ABSTRACT: Inversion of Early Cretaceous extensional basins in the Central Spanish Pyrenees

Garcia Senz, Jesus¹, Josep Anton Muñoz¹, and Ken McClay²  
(1) Barcelona University, Barcelona, Spain
(2) Royal Holloway University of London, Egham, Surrey, England

The Pyrenees is a Late Cretaceous - Early Miocene contractional orogen which is characterized by significant inversion structures at all scales. The uppermost thrust sheets of the south-central Spanish Pyrenees involve folded and thrust Early Cretaceous extensional basins that contain a thick (up to 5km thick) sequence of marls and limestones and which were inverted in the Late Cretaceous - Early Miocene orogeny. Deformation is characterized by partly inverted extensional faults, footwall short-cut faults and hangingwall fault-propagation folds. Syn-inversion, strongly subsident basins developed in front of the reversed extensional faults and were infilled with Late Cretaceous turbidites. In this paper the Tamurcia structure, where the tectono-sedimentary evolution is well constrained from outcrop, well, and seismic data, is described in detail. This is an inverted half-graben that forms a hangingwall fold above a stack of basement-involved ramp anticlines. Syn-inversion turbidites display growth stratal geometries and are thickest adjacent to the main footwall ramp of the inverted half-graben. Sequentially restored and balanced cross-sections show that initial deformation involved reactivation of a high-angle extensional fault. When shortening equalled extension in Cenomanian / Santonian, a footwall shortcut developed producing a monoclinal hangingwall fold . Continued deformation on the shortcut thrust lead to uplift of the inverted basin in the hangingwall along the thrust ramp and subsequent lateral translation for as much as 100 km along a footwall flat. The Tamurcia structure is an analogue to the Meillon gas field in the northern Pyrenees and is similar to other inverted Pyrenean Early Cretaceous extensional basins.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia