LEO F. LAPORTE Dept. Geology, Brown University, Providence, R. I.

Paleoecology of the Cottonwood

(Permian), Northern Mid-Continent

Abstract: The Cottonwood Limestone, a thin (7 abundant, and well-preserved fauna, especially feet or less), laterally persistent, fossiliferous, marine , molluscs, and ammodiscid foraminifers limestone and calcareous , has been traced in (shelly ). At the southern limit of its outcrop outcrop from southeastern to north- the Cottonwood Limestone is a medium crystalline central . Detailed field and laboratory limestone with thin, shaly layers; molluscs, Osagia, analyses reveal 5 distinct facies. From southern and quartz silt are common (silty Osagia fades). Nebraska to central the lower half of the The bioclastic and fusuline facies were deposited Cottonwood Limestone is a fine-grained buff lime- in shallow, well-lit, moderately turbulent waters stone composed of finely comminuted , es- having very small amounts of terrigenous influx; pecially the algal-foraminiferal intergrowth Osagia, water circulation was variably restricted. The , and bryozoans (biodastic facies). shelly facies was deposited in a less turbulent and The upper half of the unit in this region is fine- deeper-water environment, having good circu- grained buff limestone with abundant small fusu- lation and relatively large amounts of terrigenous lines; fossils typical of the bioclastic facies are also material entering from the south; the silty Osagia present (fusuline facies). In central Kansas the Cot- facies was formed in a shallower, more turbulent, tonwood Limestone is a fine-grained, gray, massive nearer-shore environment marginal to the shelly limestone having abundant broken thalli of the facies. Separating these two facies provinces was a calcareous alga, Anchicodium, and some Osagia broad shoal where the platy algal facies was de- (platy algal facies). The Cottonwood in southern posited; here waters were moderately turbulent, Kansas and northern Oklahoma is an mterbedded well-lit, shallow, and somewhat restricted in circu- limestone and calcareous shale with a very diverse, lation.

CONTENTS Introduction 522 General statement 541 Acknowledgments 522 Field 541 Regional setting 522 Laboratory 541 Stratigraphy 522 References cited 543 Paleogeography 523 Cottonwood facies 525 Figure Bioclastic facies 525 1. Stratigraphic section of Council Grove Group . 523 Description 525 2. Paleogeography of area during deposition of Distribution 528 Beattie Limestone 524 Fusuline facies 530 3. Restored section of Cottonwood Limestone . . 526 Description 530 4. Summary of thin section data 528 Distribution 530 5. Cottonwood Limestone sampling localities . . 529 Platy algal facies 531 Description 531 Plate Following Distribution 531 1. Cottonwood Limestone: field ' of various Shelly facies 532 facies Description 532 2. Cottonwood Limestone: photomicrographs of Distribution 532 bioclastic and fusuline facie: Silty Osagia facies 533 3. Cottonwood Limestone: photomicrographs of •534 Description 533 platy algal, shelly, and silty Osagia facies . Distribution 533 4. Cottonwood Limestone: bedding surfaces, bur- Interpretation of facies 534 row structures, and photomicrograph of General statement 534 Osagia sp y Northern facies province 534 Southern facies province 538 Table Shelly facies 538 1. Cottonwood facies mineralogy 527 Silty Osagia facies 539 2. Summary of Cottonwood facies characteristics . 536 Summary 539 3. Summary of Cottonwood facies composition . . 537 Conclusions 540 4. Environmental factors responsible for Cotton- Appendix on methods 541 wood facies differentiation 540

Geological Society of America Bulletin, v. 73, p. 521-544, 5 figs., 4 pis., May 1962 521

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Company read the manuscript and offered INTRODUCTION helpful comments for its improvement. This study describes the sedimentary facies within the Cottonwood Limestone and ex- REGIONAL SETTING plains them in terms of the primary deposi- tional environment. This stratigraphic unit of Stratigraphy the northern Mid-continent was selected for The Cottonwood Limestone Member is the study because: (1) the unit is thin (7 feet or lowest of three members comprising the Beattie less) and can be traced for a distance of more Limestone Formation of the Council Grove than 250 miles; (2) the line of outcrop transects Group, Wolfcampian Series, Permian System. the original sedimentary basin almost from The Cottonwood lies structurally within the shore to shore; (3) the fauna and flora are Prairie Plains Homocline (King, 1951, p. 47), fairly well-known, at least to the generic level; which strikes north from south-central Okla- (4) the physical stratigraphy has been worked homa through eastern Kansas to southeastern out in detail, permitting concentration of ef- Nebraska and dips at very low angles to the fort on facies description and analysis; (5) re- west. sults of a similar study of the two overlying The Council Grove Group (Fig. 1) consists units, the Florena Shale and Morrill Limestone of many thin, fossiliferous, marine and (Imbrie, 1955; Imbrie and others, 1959), pro- intercalated with non-marine sand- vide additional criteria for interpreting Cot- stones and shales. The Beattie Limestone con- tonwood characteristics; (6) several facies of tains, in ascending order, the Cottonwood the Cottonwood Limestone are found through- Limestone, Florena Shale, and Morrill Lime- out upper Paleozoic cyclic deposits of the stone, fossiliferous marine shales and limestones northern Mid-continent. having an aggregate thickness of 3-24 feet. This investigation was also undertaken to Despite this relative thinness the Beattie can discover some of the ecologic controls of the be traced in outcrop from southern Nebraska major taxa in this unit. A record of the to northern Oklahoma and, in the subsurface, distribution and abundance of fossils could westward to the Colorado-Kansas line (Imbrie serve as the basis for limited ecologic interpreta- and others, 1959). Immediately above and be- tion. Future studies may focus on the func- low the Beattie are variegated non-marine tional relationships of the fossils in meeting the shales, the Stearns and Eskridge which locally demands imposed by the environment, and on contain thin coal beds. This alternation of the dynamic relationships within and among marine and non-marine beds is typical of upper the various fossil communities. Paleozoic deposits of the northern Mid-con- tinent and records successive transgressions and ACKNOWLEDGMENTS regressions of late Paleozoic seas. The writer is indebted to Professors John Strata in this part of the geologic column are Imbrie and Norman D. Newell of Columbia laterally persistent and of uniform thickness. University for their guidance and encourage- Changes in thickness are gradual and system- ment. Detailed field work by J. Imbrie, L. S. atic. Individual beds within the upper Pennsyl- Kornicker, and W. G. Heaslip was most valu- vanian and lower Permian commonly exhibit able in verifying the correlation of the Cotton- contrasting facies along the line of outcrop. wood. Field assistance by E. G. Purdy is also The Cottonwood Limestone was first named appreciated. Chemical analyses were made by by Haworth and Kirk (1894, p. 112-114) the K. Kalle and W. Waugh, under the direction Cottonwood Falls Limestone from quarries of R. T. Runnels, of the Kansas Geological near Cottonwood Falls, Kansas. Prosser (1894, Survey. p. 37-41) renamed it the Cottonwood Forma- The author is grateful for the generous sup- tion and included within it the overlying port of the State Geological Survey of Kansas. shale. Later, Prosser (1902, p. 712) subdivided The National Science Foundation provided the this renamed formation into the Cottonwood writer with a Cooperative Fellowship during Limestone and Florena Shale. Condra and the summer of 1959, as well as funds (NSF Busby (1933, p. 13) formally proposed that the G-4535), which made the latter stages of Beattie Limestone Formation include the Cot- laboratory research possible. tonwood Limestone, Florena Shale, and Morrill Robert N. Ginsburg of Shell Development Limestone members. The type locality of the

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Beattie Limestone is a quarry in Beattie, seaway, the Kansas Strait, was bounded on the Kansas. northeast by a low-lying continental mass and on the west and south by tectonic lands in Paleogeography parts of Utah, Colorado, Arizona, New Paleogeography inferred for the northern Mexico, Oklahoma, and Texas. The Kansas Mid-continent region during deposition of the Strait had its principal connection with the Beattie Limestone is shown in Figure 2. An open ocean through the Arkansas Embayment elongate seaway extended from northeastern on the southeast; a lesser connection may also Wyoming, southeastward across Kansas to have existed to the southwest (Tanner, 1959). Arkansas and northeastern Oklahoma. This Lying between the Kansas Shelf Lagoon and

Feet tE~7 > x — Speiser Shale -300 Funston 1 s ^fi^""— *— — Blue Rapids Sh

[* L 'L i * i Grouse. Ls. ix^"^F-^3 Easly Creek Sh. V * l \Middlebura Ls. s f x—^-x — Hooser Shale Bader Limestone T — ' * Eiss Limestone x O 1 1 *— — • Stearns Shale UJ Ci— — i- * ^Morrill Limestone^ Beattie CL o - 200 ^-JL=- _ Florena Shale 3 L- L ^ L 1 Cottonwood Ls Limestone 0 i- ^E^r-rz^— i« M Eskridge a> z ¥=^*j,^j. *~

Shale o SYSTE M poc" — ^-ammm E

1 -x x PERM I A N ^J — . Neva Limestone o u. ) Salem Point Sh. Grenola _i cc LOWE R LJ ^-' L * I ' i Burr Limestone Limestone 0

