Shallow-burial diagenesis of deep-water carbonates, northern Bahamas: Results from deep-ocean drilling transects

Abstract

Rates of burial diagenesis and subsurface distribution of chalk and limestone in modern deep-water carbonate slopes were little known prior to 1985 when the Ocean Drilling Program established two drill transects in the northern Bahamas: north of Little Bahama Bank and in southwestern Exuma Sound. From these transects, different shallow-burial ( Along the accretionary north margin of Little Bahama Bank, the amount of lithified strata decreases seaward because of a decreasing volume of bank-derived aragonite. The rate of bulk carbonate calcitization increases seaward as the rate of diagenesis begins to match, then exceed, the rate of burial. Mineral-controlled diagenesis is of little consequence below about 20 m subsurface only 30 km seaward of the bank margin. Along the bypass margin in Exuma Sound, the extent of lithification increases downslope toward preferential accumulation of bank-derived aragonite; much higher accumulation rates and high percentages of aragonite along this margin sustain a still-present, mineral-controlled diagenetic potential in limestone at 300 m. From analogy of modern Bahama slopes, considerable diagenetic heterogeneity within the shallow-burial realm may be expected along some ancient carbonate margins. Our results serve to illustrate carbonate-mineral stabilization and early limestone formation with secondary porosity in a sea-water-mediated environment, and they further highlight the high diagenetic potential of periplatform carbonates.