Maysvillian Stage of the Cincinnati Arch, Indiana, Kentucky, and Ohio, U.S.A

Sequence Stratigraphy of the Late Ordovician (Katian), Maysvillian Stage of the Cincinnati Arch, Indiana, Kentucky, and Ohio, U.S.A.

A thesis submitted to the

Graduate School

of the University of Cincinnati

in partial fulfillment of the requirements for the degree of

Master of Science

In the Department of Geology

McMicken College of Arts and Sciences

Thomas J. Schramm

B.S. State University of New York College at New Paltz

S.U.N.Y. New Paltz

2009

Committee Chair: Carlton E. Brett, Ph.D.

Abstract:

Richly fossiliferous strata of the Cincinnati area have a long history of study. An abundance of lithologic names have been applied to various shallow marine depositional facies across the Cincinnati Arch in Indiana, Kentucky and Ohio, U.S.A. The current study builds upon recent, high-resolution stratigraphic studies of the Edenian Stage, Kope Formation, and applies a similar approach to the Maysvillian Stage strata of the Cincinnati Arch. Strata of the Maysvillian

Stage were deposited in shallower water conditions than the underlying Kope Fm., resulting in an increased localization of facies. Maysvillian Stage strata have previously been treated as a mosaic of local facies with little to no continuity or small-scale cyclicity; however, correlation of time-synchronous marker horizons and sequence stratigraphic units the Maysvillian Stage throughout the Cincinnati Arch demonstrates that this is not the case and suggests widespread, allocyclic controls on sedimentation.

Based upon the documentation of widely traceable horizons the current study establishes a fourth order sequence stratigraphy for the Cincinnati Arch. As an independent test of lithologic-cycle correlation, the current study has utilized magnetic susceptibility in vertical successions, and attempts to quantify small scale cycles within the Maysvillian Stage. Magnetic susceptibility in combination with field observations has revealed previously overlooked unconformities, such as the basal Bellevue Mbr. unconformity, which oversteps the Miamitown

Shale to the east of Cincinnati. In addition, intervals of relatively thick siltstone beds, commonly with soft-sediment deformation, are identified as an indicator of falling stage systems tracts, formed during forced regressions. In contrast, intervals of relatively compact skeletal pack and grainstones with evidence of condensation, such as hardgrounds indicate transgressive systems

ii tracts. Using these criteria the current study provides a newly established fourth order sequence stratigraphic framework, and a reevaluation of third order depositional sequences on the

Cincinnati Arch. Revisions include reinterpretation of key surfaces, some of which record flooding surfaces, previously identified as sequence boundaries, identification of previously unrecognized sequence boundaries, and replacement of “shazam” lines of imaginary facies transition by a more realistic framework of small-scale cycles.

Empirical evidence of sea level variation within small-scale cycles, based upon sedimentary structures in shallow water facies, e.g., changes from mud-cracked strata to fully marine carbonate deposits, suggests sea-level change as the principal mechanism for small-scale cycle generation; widespread correlation of these cycles indicates an allocyclic forcing mechanism, probably eustasy. Differences in thickness of mudstone deposits between

Cincinnatian units are attributed to tectonic and climatic changes occurring in the orogenic hinterland during the Late Ordovician, affecting the supply of fine-grained siliciclastics to offshore areas. Synthesizing sequence stratigraphy of the Cincinnati Arch with observation of coeval strata in New York, and the Southern Appalachians the current study also recognizes variations in the magnitude of base-level change to peripheral foreland bulge migration occurring during waning phases of the Taconic orogeny. Throughout the Cincinnatian, and other Paleozoic strata a three-fold motif of lithologic units has been observed: the current study offers a discussion of the naming of lithologic units and the hierarchical nature of depositional cycles associated with this phenomenon.

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Acknowledgements

First and foremost, I would like to thank my parents for their continued support of my education in geology and moral support throughout the time of the writing of this thesis. I would like to thank close friends James Thomka and Nathan Marshall for continued moral support, field support, and useful discussion to this project. Mike DeSantis offered valuable discussion and advice contributing to the completion of this thesis. I greatly appreciate the support and revisions of members of my thesis committee: Carl Brett, Arnie Miller, Dave Meyer and Ben

Dattilo. Without the teaching, guidance, hours of daily discussion, literally months spent together in the field, arguments, late night phone calls and emails, document revisions, of my advisor, Carl Brett this thesis would not be possible. I am eternally grateful for Carl’s “hit the ground running” and always “more the merrier” attitude. My introduction to Ben Dattilo, through Carl, was pivotal to the success of this project. Continuing in collaboration where Ben left off, his project advice, valuable discussion, field experience, and friendship have been critical to the success of this project.

I would further like to thank the Dry Dredgers for their help, interest, and valuable discussions of this project. Specifically, Dan Cooper and Stephen Felton have been critical to the completion of this project. Dan provided useful advice and introduction to outcrops of the

Corryville Mbr. No other living person has had more experience in the Cincinnatian strata than

Steve Felton; knowledge of Cincinnatian beds, fauna, previous workers, and literature is impeccable. The knowledge of localities and Cincinnatian fossils held by Steve dwarfs that of generations of Cincinnatian workers. Steve’s valuabe insights, in addition to valuable

v discussion, and field support have contributed strongly to this project, for which I am extremely thankful.

I would like to thank Brooks Ellwood, my current advisor at LSU, for valuable advice, training, and revisions concerning Magnetic Susceptibility. I am grateful to University of

Cincinnati undergraduate students, Adam Leu, Emily Wendler and Nick Bose for field assistantance. Likewise, advice on how to conduct a research from Attila Kilinc and Paul Potter has contributed strongly to this project.

Funding for this project was generously provided by a Dry Dredgers, Paul Sanders

Award; Geological Society of America, Student Research Grant; and an award from the

Univeristy of Cincinnati Research Council.

Preface

Research of the Cincinnatian Series over the past 10 years has been termed a

“Stratigraphic Renaissance” (McLaughlin et al., 2008), but the bulk of stratigraphic research has involved the Edenian Stage, Kope Formation. Correlation is a key component to studies of sedimentary strata, and without this knowledge other paleoecological, climatological, geochemical studies, etc. may be flawed and include errors. The intention of this research is to raise the base of knowledge out from the Edenian Stage, and up, into the Maysvillian Stage, using recent studies in the Kope Formation as a model. Together with Carl Brett and Ben

Dattilo, I have conducted this research in order to kickstart further investigations occurring in the

Cincinnatian, Maysvillian Stage. It is the hope of the author that the following chapters of this thesis will provide a refined sequence stratigraphic framework for strata of the Maysvillian Stage in its type area and will prompt other researchers to move their future studies out of the well studied Edenian, and move into the up and out, of the Maysvillian Stage and higher

Richmondian Stage, in order to gain a further understanding paleoenvironments, paleoclimates, and paleobiology occurring during the Late Ordovician of the Cincinnati Arch. Chapters two-six of this thesis are intended for publication, or as part of a publication in a peer reviewed journal.

Chapter One is provided as background reguarding sequence stratigraphic terms.

McLaughlin, P.I., Brett, C.E., Holland, S.M., Storrs, S.W. 2008. Stratigraphic Renaissance in the

Cincinnati Arch. Implications for Upper Ordovician Paleontology and Paleoecology.

Cincinnati Museum Center Scientific Contributions. Number 2.

vii

Table of contents:

Title Page: i Abstract: ii Blank Page-Copyright Notice: iv Acknowledgements: v Preface: vii Table of Contents: viii List of Table and Figures: xi

Introduction 1

References 3

Chapter 1: Definition of Stratigraphic Sequences, Terms, and Model Used 5

References 14

Chapter 2: Facies Mosaics vs. Sequence Stratigraphy: using fine scale stratigraphic

correlation to decode sedimentary facies in the Cincinnatian, Maysvillian

Stage 16

Introduction 16 Traceable Horizons 18 Fairview Formation 18 McMillan Formation 27 Fourth Order Depositional Cycles 34 Corryville Member Cycles 44 Fourth order sequence stratgraphic framework 49

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Discussion of Cycle Propagation and Development 52 Conclusions 53 References 55

Chapter 3: Regional Correlation of the Late Ordovician Cincinnatian, Maysvillian

Stage Sequences using Magnetic Susceptibility 61

Abstract 61 Specific Aims 62 Background: MS, Milankovich Cycles, Cincinnatian 62 Cincinnatian Series 64 Methods 67 Outcrop Descriptions 68 Correlation and Interpretation using MS 72 Conclusions 81 References 83

Chapter 4: Third Order Sequence Stratigraphy of the Cincinnatian, Maysvillian

Stage: Not all Unconformities are Sequence Boundaries 89

Introduction 89 The Current Sequence Stratigraphic Model 90 Inconsistancies in the Current Model 91 A Reinterpretation of Cincinnatian Sequences 92 Discussion 106 Conclusions 110 References 112

Chapter 5: Tectonically Induced Depth Changes in the Cincinnatian:

Understanding the relationship between Eustatic and Tectonic changes in

Sea-Level in the Taconic Foreland Basin 118

Tectono-Eustatic Synthesis 118 Mud Generation and Cycle Development in the Kope and Fairview Fm. 126 Conclusions 130 References 132

Chapter 6: The Cincinnatian: The Three Fold Series 137 References 145

Conclusion: 147

Appendix One: 149

List of tables and figures:

Table 1: Fairview Formation MS values Maysville, Kentucky 149

Table 2: Grant Lake Formation MS values Maysville, Kentucky 152

Table 3: Kope-Fairview-Bellevue MS values Lawrenceburg, Indiana 156

Table 4: Uppermost Miamitown-Mt. Auburn MS values Trimble-Carroll Co.

Line Kentucky 161

Table 5: Miamitown-Richmond MS values Fredericktown, Kentucky. 164

Figure 1: Idealized Sea Level Curve 169

Figure 2: Correlation Chart of Cincinnatian Lithostratigraphic Units 170

Figure 3: Regional Map 171

Figure 4: Type Cincinnatian Bellevue Member 172

Figure 5: Fairview Formation Lawrenceburg, Indiana 173

Figure 6: Fairview-Bellevue Contact Maysville, Kentucky 174

Figure 7: Bellevue-Corryville Contact Maysville, Kentucky 175

Figure 8: Mt. Auburn Mbr. Maysville Kentucky 176

Figure 9: Bellevue through Mt. Auburn Trimble-Carroll Co. Line Kentucky 177

Figure 10: Corryville Mbr. at Campbellsburg, Kentucky 178

Figure 11: Kope-Fairvew Contact Maysville, Kentucky 179

Figure 12: Strophomena Bed Maysville, Kentucky 180

Figure 13: Seismite Horizons Maysville, Kentucky 181

Figure 14: Hardground Blocks Maysville, Kentucky 182

Figure 15: Upper Fairview through Bellevue Maysville, Kentucky 183

Figure 16: Miamitown-Bellevue Contact Bedford, Kentucky 184

Figure 17: Miamitown Shale through Richmond Grp. Fredericktown, Kentucky 185

Figure 18: Cross Beds in Bellevue Mbr. Trimble-Carroll Co. Line Kentucky 186

Figure 19: Cross Beds in Bellevue Mbr. Bedford, Kentucky 187

Figure 20: Lower Corryville Oncoid Beds Bedford, Kentucky 188

Figure 21: Lower Corryville Oncoid Trimble-Carrol Co. Line Kentucky 189

Figure 22: Corryville Mbr. O’ Bannon Creek Loveland, Ohio 190

Figure 23: Fredericktown Bed through Sunset Mbr. Fredericktown, Kentucky 191

Figure 24: Mt. Auburn Mbr. Trimble-Carrol Co. Line Kentucky 192

Figure 25: Stromotoporoids in Mt. Aubrn Mbr. Flemingsburg, Kentucky 193

Figure 26: Revised Sequence Stratigraphy of the Maysvillian Stage 194

Figure 27: Fairview Fm. Magnetic Susceptibility Curve Maysville, Kentucky 195

Figure 28: Grant Lake Fm. Magnetic Susceptibility Curve Maysville, Kentucky 196

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Figure 29: Fairview-Bellevue Magnetic Susceptibility Curve Lawrenceburg,

Indiana 197

Figure 30: Maysvillian Magnetic Susceptibility Curve TrimbleCarrol Co. Line

Kentucky 198

Figure 31: Maysvillian MagneticSusceptibility Curve Fredericktown, Kentucky 199

Figure 32: Cincinnati Arch C1-6 3rd order Sequence Stratigraphic Model 200

Figure 33: Schematic Illustration of Maysvillian Sequence Stratigraphy 201

Figure 34: Sedimentological Model Comparisons with Observations of

Cincinnatian Strata 202

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Introduction

As the result of a detailed regional field study of the Maysvillian Stage, a new sequence stratigraphic framework has been established, based upon a series of small scale (~5 to 15 m thick) depositional cycles traceable across the Cincinnati Arch. The construction of this detailed stratigraphic framework in conjunction with a detailed study of Magnetic Suseptibility throughout the interval has revealed widespread unconformities and facies dislocations. These unconformities have lead to the conclusion that the current 3rd order sequence stratigraphic architecture in place on the Cincinnati Arch does not match the newly established 4th order model, or the Episodic Starvation model of sedimentation. The purposes of this paper are to: 1) demonstrate the newly established 4th order sequence stratigraphic model; 2) document the results of a detailed study of Magnetic Susceptibility, using this as a tool for correlation, and an independent proxy for sedimentation, climate, and exposing unconformities; 3) to propose a new

3rd order sequence stratigraphic framework of the Maysvillian Stage, based upon high-resolution

4th and 5th order sequence stratigraphic correlation, magnetic susceptibility, and observations of sedimentation on a broad distal to proximal transect; and 4) establish controls for sequence generations within the Late Ordovician Katian Stage on the Cincinnati Arch. An additional chapter discusses the philosophy of stratigraphy, named units, previous work, and mechanisms for patterns observed in the stratigraphic record.

Strata of the Cincinnatian Series have a long and diverse history of study, and within this

Series, the succession through the Kope Fm., Fairview Fm., and Bellevue Member have long been regarded as generally shallowing upward (Anstey and Fowler 1969; Tobin 1982; Weir et. al

1984; Holland 1993; Jennette and Pryor 1993, etc.). The current study proposes a much more

1 complex pattern of sea level change throughout this Edenian-Lower Maysvillian interval

,establishing that the Fairview Formation, including the Miamitown Shale, consists of five 4th order depositional cycles distributed through two 3rd order depositional cycles. The Bellevue

Member consists of one 4th order cycle occurring during the Transgressive Systems Tract of an independent 3rd order cycle. Strata of the Upper Maysvillian stage were grouped into the

McMillan Formation in Cincinnati consisting of the Bellevue, Corryville and Mt. Auburn members (Bassler 1906), and subsequently into the previously undifferentiated Grant Lake

Formation in the Maysville region (Peck 1966; Weir et al. 1984). These same contiguous layers of strata masquerade under a different group of names governed by local variations in facies in central Kentucky and Indiana (Ettensohn, 1992; Cuffey 1998; Brett and Algeo 2001).

The present study recognizes two fourth order cycles in the Corryville Member and two more in the Mt. Auburn Mbr. Together, the Bellevue and Corryville Mbrs. have been newly interpreted to be one independent 3rd order cycle: and the Mt. Auburn is interpreted to represent the transgressive deposits of an independent 3rd order cycle, with the Sunset Mbr. of the Arnheim

Fm. composing the highstand or falling stage systems tract. In total, the current study interprets the Maysvillian interval in its type region to consist of 10 4th order cycles and a total of 3 ½ 3rd order cycles spanning approximately 4 million years of geologic time.

References

Anstey, R.L and Fowler, M.L., 1969. Lithostratigraphy and depositional evironments of the Eden

Shale (Ordovician) in the tri-state areas of Indiana, Kentucky and Ohio: Journal of

Geology, v. 77. p. 129-149.

Bassler, R.S., 1906. A study of the James types of Ordovician and Silurian Bryozoa.

Proceedings of the U.S. National Museum, V. 30 No. 1442.

Brett, C.E. and Algeo, T.J., 2001. Stratigraphy of the Upper Ordovician Kope Formation in its

Type Area, Northern Kentucky, Including a Revised Nomenclature. in: T.J. Algeo and

C.E. Brett., eds. Sequence, Cycle, and Event Stratigraphy of Upper Ordovician and

Silurian Strata of the Cincinnati Arch Region. Field Trip Guidebook in conjunction with

the 1999 Field Conference of the Great Lakes Section SEPM-SSG.

Cuffey, R.J., 1998. An introduction to the type-Cincinnatian. in: Davis, R.A. and Cuffey, R.J.

(eds.) Sampling the layer cake that isn’t: The stratigraphy and Paleontology of the Type-

Cincinnatian. State of Ohio, Guidebook No. 13 p. 2-9, fig. 2-3.

Ettensohn, F.R. 1992. Changing interpretations of Kentucky Geology: Layer-Cake, Facies,

Flexure, and Eustacy. Department of Natural Resources. Miscellaneous, State of Ohio.