Counci l Q_ J — Legion Shale - 100 '^^.j i-j. ^ jr^v^Sollyards Ls. J Roca Shale

7E3?rr>Er^<3= Bennett Shale Red Eagle Ls. ' ^ T j^— ---^J3lenroc k Ls. ) Johnson _\L^.jI^EK Shale ^\ * * t1 1* ^F"Sv^l-ong Cl"eek Ls. y1 fr-r±--±f L-^^" Hughes Creek Sh. Foraker Limestone ', TT~ ' — i . —S I Americus Ls. _ n

Coal or lignite

Limestone Geodes in limestone r2T1 Cherty limestone Figure 1. Stratigraphic section of the Council Grove Group (after Jewett, 1960)

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EMBAYMENT

TEXAS OKLAHOMA KANSAS NEBRASKA

Uplift Subsidence

Approximate O 5O IQO ISO 20O Miles vertical scale Horizontal scale

Figure 2. Paleogeography of area during deposition of Beattie Limestone (from Imbrie and others, 1959)

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the Arkansas Embayment was the Greenwood COTTONWOOD FACIES Shoal which trended northeastwardly. The concept of the Greenwood Shoal is Bioclastic Facies critical in understanding Cottonwood facies. Description. From southern Nebraska to Because only part of the evidence for this central Kansas the lower half of the Cotton- paleogeographic feature is drawn from data wood Limestone is a buff to yellow, cherty, gathered for the present paper, a summary of fine-grained limestone composed of finely com- the several lines of evidence is given (See minuted fossils, especially the algal-foraminif- Imbrie and others, 1959, for detailed discus- eral intergrowth Osagia, echinoderms, and sion) : bryozoans (PI. 1, fig. 1). This facies averages 3 (1) ISOPACHOUS DATA: An isopachous map feet thick (Fig. 3). Well-weathered outcrops of the Florena Shale based on several thousand usually display good planar orientation of the electric logs, laterologs, and radioactivity logs component carbonate grains. Some outcrops and contoured on a 4-foot interval shows have inclined bedding which suggests either systematic thinning of the Florena over the cross-stratification or scour and fill structure site of the postulated shoal. (PI. 1, fig. 4). The few large fossil fragments (2) ZONE OF FACIES CHANGE: All three mem- have their long dimensions parallel to the bed- bers of the Beattie Limestone change facies ding; no fossils were seen in what may have across the postulated shoal. been in situ growth position. (3) LITHOLOGIC EVIDENCE: Over the site of There is often a layer of nodular chert near the postulated shoal the Morrill Limestone is the middle of the bioclastic facies. Individual characterized by breccia composed of algal- nodules, 1-3 inches thick, are, in cross section, bound carbonate and by mud-cracks, which re- elliptical or subcircular to irregularly shaped flect a very shallow and turbulent area. Clay masses. Some nodules coalesce with others, mineral suites within the Florena Shale change vertically or laterally. The nodules do not markedly across the postulated shoal. The grade into the host limestone lithology but mica-chlorite suite on the north and the illite- have sharp contacts with it. Macroscopic and montmorillonite suite on the south indicate dif- microscopic examination of the chert and ferent source areas whose erosional products limestone matrix reveal no significant differ- were not significantly mixed. Total clay abun- ences between the two in particle size, com- dance in the Florena decreases over the shoal, position, or orientation. The boundary suggesting winnowing of clay off the shoal into cuts across individual grains rather than flanking basins. A well-developed, algal lime- around them. Cottonwood chert is secondary, stone facies of the Cottonwood coincides with although primary differences in grain-size, the postulated shoal. The abundance of algae chemical composition, and physical properties suggests shallow and well-lit waters. may have controlled the site of silica deposi- (4) FAUNAL PROVINCES: Fossils within the tion. Florena and Cottonwood differ on the two sides The bioclastic facies immediately above the of the shoal. Taxonomic diversity is also Eskridge Shale has abundant, gray to black, greater on the south side of the shoal. Mol- irregularly shaped pellets averaging }^-l mm luscs, especially, are more varied and abundant in diameter (PI. 2, fig. 3). This layer is much south of the shoal. Several taxa, including less fossiliferous than the rest of the bioclastic Omphalotrochus, Bellerophontacea, Ammon- facies, and at Locality 7 stromatolite-like ob- oidea, and Nautiloidea occur south of the shoal jects are found with the pellets. The pellets are but not north of it. Apparently these molluscs composed of fine-grained organic debris, inhabited waters with freer connection to the quartz, and clay aggregates. The pellets re- open ocean. semble phosphatic pellets, but chemical analy- The Greenwood Shoal may have been tec- sis indicates that they lack significant amounts tonically controlled; that is, it was an area of phosphorous. which subsided less than areas north or south Small isolated masses of fusulines within the of it during Beattie time. This difference in bioclastic facies are found at localities 10 and subsidence rate kept the shoal topographically 38. These may be burrows dug in the bioclastic higher than the surrounding areas, thereby in- sediment which have been filled from above fluencing the depositional environments of the during deposition of the fusuline facies (PI. 4, shoal. It may have been related to activity fig. 3). along the Bourbon Arch, a post-Mississippian Most of the organic remains are 1 mm in structure of southeast Kansas (Jewett, 1951). diameter or less, with many fragments reach-

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SOUTH -OKLAHOMA^* -KANSAS- -ARKANSAS EMBAYMENT- -GREENWOOD SHOAL-

THIN SECTION POINT-COUNT ANALYSIS VERTICAL EXAGGERATION 1:21,000 THIN SECTION AND CHEMICAL ANALYSIS POINT-COUNT ANALYSIS AND CHEMICAL ANALYSI CHEMICAL ANALYSIS SAMPLE NUMBER

SILTY OSAGIA FACIES Igjj] SHELLY FACIES PLATY ALGAL FACIES £^ FUSULINE FACIES. I1- > Al BIOCLASTIC FACIES

Figure 3. Restored section of Cottonwood Limestone showii

ing 2 mm; few are larger than 2 mm (PL 4, The Osagia colonies show little host-particle fig. 2). All the inorganic grains are less than preference. Many of the colonies are abraded }/% mm. The cementing matrix is finely crystal- and disintegrated with broken pieces of the line calcite.1 Aside from the general parallelism colonies strewn throughout the matrix (PI. 2, of particles to the bedding, the distribution of fig. 4). They do not have the characteristic particles within any one thin section seems bean shape exhibited in osagite limestones random; organic grains are rarely segregated (Twenhofel, 1919). There is a wide range in into patches, stringers, or lenses. the degree of Osagia encrustations with many Recalculation of the weight per cent of the grains being entirely free of Osagia while others various oxides shows that the bioclastic facies are only partially coated. Heavily coated is a relatively pure limestone (Table 1). The particles commonly show recrystallization of free silica is fine-grained interstitial chalcedony the oldest parts of the colony (PI. 2, fig. 3). or quartz disseminated throughout the rock; Our observations agree with Johnson's (1946) very little detrital quartz is seen in thin section. that the Osagia colony is composed of an en- The fraction finer than 1/8 mm averages 59 crusting foraminifer, Nubecularia? and a lime- per cent of the total rock by volume. The precipitating (blue-green?) alga. The colonies single dominant biotic element is Osagia; apparently were rather friable when first second in abundance are bryozoans and formed, for most of the fragments from these echinoderms, with other taxonomic groups 2 More recent work indicates that Johnson's Nube- being less abundant (Fig. 4; Tables 2, 3). cularia is not Nubecularia, scnsu striao; Donald F. Toomcy (Personal communication) believes it is a 1 Terminology for matrix grain-size follows Folk "plumose calcitornellid" and has found a variety of en- (1959). crusting forms associated with Osagia.

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NEBRASKA-

KANSAS SHELF LAGOON- 9 50 25 ?4

-FACIES

.mpling control and areal distribution of facies. Sample localities shown on Figure 5.

colonies seem to have disaggregated from the sediment surface. The encrusting forammifer is parent mass instead of breaking off cleanly. not always apparent in the Osagia colonies. They were also mucilaginous and adhesive, be- This may be a preservational phenomenon, or cause some of the colonies as they grew in- it may mean that occurrence of the fora- corporated broken skeletal grains from the minifer with the algal material is not biologically

I ABLE 1. COTTONWOOD FACIKS MINERALOGY

Minor Calcite Dolomite Silica* Clay constituents** Bioclastic 84.9 2.4 3.6 7.5 1.3 Fusuline 87.7 1.8 2.8 6.2 0.9 Platy algal 91.7 0.7 1.2 6.2 0.4 Shelly lime-rich 81.1 2.6 4.7 9.6 1.6 clay-rich 46.9 3.3 13.1 32.6 3.3 Silty Osagia lime-rich 75.7 2.8 8.3 10.4 2.7 clay-rich 40.5 2.2 31.8 19.7 5.5

* See Imbrie and Poldervaart (1959) for method of calculation. Number of analyses per facies: 8 fusulinc, 6 bioclastic, 5 platy algal, 5 lime-rich shelly, 4 clay-rich shelly, 1 lime-rich .silty Osagia, and 1 clay-rich silty Osagia. t Includes detntal and interstitial quartz or chalcedony ** Includes gypsum, pyrite, hematite, rutile, apatite, and plagioclase (albite)

