Oligocene sediments are found only in the subsurface and have a patchy distribution. The early to middle Oligocene (Sewell Point Formation) is characterized by glauconite-rich sedimentation that was deposited very slowly. The entire New Jersey margin was sediment-starved not only of siliciclastics but also of pelagic carbonate.
|Sewell Point Formation from the Ocean View (1103-1104 ft) core.
The greenish color is from the mineral glauconite. There are also common shell fragments.
In the late Oligocene (approximately 27-25 Ma) sedimentation rates increased and thick prograding sequences developed. Sedimentats changed (Atlantic City Formation) and medium-to-coarse quartz sand appeared as an important constituent, along with glauconite, in the onshore boreholes. This increase in siliciclastic input clearly marks the beginning of increased sediment input from the hinterland.
|Atlantic City Formation from the Ocean View (981-982 ft) core.|