QUANTITATIVE MODELLING OF THE SOUTHERN CANTABRIAN BASIN (NW-SPAIN)

An effective tool in dynamic basin modelling is the combination of reverse basin and forward stratigraphic modelling. The model considers the spatial and temporal development of sedimentary parameters from the deposition of the oldest sediments in the basin to the time of maximal burial.

The processed transect (24km) is situated at the southern margin of the Cantabrian Mountains in NW-Spain. This part of the Variscan orogen is represented by a foreland thrust and fold belt with a thin-skinned deformation style. The setting offers magnificent outcrops in each individual thrust sheet. However structural 2D balancing of the deformed basin infill is required in order to obtain realistic approximations of the basin extension before the Variscan orogeny. Based on both qualitative and quantitative structural balancing approaches, the shortening of the Cambrian to Carboniferous basin amounted to 54%.

The main focus of the reverse modelling (backstripping) is on the development of the basin architecture in consideration of lithofacies, incremental compaction, sea-level changes and flexural loading of the crust. These parameters influence the long-term evolution of accommodation space in time. The model comprises the whole basin infill between the top of basement (Precambrian/560Ma) and the time of maximal burial (Cenozoic/34Ma). Tectonic subsidence rates during Precambrian to Ordovician are uniform in terms of time and space (-20 to 18 m/Ma) and reflect the stable conditions of a passive continental margin. Local tectonics of the basin triggered differential subsidence between the Silurian and latest Devonian (-12 to 65m/Ma). In the Carboniferous depocentres with remarkable high rates of tectonic subsidence (-131 to 239 m/Ma) moved to the east because of the approaching Variscan front.

Stratigraphic forward modelling includes subsidence/uplift, flexural loading, compaction, sea-level changes, erosion, and both siliciclastic and carbonate sedimentation. This method offers geometrical minimum/maximum models of the sedimentary geometries and lithofacies distribution in time and space. Results visualize the development of the depositional and structural characteristics with a time-series animation.