Reconstructing the stratal geometry of latest Eocene to Oligocene sequences in New Jersey: resolving a patchwork distribution into a clear pattern of progradation

Abstract

Nine latest Eocene to Oligocene (34.2‐23.9 Ma) sequences were identified and dated from eight sites situated on the onshore New Jersey Coastal Plain and nearshore region. These sequences show a patchy distribution, with more complete lower Oligocene sections updip and more complete upper Oligocene sections downdip. We projected these sequences onto a dip profile and reconstructed their original thicknesses and distributions by 2-D flexural backstripping. This demonstrated that depocenters migrated offshore during the Oligocene, indicating that the patchy distribution can be best explained by progradation of generally thin and spacially limited clinoforms over an Eocene carbonate ramp. During the late Eocene to Oligocene, the New Jersey passive margin underwent a major morphologic change. Reconstructions indicate that the margin was a relatively steeply dipping carbonate ramp (1:500 paleoslope gradient) during the Eocene and was transformed into a siliciclastic margin characterized by a gentler gradient of 1:1000 and prograding clinoforms by the Miocene. Clinoform progradation probably began during the latest Eocene. Increased sediment supply during the Oligocene resulted in the further progradation of sediments across the antecedent carbonate ramp. The heights of the clinoforms ranged from ,20 m during the latest Eocene and earliest Oligocene to nearly 50 m during the late Oligocene. Most sediment accumulated within clinoform wedges, with little or no sediment being preserved behind the clinoform inflection point. q 2000 Elsevier Science B.V. All rights reserved.