Stratigraphy and Regional 

Relationships of a Reference 

Section for the Juana Lopez 

Member, Mancos Shale, in the 

San Juan Basin, New Mexico

By CARLE H. DANE, WILLIAM A. COBBAN, and ERLE G. KAUFFMAN

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1224-H

The lithology and faunal donation 

of a well-exposed surface section 

are described, and the section is 

compared with the abnormally thin 

section at the type locality
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1966

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

Washington, D.C. 20402 - Price 15 cents

V

4'
CONTENTS

Page

Abstract_________________________-_--_---_-----_----_._-________ HI

Introduction-_____________________________________________________ 1

Stratigraphic history of the Juana Lopez Member _____________________ 2

Lithology and thickness.___________________________________________ 4

Faunal zones, age, and correlation.__________________________________ 7

Stratigraphic sections _-__-----------------_-------_---------___-- 10

References__ _-____-_______--___-________-___---___---.____-_____ 14

ILLUSTRATIONS

Page 

FIGURE 1. Map showing location of type and reference sections, Juana

Lopez Member of Mancos Shale.-.-..-__________________ H3

2. Photograph of outcrop of reference section of Juana Lopez

Member__ __________________________________________ 6

3. Diagram showing stratigraphic ranges of fossils occurring in the

Juana Lopez Member__________________________________ 8
'» .4
CONTRIBUTIONS TO STRATIGRAPHY

STRATIGRAPHY AND REGIONAL RELATIONSHIPS OF A 

REFERENCE SECTION FOR THE JUANA LOPEZ 

MEMBER, MANGOS SHALE, IN THE SAN JUAN BASIN 

NEW MEXICO

By CARLE H. DANE, WILLIAM A. COBBAN, and ERLE G. KAUFFMAN *

ABSTRACT

The Juana Lopez is a member of the Mancos Shale in northwestern New 

Mexico and southwestern Colorado 'and a member of the Carlile Shale in central 

and southeastern Colorado and northeastern New Mexico. The member is 

characterized by ridge-forming hard thin platy layers of orange-brown-weathering calcarenite, which are interbedded with dark-gray noncalcarenitic clay shale.

The member is only 3 feet 10 inches thick at its type locality near Santa Fe, 

N. Mex., where it is predominantly calcarenite. Along the east side of the San 

Juan Basin, N. Mex., however, the thickness of the member ranges from 90 to 

135 feet (the maximum known thickness of the member), and it contains much 

more shale than calcarenite. A well-exposed stratigraphic section near La 

Ventana, N. Mex., is presented as a reference section for the member in the 

San Juan Basin, and its relationship to the unusually thin sequence at the 

type locality is- discussed.

Abundant peleeypods and ammonites indicate that the Juana Lopez Member 

is of early late Turonian age (Upper Cretaceous). In New Mexico ribbed oysters 

(Lopha litQubris), Inoceramus, and the ammonites Prionocyclus, Bacitlites, Coilopoceras, and Scaphitcs dominate the faunas. Fossils in the Juana Lopez Member on the east side of the San Juan Basin are distributed in distinct laterally 

persistent faunal zones.

INTRODUCTION

The Upper Cretaceous Juana Lopez Member is one of the most 

laterally persistent and lithologically distinctive divisions of the 

Mancos Shale in northwestern New Mexico and southwestern Colorado 

and of the upper part of the Carlile Shale in central and southeastern Colorado nnd northeastern New Mexico. It is characterized by 

numerous thin, slabby to platy resistant calcarenite beds separated by 

varying amounts of dark-gray clay shale. The calcarenite beds

1 Dept. of Paleobiology, U.S. Natl. Mus., Washington, D.C.

HI
H2 CONTRIBUTIONS TO STRATIGRAPHY

weather pale to moderate yellowish brown or orange brown and are 

composed largely of bioclastic debris, predominantly calcite needles 

or rounded grains of calcite derived chiefly from the prismatic layer 

of Inoceramtus shells, and oyster-shell fragments, worn fish teeth, and 

bone fragments.

During the past 5 years the writers have measured more than 15 

surface sections of the Juana Lopez Member in the type area and along 

the eastern and northern flanks of the San Juan Basin from Seboyeta, 

N. Mex., north to Pagosa Springs, Colo., and west to the vicinity of 

Ship Kock, N. Mex. Large collections of fossils were made from 

many of the sections. It is apparent from these studies that the Juana 

Lopez Member at the type section southwest of Santa Fe is abnormally thin (3 ft, 10 in.) compared with sections exceeding a hundred feet 

in thickness over much of the San Juan Basin. In advance of more 

detailed reports on the extent, lithology, stratigraphy, and faunal 

zonation of the Juana Lopez Member, we herein describe the member 

as it occurs on the east side of the San Juan Basin, establish an outcrop reference section of the member that is substantially representative of its occurrence there, and discuss the relationships of this section to the type section. The reference section is in the SE^SW1/^ 

sec. 14, T. 19 N., R. 1 W., northeast of La Ventana, Sandoval County, 

N. Mex. (La Ventana quad.).

STRATIGRAPHIC HISTORY OF THE JUANA LOPEZ

MEMBER

. Rankin (1944, p. 12, 19, and 20) applied the name "Juana Lopez 

sandstone member" to 10 feet of "very calcareous sandstone" which 

lies "near the top of the Carlile Shale" on the Mesita Juana Lopez 

Grant, in sec. 32, T. 15 N., R. 7 E., 6 miles northwest of Cerrillos, Santa 

Fe County, N. Mex. (fig. 1). Long before Rankin's work the distinctive nature and wide extent of the beds that he included in his "Juana 

Lopez sandstone member" had been noted by other authors (Newberry, 

1876, p. 87, 107; Stanton, 1893, p. 29, 32). Rankin, however, emphasized the lateral extent and continuity of the member by identifying it in measured stratigraphic sections around the margins of the 

San Juan Basin from near Ship Rock, N. Mex., northeast to Mancos, 

Colo., east to Pagosa Springs, Colo., and south to the Rio Puerco, 

northeast of Seboyeta, N. Mex.

Three years after Rankin's work, Pike (1947, p. 22, 29, 30 and pi. 6) 

described the member as the "late Carlile zone" and noted its distinct 

fauna and lateral persistence in the northwestern part of the San Juan 

Basin. In the same paper (p. 23) he mentioned in a footnote that 

since his paper had been written Rankin had applied the name "Juana
STRATIGRAPHY, JUANA LOPEZ MEMBER, MANGOS SHALE H3

107° 106°

37'

36'

^: v.; :{:X:^:/V;'Spring^

Lr

Area shown on figure 1

de Juana 

I Lopez Grant

.... _RNALILLO 10

VALENCIAt*;^;^V:\ Vo ... __________::/;X.#y.;'j-y::-.'V';\______i Albuquerque

10MILES

FIGUEE 1. Location of the type and reference sections of the Juana Lopez 

Member of the Mancos Shale, Sante Fe and Sandoval Counties, N. Mex. 

(Stippling shows much-generalized area of outcrop of Upper Cretaceous 

rocks.)
H4 CONTRIBUTIONS TO STRATIGRAPHY

Lopez Sandstone Member of the Carlile Shale" to his "late Carlile 

zone" in areas where it was a distinct lithologic unit. The name Juana 

Lopez has since been applied to the member in the type area by Stearns 

(1953, p. 968) and along the east side of the San Juan Basin by Dane 

(1960, p. 72), and it has been mentioned in regional papers by Cobban 

and Eeeside (1952, chart lOb) and Young (1960, p. 178). Juana Lopez 

has recently been accepted by the U.S. Geological Survey as a member 

of the Mancos Shale in the Ute Mountains area of southwestern Colorado (Ekren and Houser, 1965, p. 23) and as a member of the Carlile 

Shale in the Pueblo area of eastern Colorado (Scott, 1964). Kauffman (1965) applied the name widely in southern Colorado and northern New Mexico.

Subsequent to its definition by Kankin (1944) two other stratigraphic names have been applied to rocks now incorporated in the 

Juana Lopez Member. The name "Sanastee" was applied to part or 

all of the Juana Lopez in a road log of the New Mexico Geological 

Society Second Field Conference (1951, p. 46). The name was apparently derived from the trading post of Sanostee (present spelling), 

18 miles south of Ship Rock, and was in use by petroleum geologists 

and drillers long before its publication. Bozanic (1955, p. 91) noted 

the priority of Juana Lopez over "Sanastee" and stated "As a matter 

of priority the term Sanastee should be discarded in favor of Juana 

Lopez, but in actual practice such a change is not easily made, inasmuch 

as the Sanastee name is deeply entrenched in petroleum usage." Nevertheless, as Bozanic noted, the name Juana Lopez has unquestioned 

priority, and its formal description predates the first published usage 

of "Sanastee" by 7 years.

