Cold Snaps in the Cretaceous

Abstract

GEOLOGY The Late Cretaceous, 80 to 65 million years ago, has typically been thought of as a time with a warm climate. Dinosaurs flourished all over Earth, including at sites near both poles, and it has been thought that atmospheric CO2 levels were also high during the Cretaceous. Some recent studies, however, have provided evidence for the occurrence of glacial cycles at times during the Late Cretaceous. Miller et al. now provide a detailed study of sea level changes from sediments recovered in drill cores on the Atlantic coastal plain off New Jersey, USA. The nature of the sediment (sand versus mud) provides information about ocean depth. By accounting for subsidence and compaction, and by using Sr isotopes for dating, an accurate relative sea level curve was produced. The results imply that sea level changed abruptly, by about 25 m, numerous times from about 95 to 65 million years ago. These changes may reflect the growth and demise of local ice sheets in Antarctica, supporting the notion that glacial cycles were ongoing during this period. — BH Geol. Soc. Am. Bull. 116 , 368 (2004).