Geochronology of Torrejonian sediments, Nacimiento Formation, San Juan Basin, New Mexico

Item Type text; Thesis-Reproduction (electronic)

Authors Taylor, Louis Henry, 1944-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/566500 GEOCHRONOLOGY OF TORREJONIAN SEDIMENTS,

NACIMIENTO FORMATION, SAN JUAN BASIN, NEW MEXICO

by

Louis Henry Taylor

A Thesis Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 7 STATEMENT BY AUTHOR

This th e s is has been subm itted in p a r tia l f u lf illm e n t o f re ­ quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of th is m anuscript in whole or in p a rt may be granted by the head o f the major department or the Dean of the Graduate College when in his judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

7 7 Date Associate Professor of Geosciences ACKNOWLEDGMENTS

I thank Drs. E. H. Lindsay, R. F. B u tle r, and G. G. Simpson for their guidance and constructive criticism during the course of this project. I also thank Dr. Butler, S. L. Bressler, Y. Tomida, and

R. A. Haskin for their assistance in measuring paleomagnetic specimens.

Assistance in the collection of both paleomagnetic samples and fossils was provided by Drs. Lindsay, Butler, and L. L. Jacobs, III.

Also indispensible in the field were J. G. Honey, L. J. Flynn, B. R.

Standhardt, and Y. Tomida. For their help I thank them.

I would also like to thank my wife Mary for her encouragement and fin a n c ia l support.

i i i TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS ...... vi

LIST OF TABLES ...... v l l l

ABSTRACT...... ix

1. INTRODUCTION ...... 1

2 . THE SAN JUAN B A S I N ...... 5

Geography ...... 5 Geology ...... 7 Previous Geological Investigation ...... 8

3. THE NACIMIENTO FORMATION...... 11

Stratigraphic Nomenclature ...... 11 Stratigraphy ...... 13

4 . METHODS OF CHRONOLOGICAL CORRELATION ...... 18

B io s tra ti g r a p h i c ...... 18 The T o rrejo n ian Land Mammal A g e ...... 19 Magnetostrati g ra p h ic ...... 21 Geomagnetic-Polarity Time Scale ...... 22 M e th o d s ...... 23

5. STRATIGRAPHY ...... 37

The Study A r e a s ...... 37 L ith o s tra tig ra p h y ...... 43 B io s tr a tig r a p h y ...... 45 M a g n e tic -P o la rity S tra tig ra p h y ...... 52

6. GE0CHR0N0L0GIC CORRELATION ...... 60

The Ojo End no and Big Pocket A r e a s ...... 60 The Barrel Spring Arroyo Section ...... 65

7 . SUMMARY...... 69

iv V

TABLE OF CONTENTS-Continued

Page

APPENDIX A: PALEOMAGNETIC D A TA...... 72

Locality 10, Ojo Encino A re a ...... 72 L o c a lity 11, Ojo Encino A r e a ...... 76 Composite S e ctio n , Big Pocket Area ...... 78 Radio Tower Section, Big Pocket Area ...... 87

REFERENCES CITED ...... 88 LIST OF ILLUSTRATIONS

Figure Page

1. Regional Map o f the San Juan B a s i n ...... 3

2. Geologic Map of Nacimiento, Animas, and San Jose Form ations, San Juan B a s i n ...... 12

3. AF Demagnetization Curves and NRM Vector Motions, S ite SJ342 ...... 29

4. NRM Vector Motions, Site SJ480 30

5. NRM Vector Motions, Site SJ585 31

6. AF Demagnetization Curves and NRM Vector Motions, Site SJ356 ...... 32

7. NRM Vector Motions, Site SJ309 34

8. NRM Vector Motions, Site SJ482 35

9. AF Demagnetization Curves and NRM Vector Motions, S ite SJ044 36

10. Map o f the Ojo Encino A r e a ...... 38

11. Map o f L o c a lity 10, Ojo Encino A r e a ...... 39

12. Map of Locality 11, Ojo Encino Area ...... 40

13. Map o f the Big Pocket Area ...... 42

14. Lithologic Correlation of Localities 10 and 11, Ojo Encino A r e a ...... 44

15. Magnetic Correlation of Localities 10 and 11, Ojo Encino A r e a ...... 54

16. Magnetic-Polarity Stratigraphy of the Ojo Encino Area ...... 55

17. Magnetic-Polarity Stratigraphy of the Big Pocket Area ...... 58

vi v l i

LIST OF ILLUSTRATIONS-Continued

Figure Page

18. Geochronological Correlation of the Ojo Encino and Big Pocket A r e a s ...... 61

19. Correlation of Revised Cenozoic Polarity Time Scale and Barrel Spring Arroyo Section ...... 66 LIST OF TABLES

Table Page

1. H ierarchy o f Paleomagnetic S ite s ...... 27

2. Faunal List for the Ojo Encino and Big Pocket Study A r e a s ...... 46

viii ABSTRACT

This study compares two areas o f the San Juan Basin w ith respect to biostratigraphy, lithostratigraphy, and magnetic-polarity stratigraphy. The Ojo Encino Area, near Cuba, New Mexico and the Big

Pocket Area of Kutz Canyon, near Bloomfield, New Mexico were collected for vertebrate fossils and magnetic samples.

Both study areas contained fossils of Torrejonian Land Mammal

Age. Within this age two collecting levels are recognized. The upper.

Panto!ambda, level is characterized by the presence of Panto!ambda,

Claenodon, and possib ly Mixodectes pungens and T o rre jo n ia w lls o n i. The lower, Deltatherium, level is characterized by the presence of

D e lta th e riu m , T riis o d o n , Haploconus, Mixodectes m a la ris , and possib ly

Palaechthon nacimientl. These collecting levels are also defined by their magnetic-polarity stratigraphy. Correlation of the two study areas demonstrates that the Panto!ambda level is from within a normal magnetozone and that the Deltatherium level is from within the under­ lying reversed magnetozone.

Comparison of the magnetic-polarity stratigraphy from the two study areas with the polarity time scale demonstrates that the normal magnetozone containing the Panto!ambda level is either anomaly 26 or anomaly 27.

ix CHAPTER 1

INTRODUCTION

The San Juan Basin has been Im portant to v e rte b ra te p aleo n to lo ­ gists for over a century. This region, located in northwestern New

Mexico and southwestern Colorado, is paleontologically significant be­ cause it contained the characterizing assemblages that served as the basis for the Puercan (Early Pal eocene), Torrejonian (Middle Pal eocene), and Tiffanian (Late Pal eocene) North American Provincial Ages of Wood et al. (1941), presently referred to as North American Land Mammal Ages

(Evernden et a l. 1964).

This study was undertaken to define the magnetic-polarity se­ quence in a section from Arroyo Torreon and to correlate that section with a section in Kutz Canyon that has also yielded fossils of Torre- jonian Land Mammal Age. These sections, consisting primarily of sedimentary rocks, were from two areas within the San Juan Basin. The

faunas from both areas have been known for some time but their precise

geochronological re la tio n s h ip has n o t.

Time-correlation of the two areas was attempted through the use of magnetic-polarity stratigraphy and biostratigraphy. Each area was collected extensively for magnetic samples that were used to construct magnetic-polarity columns. Comparison of their relative magnetic-

polarity columns then permitted correlation of sim ilar magnetozones,

1 2 which gives a more precise chronological framework than does either lithostratigraphy or biostratigraphy.

Areas chosen for this study were, firs t, the head of Arroyo

Torreon (Figure 1) referred to as the Ojo Encino Area; and second, an area on the west side of Kutz Canyon (Figure 1) called the Big Pocket

Area. The Ojo Encino Area includes fossil localities 10 and 11 of

Sinclair and Granger (1914) which contained the original Torrejon levels discovered by Wortman in 1896 (Matthew 1897), named by Matthew

(1897), and used to define the Torrejonian Provincial Age by Wood et a l. (1941). The Ojo Encino Area is approximately 40 kilometers (25 miles) west of Cuba, New Mexico.

The Big Pocket Area is approximately 16 kilometers (10 miles) south of Bloomfield, New Mexico. The Big Pocket Area includes the

U n iv e rs ity o f Kansas fo s s il lo c a lit y 13 (KUPV 13 in Wilson 1956b and

NM 13 in Wilson and Szalay 1972) discovered by Wilson in 1948 and de­ scribed by him (Wilson 1951) as the Angels Peak faunule. Modifications and additions to Wilson's (1951) original description of the area were made in Wilson (1956a), Russell (1967), and Wilson and Szalay (1972).

Wilson (1951), in his preliminary survey, assigned the

Angels Peak fauna to T o rrejo n ian Land Mammal Age and suggested th a t i t may not be contemporaneous with other Torrejonian faunas from the San

Juan Basin. He, at that time, did not feel justified in determining

the temporal difference between his Angel Peak fauna and those from other San Juan Basin Torrejonian localities. In 1972, Wilson and

Szalay (1972) pointed out that the Kutz Canyon local fauna (= Angels

Peak faunule of Wilson 1951) is of Torrejonian age but older than the 3

So 0 ^ 2 ^ ( Durango e Ragosa ?ADO any ^ ( S p r i n g s UTAH x COLORADO

ARIZONA y XNEW MEXICO X V V * Farmington •VeBloomfield \K u tz Canyon Barrel Spring Arroyo •z •Tsosie Kimbetoh Canyon Xb Arroyo Ojo". ( /eCuba De Chelly Encmo ) / * Nat. Mon. /A rro y o j L / / Torreon>-.j)Rio VPuerco V \ Albuquerquel

N

30 Mi. ill t i Km. Z Boundary of the ' San Juan Basin

l \ Continental Divide

Figure 1. Regional Map o f the San Juan Basin 4 upper collecting level (Panto!ambda zone) from the Ojo Endno Area.

Nevertheless, the chronological difference, or lack thereof, between similar faunal levels in the San Juan Basin has not been determined, nor has the technique of magnetic-polarity stratigraphy been available with which to do so. This was the main purpose of this study; to apply the technique of magnetic-polarity stratigraphy to sediments that con­ tain fossils of Torrejonian age. Time-correlation of vertebrate faunal remains is important to the understanding of both evolution and biogeography. Simpson (1933 , p. 79) emphasized the importance o f chronostratigraphy when he wrote, "The fittin g of all these faunas into their relative positions in a time scale and the establishment of appropriate conventional divisions of this time scale constitute one of the most important aims of mammalian paleontology." This statement is as true with respect to the faunal horizons within each Land Mammal

Age as i t was fo r the Land Mammal Ages them selves. R ecen tly, Woodburne

(1977) reiterated the need for increasing the precision and refinement of the North American Land Mammal Ages. CHAPTER 2

THE SAN JUAN BASIN

Figure 1 shows the boundaries of the San Juan Basin. It in­ cludes the areas of interest to this study as well as the geographical

features briefly discussed below.

Geography

Located in the Four Corners Region, the San Juan Basin occupies

part of McKinley, Rio Arriba, and Sandoval Counties and all of San Juan

County in New Mexico; part of Archuleta, La Plata, and Montezuma

Counties in Colorado; and a small fraction of Apache County, Arizona.

Nearly 52,000 square kilometers (20,000 square miles) in area, it is

bounded roughly by C o rtez, Durango, and Pagosa Springs in Colorado and

by Cuba, Grants, and Gallup in New Mexico.

A major portion of the San Juan Basin is drained by the SaiT

Juan River System, a tributary to the Colorado River. East of the

Continental Divide the Rio Chama System to the north and the Rio Puerco

System to the south flow southeasterly out of the basin and into the

Rio Grande River.

There is a tremendous difference in topographic re lie f between

the rim areas and the basin interior of the San Juan Basin. The eleva­

tion difference between the highest bordering peak and the San Juan

River where it leaves the basin is about 2835 meters (9300 feet)

5 6

(Kelley 1950a). The basin interior is less spectacular in relief; less than 500 meters (1609 feet) separate its highest and lowest elevations.

Cuba Mesa, Arroyo Torreon, and Kutz Canyon show some of the most spec­ tacular relief in the basin interior with topographic relief of 290 meters (950 feet), 152 meters (500 feet), and 473 meters (1550 feet), respectively.

The interior of the San Juan Basin is most important to this study. Extensive badlands in th is region have y ie ld e d numerous remains o f v e rte b ra te s . The w ell studied p o rtio n o f the San Juan Basin con­ tains geographical features that are cartographically problematical.

The geographical location, spelling, or even the name of some of these featu res remains in d is p u te . For example, Simpson (1959) f e l t i t nec­ essary to discuss the history of names and spellings applied to Tsosie,

Kimbetoh, and Torreon Arroyos as well as to provide a brief account of the change in name and location of the present town of Cuba, New Mexico.

His suggested names, spellings, and locations are used in this study.

MacIntyre (1966) also discussed some geographical features from this region. In at least one instance (Angel Peak) he is in error. Near the Big Pocket Area of Kutz Canyon is an erosional remnant variously re­ ferred to as Angel or Angels Peak1 (Figure 13, p. 42). MacIntyre (1966)

1. Sinclair and Granger (1914), Wilson (1951), and various maps refer to this feature as Angels Peak. Granger (1917), however, c a lle d i t Angel Peak. At the suggestion o f G. G. Simpson th is erosion­ al remnant w ill be referred to as Angel Peak. He pointed out that it was named by pioneers who saw, in its outline, an angel. The peak was neither thought to have been in the possession of angels nor was an in d iv id u a l w ith the surname Angel i t s eponym. 7 2 concluded that this peak is located in the NW^ of Section 5, T.27N.,

R.9W. Angel Peak is found in the NW^ of Section 23, T.27N., R.10W. on the U. S. Geological Survey Bloomfield 15 Minute Quadrangle Map.

Geology

Geologically, the San Juan Basin is the southernmost of several large intermontane structural basins among or partially bounded by the

Rocky Mountains. It occupies approximately the eastern one-half of the

Navajo Physiographic Section of the Colorado Plateau Physiographic

Province. The several structural elements that define the San Juan

Basin are discussed in Kelley (1950b) and Baltz (1967).

The geological boundaries of the San Juan Basin have not been agreed upon (Kelley 1950b). Bauer (1916) and Reeside (1924) limited the San Juan Basin to that region containing concentric inwardly dip­ ping strata. This corresponds to the northern half of the basin interior mentioned above. This Central Basin (Baltz 1967), asymmetrical with a northwest trending axis, is that part of the basin noted for its vertebrate faunas; it contains both the Ojo Encino and Big Pocket Areas.

