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INTRODUCTION

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Northeastern GeoscienceVolume 33

ORGANIC MICROFOSSILSOF THE MIDDLE RUN FORMATION (NEOPROTEROZOIC?)

OF OHIO, U.S.A.Jeffrey G. Richardson

Columbus State Community College, Columbus, Ohio 43215

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All rights and permissions beyond publication in this issue of Northeastern Geoscienceare held by the authors.

Corresponding Author: Jeffrey RichardsonDepartment of Biological & Physical SciencesColumbus State Community CollegeColumbus, OH [email protected]

The Ohio Department of Natural Resources, Division of Geo- logical Survey (DGS) Core 2627 (39°33’57”N; 84°06’51”W) from Warren County, Ohio (Figure 1) documented the first occurrence of the Neoproterozoic Middle Run Formation (Shrake, 1991). This previously unknown unit was encountered below the Cambrian Mt. Simon Sandstone and above the crystal-line basement (Figure 2). The Cambrian assignment for the Mt. Simon is based on trilobite fossils from the Eau Claire Formation and the Knox Dolomite, which both sit stratigraphically above the Mt. Simon (Babcock, 1994). The Middle Run is believed to have a total thickness of approximately 1100 m, although the core DGS 2627 only penetrated the first 582 m (Shrake et al., 1991). The 1100 m estimated thickness is based on the seismic reflection profile which was financed and managed by the Wright State University Depart-ment of Geological Sciences and Physics and Mr. Gary Sitler, formerly of Stocker and Sitler Inc. The seismic reflection profile was 12.8 km long, designated ODNR-1-88 and was shot to the northwest of the drill location in Wayne Township, Warren County, Ohio (Figure 1). The profile can be seen in several pub- lications; however, a full size seismic reflection profile is included in Shrake et al. (1990). The seismic profile revealed a deep basin structure, probably rift related, underlying the Cambrian Mt. Simon Sand-stone. Shrake et al. (1991) reported the seismic reflection profile indicated three fundamental elements: 1) a clearly defined horizon-tal Paleozoic succession, 2) an unknown clastic unit (defined later as the Middle Run), and 3) a rock sequence containing well-defined seismic reflectors. The horizontal Paleozoic rocks are not affec- ted by the thrusting that occurred during the formation of the Grenville foreland, which is discussed by Hauser (1993). The Middle Run (second element above) is defined by the seismic line as a homogenous wedge-shaped unit which contains eastward-dipping reflectors which, according to the seismic profile, may have a maximum thickness of 1800m, although the exact thickness of the unit is not known at this time. Due to the fact that the Middle Run reflectors dip to the east under the well-defined overlying Paleozoic units, the contact between the Cambrian ..

Mt. Simon Sandstone and the underlying Middle Run is an angular unconformity (Shrake et al., 1991).

Age Concerns The exact age of the Middle Run is not known. The unit has been assigned ages of either Cambrian or Pre- cambrian by several authors, including Babcock (1994), Roden-Tice and Shrake (1998), and Santos et al. (2001). Due to its stratigraphic location below the Cambrian strata in Ohio and the presence of an unconformable surface, the unit was initially believed to be older than the Cambrian. Further work has revealed that the Middle Run has a relative date of no younger than Middle Cambrian based on trilobite biostratigraphy from the overlying Eau Claire Formation (Babcock, 1994). The Eau Claire sits stratigraphically above the Mt. Simon and the Middle Run, constraining the age assignment of the Middle Run. Roden-Tice and Shrake (1998) reported zircon fission-track ages for the Middle Run to have a wide age range. These reported ages are 684±89 Ma for depths of 3480-3510 ft, 707±79 Ma for 4520-4560 ft, and 580±57 Ma for depths of 5180-5220 ft. The ages may have been reset, and indicate the Middle Run exper- ienced temperatures in excess of 200°C for at least 1 million years. Roden-Tice and Shrake (1998) also reported further work would need to be done to understand the source of the alteration. Santos et al. (2001) reported a maximum depositional age of 1012 Ma using SHRIMP U-Pb dating. Santos et al. (2001) suggest the Middle Run may be equivalent to the Neoproterozoic Torridonian of Scotland. A similar red clastic unit was encountered from a core in Putnam County, about 160km north of the DGS 2627 site; however, Fettke (1948) assigned an age of Cambrian to this unit based on its stratigraphic location.

