Isotopic and Foraminiferal Analysis of the Cenomanian - Turonian Boundary Event of the Indian Ocean
Abstract
The Cenomanian - Turonian Boundary Event (CTBE) at ODP site 762 (19o53.23S, 112o15.24E) was investigated to explore the nature of mid Cretaceous events, in particular ocean anoxia and associated climatic and oceanographic changes. Through the application of carbon and oxygen isotope analysis in conjunction with the study of changes in the foraminiferal assemblage across the boundary, the nature of the event in the Indian Ocean can be defined. Site 762 is situated on the Exmouth Plateau off the west coast of Australia at a latitude around 19oS and at a water depth of 1360 metres. During the Cretaceous the site is thought to have been located at a palaeolatitude of 47oS in a deep ocean environment with deposition dominated by nannofossil chalks and clays. These sediments have since been buried up to 819.25 metres (the base of the Cenomanian sediments) subjecting them to possible high degrees of diagenesis and alteration which could effect the isotope signatures obtained from the samples. Fine fraction samples in addition to foraminiferal species specific samples (benthic, deep dwelling planktonic and shallow dwelling planktonic) were analysed for carbon and oxygen isotopes that were used to define the oceanographic changes of the CTBE in this region. This data combined with published work show the globally recognised warming event at the Cenomanian - Turonian Boundary, albeit with some subtle differences. To support the isotope data species of foraminifera were picked and analysed from the samples using standard picking techniques and studied in part using a scanning electron microscope. This enabled the full extent of any alteration and infilling of the tests due to diagenesis to be studied and any effect on the isotope curves to be qualified, as well as enabling the biostratigraphy of the foraminifera of the Cenomanian and Turonian in the Indian Ocean to be studied This data reveals new insights into this enigmatic extreme event and aids to piecing together of what happened at this global Cenomanian - Turonian Boundary Event.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....9131F