Stratigraphy and structure of the Palen Formation, Palen Mountains, southeastern California
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Authors LeVeque, Richard Alan
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/557714 STRATIGRAPHY AND STRUCTURE OF
THE PALEN FORMATION, PALEN
MOUNTAINS, SOUTHEASTERN CALIFORNIA
by
Richard Alan LeVeque
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 8 1 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillm ent of 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 this manuscript in whole or in part may be granted by the head of 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:
^ OicjitwurTl______'Jusie /^S/ W. R. DICKINSON D ate Professor of Geology ACKNOWLEDGMENTS
I would truly like to thank the members of my committee, Drs.
B ill Dickinson, Peter Coney and Gordon Haxel. Each was instructive and of assistance, both in the office and in the field. Appreciation is also extended to Steve Richard and Lucy Harding, fellow members of the
Blythe Research Station, for friendship and discussions concerning the geology of our common areas. I feel fortunate to have been associated with a fine group of people in the Department of Geosciences.
Financial assistance and equipment was provided by the National
Science Foundation Grant EAR-8018500 awarded to Peter Coney and Lucy
Harding, the U. S. Geological Survey and the Bert S. Butler Scholarship fund of the Department of Geosciences.
i l l TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS...... v
ABSTRACT...... v i i
INTRODUCTION...... 1
P r e v io u s W o r k ...... 3 Regional Geologic Setting ...... 4 Local Geologic Setting ...... 7
STRATIGRAPHY OF THE PALEN FORMATION...... 9
I n tr o d u c tio n ...... 9 Member D e s c r ip tio n s ...... 10 Lithofeldspathic Arenite ...... 10 Polym ictic Conglomerate ...... 11 Quartzose Arenite ...... 20 Age o f th e P a le n F o r m a t i o n ...... 22 Environm ent o f D e p o s i t i o n ...... 25 Paleogeographic Interpretation ...... 27
STRUCTURAL GEOLOGY...... ^ ...... 30
I n tr o d u c tio n ...... 30 F o l d s ...... 30 F a u l t s ...... 38 T h ru st F a u ltin g ...... 38 S t r i k e - s l i p F a u lts ...... 40 R everse F a u l t s ...... 40 C l e a v a g e ...... 42 S tr u c tu r a l I n t e r p r e t a t io n ...... 46
CONCLUSIONS...... 53
REFERENCES C I T E D ...... 55
iv LIST OF ILLUSTRATIONS
Figure Page
1. Location and Generalized Geologic Map of Part of Southeastern California and Western Arizona ...... 2
2. Geologic Map of the Northern Palen M ountains ...... in p o ck et
3 . Lownangle C ro ss-b ed d in g i n th e Lower Member o f th e P a le n F o r m a tio n ...... 12
4. Microphotograph of Typical Sample of Lower Member .... 13
5. Size Variation of Clasts in Conglomerate of Middle M e m b e r ...... 15
6. Compositional Variation of Clasts in Conglomerate of Second Member ...... '...... 16
7. Cyclic Graded Bedding in Arkose Interbeds in Middle Member of Palen Formation ...... 18
8 . M icrophotograph o f th e M atrix o f th e M iddle Member . . . 19
9. Large-scale Trough Cross-beds in the Upper Part of th e Upper Member o f th e P a len F o r m a tio n ...... 21
10. Microphotograph of the Quartzose Arenite of the P a le n F o r m a tio n ...... 23
11. Microphotograph of the Upper Menter Showing Development of Micaceous M atrix ...... 24
12. Equal-area, Lower-hemisphere Plot Showing Orientation of Fold Axes (FA) and Axial Planes (AP) for Major F o ld s in th e P a len F o r m a t i o n ...... 31
1 3 . An O utcrop o f C onglom erate o f th e M iddle Member o f th e P a le n F o r m a tio n ...... 32
14. Well-developed Cleavage in Overturned Conglomerate of Middle Member of the Palen Form ation ...... 33
1 5 . S ch em atic S t r u c tu r a l S e c tio n s ...... in p o c k e t
v v i
LIST OF ILLUSTRATIONS— C ontinued
Figure Page
16. Complex Folds in the Lower Member of the Palen Forma tion in Area of Strong Deform ation ...... 35
17. Sketch and Close-up Photo of Folds in Figure 16 Showing that Fold Form is Generated by Slip along Closely-spaced Axial Planar Cleavage ...... 36
18. Imbrication of the Palen Pass T h ru st ...... 39
19. High-angle, Oblique-slip Fault on East Side of the Palen Mountains Separating Middle Member of the Palen Formation (Right) from Upper Member (Left) . . 41
20. Low-angle Reverse/Thrust Fault on Southwest Side of the Northern Palen Mountains ...... 43
21. Contoured Lower-hemisphere Equal-area Data for Cleavage in Northern Palen Mountains ...... 44
22. Deformed Clasts from Conglomerate of Middle Member . . . 45
23. Two Photos of Cleavage in the Volcanic Porphyry ...... 47
24. Schematic Drawing of "Compartmental" Deformation .... 49 ABSTRACT
The Palen Formation is comprised of three members, which consist of lithofeldspathic arenite, polymictic conglomerate and quartzose are- nite that were deposited prior to at least a portion of a Jurassic mag matic arc that existed in southeastern California and western Arizona.
The three members of the Palen Formation become more compositionally ma ture upward in the section. Gradational contacts between each member imply that sedimentation was not interrupted and that drastic changes in sedimentary environments did not occur. Bedding characteristics suggest that the depositional environments changed with time from shallow-marine to subaerial.
Intense deformation of the Palen Formation produced thrust and strike-slip faults, tight to isoclinal south-vergent disharmonic folds
and a penetrative cleavage. This deformation was the consequence of the
southward translation of upper plate Paleozoic and possible Mesozoic metasedimentary rocks along the Palen Pass thrust over a lower plate
consisting of the Palen Formation and an intrusive rhyodacite porphyry.
Strike-slip faults that are transverse to the folds in the lower plate
rocks separated the map area into discrete compartments, each of which
underwent unique deformations. The sim ilarity of fabric data from the
upper and lower plate rocks with deformed strata to the east in the Big
Maria Mountains suggests that this deformation occurred in the early
Late Cretaceous ('''90-100 m .y.B.P.).
v i i INTRODUCTION
A Jurassic magmatic arc trended northwestward across the south western Cordillera of North America (Burchfiel and Davis, 1981; Howard,
1981). Remnants of this arc in southeast California and western
Arizona are represented by granitic to monzonitic plutonic rocks, rhyo- dacitic subvolcanic intrusions and volcaniclastic to quartzofeldspathic sedimentary strata (Pelka, 1973; Harding, 1978; Howard, 1981). Most, but not all, of the sedimentary strata are quartzofeldspathic siltstones, sandstones and conglomerates of the McCoy Mountains Formation and equiv alent strata that overlie and thus postdate the volcanic rocks of the
Jurassic arc (M iller, 1970; Harding, 1978).
Within the region of southeastern California and western
Arizona, Mesozoic sedimentary rocks known to predate the Jurassic arc are rare. Intrusive relationships within the northern Palen Mountains indi
cate that the Palen Formation predates at least a portion of the Jurassic arc. This study of the Palen Formation is an attempt to establish its
age through stratigraphic position and regional geological relationships
and to interpret its depositional setting. With this knowledge it may
then be possible to place constraints on the early Mesozoic paleogeog-
raphy of -this area.
