Organic-Walled Microphytoplankton Abundance and Strategraphic
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Copyright © 1983 Ohio Acad. Sci. OO3O-O95O/83/OOO1-OOO2 $2.00/0 ORGANIC-WALLED MICROPHYTOPLANKTON ABUNDANCE AND STRATIGRAPHIC DISTRIBUTION FROM THE MIDDLE DEVONIAN COLUMBUS AND DELAWARE LIMESTONES OF THE HAMILTON QUARRY, MARION COUNTY, OHIO1 REED WICANDER, Department of Geology, Central Michigan University, Mt. Pleasant, MI 48859 ROBERT P. WRIGHT, Cities Service Company, Research Laboratory, Tulsa, OK 74102 ABSTRACT. Forty-three species representing 25 genera of organic-walled micro- phytoplankton were recovered from a 28.04—m thick section of the Middle Devonian Columbus and Delaware Limestones of central Ohio, USA. This assemblage compares closely with other Middle Devonian microphytoplankton assemblages from North America, indicating their potential use as biostratigraphic guides. Their stratigraphic distribution is probably related in part, to the Columbus-Delaware carbonate lithofacies. The organic-walled microfossils are neither abundant nor well-preserved in the porous dolomite near the bottom of the Columbus Limestone. This poor preservation is probably a consequence of dolomitization, while their paucity may reflect an original shallow- water environment of restricted circulation. Such an environment may not have been conducive to plankton growth. The microphytoplankton assemblage increases in nu- merical abundance and diversity in the overlying non-dolomitized carbonates, particu- larly the finer-grained limestones. OHIOJ. SCI. 83 (1): 2-13, 1983 INTRODUCTION rophyta (green algae) and Acritarcha The carbonates of the Columbus and (unknown affinity). They tend to be superjacent Delaware Limestone were abundant, generally well preserved, and deposited during the Early Devonian geographically widespread in distribution. (Emsian) with deposition continuing into As their stratigraphic ranges and areal dis- the Middle Devonian (Givetian). Sedi- tribution become better known, they are ment accumulation occurred east of the proving to be biostratigraphically useful Wabash Platform, a dominant paleogeo- in correlating Paleozoic rock units. Thus graphic feature of Illinois, Indiana and Ohio the description of the organic-walled mi- (Droste et al. 1975, Wright 1976, 1978, crophytoplankton from previously studied 1980). This platform, which separated the outcrop exposures such as the Columbus Illinois Basin from the Michigan and and Delaware Limestones (Stauffer 1909, Appalachian Basins, was emergent in Conkin and Conkin 1975) is important in Eifelian time. Consequently, carbonate de- establishing their stratigraphic occurrence. position in central Ohio was in proximity to carbonate flats and tidal lagoons to METHODS AND MATERIALS the west in Indiana. Planktonic algae were For this study, 18 samples were chosen repre- prolific in these sunlit waters. senting the various carbonate lithofacies and deposi- tional environments of the Columbus and Delaware Organic-walled microphytoplankton are Limestones (fig. 1). Approximately 50 g of sample the presumed cysts of marine planktonic were processed using standard palynological tech- algae. They can be divided into the Chlo- niques, which consisted of treatment in hydro- chloric, hydrofluoric, and nitric acids; removal of the undissolved "heavy" minerals by panning; and screening through either a 38 fxm of 20 fxm screen. ^anuscript received 23 November 1981 and in From the remaining residue, slides were then pre- revised form 16 April 1982 (#81-45). pared. For relative abundance data, 2—5 slides were OhioJ. Sci. DEVONIAN MICROPHYTOPLANKTON microphytoplankton. The dolomitized carbonates may have been deposited in a shallow-water environment with restricted circulation just east of the Wabash Platform. The overlying coral-stromatoporoid zone may represent a period of normal open marine conditions with good water circu- lation. Immediately above the coral- stromatoporoid horizon, the organic- walled microfossils increase in abundance and diversity and are better preserved. The fossiliferous limestone in this part of the section, up to the chert-bearing limestone at sample 28, represents a depositional site at or near wave base (Chapel 1975) with good water circulation. The 305 m of cherty fine-grained lime- stone between samples 28-34 are of inter- est because this interval does not contain many megafossils, has a high concen- tration of chitinozoans (Wright 1976), and contains 30 species of organic-walled mi- crophytoplankton. The abundance in these samples is somewhat higher than for any FIGURE 1. Map showing the location of the Ham- other interval. Chapel (1975) considered ilton Brothers Quarry, Marion, Ohio. this interval a regressive phase represent- ing a semi-restricted deposit above wave- examined, and counts were calculated on the basis of base, perhaps even somewhat lagoonal. 