of Northern >,::„:-. 

and. .---.- Central :-.- California -:-' by & Neutron " Activation '

Analysis of Glass and Comparison with 

X-Ray Fluorescence Analysis
Chemical Correlation of Some Late Cenozoic Tuffs

of Northern and Central California by Neutron Activation

Analysis of Class and Comparison with

X-Ray Fluorescence Analysis

By ANDREI M. SARNA-WOJCICKI, HARRY W. BOWMAN, and PAUL C. RUSSELL

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1147

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1979
tJNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Catalog-card No. 79-600136

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock No. 024-001-03219-8
CONTENTS

Page 

Abstract. ................... 1

Introduction. ................. 1

Tuff units. .................. 1

Sampling methods. ............... 1

Sample preparation and glass separations. ... 3

Analytical methods. .............. 3

Neutron activation analysis. ....... 3

Sample preparation for neutron

activation analyses and measurements. . 5

X-Ray fluorescence spectrometric analyses. 5

Selection of elements for correlation ..... 5

Methods of evaluating chemical data for use

in correlation .............. 5

Correlation of specific units ......... 7

Tuff in Merced(?) Formation of

Sonoma Countv ............. 7

Lawlor Tuff. ............... 10

Nomlaki and Putah Tuff Members of

Tehama Formation. ........... 10

Tuffs in uppermost part of San

Joaquin Formation ........... 13

Provincial chemical characteristics

of silicic tephra ........... 13

Comparison of analyses by X-Ray fluorescence

and neutron activation .......... 13

References cited. ............... 14

ILLUSTRATIONS

Figure 1. Generalized geologic map showing 

location of samples, central 

Coast Ranges, California. ... 2

Histograms showing ratios of 

element concentration in 

glass samples to USGS standard 

rock G-l and differences 

between ratios of selected 

sample pairs. ......... 6

Diagram summarizing correlation of 

late Cenozoic tuffs based on 

neutron activation analysis 

of glass. ........... 11

Similarity coefficient dendrogram. . 12

TABLES

Table 1. Age of tuff units studied. ..... 4

?. Analyses of USGS standard rock G-2 

by neutron activation and 

X-ray fluorescence. ...... 3

3. Neutron activation analyses of

glass of tuffs. ........ 8

4. Chemical analyses by X-ray

fluorescence. ......... 14

III

Chemical Correlation of Some Late Cenozoic Tuffs of Northern and Central California by 

Neutron Activation Analysis of Glass and Comparison with X-Ray Fluorescence Analysis

By Andrei M. Sarna-Wojcicki, Harry W. Bowman, and Paul C. Russell

ABSTRACT

Glasses separated from several dacitic and 

rhyolitic late Cenozoic tuffs of northern and central 

California were analyzed by neutron activation for 

more than 43 elemental abundances. Eighteen 

elements—scandium, manganese, iron, zinc, rubidium, 

cesium, barium, lanthanum, cerium, samarium, europium, 

terbium, dysprosium, ytterbium, hafnium, tantalum, 

thorium and uranium—were selected as most suitable 

for purposes of chemical correlation on the basis of 

their natural variability in silicic tuffs and the 

precision obtainable in analysis. Stratigraphic 

relations between tuffs and replicate chemical 

analyses on individual tuffs make it possible to 

calibrate a quantitative parameter, the similarity 

coefficient, which indicates the degree of correlation 

for the tuffs studied. The highest similarity 

coefficient (0.99) was obtained for analyses of two 

tuffs (potassium-argon dated at about 6.0 m.y.) 

exposed in the Merced(?) and Petaluma Formations of 

Sonoma County, which represent different 

paleoenvironments, shallow-water marine and fresh 

water or brackish marine, respectively. Correlation 

of these formations on the basis of criteria other 

than tephrochronoloqy would be difficult. Results of 

neutron activation analysis in general confirm earlier 

correlations made on the basis of analysis by X-ray 

fluorescence but also make it possible to resolve 

small compositional differences between chemically 

similar tuffs in stratigraphic proximity. The Law!or 

Tuff (potassium-argon dated at about 4.0 m.y.) is 

identified at two new localities: in a core sample 

obtained from a bore hole east of Suisun Bay, and from 

the Kettleman Hills of western San Joaquin Valley. 

This identification permits correlation of the 

uppermost part of the marine Etchegoin Formation in 

the San Joaquin Valley with the continental Livermore 

Gravels of Clark, the Tassajara Formation, and the 

upper part of the Sonoma Volcanics in the central 

Coast Ranges of California. A younger tuff near the 

top of the marine San Joaquin Formation in the 

Kettleman Hills has been identified at both new 

localities.

INTRODUCTION

Within the past 14 years, a number of papers have 

been published on chemical correlation of volcanic 

ashes and tuffs (Czamanske and Porter, 1965: Jack and 

others, 1968; Lajoie and Carmichael, 1968; Jack and 

Carmichael, 1968; Izett and others, 1970; Borchardt 

and others, 1972; Randle and others, 1971; Dudas and 

others, 1973; Bartow and others, 1973; see also 

Westgate and Gold, 1974). The method has been shown 

to work well using a variety of analytical techniques 

and a number of elements. Most workers, however, have 

focused their attention on specific stratigraphic 

problems or the development of a particular analytical 

method. To this time, there has not been any

Lawrence Berkeley Laboratory University of 

California, Berkeley.

comparative evaluation of the different methods which 

analytical method and what combination of elements 

work best to solve a particular problem. Nor has 

there been much statistical work done on the natural 

chemical variability of tephra what differences exist 

within individual eruptive units, between eruptive 

units, and between units erupted from different 

volcanic provinces. Such studies can make 

correlations more definitive by defining the spectrum 

of compositional types, and they can help standardize 

analyses so that data collected by different workers 

can be used in making new correlations.

The present study has three purposes: to 

determine which elements are most suitable for 

chemical correlation using neutron activation analysis 

to calibrate quantitative parameters (similarity 

coefficients) that show correlation and provincial 

relations between tuffs, and to test by neutron 

activaition analyses correlations made previously on 

the basis of X-ray fluorescence spectrometry (SarnaWojcicki, 1976).

Acknowledgments. We are grateful to Douglas 

Hamilton of Earth Sciences Associates who provided 

core samples from the Collinsvilie area used in this 

study and to John Obradovich for providing information 

on tuffs in the Kettleman Hills.

TUFF UNITS

Tuff units studied were, from youngest to 

oldest: two thin tuffs in the uppermost part of the 

San Joaquin Formation, exposed in the Kettleman Hills 

of western San Joaquin Valley (samples 2 and 3) and 

the uppermost tuff in subsurface near Collinsville, 

east of Suisun Bay (sample 1); the Nomlaki Tuff Member 

of the Tehama Formation of northwestern Sacramento 

Valley (samples 4-9); the Putah Tuff Member (samples 

10-15) of the Tehama Formation of southwestern 

Sacramento Valley, approximately the same age as the 

Nomlaki; the upper tuff in Livermore Gravels of Clark 

(1930) south of Livermore Valley (sample 16); the 

Lawlor Tuff, (samples 17-34); the tuff in the 

Merced (?) Formation of Sonoma County (samples 35-42); 

and the tuff above the Neroly Formation and below the 

Contra Costa Costa Group near Lafayette (samples 43, 

44). Sample localities for these tuffs are shown in 

figure 1; their ages, stratigraphic positions, and 

earlier sources are summarized in table 1. Results of 

neutron activation analyses of glass samples of these 

tuffs are given in table 3, and results of X-ray 

fluorescence analyses are given in table 4. Note that 

some samples are analyzed only by neutron activation 

or X-ray fluorescence analysis and consequently are 

listed in only one of the two tables.