The Palen Formation underlies approximately 11 km^ in the north
ern Palen Mountains in southeastern California (Figure 1). The Palen
Mountains are about 43 km northwest of Blythe, California and are sepa
rated from the Granite Mountains to the north by Palen Pass. Access to
1
) Figure 1 . Location and Generalized Geologic Map of Part of South eastern California and Western Arizona. — A = Arica Mountains, B = Blythe, California, BM = Big Maria Moun tains, Ch = Chuckwalla Mountains, C = Coxcomb Mountains, D = Dome Rock Mountains, E = Eagle Mountains, G = Granite Mountains, H = Hexie Mountains, LM = L ittle Maria Moun tains, Me = McCoy Mountains, M = Mule Mountains, P = Palen Mountains, PP = Palen Pass, Pi = Pinto Mountains, R = Riverside Mountains. Sources of data referenced in text; map modified from Ehlig (1981). 0 10 20 30 40 50 if i KM E l Late Cretaceous granitic rocks 3 McCoy Mountains Fm. and equivalents (J-K) 5 3 Mid-Mesozoic volcanic porphyry ZZlPalen Formation (Early J) 3 Paleozoic metasedimentary rocks SDPrecambrian granitic gneiss and meta-granite EEpPrecambrian terrane of Powell and Silver (1978; 1979) 3 the study area is by California State Route 177 (Rice Road) north from
Interstate 10 approximately 25.6 km (16 mi) and then east via dirt road to the Palen Pass area (Figure 1). The topographic base used for field mapping was a portion of the U. S. Geological Survey Palen Mountains 15' quadrangle enlarged to a scale of 1:12,000.
P r e v io u s Work
Most published geologic reports of the Palen, L ittle Maria, Big
Maria and McCoy Mountains have been reconnaissance in nature.
The work of M iller (1944) was the first that mentioned the geol ogy of the Palen Mountains. He formally named the McCoy Mountains Forma
tion for exposures in the McCoy Mountains and noted their occurrence in
the southern Palen Mountains.
The Paleozoic rocks in Palen Pass were studied by Hoppin (1951).
His report dealt primarily with the gypsum occurrences in the area, al
though his outline of the areal geology included a. description of meta
sedimentary rocks south of the Paleozoic complex (Palen Formation).
Hoppin provisionally assigned these rocks to the McCoy Mountains Forma
tion of M iller (1 9 4 4 ).
The Palen Formation was first described by Pelka (1973) in a
Ph. D. Thesis on the Palen and McCoy Mountains. He was the first to no
tice the fundamental differences in lithology and stratigraphic position
between the Palen and McCoy Mountains Formations. His description of
the areal geology provided the framework for the present study. 4
Regional Geologic Setting
The Palen Formation is not presently correlated with any of the known Mesozoic sedimentary rocks of southeastern California or western
Arizona. It is in thrust contact to the north with Paleozoic and pos sibly Mesozoic metasedimentary rocks. To the south, the Palen Formation
is intruded by a rhyodacite porphyry of probable Early Jurassic age.
Basement rocks of Precambrian age are present both to the south
and west in the Chuckwalla, Eagle, Cottonwood, Hexie and Pinto Mountains
and to the north and east in the Big Maria, Riverside and Arica Moun
tains (Figure 1) (Hamilton, 1971; Silver, 1971; Powell and Silver, 1978,
1979; Carr and Dickey, 1980). Designation of the Precambrian age in the
Riverside and Big Maria Mountains is largely arbitrary and made on the
basis of the polymetamorphic and gneissic nature of the rocks, as iso
topic age data are not present in the literature (Bishop, 1963).
The Precambrian rocks exposed in the Chuckwalla, Eagle, Cotton
wood, Hexie and Pinto Mountains consist of two lithologically distinct
suites of older metamorphic rocks that have been juxtaposed by a post-
1200 m.y.B.P., pre-165 m.y.B.P. old thrust fault (Powell and Silver,
1979). These metamorphic rocks do not correlate closely with any other
metamorphic rocks of southeastern California (Silver, 1971).
Paleozoic strata occur at scattered localities throughout south
eastern California, including the Arica, Riverside, L ittle and Big Maria
and Palen Mountains. No fossils have been found in these sequences, so
correlation is made solely on the basis of lithology and stratigraphic
succession. The Paleozoic sequences in the L ittle Maria, Big Maria and
Palen Mountains consist of low- to high-grade metasedimentary rocks that 5 have been correlated with all or parts of the Tapeats to Kaibab Forma
tions of the Colorado Plateau (Hamilton, 1971; Stone and Howard, 1979;
Howard, personal communication, 1981). Pronounced facies changes occur in the Pennsylvanian and Permian strata, which become more calcareous
toward the west.
Limestones, conglomerates and gypsiferous schists that overlie
the Kaibab Formation are particularly well exposed in the L ittle Maria
Mountains (Krummenacher, personal communication, 1981). These strata may be correlative with the Triassic Moenkopi Formation. If so, they
represent the oldest Mesozoic strata of the region. They occur in areas
of complex structure and are commonly metamorphosed to at least upper
greenschist grade. They may be present in the Palen Pass area in in
verted stratigraphic position structurally below the Kaibab Formation.
If these sediments are equivalent to the Moenkopi Formation, they are
the southernmost exposures of rocks of this age and type in the Mojave-
Sonoran Desert region.
Jurassic plutonic and subvolcanic rocks extend southeastward
from at least the central portion of the Needles 1° x 2° A.M.S. sheet
(Bishop, 1963) south of Chambliss, California (Howard, 1981) to the
Baboquivari Mountains of south-central Arizona (Haxel and others, 1980).
The Jurassic magmatic arc is represented in the study area by a rhyoda-
cite porphyry (K-Ar plagioclase, 175 m.y.) (Pelka, 1973) in the northern
Palen Mountains and by volcanic rocks dated as early to middle Jurassic
in the Dome Rocks Mountains of western Arizona (geochronology by L. T.
Silver, as reported in Growl, 1979). 6
A very thick (greater than 8 km) section of quartzofeldspathic metasedimentary rocks overlies the rocks of the magmatic arc in a number of mountain ranges in southeastern California and western Arizona
(M iller, 1970; Pelka, 1973; Harding, 1978; Robison, 1979). These rocks, the McCoy Mountains Formation and correlatives, consist of conglomerates, sandstones and siltstones that have undergone degrees' of metamorphism ranging from weak greenschist to amphibolite grade (Marshak, 1979).
Their age is constrained only by depositional contacts on the Jurassic volcanics and intrusive relationships with Late Cretaceous plutons in the Granite Wash Mountains of Arizona (Reynolds, 1980).
Phanerozoic structural elements in southeastern California are predominantly Mesozoic in age. The Paleozoic rocks of the L ittle Maria,
Big Maria and Palen Mountains have been deformed into south-vergent iso clinal synclines and anticlines that have been overturned to the south and that are, in places, cored by Jurassic plutons (Hamilton, 1971;
Demaree, 1981; E llis, Frost, and Krummenacher, 1981; Emerson and
Krummenacher, 1981). Pegmatites that have been dated at 90 m.y.B.P. by
Rb-Sr isotopic methods crosscut these folds and therefore date this folding as Late Cretaceous (Krummenacher, personal communication, 1981).
Fold axes trend east-west to northwest-southeast and plunge generally to
the west (Ellis and others, 1981).
Mesozoic deformation 90 km to the northwest, in the Old Woman
Mountains, is sim ilar in style although of different orientation (Howard,
1981). In this range a ductile southeast-verging nappe is cored by Pre-
cambrian crystalline and Cambrian supracrustal rocks. The sim ilar occur
rences of basement-involved recumbent and isoclinal folds in both 7 regions, although of different orientation, suggest that the southeast structures of the Mojave Desert may be transitional between south- verging structures in the Big Maria and L ittle Maria Mountains and east- vergent thrust faults of the Sevier erogenic belt in California and
Nevada farther to the north. High-grade metamorphic rocks are involved in the deformation in the Mojave Desert and Big Maria and L ittle Maria
Mountains whereas they are not in the Sevier orogenic belt to the north,
thus indicating that the structural styles of these areas differ.
A south-dipping thrust fault in the northern Mule Mountains,
south of the McCoy Mountains, represents another style of Mesozoic de
formation (Crowell, 1981). The upper plate of this feature consists of
gneiss and porphyritic diorite possibly correlative with PreCambrian
rocks present in the Chuckwalla Mountains to the west (Crowell, 1981, p.
