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  • Phillips, Emrys
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  • 1
    Language: English
    In: Quaternary Science Reviews, 2008, Vol.27(19), pp.1848-1871
    Description: Detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between West Runton and Sheringham (eastern England) has allowed the characterisation of the glacitectonic signature associated with the advance of a major Mid-Pleistocene (Anglian) ice sheet. The sequence of pre-glacial deposits and glacial sediments laid down during earlier southerly directed ice advances (D1–D2) is deformed and disrupted by an ice advance from the west/southwest that marks a major change in ice flow dynamics in northern East Anglia. The simplest interpretation of this deformation event (D3) is in terms of a progressive proglacial to subglacial deformation model. Proglacial deformation occurred in advance of the ice margin and was dominated by thrusting. Positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur, leading to the formation of small sub-basins between these morainic ridges. The accretion of the wedge-shaped, proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice. Thrusting and large-scale folding associated with ice-marginal deformation led to the stacking of material excavated from further up-ice onto the stoss-side of these accreted thrust-related moraines that allowed the glacier to override the obstruction. Subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting, through to more pervasive ductile shearing associated with the formation of a subglacial shear zone. The thickness and complexity of this shear zone increases up-ice, where it is characterised by a thick glacitectonic mélange. The pore water content of the deforming sediments controlled the pattern of deformation within the shear zone. However, an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water-enhanced zone of ductile shear. Evidence from north Norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone. Consequently, the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base, but occur at a deeper level within the deforming bed.
    Keywords: Sciences (General) ; Geology
    ISSN: 0277-3791
    E-ISSN: 1873-457X
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  • 2
    Language: English
    In: Quaternary Science Reviews, 2008, Vol.27(13), pp.1350-1362
    Description: This paper presents a hybrid ‘pervasive’ and ‘mosaic’ model for the progressive deformation of a stratified diamicton complex in eastern England within an active subglacial shear zone. Sedimentary evidence from undeformed low-strain zones towards the base of the sediment pile indicates that the tectonised sediments were originally deposited as a series of subaqueous flows in a glaciolacustrine basin. These sediments have subsequently been deformed during a progressive subglacial shearing event. This event is divided into three stages: ductile folding and sediment remobilisation (D1), brittle faulting in the form of Reidel shears (D2) and hydrofracturing and sediment remobilisation (D3). The dominant control on the pattern and style of deformation appears to relate to the rate of thrust-induced till accretion, and the aquifer properties and pore water content and/or pressure of the deforming sediments.
    Keywords: Sciences (General) ; Geology
    ISSN: 0277-3791
    E-ISSN: 1873-457X
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  • 3
    Language: English
    In: Proceedings of the Geologists' Association, September 2013, Vol.124(5), pp.855-875
    Description: The efficiency of subglacial drainage is known to have a profound influence on subglacial deformation and glacier dynamics with, in particular, high meltwater contents and/or pressures aiding glacier motion. The complex sequence of Middle Pleistocene tills and glacial outwash sediments exposed along the north Norfolk coast (Eastern England) were deposited in the ice-marginal zone of the British Ice Sheet and contain widespread evidence for subglacial deformation during repeated phases of ice advance and retreat. During a phase of easterly directed ice advance, the glacial and pre-glacial sequences were pervasively deformed leading to the development of a thick unit of glacitectonic mélange. Although the role of pressurised meltwater has been recognised in facilitating deformation and mélange formation, this paper provides evidence for the subsequent development of a channelised subglacial drainage system beneath this part of the British Ice Sheet filled by a complex assemblage of sands, gravels and mass flow deposits. The channels are relatively undeformed when compared to the host mélange, forming elongate, lenticular to U-shaped, flat-topped bodies (up to 20–30 m thick) located within the upper part of this highly deformed unit. This relatively stable channelised system led to an increase in the efficiency of subglacial drainage from beneath the British Ice Sheet and the collapse of the subglacial shear zone, potentially slowing or even arresting the easterly directed advance of the ice sheet.
