Horst, Peter A. and Maurrasse, Florentin J. (2006): Characterization of geochemical and fossil variabilities in Cenomanian-Turonian sediments of DSDP Leg 43, Site 386, Bermuda Rise

DSDP 43 386

Horst, Peter A.
Florida International University, Department of Earth Sciences, Miami, FL, United States

Maurrasse, Florentin J.

Characterization of geochemical and fossil variabilities in Cenomanian-Turonian sediments of DSDP Leg 43, Site 386, Bermuda Rise
In: Anonymous, Geological Society of America, 2006 annual meeting
Geological Society of America (GSA), Boulder, CO, United States
Geochemical studies of Cenomanian strata at Site 386 reveal that TOC values range from 0.0% to 31.6%, with an average of 2.0%, and highest values occur at the stratigraphic level attributable to OAE 2 (Core 43). Levels rich in TOC contain predominantly marine planktonic organisms (radiolarians, nannoplankton) and tend to be isotopically lighter compared to most Tertiary samples. The delta (super 13) C (sub org) values for bulk organic matter range between -27.8 and -19.7ppm with an average of -25.3ppm, showing a positive excursion of about 2ppm during OAE 2, preceded by a slight negative excursion. XRD analyses of clay content imply both oceanic and continental provenances. The oceanic component of Cenomanian sediments is discrete smectite, whereas the associated illite-smectite indicates a continental origin. The highly expandable illite-smectite and the kaolinite of Turonian sediments indicate a continental origin from subtropical soils, while the clinoptilolite is of marine origin. The OAE 2 interval yields abundant microscopic quartz interpreted to be diagenetically generated from remobilized biogenic silica, which reprecipitated in pore waters with lower pH due to high content of organic matter. Younger levels show systematic increase in the proportion of calcareous nannoplankton (50-75%) represented mostly by Watznaueria barnesae, a solution resistant taxon suggestive of dissolution effect. However, in the early Cenomanian this species shows a negative correlation with high productivity species and a positive correlation with carbonate content, which indicates a fluctuating CCD. The elevated organic matter content is related to the overall decreased oxygen content in the Cretaceous greenhouse oceans, particularly during that time interval. Abstract 111962 modified by on 7-10-2006
Coverage:Geographic coordinates:
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Stratigraphy; Atlantic Ocean; Bermuda Rise; Cenomanian; characterization; cores; Cretaceous; Deep Sea Drilling Project; DSDP Site 386; fossils; geochemistry; Leg 43; Mesozoic; mineral composition; nannoplankton; North Atlantic; organic compounds; paleo-oceanography; paleoclimatology; pH; plankton; pore water; precipitation; productivity; sediments; total organic carbon; Turonian; Upper Cretaceous; variations; Watznaueria barnesiae; X-ray diffraction data;