Ecosystem changes after Early Cretaceous seawater intrusion into the proto-South Atlantic Ocean
Abstract
The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil side, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from pelagophyte marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition.
Financial support at the Massachusetts Institute of Technology (MIT) was provided by an MIT Energy Initiative grant funded by Shell with additional support from the Simons Foundation Collaboration on the Origins of Life that provided instrumentation needed for this work. Funding support at Shanghai Jiao Tong University (SJTU) is provided by the National Natural Science Foundation of China (42203030, 42273075), the Shanghai Pujiang Programme and the SJTU startup grant (WH220544005). We are grateful to Shell for allowing sample access to the Fragata well.