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  • 11
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    The glacier-influenced marine record on high-latitude continental margins: synergies between modern, Quaternary and ancient evidence (2019)
    Geological Society of London
    Details
    Publication Date: 2019
    Description: 〈p〉Major glaciations or ‘ice ages’ are known to have affected the Earth's surface over the past three billion years. The best preserved records of these glaciations are often found in high-latitude continental margin settings where sediment has been delivered to, and then accumulated at, the edge of the ice sheet in thick glacier-influenced marine sequences. The composition and geometry of these deposits and the related assemblages of glacial landforms provide a wealth of information about the environmental setting during successive cycles of glaciation and deglaciation, including ice-dynamic and oceanographic processes. Here, we discuss modern (present day), Quaternary (last 2.6 myr) and ancient (last 1 gyr) high-latitude continental margin settings, and then contrast the methodologies used and glacier-influenced deposits and landforms most often identified for each time period. We use examples from the literature to identify synergies, as well as to note differences, between studies of glacier-influenced sediments from ancient to modern environments.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 12
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    Development of a palaeovalley complex on a Late Ordovician glaciated margin in NW Saudi Arabia (2018)
    Geological Society of London
    Details
    Publication Date: 2018
    Description: 〈p〉Late Ordovician glacial deposits are of great importance in North Africa and the Middle East as a result of their significance as reservoirs for hydrocarbons and groundwater. The sedimentary record of this glaciation in NW Saudi Arabia (the Sarah Formation) is generally preserved in meridionally oriented palaeovalleys cut beneath northward-flowing ice sheets. In the Tabuk region of NW Saudi Arabia, an apparently intersecting complex of north–south- and east–west-oriented palaeovalleys occurs in the Alwizam area. Field relationships show two generations of palaeovalley incision, suggesting that the north–south-oriented palaeovalley was cut subglacially, filled, subsequently deformed and then cross-cut by the east–west-oriented palaeovalley. Abundant facetted and striated quartzite clasts occur at the base of each palaeovalley, testifying to a subglacial origin. Detailed examination of the north–south-oriented palaeovalley shows it to be well-defined with symmetrical sides. Its fill is composed of nine lithofacies grouped into four facies associations. About 80% of the fill consists of three sandstone facies: a parallel-bedded massive sandstone, a stacked scoured sandstone and a massive sandstone. Centimetre-scale extensional faults developed in soft sediments are commonly found throughout the stratigraphy, along with a glacially striated surface seen mid-way through the succession. These features provide evidence for direct ice contact, synglacial fill, and consequent reworking, cannibalization and deformation by the fluctuating ice margin.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 13
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    An introduction to glaciated margins: the sedimentary and geophysical archive (2019)
    Geological Society of London
    Details
    Publication Date: 2019
    Description: 〈p〉A glaciated margin is a continental margin that has been occupied by a large ice mass, such that glacial processes and slope processes conspire to produce a thick sedimentary record. Ice masses take an active role in sculpting, redistributing and reorganizing the sediment that they erode on the continental shelf, and act as a supply route to large fan systems (e.g. trough mouth fans, submarine fans) on the continental slope and continental rise. To many researchers, the term ‘glaciated margin’ is synonymous with modern day areas fringing Antarctica and the Arctic shelf systems, yet the geological record contains ancient examples ranging in age from Precambrian to Cenozoic. In the pre-Pleistocene record, there is a tendency for the configuration of the tectonic plates to become increasingly obscure with age. For instance, in the Neoproterozoic record, not everyone agrees on the location of rift margins and some fundamental continental boundaries remain unclear. Given these issues, this introductory paper has two simple aims: (1) to provide a brief commentary of relevant Geological Society publications on glaciated margins, with the landmark papers highlighted and (2) to explain the contents of this volume.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 14
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    A tale of two rift shoulders, and two ice masses: the Cryogenian glaciated margin of Death Valley, California (2018)
    Geological Society of London
    Details
    Publication Date: 2018
