The Geology of the N.A.S.A. Arizona Sedimentary Test Site Mohave Co

The Geology of the N.A.S.A. Arizona Sedimentary Test Site

Mohave Co. Arizona

A thesis submitted in partial fulfillment of the

requirements for the degree of Master of

Science in Geology

by

Peter Anderson Brennan

University of Nevada

Reno. Nevada

June 1968 The thesis of Peter Anderson Brennan is Approved

Dept. Chairman

Dean, Graduate School

University of Nevada

Reno

June 1968 a b s t r a c t

The NASA Fundamental Sedimentary Test Site in northern

Mohave County, Arizona contains exposures of limestone, sandstone,

conglomerate and thin layers of basalt.

Structurally, the area consists of southeasterly dipping

rock units transversed by a series of minor high angle faults,

and a major low angle normal fault. The structure is complicated

by drag folding along some of the faults, and minor changes in

the direction and amount of the regional dip. The Tertiary and

Quarternary units are superimposed unconformably over the faulted

and tilted upper Paleozoic rocks.

The topography is moderate, much of the site being in a

broad flat valley. Because of the arid weathering conditions

large detrital fans have been developed in the valleys. These

fans support typical high desert vegetation.

Remote sensing aircraft flights have yielded photographs,

imagery and sensor data which, with detailed ground information provides an almost unique area in which to study the possible contributions of remote sensing to geology. Radar ultraviolet, photographic infrared, thermal infrared, microwave radiometry and scatterometry are available for the site.

A comparative analysis between each of the sensing systems and the classical geologic study shows subtle peculiarities of each system giving data not otherwise available, except by careful field and laboratory studies. By integrating the various systems, details have been added and corrections made to the existing geologic interpretations. Two systems, the radar and the thermal infrared have been completely evaluated and are in- cluded.

The degree of development of remote sensing instruments is not such that geologic mapping can be done from airborne data alone. In this study the remote sensors have provided valuable supplementary information and confirmed much of the geologic mapping. This study should enable future geology in similar areas to be done using remotely sensed data as a back­ bone, reducing field time by as much as 50 percent. TABLE OF CONTENTS A B S T R A C T ......

INTRODUCTION ...... 1

Previous W o r k ...... _ 4

Geologic S e tt in g...... 5

Remote Sensor Data ...... 7

STRATIGRAPHY ...... g

Pennsylvanian System ...... 9

Callvilie Limestone ...... 9

Permian System ...... 12

Hermit Formation ...... 12

Coconino Sandstone ...... 19

Pre-Kaibab Unconformity ...... 26

Kaibab Limestone ...... 27

Post-Kaibab Unconformity ...... 32

Cottonwood Wash Formation ...... 34

Triassic Jurassic, and Cretaceous Systems . . . 44

Tertiary System...... 46

Muddy Creek Formation...... 47

Clastic M e m b e r ...... 47

Fortification Basalt ...... 50

Quaternary Alluvium ...... 58

STRUCTURE...... 60

General Structure ...... 60

Western Boundary Fault ...... 60

Strike Slip Faults

v Jointing...... 53

GEOLOGIC HISTORY ...... 65

APPENDIX I — RADAR IMAGERY...... 70

APPENDIX II - INFRAREDIMAGERY ...... 80

R E F E R E N C E S ...... 91

vi TABLE OF FIGURES

Figure Page

1 Index m a p ...... 2

2 Index m a p ...... 3

3 Flight lines ...... 6

4 Formation names ...... 8

5 Callville Limestone ...... 10

6 Hermit Formation ...... 14

7 Hermit grain size distribution ...... 16

8 Coconino Sandstone ...... 22

9 Coconino Sandstone ...... 22

10 Coconino grain size distribution .... 24

11 Kaibab Limestone...... 29

12 Basal "Cottonwood Wash" unconformity . . 33

13 Air view of "Cottonwood W a s h " .... 35

14 "Cottonwood W a s h " ...... 35

15 "Cottonwood Wash" conglomerate ...... 37

16 "Cottonwood Wash" limestone ...... 41

17 Muddy Creek conglomerate ...... 48

18 Muddy Creek metamorphic boulders .... 48

19 Muddy Creek grain size distribution . . . 49

20 Air view of basalt f l o w s ...... 51

21 Basalt flows ...... 51

22 Basalt flows ...... 54

23 Surface of basalt f l o w ...... 54

24 Or-An-Ab triangular diagram ...... 57

vii 25 Structure contour m a p ...... 62

26 Rose diagrams and strain relationships. 64

27 Paleozoic carbonate sequence ...... 66

28 Horizontal radar returns ...... 78

29 Vertical radar returns ...... 79

30 Infrared temperature correlation chart. 87

31 Infrared imagery...... 89

32 Infrared imagery...... 90

viii TABLE OF TABLES

TABLE 1 Section of Hermit Formation...... 17

TABLE 2 Hermit grain s i z e ...... ; 19

TABLE 3 Section of Coconino Sandstone...... 23

TABLE 4 Section of Kaibab Limestone...... 30

TABLE 5 Chemical analyses of lithic sands . . . 39

TABLE 6 Section of "Cottonwood Wash" limestone. 40

TABLE 7 Mineral composition of b a s a l t ...... 52

TABLE 8 Chemical variation of basalt...... 55

TABLE 9 Experimental iron ratios of basalts . . 55

TABLE 10 Radar returns ...... 73

TABLE 11 Infrared temperatures...... 86

IX 1

INTRODUCTION

The purpose of the geologic study is to provide calibration for

instruments with potential value in the locating and mapping of earth

resources. The geology required for the interpretation of the output

of airborne and potential satellite instruments goes beyond standard

geologic mapping. Because of the pecularities of the sensors, aspects

of soil, vegetation, weathering characteristics, surface texture and

any other parameters which differentiate rock units must be studied.

The NASA Fundamental Test Site for sedimentary rocks is located

in extreme northwestern (Mohave County) Arizona, centered approxi­

mately 30° 37' N, 113° 571 W, and is oriented N-S. The 1 x 10 mile

site is most easily accessible from Mesquite, Nevada, a distance of

17 miles over unsurfaced roads. This area was chosen for the variety

of sedimentary lithologies which are readily distinguished from the

air by both color and topographic expression. The terrain has moder­

ately low relief with only one escarpment exceeding 430 feet; the

average elevation is approximately 3900 feet. Major adjacent topo­ graphic features should facilitate identification of the area from extreme altitudes.

In this arid region where rainfall amounts to only a few inches per year, no bodies of water exist on the site. Lake Mead, 40 miles south, provides a large stable body of water which may be used for sensor calibration. 0 25 40 Kilometers

SCALE

Figure 1 . Index Map of Cane Springs area, Arizona.

2

PREVIOUS WORK

Topographic coverage is supplied by the 15' Cane Springs

(Arizona) quadrangle map. The southern half of the area is covered in more detail by the Ik' Littlefield SW quadrangle.

The AMS 1:250,000 sheet for the Grand Canyon provides a large scale map of most of Mohave County.

Two geologic maps have been published. The first is a reconnaissance map by Darton (1924), at a scale of 1:500,000, the second is a county map by the Arizona Bureau of Mines (1959) at a scale of 1:375,000. Both maps have their limitations;

Darton concerned himself with bedrock and does not give adequately detailed information regarding the alluvial cover. The 1959 map is difficult to reconcile with the bedrock configuration. A revision of the Arizona Bureau of Mines map of Mohave county is now being compiled.

4 GEOLOGIC SETTING

The Virgin and Beaver Dam Mountains form a transition

zone between the Colorado Plateau and the Basin and Range

Provinces. To the west, the typical Basin and Range topography

of North-trending faulted mountains and alluvium-filled valleys

extend across southern Nevada and into California. To the east,

a series of north-south trending stop faults and long low mesas

slowly bring the land up to the level of the Colorado Plateau.

To the east the Grand Wash Fault, Hurricane Fault, and a series

of smaller faults expose Mesozoic rocks and increase the general

elevation to more than 5000 feet. These flat-lying Mesozoic

sediments are best seen in Zion National Park.

Immediately to the east of the sedimentary test site, a

series of thin, dissected basalt flows top flat mesas extending

to the Hurricane Cliffs on the east and Lake Mead on the south.

These flows are uniform sheets that issued passively from fissures.

On the east flank of the Virgin Mountains the rocks dip southeast away from the mountain core. At the north end of the site, beds dip 40° SE; at the center of the site they dip

20° ESE; further south they dip 15° ESE, and at the south end, flat-lying lavas cover the older sedimentary units.

The faulting in the area, though complex, does not greatly disturb the normal sequence of beds except at the north end of the site where the upper Permian lies between the Pennsylvanian and lower Permian section, as a result of two faults of large displacement.

5 r i y u r u o FLIGHT LINES AND STATIONS FOR MISSIONS 4 4 AND 59

6 REMOTE SENSOR DATA

The geological study of the Arizona Sedimentary Test Site

is largely the result of classical ground based geological

investigation. Subsequent to the bulk of the mapping and

sampling, two multisensor aircraft missions were flown over the

site. Three of the mapping systems, the side looking radar, the

thermal infrared (8-14 y) and the high resolution metric cameras

using color infrared film have provided valuable tools in prep­

aration of tne geologic map, delineation of large scale structures

and division of geologic units. A fourth imaging system, the near

ultraviolet imager, was of such poor quality that it could not

be used. Two nonimaging systems, the radar scatterometer and

four channel multispectral microwave radiometers show considerable

promise, but their successful interpretation requires further

research.

Our current knowledge of the interpretation of remotely

sensed data does not allow us to map from aircraft, but the sensors

do serve to enhance, subdivide, clarify and confirm the geology

of ground based investigations. If the three, above mentioned,

easily used, sensor systems had been available at the outset of

geologic investigations at this site 25% of the field time might have been saved. If all of the systems had been available in map format the entire study might have been done by one or two men in a week, at which time field checking, assignment of formation and member names and investigation of anomlies would have been the major task.

7 CORRELATION OF LITHOLOGIC UNITS

Grand Canyon Pakoon Springs Clark Co., Nev. Virgin Mtns. Virgin Mtns. Noble (1921) McNair (1951) Longwell (1965) Moore (1966) This Paper

-

Muddy Creek Muddy Creek Muddy Creek Tertiary O 0-2000' 0-500' 0-600' o M O Horse Springs LU O 0-4000'

Baseline 0-300' Cretaceous Willow Tank "Cottonwood Wash" 0-3500' 1400' i CO O >— i Aztec Navajo o Jurassic M 2000'-2500' 2500' OOO LU

*ChinIe - *Chinle *Chinle 1500' Triassic 740'-3300' Moenkopi 481' Moenkopi Moenkopi 1600' Moenkopi 1220-1630' "Cottonwood Wash" 0-700' S — , .

Kaibab 562' Kaibab+Toroweap Kaibab+Toroweap Kaibab 750' ' Kaibab 735' Permian 756' 200-600' . Coconino 330' Coconino 122' Coconino 0-100' Upper Coconino 39' i— ( Hermit 332' Hermit 710' Redbeds 1400' Hermit 0-400' O Lower Coconino 1350 hvj Queantoweap 400' Supai 800-1250' O Hermit 383' LU J c cL Supai 953' Pakoon+Cal1vil1e Call vi He 1500' Callville 1350' Callville 1000+' Pennsylvanian 1361'

includes Shlnarump member STRATIGRAPHY

The stratigraphic sequence exposed along the ten mile test strip

includes faulted and tilted blocks ranging in age from Pennsylvanian

to Permo-Triassic, capped in places by a flat lying late Tertiary

rock and partially covered with Quaternary alluvium. The Paleozoic

units consist almost exclusively of carbonates and aeolian sandstones.

The Cenozoic rocks include fluvatile sand and gravels, capped by

Pliocene olivine basalts.

PENNSYLVANIAN SYSTEM

Callville Limestone

The name Callville Limestone was first proposed by C. R. Longwell

(1921) for more than 1100 feet of predominantly dark limestone of Penn­

sylvanian age in the Muddy Mountains 50 miles southwest of the test site.

Uppermost Mississippian fossils (?) were later identified near the base

of the Callville near its type locality. Longwell comments that an

indeterminate thickness has been eroded from the top of the section in

the Muddy Mountains. He recognized similar limestones in the Virgin

Mountains and Pennsylvanian limestones at Grand Wash Cliffs which did not lithologically resemble the Callville at its type locality.

McNair (1951) described an upward extension of the Callville Lime­ stone containing Wolfcampian fusulinids at Pakoon Springs, 12 miles south of the test site. Because of its Permian age, he has divided it from the lithologically similar Callville Limestone, and called it the

Pakoon Formation. At its type locality, there are 688 feet of tan to grey, dolomitic, thinly bedded limestone assigned to the Pakoon Formation.

McNair also recognized 305-1/2 feet of Pakoon Limestone at an area along North Grand Wash Cliffs. Welch (1959) reported 630 feet of Lower

9 Figure 5 Callville Limestone north of the test site. Light colored beds at the left of the photograph and in the foreground are pink fine grained sandstones. The lower beds are mostly grey to black limestones. Several small reverse faults cut across bedding near the center of the photograph. Photograph taken looking northwest and the beds are dipping approximately 45° to the southeast. Permian limestone at Hen Springs, 10 miles to the west, which he called

Pakoon. The Callvilie sections described by McNair at Pakoon Ridge

(6731), North Grand Wash Cliffs (5181) and Hurricane Cliffs (277-1 /21)

all contain well sorted pink cross-bedded sandstones and sandy lime­

stones not mentioned by Longwell at the type locality. Bissell (1963)

also mentions calcareious sandstones, orthoquartzites and sandy lime­

stones in a 1085 foot Callvilie section from the East-Central Beaver

Dam Mountains.

The probable Callville outcrops lie along a brecciated zone

at the northwest corner of the ten mile long test strip. The outcrop

is cut along three sides by faults of large displacement and further

complicated by a series of low angle thrusts of small displacement.

The stratigraphic position of the beds is seen only at a point two

miles north of the north end of the flight lines, where the Callville (?)

is seen resting on the Mississippian Redwall Limestone. No identifiable

fossils were recovered from the section, nor has any good estimate of

its thickness been made. The resistant, pink, finely cross-bedded

sandstones at least 100 feet thick cap'all of the exposures on the

test site. To the northeast, the Callville formation is composed

primarily of grey to black limestones. A sequence of Pennsylvanian

and Permian (?) at least 1000 feet thick caps a large Middle and Lower

Paleozoic section just west of the test site. The thick sequence, stratigraphically below Permian red-beds and above Mississippian lime­ stones, is composed of pick sandstones and grey to black limestone lithologically similar to those at the north end of'the site.

11 PERMIAN SYSTEM

In Northern Arizona the Permian System contains two major

lithologic subdivisions, the upper carbonate sequence and the lower

red-bed sequence. The upper sequence is predominantly limestone

and dolomite, but contains some massive gypsum units. These

easily identified, resistant units are divided into the Toroweap

and Kaibab formations. The lower terrestrial red-bed sequences are

typified by rapid changes in lithology and thickness with no

widespread marker horizons or disgnostic fossils. These red-beds are

here referred to as the' Hermit Formation and the Coconino Sandstone.

They have been so designated on the basis of their stratigraphic posi­

tion, age, lithology and mode of deposition. The Pennsylvanian and

Permian age red-beds in Southern Utah, Northern Arizona and Southern

Nevada have caused a naming problem. Since terrestrial, lacustrine

and deltaic sediments can rapidly change color, thickness and lithology,

and since these particular sediments contain fossils only rarely and

are time transgressant, assignment of formation names which are consist- ant with characteristics noted at the type localities is often difficult.

It has been necessary in this paper to extend the use of one formation name, the Coconino Sandstone, to include sediments not usually placed under it. 1350 feet of fine grained rust colored aeolian sandstone have been included within the Coconino. They have almost the same age, the same lithology and an identical mode of deposition as the thin buff sandstone bed which lies conformably above them, and to which the name

Coconino is usually restricted. Four other formation names applying to the red-bed sequence in the region, Queantoweap, Hermit, Supai and

12 upper Callville, are not applicable because of inconsistencies of age,

stratigraphic position, lithology or mode of deposition.

Hermit Formation

The basal unit of the Permian red-bed section in the mapping

area is referred to as the Hermit Formation. The unit, because of its

thin bedding, graded-bedding and lack of cross-bedding is judged to

be marine. It lies above the Wolfcampian Pakoon (?) formation in areas

adjacent to the test site, although the contact is absent due to

faulting, and the Pakoon is not present on the test site. Similarly

it lies below the Leonardian Coconino and Kaibab formations. This

places its age as lower Permian. Lithologically it is most similar to

the Hermit formation and the Supai formation as described at their type

localities, however, as originally defined the Supai is restricted to the Pennsylvanian. Therefore, the name Hermit has been applied to these beds.

Noble (1922) proposed the name Hermit for a series of deep-red sandstones and siltstones in the Grand Canyon at Bass Trail. They lie above the Pennsylvanian Supai formation and below the Permian Coco­ nino Sandstone at their type locality. Terrestrial fossils collected by Noble have been identified as wholly Permian in age, and he has speculated that an unconformity occasionally seen at the base of the

Hermit may be the Pennsylvanian - Permian boundary, though the bound­ ary might also fall in the undated uppermost beds of the underlying

Supai formation. Noble's sections in the Grand Canyon vary in thick­ ness between 267 and 332 feet. His section (after Walcott) in Kanab

Canyon, 30 miles north of the Grand Canyon measures 775 feet.

13

Bissel1 (1963) calls 1000 feet of red fine grained sandstone

near Frenchman's Mountain Hermit. McNair (1951) published three

measured sections; 698-1/2 feet at North Grand Wash Cliffs, 710-1/2

feet in the North Virgin Mountains, and 933 feet at Hurricane Cliffs.

In the test area several hundred feet of brick-red sandstone and

siltstones appear at the base of the exposed Permian red-bed section.

Beal (1965) also comments on the presence of these beds in the

Bunkerville mining district a few miles west of the test site. In

the Bunkervi11e district they lie above the Permian Pakoon formation.

On the test site the lower portion of these beds is not exposed and

their lower contact is faulted, so their exact stratigraphic position

with regard to the underlying Paleozoic units cannot be checked. To

the west, near the Arizona-Nevada state line, these beds are present

above the undifferentiated Cal 1ville-Pakoon sequence. Just north of

the site they cannot be seen, but complex faulting in the area may

account for their absence.

At the point of best exposure the Hermit may be divided into

three lithologic members. The uppermost, is a siightly-crossbedded,

calcareously-cemented, pink, arkosic, sandstone. This unit forms

resistant ridges. The middle member is a brick-red, sandy siltstone,

which shows very faint parallel bedding, but no crossbedding. The

lower unit is composed of red siltstones and cream micaceous sands.

The upper and middle units retain their autonomy ten miles to the

southwest, where they are cut off by a large high angle fault. The

upper unit because of its resistance may be seen several miles to the

northeast protruding intermittently from the alluvium. The brick-red soils derived from the middle unit are also seen to the northeast for a distance of more than five miles, but good outcrops are lacking.

15 weight percentage 20 30- 40- 10 5 0 0 - - - - aeae f or samples four of average x RI SZ DISTRIBUTION SIZE GRAIN imtr n millimeters in diameter EMT FORMATION HERMIT 1 .2 .09 .12 .17 FIGURE 7 Six miles beyond the southern boundary of the area a series of similar

looking brick-red beds occur, but, because of faulting their strati­

graphic position is not known.

At the only good exposure on the test site, a total of 383' of

beds assigned to the Hermit were measured, though the formation's lower

contact was obscured.

TABLE 1

SECTION OF HERMIT FORMATION FOUR MILES NORTH OF CENTER OF TEST SITE

(4) Sandstone, deep .redish-pink, pi soli tic, slightly corss- bedded. Ripple marks may be found on a few surfaces. The unit is moderately bedded and breaks off in plates from a very few inches to several feet thick. This sandstone is very hard and resistant and forms a prominent ridge...... 200'

(3) Sandstone, silty, very fine grained, brick-red, thin to massive bedded. The bed appears to be very homogeneous, soft and does not crop out except in stream cuts and sheltered areas...... 175'

(2) Sandstone, cream-colored, crumbly, very fine grained, biotite bearing...... 31

(1) Sandstone, sameas bed 3 ...... 5' +

Total thickness of Hermit...... 383' +

The pisolites in bed four are due to small, up to 1cm in diameter, very hard concentrations of carbonate cement. They are well developed at the location where the above section was measured but become in­ distinct four miles to the southwest, and are not present further south or at a point two miles north of the measured section. At the two nonpisolitic localities the bed is lighter pink, but is still very hard and forms a prominent ledge.

17 One of the lower brick-red beds, probably bed 1, contains a

small amount of fiberous gypsum in an exposure just north of the Lime­

kiln Mine. There it assumes a purple, to brown, to brick-red mottled

color.

Because of the rapidly changing character of the sediments and

the softness of the lower Hermit beds, the formation is extremely hard

to trace. The uppermost beds of the Hermit, however, is the closest

unit to a marker horizon that exists in the Permian red-bed succession.

Two miles west of the Limekiln Mine, 150 feet of hard, light pink, very

fine quartz sand can be seen below the conformable contact with the

lower Coconino. This bed has much the same appearance north of the

ends of the flight lines. Just north of the Limekiln Mine the bed

is a deeper red color, four miles further north at the locality where

the section was measured cement variations cause abundant pisolites

throughout the bed. Five miles northeast of the pi soli tic section,

in Cottonwood Canyon, a thinner buff colored sandstone appears between

the Hermit and the Coconino. It contains numerous small cut and fill

structures and a few small pebbles, however, it too is basically a

very fine grained sand displaying small scale deltaic cross-bedding and is extremely well cemented. This bed is probably a continuation of the same pinkish sandstone seen to the south. Moore (1966) has traced this bed several miles further to the northeast. He considers it a local anomalous varient of the Shinarump conglomerate, which should be some 3000 feet higher in the section.

Compositionally the Hermit is distinct from the overlying

Coconino Sandstone. Feldspars are found throughout the formation,

18 and the lower beds contain other igneous to metamorphic minerals

particularly biotite and hornblende. X-ray spectrographic analysis

of the lower beds show detectable amounts of potassium, magnesium,

and sodium, not normally present in the aeolian Coconino above.

The Hermit beds, though sometimes less resistant, have greater amounts of interstitial carbonate than the overlying unit. The average grain size of the uppermost Hermit bed is

approximately the same as that of the Coconino, The soft brick-

red beds below the highest bed have smaller, more poorly sorted

grains and exhibit micro-graded-bedding observable only in thin

section. These micro-laminae, in the size range from a-mill­

imeter to several centimeters, are typified by changes in grain

size and by variations in the texture and coloration of the

cementing material.

