Fossil Communities of the Borden (Mississippian) Delta in Indiana and Northern Kentucky

Home , Borden Formation, Edwardsville Formation, Paleontology in Indiana

William I. Ausich; Thomas W. Kammer; N. Gary Lane

Journal of Paleontology, Vol. 53, No. 5. (Sep., 1979), pp. 1182-1196.

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http://www.jstor.org Fri May 11 13:10:45 2007 JOURNALOF PALEONTOLOGY,V. 53, NO. 5, P. 1182-1196, 7 TEXT-FIGS., SEPTEMBER1979

FOSSIL COMMUNITIES OF THE BORDEN (MISSISSIPPIAN) DELTA IN INDIANA AND NORTHERN KENTUCKY

WILLIAM I. AUSICH,' THOMAS W. KAMMER AND N. GARY LANE Indiana University, Bloomington, Indiana 47401

ABSTRACT-The Borden siltstone delta in Indiana and northern Kentucky contains shelly communities that are distinctive with respect to their occurrence in delta platform, delta slope, and prodeltaic environments. Isopach maps of the New Providence Shale and total Borden Group indicate that two distinct lobes of the delta existed in Indiana. The delta platform exhibits the greatest variety of habitats, including carbonate banks, distributary channel sandstones, and interdistributary mudstones and siltstones. Each of these environments was occupied by a distinctive tiered shelly community dominated by crinoids and bryozoans. The carbonate bank was dominated by large brachiopods (Spirifer, Imbrexia) and camerate (Alloprosallocrinus)and disparid (Halysiocrinus)crinoids. The distributary channel was occupied by a variety of small, short-stemmed advanced inadunates (Abroto- crinus), and the interdistributary mudstones by a great variety of fenestrate (Fenestella)and cysto- porate (Cheilotrypa)bryozoans, as well as crinoids and brachiopods. The delta slope community was generally not tiered and consisted primarily of large brachiopods (Orthotetes, Syringothyris) that could remain fixed in position on unstable slopes. The prodeltaic community included a variety of bryozoans (Rhombopora, Cystodictya) and crinoids (Halysiocrinus, Synbathocrinus) as well as gastropods and pelecypods (Bembexia, Phestia, Ctenodonta). The slope community originated by migration down from the platform by some species and up from the prodelta by others. Species diversity at individual sites on the delta platform range from 47 to 155, on the slope from 2 to 23, and on the prodelta from 35 to 103.

INTRODUCTION Kentucky and adjacent Indiana. In order to DURINGDEVONIAN and Mississippian time a integrate these various studies and provide a series of deltas gradually filled in large areas regional picture of the Borden fossil commu- of shallow marine basins of the eastern interior nities, all three of us conducted field investi- of the United States. These deltas began with gations of fossils in the Carwood and Locust the Devonian Catskill delta to the east, fol- Point formations in the fall of 1977, thereby lowed by the Devonian-Mississippian Bed- providing needed information on delta slope ford-Berea delta in Ohio, and terminated with communities. In order to provide a regional the Middle Mississippian Borden delta of In- framework within which to set our paleonto- diana, Illinois, and Kentucky (Text-fig. 1). logical efforts we undertook construction of Only seaward portions of the Borden delta are iospach maps of total Borden and New Prov- still preserved, mainly in the subsurface of idence thicknesses in southern Indiana. Those southern Illinois and southwestern Indiana, maps were constructed using information de- but also in a narrow outcrop belt in southern rived from well logs housed in the Petroleum Indiana and Kentucky. The non-marine part Section of the Indiana Geological Survey. of the delta subsequently has been eroded to This is not a taxonomic study. Most of the the north and east, the presumed source di- fossils reported here are identified only to the rections. The fossil communities of the Borden generic level, especially those from the Car- delta, as exhibited in outcrop in southern and wood and Locust Point. Specific identifica- central Indiana, are the subject of this report. tions of most of the delta platform and pro- One of us began study of Borden deltaic deltaic and basinal species are available but communities 15 years ago (Lane, 1963). Sub- not reported here because they add little to the sequently, Ausich has studied delta platform overall paleoecological interpretation based on communities in Monroe County and Kammer genera. is conducting research on the prodeltaic and contiguous basinal communities in northern PHYSICAL FRAMEWORK OF THE BORDEN DELTA 'Present address: Department of Geology, In Indiana the rocks that comprise the delta Wright State University, Dayton, Ohio 45435. and associated basinal deposits are collectively

(1965) and was based on subsurface studies in I LL. I Illinois and Indiana. Since then a series of re- IOOMiles I IND. ports on the subsurface stratigraphy of the Borden in Illinois and Indiana, by Lineback (1966, 1968; 1969), has further elaborated details of deltaic sedimentation. Our field studies of fossil communities have been confined to Borden rocks exposed at the surface in southern Indiana and northern Ken- tucky. The outcrop belt of the Borden is essentially parallel to depositional strike and represents a narrow, vertical slice through the delta (Text-fig. 2). Thus, the lowest units of the Borden Group record primarily basinal and prodeltaic deposits, represented princi- pally by the New Providence Shale. The mid- TEXT-FIG.1-Distribution of Borden rocks in dle part of the group, the Locust Point and southern Indiana, southern Illinois and northern- most Indiana. The Borden outcrop in southern Carwood formations, represents the delta Indiana and northern Kentucky is shown in slope, and the Edwardsville, at the top of the black, subsurface areas of Borden deposition are Borden Group, consists of delta platform stippled. Modified from Lineback (1969). rocks. The delta eventually filled the eastern edge of the Illinois Basin and was succeeded by shallow water carbonates of the Harrods- termed the Borden Group, which consists, in burg Limestone. sequence upward, of the New Providence We recognize that strict equating of each Shale, the Locust Point Formation, the Car- formation in the group with a specific deltaic wood Formation, the thin Floyds Knob For- environment is a first-order approximation mation, which is confined to southern Indiana, and is probably subject to revision in details and the Edwardsville Formation. This stratig- with further studies. For instance, the New raphy was elucidated by Stockdale (1931; Providence Shale may represent, at least in its 1939) long before the deltaic nature of the upper part at some localities, the lower slope rocks was known. The prograding structure of the delta. The uppermost beds of the Car- of the beds was demonstrated by Swann et al. wood, just below the Floyds Knob Formation,

- subsurface -y:yi,t-- eroded - , . ..' Edwardsville Fm.

