The Neoproterozoic-Cambrian transition was characterized by ophiolite formation (Yakubchuk et al. 1994), the formation and breakup of supercontinents (e.g., Bond et al. 1984), the Cambrian evolutionary explosion (Moores 1993; Knoll 1994), and intense climatic changes, among which the most important might be considered glacia-

Figure 5.1 Time distribution of glaciogenic sedimentary rocks, showing their sporadic nature and possible relationship with supercontinentality. Source: Modified from Young 1991.

tions (e.g., Hambrey and Harland 1985) and the shift from Neoproterozoic icehouse to Cambrian greenhouse conditions (Veevers 1990; Tucker 1992).

At least 10 major glacial periods have been recorded prior to the Pleistocene (Young 1991; Eyles 1993) (figure 5.1). Probably the most extensive and enigmatic of these occurred during the Neoproterozoic and at the beginning of the Cambrian, at ~900-540 Ma (Hambreyand Harland 1985;Young 1991; Eyles 1993;MeertandVanderVoo 1994). There are signs of four Neoproterozoic-Cambrian glacial periods (figures 5.15.2): the Lower Congo (~900 Ma), the Sturtian (~750-700 Ma), the Varangerian (~650-600 Ma), and the lower Sinian (~600-540 Ma) (Hambrey and Harland 1985; Eyles 1993; Meert and Van der Voo 1994). There are, however, also proposals for only two (Kennedy et al. 1998) or even five (Hoffman et al. 1998a; Saylor et al. 1998).

This chapter presents a brief overview of Neoproterozoic-Cambrian climate changes and events, with emphasis on the Varangerian and lower Sinian glacial periods and the subsequent global warming in the Cambrian (see also chapters in this volume by Brasier and Lindsay; Seslavinsky and Maidanskaya; Smith; and Zhuravlev).

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