Siltstone: a key to cyclicity in mixed siliciclastic–carbonate successions: example from Upper Ordovician Kope Formation (Ohio, Indiana, Kentucky)

The Upper Ordovician (mid-Katian) Kope Formation provides an example of how a detailed study of fine-grained siliciclastic sediment can provide sedimentological insights. The Kope Formation is an exemplar of mixed siliciclastic–carbonate cyclicity; however, most of the sedimentological research to date has focused on the fossiliferous limestone beds. Conversely, this paper provides a detailed investigation of siltstone within 42 metre-scale cycles from 26 locations spanning a large geographic area. The objective of the study is twofold: ( i ) to confirm the mineralogical nature of silt-sized sediment. Currently, silt-sized sediment is irregularly defined as being either carbonate or siliciclastic rich. This paper uses X-ray diffraction, thin-section, and elemental analyses to determine the mineralogy of the silt; ( ii ) to determine the stratigraphic distribution of siltstone beds. If a distinctive and reoccurring distribution of siltstone can be found, then it can provide additional information about environmental energy changes that led to cyclic fossiliferous limestone formation. This study finds that silt within the Kope Formation is siliciclastic and siltstone, therefore, records periodic minor pulses of coarser terrigenous sediment. Predominantly, metre-scale limestone–shale cycles show an increasing abundance of siltstone beds in the upper half of the shale interval, with a marked decrease just before the capping limestone. This finding supports the idea that limestone formation occurred during slowing sedimentation, perhaps at a time of maximum sea-level rise. Furthermore, decametre-scale fluctuations in siltstone abundance are similar in pattern to previously documented faunal variations, indicating that fauna assemblage might be more controlled by turbidity and not depth.

[1]  E. Holley,et al.  Abstracts with Programs , 2016 .

[2]  J. Macquaker,et al.  Capturing Key Attributes of Fine-Grained Sedimentary Rocks In Outcrops, Cores, and Thin Sections: Nomenclature and Description Guidelines , 2015 .

[3]  Benjamin F. Dattilo,et al.  Tempestites in a teapot? Condensation-generated shell beds in the Upper Ordovician, Cincinnati Arch, USA , 2012 .

[4]  J. Tomkin,et al.  Visual identification and quantification of Milankovitch climate cycles in outcrop: an example from the Upper Ordovician Kope Formation, Northern Kentucky , 2012 .

[5]  C. Brett,et al.  Subsurface Correlation and Paleogeography of a Mixed Siliciclastic-Carbonate Unit Using Distinctive Faunal Horizons: Toward a New Methodology , 2008 .

[6]  C. Brett,et al.  Use of Event Beds and Sedimentary Cycles in High-Resolution Stratigraphic Correlation of Lithologically Repetitive Successions , 2008 .

[7]  C. Brett,et al.  Magnetostratigraphy susceptibility of the Upper Ordovician Kope Formation, northern Kentucky , 2007 .

[8]  Sean R. Cornell,et al.  High-resolution sequence stratigraphy of a mixed carbonate-siliciclastic, cratonic ramp (Upper Ordovician; Kentucky–Ohio, USA): insights into the relative influence of eustasy and tectonics through analysis of facies gradients , 2004 .

[9]  A. Webber.  High-Resolution Faunal Gradient Analysis and an Assessment of the Causes of Meter-Scale Cyclicity in the Type Cincinnatian Series (Upper Ordovician) , 2002 .

[10]  G. Gehrels,et al.  Paleotectonic Implications of a Mid‐ to Late‐Ordovician Provenance Shift, as Recorded in Sedimentary Strata of the Ouachita and Southern Appalachian Mountains , 2002, The Journal of Geology.

[11]  C. Brett,et al.  Stratigraphic evidence from the Appalachian Basin for continuation of the Taconian orogeny into Early Silurian time , 2002 .

[12]  Arnold I. Miller,et al.  The Use of Faunal Gradient Analysis for Intraregional Correlation and Assessment of Changes in Sea‐Floor Topography in the Type Cincinnatian , 2001, The Journal of Geology.

[13]  W. Huff,et al.  The Ordovician Sebree Trough: An oceanic passage to the Midcontinent United States , 2001 .

[14]  Arnold I. Miller,et al.  The Detection and Importance of Subtle Biofacies within a Single Lithofacies: The Upper Ordovician Kope Formation of the Cincinnati, Ohio Region , 2001 .

[15]  Arnold I. Miller,et al.  High-Resolution Correlation in Apparently Monotonous Rocks: Upper Ordovician Kope Formation, Cincinnati Arch , 2000, Palaios.

[16]  Arnold I. Miller,et al.  Cycle Anatomy and Variability in the Storm‐Dominated Type Cincinnatian (Upper Ordovician): Coming to Grips With Cycle Delineation and Genesis , 1997, The Journal of Geology.

[17]  Richard J. Diecchio.  Stratigraphic interpretation of the Ordovician of the Appalachian Basin and implications for Taconian flexural modeling , 1993 .

[18]  W. Pryor,et al.  Cyclic alteration of proximal and distal storm facies; Kope and Fairview formations (Upper Ordovician), Ohio and Kentucky , 1993 .

[19]  Robert C. Reynolds,et al.  X-Ray Diffraction and the Identification and Analysis of Clay Minerals , 1989 .

[20]  J. C. Butler,et al.  Re-examination of Upper Cincinnatian Shale Petrology , 1973 .

[21]  J. S. Booth,et al.  The American upper Ordovician standard; XV, Clay mineralogy of insoluble residues from Cincinnatian limestones, Hamilton County, Ohio , 1971 .

[22]  J. Rodgers.  The Taconic Orogeny , 1971 .

[23]  D. R. Bassarab,et al.  Clay Mineralogy of Kope and Fairview Formations (Cincinnatian) in the Cincinnati Area , 1969 .

[24]  J. Ford.  Cincinnatian Geology in Southwest Hamilton County, Ohio , 1967 .

[25]  D. M. Scotford.  Petrology of the Cincinnatian Series Shales and Environmental Implications , 1965 .

[26]  M. Weiss.  The American Upper Ordovician Standard , 1961 .