Patterns of Sediment Compaction at Ocean Drilling Program Sites 645, 646, and 647, Baffin Bay and Labrador Sea

Abstract

With several exceptions, porosity and density measurements of sediments cored at Site 645 in Baffin Bay and Sites 646 and 647 in the Labrador Sea reveal compaction patterns typical of terrigenous sediments. Deviation from standard porosity trends is greatest at depths shallower than 350 meters below seafloor (mbsf). This depth range contains the greatest variability in porosity at the individual sites and the largest differences between the Leg 105 sites and other terrigenous sediment sections. Porosity variation in this range is attributed primarily to differences in sediment texture and composition. At greater depths, pressure is the dominant factor influencing compaction, and the patterns are more uniform. Sediments at Sites 645 and 646 parallel typical terrigenous sediment porosity profiles. The more rapid decrease of porosity at Site 647 probably reflects the greater age and diagenetic alteration of these sediments. Comparisons of porosity profiles for the three sites are based on laboratory-measured porosities corrected for sediment expansion. At Site 646, the expansion correction procedure yields a porosity profile that closely matches a profile based on porosities estimated from the borehole sonic log.

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

“…study because straight-line segments facilitate comparison, provide immediate recognition of rate effects, and are very close to more advanced models over discrete depth intervals. In addition, the exponential porosity law may not apply in all instances (Busch, 1989). At Hole NGHP-01-1A, porosity versus depth approximates the trends for deep-sea terrigenous and calcareous sediment ( Fig.…”

“…S pp /s' v at the top of Hole NGHP-01-1A exhibits pseudooverconsolidated behavior prevalent in many fine-grained sediments where electrical forces at shallow subbottom depth influence compaction more than gravitational forces (Francisca et al, 2005). Variations in clay mineralogy and sedimentation rates affect compaction patterns at low overburden stresses (Busch, 1989). This upper zone has sediment characteristics (high water content, etc.)…”

“…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).…”

“…This occurs both locally as a reservoir for individual hydrate grains and assemblages and also on a much larger scale by influencing fault patterns and characteristics (Minor and Hudson, 2006) that are responsible for regional fluid and gas flow that feed hydrate reservoirs (e.g., Riedel et al, 2010a). Furthermore, faults might serve as mechanisms to locally change sediment porosity (Busch, 1989).…”

Deep seismic reflection data across the conjugate margins of the Labrador Sea

“…The effects on densitv of increased temperatures in the younger oceanic lithosphere are included, but are quite small. Sediment thicknesses were fixed using the seismic results, and the corresponding densities were assigned using the well logs from boreholes on the Labrador shelf and from the Ocean Drilling Program in the deep basin (Busch 1989). Typical values of density were chosen for crust and mantle rocks (Ludwig et al 1970).…”