The Paleoecology of a Late Ordovician Shale Unit from Southwest Ohio and Southeastern Indiana Author(S): Robert C

Paleontological Society

The Paleoecology of a Late Ordovician Shale Unit from Southwest Ohio and Southeastern Indiana Author(s): Robert C. Frey Source: Journal of Paleontology, Vol. 61, No. 2 (Mar., 1987), pp. 242-267 Published by: Paleontological Society Stable URL: http://www.jstor.org/stable/1305320 Accessed: 14/03/2010 21:30

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http://www.jstor.org JOURNALOF PALEONTOLOGY,V. 61, NO. 2, P. 242-267, 7 FIGS.,MARCH 1987

THE PALEOECOLOGY OF A LATE ORDOVICIAN SHALE UNIT FROM SOUTHWEST OHIO AND SOUTHEASTERN INDIANA

ROBERTC. FREY Department of Geography and Geology, Centenary College, Shreveport,Louisiana 71134-0188

ABSTRACT- The Treptocerasduseri shale unit withinthe WaynesvilleFormation of LateOrdovician (early Richmondian)age in southwestOhio and the equivalentTrilobite shale unit in the same formationexposed in adjacentportions of Indianarepresent an Ordovicianshallow marinemud- bottom epeiricsea facies. These fine-grainedclastics contain a moderatelydiverse mollusk-trilobite assemblagedominated by vagrantepifaunal detritus-feeding calymenid and asaphidtrilobites, large endobyssateand infaunalfilter-feeding pelecypods, and nektonicnautiloids. Articulate brachiopods, ectoprocts,and pelmatozoanechinoderms form only minor elements of this fauna. This mollusk-trilobiteassemblage was common in Late Ordovicianshallow marineclastic en- vironmentswhere mobility was an asset and therewas an abundanceof oxygenand food resources. Such assemblagesare characteristicof the LorraineFauna of Late Ordovician(Edenian to Rich- mondian)age that occurs from the Ohio Valley north and east into New York, Ontario,Quebec, and Ireland.These early Paleozoic mud-bottom assemblageswere considerablymodified by the Late Ordovicianextinction event and were replacedin the Silurianand Devonian by distinctly differentassemblages dominated by largeepifaunal strophomenid and spiriferidbrachiopods, crinoids, and phacopidtrilobites.

INTRODUCTION from mollusks in these Ordovician marine PALEOZOICsubtidal mud-bottom environ- environments. ments have been describedas supportingas- Shale units in the CincinnatianSeries (Up- semblages dominated by relatively immo- per Ordovician)in the Ohio Valley make up bile, epifaunal suspension-feeding benthos at least 60% of the exposed Ordovician sec- (Ausich and Bottjer, 1982; Jablonski and tion. Very little has been published concern- Bottjer, 1983; Thayer, 1983) or, less-com- ing the biota of these shales and their paleo- monly, mobile infaunaldeposit-feeders (Lev- ecology. Many of the shales represent the inton and Bambach, 1975). Sepkoski and deposits of muddy epeiric sea floors that sup- Sheehan(1983), citing primarilythe work of ported moderately diverse assemblages dom- Bretsky (1969, 1970a, 1970b), have de- inated not by articulate brachiopods, but by scribedUpper Ordovicianshelf communities filter-feeding pelecypods, trilobites, nauti- in easternNorth Americaas being dominated loids, and, occasionally, echinoderms. The by a diverse assemblage of orthid, stropho- Treptoceras duseri shale unit in the Waynes- menid, and atrypidbrachiopods, trepostome ville Formation is one such unit. and cryptostome ectoprocts, phacopine trilobites, and crinoids.Most of this assemblage STRATIGRAPHY persists beyond the Ordovician to constitute The Treptoceras duseri shale unit is a blue the brachiopod-ectoproct-pelmatozoanechi- claystone unit about 1.5 m thick located with- noderm assemblage so characteristic of Pa- in the Waynesville Formation of Late Or- leozoic shelf environments.These authorslist dovician (early Richmondian) age exposed in pelecypods as part of their "Modem Fauna" southwest Ohio and adjacent portions of and indicate that members of this group were southeastern Indiana (Figure 1). Shideler locally important in the Late Ordovician in (unpublished notes) and Flower (1946) both nearshore, inner shelf environments, spa- noted that the Treptoceras duseri shale, as tially distinct from the brachiopod-dominat- typified by the occurrenceof large numbers ed "Paleozoic Fauna" of offshore shelf en- of the nautiloid Treptoceras duseri (Hall and vironments. Trilobites, an important Whitfield),is restrictedto portions of Warren component of this offshorePaleozoic Fauna, and Clinton counties in Ohio. Studies by the are inferredto have been spatiallysegregated writer have confirmed this distribution.

However, a temporally-equivalent shale unit, lithologically identical to the Treptoceras du- mo seri shale but minus the distinctive nautiloid INDIANA OHIO fauna, has been found in Butler and Preble . * counties in western Ohio and in adjacent por- 5A&4 A tions of southeastern Indiana. This shale will 2 3. be differentiated from the Treptoceras duseri shale and is referred to as the Trilobite shale 6A unit from the abundance of the calymenid trilobite, Flexicalymene meeki (Foerste). The Treptoceras duseri shale unit is located 11-13 m above the contact between the underlying rubbly limestones of the Arnheim KENTUCKY Formation and the even-bedded shales and thin limestones of the Waynesville Forma- tion (Figure 2). At most localities in Warren A* TREPTOCERASDUSERI SHALE OUTCROPS SCALE TRILOBITESHALE OUTCROPS I": 2Omi. and Clinton counties in Ohio, the basal con- f ORDOVICIAN-SILURIANBOUNDARY DAI tact of the Treptoceras duseri shale is well- defined, with the massive claystone of the FIGURE1 -Map of the Indiana-Ohioarea showing shale resting on a ripple-marked, irregularly the location of the exposuresof the Treptoceras bedded packstone composed of jumbled, duseriand Trilobiteshale units thatwere studied whole, disarticulated brachiopod valves. The and collectedas partof this investigation.Num- upper contact of the shale unit is gradational beredlocalities correspondto localities listed in with the occurrence of the localityregister. These localities include those in most places, limy where these shale units are more in the 10 cm of the extensively lenses increasing upper exposed and those exposures more intensively shale. However, at most localities the shale studied. is capped by a well-bedded, 10 cm thick packstone composed almost entirely of the disarticulated valves of the entelacean brachio- The monotonous massive claystone li- pod Onniella meeki (Miller) in a matrix of thology that makes up much of the Treptoc- clay and sparry calcite. eras duseri shale unit is interrupted locally by The predominant lithology of the Treptoc- the development of shelly beds less than 1 eras duseri shale is best termed a claystone, cm thick and by thin limestone beds from 1- using the terminology of Potter et al. (1980). 6 cm thick (Figure 3, column 1). The shelly These massive claystones, when fresh, are beds consist of calcareous indurated clays with blue-gray, hard, dense, and well-indurated. concentrations of pelecypod and nautiloid They show no evidence of bedding, with the shells and trilobite carapaces and exuviae. rock splitting conchoidally when struck with These shelly beds are usually not continuous a hammer. These rocks are remarkably uni- and rarely traceable for more than 100 m in form in texture, fine-grained, with this mo- any direction. The thin limestone beds con- notonous lithology relieved only by occa- sist of well-bedded packstones with sharp sional layers of shells and thin limestone beds basal contacts with the underlying claystones. (Figure 3). The claystones are predominantly These limestones are composed of poorly- clay in composition (illite, 70-80%) with mi- sorted biogenic allochems ranging from fine nor amounts of silt (20-24%) and carbonate shell detritus to whole, unbroken shells in a (less than 8%). The carbonate content of the matrix of clay, micrite, and sparry calcite. claystone increases adjacent to the localized The basal portions of the limestone beds are accumulations of shell debris. Biogenic struc- commonly a jumbled mass of large, random- tures are uncommon in the massive claystone ly-oriented shells. These limestones exhibit lithology, being represented by branching graded bedding, fining upwards with shells tube-like structures referable to the ichno- becoming aligned parallel to bedding and ori- genus Chondrites. No obvious sedimentary ented convex up. These grade into laminated structures were observed. silts and clays. The upper portions of these 244 ROBERT C. FREY

TIME- SOUTHEASTERNINDIANA SOUTHWESTERNOHIO NORTH CENTRAL ROCK KENTUCKY

NEW POINT SHAL

HITZ BED (Ls) SHALE PREACHERSVILLE .ELKHORN IMBR (moroon 8 green mudstone) SALUDA FM (Dol. Ls) z < DRAKES FM LLI( 0 WHITEWATER FM (Ls) ZWHITEWATER ULL(Dol. Ls 8 mudstone)

FORK FM J

< • LIBERTY FM (Ls 8 Sh) (Ls a Sh) z z WAYNESVILLE FM

z TRILOBITE SHALE UNIT T. DUSERI SHALE UNI

(Sh w/h minor Ls) ASHLOCK FM DILLSBORO FM ARNHEIM FM (Ls & Sh)

(Ls mudstones) & MT AUBURN MBR GRANT (Ls Sh) MCMILLIAN (Ls) LAKE MCMILLIAN Z - CORRYVILLE MBR (Sh) LIMESTONE

BELLEVUE LIMESTONE ( o L 0 CALLOWAY CREEK w FAIRVIEW FM (Ls & Sh) O LIMESTONE

z W KOPE FM (Sh w/h minor Ls) CLAYS FERRY FM (Sh & Ls)

