ABSTRACTS
Sanad A. Al-Khashab Ostracoda of Tanuma Formation in Borehole EB-12, Northeast Baghdad City, Iraq (M.Sc)
Ostracoda of Tanuma Formation, Borehole EB-12 have been studied in detail. Thirty-two species belonging to 10 genera are described, of which 26 of these species were recorded for the first time in Iraq, including 6 new species. Biostratigraphically, on the basis of the Ostracoda species occurrence, one biozone is proposed, which is divided into three sub-biozones (assemblage zones), correlated with Ostracoda and Formainifera biozones from the adjacent areas, confirming the Coniacian age of the Tanuma Formation in borehole EB-12. The paleoecology of the Tanuma Formation is shallow neritic marine environment, between middle shelf to outer shelf under marine salinity. The affinities of the described species are discussed from a paleogeographical view, indicating that there was a marine connection between Iraq, North Africa, and West Africa during Coniacian time. Three migration routes were outlined: the first from West Africa to east South America, the second from West Africa to North Africa and the Middle East, and the third from Iran to east Africa. Three Bioprovinces were recognized during the Coniacian: West Africa, North Africa, and Iraq and Iran.
Nicola Johnson Ostracod Biogeography during the
Cenomanian-Turonian Oceanic Anoxic Event in Europe
Podocopid ostracods from the Plenus Marls at sites in England show stepped extinctions through an interval marked by a strong positive carbon stable-isotope excursion, corresponding to the Cenomanian-Turonian Oceanic Anoxic Event (CTOAE). Platycopid ostracods, however, do not appear to be affected. Ostracods, benthonic crustaceans with no pelagic stage in their life cycles, may offer a unique insight into water mass distributions and circulation patterns during the CTOAE interval, which lasted approximately 100,000 years. From a detailed literature review concerning the CTOAE and Plenus Marls, two opposing theories are recognized. These are that either the Oceanic Anoxic Event (OAE) resulted from a transgression and expansion and intensification of the Oxygen Minimum Zone (OMZ) or from a regression coupled with climatic cooling. The distribution data of 48 species of Ostracoda from samples collected across southern England from Compton Bay (Isle of Wight), White Nothe (Dorset), Beggars Knoll (Wiltshire), Pitstone (Chilterns), Sewell (Chilterns), and from Menoya (northern Spain), Baddeckenstedt and Wunstorf (northern Germany) is presented. Correlation of the southern England Plenus Marls stratigraphy to Spanish and German sections is problematical and therefore relies heavily on the foraminifer Rotalipora cushmani and the belemnite Actinocamax plenus. The discovery of the virtual absence of Cytherelloidea from English sections has led to a detailed study of the global palaeobiogeography and biogeography of this genus and initial conclusions challenge the commonly held view that it is a warm-water indicator.
After detailed studies and analyses of the palaeobiogeography of all the ostracod species recovered across southeast England, clear biogeographical changes are evident through the Plenus Marls. It is felt that the ostracod data neither fully supports nor disproves either of the opposing theories. The data, when coupled with the delta 18O data, would appear to be best explained by an Oceanic Anoxic Event (OAE) induced by warm climate conditions leading to a brief cooling in the climate closer to the Cenomanian-Turonian boundary. This, in turn, probably terminated the OAE.