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

Sedimentologic, paleogeographic, stratigraphic, structural and tectonic stu dies in a paleo/mesoproterozoic metasedimentary succession (Espinhaco Megas equence, southeastern Brazil) indicates deposition in a rift-sag basin. Fou r basin evolution stages are recognized (prerift, rift, transitional and fl exural). The four stages can be represented by six unconformity-bounded tec tonosequences. The unconformities are recognized in the field and mappable even on a regional scale. The prerift and rift stages of the Espinhaco basi n 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. Durin g 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. Pa leocurrent patterns indicate that block tilting and half-graben subsidence/ uplift controlled sediment dispersion. The first marine incursion within th e Espinhaco basin marks the change in the subsidence regime of the basin. T he evolution of the transitional and flexural stages was probably controlle d by thermal subsidence due to thermal contraction of the lithosphere durin g cooling. The transitional stage was characterized by relatively low subsi dence rates. Higher subsidence rates and a consequent sea-level rise charac terize the flexural stage of the Espinhaco basin, in which three second-ord er transgressive-progradational sequences can be recognized. (C) 2000 Elsev ier Science B.V. All rights reserved.