RECURRENT TROPIDOLEPTUS ZONES: THE FATE OF THE HAMILTON FAUNA THROUGH THE GLOBAL TAGHANIC BIOEVENT

James Zambito

University of Cincinnati, Department of Geology, 500 Geology/Physics Bldg.

Cincinnati, OH 45221-0013

[email protected]

The purpose of this research is to document the recurring Hamilton fauna within the Upper Devonian Appalachian Basin strata and to understand the driving paleoenvironmental changes responsible for these faunal recurrences. Hypotheses include: 1) Recurrent Hamilton assemblages are distinctive from surrounding “Ithaca” faunas with little or no overlap in composition. 2) Recurrent faunas record unusual water mass conditions associated with transgressive flooding surfaces such that recurrent Hamilton assemblages occur within transgressive facies above flooding surfaces. 3) Incursions of relatively deep water masses during low sediment influx facilitated recurrence of anachronistic taxa in the Appalachian Basin.

Current progress on this project has been focused in the area of Ithaca, New York; the type section of the Ithaca Shale Member of the Genesee Formation and the oldest strata in which the Hamilton fauna is recorded as recurring. Sampling of fossils has begun for later examination as to whether “Ithaca” and Hamilton faunas have distinct compositions. Preliminary recognition of fifth- and fourth-order cycles within the deposits of the Ithaca Shale Member have been made and the associated diagnostic depositional features identified. Approximately twenty-five stratigraphic sections have been examined to date. Samples and field notes will be further reviewed during the winter of 2006-2007. Fieldwork will resume in the summer of 2007, in the vicinity of and between Ithaca and Oneonta, New York.

This research holds the potential for the further understanding of the tempo and mode of evolution and global bioevents. Appalachian Basin depositional environments will be described and a detailed account of the stratigraphic cyclicity of Middle and Upper Devonian strata will be possible. This project will document a high resolution sea level curve for these strata.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid