Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)
The Paleozoic intracratonic North African Platform is characterized by an
association of arches (ridges, domes, swells, or paleo-highs) and low
subsidence rate syncline basins of different wavelengths (75–620 km). The
Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from
east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches.
Through the analysis of new unpublished geological data (i.e., satellite
images, well logs, seismic lines), the deposits associated with these arches
and syncline basins exhibit thickness variations and facies changes ranging
from continental to marine environments. The arches are characterized by thin
amalgamated deposits with condensed and erosional surfaces, whereas the
syncline basins exhibit thicker and well-preserved successions. In addition,
the vertical facies succession evolves from thin Silurian to Givetian
deposits into thick Upper Devonian sediments. Synsedimentary structures and
major unconformities are related to several tectonic events such as the
Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound,
the Silurian–Devonian Caledonian extension/compression, the late Devonian
extension/compression, and the Hercynian compression. Locally, deformation is
characterized by near-vertical planar normal faults responsible for horst and
graben structuring associated with folding during the
Cambrian–Ordovician–Silurian period. These structures may have been
inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late
Devonian) compression and the Carboniferous (i.e., pre-Hercynian to
Hercynian). Additionally, basement characterization from geological and
geophysics data (aeromagnetic and gravity maps), shows an interesting
age-dependent zonation of the terranes which are bounded by mega-shear zones
within the arches–basins framework. The old terranes are situated under
arches while the young terranes are located under the basins depocenter.
This structural framework results from the accretion of Archean and
Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny
900–520 Ma). Therefore, the sedimentary infilling pattern and the nature of
deformation result from the repeated slow Paleozoic reactivation of
Precambrian terranes bounded by subvertical lithospheric fault systems.
Alternating periods of tectonic quiescence and low-rate subsidence
acceleration associated with extension and local inversion tectonics
correspond to a succession of Paleozoic geodynamic events (i.e., far-field
orogenic belt, glaciation).</p