COMPARATIVE SEQUENCE STRATIGRAPHY OF THE MIDDLE-UPPER ORDOVICIAN (TURINIAN-EDENIAN) OF KENTUCKY AND NEW YORK

Detailed comparisons of the upper Tyrone, Lexington, Point Pleasant, and Kope formations of northern Kentucky with biostratigraphically correlative upper Black River, Trenton and Utica formations in the Mohawk Valley, New York, show marked similarities. Using abrupt facies dislocations interpreted as sequence boundaries, eight-decameter scale sequences are recognized in both areas. The lower and upper sequence boundaries represent Holland and Patzkowsky’s (1996) M4 and C1 sequences, respectively. However, M5 and M6 are each divisible into at least three subsequences. Transgressive systems tracts are recognized as sharply based pelmatozoan, bryozoan, and/or gastropod rich pack-to grainstones. The upper contacts of these beds are sharply defined by rusty weathering (pyrite stained) and phosphatic discontinuity surfaces. Early highstands are widespread, thinly bedded calcisiltites and dark shales.

The detailed similarities of these widely separated (~900 km apart) sections suggest similar conditions over a large area of eastern Laurentia during late Turinian-lower Shermanian. Despite local variations, the upper Shermanian (Cobourgian) shows broad similarities. In both regions it consists of a succession of thin bedded calcisiltite and shale that shallows upward through wavy bedded packstones and fine-grained grainstones with significant zones of deformation (seismites) (upper Rust Fm.: NY; Bromley-Gratz: KY) and finally into skeletal grainstones (Steuben Fm.: NY; Rogers Gap: KY). Both areas show a very major deepening associated with widespread graptolite- (C. spiniferus Zone) and Triarthrus-bearing organic rich shales at or near the base of the Edenian (Cincinnatian Series; Indian Castle (Utica) black shales: NY; lower Kope Fm.: KY). These correlations suggest a strong degree of allocyclic control. Conversely, regional and local variations, and widespread seismites in the upper Lexington-Point Pleasant formations and equivalent Trenton Limestone point to tectonic influences associated with the Vermontian tectophase of the Taconic Orogeny.