ABSTRACT: The Middle Run Formation (Neoproterozoic) was sampled at seven intervals from a core drilled in Warren County, southwestern Ohio. The Ohio Department of Natural Resources, Division of Geological Survey (DGS) core DGS 2627 is the core in which the Middle Run Formation was originally encountered in 1988. The unit is composed of a fine-grained to medium-grained, grayish-red, lithic arenite with several sedimentary structures present including cross-bedding and ripple laminations. The Middle Run Formation from core DGS 2627 repre- sented approximately 582m of the estimated 1100m total thickness of the unit. The Middle Run Formation was originally described and assigned an age of Precambrian (Neoproterozoic). This age assignment resulted in part from the stratigraphic location of the formation below the Cambrian Mt. Simon Sandstone and above the crystalline basement. The sampled intervals reveal a moderately diverse suite of microfossils that contain granular organic microfossils and organic-walled microfossils. The group of microfossils discussed in this manuscript document the first occurrence of fossils from the Middle Run Formation.

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Figure 1. Location of Warren County (Ohio) with the corehole DGS 2627 and associated seismic line in the northeastern part of the county (modified from Shrake, 1991)

Depositional Environment The exact depositional environment of the Middle Run is not fully understood, although the lithologic evidence and the associ-ated sedimentary structures can provide a good framework. Since the Middle Run was not officially known before the drilling of the corehole DGS 2627, the analysis of the depositional environment was also new. The current analysis is the Middle Run was deposited in a fluvial setting as part of a rift-filling sequence (Shrake, 1991; Shrake et al., 1990). This analysis for a fluvial environment is supported by the presence of cross-bedding, horizontal and ripple laminations, and zones of massive deposition (Olsen, 1988; Shrake, 1991). The presence of calcite cement, calcareous nodules, and calcitic laminae suggests the possibility of an arid climate during deposition. The Middle Run may have formed in an arid environment such as the one described for the Miocene Rio Grande rift-filling sequence in New Mexico (Cavazza, 1989). An alternative depositional analogue may be similar to the caliche or vadose carbonate in the rift-fill sediments of the Upper Peninsula of Michigan (Kalliokoski, 1988a). Santos et al. (2001) suggested the Middle Run was equivalent to the Torridonian of Scotland and was deposited in a foreland basin associated with the uplift and erosion of the Grenville Orogeny. Several studies have compared the Middle Run from the DGS 2627 core in Warren County, Ohio with other previously-described Cambrian/Precambrian red clastic units from around the

Midcontinent. Other than the red clastic units described from other western Ohio cores, such as those by Fettke (1948) and Wasson (1932), several other stratigraphic units have been used as depositional analogues for the Middle Run. The Precambrian (Keweenawan) Oronto Group of the Lake Superior area has a similar general lithology to the Middle Run (Daniels, 1982; Morey and Ojakangas, 1982). The Oronto Group is interpreted to be a transgressive-regressive alluvial fan-fluvial-lacustrine system that fills the developing Midcontinent Rift (Daniels, 1982). Also in the northern part of the Midcontinent, the subsurface equivalent of the Oronto Group in Minnesota, the Solor Church Formation has similar lithology and similar depositional characteristics, which are associated with the filling of the Midcontinent Rift System (Dickas, 1986). In northern Michigan, the Jacobsville Sandstone is probably one of the more popular depositional analogues for the Middle Run (Kalliokoski, 1982; 1988b). Although the idea of an alluvial fan-fluvial rift-filling sequence seems to be the most common depositional environment interpretation, in part due to the lithologic characteristics and stratigraphic similarities, there have been other interpretations that are less common. The Middle Run may be associated with the Reelfoot Rift of the Upper Mississippi Valley or the previously mentioned foreland basin fill from the Grenville Front. In addition, Wasson (1932) reported approximately 244m of fractured carbona- ceous limestone below the Cambrian clastic unit from a well in Clark County, Ohio.

