The Thermal Regime of

Santa Maria Province, California

Phosphorus Geochemistry, Diagenesis, and

Mass Balances of the Miocene Monterey Formation

at Shell Beach, California

Geophysical section offshore Santa Maria basin

Geologic section onshore Santa Maria basin

U.S. GEOLOGICAL SURVEY BULLETIN 1995-F,G
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the currentyear issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey 

publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are 

listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability 

List" are no longer available.

Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of 

Commerce, Springfield, VA 22161; please include NTIS report number with inquiry.

Order U.S. Geological Survey publications by mail or over the counter from the offices given below.

BY MAIL OVER THE COUNTER

Books

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications 

of general interest (such as leaflets, pamphlets, booklets), single 

copies of Earthquakes & Volcanoes, Preliminary Determination of 

Epicenters, and some miscellaneous reports, including some of 

the foregoing series that have gone out of print at the Superintendent of Documents, are obtainable by mail from

U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY 

from the

Superintendent of Documents

Government Printing Office

Washington, DC 20402

(Check or money order must be payable to Superintendent of 

Documents.)

Maps

For maps, address mail orders to

U.S. Geological Survey, Map Distribution

Box 25286, BIdg. 810, Federal Center

Denver, CO 80225

Residents of Alaska may order maps from

U.S. Geological Survey, Earth Science Information Center

101 Twelfth Ave., Box 12

Fairbanks, AK 99701

Books and Maps

Books and maps of the U.S. Geological Survey are available 

over the counter at the following U.S. Geological Survey offices, 

all of which are authorized agents of the Superintendent of Documents.

 ANCHORAGE, AIaska^230 University Dr., Rm. 101

 LAKEWOOD, Colorado Federal Center, Bldg. 810

 MENLO PARK, California Bldg. 3, Rm. 3128, 345 Middlefield Rd.

 RESTON, Virginia National Center, Rm. 1C402, 12201 

Sunrise Valley Dr.

 SALT LAKE CITY, Utah Federal Bldg., Rm. 8105, 125 

South State St.

 SPOKANE, Washington U.S. Post Office Bldg., Rm. 135, 

W 904 Riverside Ave.

 WASHINGTON, D.C. Main Interior Bldg., Rm. 2650, 18th 

and C Sts., NW.

Maps Only

Maps may be purchased over the counter at the U.S. Geological Survey offices:

 FAIRBANKS, Alaska New Federal Building, 101 Twelfth 

Ave.

 ROLLA, Missouri 1400 Independence Rd.

 STENNIS SPACE CENTER, Mississippi Bldg. 3101
The Thermal Regime of

Santa Maria Province, California

By COLIN F. WILLIAMS, S. PETER GALANIS, JR., 

FREDERICK V. GRUBB, and THOMAS H. MOSES, JR,

Phosphorus Geochemistry, Diagenesis,

and Mass Balances of the Miocene Monterey

Formation at Shell Beach, California

By GABRIEL M. FILIPPELLI and MARGARET L. DELANEY

Chapters F and G are issued as a single volume 

and are not available separately

U.S. GEOLOGICAL SURVEY BULLETIN 1995

EVOLUTION OF SEDIMENTARY BASINS/ONSHORE OIL AND GAS INVESTIGATIONSSANTA MARIA PROVINCE

Edited by Margaret A. Keller
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names

in this publication is for descriptive purposes only

and does not imply endorsement by the U.S. Government

Text and illustrations edited by James W. Hendley II

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994

For sale by

U.S. Geological Survey, Map Distribution 

Box 25286, MS 306, Federal Center, 

Denver, CO 80225

Library of Congress Cataloging in Publication Data

The thermal regime of Santa Maria Province, California / by Colin F. Williams ... 

[et al.]. Phosphorus geochemistry, diagenesis, and mass balances of the 

Miocene Monterey Formation at Shell Beach, California / by Gabriel M. 

Filippelli and Margaret L Delaney.

p. cm. (U.S. Geological Survey bulletin ; 1995-f-g) (Evolution of 

sedimentary basins/onshore oil gas investigations Santa Maria Province ; 

ch. F-G)

Includes bibliographical references.

Supt. of Docs. no. : I 19.3:1995 F, G

1. Terrestrial heat flow California Santa Maria Basin Measurement. 

2. Geology, Stratigraphic Miocene. 3. Geochemistry California Shell 

Beach (Pismo Beach). 4. Phosphorus compounds. 5. Monterey Formation 

(Calif.) I. Williams, Colin F. II. Delaney, Margaret L. III. Filippelli, Gabriel 

M. Phosphorus geochemistry, diagenesis, and mass balances of the Miocene 

Monterey Formation at Shell Beach California. 1994. IV. Title: Phosphorus 

geochemistry, diagenesis, and mass balances of the Miocene Monterey 

Formation at Shell Beach, California. V. Series. VI. Series: Evolution of 

sedimentary basins/onshore oil and gas investigatino Santa Maria Province ; 

ch. F-G.

QE75.B9 no. 1995-F-G 

557.3 s dc20

[551.1'4] 94-27960

CIP
Chapter F

The Thermal Regime of

Santa Maria Province, California

By COLIN F. WILLIAMS, S. PETER GALANIS, JR., 

FREDERICK V. GRUBB, and THOMAS H. MOSES, JR,

U.S. GEOLOGICAL SURVEY BULLETIN 1995

EVOLUTION OF SEDIMENTARY BASINS/ONSHORE OIL AND GAS INVESTIGATIONSSANTA MARIA PROVINCE

Edited by Margaret A. Keller
CONTENTS

Abstract Fl 

Introduction Fl 

Geologic setting F2 

Temperature data F4 

Thermal conductivity data F7

Conductivity of the Gaviota Formation, Rincon Mudstone, and basement rocks F7

Conductivity of the Monterey Formation F9

Conductivity of the Sisquoc Formation Fll

Conductivity of the Foxen Mudstone Fll

Conductivity of the Careaga Sandstone and the Paso Roles Formation (part) Fll

Anisotropy Fll 

Heat flow F13 

Local disturbances to the thermal regime F16

Shallow ground-water disturbances F16

Erosion F19 

Heat flow in a regional context F19

Upper crustal disturbances F10

Extension and basin formation Fll 

Conclusions Fll 

References F13

FIGURES

1. Location map of a portion of Santa Maria province, showing major faults, oil 

fields, and general locations of heat-flow sites Fl

2. Map of onshore Santa Maria basin, showing major synclines and anticlines, oil 

fields, wells logged for temperature, and wells sampled for thermal conductivity 

F3

3. North-south cross section through onshore Santa Maria basin, showing structure 

and stratigraphy of basin relative to major oil fields F3

4. Temperature logs from West Santa Maria Valley, Guadalupe, Cat Canyon, and Orcutt Hill Oil Fields F4

5. Temperature logs from Santa Maria Valley Oil Field F5

6. Commercial temperature logs from Cat Canyon Oil Field F5

7. Temperature logs from the Point Conception, Lompoc, and Zaca Oil Fields F6

8. Temperature logs from Point Arguello Oil Field F6

9. Temperatures, temperature gradients, and calculated interval heat flow for the 

BD06well F6

10. A, Bulk thermal conductivities measured on basement-rock samples and plotted 

versus depth. B, Histogram of these conductivities F9

11. A, Bulk thermal conductivities of Monterey Formation samples plotted versus 

depth. B, Histogram of these bulk conductivities. C, Matrix thermal conductivities 

of Monterey samples plotted versus depth. D, Histogram of these matrix 

conductivities F9

12. A, Bulk thermal conductivities of Sisquoc Formation samples plotted versus depth. 

B, Histogram of these bulk conductivities. C, Matrix thermal conductivities of 

Sisquoc samples plotted versus depth. D, Histogram of these matrix 

conductivities Fll

IV Contents
13. A, Matrix thermal conductivities from Foxen Mudstone plotted versus depth divided by unit thickness for each sample well. B, Histogram of conductivities from 

upper part of Foxen Mudstone. C, Histogram of conductivities from lower part of 

Foxen Mudstone F12

14. A, Matrix thermal conductivities from Paso Robles Formation and Careaga Sandstone plotted versus depth. B, Histogram of these matrix conductivities F13

15. Ground-water-level contours (in meters above sea level) for Santa Maria Valley, 

along with the location of major oil fields and logged wells F17

16. Cross section B-B1 (figure 15) showing the approximate path of ground-water flow 

in the Santa Maria Valley and its relationship to formations and in situ 

temperatures F17

17. Comparison of modeled temperatures derived from equation (9) with measured 

temperatures along flow path shown in figures 15 and 16 F18

18. Conductive heat flow in Santa Maria province, along with published heat-flow 

values for southern and central California F20

19. A, Normalized heat flow for Santa Maria province over time for one-dimensional 

extension using the model of McKenzie (1978) for an initial lithospheric thickness 

of 50 km and various values for stretching factor, 8. B, Normalized heat flow over 

time for an initial lithospheric thickness of 60 km F22

TABLES

1. Santa Maria province wells with temperature data F5

2. Thermal conductivity sample wells F8

3. Bulk and matrix conductivity by stratigraphic unit F8

4. Santa Maria Province heat flow F14

Contents

The Thermal Regime of Santa Maria Province, California

By Colin F. Williams, S. Peter Galanis, Jr., Frederick V. Grubb, and 

Thomas H. Moses, Jr.

Abstract

Equilibrium temperature logs have been recorded in 27 

idle oil wells in the onshore Santa Maria, offshore Santa 

Maria, and western Ventura basins. Thermal conductivities 

have been measured on 365 core and cuttings samples from 

an additional 26 wells in the region. From these data, conductive heat-flow values have been determined for the Guadalupe, Santa Maria Valley, Cat Canyon, Orcutt Hill, Lompoc, 

Zaca, Point Conception, and Point Arguello Oil Fields. Examination of these thermal data reveals a complex combination 

of advective and conductive processes dominating heat transfer within the province. Over much of the Santa Maria Valley, 

temperature gradients in the Pliocene to Pleistocene Careaga 

Sandstone, Paso Robles Formation, and Orcutt Sand are 

depressed to nearly isothermal values. Geologic constraints 

and simple analytical models suggest that shallow groundwater flow accounts for most (if not all) of the heat loss within 

these shallow sediments. Temperature profiles in the older, 

underlying Foxen Mudstone, Sisquoc Formation, and Monterey Formation are linear and yield conductive heat-flow values that are relatively constant with depth. Corrected heatflow determinations for the deeper units vary from 73 to 106 

milliwatts per square meter (mW/m2 ), with an average of 84 

mW/m2 for the entire region. These values are typical of the 

Coast Range heat-flow high to the north and contrast sharply 

with low heat flow (45 to 50 mW/m2) in the central Ventura 

basin to the south. Identification of Santa Maria heat flow 

with the Coast Range high extends the southern boundary of 

the high and provides compelling evidence for the persistence 

of high heat flow at least 20 m.y. after cessation of subduction 

and the establishment of the transform margin. This suggests 

that the Coast Range high did not develop solely from asthenospheric upwelling in the wake of triple junction passage 

but may have arisen from a combination of sources within the 

crust and upper mantle.

INTRODUCTION

Heat-flow studies in California have provided valuable 

insights into the tectonics of the San Andreas Fault system 

(Lachenbruch and Sass, 1980), the nature and evolution of

Manuscript approved for publication, June 21,1994.

the Sierra Nevada (Saltus and Lachenbruch, 1991), the 

development of the Salton Trough (Lachenbruch and others, 

1985), and many other topics related to active and ancient 

geologic processes. In spite of these many achievements, 

the state's sedimentary basins remain relatively unexplored 

and unexplained by thermal studies. Of the more than 500 

published heat-flow measurements from California, fewer 

than 40 are from the petroleum-producing basins, even 

though these basins cover more than 25 percent of the 

state's surface area. This shortcoming is magnified by the 

fact that heat-flow measurements in sedimentary basins not 

only provide the same tectonic constraints provided by 

measurements in crystalline basement rocks but also yield 

unique information on the conditions for sediment maturation and petroleum generation.

One reason for the paucity of measurements from 

basins is the poor quality of thermal data typically available from oil and gas wells, in particular with the welldocumented problem of determining geothermal gradients 

from bottom-hole temperature (BHT) data (for example, 

Beck and Balling, 1988). These problems can be avoided 

through continuous temperature logging of equilibrated, 

idle wells; examples of heat-flow measurements in idle oil 

wells have been published sporadically over the years (for 

example, Benfield, 1947; Sass, Lachenbruch, Munroe and 

others, 1971). The recent paper by De Rito and others 

(1989) on heat flow in the central Ventura basin was the 

initial product of an effort by the U.S. Geological Survey 

(USGS) Geothermal Studies Project to apply these standard heat-flow techniques in a systematic study of heat flow 

in sedimentary basins. This paper reports heat-flow results 

from a second study area the Santa Maria province.

A thermal investigation of the Santa Maria province is 

of interest for a number of reasons. With its location at the 

transition between the southern Coast Ranges and the western Transverse Ranges, the Santa Maria province (fig. 1) is 

a link between two regions of contrasting tectonics and heat 

flow (Lachenbruch and Sass, 1980; De Rito and others, 

1989). As such, the province serves as an excellent location 

for testing current ideas regarding the relationship between 

present-day heat flow and late Tertiary evolution of the San 

Andreas transform margin. The importance of regional 

fluid flow to the thermal state of many sedimentary basins

The Thermal Regime of Santa Maria Province, California F1
has been recognized in recent years (for example, Hitchon,

1984), and California basins have been identified as possible sinks for fluid flowing away from the San Andreas Fault 

zone (Williams and Narasimhan, 1989). Thermal studies in 

California basins should reveal the magnitude and nature of 

any pervasive ground-water flow. Finally, the nature and 

timing of petroleum generation in the Monterey Formation, 

which is both an important reservoir and the primary source 

rock for the Santa Maria and many other California basins, 

has received extensive attention in the past decade. Maturation history models (for example, Heasler and Surdam,

1985) and exploration strategies may benefit significantly 

from a thorough understanding of regional geothermal gradients, yet the only published thermal data from the Santa 

Maria region are the BHT data of French (1940).

The following sections detail the temperature and 

thermal properties data collected from the Santa Maria 

province, the resulting heat-flow values, the nature and 

magnitude of advective and transient disturbances to the 

thermal regime, and the resulting implications for the relationship between heat flow in the Santa Maria province 

and the tectonic history of Central California.

35° 00'

34° 30'

Pacific 

Ocean

Point Arguello Point Conception

10km

120° 30'

Figure 1. Location map of a portion of Santa Maria province, 

showing major faults (dashed where approximate), oil fields 

(hachured areas), and general locations of heat-flow sites 

(solid circles). Approximate extents of the onshore Santa 

Maria basin (northern shaded region) and western Ventura 

basin (southern shaded region) are also shown. Point Arguello 

Oil Field lies in offshore Santa Maria basin. Fault abbreviations are SMVF, Santa Maria Valley Fault; WHF, West Huasna 

Fault; EHF, East Huasna Fault; NF, Nacimiento Fault; SF, Suey 

Fault; P-CF, Pezzoni-Casmalia Fault; LHF, Lions Head Fault; 

LPF, Little Pine Fault; BPF, Big Pine Fault; LF, Lompoc Fault 

(modified from Hall, 1981; McLean, 1991).

GEOLOGIC SETTING

The Santa Maria province, as defined by Crawford 

(1971), is composed of the Huasna-Pismo basin, Santa 

Maria basin (both onshore and offshore), and Cuyama 

basin. The Santa Maria province and vicinity has been the 

subject of a large number of geologic studies, and relevant 

information on many topics not treated here can be found in 

other papers of this volume or Heilbrunn-Tomson (1988). 

This study is concerned with thermal measurements in a 

portion of the Santa Maria province (the onshore and offshore Santa Maria basin) and the oil fields of the western 

Ventura basin (fig. 1). These basins are among the many 

Cenozoic basins that developed along the California continental margin during and after the cessation of subduction 

in the Miocene (Atwater, 1970; Lonsdale, 1991).

The onshore Santa Maria basin occupies a wedgeshaped region of approximately 1,800 km2 (figs. 1 and 2) 

between the Coast Ranges and the Transverse Ranges. Sediment thicknesses reach 5 km in places, although basinwide 

the average is no more than 2 to 3 km. The major structural 

features of the basin are three anticlinal trends (figs. 2 and 3) 

and the associated faults (figs. 1 and 3). Although the history 

of deformation on these faults is the subject of some controversy, convergence and transform motion have clearly predominated since the middle Pliocene (Namson and Davis, 

1990). The anticlinal, homoclinal, and stratigraphic traps 

created by this and earlier deformation have yielded more 

than 900 million barrels of oil, primarily from the Miocene 

Monterey Formation (MacKinnon, 1989).

The stratigraphy of the onshore Santa Maria basin as it 

applies to this study (fig. 3; Woodring and Bramlette, 1950; 

Dibblee, 1950; Isaacs, 198la; Namson and Davis, 1990) can 

be summarized as follows:

Basement rocks A series of Mesozoic rocks underlying the 

entire Santa Maria province, with components including 

the Great Valley sequence, Franciscan assemblage, and 

ophiolitic rocks (McLean, 1991).

Lospe Formation Early Miocene, nonmarine red to gray 

conglomerates, sandstones, and mudstones with interbedded tuffs. The Lospe lies unconformably atop the 

basement assemblage and is limited to the central portion of the basin.

Point Sal Formation Early Miocene, deep-marine sandstones and silty shales confined to the onshore Santa 

Maria basin and representative of rapid subsidence early 

in the basin history.

Monterey Formation Early, middle, and late Miocene, 

deep-marine, laminated fine-grained siliceous and dolomitic rocks, which serve as both source and -primary 

reservoir for oil fields in the region.

Sisquoc Formation Late Miocene and early and middle 

Pliocene, fine-grained, marine siliceous rocks, primarily 

diatomaceous and porcelaneous mudstones with local 

siltstone and sandstone beds.

F2 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
35° 00' '

34° 45' -

120° 30' 120° 15'

Figure 2. Map of onshore Santa Maria basin, showing major synclines and anticlines (from 

Namson and Davis, 1990), oil fields (hachured areas), wells logged for temperature (solid 

circles), and wells sampled for thermal conductivity (solid squares). Section A-A" shown in 

figure 3.

Lompoc 

Oil Field

Orcutt 

Oil Field

^^^^^^ 1 ^t^l^^^^Bi

Santa Maria 

Valley Oil Field

Orcutt - ^

A' 

North m I Ml -^ r ~^. f

QrmfVi oouin ^^*rr^\r>^~^ -*g^ v*"'trVTv- orcutt-v.^ ___

'Vv----?-"*?^' |\ \ \'f"^'/'/~1[ 'Uhx t\ PasoRobles ,^'V

1 \\ ^cSre-agaX" '» \ \ V x' / / ' /T^A^, , '>' '*

> \\ " ' /~Vf\l \ ^Careaga/ , I//< l| ^Foxen-----' ,^ " ,'/

V v \ ,,. / Nl \l \ x. / ' I ' J I M ' N Cai-caga,^" st \\\x-, sisquoc -' ,*($ \ - / '-/.if^in^ s/\ K:^S% \7 /^/fjii.....^/^ ^

I Point Sal ^< -^- x vT V\ / 7 /X" T I .7l r, /I |/V "-Monterey i ' V\ \ / ' ' ilk III Sisquoc / t\f/<

Jir ' fy \ . ' / /' Iv 1 v1" 'f ---"X ''/// *jll'i 

M Franciscan Complex \A \ SlsqUOC , / / \ LH'I» "' ^/'Ilty

5km

0

^\\ X ^-X// / / /

\» \ Monterey . / /

v\\..// / ^ V ^ Pnint Point Sol Sal / t i/ 

/

J-1 km

\ Lospe Franciscan Complex

Figure 3. North-south cross section through onshore Santa Maria basin, showing structure and stratigraphy of basin relative to 

major oil fields (from California Division of Oil and Gas, 1974). Complete unit names are: Careaga Sandstone, Foxen Mudstone, 

Lospe Formation, Monterey Formation, Orcutt Sandstone, F'aso Robles Formation, F'oint Sal Formation, Sisquoc Formation. Faults 

are heavy dashed lines; arrows show direction of relative movement.

The Thermal Regime of Santa Maria Province, California F3
Foxen Mudstone Middle and late Pliocene, shallowmarine mudstones and siltstones with fine-grained sandstone common in the upper sections of the formation. 

Careaga Sandstone Late Pliocene, shallow-marine sandstones traditionally divided into a lower fine-grained 

sandstone and an upper coarse-grained sandstone and 

conglomerate. Commonly poorly lithified. 

Paso Robles Formation (part) and Orcutt Sand In the Santa 

Maria basin, late Pliocene to Pleistocene, nonmarine 

sands, gravels, and clays, typically poorly consolidated 

and highly porous, which overlie the Careaga Sandstone. 

For the sedimentary section found in the offshore Santa 

Maria basin region (specifically the Point Arguello field), 

stratigraphic equivalents to the above units have been identified (Grain and others, 1985; Nicholson and others, 1992). 

