Abstract

A marine to non-marine transition is recorded in Frasnian rocks exposed along a 30 km west to east traverse in the Windsor-Deposit region of south-central New York. Marine rocks are dominated by mudstone with subordinate sandstone sheets, lenses and channel fills. Sandstones contain hummocky cross stratification, planar lamination and wave-ripple lamination. Sole structures on erosional sandstone bases, and sandstone- and mudstone-filled channels indicate east to west paleocurrents. Rare trace fossils within sandstones increase in abundance near their tops and into overlying mudstones. Towards the paleoshoreline sandstone bed thickness and mean grain size increases, the proportion of channel filling sandstone increases relative to sheet sandstone, and amalgamated hummocky bedsets appear. Sandstones are interpreted as deposits of storm waves with combined oscillatory and unidirectional currents; mudstone represents fair weather and/or shore-distal deposition, i.e., below storm-wave base. Channels may be formed by storm-wave induced currents or turbidity currents.

Coastal deposits are represented by trough cross-bedded and planar-bedded sandstone bodies which fine upwards from an erosional base and contain lateral-accretion surfaces. Sandstone bodies are interbedded with cross-laminated and planar-laminated siltstone and shale, with relatively thin sandstone sheets and lenses. Plant remains are abundant but marine fossils are rare. Trace fossils are rare in sandstone bodies but common in mudstones. Sandstone bodies are interpreted as deposits of distributary channels which cut through lacustrine or interdistributary bay mud deposits. An erosional-based sandstone at the top of a coarsening upward sequence, with evidence of strong westerly directed paleocurrents as well as oscillatory currents, is interpreted to be due to progradation of a distributary mouth bar. Evidence of strong tidal currents is lacking in these deposits.