SEQUENCE STRATIGRAPHIC COMPARISONS OF THE BLACK RIVER-TRENTON BOUNDARY INTERVAL: IMPLICATIONS FOR TACONIC FORELAND BASIN DYNAMICS

Despite the fact that the Ordovician Taconic Orogeny has been studied for over a century, there are still many issues concerning the timing, evolution, and impact of this tectonic event on ancestral North America. Due to the coincidence of major climatic, paleooceanographic, paleobiologic and tectonic events at this time, there is need for a high-resolution correlated framework within this interval. Sequence stratigraphic analysis allows for the construction of high-resolution models for testing the relative timing of these changes.

This study focuses on the Black River-Trenton boundary interval which records the transition from peritidal-carbonates into deeper-water, shale-influenced rocks of the Trenton. This interval has been interpreted to show diachronous cratonward migration of basin subsidence and shale accumulation. In order to test the timing and apparent diachronous nature of this transition, 5 Black River (Turinian) and Trenton (Chatfieldian) decameter-scale depositional sequences from New York and Kentucky/Ohio are compared.

Comparisons reveal similar patterns in facies development, sequence architectures, and timing of basin subsidence. Sequences and smaller-scale cycles initially are widely correlatable, show synchronous water depth histories, and gradual lateral changes in shallow facies suggesting that eustacy played a major role in their deposition. Conversely, upper sequences of the mid-to-late Trenton record abrupt lateral facies change from shallow, peritidal carbonates into deeper water nodular carbonates and shales suggesting extensive lateral topographic change after the onset of tectonism. Perhaps the most striking similarity between them is the simultaneous collapse of the Sebree Trough, and Taconic Foreland and synchronous influx of siliciclastic sediments onto the craton.

There is also some dissimilarity to be mentioned. First, the relative thickness of time-equivalent sequences show variable sedimentation rates suggesting a difference in the production/deposition of carbonates across both transects. Second, sequences deposited on the Lexington Platform show uniform, along transect thicknesses, while those deposited nearest the shelf margin show lateral thickness changes indicating local variations in sediment accumulation and preservation.