In southeastern and south-central Colorado, the term "Niobenton 

sand" has been applied informally by drillers to a very thin sequence 

of massive to slabby calcarenite beds that cap the Codell Sandstone 

Member of the Carlile Shale (Dane, Pierce, and Reeside, 1937, p. 217). 

Inasmuch as the derivation of the name does not allow it to be used 

formally in stratigraphy, and Scott (1964) and Kauffman (1965) 

correlated this unit with the Juana Lopez Member of New Mexico, 

the name "Niobenton" has been abandoned in favor of Juana Lopez 

in this area.

LITHOLOGY AND THICKNESS

The most characteristic lithologic feature of the Juana Lopez Member in outcrop in the San Juan Basin and elsewhere is its content of 

numerous hard dense slabby, platy, rarely massive beds of calcarenite 

which range from a fraction of an inch to several inches in thickness. 

The thickest beds normally occur near the top of the member; massive 

calcarenite beds, some of them exceeding a foot in thickness, are most
"STRATIGRAPHY, JTJANA LOPEZ MEMBER, MANGOS SHALE H5

common in areas where the member is abnormally thin, as at the type 

section. The thinnest calcarenite beds are ordinarily lenses of very 

limited extent. Small-scale crossbedding and extensively ripplemarked surfaces are common, particularly in the upper part of the 

member. Bedding surfaces, especially within and at the margins of 

massive calcarenite beds, are generally irregular, possibly reflecting 

small-scale scouring in an environment of vigorous wave or current 

agitation of the sea bottom.

In New Mexico, Juana Lopez calcarenite beds are light olive gray 

and, less commonly, medium gray, purplish gray, and grayish red on 

fresh fracture. They characteristically weather pale to moderate 

yellowish brown or orange brown. The beds are fine to coarse grained; 

the thinnest beds are generally finer grained than the slabby and massive units. The rock is dense, and the grains are tightly cemented with 

calcium carbonate. Many calcarenite beds are abundantly fossiliferous; most of the fossil material is broken and worn. The grains of 

calcarenite are predominantly bioclastic debris. The carbonate grains 

of most beds are predominantly fragmented calcareous needles from 

the prismatic layer of Inoceramus shells (inoceramite of Hattin, 1962, 

p. 41) together with small percentages of broken oyster shells, worn 

fish teeth and bone fragments, and shell fragments of other invertebrates. Some beds, particularly in the lower part of the member, 

include a conspicuous, though fractional, amount of greatly abraded 

grains of fish bone, teeth, and scales. Locally these beds have been 

described as "fish-tooth conglomerates," "fish-bone beds," "fish-tooth 

beds," or simply "fish beds."

Although the calcarenite beds are composed predominantly of carbonate with small percentages of phosphatic material (fish debris), a 

few beds, mostly in the lower part of the member, contain an appreciable percentage of silt- to sand-size grains of silica and some clay. 

Petrographic observation of calcarenite in measured sections has been 

random, and only a few thin sections have been studied, but the designation of almost all hard beds as calcarenite in these sections appears 

warranted.

Although the calcarenite beds constitute only a small fraction of the 

total thickness of the member in the San Juan Basin, they are resistant 

to erosion, and plates, ranging from a few inches to more than a foot 

in diameter, litter the surface of the outcrops and creep long distances 

down shale slopes where they are more conspicuous than the associated 

shales.

The dominant lithology of the Juana Lopez Member in the San 

Juan Basin is fissile medium-dark-gray to black noncalcareous clay 

shale that weathers light gray and is easily eroded. The shale in798-003 O 6'6 2
H6 v^/Hp. .- - CONTRIBUTIONS TO STRATIGRAPHY

eludes, especially in the upper part of the member, limestone and limestone-siderite concretions that are light to medium gray on fresh fracture and weather gray to grayish orange. Some of the concretions 

are septarian. They occur either isolated in the shale or localized in 

zones and range from a few inches to several feet in diameter. 

