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Sedimentary Facies and Depositional Environment of Oligo-Miocene of the Southern Shore of the Strait of Gibraltar (Rif, Morocco)

Salhi Fouad, El Khalidi Khalid, Zourarah Bendahhou

Ecological Engineering & Environmental Technology

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2024

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Vol. 25, iss. 3

233--252

EN

This paper highlights a detailed sedimentological investigation of the deposits of Oligo-Miocene age on the southern shore of the Strait of Gibraltar commonly called flyschs Numidian, micaceous-sandstone flysch of Beni Ider and merinid flysch. This study has allowed us to demonstrate the existence of different facies and environments linked to the different processes that prevail in the Maghrebian basin under the simultaneous control of sedimentary input, eustatism and the tectonic process. Our study is based on the observation and the detailed stratonomic analysis of the different facies encountered in the Oligo-Miocene age series of flyschs from the southern shore of the Strait of Gibraltar. For the first time, this analysis shows that the Numidian successions studied, except that of Oued Lihoud, were deposited in deltaic environments (deltaic cone) at the level of the North African margin (Rif chain). These are prodelta deposits where slides, slumps or turbidites of predominantly fluvial delta fronts, regular waves and storm waves, fluvial and estuarine channels and tidal plains are sometimes intercalated. The micaceoussandstone flyschs are due to gravitational sedimentation at the level of the submarine plain of the Maghreb basin. We have identified different categories of deposits: low, medium and high density turbidites, pulsation turbidites, homogenites, debris-flows and contourites. The Merinid flyschs are also due to mixed gravity sedimentation from a lithological point of view between the Numidian sandstones and the micaceous-sandstoneof Beni Ider. These deposits have therefore occupied an intermediate position between the southern and northern margins of the Maghrebian basin. In addition to the gravity facies, the deposits show high-density megaturbidites. This study also allowed the identification a major eustatic decline that was recorded during the Oligocene, the cold climate of the Oligocene and distensive (north) and compressive (south) tectonic movements depending on the position in the basin.

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Record of Late Neogene seismites in turbidite deposits of the Tafna Basin (NW Algeria)

Benzina Mostapha, Pisarska-Jamroży Małgorzata, Hebib Hakim

Geological Quarterly

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2023

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Vol. 67, No. 3

art. no. 25

EN

The wide variety of soft-sediment deformation structures (SSDS) developed within deposits of the same age may hinder the interpretation of their origin. Some types of SSDS may appear similar though have different trigger mechanisms, while others may result from a specific mechanism. Furthermore, the development of particular SSDS may be influenced by several synchronous or semi-synchronous factors. This study deals with the recognition of SSDS trigger mechanisms with respect to lithological and deformational features of the deposits concerned. Turbidite deposits of late Neogene age in the Hadjret El Gat area (Tafna Basin) contain different types of SSDS associated with (1) slope processes (e.g., slump folds) and induced overburden pressure, coupled with broken beds and overloading structures, and (2) liquefaction and fluidisation phenomena, leading to the development of load structures, ball-and-pillow structures, water-escape structures and syndepositional faults. These two mechanisms of SSDS formation in the study area are thought to result from seismically-induced triggers. Recognition of a vertically-repeated, sandwich-like arrangement of deformed and undeformed layers along with the SSDS features ("trapped" within beds) suggests that these internally-deformed beds are seismites, the first recognized in the Tafna Basin of NW Algeria. Large earthquakes may trigger seismic waves energetic enough to deform strata and induce the development of SSDS. This hypothesis is supported here by tectonic evidence, given deposition of the Tafna Basin strata in the convergence zone between Africa and Eurasia, active since the late Neogene.

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Tectonic evolution of the late Cretaceous Nysa Kłodzka Graben, Sudetes, SW Poland

Don J., Gotowała R.

Geologia Sudetica

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2008

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Vol. 40

51-63

EN

The Nysa Kłodzka Graben, located in the Sudetes of SW Poland, developed as a result of Coniacian (middle Upper Cretaceous) N-trending faulting of the Variscan crystalline basement rocks that comprise the crest of the Orlica-Śnieżnik Dome. The graben was transgressed by a late Cretaceous sea that encroached during the Cenomanian from the northwest. Up to 700 m of Coniacian shales, sandstones and conglomerates were deposited in the graben, with shales (the ~500 m thick Idzików 'clays') dominating the graben's central section. On the western side of the graben, shales grade upwards to greywackes in a style that resembles a turbidite sequence; on the eastern side, shales are overlain by sandstones and conglomerates (the Idzików conglomerates) that represent extensive late Cretaceous fan deltas. These within-graben fan deltas date the onset of fault-block movements that uplifted the Sudetes region during the late Cretaceous-Cenozoic. By the end of the Cretaceous, both the sedimentary infill and the underlying Cenomanian and Turonian strata were steepened at the graben margins and were gently folded, the fold axes paralleling the graben's marginal faults. Subsequent Cretaceous-Paleocene ('Laramian') deformations resulted in NW-trending reverse faulting, which restructured the earlier N-S template of the graben, and in transcurrent faults, which cut the N-trending folds, modified the north and south ends of the graben and strongly affected the graben's western walls. The total thickness of the Upper Cretaceous strata of the Nysa Kłodzka Graben is 3 times that of the Intra-Sudetic Synclinorium, implying that the two units developed independently.