Figure 1. Location of Warren County (Ohio), corehole DGS 2627 and the associated seismic line (in the northeast-ern part of the county). (modified from Shrake, 1991)


Northeastern GeoscienceOrganic Microfossils of Ohio

Figure 2. Lithostratigraphic column showing the cored section of the Middle Run Formation and the Cambrian-Precambrian boundary. The left side of the diagram shows the sample intervals within the unit. (modified from Shrake, 1991)

slightly finer grain size were chosen due to the fact the preservation of the organic microfossils would be more conducive in a lower energy environment. The intervals were also chosen from levels of the core with the fine-grained quartz matrix, which refers to deposi-tional energy. Additionally, the author chose the intervals that had supporting geophysical logs. The cored section of the Middle Run Formation from DGS 2627 has a wide range of clastic lithologies and sedimentary structures. The upper part of the Middle Run (3458’- 4760’) consists of grayish-red to moderate-red sandstone with sub-rounded to sub-angular grains which are moderately- to poorly-sorted (Shrake, 1991; Shrake et al., 1990). Within this interval, there are zones of siliceous cement with smaller zones of calcite cement. The interval also contains a very fine-grained to fine-grained quartz matrix with lesser occurrences of hematitic matrix. Mica and iron-magnesium rich minerals are dispersed throughout and are faintly laminated and cross-bedded. The samples taken for this study were taken from this uppermost sandstone interval. Below the sampled sandstone interval is an interval of siltstone (4760’ – 4840’). The interval is dark-reddish-brown, very fine-grained siltstone, which is well-sorted and has silica cement with some calcite-rich laminae (Shrake, 1991; Shrake et al., 1990). The final and deepest cored interval is present from 4840’ to 5380’ (total core depth). This

RESULTSThe Middle Run (Neoproterozoic) has yielded a low-diversity, moderately-abundant organic microfossil assemblage that seems to be similar to other Proterozoic assemblages previously described from around the globe. The global record of Proterozoic fossils is not very abundant, although in the past several decades there has been a marked increase in Proterozoic microfossil research. In 1996, Knoll reported there have only been approximately 200 Neoproterozoic microfossil assemblages reported worldwide. The microfossils in this report will be the first known report of such fossils from the Middle Run.

The microfossil assemblage from the Middle Run is dominated by two primary forms, granular organic microfossils (GOMs) and organic-walled microfossils (OWMs). The terms, GOM and OWM, were originally proposed by Strother (2012) for carbonized microfossils recovered from shales of the Nastapoka Group in Canada. The granular organic microfossils (GOMs) display a cohesive, granular structure, but lack a discrete cell wall. Plate 1 shows several specimens of the granular organic sphaeroids. (Each of the specimens in Plate 1 exhibits a cohesive, granular structure, especially along the distal surface; however, none of the specimens show a clearly recognizable cell wall. The overall shapes of the granular organic microfossils from the Middle Run range from sub-circular to sub-triangular (Plate 1).

There is a less numerous form then than the previously described granular organic microfossils (GOMs) and the organic walled microfossils (OWMs) in the assemblage. The Middle Run has also yielded several specimens that are extremely similar to Leiosphaeridia Eisenack, 1958. The primary shape of the Leiosphaeridia-like microfossil occurrences from the Middle Run is spherical to ovoid (Plate 2).The microfossils have no ornamentation and no surficial division into specific fields, although some folding may be present. Some the identified Leiosphaeridia-like specimens exhibit radial splits and excystment structures are rare to absent.

DISCUSSIONThis report of the granular organic microfossils organic-walled microfossils from the Middle Run adds to the 200-plus occurrences of Neoproterozoic fossil assemblages worldwide (Knoll, 1996). Sergeev (2009) reported a “working hypothesis” for the distribution of microfossil assemblages in Proterozoic rocks. In this report, Sergeev (2009) defined seven principle units from the Proterozoic.

The newly described microfossils from the Middle Run are similar to other Neoproterozoic assemblages from around the world. Yin and Sun (1994) reported on well preserved, abundant acritarchs from the Liulaobei Formation in the Huanian Region, northern Anhui Province, China. Yin and Sun (1994) reported an abundance of Leiosphaeridium spp., while Yin (1985) reported occurrences of Trachysphaeridium in the same Neoproterozoic strata. Some specimens from the Middle Run are similar reported



MATERIALS AND METHODS

The Middle Run was sampled at seven intervals throughout the core DGS 2627 (Figure 2). The core description indicates the upper contact of the Middle Run occurs at a depth of 3458 feet and contin-ues to the total depth of the core, which is 5380 feet (Shrake et al., 1990). The samples in this study were sampled at depths ranging from 4524 feet (1379 m) to 4745 feet (1446 m). The sampled intervals were chosen based primarily on grain-size. Layers of

interval consists of sandstone, but there are no geophysical logs due to a collapsed borehole (Shrake, 1991; Shrake et al., 1990). Sedimentary structures throughout the entire thickness of the Middle Run Formation include cross-bedding, fining-upwards intervals, and horizontal and ripple laminations. A more detailed description of the lithology and petrology of the Middle Run is provided by Dickas et al. (1992). Dickas et al. (1992) reported the sandstone intervals of the Middle Run consti-tute 96% of the cored section, the siltstone intervals, which include some carbonate nodules, constitute 3.5% of the cored section, and some smaller conglomerate layers constitute less than 1% of the cored interval. The samples were sent to the Kentucky Geological Survey for processing. They were processed by standard methods for extracting organic-walled microfossils using a series of acid baths. A detailed discussion of the processing methods is found in Litwin and Traverse (1989).

