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9 Campanian Through Paleocene Paleotemperature and Carbon Isotope Sequence and the Cretaceous-Tertiary Boundary in the Atlantic Ocean by Anne Boersma
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Chapter 9 CAMPANIAN THROUGH PALEOCENE PALEOTEMPERATURE AND CARBON ISOTOPE SEQUENCE AND THE CRETACEOUS-TERTIARY BOUNDARY IN THE ATLANTIC OCEAN ANNE BOERSMA Lamont-Doherty Geological Observatory INTRODUCTION The extinctions and physical-oceanographic phenomena at the Cretaceous -Tertiary boundary have elicited a vast number of astute observations from scientists for half a century. The accumulated literature documenting faunal changes among dinosaurs (Russell, 1975), marine invertebrates (Kauffman, 1973), larger foraminifera (Dilley, 1973), benthonic foraminifera (Beckman, 1960), planktonic foraminifera (Rosenkrantz and Brotzen, 1960), and marine floras (Tappan and Loeblich, 1971; Harker and Sarjeant, 1975; Percival and Fischer, 1977) complements the work on geology and tectonics which shows extensive paraconformities (Gignoux, 1950; Newell, 1963) and hiatuses in the deep sea record (Worsley, 1974) along with an extensive and rapid regression (Termier and Termier, 1969; Vail et al., 1977) from a low-lying continental system (Hallam, 1968) largely covered by marine seaways (Dunbar, 1960). A change in spreading rates along oceanic ridge systems is also documented at this time (Pitman and Hays, 1973). Recent evidence from DSDP (Deep Sea Drilling Project) Legs 39 and 43 shows that the CCD (Calcite Composition Depth) in the Atlantic dropped, then rose just below the boundary (Tucholke et al., in press), then dropped again by earliest Tertiary (Boersma, 1977). Paleobotanists have speculated on late Cretaceous climate (Whitehead, 1969; Tschudy, 1971); they have recorded that extinctions at the boundary are rare in the land plants (Sloan, 1967; Flessa and Imbrie, 1975). Oxygen isotope analysis of foraminifera in deep-sea sediments (Saito and 247 248 BOERSMA Van Donk, 1974; Douglas and Savin, 1975) and of shelf invertebrates (Lowenstam and Epstein, 1954) suggest that the marine temperatures reached a low in the Early Maastrichtian, decreased during the Maastnchtian and may have decreased across the boundary (Savin, 1977). Theories on the events that precipitated the Cretaceous/Tertiary boundary crisis include drastic climate change and decreased marine temperatures (Saito and Van Donk, 1974); supernova (Reid, 1977); magnetic reversals affecting biotic systems (Uffen, 1963); the rapid regression that reduced nutrient supplies (Tappan, 1968); and the rising of the CCD into the photic zone (Worsley, 1974). To date only ideological change has been overlooked as a possibility. During the last four years, I have been investigating marine paleotemperature and geochemical variations through the Maastrichtian, across the Cretaceous-Tertiary boundary, and through the early Tertiary using the oxygen and carbon isotopic variations in foraminiferal carbonate. To date I have analyzed sediments through the Maastrichtian and Early Tertiary of the Atlantic Ocean at DSDP Sites 152, 356, 357, 384, and in Site 2OC 21 94 95 144 151 152 327a 329 356 357 384 v26-65 Vl 6-56 V22-127 V16-55 V22-126 Latitude 28°31'S 28°35'S 24°31'N 24°09'N 09°27'N 15°0TN 15°52'N 50°52'S 50°39'S 28°17'S 30°00'S 41°21'N 26°42'S 41°2TS 41°18'S 40°14'S 41°01'S Longitude 26°50'W 30°35'W 88°28'W 86°23'W 54°20'W 73°24'W 74°36'W 46°47'W 46°05'W 41°05'W 35°33'W 51°39'W 27°51'W 26°38'E 26°43'E 25°15'E 26°30'E Table 9-1. Geographic locations of sites from which we have made isotopic measurements . PALEOCENE PALEOTEMPERATURE BOUNDARY 249 assorted Vema cores from the Agulhas Plateau and the Rio Grande Rise (Table 9-1; Boersma et al., in press). I have attempted to produce the estimated temperature and carbon isotope record across the boundary at as close a sample spacing as possible in order to evaluate some of the theories mentioned above. Because of preservational vagaries and the numerous boundary hiatuses , there are slight stratigraphic gaps in several of my records. The section at Site 384 appears to be the most complete, and I have sampled this at 2 to 10 centimeter intervals. The section at Site 356 contains a 31meter lower Paleocene interval that includes the basal Tertiary, but lacks the very uppermost Cretaceous. The records at the other sites are less complete, but they can be correlated with Sites 384 and 356 to produce meaningful coverage from almost 50 ° N to 50 ° S paleolatitude in the Atlantic Ocean. SURFACE DWELLING PLANKTONIC FORAMINIFERA In order to produce a surface temperature record it has been necessary to establish which species of foraminifera lived closest to the ocean surface. A detailed study of foraminiferal...