Comparative sequence stratigraphy of two classic Upper Ordovician successions, Trenton Shelf (New York–Ontario) and Lexington Platform (Kentucky–Ohio): implications for eustasy and local tectonism in eastern Laurentia

Comparison of the classic Upper Ordovician (Mohawkian to lower Cincinnatian; Caradoc to lower Ashgill) Black River and Trenton Groups in New York State/southern Ontario with the Tyrone–Lexington Formations exposed in the Jessamine Dome (southern Cincinnati Arch) in north-central Kentucky and southern Ohio reveals striking similarities. Previous emphasis on complex local facies mosaic has obscured widespread regional patterns. Biostratigraphy and K-bentonites provide broad constraints on inter-regional correlations; however, an allostratigraphic approach permits higher resolution correlations and a partial test of eustatic vs. strictly local tectonic models to explain stratigraphic patterns. Upper Mohawkian to lower Cincinnatian (∼455–449 Ma) depositional sequences, previously recognized for the Jessamine Dome and Nashville Dome areas, are correlated between the two main study areas and further refined; Chatfieldian (Rocklandian to Shermanian or Cobourgian of traditional terminology) sequences M5 and M6 of previous workers are interpreted to be composite sequences and are each subdivided into three smaller-scale sequences, which also have counterparts in the New York–Ontario strata. In turn, these correlations indicate at least partial allocyclic control on sedimentary cycles. Complex lateral variations within depositional sequences, especially in the late Shermanian to Edenian, indicate that tectonically controlled patterns of basinal subsidence and uplift of crustal blocks (perhaps reflecting forebulge migration) exerted a strong influence on the local facies and motif of depositional sequences. These tectonic features, however, did not obliterate the underlying allocyclic pattern. Indeed, high-resolution sequence stratigraphy enables detailed resolution of shifting patterns of minor uplift and subsidence.