Plate 2 shows occurrence of the organic-walled micro-fossils (OWMs) recovered from the Middle Run. These OWMs differ from the previously discussed granular organic microfossils (GOMs) in that the OWMs exhibit a clearly defined cell wall. The specimens displayed in Plate 2 show a distal thickening, interpreted as a cell wall. The vesicle shapes in the OWMs from the Middle Run range from circular to sub-triangular.

These units cover the interval from approximately 2 Ga to 542 Ma and are identified as Labradorian, Anabarian, Turukhanian, Uchuromayan, Yuzhnouralian, Amadeusian, and Belomorian. The microfossil assemblages from the Middle Run are morphologically most similar to the Uchuromayan unit (late Stenian–Tonian) or the Yuzhnouralian unit (Crogenian). The Uchuromayan unit covers an age range from 1.03 to 0.85 Ga and is named for the microbiota that comes from the Neryuen and Ignikan formations of the Lakhanda Group of the Upper Riphean of the Uchur-Maya Region, Siberia, (c. 1.03Ga) (Sergeev, 2009). The Yuzhnouralian unit covers an interval spanning 0.85 to 0.63Ga, and is named after the biota recovered from the Inzer Formation of the southern Ural Mountains (Sergeev, 2009). Since the Middle Run organic-walled microfossil assemblage has such low-diversity, it is difficult to assign a definite unit affiliation.



Figure 2. Leiosphaerida-type microfossils from the Middle Run Formation.

Figure 1.

Konzalová (1974) described an assemblage on sphaeromorphic and acanthomorphic acritarchs from the Upper Proterozoic and Lower-Middle Cambrian of Bohemia. Vorob’eva et al. (2009) reported on a Neoproterozoic assemblage of microfossils from the East European Platform. The Middle Run specimens are a bit older that these microfossils and have a lower diversity. The assemblage reported by Vorob’eva et al. (2009) was taken from the Vychedga Formation, which is Lower Ediacaran in age. An assemblage with similar sphaeromorphic forms have also been previously reported from the Precambrian and Lower Cambrian of eastern Siberia (Pichova, 1967). The microfossil assemblage from the Middle Run is similar to other Neoproterozoic microfossil assemblages reported from other North American locations. Vidal and Ford (1985) reported on microbiotas from the Late Proterozoic Chuar Group (northern Arizona) and the Uinta Mountain Group (Utah). Both of these assemblages described by Vidal and Ford (1985) contain numerous sphaeromorphic forms such as Leiosphaeridia and specimens with ornamentation, such as specimens of Trachys-phaeridium. The northern Arizona and Utah assemblages are compared with late Proterozoic sequences in the southern Urals, the Russian Platform, northern and southern Scandinavia, Svalbard, and Greenland, which all have an age assignment of late “Riphean” and early Vendian, approximately 800-700Ma. The other similar assem-blage was reported by Samuelson and Butterfield (2001) from the Neoproterozoic strata from the Franklin Mountains, northwestern Canada. This assemblage contains several forms of Leiosphaeridia and numerous fused and coiled filamentous forms. Butterfield (2005) also reported on occurrences of Neoproterozoic microfossils from the Wynniatt Formation of arctic Canada. The assemblage reported by Butterfield (2005) contains several forms of Leios-phaeridia along with several forms with fungal associations.

CONCLUSIONSAlthough the Middle Run organic-walled microfossils seem to have similarities with other Neoproterozoic assemblages from around the globe, the exact biological affinities of the Middle Run microfossils are not completely understood. One problem with the occurrence of the Middle Run microfossils is the inferred depositional environ-ment of the rocks from which they were recovered is that of a rift-filling, clastic sequence deposited as an alluvial fan with fluvial occurrences. Since the microfossil occurrences of the Middle Run Formation seem to have some acritarch affiliations, it may be possible that several influxes of seawater occurred during Middle Run deposition. Additionally, further work and additional sampling of other cores containing the Middle Run are needed to gain a complete understanding of the depositional environment, paleogeo-graphic implications, and age of the unit.

