Chapadas: Relict of Mid-Cretaceous interior seas in Brazil (1)

Abstract

In the mid-Cretaceous, particularly during Albian-Turonian time, the greatest eustatic sea level rise in Phanerozoic history triggered a global transgressive event. This resulted in sedimentary filling of then-existing intracontinental depressions. Following the Highstand Phase, the non-subsiding areas ceased receiving sediment and underwent erosion at their margins. In Brazil, these areas were subsequently uplifted, mainly in post-Neogene time, to constitute plateau-like geomorphologic units termed chapadas (e.g., Apodi, Araripe, Parecis, and Urucuia). The relationship between the mid-Cretaceous marine transgression and the origin of chapadas has been pointed out in our previous works. Chapadas have tabular geometry, and their lithostratigraphic units are horizontal and have notable lateral continuity. Marine fossils of some strata of the chapada units reinforce this model. The only chapada that does not have marine paleontologic evidence is Parecis. However, this may simply reflect inadequate knowledge. Paleontological and paleocurrent data available point to interconnection among the chapada-bearing basins and, moreover, their connection to the Pacific and Central and South Atlantic oceans.