The Chameis Gate Member, Chameis Group, Marmora Terrane, Namibia
Hartwig E. Frimmel, 2011. "The Chameis Gate Member, Chameis Group, Marmora Terrane, Namibia", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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The Chameis Gate Member is a poorly exposed and poorly investigated diamictite in the Chameis Subterrane of the Marmora Terrane, which forms the western, completely allochthonous part of the Pan-African Gariep Belt (southwestern Namibia). Its significance lies in its position in an entirely oceanic unit, the Dernburg Formation, which is dominated by mafic volcanic rocks. The diamictite contains exotic dropstones in a mafic volcaniclastic matrix, thus providing evidence for transport by ice away from the continental margin into an oceanic environment. No direct age data are available and stratigraphic relationships are obscured by limited outcrop and intense syn-orogogenic deformation. Preliminary chemostratigraphic data obtained on carbonate rocks below and above the diamictite, imprecise Pb–Pb age data on the largely volcaniclastic silicate fraction within associated stromatolitic reef carbonates, and imprecise Ar–Ar data on early hornblende related to sea-floor metamorphism of the associated volcanic rocks all point to an age loosely constrained between 640 and 580 Ma. Based on a comparison between the tectono-stratigraphic units of the Marmora Terrane with the continental Port Nolloth Group on the one side and the Rocha Group of the Punta del Este Terrane in Uruguay on the other side of the terrane, it is suggested that the diamictite was deposited in a back-arc basin that developed in response to the 640–590 Ma volcanic arc of the Dom Feliciano Belt in southeastern Brazil and eastern Uruguay.
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In recent years, interest in Neoproterozoic glaciations has grown as their pivotal role in Earth system evolution has become increasingly clear. One of the main goals of the IGCP Project No. 512 was to produce a synthesis of newly available information on Neoproterozoic successions worldwide similar in format to Hambrey & Harland’s (1981) Earth’s pre-Pleistocene Glacial Record. This Memoir therefore consists of a series of overview chapters followed by site-specific chapters. The overview chapters cover key topics including the history of research on Neoproterozoic glaciations, identification of glacial deposits, chemostratigraphic techniques and datasets, palaeomagnetism, biostratigraphy, geochronology and climate modelling. The site specific chapters for 60 successions worldwide include reviews of the history of research on these rocks and up-to-date syntheses of the structural framework, tectonic setting, palaeomagnetic and geochronological constraints, physical, biological, and chemical stratigraphy, and descriptions of the glaciogenic and associated strata, including economic deposits.