PRODELTA

TEXT-FIG.2-A depositional model for the Borden delta in southern Indiana. Deltaic rocks thin and disappear to the southwest in the subsurface and have been eroded to the north and east. The outcrop belt is judged to record a narrow, vertical slice through the major parts of the delta. W.I. AUSICH, T. W.KAMMER AND N. G. LANE

TEXT-FIG.3-Isopach map of the New Providence Shale in southwestern Indiana and adjacent Kentucky. Dots indicate control points, contour interval is 50 feet. Kentucky data is from Kepferle (1977), Indiana data is from the Petroleum Section, Indiana Geological Survey. at some localities, records the onset of delta mostly clay-size sediments, in front of the delta platform deposition. Nevertheless, in a broad slope. Basinal deposits are fine-grained clastics way, these units do seem to correspond to spe- basinward from the prodelta that were influ- cific parts of the delta geometry, at least in- enced very little by deltaic deposition. sofar as that geometry can be deduced by In order to provide a regional setting for study of fossil communities. studies of fossil communities in the outcrop In the terminology used here the terms delta belt of the Borden, isopachous maps of Borden platform, delta slope, and prodelta refer to the Group and New Providence Shale thicknesses geometric configuration of the delta. Topset were constructed for southern Indiana and ad- beds were deposited on the platform, foreset jacent Kentucky. These are the only two beds on the slope, and bottomset beds on the stratigraphic units that can be distinguished prodelta, the latter forming an apron of fine, with some degree of confidence using standard FOSSIL COMMUNITIES 1185

TEXT-FIG.4-Isopach map of total thickness of the Borden Group in southwestern Indiana and distribution of fossil localities in Indiana and northern Kentucky. Contour interval is 100 feet. Data is from Petroleum Section, Indiana Geological Survey. electric and lithologic logs that are available. tected on subsurface logs and does not occur The boundary between the Locust Point and with certainty north of Washington County in Carwood formations is impossible to detect in Indiana. the subsurface and is difficult to find with cer- The isopach map of the New Providence tainty in the field. It is based primarily on the indicates that the principal locus of deposition presence of common ironstone nodules in the was in south-central Indiana, with a lobe of Locust Point but we have observed sections of the deltaic slope extending to the west (Text- the Carwood that contain abundant nodules. fig. 3). The unit thins to the northwest and to The Floyds Knob bed, which serves as the the south into Kentucky. In south-central In- only reliable marker to distinguish the Car- diana this Formation may include delta slope wood from the Edwardsville, cannot be de- beds as well as the prodeltaic and more distal 1186 W.I. AUSZCH, T. W.KAMMER AND N. G. LANE