590). Northeastward-verging folds in the lower-plate volcanic and vol-
caniclastic rocks (McCoy Mountains Formation) are interpreted to have
formed as the upper plate gneiss and diorite were thrust to the
n o r th e a s t.
Local Geologic Setting
The contacts of the Palen Formation are well exposed in the
study area (Figure 2, in pocket). The northern contact is a shallowly
north-dipping thrust fault, herein termed the Palen Pass Thrust, which
trends approximately east-west across the southern Palen Pass area and
places Paleozoic and Mesozoic(?) rocks over the uppermost member of the
Palen Formation and the rhyodacite porphyry. The thrust fault is offset
by a small right-lateral fault in the middle of the map area (Figure 2). 8
The other major contact of the Palen Formation is an intrusive one. Along the south edge of the outcrops and in several other places, the formation has been intruded by a Lower Jurassic porphyry (intrusive porphyry on the map). The irregular pattern of the contact and the pres ence of small masses of porphyry injected into the Palen Formation pro vide evidence for its intrusive nature. There is no contact aureole, nor any xenoliths of the Palen Formation in the intrusion. The age of the porphyry provides the only direct evidence for the age of the Palen
F orm ation.
The 175 m.y.B.P. age of the porphyry as determined by K-Ar meth ods represents the time at which the K-Ar isotopic system was sealed and is probably younger than the actual age of intrusion. Work by Anderson
and Silver (1978), Haxel and others (1980) and Wright, Haxel and May
(1981) documents the presence of the rhyodacite porphyry arc terrane
through south-central Arizona and into northern Sonora. Uranium-lead
isotopic ages for these rocks range from 170 to 194 m.y.B.P., suggesting
that the development of the magmatic arc occurred primarily in the Early
J u r a s s ic .
Phases of an igneous complex that yields a Cretaceous K-Ar age
(66 m.y. biotite) (Pelka, 1973) occur in a small area on the western side
of the map in intrusive contact with the Palen Formation as well as on
the flank of the eastern side of the Palen Mountains. STRATIGRAPHY OF THE PALEN FORMATION
Introduction
The original lithostratigraphic subdivision of the Palen Forma tion into three members by Pelka (1973) is supported by the more detailed study described in this report and is retained. In ascending strati graphic order, the three members are: 1) lithofeldspathic arenite, 2) polymictic conglomerate, and 3) feldspathic to quartzose arenite (clas sification of Crook, 1960). The prefix "meta" should be applied to each member, as all sections examined reveal recrystallization of certain ma trix components. The contacts between members are a ll gradational and are marked by transitional zones that include lithologic types common to both the overlying and underlying members.
A complete section is not exposed. The base of the section is not seen, and the uppermost member is truncated by the rhyodacite por phyry that underlies the southern part of the study area (Figure 2) .
The absence of a complete section combined with the degree of deforma tion precludes an accurate estimate of the total thickness of the forma tion. Two partial sections of 129 and 455 m were measured. The more complete sequence of 455 m contains 275 m of the middle conglomerate member. This unit appears complete, although it is possible that it is either incomplete or locally repeated by movement along faults parallel to cleavage.
Sedimentary structures in the lower two members are rarely dis
cernible owing primarily to heavy desert varnish and probably also to
9 10 obliteration by metamorphism. The cross-bedding that is characteristic of the third member is better preserved, possibly because of its large scale. Details of the stratigraphy were culled from field observations and petrographic investigation of 33 thin sections. The thin sections were stained by conventional methods to enhance the recognition of
K -sp a r.
Member D e s c r ip tio n s
Litho feldspa thic Arenite
Distribution. The lower member is present along the lower ele vations of the northern Palen Mountains in the eastern half of the map area (Figure 2). The most complete undeformed section is found along the ridge that trends toward the southeast from h ill X1437 in the lower right-hand quadrant of the map.
Description. The dominant rock type is lithofeldspathic arenite.
Hand specimens that are not dark red-brown due to desert varnish are me
dium to dark olive green on weathered surfaces. Fresh samples are of
grayer hues. A ll samples are texturally immature and contain more than
5% matrix. In hand specimen the matrix can be recognized as a mixture
of epidote, green biotite and chlorite that is in much greater abundance
than the framework detrital grains. The framework grains are dominantly
blocky feldspar that have been altered to a chalky color. The amount of
detrital quartz in this member is low relative to the upper members. An
increase in quartz is one of the mineral parameters used to define the
transition zone between the lower and middle members. 11
In most places bedding is unrecognizable from a distance and is difficult to see at close observation. Where observed, bedding is rep resented by thin wavy laminations that are from 3-5 mm to 1-1.5 cm in thickness. Other Variations include low-angle.cross-beds with sets of
3-5 cm and rare graded beds (Figure 3). Grain size within the graded beds varies from approximately 3 to .10 mm through a vertical distance o f about .2m. No sedimentary structures indicative of either a waxing or waning hydrologic current were observed in conjunction with the size g r a d in g .
Petrography. Thin sections of the lower member contain 20-50% plagioclase (average composition about An^) , 10-20% each of secondary epidote and green biotite, and generally less than 10% of quartzite fragments, volcanic rock fragments, secondary chlorite, detrital biotite and microgranular quartz (Figure 4). Sorting is very poor, and nearly all detrital grains are angular to subangular. In all samples, except
those within the transition zone to the middle member, the matrix (meta- morphic chlorite, epidote and biotite) is the volumetrically most abun
dant component of the rock. Due to the lath-like morphology and compo
sition of the plagioclase and the presence of volcanic rock fragments,
these rocks are considered to have been derived from a volcanic source
of intermediate composition.
Polymictic Conglomerate
Distribution. The middle member of the Palen Formation is ex
posed primarily in two separate areas: 1) in the west half of the map 12
Figure 3. Low-angle Cross-bedding in the Lower Member of the Palen F orm ation.
14 area where it is tightly folded.and intruded by Cretaceous granite, and
2) in the east half of the map area where it is in stratigraphic posi tion between the lower and upper members. A partial section was meas ured in the east half of the map area where the member is best exposed.
Description. The middle member consists of about 75% polymictic conglomerate and 25% arkose. Quartzite clasts are dominant in the con glomerate. Bedding is poorly defined in the conglomerates and can be easily recognized only in the arkose interbeds. From a distance the conglomerates appear to form tabular beds, but exposures are inadequate to establish this morphology.
The transition zone between the lower and middle members con sists of coarse-grained lithofeldspathic arenite that grades up into
conglomerates of the middle member. Attendant with the size grading is an increase in the amount of quartz and a decrease in the amount of ma
trix relative to the lower member. The contact between the lower and middle members was placed at the first pebble conglomerate with clasts
that were on the average larger than three centimeters.
The conglomerate beds are in places so poorly sorted as to be a
chaotic mixture of clasts of all sizes and shapes (Figure 5). Even where
the majority of clasts are subrounded, there are always a small number
of angular clasts present. For determination of clase size and composi
tion, only clasts larger than one centimeter were counted. Clast compo
sition data (Figure 6) show that quartzite is the dominant clast type.
Other clast types, in order of decreasing abundance, are leucogranite,
carbonate, re-sedimented lithofeldspathic arenite of the lower member /
F ig u r e 5 Size Variation of Clasts in Conglomerate of Middle Member. — Section approximately 275 m t h ic k . 40-
35 -
30 - LARGEST cm 25 -
20-
15-
change 10 — in scale
AVG. cm
100 150 200 stratigraphic height above base (m) G • Quartzite A Leucogranite ° Carbonate A Member one
100 -
% 50— [only occurrence)
100 150 200 stratigraphic height above base (m)
Figure 6. Compositional Variation of Clasts in Conglomerate of Second Member. — Section approximately 275 m thick; 17 and rare volcanic porphyry. The quartzite is vitreous, tan and nonmica-
ceous. The leucogranites have subequal amounts of quartz and pheno-
crystic potassium feldspar and little or no micas or mafic minerals.