The average grain sizes of the beds are given in the table

below. These sizes are the average of diameters measured in thin

section,

TABLE 2

MEAN GRAIN SIZE OF HERMIT SAMPLES DETERMINED FROM THIN SECTION

BED SAMPLE AVERAGE SIZE

Lowermost Coconino #N5910 . 17mm Bed 4 Hermit #N5908 . 17mm II #N6174 . 16mm II #N5919 ,23mm II #N5907 . 19mm Bed 3 Hermit #N5918 . 10mm II #N6212 „ ,19mm II #N6211 ,17mm Bed 2 Hermit #N6210 ,06mm Bed 1 Hermit #N6209 ,14mm

Coconino Sandstone

Darton (1910) suggested the name Coconino Sandstone for the massive gray and white corss-bedded sandstone unit lying below the Aubrey (Kaibab and Toroweap) formations in the Grand Canyon.

Darton does not specify a specific type locality, but says that a section near Bright Angel trail total 305 feet and that one near

Hance trail measures 400 feet in thickness. No attempt was made to

subdivide the unit.

McKee (1952) considers the maximum thickness of Coconino to

be in Central Arizona and progressively thin to the Northwest

pinching out near the Arizona-Nevada border.

McNair (1951) has measured three sections within twenty-five

miles of the test site to the south and east. They range in thickness

from 42 feet to 122-1/2 feet.

Bissell (1963) believes that there is some question as to whether the sandstone encountered in several wells in southern

Utah is actually Coconino. The Coconino may be entirely absent

from these areas, and from the Muddy Mountains according to Longwell

(1949).

The description of the Coconino will include 1350 feet of aeolian red-beds which lie below the 39 foot thick cream sandstone to which the name Coconino is usually restricted. It is referred to as Coconino because it more closely resembles the Coconino Sandstone at its type location than it does either Hermit or Supai, the other two names which the red-beds are commonly placed. Since they occur above beds which,are considered Hermit they must either be included in the Coconino or placed in a new formation. Like the Coconino at the Grand Canyon the lower Coco­ nino red-beds are typified by giant aeolian cross-beds tens of feet high and hundreds of feet long, though they are somewhat finer grained and are colored red.

The lower Coconino contact with the Hermit formation seems to be conformable. In the few places where it is exposed the contact is shapr. The upper contact is unconformable where it is exposed, but the regional relationship with overlying beds is not clear.

20 The lower Coconino beds underlie the alluvium on almost all

of the northern portion of the test site. The soft sandstones have

been eroded level forming a broad flat valley which is now mostly

filled with detritus from the surrounding mountains and hills. Out­

crops occur where recent erosion has cut through older alluvial fans.

In these areas scattered knobs of Coconino protrude from shallow

valleys, whose floors are composed mainly of sand derived from the

weathering of the soft sandstone. The joints in the Coconino

control the shape of the outcrops. The outcrops take on a very

unusual banded appearance because of differential weathering along

individual cross-beds. These hoodoos are characteristic of the lower

Coconino where it crops out on flat terrain. Extremely well deve­

loped joint sets appear throughout the Coconino across the entire

test site.

The color of the lower Coconino beds varies from rusty-red- orange, to pinkish-red to cream. The color changes are not restricted to individual beds but occur in zones of blotches, or, the rock may be mottled. On the test site the sandstone is red-orange except for a zone near the base of the formation where a cream colored zone several hundred feet thick occurs. To the west the lower beds are a mottled pinkish-red and cream, and the upper beds reddish- orange. Several miles south of the mapped area, two large cream colored zones occur. The reddish coloration in all of the outcrops is due entirely to hematite staining of the grains.

McNair (1952) and Reber (1952) have recognized 1800 feet of the sandstone here described as lower Coconino in the Beaver Dam Moun­ tains, whcih are a Northward extension at the Virgin Mountains into

21 A

Figure 8 bedding. Kiln Mine.

Figure 9 Close-up of Coconino Sandstone showing differential weatheiing oi cross-beds and numerous joints.

22 southern Utah. They call the unit "Supai" and/or Queantoweap

and undivided Supai-Coconino respectively. Bissell (1963)

says that this unit is also known from oil wells in Southern Utah.

The complete Coconino section was measured four miles

west of the test site on the Lime Kiln road. At this point

the entire Coconino can be seen in a nearly vertical unfaulted

exposure.

TABLE 3

SECTION OF COCONINO SANDSTONE, FIVE MILES WEST OF SITE ON LIME KILN ROAD

UPPER COCONINO

(2) Sandstone, yellowish cream, medium to coarse grained, slightly cross-bedded. This well cemented, hard, prom­ inent cliff forming sandstone lies immediately below the Kaibab limestone...... 39'

LOWER COCONINO

(1) Sandstone, fine to very fine grained, pink to red- orange to cream. The bed has several shaley bands near the top. Near the middle is a cream band 20 feet thick, the middle section also has less prominent cross-bedding.1350

Total thickness of Coconino sandstone...... 1389

Petrographically the Coconino is a well sorted, poorly cemented quartz sandstone. In some areas cement is almost non-existent. From area to area or bed to bed the grain size varies, but the sorting is always very good. In most areas the grains are frosted. Some specimens contain several percent feldspar including some mi crocline grains, while they are lack­ ing in other samples, in all cases other igneous or metamor- phic minerals are extremely rare. Grain shapes range from sub-

23 weight percentage 40- - 0 5 aeae f he samples three of average x R I SZ DISTRIBUTION SIZE GRAIN OOIO SANDSTONE COCONINO 24 FIGURE 10 rounded to angular with subarigular grains predominating. Some

of the quartz grains display overgrowth, though none are well

developed. The hematitic coloration is restricted to areas

around the grains and does not affect the cementing material.

Apparently the limonite forms grain coatings. The grains are

very closely packed, even where the cement completely fills the

interstices it does not amount to more than ten percent of the

rock. Highly cemented rock is rare, most often only enough

cement is present to barely hold the rock together. Most of the

cement is calcite, however, X-ray diffraction detected kaolinite

in the cement of several samples.

Several structures within the lower Coconino indicate

brief periods of sub-aqueous deposition. A few miles to the north a number of small coarse lenses appear to be deltaic or fluvatile. The coarseness of the particles and the cut and fill structure exhibited in these lenses rule out aeolian deposition, even though apparently aeolean beds lie above and below the lenses. Near the north end of the test site a thin chert bed is present near the base of the lower Coconino. Although the chert has never been found in actual outcrop, interlocking blocks almost cover the surface of the weathered Coconino in several locations, so it is assumed that this chert is almost in place. The cream to green to grey chert contains a few poorly preserved fossils. One crinoid stem and two specimens of what was probably a coral were found. Further identification was impossible due to poor preservation.

25 V Bedrock outcrops of Coconino sandstone are not common nor

of great areal extent. Because of the rapid rate of Coconino

erosion they form a narrow front which is slowly retreating up

the older alluvial fans, leaving truncated outcrops at the present

level of stream erosion. The truncated beds are covered by a

veneer of sand from a few inches to many feet in thickness.

These sandy vegetation-covered areas represent a somewhat larger

area than the actual rock outcrops. Much of the sand is carried

into the major drainages, and since the Coconino erosion rate is

very high, forms most of the bed load for these intermittent

streams. Miles down stream from large Coconino outcrops a significant portion of the material in stream beds is distinctive

red-orange Coconino sand.

b Pre-Kaibab Unconformity

McKee (1938) in summarizing the evidence for unconformities in his work on the Toroweap and Kaibab Formations, states that, a Coconino-Kaibab unconformity is known to exist in many locations, but only where the Toroweap is absent. On and near the test site the alternating sequence of limestone, gypsum and red-beds of the Toroweap formation are missing from the stratigraphic sequence. Three miles east of the measured section the 39' cream colored sandstone bed at the top of the

Coconino and Kaibab formations has been hydrothermally altered and the rocks below the Kaibab have a red chalky appearance, and the characteristic cross-bedding is not preserved. Here and there small pods of manganese "wad" occur mostly pyrolusite, as

26 determined by X-ray diffraction. The alteration obscures the

exact nature of the contact, but the lack of any unit resembling

the upper Coconino from either here or along the east side of

the Coconino filled valley is evidence for an unconformity below

the Kaibab.

Kaibab Limestone

The name Kaibab Limestone was first used by Darton (1910)

to designate the unit described earlier by Gilbert (1875) on

the walls of the Grand Canyon, which Gilbert called the Aubrey

Limestone. Noble (1927) measured a number of sections, one of which, the Kaibab Gulch, Utah section, has become the type

locality. McKee (1938) redefined the formation by dividing it, calling the lower gypsiferous portion the Toroweap and re­ taining the name Kaibab for the more massive upper beds.

McKee (1938) has published the most complete work on the

Kaibab. He records thickness up to 1050+ feet in southern Utah.

His compilation shows the Kaibab seas, indicating that they covered most of central and northwestern Arizona, portions of central and south western Utah and most of the southern tip of

Nevada. The faunal studies done by McKee show the Kaibab to be Leonardian. Bissell (1962) points out that the Kaibab Sea transgressed northward and is younger in eastern Nevada.

A number of sections have been measured in the vicinity of the NASA test site. McNair (1951) measured 330 feet, six miles to the south at Pakoon Ridge and 357 feet approximately 20 miles southeast along Hurricane Cliffs. Bissell (1963) measured 900

27 feet in the South Virgin Mountains. Bissell also states that a minimum of 300 feet of Kaibab is exposed along the Hurricane

Cliffs in southern Utah. The section thickens to the west, and in the Muddy Mountains, 30 miles distance, reaches a thickness of

600 to 800 feet, according to Longwell (1949).

McKee (1938) describes the Kaibab Limestone in western

Arizona and Nevada with the adjectives light gray, massive and crystalline, but points out that sandy argillaceous and gyp­ siferous units of varying colors exist, and in many places are rather important.

Many published sections of the Kaibab probably do not include the uppermost beds. The soft Triassic beds which normally overlie the Kaibab are usually eroded, and the Kaibab forms cap rock on steep escarpments where portions of the uppermost units may be missing as the result of recent erosion. Another reason for the widely varying thickness reported is undoubtedly the major post-Kaibab erosional interval.

In the area of detailed study the Kaibab forms the highest ridge and most imposing geomorphic feature. Medium-gray cherty

Kaibab Limestone forms a massive 1100-foot hogback trending southwest-northeast at the northern terminus of the area. A detailed section was made along this ridge where it is cut nearly all of the way through by a stream valley. The bedding at the measured section is inclined at about 35° to a stream valley and exposures are good.

28

TABLE 4

SECTION OF KAIBAB LIMESTONE FOUR MILES NORTHWEST OF JACOB'S RANCH

(12) Sandstone, tan, fine grained, containing massiye chert lenses. A few sandstone and chert pebbles occur at the top of this bed. At the bottom the sand grades into sandy limestone. This bed forms small flat irons......