2. MacIntyre (1966) wrongly identified an unnamed peak at approximately 36e36l N. Lat., 107*48* W. Long, as Angel Peak. Sinclair and Granger's (1914) map places the peak at about 36*341 N. L at., 107* 53* W. Long, and Wilson's (1951) reference was to a peak at approxi­ mately 36*32' N. Lat., 107*58' W. Long. The coordinates of Angel Peak on the U. S. Geological Survey Bloomfield 15 Minute Quadrangle Map are 36*341 N. Lat., 107*52' W. Long. Also, Wilson's (1951) map showed Angel Peak to be near the head o f Armenta Canyon and eas t southeast from his fossil locality 13. The peak that MacIntyre (1966) identified as Angel Peak is east northeast of fossil locality 13. Further, Granger (1917) clearly associated Angel Peak with Kutz Canyon. 8

The stratigraphic column of the Central Basin is a succession of marine, brackish water, and fresh water strata (Bauer 1916). These strata, thickest in the center of the basin, are estimated to represent from 3050 to 4570 meters (10,000 to 15,000 feet) of sediment (Kelley

1950b). Although predominantly of Cretaceous age, these strata repre­ sent a broken sequence from Late Paleozoic to the Eocene (Simpson 1948,

Baltz 1967). This study is concerned with the Pal eocene Nacimiento

Formation. For further inquiry into the geology of the San Juan Basin see Reeside (1 9 2 4 ), Beaumont and Read (1 9 5 0 ), K elley (1 9 5 0 b ), and B a ltz

(1 9 6 7 ).

Previous Geological Investigation

The San Juan Basin has been in v e s tig a te d by many workers since

J. S. Newberry firs t traversed the region with the Macomb Expedition in

1859 (Simpson 1948, 1950). The history of investigation has been ade­ q u ately developed by Simpson (1948) and B a ltz (1967) and only those investigations pertinent to the present study are included here.

The firs t recognized Pal eocene mammals from the San Juan Basin were collected by David Baldwin while in the employ of E. D. Cope, sometime between 1880 and 1888. These fossils are now part of the

Pal eocene collection of the American Museum of Natural History (Matthew

1937). That institution began a successful association with the fossil ric h badlands o f the San Juan Basin by d eleg a tin g J . L. Wortman to lead an expedition there in 1892. Wortman led a second expedition to the

San Juan Basin during which he collected over 1500 Pal eocene specimens and discovered the Torrejonian faunal level of the Ojo Endno Area 9

(Matthew 1897, 1 93 7). The Wortman c o lle c tio n was described by Osborn and E arle (1895) and by Matthew (1 9 3 7 ).

Walter Granger briefly examined the Paleocene strata of the San

Juan Basin fo r the American Museum in 1912. The fo llo w in g year he re ­ turned with W. J. Sinclair of Princeton University to study the stratigraphy and vertebrate faunas of the area (Sinclair and Granger

1914). They recognized what they considered to be two collecting levels in the Torrejonian of Arroyo Torreon. Granger (1917) later col­ lected Torrejonian fossils from the northern portion of the Central

Basin; he found fossils in several arroyos near Aztec, New Mexico and in Kutz Canyon, south of Bloomfield, New Mexico. Further details of the two collecting levels of the San Juan Basin w ill be discussed below.

After the Second World War interest in the paleontology of the

San Juan Basin Pal eocene was revived and personnel from a number of in­ stitutions were in the area at that time. Of Interest to the present study are investigations of the Torrejonian strata and faunas. Conse­ quently no mention is made of investigations of strata and faunas of

Puercan or Tiffanian age. As mentioned above, Wilson led a University o f Kansas group in to the San Juan Basin in 1948 and returned to the area in 1956 and 1962 (Wilson 1950, 1951, 1956a, 1956b, Wilson and

Szalay 1972). C. L. Gazin collected fossils for the U. S. National

Museum from Middle Pal eocene strata in 1949 (Gazin 1968). Part of

Wilson's (1951, 1956a) collection came from Kutz Canyon while part of

Gazin's (1968) collection was found near Arroyo Torreon. Also, G. G.

Simpson, of the American Museum, collected Torrejonian fossils from near Cuba in 1949 (Simpson 1959). 10

The most recent in v e s tig a tio n o f fo s s ils and s tra tig ra p h y o f the San Juan Basin has been by the U n iv e rs ity o f Arizona p a rty under the leadership of E. H. Lindsay and R. F. Butler. This group is at­ tempting to resolve the chronology of Late Cretaceous to Eocene strata in the San Juan Basin by applying modern methods o f both v e rte b ra te paleontology and paleomagnetism. The present study is a part of the most recent scientific effort in the San Juan Basin. CHAPTER 3

THE NACIMIENTO FORMATION

Rocks deposited during the Torrejonian age In the San Juan

Basin are found within the Nacimiento Formation. The Nacimiento is one of the several lithostratigraphic units concentric about the basin in­

terior. It crops out primarily in the southern half of the central

portion of the San Juan Basin. Badlands and cliffs in the Nacimiento

Formation are exposed from the Colorado-New Mexico boundary southeast­ ward to Cuba Mesa, and along the Rio Puerco east and north of Cuba

(Simpson 1950, Fassett and Hinds 1971). The Nacimiento Formation is

thought to grade l a t e r a ll y in to the Animas Formation (Reeside 1924,

Silver 1950) which crops out in the northwestern area of the San Juan

Basin (Figure 2).

Torrejonian fossils are found throughout the extent of the

Nacimiento but especially: 1) near the head of Arroyo Torreon (Sinclair

and Granger 1914, Gazin 1968); 2) near the head of Kimbetoh Arroyo

(Sinclair and Granger 1914, Wilson 1951 , 1956c); 3) in Kutz Canyon

(Granger 1917, Wilson 1951, 1956c, Wilson and Szalay 1972); and 4) in

the Animas R iver V a lle y near Aztec (Granger 1 9 1 7 ).

Stratigraphic Nomenclature

The Nacimiento has had a long history of nomenclature! change.

It has been recognized as a unit since firs t designated the "Puerco

11 12

Durango Pagosa Springs

COLORADO NEW MEXICO

•Aztec

Bloomfield*

Jose

10 20 30 Mi. Cuba 50 Km.

Figure 2. Geologic Map of Nacimiento, Animas, and San Jose Formations San Juan Basin. — (Adapted from S ilv e r 1950; Fassett and Hinds 1971) 13

Marls" by Cope in 1874 (Simpson 1948). This three quarters of a cen­

tu ry o f Nacimiento h is to r y , as presented by Simpson (1948, 1 9 5 9 ),

includes the problem resulting from the error of confusing biostrati-

graphic and lith o s tr a tig r a p h ic u n its . The Nacimiento has long been

divided into separate lithologic and associated faunal units, the

Puerco and the T o rre jo n . Usage o f the terms Puerco, T o rre jo n , and

Nacimiento was not consistent until 1948 when Simpson (1948) aptly

pointed out that the Puerco and Torrejon are lithologically inseparable

and, consequently, cannot be considered formations, which are lith o ­

strati graphic units. He considered Puerco and Torrejon as faunal zones

within the rocks of the Nacimiento Formation; the term "Nacimiento for­

mation" had been used by Dane (1946) but had not been proposed as a

formal lithostratigraphic unit. Simpson (1959) demonstrated the occur­

rence of Torrejonian fossils from the type Puerco, emphasizing the need

to distinguish faunal concepts from stratigraphic concepts. The

Torrejonian Land Mammal Age is of importance to the present study and

is discussed in more d e ta il below.

Stratigraphy

The Nacimiento Formation consists of variously colored beds of

clay, shale, and siltstone with interbedded sandstones. The fine­

grained strata vary in color from the common gray or green-gray to red

or black. The sandstones, usually local and lenticular, vary in color

from buff or yellow to gray or white. The sandstones also vary in

their resistance to weathering; some are friable while others are in­

durated. A few restricted black carbonaceous claystone and siltstone 14 lenses occur within the Nacimiento Formation. Also present, but rare, are th in beds o f c o a l.

The upper and lower boundaries of the Nacimiento Formation are not easily recognized throughout the San Juan Basin and generally have been placed a t unconform ities w ith the underlying Ojo Alamo Sandstone and the overlying San Jose Formation. The lower unconformity was noted by S in c la ir and Granger (1 9 1 4 ), but B a ltz , Ash, and Anderson (1966) were unable to confirm its presence. Instead, they found evidence that the Nacimiento intertongues with the underlying Ojo Alamo at three lo­ cations in Barrel Spring Arroyo. More recent work on the stratigraphy of this area by Butler et a l. (1977) substantiates this intertonguing relationship.

The upper boundary of the Nacimiento is not simple either. In the southern part of the San Juan Basin an unconformity appears to sep­ arate the Nacimiento Formation from the overlying San Jose sediments

(Reeside 1924, Simpson 1 9 4 8 ). However, to the north the Nacimiento apparently grades into the San Jose with no apparent break in sedimen­ tation. The Tiffany beds of Granger (1917), here considered a part of the San Jose Formation (Simpson, in Simons 1 9 6 0 ), are thought to con­ formably overlie the Nacimiento in the northern part of the basin.

More field work is needed to determine the accurate stratigraphic relationships of the Nacimiento, San Jose, and Tiffany.

The re la tio n s h ip o f the Nacimiento to the Animas Formation is not f u ll y understood. North and west o f the N acim iento, the Animas was thought by Baltz (1967) to be contemporaneous with the former. The 15

Animas Formation is d is tin c tiv e in c o lo r (tan or green) and contains much andesitic debris. Red strata, comon in the Macimiento, are

r a re ly seen in the Animas (Reeside 1 9 2 4 ). The d iffe re n c e in lith o lo g y distinguishes the Animas from the Nacimiento, but whether their strati­

graphic relationship is lateral or partly superpositional has not been

determined (Fassett and Hinds 1971).

Baltz's (1967) measurements show the Nacimiento to be only half

as thick in the southern part of the San Juan Basin, near Cuba, New

Mexico, as in the more northerly part of the basin. This thinning,

according to Baltz (1967) is partly intraformational. It is also part­

ly due to erosion of the upper Nacimiento prior to San Jose deposition.

Simpson (1959) suggests th a t the probable lack o f Puercan fo s s ils in

the type Nacimiento area at Cuba Mesa indicates thinning of the Naci­

miento due to progressive overlap of younger rocks to the south. This,

of course, could also account for part of the southeasterly thinning

tre n d .

It is agreed generally (Baltz 1967) that the Nacimiento sedi­

ments were deposited in a fluvial environment. The many local

lenticular sandstones that represent channels and the intergrading

lenses o f clays and s i l t s mentioned by Simpson (1948) support th is

interpretation. MacIntyre (1966) suggests that streams and bodies of

water large enough to support large aquatic reptiles were present but

that enough solid ground was present to support a fairly large pop­

u la tio n o f t e r r e s t r ia l mammals. R e s tric te d p a r t ia lly paludal

environments were suggested by both MacIntyre (1966) and Baltz (1967). 16

Such an environment is evidenced by at least two areas encountered dur­ ing the present study, both of which are within Sinclair and Granger's

(1914) fossil locality 10 in the Ojo Encino Area. One area, in the NW% of Section 26, T.21N., R.5W., contains a 2 meter (6.6 foot) thick black carbonaceous clay layer exposed over a relatively fla t area of approxi­ mately 740 square meters (8000 square feet). Turtle remains and plant material were found in the stratum. A second, sim ilar, exposure was located approximately 0.8 kilometer (1.5 mile) southeast of the firs t.

S tra ta o f black carbonaceous c la y w ith numerous f is h , aq u atic r e p t il e , and p la n t fo s s ils were also seen in B arrel Spring Arroyo and Kutz Can­ yon. A further indication of paludal environment was a thin coal seam

present near the base of the locality 10 section in the Ojo Encino Area.

Baltz (1967) demonstrated the tendency toward a greater pro­

portion of sandstone in the northern part of the San Juan Basin. This

trend was noted during the present study while collecting paleomagnetic

samples in the Ojo Encino and Big Pocket study areas. The presence of

a greater amount of sandstone in the Nacimiento to the north could be

indicative of a northerly source area for the sediments of that forma­

tion. However, the detailed stratigraphic analysis of the Nacimiento,

necessary to demonstrate this concept, has not been undertaken.

The Nacimiento is considered lower and m iddle Pal eocene in age.

In the past it has been considered basal Eocene or post-Cretaceous

(Gardner 1910). The discovery of the late Pal eocene Tiffany beds,

strati graphically higher than the Nacimiento, reduced the upper age

lim it of the Nacimiento from early Eocene or late Pal eocene to middle 17

Pal eocene (Simpson 1933). Presently the Puerco, Torrejon, and Tiffany levels are considered lower, middle, and upper Paleocene, respectively, as suggested by Simpson (1933) and Matthew (1 9 3 7 ). CHAPTER 4

METHODS OF CHRONOLOGICAL CORRELATION

Two methods of time-correlation are useful in the Nacimiento

Formation of the San Juan Basin. The vertebrate fossils for which the basin has long been noted can be used b io s tr a ti g ra p h ic a lly fo r chronological correlation. Also, the fine-grained sediments of this

formation have been found to be recorders of reversals in the earth's magnetic field; they are useful in the magnetic-polarity stratigraphic method of time-correlation.

Biostratigraphic

The Nacimiento Formation has long been recognized as two distinct biological units, the Puerco and Torrejon faunas mentioned

above. The Puerco fauna is the oldest of a series of Cenozoic faunas

in North America which served to define the North American Provincial

Ages of Wood et a l. (1941). Now referred to as North American Land

Mammal Ages (Evernden et al. 1964), these units are used by vertebrate

paleontologists to correlate the Cenozoic of North America. Their de­

velopment by modifications to concepts firs t proposed in the late 1800s was well detailed by Tedford (1970). He also discussed, as did Savage

(1955) and Wilson (1967), the use of fossil mammals in correlation and

concluded that the presently developed Land Mammal Ages have proven .

useful in correlation.

