Tectonics and sedimentation in a paleo/mesoproterozoic rift-sag basin (Espinhaço basin, southeastern Brazil)

Abstract

Sedimentologic, paleogeographic, stratigraphic, structural and tectonic studies in a paleo/mesoproterozoic metasedimentary succession (Espinhaço Megasequence, southeastern Brazil) indicates deposition in a rift-sag basin. Four basin evolution stages are recognized (prerift, rift, transitional and flexural). The four stages can be represented by six unconformity-bounded tectonosequences. The unconformities are recognized in the field and mappable even on a regional scale. The prerift and rift stages of the Espinhaço basin were filled by products of continental depositional systems. The prerift stage probably represents the first product of the rifting process, before the development of the half-grabens that characterize the rift stage. During the rift stage, mechanical subsidence due to lithospheric stretching was predominant and led to episodic rising of the depositional base level. As a result, the basin fill is characterized by coarsening-upward intervals. Paleocurrent patterns indicate that block tilting and half-graben subsidence/uplift controlled sediment dispersion. The first marine incursion within the Espinhaço basin marks the change in the subsidence regime of the basin. The evolution of the transitional and flexural stages was probably controlled by thermal subsidence due to thermal contraction of the lithosphere during cooling. The transitional stage was characterized by relatively low subsidence rates. Higher subsidence rates and a consequent sea-level rise characterize the flexural stage of the Espinhaço basin, in which three second-order transgressive-progradational sequences can be recognized.