The primary differences in the offshore section compared to 

the onshore section are (1) the presence of thick (1,000+m) 

sequences of Cretaceous and Paleogene sandstones and 

shales overlying the basement rocks, (2) the appearance of 

the early Miocene Tranquillon Volcanics of Dibblee (1950) 

in the stratigraphic position of the Lospe Formation, (3) a 

thicker Miocene and younger sedimentary sequence, with 

the top of the Monterey Formation found more than 2 km 

below the sea floor, (4) the common use of different nomenclature for strata overlying the Monterey Formation (for 

example, the lower part of the Sisquoc Formation equivalent 

as the Santa Margarita Formation and the upper part of the 

Sisquoc Formation and Foxen Mudstone equivalents as the 

Pico Formation) (Grain and others, 1985), and (5) the presence of undifferentiated shallow-marine sandstone, siltstone, and shale in the stratigraphic position of the Careaga 

Sandstone, Paso Robles Formation and Orcutt Sand.

In the western Ventura Basin (Point Conception field), 

the Monterey Formation is underlain by a thick sequence 

of Cretaceous through early Miocene sedimentary rocks. 

Two of these formations are relevant to this study: 

Gaviota Formation (part; Dibblee, 1950) Oligocene, shallow marine sequence of sandstones and siltstones. 

Rincon Mudstone Oligocene and early Miocene, poorly 

bedded to massive claystones or mudstones.

TEMPERATURE DATA

The production of oil and gas from depth disturbs the 

thermal equilibrium of a well, so the successful study of 

heat flow requires that the well be idled over a period of 

time long enough for temperatures to return to near-equilibrium values. As a practical matter, this is generally an interval at least twice as long as the original period of production 

(see Lachenbruch and Brewer (1959) for a detailed discussion of the decay of thermal disturbances in boreholes). In 

the Santa Maria province, economic considerations dictated 

that many wells drilled in the early 1980's were either never 

produced or shut-in soon after completion. In addition, the

operational difficulties associated with petroleum production (for example, collapsed casing, high H2S contents, high 

water cuts) have idled many wells since the beginning of 

large-scale production in the 1930's. Taken together, these 

two oil industry problems have provided a large number of 

wells suitable for thermal studies.

With the cooperation of production companies, the 

USGS gained access to and measured temperatures in 30 

idle oil wells in the Guadalupe, Santa Maria Valley, Cat 

Canyon, Orcutt, Lompoc, Zaca, Point Conception, and 

Point Arguello oil fields (figs. 1 and 2). The USGS also 

obtained commercial temperature logs from 19 additional 

wells. Of these 49 logs, 27 (23 USGS and 4 commercial) 

were considered of sufficient quality to use for heat-flow 

determinations. The basic information on each well is summarized in table 1, and the data are shown in figures 4 to 9.

Although each temperature profile displays unique 

characteristics, it is possible to make some general observations regarding temperature data from each region of the 

Santa Maria province. In the onshore Santa Maria basin, 

mean ground-surface temperatures range between 12 and 

18°C, with a fairly consistent trend of lower temperatures 

near the coastline and higher temperatures in the interior 

valleys. Temperatures in the upper 200 to 400 m often 

show significant departures from linearity, and these deviations are typically the result of ground-water flow in the 

near-surface sediments (see the section "Shallow GroundWater Disturbances" below), depressed fluid levels, or 

temporal variations in surface temperature.

Temperature gradients are generally consistent with a 

rough division of the stratigraphic units into two groups: 

those with disturbances and (or) low gradients and those with 

consistently high gradients. The temperature profile in figure

40 60 80

400

800

1200

1600

SG44

20 40 60 

TEMPERATURE. IN DEGREES CELSIUS

80

Figure 4. Temperature logs from West Santa Maria Valley (SMV), 

Guadalupe, Cat Canyon, and Orcutt Hill Oil Fields. Temperatures are offset for presentation by the following amounts: 

SG44, -8°C; LYP6, 0°C; LYQ5, +8°C; TUN8, +20°C; LA68, 

+24°C; PL12, +32°C. See figures 1 and 2 for well locations.

F4 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
Table 1. Santa Maria Province wells with temperature data

[See figures 1 and 2 for well locations. TRS, township, range, and section; Log T.D., temperature log total depth; Elev, elevation 

above sea level]

Field Operator

Guadalupe Unocal

Santa Maria Valley Unocal

Cat Canyon Unocal

Texaco

Orcutt Hill Unocal

Lompoc Unocal

Zaca Texaco

Pt. Conception Unocal

Pt. Arguello Texaco

Well

Le Roy P6

Le Roy Q5

Union Sugar 44

Vincent 15

Battles 8

Calif. Lands 1

Wylie 2

Bradley 1-6

Bradley I- 10

Bell 83

Bell 133

Bell 165

Blochman 29

Tunnell 8A

Los Alamos 68

Final 12

Purisima 34

Purisima 39

Luton 113

State 10-6

State 13-6

State 15-6

Pt. Arguello 1

Pt. Arguello 2

Pt. Arguello 3

Pt. Arguello 4

Pt. Arguello 5

Code

LYP6

LYQ5

SG44

VN15

BT08

CL01

WY02

BD06

BD10

BL83

B133

B165

BH29

TUNS

LA68

PL12

PU34

PU39

LUTN

PC10

PC13

PC15

PA1

PA2

PAS

PA4

PAS

Latitude

(N)

34°59.9'

34°59.3'

34°55.9'

34°55.1'

34°55.2'

34°54.9'

34°54.7'

34°54.7'

34°54.7'

34°49.0'

34°49.1'

34°49.4'

34°50.0'

34°52.7'

34°48.2'

34°50.2'

34°42.7'

34°42.1'

34°44.4'

34°26.7'

34°26.7'

34°27.1'

34°28.2'

34°28.2'

34°28.2'

34°28.2'

34°28.2'

Longitude 

(W)

120°36.3'

120°36.2'

120°29.7'

120°24.3'

120°24.2'

120°23.7'

120°23.8'

120°24.9'

120°25.0'

120°19.4'

120°19.6'

120°19.4'

120°19.4'

120°19.0'

120°18.3'

120°24.9'

120°26.1'

120°26.5'

120°10.2'

120°27.5'

120°27.5'

120°28.0'

120°40.9'

120°40.9'

120°40.9'

120°40.9'

120°40.9'

TRS Log T.D. (m)

UN 35W Sec 32

UN 35W Sec 34

ION 34W Sec 19

ION 34W Sec 25

ION 34W Sec 25

ION 33W Sec 30

ION 33W Sec 30

ION 34W Sec 25

ION 34W Sec 25

9N 33W Sec 35

9N 33W Sec 35

9N 33W Sec 26

9N 33W Sec 26

9N 33W Sec 11

8N 33W Sec 1

9N 34W Sec 24

7N 34W Sec 2

7N 34W Sec 15

8N 31W Sec 29

4N 34W Sec 8

4N 34W Sec 8

4N 34W Sec 8

N/A

N/A

N/A

N/A

N/A

830

771

1477

745

674

1061

945

1241

956

869

914

747

786

762

662

288

693

817

503

824

912

976

1804

1866

1693

2460

2225

Elev (m)

44

21

56

87

91

97

116

82

81

341

340

293

232

138

259

228

152

119

327

9

9

40

-206

-206

-206

-206

-206

20

400

800

1200

1600

40 60 80

BD10

VN15

CL01

BD06

20 40 60

20 40 60 

TEMPERATURE, IN DEGREES CELSIUS

80

400

800

1200

1600

80

BL83 B133

Figure 5. Temperature logs from Santa Maria Valley Oil 

Field. Temperatures are offset for presentation by the following amounts: BD10, -8°C; BD06, 0°C; WYL2, +8°C; CL01, 

+16°C; BT08, +24°C; VN15, +32°C. See figures 1 and 2 for 

well locations.

20 40 60 

TEMPERATURE, IN DEGREES CELSIUS

80

Figure 6. Commercial temperature logs from Cat Canyon Oil 

Field. Temperatures are offset by the following amounts: 

B165, -14°C; BK29, 0°C; BL83, +7°C; B133, +18°C. See figures 1 and 2 for well locations.

The Thermal Regime of Santa Maria Province, California F5
9 provides an illustration of this for the Santa Maria Valley 

field. In the absence of obvious disturbances, temperature 

gradients in the younger sediments of the Careaga Sandstone, 

Paso Robles Formation, and Orcutt Sand generally range 

between 20 and 40°C/km. Taken together, these units are 

approximately 400 to 600 m thick in the Guadalupe and 

Santa Maria Valley fields but are often absent or greatly 

attenuated in other areas (Worts, 1951; Dibblee, 1950; Woodring and Bramlette, 1950). Profiles in the older mudstones, 

siltstones, and shales of the Monterey Formation, Sisquoc 

Formation, and Foxen Mudstone are remarkably linear, with

20 40 60 80

400

800

1200

1600

LUTN

PC10

PC13 PC15

20 40 60 

TEMPERATURE, IN DEGREES CELSIUS

80

Figure 7. Temperature logs from the F'oint Conception, Lompoc, and Zaca Oil Fields. Temperatures are offset by the following amounts: PC10, -18°C; PC13, -12°C; PC15, -4°°C; 

PU34, +12°C; PU39, +12°C; LUTN, +36°C. See figures 1 and 2 

for well locations.

40 80 120 160

1000

2000

3000

PA4 PAS

40 80 120 

TEMPERATURE, IN DEGREES CELSIUS

160

Figure 8. Temperature logs from Point Arguello Oil Field. 

Temperatures are offset by the following amounts: PA4, 

-8°C; PA1, 0°C; PA3, +12°C; PAS, +20°C; PA2, +32°C. See 

figure 1 for well locations.

gradients ranging between 45 and 60°C/km, although disturbances at the levels of producing zones are common. 

(These disturbances reflect communication with nearby producing wells and typically do not affect thermal equilibrium 

in the overlying sections of an idle well.) As with the shallow 

Pliocene and Pleistocene sediments, these formations vary 

in thickness and character throughout the basin. The Foxen 

Mudstone occupies more than half of the logged intervals in 

the data from the Guadalupe, Santa Maria Valley, and Zaca 

fields, whereas most of the temperature data for Orcutt, 

Lompoc, and Cat Canyon fields are from the Sisquoc Formation. In the Point Conception wells, the primary logged 

units are the Gaviota Formation and the Rincon Mudstone, 

and in the Point Arguello field the data cover the offshore 

sedimentary section from the Monterey and Sisquoc reservoir 

rocks up through the offshore stratigraphic equivalents of 

the Foxen, Careaga, and Paso Robles (Grain and others, 

1985). Measured temperatures are not available for the Point 

Sal Formation, Lospe Formation, or basement rocks.

THERMAL CONDUCTIVITY DATA

In the absence of advective or radiative disturbances 

to the thermal field, the vertical component of conductive 

heat flow can be calculated from the equation

(1)

where 9779z is the vertical temperature gradient, X is the 

thermal conductivity, and q is the heat flow. Ideally, accurate 

temperature and thermal conductivity data are available from 

a combination of precision well logging and continuous 

coring in the same well. In reality, for the Santa Maria 

province and other sedimentary basins, core samples are 

available from only a fraction of the total number of wells, 

and the sampled wells are generally not those idled and later 

logged for temperature. This substantially increases the 

uncertainty of heat-flow determinations unless a systematic, 

quantifiable method can be used to combine the two data sets.

The development of an adequate method must address 

two critical components of porous rock conductivity mineralogy and porosity (Horai, 1971; Sass, Lachenbruch, and 

Munroe, 1971). Changes in both mineralogy and porosity 

have a significant impact on the bulk thermal conductivity, 

and studies that rely on combining measurements from different locations must account for possible variations in 

these components. In a sedimentary basin, facies changes 

and varying compaction trends are probably the most significant sources of mineralogy and porosity changes.

For the present study, the following steps were taken 

for determining the values of thermal conductivity appropriate for each logged well. First, wherever possible, samples 

were taken from wells within 2 km of logged wells in an

F6 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
effort to minimize the effects of lateral variations in conductivity (see fig. 2). Next, thermal conductivity was determined 

by one or more of three methods. A divided bar apparatus 

(Sass, Lachenbruch, Munroe and others, 1971) was used for 

rock samples competent enough to withstand machining and 

saturating, and measurements from the divided-bar provided 

both bulk thermal conductivity (A^,) and porosity (<f>). Needle 

probe (Von Herzen and Maxwell, 1959) and half-space needle probe (Vacquier, 1985) techniques were applied on a few 

samples to obtain Xb. The crushed chip method, which yields 

a measure of the matrix conductivity (A^; Sass, Lachenbruch, 

and Munroe, 1971), was applied on ground-up samples from 

the remaining cores and cuttings. The divided-bar and needleprobe methods are typically accurate to ±5 percent and 

repeatable to ±2 percent (Sass and others, 1984). The chip 

method is accurate to ±10 percent and repeatable to ±5 

percent (Sass, Lachenbruch, and Munroe, 1971). In all, 365 

conductivity measurements were made, including a few chip 

measurements on ground-up divided-bar "cookies". Summary information on the sample wells, measurement techniques, and formations is given in table 2.

The measurements of A^, and A^ were divided among 

the major formations and examined for their variability

with depth, location, and <|>. The results for the onshore 

Santa Maria basin are summarized in table 3 and figures 10 

to 14. When trying to correctly link samples to their respective formations, there is often ambiguous or contradictory 

evidence. Ideas regarding formation characteristics and 

markers have changed over the years, as have the names of 

the formations themselves. Although every effort has been 

made to identify the correct formation for each sample, 

there are certainly a small number of mistakes. In all likelihood these misidentifications do not affect the final results, 

but they do limit the accuracy with which we can characterize the thermal properties of a given formation.

Conductivity of the Gaviota Formation, 

Rincon Mudstone, and Basement Rocks

Because samples of the basement rocks of the Santa 

Maria basin could be cut and saturated without crumbling, 

direct measurements of bulk conductivity were possible. 

For this sample set, basement rocks include undifferentiated 

samples from the Franciscan assemblage and Great Valley 

sequence, with the possible addition of a few samples from

GRADIENT, IN DEGREES 

CELSIUS PER KILOMETER

20 40 60 80 50 100 150

V) 

01 HI

ill

t

HI 

Q

300

600

900

1200

1500

Paso Roble 

Careaga

Formation 

Sandstone

Foxen Mudstone

Sisquoc Formation BD06

Monterey Formation

20 40 60 80 50 100 150

TEMPERATURE, IN DEGREES CELSIUS HEAT FLOW, IN MILLIWATTS PER SQUARE METER

Figure 9. Temperatures, temperature gradients, and calculated interval heat flow (solid circles) for the BD06 

well. Note correlation of depressed gradients and heat flow with the permeable Paso Robles Formation and 

Careaga Sandstone. See figure 2 for well location. Vertical error bars indicate depth interval over which heat 

flow was calculated. Horizontal error bars indicate uncertainty in calculated heat-flow value.

The Thermal Regime of Santa Maria Province, California F7
Table 2. Thermal conductivity sample wells

[See figures 1 and 2 for well locations. TRS, township, range, and section; N, number of samples; Mdst., mudstone; Ss., sandstone; Fm., formation]

Field Operator Well

Guadalupe Unocal

Santa Maria Valley Unocal

Shell

Unocal

Cat Canyon Mobil

Texaco

Orcutt Unocal

Lompoc

Zaca Texaco

Pt. Conception Offshore Texaco

Pt. Arguello Texaco

Le Roy 1-A

Le Roy 3

Le Roy 4

Union Sugar 2

Union Sugar A-4

Le Roy 1

Security 1

Bradley 2-3

Adam 1

Calif. Lands 1

Gallison 1

Laine 1

Rice 1

Vincent IX

Battles 2

HB Enos 1

Neotsu 11-13

Los Alamos 32

Williams 1

Newlove 51

Careaga 1

Chamberlin 1

Jade 19

Pt Arguello 6 

Pt Arguello 7 

315-1

Code

LY1A

LY03

LY04

SG02

SGA4

LY01

SEC1

BD03

AD01

CL01

GAL1

LNEl

RCE1

VN1X

BT02

EN01

NU13

LA32

WL01

NW51

CGA1

CHMl

JD19

PA6 

PA7 

T315

Latitude

N

34°58.5'

34°58.6'

34°58.7'

34°55.8'

34°54.5'

34°57.0'

34°55.8'

34°54.3'

34°56.0'

34°54.9'

34°54.7'

34°56.5'

34°56'

34°55.5'

34°56.0'

34°56.6'

34°51.8'

34°48.3'

34°49.0'

34°49.0'

34°44.0'

34°43.0'

34°25.0'

34°28.2' 

34°28.2' 

34°28'

Longitude 

W

120°33.6'

120°38.7'

120°38.7'

120°29.5'

120°31.0'

120°28.0'

120°29.2'

120°24.3'

120°24.3'

120°23.7'

120°25.5'

120°24.4'

120°23.6'

120°24.5'

120°24.2'

120°24.9'

120°18.6'

120°17.3'

120°16.2'

120°25.0'

120°24.0'

120°09'

120°23.0'

120°40.9' 

120°40.9' 

120°41'

TRS

ION 36W Sec 2

ION 36W Sec 2

ION 36W Sec 2

ION 34W Sec 19

ION 34W Sec 31

ION 34W Sec 16

ION 34W Sec 20

ION 34W Sec 36

ION 34W Sec 24

ION 33W Sec 30

ION 34W Sec 26

ION 34W Sec 13

ION 33W Sec 19

ION 34W Sec 25

ION 34W Sec 24

ION 34W Sec 13

9N 33W Sec 13

8N 32W Sec 6

9N 32W Sec 32

9N 34W Sec 25

8N 33W Sec 31

8N 31W Sec 33

4N 33W Sec 13

N/A 

N/A 

N/A

N

1

1

1

15

31

4

2

2

16

46

38

14

49

15

1

1

10

4

5

43

17

7

29

9 

4

7

Units

Foxen Mdst.

Foxen Mdst.

Foxen Mdst.

Careaga Ss., Foxen Mdst., Sisquoc Fm.

Paso Robles Fm., Careaga Ss.

Monterey Fm.

Monterey Fm.

Monterey Fm.

Foxen Mdst., Sisquoc Fm., Monterey Fm.

Monterey Fm., Point Sal Fm., Basement rocks

Foxen Mdst., Sisquoc Fm., Monterey

Foxen Mdst., Sisquoc Fm., 

Monterey Fm., Basement rocks

Carega Ss., Foxen Mdst., Sisquoc Fm 

Monterey Fm., Basement rocks

Point Sal Fm., Basement rocks

Foxen Mdst.

Sisquoc Fm.

Foxen Mdst., Sisquoc Fm.

Foxen Mdst., Sisquoc Fm.

Sisquoc Fm.

Sisquoc Fm.

Sisquoc Fm., Monterey Fm.

Foxen Mdst., Sisquoc Fm.

Monterey Fm., Rincon Mdst., 

Gaviota Fm.

Monterey Fm. 

Sisquoc Fm., Monterey Fm. 

Monterey Fm.

Fm.

"

Table 3. Bulk and matrix thermal conductivity by stratigraphic unit 

[Mdst., mudstone; Ss., sandstone; Fm., formation; N.A., not applicable]

Bulk1 (A») Matrix (Am )

Unit Number Conductivity2 (W/m-K) Number Conductivity2 (W/m-K) 

of Samples of Samples

Basement rocks

Gaviota Fm.

Rincon Mdst.

Monterey Fm.

Sisquoc Fm.

Foxen Mdst. 

Lower part 

Upper part

Paso Robles Fm. and 

Careaga Ss.

37

N.A.

N.A.

30

10

9

N.A.

N.A.

2.85±0.56

N.A.

N.A.

2.27±0.34

1.78±0.21

1.47±0.10

N.A.

N.A.

3

8

26

100

24 

7

34

N.A.

3.41±0.48

2.00±0.07

2.35±0.39

2.20±0.29

2.46±0.43 

3.10±0.13

2.93±0.45

1 Bulk conductivities were measured in the vertical direction. Printed averages are harmonic means. 

2Uncertainties given are plus or minus one standard deviation.

F8 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
the Point Sal and Monterey Formations. The measured conductivities are highly variable (fig. 10), but the absence of 

any depth dependence for the results suggests that the variability in conductivity reflects variability in both the mineralogy and porosities of the samples. The harmonic mean 

basement bulk thermal conductivity of 2.85 Watts per meter 

per Kelvin (W/m-K) is the highest of all the formations 

studied, a result which reflects both low porosity and a high 

quartz content.

Matrix conductivities of the Gaviota Formation and 

Rincon Mudstone were measured on samples from Texaco 

Jade 19, a well located in the Conception Offshore field 

adjacent to the Point Conception field (table 3). Given the 

small sample size, the uncertainties are large, and it is not 

possible to identify systematic variations with depth. The 

average results reflect the expected contrast between a 

high-conductivity sandstone (Gaviota) and a low-conductivity mudstone (Rincon).

CO 900 

ill ID

I 1200 

t

12345 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

I!I IIII

B

I m 12345 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

Figure 10. A, Bulk thermal conductivities measured on basement-rock samples and plotted versus depth. B, Histogram of 

these conductivities.

