Abstract

The cement volume in ooze, chalk and limestone drilled at Deep Sea Drilling Project Sites 504 and 505 (Pacific Ocean) was quantified by measuring porosity and consolidation characteristics. Heat flow clearly affects the lithification of pelagic ooze/chalk: the higher the temperature in the deposits, the more cemented is the sediment. When the temperature is four times higher, the cement content almost doubles. This study distinguishes between two processes which reduce the pore volume of carbonate sediments: mechanical compaction and carbonate dissolution at grain contacts. Mechanical compaction was quantified by compression tests in the laboratory. The effect of carbonate dissolution at grain contacts was then determined from the difference between the pore volume in the field and that determined for mechanical compaction. The cement volume at both sites was calculated based on laboratory and field data. Physical parameters such as compressibility and degree of induration are clearly related to the cement volume. The ratios between physical sediment parameters, determined at both sites for compressibility, degree of induration, and cement volume, are nearly parallel to the temperature ratio. This pattern very probably indicates the influence of temperature on chalk diagenesis. Increasing sediment temperature influences diagenesis by (1) lowering the density and viscosity of pore water and, hence, enhancing the dewatering of sediment, and (2) accelerating chemical reactions leading to increased cementation. The latter process is the most important.

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