The carbonate clasts are generally all recrystallized and, in the more
deformed areas, metamorphosed to marble. The quartz porphyry clasts are
light tan aphanitic volcanic rocks that bear no resemblance to the rhyo-
dacitic porphyry of the map area. Quartzite and carbonate clasts are
present throughout the section (Figure 6). In the section measured
(approximately 275 m thick) the quartz clast/carbonate clast ratio va
ried from about 2:1 to 4:1.
The arkosic interbeds in the middle member are graded laminar
beds that consist of medium- to coarse-grained feldspathic arenites.
One sequence of 1-3 cm thick graded beds is repeated through 10 cycles.
The usual bedding style is that of poorly defined fining-upward sequences
approximately .5-.75 m thick (Figure 7).
Petrography. The petrographic characteristics of the middle
member are sim ilar to those observed on the mesoscopic scale. In all
thin sections, a pronounced increase in quartz, both as separate detrital
grains and as components of polycrystalline basement rock fragments, re
lative to the first member, is apparent. The epidote-green biotite-
chlorite matrix present in the first member, although less abundant,
comprises the matrix of this member also (Figure 8). The quartz/feldspar
ratio in the arkose interbeds is about one and the quartz + feldspar/
matrix ratio is relatively low (0.3). 18
Figure 7 Cyclic Graded Bedding in Arkose Interbeds in Middle Member of Palen Formation. Figure 8. Microphotograph of the Matrix of the Middle Member. — green biotite, E = epidote, C = secondary chlorite. 20
Quartzose Arenite
Distribution. The upper member is continuously exposed in two
areas. It is present in an east-west trending belt that is in the strat-
igraphically highest position of the lower plate of the Palen Pass
Thrust. In this position many of the distinguishing characteristics of
this member are lost because of its highly deformed state. The upper
member is also present on the north-trending ridge on the east side of
the map. The lithology and sedimentary structures are best displayed in
t h is a r e a .
The upper member is in gradational contact with the underlying
conglomerates of the second member and is intruded by the rhyodacite
porphyry in both areas of exposure.
Description. The characteristic bed form of the upper member,
although not everywhere exposed, is large-scale trough cross-beds (Fig
ure 9). The size of single cross-bed sets is very large, in places
reaching approximately 5-10 m in height. Because the bedding attitudes
change along individual foresets, precise measurement of attitudes is
. difficult and therefore most readings represent a local average. The
presence of the cross-bed sets does provide an indication of facing and
aids structural mapping.
The upper member ranges in composition from subarkose to quartz
arenite. The greatest amount of feldspar is found above and within the
transition zone between members two and three. Many of the samples ex
amined were entirely quartz. Accurate appraisal of the relative 21
Figure 9 Large-scale Trough Cross-beds in the Upper Part of the Upper Member of the Palen Formation. 22 proportions of quartz and feldspar is increasingly difficult up-section because of folding and development of cleavage.
Petrography. The samples examined in thin section either had about 25-30% potassium feldspar or were entirely quartz. Original tex tural relationships have been modified by deformation; quartz occurs as angular grains that are connected by sutured grain boundaries (Figure
10). In an attempt to determine what the original grain morphology may have been, a less deformed sample was examined by luminoscope. This re vealed an essentially homogeneous quartz population. This probably in dicates that recrystallization has thoroughly redistributed the original quartz. Minor pods of non-undulous, finely-granular quartz are present which also suggest that appreciable recrystallization has occurred. A small amount of matrix is present; i t .i s now represented by muscovite
(Figure 11).
Age of the Palen Formation
All members of the Palen Formation are unfossiliferous; thus, age
assignment must be based on contact relationships and lithostratigraphic
correlations.
The only direct constraint on the age of the Palen Formation is
based on the intrusive relationship with the Lower Jurassic rhyodacite
porphyry. Regional considerations suggest that the 175 m.y.B.P. K-Ar
age may be too young and that an age of about 190 m.y.B.P., obtained by
U-Pb isotopic analysis of sim ilar rocks, may be more appropriate. The
lower contact of the Palen Formation is not exposed and thus provides no
information. 23
Figure 10. Microphotograph of the Quartzose Arenite of the Palen For mation. — Note sutured grain boundaries. 24
Figure 11. Microphotograph of the Upper Member Showing Development of Micaceous Matrix. — The matrix in the upper member com prises generally less than 10% of the rock in these samples. 25
The quartzite and carbonate clasts of the second member, though lacking unique identifying characteristics that would allow a definite choice of provenance, may have been derived from a cratonal section si milar to that exposed in the Palen Pass area.
The large-scale, high-angle cross-bedded sands of the third mem ber suggest deposition by eolian processes. Aspects of eolian deposits
(such as grain morphology and geometry of set bounding surfaces) which would provide further evidence for eolian deposition have been obscured by deformation. Nonetheless, the preserved characteristics of this unit and relative chronological position (pre-175 m.y.B.P.) suggest correla tion with the Lower Jurassic (Peterson and Pipiringos, 1979) Aztec
Sandstone.a
Therefore the age of the Palen Formation may by loosely con strained to post-Paleozoic and pre-175 m.y.B.P. (Lower Jurassic). Litho- stratigraphic sim ilarity to the Aztec Sandstone suggests a Lower Juras sic age assignment.
Environment of Deposition
Although lim ited data are available because of metamorphism and
deformation, the composition of and the bedding styles displayed by the
Palen Formation allow a partial interpretation of its depositional en vironment. Gradational contacts between a ll three members imply that
sedimentation continued without interruption and that drastic changes in
depositional environments did not occur.
The lower and middle members are compositionally distinct. The
increase in the percentage of quartz and the decrease in the relative 26 abundance of feldspar in the middle meni>er relative to the lower member
continues as a more subtle decrease in the percentage of feldspar within
the upper member. The trends indicate a gradual increase in the compo sitional maturity of the Palen Formation and most likely represent a
change in provenance from volcanic to quartz-rich rock types.
The bedding style of the Palen Formation also changes vertically.
The relative abundance of laminar bedding over cross-bedding and the lack
of coarse detritus or conglomerates in the first member argue against a
fluvial depositional system. These sediments may have been deposited by
turbidity currents (as defined by Walker and Mutti, 1973, p. 119) in a
shallow basin. A pronounced change in the depositional environment is
recorded by the conglomerates of the middle member.
Although paleocurrent data are not available, the contrasting
lithology and composition of the lower and middle members suggests deri
vation from two separate terranes. It is significant that there is a
strong volcanic component in the first member, whereas clasts of volcanic
rock are rare in the middle member. The lack of sorting and the combina
tion of matrix- and clast-supported conglomerates suggests deposition in
some type of alluvial fan environment (Rust, 1980, p. 11, fig. 3). The
interbeds of arkose may represent the remnants of channels that coursed
the alluvial fan surface.
As mentioned earlier, the cross-bedded structures of the upper
member were most likely the product of eolian processes. Although simi
lar structures do occur in continental shelf environments (Flemming,
1978), it is difficult to imagine an environmental sequence from a prob
able alluvial fan environment to a continental shelf setting traversed 27 by large sand waves. The possible correlation of the third member with the Aztec Sandstone suggests that it may have been blown into the area from the north-northeast (Picard, 1975, p. 119). The transitional zone that contains interbedded middle and upper member lithologies represents the decline of alluvial sedimentation concomitant with the encroachment of eolian sands.
The available data therefore suggest that the lower member of the Palen Formation may have been deposited by turbidity currents in a shallow basin. These deposits were succeeded by coarse debris that were very different in composition from the lower member. The lack of sorting and stratification in the conglomerates of the middle member suggest de position within the alluvial fan environment, probably adjacent to the margin of the shallow basin environment proposed for the lower member.
The trough cross-bedded quartzose sands of the upper Palen Formation are
temporally equivalent and physically sim ilar to the Early Jurassic Aztec
Sandstone and may thus represent eolian sedimentation.