3 slides/sample to maintain uniformity throughout The fossiliferous limestone of the upper- the section. We counted all specimens on each slide. The number of slides varied (2—5) because the same most Columbus Limestone, and the amount of material was used per sample to maintain 3.66 m of overlying Delaware Limestone, uniformity between samples. In some cases, only reflects a deepening of the water that con- enough residue was left to make 2 slides. As is evi- tinued into Middle Devonian time dent from fig. 2, most species exhibit low abun- dance throughout the section. (Wright 1978). This interval contains only 17 species of organic-walled microphyto- plankton from 3 samples. STRATIGRAPHY Generally, then, the occurrence and the At the Hamilton Quarry in Marion abundance of the organic-walled micro- County, Ohio (figs. 1,2) a section of the phytoplankton assemblage throughout the Middle Devonian Columbus and Delaware section appear to be a reflection of the Limestones, 28.04 m thick, was measured lithofacies and depositional environment. and sampled for organic-walled micro- The greatest diversity and abundance of fossils. The lower 6.10 m of the section is microphytoplankton occur in the cal- primarily porous recrystallized dolomite careous mudstone (except for the Delaware stained with hydrocarbons and containing Limestone). Chitinozoa are also abundant chert lenses. The dolomite contains fossil in this lithofacies (Wright 1976). How- molds of corals and is totally devoid ever, while no chitinozoans were found of chitinozoans (Wright 1976), but it in the lower dolomite facies, 20 species of does contain an assemblage of 20 species organic-walled microphytoplankton were of poorly preserved organic-walled recovered. The state of preservation of the R. WICANDER AND R. P. WRIGHT Vol. 83 Stratigraphic Distribution of Organic-Walled Microphyloplankton Taxa e Limeston e Delawar I r Membe d Marblehea e Limeston s Columbu FIGURE 2. Stratigraphic section of the Columbus and Delaware Limestones showing the carbonate litho- facies and distribution and abundance of organic-walled microphytoplankton. assemblage can generally be regarded as a All except 2 species have been previously reflection of microphytoplankton entomb- reported in the literature. These 2 species ment in a carbonate matrix and the sub- {Cymatiosphaera sp. and Induoglobus sp.)are sequent alteration due to diagenesis of probably new, but only a few specimens of those carbonates. each were found. We felt there was an in- sufficient number of specimens to justify DISCUSSION establishing new species. The range of the Forty-three species of organic-walled genus Induoglobus is now extended into the microphytoplankton were recovered from Middle Devonian, having been found pre- the Columbus and Delaware Limestones. viously only in the Lower Devonian Gedin- OhioJ. Sci. DEVONIAN MICROPHYTOPLANKTON nian of Oklahoma (Induoglobus latipenniscus not yet possible with any real precision for Loeblich and Wicander 1976). the organic-walled microphytoplankton. The organic-walled microphytoplank- It is precisely because so few Middle ton assemblage shows a high degree of Devonian organic-walled microphyto- similarity to the younger Middle Devonian plankton assemblages have been reported Givetian-aged Silica Formation of Ohio that we are describing this assemblage (Wicander and Wood 1981). Thirty of from the Columbus and Delaware Lime- the 43 species from the Columbus and stones. We hope that greater biostrati- Delaware Limestones are also found in the graphic refinement will ensue from such Silica Formation. This assemblage is also studies. similar to that of the Middle Devonian Onondaga Limestone of Ontario, Canada SYSTEMATIC PALEONTOLOGY (Deunff 1954a, 1955, 1957, 1961, 1966a, We list here only the valid name and North 1971), and contains recurring species with American geologic range (Early, Middle, Late) for the species recovered from the Columbus and the Middle Devonian Hamilton Formation Delaware Limestones at the Hamilton Quarry, of Ontario, Canada (Legault 1973) such Marion County, Ohio. For a complete synonymy as Arkonites bilixus Legault 1973, and with world-wide geologic range and geographic dis- Estiastra rhytidoa Wicander and Wood tribution, the reader is referred to Wicander and 1981, among others. Wood (1981) and Wicander (in press). All figured specimens are deposited in the Mus- The Columbus-Delaware organic-walled eum of Paleontology, Department of Geology, Cen- microphytoplankton assemblage also has tral Michigan University, Mount Pleasant, MI some species in common with the Late 48859. Numbers given as CMUMP#516O, #43 > 20 /Am 1,116.7; 16.1 refer to Central Siegenian to Givetian-aged Jaab Lake Michigan University Museum of Paleontology de- No.