18 19

Wood et a l. (1941) defined the Land Mammal Ages on the basis of the faunal assemblages within them. The faunas were separated into four aspects: 1) genera known only from the age being defined (index fossils); 2) genera found in North America for the first time (firs t appearance); 3) genera found in North America for the last time (last appearance); and 4) genera corranon in the age being defined (character­ istic fossils).

The T o rrejo n ian Land Mammal Age

This study is concerned with one of the presently recognized

North American Land Mammal Ages, the m iddle Pal eocene T o rre jo n ia n .

The Torrejonian was defined by Wood et a l. (1941, p. 9) as "-new pro­ vincial term, based upon the Torrejonian formation of the San Juan

Basin, New Mexico, type locality, the heads of Arroyo Torrejon;..."

The fo llo w in g genera were used by them to d efin e the T o rrejo n ian Land

Mammal (Provincial) Age:

First appearance: Chriacus, Psittacotherium, Didymictis, Pantolambda, Claenodon, Tetraclaenodon

Last appearance: E llip s o d o n , Eucosmodon, Haploconus

Index fossils: Conoryctes, Deltathen urn, Mloclaenus, Trlisodon

Characteristic fossils: Anisonchus, Periptychus, Ptilodus

Since the discovery of the original Torrejon fauna, the defin­ ing genera of the Torrejonian have been found outside the San Juan

Basin. Wood et a l. (1941) included some Torrejonian correlatives in their report and, more recently. Van Valen and Sloan (1966) constructed a chart listing all known Pal eocene mammal localities and faunas. 20

Since Van Valen and Sloan’s (1966) publication some localities have been discovered or found to be o f T o rrejo n ian age. A l i s t o f these localities is included below:

Tongue River: Fort Union Formation; Billings County, North Dakota; Simons (I9 6 0 ) and Brown (1962)

(?)Alberta Oil Well: Paskapoo Formation; Research Council of Alberta Core Hole 66-1; Balzac, Alberta, Canada; Fox (1968)

L ittle Muddy Creek: Evanston Formation; southwestern Wyoming; Gazin (1969)

Black Peaks: Black Peaks Form ation; Big Bend N ational Park, Texas; Schiebout (1974)

The Torrejonian of the San Juan Basin includes two horizons described by S in c la ir and Granger (1914) and named the Panto!ambda and

D eltatherium l i f e zones by Osborn and Matthew (1909) and Osborn (1 9 2 9 ).

These faunal levels, each of which was defined by and named for the genus restricted to it, have been problematical since their discovery.

Sinclair and Granger (1914) reported the Deltatherium zone 30.5 meters

(100 feet) below the Panto!ambda zone and Osborn (1929) considered the levels distinct life zones. Matthew (1937), however, believed them to be either facies differences or accidents of collecting because many of the same species were found in both levels and no significant faunal changes could be recognized. Wilson (1951, p. 10) also stated that the difference between the Panto!ambda and Deltatherium zones is "...larg e­ ly, if not entirely, facial in character." Wilson (1956a) also expanded the definition of the zones. He pointed out that, in addition to Deltatherium, Triisodon and Haploconus are restricted to the 21

D eltatherium zone and th a t Claenodon as w ell as Panto!ambda is re ­ stricted to the Pantolambda zone.

More recently, Szalay (1969) discussed the Torrejonian levels with respect to the genus Mixodectes. He found fi. malar!s to occur only in the D eltatherium zone and thought i t l ik e ly th a t M. pungens occurs only in the Pantolambda zone. He noted that the provenance of the M. pungens specimens.was, however, suspect.

Gazin (1968) obtained the primate Torrejonia wilsoni from the

Pantolambda zone and Wilson and Szalay (1972) discovered Palaechthon nacimienti within the Deltatherium zone. These primates are not re­ presented by enough m a te ria l to be considered d iag n o stic o f e ith e r horizon but at the present time are restricted to only one collecting le v e l.

The definition of the Deltatherium zone with Deltatherium,

Triisodon, Haploconus, and Mixodectes malaris restricted to it and the

definition of the Pantolambda zone with Pantolambda and Claenodon re­ stricted to it are consistent with biostrati graphic ranges determined

in the Ojo Encino and Big Pocket areas during the present study.

Magnetostratigraphic

Scientific interest in paleomagnetism began in the mid-

nineteenth century but application of this field was largely ignored

until the revival in popularity of the theory of continental drift in

the 1950s (McElhinny 1973). The volume of literature in this field

increased from about 200 to about 1500 independent studies from 1959 22 to 1973 (Cox and Doell I9 6 0 , McElhinny 1973) and continues to increase at a rapid rate.

Geomagnetic-Polarity Time Scale

One result of the renewed interest in paleomagnetism has been the magnetic-polarity time scale; it was largely the result of attempts to demonstrate Matuyama's (1929) hypothesis that a time synchronous magnetic reversal had occurred in the early Pleistocene (Watkins 1972,

Cox 1973). Calibration of the magnetic-polarity time scale is possible through radiometric age determinations made on rocks of known polarity.

The developmental history of the magnetic-polarity time scale has been chronicled by Watkins (1972) and Cox (1973).

Presently the magnetic-polarity time scale is reliably cali­ brated for only the past four m illion years but attempts have been and are being made to extend th is s c a le . Opdyke (1972) and McDougall e t a l. (1977) extended the time scale into the Miocene. Earlier,

Heirtzler et a l. (1968) had extended the magnetic-polarity time scale into the Cretaceous. However, because the dates used were extrapolated from an Interval of known age, either radiometrically or paleontolo­ gically determined, ages earlier than late Cenozoic are not as yet well determined. They should be used with caution. The Heirtzler et al.

(1968) tim e scale used the p re s e n tly accepted Hays and Opdyke (1967) convention for labeling magnetozones; magnetic epochs are labeled with

Arabic numerals and magnetic events within an epoch are labeled with

letters, both beginning with the most recent. 23

The H e ir t z le r e t a l . (1968) m a g n e tic -p o la rity tim e scale has been m odified by Larson and Pitman (1 9 7 2 ), Berggren and VanCouvering

(1 9 7 4 ), and T a rlin g and M itc h e ll (1 9 7 6 ). The T a rlin g and M itc h e ll

(1976) polarity time scale is used in this study.

A recent advance in the field of magnetostratigraphy has been

the correlation of terrestrial sediments known for their vertebrate

faunas. Early in 1975, Johnson, Opdyke, and Lindsay (1975) showed

that such correlation was possible in the San Pedro Valley of southern

A rizona. Lindsay, Johnson, and Opdyke (1975) and Opdyke e t a l . (1977)

have demonstrated the correlation of other terrestrial sediments with

the magnetic-polarity time scale. The project undertaken by workers

from The University of Arizona in the San Juan Basin is designed to

correlate the vertebrate-fossil-bearing terrestrial sedimentary se­

quences of that region through the use of magnetic-polarity

stratigraphy.

Methods / Since Johnson et a l. (1975) first pointed out that some terr­

estrial sediments have acquired stable remanent magnetization in the

form of depositional remanence (DRM), the techniques of field collec­

tion, laboratory preparation, and laboratory analysis have been refined

through further application.

For the purposes of this study 265 paleomagnetic sites were

collected and analyzed. The oriented-block technique was used in the

badlands of the San Juan Basin. Details of this sampling technique 24 are described in Lindsay et a l. (in press). At least three oriented samples were collected from each site. A stratigraphic separation of approximately three meters (ten feet) was maintained between successive sites whenever possible. Samples were collected from the finest grained clay lithologies available in the area; some siltstones were collected out of necessity. It is suggested, however, that the choos­ ing of an acceptable lithology takes priority over the maintenance of an exact stratigraphic interval. Unacceptable lithologies often pro­ vide ambiguous p o la r ity determ inations and are not u s e fu l, regardless of their stratigraphic elevation. In the laboratory each sample was cut and trimmed into a block specimen that fit into a plastic box with an inside volume of approximately 4 cubic centimeters (1.02 cubic

inches). Johnson et a l. (1975) estimate that these techniques of col­

lection and specimen preparation cause an approximate error of ±5° in

the resulting magnetic declination and inclination measurements. t One problem encountered during specimen preparation was that of

desiccation. Many samples were found to be dry and cracked su ffi­

ciently to disintegrate in preparation. For this reason some sites are

represented by only two specimens. Some of the disintegration d iffi­

culties were avoided by collecting more than three oriented samples

from sites of fissile lithology. In the laboratory some of the disin­

tegration problems were solved through the use of Elmer's Glue-All.

Sample d is in te g ra tio n m ight be avoided by trim m ing and p lacin g poorly

preserved samples in plastic boxes while at the outcrop. 25

Once prepared, the specimens were measured for natural remanent magnetism (NRM) with a Superconducting Technology C-102 cryogenic mag­ netometer. This instrument, with the capacity of measuring magnetic moments with intensities as low as 10" gauss-cubic centimeters, can easily measure the weak magnetic moments of terrestrial sediments.

Many of the rocks have acquired a secondary component, usually in the direction of the earth's present magnetic field , which must be removed to determine the polarity of the alternating field (AF) demagnetized

NRM which approximates the primary DRM. Alternating field demagneti­ zation with a Schondstedt GSD-1 demagnetizer was used to remove the secondary, viscous remanent magnetization.

Data from these measurements (Appendix A) were interpreted to

indicate the magnetic behavior, as well as the magnetic polarity, of

the sediments. Positive inclinations and northerly declinations are

indicative of normal magnetic polarity whereas negative inclinations

and southerly declinations indicate the presence of a reversely mag­

netized interval. Calculated virtual geomagnetic pole (VGP) latitudes

are also used to construct magnetic-polarity columns. A normally mag­

netized site exhibits a positive VGP latitude and a magnetically

reversed site exhibits a negative VGP latitude; positive VGP latitudes

are north of the equator and negative VGP latitudes are south of it.

As suggested by Lindsay et a l. (in press), in interpreting the data a

reversed direction is considered primary and any conflicting normal

direction is suspect because an unremoved secondary component may have

been acquired during the Brunhes Normal Epoch. 26

Opdyke et a l. (1977) recently provided a priority lis t for the reliability of magnetic data from individual sites (Table 1). Their hierarchy includes five classes: I) sites in which the data indicate all specimens are of the same polarity and the results are statisti­ cally significant; II) sites from which only two specimens are known but their directions are concordant; III) sites that show statistically random directions of magnetization but two of the three specimens are concordant and the third is widely divergent in an intermediate direc­ tion; IV) sites that demonstrate a strung distribution but the directions change with AF demagnetization in a systematic way so that polarity is determined; and V) for which no definition was given.

Lindsay et a l. (in press) redefined the above hierarchy (Table 1) such th a t i t consists o f Opdyke e t a l . ' s (1977) Class I , Classes I I and I I I combined,Class IV , and a new class fo r s ite s w ith random d ire c tio n s .

It seems that five classes are really necessary because the Class II and III sites of Opdyke et al. (1977) are not the same; Class II sites are distinct because there is not a third sample to be divergent. If present, the third sample could change the Class II into either a Class

I or a Class III site, depending upon its magnetic directions. The

five class hierarchy, as summarized in table 1, consists of the four classes o f Opdyke e t a l . (1977) and the a d d itio n a l class o f Lindsay e t al. (in press). The significance of the last (Class V) category is

that it is the only level in the hierarchy which provides no useful

data (Lindsay et al. in press). Table 1. Hierarchy of Paleomagnetic Sites

Class Opdyke e t a l . (1977) Lindsay et a l. (In press) This Paper

I All specimens of the same All specimens of one polarity Same as Opdyke e t a l . (1977) polarity with statistically and statistically significant and Lindsay et al. (In press) significant results

II Only two samples known Two samples are concordant Same as Opdyke e t a l . (1977) but their directions are and th ir d forms an angle to concordant the other two - Polarity usually clear

III S t a t is t i c a l ly random Sample directions strung Same as Opdyke e t a l . (1977) directions of magneti­ between a reversed direction zation but two of the of field and the present three specimens are direction of field concordant but the third is widely divergent in an intermediate direction

IV Strung distribution but Directions of magnetization Same as Opdyke e t a l . (1977) directions change with randomly d ire c te d and w ith o u t AF demagnetization in a useful results system atic way so th a t polarity is determined

V Mentioned but not defined Directions of magnetization randomly directed and without useful results - Class IV of Lindsay et a l. (In press) 28

Selected sites from the Ojo Encino and Big Pocket study areas provide examples of the classes listed in table 1. Site SJ342 (Figure

3) from locality 10 in the Ojo Encino Area had a relatively weak, un­ stable secondary component overprinting the NRM. The mean NRM inclination and declination (I = 71.6®, D = 358.1°) indicated that the site was normally magnetized. Removal of the secondary component by

AF demagnetization at a peak field of 200 oersteds permitted the AF demagnetized NRM inclination and declination to be revealed. These angles (I = 54.3°, D = 345.2°) indicated that the AF demagnetized NRM polarity was also in a normal direction, but with less scatter than prior to demagnetization. A site such as SJ342 provides unambiguous polarity determination and is considered a Class I site.

Site SJ480 (Figure 4), from the Big Pocket Area, also repre­ sents a Class I site. It clearly shows the polarity change resulting from the removal of the normally magnetized secondary component by AF demagnetization.

Site SJ585 (Figure 5), from locality 10 in the Ojo Encino

Area, is an example of a Class II site. It contains no third sample.

The two samples present do have concordant directions.

The magnetic vectors of site SJ356 (Figure 6) from locality 11 in the Ojo Encino Area demonstrate the removal of a stronger, more stable secondary magnetic component than that removed from site SJ342.

SJ356 had w id e ly s c a tte re d NRM d ire c tio n s ; specimens A and C showed possible reversed polarity and specimen B showed normal polarity. The mean NRM direction (I = 67.9°, D = 238.6°) was tenuously indicative of iue . F mantzto Cre ad R Vetr tos Sie SJ342 ite S otions, M NRM ector V and Curves agnetization em D AF 3. Figure

Remanent Magnetization (Gauss) ek eantzn Fed (Oersteads) Field Demagnetizing Peak N 29 30

N

SJ480

NRM

Figure 4. NRM Vector Motions, Site SJ480 31

Figure 5. NRM Vector Motions, Site SJ585 iue A Dmantzto Cre ad R Vetr i s Sie SJ356 ite S ns, tio o M NRM ector V and Curves agnetization Dem AF . 6 Figure Remanent Magnetization (Gauss) X0 r 3X10 ek eantzn Fed (Oersteads) Field Demagnetizing Peak 32 33 reversed polarity. The vector motions during AF demagnetization showed the NRM directions to be masked by a normally magnetized secondary com­ ponent. Although this normally magnetized secondary component was incompletely removed from specimen B, the mean AF demagnetized NRM d ir­ ection (I = 26.7°, D = 161.5°) indicated a reversely magnetized site.

