No abstract

Sedimentological, petrographic and radiometric data from a submerged beachrock on San Salvador Island, Bahamas, provide new information about the Late Holocene sea-level history in this area.At French Bay, on the southern shore of the island, samples of beachrock collected at a depth of 1 m below low tide level yielded an average 14C age of 965 + 60 years before present. These samples further display a well developed fenestral porosity and present an early generation of low Mg calcite meniscus cement. These features characterize intertidal and supratidal settings; they are not consistent with the present beachrock position and the reported Late Holocene sea-level history in the Bahamas. A 1 . 5 -2 m low stand of the sea about 1 000 years ago would best explain the observed particularities of the French Bay beachrock.This example from San Salvador shows that the smooth trend of Late Holocene sea-level rise proposed by previous workers might be overprinted by high frequency, low amplitude fluctuations. Recognition of these fluctuations is fundamental when calculating rates of sea-level rise and evaluating the coastal response to a marine transgression.

There are three main types of soils in the Bahamas: sandy, organic, and lateritic soils. Sandy soils occur on unconsolidated carbonate sands and consist of unaltered carbonate minerals plus organic matter. Organic soils contain abundant organic material and lack mineral matter. They are most common on flat, rocky lands of the larger Bahamian islands. Lateritic soils are thin and discontinuous, and occur on lithified Pleistocene eolian and beach ridges. They have low SiO 2 /Al 2 O 3 ratios and contain calcite, aragonite, hematite, goethite, hydroxy-interlayered clay (HIC), boehmite, and quartz. The following petrographic features were observed in pedogenically altered Pleistocene grainstones: rhizoliths, pedotubules, alveolar textures, calcified root hairs, Microcodium, laminated micrite, clotted micrite, soil pisoids, circumgranular cracking, horizontal fractures, microbial borings, and iron-rich clay accumulations. The characteristics of Bahamian soils result from a complex interaction of the five major soil-forming factors: climate, topography, vegetation, parent material and time.

No abstract

No abstract