EVIDENCE FOR A REINSTATEMENT OF THE DIXON HILL MEMBER TO THE GROTTO BEACH FORMATION, SAN SALVADOR, BAHAMAS
The measured section began near the Lighthouse cave mouth, sampling at 1.5-m intervals along the trail using a 1.5-m Jacob staff and rudimentary sighting device. This unit is present from the cave mouth to approximately the 17.4 vertical meter mark, and is recognizable in both hand samples and thin sections. Within the 14.3 to 17.4-meter interval, the grain sizes of the foraminifera and red algae fragments become slightly smaller (0.2-0.6mm). At 17.4-meter elevation along the section, algae and foraminifera grains are abruptly replaced by well-formed ooid grainstones (0.2-0.4mm), which continue to the top of the trail.
We postulate that this unit formed as sea level fell following the MIS 5e high stand of sea level, which was responsible for the development of the Cockburn Town reef facies. This marine incursion onto San Salvador likely created shallow, normal marine environments, which supplied the abundant biotic clasts present in this coarse-grained facies, and were slightly reworked during sea-level fall. This unit was subsequently draped by younger, carbonate ooid grainstones that are exposed along the road up to the lighthouse and drape the coarser-grained strata. Future research will determine the extent of this layer throughout the Dixon Hill area and the potential that it forms the core of other island ridges. We will also begin foraminifera identification to obtain potential paleoecologic and biostratigraphic information.
This easily identified unit is unlike other samples of the currently accepted formations and their members. Our data support the inclusion of an additional member within the Grotto Beach Formation, and thus providing a more detailed stratigraphy of San Salvador.