JURSSIC STRUCTURAL STEPS OF THE CENTRAL HIGH ATLAS (MOROCCO). EXAMPLE OF THE MIDELT-ERRACHIDIA TRANSVERSE SECTION

JURSSIC STRUCTURAL STEPS OF THE CENTRAL HIGH ATLAS (MOROCCO). EXAMPLE OF THE MIDELT-ERRACHIDIA TRANSVERSE SECTION IBOUH H.¹, CHAFIKI D.¹ ¹: Cadi Ayyad Univ., Laboratory of Geosciences and environment, Faculty of Sciences... [ view full abstract ]

JURSSIC STRUCTURAL STEPS OF THE CENTRAL HIGH ATLAS (MOROCCO). EXAMPLE OF THE MIDELT-ERRACHIDIA TRANSVERSE SECTION

IBOUH H.¹, CHAFIKI D.¹

¹: Cadi Ayyad Univ., Laboratory of Geosciences and environment, Faculty of Sciences and Techniques, Marrakesh (Morocco), h.ibouh@uca.ma

The Midelt-Errachidia section is located in the eastern part of the Central High Atlas. It corresponds to an accessible and studied N-S transverse.
The detailed study of the synsedimentary structures, Lower and Middle Jurassic in age, shows four tectonic steps which control the basin evolution before the compression phase leading to the creation of the present central atlasic belt.

Sinemurian: the carbonate platform settles up involving distension and flexures along the main faults. The resulting arch bends are covered with building organisms as sponges which form carbonate mounds. During the Upper Sinemurian, the persisting distension movement leads to break down, block tilting along the N70 and E-W oriented faults and halokenitic rise of Triassic series inducing collapse and relative deepening of the platform. This step is earlier and mainly recorded in the southern part of the section.

Carixian-Domerian: Distension inducing middle-sized deformation leads to synsedimentary normal faulting and slumping processes. The collapsed Sinemurian platform is converted into a deep atlasic subsiding trough. Distension is mainly present in the northern.

Upper Domerian: to Lower Toarcian boundary. A very important regional extension motion leads to the paroxysmal breakup of the Liassic platform and to the general collapse of the atlasic trough.

Aalenian-Bajocian: This step is characterized by a N120 to N160 oriented distension locally associated with a synsedimentary, horizontal, NW-SE oriented compression. This association is related to a sinistral strike slip movement along the main faults oriented N70 to E-W. The compression process is the first one within the Jurassic sedimentary record. It corresponds probably to the transition period between the opening/filling up and the closure stages of the central High Atlas basin and records the first small events related to tectonic inversion in the Midelt-Errachidia section.

The post-Jurassic atlasic compression phases are locally represented by structures related to compression oriented NW-SE, N-S or NE-SW. This compression induces really the geometry of the main megastructures oriented N70 to E-W. This organization is closely linked to a coating tectonics related to interaction between the sedimentary cover and basement.