Physical-property data of turbidites and periplatform ooze of ODP Leg 101 holes (Table 1)

Along the slopes and in adjacent basinal areas of Bahamian platforms, periplatform ooze forms the host sediment for variable proportions of carbonate turbidites. In unlithified sections, these turbidites appear as unconsolidated layers intercalated with stiffer ooze. Within an individual turbidite, differences in grain size result in variations in consolidation and physical properties. With decreasing grain size, water content and porosity decrease, and two distinct surfaces develop at the lower and upper boundaries of the turbidite. These surfaces are potential instability horizons where mass-wasting can occur. Therefore, a relation between turbidites and slumping frequency is proposed. The higher proportion of turbidites in sediments deposited on low-angle, accretionary terrains, such as the toe of the northern slope of Little Bahama Bank, probably facilitates frequent, small-scale slumping and creeping, as seen in seismic profiles. In contrast, slumping is less frequent along the steeper (12°) bypass slope in Exuma Sound, where turbidites are rarely found.Where the background sediment was initially a pelagic nannofossil ooze rather than a periplatform ooze, mineralogical composition results in lithification differences. In lithified sections having chalk as the background sediment, turbidites display a higher sonic velocity, indicating that they are the more competent beds. This lithification variation is the result of differential diagenesis between the platform-derived turbidites, enriched in metastable carbonates, and the calcitic nannofossil ooze of the background sediment. The different lithification owing to dissimilar mineralogical composition could also influence fluid migration in carbonate sequences. In a periplatform sequence, the more porous turbidite might be the fluid conduit, whereas in a pelagic sequence the chalky background sediment allows for fluid migration.