Brighan Young University Geology...

I YOUNG

f UNIVERSITY

GEOLOGY STUDIES

r' Volume 12

C O N T E N T S

December 1965

Thrusting in the Southern Wasatch Mountains, Utah ........ Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ........ B. Allen Black 55

Paleoecologic implications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Button W. Bordine 91

Paleoecology of the Twin Creek Limestone In the Thistle, Utah area .................................... .... . . . . . Ladell R. Bullock 121

Geolo of the Stockton stock and related intmsives, &1e County, Utah ................................................. John L. Lufkin 149

Stratigraphy and rifera of Ordovician rocks near Columbia I ceads , Jasper National Park, Alberta, Canada .............................................................. .. .... J. Keith Rigby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ........................... .. .......... R. L. Ethington and D. L. Clark 185

..... Publications and maps of the Geology Department ........................... .. 207

Brigham Young University Geology Studies

Volume 1 2 - December 1965

Contents

Thrusting in the Southern Wasatch Mountains, Utah ........ Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ........ B. Allen Black 55

Paleoecologic irriplications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Burton W. Bordine 91

Paleoecology of the Twin Creek Limestone in the .................................................... Thistle, Utah area Ladell R. Bullock 121

Geology of the Stockton stock and related intrusives, Tooele County, Utah .................................................... John L. Lufkin 149

Stratigraphy and porifera of Ordovician rocks near Columbia Icefields, Jasper National Park, Alberta, . . Canada .......................................................................... J. Kelth Rlgby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ............................................ R. L. Ethington and D. L. Clark 185

Publications and maps of the Geology Department ........................................ 207

A publication of the

Department of Geology

Brlgham Young University

Provo, Utah 84601

Ed~tor

J. Keith Rigby

Editorial Staff

Lehi F. Hintze Myron G. Best

Brzgham Your~g Uniuerszty Geology Studres is published annually by the Department. Geology Studies consists of graduate student and staff research in the Department and occasional papers from other contributors, and is the successor to BYU Research Studies, Geology Serier, published in separate numbers from 1954 to 1960.

Distributed December 31, 1965

Prrce $4.00

Paleoecologic Implications of Strontium, Calcium, and Magnesium in Jurassic Rocks Near

Thistle, Utah*

BURTON W. BORDINE Huvzble Oil and Refining Co. , BaRrrsfield, California

~ ~ s ' r ~ ~ c ~ . - S t r o n t i u m , calcium, magnesium, calcium carbonate and insoluble residue determinations were obtained from 75 analyses of micrite. calcareous shale, oolitic limestone, and siltstone from the Middle Jurassic Twin Creek Limestone. Sr/Ca-paleosalinity relationships suggest presence of nonmarine, marinr, and hypersaline deposits within the formation. A zoned molluscan fauna occurs in beds with a high Ca/Mg ratio, and an insoluble residue averaging 8 percent, contrasted with 31 percent in adjoining beds. Deposition in water saturated with calcium carbonate IS indicated in the high percentage of this compound throughout most of the section. Ripple marks, mud cracks, rain imprints and shoal water faunas suggest shallow water sedimentation throughout most of the lower 620 feet of the Twin Creek Limestone.

CON

TEXT

page Introduction ........................................ 92

........... Purpose and previous work 92 ................ Location and unit studied 92

.................... Regional paleoecology 92 ........................................ Field work 93

.................... Laboratory procedure 93

Acknowledgments ................................ 93

Analytical procedure ............................ 94 ........................ Sample preparation 94

................ Strontium determination 95 .................... Calcium determination 95

................ Magnesiom determination 95 Calcium carbonate determination .... 95

.... Insoluble residue determination 96 ........................ Accuracy of results 96

Paleoecologic i~nplications of ........................ element distribution 96

................ Strontium/calcium ratio 97

................ Calcium/magnesiurn ratio 100 Calcium carbonate ............................ 103 Insoluble residue ............................ 103

Environments of contained fauna and ................ relationship to elements 105

Strontium/ca~cium ............................ 105 Calcium/magnesium ........................ 105 Calcium carbonate ............................ 109 Insoluble residue ............................ 109

TENTS

ILLUSTRATIONS figure Page

1 . Index map of northern Utah. Map of Middle Jurassic seaway 93

2. Columnar section, Sr/Ca distribution, line graph, and bar graph indicating zones ............ 98

3. Columnar section. Ca/Mg distribution, line graph, and bar graph indicating zones ............ 101

4. Columnar section, CaC03 distribution, line graph ................ 104

5. Columnar section, insoluble residue distributions, line graph 106

6. Columnar section, fauna Sr/ Ca relationship ............................ 107

7. Columnar section, fauna Ca/ M g relationship ........................ 108

8. Columnar section, fauna, Ca- CO:, relationship ........................ 110

9. Columnar section, fauna-insoluble residue relationship ........ I I 1

10. Columnar section, transgression and regression of seas ................ 11 2

11. Limestone classification ............ 116 12. Sedimentary rock classification 116 13. Distribution of samples ............ 117

APPENDIX A Table of analytical results ................ I 14

Conclusions and generalized APPENDIX B

paleoecology 109 Detailed stratigraphic section. De- .................................... scripfion of lithology and sample

References cited .................................... 120 locations ............................................ 1 I 5

'A thesis submitted to the Faculty of the Department of Geology. Brigham Young University in partial fulfillment of the requirements for the degree of Master of Science.

9 1

92 BURTON W. BORDINE

INTRODUCTION Purpose and Previous Work

A means of devising valid tools for paleoecologic reconstruction has long been a problem for stratigraphers and paleontologists. Prior to the past twenty years, little was done in this field until preliminary plans for compiling a Treatise on Paleoecology were begun in 1940, stimulating interest in the subject. Early studies consisted of ecologic reconstruction based on faunal abundance, interrelationship of various groups, morphological features, and characteristics indicative of mobility and habitat. Geochemical methods have been more recently successfully employed, for example, by Ernst and Werner (1945), who discovered that sediments formed in fresh water environments contained less boron than normal marine units; Frederickson and Reynolds published similar studies in 1960; as did Harder (1961) and Walker (1962).

Studies involving calcium, strontium, and magnesium relationships have also been done in an attempt to arrive at absolute ages of sedimentary rocks, and to investigate the role of these elements in the formation of calcite and aragonite. After many analyses were correlated with lithologies and faunal distribution, the possibilities of paleoecologic implications were suggested by Odum (1950), Kulp, Turekian, and Boyd (1952), Turekian (1955), Chilin- gar (1956, 1962, 1963), and Siege1 (1961).

Purpose

The current study is an attempt to reconstruct environmental conditions in a portion of the sea which extended over eastern Utah during Medial Jurassic (Text-fig. 1 ) . Geochemical methods were employed as the primary ecologic tool. Distribution of particular elements would be of little value, however, without the aid of faunal zones, lithology, and primary sedimentary features.

