|mhorn||Дата: Tuesday, 16.10.2012, 15:55 | Сообщение # 1|
|Hammer Ø., Collignon M., Nakrem H.A. (2012) Organic carbon isotope chemostratigraphy and cyclostratigraphy in the Volgian of Svalbard // Norwegian Journal of Geology, Vol. 92., P.103-112. |
We present δ13Corg curves for the Upper Jurassic to lowermost Cretaceous of central Spitsbergen. The three sections span the Slottsmøya Member (Agardhfjellet Formation) at Janusfjellet and Knorringfjellet in the Sassenfjorden area. The results indicate that bulk organic carbon isotope chemostratigraphy can be used as a tool for high-resolution, local chronostratigraphic correlation in central Spitsbergen, resolving problems of possible overthrusts, slumping and diachronous lithological boundaries. Moreover, the curves can be compared with published data from carbonates on the Russian Platform, recording a negative δ13C trend through the Lower Volgian followed by a positive trend from the lower part of the Middle Volgian and into the Upper Volgian. The minimum in the curve in the lower Middle Volgian is sharply defined, and this negative excursion may provide a useful chemostratigraphic marker for correlation between the Barents Sea and the Russian Platform, and possibly globally. The excursion is here called VOICE (Volgian Isotopic Carbon Excursion). There are indications of a c. 400 kyr periodicity, which can be interpreted as a result of orbital forcing (long eccentricity). In contrast, inorganic carbon and oxygen isotopes from carbonates in the Sassenfjorden area mainly reflect diagenetic processes.
Middle Jurassic - Lower Cretaceous ammonites & aptychi