Principal Reference Section for the 

Santa Rosa Formation of 

Middle an<J 

U.S. GEOLOGICAL SURVEY BULLETIN 1804 

Principal Reference Section for the 

Santa Rosa Formation of 

Middle and Late Triassic Age, 

Guadalupe County, New Mexico 

Edited by WARREN I. FINCH 

This bulletin is published as chapters A through C. 

These chapters are not available separately. 

U.S. GEOLOGICAL SURVEY BULLETIN 1804 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 

For sale by the Branch of Distribution 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Principal reference section for the Santa Rosa formation of middle and late Triassic 

age, Guadalupe County, New Mexico. 

(U.S. Geological Survey bulletin ; 1804) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1804A-C 

1. Sandstone-New Mexico-Guadalupe County. 2. Geology, StratigraphicTriassic. 3. Santa Rosa Formation (N.M. and Tex.) I. Finch, Warren Irvin, 

1924- II. Series. 

QE75.B9 no. 1804 557.3 s [551.7'62'0978925] 87-600312 

[QE471.15.S25] 
CONTENTS 

[Letters designate chapters] 

(A) Description of the Principal Reference Section for the Santa Rosa Formation, by Warren I. Finch. 

(B) Interpretive Depositional History of the Santa Rosa Formation at the Principal Reference Section, by Robert Lupe. 

(C) Fossil Plants from the Mudstone Member of the Santa Rosa Formation at 

the Principal Reference Section, by Sidney R. Ash. 

Contents Ill 

Chapter A 

Description of the Principal Reference 

Section for the Santa Rosa Formation 

By WARREN I. FINCH 

With a section on PALEOMAGNETIC CHARACTER OF THE 

SANTA ROSA-PERMIAN CONTACT 

By SCOTT C. REEVE 

U.S. GEOLOGICAL SURVEY BULLETIN 1804 

PRINCIPAL REFERENCE SECTION FOR THE SANTA ROSA 

FORMATION OF MIDDLE AND LATE TRIASSIC AGE, 

GUADALUPE COUNTY, NEW MEXICO 
CONTENTS 

Abstract 1 

Introduction 1 

Historical review of nomenclature 2 

Principal reference section of Santa Rosa Formation 2 

Lower sandstone member 6 

Middle sandstone member 7 

Mudstone member 7 

Upper sandstone member 8 

Paleomagnetic character of the Santa Rosa-Permian contact 8 

References cited 10 

FIGURES 

1. Map showing the location of the Santa Rosa area in northeastern New 

Mexico 3 

2. Map of part of the Santa Rosa 7 .5-minute quadrangle showing the location of the principal reference and type sections and fossil plant 

localities 4 

3-8. Photographs showing: 

3. The measured lower sandstone member and its contacts with Permian rocks and the middle sandstone member 6 

4. An outcrop of the lower sandstone member in the railroad cut 6 

5. Angular blocks of mudstone in the middle sandstone member 7 

6. An outcrop of the conglomerate zone near the base of the middle 

sandstone member 7 

7. The nature of the contact between the mudstone member and the 

underlying middle sandstone member 8 

8. The weathering character of the upper sandstone member and its 

relation to the mudstone member 8 

9. Plot of paleomagnetic properties of the basal 9 m of the lower sandstone 

member and the upper 2m of the Grayburg and Queen Formations 9 

TABLE 

1. Stratigraphy of the Dockum Group in the Santa Rosa area, New 

Mexico 2 

VI Contents 
Description of the Principal Reference 

Section for the Santa Rosa Formation 

By Warren I. Finch 

Abstract 

Because the type section for the Santa Rosa Formation 

is incomplete and the upper contact of the section is not exposed, a principal reference section is herein established at a 

more accessible location. The principal reference section is exposed in the cuts of the railroad grade at the east edge of the 

town of Santa Rosa and continues along the banks of El Rito 

Creek and into nearby slopes. The principal reference section 

is 228ft thick and consists of four informal members, in ascending order: lower sandstone member, middle sandstone 

member, mudstone member, and upper sandstone member. 

These members can be traced over a large part of Guadalupe 

County, and some can be recognized farther to the east and 

south. The basal contact with Permian rocks is erosional. Collapse of underlying Permian salt influenced the deposition of 

the three lower members. The upper contact with the Chinle 

Formation is marked by a slight erosional disconformity and 

an abrupt change in lithology. Each member has distinct 

sedimentary structures and lithologic characteristics. 

INTRODUCTION 

The Santa Rosa Formation of Middle and Late 

Triassic age is the basal formation of the Dockum Group 

in the central part of eastern New Mexico (table 1). The 

Santa Rosa Formation consists chiefly of thick sandstone 

beds that crop out over large areas in Guadalupe, San 

Miguel, Quay, and De Baca Counties, and small areas 

in some adjacent counties (fig. 1). The Santa Rosa extends eastward along the Canadian River into Oldham 

County, Tex., where in the Trujillo 7 .5-minute quadrangle, reconnaissance mapping in 1972 revealed its probable pinchout (Finch and others, 1976). The recognition 

of the Santa Rosa along the Canadian River east of 

Tucumcari and its extension into Texas is controversial 

(Trauger and others, 1972) and is not shown on the 

geologic map of the Tucumcari Sheet (Barnes, 1983). 

More recent work by Lucas and others (1985) concludes 

that outcrops of sandstone of the Santa Rosa along the 

Canadian River are too limited to map at a scale of 

1:500,000, and they have modified the map of Dane and 

Bachman (1965) to show only the Chinle Formation. 

Dane and Bachman ( 1965) were unable to map the Santa 

Rosa at 1:500,000 scale south of the 34th parallel because 

of poor, small outcrops and southward thinning and 

probable pinching out of the Santa Rosa. The name 

"Santa Rosa Sandstone" has been used for isolated outcrops of basal Dockum sandstone and conglomerate in 

Eddy County, N. Mex., by Hendrickson and Jones 

(1952), Vine (1963), and Barnes (1976), and in Mitchell 

County, Tex., by Roberts (1941). These extensions of the 

Santa Rosa beyond its clearly recognized outcrop area 

shown by Dane and Bachman (1965) in central eastern 

New Mexico are questionable. The nature of the sandstone and conglomerate beds at and near the base of 

Dockum appear to be analogous to the Shinarump 

Member of: the Chinle Formation and other units at and 

near the base of the Upper Triassic section in the Colorado Plateau region. Early work on the Colorado 

Plateau led to the idea of a widespread occurrence of a 

single thin sheet of Shinarump over the entire Plateau and 

even beyond; whereas later detailed work showed that the 

Shinarump was not a single widespread unit but rather 

consisted of several distinct stratigraphic units each having their own separate source areas and directions of sediment transJl>ort (Stewart, 1957; Finch, 1959; Stewart and 

others, 1972; McGowen and others, 1979, fig. 4). My 

studies of sedimentary structures and pebble distribution 

and my reconnaissance mapping indicate that the Santa 

Rosa ought to be restricted to the vicinity of the outcrop 

pattern shown by Dane and Bachman (1965). 

When the "Santa Rosa Sandstone" was first introduced by Rich (1921) and described by Darton (1922), 

no type section was established, a common practice in 

early days. In 1971, I measured a section in the Santa 

Rosa area with the intention of establishing a type section. Later 1in 1972, I discovered that Vincent C. Kelley, 

University of New Mexico, had at about the same time 

measured a section nearby, which was established as the 

type sectiom (Kelley, 1972). Examination of his section 

revealed that the mudstone member, which is intermittent, was absent, and that the top of the section was not 

exposed. 1lherefore, the purpose of this report is to 

designate a' principal reference section that is complete, 

well exposed between the Permian Artesia Group and the 

Triassic Chinle Formation, and quite accessible. 

Description of the Principal Reference Section for the Santa Rosa Formation 
Table 1. Stratigraphy of the Dockum Group in the Santa Rosa area, New Mexico. 

Age Group Formation 

Redonda 

Formation 

Late Dockum Chinle 

Triassic Formation 

Group Santa 

Rosa 

Formation 

Middle 

Triassic 

1

Cuervo Sandstone Member of Kelley (1972) 

The results of the studies reported in this bulletin 

are outgrowths of a broader study of the uranium potential in Triassic rocks of the southern High Plains, mainly in eastern New Mexico and West Texas, made by J. C. 

Wright 1967-1968 and continued by me 1968-1972. 

Robert Lupe made special studies of the sedimentary environment of the principal section in 1971, and Sidney 

R. Ash studied the plant fossils in 1971; the results of 

these studies are given in chapters B and C of this bulletin, 

respectively. A study was made of the paleomagnetic 

character of rocks in the section by Scott C. Reeve (1975); 

a brief summary of that study as it relates to the lower 

contact of the Santa Rosa with Permian rocks is presented 

at the end of this chapter. Measurements of length, 

distance, thickness, elevation, and size are given in each 

chapter in either the English or metric system, whichever 

was used in the original measurement. 

HISTORICAL REVIEW OF NOMENCLATURE 

The original reference to the "Santa Rosa Sandstone" was in 1919 by Dorsey Hager and A. E. Robitaille 

(1919), who list it in their correlation table for a report 

on oil possibilities in eastern New Mexico. The "Santa 

Rosa Sandstone" was described by Rich (1921) as "a very 

definite unit exposed at Santa Rosa" and elsewhere along 

the Pecos River. The name "Santa Rosa Sandstone" was 

adopted by the U.S. Geological Survey for N. H. 

Darton's report of July, 1919, but his report was not 

published until 1922. Darton (1922) defined the "Santa 

Rosa Sandstone'' as resistant massive sandstone near 

the bottom of the Dockum Group that crops out prominently in mesas of Guadalupe County and along the 

Pecos River at Santa Rosa. He stated that ''This sandMember 

Upper shale member 

Middle sandstone member 1 

Lower shale member 

Upper sandstone member 

Mudstone member 

Middle sandstone member 

Lower sandstone member 

stone appears to occur at about the horizon of the 

Shinarump conglomerate, but no definite correlation is 

possible . . . ''. 