    Description: 〈p〉The Death Valley area of California, USA, exposes an outstanding record of a Neoproterozoic (Cryogenian) glaciated margin: the Kingston Peak Formation. Despite the quality of the exposure, however, the outcrops of glaciogenic strata are fragmentary, forming isolated, laterally offset outcrop belts at the western extremity of the Basin and Range province. Excellent evidence for glacially modulated sedimentation includes (1) ice-rafted dropstones in most ranges, (2) thick diamictites bearing a variety of exotic (extrabasinal) clasts, (3) striated clasts and (4) local occurrences of glacitectonic deformation structures at the basin margins. In tandem with this, there is a distinct signature of slope collapse processes in many ranges, including (1) up to kilometre-scale olistoliths, (2) extensional growth fault arrays, (3) dramatic proximal-distal thickness changes and (4) basalt occurrences. New sedimentological observations reinforce long-held views of rifting superimposed on glaciation (or vice versa), with both processes contributing to a complex record whereby rift and glacial processes vie for stratigraphic supremacy. We consider that a mechanism of diamictite accumulation in a series of rift-shoulder minibasins produced greatly contrasting successions across the Death Valley area, under the incontrovertible influence of hinterland ice sheets.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 15
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    Development of a palaeovalley complex on a Late Ordovician glaciated margin in NW Saudi Arabia (2018)
    Geological Society (of London)
    Details
    Publication Date: 2018-06-08
    Description: Late Ordovician glacial deposits are of great importance in North Africa and the Middle East as a result of their significance as reservoirs for hydrocarbons and groundwater. The sedimentary record of this glaciation in NW Saudi Arabia (the Sarah Formation) is generally preserved in meridionally oriented palaeovalleys cut beneath northward-flowing ice sheets. In the Tabuk region of NW Saudi Arabia, an apparently intersecting complex of north–south- and east–west-oriented palaeovalleys occurs in the Alwizam area. Field relationships show two generations of palaeovalley incision, suggesting that the north–south-oriented palaeovalley was cut subglacially, filled, subsequently deformed and then cross-cut by the east–west-oriented palaeovalley. Abundant facetted and striated quartzite clasts occur at the base of each palaeovalley, testifying to a subglacial origin. Detailed examination of the north–south-oriented palaeovalley shows it to be well-defined with symmetrical sides. Its fill is composed of nine lithofacies grouped into four facies associations. About 80% of the fill consists of three sandstone facies: a parallel-bedded massive sandstone, a stacked scoured sandstone and a massive sandstone. Centimetre-scale extensional faults developed in soft sediments are commonly found throughout the stratigraphy, along with a glacially striated surface seen mid-way through the succession. These features provide evidence for direct ice contact, synglacial fill, and consequent reworking, cannibalization and deformation by the fluctuating ice margin.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 16
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    Development of a palaeovalley complex on a Late Ordovician glaciated margin in NW Saudi Arabia (2018)
    Geological Society (of London)
    Details
    Publication Date: 2018-06-10
    Description: Late Ordovician glacial deposits are of great importance in North Africa and the Middle East as a result of their significance as reservoirs for hydrocarbons and groundwater. The sedimentary record of this glaciation in NW Saudi Arabia (the Sarah Formation) is generally preserved in meridionally oriented palaeovalleys cut beneath northward-flowing ice sheets. In the Tabuk region of NW Saudi Arabia, an apparently intersecting complex of north–south- and east–west-oriented palaeovalleys occurs in the Alwizam area. Field relationships show two generations of palaeovalley incision, suggesting that the north–south-oriented palaeovalley was cut subglacially, filled, subsequently deformed and then cross-cut by the east–west-oriented palaeovalley. Abundant facetted and striated quartzite clasts occur at the base of each palaeovalley, testifying to a subglacial origin. Detailed examination of the north–south-oriented palaeovalley shows it to be well-defined with symmetrical sides. Its fill is composed of nine lithofacies grouped into four facies associations. About 80% of the fill consists of three sandstone facies: a parallel-bedded massive sandstone, a stacked scoured sandstone and a massive sandstone. Centimetre-scale extensional faults developed in soft sediments are commonly found throughout the stratigraphy, along with a glacially striated surface seen mid-way through the succession. These features provide evidence for direct ice contact, synglacial fill, and consequent reworking, cannibalization and deformation by the fluctuating ice margin.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 17
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    A tale of two rift shoulders, and two ice masses: the Cryogenian glaciated margin of Death Valley, California (2018)
    Geological Society (of London)
    Details
    Publication Date: 2018-07-29
