Basement-cover decoupled hyperextended rifting: revisiting syn-rift sag basins of the Western Pyrenees
Abstract
Knowledge of rifting processes largely depends on our understanding of the tectono-stratigraphic record of rifted margins. While the syn- to post-kinematic evolution of half graben basins is well understood, few descriptions exist of so-called "syn-rift sag basins" commonly located in hyper-extended domains of rifted margins. Because of banana-like shape and little evidence of syn-rift deformation, they are interpreted as the record of depth-dependent crustal thinning, migration of deformation, post-kinematic thermal subsidence, sub-seismic faulting or a combination of these latter.
We use onshore record of the Arzacq Basin from Western Pyrenees (SW France) where syn-rift "sag basins" are commonly reported and associated to a regional pre-kinematic decollement in the Upper Triassic sequence. Benefitting from a century of hydrocarbon exploration, syn-rift "sag basins" from these regions are extensively imaged by 2D and 3D reflection seismic and well data or described in the field as inverted analogues into the nearby Pyrenees. These sub-surface and surface data bring the opportunity to document the anatomy of the Arzacq Basin in 3D. Above the decollement, the pre-rift sequence has the same morphology as the top-basement across the whole basin and is covered by a syn-kinematic syncline with growth strata and migrating depocenters toward the footwall. At the exception of normal faults located in the pre-rift sequence, no major faulting are reported in pre- and syn-rift cover. We show that the basin formation was controlled by a north-dipping top-basement low-angle normal fault. Dipping of less than 20° within the basement, the thin-skin counterpart of the deformation is soling out into the Upper Triassic pre-rift evaporites. Based on these results, we conclude that this type of syn-rift "sag basin" results from the interaction between top-basement low-angle faulting and an efficient pre-kinematic decollement. Based on this example, we define a "basin-decoupled" end-member mode of hyper-extension rifting from which we present kinematic restorations. We suggest that the study case of the Arzacq Basin should drastically impact basin models and exploration interests of many instances of "syn-rift sag basins" worldwide.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T43E0496D
- Keywords:
-
- 8105 Continental margins: divergent;
- TECTONOPHYSICS;
- 8107 Continental neotectonics;
- TECTONOPHYSICS;
- 8109 Continental tectonics: extensional;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS