Geology and Geotechnical Features of the Mid-Atlantic Continental Shelf

Abstract

This paper summarizes and augments the existing geological and geotechnical engineering data on the U.S. mid-Atlantic continental shelf. This study provides a basis for planning and management for shelf users and for delineating research needs. Introduction Several major construction efforts are anticipated on the U.S. mid-Atlantic continental shelf over the next decade, including oil platforms and pipelines, deepwater ports, and power plants. In addition, there are many ongoing activities on the continental shelf, such as recreation, waste disposal, fishing, public safety, and defense. In each of these proposed efforts or ongoing activities, there is an interaction with the seabed of localized or regional nature. Preliminary information on the regional geology and sediment properties is needed for proper planning and management by shelf users and for delineating research needs. In fact, the National Research Council (NRC) Committee on Seafloor Engineering has acknowledged marine sediment studies to be of the highest priority for continental shelf development. Particular needs exist for soil maps and fundamental knowledge of the physical and engineering properties of marine sediments.The overall objectives are to summarize and improve existing geological and engineering shelf sediment information. Since the location of potential seabed developments are flexible, this study covers the general area off Delaware and extends from the beach to the shelf break. The primary objectives are (1) to assemble and interpret available geological and geotechnical data in view of possible engineering developments and (2) to obtain supplementary property data from laboratory tests. The laboratory tests were performed on samples acquired by the USGS during the recent continental margin boring program. It is the intent of this study to examine the general distribution of sediments and the unique aspects of engineering behavior. A brief review of the geology will provide a basis for examining the sediment property variations in addition to defining anticipated shelf development and construction hazards. Delaware Continental Shelf The continental shelf off Delaware is typical of the shelf along eastern North America. From a bathymetric map (Fig. 1) the shelf may be described as being broad and flat with a width of about 200 km (125 miles). The average slope is only 0.05 degrees, but many morphological features of the intermediate size, such as shoals or sand waves, exhibit locally steeper slopes of 2 or 3 degrees or more. In fact, very little of the outer-shelf topography reflects the morphology of coastal elements. The Hudson Channel and Canyon to the north of the Baltimore Canyon trough area is the only major feature that cuts the continental shelf and slope. JPT P. 363＾