Isotopic composition of low-latitude paleoprecipitation during the Early Cretaceous

Abstract

The response of the hydrologic cycle in global greenhouse conditions is important to our understanding of future climate change and to the calibration of global climate models. Past greenhouse conditions, such as those of the Cretaceous, can be used to provide empirical data with which to evaluate climate models. Recent empirical studies have utilized pedogenic carbonates to estimate the isotopic composition of meteoric waters and calculate precipitation rates for the AptianAlbian. These studies were limited to data from mid- (35°N) to high (75°N) paleolatitudes, and thus future improvements in accuracy will require more estimates of meteoric water compositions from numerous localities around the globe. This study provides data for tropical latitudes (18.5°N paleolatitude) from the Tlayua Formation, Puebla, Mexico. In addition, the study confi rms a shallow nearshore depositional environment for the Tlayua Formation. Petrographic observations of fenestral fabrics, gypsum crystal molds, stromatolitic structures, and pedogenic matrix birefringence fabric support the interpretation that the strata represent deposition in a tidal fl at environment. Carbonate isotopic data from limestones of the Tlayua Formation provide evidence of early meteoric diagenesis in the form of meteoric calcite lines. These trends in δ 18 O versus δ 13 C