Magneto-biostratigraphy of the Middle to Upper Triassic transition, central Spitsbergen, arctic Norway.

Hounslow, Mark W. and Hu, M. and Mork, A. and Vigran, J. O. and Weitschat, W. and Orchard, M. J. (2007) Magneto-biostratigraphy of the Middle to Upper Triassic transition, central Spitsbergen, arctic Norway. Journal of the Geological Society, 164 (3). pp. 581-597. ISSN 0016-7649

Abstract

Palaeomagnetic and biostratigraphic data were obtained for the latest Ladinian and most of the Carnian (Botneheia Formation to basal Kapp Toscana Group), from two sections in central Spitsbergen (Svalbard archipelago). Thermal and AF demagnetisation reveal a magnetisation of both normal and reversed polarities. The mean directions pass reversal and fold tests and are similar to other European Late Triassic palaeopoles. One of the sections displays 15o of vertical-axis, clockwise, tectonic rotation on a décollement in the underlying Botneheia Formation. The magnetostratigraphy is dominated by normal polarity in the uppermost Botneheia Formation and into the Tschermakfjellet and basal De Geerdalen formations. A substantial hiatus characterizes the Ladinian- Carnian boundary in central Spitsbergen, so reverse magnetozones, identified in Tethyan sections near this boundary, are absent. Magnetostratigraphic correlation, along with palynostratigraphic constraint, indicates most of the De Geerdalen Formation is Lower Carnian. The magnetostratigraphy and palynology, indicates the Isfjorden Member (upper unit of the De Geerdalen Formation) is probably mid Carnian in age. Change in the lithologic architecture in the Isfjorden Member, compared to the underlying parts of the De Geerdalen Fm, suggests a hiatus near the base of the member, which may represent a mid Carnian unconformity, not previously recognized on Spitsbergen.