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Pyramid

ANR Blanc 4 year project, 2012-2016

PI : Mary Ford

External orogenic systems, each comprising a fold and thrust belt and its associated foreland basin, represent the most complex and challenging domains for hydrocarbon exploration due to the complexity of structural geometries and stratigraphic architectures, and the polyphase nature of fluid flow histories. Now at the end of its commercial life, the Aquitaine basin in SW France is one of the best explored foreland basins in the world. It is part of the north Pyrenean orogenic retrowedge, which is itself remarkable because of the presence of mantle and lower crustal rocks that were exhumed during pre-orogenic extension. In this large and ambitious project 3 industrial partners and 3 academic partners will collaborate in a multi-disciplinary investigation of the interactions of deformation, surface processes and climate during mountain building and of their influences on fluid flow history. For this project Total, the main operator in the Aquitaine basin, and the BRGM are providing full access to their extensive subsurface databases, thus creating a unique opportunity to apply new techniques and concepts to a full foreland orogenic system. The main objectives of the four year project are
- (1) to constrain the 3D structural style and architecture of the North Pyrenean foreland system and to define the role of crustal inheritance in contractional deformation ;
- (2) to link sediment routing systems, orogen relief and exhumation to evolution of the foreland basin and,
- (3) to quantify fluid-rock-deformation interactions throughout the extension-contraction cycle.

Three interlinked tasks are built to address these objectives. The first will use field mapping, stratigraphy, cross section construction and restoration, strain analyses to build a series of cross sections and restored templates. The second task links basin history to evolution of orogen relief (source to sink) during and after orogenesis by integrating sedimentology, subsidence analysis and double dating of zircon and apatite detrital grains in the basin with low and medium temperature geochronology, paleo-elevation and geomorphology studies in the orogen itself. The third task focuses on fluid characterization during different phases of orogenesis and pre-orogenic extension both in the basin and in different zones (and crustal levels) of the orogen. In a fourth task results of other tasks will constrain simulation and analogue modeling to build 2D and 3D models for basin history and fluid flow (petroleum systems), evolution of orogen relief and inversion of the pre-orogenic template.

Tectonic map of the Pyrenees from Verges and Garcia-Senz (2001) showing the area covered by this project (red box), major oil and gas fields, and the positions of the ECORS deep seismic profiles.

Cartoon showing the principal elements and processes controlling material and fluid flux in a foreland orogenic system. Fluid migration pulses (blue arrows) may be related to creation of relief, climate variations, metamorphic and deformation phases, diagenesis and compaction, subsidence and overpressure.

Geological map of the Pyrenean orogen (BRGM). The North Pyrenean Zone (NPZ) lies between the North Pyrenean Frontal Thrust and the North Pyrenean Fault. The provisional position of nine key transects (1 to 9) are shown. Circles represent the position of areas where exhumation of lower crust and mantle will be studied (Task 4.1). Three cross sections will cross the whole orogen to link with the southern prowedge (sections 2,4,7). At least one transverse section (10) will link all sections. NPZ basement massifs are Mouthoumet (M), Agly, Saint Barthelemy (SB), Trois Seigneurs (TS), Arize, Castillon (C).