Occurrence, Stratigraphic Distribution, and Abundance of Chitinozoa from the Middle Devonian Columbus Limestone of Ohio1

OCCURRENCE, STRATIGRAPHIC DISTRIBUTION, AND ABUNDANCE OF CHITINOZOA FROM THE MIDDLE DEVONIAN COLUMBUS LIMESTONE OF OHIO1 ROBERT P. WRIGHT, The Department of Geology and Mineralogy, The Ohio State University, Marion, Ohio Abstract. Chitinozoa from the Middle Devonian Columbus Limestone of central Ohio belong to eight species of the genera Alpenachitina, Ancyrochitina, Angochitina, Conochitina, Desmochitina, and Eisenackitina. Two new species, Ancyrochitina frankeli and Eisenackitina robusta, are described. The Chitinozoa occur in carbonate rocks such as mudstone, grainstone and packstone that represent well circulated open marine conditions. They are absent from dolomite which represents sediment deposited at a shallow water depositional site characterized by restricted water circulation. Comparison of the Columbus Limestone Chitinozoa with faunas from similar Middle Devonian strata in Iowa, Illinois, and Missouri indicates that the Middle Devonian Wabash Platform, located in Indiana, effectively restricted the distribution of chitinozoans in the Illinois and Appalachian Basins. OHIO J. SCI. 76(5): 214, 1976 Chitinozoa were first described in the America. Second, Chitinozoa appear to 193()'s by the German scientist A. be useful bathymetric indicators (Wil- Eisenack (1930, 1931) from Silurian gla- liams and Sarjeant, 1967; Gray et al, cial erratics in the Baltic region of 1974). Laufeld (1975) has noted, in the Europe. Since that time interest in this Silurian of Gotland, Chitinozoa diversity group of extinct organic-walled micro- and abundance increase away from organisms has grown in Europe and the reefoid detrital limestones in the direction Americas as exemplified by the recent of deeper water. monographic treatment of the group The dominant feature of the Middle (Combaz et al, 1967; Taugourdeau et al, Devonian paleogeography of Indiana, 1967). The interest of North American Illinois, and Ohio is now recognized as paleontologists in this group of fossils consisting of a broad shallow water car- has grown steadily since the 1950's. bonate shelf (Droste et al, 1975). That The importance of Chitinozoa is two- shelf, called the Wabash Platform, con- fold. They are abundant and easily ex- trolled the sedimentology of adjacent ba- tracted from strata of Ordovician through sins in Missouri, Iowa, Illinois, Michigan, Devonian age and, as some of the forms and Ohio. It must have influenced the may have been members of the lower spatial and temporal distribution of the Paleozoic zooplankton (Chaiffetz, 1972), marine plankton and members of the their biostratigraphic value is obvious. benthic fauna. In this regard, the de- The presence of Chitinozoa in the Co- scription of the Columbus Limestone lumbus Limestone as well as faunas from Chitinozoa is the necessary first step in strata of similar age elsewhere in the establishing the degree of Chitinozoa Midwest (Urban, 1972; Urban and New- faunal interchange in the Illinois, Michi- port, 1973; Legault, 1973; Wood, 1974) gan, and Appalachian Basins. The pur- suggest their potential importance for the pose of this paper is to describe the oc- refinement of the biostratigraphy of Mid- currence, stratigraphic distribution, and dle and Upper Devonian strata in North abundance of Chitinozoa in the Middle xManuscript received January 28, 1976 and in Devonian Columbus Limestone in north- revised form May 18, 1976 (#76-11). central Ohio. 214 No. 5 COLUMBUS LIMESTONE CHITINOZOA 215 METHODS AND MATERIALS environments represented by the various car- Collections for this study were obtained from bonate lithofacies and to attempt to identify the Hamilton Brothers Quarry near Marion, the environmental occurrence of the Chitinozoa. Ohio. The Columbus Limestone is well ex- Fresh samples were taken systematically at posed and stratigraphically complete at this two-foot vertical intervals or at every change locality (tig. 1). The strata were examined in in lithology. In all, 41 samples were treated detail in order to determine the depositional using the following techniques. Fifty grams Abundance of chitinozoans in 50 grams of rock Legend Bivalves £>J Grainstone ^J Ripple marks Bone bed |^| Horn corals |@| Sample number Brachiopods 1 Mudstone J Shale Bryozoans [—H Oil stain |^| Stromatoporoids Chert \Mi Packstone \~~[ Stylolites Dolomite |^| Pelmatozoans [<Hh] Colonial corals [^1 Calcite-filled vugs FIGURE 1. Stratigraphic section of the Columbus Limestone exposed in the Hamilton Brothers Quarry. The section shows the vertical destribution of carbonate lithofacies and Chitinozoa. 