The Upper Diamictite Formation of the West Congo Supergroup is a diamictite-dominated succession variously interpreted as a continental tillite, glaciomarinite, and glacially-influenced or non-glacial debrite. This paper presents a detailed macroand microscale analysis of soft-sediment deformation structures in order (1) to resolve the long-standing debate on the genetic origin of the Upper Diamictite Formation, and (2) to constrain the paleoenvironmental conditions during the Marinoan global event. The predominance of ductile and brittle deformations and grain-to-grain compression, considered as evidence of high strain rates and local high stress conditions, indicate that the diamictites were deposited as mass flows. The presence of probable pelagic clays, lonestones, and the absence of direct ice-contact deposits point to a subaqueous gravity flow origin. These diamictites were deposited along the margin or at the foot of the basin slope. They were probably triggered by oversteepening and/or tectonic shocks in the Araçuaí-West Congo Orogen between 630 and 660 Ma. The Upper Diamictite Formation provides no support for the postulated global Marinoan glaciation at this time and underscores the importance of a local tectonic control on the sedimentation.
- Lower Congo region
- Sediment gravity flow
- Soft-sediment deformation microstructures
ASJC Scopus subject areas
- Earth and Planetary Sciences (miscellaneous)