The "Santa Rosa Sandstone" was mapped in 

central eastern New Mexico by later workers, such as 

Gorman and Robeck (1946), Lang (1947), Bachman 

(1953), Wanek (1962), and Johnson (1969), but none of 

these authors established a type locality. Vincent C. 

Kelley, University of New Mexico, in connection with 

mapping the Fort Sumner Sheet, set up a type section 

located along the steep walls of the Pecos River in SW Y4 

sec. 35, T. 9 N., R. 21 E., about a mile north of 

downtown Santa Rosa (fig. 2; Kelley, 1972, p. 21-22). 

Because a type section has been established, the section 

described herein must be referred to as the principal 

reference section for the "Santa Rosa Sandstone." 

Lucas and others (1985) renamed the "Santa Rosa 

Sandstone" the Santa Rosa Formation because it contains significant amounts of conglomerate and mudstone. 

Even though the Santa Rosa is most distinctive as a continuous sandstone unit, this renaming as Santa Rosa Formation seems appropriate and is adopted for this bulletin. 

Future work outside the present known distribution of 

the Santa Rosa may reveal time correlative deposits whose 

lithology is not sandstone. This would allow the extension of the Santa Rosa Formation nomenclature 

throughout the Dockum Basin. 

PRINCIPAL REFERENCE SECTION OF 

SANTA ROSA FORMATION 

The principal reference section of the Santa Rosa 

Formation is adjacent to and northeast of the city of 

Santa Rosa. The section was measured along an 

2 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
COLORADO 

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ROOSEVELT 

LINCOLN 

25 50 MILES 

25 50 KILOMETERS 

Figure 1. Map of northeastern New Mexico showing the location of the Santa Rosa area. 

Description of the PrincipaiiReference Section for the Santa Rosa Formation 3 
approximately 1-mi-long, east-trending traverse through 

the railroad cuts of the Chicago Rock Island and PacificSouthern Pacific Railroad adjacent to the banks of El Rito 

Creek and onto the gentle slopes north of the westernmost lake of Tres Lagunas in NY2 sec. 1, T. 8 N., R. 21 

E., and SE Y4 sec. 36, T. 9 N., R. 22 E. (fig. 2). This site 

was chosen because of its accessibility, nearly perfect exposures, well-defined members, and exposed basal and top 

contacts of the Santa Rosa with the Permian Artesia 

Group and the Chinle Formation, respectively. No other 

complete, well-exposed single exposure of the Santa Rosa 

is known to me. Early workers such as Dorsey Hager, A. 

E. Robitaille, J. L. Rich, and N.H. Darton undoubtedly 

used the railroad as their chief means of travel to Santa 

Rosa. The Santa Rosa depot is only a mile from the base 

of the principal reference section, and these early workers 

very likely examined the section. One can drive to within 

a hundred yards of the base of the section. 

The regional dip of the rocks in the area of the section is about one degree eastward. This dip is interrupted 

locally by gentle to moderately steep folds a hundred feet 

to as much as a half mile across. These folds represent 

T. 9 N. 

T. 8 N. 

Base from U.S. Geological Survey, 

1:24,000 Santa Rosa, 1963 

deformation into sinkholes formed by the dissolution of 

salts in the underlying Permian rocks. The dips of the 

lower members of the Santa Rosa and exposed Permian 

beds are more affected by this dissolution than are the 

uppermost member of the Santa Rosa and the overlying 

Chinle Formation. Thinning and thickening of the lower 

members of the Santa Rosa are evident depositional 

responses to the dissolution of salt. The line of the measured section crosses one fold at the place where the mudstone member is exposed. Kelley (1972) mapped a fault 

through the section at this point but I observed no offset 

in measuring the section. Other folds can be examined 

along the railroad cut west of the base of the section. 

Large sinks and depressions occur in the region surrounding the area of the section. 

Principal reference section of the Santa Rosa Formation, 

Dockum Group of Middle and Late Triassic age 

[The section was measured in the cuts of the Chicago Rock Island and 

Pacific-Southern Pacific Railroad, along the north banks of El Rito 

Creek, and on the northern slopes of the westernmost lake of Tres 

Lagunas in the Santa Rosa 7.5-minute quadrangle (figs. 1 and 2). Approximate altitude of base of section is 4,630 ft. This section was 

measured by W. I. Finch, October 26-27, 1971] 

1 MILE 

1 KILOMETER 

R. 21 E. R. 22 E. 

Location within 

quadrangle 

Figure 2. Map showing the location of the line of measurement of the principal reference section of the Santa Rosa Formation, the type section of Kelley (1972), and fossil plant localities in the Santa Rosa 7.5-minute topographic quadrangle, Guadalupe 

County, N. Mex. 

4 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
Dockum Group (Triassic). 

Chinle Formation (lower shale member, incomplete): 

8. Siltstone, pale-red (5R 612), weathers light-red, 

sparse very fine grained quartz, calcareous, 

micaceous (colorless) along bedding planes; 

hard; thin wavy laminations due to pervasive 

ripple marks, which cause irregularly lined 

surface; most forms weak ledge; interfingers 

Thickness 

Feet 

with upper 5 ft of unit 7 . . . . . . . . . . . . . . 3.0 

7. Claystone and siltstone, intermixed, grayish-red 

(lOR 4/2), calcareous, micaceous (colorless), 

thinly laminated to indistinctly bedded; soft, 

shaly; most forms a covered slope . . . . . . 16.0 

Total Chinle Formation 

(incomplete) . . . . . . . . . . . . . . . 19.0 

Santa Rosa Formation (member terminology is that of 

Gorman and Robeck, 1946, except their shale member 

is here designated the mudstone member): 

Upper sandstone member: 

6. Sandstone, brown and yellowish-brown (due to 

limonite stain), speckled white and pale-gray, 

most weathers light-brown, minor pale-red 

(5R 612); very fine grained clear quartz, silty and clayey, micaceous (muscovite and 

biotite) along bedding planes, calcareous; 

shaly zone from 10 to 20 ft below top; upper part of zone is grayish- and yellowishgreen claystone; zone extends 100 yd to the 

north where it lenses out; strongly crossbedded in upper 5 ft of unit, which is welldisplayed on dip slope between top of unit 

and first outcrop of unit 7 about 700 ft to 

east; lower part thin-bedded, ripple-marked, 

and flat-bedded; unit forms two 5 ft ledges 

separated by steep slope; large rounded to 

angular blocks of lower ledge 3-40 ft across 

lie on slopes of unit 5 (fig. 8). 

Total upper sandstone member 30.0 

Mudstone member: 

5. Claystone, grayish-red (lOR 4/2), calcareous, 

soft, weakly bedded; forms covered slope 

shore of lake; base marked by irregular 6-

to 12-in.-thick brown-weathering siltstone 

bed that dips about 25 ° eastward . . . . . . 45.0 

4. Claystone, light-olive-gray (5 Y 6/1) to yellowish-gray (5 Y 7 /2), calcareous; contains carbonized leaf and twig fossils that are locally 

abundant; soft, shaly; contains sporadic, irregular, thin (1- to 6-in.-thick) brown siltstone layers that mark edges and bottoms 

of local channel-fills within unit; basal part 

lies on undulatory beds of unit 3; unit interpreted to be lacustrine or backswamp fillings of depressions formed by dissolution of 

Permian salts at depth; 12 ft well exposed 

in canal and 8ft exposed at railroad cut (fig. 

7), ground between is disturbed by fill and 

covered partly by colluvium . . . . . . . . . . . ::::::::25.0 

Total mudstone member (unit 

variable in thickness regionally 

and absent in places) ::::::::70.0 

Middle sandstone member: 

3. Sandstone, yellowish-brown, speckled white 

and light-gray, weathers light-brown to 

brown, black desert varnish on weathered 

surfaces; well-sorted beds of medium- to 

coarse-grained clear quartz; upper and basal 

beds are silty to fine grained, contain inconspicuous dark grains, calcareous, white 

interstitial clay common, hard to friable; 

iron-oxide-replaced and flattened fossil 

wood pieces and impressions on bedding 

planes throughout; beds tend to be thick 

(3-15 ft), crossbedded, undulatory (undulations caused by local subsidence), and continuous (extending for hundreds of feet); 

5-10ft above base is continuous zone 5-10 

ft thick of quartz-chert-limestone pebble 

conglomerate and greenish-gray (commonly pebbly) claystone; zone interfingers with 

adjacent sandstone beds; zone contains carbonized and limonitized wood fragments 

and logs; greenish-gray claystone and 

mudstone splits common in upper 20 ft; unit 

forms nearly continuous ledge; lies with erosional unconformity on unit 2; unit is 

distinctive and recognizable throughout 

Guadalupe, San Mig\]el, and Quay Counties, N. Mex. 

Thickness 

Feet 

Total middle sandstone member ::::::::60.0 

Lower sandstone member: 

2. Sandstone, pale-red (5R 6/2), speckled white, 

weathers brown to reddish brown; very fine 

grained to fine~grained brown-stained and 

clear quartz, interstitial white clay, 

calcareous, dirty looking, dense, hard; few 

thin (1-ft-thick) limestone-granule (1/12 to 

1/6 in. diameter) conglomerate beds scattered throughout; massive, flat-bedded and 

crossbedded, one festoon about 50 ft across 

noted near base; beds range from about 2 

in. to 8 ft thick, evenly thick to lenticular, 

3/4 in.-thick shaly breaks common; weathers 

as steep slope, partly covered, some 1- to 

3-ft-thick rounded ledges; slight erosional 

unconformity at base; bedding more or less 

parallel to that of underlying Permian rocks. 

Total lower sandstone member . ::::::::68.0 

Total Santa Rosa Formation . . . ::::::::228.0 

Total measured Dockum Group ::::::::247.0 

Artesia Group (Permian). 