The magnetic vector motion of specimen B indicated that a negative in­ clination was not reached but the positive inclination became lower in angle and the declination became clearly a southerly direction. This trend showed that, even though the normally magnetized secondary com­ ponent of specimen B was s till influencing the magnetic directions, the vector was trending toward the reversed polarity demonstrated by speci­ mens A and C. This Class III site shows the value of interpreting the

trend of magnetic vector motions.

Sites SJ309 (Figure 7) and SJ482 (Figure 8), both from the Big

Pocket Area, exhibited a magnetic vector trend toward reversed polari­

ty. These sites are also examples of Class III sites.

Site SJ044 (Figure 9), from the Ojo Encino locality 10, is an

example of a site with a strung distribution. The 200 oersted demag­

netized NRM declination was clearly Indicative of reversed polarity

and the trend in both inclination and declination was toward that of a

reversed site. This trend permitted site SJ044 to be interpreted as

reversely magnetized with a normally magnetized secondary overprint

partially removed by AF demagnetization. This site was considered a

Class IV site. 34

N

SJ309

Figure 7. NRM V ector M o tio ns, S ite SJ309 35

N

S J482

NRM :200

Figure 8. NRM V ector M otions, S ite SJ482 36

. 0 .2 -

Peak Demagnetizing Field (Oersteads)

300 NRM

S Figure 9. AF Demagnetization Curves and NRM Vector Motions, Site SJ044 CHAPTER 5

STRATIGRAPHY

The biostratigraphy, 11thostratigraphy, and magnetic-polarity stratigraphy of two study areas were determined so that the two areas could be correlated unambiguously.

The Study Areas

The Ojo Encino Area is the site of the original Torrejonian fauna (Matthew 1897). The area was studied and collected by Sinclair and Granger (1914) and la b e le d by them as two la rg e American Museum vertebrate fossil localities. Their localities 10 and 11 are on op­ posite sides of Arroyo Torreon, near its head, and approximately five kilometers (three miles) apart (Figure 10).

Locality 10 includes the badlands near the heads of Toledo

Arroyo and Encino Wash (Figure 11) and contains forty three University of Arizona (UALP) vertebrate fossil localities. It includes all or part of Sections 21, 26-28, and 34 in T.21N., R.5W. on the U. S. Geo­ logical Survey Deer Mesa 7.5 Minute Quadrangle Map.

L o c a lity 11, s itu a te d near the heads o f Lopez Arroyo and an un­

identified wash (Figure 12), is the smaller of the two Sinclair and

Granger (1914) localities and contains about one-fifth as many UALP

vertebrate fossil localities as does locality 10. It is found on the

U. S. Geological Survey Ojo Encino Mesa 7.5 Minute Quadrangle Map and

includes Sections 4 and 5 , T .2 0 N ., R.4W.

37 gur 0 Mp h Oo n o Area no End Ojo the f o Map 10. re u ig F /

/?ti v ,Wi j Ecnf - y Encinof Ojo y v |V vC / Y.:, f . % r ,c|" ^ ^ — : 3 \ 1 X:!3 , 1 i l N 1Mi. Km. 00 W UALP u Fossil Locality

y Magnetic

Figure 11. Map of Locality 10, Ojo End no Area ^.Ar

•UALP Fossil Locality /Magnetic Section 1 Mi.

4* Figure 12. Map of Locality 11, Ojo End no Area O 41

The name for this study area was derived from Ojo Encino, a spring located south of the fossil localities. This spring has been used to name several geographical and political features in the region; a wash, a school, several dams, and the mesa upon which the spring is located are all named Ojo Encino.

The Big Pocket Area (Figure 13), approximately 80 kilometers

(50 miles) north and west of the Ojo Encino Area includes R. W.

Wilson's (1951) University of Kansas vertebrate fossil locality 13, the "Big Pocket" locality. Locality 13 is on the western edge of Kutz

Canyon, approximately 16 kilometers (10 miles) south of Bloomfield, New

Mexico. It is in the SVPs of Section 14, T.27N., R.11W. The study area is much larger than locality 13 and includes most of the west side of

Kutz Canyon. It extends from the SW% of Section 33, T.29N., R.11W. southward along the edge of Kutz Canyon to the NW% of Section 5, T.26N.,

R.10W., a distance of approximately 20 kilometers (12 m iles).

The study area includes fossil localities other than that of

Wilson (1951). Granger (1917) discovered at least two Torrejonian lo­ calities in the cliffs along the west side of Kutz Canyon. Also, he located a fossil site about 1.5 or 3.2 kilometers (1 or 2 miles) west o f Angel Peak (Fig ure 1 2 ). Recent in v e s tig a tio n s in Kutz Canyon have resulted in the discovery of over twenty UALP vertebrate fossil local­ ities. These new localities w ill provide data for future research into the biostratigraphy of the San Juan Basin. Big Pocket

Angel Peak

UALP Fossil Locality Magnetic Section G ) Granger (1917) Fossil Locality 1 2 Mi.

3 Km.

Figure 13. Map of the Big Pocket Area 43

Lithostratigraphy

Figure 14 shows two measured sections taken in the Ojo Encino

Area. The lithologic section consists of various colored clays, s ilt- stones , and sandstones common to the Nacimiento Formation; the finer sediments were predominant with the sandstones represented as local channel deposits rather than as continuous horizontal strata.

The nearly 185 meter (607 foot) thick section from locality 10 contains three distinctive black carbonaceous clay beds (Marked L, M, and U on figures 14 and 15) with two probable volcanic ashes, one strat- igraphically above and the other stratigraphically below the lowest black layer. The section from locality 11 is slightly over 60 meters

(180 feet) in thickness. It contains two distinct black strata with a probable volcanic ash strati graphically below the lower black layer.

There appears to be no evidence of structural displacement in the distance separating the localities and the lithologic correlation shown in figure 14 was made by using the black layers, the probable ashes, and a capping sandstone.

The lit h o lo g ic s im ila r it y between the Big Pocket and Ojo Encino areas can be seen in the presence of gray or green-gray and red s ilt- stones and clays with interbedded white or light gray sandstone channel deposits. The Big Pocket Area, however, contains a higher number of persistent tan sandstones than does the Ojo Encino Area. In general, the Big Pocket stratigraphic column contains a higher ratio of sand­ stone to shale than found to the south. Because of the lack of 44

STRAY. LOCALITY 10 LOCALITY 11 ELEV. M. FT. r600

150-"500

PANTOLAMBDA ZONE -400

100- -300

DELTATHER1UM ZONE

-200

50-

-100 — Rock Correlation 8=a Fossil Level Clay:UPPER;MIDDLE; Siltstone L0WER o-t-o Sandstone ?Volcanic Ash Coal l

Figure 14. Lithologic Correlation of Localities 10 and 11, Ojo Encino Area 45 laterally continuous exposures, stratigraphic correlation of the two areas is made by magnetic-polarity stratigraphy and biostrati graphic methods.

Biostratigraphy

The above lithologic correlation from the Ojo Endno Area

(Figure 14) indicates that the uppermost faunal level at locality 10

is correlative with the faunal level at locality 11. Fossils recovered

from locality 10 indicate that the upper level is the Panto!ambda zone of Osborn and Matthew (1909). The lower fossil horizon from locality

10, the Deltatherium zone of Osborn (1929), appears to have no cor­

relative in locality 11. Discussion of the faunal zones and their

probable significance w ill be included below.

Granger (1917) noted that Kutz Canyon did not appear to contain

the classic faunal levels of the San Juan Basin Torrejonian. Wilson

(1951) suggested that, although his University of Kansas locality 13

(the "Big Pocket" locality) closely resembled the Deltatherium zone,

the Torrejonian of the San Juan Basin could be found to consist of more

than two characteristic levels. Or, as he (Wilson 1951, p. 11) put it,

"...a series of faunules of slightly different ages..." Paleomagnetic

data and new UALP fo s s il lo c a lit ie s in Kutz Canyon lend support to

Wilson's (1951) ideas.

Table 2 indicates the known taxa from the Ojo End no and Big

Pocket study areas. It was compiled from Matthew (1937), Wilson (1951,

1956a, 1956b), MacIntyre (1966), Russell (1967), Van Valen (1967),

Gazin (1968), and Wilson and Szalay (1972). This table shows that a 46

Table 2. Faunal List for the Ojo End no and Big Pocket Study Areas

Taxon Ojo End no Big Pocket

Class Mammalia Linneaus 1758 X xa

Subclass A llo th e r ia Marsh 1880 X xa

Order Multituberculata Cope 1884 X xa

Suborder Taeniolabidoidea (Granger and Simpson 1929) X

Family Taeniolabididae (Granger and Simpson 1929) X

Catopsalis Cope 1882 X C. foliatus Cope 1882 X C. fis s id e n s Cope 1884 X

Family Eucosmodontidae (Jepsen 1940) X

Stigim ys Sloan and Van Valen 1965 X S. t e ilh a r d i (Granger and Simpson 1929) X

Eucosmodon Matthew and Granger 1921 X E. molestus (Cope 1885) X

Suborder Ptilodontoidea (Simpson 1927) X xa

Family Ptilodontidae Gregory and Simpson 1926 X

Ptilodus Cope 1881 X P. mediaevus Cope 1881 X

Family Neoplagiaulacidae Armeghino 1890 X xa

Ectypodus Matthew and Granger 1921 xbb E.1 sp. Wilson 1956a xb

Mimetodon Jepsen 1940 x : xe M. tro vess artian u s (Cope 1882) xe M. near M. trovessartianus (Cope 1882) xe

Subclass Theria Parker and Haswell 1897 X xa

Infraclass Metatheria Huxley 1880 x i 47

Table 2. Continued, Faunal List

Taxon Ojo Encino Big Pocket

Order M arsu p ialia I l l i g e r 1811 Xj

Family Didelphidae Gray 1821

Infraclass Eutheria G ill 1872 X Xa

Order In s e c tiv o ra Bowditch 1821 X x a

Family Leptictidae G ill 1872 X x a

Prodiacodon Matthew 1929 X x a P. puercensis (Matthew 1918) X £. n. sp.? Wilson 1956a x a

Family Panto!estidae Cope 1884 X

Pantominia Van Valen 1967 X9 P. ambigua Van Valen 1967 X9

Family Pentacodontidae (Simpson 1937) X x b

Pentacodon Scott 1892 X x b P. Inversus (Cope 1888) X P. occultus Matthew 1937 X £. n. sp. Wilson 1956a x b

Coriphagus Douglass 1908 X x b C. encinensis (Matthew and Granger 1921) X x b

Family Mixodectidae Cope 1883 X x a

Mixodectes Cope 1883 X x a M. pungens Cope 1883 X M. m alaris (Cope 1883) X x b

Order Primates Linneaus 1758 X X1

Family Paromomyidae Simpson X X1

Torrejonia Gazin 1968 < T. wilsoni Gazin 1968 x h

Palaechthon Gidley 1923 P. nacim ienti Wilson and S zalay 1972 $ 48

Table 2. Continued, Faunal List

Taxon Ojo Encino Big Pocket n. gen. and n. sp. Wilson 1956a Xb

Order Deltatheridia Van Valen 1965 X x a

Family Palaeoryctidae (Winge 1917) X x a

Acmeodon Matthew and Granger 1921 X xb A. c f . A. secans Matthew and Granger 1921 x b A . secans Matthew and Granger 1921 X

Palaeoryctes Matthew 1913 X P. puercensis Matthew 1913 X P. c f . P. puercensis Matthew 1913 x a

Order Taeniodonta (Cope 1896) X x a

Family Stylinodontidae Marsh 1875 X x a

Conoryctes Cope 1881 X C. comma Cope 1881 X

Psittacotherium Cope 1882 X xb P. m ultifragum Cope 1882 X x b P. aspasiae Cope 1882 X

Order Condylarthra Cope 1881 X x a

Family Arctocyonidae Giebel 1855 X x a

Tricentes Cope 1884 X x a T. truncatus (Cope 1884) X x a

M im otricentes Simpson 1937 X x a M. subtrigonius (Cope 1881) X x a

Chriacus Cope 1883 X C. pelvidens (Cope 1881) X C. baldw ini (Cope 1882) . X

D eltatherium Cope 1881 X. x a D. fundaminis Cope 1881 X x a

Claenodon (Scott 1892) X C. ferox (Cope 1888) X C. procyonoides (Matthew 1937) X 49

Table 2. Continued, Faunal List

Taxon Ojo Encino Big Pocket

Goniacodon Cope 1888 X x ! G. levisanus (Cope 1888) X x a

Triisodon Cope 1881 X x a Y . q u iv ire n s is Cope 1881 X T. antiquus (Cope 1882) X T. sp. Wilson 1956a x b

Family Hyopsodontidae Nicholson and Lydekker 1889 X x °

Mioclaenus Cope 1881 X x a M. turgidus Cope 1881 X x a M. lydekkerianus Cope 1888 X

Ellipsodon Scott 1892 X x a E. inaequidens (Cope 1884) x X E. granger! Wilson 1956b x c

Promioclaenus Trouessart 1904 X x a P. acolytus (Cope 1882) X x P. lemuroides (Matthew 1897) X ? x c

Protoselene Matthew 1897 X x a P. opisthacus (Cope 1882) X x a

Family Phenacodontidae Cope 1881 X x a

Tetradaenodon Scott 1892 X x a Y . puercensis (Cope 1881) X x a n. gen. and n . sp. Wilson 1956a x b

Family Periptychidae Cope 1882 X x a

Anisonchus Cope 1881 X x a A. sec to riu s (Cope 1881) X x a

Haploconus Cope 1882 X H. angustus (Cope 1882) X H. corniculatus Cope 1888 X

Periptychus Cope 1881 X x a P. carinidens Cope 1881 X x a 50

Table 2. Continued, Faunal List

Taxon Ojo Encino Big Pocket

Order Carnivora Vicq d'Azyr 1792 X Xa

Family Miacidae Cope 1880 X Xa

Protictis Matthew 1937 X , Xf P. haydenianus (Cope 1882) P. vanvaleni MacIntyre 1966 j * f F. n. sp. a Wilson 1956a X f P_. n. sp. b Wilson 1956a XT

Order Pantodonta Cope 1883 X

Family Panto!ambdidae Cope 1883 X

Panto!ambda Cope X P. bathmodon Cope 1882 X P. cavirictus Cope 1883 X

a. Wilson 1951 b. Wilson 1956a c . Wilson 1956b d. MacIntyre 1966 e . Van Valen and Sloan 1966 f . Russell 1967 g. Van Valen 1967 h. Gazin 1968 i . Wilson and S zalay 1972 j . This paper

All other identifications from Matthew 1937 51 total of 18 fam ilies, 36 genera, and 18 species are common to both areas. 6 families, 11 genera, and 28 species are restricted to the Ojo

Encino Area whereas only 5 genera and 8 species are restricted to the

Big Pocket Area.