    Keywords: Subglacial Drainage ; Glacitectonism ; Middle Pleistocene ; North Norfolk ; Geology
    ISSN: 0016-7878
    Source: ScienceDirect Journals (Elsevier)
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  • 4
    Language: English
    In: Proceedings of the Geologists' Association, September 2013, Vol.124(5), pp.731-737
    Description: The role of ice masses within the Earth's climate system and in landscape change is increasingly being recognised within regions that are either currently glaciated or were glaciated during the geological past. There are many different remote and field-based approaches to studying the products of glaciation. One approach – that of , focuses on the styles of deformation and tectonic imprint (folds, fractures, fabrics, foliations and lineations) produced as ice overrides or pushes into pre-existing rocks or sediment. This approach, when used in combination with other types of evidence, can be used to infer ice-dynamics, substrate rheology and ice-bed coupling. Of equal significance is the influence of glacitectonic structure upon the applied properties of glaciated terranes such as ground stability, hydrogeology and fluid migration (e.g. water, gas hydrates and hydrocarbons). This paper provides an introduction to this Special Issue on Glacitectonics, outlining the significance and historical development of this field of glacial geology, before introducing and summarising the contributions that make up the volume.
    Keywords: Glacitectonic ; Glacitectonite ; Subglacial ; Proglacial ; Till ; Subglacial Deformable Beds ; Geology
    ISSN: 0016-7878
    Source: ScienceDirect Journals (Elsevier)
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  • 5
    Language: English
    In: Quaternary Science Reviews, Feb 1, Vol.109, p.88(23)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.quascirev.2014.09.010 Byline: Jonathan R. Lee, Oliver J.W. Wakefield, Emrys Phillips, Leanne Hughes Abstract: Subglacial drainage systems exert a major control on basal-sliding rates and glacier dynamics. However, comparatively few studies have examined the sedimentary record of subglacial drainage. This is due to the paucity of modern analogues, the limited recognition and preservation of upper flow regime deposits within the geological record, and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments (e.g. glacier outburst flood deposits). Within this study, the sedimentological and structural evolution of a subglacial to subaerial (ice-marginal/proglacial) drainage system is examined. Particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context. Facies are attributed to subglacial meltwater activity and record sedimentation within a confined, but progressively enlargening, subglacial channel system produced under dune to upper flow regime conditions. Bedforms include rare large-scale sinusoidal bedding with syn-depositional deformation produced by current-induced traction and shearing within the channel margins. Subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel-abandonment or a seasonal drainage regime. Retreat of the ice margin, led to the establishment of subaerial drainage with phases of sheet-flow punctuated by channel incision and anastomosing channel development under diurnal, ablation-related, seasonal discharge. The presence of extensive hydrofracture networks demonstrate that proglacial groundwater-levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream. Author Affiliation: (a) British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK (b) British Geological Survey, West Mains Road, Edinburgh, EH9 3LA, UK Article History: Received 30 April 2014; Revised 1 September 2014; Accepted 4 September 2014
    Keywords: Groundwater ; Bedforms ; Sedimentary Structures ; Sediments (Geology)
    ISSN: 0277-3791
    Source: Cengage Learning, Inc.