Queen and Grayburg Formations, undivided: 

1. Siltstone, moderate-reddish-orange (lOR 6/6), 

calcareous, massive, lamination suggests ripple marks; soft zone a few inches thick about 

5 ft below top; upper surface modified by 

dissolution and deposition of carbonate and 

is grayish orange (10 YR 7 I 4); forms smooth, 

irregular, and indurated ledge; measured and 

described within 150 ft of east end of 

railroad fill where thickness of unit 2 

measured; Permian exposed south of tracks 

Description of the Principal Reference Section for the Santa Rosa Formation 5 
Artesia Group (Permian)-Continued 

Queen and Grayburg Formations, undivided-Continued 

is about 25 ft thick where the beds roll upward to form small anticlinal structure; here 

individual beds are about 5 ft thick, 

separated by shaly breaks, and show flat 

Thickness 

Feet 

parallel bedding . . . . . . . . . . . . . . . . . . . . . 8.0+ 

Total measured Queen and 

Grayburg Formations 

(incomplete) . . . . . . . . . . . . . . 8.0+ 

In western Guadalupe County, the Santa Rosa Formation is divisible into four informal members: lower 

sandstone member, middle sandstone member, mudstone 

member (locally absent), and upper sandstone member 

(Gorman and Robeck, 1946). The name shale member of 

Gorman and Robeck is herein changed to mudstone 

member because the rocks lack fissility. All of the members are noticeably calcareous. These members were 

mapped in north-central Guadalupe County adjacent to 

the north edge of the Santa Rosa 7 .5-minute quadrangle 

by Gorman and Robeck (1946). In the vicinity of the 

Guadalupe (Pastura) copper-mining district about 15 mi 

southwest of Santa Rosa, the three sandstone members 

are well developed, but the mudstone member is present 

only locally. The middle sandstone member appears to 

be the most continuous and prominent member and crops 

out over wide areas. It extends northward into San Miguel 

County and is exposed where State Highway 65 crosses 

the Canadian River south of Sabinosa. Eastward in Quay 

County, a sandstone that has lithology and bedding 

characteristics identical to those of the middle sandstone 

member at Santa Rosa crops out where State Highway 39 

crosses the Canadian River at Logan (fig. 1). 

Lower Sandstone Member 

The lower sandstone member consists of a series of 

thin to thick beds of sandstone separated by paper-thin 

to a-few-inch-thick shale partings (fig. 3). Thicker beds 

form poorly developed to well-developed rounded 

boulder-like ledges (fig. 4). Gorman and Robeck (1946) 

noted several feet of "chocolate-red" shale in the upper 

part of this member in the Esterito Dome area about 10 

mi to the north, and C. B. Read and R. D. Sample (written commun., 1943) noted sandy claystone in the Pastura 

area about 15 mi to the southwest. A few thin limestonepebble conglomerate layers are scattered throughout the 

member. The sandstone beds are characteristically red and 

speckled white on fresh surfaces and dark-reddish and 

purplish shades of brown on weathered surfaces. The 

sandstone ranges from very fine grained to fine grained 

in individual beds. Iron-stained to clear quartz is the chief 

component; interstitial white clay gives much of the 

Figure 3. Photograph of the outcrop of the lower part of the 

principal reference section of the Santa Rosa Formation showing the weathering characteristics of measured lower sandstone 

member (L) and its contacts with Permian rocks (P) and the middle sandstone member (M). 

Figure 4. Photograph of lower sandstone member in railroad 

cut. Sample for paleomagnetic study being taken by Scott C. 

Reeve. 

sandstone a salt-and-pepper appearance. The sandstone 

contains enough dark grains to give it a dirty appearance. 

It is generally well cemented with calcium carbonate and 

6 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
in most places is hard and brittle. Gorman and Robeck 

(1946) described the sandstone as friable in the area to 

the north. 

Fossils are very rare in the member. Gorman and 

Robeck (1946) report bone fragments northwest of Santa 

Rosa. Recently, Lucas and Morales (1985) described an 

incomplete amphibian skull of Middle Triassic (Anisian) 

age collected from the lower sandstone member at a locality southeast of Dilia, Guadalupe County, in the area Gorman and Robeck worked. The skull was collected from 

conglomerate, mostly of sandstone and limestone fragments in a matrix of medium- to coarse-grained quartzose 

sand. The possibility of the skull's having been reworked 

from Middle Triassic beds in Late Triassic time is not addressed by Lucas and Morales, but its character does not 

appear to be that of a reworked fossil. More recent work 

has disclosed more Middle Triassic amphibians (S.G. Lucas, 

written commun., 1986). 

The lower member is 68 ft thick in the principal 

reference section. Gorman and Robeck (1946) report as 

much as 112 ft and found the member to be extremely 

variable in thickness and locally absent. Variations in 

thickness reflect subsidence due to dissolution of underlying Permian salt during sedimentation. The lower member 

lies with local erosional unconformity on the clastic beds 

of Permian age. 

Middle Sandstone Member 

The middle sandstone member is characteristically 

yellowish-brown, speckled white to light gray on fresh surfaces, and weathers light brown. Thick, continuous beds 

of sandstone consist of well-sorted, generally medium to 

coarse quartz grains and of scattered quartz pebbles averaging Y2 in. in diameter, and iron-stained fossil-wood compressions. Angular blocks of mudstone were observed 

within the sandstone in the railroad cut (fig. 5). The sandstone beds are platy to massively bedded and weather into 

"fretted" blocks. A thin zone of quartz-chert-limestone 

pebble conglomerate and greenish-gray claystone occurs at 

or near the base of the member in most places in Guadalupe County (fig. 6). This zone locally contains fossil wood 

fragments, some of which contain uranium (Finch, 1972). 

The red-bed copper deposit at Pastura is in this member. 

The thickness of this member is about 60 ft in the measured 

section and varies regionally, but not as much as the other 

members; it ranges from about 15 to 135 ft thick (Gorman and Robeck, 1946). It lies with erosional unconformity on the lower sandstone member and locally on the 

Lower Permian San Andres Limestone. 

Mudstone Member 

The mudstone member is red to gray, more commonly gray, soft claystone, locally silty, commonly arenaceous 

in basal sections, and locally leaf bearing in gray parts (see 

Figure 5. Photograph of middle sandstone member showing 

angular blocks of mudstone, one on left (arrow) is 18 in. long. 

Figure 6. Photograph of the conglomerate zone (arrow) near 

the base of the middle sandstone member (M) and its contact 

with the lower sandstone member (L). 

chapter C). The member is discontinuous; for example, it 

is absent in the type section of Kelly (1972) about 1 mi to 

the northwest. The mudstone fills depressions in undulatory beds of the underlying middle sandstone member 

(fig. 7). Its thickness is extremely variable, ranging from 

0 to 70 ft. The upper contact is planar with the overlying 

upper sandstone member. 

Description of the Principal Reference Section for the Santa Rosa Formation 7 
Upper Sandstone Member 

The upper sandstone member consists of a prominent ledge of sandstone and locally thin claystone lenses 

and conglomerate channel fillings. The sandstone is generally brown, locally gray, micaceous, calcareous, very fine 

grained to fine-grained quartz, and commonly silty and 

clayey. It is platy to massive, and weathered surfaces are 

rounded and commonly have ribbed cupholes. The lower 

part is ripple-laminated and the upper part is strongly 

crossbedded. Crossbeds dip 10°-20° N. 45 °-80° E. in the 

line of section. Characteristically, the sandstone weathers 

into large blocks (fig. 8). The claystone lenses are gray to 

green. Thin limestone-pebble conglomerate beds occur at 

and near the base of the member north of the principal 

reference section (Gorman and Robeck, 1946). The member is 30 ft thick in the principal reference section and 

regionally is variable, ranging from 11 to 115 ft (Gorman 

and Robeck, 1946). The upper contact with the overlying 

Chinle is disconformable. The red claystone and siltstone 

of the Chinle contrasts sharply with the brown sandstone 

of this member. Only 3 ft of the Chinle is exposed here, 

but 75-100 ft of dominantly claystone and siltstone and 

some thin sandstone and limestone-pebble conglomerate 

beds of the Chinle are poorly exposed in the valley to the 

southeast towards Sunshine Mesa (see Sunshine Mesa 

measured section in Finch and Wright, 1983). 

PALEOMAGNETIC CHARACTER OF THE 

SANTA ROSA-PERMIAN CONTACT 

By Scott C. Reeve1 

Paleomagnetic declinations, inclinations, and intensities across the Permian-Late Triassic unconformity in the 

principal reference section of the Santa Rosa were 

measured by Scott C. Reeve (1975) (figs. 1, 4). Above the 

unconformity is a reversed-normal-reversed-normal polarity sequence in the basal 9 m of the Santa Rosa Formation (fig. 9). The numerous polarity changes in the rapidly deposited braided stream bedforms suggest variations 

in secondary magnetization relative to varying permeability 

and grain composition. Magnetization directions, even 

though scattered, are consistent with the Triassic field 

(Pechersky and Khramov, 1973). The upper 2m of the 

Queen and Grayburg Formations, undivided, are magnetized normally. These Permian rocks either record a period 

of normal magnetic field directions during Guadalupian 

time or were almost totally remagnetized to a depth of at 

least 2 m below the unconformity, most likely before 

deposition of the lower sandstone member. 

Magnetic remanence in the Middle Triassic lower 

sandstone member is carried by detrital specular hematite 

and martized magnetite and by red hematite pigment. The 

1

Current address: 105 Rue Burgundy, Slidell, LA 70461 

Figure 7. Photograph showing nature of the basal contact of 

the mudstone member (MU) with the underlying middle sandstone member (M) along the line of measured section. 

Figure 8. Photograph of the upper sandstone member (U) 

weathered into blocks as much as 25 ft across and the upper 

part of the mudstone member (MU) near the edge of the westernmost lake of Tres Laguna. 

agreement in polarity of a portion of the detrital fraction 

with the thermally stable fraction of the pigment is consistent with a nearly contemporaneous acquisition of the 

magnetism. Unfortunately, the agreement is also due in 

8 Principal Reference Section for the Santa Rosa Formation of Middle and late Triassic Age, Guadalupe County, New Mexico 
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Figure 9. Paleomagnetic declination, inclination, and intensity of the basal 9 m of the lower sandstone member (Rs) and the upper 2 m of the 

Queen and Grayburg Formations, undivided (Pqg) (modified from Reeve, 1975). A, natural remanent magnetism (NRM): 8, magnetism after demagnetism 

at 621 °-635°C. Beds marked with W are leached of all or portions of their red hematite pigment. N, normal polarity; R, reversed polarity. 
part to further oxidation of the original magnetite portion 

of the detrital fraction during the pigment's growth and 

could have occurred long after deposition. Attempts at 

chemical demagnetization were only partly successful. 

These results suggest that the detrital fraction, in addition 

to carrying Triassic field directions, also carries a steeply 

dipping normal-field, chemical-remanent magnetization 

component of Cretaceous or Holocene age in some grains 

and some multidomain viscous magnetizations as well. 

REFERENCES CITED 

Bachman, G.O., 1953, Geology of a portion of northwestern 

Mora County, New Mexico: U.S. Geological Survey Oil and 

Gas Investigations Map OM-137, scale about 1 in. to 1 Y4 

mi. 

Barnes, V.E., project director, 1976, Geologic Atlas of Texas, 

Hobbs Sheet: The University of Texas at Austin, Bureau 

of Economic Geology Map, scale 1:250,000. 

Barnes, V.E., project director, 1983, Geologic Atlas of Texas, 

Tucumcari Sheet: The University of Texas at Austin, Bureau 

of Economic Geology Map, scale 1:250,000. 

Dane, C.H., and Bachman, G.O., 1965, Geologic map of New 

Mexico: Washington, D. C., U.S. Geological Survey, scale 

1:500,000. 

Darton, N.H., 1922, Geologic structure of parts of New Mexico: U.S. Geological Survey Bulletin 726-E, p. 173-275. 

Finch, W.I., 1959, Geology of uranium deposits in Triassic rocks 

of the Colorado Plateau region: U.S. Geological Survey 

Bulletin 1074-D, p.l25-164. 

Finch, W.I., 1972, Uranium in eastern New Mexico, in Kelley, 

V.C., and Trauger, F.D., eds., Guidebook of east-central New 

Mexico: New Mexico Geological Society Guidebook, 

Twenty-third Field Conference, East-central New Mexico, 

September 28-30, 1972, p. 172-175. 

Finch, W.I., and Wright, J.C., 1983, Measured stratigraphic sections of uranium-bearing Upper Triassic rocks of the Dockum Basin, eastern New Mexico, West Texas, and the Oklahoma 

Panhandle, with brief discussion of stratigraphic problems: 

U.S. Geological Survey Open-File Report 83-701, 118 p. 

Finch, W.I., Wright, J.C., and Davis, B.O., 1976, Unevaluated 

preliminary geologic cross section of uranium-bearing Upper Triassic rocks extending from Ute Reservoir, New Mexico to Palo Duro Canyon, Texas: U.S. Geological Survey 

Open-File Report 76-205, 1 sheet. 

Gorman, J.M., and Robeck, R.C., 1946, Geology and asphalt 

deposits of north-central Guadalupe County, New Mexico: 

U.S. Geological Survey Oil and Gas Investigations Preliminary Map 44, scale approximately 1 inch= 1 mile. 

Hager, Dorsey, and Robitaille, A.E., 1919, Geological report on 

oil possibilities in eastern New Mexico: 15 p. [unpublished 

pamphlet; copy available in U.S. Geological Survey Library, 

Reston, Va.] 

Hendrickson, G.E., and Jones, R.S., 1952, Geology and groundwater resources of Eddy County, New Mexico: New Mexico 

Bureau of Mines and Mineral Resources Ground-Water 

Report 3, 169 p. 

Johnson, R.B., 1969, Geologic map of the Villanueva quadrangle, 

San Miguel County, New Mexico: U.S. Geological Survey 

Geologic Quadrangle Map GQ-869, scale 1:24,000. 

Kelley, V.C., 1972, Geology of the Fort Sumner sheet, New Mexico: New Mexico State Bureau of Mines and Mineral 

Resources Bulletin 98, 55 p. 

Lang, W.T.B., 1947, Triassic deposits of Pecos Valley, southeastern 

New Mexico: American Association of Petroleum Geologists 

Bulletin, v. 31, no. 9, p. 1673-1674. 

Lucas, S.G., Hunt, A.P., and Morales, Michael, 1985, Stratigraphic 

nomenclature and correlation of Triassic rocks of east-central 

New Mexico: A preliminary report, in Lucas, S.G., ed., Santa Rosa-Tucumcari region: New Mexico Geological Society 

Guidebook, Thirty-sixth Annual Field Conference, 

September 26-28, 1985, p. 171-184. 

Lucas, S.G., and Morales, Michael, 1985, Middle Triassic amphibian from basal Santa Rosa Formation, east-central New 

Mexico, in Lucas, S.G., ed., Santa Rosa-Tucumcari region: 

New Mexico Geological Society Guidebook, Thirty-sixth Annual Field Conference, September 26-28, 1985, p. 56-58. 

McGowen, J.H., Granata, G.E., and Seri, S.J., 1979, Depositional 

framework of the lower Dockum Group (Triassic), Texas 

panhandle: The University of Texas at Austin, Bureau of Economic Geology Report of Investigations no. 97-1979, 60 p. 

Pechersky, D.M., and Khramov, A.N., 1973, Mesozoic paleomagnetic scale of the USSR: Nature, v. 244, p. 499-500. 

Reeve, S.C., 1975, Magnetization of the basal (Upper Triassic) Santa Rosa Sandstone, and underlying Permian Greyburg-Queen 

Formation, Santa Rosa, N.M., in Paleomagnetic studies of 

sedimentary rocks of Cambrian and Triassic age: The University of Texas at Dallas, unpublished Ph.D. dissertation, p. 

130-162. 

Rich, J.L., 1921, The stratigraphy of eastern New Mexico-a correction: American Journal of Science, 5th series, v. 2, p. 

295-298. 

Roberts, M.E., 1941, Measurement of composite section, in Scott, 

Gayle, and others, Spring field trip, Fort Worth to Midland, 

Texas, on Highway 80 along the T & P, May 10-11, 1941: 

[Midland, Texas] West Texas Geological Society [Guidebook], 

p. 57-58. 

Stewart, J.H., 1957, Proposed nomenclature of part of Upper 

Triassic strata in southeastern Utah: American Association 

of Petroleum Geologists Bulletin, v. 41, no. 3, p. 441-465. 

Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy 

and origin of the Chinle Formation and related Upper 

Triassic strata in the Colorado Plateau region: U.S. Geological 

Survey Professional Paper 690, 336 p. 

Trauger, F.D., Mankin, C.J., and Brand, J.P., 1972, Road log of 

Tucumari, Mosquero, and San Jon country, in Kelley, V.C., 

and Trauger, F.D., eds., Guidebook of east-central New Mexico: New Mexico Geological Society Guidebook, Twenty-third 

Field Conference, East-central New Mexico, September 

28-30, 1972, p. 12-45. 

Vine, J.D., 1963, Surface geology of the Nash Draw quadrangle, 

Eddy County, New Mexico: U.S. Geological Survey Bulletin 1141-B, 46 p. 

Wanek, A.A., 1%2, Reconnaissance geologic map of parts of Harding, San Miguel, and Mora Counties, New Mexico: U.S. 

Geological Survey Oil and Gas Investigations Map OM-208, 

scale 1:96,000. 

10 Principal Reference Section for the Santa Rosa Formation of Middle and late Triassic Age, Guadalupe County, New Mexico 
Chapter B 

Interpretive Depositional History of the 

Santa Rosa Formation at the 

Principal Reference Section 

By ROBERT LUPE 

U.S. GEOLOGICAL SURVEY BULLETIN 1804 

PRINCIPAL REFERENCE SECTION FOR THE SANTA ROSA 

FORMATION OF MIDDLE AND LATE TRIASSIC AGE, 

GUADALUPE COUNTY, NEW MEXICO 
CONTENTS 

Abstract 13 

Introduction 13 

Environments of deposition 13 

Paleotransport trends 15 

Modal analyses 17 

Summary 17 

References cited 17 

FIGURES 

1-4. Photographs showing: 

12 Contents 

I. Trough cross-stratification and flat beds of the lower sandstone 

member and foreset bedding of the middle sandstone member 14 

2. Tracks and trails on current-rippled sandstone of the middle sandstone member 15 

3. Lag conglomerate of pedogenic, calcareous intraclasts in the 

mudstone member 15 

4. Possible algal-laminated limestone in the mudstone member 15 

5. Rose diagrams showing transport direction in the members of the Santa 

Rosa Formation 16 

6. Ternary (QFL) diagram of clasts for Santa Rosa Formation 17 

7. Plot showing abundance of heavy minerals plus micas in the various 

members of the Santa Rosa Formation and lowermost Chinle 

Formation 18 
Interpretive Depositional History of the 

Santa Rosa Formation at the 

Principal Reference Section 

By Robert Lupe1 

Abstract 

The Santa Rosa Formation at the principal reference section consists of continental sediments, primarily sandstone and 

less claystone, siltstone, and limestone-clast conglomerate. The 

formation is divided into lower sandstone, middle sandstone, 

mudstone, and upper sandstone members. The three sandstone 

members are interpreted to have been deposited as alluvial 

sheets by braided streams, and the mudstone member was 

deposited as discontinuous strata in small lakes. 

