Sequence Stratigraphy and Diagenesis of the Miocene–Oligocene below the New Jersey Continental Slope: Implications of Physical Properties and Mineralogical Variations

Abstract

We discuss the origin and sequence stratigraphic implications of physical properties and mineralogical variations in the mid-Miocene to upper Oligocene of the New Jersey continental margin at Site 903. The thick, mostly fine-grained, strongly bioturbated, terrigenous and biogenic sediments reveal continuous long-term and cyclic compositional changes as well as abrupt short-term changes. The most important long-term changes are early compaction and diagenetic precipitation of carbonate concretions, late diagenetic precipitation and dissolution of calcite, dissolution of biogenic silica, and subsequent precipitation of opal-CT and clinoptilolite. Dissolution of biogenic opal appears to be the main cause of generally downhole decreasing wet-bulk density and increasing porosity. Opal-CT cementation strongly increases in the 40 m immediately above the Eocene chalks, and again deeper in the upper-middle Eocene chalks, forming two distinct diagenetic fronts. Integration of physical properties and mineralogical variations allows us to recognize 10 distinct intervals. The intervals and their boundaries compare well with the previously devised seismic stratigraphy of this area and its sequences and systems tracts, although some intervals are too thin to be resolved by the available seismic data. The intervals reflect changes of sediment composition with progressive continental margin progradation. In the upper Oligocene and subordinately in the Miocene, intervals characterized by high density and distinct mineralogy correlate to sediments between thin, laterally continuous reflectors. These intervals are interpreted as distal slope sediments and as lowstand fans deposited laterally or basinward from prograding deltaic wedges, that is, probably in the early lowstand systems tract. Lithological changes associated with progradation caused sediment bulk density to increase and distinctive mineralogic changes which we interpret as late lowstand and highstand systems tracts.