Late ordovician—early silurian glaciofluvial deposits preserved in palaeovalleys in South Jordan

Powell, J. H.; Moh'd, Basim Khalil; Masri, Ahmed

doi:10.1016/0037-0738(94)90099-x

Cited by 61 publications

(36 citation statements)

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“…The sea level curve derived from the mid latitude Gondwanan succession of the Prague Basin displays a pattern of post-glacial deepening episodes resembling that identified in the Welsh Basin (Brenchley et al 1991;Š torch 2006). In widely separated high latitude Gondwanan rocks described by Powell et al (1994) and Underwood et al (1998) an interval of unfossiliferous post-glacial transgressive facies, as in Wales, precedes the abrupt entry of persculptus Biozone graptolite faunas, and a sequence of similar post-glacial sea level changes can be inferred. Post-glacial maximum sea level perturbations closely comparable to those in Wales are also recognized in low latitude Hirnantian successions on the palaeoplates of both Laurentia (e.g.…”

Section: Wider Implicationsmentioning

confidence: 97%

Sedimentary and faunal events revealed by a revised correlation of post‐glacial Hirnantian (Late Ordovician) strata in the Welsh Basin, UK

et al. 2009

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The discovery of a previously unrecognized unconformity and of new faunas in the type Llandovery area underpins a revised correlation of Hirnantian strata in mid Wales. This has revealed the sedimentary and faunal events which affected the Lower Palaeozoic Welsh Basin during the global rise in sea level that followed the end-Ordovician glacial maximum and has allowed their interpretation in the context of local and global influences.In peri-basinal shelfal settings the onset of post-glacial deepening is recorded by an unfossiliferous, transgressive shoreface sequence (Cwm Clyd Sandstone and Garth House formations) which rests unconformably on Rawtheyan rocks, deformed during an episode of pre-Hirnantian tectonism. In the deep water facies of the basin centre, this same sequence boundary is now recognized as the contact between fine-grained, re-sedimented mudstones and an underlying regressive sequence of turbidite sandstones and conglomerates; it is at a level lower than previously cited and calls into question the established lithostratigraphy.In younger Hirnantian strata, graptolites associated with the newly recognized Ystradwalter Member (Chwefri Formation) demonstrate that this distal shelf unit correlates with the persculptus graptolite-bearing Mottled Mudstone Member of the basinal succession. Together these members record an important macrofaunal recolonization of the Welsh Basin and mark a key event in the post-glacial transgression. Further deepening saw the establishment of a stratified water column and the imposition of anoxic bottom water conditions across the basin floor.These post-glacial Hirnantian events are consistent with the re-establishment of connections between a silled Welsh Basin and the open Iapetus Ocean. However, a comparison with other areas suggests that each event records a separate deepening episode within a pulsed glacio-eustatic transgression, while also reflecting changes in post-glacial climate and patterns of oceanic circulation and associated biotic flux. British Geological Survey # NERC 2009. All rights reserved

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Section: Wider Implicationsmentioning

confidence: 97%

Sedimentary and faunal events revealed by a revised correlation of post‐glacial Hirnantian (Late Ordovician) strata in the Welsh Basin, UK

et al. 2009

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“…Renewed interest arose in the 1990s, when oil companies recognised the association of syn-glacial strata (reservoir rocks) with lower Silurian shales (source rocks) as one of the most significant plays in the North African Lower Palaeozoic succession (Lüning et al, 2000). Recent work has included detailed field and subsurface studies conducted in Mauritania (Ghienne, 1998;Ghienne and Deynoux, 1998;Ghienne, 2003), Morocco (Ouanaimi, 1998;Sutcliffe et al, 2000Sutcliffe et al, , 2001Le Heron et al, 2007), Algeria (Hirst et al, 2002;Eschard et al, 2005), Niger (Denis et al, 2007), Libya (McDougall and Martin, 2000;Smart, 2000;Ghienne et al, 2003;El-ghali, 2005;Moreau, 2005), Jordan (Abed et al, 1993;Powell et al, 1994;Turner et al, 2005), Saudi Arabia (Senalp and Al-Laboun, 2000) and the Horn of Africa (Ethiopia and Eritrea, Kumpulainen, 2005). In addition to these areas, studies have also been undertaken around the northern Gondwana periphery to better provide an overall understanding of the glacial record as a whole, e.g.…”

