Temporal and spatial distribution of biozones and facies relative to geochemically correlated K-bentonites in the Middle Ordovician Taconic foredeep

The Middle Ordovician rocks of the Taconic foredeep in the Mohawk Valley, New York, contain numerous altered volcanic ash beds (K-bentonites). Geochemical fingerprinting of glass inclusions within volcanic quartz phenocrysts permits unambiguous matching of the compositionally unique ash layers. The resulting correlations demonstrate that time lines based on the graptolite biozones and transgressive-regressive facies patterns parallel the K-bentonite isochrons. They also demonstrate that much of the upper Trenton Group is older than previously believed and facies relations are markedly different from previous interpretations. Although some facies patterns appear to be synchronous across the region, the likely existence of substantial structural control on facies development in the basin suggests that it is unwise to attribute these patterns to eustatic sea-level changes. -from Authors