A preliminary report on the Rare Earth Element + Yttrium (REE+Y) analysis from the Tlayúa Quarry Konservat-Lagerstätte (Tlayúa Formation; Lower Cretaceous, Albian) of Tepexi de Rodríguez, Puebla, Mexico: Results from Zone 13

Abstract

The Tlayua Quarry Konservat-Lagerstatte (Albian, Lower Cretaceous; Tepexi de Rodriguez, Puebla, Mexico) is known worldwide for the preservation of its ubiquitous fossil remains. Major and trace element concentrations of selected limestone samples from zone 13 of the Tlayua Quarry were measured in order to understand the depositional conditions and source of REE + Y. The concentrations of SiO2, Al2O3, P and Zr show little contamination by terrigenous material and phosphates in this zone, at least to instances in which the REE + Y concentrations can be both shale-normalizable and reliable. REE + Y plots display typical modern seawater signals; namely, positive La and Gd anomalies, superchondritic Y/Ho ratios (between 46.421 and 67.777) and slight depletions of LREE and MREE with respect to HREE (x Pr/Yb = 0.201; x Nd/Yb = 0.305 and (x Dy/Yb = 0.683 respectively). Furthermore, sustained negative cerium anomalies could be identified (Ce/Ce* = 0.613), which would indicate oxidating conditions as in modern seawater. The observed REE + Y patterns, which constitute the first palaeoenvironmental inference by means of element analysis performed in Tlayua, suggest that the limestones from zone 13 still retain their original seawater pattern. Considering that terrigenous and phosphate contamination is overall low in the analysed samples, REE + Y (REY) patterns from the Tlayua Formation can be useful palaeoenvironmental proxies for the Cretaceous. All this allows the conclusion that, at least during the deposition of these limestones from zone 13, a typical marine signature can be seen. This does not exclude, however, the presence of a tidally or strongly monsoonic-influenced sedimentation in other sediments from zone 13 or from other zones in Tlayua, as previous works have suggested.