Location and Unit Studied

The lower beds of the Medial Jurassic Twin Creek Limestone near Thistle, Utah (Text-fig. 1B), provide an ideal unit for such a study. Stratigraphically, the lower 620 feet of the unit rest conformably on the Nugget (Navajo) Sandstone, but are in fault contact with Early Tertiary Flagstaff and Green River Formations. Lithologically the unit consists of interbedded arenaceous, shaly, micritic, and oolitic limestone, with numerous thin beds of red siltstone and claystone. Various environments are indicated by abrupt changes in lithology and fossil zonation.

Regional Paleoecology

During Early Medial Jurassic (Bajocian), seas encrouched from the north covering much of Alberta and British Columbia. Near the border between these two provinces it split into two distinct segments and continued its transgression over parts of western United States (Text-fig. 1A) . One branch received sediments in the states of Washington, Oregon, northeast California and northwest Nevada. The other covered the present states of Montana, western North and South Dakota, all of Wyoming except the southeast quarter, eastern Idaho, and terminated in a shallow area extending through central to southwestern Utah. A section located near the center of this narrow seaway in central Utah is the area that was studied.

THISTLE JURASSIC SR, CA, MG 93

TEXT-FIGURE 1.-A, Middle Jurassic paleogeography (after Imlay, 1957). The Thistle area is in the central part of the southeastern seaway, in central Utah. B, Index tnap of the Thistle, Utah region.

Field Work

One stratigraphic section of the lower 620 feet of the formation was measured, described and sampled at each major change in lithology or fossil occurrence. A total of seventy-five samples were collected from thirty-two distinct units. Fossils, consisting chiefly of pelecypods, gastropods and crinoid fragments were collected, and utilized for correlation with chemical distribution to aid in environmental reconstruction. Primary sedimentary features and rock specimens were used for the same purpose.

Laboratory Procedure

Seventy-five samples were analyzed for strontium, calcium, magnesium, calcium carbonate and insoluble residue, using procedures described on following pages. Fossils were identified and correlated with other parameters. Rock samples and insoluble residues were observed under the binocular microscope.

Acknowledgments

Appreciation is expressed to Dr. J. Keith Rigby of the Brigham Young University Geology Department who served as committee chairman, and to Dr. W. K. Hamblin, committee member. Dr. H. J. Bissell offered beneficial suggestions regarding laboratory procedure, and observed the section in the


field. Professor John Wing of the Brigham Young University Chemistry Department provided standard samples and advised on analytical techniques. Mr. Terry Patzias, chief chemist, and the laboratory staff at the Dundee Cement Co., Dundee, Michigan, assisted by analyzing samples for comparative tests, and by offering suggestions pertaining to analytical procedure.

ANALYTICAL PROCEDURE

A Beckman Model B. Flame Spectrophotometer with flame attachment was used for the determination of strontium, calcium and magnesium. Calcium carbonate quantities were determined volumetrically by means of an acid, base titration. Insoluble residue tests were done gravimetrically. The following sample preparation and analytical procedures were utilized. A blue sensitive phototube with a range from 320 mu to 625 mu was used for all deter- m~nations. Hydrogen was favored over acetylene for fuel, chiefly because of favorable results reported by previous analysts.

Sample Preparation

Samples for chemical analysis were prepared in the following manner (Diamond, 195 5 ; Furman, 1962; Harder, 1960; Walker, 1962).

I . Dry hand samples in oven at 75OC for 12 hours. 2. Crush dried samples in jaw crusher. 3. Pulverize crushed material in a steel mortar to a -100 sieve size. 4. Place in dry, air tight bottle.

Dissolving and preparation of sample for strontium, calcium and magnesium determinations.

Weigh a 1 g. sample and place in a 50 ml. pyrex beaker. Wash with water and add 20 ml. of 6N HCI. Allow solution to boil for 1-2 minutes and place on steam or sand bath. Stir occasionally. Evaporate to dryness. Beaker should be covered with a ribbed watchglass and placed under an exhaust hood. The dried residue is treated with 10 ml. of 6 N HCI and boiling water, to put the salts into solution. Filter (using #40 filter paper) to remove silica and carbonaceous material. Wash with hot water four or five times. Evaporate filtrate to approximately 50 ml. and bring to boil. Add three or four drops of methyl red indicator, then add NH,OH (1 : l ) drop-wise stirring constantly until the color changes from red to yellow. Add no more than the drop that causes the color change; an excess will cause the CaO to precipitate. - - Allow to cool for four-five minutes, then filter into a 100 ml. volumetric flask through a 41 h filter paper. The retained residue is A1,0,, plus Fe,O, which must be removed to prevent interference with the ensuing photometric determinations. Wash AI,O, plus Fe,O,, three times with small quantities of boiling water.


11. Acidify filtrate by adding concentrated HCI drop-wise until color changes from yellow to red.

12. Allow filtrate to cool and bring volume to 100 ml. 13. The A1,0, plus Fe,O, residue is discarded. The 100 ml. of solution

is now ready for photometric determinations.

Photometric Analyses

Curves plotting ppm Sr, and percent CaO and MgO vs. percent transmission were drawn. Samples of known quantities were utilized for the curves so subsequent determinations could be determined rapidly.

Strontium Determination

A stock solution containing 200 ppm Sr was prepared by dissolving 966.10 Mg of strontium nitrate in 10 ml of 6N HCI and diluting to two liters.

Calibration samples containing from 80 to 800 ppm strontium were made from the stock and analyzed at 461 mu. The following instrument settings were used :

Oxygen 12 Hydrogen 6 Slit 1.5 mm.

Sensitivity 4 Wave length 461 mu.

Calcium Determination

Calibration for calcium was done by the following method. Samples of known concentration were prepared and analyzed by the prescribed method (Furman, 1962). The following instrument settings were used :

Oxygen 12 Hydrogen 6 Slit 1.5 mm

Sensitivity 3 Wave length 5 54 mu

Magnesium Determination

Calibration rocedure for magnesium is essentially the same as that used for calcium. d e same solution containing the dissolved unknown sample that war, used for the strontium and calcium determination was analyzed with the instrument at the following settings:

Oxygen 12 Hydrogen 6 Slit 1.5 mm.

Sensitivity 4 Wave length 371 mu.

Determination of Calcium Carbonate

A. Apparatus required 1 . Two 2 5 MI. burettes 2 . Erlenmeyer flask, 300 ml. 3 . Two ring stands 4. Two clamps

96 BURTON W . BORDINE

B. Solutions required 1. .2 Normal HCI 2. .4 Normal N a O H 3. 2% Phenolphthalein indicator solution

C. Test Procedure 1 . Weigh 0.5 g. of sample and place in a 300 ml. Erlenmeyer flask. 2. Wash the sides with water, add 25 ml. of .2N HCI and wash again

with water. ?he total amount of liquid should not exceed 75-100 ml. 3 Boil slowly for three minutes, then cool until lukewarm. 4. Add two or three drops of phenolphthalein indicator solution. 5. Titrate with .4H NaOH, swirling constantly, until a pink color is

reached.