Section: Introductionmentioning

confidence: 99%

The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform

Ghienne

Heron

Moreau

et al. 2007

Glacial Sedimentary Processes and Products

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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“…Anderson, 1999;Canals et al, 2000;Ó 'Cofaigh et al, 2002). Tunnel valleys are not restricted to Pleistocene glacial successions but have also been reported from earlier glaciations in the Earth's history including within deposits of the Ordovician (Ashgillian) glaciation of Gondwana in North Africa (Ghienne and Deynoux, 1998;Powell et al, 1994;Hirst et al, 2002) and from the Late Carboniferous-Early Permian Gondwana glaciation in Western Australia (Eyles and de Broekert, 2001). For both North American and northwest European Pleistocene examples and the Palaeozoic tunnel valleys of North Africa the stratigraphic fill, where present, consists of sandy glacifluvial sediments (locally including subglacial diamict) overlain by muddy glacilacustrine and/or glacimarine sediments (e.g.…”

Section: Introductionmentioning

confidence: 99%

Pleistocene subglacial tunnel valleys in the central North Sea basin: 3‐D morphology and evolution

Lonergan

Maidment

Collier

2006

J Quaternary Science

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Four phases of cross-cutting tunnel valleys imaged on 3-D seismic datasets are mapped within the Middle-Late Pleistocene succession of the central North Sea basin (Witch Ground area).In plan the tunnel valleys form complex anastomosing networks, with tributary valleys joining main valleys at high angles. The valleys have widths ranging from 250 to 2300 m, and base to shoulder relief varying between 30 and 155 m, with irregular long-axis profiles characteristic of erosion by water driven by glaciostatic pressures. The youngest phase of tunnel valleys are smaller and have a thinner infill than the older generations. The fill of the larger valleys comprises three seismic facies, the lowermost of which has high amplitudes and is discontinuous. The middle facies consists of wedge-shaped packages of low-angle dipping reflectors and is overlain by a facies characterised by sub-horizontal reflectors, which onlap the valley margins. The seismic character, and comparison with lithologies identified in other northwest European Pleistocene tunnel valleys both onshore and offshore, suggests that the lower two seismic facies are most likely sand and gravel-dominated, while the uppermost facies consists of glaciolacustrine and marine muds. The 3-D morphology of the valley margins combined with the geometry of the infill packages suggest that episodic discharge of subglacial meltwater was responsible for incising the valleys and depositing at least some of the infill. Proglacial glaciofluvial deposits are inferred to account for some of the fill overlying the subglacial deposits. Glaciolacustrine and marine muds filled remaining valley topography as the ice sheet retreated. The preserved valley margins are shown to be time-transgressive erosion surfaces that record changes in geometry of the tunnel valley system as it evolved through time, implying that valleys associated with each ice-sheet advance/retreat cycle were dynamic and probably long-lived. Within the constraints of the existing stratigraphy the oldest tunnel valleys in the Witch Ground area of the central North Sea are most likely to be Marine Isotope Stage (MIS) 12 (Elsterian, ca. 470 ka) in age and the youngest pre-MIS 5e (last interglacial, ca. 120 ka). If each tunnel valley phase was formed during the retreat of a major ice sheet then four glaciations with ice coverage of the central North Sea are recorded in the pre-Weichselian, Middle-Late Pleistocene stratigraphy.

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Late ordovician—early silurian glaciofluvial deposits preserved in palaeovalleys in South Jordan

Cited by 61 publications

References 5 publications

Sedimentary and faunal events revealed by a revised correlation of post‐glacial Hirnantian (Late Ordovician) strata in the Welsh Basin, UK

Sedimentary and faunal events revealed by a revised correlation of post‐glacial Hirnantian (Late Ordovician) strata in the Welsh Basin, UK

The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform

Pleistocene subglacial tunnel valleys in the central North Sea basin: 3‐D morphology and evolution

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