Report 5.

Holland, S.M. 1993. Sequence stratigraphy of a carbonate-clastic ramp: The Cincinnatian Series

(Upper Ordovician) in its type area. Geological Society of America Bulletin, 105. 306-

322.

Jennette, D.C., Pryor, W.A., 1993. Cyclic alternation of proximal and distal storm facies: Kope

and Fairview Formations (Upper Ordovician), Ohio and Kentucky. Journal of

Sedimentary Petrology 73, 306-319.

Peck, J.H., 1966. Upper Ordovician formations in the Maysville area, Kentucky: US. Geological

Survey Bulletin 1244-B, 30p.

Tobin, R. C. 1982. A model for cyclic deposition in the Cincinnatian Series of Southwestern

Ohio, Northern Kentucky, and Southeastern Indiana. Unpublished PhD dissertation,

University of Cincinnati.

Weir, G.W., W.L. Peterson, and Swadley, W.C., 1984, Lithostratigraphy of Upper Ordovician

strata exposed in Kentucky. U.S. Geological Survey Professional Paper 1151-E.

Chapter 1

Definition of Stratigraphic Sequences, Terms, and Model Used

Sequence Stratigraphy is a system in which strata are divided into a series of unconformity bounded packages resulting from variations of sea level over time. This system seeks to establish a series of time correlative surfaces and divides rock bodies not in relation to their lithology, or facies, as does lithostratigraphy, but instead, as allostratigraphic units of rock deposited approximately synchronously and bounded by key, isochronous stratigraphic surfaces.

Due to variations in, and claims of complex sequence stratigraphic terminology, definitions of the terms and the system used here will be provided in this chapter. The sequence stratigraphic system used in this paper proposes to place sequence boundaries of depositional sequences at subaerial unconformities, submarine unconformities, or their correlative marine conformities occurring at the minimum sea level bounding a depositional sequence: as opposed to a genetic stratigraphic system in which sequence boundaries are placed at maximum flooding surfaces as proposed by Galloway (1988) or an alternative Exxon system, which places the sequence boundaries at the beginning of the forced regression (see Catuneanu, 2006). This paper subdivides each depositional sequence into four systems tracts: groups of related facies deposited during particular phases of base level rise and fall and bounded by traceable surfaces, the lowstand (rarely observed in cratonic sequences), transgressive, highstand, and falling stage systems tracts, each bounded by distinctive surfaces (see below).

Orders of cyclicity can be defined on the basis of one of two hierarchical systems, one in which the hierarchy system is based upon cycle duration, considering eustasy the principal driver of cyclicity, (Vail et al. 1991; Mithchum and Van Wagoner 1991; see Catuneaunu 2006 for

5 additional definitions), and another based upon the inferred magnitude of base-level changes resulting in boundary formations, the physical attributes of the cycle’s bounding surfaces, and areal extent of unconformity (Embry 1995); the later is frequently applied where tectonic control of sequence generation is inferred. Ideally, both systems are valid in establishing a hierarchy of depositional cycles. For the purposes of this paper, cycles will be defined by the physical attributes of their bounding surfaces. Inferred durations of the different cycles range from approximately 20,000 to 100,000 year duration for 5th order cycles, 400,000 year duration for 4th order depositional cycle, and a variable cycle duration generally > 1 million years for 3rd order depositional cycle. These durations imply a combination of Milankovitch-band forced glacio- eustasy as well as tectonic control as a source of sequence generation.

Cycles defined by the physical attributes of their bounding surfaces, are interpreted to have an approximately 400,000 year 4th order depositional cycle duration (0.5 to .08 million year proposed by Vail et al. 1991), and a 3rd order depositional cycle varying in duration: Vail proposed 0.5 to 3 million years. Fourth order cycles, and corresponding depositional sequences, are representative of large scale orbital perturbations, composed of the constructive interference and overlap of a hierarchy of Milankovitch band cycles of different frequency, and for the purposes of this paper are defined chronostratigraphically to represent an approximately idealized 400,000 years of time (Brett et al. 2011). Cycles of this duration reportedly are representative of eustatic, or global phenomena, and can be widely traceable, or laterally continuous, as observed in Pennsylvanian cyclothems (Catuneaunu 2006). Coincidently, an idealized third order cycle duration of 1.25 to 1.3 million years is concurrent with long eccentricity cycle durations implying an orbital control (Shackleton et al. 1999; Berger 1977).

Due to their development in the form of a nested hierarchy of orbital perturbation, or

Milankovitch cycles, these cycles often contain smaller order 5th, ~ 100,000 year, and 6th 40,000

– 20,000 year cycles, whose trangressive deposits can often results in sediment starved beds when overprinted on the larger 4th order cycle. These same 4th order cycles can compose the different systems tracts of larger 3rd order depositional cycles (Coe 2005); however, this is not always the case, and as shown by (Brett et. al 2011; Brett 1995), the number of 4th order depositional cycles occurring in a given 3rd order cycle may vary. An ideal third order cycle of

1.25 million year duration would be composed of three fourth order cycles composing the trangressive, highstand, and falling stage systems tracts.

Physical attributes of sequence boundaries in the Cincinnatian are often sharp, parallel bedding contacts with a limestone, often containing rip-up clasts in a compact grainstone, or rubbly packstone deposit, depending on paleobathymetry, sharply overlying silty falling stage deposits. This has been the dominant morphology for the majority of sequence boundaries found within this study, none of which exhibited large scale karstification and relief. These sequence boundaries are incredibly widespread and have been traced across the entire Cincinnati arch.

Third order sequence thicknesses can vary between 30 to 15 meters. Fourth order 400,000 year cycles often display this same motif, however which a lesser degree of facies juxtaposition occurring at the boundary. Fourth order cycles can range from approximately 4 to 15 meters thick, and in extremely condensed section may be less than one meter thick. Fifth order, 100,000 year cycles often display the motif of typical Cincinnatian Limestone-Shale cycles, exhibiting a sharp base, approximately 30cm or less of condensed limestone beds, sharply overlain by mudstones, increasing in silt content upward. These cycles are approximately one meter in thickness. Concretions occurring in the shaly portions of cycles can be attributed to sediment

7 starvation occurring during accumulation of the overlying limestone bed; and these limestone beds sometimes preserves small rip-up clasts.

The term parasequence is sometimes regarded as synonymous with 4th order depositional cycle. However, as originally defined, parasequence is meant to imply asymmetrical, upward- shallowing cycles bounded by flooding surfaces with no definite temporal scale, and no preservation of the transgressive phase so the term is not appropriate for most packages herein described as 4th order sequences. Thus, this term it will not be used in the context of this paper.

In fact, these 4th order cycles display the same general components as a broader larger scale depositional sequences including a stratigraphic discontinuity at their base, a transgressive systems tract (TST) including a condensed sediment starved interval in the middle, a highstand, and regressive or falling stage systems tract. Each depositional sequence, whether third or fourth-order, is composed of a series of the same systems tracts.

All sea-level cycles begin with a Sequence Boundary (SB) occurring at the period of maximum sea level low (Figure 1). Unconformities can occur at periods of sea level lowstand; however, unconformities are not always present or easily recognizable in the field. The position of sequence boundaries can be determined by the magnitude of a stratigraphic deposit, its regional extent, evidence for regional truncation of subjacent strata, and the relationship between it and the overlying deposit. Such intervals are, predictably, succeeded by a transgressive limestone deposit, which is stratigraphically thicker in the nearshore and commonly contains numerous rip up clasts.

The Lowstand Systems Tract (LST) deposit occurs from the sequence boundary to the transgressive surface, frequently marked by a ravinement surface (TS) and occupies a point in

8 time when sea-level is rising slowly, but progradation of the shoreline seaward may be occurring in association with subsidence. Widespread submarine fans are associated with LST deposits in deep water off continental shelves but are absent in most cratonic successions. More commonly, however, LSTs are absent and the sequence boundary is combined with, and modified by, a transgressive surface, typically with wavebase erosion or ravinement, that may erase distinctive features of a subaerial unconformity. LST deposits may not be present in sequences marked by widespread aerial unconformities, and are more often associated with correlative conformities marking sequence boundaries. Such ET (erosion-transgression)surfaces, or joint sequence boundary and transgressive ravinement surfaces mark the bases of most depositonal sequences.

However, lowstand sediments, marking initial base level rise, may be represented in

Cincinnatian Series as widespread shale deposits which do not exhibit widely recognizable changes in facies across their lateral extent.

The transgressive systems tract (TST) is bounded by the Transgressive Surface (TS) or the combined SB/TS (ET) surface and the maximum flooding surface. Transgressive Systems

Tract deposits (TST) are deposited during rising base level when the rate of creation of accommodation exceeds sediment progradation. Sediments deposited during such periods display retrogradational (backstepping) patterns, when the coastline is migrating landward in response to rising sea-level, and in mixed siliciciclastic-carbonate systems such as the

Cincinnatian, are typically associated with clean carbonate buildups as terrigenous sediment is trapped in proximal areas, and distal clastic sediment starvation occurs.

Transgressive systems tracts are typically subdivided into an early and later phase by a sediment starved discontinuity. Deposits of the early TST end at the maximum rate of sea level rise, the first derivative of a rising sea level curve. The period of maximum sea level rise will be

9 referred to as the maximum starvation surface (MSS; see Baum and Vail 1988; Brett, 1995). The

MSS is often associated with widespread shales sharply, and disconformably overlie limestones, associated with widespread hardgrounds, phosphatic lag deposits, or bone beds. This, and the maximum flooding surface are equivalent to the “Drowning Unconformity” in the nomenclature of Kolata et. al (2001).

The later TST or condensed section, is bounded between the MSS and a slightly higher maximum flooding surface (MFS); this latter surface or zone records the strongest or most landward transgression of the shoreline and, though often obscure, may be identified as a shale- rich zone, recording maximum water depths, in places showing evidence of condensation.

Maximum flooding surfaces are more difficult to recognize in outcrop than the underlying MSS, and are less emphasized in this study (Figure 1).

The High Stand Systems Tract (HST) occurs during the period of generally high sea level marked from the MFS to the initial surface of forced regression, the true highest relative sea surface. The highstand systems tract (HST) occurs between the MFS and an inferred position of initial sea level fall (first surface of forced regression) recording a phase of gently rising base level during which sediment progradation outpaces the rate of accommodation increase and hence is a time of so-called “normal regression”. The Highstand Systems Tract represents two components in which sea level is continuing to rise at a lowering rate resulting in aggradational stacking of smaller scale cycles in the early portion of the HST and progradational patterns in the later HST. Highstand deposits are often associated with widespread shale deposition.

Falling Stage Systems Tract deposits (FSST) occur during the period of sea level fall from the Forced Regression Surface (FRS) to the Sequence Boundary. This may be associated

10 with shale and siltstone deposition. The point at which sea level is at its maximum height and is just beginning to fall is referred to as the first surface of forced regression. The Falling Stage systems tract represents all sediments deposited during the time of falling base level and characterized by “forced regression”, i.e., regression caused by actual base level drop, as opposed to progradation alone.

Translation of the idealized succession of systems tracts into a workable sequence stratigraphic framework in outcrops requires recognition of key patterns and surfaces in the field.

Generally, the most important surfaces are only identifiable with a regional study of strata. In an ideal Cincinnatian depositional sequence, the sequence boundary is demarcated by a sharp, joint sequence boundary and erosive trangresseive surface at the base, and overlain by a backstepping, deepening upward succession of skeletal limestones, formed during periods of siliciclastic starvation associated with transgression, the trangressive systems tract. This is sharply overlain at a surface of sediment starvation by a thin condensed interval, often phosphatic lag deposits, presumably formed while sea level is rising at its fastest rate, occur at this position. During this time siliciclastic starvation will be strongest and there may also be a period of backstepping or temporary drowning of the carbonate factory resulting in a sharply demarcated, mineralized hardground surface the maximum starvation surface.

This MSS is overlain by thin retrogradational to aggradation deposits typically rich in shale, or mixed shale and limestone. For purposes of this study the true maximum flooding surface is picked somewhat arbitrarily at the top of the finest grained-typically shaliest, most clay rich, strata above the MSS. The HST deposits are also typically fine grained but usually typified by a mixture of shales, thin silty packstones and thin siltstines. If small scale cycles are recognized they show a subtle progradational (shallowing upward) pattern.

The initial surface of forced regression (ISFR) is typically obscure but may be associated with periods of submarine erosion and may be marked by reworked concretions at the boundary between a shale and an overlying mudstone or siltstone deposit. A thin condensed horizon at this level has been termed a “precursor bed” by Brett (1995) because it occurs at the base of marked siliciclastic progradation and shallowing.

In proximal areas the later Falling Stage, typically with a somewhat irregular, channelized base is characterized by thicker and coarser terrigenous siltstones, which may show soft sediment deformation. In an idealized model an individual 4th order depositional cycle would be composed of successive, transgressive, highstand, and falling stage systems tracts..

During FSSTs clastic bodies will often prograde or downstep seaward. In a nearshore environment this could be observed in Cincinnatian strata as large and thick siltstone rich deposits, and in more distal environments may record the deposition of shales with some mixed siltstones and carbonates. In siliciclastic dominated sections sandstone deposition may occur in nearshore environments, along with increased amounts of wave base erosive incision. Silt and sandstone bodies frequently display large gutter casts and/or channel forms formed by submarine erosion Often associated with FSSTs are one or more horizons of disturbed strata, or ball and pillow structures showing soft sediement deformation typically associated with large silt-filled channels. These are interpreted as seismites by McLaughlin and Brett (2004). It is thought that rapid deposition of mixed muds and thicker siliciclastics or detrital carbonates of the FSST led to instabilities that promoted seismically induced foundering of silt-or sand-sized sediments into liquefied muds.

Just as a juxtaposition of sedimentary facies will occur at sequence boundaries, distal and proximal environments also show complementary patterns of sedimentation, in other parts of the

12 transgressive-regressive cycle. During periods of transgression, TSTs, clastic sediments will be trapped in more proximal estuarine or nearshore environments. The resulting strata in a proximal environment form stratigraphically thick deposit, and in the case of the Cincinnatian, a fossiliferous, rubbly packstone. The correlative strata in a more distal environment will be more sediment starved, resulting in shell bed accumulation, carbonate formation, and as observed, stratigraphically thin, condensed grainstone deposits occur during these times.

Using the principles of sequence stratigraphy a fairly predictable suite of depositional environments and facies will occur during different phases of base level rise and fall.

Geographically widespread surfaces showing juxtaposition of facies, in combination with high magnitude regressive followed by transgressive systems tracts adjacent to each other, the contact between these units is a sequence boundary. Likewise, 3rd order depositional sequences can be based upon, and defined by the extent and presence of widespread falling stage systems tracts, and transgressive deposits.

References

Baum, G.R. and Vail, P.R. 1988. Sequence Stratigraphic concepts applied to Paleogene outcrop,

gulf and atlantic basins. In: Sea Level Changes-and Integrate Approach, C.K. Wilgus,

B.S. Hastings, C.G. St.C. Kendall, H.W. Posamentier, C.A.Ross, and J.C. Van Wagoner,

Eds., pp. 309-327. SEPM Special Publication 42.

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North America. Palaeogeography, Palaeoclimatology, Palaeoecology V. 304 p. 21-53.

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Springer-Verlag.

Chapter 2

Facies Mosaics vs. Sequence Stratigraphy: Using Fine scale Stratigraphic

Correlations to Decode Sedimentary Facies and establish a Fourth order

sequence stratigraphic model in the Cincinnatian, Maysvillian Stage

Thomas Schramm, Carlton Brett, Benjamin Dattilo

Keywords: Late Ordovician, Cincinnatian, Maysvillian, Sequence Stratigraphy, Fourth Order

Cycles

Introduction:

Richly fossiliferous, shallow-marine Upper Ordovician strata of the type Cincinnatian have a long history of research dating back over 150 years. Meanwhile, a plethora of local stratigraphic terms, while reflecting minor local facies changes, have obscured some overarching patterns, including sedimentary sequences, sharp facies dislocations (discontinuities), and unique marker beds. These features provide a key to identifying a hierarchy of cycles and understanding of coeval facies and depositional environments in high resolution.

A long-standing perception exists that the Cincinnatian and in particular the Maysvillian stage strata, comprise a mosaic of local facies that cannot be subdivided and correlated in detail, with little small-scale cyclicity present (Figure 2) (Cuffey 1998; Ford 1967). However, the results of an intense field investigation indicate that this is not the case. Recent research has led to a stratigraphic renaissance on the Cincinnati Arch, however most of the detailed work over the

16 last decade has focused on the Edenian Stage Kope Formation. Building and expanding upward on previous research in the older Kope Formation (Jennette and Pryor 1993; Holland et al. 2000;

2001; Brett and Algeo 2001; Miller et al. 2001; Webber 2002; Brett et al. 2007 etc.), and using this previous body of work as an exemplar of a high resolution stratigraphic and paleoecological study, the present study will establish a high-resolution litho- and cyclostratigraphic framework for the slightly younger Maysvillian Stage strata, which can then be used as a basis for future paleontological, sedimentological¸ evolutionary, and climatic investigations.

