Indicadores geoquímicos das mudanças paleoambientais na formação romualdo (ne, brasil) durante a transição aptiano- albiano

Abstract

The Early Cretaceous was a period of intense global climatic and oceanographic changes, marked by oceanic anoxic events and large-scale volcanism. In Brazil, the Romualdo Formation, in the Araripe Basin, preserves an exceptional record of these disturbances. This study investigates the paleoenvironmental and paleoclimatic variations in the Romualdo Formation, Araripe Basin (Lower Cretaceous), during the Aptian-Albian transition, using a high-resolution chemostratigraphic approach. The main objective was to evaluate the relationship between large-scale volcanism and changes in paleoproductivity, paleoredox conditions, paleosalinity, and paleoclimate, as well as its influence on the mass mortality events recorded in the unit. Trace metals (Al, Cu, Pb, Cr, Zn, Mn, Sr, Ba, V), mercury (Hg), and Total Organic Carbon (TOC) were analyzed in a 2-meter sedimentary profile collected in Santana do Cariri, Ceará. The results revealed Hg anomalies associated with high TOC contents, providing robust evidence of the influence of volcanism from the Kerguelen South Plateau Igneous Province. These volcanic pulses may have acted as triggers for ocean fertilization, intensifying primary productivity and promoting the expansion of anoxic and suboxic conditions in the depositional environment, correlated with Oceanic Anoxic Event 1b (OAE 1b). The analysis of Sr/Ba and Sr/Cu ratios indicated a possible predominance of a coastal environment under a predominantly humid climate, with episodes of aridity. It was possible to conclude that the establishment of anoxic conditions was possibly decisive for the mass mortality events of the fauna, while the same environment favored the exceptional preservation of fossils, consolidating the Romualdo Formation as a world- class Konservat-Lagerstätte.