Chronostratigraphy and the sequence hierarchy of the late Turinian through early Edendian (Ordovician) Taconic foreland in New York and central Pennsylvania: Implications for active margin basin evolution

Late Turinian through early Edenian (Ordovician) Trenton Group carbonates and Utica Group shales crop out in the Mohawk Valley, New York, and central Pennsylvania. These rocks were deposited along the western margin of the Taconic basin during the Taconic orogeny. Facies changes record episodic basin deepening and simultaneous carbonate ramp shallowing, long-term margin tilting, local structural features, and changing sediment supply rates and eustatic sea level.; Differential subsidence rates observed within the Mohawk Valley increased by an order of magnitude between the Trenton shelf (western Mohawk Valley) and the basin (central Mohawk Valley). Large increases in accommodation space also occurred in central Pennsylvania during this interval. Determining synchroneity of accommodation space changes between sub-basins within the Mohawk Valley and central Pennsylvania depends on the precise timing of initial Utica Group deposition in each of the two regions.; Geochemical correlation of several regionally extensive K-bentonites, graptolite and conodont biostratigraphy, and the correlation of stratigraphic sequences provide some constraints on the spatial and temporal relations between New York and central Pennsylvania. These data suggest that differential subsidence influenced broad areas of the Taconic basin. Sequence stratigraphic development was related to the same events that produced this differential subsidence. The most profound period of relative sea rise in the study area occurs during the mid-Chatfieldian. This event may be an older manifestation of the carbonate to black shale onlap recognized elsewhere in the Appalachian Basin in the early Edenian. Sequence stratigraphic analysis of the north central Taconic basin provides information regarding the genetic origin of sequences recognized on the 10 and 100 m scales. Observations regarding the timing and variation of magnitude of accommodation space, the relationships between structural features and relative rock accumulation and the balance between sediment supply and accommodation space suggest that a multi-component facies model is needed to describe the evolution of this active margin facies mosaic.