Climate Change at the
Toni T. Eerola
Varangerian and lower Sinian glacial deposits are found in Argentina, Uruguay, Mato Grosso (Brazil), Namibia, Laurentia, and probably southern Brazil, which were all situated close together during Neoproterozoic-Cambrian times. According to continental paleoreconstructions, glacial deposits of these regions, together with those of Scotland, Scandinavia, Greenland, Russia, Antarctica, and Australia, formed the Varangerian-Sinian Glacial Zone of the supercontinent Rodinia. Tectonic activity associated with the amalgamation of Rodinia and Gondwana was probably related to the origin of these deposits, as in the case of mountain glaciers that formed in uplifted areas of fragmenting or colliding parts of this supercontinent. In such circumstances, the Pan-African and Brasiliano orogenies and the site of opening of the Iapetus Ocean would have been in key positions. However, some paleomagnetic reconstructions locate these regions near the South Pole, where glaciers could have formed even in the absence of tectonic events. In this case, the change to warm climate and the evolutionary explosion of the Cambrian could have been due to rapid shift of continents to equatorial latitudes, although these changes might also have been triggered by supercontinent breakup. These events are reflected in the isotopic records of strontium and carbon, which provide some of the best available indicators of the climatic and environmental changes that occurred during the NeoproterozoicCambrian transition. They also appear to reveal the occurrence of a discrete cold period in the Cambrian: the disputed lower Sinian glaciation.
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