FIGURE2- Lithostratigraphicunits within the Upper Ordovician CincinnatianSeries exposed in the Cincinnati, Ohio, area, showing the lateral and vertical facies relationshipsbetween these units. Relative thicknesses of these units in this diagram do not express the true thicknesses. Modified from Weir et al. (1984, fig. 50, p. E80). The Treptocerasduseri and Trilobiteshale units are informal stratigraphicunits within the WaynesvilleFormation in southwest Ohio and southeasternIndiana. shelly sets commonly have the fine laminae unit, consisting of a meter and a half of hard, disrupted by clay-filled burrows. The thin dense, massive, blue-gray claystone with mi- limestone beds are generally continuous nor thin limestone beds in the upper 50 cm throughout a particular exposure and some of the unit (Figure 3, column 2). These thin appear to be traceable across the outcrop area, limestones are less common and much thin- although thicknesses of these beds are vari- ner in the Trilobite shale and do not exhibit able. Allochems are primarily pelecypod the graded texture present in limestone beds shells and trilobite fragments. In the upper occurring in the Treptoceras duseri shale. In 10 cm of the Treptoceras duseri shale, the Franklin County, Indiana, the claystone of limestone beds become more irregular, the Trilobite shale rests upon an even-bed- pinching out rapidly in all directions. These ded, 5-8 cm thick microsparite that is uni- limestones are poorly-bedded, lensoidal, form in texture with a few recognizable large composed of whole shells in a matrix of mi- allochems. The massive claystone lithology crite, fine shell detritus, and spar. Allochems of the Trilobite shale is identical texturally in these upper limestone beds consist of ar- and mineralogically to that of the Treptoceras ticulate brachiopod valves with lesser num- duseri shale, differing only in the more com- bers of fragmentary trepostomes. mon occurrence of shelly beds within the Lithologically, the Trilobite shale unit is shale. The most obvious difference between nearly identical to the Treptoceras duseri shale these two equivalent shale units is the en- ORDOVICIAN PALEOECOLOG Y 245

SLABBY LIMESTONESWITH ONNIELLAINTERBEDDED WITHTHIN SHALE SEAMS SLABBY LIMESTONESWITH ONNIELLAa THAERODONTA INTERBEDDEDWITH THIN SHALE SEAMS ONNIELLA MEEKI LIMESTONE ONNIELLA MEEKI LIMESTONE -150cm i 5o cm HASHYLIMESTONE BEDS _ LIMYLENSES WITH FISSILE SHALE FISSILE CLAYSTONE(FOSSILIFEROUS) THIN LIMESTONEBED WITH GASTROPODS INDURATEDMUDSTONE WITH LARGE RAFINESQUINA SHELL PAVEMENT

MASSIVE CLAYSTONE(FOSSILIFEROUS)

MASSIVE CLAYSTONE(FOSSILIFEROUS) - 100 cm STHIN GRADEDLIMESTONE, BURROWED - 100I cm

E MASSIVECLAYSTONE (FOSSILIFEROUS) c SILTY CLAYSTONE

MASSIVE CLAYSTONE(LOCAL SHELL BEDS) w HASHYLAYERS OF TRILOBITE EXUVIAE - 50cm u 50cm MASSIVECLAYSTONE(FEWFOSSILS) MASSIVE CLAYSTONE(FEW FOSSILS)

cm THIN LIMESTONEWITH FLEXICALYMENEPARTS BARRENMICROSPARB ROUNIT ATBASE 0 cm RIPPLED PACKSTONEAT BASE

FIGURE3--Stratigraphic sections within the Treptocerasduseri and Trilobite shale units showing the lithologies present. Column 1, the Treptocerasduseri shale unit exposed along the north fork of HarpersRun at Camp Whip-Poor-Will,G.S.A. outdoor center, WarrenCounty, Ohio (Locality2 in Figure 1). Column 2, the Trilobite shale unit exposed at the Rt. 101 roadcut at Bon Well Hill, FranklinCounty, Indiana (Locality 4 in Figure 1). Note the sharp basal contacts at both localities (marked0 cm) and the increase in thin limestone beds toward the top of both sections. closed fauna. This fauna is more diverse in cut, 3 km northeast of Waynesville, Warren the Treptoceras duseri shale unit primarily County, Ohio, and along stream exposures because the diverse nautiloid fauna is absent on Harpers Run, Camp Whip-Poor-Will, from the Trilobite shale unit. G.S.A., also in Warren County, Ohio. Similar detailed studies were made in the Trilobite METHODS shale unit exposed at the Bon Well Hill road- Sixty-two species of invertebrates were cut on Rt. 101, just northeast of Brookville, identified from the Treptoceras duseri shale in Franklin County, Indiana (for more de- and forty-nine species were identified from tailed locality information, refer to the lo- the equivalent Trilobite shale (Tables 1, 2). cality register following the conclusions). At Individuals of each species were measured the U.S. Rt. 42 locality and Bon Well Hill and histograms prepared illustrating size-fre- localities, samples were taken at 10 cm in- quencies for collected suites of specimens. tervals and density surveys were undertaken The horizontal and vertical distribution to determine any lithologic or paleontologic within the shale was determined for each changes occurring within the shale. These species as well, with its orientation, relative density surveys consisted of studying succes- abundance, and faunal associates noted (Frey, sive bedding planes within the shale and not- 1983). These data plus information provided ing the number of species present, the num- by the physical characteristics of the strata ber of individuals per species, plus the spacing, were used to interpret the paleoecology of orientation, size, and preservation of the fos- these shale assemblages and reconstruct the sils exposed on these approximate bedding environment of deposition. plane surfaces. Detailed studies of the Treptoceras duseri The Harpers Run exposures are located shale were carried out at the U.S. Rt. 42 road- within Camp Whip-Poor-Will, a Girl Scouts 246 ROBERT C. FREY

TABLEI--Fauna of the Treptocerasduseri shale (62 species, 53 genera). Claystonelithology Limestonelithology Species Genera Species Genera 2 stromatoporoids 2 1 coral 1 3 inarticulatebrachiopods 3 1 articulatebrachiopod 1 3 articulatebrachiopods 3 5 ectoprocts 4 3 ectoprocts 3 1 monoplacophoran 1 2 monoplacophorans 2 5 gastropods 5 11 nautiloids 8 3 nautiloids 2 12 pelecypods 10 12 pelecypods 9 2 trilobites 2 2 trilobites 2 2 ostracodes 2 2 "wormtubes" 2 2 "worm tubes" 2 2 scolecodonts 2 2 scolecodonts 2 2 conodonts 2 1 graptoloid 1 43 total species 37 genera 38 total species 34 genera 43 total species identifiedfrom claystonelithology 38 total species identifiedfrom limestone lithology 19 total species common to both lithologies of America outdoor center and nature pre- caused collapse of the shelf edge, followed by serve. At this locality, detailed collections northwestwardthrusting of slices of meta- were made periodically from naturally ex- morphosed shelf margin and oceanic crustal posed stream bank exposures, with the in- material (Bird and Dewey, 1970). This up- dividual species being identified and collect- heaval led to the development of the Taconic ed, and their location and orientationwithin Highlands, a roughly northeast-southwest the shale being noted. The paleontological trendinglandmass that separatedthe epeiric censustaken here approximates the "stretched seas of the North American craton from the line" method employed by Johnson (1960) Iapetus Ocean to the south and east. This in studyingbeach cliff exposuresin the Pleis- landmass is thought to have been the major tocene of California. source of clastic sediment that was deposited in the Cincinnati area during Late Ordovi- PALEOGEOGRAPHIC SETTING cian time. The erosion of the Taconic High- Currentreconstructions of EarlyPaleozoic landsled to the developmentof a vast fluvial- plate configurationsindicate that in the latter deltaic system, the Queenston Deltaic Com- part of the Ordovician the North American plex, that spread clastics derived from these Plate was situated on the equator, rotated highlands northwardand westward into ad- slightlyclockwise from its presentorientation jacent epeiric shelf areas (Dennison, 1976). (Scotese et al., 1979; Bambach et al., 1980). In this deltaic complex, coarser sands were The Cincinnati area was situated about 15- depositedadjacent to the sourcearea (Juniata 20 degreessouth of the equatorin tropicalto Formation) and finer muds and silts farther subtropicallatitudes, under the influence of out on the shelf (QueenstonFormation). Be- westerly-flowingtrade winds. cause of the distance separating the source During the Ordovician, eastern North area from the Cincinnatiarea, the only clas- America consisted of a broad, flat, gently tics reaching the region during early Rich- sloping shelf areathat was alternatelysubject mondian time were the finer-sizedfractions; to periods of subaerial erosion and periods typically fine silt and clays. of inundation by shallow warm tropical seas The tectonic events to the (Ordovician) (Read, 1980). In the latterpart of the Middle southeasthad importantconsequences for the Ordovician, the southeasternmargin of the Cincinnati Shelf area. Periodic uplift of the North American plate (Laurentia)collided Taconic regionwould generatepulses of clas- with a volcanic arc system which initially tic sediment that would sweep onto the shelf ORDO VICIAN PALEOECOLOGY 247

TABLE2-Fauna of the Trilobite shale (49 species, 45 genera).

