Abstract
Evidence of strike-slip deformation in the Inkisi Formation was overlooked for a long time. After controversial characterization, this paper demonstrates that the Inkisi Formation underwent at least two phases of strike-slip deformation accompanied with a compressive component, which created faults that help determine paleostress. Field observations permitted to characterize NW–SE trends sinistral strike-slip faults systems and NE–SW oriented dextral strike-slip faults systems. The strike-slip faults are associated with flower structures in profile view and with damage zones along tips, wall and linking zones in plan view. Both faults systems (sinistral and dextral) initiated from joints, which show similar orientations with faults. Many kinematic indicators of slip sense or extension have enabled to determine the stress stages and the evolution of the structures. The first tectonic phase has a horizontal maximum principal compressive stress σ1 of 319 ± 21,1/03, which probably have a potential correlation with far-field stress propagation which occurs during the subduction of Gondwana south margin in the Permo-Trias. The second tectonic phase with a slightly inclined maximum principal compressive stress σ1 of 264°± 22,3/12 potentially results from the intraplate stress propagation, due to the opening of the Southern Atlantic Ocean.
PUBLIC INTEREST STATEMENT
The study of the tectonic structures that affected the Inkisi sandstone of Paleozoic age, in the southern Brazzaville has a paramount importance. A large part of the city is built on these sandstones that carry fractures that reach the topographic surface. This constitutes a large danger to the buildings and the stability of the geotechnical structures. This study can also be a good guideline in groundwater exploration.
Acknowledgements
We would like specially to thank Joachim Miyouna for English corrections of the manuscript. Instructive comments of anonymous reviewers substantially improve the quality of the manuscript and were greatly appreciated. We are also grateful to Pr. El Hadji Sow from Cheikh Anta Diop University of Dakar for his advices and encouragements.
Description
This study of deformations in the Inkisi sandstone Formation shows that it is affected by two major directions of NW–SE and WSW–ENE strike-slip faults. The NW–SE faults have displayed sinistral movement, whereas the WSW–ENE faults that offset the previous one have dextral movement. NW–SE fractures may result from the subduction of Gondwana south margin in the Permo-Trias. The second results from the interplate stress propagation due to the opening of the southern Atlantic ocean.
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Timothée Miyouna
Timothée Miyouna is an assistant professor at Marien NGOUABI University of Brazzaville, where he teaches mineralogy and petrology of sedimentary rocks. He extensively worked in gold mineralization in West Africa Belt. Actually, he is working in basin researches and tectonic deformations in the Paleozoic sandstones of Inkisi.