3. SITE 1071
Position: 39°22.9446′N, 72°43.6830′W Start hole: 1300 hr, 23 June 1997 End hole: 0355 hr, 24 June 1997 Time on hole: 14.92 hr Seafloor (drill pipe measurement from rig floor, mbrf): 99.4 Total depth (drill pipe measurement from rig floor, mbrf): 151.3 Distance between rig floor and sea level (m): 11.2 Water depth (drill pipe measurement from sea level, m): 88.2 Penetration (mbsf): 51.9 Coring totals: Type: APC Number: 7 Cored: 36.3 m Recovered: 27.75 m (76.45%)
Degree of supersaturation and precipitation of organogenic dolomite
This paper integrates the degree of carbonate saturation into a general model for the origin of dolomite in organic-rich marine sediments. Degradation of organic matter by sulfate-reducing bacteria promotes early dolomite precipitation by simultaneously increasing the carbonate alkalinity and lowering the sulfate ion concentration to near zero. The interstitial water in organic-rich sediments of several Deep Sea Drilling Project sites where dolomite is believed to be precipitating is up to 10/sup 3/ times supersaturated with respect to near-ideal dolomite and up to 10 times supersaturated with respect to calcite. The highly supersaturated interstitial waters appear to overcome low-temperature kinetic barriers to precipitate a nonideal, fine-grained calcian dolomite. The degree of supersaturation with respect to dolomite decreases, and the interstitial water approaches carbonate equilibrium with increasing burial depth at several of these sites. Removal of sulfate ion is important because sulfate ion may inhibit dolomite precipitation. A calcareous sediment is not required, but the presence of calcite or aragonite appears to greatly enhance dolomitization by providing an additional source of Ca and carbonate ions.
Naturally cemented sensitive soils
Many extremely sensitive or quick clay soils, particularly but not only those found in Canada, show characteristics of natural cementation bonding between particles. These soils include not only th...