Paleogeographic Interpretation
Sedimentation and arc magmatism complexly interacted through
most of the Mesozoic era within the region of southeastern California
and western Arizona. For the most part, a regional stratigraphic column
cannot be constructed due to the highly variable local stratigraphic
s e q u e n c e s .
Sedimentation in the region of southeastern California and west
ern Arizona during the early Mesozoic is represented by lim estones,
shales and siltstones of the Lower Triassic Moenkopi Formation, which 28 crop out in the Soda Mountains (Grose, 1959) and Old Dad Mountains
(Dunne, 1972 in Novitsky-Evans, 1978, p. 31) and possibly in the L ittle
Maria Mountains. East of the Soda Mountains the Moenkopi Formation is overlain by sandstones and conglomerates of the Upper Triassic Shinarump and Chinle Formations and to the west by volcanic flows, conglomerates and volcanielastics of the Soda Mountains Formation, or its suggested equivalent, the informally named lower volcanic unit in the Mojave Des ert (Grose, 1959; Novitsky-Evans, 1978). Both the Soda Mountains Forma tion and the lower volcanic unit occupy a stratigraphic position above the Lower Triassic Moenkopi Formation and below the Lower Jurassic Aztec
Sandstone, suggesting that these volcanic sequences may be Middle to
Late Triassic in age. The prevalence of volcanic strata west of the
Soda Mountains implies that arc volcanism was active in this region dur ing the latter part of the Triassic.
Late Triassic to Early Jurassic volcanism may not have developed synchronously along the axis of the arc. Therefore, sedimentation in the Palen Mountains area may have occurred at the same time that volcan ism was active in the Mojave Desert region. Thus, the lower member of the Palen Formation may represent the erosion of volcanic rocks sim ilar to the Soda Mountains Formation and lower volcanic unit. The lack of volcanic material in the middle and upper members of the Palen Formation suggests that arc activity was quite variable in space and time during
the Early Jurassic in southeastern California and western Arizona.
The association of quartz sandstones and intercalated silicic vol
cani cs is a regional geologic phenomenon (M iller and Carr, 1978; Bilodeau
and Keith, 1981). The close spatial association of the upper member 29 quartzose arenite of the Palen Formation with the rhyodacite porphyry is consistent with the interpretation of Bilodeau and Keith (1981) that a large sand sea existed on the craton behind the Jurassic arc and that a mixing of these different rock types occurred along their common boun dary.
In summary, the Palen Formation probably represents sedimentation synchronous with and prior to the earliest development of the Jurassic
arc terrane in southeastern California. The compositional variation of
the Palen Formation on the local scale and the temporal disparities in
volcanism between this area and the Mojave Desert region suggest that
the development of the Jurassic arc was intermittent in time and space.
The association of quartz sandstones and silicic volcanics in the Palen
Mountains provides a link between sim ilar association to the northwest
in the Mojave Desert and to the southeast in south-central Arizona. STRUCTURAL GEOLOGY
Introduction
The Palen Formation has been intensely deformed. The structural elements present include three types of faults, complex folds and a pen etrative cleavage. All of the structures possess a common fabric that most likely formed at the time of thrusting and metamorphism in the
Palen Pass area. Analysis of the kinematic history suggests that all of the structural elements formed during a single deformational event.
F o ld s
Folds possess complex, tight to isoclinal geometries. Fold axes
plunge to the northwest and have an average axial trend of N57°W and ax
ial planes have an average strike of N71°W and dip of 42°N (Figure 12).
The majority^of the folds are overturned to the south.
These folds are delineated by upright and overturned strata that
are separated by zones of intense cleavage and flattening. Hinge zones ( exhibiting folded layering are rarely exposed. The presence of inverted
bedding is indicated largely by the relationship of cleavage to bedding
(Figure 13) and to a lesser extent on facing as indicated by grading and
cross-bedding.
Internal deformation of individual layers is most pronounced in
overturned strata. This is best exposed in the conglomerates of the mid
dle member (Figure 14) and results in the development of cleavage that is
axial planar to the folds. Offset along cleavage planes is difficult to
discern owing to the lack of marker horizons. Balanced structural
30 31
FA 5N58W FA 40N40W AP N62W.37N AP N87W, 41N
FA 3N62W FA .5N67W AP N66W, 42N AP N66W, 42 N
Figure 12. Equal-area, Lower-hemisphere Plot Showing Orientation of Fold Axes (FA) and Axial Planes (AP) for Major Folds in the P.alen Formation. 32
Figure 13. An Outcrop of Conglomerate of the Middle Member of the Palen Formation. — Bedding dips more steeply than cleavage, indi cating that bedding is overturned. Natural orientation. 33
Figure 14. Well-developed Cleavage in Overturned Conglomerate of Middle Member o f th e P ale n F o rm atio n . — C la s ts a re s tro n g ly f la t te n e d .
4 34
sections (Dahlstrom, 1969) (Figure 15, in pocket) suggest that the
shortening accommodated by folding at depth is inadequate to account for bedding attitudes at the surface. It is likely that additional shorten
ing has taken place by movement along faults and cleavage planes.
Folds are approximately sim ilar (Ramsay, 1967, p. 367) in mor
phology, as shown by an exceptional exposure of a minor fold within the
lower member (Figure 16). These folds are plunging, non-cylindrical
folds that exhibit minor thickening and thinning within individual layers.
Axial planar cleavage is ubiquitous and penetrative on all scales
in these folds (Figure 17). The bedding has been separated by the cleav
age into lath-like blocks approximately 3-4 cm across. Within individual
blocks there are thin 1 cm strips that are also separated by cleavage.
Upon close examination it is also apparent that these strips are sliced
by axial planar cleavage.
Axes of a ll folds are sinuous and are commonly truncated by
transverse faults. In the southeastern part of the map, individual anti
clines and synclines occur on the east side of the high-angle fault that
strikes N45°E and dips 78°NW (Figure 2) but not on the west side of the
fault. The fault thus forms a boundary between "compartments" that have
undergone deformation that has produced non-identical structure. This
style of deformation is also well displayed in the northeastern part of
the study area. Here, a simple anticline was formed on the west side of
a left-lateral transcurrent fault, whereas a complex train of folds was
produced on the opposite side of the fault. 35
Figure 16. Complex Folds in the Lower Member of the Palen Formation in Area of Strong Deformation. — Note minor thickening and thinning of individual layers. 36
Figure 17. Sketch and Close-up Photo of Folds in Figure 16 Showing That Fold Form is Generated by Slip along Closely-spaced Axial Planar Cleavage. — The cleavage is penetrative on all scales. 1, 2 and 3 refer to decreasing magnitudes of slip, respectively. 37
Figure 17, Continued 38
F a u lts
Thrust, strike-slip and reverse faults are present in the study area. Each type of fault w ill be discussed separately.
Thrust Faulting
The Palen Pass thrust is the dominant structural feature in the area. It strikes approximately east-west and dips about 40° north. This thrust places Paleozoic and Mesozoic(?) metasediments over the intrusive porphyry and Palen Formation.
Intensity of deformation is greatest near the fault. On the westernmost side of the map area, adjacent to the thrust, the Palen For mation is isoclinally folded and the arenites of the upper member have been converted to five-grained gray phyllite. Along the thrust in both plates, the rocks are extremely fractured and lack stratification. Along the eastern end of the thrust, the middle and upper members of the Palen
Formation are less strongly deformed and ready identification of upper and lower plate strata can be more clearly made. Here, the fault dips about 20° to the north.
Repetition of both upper and lower plate strata on the northeast quadrant of the map suggest that the fault is imbricated here (Figure 18).