ACKNOWLEDGEMENTSThis project was completed with the help of several important people. I would like to thank Mr. Greg Schumacher at the Horace Collins Core Repository of the Ohio Geological Survey. I would

like to extend a special thanks to Mr. Cortland Eble at the Kentucky Geological Survey for his generous and excellent preparation of the samples. Special thanks are also extended to Mr. Ernie Slucher of the United States Geological Survey and Mr. Doug Shrake for their insight into the depositional environments and Precambrian strati-graphy. Additionally, a large thank you goes to Mr. Charles Braithwaite in the Columbus State Print Shop for his wizard-like mastery of Photoshop.

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by Yin and Guan (1999) from the Neoproterozoic Dongjia Forma-tion, Henan Province, North China. Although this assemblage is dominated by sphaeromorphic acritarchs with some spinose forms, which do not occur in the Middle Run, some of the organisms in the assemblage are similar. The Middle Run assemblage has some similarities to several previously described microfossil occurrences in Europe.

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Shrake, D.L., 1991, The Middle Run Formation: a subsurface stratigraphic unit in southwestern Ohio: Ohio Journal of Science, v. 91, no. 1, p. 49-55.Shrake, D.L., Carlton, R.W., Wickstrom, L.H., Potter, P.E., Richard, B.H., Wolfe, P.J., and Sitler, G.W., 1991, Pre-Mount Simon basin under the Cincinnati Arch: Geology, v. 19, p. 139-142.Shrake, D.L., Wolfe, P.J., Richards, B.H., Swinford, E.M., Wickstrom, L.H., Potter, P.E., and Sitler, G.W., 1990, Lithologic and geophysical description of a continuously cored hole in Warren County, Ohio, including description of the Middle Run Formation (Precambrian?) and a seismic profile across the core site: Ohio Department of Natural Resources, Division of Geological Survey, Information Circular 56, 11p.Strother, P.K., 2012, Probable Paleoproterozoic palynomorphs: Programs and Abstracts, Joint Meeting of the 45th Annual Meeting of the AASP – The Palynological Society and CIMP – Commission Internationale de la Microflore du Paléozoique Subcommissions, p. 45.Timofeev, B.V., 1959, Drevneishaya flora Pribaltiki I-ee stratigraf- icheskoe znachenie. Vsesoyuznyi Neftyanoi Nauchno – Issledovatelskii Geologora zvedochnyi Institut, Leningrad grad (VNIGRI), Trudy 129, p. 1-136. (in Russian)Timofeev, B.V., 1966, Mikropaleofitologicheskoe issledovanie dravnikhsvit: Akademiya Nauka SSSR, Isdatelsko Nauka, Moskva, p. 1-147. (in Russian)Vorob’eva, N.M., Sergeev, V.N., and Knoll, A.H., 2009, Neopro- terozoic microfossils from the margin of the northeastern margin of the East European Platform: Journal of Paleontology, v. 83, p. 161-192.Vidal, G., and Ford, T.D., 1985,Microbiota from the Late Protero- zoic Chuar Group (Northern Arizona) and Uinta Moun- tain Group (Utah) and their chronostratigraphic implications: Precambrian Research, v. 28, p. 349-389.Wasson, I.B., 1932, Sub-Trenton formations in Ohio: Journal of Geology v. 40, p. 673-687.Yin, C.Y., 1985,Micropaleoflora from the Late Precambrian in the Huanian region of Anhui Province and its stratigraphic significance: Professional Papers of Stratigraphy and Paleontology, Chinese Academy of Geological Science, v. 12, p. 97-120. (in Chinese) Yin, L., and Guan, B., 1999, Organic-walled microfossils of Neoproterozoic Dongjia Formation, Lushan County, Henan Province, North China: Precambrian Research. v. 4, p. 121-137.Yin, L., and Sun, W., 1994, Microbiota from the Neoproterozoic Liulaobei Formation in the Huanian region, Northern Anhui, China: Precambrian Research, v. 65, p. 95-114.



Knoll, A.H., 1996, Chapter 4. Archean and Proterozoic paleontology: in J. Jansonius and D.C. McGregor, eds., Palynology: Principles and Applications, American Association of Stratigraphic Palynologists Foundation, v. 1, p. 51-80.

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