A history of Neoproterozoic glacial geology, 1871–1997
Neoproterozoic glacial records have been discovered on 23 palaeocontinents, their rate of discovery changing little since 1871. Yet, half of all the resulting publications appeared since 2000. The history of research before 1998 is described in five stages defined by publication spikes; subsequent work is not covered because historical perspective is lacking. In stage 1 (1871–1907), ‘Cambrian’ (now Neoproterozoic) glaciation was recognized successively in Scotland, Australia, India, Norway, Svalbard and China. Criteria for recognition included faceted and striated pebbles in matrix-supported conglomerates resting on ice-worn bedrock pavements. In stage 2 (1908–1940), Neoproterozoic glaciation was shown to have been widespread in Africa, Asia and the Americas. Major textbooks summarized these findings, but the rejection of continental drift (to account for late Palaeozoic glacial dynamics) put a chill on research. In stage 3 (1942–1964), the occurrence of glacial deposits within carbonate successions, as well as nascent palaeomagnetic observations, suggested that Neoproterozoic glaciers reached sea-level at low palaeolatitudes, but the belated recognition of sediment gravity flowage caused glacial interpretations to be prematurely abandoned in key areas. In stage 4 (1965–1981), the extent of Neoproterozoic glaciation was rethought in light of plate tectonics. Distinctive chemical sediments (iron±manganese formations and cap carbonates) were identified. In basic climate models, modest lowering of solar luminosity resulted in global glaciation due to ice-albedo feedback, and deglaciation due to greenhouse forcing resulted from silicate-weathering feedback in the carbon cycle. Neoproterozoic glacial geologists were blind to these ideas. In stage 5 (1982–1997), reliable palaeomagnetic data combined with glacial marine sedimentation models confirmed that Neoproterozoic ice sheets reached sea level close to the palaeoequator.
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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.