Bentonite beds as much as several inches in thickness are present at 

many places. Owing to the generally poor soft-shale exposures in 

the Juana Lopez Member and the marked downslope creep of bentonitic material, the precise position and thickness of bentonite beds in 

many sections were not determined. On the eastern and southeastern

jl&fcs.

FIGUBE 2. Outcrop of reference section of the Juana Lopez Member of the 

Mancos Shale, northeast of La Ventana, N. Mex.

flanks of the San Juan Basin, the Juana Lopez Member ranges in 

thickness from 90 to 135 feet. In the reference section it is nearly 

107 feet thick, which seems to be only slightly below the average for 

this part of the basin (fig. 2).

Reexamination of the type section in 1963 demonstrated that: (1) 

although Rankin's (1944) measured section of Coloradoan sediments 

started in sec. 32, the Juana Lopez is exposed in sec. 33, T. 15 N., R. 

7 E., (2) the thickness of the Juana Lopez at the type section is only 

3 feet, 10 inches, the rest of Rankin's original estimate of 10 feet being 

made up of baked resistant shale of earliest Niobrara age (latest 

Turonian) overlying the Juana Lopez and a massive brown-weathering sill of hornblende monzonite porphyry (Disbrow and Stoll, 1957)
STRATIGRAPHY, JUANA LOPEZ MEMBER, MANGOS SHALE H7

that caps the ridge, (3) the Juana Lopez at the type section is composed predominantly of calcarenite and limestone, in view of which, 

the term "Sandstone" has been dropped from the member name, and 

(4) the Juana Lopez Member at the type section is abnormally thin 

and contains an unusually small percentage of shale as compared with 

sections more than 100 feet thick in the eastern San Juan Basin which 

are predominantly shale.

Subsurface data in the San Juan Basin corroborate outcrop observations. Bozanic (1955, p. 91) recognized the Juana Lopez Member 

in the subsurface of the northern San Juan Basin as "a persistent 

discernible interval of roughly 120 feet, which will vary somewhat 

due to occasional arbitrarily chosen boundaries. In some areas, two 

distinct units are present, whereas in other parts of the basin the 

lower part is transitional with and not distinctly separable from the 

upper development". McPeek (1965, fig. 2, sec. B-B') identified the 

Juana Lopez Member in electric logs of 12 wells on the east side of 

the San Juan Basin as an interval ranging from 115 to 135 feet in 

thickness. Other subsurface information and similarity of intervals 

from the bottom and top of the Juana Lopez to lower and higher 

horizons in the Mancos Shale indicate that the member, as identified 

in the subsurface, includes the. same stratigraphic sequence as it does 

in surface exposures.

FAUNAL ZONES, AGE, AND CORRELATION

Calcarenite, shale, and concretions in the Juana Lopez Member at 

the reference section and throughout the San Juan Basin are fossiliferous. The calcarenite beds indicate periods of abundant invertebrate 

life on the shallow sea floor, favorable living conditions for sharks and 

other fish, and long periods of negligible accumulation of terrigenous 

sediments or chemical carbonate deposits.

Seven genera of mollusks dominate the invertebrate faunas of the 

Juana Lopez almost to the exclusion of others. These are the ammonites Prionocyclus, Scaphites, Baculites, and Coilopoceras, and the 

pelecypods Inoceramus, Lopha, and LuGina. Many of the species are 

widely distributed in time-equivalent strata in the western interior and 

thus form a good basis for faunal zonation and correlation. Good 

faunal zoning can be recognized in the thick Juana Lopez sections in 

the San Juan Basin.

The ranges of the significant species insofar as they are now known 

are shown on the accompanying chart on which the Juana Lopez is 

divided arbitrarily into equal lower, middle, and upper parts (fig. 3). 

The regional applicability of this zoning has not yet been fully tested.

Coilopoceras colleti Hyatt is in the lower part of the member to-
H8

gether with a form of Prionocyclus mcwombi Meek that has a wellarched venter, but only P. macombi persists into the middle and upper 

parts, where it becomes more flat ventered, in marked contrast to the 

earlier form. Prionocyclus wyomingensis wyomingensis Meek is restricted to the basal and middle parts of the upper third of the member 

and P. wyomingensis elegans Haas to the uppermost ledges. In the 

upper part of the member distinct species of ScapMtes occur at three 

levels: 8capMtes warreni Meek and Hayden in the lower beds, Scaphites ferronensis Cobban in the middle part, and the more delicately