Claystonelithology Limestonelithology Species Genera Species Genera 1 conularid 1 2 inarticulatebrachiopods 2 2 inarticulatebrachiopods 2 2 articulatebrachiopods 2 3 articulatebrachiopods 3 2 ectoprocts 2 5 ectoprocts 4 1 monoplacophoran 1 2 monoplacophorans 2 3 gastropods 3 2 nautiloids 2 3 nautiloids 3 8 pelecypods 7 11 pelecypods 10 3 trilobites 3 4 trilobites 4 3 ostracodes 3 1 crinoid 1 2 "worm tubes" 2 2 "worm tubes" 2 2 conodonts 2 1 ?carpoid 1 23 total species 22 genera 42 total species 40 genera 23 species identifiedfrom the claystonelithology 42 species identifiedfrom the limestone lithology 16 species common to both lithologies and deposit new accumulations of silts and that extended across the northernedge of the clays. These pulses of sedimentation are platform during early Richmondian times. thought to be representedby the periodic de- The shallow water depths on this platform velopment of nearlypure claystonebeds with area are also indicated by development in only minor amounts of limestone. Pulses of northernKentucky and adjacentareas of In- sediment influx are believed to have been diana of the Marble Hill Bed of later Rich- responsible for the deposition of the shaly mondian age. Swadley (1980) has described Kope, Corryville, and Waynesville facies in these gastropod biosparruditesand biospa- the Cincinnati area (Figure 2). rites as linear, well-washedaccumulations of The Cincinnati Shelf area is reconstructed shells deposited in high-energy,shallow ma- as having been a gently sloping muddy shelf rine environments,possibly offshorebar sys- area that graded into deeper-waterbasins to tems and associated tidal channel complexes the north and east (Figure4). This mud-bot- that paralleledthe northernedge of the Blue- tom shelf area graded southwestward into grass Platform. Southwest of the platform shallowerwater environments represented by edge banks (exposed in the Bardstown,Ken- low-energy clayey limestone facies now ex- tucky, area in Figure 4) was a low-energy, posed in areasalong the Ohio River in south- mud-bottom, restricted lagoonal environ- easternIndiana and southwestOhio (the areas ment representedby the micritic and dolo- marked "shallow subtidal" in Figure 4). To mitic mudstones of the Rowlands Member the southwest was the BluegrassPlatform, a of the Drakes Formation (Weir et al., 1965). positive area that was the site of carbonate These mudstones typically lack body fossils, deposition throughoutmuch of the Ordovi- with the only abundant biogenic structures cian (Cressman and Karklins, 1970; Cress- being local bedding planes covered by the man, 1973; Weir et al., 1984). This Bluegrass trace fossil Palaeophycus. Platform was the site of very shallow water conditionsin earlyRichmondian times. Along ENVIRONMENT OF DEPOSITION the northernedge of the platform are rubbly Numerous authors (Bucher, 1917; Fox, mudstones and limestones that contain nu- 1962; Anstey and Fowler, 1969; Cressman, merousspecimens of the coral Tetradiumon- 1973; Martin, 1975; Hay, 1981; and Weir et tario and the stromatoporoid Labechia hu- al., 1984), citing evidence from the sedimen- ronensis, plus a diverse trepostome fauna. tary facies present, the associated sedimen- These deposits are thought to represent the tary structures,and the enclosed fossil biota, development of coral-stromatoporoidbanks have inferredthat the entire Upper Ordovi- 248 ROBERT C. FREY

OHIO BASIN A' WAYNESVILLE,OH

SUBTIDALBELOW WAVE BASE CINCINNATI SHELF

(TRILOBITESHALE UNIT) (TREPTOCERASDUSERI SHALE UNIT)

SHALLOWSUBTIDAL SHALLOWSUBTIDAL PACKSTONE 8 PACKSTONE WACKESTONE WACKESTONEWAESPACKSTONTONE 8

.g~Th4 TETRADIUMBANKS

BLUEGRASS PLATFORM

DOLOMITICMUDSTONE FEW BODY FOSSILS A BARDSTOWN, KY

A A'

LOW ENERGYRESTRICTED BANK SUBTIDALMUD BOTTOM

FIGURE4--A reconstruction of local paleoenvironmental conditions in the Indiana-Ohio-Kentucky area during the time of deposition of the Treptoceras duseri shale unit in southwest Ohio and the equivalent Trilobite shale unit in southeastern Indiana. Stippled pattern shows the areal extent of shelf edge bar deposits of the slightly younger Marble Hill Bed. Coral symbol marks the extent of ORDOVICIAN PALEOECOLOG Y 249 cian section exposed in the Cincinnati area conditions with normal marine salinities. The represents shallow marine subtidal deposi- two basic rock types present in these shale tion on an extensive, gently sloping shelf area, units, the massive claystones and thin-bed- termed here the Cincinnati Shelf. Weir et al. ded, shelly packstones and wackestones, are (1984), citing the observations of Bucher thought to represent distinctive depositional (1917) and Anstey and Fowler (1969) for the environments within this general environ- Kope Formation, described their lithofacies mental setting. Group I-D as being deposited in water depths Massive claystone environment. -The of from 20-25 m (66-82 ft). The Waynesville massive claystone lithology is thought to rep- Formation in Ohio is lithologically similar to resent the influx of fine clastics into the Cin- the Kope and would be classified as part of cinnati Shelf area, with the accumulation and the same lithofacies group. This suggests that preservation of these clastics in the low-en- water depths during deposition of the Trep- ergy, quiet-water bottom environments char- toceras duseri and Trilobite shale units were acteristic of the Ohio and Indiana portions similar to that of the Kope. of this shelf. The monotonous, nearly pure Wray (1977) stated that the depth range of claystones and the lack of extensive accu- living dasycladacean algae extends from just mulations of shelly debris indicate low rates below low tide to about 30 m, with the max- of colonization by shelly invertebrates on imum abundance of these algae occurring at these bottoms due to local development of depths of less than 10 m. Benthic calcareous adverse environmental conditions, possibly algae (dasycladaceans and solenoporaceans) periodically high rates of sedimentation or occur sporadically throughout the entire Cin- soft-substrate conditions. The high volume cinnatian Series in the Indiana-Ohio-Ken- of sediment relative to shell debris effectively tucky region (Blackwell and Marek, personal diluted the volume of shell debris that was commun.). The problematic dasycladacean present on these mud bottoms. Cyclocrinites darwini (Miller) had been col- These massive claystones contain a fauna lected by the writer from the basal Waynes- of mobile invertebrates whose morphologies ville Formation in Franklin County, Indiana, show adaptations to the periodically high rates only several meters below the Trilobite shale of sedimentation. The streamlined morphol- unit. The same species has also been collected ogies of infaunal burrowing pelecypods sug- from the overlying Liberty Formation in the gest that these mud bottoms were relatively same area. This also suggests rather shallow cohesive, and the large average size of many water conditions for the deposition of the individuals indicates an abundance of nu- Waynesville Formation, including the Tri- trients. Brandt (1980) suggested that the lobite and Treptoceras duseri shale unit. abundant pelecypod fauna and the low or- The Treptoceras duseri and Trilobite shale ganic content of these claystones were indic- units are inferred to have been deposited on ative of well-oxygenated bottom conditions. the gently sloping mud bottoms of the Cin- The only common biogenic structures in cinnati Shelf, an area transitional between the the claystone of the Treptoceras duseri shale very shallow waters of the Bluegrass Platform are small diameter (2-3 mm), pyrite-replaced to the south and the deeper water environ- branching networks of tubes referable to the ments of basins to the north. As indicated ichnogenus Chondrites. These structures are above, water depths in this area during the best developed in clays that immediately time of deposition of these shale units are overlie the shelly beds and thin packstones thought to have been below wave base and that occur sporadically within the claystone. probably less than 30 m deep. Lithologies and The ichnogenus Chondrites is a common ele- faunas of both shale units indicate subtidal ment in a broad variety of ichnofacies within

