The origins of glacially related soft-sediment deformation structures in Upper Ordovician glaciogenic rocks: implication for ice-sheet dynamics

Heron, Daniel Paul Le; Sutcliffe, Owen E.; Whittington, R J; Craig, Jonathan

doi:10.1016/j.palaeo.2004.12.007

Cited by 119 publications

(70 citation statements)

References 45 publications

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“…Ice flows are generally centrifugal from ice-sheet centre and so flowed from south to north in Saharan areas. A great deal of evidence of this glaciation has been reported from north and west African basins [1,14,15,16,10,17,18]. The present work concerns the Murzuq-Djado Basin, located on the north-Gondwanan continental shelf.…”

Section: Introductionmentioning

confidence: 93%

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Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

et al. 2007

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Pluridisciplinary fieldwork highlights features generated by an extended ice-sheet in the Djado Basin during the Hirnantian. Two glacial palaeovalley systems associated with glacial pavements and separated by thin glaciomarine interstadial series are revealed. Rigid glacial pavements characterised by abrasion erosion are differentiated from soft glacial pavements characterised by soft-bed deformation. Glacial pavements are associated with subglacial bedforms such as megaflutes, flutes and meltwater channels. They are also associated with clastic dykes and glaciotectonic structures such as deformed flutes, subglacial folds and duplex structures. This record demonstrates that ice was warm-based and flowed rapidly on the highfluid-pressure soft substrate, as for ice streams. The erosional glacial landscape is typical of areal scouring, and the depositional sediment-landform assemblage corresponds to subglacial processes. These data afford a reconstruction of glacial events which is consistent with the two polyphased low-frequency glacial cycles inferred in previous studies. During interstadial and postglacial stages, grabens, normal faults, radial extensional microfaults and extensional dihedrons were generated by extensional tectonics during glacio-isostatic rebound. In sectors highly affected by this tectonics, doleritic dykes reflect a basal crust fusion increase induced by adiabatic decompression.

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Section: Introductionmentioning

confidence: 93%

“…Their V-shaped cross-section is typical of intraformational pavements. Intraformational pavements are multiple stacked surfaces with striations and grooves all oriented in the same direction, corresponding to contemporaneous shear planes [27,28].…”

Section: Glacial Pavementsmentioning

confidence: 99%

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

et al. 2007

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“…The grooved sandstone surface closely resembles soft-sediment striated surfaces observed within the Mamuniyat Formation and its equivalents across large tracts of North Africa, including elsewhere in Al Kufrah Basin in Jabal Azbah (Le Heron & Howard 2010), as well as in the Murzuq Basin, Morocco and South Africa. These surfaces result from the shearing of ice over unconsolidated sand (Sutcliffe et al 2000;Le Heron et al 2005). The three types of concretions found within this facies association are of particular interest given that they are absent in other facies associations and indeed in other formations.…”

Section: Lonestone-bearing Facies Associationmentioning

confidence: 88%

“…A series of common features have been encountered in the last decade of research into the Late Ordovician glacial succession of North Africa (from Morocco in the west to the Al Kufrah Basin in the east), including striated pavements, suites of soft-sediment deformation structures, and poorly sorted deposits or diamictites (Le Heron et al 2005). It is beyond the scope of the present paper to provide a detailed sedimentological analysis of the Mamuniyat Formation at Jabal Eghei; this will be provided elsewhere.…”

Section: Sedimentologymentioning

confidence: 96%

Did lingering ice sheets moderate anoxia in the Early Palaeozoic of Libya?

Heron

Meinhold

Page

et al. 2013

JGS

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Abstract: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.

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“…Secondly, unlike other examples of loading triggers, such as cyclical (e.g. waves) (Pestana et al 2000;Alfaro et al 2002), mass flows (Postma 1984;Owen 1996) and glacial (Le Heron et al 2005), lavainduced loading is also associated with a temperature increase in the underlying sediments. Numerical models suggest that rhyolite lava flows hundreds of metres thick, like the JCR, can retain heat for decades by forming a top carapace, locking in heat, and increasing their ability to produce internal latent heat (Manley 1992).…”

Section: Loading and Heatmentioning

confidence: 99%

Extensive soft-sediment deformation and peperite formation at the base of a rhyolite lava: Owyhee Mountains, SW Idaho, USA

2016

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In the Northern Owyhee Mountains (SW Idaho), a >200-m-thick flow of the Miocene Jump Creek Rhyolite was erupted on to a sequence of tuffs, lapilli tuffs, breccias and lacustrine siltstones of the Sucker Creek Formation. The rhyolite lava flowed over steep palaeotopography, resulting in the forceful emplacement of lava into poorly consolidated sediments. The lava invaded this sequence, liquefying and mobilising the sediment, propagating sediment subvertically in large metre-scale fluidal diapirs and sediment injectites. The heat and the overlying pressure of the thick Jump Creek Rhyolite extensively liquefied and mobilised the sediment resulting in the homogenization of the Sucker Creek Formation units, and the formation of metre-scale loading structures (simple and pendulous load casts, detached pseudonodules). Density contrasts between the semi-molten rhyolite and liquefied sediment produced highly fluidal Rayleigh-Taylor structures. Local fluidisation formed peperite at the margins of the lava and elutriation structures in the disrupted sediment. The result is a 30-40-m zone beneath the rhyolite lava of extremely deformed stratigraphy. Brittle failure and folding is recorded in more consolidated sediments, indicating a differential response to loading due to the consolidation state of the sediments. The lava-sediment interaction is interpreted as being a function of (1) the poorly consolidated nature of the sediments, (2) the thickness and heat retention of the rhyolite lava, (3) the density contrast between the lava and the sediment and (4) the forceful emplacement of the lava. This study demonstrates how large lava bodies have the potential to extensively disrupt sediments and form significant lateral and vertical discontinuities that complicate volcanic facies architecture.

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The origins of glacially related soft-sediment deformation structures in Upper Ordovician glaciogenic rocks: implication for ice-sheet dynamics

Cited by 119 publications

References 45 publications

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

Did lingering ice sheets moderate anoxia in the Early Palaeozoic of Libya?

Extensive soft-sediment deformation and peperite formation at the base of a rhyolite lava: Owyhee Mountains, SW Idaho, USA

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