    Description: The Death Valley area of California, USA, exposes an outstanding record of a Neoproterozoic (Cryogenian) glaciated margin: the Kingston Peak Formation. Despite the quality of the exposure, however, the outcrops of glaciogenic strata are fragmentary, forming isolated, laterally offset outcrop belts at the western extremity of the Basin and Range province. Excellent evidence for glacially modulated sedimentation includes (1) ice-rafted dropstones in most ranges, (2) thick diamictites bearing a variety of exotic (extrabasinal) clasts, (3) striated clasts and (4) local occurrences of glacitectonic deformation structures at the basin margins. In tandem with this, there is a distinct signature of slope collapse processes in many ranges, including (1) up to kilometre-scale olistoliths, (2) extensional growth fault arrays, (3) dramatic proximal-distal thickness changes and (4) basalt occurrences. New sedimentological observations reinforce long-held views of rifting superimposed on glaciation (or vice versa), with both processes contributing to a complex record whereby rift and glacial processes vie for stratigraphic supremacy. We consider that a mechanism of diamictite accumulation in a series of rift-shoulder minibasins produced greatly contrasting successions across the Death Valley area, under the incontrovertible influence of hinterland ice sheets.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 18
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    Did lingering ice sheets moderate anoxia in the Early Palaeozoic of Libya? (2013)
    Geological Society of London
    Details
    Publication Date: 2013-03-14
    Description: The Hirnantian glaciation of West Gondwana produced a glacially sculpted topography, which is draped by organic-rich latest Ordovician and early Silurian ‘hot shales’. Although these are the most important Early Palaeozoic source rock in North Africa, organic enrichment is distributed unevenly. For example, in Al Kufrah Basin, Libya, ‘hot shales’ are elusive, but outcrop analysis at the western basin demonstrates why this is the case. The topmost Mamuniyat Formation, of Hirnantian age, comprises glaciogenic sandstones, passing upward into mixed facies of the Tanezzuft Formation, which has a latest Ordovician–early Silurian age. The basal Tanezzuft Formation contains a shelly carbonate (cool-water deposits accumulated under oxygenating conditions) and bioturbated sandstone succession. Above, hummocky cross-bedded and graded sandstone intervals are intercalated with shale and siltstone (storm influx onto a muddy shelf). These are interrupted by several lonestone-bearing intervals (ice-rafted debris), a striated pavement (of subglacial origin), and manganese oxide crusts and concretions. The concretions and bioturbation imply oxygenation of the sea floor during transgression. These putative glacial deposits were deposited following the main phase of the Hirnantian glaciation, at the same stratigraphic level as ‘hot shales’ elsewhere in northern Gondwana. Lingering ice caps may have produced well-oxygenated marine waters precluding ‘hot shale’ deposition.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 19
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    Normalograptus kufraensis, a new species of graptolite from the western margin of the Kufra Basin, Libya (2013)
    Cambridge University Press
    Details
    Publication Date: 2013-08-14
    Description: Normalograptus kufraensis sp. nov. occurs as monospecific assemblages in the Tanezzuft Formation at the western margin of the Kufra Basin (Jabal Eghei), southern Libya. These graptolites have parallel-sided rhabdosomes with long, straight virgellae, climacograptid thecae and a full straight median septum. N. kufraensis is intermediate between Ordovician graptolites from the N. angustus (Perner) lineage and the younger sister species N. ajjeri (Legrand) and N. arrikini Legrand. N. kufraensis differs from these taxa as follows: it is broader than N. angustus ; it has greater thecal spacing than N. ajjeri or N. arrikini . A table comparing measurements of N. kufraensis with 44 other Normalograptus taxa differentiates it from other members of this morphologically conservative group. Even though N. angustus and N. ajjeri are very long-ranging graptolites, a stratophenetic approach suggests that the specimens from Jabal Eghei may be of late Hirnantian or younger age. The faunal composition and preservation suggests these graptolites occupied the ‘cratonic invader’ biotope. The stratigraphic succession records deglacial flooding and fluctuating of redox in the Tanezzuft Formation, with the graptolites indicating a short-lived interval of anoxia.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 20
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    A diamictite dichotomy: Glacial conveyor belts and olistostromes in the Neoproterozoic of Death Valley, California, USA (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-12-21
    Description: Multiple intercalations of glacially derived and slope-derived diamictites testify to the drawbacks of correlating Neoproterozoic diamictites more widely, but shed new light on the close interrelationship of these processes in the Cryogenian world. In the Neoproterozoic of Death Valley, California (USA), rifting of Rodinia occurred concomitantly with a major glacial event that deposited the Kingston Peak Formation. A new sedimentologic investigation of this formation in the Silurian Hills demonstrates, for the first time, that some diamictites are ultimately of glacial origin. Abundant dropstone textures occur in interstratified heterolithic deposits, with clasts of identical composition (gneiss, schist, granite, metabasite, quartzite) to those of boulder-bearing diamictites suggesting a common source (the glacial conveyor belt). In stark contrast, megaclast-bearing diamictites, yielding clasts of carbonate and siliciclastic preglacial strata as much as 100 m across, are interpreted as olistostromes. The occurrence of syn-sedimentary faults within the succession allows glacial versus slope-derived material to be distinguished for the first time.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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