The type Cincinnatian in and surrounding Cincinnati, Ohio (Figure 3) has been long divided into a series of subunits representing the reference intervals of the Edenian and

Maysvillian stages of North American terminology. Stratigraphic units comprising the

Maysvillian Stage from oldest to youngest are; the Fairview Formation, Miamitown Shale,

Bellevue, Corryville, and Mt. Auburn Members of the McMillan Formation or the equivalent

Grant Lake Fm. in Kentucky (Figure 4). Because most of these old reference sections are covered or poorly exposed in Cincinnati nearby newly created roadcut sections of the Fairview

Formation along Rt. 48 in Lawrenceburg Indiana (Figure 5) and creek localities of the Corryville

Member provide paratype sections of the Cincinnatian. These members have been mainly traced in the Cincinnati area, those being the Miamitown, Bellevue, Corryville, and Mt. Auburn.

Ironically the type Maysvillian in Maysville Kentucky, about 100 km (60 miles) to the east of Cincinnati has never been similarly subdivided nor correlated in much detail to the reference Cincinnati sections and has been largely grouped into undifferentiated lithostratigraphic units including the Fairview, or Calloway Creek Formation, and the Grant Lake

Lithostratigraphic Formation (Figure 6, 7, 8) This, in turn has given rise to the notion of a mosaic of local facies (Figure 2). Likewise, stratigraphic successions to the southwest of Cincinnati

17 masquerade under a myriad of different names; (Figure 9, 10). This hodgepodge of names conveys the misleading interpretation that little similarity exists among these areas and that they cannot be correlated throughout the Cincinnati region. This is not the situation with sequence stratigraphic correlations.

In the present study, we bridge together these three seemingly disparate areas across the

Cincinnati Arch to produce an event and sequence stratigraphic framework for the Maysvillian

Stage. This involves the application of a sequence stratigraphic model (see Chapter 1; Figure 1).

In particular, a series of key stratigraphic surfaces, marker beds and intervals found within the

Maysvillian strata provide the necessary tools for regional stratigraphic correlation.

Traceable Horizons

Fairview Formation.

Originally named by Bassler (1906), the Fairview Formation is a combination of the previously named Mt. Hope and Fairmont divisions (Nickles 1902). Several traceable horizons have been recognized throughout the Fairview Formation. The current study attempts to duplicate high resolution stratigraphic correlations of the Kope Formation (Jennette and Pryor

1993; Holland et al. 2000, 2001; Brett and Algeo 2001a) and to establish such detailed correlations throughout the shallower water dominantly carbonate facies of the Fairview

Formation, with the purpose of providing a detailed stratigraphic framework for future studies.

The Kope-Fairview-Bellevue succession been regarded as a shallowing upward succession

(Anstey and Fowler 1969; Tobin 1982; Weir et. al 1984; Holland 1993; Jennette and Pryor 1993, etc.); however, the results of the current study imply a much more complex sea-level history for this interval. Increasingly shallow facies have been claimed to offer difficult, or too monotonous

18 to permit high-resolution stratigraphic correlations, due to a localization of depositional environments, but we demonstrate here key stratigraphic surfaces can be traced across depositional facies, thereby permitting a high-resolution correlation.

Z-Bed and Two Foot Shale of the Kope Formation.

The currently utilized base of the Fairview Formation overlies a widespread 30 to 60 cm five part cluster of limestones known informally as the Z-bed of the Kope Formation, which sharply overlies a widespread siltstone interval known as the Taylor Mill Mbr. of the Kope Fm.

(Brett and Algeo 2001) or the correlative Garrard Siltstone (Figure 11). The Z-bed has been traced over the entire outcrop belt of the Cincinnati Arch and is consistently overlain by approximately two feet (60-70 cm) of shale or mudstone, making the interval an excellent marker (Brett and Algeo 2001). Moreover, the Z-bed and two foot shale interval has been identified to the south where they sharply overlie the deformed siltstones of the Garrard

Formation, equivalent to the Taylor Mill submember of the Kope Formation. The Z-bed matches the descriptions of Nickles (1902) as an 8-16 inch thick limestone bed overlying the “Utica

Shale” (Kope Formation), rich in reddish colored Dalmanella multisecta and succeeded by several limestone layers (interpreted to be the North Bend Tongue). This (Z-bed) was considered to represent the base of the Maysvillian Stage by Fenneman (1916) and the base of the Fairview Formation Mt. Hope Member (Nickles 1902; Fenneman 1916), and according to

Fenneman, it is locally more than one foot thick bed, “probably the thickest in the Cincinnatian” which can “easily be recognized by its fossils without expert knowledge” and, “Commonly, though not always, the bed including the fossils (Dalmanella multisecta) is reddish or reddish brown.”

The rather pure mudstone unit overlying the Z-bed has been informally named the “two foot shale” (Brett and Algeo 2001) and retains a thickness of approximately 60 cm throughout most of its extent, although, on the Jessamine Dome and areas south of Sherberne, KY, where the “two foot shale” has been located has a thickness of approximately three feet or 90 cm thickness. This same “two foot shale” is represented by cycle 22 of Jennette and Pryor (1993).

In Maysville, Kentucky, this bed subsequently is interpreted to represent an obrution type deposit, containing intact, well preserved crinoid stems formed into large bundles (“log jams”) at two observed orientations. Similar “log jams” have been observed as far south as Clays Ferry,

Kentucky. Based upon observations, lithologic descriptions and unit definitions of previous workers, and consistent with our new outcrop based observations, the Z-bed and two-foot-shale of the Kope Formation were originally grouped into, and regarded as the base of the Fairview

Formation. Subsequent workers regarded the Z-bed and two-foot shale as the uppermost units of the Kope Formation (Holland, 1993; Jennette and Pryor, 1993; Brett and Algeo, 2001). We favor the original definition, however, not simply for historical reasons, but because the Z-bed is inherently related to the Fairview Formation.

North Bend Tongue-Submember

The North Bend submember represents the basal deposits of the Fairview Formation, Mt.

Hope Member, which overlie the Z-bed and two-foot shale. It overlies a single thin limestone bed and approximately 6 inch thick mudstone unit, occurring above the 2 foot shale. This individual limestone bed represents the basal most Fairview Formation and has also been widely traceable. The North Bend Tongue was originally named by Ford (1967) and is approximately three meters thick; we rename this unit North Bend submember, herein, as no interfingering between between the Kope Fm. and Fairview Fm. occurs. The North Bend submember is

20 composed of a carbonate rich, limestone lower portion, consisting of approximately five limestone beds, a thin shaly middle portion, and an upper limestone portion containing five limestone beds again. The upper beds of this interval are rich in the brachiopod Strophomena in more proximal facies such as Maysville Kentucky and rich in the brachiopod Dalmanella in more distal facies (Figure 11). These beds of the upper North Bend submember are very compact, and coquinoid with abundant edgewise, fragmental brachiopods.

Wesselman Tongue-Submember

Directely overlying the North Bend submember is the Wesselman “Tongue” (Ford 1967).

The Wesselman is a shaly unit, and has in the past been considered to be a Tongue or interfinger of the Kope Formation; however, this interpretation resulted, at least in part, from the miscorrelation of the Wesselman with the upper or Taylor Mill submember of the Kope (S.

Felton, pers. comm.). The Wesselman Tongue, is completely separated from the Kope

Formation by the underlying North Bend Tongue, and no interfingering between these units occurs (Figure 11). Hence, again, we rename the interval as a submember of the Mt. Hope

Member. Across the Cincinnati Arch the Wesselman submember exhibits a three part motif, with a lower shale-mudstone rich portion, a lower middle limestone portion, and an upper Shaly siltstone portion. The Wesselman submember appears to be thicker in more distal, deeper water settings, such as Lawrenceburg Indiana, at approximately 7 meters thick, and is much thinner in more proximal shallow water settings at approximately 3-4 meters thick, however still displaying the triad motif. This unit, and the different sub-units within it are traceable over large distances.

Un-named Submember

A unit similar in lithology to the Wesselman submember the Un-named submember occupies the upper Mt. Hope Member of the Fairview Formation. This mudstone rich interval is set apart from the underlying Wesselman Tongue by a grainstone bed containing rip up clasts.

Within this interval four major limestone beds are present, each typically contains five thinner beds composing the larger ones. The unit exhibits a general coarsening upwards following the initial grainstone, and becomes more siltstone rich in its upper portions. The un-named submember averages approximately 10 meters in thickness, thicker in more distal settings, and thinner in proximal settings. In proximal settings, such as Maysville Kentucky, the siltstones of the upper portion show small scale soft-sediment deformation, or small seismites underlying the

Strophomena Bed; frondose bryozoans are also common within this interval.

Strophomena Bed

An approximately 30cm thick rip up clast bearing grainstone bed marks the Mt. Hope-

Fairmont Member boundary (Nickles 1902). This grainstone bed occurs at or directly above the faunal boundary marking the Member contact, and is unusuallly rich in the Brachiopod

Strophomena (Figure 12). The mudstones below this bed often contain frondose colonies of the bryozoan Constellaria. This horizon is easily recognizable and has been traced across southern

Ohio, southeastern Indiana and northern Kentucky.

Hooke-Gillespie submember

Hooke-Gillespie submember is an informal name herein assigned to lower strata of the

Fairmont Member, above the Strophomena Bed composed dominantly of silty mudstones with thick (up to 1 m), locally channeled and deformed siltstones, that extends upward to a series of

22 thick rip-up clast bearing grainstone beds. This interval is named for the intersection between the AA highway, and Hooke and Gillespie Lanes, where a series of three thick deformed siltstones, interpreted as seismites, are exposed. This same stratigraphic interval has been well studied in the Maysville Kentucky region (Schumacher 2001; Brett et al., 2008) where it contains massive ball and pillow seismite horizons (Figure 13), siltstone infilled channels, and large encrusted limestone blocks associated with these seismite horizons (Figure 14), and is widely traceable. In distal sections this interval is mudstone rich interbedded with skeletal grainstones and contains a series of three approximately 10-20 cm. thick siltstone beds in its upper portions.

Lawrenceburg submember

Resting sharply above the deformed siltstone horizons of the Hooke-Gillespie interval is a cluster of three rip-up clast bearing carbonate beds and interbedded shale and thin limestone marking the base of the informally named Lawrenceburg submember. This submember of the

Fairmont Member contains thick skeletal carbonates over 4 meters in thickness at the type locality at the upper end of the large Rte. 48 road cut at Lawrenceburg Indiana, sitting on top of a series of three rip-up clast bearing beds containing clasts up to 20cm across. This same series of three rip-up clast bearing beds has also been observed in more proximal settings in the Maysville region (Figure 15). The uppermost of these compact skeletal carbonates has a sharp, somewhat corroded mega-ripple hardground top at Lawrenceburg Indiana, Immediately underlying this bed is an interval up to 10 cm thick comprised of pale orange weathering phosphatic granules with abundant phosphatic steinkerns of minute gastropods (B. Heimbrock, pers. comm.). Thinner stringers of orange phosphatic grains occur near the top of the rippled bed and in overlying lenticular hardgrounds. The Lawrenceburg beds also contain an index fossil of the interval, the brachiopod Orthorhynchula, (S. Felton, pers. comm.) which has been found rarely at

Lawrenceburg, and abundantly in the coeval strata at Richmond, Point Leavell, and Springfield

Kentucky, rendering this interval traceable across the Kentucky Bluegrass region, despite exhibiting much shallower water muddy carbonate facies, in comparison to the distal, Sebree

Trough section near Lawrenceburg.

Lower Hill Quarry Submember

Interbedded discrete limestones and shales of the Fairmont Member resting sharply on top of the tightly bedded carbonates of the Lawrenceburg submember have in the past been referred to as the “Hill Quarry Beds” based upon former quarries occurring in this stratigraphic interval in the hills surrounding Cincinnati for the production of building stones (Nickles 1902).

The interval that sits sharply on top of the tightly bedded carbonates of the Lawrenceburg submember are being called by the prior name of Hill Quarry Beds. Here a series of seven carbonate-mudstone cycles are preserved, or seven approximately “meter-scale cycles”. These cycles are typically composed of a lower prominent compact skeletal carbonate pack-grainstone overlain by a mudstone interval which coarsens upward into silty mudstone, with possible siltstone beds in the upper portions of the cycle. This series of beds has proven to be extremely traceable and widespread, including into the subsurface (Dattilo 1998, Dattilo et al., 2011 in press). Our field research has shown the widespread lateral nature of the Hill Quarry Beds, and have been numbered beginning above the Lawrenceburg submember.

In the present paper, however, we subdivide the Hill Quarry beds into two distinct packages at a very sharply based grainstone ledge, herein termed the Lower Hill Quarry submember and Upper Hill Quarry submember. The Lower Hill Quarry submember, approximately 3 m thick, directly overlies the Lawrenceburg submember at its type locality and

24 consists of the lower three of the cycles of the “Hill quarry beds”, terminating with a distinctive meter-thick, silty shale that is sharply (erosionally) overlain by a very discrete, ledge-forming grainstone (Third Hill Quarry Bed). Exceptional exposures of this interval appear at the upper end of a major roadcut on Rt. 48 at Lawrenceburg, IN. The meter-thick shale interval contains siltstone interbeds; the uppermost siltstone bed contains abundant traces (Diplocraterion) and scolecodonts.

Upper Hill Quarry (Fracta) Submember

The upper three beds of this interval have also been referred to as the “shingled

Rafinesquina zone”, or fracta Beds (after Rafinequina fracta) (Caster et al., 1961), and are characterized lithologically by a rubbly fossiliferous, possibly orange weathering, packstone interval. These (fracta) beds have been described number from the top down (Forsyth 1946), or first equal uppermost bed, and have been referred to as lower, middle, and upper shingled zones, in order to avoid any numerical confusion by Dattilo (1998), who also demonstrated the traceable nature of these horizons. Herein, we redesignate this informal interval as the Upper

Hill Quarry submember, for an excellent exposure in a hillside cut along Gage Street at the intersection of Rice Street, below the helicopter pad of the Christ Hospital, Cincinnati, Ohio

(Figure 4). Our field research his shown the widespread lateral nature of the Hill Quarry Beds.

Specifically the third discrete Hill Quarry limestone ledge above the top of the Lawrenceburg submember, has proven to be extremely distinctive. Because it appears to be genetically related to the overlying Fracta beds, this “third Hill Quarry bed” has been assigned, herein, to the overlying Upper Hill Quarry submember.

As noted above this bed overlies a meter thick mudstone interval containing siltstone interbeds; the uppermost siltstone bed contains abundant Diplocraeterion and scolecodonts. The third Hill Quarry Bed, or Hill Quarry Bed three, is an approximately 30 cm thick compact grainstone, weathering somewhat orange, and contain small granules of orange weathering phosphate, and appears prominently in outcrop and is easily distinguishable from the other Hill

Quarry Beds. Lithologically it resembles the Middle Devonian, Tichenor limestone bed of New

York State. Overlying the 3rd Hill Quarry Bed is a somewhat rubbly, muddy packstone interval.

The fourth Hill Quarry Bed is generally somewhat thinner, and less prominent than the third Hill

Quarry Bed, although may vary and increase in thickness locally, and possibly more-so than the underlying third Hill Quarry Bed on occasions. The seventh Hill Quarry Bed is also a very widespread compact pack-to-grainstone occurring directly below the basal Miamitown Shale interval.

Miamitown Shale Submember (of the Fairview Formation)

The Miamitown Shale (Ford 1967) is a dominantly mudstone unit rich in gastropods and marked by the index fossil Heterorthina. For more information on the widespread nature and morphology of this unit see Dattilo (1994, 1998). The exact stratigraphic position of the

Miamitown has been poorly defined. Herein, we define the Miamitown as a third, uppermost submember of the Fairview Formation, Fairmont Member. The Miamitown Shale can be characterized by three typical, units: a lower mudstone portion, a middle limestone portion containing five limestone interbeds, and an upper silty mudstone portion containing current aligned siltstone gutters northwest of Cincinnati. Each of these three intervals can be traced over long distances west of Cincinnati, and has been found as far as Madison, Indiana where the unit is a green mudstone (Figure 16). Meanwhile, this same seemingly widespread unit thins

26 drastically southeast of Cincinnati, and is less than one meter thick at Reidlin/Mason road Fort

Wright-Taylor Mill, Kentucky (St. Louis Diekmeyer 1998); to the southeast of this the unit disappears. In peritial facies of the Bardstown-Fredericktown KY, area, southwest of Cincinnati, this unit is approximately 10m thick and appears as muddy carbonates, which still tend to show a distinct three part system (Figure 17). In outcrops and creek exposures near Fredericktown and

Loretto KY. this unit has a calci-micritic lower portion containing marine fossils, a middle portion contain bored marine hardgrounds, mudcracks, and rippled beds, sharply overlain by a fossiliferous marine packstone containing bryozoans, brachiopods, cephalopods, and Isotelus trilobites. This change in deposition facies would be expected when tracing a unit from deep subtidal to pertidal facies.