Rocks in the area between the porphyry and the thrust imbrications con sist of both upper- and lower-plate strata that have a strong cleavage parallel to the thrust fault. Additional thrust slices are probably present in this area of poor exposure. 39
Figure 18. Imbrication of the Palen Pass Thrust. — Upper-plate Kaibab Limestone (white) overlies and is imbricated with lower- plate Palen Formation (dark green). View looking west (Cox comb Mountains in distance). 40
Strike-slip Faults
High-angle, oblique-slip faults that are transverse to folds are confined to the east side of the map area. Most of these faults strike approximately north. These faults are marked by pronounced changes in strike and rock type, but not by well-developed gouge zones. These char acteristics are best displayed in the south-central part of the map area where unequal map widths of the middle member are offset along three faults. There are no unique markers, such as lithologic contacts, that can be correlated across the faults in order to restore the complete sec tion. Similarly, a fault on the east side of the map area has a north east strike and dips 65°NW and places upper member strata over conglom erates of the middle member (Figure 19). This appears to be an oblique- slip fault.
This is also probably true for the fault, along the ridge on the
east side of the map, that strikes N45°E and dips 78°W. For orientation
purposes, this fault has a relatively long surface trace and it places middle member conglomerates over the upper member. It separates areas
that have very different structural features. A unique aspect of this
fault is the presence of volcanic porphyry within the fault zone. The
porphyry in the fault zone is sheared and has a cleavage that is parallel
to the fault.
Reverse Faults
Trends of reverse faults closely parallel axes of the folds.
They are best exposed in the southeastern comer of the map (Figure 2). 41
Figure 19. High angle. Oblique-slip Fault on East side of the Palen Mountains Separating Middle Member of the Palen Formation (Left) from Upper Member (Right). — V ertical and horizontal components of slip are indicated on photograph. View look in g w e s t. 42
These faults are best delineated by recognition of abrupt litho logic change. All are found in areas of strongly developed cleavage.
The actual fault zones are strongly brecciated and dip from 40-68° to the north. In the south-central part of the map, a well-exposed example of this type of fault reveals that individual fault planes may be warped
and non-planar (Figure 20). Rocks of the middle and upper members are placed over arenites of the upper member along a fault that dips between
35 and 54° to the north. The lower angle section of the fault is shown
as a thrust. Not only does the fault plane change dip, but its surface
trend is curvilinear. The fault is terminated at both ends by transverse
strike-slip faults.
C leavage
Cleavage is penetrative on all scales. It is axial planar with
respect to folding and changes trend in harmony with fold axes. Stereo
graphic plots reveal that there are three general domains that possess
cleavage of the same orientation (Figure 21). These domains are sepa
rated by strike-slip faults.
All of the members of the Palen Formation as well as the volcan
ic porphyry possess cleavage fabric. The strength of the fabric is not
dependent on lithologies within the Palen Formation, but is directly as
sociated with the folding. Extreme flattening and flow along cleavage
is prominent in the more deformed areas. The more competent clasts in
the second member have developed tension cracks at about 45° to the
cleavage, whereas the carbonate clasts have deformed plastically (Figure
22). 43
Figure 20. Low-angle Reverse/Thrust Fault on Southwest Side of the Northern Palen Mountains. — Fault places middle and upper members of Palen Formation over upper member. The dip of the fault changes magnitude along the structure and the surface trace is curviplanar, suggesting a non-planar fault s u r f a c e . 44
• >10% Q<6% ® > 8 % 0 > 6% n=46
• >7% ©>3% <2>>6 % Q<3% 0 > 4 % n=83
Figure 21. Contoured Lower-hemisphere Equal-area Data for Cleavage in Northern Palen Mountains. — Bottom right-hand comer is synoptic diagram. 45
a) Plastically-deformed carbonate clasts in middle member conglomerate.
b) Brittley-deformed igneous clasts in same member.
Figure 22. Deformed Clasts from Conglomerate of Middle Member 46
Cleavage within the porphyry does not have a consistent orienta tion. The attitudes on the map represent areas that have a strong cleavage fabric of one attitude, although individual outcrops of porphyry w ill often display a number of different cleavage orientations (Figure
23). Along the contact of the porphyry with the Palen Formation, it is common that a cleavage is developed that is parallel to the contact.
Steeply-dipping cleavage that strikes almost north-south is well developed adjacent to some of the transcurrent faults. This cleavage is almost normal to the cleavage described above and is weakly developed in relation to it.
Structural Interpretation
The geometrical relationships and physical style of the structur al features suggests that these structures formed synchronously due to southwest-northeast directed compression. Foremost among the geometrical relationships are folds that terminate at and are modified by transcur
rent strike-slip faults and the parallelism of cleavage, reverse faults,
fold axes and the Palen Pass thrust. The prominent aspects of the struc
tural style that are worth noting are reverse faults whose sense of move ment was southward-vergent and the southward vergence of the major folds, both of which suggest clockwise rotation (looking east) around an east- w e st a x i s .
Chronologically, the folding and transcurrent faulting developed
synchronously and relatively early in the deformation, followed by later
stage reverse faulting and cleavage development. The geometrical rela
tionships of folds and faults are identical to ones produced by . 47
a) Multiple cleavage within the interior of the porphyry.
b) Cleavage developed adjacent to the contact of the porphyry with the Palen Formation.
Figure 23. Two Photos of Cleavage in the Volcanic Porphyry. 48 experimental method (Dubey, 1980). In this set of experiments, folding and faulting occurred simultaneously. Faults act as boundaries to inde pendently deforming compartments that contain different structures yet accommodate equal amounts of strain.
The prominent transverse north-trending fault in the central part of the map separates the two halves of the area into first-order compartments. On either side of this fault, southwest-northeast com pression produced folds and faults that are unique in style and orienta tion to each half of the map area; these structures cannot be traced from east to west across the entire map.
Second-order compartments were formed in the east half of the map area. Here, mostly north-northeasterly striking faults separate com partments that have undergone unique deformations. Folds and reverse faults are terminated at these faults and are modified by them. Also the change of member thicknesses that is shown by the outcrop pattern indicates that different structures formed on either side of these trans current faults (see Figure 24 for comparison.
It is possible that some faulting formed earlier than the thrust ing event. The reverse/transcurrent fault on the east side of the map that strikes N45°W and dips 78°NW provided a conduit for the intrusive volcanic porphyry. As the intrusion of the porphyry occurred prior to thrusting, the fault must have either developed pre- or syn-intrusion.
Later, when the thrust faulting occurred, the rocks on both sides of this fault were deformed, producing non-identical structures.
Cleavage is an additional method by which shortening has been accommodated. As it is penetrative on all scales, it may be best Figure 24. Schematic Drawing of "Compartmental" Deformation. — Total percent shortening for a ll four compartments is the same. Each compartment is separated by transcurrent faults; note that folds and faults are not continuous across these faults (modified from Krantz, 1980).
vo4S 50 termed slaty cleavage (Ramsay, 1967, p. 177). An analysis of the struc ture sections (Figure 15) suggests that movement has occurred along re verse faults parallel to cleavage planes. In fact, the fold morphologies appear to be due to movement along closely spaced axial planar cleavage
(Figure 17). In the most deformed areas, the amount of movement has probably been great; this translation reaches a maximum where reverse faulting has occurred.
Cleavage within the porphyry is the primary way in which this rock has deformed. Cleavage within the volcanic porphyry that is sub parallel to the contact of the porphyry and the Palen Formation may rep
resent a transition zone between these two very differently deforming
rock types. This is represented schematically on the structure sections
(Figure 15). The other areas in the porphyry that exhibit multiple
cleavages probably represent the response of this rock to changing
stresses generated during a progressive deformation.
It has been suggested (Hamilton, personal communication, 1981)
that the Palen Formation lies stratigraphically above, although presently
structurally below, the Kaibab-equivalent limestone of the Palen Pass
area and that the thrust fault postulated in this report is no more than
an overturned contact. This would require that the stratigraphic suc
cession of the Palen Formation discussed in this report as upright is
actually inverted. Indications of stratigraphic order suggested by
cross-bedding and graded beds demonstrate that the section is upright.
Broadly speaking, the gross structure of the Palen Formation is that of
an antiform. Therefore if the Palen Formation was inverted and 51 structurally below the Kaibab Limestone, one would expect to see the first member at this contact, not the third, as is seen in the field.