Conductivity of the Monterey Formation

For the Monterey Formation, a mix of divided-bar and 

chip measurements were made. For both matrix and bulk 

conductivities, there is no apparent correlation of conductivity with depth (fig. 11), and the values are generally low, 

with a fair amount of scatter. The range of values is consistent 

with the diversity of lithologies represented in the Monterey 

(Isaacs, 1984) and also reflects variations in conductivity 

owing to silica phase changes.

Isaacs (1984) has suggested that the phase transitions 

of biogenic silica from opal-A to opal-CT at approximately 

50°C and opal-CT to quartz at approximately 80°C significantly alter the whole-rock thermal conductivity. Because 

diatomaceous rocks are common in both the Monterey and 

Sisquoc Formations (Woodring and Bramlette, 1950) and 

the present-day temperatures of these formations cover the 

range of silica-phase-transition temperatures (figs. 4-9), the 

possible role of silica phase transitions in conductivity variations should be quantified.

Both Monterey and Sisquoc diatomaceous rocks from 

the Santa Maria basin have been examined by Isaacs, Taggart, 

and others (1989), and the following observations have been 

made. The primary effect of silica diagenesis is the loss of 

porosity, with representative porosities for these formations 

in each of the three phases being 60 percent for opal-A, 40 

percent for opal-CT, and 20 percent for quartz (Beyer, written 

commun., and Isaacs, 198 Ib). In addition, mineral conductivities for each phase are ^=7.7 W/m-K for quartz (Horai, 

1971), ^=3.7 to 4.5 W/m-K for opal-CT (Horai, 1971; 

Diment and Pratt, 1988), and ^=1.4 to 1.7 W/m-K for opalA (Horai, 1971; Diment and Pratt, 1988; De Rito and others, 

1989). The changes in mineral conductivity are large and 

can dominate the bulk conductivity. De Rito and others 

(1989) measured a matrix conductivity of 1.7 W/m-K on a 

nearly pure diatomite from the Modelo Formation in the 

central Ventura basin, and the associated porosity of 55 

percent reduced the bulk-rock conductivity to 0.9 W/m-K.

In the Santa Maria basin, with some notable exceptions 

in the diatomite deposits of the Purisima Hills and Santa 

Ynez Mountains (Dibblee, 1950; Woodring and Bramlette, 

1950), the composition of a typical Monterey or Sisquoc 

sample may be approximately 30 percent by weight silica, 

65 percent detritus (clays, feldspars, and detrital quartz), 

and 5 percent carbonate (calcite and dolomite) (Isaacs, Taggart, and others, 1989, and Isaacs, Jackson, and others, 

1989). (Note that measured percentages vary over a wide 

range and that these values are intended for illustrative purposes only.) With the simplifying assumption that volume 

percentages are approximately the same as weight percentages, the matrix conductivity of this theoretical sample can 

be written as

The Thermal Regime of Santa Maria Province, California F9
where (jjj, fa, ..., (|>n are the volume fractions of the constituents with conductivities A1? A^, ..., A^ (Sass, Lachenbruch, and Munroe, 1971).

With conductivities for the detritus and carbonate 

taken as 2.0 and 4.5 W/m-K, respectively, the resulting 

matrix conductivities in each of the three silica phases are 

A^ (opal-A)=2.0 W/m-K, J^ (opal-CT)=2.7 W/m-K, and 

AH, (quartz)=3.1 W/m-K. With the aforementioned porosities of 60 percent, 40 percent and 20 percent, and a simplification of equation (2) to

(3)

where 1-<|) is the solid fraction and A^, is the conductivity 

of the saturating fluid (assumed to be water with A^O.61 

W/m-K at 25°C), the resulting bulk conductivities are Ab 

(opal-A)= 1.0 W/m-K, Ab (opal-CT)=1.5 W/m-K, and Ab 

(quartz)=2.3 W/m-K.

For a constant heat flow of 80 mW/m2, the corresponding thermal gradients would be 80, 53, and 35°C/km. However, if the porosity is constant at 40 percent, the bulk 

conductivities are 1.2,1.5, and 1.6 W/m-K, which correspond 

to gradients of 67, 53 and 50°C/km. Therefore, given the 

relatively low percentage of silica in many Monterey and 

Sisquoc Formation rocks, the effects of changing matrix 

conductivities with changing silica phase are minor compared to the effects of the concurrent decrease in porosity. 

The Monterey Formation conductivities in figure 11 are from 

samples entirely in either the opal-CT or quartz phase, and 

consequently, the use of a single average matrix conductivity 

with a locally determined porosity is justified.

Conductivity of the Sisquoc Formation

As with the Monterey Formation, thermal conductivity 

measurements on the Sisquoc Formation samples involved

Q 1 2 3 4 e

g 1000

in

in^

z

I

t

LIJ

Q 2000

3000

/A

**

* A t * *

 *

* * »

 * 

% 

1 2 3 4 e 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

8 

SAMPLES NUMBER OF

*. O310

y/////////////////A

y/AYAY///////////////A 

VAYAYAYAY//////////////A

y//////////////////////A

Y///////////Ay//Ay//AY////////A

B

'////////A

\

12345 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

V///////A

Y////////////A

|

1

S

Y/////////////////A

D

V////////////A \7////////////A

'/////////////////A

|

12345 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

12345 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

Figure 11. A, Bulk thermal conductivities of Monterey Formation samples plotted versus depth. B, Histogram of these bulk 

conductivities. C, Matrix thermal conductivities of Monterey samples plotted versus depth. D, Histogram of these matrix 

conductivities.

F10 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
both the divided-bar and chip techniques. Samples from the 

Sisquoc and younger units are generally fragile and more 

difficult to work with than Monterey and basement samples. 

Consequently, most of the thermal conductivity data from 

these formations comes from chip measurements. The Sisquoc bulk conductivities are lower than Monterey Formation 

results, a trend which reflects increasing porosity from a 

mean of 8.5 percent for the Monterey core samples to 21.1 

percent for the Sisquoc samples. The Sisquoc matrix conductivities range from a low of 1.59 W/m-K to a high of 3.18 

W/m-K (fig. 12Q, but given the apparently normal distribution about the mean of 2.2, these extremes probably reflect 

mineralogic variability within the formation.

Conductivity of the Foxen Mudstone

The strong depth-dependence of the Foxen Mudstone matrix conductivities is unique among the Santa

Maria province units (fig. 13). This result is consistent 

with both electric-log measurements and geologic studies. 

Resistivity logs from the upper 100 to 200 m of the 

Foxen Mudstone typically show high resistivities consistent with the sand-rich facies of the overlying Careaga 

Sandstone and Paso Robles Formation, and logs from the 

lower part of the Foxen reveal low resistivities similar to 

those of the underlying mudstones and diatomites of the 

Sisquoc Formation (Curran and others, 1959). Both Dibblee (1950) and Woodring and Bramlette (1950) note the 

increasing abundance of sandstone and siltstone in the 

upper part of the Foxen as it grades into the Careaga 

Sandstone.

Consequently, for consistency with thermal properties and lithologic variations, we have divided the Foxen 

Mudstone into upper and lower parts (table 3), with the 

upper part of the Foxen representing the top 30 percent 

of the unit and the lower part of the Foxen representing 

the remaining 70 percent. It should be noted that these

1.0

5001 

1.0 1.5 2.0 2.5 3.0 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

0

1.0 1 5 2.0 2.5 3.0 

BULK THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

300

1234 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

25

i 1.5 2.0 2.5 3.0 3.5 4.0 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

Figure 12. A, Bulk thermal conductivities of Sisquoc Formation samples plotted versus depth. B, Histogram of these bulk 

conductivities. C, Matrix thermal conductivities of Sisquoc samples plotted versus depth. D, Histogram of these matrix 

conductivities.

The Thermal Regime of Santa Maria Province, California F11
0.2

0.6

1234 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

III

B

i

2.0 2.5 3.0 3.5 4.0 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

c

1

Y////////A

I

V/////////////. V/////////////.

I

'/////////////A

|

1234 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

Figure 13. A, Matrix thermal conductivities from Foxen Mudstone plotted versus depth (z) divided by the unit thickness 

(H) for each sample well. Note strong depth-dependence 

and marked difference between conductivities for z/H<03 

and those for 2/H>0.3. B, Histogram of conductivities from 

the upper part of Foxen Mudstone (z/H<Q3). C, Histogram 

of conductivities from the lower part of Foxen Mudstone (zl 

H>0.3).

designations are only intended for use in these thermal 

studies and should not be construed as an attempt to 

revise the standard stratigraphic nomenclature. As table 3 

and figure 13 show, the contrast in the mean matrix thermal conductivity between the upper and lower parts of 

the Foxen is approximately 0.64 W/m-K.

Conductivity of the Careaga Sandstone and the 

Paso Roles Formation (Part)

Petroleum companies active in the Santa Maria province generally drill through these poorly consolidated 

Pliocene and Pleistocene units without taking note of formation contacts, and the few well logs from the region 

that cover both units do not always reveal a consistent 

marker between the Paso Robles and Careaga (for example, Curran and others, 1959). Water resources investigations provide some information (Worts, 1951; Upson and 

Thomasson, 1951; Miller and Evenson, 1966), but for 

many sample wells, it is not possible to conclusively tie 

the available nonmarine sandstone samples to either unit. 

Consequently, thermal data for these two units are lumped 

together and a single mean value obtained. The data do 

not reveal any depth dependence to the matrix conductivities (fig 14A), and the high mean and range of values (fig. 

145; table 3) are consistent with the dominant quartz-rich 

sandstone facies.

Anisotropy

Because geothermal studies focus on the vertical 

component of near-surface heat flow, directional variations in thermal conductivity measurements must be recognized and corrected for. For the bulk conductivity 

values summarized in table 3, all of the measurements 

are on vertically oriented samples, thereby avoiding problems with anisotropy. The matrix conductivities from 

chip measurements, however, are essentially an average 

of both the vertical and horizontal components of conductivity. If the sampled formation is substantially anisotropic, these values will not represent an accurate vertical 

conductivity.

In a sedimentary formation, anisotropy can occur on 

scales ranging from the smallest grain to an entire basin. 

From the thermal perspective, it is possible to reduce the 

problem to two scales of anisotropy: (1) anisotropy at 

scales larger than the available sample size and (2) anisotropy at scales smaller than the sample size. An example of 

the larger scale would be alternating sandstone and shale 

beds tens of centimeters to a few meters thick. Each bed 

may have an isotropic thermal conductivity, but the conductivity contrasts across the beds lead to formation-scale 

anisotropy. If the beds are horizontal, the appropriate averF12 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
age vertical thermal conductivity is obtained from a series 

model

avg (4)

where the K[ are the conductivities of each bed of thickness /i and L is the total formation thickness. If a representative number of samples are obtained from this 

formation, a harmonic mean of the measured conductivities will yield an appropriate average for the vertical formation conductivity.

Examples of the smaller scale are finely laminated 

rocks or layered rocks with preferential mineral orientations. In both of these cases, divided-bar conductivity 

measurements on centimeter-sized samples would yield 

different results for the horizontal and vertical orientations, 

and chip measurements on crushed samples would yield 

an average of the two. Given the finely laminated bedding 

of much of the Monterey Formation and the poorly laminated bedding of the Sisquoc Formation, chip measurements on these units could include substantial anisotropy. 

In order to examine this possibility, divided-bar and chip 

measurements were made on identical samples from the 

Monterey and Sisquoc Formations. The divided-bar measurements yielded the vertical conductivities, and the horizontal conductivities were calculated assuming a harmonic 

mean relationship of the form

2/3 .1/3

(5)

where Ah and Xy are the horizontal and vertical components of thermal conductivity. The resulting ratios of horizontal to vertical conductivity are Ah/Xv = 1.26 ± 0.23 for 

the Monterey Formation and A^/Ay = 1.06 ± 0.22 for the 

Sisquoc Formation.

These results indicate that the Monterey Formation is 

anisotropic and that the Sisquoc Formation is essentially 

isotropic, although the uncertainties are large relative to the 

average values. In the heat-flow results discussed below, 

heat flow determined in the Monterey Formation is based 

on oriented bulk conductivity measurements in order to 

avoid the uncertainties associated with corrections for 

anisotropy. For the Sisquoc Formation, heat flow is determined primarily from matrix conductivity measurements 

assuming isotropy, as it is for the other formations.

HEAT FLOW

Heat-flow values were determined for 27 Santa Maria 

basin wells by identifying intervals with uniform geothermal gradients within a single formation, applying an 

appropriate topography correction, determining the appropriate average thermal conductivity for a given unit, calculating an interval heat flow using equation (1), and 

combining the interval values for a single well average. 

The resulting calculations and their estimated uncertainties 

are summarized in table 4. For those bulk conductivities 

determined from applying equation (3) to matrix conductivities and average formation porosities, the associated 

matrix conductivity and porosity values are included in 

the table. Bulk conductivities measured on core samples 

are presented in table 4 with "N.A." entries in the matrix 

conductivity and porosity columns. The uncertainties in 

calculated bulk conductivities are probable errors determined from the application of standard error analysis 

techniques to equation (3).

Heat-flow determinations in the Gaviota Formation, 

Rincon Mudstone, Foxen Mudstone, Careaga Sandstone, 

and Paso Robles Formation required the calculation of bulk 

conductivities from matrix conductivities and estimated

500

12345 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

!iIiiiiii

8

12345 

MATRIX THERMAL CONDUCTIVITY, IN WATTS PER METER PER KELVIN

Figure 14. A, Matrix thermal conductivities from Paso Robles 

Formation and Careaga Sandstone plotted versus depth. B, 

Histogram of these matrix conductivities.

The Thermal Regime of Santa Maria Province, California F13
Table 4. Santa Maria Province heat flow

[See figures 1 and 2 for well locations. Pet, percent; <|>, porosity; ^5, bulk conductivity; Q, heat flow; N.A., not 

applicable. Unit abbreviations are: Car., Careaga Sandstone; L. Foxen, Foxen Mudstone (lower part); U. Foxen, Foxen 

Mudstone (upper part); Mont., Monterey Formation; P.R., Paso Robles Formation; Sisq., Sisquoc Formation]

Well

LYP6

LYQ5

SG44

VN15

BT08

CL01

WYL2

BD06

BD10

Interval (m)

275-365

550-760

60-335

365-760

305-550

670-1130

1220-1400

1220-1400

120-180

210-335

430-475

520-700

150-305

395-515

520-640

365-425

460-730

760-850

760-850

260-350

500-595

640-885

275-395

425-520

530-640

645-1155

1160-1220

1160-1220

245-400

425-520

550-700

730-915

Gradient (°C/km)

42.2±0.09

58.4±0.02

42.4±0.12

60.4±0.08

32.44±0.03

57.8U0.04

46.15±0.06

46.15±0.06

13.17±0.05

26.45±0.05

38.30±0.05

49.66±0.03

24.1U0.04

43.74±0.05

47.82±0.05

31.35±0.07

46.50±0.02

57.24±0.14

57.24±0.14

20.55±0.03

40.06±0.02

49.30±0.03

21.03±0.03

32.92±0.07

43.09±0.02

54.72±0.03

50.08±0.08

50.08±0.08

21.70±0.04

33.35±0.07

45.61±0.03

56.47± 0.06

Units

Careaga Ss.

L. Foxen

P.R./Car.

L. Foxen

Car./U. Foxen

L. Foxen

Sisquoc Fm.

Sisquoc Fm.

Paso Robles Fm.

P.R./Car.

U. Foxen

L. Foxen

P.R./Car.

U. Foxen

L. Foxen

U. Foxen

L. Foxen

Sisquoc Fm.

Sisquoc Fm.

Paso Robles Fm.

U. Foxen

L. Foxen

Paso Robles Fm.

Careaga Ss.

U. Foxen

L. Foxen

Sisquoc Fm.

Sisquoc Fm.

Paso Robles Fm.

P.R./Car.

U. Foxen

L. Foxen

Am (W/m-K)

2.93±0.45

2.46±0.43

2.93±0.45

2.46±0.43

3.10±0.13

2.46±0.43

2.20±0.29

N.A.

2.93±0.45

2.93±0.45

3.10±0.13

2.46±0.43

2.93±0.45

3.10±0.13

2.46±0.43

3.10±0.13

2.46±0.43

2.20±0.29

N.A.

2.93±0.45

3.10±0.13

2.46±0.43

2.93±0.45

2.93±0.45

3.10±0.13

2.46±0.43

2.20±0.29

N.A.

2.93±0.45

2.93±0.45

3.10±0.13

2.46±0.43

4 (Pet)

30±10

30±10

30±10

30±10

27±5

27±5

20±5

N.A.

27±5

27±5

26±5

27±5

27±5

26±5

27±5

26±5

27±5

23±5

N.A.

27±5

26±5

27±5

27±5

27±5

26±5

27±5

23±5

N.A.

27±5

27±5

26±5

27±5

At

1.83±0.35

1.62±0.30

1.83±0.35

1.62±0.30

2.03±0.20

1.69±0.25

1.70±0.21

1.78±0.21

1.92±0.26

1.92±0.26

2.03±0.20

1.69±0.25

1.92±0.26

2.03±0.20

1.69±0.25

2.03±0.20

1.69±0.25

1.64±0.20

1.78±0.21

1.92±0.26

2.03±0.20

1.69±0.25

1.92±0.26

1.92±0.26

2.03±0.20

1.69±0.25

1.64±0.20

1.78±0.21

1.92±0.26

1.92±0.26

2.03±0.20

1.69±0.25

Q(mW/m2 )

77.2±14.8

94.6±17.5

85.9±16.2

well avg.

77.6±14.8

97.8±18.2

87.7±16.6

well avg.

65.9± 6.6 1

97.7±14.5

78.5±9.6

82.1± 9.7

89.0±12.3

well avg.

25.3± 3.41

50.8± 6.9 1

77.8± 7.6

83.9±10.3

80.9±10.3

well avg.

46.3± 6.3 1

88.8± 8.7

80.8±12.0

84.8±10.5

well avg.

63.6± 6.41

78.6±11.6

93.9±11.4

101.9±12.0

88.3±11.7

well avg.

39.5± 5.3 1

81.3± 8.1

83.3±12.3

82.3±10.4

well avg.

40.4± 5.4 1

63.2± 8.6 1

87.5± 8.6

92.5±13.7

82.1±10.0

89.U10.6

88.5±11.1

well avg.

41.7± 5.6 1

64.0± 8.71

92.5± 9.3

95.4±13.9

94.0±10.4

well avg.

porosities using equation (3). In the Santa Maria Valley 

field, because of the availability of bulk conductivities from 

nearby wells, heat flow values in the Sisquoc Formation 

were determined from both calculated and measured bulk 

conductivities. Outside the Santa Maria Valley field, heatflow values in the Sisquoc were calculated solely from 

average formation matrix conductivities and locally estimated porosities. All interval heat-flow values in the 

Monterey Formation were determined from local bulk conductivity measurements.

The estimated porosities in table 4 were obtained 

from a number of sources. Beyer (1987) and Beyer and 

others (1985) published precision, downhole-gravimeter 

porosity logs for the Santa Maria Valley and Orcutt fields

F14 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
Table 4. Santa Maria Province heat flow Continued

Well

BL83

B133

B165

BK29

TUNS

LA68

PL12

PU34

PU39

LUTN

PC10

PC13

PC15

PA1

PA2

PA3

PA4

PAS

Interval (m)

335-520

550-700

305-490

520-790

335-580

460-610

615-780

365-565

230-380

400-670

45-140

150-275

135-180

215-305

335-520

580-685

365-580

585-790

380-425

340-425

455-580

350-440

455-580

380-440

455-610

1585-1800

1525-1830

1675-1770

1830-2195

1830-2130

Gradient (°C/km) Units

49.69±0.07

45.66±0.12

56.60±0.12

51.56±0.07

62.17±0.07

59.98±0.08

53.63±0.05

47.15±0.07

57.43±0.02

52.53±0.16

83.36±0.18

55.87±0.17

39.22±0.21

82.04±0.06

68.70±0.07

61.97±0.07

67.19±0.04

60.70±0.04

30.05±0.06

70.37±0.11

37.70±0.05

61.09±0.11

34.55±0.05

62.63±0.06

34.43±0.03

40.13±0.08

47.59±0.05

41.69±2.42

41.82±0.11

47.13±0.12

L. Foxen

Sisquoc Fm.

L. Foxen

Sisquoc Fm.

L. Foxen

L. Foxen

Sisquoc Fm.

L. Foxen

L. Foxen

Sisquoc Fm.

L. Foxen

Sisquoc Fm.

P.R./Car.

Sisquoc Fm.

Sisquoc Fm.

Sisquoc Fm.

Sisquoc Fm.

Sisquoc Fm.

Car./U. Foxen

Rincon Mdst.

Gaviota Fm.

Rincon Mdst.

Gaviota Fm.

Rincon Mdst.

Gaviota Fm.

Sisq./Mont.

Sisq./Mont.

Sisq./Mont.

Sisq./Mont.

Sisq./Mont.

