--> Abstract: Effects Of Early Sea-Floor Processes On Preservation Potential Of Cool-Water Skeletal Carbonates, by A. M. Smith and C. S. Nelson; #90928 (1999).

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SMITH, ABIGAIL M., Department of Marine Science, University of Otago, Dunedin, New Zealand; and CAMPBELL S. NELSON, Department of Earth Sciences, University of Waikato, Hamilton, New Zealand

Abstract: Effects of Early Sea-Floor Processes on Preservation Potential of Cool-Water Skeletal Carbonates

Cool- and cold-water carbonates are different from tropical carbonates in their sources, mineralogy, geochemistry, and modes and rates of deposition. Precipitation, cementation, and sedimentation are all slow in cool waters, so carbonate sediments remain at the sea bed for a long time. Early sea-floor processes, occurring between calcification and deposition, thus take on great importance, and have a distinctive character in cool water settings.

The physical processes of dissociation, breakage, and abrasion are mediated mainly by hydraulic regime, and are always destructive. Damage reduces the size of grains, removes structure and therefore information, and ultimately may transform skeletal material into anonymous particles. The form and structure of skeletal grains strongly influences resistance to mechanical breakdown.

Inorganic precipitation is rare in cool seas. There is conflicting opinion about the importance of diagenetic dissolution of metastable carbonate skeletons on the sea floor, but maceration and early loss of aragonite are reported. Laboratory experiments illustrate that surface-to-volume ratio and mineralogy are both important in determining skeletal resistance to dissolution.

Biological processes on the floor include encrustation, a constructive process, and bioerosion, which, in contrast, is destructive and permanent. In temperate seas, because of long sea floor residence times, bioerosion may destroy even very large shells within a 1000 years or so.

Overall, processes on the temperate sea floor combine to destroy more carbonate than they produce. This is consistent with observations that temperate production rates of carbonate are up two orders of magnitude larger than sedimentation rates.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas