Multiproxy Analysys of Ambers From the Romualdo Formation (Cretaceous), Araripe Basin, Ceará State, Brazil

This study advances the understanding of ambers as important paleobiological and paleoenvironmental archives for the Romualdo Formation of the Araripe Basin and the Lower Cretaceous (Aptian) of Gondwana. Twenty-one (21) ambers collected from the Sobradinho Site, were investigated. Modern and traditional techniques, such as confocal microscopy, petrography, and Laser Ablation ICP-MS (LA-ICPMS), were used, allowing for a detailed analysis of the physical, chemical, and taphonomic characteristics of these fossils. Among the inclusions were fungi, pollen grains of Classopollis and xylem fragments. The analyzed inclusions suggest the presence of coastal forests dominated by gymnosperms with the presence of the Cheirolepidiaceae family. Geochemical analyses revealed a significant enrichment in elements such as sulfur, phosphorus, iron, and zinc, which directly influenced the physical properties and coloration of the samples. From a taphonomic perspective, these ambers represent an allochthonous component that was transported from the forest floor to the coastal marine environment where they were finally deposited. This interpretation was corroborated by the abundance of plant and amber microfragments found in the shales associated with the samples studied. Paleoenvironmental conditions allow to infer a prevailing arid climate, with forests adapted to hydric deficits but potentially sustained by groundwater aquifers. The results offer new perspectives on the evolution of the Araripe Basin ecosystems during the Cretaceous period.