Late Ordovician Faunal Change in the Taconic Foreland Basin

One of my main interests is explaining the faunal turnover in the Katian (Late Ordovician) of the Taconic foreland basin in New York.  The King’s Falls limestone (Sandbian) of the Trenton Group is a highly fossiliferous, light gray, nearly pure limestone that contains a diverse fauna including brachiopods, trilobites, bryozoa, pelmetazoans, and corals.  As the King’s Falls grades upward into the Sugar River Formation, diversity decreases along with an increased influx of terrigenous material and gradual darkening of the limestone.  This shift in lithology has been interpreted to represent an environmental change from warm, tropical conditions to a cooler, possibly oxygen poor environment due to upwelling of deeper water onto the platform.  Another possible explanation for the faunal turnover involves the influx of siliciclastic sediment from the Taconic highlands to the east.  My goal is to try to identify which factors likely had the greatest effect on the faunas.