D. Calculations Percentage CaCO.,=lO (ml. HCL x N) - (ml. N a O H x N)

Insoluble Residue

1. Dry sample in oven at 75O for 12 hours. 2. Crush in jaw crusher. 3 . Weigh 25-50 g . samples depending on approximate percent of soluble

material. 4. Allow dissolving to take place over a two day period, adding fresh

concentrated HCI several times. 5. Filter, wash with water and weigh residue.

Accuracy of Results and Method of Instrunlent Calibration

Four limestone and argillaceous limestone samples of known composition were obtained from the Dundee Cement Company, Dundee, Michigan, for the purpose of calibrations. Curves were drawn plotting the percent transmission vs. percent element. After curves were established, standard limestone samples were provided by Professor John Wing of Brigham Young University Chemistry Department for the purpose of determining the accuracy of the instrument. The following results were observed:

Element CaO

M g O

Accuracy 0-8% 0-6%

The writer believes that for purposes of obtaining a comparative distribution of elements, it is well within limits of allowable error.

PALEOECOLOGIC IMPLICATIONS OF ELEMENT DISTRIBUTION

Reconstruction of depositional environments was based on the following data:

A . Strontium/Calcium ratio B. Calcium/Magnesium ratio C. Calcium carbonate content

THISTLE JURASSIC SR, CA, MG

D. Insoluble residue distribution E. A correlation of the above parameters with faunal zones and lithology.

Strontium-Calcium Ratio

As suggested by Turekian (1955), the Sr/Ca ratio in sediments is a function of several variables.

A. The Sr/Ca ratio in the liquid phase from which the solid phase was derived.

B. The polymorph, calcite or aragonite, into which the strontium is incorporated.

C. T h e effect of the organisms. D. The salinity of the liquid phase.

Of these variables, the one being considered in this segment of the investigation is the function of salinity.

It has been known for many years that fresh water sediments and shell bearing fauna have a lower Sr/Ca ratio than those deposited or living in a marine environment. Based on this assumption, the distribution of the two elements was investigated.

Samples of each lithologic and faunal zone were analyzed and plotted opposite the stratigraphic section. First plotting of all seventy-five samples representative of the thirty-two horizons on a line graph, presented a very irregular pattern (Text-fig. 2 ) . This necessitated lumping the units into thirteen larger units so generalized trends could be observed. - -

The Sr/Ca ratio is reported as an atom ratio, following the method used by Siege1 (1961). Calculations are as follows:

%%/atomic wt. Sr .- - - - -. x 1000

%Ca/atomic wt. C;

Results indicate the number of atoms of strontium present for every 1000 atoms of calcium.

Zones A through M were designated on the basis of lithology and the Sr/Ca ratio for the purpose of this discussion. Following is a description of the zones and implications of the Sr/Ca ratio:

Zone A.-Twenty-five feet thick consisting of Units 1-5c of the measured section. This sequence rests on the Nugget Sandstone, and consists entirely of red calcareous sandstone, siltstone and oolitic skeletal limestone. Sr/Ca ratio is .34, one of the highest of the zones. Traces of gypsum and interference ripple marks are present in the upper bed of the zone. Fauna consists of abundant fragments of Gvyphaea sp., and numerous columnals of Pentacritzus astei,/srus Meek and Hayden.

Paleoecologic data can best be obtained from the argillaceous limestone bed (Unit 3 ) , and the oolitic skeletal bed, (Unit 4 ) . The lowest Sr/Ca ratio (.30), of Zone A was found in Unit 3. This occurrence coincides with lithology and lack of fauna by suggesting an environment of reduced salinity. Upper units of the Zone (4-5c) consist of oolitic limestone and micrite, and contain an abundance of crinoid columnals, Petztnctitzu.r sp., a ~ i d pelecypod fragments. Sr/Ca ratio increased to .33 suggesting an influx of water with


TEXT-FIGURE 2.-Strontium-Calcium distribution in the Twin Creek Formation at Thistle, Utah.

THISTLE JURASSIC SR, CA. MG

a greater salinity. The salinity implied by the Sr/Ca is higher than other faunal units and can possibly be explained by the particular groups involved. Pelecypods and crinoids can perhaps adjust quite readily to changes in salinity.

Many recent oolite accumulations occur in environments of abnormally high salinity (Eardley, 1938), or in water oversaturated with calcium carbonate (Illing, 1954). Higher than normal salinity is indicated by Sr/Ca ratios, and calcium carbonate is 81.0 percent. Slightly agitated water of high salinity and abundant calcium carbonate were probably conducive to oolite formation in this zone.

Zone B.-Zone B includes Units 5d through 7, a thickness of 31.7 feet. Sr/Ca ratio is .24, a drop of . lo, suggesting that the salinity was reduced from that in Zone A. Lithologically the zone consists of micrite, interbedded calcareous shales, and several gastropod coquinites varying In thickness from two to eight inches. Pelecypods are present in the zones and abundant in certain beds. Worm borings are present, but not abundant. They are usually found in beds which are in contact with the coquinites.

Several explanations can be presented to account for the mass accumulations of fossils in particular zones. Either reduced salinities were advantageous to prolific growth, or these deposits represent beach accumulations. The writer tends to agree with the former, based on the lack of abrasion displayed by the shells. Most shells show little evidence of transportation, therefore possible reduction in salinity must have been conducive to prolific growth.

Zone C.-Zone C consists of Units 8 through 12 in the measured section, a thickness of 195 feet. Fissile and splintery calcareous shale form the dominant lithology, upon which a prominent erosion slope has been formed. The Sr/Ca ratio increased to .29 suggesting a higher salinity. The water was also probably turbid, as indicated by high insoluble residues. No fossils were collected in any part of the zone.

Zone D.-Zone D consists of Units 13 through 18 in the measured section, a thickness of 86.5 feet. Pelecypods, crinoids, algae, and twiggy unidentified structures resembling small plants were collected from the zone. A prominent ledge is formed by these units and a sharp change occurs in lithology. Lower Zone D consists of sandy limestone interbedded with shale, while the upper beds are composed of micrite. Sr/Ca ratio is reduced from .29 to .26. Fossils are abundant in some beds, but scattered in others. Insoluble residue is decreased. Oscillation ripple marks, rain imprints and numerous bottom markings are preserved in these rocks. Sandy beds in lower Zone D were probably deposited in shallow water, as indicated by ripple marks containing rain imprints. Higher in the zone, sediments are more calcareous and fossils are more abundant. The combination of salinity, temperature and reduced turbidity must have been favorable for many organisms.

Zone E.-Units 19 to 20, 20.8 feet thick, comprise this zone. It consists of red siltstone that lacks bedding and contains no fossils; the Sr/Ca ratio is .19. On the basis of the sharp reduction in Sr/Ca ratio, the red color, and the lack of fossils, a brackish or fresh water environment is suggested.

Zone F.-Zone F appears to be the beginning of a cyclic sequence that con- tinues from Unit 21 through 32 at the top of the unit. A thickness of 265.5 feet is represented by this oscillating sequence. Sr/Ca ratios fluctuate as the


lithology changes from sandy limestone to clay or siltstone to micrite. Pelecypods and gastropods are distributed throughout. Ripple marks are abundant in beds containing a higher clastic percentage.

