Abstract - The interplay between tectonics and sedimentation is reasonably well understood in non-marine rift basins and in foreland basins. However, there are fewer cases where structural controls on deep-marine turbidite deposition can be demonstrated. Gravity currents are sensitive to very small gradient changes and hence should be affected by even subtle sea floor deformation. This deformation may reflect the different types of tectonics associated with extensional basins, strike-slip pull-apart basins or with salt or shale mobility. For example, within the Gulf of Mexico, a continental slope which has been the focus of much research on tectonic controls on sedimentation, halokinetic activity has created several depressions called mini-basins. Seismic profiles and cores studies in these mini-basins show that associated slope variations can induce either changes in the mode of deposition or, if large, slope failure. Recent studies of the Marmara Sea, a pull-apart basisn in which oblique slip faults displace the deep-sea floor, highlight the importance of localised rapid basinal subsidence on associated sedimentation. In this talk, we describe the geology of a strike-slip basin in SE Spain, which illustrates the strong links between tectonics, sedimentation and associated slope failure deposits.
Our analysis is based on field observations from the very well exposed Neogene Tabernas Basin, SE Spain. The basin is a relatively small and narrow (~ 20km long and ~ 10 km wide) which is elongated in an E-W direction, sub-parallel to a bounding strike-slip fault. It contains a number of oblique-slip intrabasinal faults that propagated to the palaeo-sea bed, providing local ponded accommodation for gravity currents and influencing flow routing and slope stability. The early basin fill was characterised by extensive east-facing, axial slopes into which slope channels were incised and bypassed sediment. As the intra-basinal faults appeared at the sea bed, they bounded local areas of rapid subsidence that became deeps analogous to mini-basins into which turbidites and mass transport complexes were preferentially trapped and fully ponded. Occasional mass transport complexes and numerous slides attest to the tectonic activity and associated slope instability of the mini-basins. They are attributed to collapse of either intrabasinal fault scarps or, in most cases, the oversteepened margins of the sub-basin. Excellent outcrop exposures permit 3D definition of slumped units and reconstruction of part of their internal structure and their geometry. Detailed analysis helps define the impact of tectonics on sedimentation and slope failure, and shows how a strike-slip mini-basins are characterised by particularly unstable slopes with episodic whole scale slumping, sliding and failure of the onlap wedges.
Abstract of talk given to:
Tectonic Studies Group Annual Meeting, La Roche-en-Ardenne, Belgium, January 2008.