NEGATIVE INVERSION IN ATLASIC DOMAIN (MOR OCCO) - THE KERROUCHEN TRIASSIC BASIN, A STRUCTURAL ELEMENT OF THE ATLASIC RIFT

This specific geotraverse from Khenifra to Midelt, in addition to prev ious field observations and papers related to the early Mesozoic Atlas ic rift, provides new data concerning: (1) the centrifugal westward op ening of this ''Atlasic rift'' by reactivation of a Variscan thrust du ring the Triassic-earliest Liassic; (2) abrupt initiation of a marine flooding with a lithological change from terrigenous to carbonate depo sits during the early-Middle Liassic. The most striking point is the i mportance of pre-existing structures, particularly thrusts, in determi ning how the basement responds to extensional stress. These structures , including the thrust zone system dipping eastward between the Inner Eastern Zone (Midelt Zone) and the Intermediate Zone (Khenifra allocht honous unit), have been reactivated as extensional faults and they con trolled the development of some sedimentary basins in their hanging wa lls. In the early Liassic time, deposition of the overlying marine car bonate sequence is thought to have been at least in part induced by th e post-rift thermal subsidence stage.