Depositional architecture and sequence stratigraphic correlation of Upper Ordovician glaciogenic deposits, Illizi Basin, Algeria

Lang, Jörg; Dixon, Richard J.; Heron, Daniel Paul Le; Winsemann, Jutta

doi:10.1144/sp368.1

Cited by 26 publications

(15 citation statements)

References 83 publications

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“…This is the first indication of combinedflow tractional currents suggesting the preceding synglacial succession was below the effective wave base. † Glacial erosion surfaces have been interpreted in the subsurface at In Amenas as candidate events for periods of renewed ice sheet advance (Roussé et al 2009;Lang et al 2012). Within each of the intervals bounded by the candidate erosion surfaces, the facies types are similar, suggesting there was no significant change in depositional environment through the succession.…”

Section: Discussionmentioning

confidence: 99%

Ordovician proglacial sediments in Algeria: insights into the controls on hydrocarbon reservoirs in the In Amenas field, Illizi Basin

Hirst

2012

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Ordovician proglacial deposits form gas reservoirs in the In Amenas field, Illizi Basin, Algeria. Depositional models were developed to understand the context and disposition of the main reservoirs through an evaluation of core and analogous outcrops from the Tassili N'Ajjer.Tunnel valleys initially accumulated sandstones with tractional structures. Subsequent failures of subaqueous grounding line sediment deposited proglacial debrites comprising poorly sorted argillaceous sandstone with granules. These were interbedded with high-density turbidity sandstones; their fine grain size indicates they were dynamically disconnected from the lithologically varied debrites. A lobate geometry has been defined for one subsurface composite turbidite.Periodic catastrophic outflows, possibly evacuating subglacial lakes, incised the network of subglacial tunnels and in the process delivered sand to the turbidite outwashes. Bedforms indicate high-energy, transcritical to supercritical outflows that were stable for extended periods. During ice retreat, a period of ice margin stability may have occurred due to grounding over the In Amenas granitic palaeohighs. Outwash fan apices were located along this grounding line with feeder channels developing where the substrate was more easily eroded such as between the palaeohighs. Following further ice retreat, deposition evolved to variably sinuous channels and thence to pelagic fines with dropstones.

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Section: Discussionmentioning

confidence: 99%

Ordovician proglacial sediments in Algeria: insights into the controls on hydrocarbon reservoirs in the In Amenas field, Illizi Basin

Hirst

2012

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“…The depth of the incision ( ca 267 m) is an order of magnitude greater than lowstand fluvial incised valleys (e.g. Allen & Posamentier, 1993; Thomas & Anderson, 1994), but compares closely with deep tunnel valleys described from the Late Ordovician of Algeria (Lang et al. , 2012).…”

Section: Stratigraphic Architecture and Ice Sheet Dynamicsmentioning

confidence: 57%

An interglacial on snowball Earth? Dynamic ice behaviour revealed in the Chuos Formation, Namibia

Heron¹,

Busfield²,

Kamona

2012

Sedimentology

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The Sturtian is the oldest (ca 716Ma) of three pan-global glaciations in the Cryogenian. At Omutirapo, in northern Namibia, a 2km wide, 400m deep palaeovalley is filled by glaciogenic strata of the Chuos Formation, which represents the Sturtian glacial record. Sedimentary logging of an exceptionally high-quality exposure permits detailed stratigraphic descriptions and interpretations, allowing two glacial cycles to be identified. At the base of the exposed succession, strong evidence supporting glaciation includes diamictites, ice-rafted dropstones and intensely sheared zones of interpreted subglacial origin. These facies collectively represent ice-proximal to ice-rafted deposits. Upsection, dropstone-free mudstones in the middle of the succession, and the absence of diamictites, imply sedimentation free from glacial influence. However, the reappearance of glacial deposits above indicates a phase of Sturtian glacial re-advance. Comparison with age-equivalent strata in South Australia, where evidence for sea-ice free sedimentation has been established previously, suggests that a Sturtian interglacial may have been extensive, implying global-scale waxing and waning of ice sheets during a Cryogenian glacial event.Peer reviewe

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“…Algeria was situated towards the margin of the North African ice sheet, with the Tiguentourine field and the Tassili N'Ajjer outcrops studied here entirely beneath ice at the glacial maxima (Hirst et al 2002;Roussé et al 2009;Lang et al 2012). During the Late Ordovician Hirnantian Stage, at least two glacio-eustatic sea-level falls are interpreted in the N. extraordinarius Zone, followed by a glacio-eustatic sea-level rise in the N. persculptus Zone through to early Silurian times (Brenchley et al 1994(Brenchley et al , 1995Paris et al 1998;Underwood et al 1998;Sutcliffe et al 2000;Le Heron & Craig 2008;Le Heron & Dowdeswell 2009).…”

Section: The Late Ordovician Glaciationmentioning

confidence: 86%

Ordovician shallow-marine tidal sandwaves in Algeria – the application of coeval outcrops to constrain the geometry and facies of a discontinuous, high-quality gas reservoir

Hirst¹

2016

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The Tiguentourine field in the Illizi Basin, Algeria, is a multi trillion cubic feet (TCF) gas accumulation, with production primarily from Late Ordovician proglacial density flow deposits with permeabilities typically in the range 100-0.1 mD. The proglacial succession is truncated by an erosive surface, above which a thin interval of shallow-marine sandstones with higher permeabilites is present in a few wells. These well-sorted, high-energy sandstones were, in turn, succeeded by Silurian-age graptolitic shales that form both the seal and the source rock. Although the shallow-marine sandstone is a high-quality reservoir interval, it is thin (,12 m), discontinuous and not resolvable on seismic; it therefore represents a challenging target to predict.Coeval equivalents of the reservoir interval are exposed in the Tassili N'Ajjer, over 200 km south of the field. An erosive surface at the top of the proglacial sequence is succeeded by sandwaves with wavelengths of .100 m. The geometries and facies relationships have been documented from Landsat and outcrops; they were then compared to modern marine settings. The varied facies and the localized absence of the shallow-marine unit at outcrop serve to explain why the better quality sandstone is variably developed in the subsurface and remains a high risk target. Downloaded from Fig. 12. (a) Higher-resolution Landsat image of ridges 5, 6 and 7 (Quickbird data from Dixon et al. 2008); the white lines pick out two surface traces of the eastwards-dipping planar sets that are evident in the end view (b). These sets exhibit a higher degree of curvature in plan view than the gross sand ridge does. (c) Detail of small cross-sets resulting from bedforms that migrated eastwards down the main sets. Small clasts are also evident.

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Depositional architecture and sequence stratigraphic correlation of Upper Ordovician glaciogenic deposits, Illizi Basin, Algeria

Cited by 26 publications

References 83 publications

Ordovician proglacial sediments in Algeria: insights into the controls on hydrocarbon reservoirs in the In Amenas field, Illizi Basin

Ordovician proglacial sediments in Algeria: insights into the controls on hydrocarbon reservoirs in the In Amenas field, Illizi Basin

An interglacial on snowball Earth? Dynamic ice behaviour revealed in the Chuos Formation, Namibia

Ordovician shallow-marine tidal sandwaves in Algeria – the application of coeval outcrops to constrain the geometry and facies of a discontinuous, high-quality gas reservoir

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