Conclusive evidence for multiple deformations in this area is lacking. The poorly clustered fabric data do not fall into significant groups and is probably due to the interaction of the faults, and folds as discussed above. If this area has undergone more than one deformational event, the fabrics have been overwhelmed by the thrust faulting and re lated deformation in the Palen Formation.
Direct evidence only provides a minimum age of deformation.
Homblende-biotite and more felsic granites that intrude all of the map units have been dated at about 66 m.y. (K-Ar, biotite) (Pelka, 1973, p.
120). These rocks do not possess the structural fabric of the Palen
F orm ation.
It is more difficult to place a maximum age on the faulting and folding. The orientation and style of folding displayed by the Paleozoic rocks in Palen Pass is identical to that seen in the Little and Big Maria
Mountains to the east (Demeree, personal communication, 1981). In the
Big Maria Mountains these folds were syntectonically intruded by a por- phyritic granodiorite that has been dated at about 90-100 m.y. (Rb-Sr)
(Ellis and others, 1981; E llis, personal communication, 1981). A pos sibly correlative rock is present within the Palen Pass area and it too has a foliation that is subparallel to the thrust fault (Howard, per sonal communication, 1981). The folds in the Big Maria Mountains that are identical to those in Palen Pass are cut by 90 m.y. old pegmatites
(Rb-Sr) (Krummenacher, personal communication, 1981). If the inference is correct, that the folding of the Paleozoic strata occurred 52 simultaneously with the thrust faulting in Palen Pass, it would then be appropriate to assign an early Late Cretaceous age to the deformation in the study area. This is supported by the fact that all of the fabric elements from the folds in the L ittle and Big Maria and northern Palen
Mountains are coincident (Demaree, personal communication, 1981). CONCLUSIONS
The Palen Formation is a sequence of lithofeldspathic arenite, polymictic conglomerate and quartzose arenite that, so far as is pres ently known, occurs only in the northern Palen Mountains of southeastern
California. It is intruded by a rhyodacite porphyry that has a minimum age of 175 m.y.B.P. and a possible age of about 190 m.y.B.P. Suggested
correlation of the upper member of the Palen Formation with the Aztec
Sandstone, based on lithostratigraphic sim ilatiry and possible temporal equivalence, implies that the age of the Palen Formation is Early
J u r a s s ic .
Compositional maturity increases upward in the Palen Formation.
Detritus in the lower member is largely volcanic in composition and is
succeeded, in the middle member, by more quartzose and potassium-rich
detritus. This suggests that the lower member was of volcanic provenance
and that the middle and upper members were derived from a more cratonic
s o u r c e .
Variations in bedding characteristics also suggest changing depo-
sitional environments. Plane-laminated and shallowly cross-bedded sands
in the lower part of the Palen Formation are succeeded by conglomerates
and eolian(?) sands in the middle and upper parts. Available data sug
gest a transition from shallow-marine to subaerial environments of depo
sition. These inferences suggest that deposition occurred behind (cra-
tonward) or within a magmatic arc of Triassic and/or Early Jurassic age.
53 54
Intense deformation of the Palen Formation accompanied southward translation of upper plate Paleozoic and Mesozoic(?) metasedimentary rocks along a low to moderate north-dipping thrust fault. Structures in the Palen Formation include tight to isoclinal folds, penetrative cleav age and high-angle oblique-slip faults. Deformation is inhomogeneous across the study area. This is reflected by folds whose axes are sinuous and are truncated by transcurrent oblique-slip faults. The faults sepa rated the study area into discrete "compartments" in which strain was
accommodated by unique structures that are non-identical for each
compartment.
A comparison of fold fabrics in both the upper and lower plates of the Palen Pass thrust with those in the L ittle Maria and Big Maria
Mountains to the east suggest that deformation in both areas occurred
prior to 90 m.y.B.P. and may have been synchronous with syn-kinematic
igneous rocks intruded about 100 m.y.B.P. ago.
The lithology and suggested age of the Palen Formation suggests
that the development of the Early Jurassic magmatic arc in southeastern
California was punctuated in time and space. Volcanic rocks of presumed
Middle-Late Triassic age in the Mojave Desert suggest that arc activity
began in this area earlier than the bulk of the Early Jurassic magmatic
arc. The close apatial association of quartz sandstones of the upper
member of the Palen Formation with the intrusive volcanic porphyry pro
vides a link with sim ilar associations to the northwest in the Mojave
Desert and to the southeast in south-central Arizona. REFERENCES CITED
Anderson, T. H. and Silver, L. T ., 1978, Jurassic magmatism in Sonora, Mexico: Geol. Soc. America, Abst. w/Programs, v. 10, no. 7, p. 359.
Bilodeau, W. L. and Keith, S. B ., 1981, Intercalated volcanics and eolian "Aztec-Navajo-Like" sandstones in southeast Arizona: another clue to the Jurassic-Triassic paleotectonic puzzle of the south western U. S .: Geol. Soc. America, Cordilleran Sec. Field Trip Guide, no. 12, p. 93-111.
Bishop, C. C., 1963, Geologic map of California, Needles Sheet: Calif. Div. Mines & Geol.
Burchfiel, B. C. and Davis, G. A., 1981, Mojave Desert and environs, in The Geotectonic Development of California, Ernst, W. G. (ed .): Prentice-Hall Pub., p. 217-252.
Carr, W. I. and Dickey, D. D., 1980, Geologic map of the Vidal, California and Parker SW Califomia-Arizona Quadrangles: U. S. Geol. Sur vey Misc. Invest. Map 1-1125.
Crook, K.A.W., 1960, Glassification of arenites: Am. Jour. S ci., v. 258, p. 419-428.
Crowell, J. C., 1981, An outline of the tectonic history of southeastern California, in The Geotectonic Development of California, Ernst, W. G. (ed.): Prentice-Hall Pub., p. 583-600.
Growl, W. J ., 1979, Geology of the central Dome Rock Mountains, Yuma County, Arizona: M.S. Thesis, University of Arizona, Tucson, 74 p .
Dahlstrom, C.D.A., 1969, Balanced cross sections: Can. Jour. Earth S ci., v. 6, p. 743-757.
Demaree, R. G., 1981, Geology of Palen Pass, Riverside County, California: M.S. Thesis, San" Diego St. Univ., San Diego, 136 p.
______, 1981, Personal communication, San Diego State University, San D ieg o .
Dubey, A. K., 1980, Model experiments showing simultaneous development of folds and transcurrent faults: Tectonophysics, v. 65, p. 6 9 -8 4 .
55 56
Ehlig, P. E., 1981, Origin and tectonic history of the basement terrane of the San Gabriel Mountains, west central Transverse Ranges, iji The Geotectonic Development of California, Ernst, W. G. (ed.): Prentice-Hall Pub., p. 253-283.
E llis, M. J ., 1981, Personal communication, San Diego State University, San D ieg o .
, E llis, M. J., Frost, E. G. and Krummenacher, D., 1981, Structural analy sis of multiple deformational events in the Big Maria Mountains, Riverside County, California: Geol. Soc. America, Abst. w/Pro- grams, v. 13, no. 2, p. 54.
Emerson, W. S. and Krummenacher, D., 1981, Geological and deformational characteristics of the L ittle Maria Mountains, Riverside County, California: Geol. Soc. America, Abst. w/Programs, v. 13, no. 2, p . 6 4 .
Flemming, B. W., 1978, Underwater, sand dunes along the southeast African continental margin: Marine Geology, no. 26, p. 177-198.
Grose, L. T., 1959, Structure and petrology of the northeast part of the Soda Mountains, San Bernardino County, California: Geol. Soc. America B ull., v. 70, p. 1509.
Hamilton, W., 1971, Tectonic framework of southeastern California: Geol. Soc. America, Abst. w/Programs, v. 3, no. , p. 130.
______, 1981, Personal communication, U. S. Geol. Survey, Denver.
Harding, L. E., 1978, Petrology and tectonic setting of the Livingston H ills Formation, Yuma County, Arizona: M.S. Thesis, University of Arizona, Tucson, 57 p.
