High-Resolution Seismic Profile and Sidescan-Sonar Data Collected During June 1980 Offshore New Jersey, Whitefoot Cruise 80-1

Abstract

This survey (888 km), of the New Jersey nearshore area, extended between Corson Inlet to the south and Mlanasquan Inlet to the north and from about 8 m depth to about 25 m depth. The lines were located between latitudes 39° and 40°10'N and longitudes 73°50' and 74° 40'W. High-resolution seismic­reflection data were collected using an EG&G Uniboom (400-4000 Hz) and an ORE Mode! 1035 (3.5 kHz) subbottom profiling system in conjunction with a Klein Sidescan Sonar System (100 kHz). While the quality of the data is variable, it is virtually all usable and generally of good quality but rarely excellent. Due to equipment failure, only 880 km of 3.5 kHz and 796 km of sidescan-sonar data were recorded. Navigation was by Loran-C. and fixes were recorded at 5-minute time intervals with some gaps in the data. Analysis of the sidescan-sonar data shows five recognizable features in the study area. Megaripples (2-3 m crestal spacing) were recorded almost exclusively on coast parallel tracklines, and were most abundant at distances of 10 to 20 km offshore. Nonlinear light and dark patches were abundant in the northern half of the study area and offshore to the south. Two groups of linear light and dark bands were observed as being clearly parallel or oblique to the bathymetric contours and were noted throughout the survey area. Trawl marks were noted on only one line near the shore, just north of Barnegat Inlet. These observations indicate widespread, perhaps frequent, movement of the surface sands on the Inner New Jersey continental shelf. Directions of sediment transport are suggested by the orientation of the alternating light and dark bands and the ripples, assuming a parallel and/or transverse relative movement. Asymmetry of the ripples was not observed on the sidescan sonographs. The high-resolution seismic-reflection profiles indicate three distinct types of subbottom stratigraphy in the top 20 to 40 m of sediment. Reflectors in the area north of Barnegat Inlet dip gently (<1° ) to the south-southeast. The thirty plotted reflectors are 5 to 12 m apart (vertically), are essentially parallel, and are truncated on the updip (northern) limits where they outcrop or subcrop (under a 2-4 m overburden). Truncated by erosion, they are the dominant cause of N65° east-striking topographic ridges in this offshore region. The age of the reflectors is· inferred to be Tertiary from the strike and dip, which are the same as the Tertiary beds of adjacent New Jersey.