The glaciogenic Jequitaí Formation, southeastern Brazil
Published:January 01, 2011
A. Uhlein, C. J. S. Alvarenga, M. A. Dardenne, R. R. Trompette, 2011. "The glaciogenic Jequitaí Formation, southeastern Brazil", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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Glaciogenic deposits of the Jequitaí Formation (Fm.) are well exposed along the margins of the Serra do Cabral on the São Francisco Craton, southeastern Brazil. The Jequitaí Formation is thin (0–150 m thick), lenticular and overlies the Espinhaço Supergroup on a discrete unconformity. Sandstones show subglacial erosional structures such as grooved and striated pavements oriented ENE–WSW. The Jequitaí Fm. consists of massive and stratified diamictites with granules, pebbles and boulders of gneiss, granite, quartzite and carbonate. At the base, the diamictites are massive, whereas the upper part contains many alternating beds of clast-rich and -poor diamictites. They also contain discontinuous, fine-grained sandstones and a few laminated siltstone–mudstone intercalations. This diamictite association indicates glaciomarine sedimentation. The Jequitaí Fm. covers the São Francisco cratonic domain and its equivalent extends eastward over the Araçuaí fold belt where it is part of the metasedimentary Macaúbas Group, a thick Neoproterozoic unit with metadiamictites, quartzites and schists. The diamictite–turbidite association of the Macaúbas Group was deposited on the border of the Pan-African–Brasiliano rift as gravity flows.
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The Geological Record of Neoproterozoic Glaciations
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.