Physical Properties and Consolidation of the Calcareous Sediments of Broken and Ninetyeast Ridges

Abstract

Calcareous sediments cored at Broken and Ninetyeast ridges in the eastern Indian Ocean reveal the transitions from calcareous ooze to chalk and from chalk to limestone. Based on downhole porosity trends and laboratory mechanical consolidation tests, the compaction and lithification of these sedimentary sections occur at stratigraphically shallower depths than comparable marine calcareous sections. An exception to this case is the section at the northern Ninetyeast Ridge site. There, terrigenous silts and clays in the carbonate section appear to be normally consolidated. An analysis of porosity vs. depth trends of sediments from Sites 752 and 757 indicates an estimated 120 to 170 m of sediment were eroded during the middle Eocene uplift of this Broken Ridge.Compositional changes in the calcareous sections alter their compaction trends: inclusion of biogenic opal and/or ash results in higher porosity and lower velocity relative to the carbonate-rich horizons. The changes are observed in laboratory and log measurements and, in places, are significant enough to produce impedance contrasts giving rise to acoustic reflectors.

Comparison of the physical and geotechnical properties of gas-hydrate-bearing sediments from offshore India and other gas-hydrate-reservoir systems

“…However, there is a continual increase in the biosiliceous content of the coarse fraction beginning at about 220 mbsf from a few percent to about 30% at the bottom of the hole . High siliceous biogenic content in marine sediment has been linked to high porosity (e.g., Busch, 1989;Hamilton, 1976;Lee et al, 2013;Taylor, 1991) and even to an increase in gas hydrate saturation (Kraemer et al, 2000). In addition, it has been found to affect the engineering properties of laboratory samples (Tanaka et al, 2003).…”

“…Accurate knowledge of sediment physical properties is also necessary for borehole stability calculations and design of production-related components such as filters to prevent clogging by sediment migration (Lee et al, 2013). In addition, correlations between various properties lead to a better understanding of diagenesis and geologic history (Taylor, 1991).…”

Life cycle(s) of sediment physical properties, Ceara Rise

“…Hydraulic piston coring by the Ocean Drilling Program (ODP) has revealed for the first time the full complexity of the physical evolution of pelagic sediments. It is now clear that initial differences in the fabric of pelagic sediments are related to differences in lithology, highfrequency variations in physical properties exist in the sediment column, and primary differences in physical properties persist through at least some stages of compaction (Mienert, 1984;Wilkens and Handyside, 1985;Mayer, 1991;Herbert and Mayer, 1991;Nobes et al, 1991;Rack and Palmer-Julson, 1992;Taylor, 1991). Some simple relations often apply.…”