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

Abstract

ABSTRACT. 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.

Evolution and estimated age of the C5 Lukala carbonate-evaporite ramp complex in the Lower Congo region (Democratic Republic of Congo): New perspectives in Central Africa

“…However, recent studies of the WCB have revealed only a minor impact of these glaciations on sedimentation. On the contrary, predominantly extensional tectonic activity controlled basin formation with dolostones (at the base of the Lukala Subgroup) abruptly overlying the Upper Diamictite Formation, formerly considered as a glaciogenic deposit (Eyles and Januszcak, 2007;Delpomdor et al, 2014Delpomdor et al, , 2016Delpomdor et al, , 2017. In this paper, new detailed lithofacies associations, stratigraphic architecture and geochemistry of the C5 Formation point to a paleogeographic setting with a vast shallow back-reef lagoon stretching between a stromatolitic patch reef and a coastal sabkha plain.…”

Basinal setting and origin of thick (1·8 km) mass‐flow dominated Grand Conglomérat diamictites, Kamoa, Democratic Republic of Congo: Resolving climate and tectonic controls during Neoproterozoic glaciations

“…(). In the light of detailed sedimentological data from Kamoa it seems reasonable to argue that mass flow was a widespread (if not dominant) and diachronous process in peri‐Congolese Katangan rift basins and that such deposits cannot be used in support of a notional pan‐glacial Snowball Earth event (see also Delpomdor & Préat, ; Delpomdor et al ., , ). Regional ice covers whose timing reflect a dominantly tectonic control on basin development and topographic relief are possible but the wealth of sedimentological detail available from deep drilling at Kamoa identifies a distal and weak (if any) glacial influence.…”

“…Only a single deposit (the Lower Diamictite Formation of the West-Congo Supergroup, West Congo Belt) has been dated (694 AE 4 Ma; Straathof, 2011) and this age contrasts with the bracket obtained from radiometric dating for the Grand Conglom erat of 765 AE 5 to 735 AE 5 Ma (Key et al, 2001), the maximum age of the Grand Conglom erat obtained from Re-Os dating in the Mwashya Subgroup of 727Á3 AE 4Á9 Ma (Rooney et al, 2015) and also the 757 AE 5 Ma lower limit age obtained for the Chuos Formation of Namibia by Nascimento et al (2016). In the light of detailed sedimentological data from Kamoa it seems reasonable to argue that mass flow was a widespread (if not dominant) and diachronous process in peri-Congolese Katangan rift basins and that such deposits cannot be used in support of a notional pan-glacial Snowball Earth event (see also Delpomdor & Pr eat, 2015;Delpomdor et al, 2016Delpomdor et al, , 2017. Regional ice covers whose timing reflect a dominantly tectonic control on basin development and topographic relief are possible but the wealth of sedimentological detail available from deep drilling at Kamoa identifies a distal and weak (if any) glacial influence.…”

“…The Grand Conglom erat contains massive diamictite units consisting of poorly sorted gravel, sand and mud mixtures that are as much as 250 m thick and whose origins are elsewhere interpreted as tillites (Cahen, 1954), glaciogenic mass flows derived from glacier margins (Wendorff & Key, 2009;Master & Wendorff, 2011), or non-glacial mass flows derived from tectonically unstable margins (Binda & Van Eden, 1972;Schermerhorn, 1974;Delpomdor et al, 2014Delpomdor et al, , 2017. In general, diamictites, are prominent components of many Neoproterozoic basins worldwide, but poor exposure and limited access often hamper detailed sedimentological assessment.…”

Sedimentology and chemostratigraphy of the late Neoproterozoic carbonate ramp sequences of the Hüttenberg Formation (northwestern Namibia) and the C5 Formation (western central Democratic Republic of Congo): Record of the late post-Marinoan marine transgression on the margin of the Congo Craton

“…This isotopic "event" is followed by a positive excursion in δ 13 C values, which is marked by a rapid marine transgression as a result of extensional tectonic processes directly after the Marinoan-age glaciation event (Halverson et al, 2005;Delpomdor et al, 2016;Caxito et al, 2012;Paula-Santos et al, 2017). Such glaciations are recorded in the Ghaub Formation in Namibia, Jequitaí Formation in Brazil, and periglacial deposition in the Niari Formation in Gabon, stratigraphic-equivalent of the distal gravity deposited sediments in the Upper Diamictite Formation in DRC (Prian et al, 2009;Busfield and Le Heron, 2013;Uhlein et al 2013Uhlein et al , 2016Delpomdor et al, 2016Delpomdor et al, , 2017F. Delpomdor, S. Schröder, A. Préat, P. Lapointe, C. Blanpied Nascimento et al, 2016;Rodler et al, 2017).…”