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Lake cyclicity as response to thermal subsidence: A post-CAMP scenario in the Parnaíba Basin, NE Brazil

Cardoso, Alexandre Ribeiro, Nogueira, Afonso César Rodrigues, Rabelo, Cleber Eduardo Neri
Sedimentary geology 2019 v.385 pp. 96-109
Cretaceous period, Jurassic period, basins, lakes, lava, oxidation, periodicity, sandstone, subsidence, Atlantic Ocean, Brazil
The Jurassic-Cretaceous transition was marked by the fragmentation of the West Gondwana supercontinent and consequent opening of the Atlantic Ocean. This event resulted in extensive lava flows in the central portion of West Gondwana, composing the Central Atlantic Magmatic Province. In the Parnaíba Basin (NE Brazil), a large lacustrine system succeeded this event; nevertheless, the post-CAMP scenario and the influence of the decreasing isotherms in the Mesozoic sedimentation are poorly understood. In this sense, cyclostratigraphy and outcrop-based facies analysis were carried out in the lacustrine stratigraphic record, allowing the recognition of four paleoenvironments: central lake, sheet-like delta front, lakeshore and ephemeral fluvial channels, mainly organized in shallowing upward cycles. The upsection transition of thin black shales and limestones to thick oxidized mudstones and stratified sandstones reflects the evolution of underfilled to overfilled lake settings. The lacustrine succession is organized in four major depositional cycles, characterized by millimeter to centimeter-scale cycles, bounded by unconformities or flooding surfaces. The cycles define a retrogradational-progradational-retrogradational stacking pattern, with random and frequent changes in lithology and cycle thickness. Cyclostratigraphic data suggest that the upward increasing accommodation space was controlled by the post-CAMP thermal subsidence, as well as shifts in sedimentary supply and water inflow/outflow. The time span of this subsidence phase lasted from even before the CAMP magmatism (~200 Ma), affecting the whole deposition of the lacustrine succession, and was interrupted by the Cretaceous magmatic event (~126 Ma). Subsidence was also enhanced by crustal loading associated with thick subsurface Jurassic intrusions and probably influenced the whole basin, in consequence of flexural effects.