QUATERNARY CARBONATES IN KARSTIC LANDSCAPES OF YUCATAN PENINSULA AND THE ISLAND OF COZUMEL, MEXICO: PALEOENVIRONMENTAL RECONSTRUCTION BASED OF STABLE ISOTOPE STUDIES

In the karstic landscape (southeast Mexico), at Peninsula de Yucatan and Cozume island, three levels of Quaternary compact carbonate crusts (calcretes) interlayered with indurated coastal calcareous sediments are found, that contain significant environmental information. More precisely, the calcrete layers represent the stages of low sea level stand while the coast marine sediments are linked to sea level rise. We studied several stratigraphic sections along the shore, where samples of carbonates were collected: palustrine, calcrete and eolinite. They were analyzed geochemically (δ¹³C and δ¹⁸O), and micromorphologically, firstly to differentiate the type of carbonate, and secondly to infer their paleoenvironmental formation conditions. Under the microscope, we differentiated the calcretes by their fabrics (α-calcretes and β-calcretes), from the palustrine carbonates (with peloidal and mottled fabrics). Geochemically, calcretes compared to eolinites were depleted in δ¹³C, with values ranging between -2‰ and -10‰. The isotopic signature of palustrine carbonate showed mean values of 5.24‰ and -4.9 ‰ for δ¹³C and δ¹⁸O, respectively. These values fall in between those of calcarenites and calcretes. The δ¹³C (ranging from -10.10 to -7.50 ‰) and δ¹⁸O (-5.63 to -4.64 ‰). We interpret the isotopic δ¹³C values as the result of changes in vegetation from a predominant C3 vegetation associated with a cool-wet climate to a C3/C4 mixed vegetation, which is a plant cover that grows in a drier-hotter climate. The isotopic composition of all calcretes analyzed in this work are similar to that reported for the Pleistocene and Holocene calcretes exposed in the Caribbean Sea region.