JUANA LOPEZ MEMBER

LOWER

Lopha lugubris (finely 

plicate)

Prionocyclus macombi 

(flat venter)

Prionocyclus wy 

Luci

MIDDLE

Coilopoceras colleti 

Lopha lugubris (coarsely 

Prionocyclus macombi (ar

Scaphites warreni 

Scaphitesfe

omingensis wyomingensis

na sp. cf . L. mattiformis 

Lopha lugubris (finely 

Seal

Inocet 

Prionocyclus wyom 

Baculit

UPPER

plicate)

ched venter) 

Inoceramus dimidius

rronensis ^ 

plicate-smooth) ^ 

amus perpkxus 

ingensis elegans 

es cf . B. besairei 

FIGURE 3. Generalized stratigraphic ranges of some fossils occurring in the 

Juana Lopez Member of the Mancos Shale on the east side of the San Juan 

Basin, N. Mex. The member is divided arbitrarily into equal lower, middle, 

and upper parts which have no lithologic significance.
STRATIGRAPHY, JUANA LOPEZ MEMBER, MANGOS SHALE H9

ribbed Scaphites whitfieldi Cobban in the highest beds associated with 

Inoceramus perplexus Wliitfield, Prionocyclus wyomingensis elegans, 

and a small smooth baculite, Baculites of. B. besairei Collignon. Inoceramus dimidius White ranges from the base nearly to the top of the 

member, where it is replaced by Inoceramus perplexus. Lucina sp. cf. 

L. mattiformis Stephenson has been found thus far only in the lower 

part of the upper third of the member. Varieties of LopTia lugubris 

(Conrad) occur throughout the member, and this is perhaps the most 

abundant species. A coarsely plicate form is restricted to the basal 

third of the member; more finely plicate forms are found in the middle 

third and in the lower part of the upper third; and, in the topmost 

layers, smooth to very finely plicate forms are rare or apparently 

absent locally.

In a general way the ranges of the fossils are such that five faunal 

zones can be recognized in ascending order as follows: (1) Zone of 

Ooilopoceras colleti, coarsely plicate Lopha lugubris, and Prionocyclus 

macombi with well-arched venter, (2) zone of finely plicate Lopha 

lugubris and Prionocyclus macombi with flatter venter, (3) zone of 

Prionocyclus wyomingensis wyomingensis and Scaphites warreni, 

together with finely plicate Lopha lugubris and Prionocyclus macombi, 

(4) zone of Scaphites ferronensis along with Prionocyclus wyomingensis ivyomingensis, P. macombi (flat venter), arid Inoceramus 

dimidius in the highest part of their range, (5) zone of Scaphites 

whitfieldi, Inoceramus perplexus, and Prionocyclus wyomingensis 

elegans.

The distinctive aspect of the Juana Lopez Member facilitates its 

recognition and lithologic correlation, but time correlation of the unit 

is more difficult. The progression of ammonites and pelecypods noted 

in the thick sections of the 'San Juan Basin is not fully represented at 

the type section of the member where the lowest recognizable faunal 

zone, occurring near the base of the member, is that of Scaphites 

ferronensis. The older zones of Scaphites warreni, Prionocyclus 

macombi (late form) with finely plicate Lopha lugubris, and Prionocyclus macombi (early form) with coarsely plicate Loplia lugubris 

are absent. This suggests that the Juana Lopez of the type section 

is the lithologic and time equivalent of only the upper part of the 

reference section on the eastern flank of the San Juan Basin. It 

seems therefore that the abrupt eastward thinning of the Juana Lopez 

in north-central New Mexico is caused by facies change in the lower 

half of the section. The lower part of the Juana Lopez of the 

reference section apparently grades laterally into dark-bluish-gray 

clay shale that lacks calcarenite and lies below the Juana Lopez of
H10 CONTRIBUTIONS TO STRATIGRAPHY

the type section. Unfortunately the shale is unfossiliferous in the 

upper part, and no definite f aunal correlations can be made.

Throughout the San Juan Basin the Juana Lopez Member rests 

on shale of middle Carlile (Blue Hill, Codell) age. The contact 

between the Juana Lopez Member and the underlying Mancos Shale 

is gradational and conformable. Lateral gradation between the basal 

Juana Lopez and the top of the underlying shale unit has been 

established.

