Saturated Bulk Density, Grain Density and Porosity of Sediment Cores from the Western Equatorial Pacific: Leg 7, Glomar Challenger

Paleomagnetic Results from DSDP Site 398

“…Thus, Hamilton (1974) published average porosities for abyssal plain and hill sediments from the 0 to 30-cm depth interval; calcareous oozes of clayey-silt and silty-clay grade have an average porosity of 70 per cent, and the average porosity for terrigenous sediments of clayey-silt grade and finer is 80 per cent. Gealy (1971) found that at DSDP Sites 62 and 64, the nannofossil oozes in the uppermost few meters had porosities of about 70 per cent, and the calcareous pelagic clays at Site 63 had porosities of about 80 per cent. It would therefore seem reasonable to assume that the oozes and chalks at Site 398 originally had porosites of about 70 per cent, and the mudstones, claystones, and shales originally had porosities of about 80 per cent.…”

Site 167

“…In the limestone, the dominant component is the recrystallized micritic calcite with only few foraminifera (mainly silicified); nannofossils are still common. Gealy (1971Gealy ( , p.1103 is a correlation of density with age for nannofossil oozes, it is complicated. The density differences between the two groups of sites reflect differences in sediment porosities; the grain densities are the same.…”

Introduction

“…Assigned grain densities may be inaccurate by a few percent for most cores and by as much as 10% for radiolarian oozes; a 10% error in assigned grain density causes about a 5% error in calculated porosity. Elaboration of both methods of porosity calculation and their limitations is given by Gealy (1971b). Gealy and Gerard (1970) have shown that such calculated porosities may be lower than in situ porosities by 10% to 20%.…”

“…Continuous analog GRAPE density records can be made on all cores for which density measurement is meaningful, whereas the section weight method can only be used on sections devoid of air or water pockets, and the syringe technique can only be used on relatively plastic sediments. Gealy (1971b) gives a complete discussion of the limitations of each method. She has also compared the measurements from each method with more precise determinations of wet bulk density done on land, finding that GRAPE measurements tended to be slightly higher, in general, than shore methods, syringe technique, or section weights.…”

“…Because the grain density varies greatly with lithology, we have chosen instead to calculate porosities from the GRAPE wet bulk densities by arbitrarily assigning a grain density based on the lithology. In so doing, we have relied heavily on the shore-based measurements of grain density of Leg 7 sediments (Gealy, 1971b). Porosities were calculated from the relationship 0 = (p g -Pß)/(Pg -Pf) where 0 is porosity, PQ is grain density, pg is wet bulk density (from GRAPE), and Pf is fluid density and is assumed to be equal to 1.024 (the average density of seawater).…”