The apparent greater diversity of the fauna from the Ojo Encino

localities is at least partly due to more extensive collecting from that

study a re a . The Ojo Encino Area has been accessible to v e rte b ra te

paleontologists since its 1896 discovery whereas the Big Pocket locality

has been known only since 1948. At present the Big Pocket collection

has not received more than a preliminary description. Recent vertebrate

fossils collected from Kutz Canyon by workers from the University of

Arizona indicate that a greater diversity than now recognized is pres­

ent in that area.

Nevertheless, it is evident that some mammals are restricted

to the Ojo Encino Area. The characteristic Panto!ambda zone genera

Claenodon and Panto!ambda are not known from the Big Pocket Area. Only

one characteristic Deltatherium zone genus, Haploconus, is unknown from

the Big Pocket Area although recent University of Arizona collecting

indicates that Haploconus is present in Kutz Canyon. Deltatherium,

Triisodon, and Mixodectes malaris, other characteristic Deltatherium

zone taxa, are known from both study areas.

Table 2 indicates that the Ojo Encino study area contains both

presently recognized Torrejonian collecting levels while the Big Pocket

study area contains no taxa characteristic of the Panto!ambda collecting

zone. The Big Pocket Area does, however, contain taxa diagnostic of the 52 lower, Deltathenuro, collecting zone of Torrejonian age. Wilson (1951) concluded that the Big Pocket fossil locality bears more resemblance to the Deltatherium zone than the higher Panto!ambda zone.

Magnetic-Polarity Stratigraphy

Paleomagnetic samples were co llected from 73 s ite s in the Ojo

Encino Area; 52 from locality 10 and 21 from locality 11. The locality

10 paleomagnetic sites represent a stratigraphic interval of 171.5 meters (562.5 feet) that includes seven individual sections (Figure 11).

The three paleomagnetic sections from locality 11 (Figure 12) represent a 61.6 meter (202 foot) thick composite section. Sites from locality

10 had a geometric mean intensity of 4.0 X 10”6 gauss for the NRM. The range of intensities was 4.6 X 10”^ to 1.0 X 10~* gauss. The NRM in­ tensities from locality 11 sites ranged from 4.2 X 10“® to 1.0 X 10"^ gauss, with a geometric mean Intensity of 6.2 X 10~® gauss.

190 s ite s were co llected from the Big Pocket Area. The geo­ metric mean value for the NRM intensities of these sites was 3.24 X 10“® gauss within a range from 3.38 X 10“^ to 1.14 X 10""* gauss. The Big

Pocket Area sites fall within individual sections (Figure 13) that cover a stratigraphic interval over 300 meters (98*- feet) thick.

Paleomagnetic data from the Ojo Encino and Big Pocket study areas is included in Appendix A.

AF demagnetization a t peak fie ld s o f 100 to 300 oersteds was sufficient to remove secondary magnetization at most sites. Six sites from the Ojo Encino Area contained a secondary component stable enough to require a peak f ie ld o f 400 oersteds to remove i t . Unambiguous 53 determination of AF demagnetized polarity was possible for nearly all sites from the Ojo Encino Area. However, in the Big Pocket Area, only those sites above a stratigraphic elevation of 61 meters (200 feet) provided unambiguous polarity determinations. For some sites from both study areas it was necessary to interpret data concerning both the NRM vector motions during AF demagnetization and the resulting cluster of directions for the samples at those sites. Sites used as examples of site classes in chapter 4 indicate that the paleomagnetic polarity from the Ojo Encino and Big Pocket study areas, as interpreted from the ob­ tained inclination and declination directions and magnetic vector trends, are reliable and could be used in this study without suspicion.

The data from the Ojo Encino Area (Appendix A) were interpreted to determine the magnetic polarity of the previously constructed litho­ logic column from localities 10 and 11 (Figure 14). In figure 15 each circle represents one paleomagnetic site; closed circles represent nor­ mal polarity while open circles indicate reversed polarity. The magnetic polarity determinations for localities 10 and 11, based upon

VGP latitudes, are shown in figure 16. With the exception of two sites from locality 10, the data provide unambiguous polarity determinations.

However, the NRM vectors from these sites, SJ334 and SJ335, exhibit a definite trend towards reversed directions. The resulting magnetic- polarity stratigraphy strengthens the tenuous lithologic correlation of figure 14 by indicating a normally magnetized interval extending from the middle black stratum upward into the overlying siltstones at both localities. The minimum length of this normal interval in locality 54

STRAY. LOCALITY 10 LOCALITY 11 ELEV. M. FT. r600 r.'77_L-.;

■ L500 150-

E-.E-CrT IpANTOLAMBDA ZONE -400

100- -300 a V A V A . 0 oooo ogO;e eeeee e*ejoo ° — 8 DELTATHER1 UM ZONE

-200 Normal Polarity 50- Reversed Polarity Time Correlation -100 Rock Correlation Fossil Level Clay:UPPER;MIDDLE; E S Siltstone L1°WER EE1 Sandstone 0 - K ) IH3 ? Volcanic Ash E 3 Coal

Figure 15. Magnetic Correlation of Localities 10 and 11, Ojo Encino Area STRAT. ELEV. LOCALITY 10 LOCALITY 11 M. FT. VGP LATITUDE POLARITY VGP LATITUDE POLARITY

1 o rev.

150 -

100-

5 0 -

0

Figure 16. Magnetic-Polarity Stratigraphy of the Ojo Enclno Area 56

10 is 27.4 meters (90 feet) while in locality 11 it is represented by

24.1 meters (79 feet) of sediment. The upper, Panto!ambda, zone of the

Torrejonian is included within the upper magnetozone while the lower

fossil level, the Deltatherlum zone, is within the upper one-half of

the underlying reversed magnetozone.

The longer magnetic-polarity column from locality 10 indicates

the presence of a second, strati graphically lower, normally magnetized

interval. The length of this interval and its stratigraphic relation

to the lithology and faunal levels preclude its correlation with the

normally magnetized interval from locality 11. Figure 15 clearly dem­

onstrates that any attempt to correlate from locality 10.to locality 11

must account for lithology, paleontology, and paleomagnetism. Only the

correlation shown in figure 15 is consistent with known data from the

Ojo Encino Area.

The boundary between a normally magnetized and a reversely mag­

netized interval represents a geologic time line (Cox, Doell, and

Dalrymple 1963, 1964). Therefore, the correlation of magnetic interval

boundaries from localities 10 and 11 represents a geochronological cor­

relation. Correlation of synchronous boundaries indicates that during

the upper magnetozone the rate of sediment accumulation was slightly

more rapid at locality 10 than at locality 11. Although the paleomag-

netic data do not provide absolute dates, the data show conclusively

that 3.3 more meters (11 more feet) of sediment were deposited at

locality 10 than were deposited at locality 11 in the same amount of

tim e. 57

Also, the synchronous lower boundary of the correlative normally magnetized interval indicates that deposition of the middle black layer commenced slightly later at locality 10 than at locality 11. A greater proportion of the middle black layer is found below the time line at locality 11 than at locality 10. This demonstrates that the correlative black strata were not precisely contemporaneous but the time difference

is probably not significant. The synchronous upper boundary of this normal interval demonstrates that the opposite is true for the correl­

ative upper black strata. The upper black layer was deposited earlier

at locality 10 than at locality 11. The amount of time represented be­

tween the deposition of similar sediments in the two areas is slight

but demonstrably nonsynchronous.

The fossil evidence from localities 10 and 11 suggests that the

faunal level from locality 11 was contemporaneous with the upper fossil

horizon from locality 10. The geochronological correlation in figure

15 indicates that this was not entirely so; the faunal levels are shown

to be only partially contemporaneous. Deposition of the fossils at

local ity 11 was slightly later than at locality 10. Perhaps close ex­

amination and comparison of the earliest locality 10 fossils, from this

level and the latest locality 11 fossils would demonstrate this time

difference. This, of course, depends upon the amount of time represent­

ed by the stratigraphic difference.

Figure 17 shows the composite lithology, stratigraphic position,

VGP latitudes, and magnetic polarity for each of the 190 sites collect­

ed from the Big Pocket Area. The magnetostratigraphy of the Big Pocket

Area reveals that the upper 15 meters (50 feet) of the composite section 58

STRAT. VGP LATITUDE POLARITY ELEV. LITHOLOGY ■NOR. M. FT i i j □REV.

1 0 0 - -1 0 0 0 i o o za= c r LU $ O i -

2 0 0 - o Q < cr - 5 0 0

KL-~ 1 0 0 -

*ee # m

Lithology Symbols Same as Figures 6&10

Figure 17. Magnetic-Polarity Stratigraphy of the Big Pocket Area 59 are of normal polarity. Although the length of this normally magnetized interval is unknown, the strati graphically higher Radio Tower section contains the reversed interval above it. Unfortunately, the Radio Tower section is correlated to the composite section with only enough accuracy to determine that the normal interval from the Radio Tower section is correlative to the uppermost magnetozone of the composite section. How much sediment and time was represented by the area between the two sec­ tions, if any, is unknown. It is hoped that future investigation can lengthen the Radio Tower section and that the base of the normal mag­ netozone can be located and used to geochronologically correlate this section to the longer composite section.

A second normally magnetized interval is shown in the composite section. This interval extends for some 55 meters (180 feet) above the lowest level of reliable data. Approximately 146 meters (480 feet) of sediment with reversed polarity separate the two normally magnetized intervals. From base to top the Big Pocket magnetic-polarity column contains 55 meters (180 feet) of normal magnetization, 146 meters (480 feet) of reversed magnetization, and 15 meters (50 feet) of normally magnetized sediments. The Big Pocket fossil locality (University of

Kansas locality 13), within the Deltatherium collecting zone (Wilson

1951), is in the bottom one-third of the reversed interval. CHAPTER 6

GEOCHRONOLOGIC CORRELATION

The Ojo End no and B1g Pocket Areas can be geochronologlcally correlated by biostrati graphic and magnetostrati graphic methods. They can also be compared with a third paleomagnetic section (constructed earlier) from the San Juan Basin and with the Cenozoic geomagnetic polarity time scale of Tarling and Mitchell (1976).

The Ojo End no and Big Pocket Areas

Figures 16 and 17 show th a t the Ojo Endno and Big Pocket Areas

both have a magnetic-polarity column characterized by two normally magnetized intervals separated by a reversal. The reversal is consid­

erably thicker than the normal interval overlying it in the Ojo Endno

Area. This pattern is apparently repeated in the Big Pocket Area since

the horizontal distance between the composite and Radio Tower sections

was walked out and does not appear to allow for the 120 meters (400

feet) of sediment necessary to make the reversal and the overlying

normal interval equal in thickness. A temporal correlation of the two

areas is shown in figure 18. This correlation is consistent with the

magnetostratigraphy, biostratigraphy, and lithostratigraphy of both

areas.

The lower normally magnetized interval from locality 10 is

apparently unfossiliferous, as is that from the Big Pocket Area. The

60 61

STRAT. OJO BIG ELEV. ENCINO POCKET M. FT.

200

-5 0 0

100-

O -L -0

• UALP Fossil Level P Pantolambda Zone D Deltatherium Zone Magnetic Anomaly ■Nor. oRev.

Figure 18. Geochronological Correlation of the Ojo Encino and Big Pocket Areas 62 reversed interval from locality 10, part of which is present in locality

11, contains the Sinclair and Granger (1914) lower collecting level, the

Deltatheriurn zone. The Deltatherium horizon is situated in the middle of the approximately 64 meter (200 foot) thick reversed interval. In the Big Pocket Area the Deltatherium zone, represented by Wilson's

(1951) locality 13, is located at the stratigraphic level of about 100 meters (335 feet), about one-third of the way up section from the base of the approximately 146 meter (480 foot) thick reversed interval. The presence of the Deltatherium zone within a reversed magnetozone in the

Ojo Encino Area and the Big Pocket fauna in a similar reversed interval suggests that they are contemporaneous and within the same magnetozone.

However, because the zones are not found in the same relative strati­ graphic positions within the magnetozone, it is possible that the faunas from the Deltatherium zone in the Ojo Encino Area could have been de­ posited later than in the Big Pocket Area. How much later cannot be determined as no absolute dates are known. If they are within the same magnetozone, as they appear to be, the time difference is probably slight. Also, the rate of sediment accumulation in each area would have to be different for the temporal difference to be exactly that shown in figure 18. The correlation in figure 18 is consistent with the general thickness trend of the Nacimiento Fomation as indicated by well log data and measured sections (Baltz 1967).

The upper normally magnetized interval from localities 10 and

11 of the Ojo Encino Area contains the Panto!ambda zone of Osborn and

Matthew (1909); the upper collecting level of Sinclair and Granger 63

(1914). This, of course, does not demonstrate that the upper normal magnetozones from the two study areas are the same magnetozone. It does not, however, contradict such a correlation. It Is, therefore, consis­ tent with the above correlation of the reversed interval based upon the presence of Deltatherium, Triisodon, and Mixodectes malaris, character­ istic taxa of the Deltatherium zone (Wilson 1956a, Szalay 1969).

The Deltatherium and Panto!ambda zones of the San Juan Basin can be defined by the presence o f d is tin c tiv e genera (See pages 19 and

20 above). They can also now be defined by their magnetic-polarity stratigraphy; the Deltatherium zone is within a reversed magnetozone and the Panto!ambda zone is within the overlying normal magnetozone.

