Tectonics of a Permo-Carboniferous Trough in the Northern Foreland of the European Alps Inferred From Reprocessed and Densified 2-D Seismic Reflection Data

Abstract

Late Paleozoic basins that formed in the aftermath of the Variscian orogeny are characteristic tectonic elements of the Western European plattform. The coal bearing Permo-Carboniferous Trough of northern Switzerland (PCT) in the subsurface of the outermost Cenozoic European Alpine foreland has inspired various tectonic interpretations ever since its first characterization elaborated in the course of Nagra's exploration for a potential nuclear waste repository in the mid 80ies. Following the recent reprocessing and substantial densification of the extensive 2D-seismic dataset available across the PCT a revision of its structural interpretation was launched. The results of this re-interpretation will be presented. They shed new light on the PCT's kinematic evolution and modern seismic exploration possibilities and are considered relevant for the natural resource exploration that is anticipated for similar troughs in southward adjacent regions. Despite significantly improved seismic data quality and interpretability the tectonic interpretation of the PCT remains largely conceptual as seismic imaging of the basement is strongly influenced by the structural conditions of the sedimentary cover and its associated seismic reflection behavior. Nevertheless, due to additional interpretation support provided by newly available Bouguer anomaly maps the overall robustness of the PCT's structural interpretation could be improved. New aspects concerning the likely kinematics of trough formation and indications confirming the PCT's important role as precursor structure during post-Paleozoic tectonic events are highlighted below. The roughly ENE-WSW striking PCT shows a half graben geometry that changes laterally across a WNW-ESE striking transfer fault. The overall trough geometry strongly suggests that pull-apart tectonics. Post-Paleozoic extensional reactivation of major trough bounding faults is witnessed by the development of monoclines in the above lying Mesozoic and Cenozoic sediments. Subtle sediment thickness variations indicate that differential subsidence most likely related to this extensional reactivation of the trough already onset in Mesozoic times. Evidence for substantial Late Cenozoic inversion, reported from more westerly sections of the PCT could not be identified in the study area. A mild transpressive reactivation however cannot be fully excluded either.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016