McMillan Formation

The McMillan Formation (Bassler 1906) was created to merge together the Bellevue,

Corryville, and Mt. Auburn (Nickles 1902) into one formation and making the former divisions members, due to their close relation, and insufficient status to be mapped separately. Like strata of the Fairview Formation, strata of the McMillan Formation have yielded as series of traceable horizons through the substantial changes of depositional facies across the Cincinnati Arch.

Bellevue Member

In its current type locality at the intersection of Rice and Gage Street, Cincinnati, Ohio

(Ford 1967) the Bellevue Member overlies fossiliferous mudstones of the Miamitown Shale

(Figure 4). The Bellevue Member in this locality is a fossiliferous packstone rich in

Rafinesquina and Hebertella and bryozoans, Monticulipora. Several traceable horizons exist within this unit. Approximately 30-40 cm from the base of the unit is a 6-10 cm thick siltstone

27 bed which is traceable from Cincinnati, to Maysville. Additionally, approximately 1.5-2 meters above the base of the unit, there is a series of large mammiform bryozoan colonies, presumably of the genus Monticulipora encrusting mollusk shells, and above this more fossiliferous packstones. Overlying these beds are a fossiliferous mudstone, referred to as the “Rafinesquina shale” (Dattilo 1998). Differences have been recognized by Nickles (1903) and Dattilo (1998) between the lower, bryozoan rich portion of the Bellevue, and upper fossiliferous pack and grainstone portion, lying above the Rafinesquina Shale. In general this upper portion of the

Bellevue is increasingly compact, more grainstone rich, and less mud-rich, more sediment starved, than the lower portion. In downramp settings the Bellevue becomes a more compact skeletal-crinoidal pack-to-grainstone is reduced more in thickness, and has additional phosphate.

In upramp portions of the basin, where it is included as the basal part of the Grant Lake

Formation, the Bellevue becomes increasingly argillaceous and shows a more rubbly, fossiliferous packstone lithology, and often includes Vinlandostrophia ponderosa (formerly

Platystrophia ponderosa) (Figure 7). On the western limb of the Cincinnati Arch the Bellevue is an approximately 3.5 meter thick very compact, phosphatic grainstone, and displays large crossbeds including bimodal, “herringbone” cross stratification (Figure 16, 18, 19). At

Taylorsville Kentucky the Bellevue Member is an approximately 4 meter thick very compact hard phosphatic grainstone, and near Fredericktown-Bardstown Kentucky thins to a meter thick, then disappearing less than more mile away from Fredericktown.

Corryville Member

Strata lying above the Bellevue Member have been considered to be undifferentiable

(Ford 1967) and to have gradational and commonly concealed contact to strata unnamed. Tobin

(1980) demonstrated that the contact between the Bellevue and Corryville, although commonly

28 concealed is not gradational, and is instead a sharp contact (Tobin 1982, p. 166). He subsequently redefined the base of the Corryville as occurring at the sharp boundary between

“thin, wavy-bedded, shale poor strata, of the Bellevue, and the beginning of thicker, planar bedded shales of and limestone of the Corryville.” The Corryville Member lithologically consists dominantly of mudstones interbedded with limestones; these mudstones horizon often contain well preserved fossils interpreted as obrution deposits in deeper parts of the basin.

On the western limb of the Cincinnati Arch, near Carrollton-Bedford, Kentucky, and

Madison-Manville-China, Indiana calcareous mudstones of the lower Corryville strata sharply overlie cross-bedded calcarenitic grainstones of the Bellevue Mbr., followed by a series of four somewhat phosphatic oncolite rich grainstone beds (Figure 20, 21). In areas with increased accommodation, such as Sulphur-Campbellsburg Kentucky thick deposits of calcareous mudstones exist between the underlying Bellevue, and between the four oncolite bearing horizons of the lower Corryville (Figure 10). When traced to the area near Bardstown-

Fredericktown Kentucky, this same oncoid rich interval is represented by the upper part of the

Gilbert Member of the Ashlock Formation (Weir 1984), where four micritic beds exhibiting recrystallized stromatoporoids-coral heads are present.

In distal, Sebree trough sections of the Cincinnati Arch, such as Hamilton, Middletown,

Morrow, and Batavia Ohio, shales of the Corryville Member overlie the Bellevue Member followed by a series of four compact, approximately 20-30 cm thick grainstone beds, interbedded with mudstones correlative with the oncolite beds. In type Cincinnatian sections this interval is occupied by four beds of crinoidal pack-grainstones overlying the basal-most mudstones of the

Corryville Member; and is the equivalent facies to the Bellevue Member in Sebree Trough sections. Throughout the eastern limb of the Cincinnati Arch, Jessamine Dome, and Kentucky

Bluegrass the Corryville Member occupies part of the Grant Lake Fm. (Peck 1966), named for the undifferentiable counterparts of the McMillan Formation in the Maysville Area. This unit is prevalent across Kentucky, and is often represented by rubbly, argillaceous, packstones rich in

Vinlandostrophia ponderosa (formerly Platystrophia ponderosa). This represents the typical

Corryville Mbr. lithology across much of the Bluegrass-Maysville regions (Figure 10). The lower Corryville interval has a lower rubbly argillaceous packstone unit, overlain by a series of more compact packstone beds, equivalent to the oncoid interval.

Across Kentucky, the middle Corryville occupies this typical Grant Lake lithofacies of rubbly fossiliferous packstones rich in V. ponderosa, and is marked by the presence of

Rafinesquina nasuta, throughout the middle Corryville interval, across the Cincinnati Arch.

These strata rest sharply above the lower Corryville-equivilent Gilbert Member micritic limestones at Fredericktown KY. (Weir et al. 1984 fig. 26), and this contact is indicative of the diachronous nature of the lower contact of the “Grant Lake lithofacies” which occurs directly above the Calloway Creek-Fairview Formation as part of the Bellevue Member in the Maysville area. This can similarly be observed at this same contact when traced into the Carrollton-

Madison region, where rubbly Platystrophia/Vinlandostrophia-rich packstones (Grant Lake

Lithofacies) sharply overlie phosphatic oncoid-rich grainstones of the lower Corryville oncoid-

Gilbert interval. In downramp Sebree Trough settings, hard rubbly-nodular calcareous mudstones mark the base of this middle Corryville interval, which are subsequently overlain by

“buttery” mudstones containing well preserved trilobites, partially enrolled Flexicalymene interbedded with compact pack to grainstones. This middle Corryville interval is poorly/not presently exposed in the type area of Cincinnati and so must instead be studied in creek localities

North of Cincinnati (Figure 22). Many of these creek localities occurring north of Cincinnati

30 preserve a pelecypod rich bedding plane, with preserved black periostrocum near the base of this interval.

The upper Corryville begins at an approximately 30-40 cm thick very pronounced grainstone bed, which stands out in comparision to the surrounding strata of the Grant Lake

Formation in Fredericktown Kentucky and the surrounding region. This bed is composed of five amalgamated sub-beds and contains rip-up clasts in addition to the fossil gastropods. We have named it the Fredericktown Bed for easy refernce throughout the rest of this paper (Figure 23).

The strata above this distinct, Fredericktown Bed, show an increase in compact, tabular, micritic carbonate beds and interbedded shales. In comparison to the underlying middle Corryville, this upper portion contains more grainstone beds, muddy-micritic carbonate beds, siltstones, calcareous shales, and bryozoans. The same prominent Fredericktown bed marking the base of this upper Corryville divisions can be observed at a CSX railroad cut directly southeast of I-71 near Sulphur and Campbellsburg Kentucky (Figure 10), at Rt. 42 Bedford Kentucky, and on I-

71at the Trimble-Carroll County line. In Maysville Kentucky this interval is marked by an increased number of grainstone beds containing large (bryozoan sheathed) nautoloids. In downramp sections north of Cincinnati, mudstones are typical along with compact pack- grainstone beds. Additionally bryozoan colonies are prevalent in the upper Corryville, and siltstone beds increase stratigraphically upward. South of Maysville the Corryville quickly changes facies to become a thick compact shoaling upward grainstone unit in its upper portions.

Mt. Auburn Member

The Mt. Auburn Member of the McMillan Formation is composed of irregularly bedded nodules of limestones mixed with mainly blue shales at type localities in the Cincinnati area, the

31 lower portions of which are rich in the brachiopod Platystrophia lynx, or currently Platystrophia auburnensis (Nickles 1902; Fenneman 1916). The Mt. Auburn Member is currently the least understood Maysvillian unit within the study interval, and due to the inability to observe this unit in the type locality it subsequently had to be observed at alternante localities. The Mt. Auburn

Member where observed typically shows a lower carbonate portion, a middle mudstone portion, and an upper limestone portion, the member is typically rich in phosphate. At Todd’s

Fork/Second Creek in Morrow Ohio the Mt. Auburn Member overlies the Corryville Member directly East-southeast of the bridge on Roachester-Cozaddale Road beginning at a thick grainstone bed exposed in the low waterfall, overlying siltstone containing calcareous mudstone beds of the upper Corryville Member. The Mt. Auburn here displays a somewhat coarsening upward succession marked by several 3-4 meters of packstone beds rich in Platystrophia/

Vinlandostrophia. This, in turn, is followed by an approximately two meter thick calcareous middle mudstone interval, and an upper approximately three meter thick carbonate interval, containing a thick siltstone bed near its base, and lacking brachiopods indicative of the lower portion. Meanwhile, at the Hamilton Walmart, the Mt. Auburn is a much more phosphatic, nodular limestone mixed with shales (Holland and Patzkowsky 2008). Due to covered intervals within this outcrop only the lower portions of the Mt. Auburn were observable. The Mt. Auburn

Member at the Trimble-Carroll county line at I-71 Kentucky also shows compact phosphatic pack-grainstones of the lower Mt. Auburn, sharply overlying rubbly packstones similar to the

Corryville, Grant Lake lithology (Figure 9). This lower interval is then overlain by a shaly middle portion and an upper phosphatic grainstone. This upper phosphatic carbonate portion also contains a white colored bed with a distinct bivalve rich biofacies (Figure 24). At

Maysville, Kentucky, the Mt. Auburn once again sharply overlies the rubbly packstones mixed

32 with calci-siltstones and pack-grainstones of the Corryville Member in the Grant Lake

Lithofacies, by white, and orange, phosphatic, compact grainstones, despite claims of indifferentiability of Cincinnatian, McMillan Formation units/Members within the Grant Lake

Formation (Figure 8). The lower Mt. Auburn phosphatic grainstones are overlain by a middle mudstone mixed with nodular carbonate portion, and an upper phosphatic grainstone portion, grading into rubbly packstone portion. This upper portion also contains an unusual biofacies, at an approximately 30-40 cm thick grainstone bed containing cyclocystoids, possibly equivalent to the bivalve horizon of Trimble-Carroll county line section, at the phosphatic grainstone-rubbly packstone contact. Leptaena has been found in the upper Mt. Auburn in various localities across the Cincinnati Arch and may signify an intitial incursion of Richmondian Fauna into the basin during the latest Maysvillian Stage (S. Felton, pers. comm.) Within the 25 kilometers between

Maysville and Flemingsburg the Mt. Auburn Member drastically changes facies (Figure 25).

Pack-grainstones of the Mt. Auburn in the Maysville area composed of part of the Grant Lake

Lithofacies drastically change to stromatoporoid bioherms with a lower carbonate biohermal portion, a middle shaly portion, and an upper stromatoporoid portion. These facies are interpreted to be in much shallower water and could be interpreted as somewhat lagoonal-shoal in setting. The presence of stromatoporoid bioherms in this interval may reflect a somewhat warmer water period within the Maysvillian Stage. The presence of large amounts of phosphate occurring within the Mt. Auburn interval may be representative of sediment starvation occurring throughout the interval and resulting in the phosphatic nodular composition of the type deposit.

This large amount of phosphate could also be attributed to increased upwelling occurring during this time coincident with warm water conditions. In fact the phosphate rich carbonates forms

33 somewhat of a second “inner bluegrass” belt rich containing rich fertile soils and dairy farms occupying much of the outcrop belt in Kentucky.

Mt. Auburn overlain by Sunset

Compact carbonates of the Mt. Auburn Member are sharply overlain by shaly mudstones of the Sunset Member of the Arheim Formation. These strata mark the base of the Richmond

Group and were originally named the Warren, or Homotrypa bassleri Beds (Nickles 1902), and were later changed to Arheim due to previous occupancy of the name “Warren” (Bassler 1906).

Bluish shales of the Mt. Auburn Member mixed with compact and nodular limestones are dominantly barren (S. Felton, pers. comm.), contain Leptaena, Orbiculoid brachiopods, and a narrow zone of Retrorsirostra the the top (Caster et al. 1961).

Fourth order depositional cycles

Based upon the series of traceable horizons within the Maysvillian stage, a series of fourth order depositional cycles have been established (Figure 26). A total of 10 fourth order depositional cycles have been found. These cycles all exhibit depositional systems tracts which would be expected of larger depositional cycles, including an initial transgressive portion, and a highstand portion. Some of the cycles show well developed falling stage systems tracts, but some of these falling stage systems tracts are missing by erosion underneath the overlying transgression, or undifferentiable from the high stand systems tract. Low stand systems tracts have not been observed within all of these smaller scale cycles; however, possible LST sediments are present in two of the cycles. Key stratigraphic surfaces such as maximum starvation surfaces are generally present.

Z-bed

Due to the extremely widespread continuous nature of the Z-bed and “two foot shale”, it has previously been considered to represent the base of the Fairview Formation sequence, and represent a low stand systems tract deposit. Thickening in proximal regions may verify the interperof the “two foot shale” and consider it to represent the toe of a lowstand clastic wedge.

Obrution deposits found within the “two foot shale” further justify the interpretation as muds rapidly deposited during the intial part of rising base level. Coincidently, this bed (Z-bed) matches the original definition of Nickles, as representing the basal Mt. Hope, and Maysvillian

Stage; however, this was not the basis of our interpretation. The silty mudstones of the Taylor

Mill submember of the Kope Formation, or equivalent Garrard Siltstone of Kentucky contain siltstone guttercasts, and deformed ball and pillow structures on the Kentucky Bluegrass, and

East of Cincinnati (abandoned I-275 rest-stop, S. Felton, pers. comm). These strata are interpreted to represent a falling stage systems tract deposit due to the nature of siltstone rich siliciclastic deformed strata. The Z-bed and two foot shale are interpreted to represent the low stand systems tract of a depositional sequence independent of the Kope Formation, because of evidence of continued deposition of siliciclastics and a general progradational pattern into the overlying North Bend submember. The Z-bed contains rip up clasts in its base and is interpreted to represent a period of subaqueous sediment starvation and reworking. However, due to subaqueous deposition in a deep sub-tidal environment, this sequence boundary is being established based upon the presence of a correlative conformity. Lowstand systems tracts are poorly preserved within the Cincinnatian, and this represents the most probable LST deposit, observed within the Maysvillian Stage. Although others may be possible, the majority of other fourth order sequences are interpreted to begin with an E-T surface, or joint erosional-

35 transgressive surfaces. This again may be attributed to the deep-subtidal environment in which this sequence boundary formed.

North Bend Submember

The North Bend submember is interpreted to be represent a period of sea-level rise. The basal most contact of the North Bend Submember with the “two foot shale” is interpreted to represent a surface of transgressive ravinement, based upon its sharp contact, and some rip-up clasts appearing at its base. The North Bend Submember is interpreted to represent a transgressive systems tract deposit; the basal contact dividing between the lowstand and trangressive systems tracts, or the point at which retrogradation begins to occur. A sharp change from silty mudstones to carbonates, (pack-grainstones) associated with this lithology lead to the interpretation of a transgressive deposit. A small shaly-more mudstone rich interval within the middle North Bend submember, interval is interpreted to represent the highstand/falling stage portions of a smaller, higher-order (5th-6th order) deposit, superimposed upon this 4th order transgressive systems tract. Additionally, coquinoid brachiopod beds capping the interval, containing Dalmanella in downramp settings and Strophomena in upramp settings, are interpreted to represent the maximum starvation surface of the North Bend-Wesseman submembers interval.

Wesselman Submember

The Wesselman Submember sharply overlies the North Bend Submember; this dominantly mudstone lithology is interpreted to represent high stand and falling stage systems tract deposits. The initial mudstone portion of Wesselman Submember, overlying the brachiopod coquinas of the upper North Bend Submember, is interpreted to represent the high

36 stand systems tract portions of this deposit. No clear maximum flooding surface has been observed within this interval and may be a combined with the maximum starvation surface. A sharp offset in lithofacies exists between the compact pack-grainstones of the North Bend submember, and mudstones interbedded with lime and siltstones of the Wesselman submember.

A distinct faunal difference exists between the North Bend and Wesselman submembers as well, where Dalmanella biofacies of the North Bend Tongue, are succeeded by Flexicalymene bearing strata, showing an additional retrogradational offset to deeper biofacies within this interval.