The magnetic-polarity stratigraphic definition shows the zones to have

been deposited at different times and not the accidents of collecting or lateral facies as thought by Matthew (1937). Faunal differences

among th ree U n iv e rs ity o f Kansas v e rte b ra te lo c a lit ie s (KU 9 , 13, and

15) within the San Juan Basin, two from the Deltatherium level (9 and

13) and one from the Panto!ambda level (15), prompted Wilson (1956a)

to conclude that the zones represent different environments (facies),

slightly temporally separated. Wilson (Pers. Comm.) maintains that

environmental factors control the zones and are more important than the

temporal differences present. It is difficult to distinguish faunal

differences resulting from environmental diversity and evolutionary

change and neither has been shown to control the zones of the San Juan

Basin Torrejonian. It seems that Wilson (1956a) too easily assumed

Panto!ambda's absence at his two Deltatherium localities was controlled 64 by facies or geographical restriction. The absence of Panto!ambda could mean that it did not exist at that time, anywhere in the San

Juan Basin. A lso , the lith o lo g y o f the study areas does not d is p la y any outstanding difference that could have resulted from an environment­ al change s ig n ific a n t enough to change the faunal assemblage encased within it. The absence of such differences is particularly noticeable in the Ojo Encino Area where the two zones can be seen in the same ex­ posure at locality 10.

The final result could be that the Deltatheriurn and Panto!ambda zones may be only two of several faunal levels in the Torrejonian of the San Juan Basin, or that these zones may not be limited to only one collecting level. As mentioned above, the UALP localities in the Big

Pocket Area indicate that other collecting levels are present. It should be noted that there is no a priori reason why the Torrejonian of the San Juan Basin should be lim ite d to only two d is c re te c o lle c tin g zones. At present, however, only the Deltatherium and Panto!ambda zones can be separated.

Perhaps the most reliable use of San Juan Basin Torrejonian b io s tra tig ra p h y would be to ignore the somewhat im precise " c o lle c tin g zone" concept and utilize the more precise "range zone" concept. The known magnetic-polarity stratigraphy of the San Juan Basin permits the use of the latter concept. To do this, however, is beyond the scope of this thesis. 65

The Barrel Spring Arroyo Section

The m a g n e tic -p o la rity columns o f the Ojo Encino and Big Pocket

Areas can be compared w ith th a t o f the B arrel Spring Arroyo section o f

Butler et a l. (1977) which has been correlated with the Tarling and

Mitchell (1976) revised Cenozoic polarity time scale. Barrel Spring

Arroyo is located geographically between the two study areas; it is approximately 20 kilometers (12.5 miles) south and west of the Big

Pocket Area and approximately 60 kilometers (37 miles) north and west of the Ojo Encino Area (Figure 1). Correlation of the Barrel Spring

Arroyo section and the Cenozoic polarity time scale is shown in figure

19. The magnetic-polarity column from Barrel Spring Arroyo is char­ acterized by a basal reversed magnetozone overlain, in sequence, by a normal, a reversed, a normal, a reversed, and a topmost normal interval.

The Butler et a l. (1977) correlation shows the normal intervals to be anomalies 27, 28, and 29 o f the T a rlin g and M itc h e ll (1976) tim e scale with anomaly 29 the lowest normal interval. Anomaly 28 is shown to contain the Ectoconus and Taeniolabis Puercan collecting levels of

Osborn (1929) and is above the C re ta c e o u s -T e rtia ry boundary found near

the base of anomaly 29.

Magnetic-polarity stratigraphy of the Ojo Encino and Big Pocket

Areas compare with the Barrel Spring Arroyo section to show two pos­

sible geochronologic correlations, both of which are consistent with

the known biostratigraphy and magnetic-polarity stratigraphy of the San

Juan Basin. The lowermost normal in te rv a l from the Ojo Encino and Big

Pocket Areas is correlative with either anomaly 27 or 28 of the Tarling 66

POLARITY HIVE SCALE BARREL SPRING ARROYO c z i T ) □ m -n 2 . % i z o 2 . 3 I “ 3 5 1 ^ fD Q f s n 3 r+ <-+■* Q r+ 2 3 ! O 5 0 - 3 a CL 4 0 0 -

/ 5 z 5 5 - / r > m o O -1200 o n m m fD z z 6 0 - “ 5 m

«T 300” ■1000 6 5 - o

m c H "D U > 7 0 - a> O “j m -8 0 0 Oc cn 75—1 T-Taeniolabis Zone E-Ectoconus Zone C’•Cretaceous Level Figure 19. Correlation of Revised Cenozoic Polarity Time Scale and Barrel Spring Arroyo Section. — (Adapted from Tarling and Mitchell 1976; Butler e fa l. 1977) 67 and Mitchell (1976) geomagnetic time scale. It is not correlative with anomaly 29 because the Torrejonian Deltatherium zone is younger than the Ectoconus and Taeniolabis zones of Puercan age and must be s tra ti- graphically higher. Anomaly 26 appears to be too young to be correl­ ative with this magnetozone. This lowest magnetozone from the Ojo

Encino Area is unfossiliferous. Therefore it could represent the time during which Puercan fossils were being deposited in the Barrel Spring

Arroyo section (anomaly 28). This would mean that, for some reason,

Puercan fossils are not present in either the Ojo Encino or Big Pocket

Area and that the Deltatherium zone is absent in Barrel Spring Arroyo.

Aside from the above lim it to correlation, there is evidence which suggests that the uppermost normal magnetozone from the Ojo

Encino and Big Pocket Areas is either anomaly 26 or 27 of the Tarling and Mitchell (1976) geomagnetic polarity time scale. Sinclair and

Granger (1914) reported a Torrejonian faunal level 75 meters (245.5 feet) above the base of the Macimiento Formation in Barrel Spring

Arroyo. This locality is included within anomaly 27 of Butler et al.'s

(1977) Barrel Spring Arroyo section. Unfortunately this alleged

Torrejonian locality, based upon three specimens of Periptychus carinidens, has not been found during the recent investigation. If

present, however, it could show the uppermost normal interval from the

study areas to be anomaly 27 as this locality and the Panto!ambda zone

are both within normally magnetized rocks. Periptychus carinidens is

not a defining mammal of the Panto!ambda zone, however, and it is

conceivable that Sinclair and Granger's (1914) level in the Barrel 68

Spring Arroyo area has not yet been discovered in other areas of the San .

Juan Basin (e.g. the Ojo Encino and the Big Pocket Areas) and is older

than the Deltatherium zone. A correlation between this upper normal

Interval and anomaly 26 is suggested by the thickness of the reversed magnetozone strati graphically beneath it. Tarling and Mitchell (1976)

show anomalies 26 and 27 separated by a thick reversed Interval, over

four times as th ic k as e ith e r o f the adjacent normal magnetozones. The

reversed interval separating the two normal magnetozones in the study

areas is considerably thicker than the anomaly overlying it and is quite

unlike the reversed interval separating anomalies 27 and 28 in the

Barrel Spring Arroyo section; it is thinner than either of the adjacent

normal magnetozones. It should be noted that this comparison with the

Tarling and Mitchell (1976) anomaly thicknesses is valid only if a

constant rate of sedimentation was present in the study areas. This

has not been demonstrated. Nevertheless, this possibility should be

kept in mind.

At present, then, it is not possible to show clearly which ~

anomalies are found in the magnetic-polarity column from the Ojo Encino

and Big Pocket Areas. Biostratigraphy hints that they may be anomalies

27 and 28 while relative thickness of magnetozones hints that they may

be anomalies 26 and 27. I t is hoped th a t fu r th e r in v e s tig a tio n in the

San Juan Basin strata may supply a solution to this dilemma. CHAPTER 7

SUMMARY

This study compared two areas of the San Juan Basin of north­ western New Mexico with respect to biostratigraphy, 11thostratlgraphy,

and magnetic-polarity stratigraphy. The areas chosen for investigation were: 1) the Ojo Encino Area, including Sinclair and Granger's (1914)

American Museum of Natural History vertebrate fossil localities 10 and

11, from which the defining fauna of the Torrejonian Land Mammal Age

was collected (Wood et a l. 1941); and 2) the Big Pocket Area of Kutz

Canyon, including Wilson's (1951) University of Kansas vertebrate

fossil locality 13, from which Torrejonian fossils were collected.

Locality 13 fossils included those characteristic of the Torrejonian

Deltatherium zone, firs t recognized by Osborn (1929) and later defined

by Wilson (1956a). As shown in figure 1, the study areas are approx­

imately 80 kilometers (50 miles) apart, with the Ojo Encino to the

south and east of the Big Pocket Area.

Paleomagnetic samples were collected from both areas to con­

struct magnetic-polarity columns. Correlation of the Sinclair and

Granger (1914) localities in the Ojo Encino Area by the magnetostrati­

graphy demonstrates that the upper. Panto!ambda, zone of the Torre-

jonian Land Mammal Age is from within the upper normal magnetozone and

that the lower, Deltatheriurn, zone of the Torrejonian is from within

the medial reversed magnetozone of the area. The lower normal

69 70 magnetozone is unfossiliferous in the Ojo End no Area. This shows that the two classical collecting levels of the San Juan Basin Torrejonian are strati graphically separated and permits magnetic-polarity definition of them. The Deltatherium level is from within a reversed magnetozone and the Panto!ambda level is from within the overlying normal magneto­ zone. •

The Deltatherium zone from the Big Pocket Area is also found within the reversed medial magnetozone of that area. It is correlative with the Deltatherium zone from the Ojo End no Area and permits the above definition. The correlation is shown in figure 18 and is con­ sistent with the known biostratigraphy and thickness trends of the

Macimiento Formation.

Characteristic taxa of the Deltatheriurn zone include

Deltatherium, Triisodon, Haploconus, Hixodectes malaris, and possibly

Palaechthon nacimienti. The Panto!ambda zone is recognized by the

presence o f Panto!ambda, Claenodon, and p o ssib ly Mixodectes pungens

and T o rre jo n ia w ils o n i.

The magnetic-polarity stratigraphy of the two study areas was

compared to that from Barrel Spring Arroyo, located geographically

between them. The biostratigraphy of the Barrel Spring Arroyo section

of Butler et a l. (1977) permits the upper normally magnetized,

magnetozone from that section to be correlative with either normal

magnetozone from the study areas. Correlation of the Barrel Spring

Arroyo section with the revised Cenozoic polarity time scale (Tarling

and Mitchell 1976) by Butler et a l. (1977) demonstrates that the 71 normal magnetozones from the Ojo Enclno and Big Pocket areas are either anomalies 26 and 27 or anomalies 27 and 28. Either correlation is consistent with the known biostratigraphy but the relative thicknesses of the magnetozones suggest the former correlation. However, further study is necessary to show clearly which anomalies are present in the magnetic-polarity columns of the study areas.

v APPENDIX A

PALEOMAGNETIC DATA

Locality 10, Ojo End no Area

Site Strat. lev. AF (Oe) D (°) I (°) 0 VGP L a t. No. ( F t . ) (M.) (Gauss) (°)

559 0 0.0 000 31.0 77.3 5.9X10“ ! 100 2 6 .8 60.6 2.8X10“ ' 68.5

560 14 4 .3 000 353.0 4 8 .8 4.8X10“® 100 350.7 42.0 3.1X10"® 75.8

561 31 9 .5 000 2 6 .8 55.3 1.0X10'® 100 351.2 59.6 7.9X10“® 81.8

562 48 14.6 000 2 1 .9 32.0 2.7X10"® 100 31.6 14.5 1.8X10"® 4 9 .4

563 64 19.5 000 1 7 .4 56.0 7.6X10"® 100 1 8 .8 54.9 5.5X10“® 7 4 .8

578 67 20.4 000 350.1 52.2 1.7X10“ ® 100 344.1 48.2 1.3X10“® 64.6

564 76 23.2 000 306.1 37.0 1.7X10“* 100 346.5 25.9 2.1X10“® 75.0

579 76 23.2 000 320.2 62.9 3.4X10“® 100 319.8 60.0 1.8X10"® 5 8 .4

580 86 26.2 000 317.4 57.0 3.6X10"® 100 333.7 4 8 .8 1.6X10"® 67.1

581 96 29.2 000 358.4 38.0 2.0X10"® 100 359.0 3 2 .8 1.6X10"® 7 1 .8

583 ‘ 99 30.2 000 279.6 82.4 2.3X10"® 100 87.6 74.1 9.4X10"° 73.4

72 73

S ite Strat. Elev. AF (Oe) D (°) I (°) VGP Lat. No. ( F t . ) ( M . ) ______(Gauss) (°)

582 106 32.3 000 332.9 55.6 7.5X10"G 100 340.3 52.3 4 .7X10-6 31.8

584 109 33.2 000 327.4 62.2 2.3X10-6 100 329.0 48.1 1.7X10-6 63.1

585 124 37.8 000 311.4 70.2 I.OXIO'6 100 325.0 76.2 1.8X10-6 55.1

586 131 39.9 000 11.3 65.2 4.9X10-6 100 359.1 61.6 3.7X10-6 83.2

587 146 44.5 000 144.3 -20.9 1.7X10-6 100 155.4 -49.1 2.5X10-* -68.6

589 148 45.1 000 134.9 -36.1 1.3X10-6 100 136.4 -41.0 1.3X10-6 -50.5

588 159 48.5 000 181.7 54.0 8.eXlO'g 100 212.1 -55.8 1.1X10-6 -64.2

590 162 49.4 000 177.0 -58.8 4.0X10*6 100 178.2 -69.0 5.3X10-6 -73.4

327 176 53.6 000 159.5 -25.6 3.9X10"! 300 60.1 -76.8 4.1X10-6 -21.2

328 184 56.1 ooo 175.0 55.9 4.6X10*6 300 199.1 -15.2 2.2X10*6 -56.8

037 191 58.2 000 195.4 -43.8 2.6X10*6 300 194.1 -47.4 2.4X10*6 -76.0

038 231 70.4 000 190.1 43.5 1.3X10*6 200 200.3 -31.1 1.1X10*6 -63.7

329 241 73.5 000 165.2 35.2 4.1X10*6 200 178.0 -26.0 3.4X10*6 -67.6

330 251 76.5 000 223.3 65.9 1.3X10*6 300 204.3 -56.3 9.0X10*' -70.5

331 258 78.7 000 160.9 24.2 2.2X10*6 400 143.9 -57.2 1.6X10*6 -61.3 74

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t .) (M .)______'______’______(Gauss) (°)