SAMPLING METHODS

About 500 g of sample was collected from tuff 

outcrops. At some localities, several samples were 

collected vertically and laterally in each unit to 

test for compositional variations. At several 

localities, where two or more units are exposed in a 

stratigraphic sequence (for example, 1, ?, 15, 30), it 

was possible to test for compositional differences
O
SAMPLE PREPARATION AND ANALYTICAL METHODS

between tuffs of different ages. Replicate analyses 

of samples from individual units, together with 

analyses from multiple units in stratigraphic 

sequence, provide control for calibrating quantitative 

parameters such as the similarity coefficient of 

Borchardt, Aruscavage, and Mi Hard (1972) that 

indicate correlation or its absence where 

stratigraphic control is not available.

SAMPLE PREPARATION AND 

GLASS SEPARATIONS

Previous experience has shown that results of 

chemical analyses are markedly affected by the quality 

of glass separations ( Sarna-Wojcicki, 1971, 1976). 

The presence of phenocryst, microlite, or lithic 

particles in glass separates can produce variations in 

trace-element composition owing to enrichment or 

depletion of many elements in these particles relative 

to glass (for example, concentrations of strontium and 

eurooium in plagioclase feldspar and iron, titanium, 

scandium, manganese, and zinc in amphiboles, pyroxenes 

and opaque minerals). Contamination bv groundwater 

may cause similar variations in composition, such as 

in concentrations of strontium and barium as 

carbonates. Such variations are difficult or 

impossible to distinguish from differences due solely 

to variations in glass composition within and between 

individual tuff units. For this reason, glass 

separation is a critical laboratory procedure that 

requires great care.

Samples were disaggregated by hand or crushed in 

a mullite rotary crusher or mortar and sieved in 

plastic sieves with nylon screens. The 100-200-mesh 

size fraction1 was treated with 10-percent reagent 

grade HC1, rinsed several times in distilled water, 

etched wih 5-percent reagent grade HF, rinsed several 

times again, vibrated in an ultra-sonic probe, dried, 

and resieved. The sample was then separated in a 

Frantz magnetic separator and in acetone-bromoform and 

ace tone-methylene iodide liquid mixtures utilizing a 

density-gradient column. For some samples, these 

procedures were repeated several times before a 

satisfactory separation was obtained.

Initially, the 60-120-mesh size fraction was used; 

the smaller fraction was later chosen to reduce the 

number of glass shards containing phenocrysts and 

microlites. Size fractions finer than 200 mesh are 

difficult to work with owing to clumping during 

magnetic and heavy-liquid separations. The openings 

in nylon screens are somewhat smaller than those in 

equivalent mesh brass and stainless steel screens.

Figure 1.—Generalized geologic map showing location 

of samples, central Coast Ranges, California. 

Geology from Strand and Koenig (1965), Koenig 

(1963), Rogers (1966), Jennings and Burnett 

(1961), and Ross Wagner (written conmun., 

1974). Modified from Sarna-Wojcicki (1976).

ANALYTICAL METHODS

NEUTRON ACTIVATION ANALYSIS

When rock samples are irradiated with neutrons, 

many radioactive species are formed, and the mixture 

produces very complex gamma-ray spectra. The 

elemental sensitivities are directly related to the 

nuclear cross sections, and isotopic abundances 

inversely to radioactive half-lives, and varv 

considerably from element to element. Detailed 

computer analysis of these spectra can give very 

precise information on the abundances of a large 

number of elements. Using this method, we test for 

more than 50 elements, usually detect less than 40, 

and can actually use about 18 to 20 elements in 

correlation studies such as these.

Precision and sampling errors are tested at 

frequent intervals by analyzing a very homogeneous 

obsidian from Central America. The elemental 

precision for the 16 most precisely measured elements 

in this material varied from less than 1 percent to 

slightly more than 4 percent and resulted in an 

average standard deviation of 1.5 percent.

The accuracies here are controlled primarily by 

the uncertainties in chemical compositon of our 

composite standard, a fired clay called "standard 

pottery." Many of the analytical procedures used in 

this study were originally developed during 

archeological studies of pottery types and their 

distributions in the Middle East (Perlman and Asaro, 

1969). By our analysis of USGS standard rock G-2 by 

neutron activation analysis, using standard pottery as

Table ?.--Analyses of USGS standard rock G-2 by neutron 

activation and X-rav fluorescence

[Data for XRF analyses from Carmichael, Hempel, and Jack (1968). 

Iron in percent; other elements in ppm.]

Element

Average Neutron

concentration activation

(Flanagan, 19691 (this studyl

X-ray fluorescence 

(Carmichael and others, 

19681

Sc— ---

Ti ——— - Mn— — •

Fe ——— -

Zn- — -

Rb ——— -

Zr ——— .

Cs —— —

n -

La ——— -

PQ

Eu ———— .

Th

Dy— — -

ur

Ta —— — .

Th ———— -

n — _ _ .

3.9

ocn

1 QC

oc

168

479

12

300

1.4

1870

96

150

7.3

1.5

?

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QQ

7.35

24.2

9 n

3.70+0.07

250+7

1.90+0.04

97+15

i QCJ.OI")

1.5+ 0.2

1900+90

91+2

165+5

7.0+1

1.36+0.05

r in i

2.5+0.?

O A j.1") n O

8.4±0.7

.74±0.02

25.2±0.9

9 no.n i

1.84+0.02

175+2

465+2

10+2

320+0

110+10

175+10

10+5

30+5
CHEMICAL CORRELATION OF SOME LATE CENOZOIC TUFFS

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SELECTION OF ELEMENTS

the reference standard (table 2), other data presented 

here can be normalized to USGS preferred abundances of 

G-2.

Further information on the analytical method, 

including an explanation of the accuracies attainable, 

is given in Bowman, Asaro, and Perlman (1973).

SAMPLE PREPARATION FOR NEUTRON 

ACTIVATION ANALYSES AND MEASUREMENTS

Glass separates were ground to a powder and 100 

mg mixed with 50 mg of cellulose binder and pressed 

into small pills. The pills were placed on edge in a 

radial array along with two identical standards and 

irradiated in the central thimble of the Berkeley 

Triga reactor for 18 minutes at 1.7 x 1012 ns/cm2 , 

later for 8 hours at 3 x 1013 ns/cm2 . The two 

standards were placed opposite each other, and the 

sample capsules rotated continuously during each 

bombardment.

Six different measurements were made on each 

unknown and standard set using various gamma-ray 

counting systems. For most analyses, samples were 

handled by automatic sample-changing equipment and the 

data, counting periods, dead-time counting rates, 

date, and time of the analysis recorded on magnetic 

tape. Computer progams determined the elemental 

abundances and errors by comparing the unknowns and 

the standard gamma-ray spectral data. Checks between 

individual analyses were made, as some elements were 

determined several times.

X-RAY FLUORESCENCE SPECTROMETRIC ANALYSES

Concentrations of trace and minor elements in 

glass separates were determined earlier (SarnaWojcicki, 19Z6) by means of a Norelco Universal Vacuum 

Spectrograph using the analytical procedures 

described by Jack and Carmichael (1968). A detailed 

description of analytical methods is given in SarnaWojcicki (1971, 1976).