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necessary (i.e. some kind of symbiosis) but Some of the scarcity is due to recrystallization rather accidental owing to mutually similar re- and comminution. Recrystallization and com- quirements of habitat and attachment surface. minution, however, have occurred in other Echinoderms are important contributors to facies where brachiopods and molluscs are well the fauna of this facies. Almost all occurrences represented; moreover, most brachiopods and

5 FEETJ SCALE

20% Figure 4. Summary of thin section data showing taxonomic composition of biota. Localities 42 and 13 are within the platy algal facies; localities 10, 7, and 5 are from the bioclastic and fusuline facies; Lo- cality 35 is from the silty Osagia facies; and Locality 15 is from the shelly facies.

in thin section and at the outcrop are as certain molluscs can be identified as such even isolated ossicles or small groups of ossicles. when found as small fragments. The present Bryozoans of various growth forms, i.e. en- low abundance of these groups in the bioclastic crusting, ramose, fenestrate, and pinnate, are facies was probably a trait of the original com- common faunal elements. All the colonies are munity. seen as small fragments of what were originally The few fusulines that occur in this facies are larger colonies of unknown dimensions. Paleo- primarily members of the genus Schubertella. textularid foraminifers are more abundant in Schtvagerina, so abundant in the fusuline facies, this facies than in any of the others. is rare in the bioclastic facies. Brachiopods and molluscs are relatively rare. Distribution. The northern boundary of

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L zH \x^°'j i j J J ^"> *j*Cj-orV —J <4. '

WRRIS ~t_n IS/ JWAE^UNSEE j/LYON I

SCALE 0 5 10 20 30 40 50

Figure 5. Cottonwood Limestone sampling localities. Line AB is line of section in Figure 3.

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this facies (and the overlying fusuline facies) except for the abundance of fusulines, the is not known because of glacial cover in lithologic and biologic character of the layer in southern Nebraska. The southern boundary is each facies is typical for that facies. In this in Chase County, Kansas, where the calcareous same area, the lower part of the overlying alga, Anchicodium, is present in significant Florena Shale has a well-developed fusuline- amounts (Figs. 3, 5). The sudden appearance rich horizon, which is a continuation of the and abundance of this alga mark the transition fusuline-rich layer at the top of the Cotton- from the bioclastic facies to the platy algal wood. facies. Although the lateral extent of the bio- As in the bioclastic facies most of the organic clastic facies is more than 150 miles, the facies fragments are 1 mm or less in diameter, except seems very homogeneous, and no significant for the fusulines which average 5 mm in length. trends in lithology, biota, or mineralogy have The small amounts of inorganic material, been observed along the length of outcrop. mostly interstitial quartz and clay aggregates, are rarely greater than 1/8 mm; the matrix is T'usulme Facies finely crystalline calcite. Description. The upper half of the Cotton- This facies averages slightly more carbonate wood Limestone from southern Nebraska to than the bioclastic facies (Table 1). The fraction central Kansas is a buff to gray, cherty, fine- finer than 1/8 mm averages 56 per cent. grained limestone with abundant small fusulines Fusulines are the dominant taxonomic group; (PL 1, fig. 1). It averages 3 feet in thickness Osagia is also an important organic constituent (Fig. 3). and is about half as abundant as in the bio- The boundary between the overlying fusu- clastic facies. Other taxonomic groups are less line facies and the underlying bioclastic facies important and occur with the same frequency as seen at the outcrop is usually marked by a or less as in the bioclastic facies (Tables 2, 3; shaly parting and always by sharp textural dif- Fig. 4). ferences. Chemical solution and mechanical The fusulines in this facies belong primarily separation of fusuline tests from the fusuline to the genus Schwagsrina; Schubertella is much facies give the rock a rough and pitted texture, less common. The tests of the fusulines are while the bioclastic facies has relatively smooth often broken and worn; the greater proportion, surfaced exposures. The vertical transition be- however, are well-preserved (PI. 2, fig. 1). The tween facies is sharp and clearly seen at the fusuline tests are commonly coated with outcrop, taking place within a few inches. Osagia colonies (PI. 2, fig. 2). There is a wide However, thin-section analysis indicates that range in the size of the tests; most specimens, the transition is gradual and is completed however, seem to be in the adult or ephebic within 1 foot vertically. stage. Scour and fill structure in this facies is de- Osagia colonies encrust many kinds of or- veloped similarly to that in the bioclastic facies. ganic fragments; the shape of the colonies is No preferred azimuthal orientation of fusulines irregularly elliptical in outline. The matrix of is observed either on bedding surfaces at the the rock contains many broken and disinte- outcrop or on peels parallel to the bedding. grated parts of Osagia colonies. There is, however, a definite tendency for the Other organic elements occur as finely com- long axis of the fusulines (as well as for the long minuted fragments. Few large fossil fragments dimensions of non-fusuline organic constitu- or whole specimens are found. Isolated echino- ents) to be parallel to the bedding. derm ossicles, bryozoan debris, occasional dis- Nodular chert is present at all localities articulated ostracode, and pele- where this facies has been examined; it occurs cypod valves, and pygidia are charac- in the same way as in the bioclastic facies. Gen- teristic organic remains. Paleotextularid forams erally, the chert is confined to the middle por- are commonly present. tion of the fusuline facies. Distribution. The northern limit of this Not included within this facies is a fusuline- facies is unknown because of glacial cover in rich layer, 1-3 inches thick, which occurs at southern Nebraska. The southern boundary of the top of the Cottonwood from central the full development of the fusuline facies is Kansas to northern Oklahoma, almost to the in Chase County, Kansas (Figs. 3, 5). A very southern limit of its exposure. Each of the thin fusuline-rich layer at the top of the Cot- Cottonwood facies found in this region—platy tonwood Limestone continues southward into algal, shelly, and silty Osagia—has this layer; Oklahoma. The fusuline facies is strikingly

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similar along the full length of its outcrop. No facies. Nodular chert is occasionally found, but clear-cut differences in lithology or biology it is neither common nor characteristic for this across this area of outcrop can be demon- facies. The matrix is medium to finely crystal- strated; in the northern part of Kansas, where line. The finer than 1/8 mm fraction averages east-west control is greatest, this homogeneity 68 per cent. The platy algal facies has the of facies is maintained. highest carbonate content of all Cottonwood facies, while calculated detrital minerals in- Platy Algal Facies cluding rutile, albite, and apatite are lowest for Description. For about 40 miles across cen- all facies, as is the dolomite/carbonate ratio tral Kansas the Cottonwood Limestone is a buff (Table 1). The dominant organic constituent to gray, massive, fine-to medium-grained of this facies is Anchicodium, accounting for limestone composed of very abundant broken more than 50 per cent of the biota. Lesser con- thalli of the calcareous alga, Anchicodium ; stituents include Osagia, bryozoans, and echi- some Osagia is also present (PL 1, fig. 2). The noderms (Fig. 4; Tables 2, 3). facies displays some variation in thickness, Johnson (1946) described several species of ranging from less than 3 feet to more than 7 Anchicodium from Pennsylvanian and Per- feet, and averages about 4]/2 feet (Fig. 3). mian rocks of Kansas. The alga in this facies is On weathered outcrop surfaces the frag- referred to that genus, following Johnson's de- mented algal thalli stand in relief giving the scriptions.3 rock an irregular, crenulated texture (PI. 1, The mode of growth of this alga is unknown fig. 2). The thalli, which are thin, wavy, plate- owing to the absence of hold-fasts or definite like structures, usually have their long dimen- areas of attachment. Konishi and Wray (1961) sion parallel to the bedding. Commonly, the offer morphological evidence that Eugonophyl- algal fragments are closely appressed; in some lum, an alga closely related to Anchicodium, instances the algal debris is less abundant, and lived in an upright position. This interpreta- individual thalli lie either vertically or ob- tion seems applicable to Cottonwood Anchi- liquely to the bedding (PL 3, figs. 3, 4). These codium. positions seemingly are not in situ growth posi- Many Anchicodium fragments are partly tions, for there are no visible areas of attach- coated or encrusted by small colonies of Osagia ment of the thallus to the substrate. The net (PL 3, fig. 3). Osagia occurs predominantly as amount of algal material increases northward pieces broken and isolated from larger colonies; and southward toward Locality 42, where the there are few large and complete colonies. Cottonwood Limestone attains its maximum Distribution. The platy algal facies extends thickness and has the highest proportion of from southern Chase County to Greenwood Anchicodium. This alga occurs in a matrix of County, Kansas, interfingering northward with fine- to coarse-grained fossil debris; in some the bioclastic facies. It is found in the strati- instances, this skeletal material forms a lens graphic position of the fusuline facies at its several feet long and a few inches thick. northernmost development (Figs. 3, 5). Many of the algal thalli are curved, and The change in facies southward is more when the thallus has its concave side upward, abrupt. At the next Cottonwood exposure it is often filled with fine-grained calcite. Ap- south of the southernmost development of the parently, the shallow depression formed by the platy algal facies, there is no trace of Anchi- thallus served as a site for the accumulation of codium. At this outcrop (Locality 21) the lime mud. Areas between algal thalli are some- lithology is quite similar to the typical shelly times filled with sparry calcite, representing facies which comprises the Cottonwood Lime- secondary calcite deposition within primary stone in southern Kansas and northern Okla- voids in and around fragmented algal accumu- homa. lations. The platy algal facies, fusuline facies, and The median length of Anchicodium frag- bioclastic facies are similar in lithology and ments is about 1 cm, but many fragments are biology. All three facies are finely comminuted 3-5 cm long; the thickness of the thalli varies 3 from 1/2 to 1 mm. Aside from Anchicodium Internally, the alga resembles Johnson's Anchi- codium, although the external shape is not "cylindrical" there are few whole fossil specimens or large as described by Johnson but platy, or saddle-shaped, and organic fragments. in this regard is more like Ivanovia tenuissima (Khvorova, A thin, fusuline-rich layer occurs at the very 1946) which, however, has a different internal structure top of the Cottonwood, above the platy algal than Cottonwood Anchicodium.

