Representative sediments from each site were chosen for examination of their dry specific gravity and grain density. The determinations were made by micropycnometer; water was used as the displacing medium, and salt corrections were based on the refractive index measurements on interstitial water. For saltier brines the "salinities" derived from index of refraction are somewhat too low but, for the most part, are adequate for these corrections. Water contents are those determined on the archived samples selected for these studies. They had been kept in cold storage (4°C) in screw-capped glass bottles with poly seal lids or in heat-sealed polyethylene bags for a period of about three months.
The purpose of the measurements was to gain sufficient information on grain density to permit application of the general information or pattern to the bulk water content determinations on the small syringe samples. Bulk density, porosity, and other properties could then be calculated without using volume measurements from the syringes. Whereas the data from weight loss on drying (bulk water content) at 110-120° were considered good, the volume measurements are subject to considerable error, especially in more consolidated sediments, and are not usable at all for shales, more consolidated or cemented rocks, and anhydrite.
Detailed comparisons with the GRAPE determinations were also an objective. The Red Sea cores offer a particularly good opportunity to test the validity of these measurements, which have been increasingly questioned.