Glass samples were mixed with 20 percent by 

weight fibrous cellulose binder and pressed into 3.2- 

cm-diameter discs jn a hydraulic press at pressures of 

about 2500 kg/cm2 . The standards were similarly 

prepared in order to provide uniform surfaces for both 

sample and standard. Glass separates were then 

analyzed for titanium, manganese, iron, nickel, 

copper, zinc, gallium, rubidium, strontium, yttrium, 

zirconium, niobium, and barium. The position for each 

of these elements was calibrated with pure element 

standards, (for example RbCl for rubidium); element 

concentrations were determined by fixed-time counts at 

fixed 26 positions. Additional counts were made at 

adjoining 28 positions to determine the shape and 

intensity of the background curve. Standards used 

were G-l and G-2 for all elements except gallium, 

zinc, copper, and nickel, for which W-l was used 

(Fleisher, 1969; Flanagan, 1969).

Any use of trade names is for descriptive purposes 

only and does not constitute endorsement of these 

products by the U.S. Geological Survey.

SELECTION OF ELEMENTS 

FOR CORRELATION

For the purpose of correlation, elements were 

selected on the basis of their variability within and 

between tuff units as well as according to the 

precision attainable for each element in neutron 

activation analysis. Independent stratigraphic 

evidence and radiometric age determinations make it 

possible to select the elements on the basis of their 

natural abundance and variability in tuffs and 

limitations of the analytical procedures used.

Eighteen elements scandium, manganese, iron, 

zinc, rubidium, cesium, barium, lanthanum, cerium, 

samarium, europium, terbium, dysprosium, ytterbium, 

hafnium, tantalum, thorium, and uranium were 

particularly useful in chemical correlation of silicic 

tephra in this study (table 3).

Six elements for which the analytical precision 

was about 12 percent or better aluminum, sodium, 

potassium, cobalt, lutecium, and neodymiurn were not 

included in calculations of similarity coefficients 

(below) because they do not provide adequate 

resolution for tephra units of different ages. 

Analytical error for the remaining 19 elements-- 

magnesium, chlorine, calcium, titanium, vanadium, 

chromium, nickel, copper, gallium, arsenic, strontium, 

silver, indium, tin, antimony, tungsten, iridium, 

gold, and mercury was greater than 12 percent of 

their average concentration in these silicic tuffs.

Of 13 elements analyzed by X-ray fluorescence in 

the previous study (Sarna-Wojcicki, 1976), 8 were used 

in correlation of tuff units: titanium, manganese, 

iron, zinc, rubidium, strontium, zirconium, and 

barium. The five elements not included were copper, 

nickel, gallium, yttrium, and niobium. Because some 

elements manganese, iron, zinc, rubidium, and 

barium were analyzed by both methods, it was possible 

to compare concentrations determined on splits of the 

same samples and to derive conversion factors from 

neutron activation to X-ray fluorescence analyses by 

least-squares plots.

METHODS OF EVALUATING CHEMICAL 

DATA FOR USE IN CORRELATION

The degree of correlation between samples based 

on results of neutron activation analysis was 

determined graphically and numerically. First, 

concentrations of each of the eighteen elements used 

in correlation were ratioed to reconmended 

concentrations of the same elements in USGS standard 

rock G-l, and histograms comparing sample pairs were 

made (fig.2). Second, similarity coefficients have 

been calculated for every sample pair. This 

coefficient (Borchardt and others, 1972) is given by:
CHEMICAL CORRELATION OF SOME LATE CENOZOIC TUFFS

SAMPLE 23 24 29 31C 16 15 

RATIO OF ELEMENT CONCENTRATIONS 

IN GLASS SAMPLES TO G-l

U

23-24 24-31C 23-29 16-31C 15-23 5-31C 

DIFFERENCE BETWEEN RATIOS 

OF SELECTED SAMPLE PAIRS

0 10 10 10 10 10 1

0.96 0.97 0.96 0.88 0.81 

SIMILARITY COEFFICIENT

0.56

Figure 2.—Ratios of concentrations of elements in samples of volcanic glass to concentrations of the same e n ements in 

USGS standard rock G-l are shown on the left side of the diagram. Absolute values of the differences of these 

ratios for selected sample pairs are shown on the right side of the diagram. Corresponding values of the 

similarity coefficient for these pairs are given below the right side of the diagram, beneath the corresponding 

sample pairs. Recommended values of G-l (Fleisher, 1969) are used for all elements except for Cs, Tb, and Yb, to 

which values of 6, 1, and 2.5 parts per million, respectively, were assigned to avoid high ratios. Samples 23 

and 24 are from the Lawlor Tuff. Samples 29 and 31C are correlated with the Lawlor Tuff on the basis of glass 

chemistry and other criteria (see text). Samele 16 is from a tuff which closely overlies the tuff containing 

sample 31C. Sample 15 is from a tuff correlated with the Putah Tuff Member of the-Tehama Formation (SarnaWojcicki, 1976), which also overlies the Lawlor Tuff, but is considerably younger than both the Lawlor Tuff and 

the tuff overlying it (sample 16). All samples are from tuffs which were erupted in the Sonoma volcanic field, 

except for sample 5, from the Nomlaki Tuff Member of the Tehama Formation, which was erupted from the southern 

Cascade Range volcanic field.

where

^(A.B.) = ^(B.A.) = similarity coefficient 

for comparison between 

sample A and sample B,

•i = element number,

n - number of elements,

R£ = Z^A/J^B if X^E > Z^A; otherwise

Z.B/J.A, ^ ^

J^A = concentration of element i in 

sample A, and

J^B = concentration of element i in 

sample B.
METHODS FOR EVALUATING CHEMICAL DATA

The value of the similarity coefficient for a 

chemically identical sample pair is 1. In practice, 

the value of the coefficient for replicate analyses of 

samples from a single outcrop, or of splits of the 

same sample, ranges from about 0.93 to 0.99 owing to 

inhomogeneities in the glass, slight variations in 

degree of separation -of the glass, or analytical 

errors. For some of the earlier analyses of samples 

from the same outcrop, values of this coefficient are 

as low as 0.90, owing perhaps to incomplete separation 

of crystalline material from the glass. Values of 

similarity coefficients for tuff samples of 

demonstrably different age (for instance, tuffs 

superposed within a continuously exposed section) 

range from 0.45 to a high of 0.88. Since the ranges 

of replicate analyses from a single tuff generally do 

not overlap with those of tuffs of different ages, 

similarity coefficients can be used as quantitative 

guides to indicate correlation or its absence where 

stratigraphic control is not available.

As an example, let us consider the correlation of 

the Lawlor Tuff on the basis of its glass chemistry. 

Tuff samples taken from two outcrops of the Lawlor 

Tuff between which the tuff is continuously exposed 

(samples 23 and 24) show minor differences and a high 

similarity coefficient of 0.96 (fig.2). A comparison 

of samples 23 and 29 reveals similar minor differences 

and the same similarity coefficient of 0.96 is 

calculated, although the tuff in this instance is not 

continuously exposed between these two localities 

(figs. 1 and 2). Since samples 23 and 29 are similar 

to the same extent as samples 23 and 24, they are here 

considered correlative and support an earlier 

correlation based on X-ray fluorescence analysis and 

petrographic criteria of the same samples (SarnaWojcicki, 1976). Independent evidence supporting this 

correlation comes from potassium-argon ages of the 

tuffs at localities 23 and 29 (4.0±0.2, and 4.0+1.0 

m.y., respectively, Sarna-Wojcicki, 1976).

