Orogenically controlled sedimentation in the Lechtaler Kreideschiefer (Lechtal shale; Cretaceous) and geodynamics of the inner western NCA (Northern Calcareous Alps; Lechtal Alps)

Abstract

Only recently have sedimentological studies been integrated with orogenic research. The analysis of the “Lechtaler Kreideschiefer” (Lechtal Shale; Lower Cretaceous) demonstrates that these sediments reflect orogeny. Subduction and compressive tectonics resulted in the formation of a nappe pile. Folding of the epicontinental shelf formed long syn- and anticlines. In contrast to the uplifting anticlines the synclines represent subsiding depocenters with continuous sedimentation. Sheet-like olistostromes migrated in a broad front towards the axes of the Inner-Calcalpine synclines. The line-source character of unchannelized clastic influx from anticlines is different from fault-scarp breccias, slope aprons and the point-source of fan models. Some olistostromes document the initial tectonic elimination of various depocenters and can be recognized below following tectonic units: The Lechtal and the Inntal Nappe, the Braunarlspitz Wedge, the Hasenfluh Klippe, the Krabachjoch Thrust Outlier. These tectonic bodies arose from apparent overturning (“Ueberfaltung”Blumer, 1905; “Untermuldung”Leiss, 1988, 1989 1990) and lie on synclines filled with synorogenic sediments. The thrust distance is 5–10 km.