Curious Case of Lack of Strata Assignable to the Pterospathodus celloni Superzone (Telychian, Llandovery, Silurian) in the Eastern Portion of the Midwestern Basins and Arches Region (New York, Ohio, Kentucky, and Indiana)
Telychian strata are present throughout the eastern portion of the Midwestern Basins and Arches region (MBA) in New York, Ohio, Kentucky, and Indiana. Most conodont biostratigraphies developed for Telychian strata prior to 2000 assigned those strata to the Pterospathodus celloni and/or succeeding Pt. amorphognathoides Zone, the two zones previously recognized as comprising most/all of the Telychian. Significant revision of Silurian conodont taxonomy beginning in the late 1990s resulted in recognition of seven conodont zones belonging to three conodont superzones and one conodont zonal group comprising the same portion of the Telychian. Restudy of conodonts from research on Telychian strata conducted by the authors and others prior to 2000 and sampling and processing for conodonts from Telychian strata located in New York, Ohio, Kentucky, and Indiana conducted mostly in the last decade, as well as information published by others during the last decade, make it possible to recognize that strata assignable to the Pterospathodus celloni Superzone are mostly absent throughout the eastern part of MBA in New York, Ohio, Kentucky, and Indiana. Strata assigned to the Pterospathodus amorphognathoides amorphognathoides Zonal group typically overlie strata assigned to the Pt. eopennatus Superzone, or even older, Aeronian strata. Examples of strata assigned to the Pt. am. amorphognathoides Zonal group overlying strata assigned to the Pt. eopennatus Superzone include Willowvale Shale or Westmoreland Hematite overlying Sauquoit Shale and Rockway Dolomite overlying Merritton Limestone in New York, Estill Shale overlying Waco Formation in Ohio and Kentucky, and Osgood Formation overlying Lee Creek Formation in Indiana. One exception is a section near Rochester, New York, where both the Pt. am. amorphognathoides Zonal group and Pt. celloni Superzone (Pt. am. angulatus Zone) are recognized in the Williamson Shale. Silurian sea-level curves typically indicate high sea levels during much of the time represented by Pterospathodus celloni Superzone, and time represented by some/most of the Pt. am. amorphognathoides Zonal group, and typically indicate lower sea levels during the time represented by the Pt. eopennatus Superzone, including a significant drop in sea level near the end of the time that superzone represents. The sea-level record would seem to favor deposition of, and less erosion of, strata assignable to the Pt. celloni Superzone than strata assignable to the Pt. eopennatus Superzone. Tectonic activity along the Appalachian Orogenic Belt must have played an even more important role than eustasy in the stratigraphic record of the eastern portion of the MBA in New York, Ohio, Kentucky, and Indiana during the 1.5 to 3.0 million years of time represented by the Pt. celloni Superzone.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019