The Lawlor Tuff is also found further south in 

Livermore Valley, at locality 31. Sample 31 compares 

closely with the aforementioned Lawlor Tuff samples, 

the similarity coefficients for these comparisons 

being 0.97, 0.97 and 0.96. At locality 31, the 

Lawlor Tuff is overlain by a chemically and 

petrographically similar tuff (sample 16, table 3 and 

figs. 2 and 3). The similarity coefficient comparing 

the two superposed tuffs is 0.88. Analyses such as 

these on a number of superposed ashes and tuffs, 

combined with replicate analyses from individual 

units, have permitted calibration of similarity 

coefficients and make them a useful tool in evaluating 

tephrochronological data.

Within our experience, however, similarity 

coefficients for some tuff samples of different 

radiometric age erupted within the same volcanic 

province (for instance, the Putah Tuff Member of the 

Tehama Formation, potassi urn-argon dated at 3.3+0.2 

m.y., and the tuff in the Merced(?) Formation of 

Sonoma County, potassium-argon dated at about 5.9 

m.y.; see table 1) can be as high as 0.90. 

Consequently, similarity coefficients within the range 

0.89-0.92 represent an interval of uncertainty and are

not by themselves considered to be conclusive evidence 

of correlation or its absence.

Since similarity coefficients of tuffs of 

different ages erupted within a single volcanic 

province or field (about 0.65-0.88) are generally 

lower than those of replicate analyses from the same 

unit but are higher than those of tuffs erupted from 

different volcanic fields (about 0.45-0.65), they 

provide a criterion for determining tuff or ash 

provenance. For instance, samples 5 and 31C (fig. 2) 

were erupted from different volcanic provinces. Their 

different origins are reflected in the glass chemistry 

of these two tuffs. Samples 15, 16, and samples of 

the Lawlor Tuff are from tuffs erupted from the same 

volcanic province, the Sonoma volcanic field, and bear 

a strong family resemblance to each other, a 

reflection of their common genesis (fig. 2).

The ranges of similarity coefficients given here 

apply only to units and volcanic areas studied by the 

neutron activation analytical method for the 18 

elements used in the comparison procedure. Somewhat 

different values will be obtained if other units, 

analytical methods, or elements are used.

A matrix comparing values of similarity 

coefficients for all sample pairs in the study group 

was calculated. The relation of all analyzed samples 

with respect to the similarity coefficient is shown by 

a dendrogram (fig. 4) based on maximum individual 

values of similarity coefficients for sample pairs and 

maximum averages of coefficients for sample groups.

CORRELATION OF SPECIFIC UNITS

A summary of correlations documented in this 

study is given in a correlation chart, fig. 4. 

Discussion of correlation of specific units, from 

oldest to youngest, follows.

TUFF IN MERCED(?) FORMATION OF SONOMA COUNTY

Neutron activation analyses presented in this 

study confirm earlier correlations (Sarna-Wojcicki, 

1976) of the tuff in the marine Merced(?) Formation of 

Sonoma County (loc. 38) with the tuff in the 

estuarine(?) Petaluma Formation near Sears Point (loc. 

41, samples 41C, D, and E), and the tuff near the base 

of the continental Tassajara Formation or the top of 

the continental Green Valley Formation of Clark (1943) 

(loc. 42) (figs. 1 and 3). Ten similarity 

coefficients obtained from comparison of glass 

chemistry of samples pair range from 0.94 to 0.99 

(fig.4) with an average value of 0.96. Samples 41C, 

D, and E, replicate analyses of samples from a single 

outcrop in the Petaluma Formation, correlate at values 

of 0.95, 0.95, and 0.98, which also average 0.96. The 

highest similarity coefficient obtained in this study 

(0.99 for samples 38 and 41E, Fig. 4) is for tuff 

exposed at localities more than 60 km apart in two 

different formations representing two different 

depositional environments and facies, and consequently 

different faunal assemblages. Contact relations 

between the two formations are nowhere exposed, being 

either severed by faults or covered by younger 

alluvium.
Table 3—Neutron activation analyses of glass of tuffs

[Sample numbers are same as locality numbers shown in figure 1. Concentrations of iron in percent; all other concentrations in 

Samples with letter designations (C, D, El are replicate analyses of samples from a single locality, or of splits of the 

Sample Sc Mn Fe Zn Rb Cs Ba La Ce Sm Eu Tb Dv Yb Hf Ta 

Uppermost

1 4.48

2 5.96

ash in core near Col

610

564

2.23

2.36

100

113

1 ins ville, east

94

111

8.3

8.6

of Suisun Bay(l), and uppermost ash in San Joaquin Formation, Kettleman

590

755

28.7 63.1 7.29 1.28 1.42 9.4 6.40 9.91

31.6 69.1 8.20 1.29 1.47 10.5 6.83 10.03

Hi 1

1.2

1.0

Next-to-uppermost ash in San Joaquin Formation, Kettleman Hills, San Joaquin Valley

3 7.50

5 3.52

fc 3.69

8 3.71

9 3.63

10 7.09

J13C 7.21

*L3D 7.15

508

317

324

303

330

192

207

197

2.21

0.74

.79

.76

.80

1.13

1.16

1.18

99

27

36

36

33

57

54

49

125

89

97

104

103

Upper

165

153

160

10.1

Nomlaki

4.7

5.4

5.1

5.2

beds of

11.7

11.6

11.7

804

Tuff

959

1145

1158

1013

Put ah

832

793

864

34.2 72.8 8.17 1.15 1.54 10.3 6.56 10.40

Member of Tehama Formation, northwestern Sacramento Valley

19.7 35.7 2.19 0.51 0.34 2.4 1.56 3.96

21.4 40.1 2.39 .44 .30 2.3 1.91 4.06

20.9 40.2 2.36 .47 .32 3.0 1.74 4.32

20.7 40.8 2.36 .44 .33 2.3 1.90 4.26

Tuff Member of Tehama Formation, southwestern Sacramento Valley

30.0 67.2 6.39 0.39 1.1.4 7.7 4.75 7.29

30.3 67.0 6.45 .35 1.15 7.6 5.02 7.22

30.4 65.5 6.56 .34 1.05 7.9 5.12 7.20

1.0

0.4

.5

.5

.5

0.8

.8

.8

15 5.30 181 1.21

Thin tuff in lower part of Tehama Formation above Lawlor Tuff south of Suisun Bay

44 159 12.0 857 29.6 60.1 5.64 0.38 1.04 7.0 3.84 6.95

Upper tuff in Livermore Gravels of Clark Q930) south of Livermore Vallev

0.6

>16

117

J23

124

^9

me

*31D

32

33

34

Tuff in

'38

J41C

HID

41E

142

6.82

6.08

5.89

5.86

5.93

6.22

6.17

6.23

5.88

5.91

355

327

305

319

312

309

330

328

322

326

1.50

1.48

1.45

1.46

1.50

1.47

1.47

1.35

1.47

1.51

Merced(?) Formation

4.28

4.33

4.31

4.28

4.15

188

179

185

184

176

1.00

1.05

1.05

1.02

.99

60

68

64

65

56

63

61

76

69

68

of Sonoma

42

42

45

43

39

129

134

139

137

129

141

137

149

129

127

County,

158

157

167

163

153

10.5

9.1

9.0

8.8

8.9

9.0

9.2

9.4

9.9

9.8

in

13.7

13.2

13.6

13.7

12.4

615 24.4 53.8 5.23 0.84 1.03 6.4

Lawlor Tuff ftyoe and correlative localities)

