Print this pageEffects of Relative Sea-Level Changes on the Diagenesis of Eocene Sediment, New Jersey Slope and Coastal Plain
McHUGH, C. M. G., K. G. MILLER, and J. V. BROWNING
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.