87 Marine/Coastal Science (Posters)

A COMPARISON OF STRATAL GEOMETRY IN THE GREENHOUSE AND ICEHOUSE WORLDS FROM MULTICHANNEL SEISMIC REFLECTION AND CHIRP SONAR DATA FROM NEW YORK BIGHT

Paper number: 87-5
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

We have used 24-fold high-resolution multi-channel seismic (MCS) and swept frequency (chirp) sonar data acquired during cruise 370 of the R/V Endeavor along the New York Bight to analyze stratal geometry in sediments from the Cretaceous-Eocene “greenhouse world”. This is a time during which glacioeustatic change is thought to have been either minor or absent, in contrast to the Oligocene and younger “icehouse world” when glacioeustasy played a major role in modulating sedimentation at passive continental margins by causing 30-80-m of apparent sea-level change. While borehole data from the New Jersey coastal plain have previously been used to interpret upper Cretaceous and Cenozoic sequences and sea-level change, only upper Oligocene and younger strata had been imaged with high-resolution MCS and chirp prior to this cruise.

These new data reveal < 25 m of upper Pleistocene sediments resting unconformably on sediments that gradually thicken and dip towards the southeast. The oldest imaged strata are upper Cretaceous. Small (25-35 m) offlapping clinoforms are observed within upper Cretaceous to lower Paleocene reflections offshore Fire Island, NY. Although this geometry suggests the presence of a sequence boundary, and is consistent with sea-level modulation, it is observed on only one seismic profile and its significance is therefore uncertain. Clinoformal geometry was identified also within upper Eocene reflections thought to correlate with the upper Shark River Formation of the Sea Girt borehole, NJ located 4.5 km up dip of the nearest En370 seismic line. These upper Eocene to Oligocene clinoforms downlap onto a major regional downlap surface of late Eocene age with larger clinoforms continuing into the Miocene. The paleo-Hudson Shelf Valley erosionally truncates Paleogene strata west of a Pleistocene sediment wedge 60-70 meters thick. Data also reveal 35-45m of displacement along the 95-30 Ma New York Bight fault.