The following Sr/Ca variation exists in Zones F through M :

Zone Units Litholom Sr / Ca

21-26 low

31, 32 low 32 up

Micrite and interbedded calcareous shales Micrite Sandy limestone and micrite Sandy limestone Siltstone, micrite and sandy limestone Sandy limestone Micrite Micrite

Calcium/Magnesiurn Ratio

Early studies involving distribution of calcium and magnesium in carbonate rocks were to investigate the role of this ratio in the precipitation of calcite and aragonite. Temperature emerged as the primary control of magnesium content, thus suggesting a tool for deriving relative paleotemperatures (Chilingar, 1956; Siegel, 1961). This has been supported by other investiga- tions which suggested a relationship between evaporite conditions and a low Ca/Mg ratio.

Zonation based on Ca/Mg ratio in the section studied, showed several marked variations (Text-fig. 3 ) . One occurred in zones containing fossils, and low insoluble residue, where an abnormally high Ca/Mg ratio prevailed. Another zone displaying a low Ca/Mg ratio was found where insoluble residue was high.

For the purpose of the present analysis thirteen zones have been designated, each containing more or less uniform Ca/Mg ratios separables from zones above and below. In some instances Ca/Mg zones correspond to those based on Sr/Ca ratios. Zones where the relationship was not similar occurred where insoluble residue was high. This suggests that magnesium derived from clay minerals contributed to the amount present.

Zone A'.-Ca/Mg ratio = 3.6; Units 1-4 of measured section; thickness 19 feet.

Lithologically Zone A consists of calcareous quartz sandstone, reddish brown calcareous claystone, and oolitic limestone. Crinoid columnals of Pentacrinus califort~icus and Pentacrinus a~teriscus Meek and Hayden, and unidentified pelecypod fragments are abundant. The Ca/Mg ratio is low, suggesting deposition in extremely warm water. This zonation corresponds to the Sr/Ca ratio Zone A, which indicated above normal salinity.

Zone B1.-Ca/Mg ratio = 33.2; Units 5a-6 upper of measured section; thickness 27.25 feet.

This unit consists of micrite and calcareous shale, interbedded with several thin gastropod coquinites. Magnesium content is considerably lower than in


TEXT-FIGURE 3.-Calcium-Magnesium distribution in the Twin Creek Formation at Thistle, Utah.


the unit below, and the striking reddish color changes vertically to a pinkish tan. Fossils are scattered, except in the coquinites. Temperatures were probably dropping and conditions for faunal development were becoming more advantageous.

Zone C1.-Ca/Mg ratio = 80; Unit 7 of section; thickness 10.7 feet. This unit is micrite interbedded with thin and thick gastropod coquinites.

Environmental conditions must have been optimum, as evidenced by one of the most profuse faunal zones in the sequence. Normal marine conditions are suggested by the presence of one ammonoid, numerous pelecypods Vaugonza sp. and Astarte sp., and coquinites composed almost entirely of cerithiid gastropods.

Zone Dr.-Ca/Mg ratio = 29.1; Units 8-14 of measured section; thickness 230 feet.

This zone consists of fissile calcareous shale, with a sandy limestone unit near the top. No fossils were collected. Environmental conditions appear to have been quite uniform. Temperature and salinity were probably slightly above normal as indicated by the decreased Ca/Mg ratio and the increased Sr/Ca ratio. Insoluble residue was also high in this zone, suggesting increased turbidity was responsible for the lack of fauna.

Zone Er.-Ca/Mg ratio = 85; Units 15-19 of measured section; thickness 56 feet.

Thin to medium bedded micrite prevails. Lower beds contain matted pelecypods consisting chiefly of Camptonectes sp., Pentarrinus sp. and twiggy material, probably plants. A sharp increase in the Ca/Mg ratio occurs in the Camptonectes sp. bed. Minor fluctuations throughout the zone can be correlated with faunal abundance. Temperature could have fluctuated slightly, but at all times climatic conditions were favorable for organisms.

Zone F'.-Ca/Mg ratio = 4.3; Unit 20 of section; thickness 16 feet. This zone consists of pale reddish brown siltstone, poorly indurated. A

sharp decrease in the Ca/Mg ratio, combined with the same trend in the case of the Sr/Ca, indicates the possibility of a terrestrial origin.

Zone GI.-Ca/Mg ratio = 49.8; Unit 21 of measured section; thickness 22.6 feet.

This zone is an alternation of ledge and slope forming units consisting of thin and thick bedded micritic detrital limestone. The indicated increase in the Ca/Mg ratio must have changed environmental conditions so that it was favorable for life to exist. Reappearance of scattered pelecypods supports this.

Zone HI.-Ca/Mg ratio = 110; Units 22-24 of measured section; thickness 34 feet.

Lithologically the zone consists of thin bedded micrite and sandy limestone containing coarsely plicated pelecypods distributed throughout. Fossils are less abundant in this zone than in other peak zones, but the insoluble residue is also higher which could have been the controlling factor.

Zone It.-Ca/Mg ratio = 36.6; Units 25-29 of measured section; thickness 119 feet.


Thin to medium bedded micrite, interbedded with coarse detrital limestone, prevail as the dominant lithologic type. Ripple marks, one thin red bed, scarcity of fossils, and a reduced Ca/Mg ratio combine to indicate shallow, water and extremely warm climate.

Zones 1-M'.-Ca/Mg:

Zone Jf=15; Unit 30 Zone L'=10; Unit 31b Zone Kf=43.5; Unit 31a Zone Mf=47; Unit 32

The four uppermost zones of the sequence demonstrate a repetitive cycle consisting of two zones showing a low Ca/Mg ratio and two which are much higher. Lithologically the low zones consist of fine sand and silt in a micrite matrix. Zones with a higher Ca/Mg ratio consist of relatively clean micrite. Ripple marks are numerous in the clastic-laden beds and absent in the micritic zones. Deposition of beds containing high insoluble material must have been in shallow warm water, while micritic beds were most likely deposited in a deeper, lower temperature environment.

Calcium Carbonate

Calcium carbonate is deposited in the following ways: by chemical precipitation, as the remains of living organisms, or as detrital particles derived from erosion of older limestones (Trask, 1937). Chemical precipitation is probably the major source of calcium carbonate found in the rocks involved in this investigation. Lack of detrital calcareous material, and limited distribution of organisms eliminate both of the other means as major contributors.

Chemical precipitation is controlled chiefly by temperature, salinity, depth and organisms. Since water generally becomes under saturated in calcium carbonate below a depth of approximately 200 meters (Trask, 1937), the writer believes that the entire section was deposited in a water depth that was much less than that considered to be the point at which the solubility of calcium carbonate occurs.

Calcium carbonate distribution throughout the section is very uniform (Text-fig. 4), when the relationship of insoluble residue is considered. Calcium carbonate in the soluble percentage is usually greater than 90 percent. This suggests that environmental conditions affecting precipitation must have been relatively uniform.

Many beds containing nearly the same calcium carbonate and insoluble percentage present a very different topographic expression. Thick bedded micritic beds are in contact with thin bedded fissile calcareous shale.

