The sediments of the continental shelf off the eastern coast of the United States

Abstract

Our knowledge of clastic, shallow-water sediments over any considerable area of ocean floor is very generalized and leaves much to be desired. The notations concerning the character of the bottom found on all charts are necessarily limited to a descriptive word or two, and although suffcient for navigational purposes, are of little use to the stratigrapher. Of all the marine sediments in the geologic column, those laid down in the neritic zone bulk the largest. They grade slowly into the sediments of the bathyal zone with no sharp line of demarcation. The early oceanographers were more interested in the clays and organic oozes of the deep sea and they added but little information concerning those materials which to the geologist are the most important. From the charts one is apt to obtain the impression that bottom deposits, excepting those of the deep sea, are very patchy in their distribution, and that there is little rhyme or reason in their arrangement. On the other hand the geological text books are apt to make it appear that there is an orderly gradation of sediments from coarse to fine in an offshore direction, and that a sandstone is always an indication of shallow water deposition, with a shale the reverse. Twenhofel has called attention to the role of environment in sedimentation. Like organisms, sediments are the resultants of a long sequence of environmental factors to which they have been exposed: action by currents, wave generated and otherwise, availability of supply and its type, distance from shore, and depth of water, plus their combined effect during times of changing sea level in the past. These factors have operated in the regions of production, during the period of transportation, and at the place of deposition, and the retention of older characteristics further complicates the record. The following study was undertaken with the hope that through a detailed and systematic series of samples not only might something be learned about the characteristics and distribution of the sediments of a particular area, but something also of the environmental factors which govern conditions of sedimentation in a major ocean.