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bioclastic limestones with high lime content, few limy layers, which have a very fine-grained abundant algal remains, and one taxonomic carbonate matrix, are devoid of macrofossils. group dominating the biota. It would be dif- The organic constituents of this facies have ficult to differentiate these three facies by any a wide size-range; some whole specimens are criteria other than the dominant floral or several centimeters in diameter, while a large faunal element in each. These three facies, part of the finer than 1/8 mm fraction is broken taken together, differ considerably from the skeletal material. The median diameter of or- other Cottonwood facies developed farther ganic grains is about 1 cm. The matrix is very southward. finely crystalline to aphanitic; the less than 1/8 mm fraction averages 73 per cent and is Shelly Facies finer than the corresponding fraction in the Description. From central Kansas to north- bioclastic, fusuline, and platy algal facies. ern Oklahoma, the Cottonwood Limestone is The calculated mineralogy of this facies in- an interbedded dark-gray to reddish-gray dicates a shaly limestone to calcareous shale, limestone and calcareous shale, with a very with minor amounts of detritals. The dolo- diverse, abundant, and well-preserved fauna, mite/carbonate ratio, although low in absolute including brachiopods, molluscs, and am- terms, is highest for all the Cottonwood facies modiscid foraminifers (PI. 1, fig. 3). This facies (Table 1). Angular, fine-grained quartz sand varies in thickness from less than 1-6 feet and and silt are commonly seen in thin section in averages about 4j^ feet. There is progressive the calcareous shales and in the limestones. The thinning of the unit from Kansas into Okla- quartz content averages less than 4 per cent, homa (Fig. 3). decreasing upward in the facies. Ammodiscid Straight to slightly curved, cylindrical to forams, ophiuroids, productids, chonetids, cone-shaped objects, several inches long and an Meelylla, Meefyppora, many genera of pele- inch or less in diameter, weather out at the cypods, Amphiscapha, subulitids, a few ceph- outcrop (PL 4, fig. 3). These objects, often alopods, and other taxa are well-represented composed of fine-grained calcium carbonate, in the shelly facies but are virtually absent are casts of burrowing organisms. They usually in the other Cottonwood facies. Conversely, lie vertically or obliquely to the bedding, the fusulines and various algae, which are so larger ones penetrating several different layers abundant in the facies developed to the of sediment. The organisms responsible for north, are rare to absent in the shelly facies. these burrows are not known. However, This diversity may reflect, in part, the state of Allorisma and Schizodus, presumably burrow- preservation of fossil material, but is primarily ing pelecypods, are abundant in this facies. related to the nature of the original environ- Other objects similar to these burrow casts ment. Bryozoans and echinoderms are at least occur which have the size, shape, and cross- as abundant as in the northern facies. Paleo- sectional geometry of the pelecypod, Avi- textularid foraminifers are less abundant; culopinna. The shell material preserved on the arthropods have about the same abundance exterior identifies some of these as steinkerns. (Fig. 4; Tables 2, 3). Others may be burrow casts, for Pinna, the Although thin section analysis does not al- modern counterpart of Aviculopinna, forms ways permit generic identification of the shallow, upright burrows in loose sediment. brachiopods and molluscs, examination of Fossils in this facies are exceptionally well- weathered surfaces at numerous exposures preserved. Many whole specimens of delicate shows that the following genera are present in organisms are found intact on weathered bed- abundance: ding surfaces, including nearly complete fenes- BRACHIOPODS: Derbyia, Meekella, Chonetes, Dic- trate bryozoans, ophiuroids, and crinoid tyoclostus, andjuresania; Composita occurs occasion- calices. Articulated pelecypod and brachiopod ally, but is more abundant in the bioclastic, fusu- valves are very common. Many specimens have Ime, and platy algal facies. well-preserved surface ornamentation (PI. 4, MOLLUSCS: The gastropod that is most abundant fig. 1). Some fossils occur in original growth in the shelly facies is Amphiscapha; farther south, position, e.g., Ai'iculopinna, Allorisma, and conispiral forms (subulitids) increase in abundance. Schizodus, clams which lie vertically to the Pelecypods are particularly plentiful in the shelly bedding. However, much of the skeletal ma- facies, including Aviculopinna, Aviculopecten, Clavi- terial is coarsely comminuted with many frag- costa, Schizodus, Allorisma, and Septimyalina. ments parallel to the bedding (PL 3, fig. 2). A Distribution. The transition from the platy

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algal fades to the shelly facies is relatively of the overlying Morrill Limestone. Appar- abrupt. At Locality 21 the Cottonwood is an ently, Morrill organisms burrowed down interbedded limestone and shale. No Anchi- through the thin Florena Shale into the Cot- codium is present, but some of the limy layers tonwood. resemble the matrix of the bioclastic or platy The range in grain-size of the organic con- algal facies. Other limy beds are typical of the stituents is narrower in this facies than in the shelly facies. At the next locality to the north other Cottonwood facies; most are between (13), typical platy algal facies is present; at the J^-l mm. The matrix is medium to coarsely next locality south (14), typical shelly facies is crystalline. The amount of "recrystallized found (Figs. 3, 5). Because of the increased matrix" varies from 0 to 26 per cent and aver- clay content of the Cottonwood in southern ages 13 per cent. Following petrographic Kansas and northern Oklahoma, it is no longer criteria proposed by Bathurst (1958), some a resistant ledge-former but crops out as a of this recrystallized matrix is due to secondary rubbly, weathered-back slope beneath the infilling by calcium carbonate; the remainder more massive and resistant Morrill Limestone. is the result of recrystallization of fine-grained carbonate by grain growth where larger grains Silty Osagia Facies grow at the expense of the smaller grains. The Description. From northern Oklahoma to amount of original fine-grained carbonate the southern limit of its outcrop the Cotton- which has recrystallized is not known, but it wood Limestone is a medium crystalline, must be less than 13 per cent. Hence, the reddish-gray to light-gray limestone with sev- original fraction finer than 1/8 mm was not eral thin shaly interbeds. Molluscs, Osagia, and more than 56 per cent. quartz silt characterize this facies (PI. 3, fig. 1; The chemical analyses for this facies show PI. 4, fig. 4). The facies thins progressively it to have the largest proportion of terrigenous southward from about 4 feet to less than 1 foot detritus, undoubtedly because of its proximity (Fig. 3). The uppermost horizon lacks the to a major source area in Oklahoma (Table 1). fusuline-rich layer found at all outcrops of the Osagia is the most abundant biotic element in Cottonwood which lie north of this facies. this facies (Fig. 4; Tables 2, 3). The Osagia The silty Osagia facies is the most variable colonies may be irregular coatings on organic of all the Cottonwood facies, the lithologic and fragments, or they may be heavy, concentri- biologic aspects changing from horizon to cally arranged layers encrusting small bits of horizon. Two rock-types seem to be repre- fossil debris. These latter Osagia colonies re- sented in this facies. The first, similar to the semble those described by Twenhofel (1919) shelly facies, has abundant, well-preserved, which are the essential constituents of the large fossil fragments, especially brachiopods, osagite limestones of the Pennsylvanian and molluscs, bryozoans, and echinoderms, in a Permian of the northern Mid-continent. fine-grained carbonate matrix. The other, and Many of the Osagia encrust recrystallized the one which distinguishes this facies from the organic fragments, which, from their shape, shelly facies, is composed of fairly well-sorted, are identified as disarticulated bivalves (PL 4, sand-sized, skeletal debris with sizable quanti- fig. 4). These are probably pelecypod valves ties of quartz silt in a carbonate matrix; many because of the much greater abundance of of the fossil fragments are coated by Osagia. pelecypods than brachiopods in this facies, These two rock-types may be considered end and because pelecypod shells are more suscepti- members of a continum with most of the field ble to recrystallization (inversion from aragon- samples falling between the two extremes. This ite to calcite). This would increase the relative variation in lithology indicates a transitional frequency of pelecypods seen in thin section zone from the shelly facies to a new facies, from a few per cent to more than 13 per cent. marginal to it. Gastropods are common in this facies. Some Pellets, similar to those of the bioclastic are Amphiscapha; most are high-spired forms facies, also occur in the silty Osagia facies. They (subulitids), which are badly recrystallized and are less than 1 mm in diameter, irregular to abraded. Other organic constituents include elliptical in shape, yellow-brown to almost echinoderms (mostly echinoids), brachiopods, black, and are composed of quartz grains, clay and bryozoans. aggregates, and small bits of organic remains. Distribution. The transition from the shelly In some of the shalier layers there are bur- to the silty Osagia facies is very gradual. At row casts which have a matrix identical to that Locality 31 in northern Oklahoma, the upper