Insoluble Residue Implications

Chief factors governing the proportion of particles of clastic origin in sediments are as follows (Trask, 1937):

1 . Distance from shore. 2. Climate-sediments deposited near arid regions contain less clastic

material than those formed near humid regions. 3. Location with respect to mouths of streams. 4. The rate at which calcareous sediments are added to the water.


1 I I 8

2 b 3 0 4 0 5 0 6 0 ' 1 0 8 0 9 0 ldo X Co cos

TEXT-FIGURE 4.-Calcium carbonate distribution in the Twin Creek Formation at Thistle, Utah.


Material of clastic origin has played a major role in controlling environmental conditions which existed during deposition of the section studied. Individual mineral species were not identified, but the major contributor appears to be from clay minerals.

Primary sedimentary features are located in zones with the highest insoluble content. Ripple marks and rain imprints are found in the sandy, limestone beds, while mud cracks appear entirely in the micritic beds that contain a high clay mineral content.

Zones containing an abundance of fossils, have a low insoluble residue. A surprisingly high insoluble residue content is present in many of the clean appearing micrites (Text-fig. 5 ) .

ENVIRONMENTS OF CONTAINED FAUNA A N D RELATIONSHIP TO ELEMENTS

Fauna consists primarily of a gastropod and pelecypod assemblage. Crinoid columnals are found at various places throughout the section and are most common in the lower part. Zonation is abrupt in most instances indicating a rapid environmental change. Many beds are highly fossiliferous while others are virtually unfossiliferous. Those beds containing the greatest abundance show the sharpest contact with unfossiliferous units, and also contain only a few genera. This suggests that the environment was well suited for a particular form, but not suitable for community development.

Generally, faunal distribution is controlled by temperature, salinity, and turbidity. Temperature is probably most significant because of larvae sensitivity. Salinity is also of major importance for both larvae and adults because of inability to quickly adjust to osmotic pressure changes. Turbidity is of prime significance among filter feeders, who obtain food partcles by straining edible components from sediments. Fine clay and silt sized material tend to clog pores and gills. All three factors contributed to the sharp zonation displayed in this section (Text-figs. 6-9). Graphs are used to illustrate the contact relationships of fossiliferous to barren beds.

Strontium/Calciurn Ratio

The ratio of strontium to calcium followed a definite trend in some faunal zones, but varied from the pattern in others. In lower parts of the section evidence was not conclusive in regard to the faunal zones being associated with either an increase or decrease in salinity. In the upper beds of the section, where lithology is more homogeneous, a marked trend was observed (Text- fig. 6 ) in each unit where fossils occur, the Sr/Ca ratio is reduced, indicating a change from above normal salinity to more normal salinities.

Lack of zonation lower in the section is possibly due to allocthonous calcium or strontium contents. Clay minerals comprise the major insoluble fraction in the lower faunal units, while quartz, sand and silt are the major contributors higher in the section.

Calcium/Magnesium Ratio

Most pronounced zonation was displayed by the relationship of Ca/Mg ratios to faunal zones (Text-fig. 7 ) . In each of the eight zones, a marked increase in the Ca/Mg ratio occurred with the presence of fossils. Previous investigators, Chilinger (1956), Siege1 (1963), suggested that this ratio is

BURTON W. BORDINE

X INSOLUBLE

TEXT-FIGURE 5.-Percentage insoluble distribution in the Twin Creek Formation at Thistle, Utah.


I ABUNDANT FOSSILS

FEW FOSSILS

FOSSILS ABSENT

I I I I I I I .I0 .I5 .20 .25 .33 .35 .40 .&

ATOMS ~ r / 1000ATOMS Ca

TEXT-FIGURE 6.-Relationship of fossil abundance to the Strontium-Calcium ratio in selected units of the Twin Creek Formation.


ABUNDANT FOSSILS

FEW FOSSILS

FOSSILS ABSENT

TEXT-FIGURE 7.-Relationship of fossil abundance to the Calcium-Magnesium ratio in selected units of the Twin Creek Formation.


dependent upon temperature in recent sediments, and suggested paleo applica- tions. Magnesium is most abundant in modern sediment deposits where hypersaline conditions exist. In ancient deposits, high magnesium sediments are commonly associated with evaporite deposits.

Temperature must have dropped sufficiently, as indicated by the rapid increase in the Ca/Mg ratio, for organisms to flourish. The Sr/Ca ratio of the same beds suggest a decreased salinity in relation to faunal occurrence. The two distributions tend to support each other by suggesting the-existence of lower salinity and cooler water for fossiliferous beds.

Calcium Carbonate

Faunal zones occur in beds containing a high calcium carbonate content (Text-fig. 8 ) which is suggestive of a warm, shallow, well aerated environment. As mentioned previously, calcium carbonate is inversely proportional to the insoluble residue. This relationship supports the existence of an environment with low turbidity. Calcium carbonate content is generally high throughout the section. Fossil beds average eighty-five percent, while non-fossiliferous units in contact with the faunal zones average sixty-seven percent.

Insoluble Residue

Insoluble residue throughout the section is surprisingly high (Text-fig. 9) and consists chiefly of clay minerals. Faunal zones indicate a lower insoluble than units directly above and below. All fossils collected, except the gastropods, are filter feeders which would be sensitive to an influx of clay-sized particles. Average value for fossiliferous beds is 8.7 percent, while unfossiliferous beds in contact with those containing fauna average 31 percent insoluble.

CONCLUSIONS A N D GENERALIZED PALEOECOLOGY

Studies by Imlay (1953, 1956, 1957), indicate the boundaries of the narrow Jurassic seaway extending across eastern and central Utah. This narrow arm became isolated periodically from the main oceanic body lying to the north by localized uplift in the area of Montana and southern British Columbia. As a result, evaporite facies developed in marginal areas of the seaway to the south. Studies by the writer of the section near Thistle, Utah, express a variety of environments, caused by minor fluctuations in sea level. Based on data obtained from laboratory tests and field observations by the writer, the following is a summation of Twin Creek Limestone paleoecology in central Utah.

Source Area and Sediment Type

A source area of low relief is evidenced by the small particle size found in the clastic components. An abundance of calcium carbonate and an evaporitic facies, such as the time equivalent Arapien Shale of Central Utah, are aIso commonly associated with a low, distant source.

Directional properties were not observed, but studies by Imlay (1948, 1956, 1957) suggest an easterly origin of sediments for rocks in the Thistle region.

Transgression and Regression of Seas

Minor tectonism was responsible for most fluctations in sea level, which caused transgression and regression of the sea (Text-fig. 10). Sr/Ca ratios, fauna zones, and lithology suggest the following conclusions:


/ ABUNDANT FOSSILS

FEW FOSSILS

FOSSllS ABSENT

TEXT-FIGURE 8.-Calcium carbonate distribution in relationship to fossil abundance selected units of the Twin Creek Formation.


FEW FOSSILS

FOSSILS ABSENT

0 10 20 30 40 50 60 70 % INSOLUBLE

TEXT-FIGURE 9.-Percentage insoluble in relationship to fossil abundance in certain units of the Twin Creek Formation.