Am (W/m-K) <t> (Pet) A 4

2.46±0.43

2.20±0.29

2.46±0.43

2.20±0.29

2.46±0.43

2.46±0.43

2.20±0.29

2.46±0.43

2.46±0.43

2.20±0.29

2.46±0.43

2.12±0.12

2.93±0.45

2.20±0.29

2.20±0.29

2.20±0.29

2.20±0.29

2.20±0.29

3.10±0.13

2.00±0.07

3.41±0.48

2.00±0.07

3.4U0.48

2.00±0.07

3.41±0.48

N.A.

N.A.

N.A.

N.A.

N.A.

45±10

35±10

45±10

35±10

45±10

45±10

35±10

25±10

45±10

35±10

60±10

39±5

27±10

53±10

42±10

36±10

42±10

36±10

25±15

35±10

20±5

35±10

20±5

35±10

20±5

N.A.

N.A.

N.A.

N.A.

N.A.

1.31±0.22

1.40±0.22

1.3U0.22

1.40±0.22

1.3U0.22

1.3U0.22

1.40±0.22

1.74±0.33

1.31±0.22

1.40±0.22

1.07±0.17

1.30±0.13

1.92±0.37

1.12±0.16

1.28±0.19

1.39±0.21

1.28±0.19

1.39±0.21

2.07±0.51

1.3U0.16

2.4U0.34

1.31±0.16

2.4U0.34

1.3U0.16

2.4U0.34

2.23±0.38

2.23±0.38

2.23±0.38

2.23±0.38

2.23±0.38

Q(mW/m2 )

65.2±10.8

64.1± 9.9

64.7±10.4

well avg.

74.3±12.3

72.4±11.1

73.4±11.7

well avg.

81.6±13.5

78.8±13.0

75.3±11.6

77.1±12.3

well avg.

81.8±15.9

75.4±12.6

73.8±11.1

74.6±11.9

well avg.

89.2±14.2

72.6± 7.3

80.9±11.33

well avg.

75.2±14.6

91.5±13.5

88.2±12.9

85.9±13.5

85.2±13.6

well avg.

86.3±12.5

84. 1± 13.0

85.2±12.8

well avg.

62.1±15.42

92.2±11.3

90.9±12.8

91.6±12.13

well avg.

80.0± 9.8

83.3±11.7

81.7±10.83

well avg.

82.0± 9.4

83.0±10.0

81.8±9.73

well avg.

89.5±15.2

106.1±18.1

93.0±16.7

93.3±15.9

105.1±17.9

1 These interval values are depressed owing to groundwater flow and are not used in the well averages. 

2The value from this well may be lowered by groundwater flow. See text.

3Erosion corrections (see text) reduce these values to PL12, 76.3 milliwatts per square meter (mW/m2 ) 

PC10, 83.3 mW/m2 ; PC13, 74.3 mW/m2 ; PC15, 74.4 mW/m2 .

and parts of the Cat Canyon field. These logs provided 

most of the values used in table 4. Core data from the 

Newlove 51 well in the Orcutt field (Beyer and Isaacs, 

1990) also proved useful, as were unpublished porosity 

measurements from the Point Conception State 10-6 well 

and porosities measured on bulk thermal conductivity 

samples. For wells in the Lompoc and Zaca fields, porosity values were estimated from wells in the nearby fields 

that could be tied to the study wells on the basis of structural, sedimentary, and well log data. The unknown effects 

of lateral variability on these ties are represented in the

larger uncertainties assigned to the interval porosities. 

These uncertainties are consistent with the recorded range 

of porosities in the Santa Maria province.

The results in table 4 reveal a pattern of uniformly 

high heat flow (73 to 106 mW/m2) over the entire Santa 

Maria province. Exceptions to this are found in the shallow intervals of the Santa Maria Valley field and in the 

Luton 113 well of the Zaca field. The evidence described 

below suggests that these low values are due to groundwater flow within the shallow sediments of the onshore 

Santa Maria basin.

The Thermal Regime of Santa Maria Province, California F1 5
LOCAL DISTURBANCES TO THE THERMAL 

REGIME

Shallow Ground-Water Disturbances

The depressed thermal gradients found in the Santa 

Maria Valley field could be the result of a variety of processes, such as large changes in ground surface temperature, rapid sedimentation, or the downward flow of ground 

water. A number of geologic and thermal constraints suggest that only shallow ground-water flow can account for 

the observed disturbance.

First, the disturbance is confined to the younger, permeable Pliocene and Pleistocene sediments. It does not 

appear in wells with thin or absent Paso Robles Formation 

and Careaga Sandstone sections (for example, LA68, fig. 

2). Second, the disturbance is greatest in the eastern end of 

the Santa Maria Valley and diminishes toward the coast, 

even though the Paso Robles and Careaga section is of 

fairly uniform thickness throughout the Santa Maria Valley 

and Guadalupe Oil Fields. These two observations, taken 

together, suggest that the presence of young sediments is a 

necessary, but not sufficient, condition for existence of a 

shallow thermal disturbance.

Third, if the disturbance reflects a transient conductive 

response to a change in surface temperature, the large 

decrease in the geothermal gradient and apparent conductive 

heat flow over the upper 600 m (for example, BD06, fig. 9) 

requires a surface temperature increase on the order of 10 to 

15°C within the past 100,000 years. A change in surface 

temperature of this magnitude over a small area would be 

unprecedented in the record of natural, onshore climate 

change and its effect on subsurface temperatures (for example, Lachenbruch and others, 1988). Sea level fluctuations 

relative to the present ground surface have been common 

throughout the history of the Santa Maria basin, and the 

change from a surface covered with 5 to 8°C sea water to a 

subaerial surface at 15 to 20°C could produce the observed 

disturbance. A number of facts are in direct contradiction to 

this possibility. Pleistocene and Holocene terrace deposits 

and alluvium in the Santa Maria Valley are nonmarine in 

origin, suggesting that subaerial exposure has dominated in 

the recent geologic past (Worts, 1951). In addition, the thermal disturbance diminishes toward the coast; this trend is the 

opposite of the trend expected for sea level changes. Sea 

level high stands would have the greatest effect near the 

shoreline, yet the wells at Guadalupe are essentially equilibrated with a surface temperature of 12°C. Also, present-day 

bottom water temperatures measured at a water depth of 200 

m at the offshore Point Arguello field are approximately 

10°C (fig. 8), and the temperature in a shallow sea extending 

over the Santa Maria Valley would presumably be warmer. 

These warmer temperatures are inconsistent with the 5 to 

8°C equilibrium surface temperature required for the Santa 

Maria Valley thermal disturbance.

Fourth, the magnitude and lateral extent of the disturbance are inconsistent with the probable effects of rapid 

sedimentation. De Rito and others (1989) found similar 

shallow temperature disturbances in the top 750 m of wells 

in the Fillmore district of the central Ventura basin and 

determined that sedimentation rates on the order of 250 

meters per thousand years would be needed to generate the 

observed anomaly. Similarly high rates of sedimentation 

are also required for the wells in the Santa Maria Valley 

field, yet the known Pliocene and Pleistocene stratigraphy 

directly contradicts this possibility (figs. 2 and 9), just as 

De Rito and others (1989) found for the Fillmore wells.

Fifth, Worts (1951), Upson and Thomasson (1951), 

and Miller and Evenson (1966) document extensive 

ground-water flow systems in the Santa Maria and Santa 

Ynez River valleys. Ground-water flow in these systems 

follows a recharge path from the upland regions down 

through permeable Pliocene to Holocene sediments to 

underflow into the ocean. Water level contours determined 

by Worts (1951) are shown in Figure 15 and delineate the 

pattern of ground-water flow in the Santa Maria Valley. 

The changing pattern of well bore temperatures along the 

path of ground-water flow (fig. 16) illustrates the steady 

decay of the disturbance toward the coast line. Consequently, the thermal disturbances in the Santa Maria Valley may reflect downward flow of cold ground water into 

the Paso Robles Formation and Careaga Sandstone followed by predominantly lateral flow and gradual warming 

of the ground water as it moves westward.

This hypothesis can be tested by considering (1) 

whether the ground-water system described by Worts 

(1951) and other authors is capable of significant lateral 

heat transport and (2) whether the observed temperature 

changes across the Santa Maria Valley are consistent with 

the predominantly lateral flow of ground water heated 

from below.

For the Santa Maria Valley drainage basin, Worts 

(1951) determined that the average hydraulic conductivities 

of the Paso Robles and Careaga units were approximately 

0.003 cm/s (equivalent to a permeability of 3xlO~12 m2 for 

water at 25°C with a density of 1.0 g/cm3 and a viscosity of 

1 centipoise); these hydraulic conductivities are about an 

order of magnitude lower than the hydraulic conductivities 

of the overlying Orcutt Sand, terrace deposits, and alluvium. 

Worts (1951) found the underlying Foxen and older rocks 

to be much less permeable than the shallow sediments, and 

hydraulic conductivities published by MacKinnon (1989) 

and others for these units are less than 10"6 cm/s. Although 

the hydraulic gradient within the Santa Maria Valley varies 

significantly east-to-west (fig. 15), the average is approximately 3 m/km. These values can be applied in the onedimensional version of Darcy's Law for fluid flow in porous 

media as

dH (6)

F16 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
where v is the fluid velocity, K is the hydraulic conductiv- it enters, the total amount of heat removed by lateral

ity, and dH/dx is the hydraulic gradient. With the values 

given above for K and dH/dx, the average lateral fluid 

velocity in the Paso Robles and Careaga units is approximately 9x10~8 m/s or 3 m/yr.

If, as the temperature data indicate, ground water 

exits the Santa Maria Valley at a higher temperature than

ground-water flow can be estimated from 

Q = Pf .Cf -Ar-vAD , (7)

where pf is the fluid density, Cf is the heat capacity, AT is 

the average temperature difference between exiting and

35° 00'

34° 55'

San Rafael 

Mountains

Pacific 

Ocean

120° 30'

Figure 15. Ground-water-level contours (in meters above sea level) for Santa Maria Valley (modified from Worts, 1951), along with the location of major oil fields (shaded 

areas) and logged wells (dots). Contour interval is 7.5 meters. Section B-B1 shown in 

figure 16.

B

B'

SG44

LYQ5 TEMPERATURE. IN DEGREES CELSIUS 

TEMPERATURE. IN DEGREES CELSIUS

0 20 40 60 BO 

0 20 40 80 80

TEMPERATURE, IN DEGREES CELSIUS 

0 20 40 60 80.

LA68 

TEMPERATURE. IN DEGREES CELSIUS

20 40 60 80

Figure 16. Cross section B-B1 (figure 15) showing the approximate path of ground-water flow (arrows) in the Santa Maria 

Valley and its relationship to formations and in situ temperatures. Solid lines are measured temperatures, and dashed lines 

are estimates of formation temperatures for a constant conductive heat flow (no fluid flow).

The Thermal Regime of Santa Maria Province, California F17
entering fluid, v is the fluid velocity, and AD is the discharge area. With pf =1.0 g/cm3, Cf =4,187 J/kg-K, and 

A7=5°C (determined from variations in temperature profiles across the Santa Maria Valley, see figures 4 through 

9), the removed heat is

G=2.8xl07 W.

The surface area of the ground-water basin (AB) is approximately 4xl08 m2, so the equivalent vertical component of 

heat flow required to balance this lateral flow would be

4=e/AB=70 mW/m2.

Although there are many uncertainties in this calculation (particularly the hydraulic conductivity), the significant 

result is that the observed flow rates in the Santa Maria 

Valley ground-water system and the observed temperature 

variations across that system can account for the removal of 

almost all the vertical component of conductive heat flow.

It should be noted that this analysis assumes that all 

the temperature increase from east to west is due to conductive heating from below. Thus, as a second consequence of the fluid flow hypothesis, the observed change 

in temperature across the Santa Maria Valley should be 

attributable to the steady warming of ground water as it 

flows across the top of the impermeable Foxen Mudstone. 

This warming can be modeled with a one-dimensional 

analytical solution of the heat conduction equation if the 

following assumptions are made: (1) All downward flow is 

limited to the eastern edge of the Santa Maria Valley. 

Ground-water flow in the rest of the valley follows a horizontal path along the top of the Foxen. (2) All flow is 

oriented along the section represented by figure 16 (in 

other words, flow normal to the plane of the section is 

neglected). (3) Lateral conductive heat transfer within the 

Paso Robles Formation and Careaga Sandstone is negligible. (4) A constant surface temperature TG is maintained 

on the upper boundary, and a constant vertical heat flow q 

is maintained across the lower boundary.

These assumptions reduce the two-dimensional 

energy equation for heat and mass transport in porous 

media (Turcotte and Schubert, 1982) to

dx pfCf

(8)

where jc is the horizontal dimension, z is the vertical 

dimension, v is the horizontal fluid velocity, X is the bulk 

thermal conductivity, Pf is the fluid density, and Cf is the 

fluid heat capacity. By setting time t as x/v and defining an 

effective thermal diffusivity a as the ratio X/pfCf, the 

evolving temperature in the fluid channel is given by

T(z L (z, t) U = - T I- o +- + i 2 1*V

(Carslaw and Jaeger, 1959, p. 113), where T0 is both the 

surface temperature and the initial temperature in the 

channel, and L is the channel thickness. Figure 17 displays 

a comparison of data from the Santa Maria Valley field 

with the results of equation (9) for v=3 m/yr, (2=80 mW/ 

m2, L=400 m, o^Q.lSxKT6 m2/s, and k=1.8 W/m-K. If 

the location of BD06 is tied to x=2 km, then SG44 is at 

jt=10 km and LYP6 is at Jt=20 km. The calculated increase 

in temperature with distance shows a surprising agreement 

considering the idealization represented by equation (8).

The observations, constraints, and models discussed 

above all point to active ground-water flow as the source 

of thermal disturbances in the Santa Maria Valley. Consequently, this flow has a significant impact on temperature 

in the shallow sediments; it may also produce a transient 

conductive temperature disturbance in Monterey Formation, Sisquoc Formation, and Foxen Mudstone. If the Paso 

Robles Formation and Careaga Sandstone were initially in 

conductive equilibrium, the cooling effect of ground-water 

flow would act as a temperature change at the top of the 

Foxen. For the observed gradients in the underlying formations to be near equilibrium (<10 percent difference), 

the ground-water flow must be at least 800,000 years old 

(see De Rito and others, 1989, for a similar discussion).

However, it may not be correct to separate the flow 

system from the original sedimentation processes. Deposition of the Paso Robles Formation began as the basin floor 

emerged above sea level in response to the compressional 

tectonics active since the late Pliocene (2 to 4 Ma; Namson and Davis, 1990). As these sediments were deposited 

under a topographic gradient, they were certainly associated with an active surface water system. In addition,

20 25 30 

TEMPERATURE, IN DEGREES CELSIUS

, -a(2n+l)Vf] . 

 exp| i ^ |sm

4L 2L (9)

Figure 17. Comparison of modeled temperatures derived 

from equation (9) with measured temperatures along flow 

path shown in figures 15 and 16. Variable X represents the 

horizontal distance from point at which downward groundwater flow ceases and lateral flow begins. Temperature at 

X=0 is a constant 17°C.

F18 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
because the Paso Robles and younger units have never 

been any less permeable than they are now, some groundwater flow in response to topographic gradients has been 

ongoing since deposition. Sea level changes and the competing rates of erosion and uplift have varied over time in 

the Santa Maria Valley region (for example, Woodring and 

Bramlette, 1950; Worts, 1951; Namson and Davis, 1990), 

and these variations, along with sediment compaction, 

undoubtedly led to changes in the magnitude and direction 

of ground-water flow. It is impossible to say whether these 

changes would lead to an approximately constant, steadily 

increasing or steadily diminishing thermal effect, but given 

the fairly consistent tectonic and depositional setting over 

the past 2 m.y., the thermal conditions at depth are probably close to equilibration with present-day temperatures in 

the Paso Robles and Careaga units. In other words, the 

continuous flow of ground water may have maintained a 

relatively constant temperature at the base of the Paso 

Robles Formation since its deposition.

Erosion

The surface uplift driven by the compressional tectonics active since the Pliocene has led to extensive erosion 

in some parts of the Santa Maria province. The long-term 

erosion of material from a site will tend to increase the 

measured temperature gradients as the subsurface temperatures move toward reequilibration with the temperature of 

downward moving ground surface. Although gaps in the 

geologic record leave large uncertainties in the exact history of erosion and its thermal effects in Santa Maria 

province, the approximate magnitude of the associated disturbance can be investigated with some success. At Point 

Conception and Orcutt Hill (fig. 1), documented uplift and 

erosion rates introduce significant disturbances to the 

observed thermal gradients, and corrections for these disturbances are included in the final heat-flow estimates.

The corrections are made with a one-dimensional erosion/sedimentation model that calculates the disturbed heat 

flow as

z+Ut

(to)

(nat)

4at

, z-Ut z-Ut -(z-Ut) _erfc .+ .exp >

(4at) (nat)

(10)

where U is the erosion/sedimentation rate (positive downward for sedimentation), a is the thermal diffusivity, and 

qQ is the undisturbed heat flow (De Rito and others, 1989;

Powell and others, 1988). At the Point Conception site, 

eroded Monterey Formation rocks form the land surface, 

and geologic and structural evidence points to the erosion 

of 600 to 1,200 m of material within the past 2 to 4 m.y. 

(Dibblee, 1950; Namson and Davis, 1990). With this range 

of erosion rates, equation (10) gives ratios of observed 

heat flow to undisturbed heat flow of 1.05 to 1.15. For the 

final estimated heat flow at Point Conception, a correction 

factor of 1.10 (equivalent to an erosion rate of 250 m/m.y. 

for 4 m.y.) was applied to the measured heat flow (table 

4). For the Orcutt Hill site, evidence from silica-phasechange boundaries (R. Pollastro, written commun., 1991), 

porosity data (Beyer and Isaacs, 1990) and stratigraphy 

(Curran and others, 1959) point to approximately 600 m of 

erosion in the past 2 to 4 m.y. The erosion rates at Orcutt 

Hill lead to disturbances which increase observed gradients by a factor of 1.04 to 1.09, and the final heat-flow 

estimate includes a correction of 1.06 (PL 12, table 4).

HEAT FLOW IN A REGIONAL CONTEXT

The high average heat flow in the Santa Maria province is consistent with measurements within the Coast 

Range heat-flow high and in marked contrast with the 

lower values southeast of the Transverse Ranges (fig. 18). 

The apparent thermal tie between the Santa Maria province and the Coast Ranges may be misleading, however, 

and the possible nature and sources of the high Santa 

Maria heat flow must be characterized before any genetic 

relationship is inferred.

The Coast Range high is generally attributed to the 

thermal effects of asthenospheric upwelling into the "slab 

gap" created by triple junction passage as subduction of 

the Farallon-Monterey-Arguello plate system ceased and 

the transform margin developed (Lachenbruch and Sass, 

1980; Zandt and Furlong, 1982). A possible additional factor in the Coast Range high is the thermal effect of shear 

heating along both transform faults and detachment surfaces within and beneath the San Andreas Fault system 

(Lachenbruch and Sass, 1992). Whatever the exact nature 

and magnitude of the sources for the high heat flow, the 

available evidence suggests that they are located primarily 

in the lower crust and (or) upper mantle (Williams and 

Lachenbruch, 1991). The contrasting-heat flow pattern in 

the Ventura basin reflects the unique tectonic regime of the 

central Transverse Ranges. As De Rito and others (1989) 

pointed out, the combined effects of rapid sedimentation 

and crustal thickening have overprinted any remaining 

thermal anomaly from earlier extension and basin formation. Although the relative roles of these two processes in 

lowering the near-surface heat flow are not well understood, the overall result is consistent with the deepening 

seismicity and thick crust found within the Transverse 

Ranges (Bryant and Jones, 1992).

The Thermal Regime of Santa Maria Province, California F19
In evaluating the thermal regime of the Santa Maria 

basin, the relevant concerns center on whether the 

observed high heat flow (1) reflects regional upper crustal 

disturbances (such as the migration of oil and gas), (2) 

arises from the remaining thermal effects of extension and 

basin formation, or (3) follows from the same lower crust/ 

upper mantle sources that give rise to the Coast Range 

high. Each of these possibilities can be examined through 

considering available information on structure, sedimentation, and tectonics.

Upper Crustal Disturbances

Among the processes that can have significant effects 

on the observed heat flow in basins are cooling due to sedimentation, refraction of heat due to thermal conductivity 

contrasts, and advection due to fluid migration. As mentioned above, rapid and (or) long-term sedimentation can 

significantly lower the observed geothermal gradient relative to the background value and lead to measurable 

changes in the variation of heat flow with depth. Although 

sediment thicknesses vary significantly across the Santa 

Maria basin (fig. 3), the approximate thermal effects of sedimentation can be evaluated through the use of the onedimensional analytical model given above. Over the 15+ 

m.y. of basin history, average sedimentation rates have varied in the range of 100 to 400 m/m.y., with rates on the 

order of 100 to 250 m/m.y. for the parts of the basin from 

which heat-flow data have been acquired. For these sedimentation rates, the ratio of observed near-surface heat flow 

to the background value is given by equation (10) as q$d 

#act=0.82 to 0.90. The effects of sediment dewatering will 

raise the true ratio closer to 1.0 (Hutchison, 1985). Similarly, the contrast in thermal conductivity between a sedimentary basin and the surrounding basement rocks can lead 

to refraction of heat around the basin and consequently a 

decrease in the observed heat flow relative to the background heat flow (Lachenbruch and Marshall, 1966). However, because the depth of the Santa Maria Basin is much 

less than its width (fig. 3) and because the basement thermal conductivity is likely to decrease with increasing temperature (Birch and Clark, 1940), the associated reduction 

in observed heat flow is likely to be less than 5 percent.