Scott (1964) have shown that the New Provi- dence Shale is older to the north and becomes progressively younger to the south. Thus, in north-central Kentucky the earliest formed beds of the delta are upper Burlington to Keo- kuk in age. In west-central Indiana the upper part of the delta (Edwardsville Formation) is Keokuk in age (Lane, 1973). In Illinois the Warsaw Shale is age equivalent to all but the lowest 100 feet of the Borden (Swann et al., TEXT-FIG.5-Block diagram of the Borden delta, constructed from Lineback (1968). The diagram 1965). The Warsaw Shale overlies the Keokuk shows building of the delta into the Illinois Basin Limestone, thus indicating a younger age for from the east and north in Indiana and from the the Borden in Illinois than for any known site north and west in Illinois. The basin in front of in Indiana. This demonstrates the prograding, the delta was subsequently filled by the Fort east to west, nature of the Borden delta and Payne Chert. The thickest part of the delta has also indicates a shift in depositional loci to the been reported from west-central Indiana. These contour lines have been extended to the southeast northwest through time. beyond control points to complete the diagram. Kepferle (1977) has an excellent review of the environments of deposition for the Borden delta in Kentucky. The prodeltaic environ- basinal deposits that are present in southern- ment consists of bottomset clay shales and is most Indiana and Kentucky. represented by the New Providence Shale. The thickness of the entire Borden Group The delta slope environment is recorded by in Indiana indicates the presence of two dis- massive foreset siltstones and interbedded tinct deltaic lobes (Text-fig. 4). Both of these shales of the Locust Point and Carwood for- lobes extend from northeast to southwest. The mations. The Carwood is coarser-grained than larger lobe is centered in Knox and Green the Locust Point and probably contains the counties in southwestern Indiana and the transition from the delta slope environment to smaller one is centered on Crawford County the platform environment of the Edwards- in the extreme southern part of the state. The ville. A variety of facies is present in the maximum known thickness of the Borden in delta platform environment (Ausich, 1977; Indiana is north of these two lobes, in west- Kepferle, 1977) and includes crinoidal skeletal central Indiana, where thicknesses in excess of carbonate banks, submarine distributary 700 feet have been recorded (Text-fig. 5). Sub- sandstone channels, and interdistributary surface information in this area is too scanty mudstones. to determine whether or not a third lobe may In Kentucky and southern Indiana the have been present to the north. None of these Floyds Knob bed is representative of an ero- lobes in Indiana are as large as the deltaic lobe sional phase and depositional hiatus within the in southern Illinois delineated by Lineback. Borden delta (Peterson and Kepferle, 1970). Even though only three major lobes are de- Layers of glauconite and oolitic limestone in- fined, the delta probably prograded into the dicate a depositional pause that may be due to Illinois Basin as a series of coalescing lobes, a marine transgression across the platform. In with major distributaries shifting back and Indiana the Floyds Knob bed does not extend forth along the shoreline. Thus, the deposi- north of Washington County. The stratigraph- tional history, and hence the distribution of ic relationship of the Floyds Knob to the delta fossil communities, was probably much more front in Indiana is uncertain because the out- complex than the simple model that is used crop belt parallels depositional strike and pre- here. Future detailed studies of the sedimen- vents the tracing of the unit down into the tology, stratigraphy, and paleontology of the basin. delta will undoubtedly contribute to a better understanding of this large deltaic complex. EVIDENCE FOR FACIES CONTROLLED Some evidence indicates that the delta is COMMUNITIES younger in Illinois than in Indiana and north- The Borden Group is abundantly fossilif- central Kentucky. In Indiana Rexroad and erous at virtually every outcrop. Having said FOSSIL COMMUNITIES 1187 that, we emphasize that this statement refers demonstrate the presence of very extensive or primarily to trace fossils. Shelly fossils are strong currents. The abundant trace fossils at quite local and patchy in their distribution many localities indicate that within large bod- throughout the delta (Text-fig. 4). The shelled ies of rock, sediments were not disturbed by fauna at several localities has been preserved currents after they were deposited. at or close to living sites (Lane, 1973). In view of both faunal and lithologic evi- Completeness of preservation is thought to dence we postulate that very many of the shel- reflect rates of sedimentation. At some locali- ly fossils, and all of the trace fossils, found in ties, as at Crawfordsville, many crinoids are the Borden were buried at or close to their complete-crown, stem, and roots-and clear- living sites. Thus, the observed differences in ly were buried where they lived. At other sites the faunas from place to place can be attrib- many of the brachiopods consist of single uted to differences in depositional environ- valves, bryozoans are broken up, and crinoids ments. It seems clear that the environment did are disarticulated. These fossils are not worn exert strong control on facies and the distri- or abraded and show little or no evidence for bution of fossils. transportation. We postulate that the fossils laid on the sea floor for some time and burial was postponed for weeks or months. Thus, TIME RELATIONS OF FAUNAS differing sedimentation rates account for dif- The Borden outcrop belt extends over a ferent preservational characters at many lo- wide area in Indiana and northern Kentucky calities. and exposed deltaic rocks transgress time. The The distinctiveness of laterally contiguous possibility exists that some of the observed dif- assemblages indicates that they are commu- ferences in communities that we describe here nities of animals buried at or close to their are not due to differing deltaic environments living sites. Within a distance of 2 km along but rather to community evolution through the south shore of Monroe Reservoir, in Mon- time. roe County, three readily recognizable com- If we compare the occurrences of species munities occur. One consists primarily of present in studied faunas with known strati- small, advanced inadunate crinoids in distrib- graphic ranges of these species in areas outside utary channels, one of camerate and disparid the delta, the great majority have ranges that crinoids and large brachiopods on a carbonate include the Keokuk Limestone of the type bank, and the third is more diverse than either Mississippian. Such species as Orthotetes keo- of the others. with a wide varietv of brachio- kuk and Echinoconchus alternatus are rela- pods, bryozoans, and crinoids occurring in in- tively widespread on the delta and are con- terdistributary mudstones. These laterally fined to the Keokuk in the type area. Other contiguous but faunally distinct communities species are equally restricted in time but are provide clear evidence that faunal mixing has much more patchy in their distribution on the not occurred and that strong environmental delta. These include Syringothyris textus, control was exerted on distribution of the fos- Histocrinus coreyi, and Gilbertsocrinus tube- sils. rosus. Even some genera common to the delta The Borden rocks contain little in the way like Pellecrinus, Alloprosallocrinus, Paradi- of evidence to suggest that there was very chocrinus, and Histocrinus, are confined to strong current action during deposition of the Keokuk age rocks. Many other species could silts and muds that originally comprised the be cited that are restricted to the Keokuk. delta. Ripple marks, current bedding and cut- These provide strong evidence that the ex- and-fill structures are notably lacking or rare posed part of the delta is all very close to the at many outcrops. The best evidence for same age and was deposited within the same downslope movement and instability of sub- relatively narrow time interval. Thus we con- strate is provided by turbidite sequences on clude that a majority of the communities de- the delta slope that have been described by scribed below were near synchronous in terms Suttner and Hattin (1973), the Sedimentation of geologic time and that community evolution Seminar (1972), and Kepferle (197 7). These has not been an important factor in establish- turbidite deposits provide evidence for slope ment of differences among communities. Sub- instability and fluidity of sediment but do not surface parts of the delta may be somewhat 1188 W.I. AUSICH, T. W.KAMMER AND N. G.LANE younger than the exposed rocks but no fossil evidence is available to test this hypothesis. The deltaic fossils that have been judged to be significantly older than the Keokuk are those that occur in the prodeltaic and basinal facies in the New Providence Shale. Springer (1911) and Weller (1909) made a correlation between fossiliferous strata at Button Mold Knob and the Fern Glen Limestone or Lower Burlington Limestone.

DELTA PLATFORM COMMUNITIES Physiographically the delta platform is that part of the subaqueous delta proximal to sediment source, and therefore the delta platform is subject to more variable depositional conditions than are more distal parts of the delta. Platform facies of the Borden delta include distributary sandstone channels, sheet sandstones, interdistributary siltstones, interdistributary mudstones, and skeletal carbonate banks (Ausich, 1977). Communities with two very different basic structures are distributed among these facies. These include communities that are vertically tiered, epifaunal, and composed largely of suspension-feeding organisms and trace fossil communities with deposit feeders and possibly suspension feeders. The occurrence and taxonomic distribution of different communities in a specific facies may be a function of the available food supply (Au- TEXT-FIG.6-Diagrammatic representation of del- sich, 1978). ta platform communities. A. Carbonate bank Three different vertically tiered epifaunal community, a. Spirifer, Imbrexia; b. Alloprosal- communities are recognized in delta platform locrinus; c. Halysiocrinus; d. Eretmocrinus. B. deposits in Indiana. All these communities are Distributary channel community, a. Fenestella, composed primarily of suspension-feeding or- b. Scytalocrinus, c. Abrotocrinus, d. Cribano- ganisms, i.e., crinoids, bryozoans, brachio- crinus. C. Interdistributary mudstone community, a. Cystodictya, b. Cleiothyridina, c. Fis- pods, and corals, yet each community is fau- tulipora, d. Rugosochonetes, e. Composita, f. nally distinct. In addition to the primary Halysiocrinus, g. Platycrinites, h. Fenestella, i. groups of suspension feeders, a wide variety Cyathocrinites, Barycrinus. of feeding types are represented in these communities including the following: suspension- feeding epizoans (foraminifera, corals, bryozoans, brachiopods, annelids, etc.), deposit slope as suggested by Matthews (1973). We feeders (holothurians, trilobites?, and possibly conclude, based on our regional study, that some trace fossils), scavengers, (ostracodes? the entire Edwardsville Formation, including and trilobites?), carnivores (starfishes, sharks, the Crawfordsville site, was deposited on the gastropods?), parasites (annelids?), browsers platform. Matthews based his conclusions on (gastropods and foraminifera), and commen- a comparison of the Crawfordsville site with sals (gastropods). the modern Mississippi River delta, the struc- The Crawfordsville fossil site, Montgomery ture and composition of which is much differ- County, Indiana, (Van Sant and Lane, 1974; ent from that of the Broden delta, and con- Lane, 1973) is a well-studied delta platform sequently direct analogies between these two community rather than being on the delta deltas cannot be made with a high degree of FOSSIL COMMUNITIES 1189