(11) Limestone, medium grained, gray fossiliferous...... 8'

(10) Gypsum, white, massive, forming generally covered slopes.... 4'

(9) Limestone, gray, mostly covered slope...... 38'

(8) Sandstone, gray and tan, medium grained, with knots of brown chert...... r i

(7) Limestone, gray, fine grained, very hard and dense...... 35'

(6) Limestone, gray, with 8" white chert bed at top...... ,12'

(5) Limestone, gray, fine grained with many blebs of brown chert. The base of this, unit is covered...... i

(4) Limestone, gray, fossiliferous, medium grained, cherty ridqe former Many fossils preserved in the chert...... 15'

(3) Limestone, gray, fossiliferous, medium grained, slope former.225'

(2) Limestone, dark grey, fine grained. This bed contains very few fossils and only a little chert. Unit weathers into blocks with sandpaper-like surfaces. The beds form a series of low ridges. Locally joints are filled with white cal cite, in these areas a few fossils are preserved...... 3401

(1) Sandstone, orangish-tan, fine grained well cemented...... 25'

* Limestone and sandstone rubble along faulted contact

Total thickness of Kaibab Limestone...... 715' +

In this section, beds are probably missing from both the top and bottom. Generally the exposures were very good, but thin non-resistant units such as gypsum beds may be present under covered slopes in the lower portion of the section. Bed (2) represents an interesting horizon. The limestone is lithographic quality in some places and is exceptionally pure calcium car­ bonate having only about 1% insoluble residue in the forms of small quartz grains. If this bed were continuous to areas of

inexpensive transportation it might be of commercial value as

chemical lime or cement. Several of the darker units have a fetid odor when freshly broken, indicating a fairly high organic

content, which accounts for the dark color.

Thin section of many Kaibab beds reveali large numbers of fairly well preserved fossils irv a medium grained calcite rock.

A few detrital quartz grains are present in most of the beds.

Beds near the base of the formation which do not appear to have fossils are completely recrystallized into an even grained calcium carbonate micrite. This micrite exhibits shadowy relect structures indicating the former presence of fossils.

The Kaibab carbonates are rather pure, exhibiting a few fine quartz grains and no other igneous or metamorphic minerals.

Kaibab outcrops are restricted to the narrow band at the north end of the test site. This hogback is separated from the

lithologic sequence to the south by a concealed fault which has dropped the Kaibab at least 2000 feet stratigraphically. The

Kaibab beds rise from the alluvium at approximately a 45°

inclination at the crest of the hogback the dip has flattened to about 30°. On the south slope curved flatirons are developed by the more resistant units; but the relatively gentle 35° slope has allowed rubble to collect obscuring some of the less prominent beds.

The north face of the hogback has a vertical exposure of Kaibab. The identification of this limestone as Kaibab is achieved

by its lithology, its stratigraphic position above the Coconino

and its fossils. In addition to numerous crinoid stems and bryozoa

several brachiopods were tentatively identified. They include

Pi^ductus bassi. McKee, P r o d u c t ive£ Newberry (?), Productus

£ a m n d i c u s McKee (?), Producte Sp., Composite subtilita Hall

and Composita sp. Approximately 50 thin sections were cut for

petrographic study and for a microfossil search. No fusulinids

were found although numerous rock specimens were examined in detail.

Post-Kaibab Unconformity

Many early workers recognized an erosions! unconformity at

the top of the Kaibab Limestone. McKee (1938) compiled many of

the earlier stratigraphic sections and added his own. He noted

that the unconformity seems everywhere present, but that it was

usually of low relief with channels cut into the upper beds of

the Kaibab and filled with the basal Triassic elastics. In

western Arizona, southwestern Utah and southern Nevada the uncon­

formity becomes more pronounced. Reeside and Bassler (1922) report

a 250-foot deep channel cut in the top of the Kaibab just south of Hurricane Utah. Longwell (1921) mentions gashes 100 feet deep in several places in the Muddy Mountains. In the

Kaibab's most western known exposure, in the Spring Range near

Las Vegas, the post-Kaibab unconformity displays great relief,

According to Longwell (1925) the entire Kaibab and most of the underlying Supai Formation have been eroded, making the total

32 Figure 1t Basal unconformity of the "Cottonwood Wash Formation. Quartz pebble conglomerate fills channels cut into the lower Coconino Sandstone. post-Kaibab erosion at least 1400 feet. Longwell considers

local upwarping in post-Kaibab, pre-Moenkopi (Lower or Middle

Triassic) time to account for the greater erosion in the southern

Nevada area. He also points out that the calcareous character

of the basal Moenkopi in southern Nevada indicates a rapid,

very quiet inundation.

In the area of the test site no Kaibab-Moenkopi contacts

sre exposed. The soft Moenkopi beds have been eroded away leaving

the resistant Kaibab as ridge caps.

On the test site an erosional unconformity of major pro­

portion cuts deeply into the Coconino Sandstone. Where this

unconformity can be observed the entire Kaibab Limestone has

apparently been eroded away. Above the erosional surface up to

500 feet of conglomerates and limestone lithologically dissimilar

to both the Kaibab and the Moenkopi. This unconformity is

tentatively correlated with the post-Kaibab unconformity and the

beds immediately above it assigned to the Permo-Triassic thick

sections of Kaibab may be seen. Outcrops of the post-Kaibab

limestones and conglomerates resting on Coconino sandstone

extend on a northeast-southwest trending band for at least five miles to the south and six miles to the north of the good exposures near the center of the test site. Going east, no pre-Tertiary units are exposed.

"Cottonwood Wash" Formation

Lying above the post-Kaibab unconformity on the test site is a series of as yet undescribed beds. Because of the lithology Figure 13 Slightly oblique photo of gently dipping "Cottonwood Wash" limestone hogback near the center of the test site. West is at the top and the beds are dipping to the east. The area covered by the photo is approximately 1 x 1 miles.

Figure If East dipping "Cottonwood Wash" limestones are shown in the middle ground. Kaibab Limestone forms the ridge on the skyline.” The photo was taken looking due north down the flight lines. of the upper limestone unit, its stratigraphic position and its

topographic expression, it was mapped in reconnaissance surveys

or Longwell (1949) and the Arizona Bureas of Mines (1959) as

Kaibab. In a revised country map of Mohave Co. Arizona now in

preparation by the Arizona Bureau of Mines this unit is called the

"Cottonwood Wash", named for the major drainage just west of the

test site. In this preliminary map it is assigned a Cretaceous (?) Age.

The "Cottonwood Wash" beds may be separated into two distinct

units, the lower conglomerate member and the upper limestone

member. The conglomerate member is composed entirely of clastic

sediments, sands, shales and conglomerates, the limestone member

is almost entirely chalk-white chemical limestone.

Conglomerate member: The conglomeratic member attains a maximum

thickness of approximately 200 feet. The section is not generally

well exposed, because of the non-resistant nature of some of the

beds and concealing rock, which have fallen from the overlying

limestone member. Where the basal unconformity has its greatest

relief the lowermost bed consists of a chert conglomerate composed entirely of well rounded chert, quartzite and reworked siliceous breccia cobbles. It is weakly cemented by carbonate in a matrix of sand. Lying above the siliceous conglomerate, and forming the base of the conglomerate member in several places, is a series of sandstones and shales, deep red, maroon, gray, and brown in color. * Above the sands and shales'lies a resistant limestone boulder

36

conglomerate up to 75 feet thick. The conglomeratic bed is

composed entirely of Paleozoic rock and in places contains

limestone blocks up to three of four feet across. Kaibab Limestone

seems to make up most of the fragments. Other dark non-fossil -

ifereous carbonate rocks and some well cemented sandstone

cobbles are probably Mississippian or Pennsylvanian in age, but might be Kaibab. The boulders are surrounded by a matrix of

smaller cobbles, pebbles and sand, are firmly held by carbonate

cement. This brown to grey resistant unit forms low ridges or

ledges beneath the cliff forming limestone member.

The uppermost beds in the conglomerate member are gray-green cross-bedded lithic sandstones. They forms a slope below the limestone member and good exposures are found only in stream cuts. Fluvatile cross-bedding and cut and fill structures are common. Some lenses become coarse and even conglomeratic.

Although the mineralogy of the lithic sandstone is variable, it is distinct from all of the lower beds in that it contains abundant metamorphic minerals. Glassy quartz, anorthite, biotite, zircon, garnet, and a high percentage of clay have been identified in thin section. Lithic fragments and euhedral heavy mineral grains indicate a nearby source area. Two compositions, determined by X-ray spectrography, lie within the range of normal igneous rocks. One half to two percent CO2 , as indicated by thin sec­ tion work, probably should be added to the chemical compositions.

Approximately two percent minor and trace elements might be expected. Many of the coarser bands are almost entirely

38 chert and quartz fragments, and their si.lica content probably

exceeds ninety percent.

TABLE 5

CHEMICAL ANALYSES OF TWO LITHIC SANDSTONE SAMPLES'

N6161 N6162 Si02 58.35 72.96

A12°3 16.80 10,84

*Fe2°3 6,70 4,05

CaO 5,72 3.79

MgO 3,08 1.05

k 2o 1,82 3.04

Na20 2.24 2.09

Ti02 1.20 .32

MnO .071 .046

96.58% 98.19%

*Total iron as Fe203

In addition to petrographic and chemical evidence the omnipresence of small well rounded black chert pebbles attests to a metamorphic provenance as a source of sediments. The chert pebbles serve as a guide to mapping in areas where ex­ posures are poor or non-existent.

39 Limestone member: The limestone member of the "Cottonwood Wash"

diagonally crosses the site just south of its midpoint. The

limestone member consists of 300 feet of chalky to medium

grained white limestone forming a resistant hogback. Individual

beds are not distinct enough to be traced over any distance and

prominent marker units are lacking. Extensive recrystallization

may account for the lack of fossils and the unusual chalk-

white color of the carbonates. Some beds display very thin,

uneven, undulatory beddinq like that fmmri ,• y IKe tnat foun(J in massive travertine deposits.

TABLE 6

SECTION OF "COTTONWOOD WASH" CARBONATE MEMBER, SIX MILES SOUTHEAST

OF JACOB'S RANCH

(25) Limestone, white, fine grained, with many small cavities... 18'

(24) Limestone, white resistant, cliff former. Bed is vuqqy and zation.y .L erty and Sh°WS evidence of massive recrystalli-

C23) i s - " - " 1 ,

(22) Limestone, white to light grey. Exhibits pearly luster on

(21) Limestone, grayish white.- Brown chert formed along bedding plQHGS..,...,.,...... l ^ 1

(20) Limestone, white, slope forming......

(19) L1^ neV Whlte> V6ry re^istant> blocky. Two chalky parting occur. Contains mossy brown chert...... y ■

(18) Limestone, white, weathers tan, resistant. Major ridge form- iHy Util t « g i Figure 16 Close up of chalk-white "Cottonwood Wash" limestone in tvDical exDOSure. (17) Limestone, white plaster-like, moderately resistant.,,.,.,.. 1 3 '

(16) Limestone, white, rronresistant...... ,.... 5'

(15) Sandstone, lithic, biotifereous, calcareously cemented.....

(14) Limestone, white to light grey, non-resistant slope forming. Partially oolitic, red, brown, gray and white chert irreg- ularly distributed near base...... 59'

(13) Limestone, white, resistant ledge forming...... 6 '

( 12) Limestone, white, fine grained, irregular travertine-like beddi ng...... 12'

( 11) Limestone(?) covered slope...... 7'

( 10) Limestone, white, porous, semi resistant...... 9'

(9) Limestone, white, vuggy, travertine-like features...... 7'

( 8 ) Limestone, white. Alternating bands of resistant medium grained limestone and soft chalky layers...... 17'

(7) Limestone, oolitic, white. 4'

( 6 ) Limestone, white, non-resistant...... 14'

(5) Limestone, cream, porous...... 6 '

(4) Limestone, bright-white, hard, fine grained, forms slopes, Portions are porous. Layers of pea sized chert occur,.... 45'

(3) Limestone, cream, conglomeratic, chertified...... 2 '

( 2 ) Sandstone, sandy, limey, grey green..---.... ,...... 1'

( 1 ) Breccia, chertified, bright varigated coloration.,.,.... . 1%'

Total thickness of "Cottonwood Wash" limestone. Member 300' V.

