Abstract

The ante-Turonian Cretaceous from the southern Middle Atlas and the High Moulouya, Morocco, apparently composes a continuous series that includes the Midelt and Amghourzif pro parte formations. The Midelt Formation, described in this work, is divided in three members. The lower member, undated, is composed by gullying and lenticular conglomerates or microconglomerates, showing facies of channel bottom, sandstones of anastomosing channel bars, and red clays of flood plain. The intermediate member is azoic, constituted by the piling up of parasequences (4th or 5th order) showing clays, dolomites and sandstones, deposited in a dolomitic and evaporitic sebhka environment, without direct connections to the sea. The upper member is organized by four parasequences (4th or 5th order), with marls-dolomites or marls-limestones, showing the progressive flooding of the environment due to the eustatic transgression of the Upper Cenomanian-Lower Turonian interval. The bioclastic sedimentation of the basal limestones of the Amghourzif Formation is produced by two transgressive-regressive cycles, constituting two high frequency units (4th order sequences), dated by Upper Cenomanian ammonites, and by a third transgressive semi-cycle (4th order) at the Upper Cenomanian-Lower Turonian interval. The deposits develop, in space and time, from an inner carbonate platform environment, in a confined, freshened, and shallow water subtidal environment, to an open platform, with black shale deposits bearing planctonic foraminifers or ammonite-bearing limestones. The sedimentary dynamics during the Cenomanian are controlled by extension that infers four tilted blocks towards the Tethysian domain.

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