ABSTRACT: Paleoclimatic Implications of the Distribution of the Bivalve Calva
SAUL, L. R., Natural History Museum, Los Angeles County, Los Angeles, CA
The venerid genus Calva lived along the Pacific Coast during the Cretaceous. Calva has been recognized in deposits from Alaska to Baja California ranging in age from Albian through Maastrichtian. The genus comprises four subgenera and 16 species. Present latitudinal distributions of contemporaneous species of two of these subgenera, Calva and Egelicalva, form a north-south pattern with species of Calva (Calva) displaying a more southerly distribution vis a vis species of Calva (Egelicalva). Calva (Egelicalva) and Calva (Calva) species retain their north-south relationship despite distributional offsets due to terrane displacements, but the northernmost records for Calva (Calva) and the southernmost for Calva (Egelicalva) shift through time. The genus Calva apparently was a component o warm-temperate to temperate faunas rather than of tropical faunas. In modern molluskan province terms, the Cretaceous faunas with Calva (Calva) resemble those of the modern Surian Province and those with Calva (Egelicalva) are more Californian in composition. If the distributions of Calva (Calva) and Calva (Egelicalva) are, in part, temperature dependent, they suggest a warm Cenomanian-Turonian followed by a cooler Coniacian and Santonian. Oceanic temperatures in the late Campanian appear to have been slightly warmer than those of the early Campanian. The early Maastrichtian may have been the coolest interval, followed by a considerable warming in the late Maastrichtian.