332 268 81.7 000 105.7 9.8 2.6X10"® 300 155.0 -63.2 3.4X10"* -69.2

333 279 85.0 000 155.5 - 2 .5 1.0X10"® 300 162.7 -2 2 .0 8.4X10’* -60.9

334 288 87.8 000 346.9 73.2 8.5X10"® 400 63.4 -1 6 .6 3.3X10"* 15.8

039 299 91.1 000 8 7 .8 70.7 5.1X10’ ® 400 169.4 -1 1 .7 1.3X10’ ® -5 8 .4

335 308 93.9 000 44.6 70.0 1.3X10"® 300 8 3 .3 65.4 1.9X10’ * 2 9 .8

336 314 95.7 000 208.3 56.7 1.6X10"® 300 161.9 —38.5 1.6X10’® -62.7

040 339 103.3 000 265 .8 68.9 2.5X10"® 300 119.4 -4 5 .3 9.2X10"° -38.3

337 349 106.4 000 334.2 70.2 5.2X10"? 200 318.5 6 0 .8 8.2X 10"° 57.5

338 355 108.2 000 336.1 42.0 1.2X10’ ® 300 353.0 21.7 6 .0 X 1 0 "' 64.5

041 365 111.3 000 342.5 68.6 1.7X10"® 300 326.9 66.8 8.6X10"' 62.5

339 380 115.8 000 357.0 6 2 .4 4.6X10"® 200 359.3 56.9 3.5X 10"* 88.4

340 390 118.9 000 359.2 48.7 l.O X IO ’ J 200 359.2 4 5 .4 6.4X10"® 8 0 .9

042 000 7 .0 57.4 1.3X10"® 200 5 .0 58.4 8.4X 10"* 84.9

341 400 121.9 • 000 358.1 47.6 5.3X10"® 200 351.3 4 3 .8 3.5X 10"* 77.2

342 409 124.7 000 358.1 71.6 2.7X10"® 200 345.2 57.3 1.6X10’* 77.9 75

S ite Strat. Elev. AF (Oe) D (°) i.C) J VGP Lat No. ( F t . ) (M .) (Gauss) ( ° )

343 419 127.7 000 11.5 63.6 2.1X10’ ® 200 5 .2 66.4 1.1X10’* 76.6

043 428 130.5 000 358.1 68.7 2.0X10’ % 200 ’ 4 .3 64.5 1.2X10’ * 79.2

344 429 130.8 000 353.1 22.9 1.9X10'® 200 355.7 6 9 .2 8.6X10"* 73.0

345 439 133.8 000 5 .7 63.1 2.4X10’ ® 200 351.8 60.3 7.0X10'* 81.7

044 453 138.1 000 231.1 6 4 .4 4.2X10’ ® 300 187.9 26.1 8.1X10’ ° -3 9 .7

346 463 141.1 000 134.1 38.1 2.0X10’ ® 400 114.0 -1 1 .4 6 .4X 1 0"' -2 2 .7

347 473 144.2 000 112.5 -6 0 .2 6.6X10’ ® 300 118.2 -6 3 .3 6.2X10"* -43.3

348 483 147.2 000 128.4 -5 4 .4 6.5X 1O’ Z 200 138.3 -6 3 .2 7 .4 X 1 0 "' -5 7 .4

349 493 150.3 000 121.1 -4 8 .0 8.6X10'® 200 127.3 -5 5 .6 9.1X10’ * -1 2 .0

350 508 154.8 000 114.6 70.9 1.7X10’ S 400 174.7 -1 6 .9 2 .2 X 1 0 "' -6 2 .2

351 542 165.2 000 248.2 36.1 1 .2 X 1 0 "! 300 138.1 -4 9 .3 4.8X10"' -54.6

352 549 167.3 000 340.0 36.0 1.7 X 1 0 "! 300 7 4 .4 -7 1 .2 2 .3 X 1 0 "' -2 1 .3 76

Locality 11, Ojo Encino Area

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No, ( F t . ) (M .)______(Gauss) (°)

353 0 0.0 000 100.3 -1 7 .5 4.0X10"® 300 147.0 -4 6 .7 2.6X10"b -61.0

354 10 3.1 000 4 6 .9 68.2 1.6X10'® 400 178.5 -1 8 .9 8.1X 10"b -6 3 .7

355 20 6.1 000 147.1 -6 1 .9 2.7X10"® 200 174.1 -7 3 .1 1.7X10"® -67.0

356 30 9.1 000 238.6 67.9 1.4X10"® 300 161.5 -2 6 .7 8 .3X 1 0"' -6 2 .6

357 40 12.2 000 137.8 -1 6 .9 6.4X10"® 200 155.3 -3 2 .4 6.6X10"b -61.4

358 60 18.3 000 184.0 -1 4 .6 3.3X10"® 200 192.5 -3 2 .2 3.4X10"6 -68.4

359 70 21 .3 000 228.4 38.1 4.6X10"? 200 192.7 -6 3 .7 4 .9 X 1 0 "' -7 6 .6

360 70 21 .3 000 94.3 29.0 1.2X10"® 200 158.4 -5 7 .3 1.6X10"® -7 2 .7

361 81 24.7 000 5 4 .7 74.1 5.8X10"? 300 147.6 -5 8 .1 1.0X10"' -64.2

362 91 27.7 000 1 5 .3 55.5 3.5X10"® 200 2 5 .2 51.8 2.0X10"® 68.9

363 101 30.8 000 1 9 .7 72.9 4.9X10"® 200 349.7 73.6 2.2X10"® 65.6

364 111 33.8 000 26.3 78.6 4.7X10"® 200 1 5 .3 74.1 3.1X10"® 63.8

365 121 36.9 000 4 .9 6 3 .4 6.6X10"® 200 355.2 75.9 4.1X10"® 62.5

366 131 39.9 000 357.7 88.4 4 .0X 1 0"! 200 357.8 88.2 3.3X10"® 39.6 77

S ite S t r a t . m AF (Oe) D ( ° ) I ( ° ) J VGP Lat

No. ( F t .) m 3: • < (Gauss) ( ° )

367 141 43.0 000 22.0 67.9 1.7X10"® 200 2 .2 59.2 5.8X10"b 85.7

368 151 4 6 .0 000 340.8 58.6 6 .7 X 1 0 "| 200 335.0 55.9 4.1X10"® 69.9

369 160 4 8 .8 000 354.8 4 9 .2 1.0X 10"* 200 349.8 44.5 5.4X10"* 76.9

370 170 51.8 000 354.8 59.7 3.7X10"® 200 351.3 57.6 1.5X10"® 82.7

371 182 55.5 000 342.8 67.1 1.3X10"! 400 137.8 -1 7 .7 2.1X10"® -43.2

372 192 58.5 000 8 0 .2 80.5 2 .0 X 1 0 "! 300 168.7 -4 1 .3 2 .7 X 1 0 "' -7 4 .3

373 202 61.6 000 181.2 -2 3 .5 7 .8X 1 0"! 200 184.7 -3 5 .4 9.1X10’ ® -7 3 .1 78

Composite Section, Big Pocket Area

S ite Strat. Elev. AF (Oe) D (°) I (°) 0 VGP Lat. No. ( F t . ) (M .)______(Gauss) (*)

251 198 60.4 000 300.9 57.2 1.8X10"® 200 285 .8 1 6 .8 8.7X 10"6 1 7 .8

252 226 68.8 000 2 .6 6 9 .3 1.7X10"® 200 9 .6 37.8 1.4X10"® 73.0

253 226 68.8 000 9 .6 57.8 4.3X10"® 200 7 .4 49.5 3.7X10"® 81.7

254 256 78.0 000 310.7 53.2 1.4X10"S 200 334.1 33.9 7 .2 X 1 0 "' 61.3

255 262 79.9 000 332.0 35.0 6.8X10“® 200 334.2 30.2 4.8X10'b 59.7

256 260 79.3 000 325.7 56.9 3.8X10"® 200 350.6 4 3 .3 1.2X10"® 76.6

257 270 82.3 000 335.9 48.5 1.0X10"® 200 331.9 44.3 6.6X10"® 64.0

258 282 86.0 000 346.0 30.3 4.7X10"® 200 349.2 25.8 3.5X10"® 65.6

259 292 89.0 000 355.6 63.9 8.9X10'® 200 355.0 6 2 .3 7.6X10"® 81.5

260 302 92.1 000 13.1 6 3 .3 3.4X10"® 200 23.5 65.0 2.6X10"® 6 9 .4

261 313 95.4 000 337.1 60.5 2.6X10"® 200 334.5 6 3 .8 1.2X10"® 6 8 .6

262 327 99.7 000 2 1 .4 31.7 2.3X10"® 200 0 .2 2 0 .4 8 .9 X 1 0 "' 6 4 .5

263 330 100.6 000 317.4 36.8 3.1X10"® 200 325.3 26.9 1.2X10'® 52.1

264 336 102.4 000 333.0 23.5 8 .1 X 1 0 "! 200 326.1 4 2 .4 3 .0 X 1 0 "' 5 8 .8 79

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t . ) ( M . ) ______(Gauss) (°)

265 235 71.6 000 2 2 .8 52.1 3 .3X 1 0"! 200 20.6 49.9 2.1X10"6 72.0

266 245 75.7 000 339.4 55.9 7.8X 1 0"! 200 348.3 50.4 6.6X 10"* 79.1

267 255 77.7 000 165.1 8 7 .3 2 .3X 1 0"! 200 288.1 56.9 1.2X10"6 33.9

268 266 81.1 000 354.2 44.0 1.7X 1 0"! 200 355.1 41.5 1.3X 10"* 77.1

269 276 84.1 000 325.6 59.4 3.5X 10"! 200 334.2 51.1 2.0X 10"* 6 8 .3

270 286 87.2 000 300.1 45.9 4.5X 10"6 200

271 296 90.2 000 28.7 73.8 3.5X 10"! 200 3 .7 79.8 1.8X 10*6 55.7

272 266 81.1 000 323.2 71.0 5.1X 10"! 200 303.5 61.1 3.4X10“* 46.5

273 276 84.1 000 278.9 54.1 3.7X1 O '6 200 327.0 52.8 1.6X10"* 62.9

274 286 87.2 000 24.9 50.3 6 .9X 1 0"! 200 343.8 36.0 3.2X10"* 68.6

275 296 90.2 000 0 .6 6 0 .8 1.1X 10"6 200 337.0 49.7 7.4X10'6 70.1

276 306 93.3 000 357.3 55.7 2 .4 X 1 0 "! 200 335.4 61.7 7.9X10"' 69.9

277 316 96.3 000 28.7 65.1 5.4X10"6 200 353,8 62.2 3.2X10"* 81.2

278 326 99.4 000 0 .4 60.2 5.7X 1 0"! 200 349.3 58.2 2.7X 10"* 8 1 .0

279 336 102.4 000 60.2. 86.5 6 .2X 1 0"! 200 338.0 75.6 2.3X10“* 60.0 80

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t . ) (M .)______(Gauss) (°1

280 345 105.2 000 59.3 77.5 3.7X10"® 200 14.0 61.5 2.3X 10"6 77.3

281 356 108.5 000 328.9 69.6 3 .6X 1 0"! 200 333.5 60.9 2.6X 10"* 68.6

282 366 111.6 000 308.5 8 0 .4 3 .6X 1 0"! 200 344.7 6 0 .3 2.2X10"* 77.0

283 376 114.6 000 31.7 65.4 4 .5 X 1 0 "! 200 34.0 70.1 3.2X10'* 60.4

284 356 108.5 000 343.9 68.9 6.3 X 1 0 "! 200 3 .0 64.3 3.9X 10"* .79.6

285 370 112.8 000 1 3 .3 51.2 4 .9 X 1 0 "! 200 18.5 - 9 .8 2.3X 10"* 4 5 .6

286 382 116.4 000 38.9 75.7 4 .4 X 1 0 "! 200 14.1 57.9 2.6X10'* 78.5

287 412 125.6 000 112.9 44.7 2 .4 X 1 0 "! 200 135.6 - 4 .6 1 .1 X 1 0 '* -3 6 .9

288 350 106.7 000 15.2 6 5 .3 5 .3X 1 0"! 200 351.1 54.1 3.1X10"* 82.6

289 360 109.7 000 353.8 6 6 .8 1 .1X 1 0"! 200 0.1 58.2 7.8X10"* 87.1

290 370 112.8 000 24.9 80.5 3.4X 1 0"! 200 1 .5 72.9 1.9X 10"* 67.6

291 380 115.8 000 7 0 .8 52.5 3.8X 1 0"! 200 5 4 .8 4 2 .7 1.6X10"* 42.1

292 390 118.9 000 186.5 5 .4 3 .2X 1 0"! 200 174.8 -3 5 .9 3.6X 10"* -7 3 .3

293 400 121 .9 000 111.1 33.1 2 .5 X 1 0 "! 200 214.6 -5 4 .2 1.6X10"* -61.9

294 410 125.0 000 135.7 76.1 1 .3 X 1 0 "! 100 192.8 -5 5 .5 1.0X10"6 -79.7 81

S ite S tr a t. E le v . AF (Oe) D (°) I ( ° ) J VGP L a t. No. ( F t . ) (M.) (Gauss) ( ° ) -6 295 394 120.1 000 151.4 44.2 1.1X10 100 155.7 -4 7 .7 9.6X10' -6 8 .3 -6 296 404 123.1 000 184.1 - 0 .9 3.6X10 -6 200 179.2 -3 3 .3 3.5X10 -7 2 .2

297 414 126.2 000 159.5 -2 2 .9 6.3X10 -6 -6 200 161.7 -3 6 .8 6.0X10 -6 7 .7 -6 298 425 129.5 000 158.5 -3 3 .5 3.6X10 200 161.9 -4 5 .7 4.0X10" -7 2 .3 -6 299 435 132.6 000 184.8 -1 4 .9 2.4X10 200 167.8 -4 4 .4 4.1X10" -7 5 .6 -6 300 445 135.6 000 132.1 - 22.0 1.4X10 -6 200 127.1 -5 4 .5 2.3X10 -4 7 .5 -6 301 455 138.7 000 163.6 0.1 2.7X10 200 154.3 -4 0 .7 3.2X10" -6 4 .4

