Upper Cretaceous planktonic foraminiferal zoogeography and ecology—eastern Pacific margin

Abstract

Provincial- and depth-related distribution patterns are inferred for Upper Cretaceous planktonic foraminifers along the eastern Pacific margin. The geographic distribution of 31 species of Late Campanian to Early Maestrichtian planktonic foraminifers from Baja California to Alaska define four faunal provinces—Tethyan, Central, Intermediate, and Boreal. Suggested provincial boundaries occur near 20–23°N, 33–36°N, and 45°N latitude. These correspond closely to boundaries of present marine provinces at Cabo San Lucas, Point Conception, and Puget Sound. Hence, circulation patterns and water-mass distributions in the North Pacific during the Late Cretaceous, although occurring during a time of lessened thermal gradient, resembled those of the present but differed in thermal characteristics. Distribution patterns related to water depth are inferred also for Cretaceous planktonic foraminifers from southern California. Campanian outcrops contain 24 planktonic species;three of these are restricted to slope waters ( Globotruncana goudkoffi, G. stuartiformis, and Globotruncanella havanensis) and one to inner-slope to shelf waters ( Pseudoguembelina costulata). Heterohelix globulosa, Pseudotextularia elegans, Hedbergella holmdelensis and Globotruncana cretacea occur in both assemblages but are common in inner-slope and rare in outer-slope faunas. Heterohelicids dominate the inner-slope to shelf faunas whereas globotruncanids characterize the slope assemblages. These variations in faunal composition and abundance probably reflect the tolerance and adaptive response of each planktonic species to different ocean-margin water depths.