Effects of Submarine Cementation on Microfabrics and Physical Properties of Carbonate Slope Deposits, Northern Bahamas

Petrographic evidence from slope rocks in the northern Bahamas reveals the widespread alteration of sedimentary facies by interstitial precipitation of fine-grained magnesian calcite. Most cementation occurs at slope depths within the permanent thermocline (200 to 800 m) and in areas of well-developed, long-slope currents.The overall effect of this process is to create muddy (micritic) lithologic units from originally mud-free sediments, thereby altering both initial textural relationships (microfabric) and the physical properties of the slope.Precipitation of magnesian calcite begins with a multiple-nucleation phase, proceeds through a period of peloid formation and is eventually terminated in a sparry overgrowth phase. The record of precipitation is found in geopetal fills contained within the rocks. Sequential precipitation, in combination with internal sedimentation, leaves a microstratigraphic record that changes upsection from amorphous micrite, through clotted and peloidal fabrics, to a capping unit of epitaxial spar. Although the micritic cement is originally deposited as a paste, continued crystal growth during sequential precipitation results in dense, hard limestone units.In this chapter we present petrographic evidence from rocks obtained by submersible, dredging and cores from the thermocline-depth slopes of the Straits of Florida and Northwest Providence Channel. This evidence demonstrates the widespread occurrence and advanced degree of cementation in the slope environment and the significance of this process in altering pre-existing sedimentary properties.