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and lower parts of the Cottonwood are typical Northern Facies Province shelly facies; the middle of the unit is silty Osagia facies (Figs. 3, 5). Continuing south- The three facies of this province are fine- ward into Oklahoma, the silty Osagia facies grained, relatively pure limestones, composed becomes more dominant, although there are of the finely comminuted remains of fossil always beds similar to the shelly facies. The organisms. The wide areal extent and homo- southern limit of the silty Osagia facies is not geneity of these limestones preclude a detrital known because of its thinness (6 inches at origin. Constituent particles coarser than 1/8 Locality 44). mm show no observable geographic trends in median grain-size or variations in composition; INTERPRETATION OF FACIES nor are there any rock fragments within these facies. Osagia and fusulines in the bioclastic General Statement and fusuline facies exhibit regular vertical The five facies recognized in the Cottonwood abundance patterns over wide areas, indicating Limestone can be relegated to either one of in situ accumulation of these materials. Recent two facies provinces on the basis of lithologic, studies in modern carbonate sedimentation biologic, petrographic, and geographic con- show that material coarser than 1/8 mm gener- siderations. The silty Osagia and shelly facies ally accumulates in the general locale where it belong to a southern facies province, character- is secreted or precipitated. Ginsburg (1956, ized by a diverse, well-preserved fauna with p. 2419) in his study of Florida sediments has minor but significant amounts of detrital demonstrated "that the bulk of the reef-tract quartz. The bioclastic, fusuline, and platy algal sediment larger than 1/8 mm accumulates in facies belong to a northern facies province, the same sub-environment in which it is pro- characterized by a restricted biota, which is duced, and the reefs are not major sources of finely comminuted, in a fairly pure carbonate sand sized sediment for the adjacent areas." matrix. The organisms which occur abundantly Kornicker (1958) has shown that dead ostra- in one facies province are less well-represented codes in Bahamian sediment are taxonomically in the other (Table 2). the same as the living ostracode populations

PLATE 1. COTTONWOOD LIMESTONE: FIELD VIEW OF VARIOUS FACIES Figure 1. Outcrop of bioclastic and fusuline facies (Locality 10). Upper half of the limestone represents fusuline facies; lower half, bioclastic facies. Overlying and underlying units are Florena and Eskridge shales. Thickness is about 5}^ feet. Figure 2. Outcrop of the platy algal facies (Locality 42). The thalli of the calcareous alga Anchicodium weather out on surface. Upper 2 feet shown Figure 3. Outcrop of shelly facies (Locality 15). Interbedding of limestone and calcareous shale is shown. Upper 4 feet shown Figure 4. Outcrop of bioclastic facies showing scour and fill structure (Locality 9). Chert nodules weather out of matrix at top of photograph. Middle 2 feet shown PLATE 2. COTTONWOOD LIMESTONE: PHOTOMICROGRAPHS OF BIOCLASTIC AND FUSULINE FACIES Figure 1. Thin section of fusuline facies (Locality 10). Abundant fusulines, some heavily coated by Osagia. Foraminifer Nubecularia within Osagia colony coats fusuline at center left. Fragments of Anchicodium present. Transverse sections of bryozoans in upper left and center. Here, and in remaining figures, thin section cut normal to bedding; top of section at top of photograph. 9X Figure 2. Thin section of fusuline facies (Locality 5). Fusulines and Osagia colonies. Large Osagia colony in upper left has grown around fragment partially replaced by silica. Several of the fusulines are abraded and worn. 9X Figure 3. Thin section of pellet zone of bioclastic facies (Locality 7). Dark rounded masses are pellets; small white specks are quartz silt grains included within the pellets. Cast of high spired snail in lower right; hyperamminid foraminifer in center left; stromatolite-like fragment at top, with included fine- grained quartz. 9X Figure 4. Thin section of bioclastic facies (Locality 10). Many small pieces of Osagia strewn throughout matrix; many finely comminuted skeletal fragments coated by Osagia. Trilobite in lower left; foram- inifer in upper left; echinoid spine in center left. 9X

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COTTONWOOD LIMESTONE: FIELD VIEW OF VARIOUS FACIES

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------COTTONWOOD LIMESTONE: BEDDING SURFACES, BURROW STRUCTURES, AND PHOTOMICROGRAPH OF OSAGIA SP.

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inhabiting the area where the sediment is portant organisms which reduce the grain-size forming. Hence, grains larger than 1/8 mm of modern sediments are fish, crustaceans, are found today in the Cottonwood in about echinoderms (eleutherozoans), and molluscs. the same place as that where they were first Other organisms (blue-green filamentous algae produced. Whatever transportation of grains and certain sponges) bore into skeletal debris there might have been, the distances involved and sedimentary grains for food and protection. were probably small, relative to the over-all Undoubtedly such organisms lived in ancient dimensions of the Cottonwood sea. This marine environments and destroyed or modi- postulate is only true in a. general way, because fied carbonate grains then as now. It is difficult the detrital quartz, having some grains slightly to estimate the quantitative significance of larger than 1/8 mm, must have been trans- organic disintegration and modification of ported significant distances. sediments in any given situation in relation to After the death of the carbonate-secreting other destructive forces; nevertheless, Cotton- and carbonate-precipitating organisms, the wood sediments were presumably subject to following three agents were presumably re- comminution and mixing brought about by sponsible for the disarticulation and fragmen- organic activity. tation of the organically derived grains within CURRENTS: Bottom currents were relatively the Cottonwood. vigorous in the northern province of the Cot- ORGANISMS: Organisms play an important tonwood sea. Many colonies of Osagia, which role in early diagenesis of the sedimentary have ill-defined concentricity of growth layers, substratum. Burrowing by organisms for food show truncation by abrasion. Strewn through- or shelter destroys the initial stratification of out the matrix of the bioclastic, fusuline, and the sediments. Voiding of sedimentary grains platy algal facies are particles of Osagia colonies by organisms often binds the passed sediments broken off from larger colonies. Bottom scour into elliptical, spherical, or amorphous aggre- of the substrate and subsequent infilling by gates. Feeding by organisms, which may in- sediments point to intermittent current volve the breaking of shells, carapaces, and action. These inferred bottom currents rubbed tests of animals, as well as the ingestion of sedi- particles against one another, thereby decreas- ments for their included organic matter, com- ing their size. Abrasion of cobble- and pebble- minutes skeletal material. Particularly im- sized material produces silt- and clay-sized

PLATE 3. COTTONWOOD LIMESTONE: PHOTOMICROGRAPHS OF PLATY ALGAL, SHELLY, AND SILTY OSAGIA FACIES Figure 1. Thin section of silty Osagia facies (Locality 44). Abundant comminuted skeletal remains, many recrystallized. Many fragments have thin coating of Osagia. Small spherical white specks are quartz silt grains. Matrix is mostly secondarily precipitated calcite. 9X Figure 2. Thin section of shelly facies (Locality 15). Large fragments of recrystallized bivalves in center; bryozoan remains along top; productid fragment in upper right; fenestrate bryozoan at center right; Nubecularia in lower right. Note fine-grained matrix. 9X Figure 3. Thin section of platy algal facies (Locality 13). Long thin fragments of Anchicodium thalli. Dark irregularly shaped masses are Osagia colonies. 9X Figure 4. Thin section of platy algal facies (Locality 42). Most of the thalli are recrystallized; fragment at top best displays internal structure of thallus. 9X PLATE 4. COTTONWOOD LIMESTONE: BEDDING SURFACES, BURROW STRUCTURES, AND PHOTOMICROGRAPH OF OSAGIA SP. Figure 1. Shelly facies bedding plane (Locality 15). Fossils well-preserved and articulated. Specimens include Derbyia, Meekella, Septimyalina, Clavicosta, Juresania, Amphiscapha, and a fenestrate bryozoan. 0.74X Figure 2. Bioclastic facies bedding plane (Locality 13). Skeletal remains very finely comminuted. 0.9X Figure 3. Large specimen infilled burrow from bioclastic facies (Locality 38); material in burrow has typical fusuline facies lithology. Smaller specimens are burrow casts from shelly facies (Locality 15). 0.28X Figure 4. Thin section of silty Osagia facies (Locality 44). Replaced shell material in upper and lower part of photograph. Dark mass on lower shell fragment is Osagia. Light angular areas between shell fragments are quartz silt grains. 74X

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grains (Marshall, 1927; Pettijohn, 1949). Cal- attributed the origin of mud banks in Florida cite and aragonitc are among the minerals most Bay to such a phenomenon. There, carpets of susceptible to abrasion (Pettijohn, 1949, p. turtle grass (Thalassia testudinum) slow currents 416). so that lime mud settles out of suspension and If vigorous bottom currents are postulated accumulates. Southeast of the Isle of Pines, for the northern facies province, we must ac- Cuba, a 6-inch layer of soupy calcareous mud count for the relatively large proportion of was found below the root mat of a grass bank grains finer than 1/8 mm. One expects removal that is in water less than one foot deep. Har- of this fine fraction by winnowing and trans- baugh (1959) and Konishi and Wray (1961)

TABLE 2. SUMMARY OF COTTONWOOD FACIES CHARACTERISTICS*

Osagia Shelly Platy algal Fusuline Bioclastic Osagia c c c D Fusulines D Anchicodium D Brachiopods c c Molluscs c c Echinoderms c c c c c Bryozoans c c c c A-H c Finely comminuted XXX Coarsely comminuted x X Quartz 0-1 per cent XXX 2-5 per cent X 6 per cent or more x Carbonate 40-84 per cent x X 85-90 per cent X X 91 per cent or more X Fines 55 per cent or less x 56-70 per cent XXX 71 per cent or more X

* D indicates dominant biotic element; c indicates taxon is one of several common biotic elements, A-H foraminifers are ammodiscid and hyperamminid fbraminifers.

porting to quiet water. If, however, the rate have reached similar conclusions regarding the of production of fine-grained sediments in the sediment-trapping potential of Anchicodium Kansas Shelf Lagoon—the depositional site of and related algae from their studies of upper the bioclastic and fusuline facies—was more Pennsylvanian limestones from the Mid-con- rapid than the removal of this material from tinent and Southwest. the Lagoon across the Greenwood Shoal and SKELETAL DECOMPOSITION: The skeletons of into the Arkansas Embayment, an area of many marine invertebrates consist of small quieter water, the Lagoon sediments should masses of crystalline carbonate (calcite or have a relatively high proportion of material aragonite) intimately intermixed with organic less than 1/8 mm. This suggests that circulation tissue. While the details vary from one taxo- between the Lagoon and the Arkansas Em- nomic group to another, there usually is this bayment may have been somewhat restricted. mixture of organic tissue with inorganic The vertical stands of Anchicodium located crystalline material. When the organic matrix on the Greenwood Shoal may have behaved of skeletal material begins to decompose as current baffles checking currents in and through oxidation or bacterial activity, the around the algal growths so that fine-grained imbedded crystalline fraction is freed. Hence, sediments settled out and became trapped. post-mortem decomposition of skeletal matter Ginsburg and Lowenstam (1958, p. 313) produces fine carbonate grains. The kinds of

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carbonate grains vary with the parent organ- Secretion and precipitation by marine organ- isms. Thus, aragonitic secreting corals produce, isms of calcium carbonate from sea water ac- upon total decomposition, a fine-grained mud counts for the lime content of the northern composed of acicular crystals of calcium carbon- facies. The abundance of algae in the northern ate. Calcite secreting molluscs, e.g., Pinna, pro- facies suggests that utilization of carbon di- duce larger, single, hexagonal prisms which oxide by the algae during photosynthesis might range from silt to fine sand. This process of have raised the pH of the surrounding water skeletal decomposition and disintegration could enough to induce precipitation of fine-grained account for much of the finely comminuted carbonate directly from the sea water; how-

TABLE 3. SUMMARY OF COTTONWOOD FACIES COMPOSITION BY VOLUME These intervals are "confidence intervals of the mean." In 19 of 20 samples drawn from a specific facies, the frequency of a particular constituent will fall within the interval calculated. Thus, 19 of 20 samples from the fusuline facies will have fusulmes occurring between 33-53 per cent of the total biota. Upper part of table shows relative percentage of each category expressed in terms of total biota; lower part shows relative percentage of rock-forming elements in terms of total roc\.

Bioclastic Fusuline Platy algal Shelly Siltv Osagia (n = ll) (n = 12) 0 = 15) (n = ll) (n = 6) 2-3 1-3 1-2 1-4 1-4 Ostracodes 1-3 1-3 0-2 0-9 0-1 Echinoderms 5-11 4-11 4-10 15-32 5-28 Brachiopods 2-4 1-3 1-5 9-15 0-15 Bryozoans 7-19 3-6 4-13 12-25 0-10 Molluscs 0-1 0-2 tr-1 3-12 0-13 Fusulines 0-2 33-53 0-1 0-2 0-1 Anchicodium 0-2 1-4 34-67 0 0 Osagia 47-60 15-35 4-20 0-1 5-52 F^pimastopora 0-tr 0-tr 0 0 0-tr Paleotextularids 1-2 0-2 0-2 0 0-tr A-H Foraminifera 0 0 0 0-17 0-1 Rext. valves 0 0 0 0 0-27 ? Organic 13-17 7-16 10-22 19-27 12-32 Total organic 33-44 39-50 23-35 13-24 16-52 Pellets tr-2 0 0 0-tr 0-12 Quartz 0-1 tr-1 0 2-5 4-11 Less 1/8 mm 55-64 47-65 62-74 66-81 17-69 Rext. matrix 0 0 0-6 2-8 0-26

material in the northern facies of the Cotton- ever, unequivocal evidence is difficult to find. wood. Even in areas of recent carbonate sedimenta- These three agents or processes, then, may tion, the importance of this kind of carbonate explain the poor state of preservation of the deposition is strongly disputed. fossil remains in the northern facies. Further- One of the most striking phenomena of the more, the homogeneity of each of the three northern facies province is the strong domi- facies and the fine texture of their sediments nance of one taxonomic group over the others; suggest that rates of sediment accumulation Osagia composes 54 per cent of the total biota must have been less rapid than the rates of in the bioclastic facies, fusulines, 43 per cent mixture and comminution. in the fusuline facies, and Anchicodium, 51 per The high carbonate and low clay and quartz cent in the platy algal facies. In terms of content of the northern facies indicates that absolute abundance, expressed as volume of the little terrigenous detritus entered the Kansas total rock, 15-20 per cent of each facies is Shelf Lagoon from the low-lying continent composed of the remains of the dominant to the north and east. Terrigenous detritus organism in that facies. Such relative and coming from the erosion of the tectonic lands absolute abundance of rather narrowly defined to the south was trapped in the Arkansas taxonomic groups suggests special circum- Embayment. stances of environment. The decrease in taxo-

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nomic diversity is thought to be due to the PRESERVATION: Many excellently preserved, existence of an ecologic gradient which de- whole, and articulated specimens can be seen parted from "normal" marine conditions. on the outcrop; these specimens are often still Various marine organisms having narrow ranges in growth position. Compared to the northern of tolerance survived and reproduced in the facies the amount of comminution of skeletal southern facies province but were gradually material is small. Fragmentary remains, while excluded in the northern facies province. Those common, are relatively large and show little taxa able to maintain themselves in the north abrasion. External ornamentation (e.g. costellae proliferated in great abundance, reacting to of Derbyia, intact spines of the productids, decreased selection pressures, as competing lamellar rugosities of Septimyalina) is preserved groups, less favored, were gradually eliminated. in great detail (PL 4, fig. 1). It is difficult to specify in what way the FINE-GRAINED MATRIX: The relatively large northern facies province might have been an amount of fine-grained material in the shelly "unusual" environment. It is possible, how- facies, including clay, quartz silt, and fine ever, to narrow the range of alternative hy- carbonate, suggests quieter water where these potheses. In the northern province the facies materials could settle and accumulate. Not were deposited in moderately turbulent water only is the finer than 1/8 mm fraction greater where rates of sediment accumulation were in amount in the shelly facies than in the slow and even. The abundance of algal remains northern facies, it is also finer textured. The suggests well-lit, shallow, marine waters having less than 1/8 mm fraction in the bioclastic and abundant calcium carbonate. fusuline facies is mostly fine sand and coarse Whatever critical ecologic factor is invoked, silt, while in the shelly facies this fraction is it must be one which is compatible with the mostly fine and medium silt. The fine-grained environment so far inferred; it must be one terrigenous material undoubtedly came from which varied in intensity, and as it varied, the shallower and more turbulent areas to the particular dominant taxonomic group varied south, marginal to tectonic lands in Oklahoma. from Anchicodium to Osagia to fusuline; Fine-grained carbonate probably came from furthermore, it must be a factor which, when the Greenwood Shoal or from the area north varied, is not recorded in the physical character of it, for the amount of fine carbonate decreases of the sediment, because the matrices of the in the shelly facies southward from the Shoal. northern facies are mutually very similar. PRESERVATION OF PRIMARY STRUCTURES: These requirements exclude differences in Preservation of burrow casts in abundance depth, turbulence, and substrate. However, indicates that stirring of the substrate by cur- lithologically less detectable factors as salinity, rents was minimal and confined to the upper nutrient salts, food, temperature, oxygen con- few inches of sediment. Constant and strong tent, and illumination may have exerted current activity would have mixed the sedi- strong ecologic control. Each of these, except ments and stirred them to depths equal to illumination, is influenced by water circulation. that of the burrowing capabilities of the bur- Change or restriction in circulation, therefore, rowing organisms. Under such conditions is postulated to have been the critical environ- preservation of burrow casts in abundance mental factor in differentiating the northern seems unlikely. In the northern facies the province facies. Restriction may have increased turbulence of the water inhibited the preserva- or decreased with time in the Shelf Lagoon so tion of burrows. Preservation in the shelly that the Osagia-rich community was replaced facies of lime-rich and clay-rich interbeds, by a fusuline-rich community. Restriction of fossils, and in situ growth positions supports circulation resulting in high salinities must this conclusion. have occurred shortly after Cottonwood time, Preservation of primary sedimentary struc- for there is an 8-foot thick gypsum bed, which tures is a direct function of the rates of sedi- lies some 40 feet higher in the stratigraphic ment accumulation and an inverse function of section (Easly Creek Shale), in northern the rates of sediment turnover and reworking Kansas. by currents and organisms. The preservation of Southern Facies Province such structures in the shelly facies indicates that sediment accumulation was more rapid Shelly facies. Relatively quiet water deposi- than sediment turnover. Non-preservation of tion is indicated for this facies from the follow- these structures in the northern facies indicates ing lines of evidence. that sediment accumulation was less rapid than