Kinneya sedimentary structures indicate paleobathymetries within the photic zone, and are interpreted to represent gas bubbles bound by algal mats (A. Seilacher pers, comm). Together, based on lithology, paleontology and sedimentary structures, the Wesselman submember is interpreted to represent water depths/facies analogous to the Fulton submember, and especially the Taylor Mill submember of the Kope Formation. A change from dominantly mudstone mixed with pack to grainstones mixed with mudstone represents initial forced regression occurring during the Wesselman interval. The series of five closely spaced limestone beds, containing rip- up clasts, within the middle of the Wesselman interval are interpreted as small scale (5th-6th order) transgressive deposits in which progradation occurs. This minor transgressive interval imposed on the larger 4th order falling stage systems tract is analogous to shell-coral beds occurring during the Devonian Hamilton Group in New York State (Brett and Baird, 1996). The falling stage systems tract continues through the base of middle carbonate beds and into the mudstone mixed with siltstone bed portion, some of which contain gutter casts. The trace fossil

Diplocraterion corophioides is particularly common in these silts, as it is in the upper Taylor

Mill submember of the Kope, especially at Lawrenceburg, Indiana.

North Bend-Wesselman Cycle/lower Mt. Hope Cycle

Together the Z-bed, “two foot shale”, North Bend Tongue, Wesselman Tongue submember is interpreted to represent one fourth order depositional cycle. Together the different systems tracts within this cycle form an idealized depostional cycle with the following divisions: a sharp, although parallel sequence boundary between silty mudstone falling stage systems tract deposits and widespread compact rip-up clast bearing grainstones; a lowstand systems tract marked by widespread grainstones, and mudstones of the Z-bed and two foot shale; a transgressive ravinement surface occurring at the base of the North Bend submember; a transgressive systems tract deposit occurring during widespread carbonate deposition; a brachiopod shell pavement/coquina representing a maximum starvation surface; sharply overlain by a major facies offset of mudstone deposition of the Wesselman submember, regarded as the highstand systems tract; a series of carbonate beds occurring below siltstone deposits marks the surface of forced regression, and a final silty mudstone interval of the upper Wesselman submember represents the fallings stage systems tract of this fourth order depositional cycle.

This lower Mt. Hope Member cycle varies from other cycles in showing a pronounced lowstand systems tract, absent in virtually all other observed fourth order cycles.

Un-named Submember/upper Mt. Hope Cycle.

Strata of the informally designated Un-named submember together compose the next 4th order depositional cycle overlying the Lower Mt. Hope cycle. Strata of the Upper Mt. Hope

Cycle sharply overlie the siltstone bed rich mudstone deposits of the upper Wesselman

Submember, beginning with rip-up clast containing pack-to-grainstone horizons, marking its base. The basal five grainstone bed interval is interpreted to represent the transgressive systems

38 tract, and the sharp contact on underlying silty mudstone at its base is interpreted to represent the joint sequence boundary and transgressive ravinement surface, or ET surface of this 4th order depositional cycle. Overlying the transgressive carbonate deposits, mudstones interbedded with skeletal limestone beds form a fourth order highstand. The contact between this dominantly carbonate unit is interpreted to represent the maximum starvation-flooding surface of this cycle, however, is not as sharp as that of the lower, North Bend-Wesselman submembers contact.

Mixed mudstones and carbonates of the middle Un-named submember are interpreted to represent the highstand systems tract. The upper portion of the Un-named submember contains mudstones, mixed with siltstones, and carbonates. In the Maysville Kentucky region, this interval contains small, but locally deformed seismite/ball and pillow horizons. This silty- mudstone portion is interpreted to represent the falling stage systems tract of the upper Mt. Hope

4th order depositional cycle. Bryozoan colonies are common in the upper portions of this systems tract, and may reflect decreasing paleobathymetries associated with backstepping.

Strophomena Bed-Hooke Gillespie/ Lower Fairmont Cycle

The rip-up clast bearing, grainstone bed contact marking the Mt. Hope-Fairmont

Members contact is interpreted to represent the base of the next/Lower Fairmont fourth order depositional cycle. The basal rip-up clast bearing grainstones of the Stophomena Bed sharply overlying muddy siltstone, and locally deformed siltstone horizons is interpreted to represent the basal sequence boundary-ET surface of this cycle. This corresponds precisely with the basal

Fairmont Member as originally defined by Nickles (1902). Subsequently, this compact grainstone of the Strophomena Bed is interpreted to represent the transgressive systems tract of the Lower Fairmont Cycle. The upper contact of the Strophomena Bed is a highly sediment starved, rusted, orange colored (from weathered pyrite), brachiopod (Strophomena) shell

39 pavement, overlain by shales. This surface is interpreted to represent the joint maximum starvation-maximum flooding surface of the Lower Fairmont fourth order cycle. This compact shell bed is analogous to the widely traceable shell beds of the Hamilton Group, such as the

Stafford Limestone, or the Hallihan Hill Bed (Ver Straeten 1994; Brett and Baird 1996). The mudstones mixed with skeletal carbonates of the middle Hooke-Gillespie interval are interpreted to represent high stand systems tract portions of this cycle. The Hooke-Gillespie submember is generally a coarsening, silting, upward cycle, the upper portions of which contain thick deformed siltstone horizons with ball and pillow structures, interpreted as seismites, siltstone infilled channels, 50 cm plus reworked hardground blocks, and carbonate hardground surfaces. This upper Hooke-Gillespie interval is interpreted to represent forced regression, during a falling stage systems tract, in which progradation is occurring. This particular deposit of the upper

Hooke-Gillespie sub-member is one of the most intensely developed falling stage deposits within the entire Cincinnatian Series, comparable to the Garrard Siltstones at the top of the Kope

Formation, and represents a major period of sea-level draw down in the Ordovician Katian Stage, in addition to representing a major change in basin dynamics/structure. Faunal boundaries marking the base of the Fairmont Member match the interpretation of Brett and Baird (Pers, comm.) in which faunal incursions/boundaries often occur during falling stage systems tract deposits.

Lawrenceburg-Lower Hill Quarry Submembers/Middle Fairmont Cycle

Following one of the largest falling stage deposits within the Cincinnatian is one of the largest transgressions: the Lawrenceburg submember. A similar scenario has been observed in the Devonian of New York, where following the most intense sea-level lowstands, are the most intense deepenings, i.e. the Tully-Genessee interval (Brett pers, comm.). Sharply overlying

40 deformed siltstone horizons of the Hooke-Gillespie submember, are a series of three compact carbonate beds containing large rip-up clasts. These strata represent the widely traceable basal- most Lawrenceburg interval, the base of which is interpreted to represent a major sequence boundary occurring between the Hooke-Gllespie and Lawrenceburg intervals. In between each of these three rip-up clast bearing horizons are mudstone horizons. This interval is interpreted to represent a low stand to early transgressive systems tract, marked by a series of ravinement/transgressive ravinement surfaces. Overlying these three rip-up clast bearing carbonate beds is a massive limestone buildup, the Lawrenceburg submember, marked by approximately 3 meters of compact pack-grainstone in downramp settings, and approximately .5 to 1 meter in upramp settings. This carbonate buildup is interpreted to represent a major transgressive systems tract, possibly the biggest in the Fairview Formation. A phosphatically stained surface overlain by a small-medium shale may represent a starvation surface within the

Lawrenceburg Member, however, a hardground topped, phosphate stained mega-rippled bed in

Lawrenceburg Indiana is currently regarded as the maximum starvation surface of this cycle.

During the Lawrenceburg interval retrogradation is interpreted to occur, however following it, progradation is interpreted to occur, represented by the series of widely traceable skeletal limestone horizons of the lower Hill Quarry submember interval. Deepening continues to occur into the lower Hill Quarry Bed submember, as shown by a 50cm shale in Maysville, 1m thick mudstone interval in Lawrenceburg: a maximum flooding is believed to occur somewhere within the lower hill quarry beds. Bivalves, gastropods and other mollusks, and orange weathering beds are common within the Hill Quarry Bed interval. The silty mudstones occurring before Hill

Quarry Bed three (The base of the Upper Hill Quarry submember) are interpreted to represent the falling stage systems tract portion of this cycle, but represent quite deep water conditions

41 based upon the presence of the trilobite Ceraurus in Lawrenceburg Indiana, and Riedlin/Mason

Road Kentucky (S. Felton; D. Meyer pers. comm.): Throughout this entire interval sea level is interpreted to have risen. This cycle is very similar in morphology and composition to the Lower

Mt. Hope cycle with a well-developed low stand systems tract, compact carbonate buildup transgressive systems tract, and a mudstone rich highstand systems tract.

Upper Hill Quarry Submember-Miamitown Shale submembers/Upper Fairmont Cycle

The third Hill Quarry Bed at the base of the Upper Hill Quarry submember sharply overlies mudstones rich in scolecodont bearing siltstone beds. This compact very hard, prominent, skeletal grainstone, with a sharp base, and sharp phosphatic top is interpreted to represent the transgressive systems tract portion of Upper Fairmont Cycle. The sharp base of the cycle is interpreted to represent the combined sequence boundary and transgressive ravinement surface, or ET surface, and the top of this bed is interpreted to represent the maximum starvation surface of this cycle. Deepening continues to occur until the fourth Hill Quarry Bed which represents the maximum flooding surface of this cycle. Progradation occurs in the upper Fracta-

Bed interval, which is interpreted to represent the highstand systems tract portions of this cycle.

The seventh Hill Quarry Bed occurring immediately prior to the Miamitown Shale is interpreted to represent the forced regression surface of this cycle, is a compact grainstone, and widely traceable across the Cincinnati arch. Mudstones mixed with carbonates and siltstones of the

Miamitown Shale/submember are interpreted to represent the falling stage systems tract portions of the Upper Fairmont Cycle. This cycle is very similar in morphology and composition to the

Lower Fairmont Cycle, where the transgressive systems tract third Hill Quarry Bed is analogous to Strophomena Bed, and the deformed siltstone horizons of the Hooke-Gillespie submember are equivalent to fossiliferous mudstones of the Miamitown Shale.

In total the Fairview Formation and Miamitown Shale are interpreted to be composed of five fourth order depositional cycles. Independent fourth order sequence stratigraphic interpretation places sequence boundaries at key stratigraphic surfaces matching the basal

Mt.Hope and Fairmont Members contacts, based upon the original definitions of Nickles. All fourth order sequences within the Fairview formation show discrete transgressive, highstand, and falling stage systems tracts. Additionally major transgressive deposits occur during the North

Bend Tongue-Lawrenceburg submembers, major high stands occur during the Un-named tongue-Hill Quarry Beds intervals, and major falling stage systems tracts during the Hooke-

Guillespie-Miamitown intervals.

McMillan Formation Bellevue Member/ Bellevue Member Cycle

The sharp base of the Bellevue Member overlying silty mudstones of the Maimitown

Shale represents a sequence boundary occurring between these two units. A siltstone bed near the base of this interval may be interpreted as a low stand systems tract deposit, however, was not in this instance. Instead, the base of the Bellevue Member is interpreted to represent a combined sequence boundary and transgressive ravinement surface (ET surface). This significant amount of ravinement associated with the base of this interval is recognized by absence of the Miamitown Shale on the eastern limb of the Cincinnati Arch. Retrogradation is interpreted to occur throughout the Bellevue interval marked by brief progradational pulses during minor, highstand systems tracts of smaller cycles, such as the Rafinesquina Shale.

Increased sediment starvation occurs upwards. A maximum flooding surface occurs at the top of the Bellevue Member, with a highstand-falling stage portion occurring at the lowermost

Corryville Member overlying the Bellevue Member.

Corryville Member Cycles

Determining the number of depositional cycles within the Corryville Member has offered one of the more challenging tasks associated with the development of this fourth order sequence stratigraphic framework. Three separate hypothesizes exist for cycle abundance within the

Corryville interval, they are: The entire Corryville Member is consistent of just one fourth order depositional cycle; the Corryville member is composed of two fourth order cycles; and finally the Corryville member contains three fourth order cycles each marked by the lower, middle, and upper units elucidated upon earlier.

Option 1: The Corryville Member consists on a single fourth order depositional cycle

(excluding the small bit of strata assigned to the Highstand/Falling Stage portions of the previously occurring Bellevue Cycle). In this case the three: lower, middle, and upper divisions of the Corrville Member each represent different systems tracts within one fourth order depositional sequence. In this case the lower Corryville, oncoid interval is interpreted to represent the transgressive systems tract of this cycle, marked by carbonate build-ups associated with high energy environments across the Cincinnati Arch. The base of these oncolite rich grainstone beds would be the sequence boundary/ET surface of this cycle. A sharp phosphate stained oncoid rich top to this interval represents maximum starvation surface to this fourth order cycle. The middle rubbly pack-stone interval would subsequently represent the highstand systems tract portion of this cycle. Beginning with the rip-up clast bearing Fredericktown Bed, marking the base of the upper Corryville subdivision, and continuing stratigraphically upward until the base of the Mt. Auburn is representative of the falling stage systems tract of the one fourth order cycle option, represented by shaly siltstone, and thin tabular silty limestones alternating with shales. In this case the compact bed marking the base of this systems tract is

44 interpreted as the surface of forced regression of the Corryville 4th order cycle. In this option like all other Maysvillian cycles the Corryville Member would contain a distinct trangressive, high stand, and falling stage systems tracts. However, we also understand that these interpretations may be bordering on the third order cycle scale.

Option 2: The Corryville Member is composed of two fourth order depositional cycles.

In this option the lower Corryville oncoid interval makes up the transgressive portion of one 4th order cycle, the overlying Grant Lake fossiliferous packstone represents a minor highstand deposit. A minor sediment starved phosphatic carbonate bed, thinner and formed in deeper water, at the stratigraphic height of approximately 9 meters at the I-71 roadcut on the Trimble-

Carroll Co. line and 17 meters at Fredericktown Kentucky, represent the sequence boundary between the lower and upper Corryville fourth order cycles. In this case, this bed would represent the sequence boundary/ET surface, transgressive systems tract, and maximum starvation surface of the upper cycle. Overlying muddy argillaceous packstones, represent the high stand systems tract of this cycle, and beginning with the rip-up clast bearing bed until the base of the Mt. Auburn is the falling stage systems tract, with the rip-up clast bearing

Fredericktown bed represents the forced regression surface. This option has most consistently matched MS data in which 8 MS cyles have been measured, so is most reflected of measured values. In deeper water sections North of Cincinnati in Sebree Trough/high accommodation areas, 6-8 major calcareous grainstone cycles occur, as exhibited at Second Creek in Morrow,

Ohio and interpreted as 5th order (100,000 year) cycles. In these downramp sections (Keehner

Park, Westchester, Ohio and O’Bannon Creek, Loveland, Ohio) a compact calcareous mudstone overlies the four grainstone beds, probably equivalent to the oncolite beds. This interval is rich in Rafinequina, and could be described as a deep-water progradational tongue of the Grant Lake

45 lithofacies. Capped with a compact, waterfall-forming limestone bed, this interval is interpreted to represent the transgressive systems tract in basinward areas. Likewise the falling stage systems tract terminating this interval is more pronounced with compact carbonates mixed with soft fossiliferous mudstones (“butter shale”), tabular siltstone beds, abundant bryozoan colonies at Second Creek and elsewhere, resembling a general shallowing upward succession. Based upon consilience of MS and lithologic data, Option 2, consistent of two fourth order cycles, is the currently supported interpretation.

Option 3: The Corryville Member represents an amalgamation of three fourth order depositional cycles. This option is based upon the readily traceable typical Corryville, lower, middle, and upper divisions, in which each of these represents an individual fourth order depositional cycles. The lower Corryville oncoid interval consists of four grainstone beds in proximal settings represents and the first fourth order sequence of this interpretation. The middle

Corryville division consisting of the Grant Lake Lithofacies across the Kentucky Bluegrass region, containing the index fossil Rafinequina nasuta represents the middle fourth order cycle of this subdivision. Strata beginning at base of the Fredericktown Bed represent the upper most fourth order depositional cycle. This upper cycle contains a well-developed sequence boundary- erosional transgressive surface at the basal Fredericktown Bed contact. The Fredericktown Bed itself represents the transgressive systems tract of this cycle, and its sharp compact top, the maximum starvation surface. Shaly strata overlying it in the Fredericktown area represent the highstand systems tract, and mudstones mixed with silty laminar-lenticular beds represent the falling stage systems tract. Bryozoans are common in this interval and are also found in more basinal sections.

Corrville Sequence Stratigraphic Discussion:

We currently interpret the Corryville Member to be composed of two depositional cycles, however, we realize the potential short comings of our interpretation. For a more fundamental understanding of the Corryville Member it is critical to gain increased knowledge of this unit in sections north of Cincinnati, and in the sub-surface entering the Sebree trough. Further, an absence or destruction of Cincinnatian type localities of this interval, rapid weathering of mudstone rich outcrops in the Cincinnati vicinity, in combination with sparse outcrops of this

Member limit the ability to completely resolve this problem. We have gained a large amount of knowledge of the Corryville equivalent strata of the Grant Lake Formation and the Corryville in creek localities adjacent to Cincinnati, and within these two seemingly temporally disparate areas found a series of units, lower, middle, and upper coincident with both regions. An ability to more closely link the framework of these regions would provide increased confidence in our interpretation. Packstones common in the Grant Lake Lithofacies change laterally into grainstones mixed with thick mudstone deposits, providing a degree of ambiguity when tracing individual beds/horizons.

Magnetic susceptibility data of the Corryville Member strata in Kentucky demonstrate 8

MS cycles within this interval, favoring the interpretation of two fourth order depositional cycles, if each of those MS cycles is representative of a 100,000 year eccentricity cycles.

However, due to some of these MS half-cycles based upon single data points, and the poor stratigraphic sampling interval of this study, it has not been possible to provide increased temporal resolution to this member. Yet, heretofore no additional data was present, and frankly, is the best/only we’ve got. Additional biases exist in interpreting these as eccentricity cycles, and the possibility of their being obliquity or precession would alter our crude at best attempts of

47 confining a geochronologic framework to the Corryville Member. Yet, our cycle interpretations do match the definitions of fourth order cycles (Brett et al. 2011) and approximate cycle durations outlined in the opening chapter. If interpreting the Corryville Member to represent three independent fourth order depositional cycles as we originally interpreted in the field

(option three), the possibility exists that some fourth order sequences, such as the upper

Corryville sequence of option three, could in fact be representative of instead fifth order (100k) cycles. In this case the rip-up clast bearing bed would be equivalent to the middle Wesselman, or middle Miamitown limestone bed representing a minor 100,000 years transgressive deposit, and the forced regression surface of the falling stage systems tract of the fourth order cycle. In thick sections of the Corryville such as the Sebree Trough this may leave fourth order cycles expanded, while condensed in upramp areas, where carbonate beds are not separated by thick shales due to increased accommodation in downramp areas. This same issue arises in option one, in which the Corryville, single fourth order cycle, is highly stratigraphically expanded in downramp, Sebree Trough sections, while still somewhat stratigraphically expanded relative to other fourth order cycles in an upramp position, but to a lesser degree. In all models the widely traceable Fredericktown Bed represents the base of falling stage systems tract deposits: This bed

(rip-up clast bearing grainstone), interpreted to represent the forced regression surface and a smaller transgressive systems tract cycle is exactly analogous to the Strophomena Bed marking the Mt. Hope-Fairmont Member boundary of the Fairview Formation on some scale. In which case, rip-up clast bearing grainstone bed with sharp top and base overlain by shale, represent the

ET surface/sequence boundary, the transgressive deposit, and the maximum starvation surface of its own fourth order sequence. It is sharply overlain by highstand shales, and falling stage silty mudstones. And likewise on a broader order scale this Strophomena Bed, and its upper

Corryville counterpart represent the forced regression surface, and falling stage systems tract of a larger, high order, low frequency cycle, and agree with all three cycle abundance options.

Mt. Auburn: lower Mt. Auburn Cycle

Two 4th order cycles are interpreted to occur in the Mt. Auburn Member. Compact phosphatic grainstones overlying silty mudstones of the upper Corryville Mbr mark the base of this Member. The lower Mt. Auburn fourth order cycle begins at this contact, and is interpreted to represent the combined sequence boundary and ET surface of this cycle. The majority of this cycle marked by phosphatic carbonates is representative of transgressive systems tract deposits.

A sharp contact between these phosphatic carbonates and overlying shaly-silty mudstones of the middle Mt. Auburn and the lower carbonates marking the maximum starvation-maximum flooding surface of the lower Mt. Auburn fourth order cycle. Theses mudstone rich strata represent the highstand falling stage portion of this cycle.

Mt. Auburn: upper Mt. Auburn Cycle

Phosphatic carbonate grainstones overlying the middle shaly interval mark the base of the upper Mt. Auburn fourth order cycle. This surface is interpreted represent the sequence boundary-erosion trangsressive surface of this sequence. Trangression is interpreted to occur throughout the majority of this interval. The upper cyclocystoid bed in this interval may mark the maximum flooding surface at its base and forced regression surface at its top. Strata occurring above this are more rubbly nodular, and may represent the falling stage systems tract of this cycle. The sharp base of the Sunset Member of the Arnheim Formation terminates this interval and is marked by a regional unconformity and marking the base of the Richmond Grp.

(Holland 1993).

4th order sequence stratigraphic framework

Despite claims of wide variations in facies occurring across the Cincinnati Arch; claims of stratigraphic indifferentiability of the Maysvillian Stage, and a myriad of stratigraphic nomenclature occurring across the states of Ohio, Indiana and Kentucky (Figure 2), the current study has attempted to bridge together coeval strata of these seemingly disparate regions using a fourth order sequence stratigraphic framework (Figure 26). A series of fourth order cycles have been found to exist across subtle changes in depositional facies on the Cincinnati Arch making correlation between strata possible between the North, Southwest, and Eastern portions of the

Arch. In an attempt to confine to original stratigraphic names and definitions the current study has chosen to utilize the widely used and recognized stratigraphic nomenclature of the type

Cincinnatian as opposed to local, and or lithostratigraphic/facies names (i.e. Excello, Station

Hollow, Tanners Creek, Brookville, Dillsboro, etc.: Figure 2), causing this previous notion of regionally segregated time equivalent units, while embracing names with increased stratigraphic resolution and trying to limit the use of newly manufactured names. As shown by the Gilbert

Member of Ashlock Formation-Grant Lake Formation contact not all lithostratigraphic-facies boundaries coincide stratigraphically with the classic Cincinnatian equivalent nomenclatural and sequence boundaries, and demonstrate the diachronous nature of some of these lithostratigraphic terms defined on the basis of facies. Likewise, in order to reduce confusion and later reinterpretation of fourth order sequences, no numbering, or alphabetical scheme will be used for the naming of cycles, in order to avoid confusion in mis-lettered-numbered cycles. Instead cycles have been named based upon their Member, and position within Member, i.e. lower

Corryville cycle. A lowercase character prior to the Member is used to denote the non-

50 formalized divisions of lower, middle, and upper used outside the context of this paper within established Members, and their established definitions.

A total of ten ± one fourth order depositional sequences have been identified concurrent with the Maysvillian Stage (Figure 26). Five of these cycles have been identified in the Fairview

Formation-Miamitown Shale interval, these include from oldest to youngest the: lower Mt. Hope

Member fourth order cycle, consistent of the Z-bed, North Bend and Wesselman

Tongues/submembers; the upper Mt. Hope fourth order cycle, consistent of the Un-named submember; the lower Fairmont Member fourth order cycle, composed of the Strophomena Bed and Hooke-Gillespie submember; the middle Fairmont fourth order cycle, composed of the

Lawrenceburg submember and lower Hill Quarry Beds; and the upper Fairmont-Maimitown fourth order cycle, composed of the Upper Hill Quarry submember (Hill Quarry Bed Three and the Fracta Beds) and the Miamitown Shale/ submember. The McMillan Formation and coeval

Grant Lake Formation in Maysville Kentucky are similarly composed of five fourth order cycles.

The Bellevue Member consists of one fourth order cycle, the Bellevue Member fourth order cycle. Strata of the Corryville Member is currently grouped into two fourth order cycles: the lower Corryville fourth order cycle composed of the oncoid or time equivalent interval, and the upper Corryville fourth order cycle, composed of the middle and upper portions of the Corryville

Member. Likewise the Mt. Auburn Member is divided into two fourth order cycles: the lower

Mt. Auburn Mbr. cycle composed of the lower Mt. Auburn carbonates and middle Mt. Auburn shales, and the upper Mt. Auburn cycle composed of the upper carbonates of the Mt. Auburn

Member.

These aforementioned cycles have provided the basis for tying together stratigraphic sections on the Cincinnati Arch using this fine scale sequence stratigraphic framework. The

51 ability to trace time-correlative surfaces across the Tri-State region additionally provides the framework necessary for future high resolution paleontological, paleoecologic, paleoclimatologic, and sedimentation studies on the Cincinnati Arch. Widespread stratigraphic discontinuities, truncations, and facies variations have also been discovered and observed based upon the foundation of this framework. Often smaller order cycles have composed the different depositional systems tracts of larger sequence stratigraphic cycles; it has been noted that the majority of fourth order cycles in the Maysvillian Stage show systems tracts which would be expected to occur in larger cycles. The ability to trace these depositional cycles across the

Cincinnati Arch has allowed the evaluation/re-evaluation of larger, high order, low frequency cycles in place during the Late Ordovician Katian Stage across the Cincinnati Arch allowing a greater understanding to basin development, and tectonic vs. eustatic changes occurring in the

Taconic Foreland Basin.

Discussion of Cycle propagation and Development

Widely laterally continuous fourth order cycles deposited across the Cincinnati Arch are attributed to eustatic processes for the mechanism for cycle development. Fourth order cycles are representative of ~405 k eccentricity cycles (Brett et al. 2011) and formed as a result of a non-tectonic origin: orbital forcing. Smaller scale 5th and 6th order cycles composing these larger fourth order cycles are represented by “meter-scale cycles” occurring within the interval, and are attributed to obliquity and precessional cycles respectively. These findings argue for the presence of small scale cyclicity within the Maysvillian Stage. When individual horizons have been traced from deep to shallow water settings, a distinct suite of changing sedimentary structures have indicated qualitative evidence of sea-level variability occurring within these cycles; allowing us to refine our modes of cycle genesis. This contradicts the notion that differences in

52 storm intensity in the absence of sea-level change caused cyclicity (Holland et al. 1997; Webber

2002; Holland 2008), and instead identifies changes in sea-level associated with small scale cycles as the principal cycle generator. Wide recognition and traceability of fourth order depositional cycles identify these cycles as the principal cycles within a sequence stratigraphic hierarchy and offer the greatest opportunity for observation in the field (Brett pers comm.): fourth order cycles are not an artifact composed of the stacking patterns of other cycles, requiring a somewhat eye-squinting/smoothing to understand their nature and development, as may be the case in 3rd order depositional cycles. In other words, fourth order cycles are “real” cycles, that are probably of eustatic/Milankovitch origin, providing a high-resolution geochronology, and offer the key building blocks for the development of larger-high order-low frequency cycles, and additionally may compose the various systems tracts of these broader cycles.

Conclusions

A set of regional Maysvillian strata that were previously viewed as laterally disjunct across the study area (Figure 2), for which a multitude of names exist, have now been adjoined based on a series of traceable horizons, and a fourth order sequence stratigraphic framework of ten cycles has been established for the Maysvillian Stage (Figure 26), driven by Milankovitch- related eustascy. Many of the key sequence boundaries occurring within this fourth order sequence stratigraphic framework fortuitously coincide with originally defined boundaries of

Cincinnatian strata by earlier Cincnnatian workers (such as the Mt. Hope and Fairmont Member contacts), as these early workers certainly noticed major facies discontinuities. Changes in sea- level recorded by sedimentary structures offer indisputable evidence of sea level variability occurring during small scale depositional cycles within the Late Ordovician, (Katian)

Cincinnatian Stage. Based upon this series of laterally continuous fourth order cycles the notion

53 of a mosaic of local facies has been eliminated, restoring the Maysvillian Stage of the

Cincinnatian Series to a “layer-cake” framework.

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Chapter 3

Regional Correlation of the Late Ordovician Cincinnatian, Maysvillian Stage

Sequences using Magnetic Susceptibility

Thomas Schramm, Carlton Brett, Benjamin Dattilo, Brooks Ellwood

Keywords: Late Ordovician, Cicninnatian, Maysvillian, Magnetic Susceptibility

Abstract:

Magnetic Susceptibility (MS) provides an excellent tool for regional and global correlation of strata, and is often reserved for studies at the Global Boundary Stratotype Section and Point (GSSP), or in stratigraphic sections with biostratigraphic or isotopic control capable of global correlation. Although the current study does not take place at a Global Stratotype, it does however, take place at North America Stage type locality for the Maysvillian Stage, and the surrounding type locality of the Late Ordovician, Katian Global Stage, Cincinnatian Series: the

Cincinnati region. Based upon the creation of a MS dataset along with intense field reconnaissance, regional correlation and differentiation of the Maysvillian Stage has been possible in shallow marine strata plagued with a broad stratigraphic nomenclature and wide changes in facies. Additionally, strata of the Cincinnatian are well known for high frequency, low-order cycles, or small scale, limestone-shale cycles; the current study delineates eustacy as a mechanism for MS and litho-cyclic variations. This investigation of the Maysvillian Stage, while preliminary, is a critical step toward understanding the relationships between MS, climate, and sea level variability during the Late Ordovician Katian Stage.

Specific Aims

Small-scale cycles preserved in the rock record are thought to relate to cyclicity of global climate, which will affect global sea-level, local water depth, and, therefore the nature of sedimentary deposition. Strata of the Cincinnatian Series have been widely recognized for preserving small scale alternating limestone-shale cycles, and along with this an array of potential mechanisms have been proposed to explain their occurrence.

The specific goals of this project are: a) to further refine the Maysvillian stratigraphic framework using sequence-stratigraphic methods to establish a series of traceable horizons and packages of sediment; b) to identify different scales of sedimentary cyclicity within this interval; and c) to test for correlations between patterns of sea level change, Magnetic Susceptibility (MS) and Milankovitch cyclicity. The present study has produced detailed MS curves for reference sections of these strata as a test of periodic cyclicity and as a correlation tool. Study of these small scale cycles could potentially identify a hierarchical series of Milankovitch scale climatic changes and lead to a refinement of the relative sea-level curve and the time-scale.

Background: MS, Milankovitch Cyclicity, and Cincinnatian

Magnetic Susceptibility (MS) is the degree of induced magnetism of a material in response to an imposed magnetic field (Ellwood et. al 1999), and can be used to test the degree of magnetism in rocks or sediments, which is linked to the deposition of detrital, terrestrial components entering the marine system and eolian iron driven by variations in weathering, climate, and erosion. MS variations in vertical stratigraphic successions may reveal small-scale cycles not recognizable in outcrop and have been used successfully as a tool for making worldwide correlations of strata (Crick et. al 1997). In the Cincinnati region MS has also been

62 used successfully in the Late Ordovician Kope Fm., demonstrating fluctuations associated with different small-scale cycles (Ellwood et. al. 2007, 2011 submitted). To date, however, no other studies of MS of the Maysvillian Stage have been conducted, and this represents the first of study of its kind on the type Maysvillian. Milankovitch cyclicity consists of a series of periodic changes in the earth’s eccentricity (orbital shape), obiliquity (axial tilt), and precession (axial wobble). These perturbations have predictable effects on global climate that may be recorded in multiple orders of sedimentary cycles. If these cycles can be identified in ancient sediments they may provide both a geological metronome for quantifying rates of processes and a record of climatic changes (Bai 1995). Through the use of MS, small scale oscillations measured in a vertical stratigraphic succession can potentially be used to observe nested hierarchical cycles. In the present paper we use a correlated framework to examine the pattern of MS in different areas, proximal to distal, and use the patterns of MS to aid in sequence interpretation.

Low-field MS measurements indicate the strength of a materials transient magnetism when it is in the presence of an external magnetic field, and the material becomes “susceptible” to magnetization (Ellwood et al., 2000). This transient, or susceptible magnetism is much different than remnant magnetism, which relies on the intrinsic magnetism of a material, and these two measurements can be very different for the same samples (Ellwood et al. 2006). MS in marine strata/settings is dominantly controlled by detrital iron-containing paramagnetic and ferromagnetic grains, composed of clays, and eolian grains. Diamagnetic materials such as calcite and quartz are the dominant mineral components of marine sediments, but due to their incredibly low magnetic susceptibility values (diamagnetic, exhibiting a negative MS) they are not the principal MS drivers (Ellwood et al., 2000). This small percentage of detrital and eolian components controlling susceptibility values is used as an independent proxy of weathering and

63 climate. Single beds traced over long distances have demonstrated non-varying MS values and provide a powerful tool for correlation (Ellwood et al. 1999). Used in a vertical sucession this allows an independent dataset to adjust and evaluate stratigraphic position of sequences to improve correlation, and can be used to establish MS zones to correlate stratigraphic sections with high precision, even when biostratgraphic enigmas or small unconformities are known to occur (Ellwood 2007). Additionally, the use of abiotic methods in conjunction with conventional biostratigraphy is being stressed by the ICS for boundary correlation.

Cincinnatian Series:

Shallow marine fossiliferous strata of the Cincinnatian Series have long been recognized for preserving cyclic limestone shale oscillations observable in outcrop (Tobin 1982; Jennette and Pryor 1993; Holland et al. 2000; Brett et. al 2008; Dattilo et. al 2008; etc.). The strata of the lower Cincinnatian are composed of the Edenian Stage, Kope Fm., and the Maysvillian Stage,

Fairview Fm., Miamitown Shale, and Bellevue, Corryville, and Mt. Auburn Mbrs. of the

McMillan Fm. in Ohio, or coeval Grant Lake Formation in Kentucky (Peck 1966). The Kope-

Fairview-Bellevue succession has long been described as a broad, shallowing upward cycle or succession (Anstey and Fowler 1969; Tobin 1982; Weir et. al 1984; Holland 1993; Jennette and

Pryor 1993, etc.) Workers have provided a series of interpretations on possible mechanisms for cycle propagation, dominantly revolving around climatic cycles as a driver for sedimentation, which became possible once the traceable lateral extent of these deposits was realized (Jennette and Pryor 1993, Brett and Algeo 2001). Previous to this limestone and shale beds were perceived to be untraceable from outcrop to outcrop and the result of local storm effects superimposed upon subtle variations in basin topography (Weiss et al. 1965; Tobin and Pryor 1981). Tobin emphasized storms as a creator of cyclic deposits occurring in a hierarchical arrangement, and

64 estimated cycle duration based on the age length of the study interval divided by the number of cycles (Tobin 1982). Jennette and Pryor later successfully traced a series of depositional cycles of 3 different orders in the upper Kope and lower Fairview Fms. in a series of 15 outcrops across the Cincinnati area. They proposed the alternating limestone-shale cycles of the Cincinnati arch were driven by flucations in glacio-eustatic sea-level driven by Milankovitch-Orbital perturbations (Jennette and Pryor 1993).

In recent years a stratigraphic renaissance has occurred on the Cincinnati Arch mostly owing to recognition of the wide-spread lateral traceability of individual beds and cycles in the

Edenian Stage Kope Fm. (Brett and Algeo 2001; Brett et al. 2007), and has led to a wide variety of paleoecological work and gradient type analyses in this interval (Holland et al., 2001; Miller et al., 2001; Holland and Patzkowsky, 2007; etc.). Meanwhile, the debate of the mechanism for cycle generation in the Cincinnatian is still ongoing. Holland attributes climatically driven storm cycles as the mechanism for meter scale cycles (Holland et al., 1997; Holland 2008).

Alternatively by testing the possibility of storm winnowing as a mechanism for sedimentation on the Cincinnati arch, a new model for cyclic deposition has been proposed: the Episodic

Starvation Model (Brett et al., 2008; Dattilo et al. 2008; Dattilo et al. submitted 2011) invoking eustasy as a mechanism for sediment starvation, and small scale cycle generation. A non- eustatic mechanism had previously been suggested based on the use of quantitative, DCA analysis of fossil-bearing assemblages throught the shale and limestone-rich portions of these cycles (Webber 2002). The analysis recognized no consistent differences in the biofacies preserved in the shale and limestone rich portions of the cycles, calling into question whether they represented different water depths (Webber 2002). MS studies using composite sections of the Kope formation provide strong evidence for cycle correlation and have been used to quantify

65 visual cycles as Milankovitch band orbital perturbations (Ellwood et al., 2007; Ellwood et al.,

2011 submitted).

Expanding upward and outwards from the interval studied in Jennette and Pryor (1993), and Ellwood et al. (2007, 2011); the current study utilized MS in an attempt to recognize cyclic variations in the Maysvillian Stage. Strata of the Maysvillian Stage are typically shallower than their older Edenian Stage counterparts, and in a vertical section distally deposited muds typical of the Kope Fm. may be absent, or decrease upwards, as in the shallower cycles like the

Bellevue. Strata of the Maysvillian stage have in the past been considered a local mosaic of facies that are not laterally continous or differentiable, and containing little to no small scale cyclicity (Cuffey 1998, Ford 1967). In conjunction with a detailed field study, the current study has attempted to correlate different time equivalent units across depositional facies using the MS method as an independent proxy and possibly to recognize small scale cycles not observable in outcrop. Strata of the Maysvillian Stage are composed of the Fairview Formation, Miamitown

Shale, Bellevue, Corryville, and Mt. Auburn Mbrs. of the McMillan Formation near Cincinnati

Ohio, where these units were originally named. At the Maysvillian Stage type locality in

Maysville Kentucky however, the McMillan Formation strata are undifferentiated and grouped into the Grant Lake Formation of Kentucky (Lithostratigraphically Defined) (Peck 1966).

Across the Cincinnati Arch an abundance of redundant and/or inconsistently applied stratigraphic nomenclature poise potential problems for stratigraphic correlation.

One potential problem is the lateral loss of the Miamitown Shale interval on the Eastern

Limb of the Cincinnati Arch. Near its type locality in Miamitown, Ohio (Fig. 3 Locality 5) the

Miamitown Shale is an approximately 4 meter thick shale, with a lower shaly interval, a middle limestone interval, and an upper, shaly siltstone interval containing current aligned gutter casts.

The unit thins to approximately 2 meters thick in Cincinnati, and at nearby Riedlin Road

(Northern Kentucky, Fig. 3 Locality 6) the unit is extremely thin (and the upper portions of the

Miamitown Shale may be missing). In Maysville KY. it is very difficult to differentiate the basal

Bellevue Limestone from the underlying Fairview Fm. By studying magnetic susceptibility of the interval one goal of the current study is to establish whether the Miamitown Shale is absent in the Maysville KY. region, or if the Miamitown Shale time equivalent (and upper Fairview) has changed facies, and instead, appears to exhibit an identical, or similar facies to the Bellevue

Mbr., in a Waltherian sense/manner. The current hypothesis is that an unconformity exists at the base of the Bellevue Mbr. (Grant Lake Fm.), and that the Miamitown Shale and upper Fairview

Fm. are removed at this unconformity.

Methods

Outcrops of the Cincinnatian series are very prevalent throughout the study region, but weathering of mudstone in these strata causes them to slump and become overgrown within a few years of creation. Outcrops were chosen for this study based upon exceptional preservation of strata of the Maysvillian Stage, in large contiguous sections containing much of this interval.

Four particularly good outcrops were sampled and measured at cm resolution, while many other, less complete sections were also studied. The four outcrops measured and sampled from east to west along the Cincinnati Arch were: 1) Rt. 11 in Maysville, Kentucky; 2) Rt. 48 Lawrenceburg,

Indiana; 3) I-71 at the Carroll-Trimble County Line, Kentucky (near Carrollton, and Bedford,

Kentucky); and 4) Rt. 150 in Fredericktown, Kentucky (about 13 km southwest of Bardstown,

Kentucky) (Figure 3). These outcrops were measured at centimeter scale resolution, and samples were taken at a regularly spaced, 30 cm interval; approximately 650 samples were taken in total.

Correlation of the lithologic units at each outcrop has been achieved by tracing individual marker

67 beds, faunal epiboles, and depositional cycles from small to large scale in order to provide an independently correlated framework for comparison with MS vatiations.

Outcrop Descriptions

1.) Outcrops along Rt. 11 in Maysville Kentucky expose a composite section of the entire

Maysvillian Stage. Rt. 11 runs approximately North-South, and dips downhill to the north, toward the Ohio River (Fig. 3 Locality 1; see figure 27 and 28 for MS graphs; Appendix 1: Table

1 and 2). Strata of the Edenian Stage Kope Fm. are exposed near the bottom of the hill, or the northern end of the road. An outcrop of the upper Kope Fm. opposite Taylor Mill Road, or on the West Side of Rt. 11, exposes strata of the Grandview, Grand Avenue, and lower Taylor Mill submembers of the Kope Fm. The outcrop directly south of Taylor Mill Road (on the east side of Rt. 11), exposes the upper Taylor Mill submember (not in its type locality) of the Kope Fm. and its contact with the basal Fairview Fm. The North Bend and Wesselman Tongues of the

Fairview Fm. exposed here, are approximately 7 meters thick. Following an approximately 120 m wide grassy patch the remaining approximately 21 meters of the Fairview Fm. and the contact with the overlying Bellevue Mbr. are exposed at the next outcrop to the south (also on the east side of Rt.11). On the west side and farther south along the road, moving stratigraphically upward, the Fairview-Bellevue contact is present, along with the entire Bellevue and its upper contact with the Corryville. Moving back to the east side of the road the Corryville Mbr. is exposed, and high up on the outcrop is the base of the Mt. Auburn Mbr, also visible on its southern end. Parallel to this on the west side of Rt. 11 is another outcrop of the middle and upper Corryville. There is a grassy gap crossing a driveway on the west side of Rt. 11 in between Corryville-Mt. Auburn contact the next outcrop of the lower Mt. Auburn., and a final grassy gap, before the final outcrop on the southwest end of Rt. 11 before reaching the AA

68 highway. This final outcrop preserves the upper most Mt. Auburn Mbr. Strata of the basal

Richmond Grp. can be found a few meters stratigraphically higher, directly to the West, at the first outcrop exposed on the north side of the AA highway. Together the 7 outcrops of the

Maysvillian stage create a composite section of the entire Maysvillian Stage in its type locality and have allowed for detailed sampling to occur throughout this stratigraphic interval.

2.) Newly cut exposures along Rt. 48 in Lawrenceburg preserve continuous exposures of the upper Kope Fm. through Bellevue Mbr. interval (Fig. 3 Locality 2; see figure 29 for MS graph; Appendix 1: Table 3). Strata of the middle to upper Kope Fm. including the Grandview,

Grand Avenue, and Taylor Mill Submembers are exposed near the base, or southern end of the

Hill. Within the Fairview Fm. faunal divisions between the Mt. Hope and Fairmont Mbrs. were recognized. Additionally the North Bend, and Wesselman Toungues of the lower Fairview Fm.

(Ford 1967) and Hill Quarry Bed, “Fracta” interval of the upper Fairview were recognized. This section has been paramount to the development of a sequence stratigraphic model throughout the

Fairview Fm. on the 3rd and 4th order scale, as it represents a distal stratigraphic section on the edge of the Seebree trough (Kolata et al., 2001). Due in part to ample accommodation and distal sediment starvation this section is interpreted to represent idealized Fairview Fm. deposition in a mixed carbonate-clastic dominated environment. Samples were taken on the east side of Rt. 48 beginning in the Taylor Mill Sub Mbr. of the Kope Fm. and extending upwards into the continuous exposures of the Fairview Fm., Miamitown Shale, and Bellevue Mbr through approximately 47 meters of strata. Adjacent exposures on the west side of Rt. 48 duplicate this sequence but were not examined.

3.) Cuts along the northern side of I-71 at the Trimble-Carroll County line near

Carrollton and Bedford Kentucky preserve exposures of the mid-upper Maysvillian Stage (Fig. 3

Locality 3; see figure 30 for MS graph; Appendix 1: Table 4). This series of two outcrops exposes the uppermost Miamitown Shale, Bellevue, Corryville, and Mt. Auburn. The Fairview

Fm. is visible in a nearby railroad cut/tunnel operated by CSX; however, due to steep slope and lack of permission, the Fairview Fm. was not sampled here. The lowest strata at the I-71 cut is the uppermost green Miamitown Shale exposed in the ditch/culvert. The contact between the green Miamitown Shale and the overlying cross-bedded calcarenite Bellevue Mbr. is exposed near the base of the outcrop. The sharp contact between the Bellevue cross-bedded limestones and the shaly Corryville Mbr. is easily distinguishable and interpreted to represent a Maximum

Starvation Surface. The lower Corryville Mbr. has a series of four oncoid rich beds and the middle and upper Corryville here is typified by shale to argillaceous rubbly packstone mixed with occasional grainstone and abundant Platystrophia. The lower Corryville Mbr. is interpreted to be deposited in a shallow marine environment perhaps equivalent to what may be called a

“Shoal” like facies. The Corryville Mbr. is sharply overlain by phoshatic carbonates of the Mt.

Auburn at the lower, eastern outcrop, and near road level at the upper western outcrop, the two of which are divided by a small drainage. Approximately 10 meters of the Mt. Auburn is exposed at the upper outcrop with a carbonate rich lower portion, a shaly middle portion, and an upper phosphatic carbonate portion. This section along with Wolf Run Creek in nearby Manville

Indiana, and Rt. 42 in Bedford Kentucky, offer excellent Maysvillian exposures in the Madision

In-Carrolton Ky, area.

4) Rt 150 in Fredericktown Kentucky located about 13 km southwest of Bardstown,

Kentucky (Fig. 3 locality 4; see Figure 32 for MS graph; Appendix 1: Figure 5) exposes Late

Ordovician Maysvillian and Richmond Grp. Strata. Representing a proximal section, this road cut has been studied by Weir et. al (1984), Noger (1986), and Holland (1993). The section

70 includes equivalents of the upper Fairview, Miamitown, Bellevue, Corryville, Mt. Auburn and

Sunset Mbr. of the Arnheim Fm., or in the nomenclature of Noger 1986 the Tate Mbr. of the

Ashlock Fm. (Upper Fairview and Miamitown Shale), Gilbert Mbr. of the Aslock Fm. (Bellevue

Mbr. and lower Corryville Mbr.), Grant Lake Fm. (Corryville Mbr.), Terril Member of the

Ashlock Fm. (Mt. Auburn), and the Reba Mbr. of the Ashlock Fm. (Sunset Mbr. of the Arnheim

Fm.). The section continues upward into the Richmond Grp. and into the basal Silurian (Noger

1986) units include the Rowland Mbr. of the Drakes Fm., Bardstown Mbr. of the Bullfork Fm.,

Saluda Member of the Drakes Fm., and the Silurian Brassfield Dolomite. This section is represents the most shallow water environment sampled, and may be representative of a peritial environment oscillating from subaerially exposed sabkha like environments, to peritdal, lagoonal argillaceous calci-micrites. Despite deposition in very shallow water this section shows rather low terrestrial siliceous sediment input, perhaps due to the large distance between the Taconic

Foreland Basin and these midcontinent peritidal settings.

Un-weathered samples were broken into pebble-sized pieces and weighed to approximately 10 g. Samples were then measured using the Magnetic Suseptibility Bridge at

Louisiana State University under the direction of Professor Brooks Ellwood, using the procedure outlined in Ellwood et al. (1999). Composite curves of measured MS in a vertical profile were plotted. These curves were then smoothed using splines provided by JMP an SAS statistical software package. Barlogs have been constructed of the smoothed MS profiles marking the maximum rate of change per cycle. Each white-black couplet on a barlog is interpreted to represent approximately 100,000 years of geologic time (See Miamitown Shale Fredericktown section for varying interpretation).

Correlation and Interpretation using Magnetic Susceptibility

Using MS Stratigraphy it is possible to recognize the presence of widespread, suspected unconformities not recognizable in outcrop, and confirm the presence of certain unconformites, in addition to MS anomalies which can aid in correlation (Crick et. al 1997; Ellwood et. al 1999).

Although no MS anomalies were detected in this study, several possible cryptic unconformities detectable using MS were revealed. These are indicated by large shifts in measured MS between a collected sampele and the one directly above it, when supported by relatively consistent values above and below this shift, as opposed to an apparently spurious data point, whose measurement may be suspect. These unconformities can be critical in the correlation of strata across facies, because they provide the fundamental bounding surfaces in a sequence stratigraphic model.

Lower Fairview Fm. North Bend, Wesselman ,Un-named Tongues,and Hooke-Gillespie

submembers

The current study interprets the “Z-bed” of the Kope Fm. to represent the base of a 3rd order depositional sequence containing the Fairview Fm. The Taylor Mill Mbr. of the Kope Fm. consistently shows values approaching smaller values (left) until reaching the “Z-bed”. Low values at the “Z-bed” “2 foot shale” interval quickly spike to larger values (right) upward to the

North Bend submember of the Fairview Fm. There is a small shift to lower values, in the middle of the North Bend submember, which then continue trend towards higher values and then sharply back to low values at the Base of the Wesselman submember. The Wesselman submember shows a spike to the higher values, a middle portion of low values, and an upper portion of high values (meters 4-7 Maysville; Figure 27, meter 4-11 Lawrenceburg; Figure 29).

This may reflect the nature of sedimentation of the Wesselman submember, with a lower shaly

72 portion, a middle portion of approximately five limestone beds, and an upper shaly-siltstone portion. The Wesselman submember follows the same motif as the younger Miamitown shale in this form, and is interpreted to represent the high stand and falling stage portions of a 4th order depositional cycle containing the “Z-bed”, “2 foot shale” “North Bend Tongue” and “Wesselman

Tongue” occurring during a period of overall (3rd order) sea level rise.

Promising correlation exists between the stratigraphic interval of the upper Wesselman submember contact, and a compact approximately 30cm thick rip-up clast containing grainstone with abundant Strophomena that occur directly above the Mt. Hope-Fairmont Mbrs. faunal boundary across the Cincinnati Arch. This interval is interpreted to represent one 4th order depositional cycle and the a high stand systems tract of a 3rd order depositional cycle. This interval contains four MS cycles observed between meters 7 and 15 at Maysville KY. and meter

11 and 23 at Lawrenceburg IN (Figures 27; 29). These four MS cycles are each interpreted to represent 100,000 years of time and this stratigraphic interval informally called the “Un-named

Tongue” is interpreted to represent about 400,000 years of geologic time.

The rip-up clast-bearing bed rich in Strophomena, occurring directly above the Mt. Hope-

Fairmont members boundary is interpreted to represent a time of intense sediment starvation.

The base of this bed is interpreted to represent a 4th order sequence boundary, and this bed is interpreted to represent the Transgressive Systems Tract portion of this 4th order depositional cycle. On a 3rd order scale this bed is interpreted to represent a Surface of Forced regression, occurring as sea level falls at its maximum rate. This is achieved by the small scale (4th order) rise in sea-level imposed on a larger period of sea-level fall resulting in intense sediment starvation. In MS profile this is represented by fairly low values. The interval above the

Strophomena Bed has been informally termed the “Hooke-Gillespie” sub-member named after

73 exposures near the intersection of Hooke, and Gillespie Lanes with the AA Highway (Rt. 9) (Fig.

3, Locality 7), bearing thick deformed siltstones typical of this interval. At Rt. 11 in Maysville this interval is characterized by three horizons of large deformed seismite horizons, siltstone infilled channel forms, and a series of large encrusted limestone blocks associated with each of these deformed horizons. This interval is interpreted to represent a 3rd order falling stage systems tract deposit and a 4th order depositional cycle shown at meters 23-27 at Lawrenceburg

IN., and meters 15-22 in Maysville KY (Figures 27; 29). The equivalent deposit is interpreted to be much thicker in Maysville KY. due to increased sediment proximity and nearshore sediment trapping and deformation associated with Falling Stage deposits. In distal sections at

Lawrenceburg IN. equivalent siltstone horizons are still present but thin due to less sediment supply. Both sections show two MS barlog cycles.

Upper Fairview Fm.: Lawrenceburg, Hill Quarry Beds, Fracta Beds

Sharply overlying the deformed siltstone horizons of the Hooke-Gillespie sub-mbr. are a series of three coarse carbonate grainstone beds containing a series of large (up to 20 cm across) rip-up clasts. This occurs at approximately meter 22 in Maysville KY. and meter 27 in

Lawrenceburg Indiana (Figures 27; 29). This series of rip-up clast bearing beds is overlain by a series of grainstone beds occurs up to approximately meter 24 in Maysville KY. and meter 32 in

Lawrenceburg IN. Due to the widespread nature of these rip-clast bearing deposits overlain by coarse grained carbonates sharply overlying a deformed siltstone interval, this interval, informally named the Lawrenceburg submember for well exposed localities along Rt. 48 in

Lawrenceburg IN., is interpreted to represent a major sequence boundary and transgressive deposit. This interval shows a major period of low MS values in Lawrenceburg IN., and a minor period of low measured MS values in Maysville KY. sharply overlain by a rapid shift to higher

MS values at the top of this interval. In downramp, distal sections such as Lawrenceburg IN., thick skeletal carbonates associated with intense basinal clastic sediment starvation are indicated.

This matches sequence stratigraphic predictions that basin sediment starvation is associated with periods of sea-level rise. A more minor shift to low values in measured MS as observed in

Maysville Kentucky may indicate increased levels of clastic sedimentation in upramp, proximal environments during periods of transgression.

The stratigraphic interval from the basal Lawrenceburg beds through uppermost

Miamitown shale is interpreted to represent one complete depositional sequence. This interval displays eight MS cycles each interpreted to be 100,000 year cycles and is estimated to represent approximately 800,000 years of geologic time, and two 4th order depositional cycles. The strata in between the Lawrenceburg Beds, and the Miamitown shale are known as the Hill Quarry

Beds, and the thick grainstones which were quarried on the hills above Cincinnati for building stones in the late nineteenth century. These beds span the interval from meter 32 to meter 37 at

Lawrenceburg IN. (Figure 29) Above these beds are a series of three rubbly fossiliferous packstone interbedded with mudstone beds resembling the Bellevue Member in lithology termed the Fracta Beds (See Dattilo 1998) (Named after the Brachiopod Rafinequina fracta). These beds span the interval from 37 to 40.3 meters at Lawrenceburg IN.

Miamitown Shale

The Miamitown shale interval displays a three part division with a shaly lower portion, a middle carbonate portion, and an upper shaly siltstone portion. This interval shows a sharp change to high values at its base associated with increased shale deposition, a middle change to low values, and upper portion with high measure MS values rapidly shifting back to low values

75 at the Bellevue Mbr. contact. This occurs between approximately meter 40 and meter 43 in

Lawrenceburg IN. (Figure 29). In this case barlogs half cycles have been placed at a single point data shift within the Miamitown Shale middle portion because this unit is widespread and visible in other MS profiles (i.e. Fredericktown; Figure 31). The MS profile at the Trimble-Carrol Co. line begins in the uppermost Miamitown Shale, and also shifts to high values as observed up to

Meter 0 (Figure 30). When traced to shallow water peritidal facies of the Kentucky Bluegrass the Miamitown Shale displays evidence of fluctuating water depth based upon shallow-water and subaerial sedimentary structures, with a calci-mudstone deposit, moving upwards into mudcrack bearing horizons, sharply overlain by marine deposits with evident strictly marine fossils such as cephalopods, trilobites and brachiopods. This sharp change in water depth associated facies in a shallow water environment is evidence of small scale sea-level oscillations, when in a peritidal environment,contrasts the claims of Holland (2008) that Cincinnatian peritidal deposits are not cyclic, and supports the idea that sea-level fluctuations could be responsible for cyclogenesis throughout the basin, in opposition to the conclusions of Webber (2002), etc. In Fredericktown

KY. the Miamitown Shale is very thick and exposed from approximately .3 meters to 11.7 meters (Figure 31). The three part motif of the Miamitown interval is demonstrated in measured

MS values with a gradual increase to higher values from 0 to 2.3 meters, a return to low values between 2.3 and 4 meters, and then a shift to high values again before gradually returning to lower values until the basal Bellevue Mbr. (A short spike to high values correspond with a hardground surface at approximately 4.3 meters. Despite these broad changes in MS throughout this interval a series of 10 minor MS cycles are indicated by the MS barlogs from meter 0-12 at

Fredericktown KY. These 10 minor cycles may be interpreted to represent approximately

20,000 year, precessional cycles, occurring superimposed upon two larger 100,000 year

76 eccentricity cycles during the Miamitown Shale interval, here part of the Tate Mbr. of the

Ashlock Fm. If this is true, then a nested hierarchy of depositional cycles does in fact exist, and is present in the Maysvillian Stage Miamitown Shale interval. Despite having increased MS resolution of the Miamitown Shale due to its large thickness in pertidal, lagoonal deposits of the

Kentucky Bluegrass, these same small scale cycles believed to represent variations in sedimentation due to orbital perturbations in the Miamitown Shale interval are inferred to occur throughout the remainder of the Maysvillian Stage interval, and may be quantified using extremely high resolution sampling methods, or sampling thicker intervals.

Together the eight MS cycles in the Upper Fairview (above Hooke-Gillespie) and

Miamitown interval are interpreted to represent two 400,000 year cycles, spanning approximately 800,000 years of geologic time. Within this approximately 800,000 year succession, three depositional systems tracts have been observed. The transgressive systems tract represented by the Lawrenceburg Sub-Mbr., the high stand systems tract represented by the

Hill Quarry Beds, and the Falling Stage Systems Tract represented by the Fracta Beds, and

Miamitown Shale. In Maysville Kentucky the “Fracta Beds” interval appears to be absent, with possibly the lower bed of the interval exposed, meanwhile, the Hill Quarry Beds are present and appear undisturbed. Only three MS cycles existing above the Lawrenceburg interval. A total of

20 MS cycles have been measured in the Fairview Fm., Miamitown Shale interval. Each of these MS cycles is interpreted to represent approximately 100,000 years of geologic time.

Although this has not been quantified using the Fourier Transform Method or other means of

Time Series Analysis, the Fairview-Miamitown interval is interpreted to represent an estimated approximately 2 million years of geologic time.

Bellevue Member-McMillan Fm.

A widespread unconformity is observable at the base of the Bellevue Mbr. at numerous localities in outcrop, and is visible in the four Magnetic Susceptibility profiles demonstrated in this paper. This can be observed at meter 29.7 of the Maysville KY. MS profile (Figure 27), where a cryptic unconformity exists between packstones of the Upper Fairview (Hill Quarry

Beds) and Bellevue Mbrs. This can be observed at meter 42.7 in Lawrenceburg IN. (Figure 29) where the Miamitown Shale is sharply overlain by argillaceous pack-grainstone of the Bellevue

Mbr., and meter 0 at the Trimble-Carroll County Line (Figure 30), where green mudstones of the

Miamitown Shale is sharply overlain by cross-bedded calc-arenitic grainstone of the Bellevue

Mbr.: A large offset to lower measure MS values is visible at each of these localities. This occurs at meter 11.7 of the Fredericktown KY. MS profile and may not be as recognizable due to the peritidal nature of the deposit.

The Bellevue Mbr. is interpreted to represent one fourth order 400,000 year depositional cycle. In the Trimble-Carroll County line section (Figure 31) four small scale magnetic susceptibility oscillations occurring from meter 0 to meter 4.5 are interpreted as four 100,000 year, 5th order depositional cycles. Approximately four minor (5thorder) cycles were recognized in the Maysville KY. section as well. This same number of MS cycles was not recognizable in the Fredericktown KY. MS profile where the Bellevue interval is strongly condensed. The rather uniform MS profile and may reflect the rather monotonous lithology of the rubbly fossiliferous packstone, (associated with nearshore sequestration of sediments) of the Bellevue Mbr. in this locality. In all localities the Bellevue Mbr. shows a gradual shift towards lower values, possibly indicating increased amounts of sediment starvation upwards in the Bellevue interval.

Corryville Member

The Corryville Member in its type locality is a mudstone deposit with a series of compact pack-to-grainstones occurring in distal settings. In proximal environments the Corryville Mbr. is generally a fossiliferous rubbly packstone rich in Platystrophia, and has been mapped as part of the Grant Lake Fm. in KY. The Corryville Mbr. appears to be divided lithologically into three minor sub divisions correspondent with deposition systems tracts. A lower transgressive portion containing four thick grainstones mixed with shales in downramp settings. These are typically skeletal crinoidal grainstones in Cincinnati, and contain four oncolitic packstone beds in shoal- like settings. In peritidal settings this lower interval contains a series of micritic carbonate beds exhibiting recrystallized stromatoporoids. The middle portion of the Corryville in downramp facies begins with a compact calcareous shale, grading into mudstones mixed with grainstones, in KY. this is mostly typified by shallow fossiliferous packstones of the Grant Lake Fm. across the Kentucky Bluegrass, and often contains Rafinequina nasuta across different depositional environments. The upper portion of the Corryville has more mudstone obrution deposits and compact grainstones. In more proximal settings these can be more calcareous mudstones and carbonates. Typically these strata display eight MS cycles and are interpreted to represent two fourth order depositional cycles. The Bellevue Mbr. representing an early transgressive systems tract deposit, the lower Corryville oncoid interval a condensed portion of continued sea level rise, the middle Corryville representing the late highstand deposit, and upper Corryville representative of a falling stage systems tract deposit. The Corryville Mbr. can be observed from meter 34.5 to 45 meters at Maysville KY. (Figure 28), 4.5 to 16.8 meters at the Trimble-Carroll

Co. line (Figure 30), and 13-24.6 in Fredericktown KY. (Figure 31). MS values within the

Corryville Mbr. are fairly monotonous, which may be attributed to the lithologic nature shallow

79 marine packstones of the Grant Lake lithofacies. It is interpreted that in downramp sections of the Corryville Mbr. showing abrupt changes between shale-limestone cycles, such as that north of Cincinnati in the Sebree Trough, increased variability in measure MS values would occur due to increased accommodation in these settings, trapping detrital minerals and clay sediments, driving further MS values: it is necessary to sample the Corryville Mbr. in such a locality to evaluate this. The Fredericktown KY. section does show a gradual shift to higher MS values, which would be expected during highstands, but, the Trimble-Carroll County Line section does not exhibit this same trend and on a broad scale values shift from high, gradually to low, gradually to high, and gradually to low again.

Mt. Auburn Member

The Mt. Auburn Mbr. represents the uppermost portion of the McMillan Fm. of Ohio, and the Grant Lake Fm. of Kentucky. This unit also represents the uppermost strata of the

Maysvillian Stage. The Mt. Auburn is generally a grainstone deposit with a lower carbonate portion, middle shaly portion, and upper carbonate portion. Field-based investigations interpret the Mt. Auburn to be composed of two fourth order depositonal cycles. This is confirmed byeight measured MS cycles occurring at the Trimble-Carroll Co. line between meters 16.8 and

27.8 (Figure 30). In Maysville KY. between meter 45 and 62 only 6 MS cycles are observed

(Figure 28). The missing MS barlog cycles are equated to gaps in MS sampling between meters

45-47.1, 53.7 and 55.2-56.1, due to steep and unaccessable, or covered exposures. In

Fredericktown KY. the Mt. Auburn Mbr. is a massive, compact phosphatic grainstone occurring from meter 24.8 to meter 26, low MS values correspond with these cross-bedded compact carbonates. No middle shaly portion of the Mt. Aurburn member has been observed here and this interval is interpreted to be missing, or condensed. The sharp spike occurring at meter 26

80 from low to high values at the basal Richmond Grp. Sunset Mbr. of the Arnheim Fm. contact is interpreted to represent an unconformity. However, the sharp change from cross-bedded phosphatic carbonates to marine shale, marked by a rapid change from low to high MS values indicates that this unconformity is not a sequence boundary, but instead represents a maximum flooding surface, or early highstand deposit. Ideally an unconformity representing a sequence boundary would show a sharp change to low values associated with transgressive marine limestones sharply overlying silliclastic sediments of the Highstand or Falling Stage systems tract of the underlying cycle.

Establishing a Chronostratigraphic Framework and Future Work

Future research will attempt to generate time-series analyses of the MS data set using the

Fourier Transform method in order to establish a chronostratigraphic framework for the

Maysvillian Stage. Future and ongoing work hopes to fill in regional gaps of this study by sampling additional sections preserving proximal and distal environments by sampling outcrops in Point Leavell KY., and Morrow, and Hamilton Oh. respectively. Building on research of the

Fredericktown KY. section, additional samples have been collected stratigraphically upward throughout the Richmond Grp. strata.

Conclusions

In conjunction with careful field based lithostratigraphic measurements MS has provided a widespread correlation tool for the Late Ordovician, Maysvilian Stage strata of the Cincinnati

Arch. Studies of MS are generally reserved for globally studied sections with excellent biostratigraphic or istopic control. MS provides a powerful tool for the global correlation of strata, but is also a powerful tool in basin-scale stratigraphy. The current study presents the

81 results of a preliminary study of MS of the Maysvillian Stage Strata of the Cincinnati Arch, in its type locality, a premier Upper Ordovician succession with a wide and diverse history of study.

Using MS in vertical profiles has uncovered and allowed widespread correlation of major unconformities throughout the Maysvillian interval. These include the unconformities at the base of the Lawrenceburg Sub Mbr. of the Fairview Fm., the base of the Bellevue, and the base of the Richmond Group. Combining MS stratigraphy with field based investigations we conclude that the Miamitown Shale has not changed in a Waltherian manner to into a Bellevue- like facies on the Eastern Limb of the Cincinnati Arch, but is instead cutout below the basal

Bellevue Mbr. unconformity, while the beds below this unconformity remain unchanged. Thus, mixed fieldwork and MS provides a powerful tool for sequence stratigraphic interpretations. For example, the basal Bellevue Mbr. contact represents a major sequence boundary. Another major sequence boundary occurs in the mid-upper Fairview Fm., and the Mt. Auburn-Sunset Mbrs. contact as a maximum flooding surface as opposed to a sequence boundary. MS cycles used in conjuction with outcrop-based lithofacies studies and the tracing of individual beds and units, show that changes in water depth affecting sedimentation are reflected by MS cycle variation.

Additionally, a hierarchy of MS cycles has been observed within the Miamitown Shale interval, and is interpreted to reflect orbital perturbations. Together this observed variation in water depth indicators and hierarchy of depositional cycles aids in interpreting the mechanism for cycle development in the Cincinnatian Series Maysvillian Stage. In total the Fairview Fm. and

Miamitown Shale together appear to represent 2 mys of geologic time, and the entire Maysvillian

Stage occupying 4 mys of geologic time. Future research hopes to quantify the temporal scope of the Maysvillian Stage using Fourier Transform Analysis.

References:

Anstey, R.L and Fowler, M.L., 1969. Lithostratigraphy and depositional evironments of the Eden

Shale (Ordovician) in the tri-state areas of Indiana, Kentucky and Ohio: Journal of

Geology, v. 77. p. 129-149.

Bai, S.L. 1995. Milankovitch Cyclicity and Time Scale of the Middle and Upper Devonian.

International Geology Review. Vol. 37. p 1109-1114.