The birth and demise of the vast epicontinental Permian Irati-Whitehill sea: Evidence from organic geochemistry, geochronology, and paleogeography

Organic-rich shale deposits of the Irati (Brazil) and Whitehill (South Africa) formations represent the most important sedimentary remnants of a huge Permian sea that occupied an estimated 5 million km 2 before drying out and disappearing. To unravel the evolution and final demise of the Irati-Whitehill sea, we present a paleogeographic and organic geochemical characterization as well as a precise tephrochronology of the sea. Constrained by new high-resolution chemostratigraphic data (biomarker data combined with carbon and nitrogen isotopes) of two boreholes from central and southern areas of the Parana Basin (Brazil), the evolution of the sea is divided into five stages. These stages reflect the transition from a marine realm (stage I) to an environmentally restricted sea characterized by major ecosystem changes (stages II and IV) where water renewal controlled the post-salinity environmental dynamics (stages III and V). A zircon U-Pb TIMS age of 277.26 +/- 0.62 Ma of stage V correlates with the age of the San-Rafaelic omgeny along the paleo-Pacific South American margin and the rising of the Cape Fold Belt. We conclude that the convergent tectonic dynamics may have acted as the main agent in the entrapment and disappearance of the sea, ending a history of no more than four-million-year of the Irati-Whitehill sea.

Automated summary

The evolution and demise of the Irati-Whitehill sea can be unraveled through the study of organic geochemical characteristics and tephrochronology, constrained by new high-resolution chemostratigraphic data, the evolution of the sea is divided into five stages.