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sediment mixing. Yet, the absolute rates of ness in the northern facies province provided sediment accumulation must have been about good illumination for algal growth. the same in both facies provinces, because the The taxonomic diversity of the biota in the stratigraphic section for each is virtually the shelly facies is greatest for all Cottonwood same thickness. This, then, implies different facies. Many genera of brachiopods and mol- rates of sediment turnover and reworking for luscs, in particular, which are rare to absent in the two facies provinces. Specifically, current the other facies are very abundant in the shelly action must have been greater in the north facies. Such diversity suggests more nearly than in the south. The presence in the north normal marine conditions, which are related of inclined bedding (scour and fill or cross- to the proximity of the Arkansas Embayment stratification) supports this. to the open ocean. Access to the open ocean Not only is there terrigenous detritus in the presumably provided sufficient circulation of calcareous shales, but the interbedded lime- the water masses so that no unusual environ- stones have up to 5 per cent quartz which is mental conditions could develop. While the coarser than 1/8 mm. The presence of detrital abundance of molluscs in the shelly facies quartz in the limestones means that during might suggest brackish conditions, the abun- periods of carbonate deposition some of the dance of stenohaline forms such as brachiopods, coarser terrigenous detritus was entering the bryozoans, and echinoderms would preclude area. Apparently, erosion and deposition of this. terrigenous material was fairly continuous Silty Osagia facies. This facies is character- throughout Cottonwood time, not being re- ized by coarsely comminuted fossil debris stricted to certain intervals of time. The which is better sorted than that in the shelly alternating lithology of the shelly facies might facies. These data suggest that the silty Osagia record alternating patterns of sedimentation, facies was deposited in water of greater turbu- so that at one time large amounts of clay and lence than existed in the shelly facies environ- silt were deposited, and at other times only ment. The greater abundance of algal material quartz sand and silt entered the lime-depositing in the silty Osagia facies also suggests that the sea while the clay fraction was winnowed and water was shallower and better illuminated than transported elsewhere. The causes of such in the shelly facies. changes in sedimentary patterns can only be The greater amount of detrital quartz indi- speculated upon. Oscillations in patterns of cates that this environment was nearer shore. deltaic sedimentation have been invoked by There is not a proportional increase in clay D. Moore (1959) to explain cyclic deposits in content; in fact, there is less total clay than in the lower Carboniferous of Great Britain; the shelly facies. Evidently, most of the clay Garner (1959) has shown that lithologic varia- entering the silty Osagia facies environment tions can be controlled by periodic climatic was bypassed to quieter water. changes as well as by variations in relief of The biota of the silty Osagia facies is rather source and distance from sedimentary basin. restricted; major organic constituents include The ecologic influence exerted by the Osagia, gastropods, pelecypods, and echinoids; terrigenous detritus is uncertain. The terrige- brachiopods and bryozoans are minor elements. nous material may have had a significant Most of the organic remains are broken and portion of organically derived detritus which abraded; some are rounded. The restriction replenished the organic carbon, phosphate, of the preserved biota may be evidence for a and nitrate concentrations in the waters of the rigorous environment. Substrate instability southern province; in the northern province and variations in salinity and turbidity, associ- where the influx of terrigenous materials was ated with nearness to shore, may have caused very low and where circulation of the water biotic restriction. mass was restricted, the organic carbon, nitrate, and phosphate content of the water may have Summary been in short supply. The differing abundances The fusuline and bioclastic facies were of nutrient elements may, therefore, have deposited in a shallow, well-lit, moderately affected biological productivity. The opacity turbulent, offshore environment which had of the water because of the terrigenous influx some restriction of circulation that increased and relatively greater depth may have pre- (or decreased) with time. The shelly facies vented or inhibited the growth of algae in the was deposited in a less turbulent, offshore shelly facies; clarity of the water and shallow- environment having good circulation; the

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more southerly, silty Osagia facies represents a nearer-shore, shallower, and more turbulent CONCLUSIONS environment marginal to the shelly facies. The following conclusions are drawn from Separating these two facies provinces was a the results of this study: broad shoal bisecting the Cottonwood sea (1) Depth is not the critical factor in the where the platy algal facies was formed; this genesis of Cottonwood lithologies. Turbulence, was an area of moderately turbulent, shallow, terrigenous influx, and circulation are the chief well-lit water, with some restriction of circu- causes of facies differentiation within the lation. Cottonwood Limestone. This suggests that Depth difference alone cannot be invoked as Elias' (1937) interpretation of lithologic differ- the single controlling factor in Cottonwood ences within the Big Blue Series of the northern facies genesis. At least three other environ- Mid-continent must be revised. The non- mental conditions were equally as important: marine, marine, non-marine, stratigraphic se- (1) rate and amount of terrigenous influx, quence demands change of sea-level, i.e. regres-

TABLE 4. ENVIRONMENTAL FACTORS RESPONSIBLE FOR COTTONWOOD FACILS DIFFERENTIATION

Terrigenous influx Circulation Turbulence Bioclastic facies low poor intermediate Fusuline facies low poor intermediate Platy algal facies low intermediate intermediate Shelly facies lime-rich intermediate good low clav-rich high good low Silty Osagia facies high good high

which is partially correlated to nearness and sion, transgression, regression of early Permian relief of source; (2) turbulence, which is com- seas; within the major part of the marine monly inversely proportional to depth of sequence, however, there is little evidence to water; (3) circulation of water, which is a support the depth-control theory of facies function of basin geometry. Other factors may genesis. The results of this study, coupled with be cited which are intimately associated with those of Imbrie (1955) and Imbrie and others these: differential subsidence of the basin, (1959) indicate that, for the Beattie Limestone influencing basin topography and rates of sedi- at least, this theory must be modified.4 ment accumulation; climate, which may effect (2) The fusuline facies of this study, which strong changes in salinity and water tempera- is synonymous with the fusulinid phase of ture as well as erosion rates in the source area; Elias (1937), R. C. Moore (1950, 1959), and and a host of biological phenomena, including others, does not represent the deepest water predator-prey relationships, ecologic succession phase of sedimentation. The average depth of animal and plant communities, and food figure postulated by Elias seems excessive, and chain structures. the relative depths of deposition for the fusu- Table 4 summarizes the interaction of the linid and mixed phases also seem wrong. The three environmental factors believed to have Cottonwood shelly facies, corresponding to the been chiefly responsible for Cottonwood facies mixed phase of Elias but with some elements of differentiation. While identification of these the molluscan and brachiopod phases, was environmental factors is possible, precise certainly formed in an environment as deep explanation of how each affected Cottonwood as, if not deeper, than that of the fusulinid organisms is not. Because our knowledge of the phase. Other investigators have commented on autecolology of Permian marine organisms is 4 Because it might be argued that the Beattie Lime- very scanty, any discussion of the way the stone is somehow "not typical," it should be noted that organisms reacted to these environmental in- Elias cited the Beattie as one of the best examples of fluences, beyond what has already been given, cyclical, depth-controlled deposition within the Big is premature. Blue Series (Elias, p. 411).

