PALEOSOLS FROM ELEUTHERA, THE BAHAMAS: GEOCHEMISTRY AND MINERALOGY

Field reconnaissance of paleosols on Eleuthera, The Bahamas occurred during winter 2015 field season. During this work, 50 samples were collected and consisted of terra rossa paleosols, micritic crusts, and cave minerals developed on terra rossa paleosols in flank margin caves. Major element (Calcium, Magnesium, Aluminum, Silicon, and Iron) and trace element (Potassium, Sodium, and Strontium) analyses using ICP-AES and mineralogic determinations using x-ray diffraction (XRD) were conducted Two terra rossa paleosols were selected to analyze insoluble residue by size fraction.

Elemental analysis differentiated paleosol type and corresponds well to macroscopic field interpretations. Geochemical relationships exist between the abundance of Fe, Al, and Si in paleosol samples, allowing for determination of palesol type. Elemental differences between paleosols and micritic crusts are further demonstrated by examining the abundance of Mg, Al, and Fe. Paleosol samples had higher relative abundances of Al and Fe while micritic crusts had higher relative abundance of Mg.

To isolate insoluble residue, samples were treated with pH 5 NaAoC solution, hydrogen peroxide, and centrifuged for size fractionation. Silt and coarse clay fractions were analyzed using x-ray diffraction. Chemical and heat treatments were performed on coarse clay fractions. These fractions were K-treated and heated to 350 and Mg-glycol treated. Dominant mineralogy of coarse clay is Fe-rich Chlorite, Illite, and possibly Boehmite.

While sampling paleosols in Hatchett Bay Cave, earthen nodules were identified on the outcrop of paleosol. Three cave mineral samples were collected from a guano-coated exposed paleosol within Hatchett Bay Cave. The mineral samples were rusty brick-red with earthen nodules. These samples were powdered and analyzed using x-ray diffraction. Woodhouseite (CaAl₃(PO₄)(SO₄)(OH))₆, was the dominate mineral identified within these three samples. This complex phosphate mineral forms by the degradation and leaching of guano into underlying paleosols. This is the first documented occurrence of Woodhouseite in the Bahamas, which is a function of the infrequency of exposed paleosols in a phosphate-rich environment (guano deposits in a cave).