11 2 BURTON W. BORDINE

TRANSGRES

7 - Brackish - Calc. s a n d - s i l t s t o n e Marine - Micr i te

Brackish - Calc . , s a n d - s i l t s t o n e

- M a r i n e - A r g i l l a - ceous l imestone and - ca lcareous s i l t s t o n e . Al te rna t ing beds. S c a t t e r e d Gryphaea a; P l i c a t u l a s p .

Nonmarine - Brackish Red c l a y and s i l t - s tone.

l ~ a r i n e - Micr i te - Abundant Campton- e c t e s & Crlnoids , Pentacrinus a and twiggy p l a n t - l i k e m a t e r i a l . Brackish - Calc. - - sandstone, r i p p l e - - marks, r a i n impr in ts , mudcracks, worm t r a i l s .

Marine - Calcareous f i s s i l e s i l t and c lay s t o n e .

T-LT

- 1 . 1 -\ Marine - m i c r i t e ; I / abundant ~ e l e c v ~ o d s . .. Vauzonia a and Astar te a m o - no id ; c r i n o i d s , and oys te r fragments. Abundant m- crinus s p . -

. I S r / ~ a Ratio

TEXT-FIGURE 10.-Summary of interpreted transgressive-regressive history of the Twin Creek Formation at Thistle, Utah.

Basal units represent nonmarine to brackish depositional environments which were followed by an influx of marine waters during deposition of the near basal beds. Crinoid stems and pelecypod fragments found in oolitic limestone evidence a marine origin.

This initial penetration was followed by deposition of marine calcareous shale and fossiliferous micrite. Sr/Ca ratios are slightly higher in the micrite


than in the underlying shales, and the presence of crinoids and abundant pelecypods support the presence of a normal marine environment. Unfos- siliferous, thin and papery shale and red siltstone overly the marine micrite. The Sr/Ca ratio for these latter beds is one of the lowest of the section. This is interpreted by the writer as nonmarine to brackish deposit, similar to the beds immediately overlying the Nugget Sandstone at the base of the Twin Creek sequence.

An oscillating sea is indicated by the Sr/Ca -ratio in the upper units. Sediments containing a high clastic content show a low Sr/Ca ratio, while those with a low insoluble content, have a high Sr/Ca ratio. This upper sequence must have been deposited in a transitional environment, as indicated by ripple marked clastic beds which contain shallow water fauna, and thick bedded micrite. The dense micritic units were probably deposited in a shallow, quiet water, marine environment.

Climate

Climatic conditions were presumably very warm as indicated by scarcity of fossils, and an abundance of calcium carbonate and magnesium. Traces of gypsum were observed in the lower beds and occurs in abundance in the equivalent Arapien Shale, located south of the section at Thistle. Precipitation was low and vegetation on the surrounding source areas was sparse as implied by lack of carbonaceous material in the sediments.

Bottom Conditions

T h e abundance of clay and silt sized material in the insoluble fraction leads the writer to believe that the water was generally turbid during most of the Twin Creek deposition. Practically all of the rocks comprising this section originated from the induration of fine muds and ooze. The presence of turbid cond~tions is supported by the concentration of fossils chiefly in units of low insoluble residue. It is probable that migration of the loosely compacted sediments was responsible for the restriction of filter feeding pelecypods to zones that were relatively clean. All fossils collected are benthonic forms, with the exception of one ammonite. Animals apparently thrived in other areas of the seaway and rapidly migrated to this section when environmenta! conditions became favorable.

Depth of Deposition

Most of the deposition took place in a shoal environment as supported by primary sedimentary features, and the occurrence of red beds at frequent intervals. A n abundance of pelecypods, known shallow water inhabitants, also support this assumption.

Salinity

Trends displayed by strontium/calcium ratios suggest normal marine and hypersaline conditions during much of the Twin Creek deposition. Salinity appears to be reduced slightly in most faunal zones and depressed markedly in red siltstone units, associated with non-marine or brackish conditions.

Three significant features have developed from this study:

(1) T h e section was divided into various environments on the basis of Sr/Ca ratios, which were correlated with faunal zones and lithologic units.

BURTON W. BORDINE

Five distinct facies, consisting of poorly indurated red silt and claystone, calcareous sandstone, calcareous shale, oolitic limestone and micrite are present in the section. Low Sr/Ca ratios indicate below normal salinity during the red bed and calcareous sandstone deposition, suggestive of subaerial and near shore deposits respectively. Calcareous shales appear to be of normal marine origin, being deposited in extremely turbid waters. Sr/Ca ratios, fauna occurrence, and low insoluble residue indicate that the oolitic beds were deposited in a shallow, clean, normal marine environment.

Micrite beds that contain few fossils or sedimentary features have a high insoluble residue, and a Sr/Ca ratio, which indicates deposition in turbid normal marine water.

( 2 ) Beds containing fauna displayed an abnormally high Ca/Mg ratio. Most fossils are concentrated in thin zones, bordered sharply by

unfossiliferous beds. In all cases a marked increase in the Ca/Mg ratio occurred with the presence of fauna. Temperature is the major factor controlling magnesium precipitation, therefore, cooler water was favorable for maximum organic development.

( 3 ) Insoluble residue is lower in faunal zones than in adjacent beds. Large accumulations of fossils, consisting chiefly of filter feeding

pqlecypods, occur only where insoluble residue content is low. Clay m~nerals comprise the major insoluble fraction. This combination of pelecypods, clay-size material and cooler water (discussed above) is probably responsible for the sharp zonal concentration of fauna.

APPENDIX A

Table of Analytical Resiilts

Sample No. % CaO Sr ppm % MgO St/& Ca/Mg "/o CaCo. Insol.

5a-L 5c-L 5e-L 5-F 6-L (low) 6-L (mrd) 6-L ( U P ) 7 (UP coq.) 7-F (Pele.) 7-L (UP) 8-L ( low) 8-L (mid) 8-L jup)' 9-L

10-L ( low) 10-L (up) I I -L 12-L ( low) 12-L (mid) 13-L ( low) 13 (comp.) 14-L

THISTLE JURASSIC SR, CA, MG 11 5

15 (comp.) 16-F ( low) 16-F 16-F (mid) 16-F ( u p ) 17-F (]OW) 17-L (mid) 17 (plant) 17-L ( U P ) 18-L (low) 18-L ( u p ) 19-L 20-L (RB) 20-L ( IB) 21-L (low) 21-L (low) 21-L (mid) 21-L (top) 22-L 23-L 24-L 25-L 26-LA 26-LB 26-LD 26-LE 26-L (mid) 26-L ( u p ) 27-L (Iow) 27-F 28-L 29-L (low,) Red Bed In 29 29-L (UP) 29-FL 29-L ( u p ) fresh 29-LF fresh 30-LA 30-LB 31-LA 3 1 -LB 32-L (low) 32-L (UP)