This limestone unit is unique in the stratigraphic column

in many ways. It is an unusual, bright white color, very porous and vuggy, and contains unusual textures. In thirty thin sections examined all were mostly or completely recrystallized. In specimens where travertine-like structures occur, microscopic examination reveals alternating layers of micrite and radially crystallized sparite growing into irregular cavities and cracks. No original structures are preserved in these specimens. Clay bands are developed along some of the bands as a result of the cleansing processes during recrystallization. In other medium grained limestone specimens, ghosts of primary structures are sometimes present. The identity of most of these allochems is not known, however the shapes of some suggest fossil fragments. The allochems in the oolitic units are somewhat better preserved. Although the oolites have undergone partial recrystallization and their original structure is not preserved, the original seed fragments around which the oolites grow can sometimes be identified as angular fragments of plagioclase and quartz.

Besides the cal cite recrystallization, extensive silicification has occurred. In nearly all of the thin sections examined quartz veinlets or cherty replacements occur. The chert replacement is later than the main portion of cal cite recrystallization. Silica replaces recrystalTized calcite structures as well as relect primary structures. Quartz replacing calcite is most common, but some evidence exists for calcite replacing quartz.

Detrital quartz is common throughout the unit, feldspars occur in the oolitic beds and numerous igneous or metamorphic minerals occur in one, and possibly two lithic sandstones near the middle of the unit. This minor clastic deposition seems to indicate a genetic kinship between the limestone and the underlying lithic

sandstone unit. At the measured section, a distinct break between

these two units is seen, a mile further south the black chert

pebbles and sandy material grade up into limestone over a thick­

ness of ten feet.

Despite the continuous deposition of resistant elastics no

detrital carbonate textures can be seen, and since good evidence

for biologic carbonate accumulation exists, the unit is presumed

a chemical precipitate.

If the interpretation of the unconformity at the base of the

Cottonwood Wash" beds as the post-Kaibab erosion surface is

correct, this unit must be Upper Permian or Lower Triassic in age.

According to Longwell (1925) the invasion of the Triassic seas

depositing the carbonates beds near the base of the Moenkopi were

quick and not accompanied by continuing erosion. The "Cottonwood

Wash" limestone beds, however, were apparently formed at a time of continued erosion and are therefore pre-lower Moenkopi, hence, are assigned a Permo-Triassic (?) age.

TRIASSIC, JURASSIC AND CRETACEOUS SYSTEMS

In this report no definitely Mesozoic age rocks are recognized on the test site with the exception of the Permo-

Triassic (?) "Cottonwood Wash Formation" whose description is included in the Permian discussion.

An alternative explanation for the stratigraphy has been proposed by R.t. Moore in an "in press" map of Mohave Co. Arizona by the Arizona Bureau of Mines. His explanation places all of the beds east of the Lime Kilm Fault, the boundary fault separating

the broad valley from the ridge of Paleozoic rocks to the west and

south of the Cottonwood fault, which runs across the north end of the

site, in the Mesozoic. He calls the red aeolian sandstone, described

here as Permian Coconino, Jurassic Navajo, and assigns the overlying

"Cottonwood Wash" to the upper Cretaceous. The Triassic Moenkopi

and Chinle formations would be mostly hidden benearth alluvium at the

north end of the site. Since the Triassic is not exposed and neither

the Coconino (Navajo) nor the "Cottonwood Wash" has identifiable

fossils or good marker beds correlation must be done on lithology

alone, a tenuous line of evidence. Moore (1966) admits that the

sequence is dated on lithologic similarity alone and that his assign­

ment of an upper Cretaceous age to the "Cottonwood Wash" rests on the

facts that the unit lies above a sandstone which he considers Jurassic

and that carbonate basin fill deposits of this age are known in

Southern Nevada.

It is significant to note several facts in deciding between the

Mesozoic and the Paleozoic hypotheses. 1) In the Mesozoic hypothesis

the Kaibab-Moenkopi contact, except in one location, must be faulted

or folded in such a way that the thickness of the Moenkopi is reduced

to a point where it may be hidden beneath the existing alluvium. The

one exception to the case is on the south flank of Bunkerville Mountain.

Here a thin, white, chalky limestone resembling, though not lithologically

identical to the "Cottonwood Wash" overlies the Kaibab and is followed

by chocolate-brown shales and gypsum of the Moenkopi. 2) Even though

the red-beds vary rapidly laterally, three distinct zones can be tentatively correlated across the Lime Kiln Fault from known Permian exposures.

The three units are the upper■red-bed sequence, the pink well cemented

45 sandstones and siltstones. 3) Most of the clasts in the conglomerate at the base of the "Cottonwood Wash" beds can be identified as Paleozoic rock fragments, but none are positively Mesozoic in age. 4) If the sequence is actually Navajo sandstone very unusual movement must be postulated for the Lime Kiln Fault. It must have a displacement of about 4000 feet, a little less than a mile from its origin, and only a few thousand additional feet several miles further north where it can be best seen. If the sequence is Permian in age, a uniform "hinged" movement can be postulated. 5) The sequence of rocks are typical of the Permian section but not of the Triassic and Jurassic rocks of surrounding areas. If the younger age for the rocks is to be accepted several anomalies must be explained: a) the Navajo Sandstone must be very thin, about 1500 feet as opposed to 2000 to 2500 feet reported in surrounding areas, b) The Chinle also must be very thin, 500 feet as opposed to 1600 feet quoted by Moore (1966). c) The Shinarump conglomerate is hardly more than a coarse sandstone where as it is well developed and very coarse in Utah and Northern Arizona.

46 t e r t i a r y s y s t e m

Muddy Creek Formation

Red and yellow clastic beds containing mammalian fauna of

Pliocene (?) age were first studied in detail by Stock (1921).

The clastic section from Meadow Valley 40 miles to the northwest

is thought to be identical with a known Pliocene section near

Panaca, Nevada. He traced the unit south from Meadow Valley to

the Muddy River Valley where excellent exposures more than 2000

feet thick can be seen. Longwell et al (1965) mentions that the

Muddy Creek becomes coarser and more conglomeratic near mountain

ranges. Longwell (1963) mentions several cases of rapid lateral

gradations from coarse conglomerates to fine silts in a few

hundreds of feet in the area around Hoover Dam. Similar relation­

ships can be in road cuts just west of Bunkerville, Nevada.

Longwell (1963) considers deposition in standing bodies of water

necessary to account for these rapid lateral changes.

Just east of the test site 500 feet of water lain red-

orange, sands and gravels of the Muddy Creek Formation stand in a basalt-capped mesa. They appear to interfinger with conglomerates which are generally capped by thin layers of Basalt. Along the eastern edge of the test site, the conglomerate is not basalt covered.

The alluvial material represented a topographic high at the time of the basalt flows, and was left as an island. A paleo-drainage system remains on top of this remnant surface in which drainage flows at approximately right angles to present drainage.

47 Figure 17 Close up of Muddy Creek conglomeratic material showing typical surface and variety of cobbles.

Figure 18 Metamorphic boulder in the Muddy Creek, indicating the extremely large size of some clastic fragments.

48 weight percentage The Muddy Creek conglomerate clasts are primarily of meta-

morphic material with some Lower Paleozoic limestones and Sandstones.

The lithologies are unmistakeble as 90 percent of the material is

angular particles larger than eight millimeters in diameter, and

blocks have been found up to seven feet in length. Locally this

unit is cemented by a white caliche.

The conglomeratic material forms a 400-foot high mesa just

north of the basalt outcrops at the south end of the test site.

It is also seen mixed with basaltic rubble in valleys where the

basalt cap has been eroded south to the end of the flight lines.

Fortification Basalt member: Longwell (1963) describes a basalt

occurring near the top of the Muddy Creek Formation and calls it

the Fortification Basalt. The unit is named for excellent exposures at Fortification Hill, three miles northeast of Hoover Dam. At

Fortification Hill Muddy Creek clastic beds occur both above and below the basalt, in other places no sediments occur above the f1ows.

A large portion of the area between the Virgin Mountains and the Grand Wash Cliffs is covered by basalt flows. They conformably overlie the red-beds and the conglomerates of the Muddy Creek

Formation. The contact between the basalt and toe underlying conglomerate on the test site is typified by a layer of "burned earth" a foot or so thick. The basalt is dark gray to black in color, with pumice fragments red-brown in color locally abundant.

Textures vary from a pumicy to vesicular to dense. Flow thicknesses range from a feather edge to almost 50 feet on the site, but they

50 Figure 20 Thin basalt flows capping Muddy Creek conglomerates seen in slightly oblique photo. The picture covers approximately 1 x 1 miles at the south end of the test site.

wr

Figure 21 Thin basalt cap above Muddy Creek conglomerates seen from the ground. can be seen as thick as 100 feet on surrounding mesas, As many as four flows may be seen, but their compositions are similar and no erosional surface occurs between them.

Samples N6192-N6197 are from a vertical section through two thin flows each six to seven feet thick. Samples were taken near the bottom, middle, and top of each of the flows.

TABLE 7

VARIATIONS IN MINERAL COMPOSITION .FROM POINT COUNTS OF THIN SECTIONS

Flow #2 Flow #1 N6197 N6196 N6195 N6194 N6193 N6192 Total Feldspar 77.9 80,7 82.6 72,8 76,6 81.0

Olivine 14.8 11.6 9.2 15.0 12.3 10.4

Horn- 1.7 1.5 1.3 2.0 1.6 0,7 blende

Ilmenite 5.0 5.1 3.5 4.5 5.3 4.4 Magnetite * Secondary 0.2 0.7 2.5 5,3 3,5 2,6

Cal cite *

Secondary 0.5 0.2; 0.8 0,0 0.2 0,8 Quartz

Augite 0.0 0.2 0.1 0,4 0,5 0,1

52 MINERAL COMPOSITIONS AS COMPUTED BY CIPW NORM CALCULATIONS

Flow #2 Flow #1 N6197 N6196 N6195 N6194 N6193 N6192 Plagioclase 45.35 47.06 44.06 45.75 45.92 46.36

Orthoclase 9.26 9.74 9.60 9.43 9.36 9.49

Total 54.61 56.78 53.66 55.18 55.28 55,85 Feldspar

Olivine 13.21 11.39 11.74 10.27 15.12 14.72

Augite 18.61 14.90 12.26 :4;60 12,69 12,85

Hypersthene 5.02 8,15 12,30 16,30 5.32 5.95

Magnetite 3.17 3.20 3.16 3.18 3,13 3.12

Ilmenite 4.57 4.57 4.54 4.46 4.37 4.40

Ilmenite & 7.74 7.77 7.70 7.64 7.50 7.52 Magneti te

Calci te .22 .78 2.78 5.79 3,87 2,88

53 F ig u re 22 Typical exposures which can be expected on basalt flow surfaces in the area.

Figure 23 Close up of a portion of one of the flow surfaces TABLE 8

VARIATIONS IN CHEMICAL COMPOSITIONS

Sample No. Si02 Ti02 A12°3 *Fe203 CaO MgO MnO K20 Na20 Total

N6197 50.10 2.44 14.62 12.14 9.52 8.77 .163 1,65 2.76 102.16 N6196 50.43 2.44 14.97 12.20 8.88 8.31 .162 1.67 2.98 102.04 N6195 49.82 2.44 14.22 12.16 9.15 9.38 .171 1.66 2.80 101.40

N6194 49.67 2.44 14.65 12.48 8.92 9.12 ,181 1.66 3.15 102.27 N6193 49.37 2.37 14.50 12.14 9.77 • 8.95 .173 1.63 3.15 101.94 N5192 49.95 2.38 14.62 12.09 9.26 9.02 .178 1.65 3.18 102.33

Average 49.89 2.42 14.60 12.20 9.17 8.94 .171 1.65 3.00 102.33 of 6

*Total Iron as Fe203

The differences in chemical compositions through the flows do not seem

significant. Values for manganese and sodium seem to be the best indexes

for differentiating the flows in a closely spaced section, however deviation within a given flow over the 500-foot sample grid show greater deviations

than the analyses between flows. The h.igl) totals can probably be explained

by slight systematic errors in Si02 and A12O3 determinations and negative oxygen which has not been subtracted to account for the Fe+^; Fe+^ ratio.