The lower sandstone member is marked at the base by 

a high-energy depositional pulse that deposited a one-half- to 

one-meter-thick lag concentrate of Permian intraclasts and interbeds of trough-crossbedded, fine-grained sandstone. Lower 

energy fluvial channel-fills interpreted to have been deposited 

by a braided-stream system make up the rest of the unit. 

The base of the middle sandstone member is marked by 

an extensive lag conglomerate of resistate clasts. Structureless, 

flat beds of sandstone deposited during a high-flow regime immediately overlie the conglomerate. This episode of deposition waned quickly, and the upper part of the middle sandstone 

member consists of planar crossbeds interpreted to be deposits 

of transverse bars and related low-flow sedimentary structures. 

This unit grades upward into the overlying mudstone member. 

The mudstone member consists of claystone and minor 

sandstone and is interpreted to have been deposited in lakes. 

Intermittent desiccation is indicated by pedogenic calcrete and 

mudcracked surfaces. The mudstone member was apparently 

coursed rarely by streams that left narrow channel-fills of lag 

gravel, claystone, and sandstone. The claystone beds contain 

well-preserved organic fossil plant remains. Near the top, the 

mudstone member contains nonelastic limestone beds that are 

burrowed and display probable algal structures. 

The upper sandstone member is lithologically and structurally similar to the lower and middle sandstone members and 

was deposited in similar environments. 

Paleotransport trends within each member indicate changes 

in basin attitude and probable changes in sediment source area. 

Flow changed from dominantly northward during deposition 

of the lower sandstone member to southward during deposition of the middle sandstone member and back to northward 

during deposition of the upper sandstone member. 

1

Current address: Amerada Hess, 1200 Milan, Houston, TX 

77008 

INTRODUCTION 

The Triassic Santa Rosa Formation is interpreted 

to have been deposited by braided streams and in lakes 

or on floodplains in the area of the principal reference 

section. The rocks of each member of the formation differ in their history of deposition as indicated by sedimentary structures and composition; therefore, subdivision of 

the formation into members is genetic as well as 

descriptive. 

Thanks are expressed to J. A. McGowen, University of Texas at Austin, for his field introduction to fluvial 

depositional systems and to Carolyn Lupe for assistance 

in the field. Preliminary results of this study were 

previously reported orally (Lupe, 1977). 

ENVIRONMENTS OF DEPOSITION 

All members of the Santa Rosa Formation except 

the mudstone member were deposited as alluvial sheets 

by braided streams. In general, the deposits of these 

braided-stream systems have the following properties. The 

depositional packages (rock or sediment bodies that were 

laid down during the same depositional episode and are 

bounded by surfaces of erosion or nondeposition) are lenticular in cross section and vary little in grain size. They 

have erosional bases and the basal deposits contain intraclasts. Furthermore, the variety of sedimentary structures is small, and these structures reflect waning flow. 

The basal beds of the sandstone members are 

characterized by flat beds and trough crossbeds as shown 

for the lower sandstone member in figure IA. On the basis 

of criteria given by Harms and others (1975), these bedding features are interpreted as having formed during high 

flow. The upper parts of the sandstone members are 

characterized by current ripples and by tabular foreset 

beds as typified in the middle sandstone member (fig. lB). 

On the basis of criteria given by Smith (1970), these 

features are interpreted as migrating transverse bars. They 

are similar to those in the Upper Triassic Trujillo 

Interpretive Depositional History of the Santa Rosa Formation at the Principal Reference Section 13 
Figure 1. Photographs showing A, trough crossbeds and flat 

beds of the lower sandstone member; 8, foreset bedding 

formed by migrating sand waves interpreted to be transverse 

bars in the middle sandstone member of the Santa Rosa 

Formation. 

Sandstone in West Texas (Asquith and Cramer, 1975). 

The sedimentary rocks of each of the three sandstone 

members have these characteristics in common and are 

interpreted as braided-stream deposits; however, the 

typical dimensions of sedimentary structures in each is 

different. The dominant alluvial environment was broken 

after the middle sandstone episode by lacustrine deposition of the mudstone member. 

The lower sandstone member of the Santa Rosa 

rests unconformably on the Permian Artesia Group, 

which has less than 1 m of local relief. At its base, the 

lower sandstone member contains local lag-concentrates 

of Permian lithic intraclasts in conglomeratic lenses less 

than 1 m thick. This intraconglomerate is the most 

widespread conglomerate in the member. During the remainder of the high-energy depositional pulse that deposited the lower sandstone member, trough-crossbedded, 

poorly-sorted, fine- to medium-grained, red arkosic 

quartz sandstone was deposited in beds 0.5-1 m thick. 

Strata of this initial depositional episode are approximately 3 m thick. 

After this first high-energy episode of the lower 

member, the style of deposition changed sharply in the 

upper part of the member. Rock bodies deposited after 

this episode are thinner, repetitious, and reflect lower, 

but still high, depositional energy. Packages of episodically deposited foreset- and flat-bedded strata are approximately 0.5-1 m thick and 5-30 m wide. Many are 

separated by thin, current-rippled siltstone and mudstone 

laminae. These packages represent channels within a 

braided-stream system. 

The middle sandstone member consists mainly of 

tan feldspathic quartz sandstone, which is more mature 

than the lower member. It represents a second major 

depositional event by braided streams. The onset of 

deposition was similar to, but stronger than, that of the 

lower sandstone member and is marked by an extensive 

regional unconformity measured in tens of meters of 

relief. Local relief on the unconformity is 1-2 m, and the 

lag conglomerate at the base not only is more extensive 

than that at the base of the underlying member, but it 

contains resistate clasts of quartz as large as 5 em in 

diameter in addition to intraclasts of mudstone. These 

resistate clasts of quartz are from a source different and 

more distant than the source of the lithic intraclasts of 

the lower sandstone member. The structureless and flat 

beds of the rocks immediately above the conglomerate 

indicate deposition during high flow, as was the case with 

the lower sandstone member, but the beds are thicker 

(1-3 m) and total approximately 8 m. This high-flow 

depositional episode, like that of the lower sandstone 

member, apparently waned rapidly, for the rest of this 

member was deposited as transverse bars and other 

sedimentary structures characteristic of low-flow regimes 

(fig. 1B). Well-preserved delicate animal tracks and trails 

(fig. 2) attest to deposition in still water. These low-energy 

conditions represent the gradual transition into the lacustrine environment of the overlying mudstone member. 

Regionally, the mudstone member is discontinuous 

and appears to have been deposited mainly in lakes developed by local subsidence caused by dissolution of Permian salt. In the principal reference section, this member 

consists of about 20 m of predominantly weakly bedded 

claystone. The lower 8 m is olive gray and contains abundant well-preserved organic fossil plant material (see 

chapter C), which indicates local ponding, low-energy 

conditions, and high water tables. The upper 15 m is 

dominantly red, which indicates open-water oxidizing 

conditions and a gradual return to the fluvial environment of the upper sandstone member. 

Sparse thin lenses of siltstone and sandstone typically less than 1 m thick and 5 m wide scattered throughout 

the claystone indicate that the member was coursed by 

streams. The channels contain lag gravel of pedogenic 

calcareous clasts (fig. 3) overlain by current-rippled siltstone and sandstone. The surfaces of these channel 

14 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
Figure 2. Photograph showing tracks and trails on the lower 

bedding plane of current-rippled sandstone in the midd le sandstone member of the Santa Rosa Formation. 

deposits are commonly covered by oscillation ripples, 

tracks, and trails that attest to deposition in standing 

water and by mudcracks that indicate desiccation took 

place. These thin units are commonly burrowed. 

Within the red claystone section are scattered 

calcrete layers less than 1 m thick containing nodules and 

filaments that are characteristic of desert soils described 

by Gile and others (1966). Underlying each calcrete layer 

is a zone of ochre, purple, and white alteration from the 

normal red that probably developed as part of the soilforming process, a process described by Cooke and 

Warren (1973). 

In the vicinity of the measured reference section and 

in the upper part of the member are minor thin nonelastic 

Figure 3. Photograph showing lag conglomerate of pedogenic, 

calcareous intraclasts deposited in small channels within the 

mudstone member of the Santa Rosa Formation. 

Figure 4. Photograph showing thin, possibly algal-laminated 

limestone (arrow) in the mudstone member of the Santa Rosa 

Formation . 

limestone beds that are burrowed and display structures 

of possible algal origin (fig. 4). 

The upper sandstone member was deposited in 

depositional environments similar to those of the lower 

and middle sandstone members; however, the basal contact of the upper sandstone member with the mudstone 

member is gradational, so no significant erosional event 

marked the beginning of the upper sandstone depositional 

episode. Rather, all sediments were deposited as transverse bars and related low-flow bed forms, much as in 

the upper part of the middle sandstone member. 

PALEOTRANSPORT TRENDS 

Each member of the Santa Rosa has different 

paleotransport trends, which implies a change in basin 

attitude and a possible change in sediment source area. 

Sediment transport during the deposition of the lower 

Interpretive Depositional History of the Santa Rosa Formation at the Principal Reference Section 15 
sandstone niember was dominantly to the north (0 ~ as 

determined by measuring azimuths of trough crossbed 

axes, foreset bed dips, and, to a minor extent, parting 

lineations (fig. 5A). Transport direction changed sharply in the middle sandstone member to nearly the opposite 

direction (210~ (fig. 5B). Regional studies by McGowen 

and others (1979), done after my local studies, confirmed 

these changes in transport directions. Therefore, the 

Figure 5. Sediment transport trends of the Santa Rosa Formation. A, lower sandstone member; 8, middle sandstone 

member; C, mudstone member; 0, upper sandstone member. 

source of sediment for the middle sandstone member 

must have been within the formerly more distal part of 

the depositional basin than the source for the lower sandstone member. This conclusion is supported by the modal 

analysis data given below. Early work by Cazeau (1960) 

before subdivision of the Santa Rosa into members 

showed two opposing source areas for the "Santa Rosa 

Sandstone.'' 