The beds above the Juana Lopez Member on the eastern and southern 

flanks of the San Juan Basin in New Mexico are of latest Carlile age, 

where an age has been established, and are composed predominantly 

of dark clay shale. On the south side of the San Juan Basin the Juana 

Lopez Member is overlain by shale of late Carlile age that lies below 

one of the tongues of the Gallup Sandstone of the Mesaverde Group. 

For the present, it seems practicable to consider the Juana Lopez 

throughout the San Juan Basin as a member of the Mancos Shale 

rather than to attempt to apply Colorado Front Range nomenclature 

to the sequence. Even in the northeastern part of the basin in New 

Mexico, where the name "Carlile shale member" was used by Dane 

and Bryson (1938), it appears that Carlile is of debatable value as a 

lithologic unit because of the uncertainty of the upper contact south 

of the geographic extent of the Fort Hays Limestone Member.

At its type section the Juana Lopez Member is succeeded disconf ormably by rocks equivalent to the basal part of the Niobrara Formation in southeast Colorado, and the younger Carlile rocks of the east 

and south sides of the 'San Juan Basin are missing.

Stratigraphic sections of the Juana Lopez Member at the new reference section and at the type locality follow.

STRATIGRAPHIC SECTIONS

Reference section of the Juana Lopez Member of the Mancos Shale, SE%SW% sec. l4

T. 19 N., R. 1 W.

[Measured 3 miles southeast of San Miguel School and just east and northeast of Ruben Tafoya detention 

dam, in La Ventana quad., Sandoval County, N. Mex., by C. H. Dane, October 1959, and C. H. Dane, 

W. A. Cobban, and E. R. Landis, Aug. 1963. Additional fossil collections made by Erie G. Kauffman 

and G. R. Paulson in June 1964]

Mancos Shale (part): 

Shale, dark-gray. 

Juana Lopez Member (top):

Siltstone, calcareous, with minutely comminuted fish re- Ft in. 

mains. _________-_______---____--__-__--__.----_____ 2

Shale, dark-gray _____________________________________ 10

Bentonite, thickness only determinable approximately___ 6 

Shale, dark-gray_______-__-_____-_---_____-_--______ 5
STRATIGRAPHY, JUANA LOPEZ MEMBER, MANCOS SHALE Hll

Reference section of the Juana Lopez Member of the Mancos Shale,

sec. 14 T. 19 N., R. 1 W. Continued 

Mancos Shale (part) Continued

Juana Lopez Member (top) Continued

Calcarenite, fine-grained, in beds % to 2 in. thick, and thinbedded very fine grained calcarenite. Unit thickens Ft in. 

along outcrop to as much as 2 ft 8 in -----_-_---_____ 2 2

USGS D3672:

In.oceramus perplexus Whitfield 

Lopha lugubris (Conrad)? 

Anisomyon apicalis Sidwell 

Baculites cf. B. besairei Collignon 

Scaphites whitfieldi Cobban

Prionocyclus wyomingensis Meek var. elegans Haas 

Shale.-----.-----------------------------------..--. 2 2

Calcarenite, very silty_______--_----_______-__-________ 5

Shale, dark-gray____- _________________________________ 1 8

Bentonite __ ________________________________________ 1

Shale, dark-gray___-__-__-__-___-_-_--_---__-_--______ 3

Calcarenite, in beds % to 1 in. thick; unit thins along outcrop to as little as 2 in_ ___-___----__-----_-___---.__ 8

Shale, dark-gray_-_-----____-_---_-_---___--- --------- 1 6

Calcarenite, lenses out within 100 ft along outcrop.----..- 2%

Shale, dark-gray _ ___________________________________ 1 3

Bentonite __ _ _-__-_---____-___-_-____-__-__-____-___ 4

Shale, dark-gray __ __________________________________ 9

Calcarenite, fine-grained, very slightly silty, with some 

comminuted fish remains; in beds Mo to % in. thick; unit 

as much as 6 in. thick locally-. ______________________ 3

Shale, dark-gray____ --------- _________________________ 6 8

Zone of concretions, large, rounded, y.ellowish-gray-weathering; dense carbonate but with dusky-brown crystalline 

carbonate patches. Concretions are 1 to 2 ft thick and 

1 to 3 ft long.. _.----..__._._______...____---_-.---_ 2 0

Shale, dark-gray __ _ _________________________________ 4 10

Limestone, very finely granular, in two beds each % in.

thick with intervening shale _ _ _ _____________________ 2

Shale, dark-gray-__-----_--_-_---_----__---------_---- 10 0

Bentonite. _ - --------__________--__-___-____________ 1

Shale, dark-gray______-___ _._____.-___________-____.-_ 7 0

Calcarenite, very fine grained, hard, in two beds each % in.

thick with intervening shale __ _ _ ____________________ 2}_

USGS D4411: Lucina sp. 

