Carbonate mineral cycles in ramp slope sediment: Eastern Gulf of Mexico


  • Anne F. Gardulski,

  • Henry T. Mullins,

  • Bronya Oldfield,

  • Joe Applegate,

  • Sherwood W. Wise Jr.


Carbonate mineral cycles, controlled by Pleistocene climatic rhythms, have been discovered in a 11.6 m-long-piston core from the west Florida carbonate ramp slope at 890 m of water depth in the eastern Gulf of Mexico. Relatively high concentrations of aragonite, magnesian calcite, and dolomite, as well as insoluble residues, total organics, and mud-sized sediment, all correlate with glacial periods defined by oxygen isotope stratigraphy. The aragonite is a low-strontium variety derived from pteropods, and there is no evidence that concentration variations are controlled by dissolution. We propose that these mineral and textural cycles are the product of a combination of increased biological productivity and dilution by fine-grained terrigenous mud during glacial episodes. Aragonite cycles in Bahamian periplatform slope sediment have also been correlated with climatic change. There the aragonite is a high-strontium variety derived from shallow-water calcareous algae, with relatively high concentrations correlated with high sea levels during interglacial periods. The carbonate mineral cycles along the west Florida ramp slope are 180° out of phase with Bahamian examples and also lack their marked asymmetry. It is now apparent that for deepwater, continental margin carbonates there are two types of carbonate mineral cyclicity: one that is “pelagic driven” during glacial periods, and one that is “platform driven” during interglacials. These contrasts emphasize the differences in deep water cyclic sedimentation on carbonate ramps versus rimmed carbonate platforms that are controlled by physiography, sediment source, oceanographic setting and proximity to terrigenous input. The productivity-dilution model proposed here may be a valuable modern analog for ancient carbonate sequences deposited in epicontinental seas or on ramps attached to continental margins.