794 32.1 65.5 6.50 0.71 1.16 7.6

881 32.2 67.0 6.50 .76 1.25 7.7

759 30.5 66.9 6.38 .85 1.30 8.1

750 31.2 66.2 6.28 .71 1.16 7.9

755 31.3 69.3 6.41 .75 1.28 7.4

788 32.7 69.6 6.61 .72 1.19 7.8

800 31.9 70.7 6.66 .73 1.19 7.8

752 31.7 68.4 6.42 .72 1.14 7.5

763 33.3 67.5 6.54 .71 1.10 7.7

Petal uma Formation, and in base of Tassajara Formation

720 29.1 58.9 4.79 0.34 0.81 5.6

673 26.9 56.4 4.52 .31 .90 5.6

700 27.9 59.0 4.81 .33 .85 5.6

715 28.4 59.4 4.78 .33 .78 5.6

707 27.9 55.7 4.58 .35 .86 6.0

3.84

4.93

4.70

4.59

4.55

4.55

5.10

5.28

5.34

5.29

or top

3.86

3.49

3.88

3.79

3.26

7.32

7.85

8.07

7.88

7.98

7.93

8.02

8.44

8.15

8.10

of Green

6.16

5.89

6.23

6.02

5.79

0.9

0.9

.9

.9

1.0

1.0

.9

.9

.9

.9

Valley 

0.8

1.0

.8

.8

.7
Table 3.— Neutron activation analyses of glass of tuffs—Cont.

Sample Sc Mn Fe Zn Rb Cs Ba La Ce Sm Eu Tb Dy Yb Hf 

Tuff above Neroly Formation, below Contra Costa Group near Lafayette 

44 5.47 184 1.05 46 132 13.7 637 3?.? 70.2 6.20 0.35 1.10 7.4 4.99 6.72 0

Group averages

Uppermost ash in core near Col linsville, east of Suisun Bay (1), and uppermost ash in San Joaquin Formatio

Kettleman Hills, San Joaquin Valley (2)

AVR.(2) 5.22 587 2.30 107 103 8.5 673 30.1 66.1. 7.75 1.29 1.45 10.0 6.62 9.97 1

Next-to-uppermost ash in San Joaquin Formation, Kettleman Hills, San Joaquin Valley

3 7.50 508 2.21 99 125 10.1 804 34.2 72.8 8.17 1.15 1.54 10.2 6.56 10.40 1

Nomalaki Tuff Member of Tehama Formation, northwestern Sacramento Valley 

AVR.(4) 3.64 319 0.77 33 98 5.1 1069 20.7 39.2 2.33 0.47 0.32 2.5 1.78 4.15 0

Upper beds of Putah Tuff Member of Tehama Formation, southwestern Sacramento Valley 

AVR.(3) 7.15 199 1.16 53 159 11.7 830 30.2 66.6 6.67 0.36 1.11 7.7 4.96 7.24 0

Thin tuff in lower part of Tehama Formation and above Lawlor Tuff, south of Suisun Bay 

15 5.30 181 1.21 44 159 12.0 857 29.6 60.1 5.64 0.38 1.04 7.0 3.84 6.95 0

Upper tuff in Livermore Gravels of Clark (1930), south of Livermo^e Valley 

16 6.82 355 1.50 60 129 10.5 615 24.4 53.8 5.23 0.84 1.03 6.3 3.84 7.32 0

Lawlo^ Tuff (type and correlative localities)

AVR.(9) 6.02 319 1.46 66 136 9.2 782 31.9 67.9 6.48 0.74 1.20 7.7 4.93 8.05 0

Tuff in Mercedf?) Formation of Sonoma County, in Petaluma Formation, and in base of Tassajara Formation or top of Green Valley 

AVR.(5) 4.27 182 1.02 42 160 13.3 703 28.0 57.9 4.70 0.33 0.84 5.7 3.66 6.02 0

Tuff above Neroly Formation, below the Contra Costa Group, near Lafayette 

44 5.47 184 1.05 46 132 13.7 637 32.2 70.2 6.20 0.35 1.10 7.4 4.99 6.72 0

Average analytical error 

±0.03 ±3 ±0.02 ±3 ±7 ±0.2 ±20 ±0.6 ±0.6 ±0.01 ±0.02 ±0.04 ±0.1 ±0.06 ±0.09 ±

•'•Samples analyzed by both NA and XRF analyses. 
10 CHEMICAL CORRELATION OF SOME LATE CENOZOIC TUFFS

The tuff overlying the Neroly Formation and 

underlying the Contra Costa Group near the town of 

Lafayette at locality 44 (fig. 1), previously 

tentatively correlated with the tuff in the Merced(?) 

Formation of Sonoma County (Sarna-Wojcicki, 1976), 

does not correlate with that tuff or with any other 

unit in this study. Chemically, the tuff at locality 

44 is most similar to the Putah Tuff Member of the 

Tehama Formation (similarity coefficients of 0.89 to 

0.91) and the tuff in the Merced(?) Formation of 

Sonoma County (similarity coefficients of 0.85 to 

0.88), (fig. 4). Stratigraphic and radiometric age 

data (table 1, fig. 3) together with earlier 

petrographic and X-ray fluorescence data (SarnaWojcicki, 1976), suggest that this tuff is as old or 

older than the tuff in the Merced (?) and much older 

than the Putah. Correlation of the tuff at locality 

44 remains uncertain.

LAWLOR TUFF

As mentioned earlier, sample 31 (C and D), from 

the lower tuff in the Livermore Gravels of Clark 

(1930) south of Livermore Valley (fig. 1), is 

correlated with samples 23, 24, and 29, the similarity 

coefficients being 0.97, 0.97 and 0.96, respectively 

(fig. 4). A potassium-argon age of 4.5±0.5 m.y. on 

the tuff at sample locality 31 compares closely with 

dates obtained at localities 23 and 29 (4.0+0.2 and 

4.0+1.0 m.y.).

A light-gray, water-deposited, watertransported^) fine-grained vitric tuff (sample Iocs. 

33 and 34) near the uppermost part of the Etchegoin 

Formation in the Kettleman Hills of western San 

Joaquin Valley (Woodring and others, 1940) is here 

correlated with the Lawlor Tuff (figs. 1 and 3). 

Trace- and minor-element chemistry of the glass in 

this tuff is essentially identical to that of the 

Lawlor and its other correlatives. Similarity 

coefficients between samples of the tuff in the 

Etchegoin Formation and samples of the Lawlor Tuff and 

its correlatives range from 0.94 to 0.97 with an 

average of 0.96 (fig 4).

A gray pumice-lapilli tuff, the middle one of 

three obtained from an exploratory bore hole near 

Collinsvilie east of Suisun Bay at a depth of 205 m 

(courtesy of Douglas Hamilton, Earth Science 

Associates), also correlates well with the Lawlor Tuff 

and its other correlatives. Similarity coefficients 

between the tuff from Collinsville (sample 32) and the 

Lawlor Tuff and other correlatives range from 0.93 to 

0.96, with an average of 0.95.

In summary, the chemical data presented here make 

it possible temporally to correlate the uppermost part 

of the marine Etchegoin Formation of western San 

Joaquin Valley (Iocs. 33, 34) with certain formations 

in the central Coast Ranges: basal (?) lacustrine or 

alluvial deposits of the Livermore Gravels of Clark 

(1930) (loc. 31); alluvial gravels of the Tassajara 

Formation (loc. 29); the Lawlor Tuff south of Suisun 

Bay, which overlies the Neroly Formation and is 

overlain by the Tehama Formation (Sims and SarnaWojcicki, 1975) (Iocs. 23 and 24); unnamed alluvium in

the subsurface near Collinsville, east of Suisun Bay 

(loc. 32); and the upper part of the Sonoma Volcanics, 

north of San Pablo and Suisun Bays (loc. 17) (fig. 3).

These correlations illustrate advantage of the 

correlation method employed here. Samples 17, 23, 24, 

and 29 are from an ash-flow facies, sample 31 is from 

a water-laid lacustrine facies, and samples 33 and 34 

are from a water-laid marine facies; all of these are 

now identified as the Lawlor Tuff. It would be 

difficult or impossible to make these correlations on 

the basis of field observations or paleontologic 

criteria alone.

At a locality south of Livermore, two tuffs 

(sample 16, is from the upper tuff, and samples 31, C 

and D, from the lower tuff) separated by about 8 m of 

tuffaceous deposits, are difficult to distinguish on 

the basis of X-ray fluorescence analysis or 

petrographic data (Sarna-Wojcicki, 1976) but are 

clearly distinguishable by chemical differences 

determined by neutron activation (table 3; figs. 2, 

4). The similarity coefficients between sample 16 and 

31 (C and D) are 0.88 and 0.88. The average of all 

similarity coefficients between sample 16 and samples 

of the Lawlor Tuff is also 0.88.

NOMLAKI AND PUTAH TUFF MEMBERS 

OF TEHAMA FORMATION

Three samples of the Nomlaki Tuff Member analyzed 

by neutron activation, samples 5, 6, and 8, are from a 

single outcrop at its type locality in the former 

Nomlaki Indian Reservation, but from different 

Stratigraphic positions in the unit. Sample 9 is from 

a locality about 50 km farther north (fig. 1, inset 

map). Samples 6, 8, and 9 are very similar chemically 

(similarity coefficients of 0.95, 0.95, and 0.97, fig. 

4). Sample 5, compared with 6, 8, and 9, has lower 

similarity coefficients (0.89, 0.90, and 0.91) perhaps 

owing to chemical inhomogeneities in the glass or to 

vertical variations within the Nomlaki Tuff Member, 

even though this unit appears to be texturally 

homogeneous. An alternative explanation is that the 

greater differences may result from inadequate 

separation of crystalline material from the glass, as 

sample 5 was one of the earlier samples processed in 

these studies (Sarna-Wojcicki, 1971; Sims and SarnaWojcicki, 1975; Sarna-Wojcicki, 1976), prior to 

several improvements in separation techniques.

Samples of the Putah Tuff Member analyzed by 

neutron activation, 10, 13C, and 13D, are from the 

type locality (fig. 1), a water-laid, composite unit 

probably produced by several eruptions within a short

Figure 3. Surrmary of correlation of late Cenozic 

tuffs based on neutron activation analysis of 

glass. Solid horizontal lines indicate 

correlation certain; dashed horizontal lines, 

correlation probable; queries, correlation 

uncertain. Sample numbers are the same as in 

figure 1 and tables 3 and 4. For sources of 

potassium-argon ages, see Sarna-Wo.icicki, 

(1976).
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(55^4d E

Tuff in Mercedf?) Format on of-Z^ .,,,., / ' ' (4JX lit)t)

v / -.^^ Y^Qi. 

Sonoma County o «v

3 -c

£«

)---^

w

o

.c

O

c .2

^^

a>

o

c 

c

V V V

— ,x —

-2 

0 .2 

3 C 

o § 

< 

§ 

Uppermost tuff, Kettl

•> . ? 

r^'~ 

g

2 > 

o = 

"S i 

——— Upper tuft in Livermore Gravels of 

. . _ „ _ Clorkv

. —— ^ Lawlor Tuff F^-'~l /io-3r\

lX/Jxot.2

*-(Age uncertain)

1 1 ^ O

w)"^^

^^

Unnamed beds^.

0 Ol?

c 5 §

^(SS

rVi

(4l) (441 ^-^ " - vvv

Neroly

Fm. — — _a.

(Marine)

@s

,K 8.0*2

LL. - — -

n u

!<

*

o^

_^

0

u_

dl

.^i

J)

c

a>

O

v c*"c' 

4.0*1 

L-— ~ 1 
12 CHEMICAL CORRELATION OF SOME LATE CENOZOIC TUFFS

1.00 0.90

I i i i I I i i i i I

SIMILARITY COEFFICIENT

0.80

I I I

0.60 

I

0.50

_J

Lawlor Tuff (type and correlative tuffs, including 

lower tuff in Livermore Gravels of Clark (1930), 

south of Livermore)

34

J33 

17 

31D

sTc

23

24

29

32

Ih

Upper tuff in Livermore Gravels of Clark( 1930), _T "771 

south of Livermore

Upper beds of Putah tuff member of Tehama 

Formation, southwestern Sacramento Valley

10 

13C 

13D

Thin tuff in lower part of Tehama Formation and I ~iTL 

above Lawlor Tuff, south of Suisun Bay

Tuff above Neroly Formatiom and below Contra _T~ ~T7L 

Costa Group near Lafayette

Tuff in Merced (?) Formation of Sonoma County, 

in Petaluma Formation, and in base of Tossajara 

Formation or top of Green Valley Formation of ~ 

Clark (1943)

38 

41E 

41D 

41C

42

Uppermost Tuff in core near Collinsville and uppermost tuff in San Joaquin Formation, Kettleman 

Hills, San Joaquin Valley

Next-to-uppermost tuff in San Joaquin Formation, _T~ ~~3~L 

Kettleman Hills, San Joaquin Valley

Nomlaki Tuff Member of Tehama Formation, 

northwestern Sacramento Valley

Figure 4. Similarity coefficient dendrogram. Samples are grouped according to maximum individual values of similarity 

coefficients for sample pairs and maximum averages of coefficients for sample groups.
COMPARISON OF ANALYSES 13

period. Values of the similarity coefficient of these 

three samples, all from the upper part of this unit, 

are 0.97, 0.96, and 0.96 (fig. 4). On the basis of Xray fluorescence analysis of trace and minor elements 

of the glass and petrographic characteristics (Sims 

and Sarna-Wojcicki, 1975; Sarna-Wojcicki, 1976), the 

base of this unit (sample loc. 14) has been correlated 

with a thin tuff that overlies the Lawlor Tuff south 

of Suisun Bay (sample loc. 15, fig. 4). Since 

analyses by neutron activation have not been made on 

the basal part of the Putah, comparison of neutron 

activation and X-ray fluorescence analyses cannot be 

made for these samples.

TUFFS IN UPPERMOST PART 

OF SAN JOAQUIN FORMATION

Of two thin tuffs (Iocs. 2 and 3, fig. 1) in the 

uppermost part of the San Joaquin Formation in the 

Kettleman Hills, Kings County, the upper tuff (loc. 2) 

is chemically similar to a tuff (loc. 1) found in a 

core near Collinsville, Solano County, at a depth of 

184 m below the surface (courtesy of Douglas Hamilton, 

Earth Science Associates). Sample 1 is more similar 

to sample 2 than to sample 3 (similarity coefficient 

0.91, 0.86), but as similar to sample 3 as the two 

thin tuffs (samples 2 and 3) are to each other 

(similarity coefficient 0.91K These values of the 

similarity coefficient are too low to permit a 

definitive statement on the correlation of these 

units, but the similar stratigraphic position (above 

the Lawlor Tuff) of the tephra at both localities, 

combined with the unusual trace- and minor-element 

composition of the glass (high content of iron, 

manganese, zinc, europium, terbium, dysprosium, 

ytterbium and hafnium, table 3) suggests the 

possibility of a correlation between samples 1 and ?.

