Facies and micromorphology of the Neoproterozoic Upper Diamictite Formation in the Democratic Republic of Congo: New evidence of sediment gravity flow

Abstract

1. IntroductionSince over a decade, numerous studies have postulated that extremely low global temperatures (-50 °C) existed during successive separate glaciations in the Cryogenian period (770–580 Ma). This would explain not only the presence of ice at sea level near the equator, but also an icy cover on all oceans (Snowball Earth Hypothesis; Kirschvink, 1992; Hoffman et al., 1998; Hoffman & Schrag, 2002). The original suggestion of a “global” glaciation in the Neoproterozoic by Harland (1964) was partly based on paleomagnetic data (Harland & Bidgood, 1959) pointing to low paleolatitudes for these glacial deposits. The latter, widely distributed on all continents, are sharply overlain by a cap carbonate unit, interpreted as the result of a sudden switch back to a greenhouse climate related to the increase of atmospheric carbon dioxide due to volcanic degassing (Hoffman & Schrag, 2002). Despite the absence of many typical “glacial” features (e.g., faceted and striated clasts, dropstones, etc.), most Neoproterozoic diamictites were considered as glacial or periglacial deposits. However, not all reported Neoproterozoic diamictites were interpreted in this way, but also as the result ofsyntectonic sedimentgravityflows (Eyles & Januszczak, 2004, 2007) associated with widespread rifting of the Rodinia Supercontinent.In this paper, we present a new macro- and microscale structural analysis of the Upper Diamictite Formation (UDF) in the West Congo Supergroup (WCS) of the Democratic