302 465 141.7 000 134.0 -3 3 .3 5.3X10 -6 200 140.0 -5 3 .6 6.5X10 -5 7 .4

303 455 138.7 000 194.6 61.6 2.4X10 -6 200 142.8 -3 4 .6 2.0X10 -5 3 .2 -6 304 462 140.8 000 305.9 67.2 1.7X10 -6 200 219.2 -8 1 .1 1.1X10 -4 8 .4 -6 305 472 143.9 000 190.3 59.5 3.2X10 200 166.5 -3 7 .4 3.3X10* -7 0 .9

306 482 146.9 000 178.5 -2 2 .3 7.0X10 200 179.4 -3 0 .0 7.1X10 -7 0 .1

307 492 150.0 000 163.1 11.7 3.0X10 c : 200 179.7 - 21.8 2.6X10 -6 5 .3 308 502 153.0 000 167.3 -2 3 .2 3.6X10 :: 200 169.1 -3 8 .5 6.0X10 -7 2 .8

309 512 156.1 000 353.7 77.7 1.1X10 200 231.0 31.1 4.4X103 -1 8 .5 82

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t . ) (M .)______(Gauss) (°)

310 502 153.0 000 100.8 77.1 1.1X10"® 200 181.4 18.6 3.7X10"' -44.5

311 512 156.1 000 159.6 -1 4 .6 1.7X10"® 100 167.6 -5 0 .5 2.5X10"® -78.6

312 522 159.1 000 140.4 35.6 8.0X 10*5 400 152.3 17.5 8 .5 X 1 0 "' -3 8 .0

313 546 166.4 000 9 0 .4 42.2 3.0X10"® 200 136.7 -6 7 .1 3.0X10"* -56.0

314 557 169.8 000 198.0 -1 8 .8 2.2X10"® 200 180.2 -44.1 3.5X10"® -7 9 .9

B004 535 163.1 000 192.7 -4 6 .3 7.1X10"® -56.0

321 197 60.1 000 272.5 42.8 2.7X10"® 300 267.1 18.7 1.9X10"® 3 .3

322 220 67.1 000 301.4 78.9 2.2X10"® 200 317.0 6 1 .8 7 .4 X 1 0 "' 56.5

323 226 68.9 000 0 .5 46.0 1.3X10"® 200 357.2 41.8 1.0X10"* 77.8

324 241 73.5 000 1 8 .9 38.7 3.5X10"® 200 1 5 .3 5 6 .3 3.7X 10"* 77.7

421 535 163.1 000 158.3 -4 0 .1 3.8X10"® 200 159.1 -4 3 .8 4.0X 10"* -6 9 .4

422 548 167.0 000 235.2 61.9 1.1X10"® 200 202.0 -3 9 .8 7 .9 X 1 0 "'

423 558 170.1 000 177.5 -2 4 .3 1.2X10"® 200 180.4 -3 3 .8 3.3X 10"* -7 2 .5

424 568 173.1 000 150.1 - 2 .7 1.4X10"® 200 147.9 -2 9 .6 1.6X10"® -55.0

425 588 179.2 000 193.4 8 .0 3.7X10"® 200 199.9 - 7 .3 3.8X10"* -52.8 83

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t . ) (M .)______(Gauss) (°)

426 615 187.5 000 274.8 14.9 1.7X10"? 200 181.1 -6 0 .5 9.4X10"' -84.4

427 624 190.2 000 164.5 -3 4 .3 5 .0X 1 0"! 200 161.7 -4 7 .5 5.1 XI0"6 -72.9

428 664 202.4 000 156.0 -3 3 .5 6.4 X 1 0 "! 200 156.3 -4 0 .0 6.2X 10"* -6 5 .6

429 677 206.4 000 149.2 32.0 1 .7 X 1 0 "! 200 150.5 -2 9 .4 1.7X 10"* -5 6 .9

430 355 108.4 000 1 .8 46.5 2 .7X 1 0"! 200 1 5 .3 58.7 2.0X 10"* 77.5

431 365 111.3 000 332.3 5 1 .4 2 .2 X 1 0 "! 200 325.3 50.5 1.8X 10"* 60.9

432 376 114.6 000 8 5 .5 -3 7 .5 2.9X 1 0"! 200 93.1 -3 8 .8 2.4X10"* -15.1

433 383 116.7 000 1 2 .3 -3 7 .5 2 .9X 1 0"! 200 308.1 -8 0 .5 1.7X 10"* -2 3 .5

434 391 119.2 000 179.5 -2 1 .5 4 .0X 1 0"! 200 180.4 -2 4 .8 4.3X 10"* -6 7 .0

435 404 123.1 000 179.5 -2 1 .5 4 .0 X 1 0 "! 200 202.1 -6 6 .6 1.7X10"* -69.3

436 414 126.2 000 34.5 2 4 .0 1.1X10"? 200 250.8 -4 5 .1 7 .8 X 1 0 "' -3 0 .1

437 428 130.5 000 327.8 -1 7 .2 7 .6 X 1 0 "! 200 206.5 -5 3 .0 6 .9 X 1 0 "' -6 8 .2

438 440 134.1 000 108.7 -2 7 .2 2 .6 X 1 0 "! 200 138.8 -6 2 .7 2.1X 10"6 -5 7 .8

439 450 137.2 000 111.3 -6 2 .8 5 .9X 1 0"! 200 128.1 -6 5 .5 5.8X 10"* -5 0 .8

440 460 140.2 000 82.8 -4 9 .6 1 .4X 1 0"! 200 111.2 -5 2 .5 1.4X 10"* -3 4 .5 84

S ite Strat. Elev. AF (Oe) D (°) I (°). J VGP Lat. No, ( F t . ) (M ,)______(Gauss) (°) -6 470 143.3 000 231.9 - 66.2 2.9X10 441 -6 200 185.3 -5 6 .7 2.9X10 -8 5 .6

442 480 146.3 000 140 .4 -1 9 .4 9.5X10 200 159.0 -3 6 .3 1.2X10 -6 5 .7 -6 443 351 106.8 000 333.8 43.2 3.4X10 :-e 200 314.1 3 8 .3 2.4X10 47.7

444 452 137.8 000 109.1 -5 5 .7 3.3X10 200 123.7 -5 8 .6 2.8X10 :: -4 6 .0 -6 445 464 141.4 000 159.5 5.1X10 -5 2 .4 -6 200 154.5 -5 1 .4 5.0X10 - 68.6

446 466 142.0 000 167.5 -5 1 .0 7.1X10 200 167.1 -4 8 .5 6.9X10 -7 7 .3 -6 447 484 147.5 000 235.7 -3 7 .9 1.2X10 200 200.8 -3 9 .2 1.5X10 -6 -6 7 .3 ,-5 448 452 137.8 000 114.2 -4 5 .6 1.0X10 -5 200 120.8 -5 7 .6 1.2X10 -4 3 .6 -6 449 462 140.8 000 -5 3 .6 4.3X10 155.6 -6 200 162.8 -5 4 .5 4.0X10 -7 6 .0 -6 450 472 143.9 000 192.6 -6 4 .2 3.4X10 -6 200 189.4 -5 7 .0 4.2X10 -8 2 .3 -6 451 000 495 150.9 199.1 -2 6 .0 6.4X10 -6 200 195.0 -3 6 .2 5.4X10 -6 9 .4

452 495 150.9 000 200 183.8 -3 7 .6 8.0X10"6 -74.7

453 510 155.4 000 193.9 -6 6 .8 1.3X10";! 200 192.1 -6 5 .1 1.3X10"* -75.7

454 541 164.9 000 180 .4 2 8 .7 8.4X10"? 200 185 .8 -1 4 .2 1.4X 10"* -6 0 .7

455 519 158.2 000 137.7 -4 2 .4 4 .3 X 1 0 '* 200 160.5 -4 7 .5 4.2X1 O '6 -7 2 .0 85

S ite S tr a t. E lev. AF (Oe) D ( * ) i o J VGP Lat No. ( F t . ) (M.) (Gauss) (')

456 528 160.9 " 000 6 9 .4 -6 9 .1 1.4X 1 0"! 200 151.2 -55.2 . 1.8X10"6 -6 6 .8

457 538 164.0 000 117.8 -6 9 .6 9.8X 10"! 200 157.6 -6 6 .1 9 .1 X 1 0 "' -6 9 .4

458 544 165.8 000 150.8 -5 4 .9 2.5 X 1 0 "! 200 151.0 -61.4 2.2X10"* -68.7

459 554 168.9 000 158.3 -59.5 1 .7X 1 0"! 200 166.3 -5 6 .6 2.2X 10"* -7 8 .9

460 565 172.2 b o o 137.9 -5 8 .6 2 .2 X 1 0 "! 200 141.8 -5 4 .8 2.2X 10"* -5 9 .2

461 581 177.1 000 145.0 -4 2 .3 3 .1X 1 0"! 200 152.3 -4 1 .5 3.4X10"* -63.3

462 591 180.1 000 80.0 -7 3 .6 1 .3 X 1 0 "! 200 288.5 -6 9 .0 7.8X10"' -18.0

463 601 183.0 000 156.6 -3 4 .4 1 .7 X 1 0 '* 200 156.9 -3 4 .8 1.5X10"* -63.6

464 601 183.0 000 172.6 -5 2 .8 6.8X 10"* 200 174.3 -5 2 .9 7 .2 X 1 0 '* -8 4 .7

465 618 188.2 000 120.2 -6 4 .7 1 .4 X 1 0 '* 200 143.9 -59.2 1.5X10"* -45.0

466 625 190.4 000 157.1 -5 1 .0 3.2X 10"* 200 155.4 -5 0 .8 3.3X 10"* -6 9 .1

467 636 193.7 000 164.3 -33.3 3 .4 X 1 0 '* 200 167.2 -3 6 .5 3.6X10"* -70.7

468 646 196.8 000 172.7 -4 4 .8 2 .0 X 1 0 '* 200 172.1 -4 7 .7 2.0X10"* -80.1

469 662 201.6 000 145.6 -50.0 2.9X10"* 200 156.3 -47.9 3 .2 X 1 0 '* -6 8 .9

470 676 206.0 000 160.3 - 7 .5 4 .9 X 1 0 "! 200 165.2 -11.0 4.7X10"* -56.6 86

S ite S tr a t. E lev. AF (Oe) D ( ° ) I ( • ) J VGP Lat No. ( F t .) (M.) (Gauss) C)

471 687 209.4 000 178.5 -3 6 .3 5.2X 10-7 200 164.3 -4 6 .0 6 .1X 1 Q -' -7 5 .5

472 705 214.9 000 314.8 -8 0 .4 1.9X10"® 200 179.5 -6 9 .0 1.7X1 O'6 -73.6

473 722 219.9 000 206.0 10.1 5.3X10” ! 200 192.6 -4 5 .3 7.4X10”' -75.9

474 733 242.1 000 147.1 -39.1 1.8X10”® 200 163.4 -46.3 2.1X10”* -73.6

475 748 228.1 000 6 6 .5 -5 9 .7 2.6X10”® 200 151.5 -71.1 2.5X10” ® -6 2 .5

476 763 232.4 000 157.0 -5 5 .6 7.6X10"® 200 158.0 -5 5 .9 7.9X10” ® -7 2 .2

477 776 236.5 000 176.4 -5 3 .0 2.1X10” ® 200 180.7 -5 0 .1 2.4X10’® -84.9

478 788 240.2 000 147.2 -6 0 .4 2.5X10”® 200 164.5 -6 5 .9 3.4X10’ ® -7 3 .3

479 795 242.3 000 248.2 -7 3 .7 4.0X10”! 200 190.4 -4 6 .9 6.2X10”' -78.2

480 835 254.5 000 80.6 13.1 3.9X10”® 200 160.3 -3 9 .4 1.6X10” ® -6 8 .1

481 847 258.2 000 132.3 -6 9 .0 2.9X10’ ® 200 144.3 -64.9 3.6X10”® -6 1 .4

482 859 261.8 000 246.0 2 2 .0 5.0X10”! 200 235.8 7.6 4 .2 X 1 0 "' -4 0 .8

483 882 268.8 000 337.5 37.0 1.8X10”® 200 340.8 4 4 .6 1.5X10’® 70.9

484 907 276.5 000 8 .0 53.3 3.2X10”® 200 13.0 53.5 2.4X10”® 79.2

485 926 291.4 000 356.9 36.5 4.7X10” ® 200 358.5 29.4 3.8X10’® 69.7 87

Radio Tower Section, Big Pocket Area

S ite Strat. Elev. AF (Oe) D (°) I (°) J VGP Lat. No. ( F t . ) (M .)______'______(Gauss) (°) -6 486 0 0.0 000 1 6 .4 6 1 .6 2.2X10 -6 200 3 .5 65.0 1.5X10 78.7 -6 487 29 8 .3 000 1 6 .8 6 8 .7 1.1X10 -7 200 120.1 84.1 5.3X10 - 3 .9 -6 488 43 13.1 000 347.1 4 4 .7 1.2X10 -7 200 346.8 50.1 5.1X10 77.9 -6 489 28.4 000 157.5 -1 1 .3 4.7X10 93 -6 200 140.2 -2 3 .5 5.2X10 -4 7 .1 -7 490 104 31.7 000 244.9 83.2 4.6X10 -7 200 199.9 -3 0 .9 6.0X10 -6 3 .8 -7 491 121 36.9 000 314.1 16.3 5.7X10

492 130 39.2 000 193.6 -2 1 .6 6.4X10"® 200 196.5 -2 9 .8 5.2X 10"6 -6 5 .2

493 141 42.9 000 98.6 -4 5 .9 5.9X10"? 200 125.2 -4 5 .5 7.0 X 1 0 "' -6 4 .1

494 150 45.9 000 147.4 -5 8 .4 1.1X10"® 200 164.9 -5 4 .4 1.8X10"® -7 7 .7

495 161 49.1 000 343.4 37.4 2.8X10"? 200 192.6 -2 5 .5 1.1X10“' -64.7

496 189 57.6 000 155.3 8 .6 1.4X10"® 200 174.5 -2 6 .0 1.6X10"®

497 197 60.1 000 186.9 -4 3 .9 3.5X10"® 200 189.2 -5 3 .2 3.4X10"® -8 2 .2 REFERENCES CITED

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