Chapter 50 Moema laminites: a newly recognized Neoproterozoic (?) glaciogenic unit, São Francisco Basin, Brazil

Abstract

AbstractA recently identified diamictite and silt-clay laminite, which discordantly overlie the Archaean basement and underlie the Neoproterozoic Bambui Group, have been informally named as the Moema Laminites. They are preserved at the southwestern margin of the São Francisco Basin in southeastern Brazil, and are widely distributed in the central-western Minas Gerais state. They crop out discontinuously over at least 140 km along a north–south direction. The nomenclature of and stratigraphic relationships between the Moema Laminites and other isolated Neoproterozic occurrences of similar rocks are in a state of flux. Two exceptionally good exposures of the Moema Laminites show good evidence for deposition under glacial conditions. At the Formiga locality, a single glacial advance is registered by a deformation tillite, while overlying laminite records deposition in a post-glacial, probably marine basin following deglaciation. At the SAFFRAN quarry, striations on a bedding plane may have been caused by floating sea-ice that just touched the bottom of the basin. Much additional work is needed to establish relationships between the Moema Laminites and other similar occurrences. If these and Moema Laminites are shown to be Cryogenian glacial deposits, the area covered by the Cryogenian glaciations in the São Francisco basin is much larger than formerly believed.