Stratigraphic evolution of a salt-walled basin: the influence of diapirism and compressional tectonics on the sedimentary record of the Estopanyà syncline (South-Central Pyrenees)

Abstract

This contribution describes the influence of diapirism and compressional tectonics in the sedimentary record ofthe Estopany`a and Boix synclines (salt-walled basins) in the South-Central Pyrenees (NE Spain). Based onmapping and logging of five stratigraphic sections, two lithostratigraphic units (LU-1 and 2) along the easterndiapir margin of these synclines and five more (LU-3 to 7) in their inner parts are defined. LU-1 and 2 consist ofmonomictic breccias deposited probably during the Upper Triassic-Oligocene and the Upper Cretaceous,respectively. LU-3 to 7 constitute a marine to fluvial succession of the Tremp Group deposited during the UpperCretaceous to Paleocene. The stratigraphic and sedimentological record indicates that the topography, position,and accommodation space of the Estopany`a and Boix synclines was actively controlled by the evolution of saltstructures from the Late Cretaceous to the Oligocene in response to the advance of the Alpine compression in theSouth-Central Pyrenees. The growth of salt-inflated ridges with a near parallel orientation to the axis of thestudied synclines since the Upper Cretaceous, progressively compartmentalized the Boix syncline until inhibitingsedimentation during the lower Paleocene. In the upper Paleocene, the Alpine compression approached the studyarea increasing salt evacuation and the subsidence of the Estopany`a and Boix synclines. During the early tomiddle Ypresian, onset of compression led to salt expulsion by piercing the sedimentary roof of the inherited saltinflatedridges and forming two salt walls at the eastern margin of the Estopany`a and Boix synclines that weresqueezed and welded (possibly through secondary welds) due to tectonic compression during the Oligocene. Thiscontribution provides a new interpretation of the structural and stratigraphic evolution of the Estopany`a andBoix synclines, proposing an evolutionary model that includes the rejuvenation, growth, and extrusion of saltwalls as deciphered from the stratigraphy, sedimentology, and petrology of the diapir margin breccias and thesedimentary succession of the adjoining salt-embedded basins. Hence, it provides a new analogue study forunderstanding the interplay between compressional tectonics, diapirism, and sedimentation to other inverted saltbasins with precursor salt walls worldwide.