EARLY ORDOVICIAN MICROBIAL REEF MOUNDS OF THE TRIBES HILL FORMATION, MOHAWK VALLEY, NEW-YORK

Tribes Hill domal thrombolites, termed here microbial reef mounds, occ upied the basal part of meter-scale shallowing-upward cycles. They are part of a high-energy facies that a sharp, transgressive surface sepa rates from an underlying low-energy peritidal setting. This erosional surface served as the surface on which one of the reef mounds establis hed itself during initial transgression before further deepening. The others overlie a floor of skeletal grainstone reflecting a high-stand sea-level facies tract. Skeletal grainstone composes the fill between the mounds. One channel and several aggrading hummocks occupy inter-re ef mound areas resulting from storm events in a subtidal setting.