U.S. Geological Survey Open-File Report 94-152

Geologic Features of the Sea Bottom Around a Municipal Sludge Dumpsite near 39鑞, 73鱒, Offshore New Jersey and New York: U.S. Geological Survey Open-file Report 94-152

INTRODUCTION

An area of the sea floor south of Hudson Canyon off New Jersey was mapped as part of a study to determine the effects of offshore dumping of municipal sewage sludge on the sea bottom. The dump site for municipal sludge lies within a large area of continental slope and continental rise that has been used for offshore dumping since the 1950's. The area is called Deep Water Dumpsite 106, because the original site lay approximately 106 miles offshore.

An Index Map showing the continental margin off the mid-Atlantic Coast of the U.S. Areas of the following GLORIA mosaic illustration and the site-mapping studies are outlined as rectangles; an area mapped using Sea Beam bathymetry is shown as an irregular polygon; and the most recent sludge dumpsite area is outlined as a smaller north-south rectangle.

Previous stratigraphic investigations of this offshore region using data from boreholes and seismic profiles show that sequences of continental rise sediments lap onto eroded, slightly seaward-dipping strata of the lower continental slope.

Airgun seismic-reflection profile across the central part of the study area. Nearly flat continental-rise sediments of Neogene age lap onto an unconformity on seaward-dipping Eocene strata of the continental slope.

Brecciated rocks and exotic sediments that are found in borehole samples, and faults and chaotic and distorted seismic facies that are revealed in profiles show that submarine landsliding has been the principal agent of deposition on the upper rise during the Cenozoic (Poag and Mountain, 1987).

Previous environmental geologic studies of the dumpsite area include those of Neiheisel (1979, 1983), who investigated geochemical and physical parameters of surface sediment samples. Hanselman and Ryan (1983), and Rawson and Ryan (1983) reported bottom observations from the deep sea research vessel (DSRV) Alvin. Ryan and Farre (1983) discussed geologic processes in the dumpsite area and inferred that both mass wasting and turbidity currents have been active and may presently be active within this area. Pratson and Laine (1989), mapped the surficial character of the sea bottom using 3.5-kHz echo-sounding profiles.

To study the geologic context and processes of this submarine dumpsite and to provide information for choosing appropriate sample sites where fine-grained material might be more likely to accumulate, the sea-floor of the dumpsite area was mapped using multibeam bathymetry, sidescan-sonar images, subbottom profiles, bottom photographs and video, and bottom-sediment samples.

ACKNOWLEDGEMENTS

Fred Grassle of Rutgers University organized the program to study the benthic environment of the deep-water dumpsite region near 39鑞, 73鱒, of which this investigation is one part. I thank the officers and crews of RV Atlantis II, Rv Oceanus, and RV Betty Chouest, the Alvin group and the Deep Submergence Laboratory of the Woods Hole Oceanographic Institution, and the Sea Beam processing group of the Graduate School of Oceanography, University of Rhode Island; Joyce Miller shepherded the collection and processing of the Sea Beam bathymetric data aboard Atlantis II. This research was funded by the National Undersea Research Program (NURP) of the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS).

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