APPENDIX A (Cont

49.0 235 0.25 45.9 235 0.65 54.0 330 1.65 53.4 300 1.55 49.0 300 1.00 52.5 330 1.20 52.9 355 1 .OO 46.3 350 1 .O 52.6 300 0.80 50.8 235 0.90 42.8 216 1.30 42.5 167 1.10 15.5 70 3.60 16.0 105 3.75 31.8 275 0.80 46.0 332 1.10 49.2 355 0.80 33.5 234 0.80 51.0 316 0.45 45.0 300 0.42 41.2 280 1.05 53.8 332 1.15 47.6 300 1.20 45.6 266 2.10 48.8 250 1.20 49.0 300 1.25 33.1 332 1.15 35.9 348 1.60 46.4 284 1.30 47.2 300 0.80 41.8 250 2.15 41.8 218 1 .OO 24.6 118 1.60 44.5 218 1 .OO 42.6 218 0.90 43.5 235 0.65 46.3 235 1.10 23.4 68 1.15 25.5 168 2.55 45.5 232 1.05 15.4 30 2.75 38.0 395 2.60 5 5 270 1.10

inued )

.22

.23

.28

.26 .28 .29 .31 .35 .26 .21 .23 .18 .20 .30

APPENDIX B

Detailed Stratigraphic Section

The following standards and classification tables were utilized in describing the section:

Bedding (Modified after Kelly and Silvers, 1952)

Thick 3 to 6 feet Medium 1 to 3 feet Thin 0.5 inch to 1 foot Laminated 2 mm. to 1 inch Papery less than 2 inm.


1.10% - Micritic Limestone

la) Mlcrite - lime mud or its conwlidatad equivalent ( D l Parcentopes should be computed on o cement 8 pore free bosis

TEXT-FIGURE 11 .-Limestone classification (after Leighton and Pendexter. 1962) used in the present study.

Calcite or dolornlte

Sandy Argillaceous limestone limestone

or dolostone or dolostone

Calcareous or dolorn~tlc s~ltstone

Sand 9: 1 1 : l 1 :9 S~lt or clay

TEXT-FIGURE 12.-Classification of major subdivisions of sedimentary rocks used in the present study (after Gilbert, in Williams, Turner, and Gilbert, 1954).


OOLITIC LIMESTONE

12L (mid)

12L (low) - - -- I I L

IOL (UP)

- - \- 8L (mid)

VJ . . . .

SANDY LIMESTONE

k U M P L I ESTONE

1: : 3 - - - - RED CLAY- SILTSTONE

SPLINTERY CALC. SHALE

F lSSlLE CALC. SHALE

(UP coq)

. (mid)

TEXT-FIGURE 13.-Distribution of samples in the Twin Creek Formation at Thistle. Utah.


Color

Colors were determined by comparison with those contained in the Rork- Color Chart, distributed by the Geological Society of America, reprinted 1963.

Unit Description Thickness

in feet

Micrite-Thin to medium bedded, pale yellowish brown. Contains scattered pelecypods, Plica/ula sp. ....................................................................................

Detrital Micritic Limestone-Laminated to thin bedded, very pale orange, weathers dark gray. Upper part consists of grayish orange pink. Thin bedded calcareous siltstone; interbedded with micrite. Detrital beds contain oscillation ripple marks and burrows. ........................................................................

Calcareous Sandstone-Thin to medium bedded, very pale orange, contains abundant ripple marks. Upper part contains laminated siltstone, grayish pink interbedded with pale yellowish brown calcareous sandstone. ............

Micrit-Thick to thin bedded ledge forming unit, light olive gray, weathers grayish orange. Contains thin bed of pale red calcareous siltstone. Micrite is thicker bedded in upper portion than in lower. Scattered pelecypods; Gryphaea sp. ........................................................................................................

Micete-Platy to thin bedded slope forming unit. Light olive gray, weathers grayrsh orange. ....................................................................................................

Detrital Micrite-Prevails in lower beds; thin bedded, yellowish gray, weathers light olive gray. Lumpal micritic limestone is present in upper beds, . pale . yellowish brown. Laminated interbeds of calcareous sandstone wlth rlpple marks. ............................................................................................

Limestone-Alternating medium to thin bedded; one calcareous sandstone unit near middle. Very pale orange, weathers pale yellowish brown. Con- tains scattered pelecypods, Gryphaea sp. and compaction features or intra- formational folds. ................................................................................................

Micrite--Laminated, pale yellowish brown. Upper beds are more argillaceous, pale red color, thin bedded. ............................................................

Sandy Limestone--Prominent ledge forming unit, yellowish gray color, contains numerous stylolites perpendicular to bedding. Pelecypods, Gryphaea sp. are present but not abundant. ................................................

Fcrite-Thin bedded, pale yellowish brown, weathers light tan, bedding 1s very even. ........................................................................................................

Detrital Limestone-Thin wavy bedded pale yellowish brown on both fresh and weathered surfaces. ....................................................................................

Alternating ledge and slope forming units. Micritic detrital limestone- Laminated, yellowish gray; forms slope at top of unit. Crystalline detrital limestone--very porous, very pale orange, weathers grayish orange; thin bedded. Detrital Micrite-Yellowish gray, medium bedded; weathers grayish orange and has bitted appearance. Detrital ' Limestone-Fine to coarsely crystalline, pale yellowish brown, weathers dark gray. Detrital Limestone--Slope former, lacks bedding, poorly indurated; very

........................................................................................................ pale orange.

Calcareous Siltstone-Pale reddish brown, poorly indurated, lacks fissility and bedding. Contains one 6 inch bed of light gray material. Sharp contact between red, and light beds. ....................................................................

Calcareous Siltstone-Dark yellowish tan on both fresh and weathered surfaces. Papery beds, easily parted. ...................................................................

Micrite--Thin bedded in lower beds, laminated in upper. Light olive gray, weathers light brown. More argillaceous in upper beds. ................................


APPENDIX B (Continued)

Limestone-Thin and medium bedded. Thick beds consist of micrite; thin- ner beds of skeletal micritic limestone. Prominent ledge f o r m i 9 unit. Skeletal material abundant in lower beds. (Pelmypod fragments, crinoid columnals, and twiggy material, probably plants. Fossils sparse in upper part, pelecypods scattered.) Lower beds moderate yellowish brown; upper

........................................................................................ pale yellowrsh brown.

Micrite--Thin bedded, consists of lower slope former and upper poor ledge forming unit. Contains skeletal material, (crinoid columnals, pelecypod fragments). Light olive gray, weathers to a light medium gray. ................

Pelecypod skeletal limestone-Very pale orange weathers darkgray. Highly calcareous, small quantity of argillaceous material. Contains two pelecypod beds, each approximately one foot thick, cemented by a clean crystalline

.......................................................................................................... limestone

Micri tePlaty, light olive gray, well bedded, dense, weathers to a light tan. Prominent slope forming unit. ................................................................

Sandy LimestoneLaminated to thin bedded, grayish orange color, weathers to a pale yellowish brown. Middle beds consist of fissile calcareous siltstone with abundant primary sedimentary features; ripple marks, rain imprints, worm trails are abundant on some bedding planes. Medium tan color weathers light gray. Pillow structures (6" - 12" x 3") on some horizons, underlain by cross bedded shale. ....................................................................

