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Low-latitude glaciation in the Palaeoproterozoic era

Evans, D. A. and Beukes, N. J. and Kirschvink, J. L. (1997) Low-latitude glaciation in the Palaeoproterozoic era. Nature, 386 (6622). pp. 262-266. ISSN 0028-0836. http://resolver.caltech.edu/CaltechAUTHORS:20130130-100731416

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Abstract

One of the most fundamental enigmas of the Earth's palaeoclimate concerns the temporal and spatial distributions of Precambrian glaciations. Through four billion years of Precambrian history, unequivocally glacial deposits have been found only in the Palaeoproterozoic and Neoproterozoic record. Nonetheless, some of these deposits are closely associated with tropical— rather than just polar—palaeolatitudinal indicators such as carbonate rocks, red beds, and evaporites. These observations are quantitatively supported by palaeomagnetic results indicating a ~5° latitude for Neoproterozoic glaciogenic rocks in Australia. Similarly reliable palaeolatitudes for the older, Palaeoproterozoic glaciogenic rocks have not yet been obtained, as such deposits commonly suffer from poor preservation and secondary magnetic overprinting. The Archaean–Palaeoproterozoic 'Transvaal Supergroup' on the Kaapvaal craton in South Africa is, however, exceptionally well preserved, and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes. Within this supergroup the ~2.2 billion-year old Ongeluk lavas are a regionally extensive, largely undeformed and unmetamorphosed, extrusive volcanic succession, which conformably overlies glaciogenic deposits (the Makganyene diamictite). Here we report a palaeomagnetic estimate of 11 ± 5° depositional latitude for the lavas, and hence for the underlying contemporaneous glacial rocks. The palaeoclimate enigma is thus deepened; a largely ice-free Precambrian world was apparently punctuated by two long ice ages, both yielding glacial deposits well within tropical latitudes.


Item Type:Article
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http://dx.doi.org/10.1038/386262a0DOIUNSPECIFIED
http://www.nature.com/nature/journal/v386/n6622/abs/386262a0.htmlPublisherUNSPECIFIED
Additional Information:© 1997 Nature Publishing Group. Received 28 October 1996; accepted 4 February 1997. We thank J. Grotzinger, P. Hoffman, R. Powell and D. Sumner for discussions that improved the manuscript; A. J. Kaufman, R. Van der Voo and G. Young for constructive comments; C. Jones for updating the Paleomag program used to analyse palaeomagnetic data; and S. van der Merwe and Samancor for access to subcrop and borehole material at Hotazel and Wessels mines. This work was supported by the FRD in South Africa and the US NSF. D.A.E. was supported by a US NSF graduate research fellowship.
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FRD South AfricaUNSPECIFIED
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NSF Graduate Research FellowshipUNSPECIFIED
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ID Code:36685
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:30 Jan 2013 19:24
Last Modified:30 Jan 2013 19:24

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