TABLE 9

DIVISION OF IRON ASSUMING 4:1 FeO:Fe203 RATIO

Sample no. total Fe as Fe203 FeO Fe203 -Oxygen adjusted totals

N6197 12.14 8.93 2.22 .89 101.27 N6196 12.20 9.05 2.24 .91 101.13 N6195 12.16 8.96 2.23 .90 100.50

N6194 12.48 9.18 2.28 .92 101.35 N6193 12.14 8.93 2.22 .89 101.05 N6192 12.09 8.89 2.21 .89 101.44

Average 12.20 8.99 2.23 .90 of 6 The ferric-ferrous iron ratios were determined approximately

using CIPW norm calculations, trying a series of experimental

values to obtain correct olivine percentages for samples on which

point counts from thin sections had been made. Olivine was used

because it occurs as large well defined crystals and the percentages

determined by point counting are felt to be fairly accurate.

Olivine was: the only mafic mineral having these qualifications,

though its choice is unfortunate because of possible iron,

magnesium substitutions. The best fit using this method was an

Fe+2 to Fe+3 ratio of 4:1 which is acceptable for a basalt.

The CIPW norm calculations also demonstrated some of the short­

comings of the point counting techniques. The mafic content of the

rock was underestimated in point counting because most of the amphibole,

pyroxene, magnetite, and ilmenite occurs as indistinct grain in the

ground mass of the basalt.

The triangular diagrams produced from the CIPW norm calculations

as well as classifying the basalts show several interesting analytical

anomlies. The alkali, iron, magnesia diagram shows a clustering

expected from experimental data, while the other two diagrams show

linear tends independent of possible variations in the original magma. These linear trends are largely due to varying calcium per­

centages due to introduction of secondary cal cite, and to the high

deviations in Alumina determinations. C02 and P^Og were not quan­

titatively determined, they were arbitrarially entered as 11 and .1%,

respectively, as both are present in some quantity. These values

represent mere guesses, though the CO2 content of the basalts deter­ mined from thin section was 1.12%.

56 - \ ORTHOCLASE T 29 riangular diagram diagram riangular

somples of of Fortification plotting the basalt normative feldspars orthoclase, albife and anorthite anorthite and albife orthoclase, feldspars normative IUE 24 FIGURE Most of the flows probably originated to the northeast of

the test site. In this direction the flows thicken and the

elevation of the top of the flow surfaces increases at about 50

feet per mile. The northwest most knob of basalt at the south

end of the site is topographically higher than the surrounding

flow tops. It is irregular in shape about % mile long a

1/8 mile wide, containing a number of dikes. This acted

as a source for some of the basalt.

The thin layers of basalt no longer form continuous sheets but

are dissected by erosion. The long northwest trending basalt

ridges follow the trends of the pre-basalt drainage system suggest­

ing that valleys now flow through areas where the basalt sheets were thinned or were not deposited over pre-existing topographic

highs. The present flow tops are rough and brecciated, and some­

times covered with thin layers of caliche.

Ouarternary alluvium

Alluvium covers a large portion of the area studied. One

level representing earlier valley filling can be seen above the

present drainage level. The older level is represented by the

large fan developed across much of the northern half of the site.

Although the upper portions of the fan are still receiving a

little material the lower parts are being eroded back faster than

it can accumulate. This process leaves large windows between

the older surface and recent alluvium, through which the Coconino

outcrops can be seen. The most recent level of alluviation,

represented by the present drainages, is compositionally

58 different than the older level sand. It contains much larger proportions of the easily eroded Coconino sand.

Physically the high-standing, older alluvium is composed of a poorly sorted mixture of Paleozoic limestones and sandstones with some clay development. Boulders in the alluvium range up to two or three feet in diameter. The younger material is distinctly bimodal in size distribution, having modes in the fine sand or the clay size range and in the very coarse sizes, representing Coconino sand or limestone residue and limestone fragments respectively.

Because of reworking of older alluvium rejuvination of old channels and lithologic heterogeniety the two alluviums are not always topographically or compositionally distinct.

59 STRUCTURE

The principal structural features in the area are a boundary

fault extending north-south on the west side of the valley, and

branching around to the northeast across the northwest corner of

the test site, and a conjugate set of strike-slip faults probably

associated with east-west compression. Another major northeast

trending fault, not directly associated with either the west

boundary fault or the strike-slip faulting, drops the large

Kaibab ridge at the north end of the site. Folding is of minor

importance. The large scale tilting and sharp folding are the

result of hinged faulting and large scale drag developed along major fault planes.

Western Boundary Fault

The boundary fault at the western edge of the valley extends

from near the south end of the area parallel to the strike of the

beds, the other portion continues northwest. The north-south

portion of the fault, and the northwest branch are nearly vertical,

and exhibit a maximum displacement in excess of two thousand

feet. The displacement decreases to the south until the fault

can no longer be seen two miles south of the Lime Kiln road.

The upthrown western block of the fault forms a nearly vertical

cliff composed primarily of Pennsylvanian-Permian Callville

Limestone, Mississippian Redwall Limestone and undifferentiated

Cambrian through Devonian Carbonates. At the Lime Kiln Mine the

fault divides for a short way isolating a block of twisted Kaibab

60 Limestone between the east and west branches. This small mineralized block is downdropped with respect to both sides of the fault. It lies approximately 1300 feet below the eastern block and approximately

1600 feet below the western block.

The northeast branch of the fault dips to the southeast at approximately 40°. It runs roughly parallel to the strike.direction of the beds and dips at almost the same angle as the beds. The displace­ ment probably does not exceed 1000 feet, though, because it is a bedding plane fault the amount of movement cannot be determined exactly.

Cottonwood Fault

A northeast trending fault having a displacement of 2000 to

3000 feet repeats the Permian section. On the test site this fault

is completely covered by alluvium. Five miles northeast a narrow

valley is formed along the fault trace. This fault should intersect

the northeast branch of the western boundary fault beneath the

alluvium. Because this fault parallels the boundary faults to the

north, is of large displacement and dips at a high angle, the fault

is probably genetically related to the boundary fault set. Moore (1966)

cites evidence for a dip of 70° to the north for this fault near the

head of Cottonwood Canyon 7 miles northeast of the test site. If the

fault first shown on radar and later located as a minor break with

little or no displacement on the west side of the Lime Kiln fault is

really a continuation of the Cottonwood Fault, the dip must change

for the section in the western block dips 50° to the south.

Strike-Slip Fault Set

A conjugate set of NNE and NW trending strike-slip faults is

present. Only three faults are present in the northwest set, one

cutting diagonally through the middle at test site, another passing

through the Kaibab ridge to the northeast of the northern end of the

61 site and a third near Jacob's Ranch. The first has a maximum strike-sliD component of several hundred feet, the second is displaced by only a few feet, the third has no visible displace­ ment. The north-northeast set is represented by several large faults with strike-slip components of several hundred feet and numerous small faults developed in the Cottonwood Wash limestones where displacements are too small to determine. The generating forces can be expressed by placing a strain elipse, long axis

N15°W over the area, indicating the directions of relative compression, extension and shear movement.

JOINTING

Joints are well developed within the Coconino Sandstone.

Jointing was measured in several small areas, and almost all were found to be nearly vertical. Therefore, detailed plotting from high resolution aerial photographs is assumed adequate, for the forces producing the joints were very nearly in the horizontal plane.

Each of the three large Coconino outcrops which were sampled yielded different rose diagrams and stress-strain elipses, none of which corresponded to the suggested forces' causing slip faults.

Since the strike-slip faulting maintains consistant direction over a large area and the jointing direction changes rather rapidly from area to area it is concluded that the two were not generated by the same forces.

6 3

Joint measurements from surrounding areas might lead to a

more definitive solution of the stress field which formed the

joints. The conclusion suggested by the limited data is than an

anisotropic stress was developed which manifests itself not only

as jointing, but also as a change in general strike of the

Paleozoic and Mesozoic rock units. At the south end of the

test site, east of the boundary fault, the strike is north-south

gradually changing northward to northeast-southwest. The most

probable combination of forces involve a southward compression

away from the core of the Beaver Dam Mountains, which lie directly

to the north, and as eastward compression from the core of the

North Virgin Mountains which lie to the west and southwest. This

force couple would impart northeast-southwest compression in

the southeast quadrant, northeast-southwest extension in the

northwest quadrant and a neutral surface in between. The stress

and strain elipses summarizing the three major outcrops of

Coconino sandstone along the north-south flight lines bear out

these relationships.

■ GEOLOGIC HISTORY

The regional history of the Nevada-Arizona-Utah corner area has not been thoroughly studied. This area represents a narrow portion of the Cordillerian Miogeosyncline during Paleozoic times, the western edge of the Colorado Plateau during the Mesozoic Era and the eastern limit of the Basin and Pange Province during the

Cenozoic. Because of its peripheral position to major tectonic Figure 27 Paleozoic age carbonate rocks west of the test site. Uppermost, tree covered, thin bedded unit is Callville Limestone, the three massive grey and buff units below are the Redwall Limestone and the mostly covered slope and exposures to extreme right of photo are Cambrian through Devonian in age. Picture taken looking northwest. provinces, sedimentary units vary rapidly in thickness and

lithology.

The Lower and Middle Paleozoic units above a thin basal

sandstone and shale are part of a miogeosynclinal carbonate

sequence. The rock is limestone and dolomite with only an

occasional thin clean sandstone or shale bed. Below the massive

Mississippian Redwall Limestone the sequence has not been studied

in enough detail to determine where disconformities occur and what

the various .beds are.

The Redwall limestone is an Arizona name for the massive

cliff-forming;Lower Mississippian carbonate unit which is present

throughout most of the Western United States and Western Canada.

In Southern Nevada this unit is known as the Rogers Springs Limestone, which further to the west included some Upper Mississippian beds.

Above the Redwall Limestone, a Pennsylvanian and Lower

Permian unit known as the Callvilie Limestone occurs. The

Callvilie is a continuation of the carbonate deposition, but shallow water sandstone units are more numerous. At the end of the Callvilie deposition, in the Lower Permian, conditions changed abruptly. Although the succeeding Hermit formation is water laid, the red clastic indicates a nearby positive source-area and shallow water conditions, perhaps flood plain or shallow seas with an arid climate.

Complete emergence occurred in the Middle Permian at the beginning of the Coconino Sandstone deposition. The entire Coconino is typified by huge aeolian cross-bedding, possible only with an

67 arid climate in vast flat desert area. McNair (1951) notes

that the current cross-bedding in Pennsylvanian and Permian mar­

ine sediments and the wind direction indicated by aeolian cross­

bedding in the Coconino both show a dominant north to south trans­

port direction.