Oil and gas movement within basins can arise from 

buoyancy forces and sediment decompaction effects alone 

or take place within a regional flow system. In recent 

years, the locations of a number of oil fields have been

117°

Figure 18. Conductive heat flow (in milliwatts per meter squared) in Santa Maria province (solid 

squares), along with published heat-flow values for southern and central California (solid circles). 

Numbers with "A" are averages of two or more closely spaced measurements. Note consistency of 

Santa Maria province values with those in Coast Ranges. BPF, Big Pine Fault; CF, Carlock Fault; SAF, 

San Andreas Fault; SCF, San Gabriel Fault; SMF, Santa Monica Fault.

F20 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
tied to positive surface heat-flow anomalies, and these 

anomalies have been attributed to the upward flow of fluid 

in the subsurface (for example, Hitchon, 1984). Because 

the heat-flow measurements in the Santa Maria province 

were made exclusively in producing oil fields, it is possible that the thermal effects of petroleum migration within 

the reservoir rocks could be masking a lower value of 

background heat flow.

Lillis and King (1991), on the basis of structural, 

chemical, and physical properties data, have divided the 

reservoirs of the onshore Santa Maria basin into two age 

groups those older than 2 to 4 Ma (Guadalupe, Santa 

Maria Valley, and parts of Cat Canyon) and those younger 

than 2 to 4 Ma (Orcutt Hill and Lompoc). Although the 

relative structural ages of these traps correspond with the 

relative age of the entrapped oil (Lillis and King, 1991), 

the heat-flow data do not vary consistently between the 

two age groups (table 4 and fig. 18). An examination of 

the constraints on fluid flow within the Monterey Formation provides a ready explanation for this. Fractured reservoirs in the Monterey Formation are highly permeable 

(Regan and Hughes, 1949), but they are isolated from the 

regional ground-water system by the low permeability Sisquoc Formation and Foxen Mudstone. This leaves the 

Monterey as both the primary source and reservoir rock 

and limits most of the potential petroleum migration to 

less than 2 km vertically and 10 km laterally (fig. 3). 

Rapid sedimentation within the synclines will tend to 

lower the local geothermal gradient (see above), and 

petroleum moving updip will not introduce a large thermal 

anomaly unless the flow rates are large. For a 20 percent 

increase in the observed heat flow, the vertical component 

of fluid flow within the Monterey must be about 1 cm/yr 

(Bredehoeft and Papadopulos, 1965), a result which, given 

the low angle path the fluid must travel within the formation (fig. 3), requires a lateral flow rate of 5 to 10 cm/yr. 

This flow rate is large enough to sweep out the entire pore 

space of the Monterey (assuming 20 percent porosity) 

within 100,000 to 200,000 years, a time span inconsistent 

with the postulated age of reservoirs in the onshore Santa 

Maria basin.

In addition, as England and others (1991) pointed out, 

petroleum migration by buoyancy effects alone will be 

limited by the rate of petroleum generation, which is generally orders of magnitude smaller than the flow rates possible given an unlimited fluid supply, typical buoyant 

driving forces, and significant permeability. Compaction of 

the sediment column will also drive fluid up toward the 

surface as porosity decreases, but as mentioned above, the 

warming effects of sediment dewatering will be equaled or 

exceeded by the cooling effects of sedimentation. Given 

possible spatial and temporal focusing of both dewatering 

and petroleum migration, however, the only definite conclusion is that the available evidence is not consistent with 

a tie between deep fluid flow and measured heat flow.

Extension and Basin Formation

The formation of a sedimentary basin often involves 

the extensional thinning of some portion of the lithosphere. This thinning not only accounts for much of the 

subsequent basin subsidence but also leads to an increase 

in surface heat flow as hot material from depth is brought 

closer to the surface. In this case, the relevant question is 

whether the transient thermal effects of extension are augmenting the initial background heat flow and leading to a 

superficial thermal consistency between the Santa Maria 

province and the Coast Ranges.

For a small basin like the onshore Santa Maria, twodimensional numerical modeling is required to account for 

the precise quantitative effects of heterogeneous crustal 

structure, spatially variable extension, sedimentation, finite 

extension rates, and lateral heat losses (for example, Sawyer and others, 1987). These complications, however, tend 

to lower the predicted value of heat flow over time, so a 

maximum estimate of the thermal effects of extension can 

be derived from the use of the simpler one-dimensional 

analytical model of McKenzie (1978). In the McKenzie 

(1978) model, the relevant parameters are the age of 

extension, the initial lithospheric thickness (a) and the 

stretching factor (8). Extension and subsidence of the 

Santa Maria basin began approximately 18 Ma (McCrory 

and others, 1991; Stanley and others, 1991), and the available data (in particular the small size and limited thickness 

of the basin) suggest that the amount of stretching was 

small (less than 50 percent; Pitman and Andrews, 1985). 

This leaves the initial lithospheric thickness as the primary 

uncertainty.

Thermal models have identified triple junction migration and exposure of the North American plate to asthenospheric upwelling as the main causes of the Coast Ranges 

heat-flow high (Lachenbruch and Sass, 1980; Zandt and 

Furlong, 1982). These models predict lithospheric thicknesses on the order of 20 to 30 km in the wake of Mendocino triple junction passage, but they may not apply to the 

southern Coast Ranges and the Santa Maria province. 

Lonsdale (1991) and Fernandez and Hey (1992) have 

identified the stalled remains of a subducting microplate 

(Monterey) off the central California continental shelf, and 

recent seismic surveys have delineated what may be subducted oceanic crust under much of the Santa Maria province (for example, Trehu, 1991). If this portion of the crust 

is oceanic and not the product of magmatic underplating, 

the total lithospheric thickness at the time of basin formation would have been on the order of 50 to 60 km (Howie, 

in press).

The stretching factors appropriate to both these lithospheric thicknesses and the available data lie in the range 

of 6=1.1 to 1.5. The application of these values in McKenzie's (1978) model of extension and subsequent cooling is 

shown in figure 19 for heat flow normalized to its value

The Thermal Regime of Santa Maria Province, California F21
before the onset of extension. Given the 18-m.y. age of the 

onshore Santa Maria basin, the maximum present-day normalized heat flow is approximately 1.15. With an observed 

average heat flow of 84 mW/m2, this leaves an initial 

background value of 73 mW/m2. Given the complexities 

discussed above, the actual initial heat flow is likely to be 

much higher, a conclusion which suggests that the high 

heat flow of the Santa Maria province reflects crust and 

mantle processes unrelated to the thermal effects of basin 

formation.

Extrusive magmatism around the margins of the 

onshore Santa Maria basin at the time of basin formation 

(preserved at the Tranquillon and Obispo volcanics; Hall, 

1981) is unlikely to affect present-day heat flow. The volcanics are confined almost exclusively to the margins of 

the basin (McLean, 1991), and the thermal anomaly associated with elevated temperatures in the upper 10 km of

I

Q 1.25

5 10 15 20 25 

TIME, IN MILLIONS OF YEARS BEFORE PRESENT

HEAT FLOWLIZED 

^83

<?

cc 

o

Z 1.00 

0.75

8

B--B-- E3-S-{

o-o~o-o-^

3~&«-o

°-Q-.E

^ Q-e-e-Q

^^-1

G -o Beta = 1.1 

B -D Beta = 1.25 

v v Beta = 1.5

^:-S^

) 5 10 15 20 25 3

TIME, IN MILLIONS OF YEARS BEFORE PRESENT

Figure 19. A, Normalized heat flow for Santa Maria Province over time for one-dimensional extension using the 

model of McKenzie (1978) for an initial lithospheric thickness of 50 km and various values for stretching factor, ft. B, 

Normalized heat flow over time for an initial lithospheric 

thickness of 60 km.

the crust would have dissipated within a few million years 

(for example, Lachenbruch and Sass, 1980). If extensive 

magmatic underplating at depths of 20 km or greater was 

the source of the marginal extrusives, then magmatic 

sources could account for a portion of the observed high 

heat flow. However, the limited amount of extension associated with formation of the Santa Maria basin is inconsistent with extensive magmatic underplating (Howie, in 

press), a fact which suggests that a large portion of the 

high heat flow of the Santa Maria province reflects crust 

and mantle processes unrelated to the thermal effects of 

basin formation.

Consequently, the similarity of Santa Maria province 

heat-flow values to Coast Ranges heat-flow values probably 

does reflect a common thermal source. Given the complexity of the Miocene transition from a convergent margin to a 

transform margin, the poorly understood geometry of the 

stalled microplates, the subsequent variations through 

extensional, strike-slip and compressional tectonics, and the 

uncertain role of the plate boundary mechanical deformation in generating heat, the comprehensive modeling of the 

Santa Maria province and southern Coast Ranges heat flow 

is the appropriate subject of another paper. The basic result 

of importance here is that the thermal regime of the Santa 

Maria province is properly considered in a regional rather 

than local context. The thermal processes peculiar to the 

basins within the Santa Maria province are either easily 

corrected for or are minor compared to the thermal effects 

of regional tectonics. These effects must be understood and 

accounted for in any comprehensive understanding of the 

origin and migration of hydrocarbons within the Santa 

Maria province.

CONCLUSIONS

The results of heat-flow studies in the Santa Maria 

province not only demonstrate the viability of utilizing 

idle oil wells for investigating the thermal regime of 

sedimentary basins but also provide quantitative constraints on the thermal effects of sedimentary and tectonic processes.

Temperature measurements in the permeable Careaga 

Sandstone, Paso Robles Formation, and Orcutt Sand reveal 

the presence of an active ground-water flow system within 

the Santa Maria Valley (and possibly other nearby valleys). 

The ground-water flow depresses thermal gradients in the 

eastern part of the valley to nearly isothermal values, 

through the circulation of cold meteoric water to depths of 

400+ meters. This meteoric water then flows out across the 

basin and, with its passage, carries a great part of the background conductive heat flow into the ocean. Linear temperature profiles with high geothermal gradients are found 

below the ground-water system within the consolidated 

Monterey Formation, Sisquoc Formation, and Foxen MudF22 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
stone, and thermal conductivity measurements on cores and 

cuttings confirm that these high gradients are the result of 

high conductive heat flow. The thermal effects of topography, erosion, sedimentation, and the shallow ground-water 

system have been examined, and although there are measurable disturbances to the thermal field, the high heat flow 

(73 to 106 mW/m2) is apparently the product of regional 

thermal sources located at depth within the crust and mantle. This observation brings the Santa Maria province and 

western Ventura basin into the Coast Ranges heat-flow high 

and extends the southern limits of the Coast Ranges high 

down to the western Transverse Ranges and the Santa Barbara Channel.

The source of the Coast Ranges high has generally 

been identified and modeled as asthenospheric upwelling 

behind the Mendocino Triple Junction during its northward migration (for example, Lachenbruch and Sass, 

1980; Zandt and Furlong, 1982). These models predict a 

decrease in surface heat flow in the southern Coast Ranges 

owing to the passage of approximately 20 m.y. since the 

cessation of subduction, yet the Santa Maria measurements produce values as great as those commonly found 

in the northern Coast Ranges. In addition, plate tectonic 

reconstructions (Lonsdale, 1991; Fernandez and Hey, 

1991) and crustal structure studies (Trehu, 1991) in the 

Santa Maria province suggest that the subducting Farallon 

plate stalled beneath the Santa Maria province, leaving a 

substantial thickness of oceanic lithosphere between the 

asthenosphere and the shallow crust. These observations, 

together with the inconsistency of the observed heat flow 

with the triple junction models, suggest that the nature and 

causes of the Coast Ranges high are complex and varied. 

Even though the uniformity of the high heat flow suggests 

a common source, it may be that a number of processes 

associated with evolution of the transform margin (for 

example, asthenospheric upwelling, magmatic underplating, extension, and mechanical heating of the crust during 

deformation) have contributed to the fairly homogenous 

heat-flow pattern observed today.

REFERENCES

Atwater, Tanya, 1970, Implications of plate tectonics for the 

Cenozoic tectonic evolution of western North America: Geological Society of America Bulletin, v. 81, p. 3513-3536.

Beck, A.E., and Balling, Niels., 1988, Determination of virgin 

rock temperatures, in Haenel, R., Rybach, L., and Stegena, 

L., eds., Handbook of heat-flow density determinations: Kluwer, p. 59-86.

Benfield, A.E., 1947, A heat flow value for a well in California: 

American Journal of Science., v. 245, no. 1, p. 1-18.

Beyer, L.A., 1987, Porosity of unconsolidated sand, diatomite, and 

fractured shale reservoirs, South Belridge and West Cat Canyon oil fields, California, in Meyer, R.F., ed., Exploration for 

heavy crude oil and natural bitumen: American Association of 

Petroleum Geologists Studies in Geology, v. 25, p. 395-413.

Beyer, L.A., and Isaacs, C.M., 1990, Mass properties of conventional core samples from the Sisquoc, Monterey, and Point Sal 

formations, Unocal Newlove 51 well, Orcutt oil field, Santa 

Maria Basin, California: U.S. Geological Survey Open-File 

Report 90-14.

Beyer, L.A., Robbins, S.L., and Clutsom, F.G., 1985, Basic data 

and preliminary density and porosity profiles for twelve 

borehole gravity surveys made in the Los Angeles, San Joaquin, Santa Maria, and Ventura Basins, California: U.S. Geological Survey Open-File Report 85-42.

Birch, Francis, and Clark, Harry, 1940, The thermal conductivity 

of rocks and its dependence upon temperature and composition: American Journal of Science, v. 238, p. 529-558 and 

p. 613-635.

Bredehoeft, J.D., and Papadopulos, I.S., 1965, Rates of vertical 

groundwater movement estimated from the Earth's thermal 

profile: Water Resources Research, v. 1, no. 2, p. 325-328.

Bryant, A.S., and Jones, L.M., 1992, Anomalously deep crustal 

earthquakes in the Ventura Basin, southern California: Journal of Geophysical Research, v. 97, no. Bl, p. 437-447.

California Division of Oil and Gas, 1974, California oil and gas 

Fields, south, central coastal, and offshore California: California Division of Oil and Gas Report No. Trl2, v. 2.

Carslaw, H.S., and Jaeger, J.C., 1959, Conduction of heat in solids: Oxford, Clarendon, 510 p.

Grain, WE., Mero, WE., and Patterson, Don, 1985, Geology of 

the Point Arguello discovery: American Association of 

Petroleum Geologists Bulletin, v. 69, no. 4, p. 537-545.

Crawford, F.D., 1971, Petroleum potential of Santa Maria province, California, in Future petroleum provinces of the United 

States their geology and potential: American Association of 

Petroleum Geologists Memoir 15, p. 316-328.

Curran, J.F., chairman, and others, 1959, Correlation section 

across Santa Maria basin from Cretaceous outcrop in Santa 

Ynez Mountains northerly to Franciscan outcrop north of 

Santa Maria River, California: American Association of 

Petroleum Geologists Section 12.

De Rito, R.F., Lachenbruch, A.H., Moses, T.H., Jr., and Munroe, 

R.J., 1989, Heat flow and thermotectonic problems of the 

central Ventura basin, Southern California: Journal of Geophysical Research, v. 94, no. Bl, p. 681-699.

Dibblee, T.W, Jr., 1950, Geology of southwestern Santa Barbara 

County, California Point Arguello, Lompoc, Point Conception, Los Olivos, and Gaviota quadrangles: California Division of Mines and Geology Bulletin, v. 150, 95 p.

Diment, W.H., and Pratt, H.R., 1988, Thermal conductivity of 

some rock-forming minerals a tabulation: U.S. Geological 

Survey Open-File Report 88-690.

England, W.A., Mann, A.L., and Mann, D.M., 1991, Migration 

from source to trap, in Merrill, R.K., ed., Source and migration processes and evaluation techniques: Tulsa, American 

Association of Petroleum Geologists, p. 23-46.

Fernandez, L.E., and Hey, R.N., 1991, Late Tertiary tectonic evolution of the seafloor spreading system off the coast of California between the Mendocino and Murray fracture zones: 

Journal of Geophysical Research, v. 96, no. Bll, p. 17955- 

17979.

French, R.W., 1940, Geothermal gradients in California oil wells, 

in Drilling and production practice 1939: New York, 

American Petroleum Institute, p. 653-658.

The Thermal Regime of Santa Maria Province, California F23
Hall, C. A., Jr., 1981, San Luis Obispo transform fault and middle 

Miocene rotation of the Western Transverse Ranges, California: Journal of Geophysical Research, v. 86, no. B2, p. 1015- 

1031.

Heasler, H.P., and Surdam, R.C., 1985, Thermal evolution of 

coastal California with application to hydrocarbon maturation: American Association of Petroleum Geologists Bulletin, 

v. 69, no. 9, p. 1386-1400.

Heilbrunn-Tomson, Janice, 1988, A bibliography of the Santa 

Maria Province and vicinity, south central coastal California: 

U.S. Geological Survey Open-File Report 88-509.

Hitchon, Brian, 1984, Geothermal gradients, hydrodynamics and 

hydrocarbon occurrences, Alberta, Canada: American Association of Petroleum Geologists Bulletin, v. 68, p. 713-743.

Horai, Ki-iti, 1971, Thermal conductivity of rock-forming minerals: 

Journal of Geophysical Research, v. 76, no. 5, p. 1278-1308.

Howie, John, in press, Time transgressive evolution of the San 

Andreas Fault system in central California: Constraints from 

crustal structure: Geological Society of America Bulletin.

Hutchison, lan, 1985, The effects of sedimentation and compaction on oceanic heat flow: Geophysical Journal of the Royal 

Astronomical Society, v. 82, p. 439-459.

Isaacs, C.M., ed., 1981a, Guide to the Monterey Formation in the 

California coastal area, Ventura to San Luis Obispo: Pacific 

Section, American Association of Petroleum Geologists, 

v. 52, 83 p.

Isaacs, C.M., 198Ib, Porosity reduction during diagenesis of the 

Monterey Formation, Santa Barbara coastal area, California, 

in The Monterey Formation and related siliceous rocks of 

California: Society of Economic Paleontologists and Mineralogists, p. 257-271.

Isaacs, C.M., 1984, Geology and physical properties of the Monterey Formation, California: Society of Petroleum Engineering Proceedings, Paper 12733, p. 83-92.

Isaacs, C.M., Jackson, L.L., Stewart, K.C., and Scott, Norman, 

1989, Analytical reproducibility and abundances of major 

oxides, total carbon, organic carbon, and sedimentary components of Miocene and early Pliocene cuttings from the 

Point Conception deep stratigraphic test well, OCS-CAL 78- 

164 No. 1, offshore Santa Maria basin, southern California: 

U.S. Geological Survey Open-File Report 87-75.

Isaacs, C.M., Taggart, J.E., Jr., Jackson, L.L., and Scott, Norman, 

1989, Analytical reproducibility and abundances of major 

elements and sedimentary components in cores from the Sisquoc, Monterey, and Point Sal formations, Union Newlove 

51 well, Orcutt oil field, onshore Santa Maria Basin, California: U.S. Geological Survey Open-File Report 89-459.

Lachenbruch, A.H., and Brewer, M.C., 1959, Dissipation of the 

temperature effect of drilling a well in Arctic Alaska: U.S. 

Geological Survey Bulletin 1083C, p. 73-109.

Lachenbruch, A.H., Cladouhos, T.T., and Saltus, R.W., 1988, Permafrost temperature and the changing climate, in Senneset, 

K., ed., Permafrost, v. 3, International Conference on Permafrost, 5th: Trondheim, Norway, Tapir Publishers, p. 9-17.

Lachenbruch, A.H., and Marshall, B.V., 1966, Heat flow through 

the Arctic Ocean floor: the Canada Basin-Alpha Rise boundary: Journal Geophysical Research, v. 71, p. 1223-1248.

Lachenbruch, A.H., and Sass, J.H., 1980, Heat flow and energetics of the San Andreas Fault zone: Journal of Geophysical 

Research, v. 85, p. 6185-6223.

Lachenbruch, A.H., and Sass, J.H., 1992, Heat flow from Cajon 

Pass, fault strength, and tectonic implications: Journal of 

Geophysical Research, v. 97, p. 4995-5015.

Lachenbruch, A.H., Sass, J.H., and Galanis, S.P., Jr., 1985, Heat 

flow in southernmost California and the origin of the Salton 

Trough: Journal of Geophysical Research, v. 90, no. B7, 

p. 6709-6736.