Calcareous Siltstone-Slope forming unit, laminated to thin bedded. Pale yellowish gray, weathers dark gray. Contains one ledge fotming unit near the middle, olive gray, weathers into splintery fragments. ............................

Calcareous Fissile Siltstone-Ledge forming unlt, dark yellowish gray; weathers light olive gray. Weathering produces splintering material. ........

Calcareous Fissile Siltstone-Slope forming unit, very calcareous, thin bedded. Light olive gray, weathers tan. Grades into platy material near top .....

Calcareous, Fissile Siltstone--Ledge unit, light olive gray, very thin bedded, weathers into splintery fragments. Highly calcareous. ....................................

Argillaceous Limestone-Prominent slope forming unit, covered with several feet of rubble. Three trenches were dug at 20 ft. intervals. a. Laminated, pale yellowish brown to gray. b. Thin bedded, high argillaceous content. Dark tan to dark gray color. c. Laminated to thin bedded, light brown to gray, very dense, exhibits

conchoidal fracture. ....................................................................................

Prominent ledge forming unit divided into three zones. a. Micrite-Thick bedded, homogeneous, contains two thin coquinas. Small

pockets containing coquinoid material above and below coquina. ........ .................................... b. Calcareous Shale-Thin bedded, dark olive gray.

c. Argillaceous Limestone-Thin bedded, yellowish gray. Contains abundant pelecypods Vaugonia sp. and Asiarie sp. One ammonite was collected.

............................................................................................................

Calcareous Siltstone-Thin bedded, yellowish gray in lower beds, very pale .................................................................................... orange in upper beds.

Lithology changes sharply, unit was divided into five subunits. a. Calcareous Siltstone-Fissile, pale yellowish brown; some beds of micrite. b. Gastropod skeletal limestone-Brownish gray on both fresh and weath-

ered surfaces. ................................................................................................ c. Micrite-Medium bedded, pale red weathers moderate orange pink. ........ d. Gastropod skeletal limestone-Dark yellowish brown, weathers pale

yellow ........................................................................................................ e. Micrite-Medium bedded, pale red, weathers moderate orange pink. ....

Oolitic Skeletal LimestoneThin bedded, pale red weathers grayish pink. Skeletal material abundant. Crinoid stems (Penirrinus sp.), pelecypod fragments and possible corals. ..............................................................................


APPENDIX B (Continued)

3 Argillaceous Limestone-Thin bedded, slope forming unit. Moderate reddish brown. Poorly indurated. High clay mineral content. ........................ 8.5

2 Quartzose Calcareous Sandstone-Fine grained, prominent ledge former. Pale reddish brown, weathers moderate orange pink. Good lateral continuity. 2.5

1 Quartz Calcareous Sandstone--Medium bedded, pale reddish brown. Clastic material appears to have been derived from underlying sandstone. Weather- ing produces moderate reddish brown color. ............................................ 4.5

REFERENCES CITED

Chilingar, G. V., 1956, Use of Ca/Mg ratio of limestones and dolomites as a geologic tool: unpub. Ph.D. thesis, Univ. of Southern Calif., 140 p.

---- , 1962, Dependence on temperature of Ca/Mg ratio of skeletal structures of organisms and direct chemical precipitation out of sea water: Southern Calif. Acad. Sci. Bull., v. 61, part 1 , p. 45-60.

---- , 1963, Ca/Mg and Sr/Ca ratios of calcareous sediments as a function of depth and distance from shore: Jour. of Sed. Pet., v. 33, no. 1, p. 236.

Diamond, J. J., 1955, Flame photometric determination of strontium in Portland cement: Anal. Chemist, v. 27, no. 12, p. 913.

Eardley. A. I., 1938, Sediments of Great Salt Lake, Utah: Amer. Assoc. Petrol. Geol. BLII., v: 22, p. 1359-1387.

Frederickson, A. F. and Reynolds, R. C., 1960, How measuring paleosalinity aids exploration: Oil and Gas Jour., v. 58, p. 154-158.

Furman, N. H., Editor, (1962), Scotts standard methods of chemical analysis, 6th ed., v. 1, The Elements: D. Van Nostrand Company, Inc., Princeton, New Jersey.

Harder, H., 1961, Einbau Von Bor in detritische tonmlnerale: Geochimica Et Cos- mochimica Acta, v. 21, p. 284-294.

Illing, L. V., 1954, Bahaman calcareous sands: Amer. Assoc. Petrol. Geol .Bull., v. 38, p. 1-95.

Imlay, R. W., 1948, Characteristic marine Jurassic fossils from the western interior of the U.S.: U. S. Geol. Survey Prof. Paper 214-B.

---- , 1953, Characteristics of the Jurassic Twin Creek Limestone in Idaho, Wyo- ming and Utah: Intermountain Assoc. Petrol. Geol. Guide to the Geology of Northern Utah and Southeastern Idaho, 4th Ann. Field Conf., p. 54-62.

---- , 1956, Paleogeographic maps of the United States during the Jurassic Period: in Paleotectonic Maps Jurassic System, U. S. Geol. Survey, Washington, D.C.

---- , 1957, Paleoecology of Jurassic in the Western Interior of the United States: Treatise on Marine ecology and paleoecology, Memoir 67, v. 2, Paleoecology, p. 438-469.

Kelley, V. C., and Silver, C., 1952, Geology of the. Caballo Mountains; N. Mex. Univ. Pub. Geol., no. 4, 286 p.

Kulp, J. L., Turekian. K. and Boyd, D. W., 1952, Strontium content of Limestone and Fossils: Bull. Geol. Soc. Amer., v. 63, p. 701-716.

Leighton, M. W . and Pendexter, C., 1962, Carbonate rock types: Classification of carbonate rocks, Amer. Assoc. Petrol. Geol., Memoir 1, p. 33-62.

Odum, H. T., 1950, Strontium bi~geochemistr~, ecosystems, and paleoecological tools; Nat. Research Council Comm. Treatise marine ecology and paleoecology, Rept. 1949-50, no. 10, p. 55-58.

Siegel, F. R., 1961, Variations of Sr/Ca ratios and Mg contents in recent carbonate sediments of northern Florida Keys area: Jour. Sed. Pet., v. 31, no. 3, p. 336-342.

Turekian, K.. 1955, Paleoecologic significance of the strontium-calcium ratio in fossils and sediments; Bull. Geol. Soc. Amer., v. 66, p. 155-158.

Trask, P. D., 1937, Relation of salinity to calcium carbonate content in marine sediments: U. S. Geol. Survev Prof. Paoer 186 N. a. 27.

Walker, C. T., 1962, Separation techniques in sehihentary geochemistry illustrated by studies of boron: Nature, v. 194, p. 1073-1074.

Williams, H., Turner, F. J., and Gilbert. C. M.. 1954. Petrographv: W. H. Freeman - . and Co., San ~rancisco, p. 270.

Manuscript received May 12, 1965

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