PROVINCIAL CHEMICAL CHARACTERISTICS

OF SILICIC TEPHRA

- Analyses of the Nomlaki and Putah Tuff Members of 

the Tehama Formation illustrate differences between 

silicic tephra units erupted from different volcanic 

fields. The Nomlaki Tuff Member (Iocs. 4-9), situated 

near the base of the Tehama Formation in northwestern 

Sacramento Valley, was erupted from a source northeast 

or east of Sacramento Valley, in the southern Cascade 

Range volcanic province (Anderson and Russell, 1939; 

Russell, 1931; Lydon, 1967). The Putah Tuff Member 

(Iocs. 10-14), also in the lower part of the Tehama 

Formation in southwestern Sacramento Valley, was 

erupted from a source in the central Coast Ranges 

(Miller, 1966), probably from the Sonoma volcanic 

field (Sims and Sarna-Wojcicki, 1975; Sarna-Wojcicki, 

1976). The large differences in glass chemistry of 

these two units reflect differences in provenance and 

differences in the magmas from which the glass was 

derived. Similarity coefficients between samples of 

the Nomlaki and Putah Tuff Members range from 0.54 to 

0.59 and average a low 0.57.

Tuffs erupted within the same volcanic field are 

chemically more similar than those erupted from 

different fields. Independent evidence regarding the

eruptive sources of some of the tuffs can be obtained 

from observations of changes in their stratigraphic 

thickness and textural gradients. For example, both 

the Lawlor Tuff and the Putah Tuff Member were erupted 

from the Sonoma volcanic field, as inferred from 

thickening of these units and increase in particle 

sizes toward this volcanic field. Chemical data from 

neutron activation analysis supports this 

interpretation since similarity coefficients between 

samples of these two tuffs are rather high, averaging 

0.81 (fig. 4).

Other tuffs erupted in the Sonoma volcanic field, 

as inferred from physical evidence and glass 

chemistry, are the tuff (loc. 15) overlying the Lawlor 

Tuff (loc. 16) south of Livermore Valley, the tuff in 

the Merced(?) Formation of Sonoma County and its 

correlative tuffs (Iocs. 38, 41, 42), and the tuff 

overlying the Neroly Formation and underlying the 

Contra Costa Group near the town of Lafayette (loc. 

44). The two thin tuffs near the top of the San 

Joaquin Formation in the Kettleman Hills (Iocs. 1 and 

2) are more similar to the tuffs erupted from the 

Sonoma Volcanic field (similarity coefficients of 0.61 

to 0.83) than to the Nomlaki Tuff Member (similarity 

coefficients of 0.48 to 0.54) and probably have been 

derived from this volcanic field.

COMPARISON OF ANALYSES BY X-RAY 

FLUORESCENCE AND NEUTRON ACTIVATION

A comparison of element concentrations determined 

by both neutron activation and X-ray fluorescence 

analyses for the same samples shows barium, rubidium, 

and zinc concentrations to be fairly similar, but 

large discrepancies exist for iron and manganese, both 

elements being consistently higher in the X-ray 

fluorescence analyses. These differences may be due 

to differences in standards or absorption corrections 

used in the two analytical procedures. (Absorption 

corrections were not used for iron and manganese in Xray fluorescence analysis, since bulk compositions of 

samples and standards were approximately the same; 

Sarna-Wojcicki, 1971, 1976). Linear regression 

analyses indicate that best correspondence between Xray fluorescence and neutron activation analyses was 

obtained for iron (correlation coefficient rz of 0.98) 

followed by rubidium, barium, and zinc (r2 of 0.95, 

0.95, and 0.92, respectively). Greater scatter of data 

was found for analyses of manganese (r^ of 0.82).

Although absolute concentrations of iron, 

manganese, and, to a lesser extent, rubidium differ 

between splits of the same samples, relative 

differences are about the same, and correlations based 

on neutron activation analyses are essentially the 

same as those based on X-ray fluorescence analyses. 

Somewhat better discrimination between units was 

obtained using neutron activation analysis, probably 

because a greater number of elements were analyzed and 

greater precision is obtained for some elements, 

permitting discrimination between chemically similar 

tuffs in stratigraphic proximity, for example, samples
14 CHEMICAL CORRELATION OF SOME LATE CENOZOIC TUFFS

Table 4.--Chemical analyses by X-ray fluorescence

[Sample numbers same as locality numbers in figure 

1. Concentrations of Fe in percent; all others in 

parts per million. Samples with letter designations 

(A, B) are replicate analyses of samples from a single 

locality or of splits of the same sample. X-ray 

fluorescence data from Sarna-Wojcicki (1976). See 

table 2 for analytical error for these elements.]

Sample 

No. Ti Mn Fe Zn Rb Sr Y Zr Ba

16

7

Nomlaki Tuff Member of Tehama Formation

1332 419 0.94 33 107 169 12 182 1055

1372 518 .90 28 102 177 9 169 1052

1168 387 .87 28 103 162 14 181 965

1453 420 1.08 32 99 168 9 161 1003

Upper beds of Putah Tuff Member of Tehama Formation

11 1131 244 1.40 37 158 68 24 263 981

12 1251 278 1.36 45 153 27 28 276 814

13 1088 262 1.34 43 174 35 27 256 794

Lower beds of Putah Tuff Member of the Tehama

Formation, and thin tuff in lower part of

Tehama Formation, south of Suisun Bay

14 1018 244 1.39 39 170 37 21 261 838 

a !5 1006 247 1.44 41 186 38 17 274 875

Upper tuff in Livermore Gravels of Clark (1930) 

south of Livermore Valley

a !6A 1136 502 1.82 60 135 74 23 306 684 

1 16B 1137 517 1.82 56 137 82 24 290 718

16 and 31C, D (fig. 2). Precision for analyses of 

titanium, zirconium, strontium, and yttrium, elements 

useful in correlation of silicic tephra, is greater in 

X-ray fluorescence than in neutron activation 

analysis.

REFERENCES CITED

Anderson, C. A., and Russell, R. D., 1939, Tertiary 

formations of northern Sacramento Valley, 

California: California Journal of Mines and 

Geology, v. 35, no. 3, p. 219-253.

Bartow, J. A., Sarna-Wojcicki, A. M., Addicott, W. 0., 

and Lajoie, K. R., 1973, Correlation of marine and 

continental Pliocene deposits in northern 

California by tephrochronology Tabs.]: American 

Association of Petroleum Geologists Bulletin, v. 

57, no. 4, p. 769.

Table 4.—Continued.

Sample

No. Ti Mn Fe Zn

Law! or

M7

18

19

20

21

22

a 23

1074

1174

1283

1473

1174

1211

1048

366

459

448

436

433

440

428

1

1

1

1

1

1

1

.62

.73

.62

.75

.72

.72

.68

60

58

57

59

54

57

59

Rb

Tuff

154

154

157

143

148

145

147

Sr

51

59

56

68

58

50

48

Y

47

26

24

27

26

24

?5

Zr

312

326

336

339

301

297

303

Ba

836

817

840

801

758

812

755

Tuff in the Merced (?) Formation of Sonoma County,

in Petaluma Formation, and in lower part of

Tassajara Formation or top of Green

Valley Formation of Clark (1943)

1

1

24

25

26

27

28

29

30 J 31

a

35

36

37

38

39

40

a 41A

a

i

41B

42

1180

1203

1173

1129

1258

1183

1134

1213

876

803

710

766

750

755

729

775

738

470

447

437

454

456

449

422

431

237

233

250

259

310

285

278

215

240

1

1

.81

.78

1.73

1

1

1

1

1

1

1

1

1

1

1

1

1

1

.72

.68

.83

.70

.75

.18

.18

.21

.13

.09

.11

.07

.16

.16

63

56

59

56

67

61

59

58

40

43

40

44

44

48

41

48

39

149

152

143

146

144

148

148

143

181

176

174

190

179

183

181

177

179

62

62

54

57

71

53

71

60

41

39

40

28

27

27

44

29

59

25

25

18

18

32

24

29

25

24

21

19

28

24

28

23

29

20

304

326

329

319

313

304

305

297

247

242

216

225

249

228

221

219

261

796

845

830

768

913

849

809

733

686

698

759

817

751

755

724

767

667

Tuff above Neroly Formation and below the 

Contra Costa Group, near Lafayette

43 857 250 1.27 46 169 39 41 279 654

Sample analyzed by both neutron activation 

and X-ray fluorescence.