Lillis, P.G., and King, J.D., 1991, Controls on the variation of crude 

oil quality, Santa Maria basin, California: American Association of Petroleum Geologists Bulletin, v. 75, no. 2, p. 372.

Lonsdale, Peter, 1991, Structural patterns of the Pacific floor offshore of peninsular California, in The Gulf and Peninsular 

province of the Californias: American Association of Petroleum Geologists Memoir, v. 47, p. 87-125.

MacKinnon, T. C., 1989, Origins of the Miocene Monterey Formation in California, in MacKinnon, T. C., ed., Oil in the 

California Monterey Formation, 28th International Geological Congress field trip guidebook T311: Washington, D.C., 

American Geophysical Union, p. 1-10.

McCrory, P.A., Arends, R.G., Ingle, J.C., Jr., Isaacs, C.M., Stanley, R.G., and Thorton, M.L.C., 1991, Geohistory analysis of 

the Santa Maria Basin, California, and its relationship to tectonic evolution of the continental margin: American Association of Petroleum Geologists Bulletin, v. 75, no. 2, p. 374.

McKenzie, Dan, 1978, Some remarks on the development of sedimentary basins: Earth and Planetary Science Letters, v. 40, 

p. 25-32.

McLean, Hugh, 1991, Distribution and juxtaposition of Mesozoic 

lithotectonic elements in the basement of the Santa Maria 

Basin, California: U.S. Geological Survey Bulletin 1995-B.

Miller, G.A., and Evenson, R.E., 1966, Utilization of ground 

water in the Santa Maria Valley area, California: U.S. Geological Survey Water Supply Paper 1819-A, p. 24.

Namson, Jay, and Davis, T.L., 1990, Late Cenozoic fold and 

thrust belt of the southern Coast Ranges and Santa Maria 

basin, California: American Association of Petroleum Geologists Bulletin, v. 74, no. 4, p. 467-492.

Nicholson, Craig, and Sorlien, C. C., Luyendyk, B.P., 1992, 

Deep crustal structure and tectonics in the offshore southern 

Santa Maria basin, California: Geology, v. 20, no. 3, p. 239- 

242.

Pitman, W.C., and Andrews, J.A., 1985, Subsidence and thermal 

history of small pull-apart basins, in Strike-slip deformation, 

basin formation, and sedimentation: Society of Economic 

Paleontologists and Mineralogist, Special Publication No. 37, 

p. 45-49.

Powell, W.G., Chapman, D.S., Balling, Niels, and Beck, A.E., 

1988, Continental heat-flow density, in Haenel, R., Rybach, 

L., and Stegena, L., eds., Handbook of heat-flow density 

determinations: Kluwer, p. 167-222.

Regan, L.J., and Hughes, A.W., 1949, Fractured reservoirs of 

Santa Maria District, California: American Association of 

Petroleum Geologists Bulletin, v. 33, no. 1, p. 32-51.

Saltus, R.W, and Lachenbruch, A.H., 1991, Thermal evolution of 

the Sierra Nevada: tectonic implications of new heat flow 

data: Tectonics, v. 10, no. 2, p. 325-344.

Sass, J.H., Kennelly, J.P., Jr., Smith, E.P., and Wendt, WE., 1984, 

Laboratory line-source methods for the measurement of thermal conductivity of rocks near room temperature: U.S. Geological Survey Open-File Report 86-468, p. 84-91.

F24 Evolution of Sedimentary Basins/Onshore Oil and Gas Investigations Santa Maria Province
Sass, J.H., Lachenbruch, A.H., and Munroe, R.J., 1971, Thermal 

conductivity of rocks from measurements on fragments and 

its application to heat flow determinations: Journal of Geophysical Research, v. 76, p. 3391-3401.

Sass, J.H., Lachenbruch, A.H., Munroe, R.J., Greene, G.W., and 

Moses, T.H., Jr., 1971, Heat flow in the western United 

States: Journal of Geophysical Research, v. 76, p. 6376- 

6413.

Sawyer, D.S., Hsui, A.T., and Toksoz, M.N., 1987, Extension, 

subsidence and thermal evolution of the Los Angeles Basin a 

two-dimensional model: Tectonophysics, v. 133, p. 15-32.

Stanley, R.G., and others, 1991, Age, correlation, and origin of 

the type Lospe Formation (lower Miocene), Santa Maria 

basin, central California: American Association of Petroleum 

Geologists Bulletin, v. 75, no. 2, p. 382.

Trehu, Anne, 1991, Tracing the subducted oceanic crust beneath 

the central California continental margin: results from ocean 

bottom seismometers deployed during the 1986 Pacific Gas 

and Electric EDGE experiment: Journal of Geophysical 

Research, v. 96, p. 6493-6506.

Turcotte, D.L., and Schubert, Gerald, 1982, Geodynamics applications of continuum physics to geological problems: New York, Wiley, 450 p.

Upson, J.E., and Thomasson, H.G., Jr., 1951, Geology and water 

resources of the Santa Ynez River Basin, Santa Barbara

County, California: U.S. Geological Survey Water Supply 

Paper 1107.

Vacquier, Victor, 1985, The measurement of thermal conductivity 

of solids with a transient linear heat source on the plane surface of a poorly conducting body: Earth and Planetary Science Letters, v. 74, p. 275-279.

Von Herzen, R.P., and Maxwell, A.E., 1959, The measurement of 

thermal conductivity of deep-sea sediments by needle probe 

methods: Journal of Geophysical Research, v. 64, p. 1557- 

1563.

Williams, C.F., and Lachenbruch, A.H., 1991, The San Andreas 

Fault geotherm revisited: Eos, v. 72, no. 44, p. 443.

Williams, C.F., and Narasimhan, T.N., 1989, Hydrogeologic constraints on heat flow along the San Andreas Fault a testing 

of hypotheses: Earth and Planetary Science Letters, v. 92, 

p. 131-143.

Woodring, W.P., and Bramlette, M.N., 1950, Geology and paleontology of the Santa Maria District, California: U.S. Geological Survey Professional Paper 222.

Worts, G.F., Jr., 1951, Geology and groundwater resources of the 

Santa Maria Valley area, California: U.S. Geological Survey 

Water Supply Paper 1000, 169 p.

Zandt, George, and Furlong, K.P., 1982, Evolution and thickness 

of the lithosphere beneath coastal California: Geology, v. 10, 

p. 376-381.

The Thermal Regime of Santa Maria Province, California F25

Chapter G

Phosphorus Geochemistry, Diagenesis,

and Mass Balances of the Miocene Monterey

Formation at Shell Beach, California

By GABRIEL M. FILIPPELLI and MARGARET L. DELANEY

U.S. GEOLOGICAL SURVEY BULLETIN 1995

EVOLUTION OF SEDIMENTARY BASINS/ONSHORE OIL AND GAS INVESTIGATIONSSANTA MARIA PROVINCE

Edited by Margaret A. Keller
CONTENTS

Abstract Cl 

Introduction Gl

Acknowledgments G3 

Methods G3 

Results and discussion G5 

Conclusion G10 

References G10

FIGURES

1. Reconstruction of onshore and offshore Neogene paleobasins along south-central 

California coast, showing field area at Shell Beach in Pismo basin and location of 

Exxon Hondo Well B G2

2. Schematic columnar section for portion of Monterey Formation exposed at Shell 

Beach, California, including portion of Shell Beach section studied here G3

3. Phosphorus concentration results from metaborate/tetraborate fusion with determination by X-ray fluorescence fusion versus values determined by five-step sequential extraction for 10 samples from Exxon Hondo Well B G4

4. Phosphorus concentration versus sequential-extraction steps for three samples from 

Shell Beach dolomite, porcellanite, and phosphatic shale G5

5. Stratigraphic height in meters from base of section shown in figure 2 versus phosphorus concentrations G7

6. Phosphorus concentrations extracted using standard extraction procedure and same 

procedure with an extra buffered acetic-acid wash during extraction step that releases reactive P G9

7. Reactive phosphorus versus unreactive phosphorus in phosphatic shales and dolomitic and siliceous lithdlogies from Shell Beach G9

TABLES

1. Sample descriptions and phosphorus concentrations from Shell Beach, California 

(Miocene Monterey Formation) G6

2. Mean phosphorus (P) concentrations and error estimates for lithologies, P components, and fades at Shell Beach G8
Phosphorus Geochemistry, Diagenesis, and

Mass Balances of the Miocene Monterey Formation

at Shell Beach, California

By Gabriel M. Filippelli 1 and Margaret L. Delaney2

Abstract

Continental margins can be important areas of oceanic 

phosphorus (P) accumulation, especially given diagenetic 

reactions that transform organic P in sediments to authigenic 

P by phosphogenesis in continental margin deposits with high 

organic productivity like the Miocene Monterey Formation of 

California. To determine P concentrations and P stratigraphy, 

we tested a five-step sequential-extraction technique, which 

differentiates five sedimentary P-bearing components, for 

application to a well-dated Miocene phosphatic sequence at 

Shell Beach, California. The lower facies at the Shell Beach 

section (upper part of the phosphatic facies) is interbedded 

calcareous and laminated phosphatic shale, and the upper 

facies (lower part of the siliceous facies) is interbedded siliceous and laminated phosphatic shale with rare calcareous 

strata. We sampled from the entire exposure of the phosphatic 

facies (75 m) and the lower third (62 m) of the siliceous facies, 

as exposed in the Shell Beach section. Sequential-extraction 

results revealed that greater than 95 percent of P in these strata 

occurs as reactive P (Pr; as authigenic and biogenic sedimentary components) and unreactive P (Pur; as detritally associated sedimentary components). Less than 5 percent of P 

occurs as a combination of loosely bound, iron-bound, and 

organic P. Organic matter predominates as the main carrier of 

P to modern continental margin sediments; therefore, our 

extraction results indicate that extensive reorganization of P 

between sedimentary components has occurred at Shell 

Beach, presumably as a result of phosphogenesis.

On the basis of optimization experiments with these sedimentary rock samples, we used a two-step modification of 

Ruttenberg's (1990, 1992) procedure to determine Pr and Pur 

Shales at Shell Beach generally have higher P concentrations 

than other lithologies (for example, dolomitic and siliceous 

strata). Pr concentrations range from 0.01 to 0.27 weight per1Earth Sciences Board and Institute of Marine Sciences, University 

of California, Santa Cruz, CA 95064.

Institute of Marine Sciences, University of California, Santa Cruz, 

CA 95064.

Manuscript approved for publication, June 21,1994.

cent (wt pet) P in dolomitic and siliceous strata and from 0.34 

to 2.10 wt pet P in phosphatic shales. Pur concentrations range 

from 0.00 to 0.08 wt pet P in dolomitic and siliceous strata 

and from 0.02 to 2.50 wt pet P in phosphatic shales. Total P 

(PT) concentrations (Pr+Pur) range from 0.02 to 0.42 wt pet P 

in dolomitic and siliceous strata and from 0.36 to 3.90 wt pet 

P in phosphatic shales. Mean Pr concentrations in shales of the 

siliceous facies (1.41±0.35 wt pet P) are slightly higher than 

those of the phosphatic facies (0.98±0.21 wt pet P), mean Pur 

concentrations in shales of the siliceous facies (1.21±0.52 wt 

pet P) are higher than those of the phosphatic facies (0.48±0.40 

wt pet P), and mean Pj concentrations in shales of the siliceous 

facies (2.62±0.73 wt pet P) are higher than those of the phosphatic facies (1.46±0.41 wt pet P).

We calculated the weighted mean P concentrations, taking into account the mean P concentration in each lithologic 

type and the thickness of the section occupied by that lithology. The phosphatic facies has a higher mean PT concentration (1.09±0.31 wt pet P) than the siliceous facies (0.66+0.22 

wt pet P). Although shales of the siliceous facies have a higher 

mean P concentration than those of the phosphatic facies, the 

dominance of shales in the phosphatic facies results in it having higher mean P concentrations than the siliceous facies.

Determining the dominant P-bearing components that 

reflect a variety of depositional and postdepositional processes 

has important implications for understanding P diagenesis and 

burial in a continental margin setting with high organic productivity. The high PT concentrations observed for phosphatic 

shale strata from Shell Beach, which are minimum estimates, 

indicate that most of the P is probably retained and argue for 

redistribution of P from organically bound P to other forms 

after burial. High authigenic/biogenic P concentrations indicates that phosphogenesis plays an important role in the conversion of organic P to CFA (the authigenic mineral carbonate 

fluorapatite), and the correlation between Pr and Pur in phosphatic shales from Shell Beach indicates that there may be 

additional post-phosphogenesis transformations of P, which 

need to be investigated.

INTRODUCTION

Quantifying the reservoirs and fluxes in the marine 

phosphorus (P) cycle is important because P, in the form of

Phosphorus Geochemistry, Diagenesis, and Mass Balances of the Miocene Monterey Formation at Shell Beach, California G1
dissolved phosphate, is an essential limiting nutrient for 

primary organic productivity. The marine phosphorus (P) 

cycle has been the subject of a number of studies (for 

example, Froelich and others, 1982; Froelich, 1984, 1988; 

Mach and others, 1987; Baturin, 1988; Ruttenberg, 1990). 

The main input of phosphate into the ocean is from rivers, 

and the sole output is burial in continental-margin and 

deep-sea sediments in various forms (Froelich, 1984, 1988; 

Ruttenberg, 1990; Ruttenberg and Berner, 1993). Phosphorus enters the ocean system in two forms dissolved (or 

reactive) and detrital (or unreactive). Dissolved phosphate 

is mostly taken up by microorganisms during surface productivity and is transported to sediments in the form of 

organic matter, with a small fraction of what is produced 

being buried. Unreactive phosphorus is associated with 

detrital grains. Recent work on the kinetics of P mobility 

shows that detrital-P phases are refractory in the marine 

environment and do not exchange with the oceanic dissolved-P reservoir (Froelich, 1988; Ruttenberg, 1990; Ruttenberg and Berner, 1993). Although continental margin 

sediments may receive the majority of the total riverine-P 

flux (including reactive and unreactive forms) (Baturin, 

1988), the rate of removal of reactive/dissolved P from the 

oceanic P reservoir is roughly equal in continental margin 

and deep sea sediments (Froelich and others, 1982). Reactive-P fluxes to continental margin sediments are especially 

high beneath areas of high productivity (for example, Peru 

margin, Namibian shelf; Baturin, 1972; Burnett and others, 

1982; Froelich and others, 1988). High organic-matter rain 

rates and accompanying organic matter regeneration in sediments beneath these areas can lead to elevated pore-water 

phosphate concentrations, which in turn can drive phosphogenesis (authigenic precipitation of solid P-bearing mineral 

phases, mainly carbonate fluorapatite (CFA)) in near-surface sediments (Burnett, 1977; Sheldon, 1981; Kolodny, 

1983). Phosphogenesis effectively "locks" P into the sediments, leading to its removal from the oceanic system. 

Continental margin sediments are presently important areas 

of marine P accumulation, as they were in ancient oceans 

as well (Filippelli and Delaney, 1992), and these accumulations provide an opportunity to examine variations in P 

diagenesis and burial in detail.

Changes in oceanic circulation, surface biological productivity distribution, and biogenic sedimentation during 

the Miocene are reflected in changing continental margin 

sediment compositions. The accumulation of organic carbon-rich, and presumably P-rich, sediments in low-oxygen 

basins is thought to have resulted in the positive shift in the 

oceanic carbon-isotope record during the middle Miocene 

(Vincent and Berger, 1985; Compton, Snyder, and Hodell, 

1990). Phosphatic sedimentary rocks of Miocene age are 

widely distributed. Notable examples are the phosphatic 

sands of the Hawthorn and Pungo River Formations in the 

southeastern United States (Riggs, 1984; Riggs and Sheldon, 1990; Snyder and others, 1990; Compton, Snyder, and

Hodell, 1990; Compton, Hodell, Garrido, and Mallinson, 

1993) and the Monterey Formation of California (Pisciotto 

and Garrison, 1981; Garrison, Kastner, and Kolodny, 1987; 

Garrison, Kastner, and Reimers, 1990). The Monterey Formation was mainly deposited in marginal fault-bounded 

basins which developed since the Oligocene as transtensional basins along the San Andreas Fault system (Blake 

and others, 1978; Howell and others, 1980; Graham, 1987). 

The general depositional facies of the Monterey Formation, 

characterized by the succession of calcareous, phosphatic, 

and siliceous rocks (fig. 1), are wide-spread and have been 

recognized and described by many workers (Canfield, 

1939; Woodring and others, 1943; Woodring and Bramlette, 

1950; Isaacs, 1980, 1984; Pisciotto, 1978, 1981; Pisciotto 

and Garrison, 1981). However, characteristic lithologies do 

not occur in all locations, facies transitions do not occur 

simultaneously in California continental-borderland basins, 

and the terminology used and subdivisions assigned differ 

between different studies and for different localities. We 

chose the informal nomenclature of Pisciotto (1978, 1981), 

as it best describes the lithotypes encountered in our study 

(lower calcareous facies, middle phosphatic facies, and 

upper siliceous facies; only the upper part of the phosphatic 

facies and siliceous facies are present in our study area at 

Shell Beach). The Monterey Formation is an excellent 

record of changing continental margin deposition, recording calcareous deposition during the early middle Miocene

Figure 1. Reconstruction of onshore and offshore Neogene 

paleobasins (stippled area) along south-central California 

coast, showing field area for this study at Shell Beach in 

Pismo basin and location of Exxon Hondo Well B (after Garrison, Katner, and Kolodny, 1987).

G2 Evolution of Sedimentary Basins Santa Maria Province
(calcareous fades), a transitional period of calcareous and 

abundant phosphatic deposition during the middle Miocene 

(phosphatic facies), and mainly siliceous deposition during 

the late middle Miocene (siliceous facies). The calcareous 

and phosphatic facies have been interpreted as corresponding to warm oceanic conditions with relatively sluggish 

oceanic circulation and the siliceous facies to the development of polar glaciation, cold-water upwelling, higher 

nutrient levels, and higher organic matter productivity 

(Ingle, 1981; Pisciotto and Garrison, 1981; Barron and 

Keller, 1983; Garrison, Kastner, and Reimers, 1990).

The phosphatic sedimentary rocks in the Shell Beach 

section of the Monterey Formation, exposed in seacliffs 

about 15 km south of San Luis Obispo on the central California coast (fig. 1), were deposited in the Pismo basin 

during the middle Miocene (Omarzai, 1992). The Shell 

Beach section includes part of the phosphatic and siliceous 

facies of the Monterey Formation (fig. 2) and consists of 

calcareous-rich phosphatic mudrocks, marlstones, and 

shales (dark, laminated, and organic rich with thin (0.5-10 

mm), white, discontinuous laminae and micronodules of 

CFA) interbedded mainly with dolomites in the phosphatic 

facies and mainly with siliceous mudstones, porcellanites, 

and cherts in the siliceous facies. The 290 m of section at 

Shell Beach begins in the phosphatic facies at 15.2 Ma, is 

interrupted by a period of nondeposition from 14.3 to 13.25

Pismo Fm.

c

0

CO

E

o 

u.

0>

Q>

C

o

5

w

o

o

CO

0)

0

o 

o

~

£ W

Q.

Obispo Fm.

Height 

(m)

-300- 

-250-

-200-

-150-

-100-

-50 -

V

S

s

s 

s

Sampling range 

of this study

X

x

Figure 2. Schematic columnar section for portion of Monterey Formation exposed at Shell Beach, 

California (after Omarzai, 1992), 

including portion of Shell Beach 

section studied here.

Ma marked by phosphatic hardgrounds, and continues with 

the siliceous facies from 13.25 Ma to the top of the section 

at approximately 11.0 to 11.4 Ma (Omarzai (1992), on the 

basis of magnetic age model of Harland and others (1982)). 

This study focused on the interval from 15.2 Ma (0 meters 

stratigraphic height in the field section) to the 14.3-Ma base 

of the phosphatic hardgrounds (75 meters stratigraphic 

height), and the interval from the top of the phosphatic 

hardgrounds at 13.25 Ma to 12.85 Ma (137 meters stratigraphic height). Average lithologic abundances by thickness for the section studied here are 73 percent phosphatic 

shale and 27 percent dolomitic strata in the phosphatic 

facies and 20 percent phosphatic shale and 80 percent siliceous strata in the siliceous facies (Omarzai, 1992). Mean 

sedimentation rates are 88 m/m.y. for the interval of the 

phosphatic facies and 154 m/m.y. for the interval of the 

siliceous facies studied here (Omarzai, 1992).

Acknowledgments

We thank the Department of Defense (National Defense 

Science and Engineering Graduate Fellowship to Gabriel 

Filippelli), the National Science Foundation (grant OCE89- 

11530 to Margaret Delaney), and the University of California, Santa Cruz, Earth Sciences Board (Research grant to 

Gabriel Filippelli) for support of this research. We thank 

Robert Garrison, Caroline Isaacs, Margaret Keller, Casey 

Moore, Ken Bruland, Flip Froelich, Kathleen Ruttenberg, 

Sally Catlin, Sheraz Omarzai, and Laura Linn for valuable 

discussions. We also thank Rob Franks and the University of 

California, Santa Cruz, Institute of Marine Sciences Marine 

Analytical Laboratory for technical assistance and advice, 

and Suzanne Ware and Emily Oatney for careful and diligent 

assistance with sample preparation and analysis. Caroline 

Isaacs graciously donated samples from Exxon Hondo Well 

B for correlation of P results, and we acknowledge Exxon 

for the samples and permission to report the results of the P 

determinations. Margaret Keller provided helpful comments 

and excellent editorial handling. Reviews by Caroline Isaacs 

and David Piper greatly improved the content and clarity of 

this paper.

