Abstract

The New Jersey margin is a classic example of a siliciclastic passive margin which prograded during the Miocene and Pliocene, forming well-defined clinoforms on seismic data. It has been explored by the petroleum industry since the 1970s and more recently by Deep Sea Drilling Program and Ocean Drilling Program legs. Within this well-constrained geological framework, the stratigraphic and spatial distribution of sedimentary organic matter (OM) in fine-grained sediments has been analyzed along a transect from paleoshelf to paleoslope provided by four ODP Sites. This led to the establishment of a depositional model for sedimentary OM in prograding clinoforms, which can be applied worldwide to other similar environments of deposition.

The most significant factor influencing the type of OM sedimentation (palynofacies) is the location of the sites with respect to the shelf break. The correlation of palynofacies parameters with gamma-ray, Rock-Eval pyrolysis, and seismic data has permitted the establishment of a model for the sedimentation of OM across the margin. Various parameters indicative of proximal–distal trends have been tested, their validity tending to deteriorate distally. The most reliable ones are: (1) the continental/marine ratio (based on palynomorphs), (2) the relative percentage of amorphous OM, and (3) phytoclasts. The variations in the continental/marine ratio permits the identification of stacked transgressive–regressive intervals related to accommodation cycles and of associated condensed intervals. This palynofacies parameter can be correlated with the seismic facies at the locations of the sites.

Total organic carbon (TOC) content usually varies similarly to the continental/marine ratio, which implies that most sedimentary OM is of continental origin. The only exception is in transgressive intervals, where it varies in the opposite way, thereby indicating a change in the source of sediment and an increased concentration of marine OM. Similarly, the gamma-ray log is a good proxy for proximal–distal trends (coarse to fine sediments) at all sites, where it varies similarly to the continental/marine ratio, except in condensed intervals in the distal part of clinoforms where it records the settling of uranium-rich clay particles. Furthermore, the positive correlation between the gamma-ray data, TOC data and the continental/marine ratio confirms that the hydrodynamic behavior of continental sedimentary OM is close to that of clay and silt particles.

This research illustrates the contribution of sedimentary OM to the study of fine-grained sediments prograding on a passive margin. Some parameters, especially the continental/marine ratio, can be used as proxies for the sedimentological interpretation of sites and for distinguishing transgressive–regressive trends within prograding clinoforms.