A review of the Chemical Index of Alteration (CIA) and its application to the study of Neoproterozoic glacial deposits and climate transitions
Heinrich Bahlburg, Nicole Dobrzinski, 2011. "A review of the Chemical Index of Alteration (CIA) and its application to the study of Neoproterozoic glacial deposits and climate transitions", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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The Chemical Index of Alteration (CIA) is the most accepted of available weathering indices. Past conditions of physical and chemical weathering can be reliably inferred if application of the CIA is combined with a comprehensive facies analysis. When applied to the reconstruction of climate conditions during Neoproterozoic times, CIA data provide crucial insights into the changes in the relative contributions of chemical and physical weathering in the production of sedimentary detritus. CIA data are thus instrumental not only in documenting changes between icehouse and greenhouse climates, but also in recognizing shorter-term climate oscillations between glacial and warm–humid conditions. Concerning the Neoproterozoic glacial periods, sedimentological and CIA data sets give strong evidence of a functioning hydrological cycle, operative sediment routing systems, and variable climate conditions oscillating between dry–cool and glacial, and warm–humid and interglacial. These findings are incompatible with the hypothesis of a totally ice-covered Snowball Earth.
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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.