the developmentof shelf edge coral-stromatoporoidbanks. Both of these featuresmark the northern margin of the BluegrassPlatform relative to the adjacentCincinnati Shelf area. Cross section from Bardstown,Kentucky, to Waynesville,Ohio (A-A') illustratesthe reconstructedenvironments from the platform(in the south) to the gently sloping shelf area (in the north). From Hay (1981) and field studies by the writer. Distribution of the Marble Hill Bed from Swadley (1980). 250 ROBERT C. FREY shallow marine shelf environments and has thick) packstones with sharp basal contacts little paleodepth significance.Brandt (1980) that demonstratea graded,fining-upward se- suggestedthat the lack of abundantbiogenic quence. These gradedpackstones are similar structuresin these claystones was the result to limestones describedby Sprechtand Bren- of rapid and recurrentinfluxes of fine clastics ner (1979), Kreisa (1981), and Hinterlong which were thoughtto prevent extensive dis- (1981). These writersdescribed these graded ruption of the substrateby burrowingorgan- carbonates as "tempestites" and attributed isms. The fine-grainedsubstrate may also be their formation to the effects of storm pro- a factor in the scarcityof preservedbiogenic cesses on open shelf bottoms. The muddy structures.Ausich et al. (1979) suggestedthat fabrics and associated siliciclastic lithology the scarcity of trace fossils in the Mississip- indicate originalskeletal accumulation under pian New Providence Shale was, in part, a nonturbulent conditions on mud bottoms. function of compression during lithification The fining-upsequence and many unabrad- and the lack of contrastingsediment types to ed, unbrokenshells suggestreworking of these enhance preservationof the trace fossil, with mud bottoms by wave energyof greaterthan the only preserved trace being infilled with normal magnitudeand of short duration. pyrite. Carney (in Boucot, 1981) described The second limestone type present in the what he termed "intermittently reworked Treptocerasduseri shale is similar to the first bottoms" as being trace fossil poor as the in texture,but lackingthe comparativelywell- result of these biogenic structures being defined graded bedding characteristicof the "erased"from the upper 10 cm of sediment limestone type described above. These beds by storm currentswhich cause extensive ero- are similar to what Fursich (1978) described sion, transport,and redeposition of bottom as condensedbeds. These can develop locally sediments in open shelf areas. on shelf bottoms if shell production exceeds The scarcity of biogenic structuresand of the rate of sedimentation,or if there is small- shells in inferred life position in these clay- scale reworkingof the bottom by weak storm stones is, in part, attributedto the periodic currents. In the latter case, these weak cur- disruption of the bottom by storm currents. rents put the muds into suspension but are These are indicated in the massive claystone not strong enough to generatethe graded se- lithology of the Treptocerasduseri shale by quence. the local development of lag deposits of tri- Development of both limestone types in lobite exuviae and aligned molluscan shells the upper 50 cm of the Treptocerasduseri which are followed by barren claystone lay- shale (Figure 3, column 1) indicates an in- ers. At the Harpers Run locality, detailed crease in shelly organisms on these bottoms analysis of the distribution of these beds in- associated with a slowing of the rate of sedi- dicates the occurrenceof such shell-richbeds mentation. This is indicated by the fauna as- at regular 10 cm intervals (Frey, 1983). The sociated with these limestone beds, which is occurrence of aligned orthoconic nautiloid characterizedby its relatively high diversity shells, overturnedcoralla and coenostea, and and an abundanceof sessile, epifaunalfilter- sets of shell-rich and shell-poor claystones feeders, most of which are not present in the reflects storm reworkingof the bottom, dis- underlyingclaystone lithology. The presence placing the large allochems and throwing of these functional types indicates stabiliza- smallerallochems and sediment into suspen- tion of the bottom with a slowingof the influx sion with both settling back to the bottom of clastics onto the shelf. afterthe storm passes. A similardepositional Thin limestones occurringin the equiva- model has been proposed for the Kope For- lent Trilobite shale unit in Indiana consist of mation by Meyer et al. (1981) and for the limestones of the second type only, lacking lithologically similar Corryville Member of any evidence of graded bedding. As major the McMillan Formation by Hinterlong storm systems are thought to have had their (1981). origin in subtropical highs developing in the Thin limestone environment.--The thin ocean basin to the east (Kreisa, 1981; Mar- limestone lithologies in the Treptoceras du- saglia and Klein, 1983), much of the energy seri shale are comprised of two related lime- of these storms may have been expended in stone types. The first consists of thin (1-6 cm crossing the eastern portions of the Cincin- ORDOVICIAN PALEOECOLOG Y 251 nati Shelf area. Upon reaching the Indiana the mud substrate. Articulate brachiopods region, there was little energy left to rework and ramose trepostomesare generallyabsent these sediments in the thoroughmanner nec- from this lithology. These fixed, epifaunalfil- essary to generate the graded packstone li- ter-feeders would have been quickly over- thology. There is no evidence to suggestthat come by the influx of fine sediments. Suitable the Indiana portion of the shelf was signifi- stable attachment sites for immature bra- cantlydeeper than in Ohio. In fact, Hay (198 1) chiopods and ectoproctsmay have been rare has suggested that this portion of the shelf or absent in this specific environment. might have been slightly shallower than ad- Fossil specimens in these claystone beds jacent portions in Ohio due to the incipient are remarkably well-preserved, generally development of the Cincinnati Arch at this consistingof whole completespecimens (Frey, time. 1983). Specimens of Tetradium and stromatoporoids are commonly overturned but PALEOCOMMUNITY RECONSTRUCTIONS remain intact and unabraded.Bases of over- Each lithological type present in the Trep- turnedcoenostea are commonly colonized by toceras duseri and Trilobite shale units is a variety of encrustingand boring organisms. thought to represent a distinctive sedimen- These isolated coralla and coenostea are up tary environment. Each of these environ- to 40 cm in diameter. Nautiloid specimens ments, in turn, had its own set of limiting consist of entire conchs, includingthe phrag- factors that governed the types of organisms mocone and much of the fragileliving cham- living in these environments. Paleocommu- ber. Specimens occasionally demonstrate a nity reconstructionspresented here are based preferredalignment within individual beds. on data derived from observations of the Pelecypods are articulated although com- shales at all outcrops studied, plus informa- monly "butterflied." In place, articulated tion obtained from more detailed studies at specimens oriented in a functional life posi- the U.S. Rt. 42, HarpersRun, and Bon Well tion do, however, occur in this lithology. Tri- Hill localities. lobites are characteristicallycompletely ar- Massive claystone communities.--Faunal ticulated, enrolled or reflexed. Incomplete, assemblages contained in the massive clay- disarticulated specimens are common and stone of both the Treptocerasduseri and Tri- may represent exuviae. A few specific beds lobite shale units are dominated by mobile occur in the shale in which all trilobite re- forms: nektonic predators (orthoconic nau- mains are disarticulated,showing some evi- tiloids), vagrantepifaunal deposit or detritus dence of reworkingalthough these deposits feeders (trilobites), and sedentary endobys- (Figure 3, column 1 at the 50 cm mark) are sate and infaunal filter-feeders(pelecypods). poorly sorted and do not show evidence of All of these organismswere capable,to some extensive currentactivity. Crinoids are rare extent, of adjustingtheir position relative to in these claystone faunas with the only oc- the sediment-water interface. These mobile currencenoted being a cluster of articulated forms show adaptationsto living on mud bot- calyceswith stems of locrinussubcrassus from toms subjectto periodicallyhigh rates of sed- the claystone lithology of the Trilobite shale iment influx. Their mobility was a crucial unit at Collins Run, ButlerCounty, Ohio (Lo- factorthat allowed them to avoid, at least for cality 7). Preservationof fossil specimens in a time, smothering by these muds. The few these claystones attests to the normally low- sedentaryorganisms present, the coral Tetra- energy conditions on these bottoms and the dium, the stromatoporoid Stromatocerium, in-placeoccurrence of these biotas. Displaced and the trepostome Cyphotrypa,also show and fragmentedspecimens indicate the peri- adaptations to living on mud bottoms with odic reworking of these bottoms by storm periodicallyhigh sedimentationrates. This is processes or the disruptive activities of large expressed by the rounded living surfaces of surface crawlers like the asaphid trilobite Iso- these taxa, inferred to be a sediment-shed- telus. ding morphology (Manten, 1971). These A total of 43 species have been identified species also have a strong vertical growth vec- from the claystone of the Treptoceras duseri tor which is thought to have permitted these shale in Warren and Clinton counties in Ohio forms to maintain their living surfaces above (Table 1). Mobile mollusks make up 24 of 252 ROBERT C. FREY

TABLE 3--List of taxa and their occurrenceand abundancein the claystonelithology of the Treptocerasduseri and Trilobite shale units within the WaynesvilleFormation. Percentages given for those species that constitute 1% (in terms of numbersof individuals)or more of the assemblage.X = species presentbut less than 1%of the total fauna. Based on detailed studies of the shale carriedout at the three localities listed below.

HarpersRun Bon Well Hill Taxon U.S. Rt. 42 roadcut exposures roadcut STROMATOPOROIDEA Labechiahuronensis X X Stromatoceriumgranulosum 1% 3.5% COELENTERATA- TABULATA Tetradiumontario 1% 1% COELENTERATA- CONULATA Conulariaformosa X ECTOPROCTA OrderCtenostomata* Ropalonariavenosa X X X Order Cyclostomata** Palescharabeani X X X Spatioporamaculosa X X X Spatioporatuberculata X X X OrderTrepostomata Cyphotrypaclarksvillensis 1% 4% X Parvohalloporaonealli X X BRACHIOPODA- INARTICULATA Lingulopsvanhornei 9% 2% 14% Trematiscrassipunctata X X 3.5% BRACHIOPODA-ARTICULATA OrderOrthida Onniella meeki X OrderStrophomenida Rafinesquinaloxorhytis X X X Order Spiriferida Zygospiramodesta X MOLLUSCA- MONOPLACOPHORA Sinuites subcompressus 6% 13% 3.5% MOLLUSCA- CEPHALOPODA (Nautiloidea) OrderEndocerida Camerocerasinaequabile X X X Order Michelinoceratida Treptocerasduseri 20.5% 26% 3.5% Gorbyocerascurvatum X Isorthoceras(?)sp. X X X OrderAscocerida Schuchertocerasobscurum X OrderOncocerida Oncocerasdeliculatum X X Manitoulinocerastenuiseptum X X Manitoulinoceraswilliamsae X X MOLLUSCA- PELECYPODA Subclass Palaeotaxodonta Cleidophorusplanulatus 6% X Subclass Pteriomorphia Ambonychiacasteri 1% Ambonychiasuberecta 6% 2% 18% Anomalodontagigantea X Caritodensdemissa 3% X X SubclassIsofilibranchia Corallidomusversaillesensis 3% X 24% Modiolopsisvalida X Orthodesmacurvatum X 5% Pholadomorphapholadiformis 9% 10% 4% ORDOVICIAN PALEOECOLOGY 253

TABLE3-Continued.

HarpersRun Bon Well Hill Taxon U.S. Rt. 42 roadcut exposures roadcut SubclassOrthonotia Cymatonotasemistriata X 5.5% Psiloconchagrandis X 1% Psiloconchasuberecta X X 5% SubclassAnomalodesmata Cuneamyamiamiensis 12% 11.25% Rhytimyacf. R. byrnesi X X X ARTHROPODA- TRILOBITA Flexicalymenemeeki 15% 13% 17% Platycorphechristyi X Isotelus maximus 12% 6% 7% ANNELIDA- POLYCHAETA Rhamphoprionsp. X X Atraktoprioncornutus X X ANNELIDA- PROBLEMATICA("worm" tubes) Ancientaohioensis X X X Cornulitesflexuosus** X X X ECHINODERMATA- CRINOIDEA locrinus subcrassus X GRAPTOLITHINA Mastigograptusstictus X X * Found encrustingsemi-infaunal pelecypods. ** Only found encrustingorthoconic nautiloids.

these 43 species. These include the mono- cally the same taxa dominant at the Rt. 42 placophoran Sinuites, 11 species of nauti- locality. These include the nautiloid Trep- loids, and 12 species of pelecypods. Many of toceras duseri, the calymenid trilobite Flex- the nautiloids and some of the pelecypod icalymene meeki, the cyclomyan monopla- species are known, however, from only a sin- cophoran Sinuites subcompressus,and the gle specimen. Only seven sessile epifaunal pelecypod Cuneamya miamiensis. specieswere identified and, ofthese, only three In terms of abundance, the massive clay- are common. Species abundance was tabu- stone biota of the Treptocerasduseri shale is lated for collections from the U.S. Rt. 42 and dominatedby vagile epifaunaldeposit- or de- Harpers Run localities. These data are pre- tritus-feeders, primarily trilobites and the sented in Table 3, which shows the occur- monoplacophoranSinuites (33% and 32%), rence and relative abundance of the more by large endobyssate filter-feeding pelecy- common taxa present at both localities. At pods (30% and 28%), and by nektonic nau- the U.S. Rt. 42 locality, data were recovered tiloids (20.5%and 26%).Infaunal pelecypods from bedding plane density surveys done at make up a smaller percentage of the total 10 cm intervalsin the upper 1 m of the shale. fauna (6% and 6.5%), as do fixed, epifaunal The four most abundant species at this lo- filter-feeders,including the coral Tetradium, cality account for 60% of the total fauna. the stromatoporoidStromatocerium, and the These include the nautiloid Treptocerasdu- trepostome Cyphotrypa(3% and 8%). A re- seri, the calymenid trilobite Flexicalymene constructionof the claystoneassemblage from meeki,the pelecypodCuneamya miamiensis, unit G of the Treptocerasduseri shale at the and the asaphid trilobite Isotelus maximus. HarpersRun locality (Figure 3, column 1) is At the Harpers Run locality, species census presentedin Figure 5. was taken using a modified version of the Similar studies were made of the claystone "stretchedline" method. The entireshale unit fauna of the equivalent Trilobite shale unit was sampled at random intervals at this lo- in western Ohio and adjacentportions of In- cality. The four most abundantspecies made diana. The fauna of this unit is less diverse up 63% of the total fauna and include basi- comparedto that of the same lithology in the 254 ROBERT C. FREY

4 ~ `j)2 ~7~i~V~3

- ~XC~s~d~ _i~d~ A\ C~ 1 r4~ 1? -? ~? ";"_:/? r, 'Qa~ I~ rr --?;??\?"` ~C1 ~Sh 8 5 6 tl \ / 8.,~3~ts~P~ ~

ii~'?l 2cl

FIGURE5--A reconstructionof the paleocommunityassociated with the massive claystone lithology of the Treptocerasduseri shale showing the organismsand trophicgroups typical of this assemblage. From claystoneunit G exposed at the HarpersRun locality in WarrenCounty, Ohio. 1, stromatoporoid Stromatoceriumgranulosum. 2, monoplacophoranSinuites subcompressus.3, nautiloid Trep- toceras duseri. 4, nautiloid Oncoceras delicatulum. 5, modiomorphid pelecypod Pholadomorpha pholadiformis.6, orthonotidpelecypod Cymatonota semistriata. 7, orthonotidpelecypod Psiloconcha grandis.8, anomalodesmatidpelecypod Cuneamya miamiensis. 9, calymenidtrilobite Flexicalymene meeki. 10, asaphid trilobite Isotelus maximus. 11, ichnofossil Chondritessp.