16 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
Data on transport directions for the discontinuous 

mudstone member deposited mainly in lakes are inconclusive (fig. 5C). It appears that the intermittent channels were haphazardly coursing through flat-lying, 

overbank-lacustrine sediments. 

Trends for the upper sandstone member, however, 

are restricted enough in distribution to show that unidirectional flow was to the northeast (70~ (fig. 5D), which 

contrasts to the southwest flow of the middle sandstone 

member. Thus, there was a final apparent change in the 

basin attitude. 

MODAL ANALYSES 

Modal analyses of 40 sandstone samples of the 

Santa Rosa indicate differences in composition between 

the red lower sandstone member and the tan middle and 

upper sandstone members. The differences in composition not only reflect differences in source material, but, 

when considered together with changes in sediment 

transport trends (figs. 5A, 5B, 5D), confirm changes in 

basin attitude. 

The sandstone of the lower sandstone member is 

compositionally more immature than that of the remainder of the formation, as shown in figure 6. The sandstone of the lower member has more than 10 percent lithic 

fragments, more than 10 percent feldspar, and less than 

70 percent quartz. In contrast, the sandstone of the remaining part of the formation generally has less than 20 

percent lithic fragments, less than 10 percent feldspar, 

and more than 75 percent quartz. If the source material 

for the three sandstone members was similar, the more 

unstable constituents must largely have been destroyed 

prior to deposition of the upper two members. 

Similar changes in composition are shown by comparison of abundances of heavy minerals plus micas for 

each member (fig. 7). Generally, the lower sandstone 

member has more than 2.5 percent heavy minerals plus 

micas, and the upper sandstone member contains less 

than 2.5 percent of these constituents. 

SUMMARY 

After the first cycle, during which immature sediments of the lower sandstone member were deposited on 

the Permian Artesia Group erosional surface by braided 

streams moving from south to north into the basin, the 

attitude of the basin changed. Braided streams were 

forced to flow in nearly the opposite direction; they 

eroded sediments of the lower sandstone member, which 

were matured in the process, picked up resistant clasts 

from the new source, and deposited the middle sandstone 

member. 

Q 

• 

60\ • 40 

•• X • • 50 • • • 50 

• • 40 60 

30 70 

20 80 

10 90 

F 90 80 70 L 

EXPLANATION 

X Chinle Formation 

Santa Rosa Formation 

o Upper sandstone member 

A. Mudstone member 

• Middle sandstone member 

• Lower sandstone member 

Figure 6. Ternary diagram of quartz plus chert(Q), felds~ar 

(F), and lithic fragments (L) for Santa Rosa Format1on 

samples. 

The depositional episode of the middle member 

gradually subsided to lower energy levels until overbanklacustrine sediments of the mudstone member were 

deposited. Under apparently stable conditions over a considerable length of time, soils developed. Intermittent 

streams flowing in diverse directions coursed the lowrelief surface of the mudstone until finally the braidedstream sediments of the upper sandstone gradually took 

over deposition in the area of the principal reference 

section. 

REFERENCES CITED 

Asquith, G.B., and Cramer, S.C., 1975, Transverse braided bars 

in the upper Triassic Trujillo Sandstone of the Texas 

Panhandle: Journal of Geology, v. 83, p. 657-661. 

Cazeau, C.J., 1960, Cross-bedding directions in Upper Triassic 

sandstones of northeastern New Mexico: American Association Petroleum Geologists Bulletin, v. 44, p. 638-640. 

Cooke, R.U., and Warren, Andrew, 1973, Geomorphology in 

deserts: Berkeley, University of California Press, 374 p. 

Gile, L.H., Peterson, F.F., and Grossman, R.B., 1966, Morphological and genetic sequences of carbonate accumulation in desert soils: Soil Science, v. 101, p. 347-360. 

Interpretive Depositional History of the Santa Rosa Formation at the Principal Reference Section 17 
c 

0 

·~ 

co 

E 

0 

u. 

co 

(/) 

0 

Ct: 

co 

E 

co 

(J) 

Chinle 

Formation 

Upper 

sandstone 

member 

X X 

I 

I 

I 

I 

I 

I 

I 

Xi ---~~----~-~--------------~~--

1 

I 

I 

I 

I 

I <> ~----~~~-----jr--~-------~-~+----------------~~--~--

Mudstone 

member 

"' 

;.::1 

..-I 

cl 

~I 

Qj I 

a. I 

A A U: I 

1-----+-------------N+----------------------

Middle 

sandstone 

member 

Lower 

sandstone 

member 

• I 

• • 

• I 

• 

• 

I 

I 

I 

I 

I 

• 

~----~-----1-----------------------

• 1 • 

I 

I 

I 

I 

I • 

• • • 

• 

• 

5 samples 

: > 7 percent 

: (7.4-22 percent) 

·--~------~--------~~---·----~~----~11 _· __ ~1 ________ 1~------~~--------~1 _______ 1. 

0 2 3 4 5 6 7 

PERCENT HEAVY MINERALS PLUS MICAS 

Figure 7. Abundances of heavy minerals plus micas in the framework of sandstone from various members of the Santa Rosa 

Formation and lower beds of the Chinle Formation. Thin sections are not located precisely in the stratigraphic section, and relative 

thickness of units is not shown. Symbols for samples are the same as in figure 6. 

Harms, J.C., Southard, J.B., Spearing, D.R., and Walker, 

R.G., 1975, Depositional environments as interpreted from 

primary sedimentary structures and stratification sequences: 

Society of Economic Paleontologists and Mineralogists 

Short Course no. 2, Dallas, 161 p. 

McGowen, J.H., Granata, G.E., and Seri, S.J., 1979, Depositional 

framework of the lower Dockum Group (Triassic), Texas panhandle: The University of Texas at Austin, Bureau of Economic Geology Report of Investigations no. 97-1979, 60 p. 

Lupe, Robert, 1977, Depositional history of the Triassic Santa 

Rosa sandstone, Santa Rosa, New Mexico [abs.]: Geological 

Society of America, South Central Section, 11th Annual 

Meeting, March 17-18, 1977, El Paso, Texas, p. 61. 

Smith, N.D., 1970, The braided stream depositional environment: Comparison of the Platte River with some 

Silurian clastic rocks, north-central Appalachians: 

Geological Society of American Bulletin, v. 81, 

p. 2993-3014. 

18 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
Chapter C 

Fossi I Plants from the 

Mudstone Member of the 

Santa Rosa Formation at the 

Principal Reference Section 

By SIDNEY R. ASH 

U.S. GEOLOGICAL SURVEY BULLETIN 1804 

PRINCIPAL REFERENCE SECTION FOR THE SANTA ROSA 

FORMATION OF MIDDLE AND LATE TRIASSIC AGE, 

GUADALUPE COUNTY, NEW MEXICO 
CONTENTS 

Abstract 21 

Introduction 21 

Systematic descriptions 21 

Division Pteridophyta 21 

Division Cycadophyta 22 

Division Coniferophyta 22 

Division uncertain 23 

Conclusions 24 

References cited 24 

PLATE 

1. Photographs of fossil plants from the mudstone member of the Santa Rosa 

Formation near Santa Rosa and the Chinle Formation near Fort Wingate, 

New Mexico 

TABLE 

1. Summary of known distribution of plants from the Santa Rosa Formation in 

other stratigraphic units 24 

20 Contents 
Fossi I Plants from the 

Mudstone Member of the 

Santa Rosa Formation at the 

Principal Reference Section 

By Sidney R. Ash1 

Abstract 

Systematic descriptions are given for six species of plant 

megafossils from the mudstone member of the Santa Rosa Formation. They are the fern Cynepteris lasiophora, the bennettitalean Zamites powellii, the conifer Pelourdea poleoensis, 

Dinophyton spinosus of uncertain classification, Samaropsis sp, 

and a pithcast not assigned a name. Four of these are well 

known and characteristic of the Chinle Formation to the west 

in the Colorado Plateau region. Several of the species also occur in the Triassic part of the Newark Supergroup in eastern 

North America. The flora in the mudstone member of the Santa 

Rosa at the reference section area is typical of the floral 

Dinophyton zone. 

INTRODUCTION 

This report concerns seven species based on plant 

megafossils collected from the mudstone member of the 

Santa Rosa Formation. Four are from the principal 

reference section of the Santa Rosa Formation (fossil 

locality A, fig. 2, chapter A), and three were obtained 

from the mudstone member at a nearby locality (fossil 

locality B, fig. 2, chapter A). They were collected mainly by W .I. Finch, R.A. Scott, and me during the spring 

of 1972, although a few were found by Finch in 1971. 

Most of the fossils considered here are preserved 

as faint iron-stained impressions, but there is a small 

amount of carbonaceous residue on several impressions. 

The impressions from the principal reference section are 

preserved in fairly hard, dusky yellow (5 Y 61 4) claystone; 

those from the adjacent locality are in soft, yellowishgray (5 Y 7 /2), silty, micaceous, fine-grained sandstone. 

One fossil from the adjacent locality is a pithcast composed of grayish-yellow (5 Y 81 4), medium- to coarsegrained sandstone. The exterior of that fossil is ironstained and bears traces of woody material. 

1

Weber State College, Ogden, Utah 84408 

Cuticles, epidermises, and sporangia are not 

preserved on the Santa Rosa compressions, so data about 

those features in the following descriptions were taken 

from previous publications. 

The fossils described here have been deposited 

in the U.S. National Museum (USNM), Washington, 

D. C. 

SYSTEMATIC DESCRIPTIONS 

Division PTERIDOPHYTA 

Order FILICALES 

Family CYNEPTERIDACEAE 

CYNEPTERIS LASIOPHORA Ash, 1970a 

Plate 1, figure 4 

Description. The leaf of this fern is twice pinnate 

with oblong decurrent pinnules that have acute to obtuse 

apices and obtusely dentate to smooth margins. A strong 

midvein enters each pinnule and gives off several 

anastomosing lateral veins that form a coarse reticulum. 