confidence as was attempted by Matthews adunates (Pachylocrinus), flexible~(Taxocri- (1973). nus), monobathrid camerates (Platycrinites), The trophic structure of the Crawfordsville diplobathrid camerates (Gilbertsocrinus), are fossil site is typical for delta platform, tiered, more equitably distributed both in terms of epifaunal communities. The percentage of abundance and diversity in this community species in each trophic group is as follows: sus- type than in either of the other two tiered com- pension feeders, 75; browsers, 14; deposit munities. Brachiopods (Composita) and bryo- feeders, browsers or scavengers, 7; carnivores, zoans (Fenestella) may also be quite abundant 3; deposit feeders, 1, and commensal copro- in this community type. This community oc- phagous feeders, 1; but in terms of percent curs in siltstones in Montgomery County, In- abundance, as many as 99 percent of the indiana, in the lower community at Crawfords- dividuals are suspension feeders. ville and at Country Club Road (Lane, 1973). One type of tiered community is character- It also occurs in mudstone deposits at Patrick ized by the upper community at Crawfords- Farm, Morgan County, Indiana (NW G, ville (Lane, 1973). This community is domi- NEG, sec. 8, T1IN, R2E), and the Boy Scout nated by poteriocrine inadunates, such as Camp, Monroe County, Indiana (SE%, S W%, Scytalocrinus and Abrotocrinus. In addition SWG, and SW%, SE%, SW%, sec. 8, T7N, to Crawfordsville, this community is recog- RlE). nized at the County Farm, Montgomery Trace fossil communities are present in in- County, Indiana (Lane, 1973, p. 65) and at terdistributary siltstone facies, in sheet sand- the Waldrip Site, Monroe County, Indiana stone facies and in distributary sandstone (SEG, SW%, NEG, sec. 8, T7N, RlE). It channel facies on the delta platform. "Little occurs in interdistributary siltstones at the curly worm marks" (Stockdale, 1931, fig. 8; County Farm and at Crawfordsville and in Lane, 1973) are the dominant trace fossils on distributary channels at the Waldrip Site the delta platform as well as on the entire del- (Text-fig. 6B). ta. Other common, named, delta platform The second type of tiered epifaunal com- trace fossils are Zoophycus and Scalarituba. munity is dominated in numbers of specimens The "little curly worm marks" dominate in an and of species by monobath~idcamerates (Al- estimated 99 percent of the preserved volume loprosallocrinus, Macrocrinus, Eretmocrinus) of the delta platform sediments. Whatever or- and disparid inadunates (Synbathocrinus, ganism(~)left this trace or traces was the dom- Halysiocrinus) and occurs in coarse to fine, inant organism(s) on the delta platform. very poorly sorted crinoidal sands that accumulated in biohermal deposits (Text-fig. 6A). DELTA SLOPE COMMUNITIES Seven such deposits were reported in Monroe, The delta slope environment in Indiana in- Morgan, and Brown Counties, Indiana by cludes the sediments of the Locust Point and Stockdale (1931), and he termed these struc- Carwood Formations. Siltstone and silty tures bioherms. Carozzi and Soderman (1962) shales are the dominant lithologies, and much studied one of these seven near Stobo and of these sediments may have been deposited termed it a crinoidal mound-like mass; where- by turbidity currents from local small canyons as, Ausich studied another at Allens Creek and on slopes which ranged from 4.7 to 22.7 mlkm considered it to be a carbonate bank deposit. (25 to 120 ftlmile or dips up to slightly more In addition Lane (1964; 1973) reported two than lo) (Kepferle, 1977). Similar slopes are similar deposits in Montgomery County, In- found on modern deltas (Fisk, 1961; Mathews diana. Large spiriferid brachiopods (Spirver, and Shepard, 1962; Allen, 1970). Kepferle Zmbrexia) and siliceous sponges are common (1977) suggested that the Lampkins Sandstone on these banks as well as the predominant Member of the Carwood Formation may be a groups of crinoids. subsea fan formed of turbidites. The third tiered suspension-feeding com- The fauna of the delta slope environment munity predominated in interdistributary was scattered and where present was of rela- mudstones and siltstones (Text-fig. 6C). The tively low diversity. The fauna from all the major groups of crinoids: disparid inadunates sites studied (Table 1) comprises 57 taxa of (Halysiocrinus), cyathocrine inadunates which no more than 24 are found together as (Cyathocrinites, Barycrinus), poteriocrine in- a community. Seven sites were sampled, three 1190 W. I. AUSICH, T. W.KAMMER AND N. G. LANE

