Textural Analysis of Benthic Sediments

Textural analysis involved the handling of approximately 3,700 benthic samples by the Sedimentation Laboratory of the Bureau of Economic Geology. In addition to determination of gravel-sand-mud ratios, particle-size distribution within the sand fraction (-1.0 phi to 4 phi) was determined using a Rapid Sediment Analyzer and included sand-sized shell material. Most of the shell material was broken and apparently transported. Size distribution within the mud fraction (4.0 phi to 10.62 phi) was determined with a Coulter TA II electronic suspended particle counter. Because the gravel fraction (larger than -1.0 phi) consisted largely of unbroken shell material (much of which was probably not transported), no size distribution within this fraction was determined. Most aspects of the basic sample preparation, and particle-size analysis used by this laboratory, have been treated by Krumbein and Pettijohn (1938), Ingram (1971), and Folk (1974), among others. This paper outlines a procedure for sample preparation and determination of particle-size distribution, with special attention given to problems associated with the handling of marine benthic sediments containing an abundance of soluble salts, organic matter, and shell material. The objectives of this procedure are as follows:

1. the removal of soluble salts which affect clay flocculation;
2. removal of disseminated organic matter which bonds otherwise discrete mud particles and generates misleading mud analysis data;
3. preservation of shell material in its original form so that sand analysis reflects original sediment texture more accurately.