Metallogenesis of cratonic oolitic ironstone deposits in the Bled el Mass, Azzel Matti, Ahnet and Mouydir basins, Central Sahara, Algeria

Guerrak, Salah

doi:10.1007/bf01821072

Cited by 20 publications

(5 citation statements)

References 23 publications

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“…In two more detailed, petrographic and geochemical studies, Guerrak (1987a,b) distinguished nine iron-oolitic levels in the Devonian of the Ahnet and Mouydir. Guerrak (1987b) interpreted them as related to sedimentary cycles which were caused by eustatic sea-level changes or epeirogenic movements. Guerrak (1987b) interpreted them as related to sedimentary cycles which were caused by eustatic sea-level changes or epeirogenic movements.…”

Section: Ironstonesmentioning

confidence: 99%

Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara)

et al. 2006

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The Ahnet and Mouydir regions of southern Algeria are part of one of the world's largest, almost undeformed exposures of Palaeozoic rocks which exemplify a hitherto poorly known early Variscan development of a Devonian basin and ridge system. This area includes a series of intracratonic basins along the northern margin of the West African Craton which consists (from W to E) of the Reggane Basin, Azel Matti Ridge, Ahnet Basin, Foum Belrem Ridge and Mouydir Basin. The depositional and palaeogeographic interpretation is based on 71 sections in this region, which for the first time were biostratigraphically calibrated by means of conodonts, goniatites and brachiopods. The structural evolution during Devonian times was probably controlled by reactivation of ancient N-S-to NW-SE-running faults in the Precambrian basement, which caused differential subsidence and uplift of a previously largely unstructured siliciclastic shelf. A hiatus during Emsian times indicates widespread emergence during this interval. The entire area was flooded during the earliest Eifelian, when the first vestiges of the Azel Matti Ridge become evident by stratigraphic condensation. The palaeogeographic differentiation is most apparent during the Givetian, when a shoal with reduced carbonate sedimentation was established on the Azel Matti Ridge passing towards the west and east into basinal environments of the Reggane and Ahnet basins, respectively. The Foum Belrem Ridge is distinguished by increased subsidence during the early Givetian and by revived uplift during the late Givetian. In the Mouydir Basin further east, up to 1000 m of shales were deposited during the Givetian. The early Frasnian is marked by the ubiquitous sedimentation of black shales and bituminous styliolinites. These lithologies occur repeatedly already during the Middle Devonian and document intermittent anoxic conditions. The basin and ridge topography is levelled by the shallowing-up sequence of up to 1400 m thick upper Frasnian and Famennian shales which grade into a deltaic sequence of uppermost Famennian/Tournaisian sandstones. The up to now only vaguely discriminated lithostratigraphic formations of the Devonian have been biostratigraphically defined in suitable type sections.

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Section: Ironstonesmentioning

confidence: 99%

Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara)

et al. 2006

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“…In Type A ooids and pisoids, the nucleus can be a fragment of an older ferruginous ooid or an indeterminate ferruginous lump. The nuclei of the Fe pisoids studied here are always formed by and indeterminate ferruginous lump, so following the classification given by Guerrak (1987) they can also be classified as simple pisoids.…”

Section: Pisoid Datamentioning

confidence: 75%

Weathering events recorded in uppermost Hauterivian–lower Barremian clay-dominated continental successions from the NW Iberian Range: climatic vs. tectonic controls

et al. 2021

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The facies and clay mineral study of clay/marl-rich levels from the Torrelapaja Formation (latest Hauterivian–early Barremian, NW Iberian Range, NE Spain) allowed to establish the palaeoclimatic and palaeoenvironmental conditions under they were generated. The muddy levels and pisoids contained therein of two logs were sampled and studied by X-ray diffraction and optical and electron microscopy. A similar mineralogical upwards trend is recorded in both logs, with a decrease in calcite coupled with an increase in quartz and orthoclase content and constant proportions in goethite, hematite, diaspore, anatase, rutile, ilmenite, and clay mineral content. The lower muddy levels have higher kaolinite content than the upper levels, where illitic phases are the dominant clay minerals. Smectite and intergrowths of illitic phases and kaolinite are also detected upwards. The kaolinite and smectite textures indicate an authigenic origin, whereas the illitic phases are former phases acting as a substrate for kaolinite crystallization. Pisoids mineralogy and texture show an in-situ origin, but some are fractured, indicating reworking processes. The mineral association found in the muddy levels is characteristic of oxisols formed under warm and humid conditions. The upward decrease in kaolinite content is coeval with an increase in the illitic phases and quartz content, related to siliciclastic input, but is also coeval with the presence of authigenic smectite. This indicates a decrease in chemical weathering, not fully registered due to the siliciclastic contribution, which was possibly associated with a change to colder, drier conditions during the latest Hauterivian–early Barremian in the studied area.

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“…Goniatites are rare and can only rarely be used for biostratigraphy. In the lower part of the sections, chamosite-oolitic intercalations indicate several transgressive cycles (Bertrand-Sarfati et al 1977;Guerrak 1987). The upper part of the sequence, corresponding to the disparilis-Lower asymrnetricus interval, is distinguished by a high bituminous content.…”

Section: Devonian Biostratigraphymentioning

confidence: 96%

Mud buildups on a Middle Devonian carbonate ramp (Algerian Sahara)

Wendt¹,

Kaufmann²

1998

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During sea-level highstand in late Mid-Devonian time, a carbonate ramp was established on the vast shelf of the Northwest African Craton, in the Ahnet and Mouydir Basins of southern Algeria. The ramp was at least 400 km wide and 700 km long and sloped, in front of a local shoal of rugose-tabulate-stromatoporoid dominated biostromes, towards the west into the Reggane Basin and towards the north into the B6char Basin. Mid-and inner ramp zones were presumably situated in the area of the present Hoggar Massif and have been removed by erosion. Subsidence rates during Mid-Devonian time were considerably lower than during the preceding and subsequent periods of clastic sedimentation in Early and Late Devonian time. Spectacular mud buildups formed in an outer ramp setting and developed from small, lens-shaped, to steep, conical mounds, which eventually amalgamated into mud ridges and mud 'atolls'. Orientation of mound rows and ridges matches older NW-SE and N-S tectonic lineaments, which were probably rejuvenated during Mid-Devonian time. Stable isotope values of early marine cements, composition of the buildup fauna, and the emplacement and orientation of neptunian dykes do not indicate, however, that buildup growth was triggered by hydrothermal activity or cold seeps.

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Metallogenesis of cratonic oolitic ironstone deposits in the Bled el Mass, Azzel Matti, Ahnet and Mouydir basins, Central Sahara, Algeria

Cited by 20 publications

References 23 publications

Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara)

Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara)

Weathering events recorded in uppermost Hauterivian–lower Barremian clay-dominated continental successions from the NW Iberian Range: climatic vs. tectonic controls

Mud buildups on a Middle Devonian carbonate ramp (Algerian Sahara)

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