Haxel, G., May, D. J. , Wright, J. E., and Tosdal, R. M., 1980, Reconnais sance geology of the Mesozoic and lower Cenozoic rocks of the southern Papago Indian Reservation, Arizona: a preliminary re port: Ariz. Geol. Soc. Digest, v. 12, p. 17-30.
Hoppin, R. A., 1951, The geology of the Palen Mountains gypsum deposit. Riverside County, California: Ph.D. Thesis, Cal. Inst. Tech., p . 9 1 .
Howard, K. A., 1981, Personal communication, U. S. Geol. Survey, Menlo Park, California.
______, 1981, Mesozoic framework of the southeastern Mojave Desert re gion, California: Geol. Soc. America, Abst. w/Programs, v. 13, no. 2, p. 62. 57
Krantz, R., 1980, Geology of the Museum Embayment, Tucson Mountains, Tucson, Arizona: Unpublished manuscript.
Marshak, R. S ., 1979, A reconnaissance of Mesozoic strata in northern Yuma County, southwestern Arizona: M.S. Thesis, University of Arizona, Tucson, 110 p.
M iller, E. L. and Carr, M. D., 1978, Recognition of possible Aztec- equivalent sandstones and associated Mesozoic metasedimentary deposits with the Mesozoic magmatic arc in the southwestern Mo jave Desert, California, in Howell, D. G. and McDougall, K. A. (eds.), Mesozoic paleogeography of the western United States, Pac. Coast Paleogeog. Symp. 2: Soc. Econ. Paleon. M ineral., Pac. Sec., p. 283-289.
M iller, F. K., 1970, Geologic map of the Quartzite quadrangle, Yuma County, Arizona: U. S. Geol. Survey Quad. Map, GQ-841.
M iller, W. J ., 1944, Geology of Palm Springs-Blythe strip, Riverside County, California: Calif. Jour. Mines & Geol., v. 40, p. 12-70.
Novitsky-Evans, J. M., 1978, Geology of the Cowhole Mountains: struc tural, petrologic and geochemical studies: Ph.D. Thesis, Rice University, Houston, Texas, 128 p.
Pelka, G. J ., 1973, Geology of the McCoy and Palen Mountains, southeast ern California: Ph.D. Thesis, University of California at Santa Barbara, 162 p.
Peterson, F. and Pipiringos, G. N., 1979, Stratigraphic relations of the Navajo sandstone to Middle Jurassic formations, southern Utah and northern Arizona: U. S. Geol. Survey Prof. Paper 1035-B, 43 p .
Picard, M. D., 1975, Facies, petrography and petroleum potential of Nug get Sandstone (Jurassic), southwestern Wyoming and northeastern Utah: Rocky Mtn. Assoc. Geol., Symp. on Deep Drilling Frontiers, p. 109-128.
Powell, R. E. and Silver, L. T., 1978, Crystalline rocks of a portion of the eastern Transverse Ranges, Riverside County, California: Geol. Soc. America, Abst. w/Programs, v. 10, no. 3, p. 142.
______, 1979, Tectonic superposition of crystalline terranes in the Chuckwalla to Pinto Mountains region, eastern Transverse Ranges, southern California: Geol. Soc. America, Abst. w/Programs, v. 11, no. 7, p. 498.
Ramsay, J. G., 1967, Folding and Fracturing of Rocks: McGraw-Hill Book Co., 568 p. 58
Reynolds, S. J ., 1980, Geologic framework of west-central Arizona: Ariz. Geol. Soc. Digest, v. 12, p. 1-16.
Robison, B. A., 1979, Stratigraphy and petrology of some Mesozoic rocks in western Arizona: M.S. Thesis, University of Arizona, Tucson, 138 p .
Rust, B. R., 1980, Coarse alluvial deposits, in Facies Models, Walker, R. (ed.): Geol. Assoc. Canada, p. 9-22.
Silver, L. T., 1971, Problems of crystalline rocks of the Transverse Ranges: Geol. Soc. America, Abst. w/Programs, v. 3, no. ,, p. 193-194.
Stone, P. and Howard, K. A., 1979, Paleozoic metasedimentary rocks in the eastern Mojave Desert, California: Geol. Soc. America, Abst. w/Programs, v. 11, no. 3, p. 130.
Walker, R. G. and Mutti, E., 1973, Trubidite facies and facies associa tions, in Turbidites and deep water sedimentation: Soc. Expl. Paleon. Mineral., Short Course Notes, p. 119-158.
Wright, J. E., Haxel, G. and May, D. J ., 1981, Early Jurassic uranium- lead isotopic ages for Mesozoic supracrustal sequences, Papago Indian Reservation, southern Arizona: Geol. Soc. America, Abst. w/Programs, v. 13, no. 2, p. 115. s.f f t 5 9 ^ 331 Alluvium
2000 - [ Kgl Cretaceous granite 1 5 0 0 - [jvp] Jurassic volcanic porphyry
1000 - [JPl] Upper
| Jpt | Middle Jurassic Palen Formation
\ \ \ , ^ [ j p ] Lower
P 1 Paleozoic, undivided
3 0 0 0 -
2 5 0 0 -
2000 -
1 5 0 0 - V \ v
1000 -
LEVEQUB , M-5. TUE5I5, Geos^teNCES, l^ftl
Figure 15. Schematic Structural Sections. — Surface bedding attitudes were used to construct the fold form at the surface. These folds cannot continue with depth without modification and so thrust and reverse faults and layer thickening were drawn to portray additional methods by which shortening occurred. See Dahlstrom (1969) for an explanation of the methods employed. The S pattern along the contact of the volcanic porphyry is a schematic representation of movement that occurred along this contact during deformation.
FIGURE 2 EXPLANATION
O Alluvium - includes talus and stream deposits; O unconsolidated surface debris N O Z TIs Landslide unit - consists of angular clasts of UJ Jpg and Jp3 in mud matrix; clasts as large O as 5M in size Granite - includes two phases; I) porphyritic H LU IT quartz monzonite and 2) leucocratic quartz O monzonite; K-Ar age of 66 my (Pelka,l973)
Jip Intrusive porphyry- hypabyssal rhyodacite porphyry consisting of light gray aphanitic groundmass with phenocrysts of feldspar O CO and quartz; K-Ar age of 176 my(Pelka,1973) (/) < cr 4j JP3 'Upper member - tan, vitreous feldspathic to 3 quartzose arenite; prominent high-angle o trough crossbeds o N Jpu Jpg Middle member - light ton to green polymictic O CO o conglomerate ; includes clasts of quartzite, LU E X- carbonate and leucogranite; minor interbeds £ of arkose c QJ J p i o Lower member -medium to olive green litho- CL feldspathic arenite; consist of angular plag- ioclase feldspar in matrix of epidote,chlor O O a te and green biotite N FAULT O Paleozoic rocks undivided- includes prob LU _ l able Supai Formation, Coconino Sandstone, < CL Kaibab Limestone and unnamed gypsiferous schists (possibly Mesozoic)
CONTACTS \ Dashed where uncertain gradational FAULTS
Thrust faults;dashed where uncertain 78 u
High-angle faults showing dip and relative movement (U on upthrown side); dashed where uncertain ■ FOLDS
4 - —i— -ft- ' t i - Axial trace of plunging anticline, syncline,overturned syncline and anticline shewing plunge of fold axis BEDDING
f -
Strike and dip of bedding: inclined, overturned and vertical ea CLEAVAGE 90 — A— — fy— Strike and dip of inclined and vertical cleavage
SCALE
FEET
1000 500 1000 2000 3000 i . « ___ i GEOLOGIC MAP OF THE NORTHERN PALEN MOUNTAINS 21 0 100 400 800 METERS by 1:12000 ______Richard A. LeVeaue ______Geology mapped Jon.-March 1981. LE VEQUE.M.S. THESIS, GEOSCIENCES, 1981