TAPHONOMY OF CONODONTS AND MICROVERTEBRATES IN REMAINIÉ HORIZONS: NEW APPROACHES TO UNRAVELING STRATIGRAPHIC RELATIONS AROUND THE MIDDLE-UPPER (GIVETIAN-FRASNIAN) BOUNDARY IN WESTERN NEW YORK

The upper Givetian and lower Frasnian succession in New York includes a series of thin remanié (lag) deposits which record discontinuities within the clastic sediments of the lower Genesee Group. These horizons and the meters to tens of meters between them converge westward toward the basin margin where their positions are occupied by a single horizon, the North Evans Limestone, a fossil concentrate of conodont and fish debris sandwiched between the gray shales of the upper Hamilton Group and the styliolinid Genundewa Limestone (middle Genesee Group). At its type section at Eighteenmile Creek near Buffalo in western Erie County, the North Evans is ten centimeters thick. The taphonomic signatures of the microfossils in the North Evans and the other remanié horizons suggest the following stratigraphic relations:

1. The upper Givetian Leicester Pyrite, which records the compound Taghanic Unconformity and early stages of the Taghanic Onlap, and the succeeding Geneseo Shale, both project to a level beneath the North Evans at Eighteenmile Creek. 2. The basal 0.7 cm of the North Evans at Eighteenmile Creek (with Ancyrodella rotundiloba) corresponds to the interval from the Givetian-Frasnian boundary horizon just above the top of the Geneseo Shale (MN Zone 1) to the top of the Penn Yan Shale (MN Zone 2). 3. The middle (6 cm) and upper (3 cm) units of the North Evans at Eighteenmile Creek, with the youngest zonal conodont in the North Evans, Ancyrodella recta (MN Zone 3), is a record of a sub-Genundewa disconformity with parts of the upper Penn Yan Shale reworked or removed prior to the Genundewa transgression. 4. The North Evans is primarily a record of this sub-Genundewa disconformity rather than the Taghanic Unconformity and Taghanic Onap. The previously reported occurrences of the North Evans fossils (including An.recta) in eastern Erie, Genesee and Livingston counties are now believed to be indigenous to those areas and not offlap debris transported from the basin edge. A Frasnian (MN 3) age for all but the base of the North Evans at Eighteenmile Creek is supported by the discovery of pyritic goniatites (Koenenites?) at the top of the North Evans at Eighteenmile Creek and in the 5 cm-thick North Evans at Linden in Genesee County, some 67 kilometers to the northeast.