Stratigraphy and geochronological constraints of the Serra Sul formation (Carajás Basin, Amazonian Craton, Brazil).

Abstract

The Carajás Basin, Amazonian Craton, hosts extensive Neoarchean to Paleoproterozoic sedimentary archives, which are still poorly constrained regarding their depositional settings, ages, and type of basin in which they have been deposited. In this study, we performed detailed sedimentological investigations and U-Pb dating of detrital zircon in four drill cores intercepting the recently defined Serra Sul Formation. Our data show that this formation corresponds to various shallow to deep subaqueous environments. Shallow water environments are characterized by local occurrences of microbially-mediated structures, while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow. Both sedimentary facies and common occurrence of syn-sedimentary deformations attest for recurrent slope instabilities. Geochronological investigations allow to define a maximum depositional age of 2684 ± 10 Ma, that is several tens million years younger than other Neoarchean sedimentary units of the Carajás Basin. Major peaks in age distribution indicate that the Serra Sul Formation derives from local sources that constitute the basement of the Carajás Basin. The infilling of the Carajás Basin by local sources, together with sedimentary facies and depositional environments attesting for slope instabilities, suggest that the Serra Sul Formation was deposited during an active extensional tectonic phase. Such Neoarchean to early Paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break-up of one of the first documented supercontinent.