DYNAMIC RECORD OF LOCAL AND REGIONAL SEDIMENTOLOGICAL CONTROLS IN THE EVOLVING EARLY LATE ORDOVICIAN TACONIAN FORELAND BASIN, EASTERN NEW YORK STATE: NEW INFORMATION CONCERNING THE STEUBEN – DOLGEVILLE EVENT

The Taconic Orogeny, closely associated with an evolving peripheral foreland basin during the early Late Ordovician (Mohawkian Series), was accompanied by heterochronous carbonate shelf/ramp collapse along its cratonward margin. Past work by the present authors and others demonstrates that a general east-to-west (stepwise) pattern of extensional fault movement, westward flexural basin subsidence, and upslope pycnocline migration, all interacted to produce a spatially diachronous, and locally erosional, boundary between underlying carbonates and onlapping organic-rich, basinal mud deposits. Ongoing work shows that tilting of faulted blocks produced localized multidirectional patterns of basinal shale onlap and slumping, particularly in the vicinity of the Little Falls Fault. Eastward thinning of the lower part of the Flat Creek Shale between Amsterdam and the Hoffmans Fault is suggestive of westward rotational block motion in that area as well. K-bentonite analyses will serve as a critical test of this interpretation.

The Steuben/Dolgeville sedimentary succession in central – eastern New York marks a major late highstand (falling stage) – to – lowstand event on the basin margin cratonic platform. This regression triggered the eastward export of large volumes of turbiditic carbonate into the foreland basin largely timed with the Orthograptus ruedemanni Zone.  Normalograptus mohawkensis, recently discovered in proximal shelf facies of the Snake Hill Formation, serves as a key index of the O. ruedemanni Zone. Given that we restrict use of the term Snake Hill Formation to strata of this slice in the Taconic mélange, (it’s type locality), rather than to various other older and younger, basinal exposures west of the Taconic Front, these data suggest that the Snake Hill may correlate to part of the Steuben/Dolgeville succession and indicate that the richly fossiliferous Snake Hill succession, characterized by storm bed features, sediment winnowing, and internal marine discontinuities, may mark the active margin signature of the Steuben lowstand event.