Mineralogy, chemistry, and petrography of soils, surface crusts, and soil stones, San Salvador and Eleuthera, Bahamas

Abstract

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.

Soil genesis on the island of Bermuda in the Quaternary: The importance of African dust transport and deposition

“…The dominant clay mineral in soils and paleosols of all ages is hydroxy‐interlayered clay (HIC), as determined by a four‐treatment XRD process. The presence of HIC as the main clay mineral in Bermuda's soils and paleosols is consistent with similar observations of HIC we have made for soils on carbonate beach deposits in the Bahamas and in soils on Quaternary carbonate reefs in the Florida Keys Foos and Bain [1995]. also reported HIC in soils on carbonate aeolianites in the Bahamas.…”

“…We found boehmite in both the A and B horizons of the paleosol developed on aeolianite of the Walsingham Formation at Ireland Island‐North (Figure 14). Boehmite is also present in the surface soil developed on a last‐interglacial‐age reef on Key Largo, Florida (Figure 15) and Foos and Bain [1995]reported boehmite in a soil developed on carbonate aeolianite on Eleuthera Island, Bahamas. Goethite was found in a number of paleosols, as was clay‐sized quartz, but where they occur, abundances of both of these minerals are much lower than the amounts of clay‐sized HIC, woodhouseite or boehmite, based on relative peak heights.…”

“…However, they rejected an HIC identification of the Bermuda soil clays and interpreted their XRD patterns to indicate a mixed‐layer chlorite‐vermiculite. Their interpretation is based on a shift of the 14.2Å peak to 12.5Å, rather than 10Å, with heat treatment (550°C) Foos and Bain [1995]. pointed out, however, that heat treatment of HIC can shift the 14.2Å peak to either 12.5Å or, with low levels of interlayering, to 10Å.…”

“…Their interpretation is based on a shift of the 14.2Å peak to 12.5Å, rather than 10Å, with heat treatment (550 C). Foos and Bain [1995] pointed out, however, that heat treatment of HIC can shift the 14.2Å peak to either 12.5Å or, with low levels of interlayering, to 10Å.…”

Microcodium Revisited: Root Calcification Products of Terrestrial Plants on Carbonate-Rich Substrates

“…Microcodium does not appear to exist today, although it has been reported from Quaternary carbonate eolianites on Isla Contoy, off the Yucatan Peninsula (Ward 1975;McKee and Ward 1983), the Mediterranean island of Mallorca (Calvet et al 1975), and from calcrete crusts on San Salvador, Bahamas (Bain and Foos 1993;Foos and Bain 1995). Accumulations of Microcodium are abundant in Cretaceous, Paleogene, and Miocene continental and marine carbonate successions, especially in the peri-Mediterranean area.…”