The resulting vein meshes never contain blind vein endings. The epidermal cells on the pinnules are polygonal 

and have wavy to slightly sinuous anticlinal walls. The 

outer periclinal walls of the cells occasionally bear a simple or stellate hair. Some pinnules bear few to many 

solitary sporangia on the lower surface. They are more 

or less inversely pear shaped and have a complete apical 

annulus. The spores produced in the sporangia are round, 

each has a simple, narrow triradiate mark, and the surfaces bear low reticulations. 

Remarks. Cynepteris lasiophora can be easily 

recognized and separated from all other ferns known in 

the Upper Triassic rocks of the southwestern United 

States. Almost all of them have simple forking venation 

in contrast to the present species which has reticulate 

venation. The only other Chinle or Dockum fern having 

reticulate venation is Clathropteris walkeri. However, it 

has a palmately compound leaf whereas Cynepteris 

lasiophora has a pinnately compound leaf. Also, the vein 

Fossil Plants from the Mudstone Member of the Santa Rosa Formation at the Principal Reference Section 21 
meshes of Clathropteris walkeri commonly contain blind 

vein endings (Ash, 1970a, fig. 18H, I), which are always 

absent in Cynepteris lasiophora. 

Distribution. This fern has been found in the 

Monitor Butte Member of the Chinle Formation in 

western New Mexico, in the lower part of the Petrified 

Forest Member of the Chinle in Petrified Forest National 

Park (Ash, 1970a), and in the Shinarump Member of the 

Chinle in Utah (Ash, 1975b). It is also known from the 

Pekin Formation of Late Triassic age in the Newark 

Supergroup in North Carolina (Hope and Patterson, 

1969). Otherwise it is rarely known. However, two closely 

related species do occur in the Santa Clara Formation in 

Sonora, Mexico (Reinhard Weber, Institute of Geology, 

Autonomous National University of Mexico, Mexico, 

D. F., written commun. 1984). 

Material. USNM 172305, 172307, 172308. 

Division CYCADOPHYTA 

Order BENNETTITALES 

ZAMITES POWELLII Fontaine (in Fontaine and 

Knowlton, 1890) 

Plate 1, figures 2, 9 

Description. This form has oblanceolate to elliptical leaves that are once pinnate. The pinnae are linear 

and have distinctly parallel sides and truncate apicies. 

Small, poorly developed expansions or auricles occur in 

the basal angles of the pinnae. The pinnae usually arise 

alternately from the rachis at a high angle (55 °-70 ~, except near the leaf apex where they arise at a much lower 

angle and a pinnae terminates the rachis. The veins are 

commonly distinct in the pinnules and arise from one or 

two veins in the bases of the pinnae. They are generally 

parallel except in the pinnae bases where they diverge. 

Most of the veins continue to the apices of the pinnae 

and end in the margin there. One or two veins commonly enter each auricle where they end in the margins. The 

cuticle is thin and shows more or less rectangular epidermal cells with fairly sinuous side walls and wavy to 

straight end walls. Frequently the outer wall bears a small 

sac or stellate hair. The stomata are syndetocheilic and 

irregularly oriented and occur mainly between the veins. 

Remarks. Many specimens of Z. powellii have been 

collected from the principal reference section. They range 

considerably in size as is usual in this species. The pinnules vary from 3 mm to 7 mm in width and from 1.5 em 

to 2.5 em in length. 

The only species in the Upper Triassic flora of the 

southwest with which Z. powellii might be confused is 

Otozamites macombii Newberry (1876). Both have once 

pinnate leaves but they have somewhat different proportions; those of 0. macombii are narrower than the leaves 

of Z. powellii. The pinnules also have slightly different 

proportions; they are usually shorter and wider in 0. 

macombii than in the present species. Probably the most 

obvious difference is venation. In 0. macombii the veins 

follow fairly straight courses from their place of origin 

and end in the lateral as well as the apical margins. Only 

a few of the veins in Z. powellii end in the lateral margins 

of the auricles. Most change their courses a short distance 

from their place of origin, so they come to parallel the 

lateral margins and continue to the apical margins, where 

they end. 

Distribution. Zamites powellii is probably the most 

common leaf found in the lower part of the Dockum 

Group as well as in the Chinle Formation west of the Rio 

Grande (Ash, 1975a). The species was first described from 

the lower few feet of the Upper Triassic sequence in 

northern New Mexico by Fontaine (Fontaine and 

Knowlton, 1890). Since then it has been reported from 

the lower part of the Chinle Formation at many localities 

in southern Utah by Berry (1927) and Ash (1975a, 1975b), 

in northeastern Arizona by Daugherty (1941), and in 

western New Mexico by Ash (1967, 1975a), from the 

Tecovas and Trujillo Formations in Texas and the Chinle 

Formation in eastern New Mexico by Ash (1972), and 

from unspecified positions in the Dockum Group in Texas 

by Daugherty (1941). It has also been reported from the 

lower part of the Pekin Formation of the Newark 

Supergroup of Late Triassic age in North Carolina (Hope 

and Patterson, 1969). Except for this one occurrence, Z. 

powellii is unknown outside the southwestern United 

States. 

Material. USNM 172299, 172300. 

Division CONIFEROPHYTA 

Order CORDAITALES 

PELOURDEA POLEOENSIS (Daugherty) Arnold, 1964 

Plate 1, figure 5 

Description. This form has lanceolate to linear 

lanceolate leaves that have entire margins and acute to 

acuminate apices. The bases of the leaves narrow slightly to clasp the stems. Veins are narrow and distinct and 

are generally parallel, except in the left bases where they 

originate. The leaves are as wide as 5.2 em and are 34 em 

or more in length. 

Remarks. Four fragments of finely striate, linear 

leaves have been obtained from the principal reference 

section. They fit the general concept of Pelourdea 

poleoensis and thus are tentatively referred to that taxa. 

I know that most of the fragments are parts of the central regions of leaves because the margins of the fossils 

are more or less parallel. The illustrated specimen (pl. 1, 

fig. 5), however, apparently comes from near the apex 

of a leaf because the margins converge whereas the veins 

remain parallel and end in the margins, which is typical 

of the apex of the leaf of Pelourdea. The other specimens 

vary from 1.5 em to 3 em in width. 

22 Principal Reference Section for the Santa Rosa Formation of Middle and Late Triassic Age, Guadalupe County, New Mexico 
Distribution. Similar fragments have been reported 

from the Upper Triassic Dolores Formation in southwestern Colorado by Arnold (1964), from the Upper Triassic 

Poleo Sandstone Lentil of the Chinle in northern New 

Mexico (Daugherty, 1941), from an unspecified position 

in the Dockum of Texas (Daugherty, 1941), and I have 

collected them from the upper part of the Chinle Formation in southeastern Utah, the lower part of the Chinle 

Formation in northern Arizona and western New Mexico, and the Tecovas Formation of the Dockum in Texas. 

Pelourdea leaves are not very good index fossils because 

similar leaves have been found in rocks that range in age 

from Pennsylvanian to Jurassic from many parts of the 

world. Some of these leaves may represent different 

species, but they are difficult to distinguish and little 

significance can be attached to their occurrence in the 

Santa Rosa at this time. 

Material. USNM 172306, 172309. 

Division uncertain 

DINOPHYTON SPINOSUS Ash, 1970b 

Plate 1, figures 3, 6-8 

Description. The long, narrow leaves of this species 

are spirally arranged on a narrow stem but in the fossil 

are flattened into one plane. They are round in section, 

contain two veins, and have more or less acuminate apices. 

Petioles are absent and the basal attachment of the leaves 

is broad. Some of the axes show narrow stumps of unknown function between the leaves. The possible female 

reproductive organ consists of a pinwheel-like structure 

composed of four appendages attached at right angles to 

a small, hollow central cup-like body. The cuticle of this 

species is tough and thick and shows polygonal to rectangular epidermal cells that have curving to straight anticlinal 

walls. Each cell commonly bears a low papillae or unicellular hair. The stomata are haplocheilic with rectangular 

pores. They are typically longitudinally oriented and occur 

on all surfaces of the leaves, axis, and pinwheel structure. 

Remarks. Five recognizable examples of the leafy 

shoot of D. spinosus have been collected from the principal reference section in addition to two specimens of 

the pinwheel structure. The leaves on the shoots vary 

from 0.3 to 1.0 mm in width and from 0.8 to 2.9 em in 

length, well within the range known for the species. The 

two pinwheels are about 1. 5 em in diameter. The pinwheel 

structures and leafy shoots are attributed to the same 

plant on the basis of their very similar cuticles and their 

close association in the outcrop. 

Dinophyton spinosus does not resemble any other 

known plant in the Upper Triassic rocks of the Southwest 

U.S., and there is no doubt that the specimens described 

here are correctly identified. 

Distribution. Dinophyton spinosus is one of the 

most common plant fossils in the Dockum Group and 

the Chinle Formation west of the Rio Grande. It has been 

reported from the lower part of the Chinle Formation 

in northeastern Arizona, western New Mexico, and 

southeastern Utah (Ash, 1975b), and the Tecovas Formation in Texas (Ash, 1970b). D. spinosus has been 

reported from only one other place in the world, namely 

in the Upper Triassic New Oxford Formation of the 

Newark Supergroup in Pennsylvania (Cornet, 1977). 

Material. USNM 177301-177304. 

SAMAROPSIS SP. 

Plate 1, figure 1 

Description. This seed is about 8 mm by 15 mm and 

consists of a thick, oval central carbonaceous body surrounded by a thin membraneous wing 1-3 mm wide. The 

wing is wider in the basal and apical parts of the seeds 

than along the sides and is apparently divided into two 

long, narrow basal lobes. 