Treptoceras duseri shale, with only 23 species represent short periods of decreased sedi- being identified (Table 2). Mollusks again mentation during which opportunistic mo- dominate the fauna: 11 of 23 species. These diomorphid and ambonychiid pelecypods include one monoplacophoran, two nauti- colonized the mud bottom in patchy, high- loids, and eight species of pelecypods. Only density populations (Figure 6). The interven- four sessile epifaunal species were found in ing mudstone supports a meager fauna of this lithology. These include one inarticulate linguloid brachiopods, trilobites, and mono- (Trematis) and three uncommon articulate placophorans. Local shelly accumulations brachiopods. Data from bedding plane sur- developed within the Treptoceras duseri shale veys at the Bon Well Hill locality (Table 3) but did not support the large numbers of en- indicate species abundance rankings different dobyssate pelecypods characteristic of these from those of the Treptoceras duseri shale deposits in the Trilobite shale. unit. The top four species at this locality made Although the Trilobite shale and Treptoc- up 75% of the total fauna and include the eras duseri shale share many of the same endobyssate pelecypods Corallidomus ver- species and trophic groups, the relative im- saillesensis and Ambonychia suberecta, the portance of these groups in these shales is trilobite Flexicalymene meeki, and the lin- different. The claystone fauna of the Trilobite guloid brachiopod Lingulops vanhornei. shale is dominated by endobyssate, filter- The prevalence of the large endobyssate feeding pelecypods (47%), vagile epifaunal pelecypods in these samples is a product of deposit- or detritus-feeders, primarily trilo- several high-density shell beds with large bites (28%), with lesser numbers of infaunal numbers of individuals. These consist of lo- pelecypods (5%), and sessile epifaunal filter- cal clusters of specimens, typically reworked feeders (4%). Nektonic nautiloids, a promi- but remaining articulated and complete. nent part of the claystone biota in the Trep- These shelly accumulations are thought to toceras duseri shale, make up less than 5% of ORDOVICIAN PALEOECOLOGY 255

2cm

FIGURE6 -A reconstructionof the paleocommunityassociated with the shelly beds within the massive claystonelithology of the Trilobiteshale unit showingthe organismsand trophicgroups characteristic of this assemblage.From claystoneunit B exposed at the Rt. 101 road cut at Bon Well Hill, Franklin County,Indiana. 1, inarticulatebrachiopod Lingulops vanhornei. 2, inarticulatebrachiopod Trematis crassipunctata.3, monoplacophoranSinuites subcompressus. 4, ambonychiidpelecypod Ambonychia suberecta.5, modiomorphid pelecypod Corallidomusversaillesensis. 6, modiomorphid pelecypod Modiolopsisvalida. 7, modiomorphidpelecypod Pholadomorpha pholadiformis. 8, pterineidpelecy- pod Caritodensdemissa. 9, anomalodesmatid pelecypod Rhytimya cf. R. byrnesi. 10, calymenid trilobite Flexicalymene meeki. the fauna in the same lithology in the Tri- The shelf in southeastern Indiana is implied lobite shale unit. There are other faunal dif- to have been slightly shallower water than ferences between these two claystone units, that in southwestern Ohio. These shallower including the near absence of the pelecypod water conditions may not have been optimal Cuneamya miamiensis, a prominent element for many of the organisms that are charac- of the claystone fauna in the Treptoceras du- teristic of the Treptoceras duseri shale in Ohio seri shale, from similar claystones in the Tri- but absent from the Trilobite shale in In- lobite shale. Similarly, the soleniform pe- diana. lecypods Cymatonota semistriata and Deposit-feeding pelecypods, which are re- Orthodesma curvatum, the trepostome Cy- ported to be dominant elements in some early photrypa clarksvillensis, the coral Tetradium Paleozoic mud-bottom environments (Bret- ontario, and the stromatoporoid Stromato- sky and Bretsky, 1975; Levinton and Bam- cerium granulosum, all common in the clay- bach, 1975), are represented in the claystone stone lithology of the Treptoceras duseri shale, lithology of the Treptoceras duseri shale by a are either rare or absent from the same li- small number of sporadically distributed in- thology in the Trilobite shale unit. dividuals of the palaeotaxodont Cleidopho- The cause or causes of the faunal variation rus planulatus. The palaeotaxodont pelecy- between the two claystone assemblages is dif- pod Deceptrix is locally abundant in several ficult to establish. These differences seem to thin wackestone beds that occur in the upper result from subtle variations in the bottom 50 cm of the unit but has not been collected environment, variations not reflected in the from the massive claystone lithology. By lithologies of the two units. Hay (198 1) has analogy with living palaeotaxodont taxa, both suggested that the Cincinnati Arch had some of these genera are inferred to have been shal- affect on sedimentation during the time of low-burrowing, infaunal non-siphonate, palp- the deposition of the Waynesville Formation. proboscide deposit-feeders. The lack of 256 ROBERT C. FREY

CORALLIDOMUSVERSAILLESENSIS tims" of trophic group amensalism generated 6 by the burrowing activities of a mobile in- fauna. This detrimental effect is generated TREPTOCERASDUSERI SHALE either through fluidization of the substrate, WARRENCOUNTY, OHIO clogging of filtering devices, or burial beneath resuspended sediment. The lack of infaunal z in these coincides w deposit-feeders claystones with an abundance of several vagile epifaunal 3 c species that are interpreted as having been surface deposit-feeders. These include the cy- 2 clomyan monoplacophoran Sinuites and the trilobites Flexicalymene and Isotelus. Larson and Rhoads (1983) have indicated that crawl- ing or surface deposit-feeding activities are unimportant in bioturbating large volumes 10 20 30 40 50so 60 70 of sediment relative to infaunal deposit-feed- SHELL LENGTH (mm) ing activities. Apparently the activities of these mobile surface deposit-feeders did not have any adverse effect on these sedentary TRILOBITESHALE filter-feeding pelecypods as both groups com- FRANKLINCOUNTY, monly share bedding plane surfaces in both INDIANA of these shale units. Another characteristic of these claystone N= 69 faunas is the tendency for larger-sized indi- 4 viduals to be numerically predominant in the z This is w preserved assemblages. particularly evident in the pelecypods where size-fre- w indicate mean shell lengths clus- LIL quency plots