TABLE1-Distribution of delta slope taxa found at the seven study sites. Locality numbers from Stockdale (1931). Numbers in parenthesis provide further details as follows: 1-Nashville site; 2-silty shale immediately below Floyds Knob bed; 3-"Rotten Zone" of Stockdale (1931, p. 111); 4-section of Carwood below "Rotten Zone." LOCALITIES Locust Point Carwood Taxa Crinoids Agaricocrinus Barycrinus Camptocrinus Catillocrinus Cyathocrinus Eretmocrinus Gilbertsocrinus Halysiocrinus Platycrinites Synbathocrinus flexible plates Brachiopods Athyris Chonetes Dielasma Echinochoncus Marginatia Orthotetes keokuk OYatia Punctospirifer Rhipidomella Rugosochonetes Schuchertella Spirifer cf. S. mundulus S. washingtonensis Tylothyris Syringothyris textus Setigerites small chonetid rhynconellid Bryozoans Cheilotrypa Corynotrypa Cystodictya Fenestella Fistulipora Hemitrypa Penniretopora Rhombopora Streblotrypa Thamniscus LVorthenopora stenoporid Gastropods Bembexia Neilsonia Platyceras Spiroscala bellerophontid Bivahes Aviculopecten Cypricardinia Myalina Nuculopsis Phestia Miscellaneous Amplexus - - - Cladoconus - - - Cyathaxonia - - - Griffithides - - - Mooreoceras ?C - - echinocystitoidid echinoid - - - FOSSIL COMMUNITIES 1191

from the Locust Point and four from the Car- wood. Six of the sites are listed in Stockdale (1931)and the seventh site is located at Hardin Hollow, one mile west of Nashville, Brown County, Indiana (NW%, NW% sec. 24, T9N, R2E). The Carwood contains faunas with a greater diversity and abundance than does the Locust Point. Brachiopods are by far the dominant group of organisms on the slope (Text-fig. 7C). Sev- eral large, broad forms are common (Ortho- tetes and Syringothyris) and often occur in thin beds one brachiopod thick or randomly scattered through thick sections of sediment. Both Orthotetes and Syringothyris have been found in living position with Orthotetes resting on the pedicle valve and Syringothyris resting on the large interarea. Other brachiopods include forms with long spines for sta- bility on a soft substrate (Marginatia, Ovatia, and Setigerites). The wide variety and abundance of brachiopods may be a reflection of soft unstable substrate that discouraged settle- ment by other organisms. Other groups, in order of decreasing abundance, include bryozoans, molluscs, crinoids, corals, and trilobites. In the Locust Point Formation crinoids are nearly absent and bryozoans are rare. Mol- luscs and brachiopods are the dominant groups. At the Nashville site the following molluscs are locally abundant: Bembexia, Phestia, Platyceras, a bellerophontid, and Mooreoceras?; Schuchertella and other brachiopods are also present. The enclosing ma- TEXT-FIG.7-Diagrammatic representation of trix is a massive fine-grained sandstone lack- prodelta and delta slope communities. A. Pro- ing sedimentary structures. The lack of delta, base of slope community, a. Synbathocri- abrasion of the fossils and the absence of sed- nus, b. Barycrinus, c. Platycrinites, d. Halysi- imentary structures are offered as evidence of ocrinus, e. Rhipidomella, f. productoid in situ burial. This relatively coarse-grained brachiopod, g. Cyathaxonia, h. Cladoconus, i. substrate may have been ideal for the brows- Rhombopora, j. Cystodictya, k. Fenestella. B. Delta, basin floor community, a. Bembexia, b. ing Bembexia and the deposit feeding Phestia. Sinuitina, c. Loxonema, d. Phestia, e. GriJj- The presence of Platyceras and the near ab- thides, f. Amplexus, g. Scalarituba. C. Prodelta sence of crinoids (a few stem ossicles were ob- slope community, a. Orthotetes, b. Syringothy- served) is an enigma. The relative high diver- ris, c. Marginatia, d. Bembexia, e. Phestia, f. sity and abundance of organisms at this site is Fenestella. unusual for the Locust Point and is not char- acteristic of the Locust Point as a whole. Other the Borden Delta have not been defined and environments where molluscs are present in- are in need of further study. clude the basin-floor environment (Coral In the Carwood Formation brachiopods are Ridge community) and the delta platform en- also the dominant group although a wide va- vironment (upper community at Crawfords- riety of crinoids and bryozoans are present ville). The specific environmental factors re- (Table 1). At Section 22 (Stockdale, 1931) the sponsible for the distribution of molluscs on Carwood is 125 ft thick (Stockdale, 193 1). The W. I. AUSICH, T. W. KAMMER AND N. G. LANE

basal 35 m consists of siltstone and sandstone posit feeders4 percent, browsers-9 percent, and contains the brachiopods Orthotetes, Sy- carnivores-2 percent, deposit feeders, brows- ringothyris, and Setigerites. Just above this is ers, or scavengers-2 percent, and commen- a thin zone approximately 15 cm thick and sals-2 percent. This distribution represents termed the "rotten zone" by Stockdale because the dominance of suspension-feeders on the of its high porosity due to the dissolution of slope although browsers and deposit feeders skeletal material. This "rotton zone" has a are locally very abundant (i.e., the Nashville fairly diverse fauna with brachiopods, bryo- site). Thus there appears to be facies control zoans, and molluscs present. The unabraded of benthic organisms due to the high rate of nature of the fossils again indicates that the sedimentation and the unstable substrate of community is in place. In gross taxonomic the delta slope environment. composition this community appears to be similar to that at the Nashville site in the Lo- PRODELTAIC COMMUNITIES cust Point. The prodeltaic environment includes those The upper 3.6 m of section 22 is shale with sediments of the bottomset beds which were a crinoid-bryozoan community near the top. deposited in front of and at the base of the The crinoids and bryozoans present in this delta. For purposes of this discussion the pro- community are similar to those at delta plat- deltaic environment will be subdivided into form sites, i.e., the lower community at Craw- the basin-floor and base-of-slope environments fordsville, the interdistributary mudstone (Kepferle, 1977). Each of these environments community near Allens Creek Bank, and the has its own distinct community. Button Mold Knob community. The basin-floor environment is character- At section 39 (Stockdale, 1931) in siltstones ized by green clayey pelagic sediments which of the Carwood Formation there is an in place accumulated under conditions of little bottom community of crinoids, bryozoans, and bra- current and low oxygenation (Kepferle, 1977). chiopods which in overall gross taxonomic Water depth may have been as great as 150 m composition is similar to the lower community (500 ft) (Griffith, 1978). The lower clayey shale at Crawfordsville but its patchy distribution of the New Providence Shale (Coral Ridge and low number of individuals is more char- Member of Conkin (1957)) was deposited in acteristic of the slope environment. It was at the basin-floor environment. This community this locality that a specimen of :Marginatia is extremely patchy in distribution and is with spines extending 4-5 cm into the sur- known only from four sites in Kentucky and rounding matrix was found. The upper parts Indiana. The community is dominated by of both sections 22 and 39 contain crinoid- browsing gastropods, most notably by Bem- bryozoan communities that are reminiscent of bexia ellenae which accounts for over 50 per- the delta platform communities and may be cent of macrofossil specimens collected indicative of the gradual change from the delta (Text-fig. 7B). Other elements of the commu- slope to delta platform environment. How- nity listed in order of abundance include: Am- ever, the low diversity and abundance of or- plexus, Sinuitina, Loxonema, Grif$thides, ganisms is indicative of the delta slope envi- Rhynchopora, Phestia, Ctenodonta, Conocar- ronment. dium, and rare additional corals, blastoids, Overall the delta slope environment may be and crinoids (Conkin, 1957). The goniatites viewed as a difficult environment for benthic Pericyclus and Protocanites comprise nearly organisms. A total of 57 taxa (microfossils not 20 percent of the macrofossil specimens col- studied) have been found in this environment, lected, but it is uncertain if they can be in- and this is in sharp contrast to other environ- cluded in the community for they may have ments where as many as 155 species have been lived well above the sea floor. The trace fossil reported from the delta platform (Lane, 1973) Scalarituba is fairly common in this environ- and at least I38 species have been listed from ment. The Coral Ridge community is distinc- the prodeltaic environment (Butts, 1922; Con- tive in that the dominant organisms are brows- kin, 1957). The percentages of species in var- ing and detritus feeding gastropods, bivalves, ious trophic groups from the delta slope are as and trilobites. Suspension-feeding corals, bra- follows: suspension-feeders-82 percent, de- chiopods, blastoids, and crinoids play a minor FOSSIL COMMUNITIES role though there are a large number of these community is also similar to the fauna found species. The percentages of species in various in the interdistributary mudstones found on trophic groups from the basin-floor is as fol- the delta platform at Allens Creek (Ausich, lows: suspension feeders-5 7, deposit feed- 1977). ers-1 1, browsers-1 1, carnivores-1 1, de- With the exception of Scalarituba that is posit feeders, browsers, or scavengers-6, and found in the lower New Providence Shale, commensals-3. Though there is a high diver- trace fossils are rare in the prodeltaic shales. sity of suspension feeders the browsers and This may be a function of compression during deposit feeders are numerically dominant. lithification and the lack of contrasting sedi- The upper silty clay shales of the New Prov- ment types to enhance preservation of the idence Shale were deposited in the base- trace fossil. Scalarituba is probably preserved of-slope environment (Button Mold Knob because the low sedimentation rate character- Member of Conkin (1957)). The depositional istic of the basin-floor, and the reducing con- conditions in this environment were essentially ditions, allowed the burrows to be infilled with flat-lying beds, relatively low energy, gravity- pyrite. The Kenwood Siltstone which directly driven currents from a slope that faced west overlies the New Providence Shale in southern with debouching- from at least two minor can- Indiana and north-central Kentucky has a well yons (in Kentucky), low oxygenation, and a developed trace fossil assemblage which in- muddy bottom with increasing amounts of silt cludes Zoophycus, Chondrites, Scalarituba vertically (Kepferle, 1977). Water depth slow- and others (Kepferle, 1977). Trace fossils are ly decreased as the delta prograded. The But- commonly preserved on siltstone surfaces ton Mold Knob community is found in these which were in contact with interbedded sediments (see Butts (192 2), p. 5 1-53 for a fau- shales. The silt probably provided a firmer nal list) and is characterized by a high diver- substrate to allow preservation of the trace fos- sity and abundance of suspension-feeding or- sils. Often burrow walls are defined by traces ganisms (96 percent), i.e., crinoids, bryozoans, of iron oxide. The fine-grained sediments of brachiopods, and corals (Text-fig. 7A). Other the New Providence Shale may have had a feeding types include deposit-feeding trilobites diverse trace fossil assemblage but the physical (1 percent), commensal gastropods (1 percent), characters of the sediment prevented their and a rare carnivorous orthocone cephalopod preservation. (1 percent). In southern Indiana and north-central Ken- The faunal composition of the Button Mold tucky the prodeltaic communities are best de- Knob community is most similar to other com- veloped in the geographic area termed the Sil- munities found under conditions of low sedi- ver Hills facies by Stockdale (1939). The Silver mentation rates and soft muddy bottoms in Hills facies area is one of the most fossiliferous other environments of the Borden Delta. The areas of the New Providence Shale and is lower community at Crawfordsville (Lane, based on the presence of the Kenwood Silt- 1973), on the delta platform, shares many of stone, a turbidite which was emplaced from the same genera of crinoids and bryozoans two submarine canyons on the Borden delta which are also a part of the Button Mold Knob (Kipferle, 1977). These canyons were probably community. Common crinoids in both com- present during the deposition of the New munities include the disparid inadunates Hal- Providence Shale and may have funnelled nu- ysiocrinus and Synbathocrinus, the cyatho- trients downslope by way of density driven crine inadunates Cyathocrinites and currents to allow the colonization of these Barycrinus, the poteriocrine inadunate areas by benthic faunas. Despite the presence Springericrinus, and the camerates Platycrin- of fossiliferous patches, much of the Silver ites and Eretmocrinus. Common brvozoans in Hills facies is unfossiliferous. This may be re- each community include the rhabdomesonid lated to the problem of colonizing a muddy cryptostomes Rhombopora, Streblotrypa, and substrate and disparities in food distribution. Nikiforovella; the cryptostome bifoliate Cys- The pioneering organisms are unknown, todictya; the fenestrate cryptostomes Fenes- though they may have been brachiopods (as in tella, Hemitrypa, Penniretepora, and Tham- the Ordovician of Tennessee, Walker and Par- niscus. The fauna of the Button Mold Knob ker, 1976) and there is some evidence for this W. I. AUSICH, T. W. KAMMER AND N. G. LANE

