A study of carbonate beach sands from the Yucatan Peninsula, Mexico: a case study

Abstract

Sedimentological, geochemical, and X-ray diffraction (XRD) analyses in addition to the determination of biogenic fraction components (BFC) were performed in mollusk shells from carbonate beach samples collected on the northern coast of the Yucatan Peninsula, Mexico. The most abundant components of the BFC were bivalves and gastropods shells, ranging from 88.1 to 99.2 % and from 0.1 to 6.0 %, respectively, followed by minor percentages of foraminifera, coral fragments, bryozoa, oolites, spicules, and ostracods. A combination of major element, trace element, and XRD techniques were performed to show how the Mg/Ca and Mg/Sr ratios determine the possibility of a recrystallization process in bivalves and gastropods, which may be attributed to early diagenetic mechanisms caused by groundwater flows, subaerial exposure, high evaporation rates, and neomorphism. The rare earth element analyses gave the average anomalies for the following ratios (Pr/Yb)PAAS and MuQ ratio > 1, (Eu/Eu*)PAAS and MuQ and (Ce/Ce*)PAAS and MuQ < 1, suggesting little incorporation of sea water in the BFC of the shells from the Yucatan beach sands. This is also supported by the flat pattern trends of bivalves and gastropods based on the normalized patterns of light rare earth element compared to heavy rare earth element concentrations. This paper is also a contribution to the methodology of analysis of carbonate sands, i.e., whole bulk composition isolation into their main biogenic components and the accumulation of major, trace, and rare earth elements deposited into their shells, initially under subaquatic marine conditions and currently exposed to subaerial coastal influences based on the allochthonous character of the shells.