2 tered at the larger end of the size range for each species (Figure 7). Bretsky (personal commun.) has suggested that these size-distribution patterns can be open to a variety of interpretations. These include limited selection hence limited in 10 20 30 40 50so 60 70 pressure, mortality post- SHELL LENGTH (mm) larval juvenile growth stages, high mid-mortality rates, or relatively high rates of growth of FIGURE7--Size-frequency histograms speci- in juveniles. Jackson (1972) noted similar mens of the modiomorphidpelecypod Coralli- trends in in recent shallow domus versaillesensis(Miller) from the Treptoc- pelecypods living eras duseri shale unit in WarrenCounty, Ohio shelf environments, indicating that there was (upper) and from the Trilobite shale unit in strong selection for more rapid growth in pe- FranklinCounty, Indiana (lower). Specimens of lecypods in high-stress environments, which this speciescollected from these shaleunits range would increase the number of individuals from 21 to 64 mm in length. Note the predom- reaching full adult size. It is also speculated inance of individuals in these larger-size pre- that, in the endobyssate pelecypods in par- served suites of specimens. ticular, the rapid growth rates and larger size (up to 10 cm in length) may have been an abundant infaunal deposit-feeders may have attempt by these largely sedentary organisms been a factor in the development of locally to cope with the periodically high rates of dense populations of large, sedentary endo- sedimentation and possibly turbid bottom byssate and infaunal filter-feeding pelecypods conditions thought to have been character- in these muddy substrates. Thayer (1983) has istic of these claystone environments. The noted that these types of low-level, relatively large size of individuals would allow the shell immobile filter-feeders are usually the "vic- to protrude further above the sediment-water ORDOVICIAN PALEOECOLOGY 257 interfacewhile maintainingphysical stability formations. Claystones in the Kope Forma- by remaining deeply-embedded in the sub- tion and at the base of the overlyingFairview strate.Thayer (1983) has documented a sim- Formation (Figure 2) in the Cincinnati area ilar case from the Recent, describing the contain a fauna similar in composition to common occurrenceof the largeendobyssate Bretsky's Nuculites-Colpomya Community filter-feedingpelecypods Pinna and Modiolus from strata of the same age in New York. colonizing unstable substrates in shallow This fauna is dominated by small infaunal waters in Jamaica. He suggested that Pinna deposit-feedingpalaeotaxodont and semi-in- grows rapidlyto large size to avoid burial by faunal filter-feedingorthonotid and anom- shiftingsubstrates. He noted that growthrates alodesmatid pelecypods, indicating a mud- of 20 cm/year had been recorded by Butler bottom community of a somewhat different and Brewster(1979) in specimens of Pinna aspect than those in the Treptocerasduseri from Australia and a growth rate of 15 cm and Trilobite shale units (Giuseffi, 1982). A in the first three months for species of Atrina distinctive featureof these faunasis the small in Hawaii. size of individuals, with most specimens less Very few similar paleocommunities have than 30 mm in length. Giuseffi (1982) has been describedfrom Ordovicianstrata. Bret- suggested that the small size of individuals sky (1970b) described the Ambonychia-Mo- in the basal Fairview claystones may have diolopsis Community from the upper part of been the result of decreased nutrient supply the Pulaski Formation (Upper Ordovician, in these deeper water shelf-slope mud bot- Maysvillian) in New York. This assemblage toms, or the result of unstable substratecon- occurs in thin- to medium-bedded, fine- to ditions. In the soupy mud substrateshe pos- medium-grainedsandstones thought to have tulated for this unit, small size and lowered been deposited under moderate- to high-en- whole-animal densities might have been se- ergy conditions in nearshore,infralittoral en- lected for. Harrison(1984) indicated that the vironments. This community is dominated small size of individuals in the Kope For- by largefilter-feeding pelecypods, particular- mation might reflect a selective "census" of ly Ambonychiaand Modiolopsis. This is an juvenile specimens by disruptive storm association similar to that found in the Am- events, removing and buryingpopulations of bonychia-Corallidomusshell beds in the Tri- mollusksat differentstages of growth.He also lobite shale. In the same paper, Bretsky de- suggestedthat unstable substrateconditions scribedthe Nuculites-ColpomyaCommunity may have enhancedjuvenile mortality rates from gray silty shales in the upper Pulaski. due to foundering of organisms in the soft This community is thoughtto have been rep- muds. resentative of widespread offshore and on- Assemblages more similar to those in the shore low-energy mud bottoms. This com- Treptocerasduseri and Trilobite shale units munity is dominated by small infaunal are encountered in several thick claystone deposit- and filter-feeding pelecypods and units within the Corryville Member of the contains a few taxa found in the Treptoceras McMillan Formationof late Maysvillian age duserishale, particularlyCleidophorus (=Nu- (Figure2). These claystonebeds containmany culites),Cuneamya, and Psiloconcha.Bretsky of the same taxa that occur in the overlying and Bretsky(1976) described several assem- Treptocerasduseri and Trilobite shale units. blagesfrom the Nicolet River section in Que- These include the nautiloids Treptoceras, bec (UpperOrdovician, Maysvillian) that also Cameroceras,and Oncoceras, the large en- contain taxa of the claystone community de- dobyssate mussels Ambonychia, Corallido- veloped in the Treptocerasduseri shale, es- mus, and Orthodesma, and the trilobites pecially those from the shallow water, silt- Flexicalymeneand Isotelus. Unlike the Trep- sand section representedby sample intervals toceras duseri shale unit, within these Cor- T4 and T5 (Bretskyand Bretsky, 1976, Table ryville claystone beds local concentrations of 3). the crinoids locrinus and Glyptocrinus are Elsewhere in the Upper Ordovician of the common (Giuseffi, 1982; Hinterlong, 1981). Cincinnati area, several similar assemblages The Treptoceras duseri shale claystone bio- are found in similar lithologies in different ta recurs at the top of the Waynesville For- 258 ROBERT C. FREY

TABLE 4--List of taxa and their occurrencein the thin limestone beds that occur in the Treptocerasduseri and Trilobiteshale units within the WaynesvilleFormation. Abundance data is a roughestimate only as the shelly debrisin thesebeds is not commonlyin placeand often disarticulated(bivalved organisms and ramoseectoprocts). To locate these limestone beds within the two shale units, referto Figure3. A = abundant(represented by 50 or more specimensin sample suite),C = common (representedby 20-50 specimens),UC = uncommon(represented by 10-20 specimens),R = rare (representedby less than 10 specimens).

HarpersRun exposures Bon Well Hill roadcut Taxon Bed B Bed F Bed H Bed I Bed E Bed G ECTOPROCTA OrderTrepostomata Batostomellagracilis UC UC UC C A Cyphotrypaclarksvillensis UC C Parvohalloporaonealii C C C UC OrderCryptostomata Arthroporashafferi C C UC C C Heloporasp. C C A BRACHIOPODA- INARTICULATA unidentifiedlinguloid A Petrocraniascabiosa* C A A BRACHIOPODA- ARTICULATA OrderOrthida Onniella meeki R C A UC C OrderStrophomenida Rafinesquinaloxorhytis R A C A C OrderSpiriferida Zygospiramodesta R C UC UC UC MOLLUSCA- MONOPLACOPHORA Cyrtolitesretrorsus C R UC Sinuitessubcompressus C R C MOLLUSCA- GASTROPODA Clathrospiraconica UC UC Donaldiellabowdeni UC Liospiramicula C UC C Holopea(?)pulchella C A C Schizolophatropidophora UC C C R MOLLUSCA- CEPHALOPODA(Nautiloidea) OrderEndocerida Camerocerasinaequabile UC UC OrderMichelinoceratida Treptocerasduseri C C Isorthoceras(?)sp. C C OrderOncocerida Oncocerasdeliculatum UC Manitoulinocerassp. C MOLLUSCA- PELECYPODA Subclass Palaeotaxodonta Cleidophorusplanulatus UC Ctenodontaiphigenia UC Deceptrixalbertina A C C SubclassPteriomorphia Ambonychiasuberecta UC R C UC Ambonychiaalata R C Anomalodontagigantea C UC Caritodensdemissa C UC C Subclass Isofilibranchia Corallidomusversaillesensis UC C UC Orthodesmacurvatum UC R UC Pholadomorphapholadiformis C R UC Subclass Heteroconchia Cycloconchamilleri UC Lyrodesmamajor A ORDOVICIAN PALEOECOLOG Y 259

TABLE4-Continued.

HarpersRun exposures Bon Well Hill roadcut Taxon Bed B Bed F Bed H Bed I Bed E Bed G

ARTHROPODA-TRILOBITA Flexicalymenemeeki A A A A A A Platycorphechristyi R Isotelus maximus C A A Odontopleura(?)sp. UC UC ARTHROPODA-OSTRACODA Quadrijugatorregularis UC A A Milleratiacincinnatiensis UC C A A ANNELIDA-POLYCHAETA Rhamphoprionsp. C C C C Atraktoprioncornutus C C C C ANNELIDA-- PROBLEMATICA("worm" tubes) Ancientaohioensis C A A A Cornulitesflexuosus* C C C ECHINODERMATA- CRINOIDEA Iocrinussubcrassus C A C Thick round columnals A UC petaloid lumen Thin round columnals C A A with crenella ECHINODERMATA- HOMALOZOA(?) Lepidocoleusjamesi (plates) UC UC A A CONODONTOPHORA Drepanoistodussuberectus C C C Plectodinafurcata C C C * Occurs encrusting other invertebrates, especially ambonychiid shells.

mation in Indiana and Ohio. The fauna of thin limestone beds is dominated by sessile this claystone bed differs from that of the epifaunal forms in contrast to the predomi- Treptocerasduseri shale in the occurrenceof nantly mobile species presentin the claystone several new taxa. These include the pelecy- facies (Table 4). Although these thin lime- pod species Cuneamya scapha and Cyrto- stones show evidence of current-reworking, dontula ohioensis and a locally abundant the disarticulatedbut complete nature of the echinoderm fauna that includes crinoids and shells composing these wackestones and asterozoans. This claystone fauna makes its packstones suggests a lack of sustained cur- last appearancein the Upper Ordovician of rent-reworkingwith many thin-walled, deli- the Cincinnati area in several thin claystone cate specimens unbroken and unabraded. beds at the base of the overlyingLiberty For- These limestones are believed to be the result mation (Richmondian).In the overlyingpre- of hurricanestorm surgesreworking the bot- dominantly carbonate strata, faunas in the tom sediments, which are thought to have Cincinnatiarea are distinctly different,dom- been more stable and firmerthan those rep- inated by taxa derived from the Arctic or Red resented by the massive claystone lithology. River Fauna associated with carbonateplat- This suggests a slowing of sediment influx form facies to the north and west (Frey, 1981, into these shelf areas, allowing a higher rate 1985). of colonization of these bottoms by shelly Thin limestone communities.-Faunal as- invertebrates.The more stable environments semblagesin the thin limestone beds that oc- represented by these limestone beds sup- cur in the upper 50 cm of both the Treptoc- ported a diverse fauna of articulatebrachio- eras duseri and Trilobite shale units present pods, ramose trepostomesand cryptostomes, a differenttype of community structurethan gastropods, pelecypods, trilobites, ostra- that present in the associated massive clay- codes, and crinoids (Table 4). stone lithology. The fauna typical of these The thin limestone lithology of the Trep- 260 ROBERT C. FREY

tocerasduseri shale unit in Warrenand Clin- monospecificassemblages throughout the en- ton counties in southwest Ohio has yielded tire Upper Ordoviciansection in the Cincin- 38 species of fossil invertebratesbelonging to nati area. 34 genera (Table 1). These limestone biotas Faunalassemblages occurring in thin lime- represent patchy benthic communities oc- stone beds in the Trilobite shale unit in In- cupying locally stable bottom environments diana are distinct from those that occur in on these shelf areas. The physical presence similar beds in the Treptocerasduseri shale. of the limestone beds themselves indicates Trilobite shale limestone biotas consist of that shell production locally increased rela- higher diversity faunas that contain more tive to sedimentation. Low local sedimen- abundantcryptostomes, ostracodes, and cri- tation rates enhanced colonization of the noids (Table 4). These faunas are dominated bottom by numerous fixed, epifaunal filter- by vagrantepifaunal grazing gastropods, de- feeding organisms, leading to the develop- tritus-feedingostracodes and trilobites, and ment of patchy clusters of shelly organisms. sessile epifaunal filter-feedingarticulate bra- These clustersare usually built upon a foun- chiopods, ectoprocts, endobyssate pelecy- dation provided by anastomosingthickets of pods, and crinoids.As in the case of the Trep- the ramose trepostome Parvohallopora or toceras duseri shale in Ohio, the Trilobite shell pavements composed of the valves of shale unit is capped by packstone composed the large,flat strophomenidbrachiopod Raf- almost entirelyof the disarticulatedvalves of inesquina. These patchy communities were the small orthid Onniella meeki (Figure 3). periodically destroyed by hurricane storm The faunal assemblages present in these surgeswhich also reworked,to some degree, thin limestone beds in both the Treptoceras these shelly accumulations.Resuspension of duseriand Trilobite shale units are modified the muddy substrateand continued influx of versions of the Onniella-SowerbyellaCom- fine sediments onto these shelf areas would munity describedby Bretsky(1970a, 1970b) also smother these patchy communities and from outer infralittoralshelf muds and silts returnbottom conditions to those typical of in the central Appalachiansand New York. the massive claystone lithology. Lorenz (1973) and Meyer et al. (1981) de- In limestone beds that occur in the upper scribed the same assemblagefrom the Kope 10 cm of the Treptocerasduseri shale, there Formation (Edenian)in the Cincinnati area. is the development of nearly monospecific Studiesby the writerin the Cincinnati,Ohio, assemblages consisting of large numbers of area indicate the recurrenceof this assem- the orthid brachiopod Onniella meeki. The blage in thin limestones and shales at the base cause or causes of the development of these of the overlying Fairview Formation (Mays- monospecific brachiopod beds is unknown. villian) and throughoutmost of the Waynes- Possible causes include increasedperiodicity ville Formation (lower Richmondian). The of destructive storms, generating unstable Isotelus shale unit at the top of the Waynes- bottom conditions and preventing the de- ville Formation marks the last occurrenceof of more diverse benthic velopment complex, typical Onniella in the Cincinnati area al- communities. Steele-Petrovic (1979) sug- though a modified version of this assemblage that brachiopodsrequire less food than gested occurs in the basal portions of the overlying many other groups of filter-feedinginverte- brates. The decline and eventual absence of Liberty Formation (Figure2). This commu- does not occur in the White- mollusks, nity overlying especially filter-feeding pelecy- Formation or its in the In- pods, from these communities may then in- water equivalents dicate a decreasein the available food supply diana-Kentucky-Ohioarea, being replacedby with the orthidOnniella meeki being a species new assemblagesderived from the carbonate adapted to such conditions and exploiting platformArctic Fauna to the north and west. them in the absence of competition. Species This Arctic brachiopod-coralfauna is entire- of Onniella, as well as those of the stropho- ly different from the invertebrate faunas char- menid Rafinesquina and the atrypid Zygo- acteristic of the older Edenian-lower Rich- spira, apparently were ecological "opportun- mondian section exposed in the Cincinnati, ists" as they commonly occur in high-density Ohio, area (Frey, 1981). ORDOVICIAN PALEOECOLOG Y 261

DISCUSSION bottom conditions with periods of rapid sedimentation. Interpretationof these organisms The Treptocerasduseri and Trilobite shale as current-generating filter-feeders (i.e., units within the Waynesville Formation in sponge-like) rather than passive micro-car- Ohio and Indianarepresent examples of early nivores (coral-like)also allows these forms to Paleozoic mud-bottom epeiric sea facies that exist in lower energy, mud-bottom environ- supported moderately diverse faunas of ments. largely mobile organisms, especially trilo- Similarly,many large (up to 10 cm in length) bites, large endobyssate and semi-infaunal Late Ordovician byssally-attached filter- filter-feedingpelecypods, and nekto-benthic feeding pelecypods have been thought of as nautiloids. These forms, as well as the few primarilybeing epibyssate(living on the sur- fixed species present,show adaptationsto liv- face) on hard substratesin current-swepten- ing on mud bottoms subject to periodically vironments (Bretsky, 1970a, 1970b; Pojeta, high sedimentationrates. These mollusk-tri- 1971; Stanley, 1972). These pelecypods are lobite communities are common in Late Or- shown to have been most abundant in the dovician shallow marine clastic facies rep- Upper Ordovicianof the Ohio Valley in clay- resentativeof well-oxygenatedenvironments ey strata representativeof low-energy,mud- where mobility was an asset and in which bottom environments where they lived in a there was an abundance of food. Such mol- semi-infaunalmanner (endobyssate) with the lusk-trilobite assemblages are characteristic anterior three-fourthsof the shell buried in of the Lorraine Fauna of Late Ordovician the substrate(Frey, 1980, 1983). These large (Edenian-early Richmondian) age that has endobyssate filter-feedingpelecypods make been described from the central Appala- up a significantcomponent of the fauna as- chians (Bretsky, 1970a), New York (Foerste, sociated with the massive claystones of both 1914; Ruedemann, 1926; Bretsky, 1970b), the Treptocerasduseri and Trilobite shale Ontario (Foerste, 1916, 1924), Quebec units (30%and 47% of the fauna, respective- (Foerste, 1914, 1916; Bretsky and Bretsky, ly). Steele-Petrovic(1975) has stated that fil- 1976), and Northern Ireland (Tunniclift, ter-feeding pelecypods are generally absent 1982), as well as the Cincinnati region. from fine-grained Paleozoic marine sedi- Studiesof these Late Ordovicianmud-bot- ments and that articulatebrachiopods are the tom faunas suggest that a number of gener- dominant epifaunalfilter-feeders in these fa- alities concerningthe occurrenceof large fil- cies. She has suggested that this absence of ter-feedingorganisms in these mud substrates filter-feedingpelecypods was the result of an need to be modified. Data from this study intolerance of turbid water conditions, with suggest that some tabulate corals and stro- the gills in these organisms being unable to matoporoidswere well-adaptedto life on pe- shed fine sedimentsand eventuallybecoming riodically unstable mud bottoms with the clogged with sediment. Tevesz and McCall coral Tetradiumontario and the stromatop- (1979) have pointed out that large, slow-bur- oroid Stromatocerium granulosum both rowing filter-feedingpelecypods can live in being common in the claystones of the Trep- muddy substratesdespite not having any spe- toceras duseri shale unit. These occurrences cialized equipment to handle the unstable, are in conflict with most conventional paleo- occasionallyturbid bottom conditionsin these ecological descriptionsof these forms, which environments. Specific morphological ad- suggest that tabulate corals and stromatop- aptations for life in muddy substrates cited oroids were intolerant of mud bottoms and by these authors include a moderately-in- restrictedto current-swept,hard-bottom en- flated, thin shell to aid in shell buoyancy and vironments (Lecompte, 1956; Galloway, lower bulk density, large size to prevent 1957; and for a less rigorousviewpoint, Wells, smothering by resuspendedmuds, and spe- 1957). The development of rounded, sedi- cific behavior patterns to cope with the pe- ment-shedding living surfaces plus a variety riodically unstable habitat. These authors of coenosteum morphotypes, including um- contend that under a certain selective regime, brella-like sediment "snowshoes" and nearly including reduced competition, a lack of in- columnar growth, indicate adaptation to mud- tense predation, and a lack of extensive bio- 262 ROBERT C. FREY turbationby infaunalburrowers, large filter- tiloids "Orthoceras,"Dawsonoceras, and a feeding pelecypods may occur in abundance poorly-preservedbarrandeocerid. on soft, muddy substrates.The abundanceof The paleoecology of the Silica Shale of large endobyssate and semi-infaunal filter- Middle Devonian (Givetian) age in Lucas feeding pelecypods in the claystone facies of County, Ohio, has been described by Nuss- both the Treptocerasduseri and Trilobiteshale man (in Kesling and Chilman, 1975) and the unit indicatesthat these organismscould and same shale in adjacent portions of Indiana did thrive on muddy substrates in shallow has recentlybeen studiedby Wiedman(1985). marineenvironments of Late Ordovicianage Nussman's lithologic unit 9 is a massive dark where the above set of conditions existed. graycalcareous claystone with only a few thin Steele-Petrovic (1979), Jablonski and limestone lenses. Fourtaxa are dominant and Bottjer (1983), Larson and Rhoads (1983), three of these are epifaunal, reclining filter- and Thayer (1983) pointed out the domi- feedingbrachiopods. These include the small nance of sedentary epifaunal suspension- chonetid Devonchonetesand the large spirif- feeding organisms in Paleozoic soft-bottom erids Paraspirifer and Orthospirifer. The environments. Investigations of Paleozoic fourth common taxon in this fauna is the mud-bottom biotas currentlyin preliminary trilobite Phacops, a presumed vagrant epi- stages of study also support these observa- faunaldetritus-feeder. The total fauna of this tions. All of the stratigraphicunits under study unit comprises 42 common species, domi- are similar, consisting of massive, blocky nated in terms of numbers of taxa by artic- claystonesthat contain well-preservedshelly ulate brachiopods and encrusting cystopo- faunas. All were deposited in low-energy, rates and cyclostomes. Pelecypods and mud-bottom environments at a variety of nautiloids are rare. Crinoids occur in the un- depths, most below wave base and less than derlying unit and in the limestone lenses. 30 m in depth, with normalmarine salinities. Structurally,this assemblageis similar to the As indicated above, Late Ordovician mud- WaldronShale in the dominance of stropho- bottom assemblages,as characterizedby those menid and spiriferidbrachiopods and large in the Treptocerasduseri and Trilobite shale phacopine trilobites, with reduced numbers units in the Cincinnatiarea, consist of mod- of mollusks. The stabilizing crinoids, how- erately diverse faunas of vagrant epifaunal ever, are less important in the Silica Shale deposit-feeders, primarily trilobites and community. monoplacophorans, large endobyssate and The Francis Shale of Late Pennsylvanian shallow-burrowinginfaunal filter-feeding pe- (Missourian) age, exposed at Ada, Okla- lecypods, and nekto-benthicnautiloids, with homa, consists of a thick sequence of mas- lesser numbersof crinoids, stromatoporoids, sive-bedded, silty blue-grayclaystone. Mor- and linguloid brachiopods. gan (1924) has listed 50+ species from the Studies by the writerof the WaldronShale Francis Shale at this locality. The fauna is (Silurian,late Llandoverian-earlyWenlock- dominated by large, epifaunal, reclining ian) at St. Paul, Indiana, indicate mud bot- productid brachiopods, chonetids, pectinids toms stabilizedin partby the branchingroot- (Acanthopectenand Aviculopecten),shallow- lets of crinoid holdfasts and burrowing infaunal actinodont pelecypods encrusting and small growths of cystoporates. Faunas are domi- (Astartella Schizodus), gastropods, nated attached bra- the echinoid Archaeocidaris,and the trilobite by small, rhynchonellid This fauna a and favositid Ditomopyge. represents typical chiopods corals, a variety of Carboniferous Productid-Chonetid com- crinoids, plus a number of large, reclining dominated re- and munity (Bretsky, 1969), by strophomenid, spiriferid, rhynchonellid clining epifaunal filter-feedersthat included brachiopods(Fardenia, Leptaena, Eospirifer, productidand chonetidbrachiopods and pec- and Uncinulus.) The large phacopine trilo- tinid pelecypods. This community marks a bites Calymene and Dalmanites are also change from the Waldron-Silica type in the common elements. Pelecypods and nauti- replacement of strophomenids and spirifer- loids are poorly-represented in the Waldron ids by productids and chonetids plus the re- fauna, represented only by the epifaunal pter- turn of molluscs to these muddy epeiric sea ineids Pterinea and Newsomella and the nau- bottom environments in the form of epibys- ORDOVICIANPALEOECOLOG Y 263 sate pectinids and infaunal-burrowingacti- in the Upper Ordovician of eastern North nodonts. The largephacopine trilobites have America. Offshore shelf environments are been replacedby smaller phillipsiid forms. described as supportingdiverse assemblages dominated by articulate brachiopods, ecto- CONCLUSIONS procts, trilobites, and crinoids. Steele-Pe- Late Ordovicianshallow marine mud-bot- trovic (1979) noted a similar distribution of tom environments support moderately di- these groups in the Paleozoic, pointing out verse mollusk-trilobite assemblages domi- the failure of pelecypods to become estab- nated by vagrant epifaunal deposit-feeding lished in more offshore shelf environments calymenid and asaphid trilobites, large en- until the close of the era. Sepkoskiand Shee- dobyssate and semi-infaunal filter-feeding han (1983) described inner shelf environ- pelecypods, and nekto-benthonicnautiloids. ments as being above wave base. As indicated Articulatebrachiopods, ectoprocts, and pel- above, the CincinnatiShelf areais considered matozoan echinoderms form subordinate to have been part of a uniformly shallow portionsof these faunas,if presentat all. These epeiric sea. Depth gradients were low, con- mollusk-trilobite assemblages are common sisting of a slight slope off the BluegrassPlat- in shallowmarine clastic environments where form to the south. Water depths during the mobility was an asset and where there was deposition of these Late Ordovician shale an abundance of food. These Ordovician units have been estimatedto have been about epeiric sea mud-bottom biotas were consid- 20-30 m. The sedimentological evidence erably modified by the Late Ordovician ex- suggestsconditions below fair-weatherwave tinction event which had a particularly base on bottoms reworkedonly by abnormal devastating effect on the endobyssate am- currentsassociated with storms. This would bonychiid and modiomorphid pelecypods seem to approximate at least middle shelf and the trilobites (Sepkoski, 1982). conditions, using the model of Sepkoski and Similar Siluro-Devonian mud-bottom fa- Sheehan.Indeed, these authorsplot Fox's cri- cies supported distinctly different assem- noid-trilobite community as an outer shelf blages dominated by largeepifaunal stropho- assemblagein their figure6. From Fox's de- menid and spiriferid brachiopods, crinoids, scriptionof this community(1968), this com- and phacopine trilobites. Mollusks, particu- munity includesthe Trilobiteshale unit with- larly pelecypods, are poorly-representedand in his Resserella-Zygospiraassemblage zone make up minor portions of these faunas. Fol- in southeasternIndiana. This offshore shelf lowing the Late Devonian extinction event, mollusk-trilobite assemblage suggests that this strophomenid-spirifer-trilobiteassem- some aspects of more recent models of the blage was replaced in the Carboniferousby evolutionaryhistory of the marinerealm, such one dominated by large epifaunal reclining as that of Sepkoski and Sheehan, may need productids, chonetids, epibyssate reclining to be revised to account for the occurrence and shallow-burrowing pelecypods, echi- of this assemblagein the Late Ordovician. noids, and phillipsiid trilobites. This assem- It is believed that large filter-feedingpe- blagewould dominate muddy epeiric sea bot- lecypods were able to successfully colonize tom environments until the end of the mud-bottom environments that were possi- Permianand contains elements which would bly too unstableto supportlarge populations dominate these mud-bottom facies in the of articulate brachiopods and trepostomes. succeeding Mesozoic (i.e., the reclining pe- These first intrusions into offshore shelf en- lecypods and echinoids). vironments by pelecypodswere truncatedby The occurrenceof large numbers of filter- the Late Ordovicianextinction event. Filter- feeding pelecypods with trilobites in these feeding pelecypods did not successfully re- Late Ordovicianclaystone facies in Ohio and establish themselves in these environments Indiana suggests that these mollusks were be- until the Late Devonian or Carboniferous. ginning to invade offshore shelf environ- These younger faunas are dominated by re- ments previously dominated by articulate clining epibyssate and shallow-burrowing brachiopods. Sepkoski and Sheehan (1983) forms rather than the endobyssate taxa that noted the clustering of bivalved mollusks in were dominant in Late Ordovician mud-bot- what they termed inner shelf environments tom environments. 264 ROBERT C. FREY

