Abstract:
Ocean Drilling Program (ODP) Legs 150 and 150X were drilled on the New Jersey slope and coastal plain, respectively, to evaluate the effects of glacioeustatic changes on continental margin sedimentation. An extensive array of seismic lines permitted the tracing of seismic reflections to the slope where they were dated and correlated to sequence boundaries. Coastal plain sequences were identified on the basis of physical, well-log stratigraphy, and paraconformities inferred from biostratigraphy and/or Sr isotopes. During the Eocene, the New Jersey continental margin was a ramp-type dominated by pelagic sedimentation. The gentle slopes permit to evaluate the diagenetic changes with increasing distance from the shoreline. Coastal plain sediment is characterized by carbonate (with formation of micrite, sparry calcite, ferroan carbonates) and silica (opal-A to -CT, to chert, filling of microfractures) diagenesis, within sequences and at sequence boundaries. Generally, glauconite occurs at the bases of the sequences and quartz-rich sediments at the top. Sediment adjacent to two main Eocene slope unconformities records additional episodes of diagenesis than in between the sequences. EDX analyses indicate a local source for the fluids. The most extensive diagenetic alterations (transformation of biosiliceous chalks to a mosaic of dolomite rhombs) occur in upper Eocene slope sediment beneath the contact with upper Oligocene silty clays. This contact represents a major sequence boundary. It also represents a transition from an Eocene pelagic carbonate-dominated to an Oligocene hemipelagic siliciclastic margin. After the margin's siliciclastic switch, slope sequence boundaries are commonly correlated to mass-transport deposits especially from the late Miocene to Holocene when sediment progradation dominated the margin's sedimentation.