Borchardt, G. A., Aruscavage, P. J., and Millard, H. 

T., Jr., 1972, Correlation of the Bishop ash, a 

Pleistocene marker bed, using instrumental neutron 

activation analysis: Journal of Sedimentary 

Petrology, v. 42, no. 2, p. 301-306.

Bowman, H. W., Asaro, Frank, and Perlman, Isidore, 

1973, On the uniformity of composition in obsidian 

and evidence for magmatic mixing: Journal of 

Geology, v. 81, no. 3, p. 312-327.
REFERENCES CITED 15

Carmichael, I. S. E., Hempel, Joachim, and Jack, R. 

N., 1968, Analytical data on the U.S.G.S. standard 

rocks: Chemical Geology, v. 3, p. 59-64.

Clark, B. L., 1930, Tectonics of the Coast Ranges of 

middle California: Geological Society of America 

Bulletin, v. 41, no. 4, p. 747-828.

Clark, B. L., 1943, Notes on California Tertiary 

correlation, in Geologic formations and economic 

development of the oil and gas fields of 

California: California Division of Mines Bulletin 

118, p. 187-191.

Czamanske, G. K., and Porter, S. C., 1965, Titanium 

dioxide in pyroclastic layers from volcanoes in the 

Cascade Range: Science, v. 150, no. 3699, p. 1022- 

1025.

Dudas, M. J., Harward, M. E., and Schmitt, R. A., 

1973, Identification of dacitic tephra by 

activation analysis of their primary mineral 

phenocrysts: Quaternary Research, v. 3, p. 307-

OX0 •

Evernden, J. F., Savage, D. E., Curtis, G. H., and 

James, G. T., 1964, Potassium-argon dates and the 

Cenozoic mammalian chronology of North America: 

American Journal of Science, v. 262, p. 145-198.

Flanagan, F. J., 1969, Survey standards--!!, First 

compilation of data for the new U.S.G.S. rocks: 

Geochimica et Cosmochimica Acta, v. 33, p. 81-120.

Flanagan, F. J., 1973, 1972 values for international 

geochemical reference samples: Geochimica et 

Cosmochimica Acta, v. 37, p. 1189-1200.

Fleischer, Michael, 1969, U.S. Geological Survey 

standards--!, Additional data on rocks G-l and W-l, 

1965-1967: Geochimica et Cosmochimica Acta, v. 33, 

p. 65-79.

Huey, A. S., 1948, Geology of the Tesla quadrangle, 

California: California Division of Mines Bulletin 

140, 75 p.

Izett, G. A., Wilcox, R. E., Powers, H. A., and 

Desborough, G. A., 1970, The Bishop ash bed, a 

Pleistocene marker bed in the western United 

States: Quaternary Research, v. 1, p. 121-132.

Jack, R. N., and Carmichael, I. S. E., 1968, The 

chemical "fingerprinting" of acid volcanic rocks: 

California Division of Mines Special Report 100, p. 

17-32.

Jack, R. N., Lajoie, K. R., and Carmichael, I. S. E., 

1968 "Fingerprinting" of obsidian and pumice from 

the western United States [abs.]: Geological 

Society of America Special Paper 115, p. 107.

Jennings, C. W., and Burnett, J. L., 1961, Geological 

map of California, San Francisco sheet: California 

Division of Mines and Geology, scale 1:250,000.

Koenig, J. B., 1963, Geologic map of California, Santa 

Rosa sheet: California Division of Mines and 

Geology, scale 1:250,000.

Lajoie, K. R., and Carmichael, I. S. E., 1968, Late 

Pleistocene and Recent volcanism in the Mono Basin 

abs. : Geological Society of America Special 

Paper 115, p. 127.

Lydon, P. A., 1967, The origin of Tuscan Buttes and 

the volume of the Tuscan Formation in northern 

California, in Short contributions to California 

geology: California Division of Mines Special 

Report 91, p. 17-26.

Miller, W. L., 1966, Petrology of the Putah Tuff 

Member of the Tehama Formation, Yolo and Solano 

Counties, California: Davis, University of 

California, M. S. thesis, 85 p.

Oestreich, E. S., 1958, Geology of the Tassajara 

quadrangle: Berkeley, University of California, 

M. S. thesis.

Patten, P. R., 1948, The San Pablo Formation north of 

Mount Diablo, California: Berkeley, University of 

California, M. S. thesis.

Perlman, Isadore, and Asaro, Frank, 1969, Pottery 

analysis by neutron activation: Archaeometry, v. 

11, p. 21-52.

Randle, Keith, Goles, G. G., and Kittleman, L. R., 

1971, Geochemical and petrological characterization 

of ash samples from Cascade Range volcanoes: 

Quaternary Research, v. 1, p. 261-282.

Rogers, T. H., 1966, Geological map of California, San 

Jose sheet: California Division of Mines and 

Geology, scale 1:250,000.

Russell, R. D., 1931, The Tehama Formation of northern 

California: Berkeley, University of California, 

Ph.D. thesis.

Sarna-Wojcicki, A. M., 1971, Correlation of late 

Cenozoic pyroclastic deposits in the central Coast 

Ranges of California: Berkeley, University of 

California, Ph.D. thesis, 174 p.

Sarna-Wojcicki, A. M., 1976, Correlation of late 

Cenozoic tuffs in the central Coast Ranges of 

California by means of trace- and minor-element 

chemistry: U.S. Geological Survey Professional 

Paper 972, 30. p.

Sims, J. D., and Sarna-Wojcicki, A. M., 1975, New and 

revised stratigraphic names in the western 

Sacramento Valley, California, in Changes in 

stratigraphic nomenclature by the U.S. Geological 

Survey, 1973: U.S. Geological Survey Bulletin 

1395-A, p. A50-A55.

Strand, R. G., and Koenig, J. B., 1965, Geologic map 

of California, Sacramento sheet: California 

Division of Mines and Geology, scale 1:250,000.

Travis, R. B., 1952, Geology of the Sebastopol 

quadrangle, California: California Division of 

Mines Bulletin 162, 33 p.

Weaver, C. E., 1949, Geology and mineral deposits of 

an area north of San Francisco Bay, California: 

California Division of Mines Bulletin 149, 135 p.

Westgate, J. A., and Gold, C. M., 1974, World 

bibliography and index of Quaternary 

tephrochronology: Alberta, Canada, Alberta 

University, 528 p.

Woodring, W. P., Stewart, Ralph, and Richards, R. W., 

1940, Geology of the Kettleman Hills oil field, 

California: U.S. Geological Survey Professional 

Paper 195, 170 p.