The Permian Toroweap Formation, normally above the Coco­ nino, is locally absent, contains many evaporite beds, an in­ dication of continued arid conditions, though the evaporites are deposited in shallow seas. The overlying Kaibab, though mostly normal marine sediments, contain a few evaporite and red beds,

is indicative of still more shallow water and aridity.

Following the Middle Permian Kaibab formation, uplift and erosion occured over most of Arizona, Southern Utah and Southern

Nevada. Throughout Central Arizona and Southern Utah the erosion- al unconformity is everywhere present, but of small relief. Long- well (1925) summarizes the post-Kaibab erosion in Nevada, and points out that the thinning and final disappearance of the Kaibab west of Las Vegas is the result of erosion rather than nondeposition.

At the Arizona-Nevada boundary up to 1000 feet of Kaibab is local­ ly present, but areas of complete removal do occur. The only record of post-Kaibab, pre-Lower Middle Triassic Moenkopi deposition occurs in the channels where the Kaibab has been removed. These beds, the''Cottonwood Wash" formation, mark a period of coarse clas­ tic deposition, and a period of precipitation of carbonates.

The overlying Mesozoic sediments are essentially those found on the Colorado Plateau, until the Lower Cretaceous. They consist

68 of great thicknesses of aeolian, fluvatile and deltaic red beds which include sandstone, conglomerates and a few shales, with a notable absence of limestones.

During the late Cretaceous and early Tertiary, folding and faulting occurred. Remnants of thrust sheets can be seen to the north and west. After the initial period of orogenic activity granitic plutons were intruded. In the North Virgin Mountains no large granitic masses are exposed, but numerous small intrusion and pegmatites can be seen in the core of the range. Following the periods of thrusting and intrusion, large scale normal fault­ ing occurred.

Beginning in the Late Cretaceous, the sedimentary record is very irregular. Intermittent clastic wedges and basin deposits of questionable age are all that have survived. Intercalated with the sediments are volcanics of various compositions that serve as marker horizons in some areas. The only elastics that remain in the region of the test site are those of the Pliocene (?)

Muddy Creek Formation. In only a few cases, all some miles distant, are these sediments disturbed by minor faulting or folding.

The Quaternary is represented by uncemented to poorly cemented alluvium and fan material. At least one period of rejuv- ination has occurred, leaving bluffs of older detritus which are currently being eroded and redeposited. Much of the recent alluvial deposits on the test site represents reworked older material, but erosion of the Coconino, Kaibab and 'Cottonwood Wash"formations froms the bulk of the recent sediments.

69 APPENDIX I

CONTRIBUTIONS TO GEOLOGY FROM AIRBORNE IMAGING. RADAR

Side-looking airborne radars (SLAR) are active remote sensors which function in the microwave portion of the electro­ magnetic spectrum. The instrument used over the Arizona Sed­ imentary Test Site was a Westinghouse AN/APQ 97, K-band radar.

K-band lies between the frequencies of 36.0 ghz and 10,9 ghz

(183 to 2.74 cm.). This particular system is capable of both transmitting and receiving on horizontal and vertical polar­ izations, affording four different combinations of coverage.

The SLAR produces almost photographic quality images day or night, independent of weather. ; Although radar imagery looks much like aerial photography, the parameters effecting the returning signal are vastly different.

Much of the radar return is a result of scattering are re­ radiation rather than simple reflection. Properties of the rock, its environment, the surface geometry, and the radar instrument parameters all influence the intensity and polarization of the returning radar signal.

One of the important rock parameters is surface roughness.

This is a manifestation of the weathering characteristics of the rock type and the specific lithologic unit. In radar, as in other wavelengths in the electromagnetic spectrum, the effect of surface roughness or surface geometry can be divided into two categories, dependent on the wavelength of the sensor. Surfaces whose dominant ( root mean square relationship; ) surface

70 roughness is greater than the wavelength, /\ , appear "rough". Sur­ face roughness approximately /10 and less appear smooth.

A second contributing rock property is the Complex dielectric constant. These dielectric constants are not simple summations of dielectric constants of the mineralogical components of the rocks because voids and electrolite solutions are universally present, and the minerals grains are not homogeneous single cry­ stals, Like surface roughness, electrical properties tend to be rather uniform within a particular rock unit.

A third major factor effecting the radar signal is the incidence angle. Because the radar is side-looking, the inci­ dence angle is relative to the position of the aircraft rather than a surface slope angle. Although the effect of incidence angle is modified by surface roughness and vegetation, in general, the returning signal diminishes rather slowly as the angles increase from 0O to about 70° and much more rapidly for about 70° to 90°.

High incidence angles on radar imagery are analogous to photo­ graphy with a very low sun angle,

A fourth influencing factor is vegetation. Although radar generally "cuts through" vegetation, living material scatters

and dissipates radar energy. Much of the returning signal is

a function of the material beneath the vegetation cover, but

signals from vegetated terrain and non-vegetated terrain where

identical rock outcrops are different both in strength and polariza­

tion, Fortunately this vegetation effect is small, and some vegetation

is lithology dependent, so that the radar signature includes the

ubiquitious floral cover.

71 Polarization is the single adjustable instrument para­ meter important in radar mapping, Transmission vertical and transmission horizontal imagery are not directly comparable because they are not produced at the same time, Transmission of either polarization and reception of like-polarized and cross-polarized yields images which may be directly compared.

This type of comparison can determine the depolarizing effects of the targets. Cross-polarized imagery, in general, is not as distinct as like-polarized imagery because few targets are capable of complete depolarization. However, contrasts between different materials may be enhanced using cross-polarized imagery because of the relative depolarizing capability of varied targets,

The imagery used in this study was generated on November

5th, 1965. Two passes were made, one flying north, looking east, transmitting horizontal, the second flying south, looking west, transmitting vertical. On both passes the aircraft was record­ ing both like-polarized and cross-polarized images.

The vertical transmission was chosen for primary comparative purposes because it minimized areas where incidence angles were very large (steep slopes face predominantly east and southeast).

Results of cross-polarized and like-polarized imagery were essentially the same for all targets except for surfaces of the Muddy Creek

Formation, where the cross-polarized signal was more uniform, allowing for easier differentiation from the adajacent basalt flows.

Relative signal estimations were made from high contrast prints of the film imagery. A grey scale was used for digitizing

72 the imagery (0 being black, indicating little or no signal;

9 being white indicating high returns).

TABLE 10

RELATIVE RADAR RETURNS FROM LITHOLOGIC UNITS*

UNIT LITHOLOGY RESPONSE VV RESPONSE HH

Cottonwood Wash Limestone 8 6-7 (high incidence angle) Kaibab Limestone 7-8 7

Callvilie Limestone 6-7 8

Muddy Creek Conglomerate 5-7 7

Alluvium Conglomerate 5-7 6-7

Fortification (Flat Flows) Basalt 4 6

Fortification (Irregular) Basalt 2 6

Coconino Sandstone 1-2 4

Vertical Polarization Averages; 3 Limestones=7; 2 Conglomerates=6; 2 Basalts=3; 1 sandstone=2.

Several anomalies occur where unexpected signals return from seemingly homogeneous areas. These anomalies have not in general been plotted on the geologic maps, because they are not radical departures from the surrounding lithologies. Some were field checked after examining the radar imagery, others had been noted before hand, still others have not been field checked or the results of such checking were inconclusive. These anomalous features fall into two categories, areas of anomalous return and lineaments. Several of the lineaments are continuations of known faults, others are of unknown origin.

Seven prominent, anomolies of mappable size may be readily seen. 1. ) An extremely low return area lies along the east side of

the large Coconino valley. This low return area is composed

almost entirely of well washed sand, derived from the Coco­

nino. It is very fine, A./25, or less, resulting in a uniform

specular response. The anomaly also occurs along a major

drainage, and the water content is slightly higher than in

most Coconino exposures, which probably contributes to the

lower signal.

2. ) A second low return anomaly occurs in the same valley, just

north of the northmost Coconino outcrop. An irregular low

response area lies in the alluvium. Field checking showed

that some sand, presumably wind transported, is mixed with

the alluvium. This has two effects, lowering the average

size of the surface roughness and forming a soft spongy soil,

which acts as a radar absorber. The subsequent returns are

lower than that of the alluvium, but still higher than that

of the adjacent Coconino sandstone. Upon close examination

several other smaller areas of lower returns were found in

alluvium adjacent to other sandstone outcrops.

3. ) An area of very low return occurs at a high point in the

generally flat basalt cap just south of the major Cotton- /

wood Wash out crops. The basalt on the peak is physically

a bit more weathered, but chemically indistinguishable from

the surrounding flows. The entire hill is crisscrossed by

almost vertical basalt dikes which are slightly more resis­

tant than the flows. The transmit vertical imagery dif­

ferentiates this area best, because the radar was looking

74 west down the predominantly west facing basalt slope, yielding

higher incidence angles and thus lower returns. The east

looking horizontal polarization also gives slightly lower

returns, These are probably due to the slightly finer texture

of the weathered material, and a higher porosity and soil

water content. The area was examined specifically in an attempt

to explain the radar anomaly, but no definite quantative

conclusions could be drawn.

4.) A distinct lineation trending north-northwest occurs on the

north side of the large Coconino sandstone outcrop at the

center of the large valley through which the flight lines run.

The lineation does not cross good bedrock outcrops of sand­

stone, only loose, weathered sand and alluvium. It cannot be

seen in the valley walls or in lithologies other than the

Coconino, on radar imagery or in the field. Where the feature

crosses the alluvium it is marked by a narrow straight dry

wash. The radar anomaly can thus be accounted for by topo­

graphy where it bisects alluvium, however, where it crosses

flat, loose, uniform sand it can be accounted for by a moisture

and, or, textural difference. The most logical conclusion

is that the lineation, since it cuts across bedding, must be

either a major joint or a minor fault which extends only

through the relatively incompetent Coconino sandstone and

not other more competent lithologies. The subparallelism of

the lineament to a major fault, just to the south, and a

major jointing direction strengthen this hypothesis.

75 5. ) Just south of the lineation discussed, a subparallel lin­

eament extends from the western boundary fault across the

Coconino and the'Cottonwood Wash" beds and under the lava caps

to the east. This lineament can be clearly recognized as a

strike-slip fault with a transitional displacement of at least

350 feet near the western boundary fault. To the east where

it crosses 'Cottonwood Wash"limestones and then disappears

beneath the lava caps, no movement is discernible, although

several hundred feet of displacement may be present. Evi­

dence for continuation of the fault beneath the lava cap

exists as several short linear streaks in places where the

flows are thinned by erosion. These hints of faulting

continue for more than a mile across the flat flow surfaces.

6. ) The transmit vertical radar imagery, which was flown look­

ing west, casts long shadows on the north and west facing

slopes of the large Paleozoic age carbonate block west of

the test site. This low angle illumination emphasizes at

least one linear feature which extends east-northeast across

block and can be traced down the well illuminated east face.

On the east face it appears as a subtle dark lineation dipping

to the north almost vertically. This may be the western

extension of the large displacement northeast trending fault

separating the Coconino filled valley from the sharp ridge

of Kaibab limestone. Since the fault across the western

block is not evident in the field it is probable that little or

no movement is involved, and if it is a portion of the large

76 displacement northeast trending fault, the western fault

must have been separated before major movement occurred.

7.) A distant linear feature extending from the proximity of

Jacobs Ranch northwest for lh miles appears on the imagery.

