Late Ordovician glacial pavements revisited: a reappraisal of the origin of striated surfaces

Deynoux, Max; Ghienne, Jean‐François

doi:10.1111/j.1365-3121.2005.00640.x

Cited by 13 publications

(4 citation statements)

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“…In the Libyan portion of the basin, striated surfaces and glacial deposits are recognized in Jabal Azbah at the eastern flank of the basin (Late Ordovician; Le Heron et al, 2010) and in correlative strata in Jabal Eghei to the west (Le Heron et al, 2015). The character of striated surfaces is identical to those reported from more accessible areas (e.g., Deynoux and Ghienne, 2004;Le Heron et al, 2005;Denis et al, 2010;Girard et al, 2015). Apart from largescale geological maps (Wolff, 1964), the Ennedi-Bourkou range is virgin geological territory.…”

Section: Introductionmentioning

confidence: 61%

“…(1) they represent successive glacial cycles and the repeated occupation of the same paleodepression by ice streams, and (2) MSGLs formed by large-scale intraformational detachments and shearing of the deforming bed. In the latter model, MSGLs are seen as scaled-up versions of softsediment striated surfaces (Sutcliffe et al, 2000;Deynoux and Ghienne, 2004;Le Heron et al, 2005;Denis et al, 2010).…”

Section: Data Interpretationmentioning

confidence: 99%

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An exhumed Paleozoic glacial landscape in Chad

Heron

2017

Geology

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In northern Chad, an outcrop belt of Paleozoic rocks occurs in the Ennedi-Bourkou range. There, satellite image interpretation reveals a series of clearly expressed paleo-ice stream pathways, which are encased in sandstone plateaux. At least five paleo-ice stream pathways are recognized, measuring 5-12 km wide. Each contains well-expressed belts of mega-scale glacial lineations (MSGLs) with occasional drumlins. The paleo-ice stream tracks are confined to present-day low-lying areas, representing ancient valley networks, and have sinuous geometries. The features occur on multiple plateau and/or stratigraphic levels. Their dissection by late Neogene rivers discounts a modern-day origin as eolian features, and offset suites of MSGLs by east-west-striking faults confirms their geologic antiquity. The paleo-ice stream pathways appear to have drained a newly discovered late Paleozoic paleo-ice sheet of probable Visean age that flowed northward toward presentday Libya, with an estimated <250-m-thick tidewater ice margin. This discovery has wide-ranging implications, increasing the known extent of late Paleozoic ice sheets, and potentially their effects on sea-level changes.

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Section: Introductionmentioning

confidence: 61%

Section: Data Interpretationmentioning

confidence: 99%

An exhumed Paleozoic glacial landscape in Chad

Heron

2017

Geology

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“…7A), this minimum-sized ice sheet must have reached Central Africa. A maximum-sized Hirnantian ice sheet may, in addition, have overridden South America and South Africa where subglacial deformation zones have been also identified (Blignault, 1981;Martinez, 1998;Deynoux and Ghienne, 2005) (Fig. 7C).…”

Section: Ice Sheet Size: the Glacial Maximummentioning

confidence: 99%

The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform

Ghienne

Heron

Moreau

et al. 2007

Glacial Sedimentary Processes and Products

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133

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The Late Ordovician (Hirnantian) glaciation is examined through the North Gondwana record. This domain extended from southern high palaeo-latitudes (southeastern Mauritania, Niger) to northern lower palaeo-latitudes (Morocco, Turkey) and covered a more than 4000 km-wide section perpendicular to ice-flow lines. A major mid-Hirnantian deglaciation event subdividing the Hirnantian glaciation in two first-order cycles is recognised. As best illustrated by the glacial record in western Libya, each cycle comprises 2-3 glacial phases separated by ice-front retreats several hundreds kilometres to the south. From ice-proximal to ice-distal regions, the number of glacial surfaces differentiates (i) a continental interior with post-glacial reworking of the glacial surfaces), (ii) a glaciated continental shelf that is subdivided into inner (1-2 surfaces), middle (2-5 surfaces) and outer (a single surface related to the glacial maximum) glaciated shelves, and (iii) the non-glaciated shelf. Ice-stream-generated glacial troughs, 50-200 km in width, cross-cut these domains. These troughs are zones of preferential glacial erosion and subsequent sediment accumulation. A glacial depositional sequence, bounded by two glacial erosion surfaces, records one glacial phase. The position either within or outside a glacial trough controls the stratigraphic architecture of a glacial sequence. Glaciomarine outwash diamictites are developed at or near the maximum position of the ice-front. During ice-sheet recession, and in an ice-stream-generated trough, a relatively thin sediment cover blankets the foredeepened erosion surface. An initial rapid ice-sheet withdrawal is inferred. Marine-terminating ice fronts then evolve later into more slowly retreating, land-terminating ice fronts. In adjacent inter-stream areas where a more gradual ice-sheet recession occurred, fluvioglacial deposits prevailed. The progradation of a delta-shelf system, coeval with fluvial aggradation, that may be locally interrupted by a period of isostatic rebound, characterises the late glacial retreat to interglacial conditions. This model should facilitate the sequence stratigraphic interpretation of Late Ordovician glacial deposits and other ancient glacial successions.

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“…Similar stacked surfaces with parallel striations are not known from Pleistocene deposits where it is known that glaciers were the final depositional agent. They are similar to so-called tectonic hydroplastic slickensides or internal grooves and striations that form in soft sand and mud (Enos, 1969;Petit & Laville, 1987;Simms, 2007;Cesta, 2015;Le Heron et al, 2014), but they are sometimes interpreted as internal movements in sand caused by overriding ice (Deynoux & Ghienne, 2004;Le Heron et al, 2005, 2019.…”

Section: Pavements/striated Surfacesmentioning

confidence: 94%

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

Molén

Smit²

2022

Geologos

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The Gondwana Late Palaeozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to have formed subglacially, as are diamictites which have been interpreted as in-situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well-studied areas, throughout South Africa. Detailed analyses have focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4,271 quartz sand grains were subsampled from outcrops that are considered mainly to be tillites formed by continental glaciation. These grains, analysed by SEM, do not demonstrate the characteristic surface microtexture combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

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Late Ordovician glacial pavements revisited: a reappraisal of the origin of striated surfaces

Cited by 13 publications

References 13 publications

An exhumed Paleozoic glacial landscape in Chad

An exhumed Paleozoic glacial landscape in Chad

The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

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