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the likelihood of fusulines being characteristic had the same results as those recorded here, it of shallow and generally turbulent water should be emphasized that detailed paleoecological (Newell and others, 1953; Harbaugh, 1959; studies are necessary to build up an inventory of Myers and others, 1956). While the ecologic information, much of which, initially, seems gratui- tous, in order to make sound judgments in the controls for fusulines are not known and un- future about the complex relationships between doubtedly vary according to species, the evi- fossil organisms and their environment. dence is strong that fusulines are more typical of shallow water—perhaps water depths closer Field to 50 feet than 160-180 as suggested by Elias. Forty-five localities along some 250 miles of out- (3) R. C. Moore (1950; 1959) favors the crop from Nebraska to Oklahoma were studied in offshore-onshore theory of facies genesis for detail (Fig. 5) for thickness, primary structures, the late Paleozoic cyclic deposits of the north- fossil occurrences, and lithologic character. Hand- ern Mid-continent, rather than Ellas' depth- specimen sized samples were taken at about one-foot control theory. The results of this study are intervals from 27 of the localities. Before removing the sample from the outcrop a bedding plane direc- not inconsistent with that theory. However, tion was marked on the specimen. Where the rock fusulines occur relatively near the northern was too shaly to obtain a single massive specimen a shoreline of the Cottonwood sea and are absent trench was dug, the surface swept clear of loose in the offshore position occupied by the shelly rock, and 5-pound samples were taken at one-foot facies. The paleogeography probably did not vertical intervals. In all, 170 field samples were change significantly from early to late Cotton- collected. wood time in the northern part of the Cotton- Laboratory wood sea, so the change from bioclastic to fusuline facies cannot be explained by a change Chemical analyses of 40 samples of limestone and in shoreline position. Other ecologic controls, calcareous shale were made by the geochemical laboratory of the State Geological Survey of turbulence, terrigenous influx (which, at times, Kansas. These were expressed as weight per cent may be inversely related to offshore position), of the following constituents: CaO, MgO, K O, and circulation, are judged to be more im- 2 Na2O, A12O3, Fe2O3, TiO2, P2O5, SO3, CO2, S portant. and SiO2. Using methods developed by Imbrie and Poldervaart (1959) these analyses were recalcu- APPENDIX ON METHODS lated as sedimentary mineral norms (Table 1). In order to study rock fabric and texture many General Statement of the field samples were cut and polished at right The five facies within the Cottonwood Limestone angles to the bedding and etched with dilute can be clearly recognized and delineated in the hydrochloric acid. From these etched surfaces field using megascopic criteria. Each facies, thus de- cellulose peels were made. Enlargements made fined, becomes a statistical universe from which directly from the peels on Kodabromide paper samples are drawn. These samples, which include illustrated the composition, size, orientation, and thin sections, chemical analyses, peels, and insoluble abundance of the various rock-forming elements. residues, help to characterize each facies. It is on the Fifty grams of crushed rock was taken from basis of these samples, particularly the thin sections each of a number of samples and dissolved in 30 per which have been quantitatively analyzed by point- cent acetic acid. The resulting residues were counting, that the facies are described, compared washed, dried, and scanned with a binocular and contrasted (Fig. 3). microscope. The use of quantitative analytical methods pro- Standard petrographic thin sections, oriented motes objectivity. Quantitative data can be pre- normal to the bedding, were made from 100 of the sented graphically, handled statistically, and com- limestone samples. Five thin sections were made pared with other data from similar studies. The from the calcareous shales in the following way: major disadvantage in the use of these methods is the shales were disaggregated (Imbrie's method, that they are time-consuming. Several hours can 1955, p. 654), washed, dried, and sieved. The frac- be spent examining a single thin section owing to tion between 2 mm and 1/8 mm was impregnated the difficulty of recognition of organic grains. After with a commercial, quick-drying, isotropic plastic. the initial learning process, however, point-count When hardened the plastic was thin sectioned. This analysis can be performed relatively rapidly. One technique was necessary so that quantitative data may prefer to reserve it for "typical" thin sections from the shales would be comparable with data only, in order to get quantitative data for sum- from the thin-sectioned limestones. The 105 thin marization and characterization of a much larger sections were then examined with a binocular and number of sections which have already been ex- petrographic microscope. amined qualitatively. Five thin sections from the shales and 50 thin Although a more generalized approach may have sections from the limestones were selected for

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quantitative studies (Fig. 4). A Chayes point- light. Most ossicles either lack the proper orientation or counter was fixed to the petrographic microscope are too small for accurate subdivision. so that equally spaced traverses could be made BRACHIOPODS: Few genera identifiable in thin section. Punctuation, impunctation, or pseudo-punctation of across the thin section (Chayes, 1949). At each stop the shell are best criteria for subdivision, but most the particle beneath the ocular cross-hair was genera in the Cottonwood are pseudopunctate (e.g., identified, if possible. In this way a quantitative Juresania, Dictyoclostus, Choneies, Derbyia, Meefyelld); (volumetric) estimate of the organic and inorganic rarer forms are punctate (Dielasma) or impunctate rock-forming elements could be obtained. To get (Composita, Crurithyris). Productid and chonetid spines reproducible estimates of the proportion of or- common. They are hollow-centered and often filled with ganically derived constituents of the rock, about secondary calcite; inner, fibrous, calcitic layer covered 400-500 organic grains had to be counted per slide. by structureless, hyaline layer. Under crossed nicols spine shows progressive extinction. Spine cut normal to Because only about 1 /3 of the rock is composed of long dimension shows pseudo-umaxial extinction cross; identifiable organically derived material, a grid superficially, this particular orientation of a spine re- 0.67 by 0.50 mm was chosen so that of the ap- sembles an ooid in section. proximately 1400 determinations per slide, some ANCHICODIUM: Most species described by Johnson 400 or more would be organic. (1946) occur in Cottonwood. No specific identifications Only grains larger than 1 /8 mm were identified, are made because of recrystallization. Characterized by because the limit of successful identification is ap- shape of the thallus (platy to wavy) and internal struc- proached at about this size; studies of recent car- ture (spongy and pith-like) (PI. 3, figs. 3, 4). OSAGIA: In plane-polarized light algal part of colony bonate sediments (Ginsburg, 1956; Purdy, E. G., is almost opaque. Within this dark mass lighter threads or 1960, unpub. Ph.D. thesis, Columbia University) tubes (encrusting foraminifers) are irregularly distributed. indicate that grains larger than 1/8 mm accumu- EPIMASTOPORA: Internal morphology of this alga is late in the local environment where they are very distinctive (sec Johnson, 1946, p. 1095) and easily formed, whereas, the fraction finer than 1/8 mm recognized in thin section. has a considerable proportion of grains formed in PALEOTEXTULARIDS: Identifiable by test shape and other environments; the results of this study should morphology; most forms seem referable to Paleotex- be comparable to similar studies of recent and tularia and Climacammina. ancient sediments where the same or nearly the AMMODISCIUS AND HVpERAMMiNiosi Mainly tubular same grain-size limit was used. forams irregularly coiled (Ammodiicus) or straight (Hyperammind). Most are yellow brown in polarized Every stop made on the slide was assigned to light. (Referred to as A-H foraminifers in tables.) one of the following categories described below. UNKNOWN ORGANIC: Particles which cannot he posi- These descriptions are necessarily abbreviated, but tively assigned to any of the foregoing categories and more ample discussion can be found in Cayeux yet which by their shape or internal structure are known (1931) and Johnson (1951). to be organically derived. TRILOBITES: Only one genus, Ditomopyge, known PELLETS: Aggregate grains composed of fine skeletal from the Cottonwood. Pale, bronze-colored carapace in and nonskeletal debris; elliptical to irregular shape. In plane-polarized light, shows no layering; undulating plane-polarized light these pellets are brown to pale and opposite extinction under crossed nicols. orange with thin dark peripheries; no distinctive optical OSTRACODES: Carapace shows two finely perforate behavior under crossed nicols. layers in plane-polarized light; progressive extinction QUARTZ: Angular detrital quartz grains; interstitial under crossed nicols. No attempt is made to subdivide quartz and chalcedony are not included. ostracodes, although a number of different genera are RECRYSTALLIZKD MATRIX: Some thin sections show found in washed, disaggregated shales. partial recrystallization of the original calcium carbonate BRYOZOAXS: Identifiable by skeletal morphology. into calcite mosaics. Points are assigned to this category Many fragments show perforate texture in outer part when recrystallization has obliterated the original struc- of cocnosteum. Under crossed nicols a black extinction ture so that identification is impossible. line often outlines periphery of zooecium. No further RECRVSTALLIZED VALVES: Osagia encrustations pre- subdivision possible, although fenestrate and encrusting serve the external shapes of fragments. Some are shaped growth forms can be recognized. like valve fragments and when internal structure is re- MOLLUSCS: Pelecypods recrystallize to coarse, hyaline, crystallized, they are assigned to this category. calcite mosaic except those having an original outer shell LESS THAN 1/8 MM: Includes any particle whose layer of calcite. Original prismatic structure of Avi- largest dimension is less than 1/8 mm—inorganic grains culopmna, Aviculopccten, and Pseudomonotis is seen. and finely comminuted skeletal material. Limit of re- Shape and ornamentation of fragments used to dis- producibility for organic grains reached at about 1/8 tinguish pelecypods. mm. On the average a grain is cut at a smaller diameter All gastropods have rccrystallized to a coarser calcite than its true diameter, and consequently, the per cent mosaic except Amphiscapha which has an original, of this fraction will always be a maximum estimate. fibrous, calcitic, outer ostracum. Conispiral (subuhtids) Natural pore-space (interseptal area of fusulines, forms are distinguished by shell shape. zooecia of bryozoans, hollow centers of brachiopod FusuLiNKs: Identifiable by morphology of the test spines) is assigned to group to which parent fragment and microstructure of spirotheca. Schtvagerina and belongs; small in area and usually filled with secondarily Schubertella especially abundant in the Cottonwood. deposited calcite, or fine-grained matrix material when Discrimination made by wall structure differences and pores are at or near periphery of fragment. Large cavi- test size. ties within articulated bivalves and gastropods are not ECHINODERMS: Chief distinguishing characteristic is so tabulated because they are filled with relatively large unit extinction of individual ossicles under crossed amounts of skeletal debris, quartz grains, or matrix, and nicols and their reticulate texture in plane-polarized this infilling must be counted separately.

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MANUSCRIPT RECEIVED BY THE SECRETARY OF THE SOCIETY, JULY 25, 1960

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