PALEONTOLOGICAL RECORD OF A GONDWANA CRETACEOUS PALEOLAKE AS PROXY FOR PALEOCLIMATE RECONSTRUCTION

Abstract

The La Cantera Formation (Aptian) represents an underfilled lake system developed in an extensional basin during the Cretaceous hothouse and it bears an abundant and diverse fossil record. Our goal was to investigate paleoclimate conditions of the unit from a multiproxy approach. We analyzed two proxies: a) the stable isotope (carbon and oxygen) composition of basal Actinopterygii and Neopterygii fish remains and from indeterminate plant remains; and b) the clay mineral assemblage composition; providing two independent lines of evidence to reconstruct paleoclimate conditions including paleotemperature calculations for lake waters. The values obtained for fish remains for δ13C range between -8.4 and -1.3 ‰ (δ13C= χ -5.57‰; σ ± 2.25); and δ18O values that vary between -5.7 and -3.6‰ (δ18O= χ -4.33‰; σ ± 0.84); in the case of plant remains δ13C values range between -25.8 and -22.8‰ (δ13C= χ -25‰ -4.33). Paleotemperatures obtained from δ18O for the water column ranged between 23.33 to 35.80 °C. Plant δ13C signature allowed obtaining a δ13CCO2 composition of -5 ‰. This agrees with the interpretation of the La Cantera originating from sediment deposition in an underfilled lake basin and with the global climate context of the Cretaceous. The clay mineral assemblage is dominated by illite-smectite indicating enhanced hydrolysis and seasonal rainfall supporting temporal warmup of the lake. Our data supports aridity conditions during the La Cantera paleolake existence. These findings suggest that geochemical proxies of paleontological datasets are accurate for paleoclimate reconstructions for the deep time records of the La Cantera lacustrine system.

Keywords

• La Cantera Formation
• Lacustrine
• Underfilled lake
• Stable isotopes
• Fossil fish
• Fossil plant