at Button Mold Knob. Once a substrate was munities of the platform, though lower in di- colonized the skeletal material of previous or- versity. More basinward communities are ganisms may have served as larval settling dominated by molluscs and are unique among sites for later organisms. This may explain delta communities. why certain sites remained colonized through Taking the delta as a whole, the dominant time while the rocks of adjacent sites are un- shelly organisms were the bryozoans, espe- fossiliferous. cially fenestrates and cystoporates. Problems of preservation, sampling, and identification DISCUSSION of bryozoans cause difficulties in demographic The dominant deltaic community was com- and trophic considerations of this group. As a posed of soft-bodied organisms, but the troph- result they are commonly ignored in commu- ic structure and diversity of this community is nity studies. Yet bryozoans were the most poorly known. Shelly communities were also common and among the most diverse groups present scattered over the entire delta. These of organisms in certain communities studied communities, where present, generally had here and in many other late Paleozoic com- high diversity and abundance and were dom- munities. Any Paleozoic community study in inated by suspension feeding organisms. In an open marine environment that docs not these communities the diversity was highest consider bryozoans may have serious flaws. among those on the platform, lowest on the Within small individual sites on the Borden slope, and intermediate in the prodeltaic set- delta, we have collected up to 155 species that ting. belong to a single community of level bottom The high diversity delta platform commu- invertebrates. Examples of specific diversity nities were all tiered. Some were dominated on the delta platform include Waldrip Site, 49; by crinoids, especially by small inadunates in Allens Creek Bank, 104; Boy Scout Camp, distributary channels and by camerates and 135; lower community at Crawfordsville, 75; disparids on skeletal carbonate banks. Bryo- upper community at Crawfordsville, 155; and zoans dominated in tiered communities that in the prodeltaic setting Button Mold Knob, were present in mudstone and siltstone facies. 103. These figures contrast sharply with those Slope communities were not tiered and were presented recently by Bambach (1977) who low in diversity or even monospecific. These stated that 30 is the average number of species communities are dominated by large brachio- in an open marine level bottom community in pods that were able to inhabit unstable sub- the upper Paleozoic, and that the highest di- strates. No fossils, identified in this investi- versity in the upper Paleozoic was Crawfords- gation, are endemic to slope communities, ville with 73 species (p. 159). How he arrived instead faunal elements of the slope lived on at this number is not clear. Apparently only other parts of the delta as well. Orthotetes and certain taxa were considered to have belonged Syringothyris range from the platform down to the level bottom community. This restric- onto the slope but do not extend to the pro- tion severely distorts the true nature of many delta, and Bembexia and Phestia range from Mississippian communities that are tiered and the prodelta up onto the slope but not onto the have higher level feeding organisms such as platform. Some faunal elements, Halysiocri- crinoids and bryozoans. The tiered community nus, Cheilotrypa, and Cystodictya, had ranges was the normal type of upper Paleozoic open that extended over the entire delta. Thus the marine level bottom community. The high di- slope communities consist of a mixture of pi- versity within individual communities on the oneering organisms that migrated from adja- Borden delta is not atypical of Mississippian cent delta settings and that could survive on communities in general and many other as- soft sediments in the relatively unpredictable semblages for both younger and older Carbon- environments of the slope. iferous rocks are equally as diverse. Recogni- Prodeltaic communities have diversities that tion that upper Paleozoic communities are are intermediate between those found on the generally much more diverse than suggested platform and the slope. At the base of the by Bambach (1977)lends support to the idea slope, prodeltaic communities were tiered and that diversity may have been in equilibrium are similar to siltstone and mudstone com- during much of the Phanerozoic (Raup, 1976a, FOSSIL COMMUNITIES

1976b), rather than having increased through -. 1973. Paleontology and paleoecology of the the Phanerozoic as suggested by Bambach Crawfordsville fossil site (Upper Osagian: In- (1977) and Valentine et al. (1978). diana) with sections by J. L. Matthews, E. G. Driscoll, and E. L. Yochelson. Univ. Calif. Pubs. Geol. Sci. 99:l-147. ACKNOWLEDGMENTS Lineback, J. A. 1966. Deep-water sediments ad- Alan Horowitz introduced us to the Nash- jacent to the Borden Siltstone (Mississippian) del- ville, Ind., site in the Locust Point Formation. ta in southern Illinois. Ill. Geol. Survey Circ. Ronald S. Hattin and Stuart M. Kelly helped 410, 48 p. -. 1968. Turbidites and other sandstone bodies with field work. Alan Horowitz read a prelim- in the Borden Siltstone (Mississippian) in Illinois. inary version of the manuscript. Ill. Geol. Survey Circ. 425, 29 p. - 1969. Illinois basin-sediment starved during Mississippian. Am. Assoc. Petiol. Geol. Bull. REFERENCES 53:112-126. Allen, J. R. L. 1970. Sediments of the modern Matthews, J. L. 1973. Sedimentation, p. 17-30. Niger delta: a summary and review, p. 136-15 1. In N. G. Lane (ed.), Paleontology and Paleo- In J. P. Morgan and R. H. Shaver (eds.), Deltaic ecology of the Crawfordsville fossil site (Upper sedimentation, modern and ancient. Soc. Econ. Osagian: Indiana), Univ. Calif. Pub. Geol. Sci. Paleontol. and Mineralogists Spec. Pub. 15. 99. Ausich, W. I. 1977. Case study of some deltaic Mathews, W. H. and F. P. Shepard. 1962. Sedi- filter-feeding communities: Edwardsville For- mentation of Fraser River delta, British Colum- mation (Borden Group) in Indiana. Geol. Soc. bia. Am. Assoc. Petrol. Geol. Bull. 46:1416- Amer. Abstracts with Programs 9:884-885. 1443. -. 1978. Community organization, paleontol- Peterson, W. L. and R. C. Kepferle. 1970. Deltaic ogy, and sedimentology of the Lower Mississip- deposits of the Borden Formation in central Ken- pian Borden delta platform (Edwardsville For- tucky, p. D49-D54. In Geological Survey re- mation, southern Indiana). Ph.D. dissertation, search 1970. U.S. Geol. Survey Prof. Paper Indiana University, 430 p. 700-D. Bambach, R. K. 1977. Species richness in marine Raup, D. M. 1976a. Species diversity in the Pha- benthic habits through the Phanerozoic. Paleo- nerozoic: a tabulation. Paleobiology 2:279-288. biology 3:152-167. -. 1976b. Species diversity in the Phanerozoic: Butts, C. 1922. The Mississippian series of eastern an interpretation. Paleobiology 2:289-297. Kentucky. Kentucky Geol. Survey, Ser. 6, 7:188. Rexroad, C. B. and A. J. Scott. 1964. Conodont Carozzi, A. V. and J. G. W. Soderman. 1962. Pe- zones in the Rockford Limestone and the lower trography of Mississippian (Borden) crinoidal part of the New Providence Shale (Mississippian) limestones of Stobo, Indiana. J. Sed. Petrol. in Indiana. Ind. Geol. Survey Bull. 30, 54 p. 32:397-414. Sedimentation Seminar. 1972. Sedimentology of Conkin, J. E. 1957. Stratigraphy of the New Prov- the Mississippian Knifley Sandstone and Cane idence Formation (Mississippian) in Jefferson and Valley Limestone of south-central Kentucky. Bullitt Counties, Kentucky, and fauna of the Kentucky Geol. Survey Rept. Inv. 13, ser. 10, Coral Ridge Member. Bull. Amer. Paleont. 30 p. 38(168): 109-157. Springer, F. 1911. The crinoid fauna of the Knob- Fisk, H. N. 1961. Bar-finger sands of Mississippi stone formation. Proc. U.S. Nat. Mus. 41:175- delta, p. 29-52. In J. A. Peterson and J. C. Os- 208. mond (eds.), Geometry of sandstone bodies-a Stockdale, P. B. 1931. The Borden (Knobstone) symposium, 45th Ann. Mtg., Atlantic City, N. rocks of southern Indiana. Ind. Dept. Conserv., J., 1960. Tulsa, Am. Assoc. Petroleum Geolo- Div. Geology, Pub. 98, 330 p. gists. -. 1939. Lower Mississippian rocks of the east- Griffith, C. 1978. Depositional environment of the central interior. Geol. Soc. Am. Spec. Paper 22, New Albany Shale (Upper Devonian) in north- 248 p. central Kentucky. Geol. Soc. Am. Abstr. Prog. Suttner, L. J. and D. E. Hattin (eds.). 1973. Field 10:255. conference on Borden Group and overlying lime- Kepferle, R. C. 197 7. Stratigraphy, petrology, and stone units, south-central Indiana. Soc. Econ. depositional environment of the Kenwood Silt- Paleontol. and Mineralogists, Great Lakes Sec., stone Member, Borden Formation (Mississippi- 3d Ann. Mtg., Bloomington, Ind., 113 p. an), Kentucky and Indiana. U.S. Geol. Survey Swann, D. H., J. A. Lineback and E. Frund. Prof. Paper 1007, 49 p. 1965. The Borden Siltstone (Mississippian) delta Lane, N. G. 1963. The Berkeley crinoid collection in southwestern Illinois. Ill. State Geol. Surv. from Crawfordsville, Indiana. J. Paleontol. Circ. 386, 20 p. 37:1001-1008. Valentine, J. W., T. C. Foin and D. Peart. 1978. 1196 W.I. AUSICH, T. W.KAMMER AND N. G. LANE

A provincial model of Phanerozoic marine diver- Weller, S. 1909. Kinderhook faunal studies-V, sity. Paleobiology 4:55-66. the fauna of the Fern Glen formation. Geol. Soc. Van Sant, J. F. and N. G. Lane. 1964. Crawfords- Am. Bull. 20, pp. 265-332. ville (Indiana) crinoid studies. Univ. Kansas Pa- MANUSCRIPT RECEIVED JUNE 5, 1978 leontol. Contrib., Art. 7, 136 p. REVISEDMANUSCRIPT RECEIVED FEBRUARY3, Walker, K. R. and W. C. Parker. 1976. Popula- 1979 tion structure of a pioneer and later stage species in an Ordovician ecological succession. Paleo- Indiana University Foundation contributed $150 biology 2:191-201. in support of this article. http://www.jstor.org

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You have printed the following article: Fossil Communities of the Borden (Mississippian) Delta in Indiana and Northern Kentucky William I. Ausich; Thomas W. Kammer; N. Gary Lane Journal of Paleontology, Vol. 53, No. 5. (Sep., 1979), pp. 1182-1196. Stable URL: http://links.jstor.org/sici?sici=0022-3360%28197909%2953%3A5%3C1182%3AFCOTB%28%3E2.0.CO%3B2-H

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References

Species Richness in Marine Benthic habitats through the Phanerozoic Richard K. Bambach Paleobiology, Vol. 3, No. 2. (Spring, 1977), pp. 152-167. Stable URL: http://links.jstor.org/sici?sici=0094-8373%28197721%293%3A2%3C152%3ASRIMBH%3E2.0.CO%3B2-C

The Berkeley Crinoid Collection from Crawfordsville, Indiana N. Gary Lane Journal of Paleontology, Vol. 37, No. 5. (Sep., 1963), pp. 1001-1008. Stable URL: http://links.jstor.org/sici?sici=0022-3360%28196309%2937%3A5%3C1001%3ATBCCFC%3E2.0.CO%3B2-E

Species Diversity in the Phanerozoic: A Tabulation David M. Raup Paleobiology, Vol. 2, No. 4. (Autumn, 1976), pp. 279-288. Stable URL: http://links.jstor.org/sici?sici=0094-8373%28197623%292%3A4%3C279%3ASDITPA%3E2.0.CO%3B2-O

Species Diversity in the Phanerozoic: An Interpretation David M. Raup Paleobiology, Vol. 2, No. 4. (Autumn, 1976), pp. 289-297. Stable URL: http://links.jstor.org/sici?sici=0094-8373%28197623%292%3A4%3C289%3ASDITPA%3E2.0.CO%3B2-L http://www.jstor.org

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A Provincial Model of Phanerozoic Marine Diversity James W. Valentine; Theodore C. Foin; David Peart Paleobiology, Vol. 4, No. 1. (Winter, 1978), pp. 55-66. Stable URL: http://links.jstor.org/sici?sici=0094-8373%28197824%294%3A1%3C55%3AAPMOPM%3E2.0.CO%3B2-J

Population Structure of a Pioneer and a Later Stage Species in an Ordovician Ecological Succession Kenneth R. Walker; William C. Parker Paleobiology, Vol. 2, No. 3. (Summer, 1976), pp. 191-201. Stable URL: http://links.jstor.org/sici?sici=0094-8373%28197622%292%3A3%3C191%3APSOAPA%3E2.0.CO%3B2-1