EAST-COAST SEDIMENT TEXTURE DATABASE

Introduction

Because many scientific questions and policy issues related to sediments require data of historical, regional and interdisciplinary scope. Existent data is often geographically clustered and its references are widely dispersed and not always accessible. Acquisition of new data is expensive and may duplicate previous efforts if there has not been a full interpretation of existent data. Consequently, existing data need to be utilized to their maximum so that they can serve as a foundation, baseline, and starting point for further work. An accessible, documented, and simple-to-use compilation of existing data on sediment properties is essential for environmental managers, policy-makers, scientific researchers, and interested members of the public. We have compiled, edited, and integrated the available data on sediment texture and bottom descriptions produced at the Woods Hole Science Center of the Coastal and Marine Geology Program of the U.S. Geological Survey in order to produce a regional database.

This sediment database contains information on collection, location, description, and texture of samples taken by the marine sampling programs of the Coastal and Marine Geology Program of the U.S. Geological Survey. Most of the samples are from the Atlantic Continental Margin of the United States, a small number of samples have been collected from a variety of other locations such as Lake Baikal, Russia, the Hawaiian Islands region, Puerto Rico, and Lake Michigan. At present, the database contains about 23,000 samples, including texture data for approximately 3800 samples taken or analyzed by the Atlantic Continental Margin Program, a joint U.S. Geological Survey/Woods Hole Oceanographic Institution project conducted from 1962 to 1970 (Emery and Schlee, 1963). The data from this program were originally reported by Hathaway, J.C., 1971. Texture data for approximately 19,500 samples analyzed by the Sediment Laboratory of the Coastal and Marine Geology Program of the U.S. Geological Survey, Woods Hole MA after 1980 make up the rest of the database. Considerable data from the period 1970 to 1980 are yet to be digitized and added. Although most records contain complete grain size analyses, some are simple bottom descriptions from rocky and bouldery locations where samples were not taken. Most of the samples were collected with some type of grab sampler; a few were obtained by coring.

Individuals should be careful when assuming geodetic controls for the textural data because different systems, datums, and navigational equipment were used to locate the sample sites. Geodetic systems and datums define the assumed shape and size of the earth and the origin and orientation of the coordinate systems used to map its surface. Referencing latitude and longitude coordinates to the wrong system or datum may result in significant position errors. Most of the sampling conducted prior to 1971 was navigated with LORAN-A and is based partly on the Clarke 1866 and partly on World Geodetic System 1964 (WGS-64) reference ellipsoids, and most of the sampling conducted between 1972-1988 was navigated with LORAN-C and is based on the World Geodetic System 1972 (WGS-72). The Loran shore stations for the North American sample sites were surveyed on the 1927 North American Datum (NAD 27). Finally, most of the sampling conducted after 1988 was navigated with the Global Positioning System (GPS) and is based on the World Geodetic System 1984 (WGS-84). Conversion programs that adjust between the different reference ellipsoids and cartographic datums (e.g. NADCON) are available on the World Wide Web. Horizontal errors associated with the above mentioned navigational equipment vary spatially and average 185-460 mm (absolute accuracy), <100 m, and <10 m for Loran-C, GPS, and differential GPS, respectively (D. Olmsted, Woods Hole Oceanographic Institution, Oral Communication). Generally, LORAN-A had an average expected accuracy of 1 percent of the distance between the navigator and the shore stations (U.S. Coast Guard, 1949).