Abstract

Because the shallow isolated carbonate banks on the northern Nicaragua Rise, the Nicaragua/Honduras and southern Jamaica carbonate shelves, and many other modern carbonate banks worldwide, are covered by an average of 20 to 30 m of water and by a thin blanket of coarse carbonate sediments, other carbonate sedimentologists have considered these banks good examples of "incipiently drowned", or even "drowned" carbonate banks. However, based on recent research on the northern Nicaragua Rise, we can demonstrate that these banks currently are healthy producers of large volumes of periplatform sediments (fine aragonite and magnesian calcite), which are exported almost entirely to the deep surrounding slopes. These sediments, which were deposited during the past 9000-10,000 years, form periplatform wedges on the middle and upper slopes, which are seen clearly on 3.5 kHz seismic profiles. Radiocarbon ages of the wedge surface sediment range between 230 and 610 YBP and provide clear evidence for the contemporaneous production of sediments on the shallow bank and shelf and their instantaneous export to the upper slopes. For the last 5000 years, sedimentation rates ranged from 2000 mm/ky off Pedro Bank to 1300 mm/ky off Jamaica. These rates are somewhat lower than, but of the same order of, magnitude as sedimentation rates on the western (leeward) slopes of Great Bahama Bank. Deposition of the metastable carbonate sediments discussed in this paper occurred as soon as sea level rose to flood the bank and shelf which flank Walton Basin, following the last glacial lowstand. They comprise a wedge-shaped package of transgressive and highstand sediments on the upper and middle slopes of Pedro Bank and the southern Jamaica shelf.

You do not currently have access to this article.