TEMPORAL AND SPATIAL-DISTRIBUTION OF BIOZONES AND FACIES RELATIVE TO GEOCHEMICALLY CORRELATED K-BENTONITES IN THE MIDDLE ORDOVICIAN TACONICFOREDEEP

The Middle Ordovician rocks of the Taconic foredeep in the Mohawk Vall ey, New York, contain numerous altered volcanic ash beds (K-bentonites ). These synchronous beds have the potential to link disparate facies in a way that is not feasible with biostratigraphy or sequence stratig raphy alone. Geochemical fingerprinting of glass inclusions within vol canic quartz phenocrysts permits unambiguous matching of the compositi onally unique ash layers. The resulting correlations demonstrate that time lines based on the graptolite biozones and transgressive-regressi ve facies patterns parallel the K-bentonite isochrons. They also demon strate that much of the upper Trenton Group is older than previously b elieved and facies relations are markedly different from previous inte rpretations. Although some facies patterns appear to be synchronous ac ross the region, the likely existence of substantial structural contro l on facies development in the basin suggests that it is unwise to att ribute these patterns to eustatic sea-level changes.