LOCALITIES toceras duseri shale unit directed by J. K. The followinglist of localitiesincludes those Pope and completed as partial fulfillmentof sections that received most study and from the requirements for the Ph.D. degree at which most of the data upon which this paper Miami University, Ohio. J. K. Pope provided was based was collected. much encouragementand assistancetowards the of this 0. L. Treptocerasduseri shale unit: completion study. Karklin, R. C. Titus, and P. W. Bretskyreviewed the 1) Roadcut along U.S. Rt. 42, west side of initial manuscriptand provided many help- the road, 3 km northeast of Waynesville, ful suggestions.R. Landryprepared most of WarrenCounty, Ohio. (Waynesville, Ohio the charts and diagrams.I would also like to 7.5' Quadrangle, NE?4, SE?4 sec 26, thank C. Koss, Outdoor Program Director, R4,T4.) B. Ferguson,Camp Ranger,and the Buckeye 2) Streambankexposures along the north and Trails Girl Scout Council for permitting ac- southforks of HarpersRun, south of Strout cess to the critical exposures of the shale at Road at Camp Whip-Poor-Will, G.S.A. the Camp Whip-Poor-Willfacility in Warren outdoor center, Warren County, Ohio. County, Ohio. Field expenses for this study (Oregonia, Ohio 7.5' Quadrangle,Long. were partiallydefrayed by a grantfrom Sigma 84005'W,Lat. 39023'N;and NE?4,NW?4 Xi. Pleasant Plain, Ohio, 7.5' Quadrangle.) 3) Streambankexposures along Stony Hol- REFERENCES low, just north of Todd's Fork, imme- ANSTEY,R. L. ANDM. L. FOWLER.1969. Litho- diately north of Clarksville, Clinton stratigraphyand depositional environment of County, Ohio. (Clarksville, Ohio 7.5' the Eden Shale (Ordovician)in the tri-statearea Quadrangle, Long. 83059'W, Lat. of Indiana,Kentucky, and Ohio. Journalof Ge- 39024'30"N.) ology,77:668-682. AUSICH,W. I. ANDD. J. BOTTJER.1982. Tiering Trilobiteshale unit: in suspension-feedingcommunities on soft sub- stratathroughout the Phanerozoic.Science, 216: 4) Roadcut along Rt. 101, along the north 173-174. side of the road at Bon Well Hill, plus an , T. W. KAMMERAND N. G. LANE. 1979. exposure in the wall of the emergency Fossil communities of the Borden (Mississip- spillway, 1.5 km to the west, Franklin pian) Delta in Indiana and northernKentucky. County,Indiana. (Mount Carmel, Indiana Journalof Paleontology,53:1182-1196. 7.5' sec. 16, T9N, BAMBACH,R. K., C. R. SCOTESEAND A. F. ZIEGLER. Quadrangle,SE4 R2W.) 1980. Before Pangea:the geographyof the Pa- 5) Small streambankexposures along Whis- leozoic world. American Scientist, 68:26-38. tle Creek where Whistle Creek Road BIRD,J. M. ANDJ. F. DEWEY 1970. Lithosphere crosses the stream,north side of the road, plate-continentalmargin tectonics and the evo- Franklin County, Indiana. (Metamora, lution of the Appalachian orogen. Geological Indiana 7.5' Quadrangle, cent. sec. 4, Society of America Bulletin, 81:1031-1060. T11N, R12E.) BRANDT, D. S. 1980. Biogenic structuresas in- Roadcut north side of the dicators of depositional rates. American Asso- 6) along1-74, road, ciationof PetroleumGeologists Bulletin, 64:680. 1.6 km east of junction with State Rt. 1 BRETSKY,P. W. 1969. Evolution of Paleozoic at St. Leon, Dearborn County, Indiana. benthic marine invertebratecommunities. Pa- (Cedar Grove, Indiana 7.5 Quadrangle, laeogeography,Palaeoclimatology, Palaeoecol- sec. 13, R2W, T7N.) ogy, 6:45-59. 7) Streambankexposures on the south side . 1970a. Upper Ordovician ecology of the of Collins (Bull)Run, at PfiefferPark, just central Appalachians. Peabody Museum of south of the Miami Natural History, Yale University, Bulletin 34, University campus, 150 p. Oxford, Butler County, Ohio. (Millville, . 1970b. Late Ordovician benthic marine Ohio 7.5 Quadrangle,cent. SE4 sec. 27, communities in north-centralNew York. New T5N.) YorkState Museum and Science Series Bulletin, R1E, 414:1-34. ACKNOWLEDGMENTS - AND S. S. BRETSKY.1975. Succession and repetitionof Late Ordovicianfossil assemblages This paper is part of a larger study of the from the Nicolet River valley, Quebec. Paleo- paleontology and paleoecology of the Trep- biology, 1:225-237. ORDOVICIAN PALEOECOLOGY 265

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