Análise isotópica de oxigênio e carbono em microfósseis da Formação Romualdo, cretáceo inferior, bacia do Araripe, Pernambuco, nordeste do Brasil

Abstract

This work examined the behavior of C and O isotope in carapaces of ostracodes and foraminifera from the Romualdo Formation, Araripe Basin – PE. The analyzed samples were collected from three outcrops (Arrojado, Canastra and Cedro) located in the cities of Exu and Araripina. The de δ¹⁸O values ranged from -10.1‰ to -10.2‰ VPDB and the δ¹³C values ranged from -12.6‰ to +2.7‰ VPDB. Oxygen stabe isotope data indicate high temperature of waters and the deposition of marine limestones in all outcrops. For Arrojado and Canastra outcrops, δ¹³C values indicate an anoxic environment with high content of organic matter. In Cedro outcrop, a positive variation occurs indicating an increase in primary production, also associated to an anoxic event, and the positive values are interpreted as a marine pulse. These results indicate that Cedro outcrop, located in the midsouthern portion of this basin, has environmental characteristics with greater marine influence than in the Arrojado and Canastra outcrops, located in the southwestern portion of this basin.