Abstract:
This thesis presents chemical paleoceanographic results from fossil Paleocene biotic carbonates. Benthic and planktonic foraminifera from globally distributed deep-sea sediments were analysed for stable isotopes as well as for trace elements. Stable isotope data for mollusk shells from the North Sea region are also presented. In Paper I, stable isotope (delta (super 13) C, delta (super 18) O) and Ba (super *) profiles were established for three Deep Sea Drilling Project (DSDP) Sites in order to study the nature of the late Paleocene delta (super 13) C maximum. DSDP Holes 384 and 527 in the North and South Atlantic respectively, and DSDP Hole 577 in the equatorial Pacific show increasing Ba (super *) values contemporary with the evolution of the late Paleocene global delta (super 13) C maximum, illustrating how marine surface primary production as well as formation of biogenic barite increased at this time. At the two oligotrophic Atlantic locations, Ba (super *) increased from 160-360 ppm in the early Paleocene to 1100-3000 ppm during the delta (super 13) C maximum. At the equatorial Pacific site, which during the Paleocene was positioned adjacent or within the high-productivity belt, values increased from an early Paleocene level of 15,000 ppm to approximately 25,400 ppm in conjunction with late Paleocene maximum delta (super 13) C values. New insight into the origin of biogenic barite is provided by linear fitted correlation plots of sediment Ba (super *) content versus surface water delta (super 13) C. All three regions support biogenic barite originating in the euphotic zone. An estimation of the increase in burial rates of C (sub org) (relative to Al (sub 2) O (sub 3) ) based on the early to late Paleocene relative increase in Ba (super *) is presented. Accumulation rates of marine organic carbon accelerated by a factor approximately 1.8 and approximately 6.0 in the eutrophic and oligotrophic regions, respectively. When weighed for the entire ocean a tentative estimation suggests that C (sub org) burial rates doubled during the late Paleocene delta (super 13) C maximum. In Paper II, stable oxygen and carbon isotope profiles for Selandian (60.3-58 Ma) mollusk shells that formed at two different water depths at the marginally marine environment of Vestre Gasvaerk in Denmark, were established in order to provide new insight into the early Late Paleocene North European climate. In a paleoenvironment such as at Vestre Gasvaerk continental freshwater run-off may bias the water temperature record, which consequently must be accounted for when interpreting the paleotemperature record. The delta (super 18) O profiles of the deeper dwelling mollusks and the benthic foraminifera, respectively, indicate no such influence. The paleotemperature record for the surface dweller is, however, most certainly an artefact of a freshwater component. Surface water delta (super 18) O data implies a tropical climate in the region, contrary to paleobotanical and foraminiferal isotopic data respectively, which indicate subtropical conditions. By comparing the Selandian data to a modern analogy, such as in the eastern Mediterranean, the freshwater component in the paleo-delta (super 18) O record of Selandian surface waters could be distinguished and estimated. The study shows that continental run-off fluctuated seasonally, with higher freshwater influx in the winter. The stable carbon isotope record for the surface dwelling mollusk supports this observation. With winter rainfall diluting surface waters, salinity stratification in the water column intensified. Temperature stratification, however, was practically non-existent, as temperatures gradually decreased and grew uniform in the water column, which ultimately lead to a seasonal thermal breakdown.