Shale, dark-gray __ __________________________________ 3

Bentonite __ _ ___---_--_____-________-____-_____-__-_ %

Shale, dark-gray __ __________________________________ 14 6

Calcarenite, very fine grained, in irregular bed % to 2 in. 

thick with associated tan-weathering limestone concretions. __------_-_-_-________--_____---__-_-___-_ 2

USGS 4410: Lopha lugubris Conrad, finely plicate

variety 

Shale, dark-gray _ ___________________________________ 8 0
H12 CONTRIBUTIONS TO STRATIGRAPHY

Reference section of the Juana Lopez Member of the Mancos Shale,

sec. 14 T. 19 N., R. 1 W. Continued 

Mancos Shale (part) Continued

Juana Lopez Member (top) Continued

Shale, dark-gray; contains gray septarian limestone concre- Ft in. 

tions near the top with finely plicate oysters__.___._. 26 0 

USGS D4409: Lopha lugubris Conrad, finely plicate

variety

Shale, black; in the upper part contains rounded yellowishgray carbonate concretions weathering pale brown to 

grayish orange; from 1 to 2 ft thick and 1 to 2 ft long... 3 4 

Calcarenite, very fine-grained, in beds ^ to 4 in. thick; contains coarsely plicate oysters and other fossils.__-_____- 4

USGSD3671:

Lopha lugubris Conrad, coarsely plicate variety 

Inoceramus dimidius White 

Prionocyclus macombi Meek 

Concealed-.----------------------------------------- 3 0

Calcarenite, thin-bedded, lenticular.__--_-_-----_-___.__ 1

Shale, black....--_..-___.........-_-_...............- 1 10

Bentonite _ _________________________________________ Yz

Shale, black__..._._______.._._____.._....._..._.__. 10

Bentonite _ _________________________________________ Vi

Shale, black____.__...________._____.___...___._._ 3

Calcarenite, fine-grained, silty, with some comminuted fish 

remains in beds % to 1% in. thick; crossbedded; contains 

coarsely plicate oysters and other fossils.__-_____.-__ 8

USGS D4408:

Lopha lugubris Conrad, coarsely plicate variety 

Inoceramus dimidius White 

Prionocyclus macombi Meek 

Shale, black.--_---__----........-----__---------_---- 1 8

Calcarenite, hard.____________________________________ }i

Shale, black_-_-----------_-_-_-_---_--------_--._-__- 1 1

Siltstone, calcareous, hard, crossbedded, with abundant 

grayish-brown to dusky-brown minutely fragmented fish 

remains ____________-____________--_-_-__-_-_---__- 2

(Base of member.)

Total Juana Lopez Member____________------_____---_ 106 11

Shale, black______________..__.____-__--_-________. 1 9

Bentonitic zone; includes one bed about 1 in. thick and

several thinner beds._.__-______-_-_--________-____ 4}

Shale, black-------.-...._.-.-..---_-__-_----__-___ 6 0

Shale, black; at the top is a zone of concretions that weather 

grayish orange and pale brown; up to 1 ft thick and 

several feet long. Concretions are mostly dense gray 

carbonate but have some dark-brown crystalline carbonate patches.
^ STRATIGRAPHY, JUANA LOPEZ MEMBER, MANCOS SHALE H13

v Type section of Juana Lopez Member of the Mancos Shale, NW%SEy^ sec. 33, T. 15

N., R. 7 E.

[Measured on property of Sam Brown, realtor, Albuquerque, Madrid quad., Santa Fe County, N. Mex., 

_, by E. G. Kauflman and G. R. Paulson, July 1963. This Is section at type locality originally stated by

- Rankin (1944) to be in sec. 32, T. 15 N., R. 7 E., on the Mesita Juana Lopez Grant 6 miles northwest of 

Cerrillos]

^> Massive sill (mapped by Disbrow and Stoll, 1957, as Ti 1, which ft in. 

includes principally hornblende monzonite porphyry )..__._____ 3 0

y Mancos Shale (part) :

Niobrara Shale equivalent:

Shale, baked, thin-bedded to platy, brittle, resistant, 

> dark-gray, light-gray-weathering; contains a fauna of

earliest Niobrara age (late Turonian) ________________ 2 6

^ >. ' USGS 28766:

Scaphites sp. aff. S. geinitzi d'Orbigny

 * Prionocyclus wyomingensis elegans Haas

Worthoceras"? sp. 

Baculites sp. (smooth) 

j Trace of ammonite with constrictions

Inoceramus ex. gr. /. labiatus (Schlotheim)

>, ^, ( = problematicus Schlotheim of Meek; aviculoides Meek and Hayden)

->' Pycnodonte? sp. aff. P.? congesta (Conrad)

Nuculana sp.

 -* Hoploparia sp.

Hamulust sp. 

"*" Solitary coral, indet.

fish bone, teeth, scales 

Juana Lopez Member (top) :

_ ;, Calcarenite, dark-gray, brown- and rusty-weathering, 

fine- to medium-grained, granular, very dense and

 i. hard; in\3 distinct massive beds separated by 1 in. 

layers of shaly calcarenite and calcareous shale; forms

"^ a ledge and has a petroliferous odor. ___-____-_---___ 1 4>_ 

USGS 28765:

Inoceramus perplexus Whitfield 

Ostrea sp.

Scaphites whitfieldi Cobban 

, $ Prionocyclus wyomingensis elegans Haas

fish debris

' Calcarenite, dark-gray, rusty- and tan-weathering, finegrained, granular, well-cemented, moderately resistant,

*>" platy to shaly; interbedded with dark-gray calcarenitic

USGS 28764:

Inoceramus perplexus Whitfield 

Lopha lugubris (Conrad)? (smooth right valves) 

Scaphites whitfieldi Cobban

Calcarenite, dark-gray, rusty-brown-weathering, finegrained, petroliferous; grades to bioclastic limestone 

and forms a hard ledge.- _ _________________________ 3}_
H14 CONTRIBUTIONS TO STRATIGRAPHY

Type section of Juana Lopez Member of the Mancos Shale, NWy^SEy^ sec. 83,

T.15N.,R.7 #. Continued 

M&ncos Shale (part) Continued

Juana Lopez Member (top) Continued

Calcarenite, dark-gray, fine-grained, slabby to platy, 

interbedded with dark-gray thin-bedded calcareous Ft inshale.-_______________________J__________________ 4

USGS 28763:

Inoceramus sp. aft. /. dimidius White

Lopha? sp. aflf. L. lugubris (Conrad) (smooth

valves only)

Prionocyclus wyomingensis Meek subsp. indet. 

Scaphites whitfieldi Cobban 

fish debris

Limestone, dark-gray, brown-weathering, bioclastic, massive, hard, fine-grained, petroliferous._______________ 4

USGS 28762:

Inoceramus dimidius White 

Scaphites ferronensis Cobban 

Prionocyclus wyomingensis Meek subsp. indet. 

fish scales and bone and tooth debris 

Limestone, medium-gray, fine-grained, resistant._______ 1

Siltstone, soft, granular, and silty, sandy hard calcarenite; interbedded dark-gray carbonaceous platy 

to fissile shale. Entire unit calcareous and petroliferous. ___--_--__-_-------_----__-___---_-___-__ 9

Limestone, medium-gray, brown-weathering, bioclastic,

fine-grained, granular, dense, slabby...-___-______.__ 1-2

Total Juana Lopez Member..__________________________ 3 10

Shale, black, bluish-black-weathering, thin-bedded, soft, noncalcareous; weathers- papery. Poorly exposed but complete fresh section dug out in gully..____________________ 3 4

Bentonite, orange and buff, clayey..______________________ 1

Shale, black, blue-black- and dark-gray-weathering, soft, non-

- calcareous, thin-bedded; weathers thin-bedded to papery.

Lies on a zone of septarian limestone concretions. Well

exposed at base, poorly exposed at top, but completely dug

out in a gully._______________________________________ 29 5

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w* STRATIGRAPHY, JUANA LOPEZ MEMBER, MANGOS SHALE H15

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U.S. GOVERNMENT PRINTING OFFICE: 1966 O 798-003