Tecto-sedimentary cycles and depositional sequences of the Mesozoic and Tertiary from the Pyrenees

Abstract

Tectonic deformation in the Pyrenees is the result of an essentially continuous process which has a discontinuous effect in the style of deformation and consequently, in the sedimentary record. Tecto-sedimentary discontinuities can be correlated on a regional scale, allowing the differentiation of tecto-sedimentary cycles and depositional sequences. The relations between tectonics and sedimentation in the Pyrenees are expressed in the Mesozoic and Tertiary cyclicity. Ten tecto-sedimentary cycles have been distinguished. They are controlled by basin-forming and basin-modifying tectonics (rifting, wrenching, convergence) and are related to different successive basin-types. A first group of cycles corresponds to the episodic rifting: post-Hercynian interior fracture basin (cycle 1), spreading of the Ligurian Ocean (cycle 2), spreading of the central North Atlantic Ocean (cycle 3) and rifting of the Bay of Biscay in the context of the rotation of Iberia (cycle 4). A second group corresponds to the opening of the North Atlantic Ocean and to the change in the trajectory of Iberia along a W-E direction (cycle 5). The third group corresponds to prevailing wrench conditions grading from strike-slip plate displacement (cycle 6) to progressive oblique convergence (cycle 7). The fourth group of cycles (8, 9 and 10) corresponds to the generalization of convergence conditions; cycle 8 is the transition from wrench to foreland basin; cycle 9 corresponds to the development of migrating foreland basins in relation to thrust sheet emplacement; cycle 10 includes the unconformable clastic wedge ahead of the last thrust. These tecto-sedimentary cycles include one or several depositional sequences in which sedimentation is controlled by the interrelations between local tectonics, subsidence, eustacy and sediment supply. The analysis and definition of these sequences is given for the Cretaceous and Tertiary cycles. The depositional sequences from the Cretaceous wrench basin are essentially related to eustacy (sea level rise) together with subsidence during cycle 6, and wrench structuring during cycle 7. The depositional sequences from the foreland basins (cycles 8, 9 and 10) are related to changes in the type of basin.