216 ROBERT P. WRIGHT Vol. 76 from each sample were placed in beakers and water circulation. At the Hamilton covered with concentrated HC1. After the re- action ceased, the acid was diluted and sedi- Quarry, the so-called "coral-stromato- ment washed by filling the beaker with tap poroid zone" is well developed, and water and sieved according to a procedure de- marks the beginning of open marine con- scribed by Laufeld (1974). The sieving cloth ditions. The association of stromatopor- had a mesh distance of 45 microns. After sieving and washing, the residue was oid sponges, tabulate and rugose corals poured into a beaker and treated with concen- that characterizes this unit represents trated HF, and allowed to stand for 24 hours stabilization of the mud substrate by until the silica was digested. The acid was bottom dwelling "carpeting" organisms. then diluted with water and the residue sieved, washed, and stored in small vials filled with The skeletal-poor mudstone above the distilled water. Identification and counts of biostrome is a low energy, below wave- each taxon were made and recorded. The best base deposit (Chapel, 1975). The oc- specimens were removed from the beakers with currence of the mudstone above the bio- a finely drawn glass pipette and prepared for scanning electron microscopy. Four to six strome indicates deepening of the water specimens were mounted on a glass coverslip over the coral-stromatoporoid studded using a graphite adhesive. The specimens were shallow platform. coated with gold in a vacuum apparatus and studied using a Cambridge S4 Stereoscan The fossiliferous packstone midway (SEM). through the section records regression or All specimens were deposited in the Orton shallowing of the water. The abundance Museum at The Ohio State University in of specimens of Brevispirifer gregarious as Columbus, Ohio and designated with OSU num- well as the appearance of other species of bers. SEM stubs containing the specimens are coded thusly: In 1-29, 1 = stub number, 29= field brachiopods, corals, molluscs, bryozoans, number. and pelmatozoans indicate that circulation kept the bottom relatively free of GENERAL STRATIGRAPHY AND large amounts of carbonate mud that DEPOSITIONAL FRAMEWORK would have smothered many of the filter Columbus Limestone crops out in a and suspension feeders. narrow belt from the Columbus area The cherty mudstones near the top of north to Kelly's Island in Lake Erie. the stratigraphic section do not contain In central Ohio the formation consists of large quantities of skeletal material, ex- a lower dolomite unit and an upper lime- cept Chitinozoa. The mudstones repre- stone unit. At the Hamilton Quarry the sent a semi-restricted above wave-base dolomite is less than 25 feet thick, rela- deposit, perhaps deposited in an environ- tively unfossiliferous and banded with ment that was somewhat lagoonal. The hydrocarbons (fig. 1). The dolomite was peaks in abundance of the Chitinozoa in deposited in shallow water with restricted the cherty mudstone indicate that the circulation when submergence of the low- rate of sedimentation at this time was lying weathered craton took place during less than when the packstones and grain- Early and Middle Devonian. The over- stones were deposited. lying fossiliferous limestone was deposited The grainstone in the uppermost por- in an open marine environment with good tion of the Columbus Limestone, with its EXPLANATION OF FIGURE 2 No. 1-6. Scanning electron micrographs of Ancyrochitina frankeli Wright, n. sp. 1. Paratypc, OSU 32159, X600, 4-32. 2. Paratype, OSU 32158, X900, 4-32, high magnification showing the oral end of the specimen. 3. Paratype, OSU 32157, X450, 4-32. 4. Paratype, OSU 32156, X525, 3-31, note the clavate basal spine. 5. Holotype, OSU 32155, X525, 3-31, specimen shows the long neck in proportion to the body chamber and the bifurcating neck and basal spines. 6. Paratype, OSU 32154, X525, 3-31, note absence of neck spines. No. 7-9. Scanning electron micrographs of Alpenachitina eisenacki Dunn and Miller, 1964. 7. Note the small spines at the base, OSU 32153, X575, 2-35. 8. Specimen showing the delicate branching of the vesicle spines, OSU 32152, X575, 2-40. 9. Note the length of the neck in comparison to the body chamber, OSU 32151, X575, 1-29. No. 5 COLUMBUS LIMESTONE CHITINOZOA 217 FIGURE 2 218 ROBERT P. WRIGHT Vol. 76 crinoidal debris, abraded ripples (Bates, to the relative abundance of the other 1971), and bone beds representing lag species throughout the rest of the section. concentrations, abruptly changing to Cramer (1970) has suggested that an mudstone in the overlying Delaware enormous increase in the abundance of Limestone indicates transgression and Chitinozoa within just a few inches of submergence. rock may represent a planktic bloom similar to blooms in modern coastal CHITINOZOA waters. An alternative, and probably Representatives of six genera and eight correct, explanation is that the increase species of Chitinozoa

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