Global climate during Cambrian time was probably warmer and more equable than today. An absence of either land or landlocked seas at the Cambrian poles may have prevented the accumulation of polar ice caps. The general absence of glacial till deposits of Cambrian age is more notable, because these deposits are common and widespread in upper Precambrian strata. They accumulated again during the Ordovician Period in northern Africa as Gondwana began to move over the South Pole. Otherwise, the presence of persistent and widespread limestone deposits found on the margins of a centralized transcontinental arc in North America, for example, indicates that a subtropical climate existed in latitudes between 30° N and 30° S. In addition, arid to semiarid conditions at latitudes around the Tropics of Cancer and Capricorn (approximately 23°27′ N and S latitude, respectively) are suggested by deposits that include sandstone with quartz grains frosted by abrasion through wind transport, ventifacts (wind-polished stones), and evaporites.
More sophisticated research on paleoclimates relies on the detection of changing patterns in the amounts of isotopic oxygen, carbon, and strontium retained in limestone samples to correlate the timing of different geological events. Much remains to be accomplished regarding this promising line of research on Cambrian strata, but certain trends and events are becoming better defined. Strong reductions in isotopic carbon (13C), for example, are correlated from Lower Cambrian strata at localities as distant from one another as the Lena River area of Siberia and the Atlas Mountains of Morocco. Another substantial drop in 13C is believed to mark the transition between the early and middle parts of the Cambrian in the Great Basin of North America. Such decreases may represent a global rise in temperature occurring at the same time as a rise in global sea level. In addition, the delivery of anoxic (oxygen-depleted) ocean waters with reduced amounts of 13C also may have been aided by rising sea level.
More sophisticated research on paleoclimates relies on the detection of changing patterns in the amounts of isotopic oxygen, carbon, and strontium retained in limestone samples to correlate the timing of different geological events. Much remains to be accomplished regarding this promising line of research on Cambrian strata, but certain trends and events are becoming better defined. Strong reductions in isotopic carbon (13C), for example, are correlated from Lower Cambrian strata at localities as distant from one another as the Lena River area of Siberia and the Atlas Mountains of Morocco. Another substantial drop in 13C is believed to mark the transition between the early and middle parts of the Cambrian in the Great Basin of North America. Such decreases may represent a global rise in temperature occurring at the same time as a rise in global sea level. In addition, the delivery of anoxic (oxygen-depleted) ocean waters with reduced amounts of 13C also may have been aided by rising sea level.
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