This lineament cannot be seen on photographs and is not

apparent on the ground. Since it cuts both Cottonwood

Wash and Coconino formations and is apparent through the lava

caps, it is probably not a joint, but a fault of small dis­

placement. No scarp or offset can be observed at either

Jacobs Ranch or further west, however, since it is more

than a mile long,the lineation must be regarded as an

important structural feature.

77 Figure 28 Radar Imagery - Horizontal polarized transmission with like polarized reception above and cross- polarized reception below. Numbers correspond to anomalies listed in text, north is at right. ______;______iu Figure 28 Radar Imagery - Horizontal polarized transmission with like polarized reception above and cross- polarized reception below. Numbers correspond to anomalies listed in text, north is at right.

Figure 29 9adar Imagery - Vertical polarized transmission with like polarized reception above and cross-polarized reception below. Numbers correspond to anomalies listed in text, north is at right. APPENDIX II

THERMAL INFRARED IMAGING

The primary thermal infrared system aboard the NASA 926

remote sensing aircraft yields thermal images in a photographic

format in the 8-14 y region of the electromagnetic spectrum. This

instrument, a Reconofax IV, manufactured by H.R.B. Singer Co. is a

rather old model, however, most of the imagery and instrument

parameters are still classified.

A passive imaging system like the Reconofax IV is rather

simple in design. Naturally emitted energy from the earth passes

through a side to side scanning optical system where it is focused and filtered. Then the radiation impinges on a detector where the signal is converted to an electrical current, which is immediately amplified. The amplified signal is in turn used to drive a lamp filament whose image is passed back and forth across the film as a detector and optics scan from side to side. The film is moving synchronously with the forward motion of the aircraft to give a uniform scale both across and the length of the film. The differ­ ing film densities caused by fluctuations in the voltage to the lamp filament correspond to the changes in radiation flux at the detector in a linear manner. The radiation flux at the detector may likewise be correlated with the infrared temperature of the targets.

Both the radiation flux and wavelength of the maximum radiation are the result of the temperature of the radiating body.

80 The infrared radiation of the earth is a result of the con­ tribution of two sources, emitted thermal radiation and diffusely reflected s0]ar radiation. The earth radiates an energy spectrum approximating that of a 300° K black body, which corresponds to a maximum radiation flux at a wavelength of 9.7 y. To detect differences in the apparent temperatures of targets the imager takes advantages of the differences in radiation flux rather than the shifts in wavelength of the maximum flux. No simple, precise relationship exists relating total radiation flux and temperature for a finite width window, looking through an absorbing atmos­ phere at targets exhibiting absorption spectra, as is the case with airborne infrared imaging. However, fairly accurate empirical scales may be produced by ground monitoring, if the targets exhibit fairly similar spectral and emissive characteristics and if the temperatures are moderately uniform. During the day reflected solar energy does not drown the signal from terrestrial targets as would be suggested by the 6000° K source temperature.

Atmospheric absorption brings the total flux of the incoming signal below that of 300° K rocks, and low reflectances makes the contribution to the signal almost negligible.

i A large number of rock parameters affect the total infrared radiation flux emitting fyom a lithologic target. These parameters, including surface geometry, color, grain size, grain angularity, porosity, water content, chemical composition, mineralogy, textural lineation, weathering charac te ri se s, etc., influence how much thermal energy is absorbed, how it is stored and how is is re-

81 radiated. In order to easily classify how and why rocks emit in

a particular manner all of the parameters may be incorporated into

three measurable, independent variables: albedo, thermal dif-

fusivity and emissivity.

The albedo is the fraction of the total radiant energy

returned by reflection of the total solar energy received by

a body. Albedo is important in controlling the surface temperature

of rocks on clear, sunlit days. It has no direct influence on

nighttime temperatures. Since the peak solar radiation lies in

the visible portion of the spectrum, the easily visible properties such

as color surface "finish" dominate the contributing rock patameters.

Thermal diffusivity is a measurement of the rate of heat

flow within a rock. It is related to thermal conductivity,k; specific heat, s; and density, d.

6 = k/sxd

The diffusivity is measured in units of cm2/sec. Because remote sensing flights are made predawn and midday, they avoid periods of rapidly changing temperatures. In these periods of relatively stable temperatures the residual surface heat, or lack of heat is gone and the temperatures are related to the ability of the rock to transmit heat to or away from its surface.

Rocks and soils have very low to moderate thermal diffusivities.

Soils and poorly cemented rocks have extremely low thermal dif­ fusion rates. because of the large amounts of pore space and relatively small numbers of intergrain contacts. High density,

82 low porosity rocks are much better thermal diffusers by virtue of their high conductivities.

Emissivity may be defined as the ratio of the energy emitted by a target to that emitted by a black body at the same temperature. The absorbtivity («x ) of a body plus the reflectivity

(p x) is equal to one. According to one statement of Kirchhoff's

Law, the absorbtivity equals the emissivity (ex) for any given wave length, therefore the emissivity plus the reflectivity equals one,

“ A + pa =1

ea = aA Kirchhoff's Law

ea + pa =1; pa = (1_£a)

This simply means that the radiation received from rocks, because they have emissivities less than 1,0 is a contribution of both the rock temperatures (Tr) and the environmental temperature, primarily sky temperature (Ts). They are specifically related by the expansion of the above formulae.

T = TreA + Ts (l-ex)

The above relationships hold true only for monochromate radiation except when the emissivities and absorbtivities are constant over the entire range of wavelengths being considered.

For rocks this is never the case, but in geologic applications it is a good enough approximation. It can be seen from this that in order to identify rocks through emissivities sky temperature contrast must be obtained. This can be accomplished with clear,

83 cloudless skies where sky temperatures are normally below -50°C during periods when rock temperatures are at maximums. If true rock temperatures are to be measured ground measurements should be made to calibrate the imager's signal.

IMPORTANT ROCK PARAMETERS AFFECTING INFRARED PARAMETERS ----, .. . • - ■—•— '— 1------" 1------Albedo Diffusivi ty Emissivity

Color Density Surface geometry

Surface Texture Porosity Chemical Composition

Water Content Mineral Composition

Mineral Composition Grain Size

Grain Size and Angularity Water Content

Unlike radar, infrared is not a system with significant penetration capability. It is highly affected by vegetation, water content and adverse weather conditions. Because of this, variations within lithologic units are often as great as vari­ ations between units, due to thin soil covers, water differences and vegetation. Geologic mapping is therefore not a primary function of an infrared system. The system cannot be used effectively alone to detect gross lithologic units, however, togeth er with other systems it becomes a useful supplementary tool because of its extreme sensitivity to surface phenomena. It is a very good tool with which to add detail to mapping done by other means. Infrared is good for tracing out certain lithologic contacts and individual beds that have subtle differences from surrounding lithologies. Because vegetation is so pronounced

84 it is good for mapping the quantity and vigor of growing plants.

Very importantly it is able to differentiate bedrock outcrops

from weathered material through differences in thermal diffusivity

and water content. And finally it can help in mapping drainage

patterns even though streams are dry or almost dry.

A summary of the infrared returns from the various litho­

logic units represent rough averages of clean unweathered out­

crops and may not be typical of the unit as it most often appears.

The figures were obtained by averaging several spots on two

different missions flown over a year apart. The numbers were

obtained by visual estimates from prints of the mapping using a

0-9 grey scale; 9 being white and representing a relatively high

temperature; 0 being black and representing a relatively "low

temperature. This grey scale will vary from print to print

depending upon the exposure times, however, the differences

rather than the actual grey scale numbers are the only im­

portant thing.

The midday and predawn imagery temperatures cannot be

directly correlated because of different gains on the infrared imager. Because of large diurnal temperature changes in the desert environment it can be safely assumed that the lowest daytime temperatures are well above the highest nighttime temperatures.

Despite the fact that albedo, thermal diffusivity and emissivity are competing variables and often cancel the effects of each other, it is possible to make a few simple statements about the infrared

85 temperatures of rocks, During the day, a rock with low thermal

diffusivity, low albedo and high emissivity will be the hottest.

At night one with high thermal diffusivity and high emis-

isivity will be the hottest. In each situation rocks with the

opposite characteristics will be coldest.

The absolute effects of thermal diffusivity may be seen

in two materials on the test site. The examples are the sand­

stone compared to the loose sand, and the conglomerate compared

to the alluvium. In each case the constituent materials are

similar and the only major difference is the consolidation in the

thermal diffusion rate. Because the diffusivity is less in un­

consolidated materials, it can be predicted that the loose mater­

ial will be relatively hotter in the day and relatively cooler at

night than the corresponding well indurated material,

TABLE 11

RELATIVE INFRARED TEMPERATURES FOR VARIOUS ROCK UNITS

Formation Rock Type Midday Predawn

Coconino sandstone 4 8

Coconino sand, loose 5 6

Kaibab limestone 7 7

’’Cottonwood Wash" limestone 5% 7% "Cottonwood Wash" conglomerate 5 1h

Muddy Creek alluvium 6 6

Fortification basalt lh 7

Qal alluvium 4% 6

86 MIDDAY

GREYNESS Figure: 3q PREDAWN Assessing what will happen when more than one variable is

involved is a much more difficult problem, It is necessary to

look at the data before deciding what parameters dominate the

temperature determining qualities of the rock. in j^e data from

the Arizona Sedimentary site it appears that the thermal diffusiv-

ity differences mask the differences in emissivity in the pre­

dawn data. This is illustrated by the fact that the order of

temperature of the rocks observed during the day is exactly op­

posite those observed at night. The thermal diffusivity is not

always dominant to emissivity and albedo. The notable lower emis­ sivity of the sandstone should make it a rather cool body at night instead of the warmest, and the low albedo of the basalt should make it very warm during the day. In this particular case the low sun angles and slightly hazy conditions have mini­ mized the solar radiation and therefore lessened the importance of albedo. The contribution of emissivity is lessened by rela­ tively high sky temperatures and low rock temperatures. It can thus be seen that the relative temperatures under a single set of conditions are not a definite fingerprint that may be used in identification, and that the infrared appearance of rocks can change relative to one another with slight, hardly notice­ able, shifts in conditions. These characteristics of the infrared' should not be a deterrent to its use if the user is cognizant of the possible effecting parameters.

88 me

f b gure 31 Infrared imagery of south eti£ of fligTrE" 1 ines. Predawn imagery on right, mid-day imagery on left. Features which may be particularly well seen on infrared are labeled al = alluvium; me = Muddy Creek conglomerates; fb = Forti­ fication basalt; cwl = "Cottonwood Wash" limestones; ewe = "Cottonwood Wash" conglomerates. Scale = approx. 1:30,000. 89 :igure 31 Infrared imagery of south end of flight lines. Predawn imagery on right, mid-day imagery on left. Features which may be particularly well seen on infrared are labeled al = alluvium; me = Muddy Creek conglomerates; fb = Forti­ fication basalt; cwl = "Cottonwood Wash" limestones; ewe = "Cottonwood Wash" conglomerates. Scale = approx. 1:30,000. Figure 32 Infrared imagery of north end of flight lines. Predawn imagery on right, mid-day imagery on left Features w h ^ h my be particularly well seen o infrared are labeled ~looseVsa™,3. ' He r m U SandSt°"e; C ■ Coconino Sandstone; 90 9 32 Infrared imagery of north end of flight lines. Predawn imagery on right, mid-day Imagery on left. Features which may be particularly well seen on infrared are labeled s =~looseVsaUnd. = Sandstone’ c = Coconino Sandstone; 90 REFERENCES

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93