Early Jurassic normal faulting in a carbonate extensional basin: characterization of tectonically driven platform drowning (High Atlas rift, Morocco).
Résumé
This paper describes a tectonostratigraphic model of the synrift evolution of the Early Jurassic High Atlas rift of Morocco. The model is constrained by mapping of a set of inverted extensional blocks, by facies analysis of carbonate platform and turbiditic to hemipelagic synrift deposits, and by high-resolution (n 3 100 ka) biostratigraphy of the Early Jurassic succession. The chronostratigraphic packages of the High Atlas of Rich vary significantly in thickness, facies and architecture from one tectonic block to another. Our study shows how synrift strain varied in space and time over a long time interval (14 Ma) around the High Atlas rift. Initially, in Sinemurian time, the High Atlas rift was affected by low-strain normal faulting that controlled the growth of an extensive, low-gradient carbonate platform, except in the northern domain (towards the rift axis), where hemipelagic deposition related to high-rate faulting prevailed. Subsequently, in Carixian–Domerian time, a rapid increase in accommodation space and block subsidence caused by highstrain normal faulting brought about localized drowning of the carbonate platform and the development of calciturbidites and of starved deposits towards the rift axis. During this interval, high-strain, upper-crustal normal faulting migrated rapidly (over a period of 5 Ma) towards the rift periphery.