Remarks. This fossil is somewhat similar to the one 

Daugherty (1941) described from the Chinle Formation 

in Petrified Forest National Park, but it is not as well 

preserved. As in the case of Pelourdea poleoensis, this 

general type of fossil is also known from rocks that range 

in age from Pennsylvanian to Jurassic; thus, it is not 

judged to be an important index fossil at this time. 

Material. USNM 172298a, b. 

PITH CAST 

(not illustrated) 

Description. The pithcast is slightly flattened and 

is about 4.5 em wide along the longest axis and 1.5 em 

along the shortest. It is about 5 em long. The surface 

bears spirally arranged, narrow, spindle-shaped raised 

areas that are about 5 mm wide. Some of the areas show 

a narrow slit at one end. As noted above, a small amount 

of woody material adheres to the case in places. 

Remarks. Casts similar to the one described here 

are known from rocks of Pennsylvanian through 

Cretaceous age in many parts of the world. Some are 

thought to be cordiatean, others coniferous, and still 

others clearly are cycadean. They have been given a variety of names, commonly on the basis of very slight differences. According to Seward (1917, 1919), those from 

Pennsylvanian and Permian rocks have been called 

Tylodendron and also Schizodendron; those from 

Triassic and younger rocks have been referred to as 

Voltzia, Endolepsis, and Cycadeomyelon. Specimens 

from the Upper Triassic part of the Newark Supergroup 

in New Jersey were called Palissya? sp. by Newberry 

(1876), and some from the Newark in New Brunswick 

were referred to as Voltzia coburgensis by Holden (1913). 

Because the validity of most of these names is questionable, it seems best to refrain from assigning the 

specimen described here to any genus at this time. 

Fossil Plants from the Mudstone Member of the Santa Rosa Formation at the Principal Reference Section 23 
Distribution. Little stratigraphic significance can be 

attached to the occurrence of this pithcast in the Santa 

Rosa as it appears to be a wide-ranging form. Nevertheless, similar pithcasts are known from the Upper 

Triassic of eastern North America and also from the Upper Triassic rocks of northern New Mexico according to 

C. B. Read (oral commun., U.S. Geological Survey, 

1964). 

Material. USNM 172310 

CONCLUSIONS 

The mudstone member of the Santa Rosa Sandstone in the principal reference section contains a small 

flora consisting of six forms, four of which are well 

known and characteristic of the lower part of the classical 

Chinle Formation west of the Rio Grande (table 1). They 

are Cynepteris lasiophora, Zamites powellii), Pelourdea 

poleoensis, and Dinophyton spinosus. Two others, 

Samaropsis sp. and the pithcast, may also occur in the 

Chinle, but this is uncertain. No other Triassic unit in 

the western United States contains as many Santa Rosa 

species, and it is evident that the two floras correlate fairly 

closely. The flora in the mudstone member of the Santa 

Rosa Sandstone is typical of the Zone of Dinophyton as 

proposed by Ash (1980). Recent investigations indicate 

that the Zone of Dinophyton correlates with the Carnian 

Stage of the Upper Triassic (Ash and others, 1986). 

The relation of this flora to those in the other 

members of the Dockum is less clear because they are so 

poorly known at the present time. Two and possibly three 

of the Santa Rosa forms occur in the Tecovas Formation, and only one is known in the Chinle Formation east 

of the Rio Grande and in the Trujillo Formation. The 

only other unit that definitely contains some of the Santa Rosa forms is the Upper Triassic part of the Newark 

Supergroup in eastern North America, which contains 

three or possibly four forms. 

RE FE RE NCES CITED 

Arnold, C.A., 1964, Cordiates-type foliage associated with 

palm-like plants from the Upper Triassic of southwestern 

Colorado: Indian Botanical Society Journal, v. 42A, p. 4-9. 

Ash, S.R., 1967, The Chinle (Upper Triassic) megaflora of the 

Zuni Mountains, New Mexico, in, Trauger, F.D., ed., 

Guidebook of Defiance-Zuni-Mt. Taylor region [Arizona 

and New Mexico]: New Mexico Geological Society, 18th 

Field Conference, 1967, p. 125-131. 

___ 1970a, Ferns from the Chinle Formation (Upper Triassic) 

in the Fort Wingate area, New Mexico: U.S. Geological 

Survey Professional Paper 613-D, p. Dl-D52. 

___ 1970b, Dinophyton, a problematical new plant genus 

from the Upper Triassic of the southwestern United States: 

Paleontology, v. 13, p. 646-663. 

___ 1972, Upper Triassic Dockum flora of eastern New Mexico and Texas, in Kelley, V.C., and Trauger, F.D., eds., 

Guidebook of east-central New Mexico: New Mexico 

Geological Society Guidebook, 23rd Field Conference, 

East-central New Mexico, September 28-30, 1972, 

p. 124-128. 

___ 1975a, Zamites powellii and its distribution in the Upper Triassic of North America: Palaeontographica, pt. B, 

v. 149, p. 139-152. 

__ l975b, The Chinle (Upper Triassic) flora of southeastern Utah, in, Fassett, J.E., ed., Canyonlands Country: A Guidebook of the Four Corners Geological Society, 8th Field Conference, September 22-25, 1975, 

p. 143-147. 

___ 1980, Upper Triassic Floral Zones of North America, 

in Dilcher, D.L., and Taylor, T.M., Biostratigraphy of 

fossil plants: Stroudsburg, Pa., Dowden, Hutchinson & 

Ross, p. 153-170. 

Ash, S.R., Litwin, R.J., and Long, R.A., 1986, Biostratigraphic 

correlation of the Chinle Formation (Late Triassic) on the 

Colorado Plateau, a progress report [abs]: Geological 

Society of America Abstracts with Programs, v. 18, 

p. 338-339. 

Berry, E.F., 1927, Cycads in the Shinarump conglomerate of 

southern Utah: Journal of the Washington Academy of 

Sciences, v. 27, p. 303-307. 

Table 1. Summary of the known distribution of the plants from the Santa Rosa Formation 

in other stratigraphic units 

[X, definite occurrence; ? , possible occurrence; --, absent] 

Chinle Dockum Group, Newark Supergroup in 

Santa Rosa Formation, New Mexico and Texas eastern North America 

Formation west of the 

Rio Grande Chinle Trujillo Tecovas 

Formation Formation Formation 

Cynepteris lasiophora X X 

Zamites powellii X X X X X 

Pelourdea poleoensis X ? 

Dinophyton spinosus X X 

Samaropsis sp. ? 

pithcast ? ? 

24 Principal Reference Section for the Santa Rosa Formation of Middle and late Triassic Age, Guadalupe County, New Mexico 
Cornet, Bruce, 1977, Preliminary investigations of two Late 

Triassic conifers from York County, Pennsylvania: 

Geobotany, p. 165-172. 

Daugherty, L.H., 1941, The Upper Triassic flora of Arizona: 

Carnegie Institute of Washington Publication 526, 

108 p. 

Fontaine, W.M., and Knowlton, F.H., 1890, Notes on Triassic 

plants from New Mexico: U.S. National Museum Proceedings, v. 13, p. 281-285. 

Holden, Ruth, 1913, Some fossil plants from eastern Canada: 

Annals of Botany, v. 27, p. 243-255. 

Hope, R.C., and Patterson, O.F., III, 1969, Triassic flora from 

the Deep River Basin, North Carolina: North Carolina 

Department of Conservation and Development Special 

Publication 2, 12 p. 

Newberry, J.S., 1876, Geological report in Report of exploring expedition from Santa Fe, New Mexico, to the junction of the Grand and Green Rivers of the Great Colorado 

of the West, in 1859, under Captain J.N. Macomb: U.S. 

Army Engineering Department, p. 9-118. 

Seward, A.C., 1917, Fossil plants, v. III, Pteridospermeae, 

Cycadofilices, Cordaitales, Cycadophyta: Cambridge, 

England, Cambridge University Press, 656 p. 

Seward, A.C., 1919, Fossil plants, v. IV, Ginkgoales, Coniferales, Gnetales: Cambridge, England, Cambridge 

University Press, 543 p. 

Fossil Plants from the Mudstone Member of the Santa Rosa Formation at the Principal Reference Section 25 
PLATE 1 

Fossil plants from the mudstone member, Santa Rosa Formation, near Santa Rosa and the 

Chinle Formation near Fort Wingate, N. Mex. 

Figure 1. Samaropsis sp. USNM 172298a, X 1. 

2,9. Zamites powellii (Fontaine in Fountaine and Knowlton, 1890). Many of the 

pinnules in the figures show parallel margins and truncate apices, which are 

so characteristic of the species. In a few pinnules, slight ear-like projections 

of the lamina are visible in the basal angles. 

2. Apical part of a leaf. USNM 172299, X 1. 

9. Middle part of a leaf. USNM 172300, X 1. 

3,6-8. Dinophyton spinosus Ash, 1970b. 

3, 7, 8. Typical leafy shoots showing the variation in size commonly noted 

in the species. The needle-like leaves are clearly evident in the figures. USNM 

172301, 172302, 172303, all x 1. 

6. Specimen from the Monitor Butte Member of the Chinle Formation near 

Fort Wingate, N.Mex. Example of a pinwheel-like structure attributed to the 

species. In this specimen parts of three of the appendages and the central cuplike body are preserved. USNM 172304, X 1. 

4. Cynepteris /asiophora Ash, 1970a. Pinna from the upper part of a leaf showing a more or less entire margin. Reticulate venation typical of the species is 

visible in many places. USNM 172305, X 1. 

5. Pelourdia poleoensis (Daugherty, 1941) Arnold, 1964. The apical part of 

a leaf showing the converging margins and parallel veins. USNM 172306, X 1. 
DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

BULLETIN 1804 A-C 

PLATE 1 

FOSSIL PLANTS FROM THE MUDSTONE MEMBER, SANTA ROSA FORMATION, AND THE CHINLE FORMATION 

-t.r U.S. GOVERNMENT PR INTING OFFICE: 1988-573-047/66,026 REGION NO.8