Holocene Salina Sediments of West Caicos, British West Indies: Stratigraphy, Mineralogy, and Pore-Water Geochemistry

D. B. Rosoff, G. S. Dwyer, J. Leaver, R. D. Perkins, R. M. Lloyd

A study of "east salina" on West Caicos, British West Indies, has shown it to be the site of active gypsum and dolomite formation. East salina, 3 km long and 0.25 km wide, is situated in an elongate depression between Holocene oolitic dunes to the east and eolianite ridges of Pleistocene age to the west. The thickness of the Holocene sediment package in the salina ranges from 3 m in the center to less than 0.5 m at the edges. The salina sediments exhibit an overall restrictive-upward sequence which grades from open-marine packstone and grainstone at the base through algally laminated mud and into a gypsum mush in the uppermost part of the section. A thin algal mat encrusted with gypsum and ephemeral halite covers the salina surface. This sequence is virtually identical in scale and appearance to prograding sabkha sequences reported from the Persian Gulf.

Carbonate phases present in these sediments include aragonite, high- and low-magnesium calcite, and protodolomite. Protodolomite is found as an alteration product in the open-marine sediments and within a thin, lithified Holocene basal layer that overlies laminated calichecrust on the underlying Pleistocene bed rock. Analyses of pore waters reveal that they approach normal marine salinity at the base of the salina sequence and become hypersaline upward. Mineralogical changes in the salina sequence are reflected in the ionic character of the pore waters. Field observations indicate that interstitial water within the sequence is under hydraulic head and rises and falls with the tides.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.