METHODS

Samples were collected at low tide using a rock hammer, and sample positions were correlated to the stratigraphic column of Omarzai (1992). Sample sizes ranged 

from about 2 to 100 cm3 . Sampling focused on the phosphatic shale in both facies, which was assumed to contain a 

majority of the P in this section; a few samples were taken 

from dolomitic, siliceous, and tuffaceous strata as well. 

Samples were rinsed with deionized water to remove surface salts, dried at 60°C, and ground, first in a mechanical

Phosphorus Geochemistry, Diagenesis, and Mass Balances of the Miocene Monterey Formation at Shell Beach, California G3
agate mortar and pestle grinder and then by hand in a 

ceramic mortar and pestle. The samples were ground to 120 

mesh (125 (im) and passed through a clean metal sieve. The 

samples were sieved frequently during grinding into a 

metal collection dish to ensure that particle size remained 

consistent and that the sample was not ground too finely for 

the chemical extraction procedure. After grinding, samples 

were stored in 22 mL glass scintillation vials.

The chemical sequential-extraction technique used in 

this study was based on that developed by Ruttenberg (1990, 

1992) for the determination of P concentrations in different 

P-bearing phases in modern sediments. This sequentialextraction technique uses the solubility differences of five 

sedimentary P-bearing phases by treating the sample powder 

with various complexing, reducing, and acidic solutions to 

separate different P fractions (loosely bound or adsorbed, 

iron oxides and oxyhydroxides, authigenic and biogenic 

minerals, and organic matter, all of which are reactive, and 

detrital phases, which are unreactive). This technique, which 

distinguishes five forms of sedimentary P with different 

geochemical significance, is an improvement over methods 

that distinguish only inorganic and organic forms of P (for 

example, Aspila, X-ray fluorescence (XRF) fusion), where 

inorganic forms include some reactive P and some unreactive P. There have been criticisms of sequential-leaching 

extraction techniques (see Nirel and Morel (1991) for discussion), because the determined components are operationally defined and the results require careful interpretation, 

owing to the limitations and assumptions of the particular 

technique. Ruttenberg (1990, 1992) carefully optimized her 

procedure by using model mineral phases along with evaluation of optimal reagent concentrations and leaching times. 

Her procedure yielded total P values (the sum of the P 

components) comparable to total P values determined by 

other methods (for example, Aspila, XRF fusion; Ruttenberg, 1990,1992).

The Monterey Formation rocks at Shell Beach have 

undergone widespread diagenesis due both to the near-seafloor authigenic precipitation of CFA and to compaction 

and porosity reduction of all strata. Therefore, P distributions in these rocks may differ substantially from those in 

modern sediments, for which the five-step sequentialextraction technique was developed. To test the efficiency 

of the five-step sequential extraction technique for determining P concentrations in diagenetically altered lithologies (Ruttenberg, 1990, 1992), we compared the sum of the 

five P components for 10 samples from Exxon Hondo Well 

B (fig. 1) (with lithologies similar to those encountered at 

Shell Beach) to P determinations on the same samples 

using the standard total P analyses (metaborate/tetraborate 

fusion with determination by XRF) presented in Isaacs and 

others (1992). The sequential extraction P results agreed 

closely with the XRF fusion P results (fig. 3). Sequential 

extraction total P results are consistently slightly lower than 

total P results determined by XRF fusion, a condition

which may be the result of an uncorrected blank in the XRF 

determinations (possibly indicated by the nonzero intercept 

of the regression line) or of a greater efficiency of the 

fusion technique in extracting P from more refractory mineral phases. Nevertheless, the two different techniques yield 

comparable P results, supporting the accuracy of total P 

measurements determined by the sequential-extraction 

technique.

To evaluate the significance of the different P-bearing 

components in samples from Shell Beach, we analyzed 

three Shell Beach samples representing a range of lithologies (phosphatic shale, porcellanite, and dolomite) and total 

weight percent (wt pet) P. Phosphorus concentrations associated with adsorbed P, iron-bound P, and organic P were 

low compared to authigenic/biogenic P and detrital P 

(fig. 4). Greater than 95 percent of the P in each sample was 

present as authigenic/biogenic and detrital P components, 

as compared to about 70 to 80 percent in typical deep sea 

sediments (Ruttenberg and Berner, 1993). This difference is 

due both to extensive phosphogenesis (enriching the sediment in authigenic/biogenic P forms) and a relatively close 

proximity of the Shell Beach sediments during deposition 

to detrital sources. Owing to the diagenetic changes in these

o

ex

0.8

0.6

0.4

0.2

0.0

0.0 0.2 0.4 0.6 0.8

Wt pet P (sequential extraction)

Figure 3. Phosphorus concentration (weight percent (wt pet)) 

results from metaborate/tetraborate fusion with determination 

by X-ray fluorescence (XRF) fusion (data from Isaacs and others, 1992) versus values determined by five-step sequential 

extraction (total of all steps) for 10 samples from Exxon 

Hondo Well B. These results show that these two techniques 

yield comparable total phosphorus concentration values, 

with a linear regression slope of 1.07±0.10, an intercept of 

0.03±0.04 (both at 95-percent confidence level on calculated slope and intercept), and an r2 of 0.982 (correlation 

significant at greater than 99-percent confidence level).

G4 Evolution of Sedimentary Basins Santa Maria Province
rocks, P concentrations of the less abundant P-bearing 

phases probably do not reflect original depositional conditions and may only be useful for understanding long-term P 

diagenesis. We, therefore, streamlined Ruttenberg's (1990, 

1992) technique to a two-step sequential extraction, which 

isolated reactive P components (Pp equivalent to the sum of 

adsorbed, iron-bound, and authigenic/ biogenic P) and 

unreactive P components (Pup detrital P). Organic-P forms 

(a relatively insignificant portion of total P in all samples) 

are not released in this modified extraction scheme.

In the first step of our modified extraction technique, 

which isolates reactive P (Pr), 0.5 g of ground sample was 

placed in a 50-mL polyethylene centrifuge tube. There were 

four sequential sample treatments: (1) solid treated with 50 

mL of 1.5 molar Na-acetate solution buffered to pH 4 with 

acetic acid and shaken on an orbital shaker for 6 hours, (2) 

solid treated with 50 mL of 1 molar MgCl2 and shaken for 

two hours, (3) solid treated again as in treatment (2), and 

(4) solid treated with 50 mL of glass-distilled water and 

shaken for 2 hours. After each treatment, samples were centrifuged for 10 minutes, and a known volume (10 mL) of 

the homogeneous supernatant was transferred with a pipette

1.4

0.8

0.6

0.4

0.2

0.0

n

I II III IV V I II III IV V I II III IV V

Dolomite Porcellanite Phosphatic shale 

(£ Wt pct=0.096) (£ Wt pct=0.553) (£ Wt pct=2.25)

Figure 4. Phosphorus concentration (weight percent (wt pet)) 

versus sequential-extraction steps for three samples from 

Shell Beach dolomite, porcellanite, and phosphatic shale. 

Note scale break in y-axis. Extraction steps on x-axis are I, 

adsorbed P; II, iron-bound P; III, authigenic/biogenic P; IV, 

detritally associated P, and V, organic P. Plot shows that 

almost all P (greater than 95 percent) determined for these 

samples occurs as authigenic/biogenic P and detritally associated P.

to an acid-cleaned polyethylene bottle, combining the 

supernatants from all four treatments for sample P determinations. The remainders of the supernatants were discarded. 

This step releases adsorbed P, iron-bound P, and authigenic/ 

biogenic P from the sample. All of these P forms are reactive in the oceanic system, and we call the sum of them Pr 

in this study. In the second step of the extraction, 50 mL of 

1 N HC1 was added to the residual sample and the sample 

was shaken for 16 hours. The sample was centrifuged and 

supernatant collected as above for P determinations. This 

step releases detrital P forms, which are unreactive in the 

oceanic system and which we call PUP from the sample.

Phosphorus concentration determinations in extraction 

solutes were performed with the standard molybdate blue 

acetic-acid method (Strickland and Parsons, 1972) using a 

Shimadzu UV-2101 PC UV-VIS scanning spectrophotometer at 885 nm, with the Sipper 260 autosipper attachment 

and the Shimadzu computer interface program for absorption determinations and concentration calculations. Because 

of their high P concentrations, samples were commonly 

diluted by a factor of 100 to 1,000 with glass-distilled water 

before analysis, and P standards were prepared in glassdistilled water, as the high dilution factors resulted in no 

significant sample-matrix effect.

Relative errors on solid sample splits were from 1 to 

20 percent (typically about 6 percent). Relative errors on 

solution replicates ranged from 0 to 5 percent (typically 

about 2 percent). Dilution of sample solutions (100 to 

1000 times with glass-distilled water) before analysis was 

adjusted to yield high signal to noise ratios, resulting in a 

low detection limit (typically about 0.0005 wt pet P).

RESULTS AND DISCUSSION

Phosphorus concentrations and standard deviations for 

the 35 samples analyzed in this study are presented in 

table 1 and figure 5. Phosphorus concentrations for the 

reactive component (Pr) ranged from 0.005 to 2.41 wt pet P 

(equivalent to 0.01 to 5.5 wt pet P2O5) for all samples 

(table 1; fig. 5). Shale samples generally had relatively high 

reactive P concentrations, ranging from 0.339 to 2.12 wt 

pet P. Dolomitic, siliceous, and tuffaceous samples had relatively low P concentrations, ranging from 0.050 to 0.271 

wt pet P. The phosphatic hardground, formed during a 1- 

m.y. hiatus, had the highest Pr observed (2.41 wt pet P); on 

the basis of the presence of reworked and extensively bored 

phosphatic clasts and nodules, this hardground probably 

represents a winnowed, phosphatized sedimentary layer. 

Standard deviations (la) for replicate P determinations on 

solid samples ranged from ±0.00 to ±0.21 wt pet P, with an 

average error of about ±0.04 wt pet P (equivalent to ±5 

percent relative error).

Phosphorus concentrations for the unreactive component (Pur) ranged from 0.001 to 2.48 wt pet P (equivalent

Phosphorus Geochemistry, Diagenesis, and Mass Balances of the Miocene Monterey Formation at Shell Beach, California G5
Table 1. Sample descriptions and phosphorus (P) concentrations from Shell Beach, California (Miocene Monterey Formation)

[--, value not determined or indeterminable; wt pet, weight percent; s.d., standard deviation]

Height1 

(m)

137

135

132

130

121

118

116

115

110

110

109

108

105

104

86

78

75

74

57

53

52

40

36

25

24

21

20

10

9

7

5

4

3

2

1

Description

Siliceous

Siliceous

Siliceous

Siliceous

Siliceous

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Siliceous

Phosphatic shale

Siliceous

Phosphatic shale

Phosphatic shale

Hardground

Phosphatic shale

Phosphatic shale

Dolomite

Phosphatic shale

Dolomite

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Phosphatic shale

Dolomite

Phosphatic shale

Dolomite

Phosphatic shale

Phosphatic shale

Tuff

AGE* 

(Ma)

12.85

12.86

12.88

12.89

12.95

12.97

12.98

12.99

13.02

13.02

13.03

13.04

13.06

13.06

13.18

13.23

-

14.31

14.50

14.55

14.56

14.70

14.74

14.87

14.88

14.91

14.92

15.04

15.05

15.07

15.09

15.10

15.12

15.13

15.14

Reactive phosphorus

Wtpct3

0.018

0.047

0.050

0.020

0.151

0.564

1.75

1.63

1.03

2.12

2.05

0.227

1.15

0.271

0.997

1.42

2.41

1.58

1.39

0.063

0.472

0.055

1.36

1.21

1.16

1.19

0.862

1.07

0.758

0.049

0.864

0.112

0.497

0.339

0.005

S.d.4

0.001

0.001

0.000

0.001

0.004

0.025

0.205

0.050

0.025

0.053

0.015

0.008

0.030

0.023

0.040

0.070

0.061

0.032

0.051

0.002

0.027

0.005

0.057

0.094

0.017

0.063

0.015

0.087

0.078

0.008

0.121

0.002

0.013

0.012

0.000

Unreactive phosphorus

Wtpct

0.002

0.006

0.016

0.001

0.270

0.380

1.22

0.880

0.145

1.68

1.05

0.020

2.20

0.079

0.816

2.48

5.93

1.23

0.712

0.013

0.058

0.015

0.323

0.980

0.889

0.566

0.614

0.427

0.330

0.013

0.046

0.019

0.037

0.015

0.020

S.d.

0.000

0.000

0.001

0.000

0.033

0.031

0.142

0.031

0.003

0.105

0.003

0.000

0.029

0.009

0.007

0.033

0.204

0.029

0.028

0.001

0.003

0.003

0.007

0.130

0.011

0.027

0.017

0.032

0.020

0.002

0.021

0.000

0.009

0.000

0.003

Total phosphorus 

Wt pet S.d.3

0.020

0.053

0.066

0.021

0.421

0.944

2.97

2.51

1.18

3.80

3.10

0.247

3.35

0.350

1.81

3.90

8.34

2.81

2.10

0.076

0.530

0.070

1.68

2.20

2.05

1.76

1.48

1.50

1.09

0.062

0.910

0.131

0.534

0.354

0.025

0.001

0.001

0.001

0.001

0.033

0.040

0.249

0.059

0.025

0.118

0.015

0.008

0.042

0.025

0.041

0.077

0.213

0.043

0.058

0.002

0.027

0.006

0.057

0.160

0.023

0.069

0.023

0.093

0.081

0.008

0.123

0.002

0.016

0.012

0.003

Stratigraphic height in meters from base of section shown in figure 2.

Detennined from our measured stratigraphic height in section shown in figure 2 and the age model of Omarzai (1992), 

assuming linear sedimentation rates between age control points. Ages are reported to the ten-thousand-year level for age 

comparison between samples only and are not meant to represent true accuracy or precision of age determinations.

Wt pet P results as mean value for two solid sample replicates.

Standard deviation as la deviation from mean value of wt pet P determined for two solid sample replicates.

Standard deviation is 2aA/n error of reactive phosphorus and unreactive phosphorus propogated through calculations.

G6 Evolution of Sedimentary Basins Santa Maria Province
to 0.002 to 5.68 wt pet P2O5), with the phosphatic hardground sample having 5.93 wt pet P (13.6 wt pet ?2O5 ; 

table 1; fig. 5). Standard deviations (la) for replicate P 

determinations on solid samples ranged from ±0.000 to 

±0.20 wt pet P (±8 percent relative error). As with Pp 

higher Pur concentrations were generally found for phosphatic shales (from 0.015 to 2.48 wt pet P) and lower Pur 

concentrations tended to be from dolomitic, siliceous, and 

tuffaceous samples (from 0.002 to 0.27 wt pet P) although 

there was some overlap in values.

Phosphorus concentrations for the sum of both components (PT) ranged from 0.025 to 3.90 wt pet P, with the 

phosphatic hardground sample having 8.34 wt pet P (table 

1; fig. 5). Standard deviations (la) ranged from ±0.001 to 

±0.249 wt pet P (±5 percent relative error).

The mean Pr concentration for shales in the siliceous 

facies was 1.41±0.34 wt pet, and that for shales of the 

phosphatic facies was 0.98±0.21 wt pet (table 2). The 

mean Pr concentration for siliceous strata of the siliceous 

facies was 0.11 ±0.08 wt pet P, and for the mainly dolomitic strata of the phosphatic facies was 0.06±0.03 wt pet 

(table 2). For the entire Shell Beach section, the mean Pr 

concentration in shale strata was 1.16±0.20 wt pet P and 

in other strata was 0.09±0.05 wt pet P. This observation 

indicates that shale strata generally contain much more Pr 

than dolomitic or siliceous strata.

Mean Pm concentrations in shales of the siliceous 

facies (1.21±0.52 wt pet) are generally higher than in

shales of the phosphatic facies (0.48±0.22 wt pet; table 2), 

though there is some overlap. Mean Pur concentrations in 

the siliceous strata of the siliceous facies was 0.06±0.07 

wt pet P and in the mainly dolomitic strata of the phosphatic facies was 0.016+0.003 wt pet (table 2). For the 

entire Shell Beach section, the mean Pur concentration in 

shale strata was 0.78±0.28 wt pet P and in other strata was 

0.04±0.07 wt pet P. This observation indicates that shale 

strata generally contain much more Pw than dolomitic or 

siliceous strata (assuming linear and equivalent sedimentation rates for these lithotypes; see Filippelli and others 

(1994) for discussion).

Compared to the terrigenous-flux calculations of 

Isaacs and others (1992) for other Monterey Formation 

deposits, PU,. concentrations in some samples from this 

study were higher than expected, if these concentrations 

record only detrital influx. To examine whether the extraction technique completely dissolved Pr components (an 

incomplete dissolution of this component would lead to 

apparently high Pur values), we compared our results to P 

concentration results for a small set of samples that we 

treated with two (instead of one) buffered acetic-acid 

washes (fig. 6). This also helped to evaluate concerns of 

reagent P saturation due to the high P concentrations in 

many of the samples. Experiments to determine experimental separation between Pr and Pur show that the original Pr 

results, with one buffered acetic-acid wash, yielded essentially the same results as the efficiency experiments with

1JU

125

100

g

£ 75 Ml '5

ffi

50

25

0 

(

A

1

?

« 

1 _

° '

n 

m

f 

m 

a

1 1 B

1 P

 

 D 

-

'

"

S

n 

m

% '"

! D i i

i 

i

 i i i i i

C

1 ^

D

 

°D "

'

-

^ m

D

- ..-

: 

i " i i i i i

) 1 2 30 1 2 3 0 1 2 3 4 5 e

Wt pet Pr Wt pet Pur Wt pet PT

Figure 5. Stratigraphic height in meters from base of section shown in figure 2 versus 

phosphorus concentrations (weight percent (wt pet)). A, wt pet reactive P (Pr); B, wt pet 

unreactive P (Pur); C, wt pet total P (PT), which is the sum of Pr and Pur Solid squares are 

phosphatic shale samples and open squares are other strata, which have mainly dolomitic 

and siliceous lithologies.

The Thermal Regime of Santa Maria Province, California G7
Table 2. Mean phosphorus (P) concentrations and error estimates for lithologies, P components, and facies at Shell Beach

[NA, not applicable; wt pet, weight percent]

No. 1

Lithologic 

fraction

Reactive phosphorus 

Mean S.d.' 

wtpct

Unreactive phosphorus Total phosphorus

Mean S.d. 

wtpct

Mean 

wtpct

S.d.

Siliceous facies

Shale

Siliceous

Weighted mean

9

7

NA

0.20

0.80

NA

1.41

0.11

0.37

0.34

0.08

0.12

1.21

0.06

0.29

0.52

0.07

0.14

2.62

0.17

0.66

0.73

0.13

0.22

Phosphatic facies

Shale

Dolomitic

Weighted mean

13

5

NA

0.73

0.27

NA

0.98

0.06

0.73

0.21

0.03

0.16

0.48

0.02

0.35

0.22

0.00

0.16

1.46

0.07

1.09

0.41

0.03

0.31

Shell Beach total

Shale

Other lithologies

Weighted mean

22

12

NA

0.47

0.53

NA

1.16

0.09

0.59

0.20

0.05

0.11

0.78

0.04

0.38

0.28

0.04

0.14

1.94

0.13

0.97

0.44

0.08

0.23

Number of samples.

Fraction of section (by stratigraphic height) occupied by that lithology. We assume an absolute error of 0.05 on 

lithology thickness.

Standard deviation (2aA/n) on means for each lithology; 2erA/n standard deviation propogated through the calculations 

for weighted mean values.

Weighted mean P concentration based on the mean P concentrations of each lithology and the fraction of the section 

occupied by that lithology.

With the exception of one tuffaceous sample.

two buffered acetic-acid washes (fig. 6). Therefore, the 

technique we use does result in complete removal of CFA, 

which is acetic acid (buffered) soluble. The apparently high 

Pur concentrations may be explained by the chemistry and 

mineralogy of the CFA minerals themselves and may be the 

result of a transformation through time of "reactive" P to 

"unreactive" P, a process which yields apparent unreactive 

P concentrations that are higher in shale strata, which originally contained much higher reactive P concentrations than 

dolomitic or siliceous strata, than in dolomitic or siliceous 

strata. On the basis of Fourier Transform Infrared Spectroscopy (FTIR) analyses of sedimentary apatites including 

samples from the Monterey Formation, recent work indicates that CFA can nonsystematically convert with time to 

a "purer" fluorapatite form owing to decarboxylation and 

loss of the carbonate ion, which partially substitutes for the 

phosphate ion in the CFA mineral lattice (Shemesh, 1990).

Because fluorapatite is not readily soluble in buffered acetic 

acid, this decarboxylation process could result in lower Pr 

concentrations (and higher Pur concentrations) compared to 

the postphosphogenesis composition of the sediments. Our 

results, indicating relatively high Pm concentrations for 

some samples from Shell Beach, lend further evidence in 

support of this transformation of CFA. These results also 

have bearing on the interpretation of our Pr and Pur concentrations. If decarboxylation with time is the cause of apparently higher P^ concentrations, then our Pr concentrations 

are minimum values for the post-phosphogenesis reactive-P 

concentration. There is a positive correlation between Pr 

and Pur in phosphatic shales but not in other lithologies 

(fig. 7). This correlation may represent the diagenetic transformation of Pr to apparent Pur or may be tracking a relationship between sedimentation rate (indicated by Pur 

concentrations) and reactive P burial.

G8 Evolution of Sedimentary Basins Santa Maria Province
The mean PT concentration in shales of the siliceous 

facies (2.62+0.73 wt pet) is higher than those of the phosphatic facies (1.46+0.41 wt pet; table 2). The mean PT 

concentration in the siliceous strata of the siliceous facies 

was 0.17±0.13 wt pet P and in the mainly dolomitic strata 

of the phosphatic facies was 0.07+0.03 wt pet (table 2). 

For the entire Shell Beach section, the mean PT concentration in shale strata was 1.94±0.44 wt pet P and in other 

strata was 0.13±0.08 wt pet P. These data indicate that 

shale generally contains much more PT than dolomitic or 

siliceous strata at Shell Beach.

To compare the mean concentration of P contained in 

each of the facies, we calculated a weighted mean of P 

concentrations in each lithology (shale, dolomite, siliceous) 

versus the fraction of the thickness of each facies repre10

PL.

 »-»

o

0.

0

I

234 

Sample number

Figure 6. Phosphorus concentrations (weight percent (wt pet)) 

extracted using standard (two-step) extraction procedure (first 

bar of each sample number) and same procedure with an extra 

buffered acetic-acid wash during extraction step that releases 

reactive P (second bar of each sample number). Sample numbers represent following samples from Shell Beach (identified 

by sample height): 1, 2 m; 2, 121 m; 3, 105 m; 4, 110 m; 5, 

phosphatic hardground at 76 m. Open portion of each bar 

represents wt pet reactive P (Pr), closed portion represents wt 

pet unreactive P (Pur), and entire bar is the sum of these two 

components (total P (PT)). Typical 1o standard deviation on 

replicate analyses for PT determinations is depicted on error 

bar at 5 wt pet, and typical 1o standard deviations on replicate 

analyses for Pr and Pur is depicted on error bar at 2 wt pet. 

There are no systematic differences between wt pet Pp PUP and 

total P for the two procedures used to analyze each of these 

five samples. Differences in total-P values for standard and 

extra buffered acetic-acid extractions for sample number 5 

(phosphatic hardground) probably represent sample heterogeneity for this sample rather than real differences in ability of 

techniques used to extract P.

sented by that lithology. For the siliceous facies, the mean 

Pr concentration (0.37+0.12 wt pet) was lower than that of 

the phosphatic facies (0.73±0.16 wt pet), the mean Pm concentration (0.29±0.14 wt pet) was about the same as that of 

the phosphatic facies (0.35±0.16 wt pet), and the mean PT 

concentration (0.66+0.22 wt pet) was lower than that of the 

phosphatic facies (1.09±0.31 wt pet) (table 2). Thus, 

although shale of the siliceous facies has higher mean P 

concentrations than shale of the phosphatic facies, the dominance of shale strata in the phosphatic facies results in it 

being equal to or more important than the siliceous facies in 

terms of sedimentary-P concentrations. For the portion of 

the Shell Beach section studied here, the weighted mean Pr 

concentration is 0.59±0.11 wt pet P, the weighted mean P^ 

concentration is 0.38±0.14 wt pet P, and the weighted mean 

PT concentration is 0.97±0.23 wt pet P (table 2).

Determining the dominant P-bearing components that 

reflect a variety of depositional and postdepositional processes has important implications for P diagenesis and 

burial in a high organic-matter productivity continental 

margin setting. The P flux to modern continental margin 

sediments is dominated by organically bound P (Froelich, 

Bender, Luedtke, Heath, and DeVries, 1982; Ruttenberg, 

1990; Ruttenberg and Berner, 1993). Because organic P is 

a minor portion of total P in our samples (about 1 percent;

0

Wt pet Pr

Figure 7. Reactive phosphorus (Pr) versus unreactive phosphorus (Pur) in phosphatic shales (filled squares) and dolomitic and 

siliceous lithologies (open squares) from Shell Beach in weight 

percent (wt pet). There is a correlation between Pr and PUI. for 

phosphatic shales, with a linear correlation coefficient r of 

0.394 (significant at the 99-percent confidence level with 

n=22). There is no correlation between Pr and Pur for dolomitic 

and siliceous lithologies.

Phosphorus Geochemistry, Diagenesis, and Mass Balances of the Miocene Monterey Formation at Shell Beach, California G9
fig. 4), P originally deposited as organic P must either be 

redistributed or lost out of the sediments. The high total P 

concentrations observed for phosphatic shale of Shell 

Beach, which are minimum estimates, indicate that most 

of the P is probably retained and argue for redistribution 

of P from organically bound to other forms after burial. 

High authigenic/biogenic P concentrations indicate that 

phosphogenesis plays an important role in the conversion 

of organic P to CFA, and the correlation between Pr and 

Pur in phosphatic shales indicates that there may be additional post-phosphogenesis transformations of P, which 

need to be investigated.

CONCLUSION

A modified two-step chemical-extraction technique is 

effective for determining P concentrations in sedimentary 

rocks from the Miocene Monterey Formation. The two-step 

technique also enables the separation of reactive P from 

unreactive P for the purpose of determining P dynamics 

within the reactive marine-P cycle. Greater than 95 percent 

of P in the strata studied occurs as reactive P (as authigenic 

and biogenic sedimentary components) and unreactive P (as 

detritally-associated sedimentary components). Less than 5 

percent of P in the strata studied is loosely bound, ironbound, and organic P. Organic matter predominates as the 

main carrier of P to modern continental margin sediments; 

therefore, our results indicate that extensive reorganization 

of P between sedimentary components has occurred, probably as a result of phosphogenesis.

Shales are much more important than other lithologies 

(for example, dolomitic, siliceous) in terms of P concentrations at Shell Beach. In shales of the siliceous facies studied 

here, mean Pr concentrations (1.41+0.34 wt pet P) are 

slightly higher than those of the phosphatic facies (0.98+0.21 

wt pet P), mean Pur concentrations (1.21±0.52 wt pet P) are 

higher than those of the phosphatic facies (0.48±0.22 wt pet 

P), and mean PT concentrations (2.62±0.73 wt pet P) are 

higher than those of the phosphatic facies (1.46+0.41 wt pet 

P) (table 2).

The weighted mean P concentrations, taking into 

account the mean P concentration in each lithology type 

and the thickness of the section that that lithology occupies, indicate that the phosphatic facies has a higher mean 

PT concentration (1.09+D.31 wt pet P) than the siliceous 

facies (0.66+0.22 wt pet P) (table 2). Thus, though shale 

of the siliceous facies has a higher mean P concentration 

than shale of the phosphatic facies, the dominance of shale 

in the phosphatic facies results in it having higher P concentrations than the siliceous facies.

The high total P concentrations observed for phosphatic shale strata of Shell Beach, which are minimum 

estimates, indicate that most of the P is probably retained 

and argue for redistribution of P from organically bound to

other forms after burial. High authigenic/biogenic P concentrations indicate that phosphogenesis plays an important role in the conversion of organic P to CFA.

REFERENCES

Barren, J.A., and Keller, Gerta, 1983, Paleotemperature oscillations in the middle and late Miocene of the northeastern 

Pacific: Micropaleontology, v. 29, p. 150-181.

Baturin, G.N., 1972, Phosphorus in interstitial waters of sediments 

on the South West Africa Shelf: Oceanology, v. 12, p. 849-855.

 1988, Disseminated phosphorus in oceanic sediments A 

review: Marine Geology, v. 84, p. 95-104.

Blake, M.C., Jr., Campbell, R.H., Dibblee, T.W., Jr., Howell, D.G., 

Nilsen, T.H., Normark, W.R., Vedder, J.C., and Silver, E.A., 

1978, Neogene basin formation in relation to plate-tectonic 

evolution of San Andreas fault system, California: American 

Association of Petroleum Geologists Bulletin, v. 62, p. 344- 

372.

Burnett, W.C., 1977, Geochemistry and origin of phosphorite 

deposits from off Peru and Chile: Geological Society of 

America Bulletin, v. 88, p. 813-823.

Burnett, W.C., Beers, M.J., and Roe, K.K., 1982, Growth rates of 

phosphorite nodules from the continental margin off Peru: 

Science, v. 215, p. 1616-1618.

Canfield, C.R., 1939, Subsurface stratigraphy of the Santa Maria 

oil field and adjacent parts of the Santa Maria Valley, California: American Society of Petroleum Geologists Bulletin, v. 23, 

p. 45-81.

Compton, J.S., Hodell, D.A., Garrido, J.R., and Mallinson, D.J., 

1993, Origin and age of phosphorite from the south-central 

Florida Platform: Relation of phosphogenesis to sea-level 

fluctuation and 8 13C excursions: Geochimica et Cosmochimica Acta, v. 57, p. 131-146.

Compton, J.S., Snyder, S.W., and Hodell, D.A., 1990, Phosphogenesis and weathering of shelf sediments from the southeastern 

United States Implications for Miocene 8 13C excursions and 

global cooling: Geology, v. 18, p. 1227-1230.

Filippelli, G.M., and Delaney, M.L., 1992, Similar phosphorus 

fluxes in ancient phosphorite deposits and a modern phosphogenic environment: Geology, v. 20, p. 709-712.

Filippelli, G.M., Delaney, M.L., Garrison, R.E., Omarzai, S.K., and 

Behl, R.J., 1994, Phosphorus accumulation rates in a Miocene 

low oxygen basin The Monterey Formation (Pismo basin), 

California: Marine Geology, v. 116, p. 419-430

Froelich, P.N., 1984, Interactions of the marine phosphorus and 

carbon cycles, in Moore, B.C., and Dastoor, M.N., eds., The 

interactions of global biogeochemical cycles: California 

Institute of Technology, Pasadena, California, NASA-JPL 

Publication 84-21, p. 141-176.

 1988, Kinetic control of dissolved phosphate in natural 

rivers and estuaries A primer on the phosphate buffer 

mechanism: Limnology Oceanography, v. 33(4, part 2), 

p. 649-668.

Froelich, P.N., Arthur, M.A., Burnett, W.C., Deakin, M.L., Hensley, 

V.M., Jahnke, R.A., Kaul, L.A., Kim, R.-H., Roe, K.C., Soutar, 

Andrew, and Vathakanon, C.B., 1988, Early diagenesis of 

organic matter in Peru continental margin sediments: Phosphorite precipitation: Marine Geology, v. 80, p. 309-343.

G10 Evolution of Sedimentary Basins Santa Maria Province
Froelich, P.N., Bender, M.L., Luedtke, N.A., Heath, G.R., and 

DeVries, T.M., 1982, The marine phosphorus cycle: American Journal of Science, v. 282, p. 474-511.

Garrison, R.E., Kastner, Miriam, and Kolodny, Yesu, 1987, Phosphorites and phosphatic rocks in the Monterey Formation 

and related Miocene units, coastal California, in Ingersoll, 

R.V., and Ernst, W.G., eds., Cenozoic basin development in 

coastal California, Rubey volume VI: Prentice-Hall, Englewood Cliffs, N.J., p. 348-381.

Garrison, R.E., Kastner, Miriam, and Reimers, C.E., 1990, Miocene phosphogenesis in California, in Burnett, W.C., and 

Riggs, S.R., eds., Phosphate deposits of the World, volume 

3 Neogene to modern phosphorites: Cambridge, England, 

Cambridge University Press, p. 285-299.

Graham, S.A., 1987, Tectonic controls on petroleum occurrence in 

central California, in Ingersoll, R.V., and Ernst, W.G., eds., 

Cenozoic basin development in coastal California, Rubey volume VI: Prentice-Hall, Englewood Cliffs, N.J., p. 47-63.

Harland, W.B., Cox, A.V., Llewellyn, P.O., Pickton, C.A.G., 

Smith, A.G., and Walther, R.A., 1982, A geologic time scale: 

New York, Cambridge University Press, 131 p.

Howell, D.G., Crouch, J.K., Greene, H.G., McCulloch, D.S., and 

Vedder, J.G., 1980, Basin development along the late Mesozoic and Cenozoic California margin A plate tectonic margin 

of subduction, oblique subduction, and transform tectonics, in 

Ballance, P.P., and Reading, H.G., eds., Sedimentation in 

oblique-slip mobile zones: Los Angeles, International Association of Sedimentologists, Special Publication No. 4, p. 43-62.

Ingle, J.C., Jr., 1981, Origin of Neogene diatomites around the 

north Pacific rim, in Garrison, R.E., and Douglas, R.G., The 

Monterey Formation and related siliceous rocks of California: Society of Economic Paleontologists and Mineralogists 

Publication, Pacific Section, p. 159-180.

Isaacs, C.M., 1980, Diagenesis in the Monterey Formation examined laterally along the coast near Santa Barbara, California: 

Stanford University, Ph.D. dissertation, 329 p.

 1984, Hemipelagic deposits in a Miocene basin, California: Toward a model of lithologic variation and sequence, in 

Stow, D.A.V., and Piper, D.J.M., eds., Fine-grained sediments Deep water processes and environments: Geological 

Society of London Special Publication, v. 15, p. 481-496.

Isaacs, C.M., Tomson, J.H., Stewart, K.C., and Jackson, L.L., 1992, 

Abundance of major elements and sedimentary components in 

cuttings from the Repetto, Sisquoc, and Monterey Formations, 

DCS P-0188 H-l and H-2 wells, Hondo oil field, offshore 

Santa Barbara-Ventura basin, southern California: United 

States Geological Survey Open-File Report 92-383, 46 p.

Kolodny, Yesu, 1983, Phosphorites, in Emiliani, E., ed., The sea: 

Wiley, New York, v. 7, p. 981-1023.

Mach, D.L., Ramirez, A.N., and Holland, H.D., 1987, Organic 

phosphorus and carbon in marine sediments: American Journal of Science, v. 278, p. 429-441.

Nirel, P.M.V., and Morel, F.M.M., 1991, Pitfalls of sequential 

extractions: Water Research, v. 24, p. 1055-1056.

Omarzai, S.K., 1992, Monterey Formation of California at Shell 

Beach (Pismo basin) Its lithofacies, paleomagnetism, age, 

and origin, in Schwalbach, J.R., and Bohacs, K.M., eds., 

Sequence stratigraphy of fine-grained rocks Example of the 

Monterey Formation: Pacific Section, Society of Sedimentary Geology Special Publication, v. 70, p. 47-65.

Pisciotto, K.A., 1978, Basinal sedimentary facies and diagenetic 

aspects of the Monterey Shale, California: University of California, Santa Cruz, Ph.D. dissertation, 450 p.

 1981, Notes in Monterey rocks near Santa Maria, California, in Isaacs, C.M., ed., Guide to the Monterey Formation 

in the California coastal area Ventura to San Luis Obispo: 

Pacific Section, American Society of Petroleum Geologists, 

v. 52, p. 73-82.

Pisciotto, K.A., and Garrison, R.E., 1981, Lithofacies and depositional environments of the Monterey Formation, California, 

in Garrison, R.E., and Douglas, R.G., The Monterey Formation and related siliceous rocks of California: Society of 

Economic Paleontologists and Mineralogists Publication, 

Pacific Section, p. 97-122.

Riggs, S.R., 1984, Paleoceanographic model of Neogene phosphorite deposition, U.S. Atlantic continental margin: Science, 

v. 233, p. 123-131.

Riggs, S.R., and Sheldon, R.P., 1990, Paleoceanographic and 

paleoclimatic controls of the temporal and geographic distribution of Upper Cenozoic continental margin phosphorites, 

in Burnett, W.C., and Riggs, S.R., eds., Phosphate deposits 

of the World, volume 3 Neogene to modern phosphorites: 

Cambridge, England, Cambridge University Press, p. 207- 

222.

Ruttenberg, K.C., 1990, Diagenesis and burial of phosphorus in 

marine sediments Implications for the marine phosphorus 

budget: Yale University, Ph.D. dissertation, 375 p.

 1992, Development of a sequential extraction method for 

different forms of phosphorus in marine sediments: Limnology and Oceanography, v. 37, p. 1460-1482.

Ruttenberg, K.C., and Berner, R.A., 1993, Authigenic apatite formation and burial in sediments from nonupwelling, continental 

margin environments: Geochimica Cosmochimica Acta, v. 57, 

p. 991-1007.

Sheldon, R.P., 1981, Ancient marine phosphorites: Annual 

Review of Earth Planetary Sciences, v. 9, p. 251-284.

Shemesh, Aldo, 1990, Crystallinity and diagenesis of sedimentary 

apatites: Geochimica Cosmochimica Acta, v. 54, p. 2433-2438.

Snyder, S.W., Hine, A.C., and Riggs, S.R., 1990, The seismic 

stratigraphic record of shifting Gulf Stream paths in response 

to Miocene glacio-eustacy: Implications for phosphogenesis 

along the North Carolina continental margin, in Burnett, W.C., 

and Riggs, S.R., eds., Phosphate deposits of the World, volume 

3 Neogene to modern phosphorites: Cambridge, England, 

Cambridge University Press, p. 396-423.

Strickland, J.D.H., and Parsons, T.R., 1972, A practical handbook 

of seawater analysis: Ottawa, Canada, Fisheries Research 

Board of Canada.

Vincent, Edith, and Berger, W.H., 1985, Carbon dioxide and polar 

cooling in the Miocene The Monterey hypothesis, in Sunquist, E.T., and Broecker, W.S., eds., The carbon cycle and 

atmospheric CO2 Natural variations Archean to present: 

American Geophysical Union Monograph 32, p. 455-468.

Woodring, W.P., and Bramlette, M.N., 1950, Geology and paleontology of the Santa Maria district, California: United States 

Geological Survey Special Publication, no. 222, 185 p.

Woodring, W.P., Bramlette, M.N., and Lohman, K.E., 1943, Stratigraphy and paleontology of the Santa Maria district, California: American Society of Petroleum Geologists Bulletin, 

v. 27, p. 1335-1360.

Phosphorus Geochemistry, Diagenesis, and Mass Balances of the Miocene Monterey Formation at Shell Beach, California G11

U.S. GOVERNMENT PRINTING OFFICE: 1994-583-048A0006



SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports of wide and lasting interest and importance to professional 

scientists and engineers. Included are reports on the results of 

resource studies and of topographic, hydrologic, and geologic investigations. They also include collections of related papers addressing 

different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the 

results of resource studies and of geologic and topographic investigations, as well as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of wide 

interest to professional geologists, hydrologists, and engineers. The 

series covers investigations in all phases of hydrology, including 

hydrogeology, availability of water, quality of water, and use of 

water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for 

distribution at no cost to the public. Information is usually of shortterm interest.

Water-Resource Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS 

publications series. Copies are reproduced on request unlike formal 

USGS publications, and they are also available for public inspection 

at depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may 

be cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7 1/2- or 15-minute quadrangle formats (scales 

mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps 

include structure and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric bases at various scales; they show results of surveys using 

geophysical techniques, such as gravity, magnetic, seismic, or 

radioactivity, which reflect subsurface structures that are of economic or geologic significance. Many maps include correlations 

with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; 

they present a wide variety of format and subject matter. The series 

also includes 7 1/2-minute quadrangle photogeologic maps on planimetric bases that show geology as interpreted from aerial photographs. Series also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic 

or planimetric bases at various scales showing bedrock or surficial 

geology, stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum 

potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or 

irregular areas at various scales. Pre-1971 maps show bedrock 

geology in relation to specific mining or mineral-deposit problems; 

post-1971 maps are primarily black-and-white maps on various 

subjects, such as environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolor or black-andwhite maps on topographic or planimetric bases presenting a wide 

range of geohydrologic data of both regular and irregular areas; 

principal scale is 1:24,000, and regional studies are at 1:250,000 scale 

or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under the conditions indicated below from the U.S. Geological 

Survey, Books and Open-File Reports Sales, Federal Center, Box 

25286, Denver, CO 80225. (See latest Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be 

purchased by mail and over the counter in paperback book form and 

as a set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be 

purchased by mail and over the counter in paperback book form and 

as a set of microfiche.

"Publications of the Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by 

mail and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by 

mail and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback 

booklet form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" are available free of charge by mail or may 

be obtained over the counter in paperback booklet form only. Those 

wishing a free subscription to the monthly catalog "New Publications 

of the U.S. Geological Survey" should write to the U.S. Geological 

Survey, 582 National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, and publications.