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  • 6
    In: Journal of Quaternary Science, February 2017, Vol.32(2), pp.231-260
    Description: Byline: Emrys Phillips, David Hodgson, Jonathan R. Lee, Emrys Phillips, James Rose, David Vaughan-Hirsch ABSTRACT The Middle Pleistocene glacial history of northern East Anglia is a controversial topic with differing opinions surrounding chronology, provenance and the relative stratigraphic framework. Reconciling the stratigraphic framework of the region is an essential first step to developing onshore-offshore geological models and a robust event-driven chronological framework. Within this study a dynamic tectonostratigraphic-parasequence methodology is applied to deposits traditionally attributed to the Anglian Glaciation (Marine Isotope Stage 12). This approach offers an insight into ice-bed coupling during glaciation and how evolving boundary conditions influenced glacier dynamics. Six major tectonostratigraphic-parasequence assemblages (A1-A6) are recognized in northern East Anglia and correlate with successive advances into the region of North Sea or Pennine lobes of the British Ice Sheet. Individual tectonostratigraphic-parasequence assemblages are bound at their base by a sedimentary contact or, more commonly, a glacitectonic zone. The geometry and structural characteristics of these glacitectonic zones reflect temporal and spatial variations in ice-bed coupling (traction), a function of substrate rheology and, in turn, variations in lithology, porewater availability and thermo-mechanical properties. The role of permafrost may also be significant, promoting proglacial/ice-marginal thrust stacking in front of advancing ice and enhanced ice-bed decoupling during subsequent overriding and subglacial till accretion. [c] 2016 British Geological Survey, NERC Journal of Quaternary Science [c] 2016 John Wiley & Sons Ltd
    Keywords: East Anglia ; Glacitectonic ; Middle Pleistocene ; North Sea ; Stratigraphy
    ISSN: 0267-8179
    E-ISSN: 1099-1417
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  • 7
    In: Boreas, April 2013, Vol.42(2), pp.376-394
    Description: The ability of glaciers to detach and transport bedrock as glaciotectonic rafts is widely observed throughout Quaternary sections. However, the glaciological, hydrological and geological parameters controlling rafting are currently poorly constrained. There is a lack of structural and sedimentary evidence concerning rafting, and therefore the processes driving raft detachment, transport and emplacement are poorly understood. This paper contributes to our understanding by presenting a macro‐ and microstructural study of deformation associated with a chalk raft at est unton, north orfolk. Detailed thin‐section analysis reveals several discrete micro‐fabric orientations, representing poly‐phase deformation occurring during raft transport and emplacement. A four‐stage conceptual model for raft transport and emplacement is proposed, with deformation being partitioned into the relatively weaker Happisburgh Till member, the latter forming the host to the raft. Stage 1 is the main transport phase of the chalk raft, and was dominated by easterly (down‐ice) directed ductile shearing. During Stage 2 a narrow ductile shear zone within the Happisburgh Till member propagated upwards through the base of the raft, leading to the detachment of an elongate block of chalk. Attenuated lenses of diamicton in this shear zone possess kinematics recording an easterly directed sense of shear. As deformation progressed, during Stage 3, the detached block impinged on the ‘high‐strain’ zone wrapping the base of the raft, influencing the style of deformation partitioning and leading to localized, up‐ice‐directed kinematics. Stage 4 represents the final stages of raft emplacement, when the detachment zone at the base of the raft began to ‘lock‐up’. These results demonstrate the relative importance of the hydrological controls associated with raft transport and emplacement underneath an actively advancing glacier. Furthermore, the model represents an example of how micromorphological analysis can reveal detailed poly‐phase deformation histories in deformed glacial sediments.
    Keywords: Quaternary Geology ; Alteration ; Bedrock ; Carbonate Rocks ; Cenozoic ; Chalk ; Clastic Sediments ; East Anglia ; England ; Europe ; Fabric ; Glacial Geology ; Glacial Transport ; Glaciotectonics ; Great Britain ; Happisburgh Till Member ; Kinematics ; Microstructure ; Middle Pleistocene ; Norfolk England ; Petrography ; Pleistocene ; Pore Pressure ; Quaternary ; Sedimentary Rocks ; Sediments ; Shear ; Strain ; Till ; Transport ; United Kingdom ; West Runton England ; Western Europe;
    ISSN: 0300-9483
    E-ISSN: 1502-3885
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  • 8
    Language: English
    In: Quaternary Science Reviews, 2011, Vol.30(23), pp.3481-3500
    Description: Sand intraclasts are common within the Bacton Green Till Member, a glacitectonic mélange subjected to polyphase deformation during the Middle Pleistocene in North Norfolk, UK. The intraclasts range from a few tens of centimetres to 〉10 m in length and have sharp contacts with the surrounding till. Sand within the intraclasts is unconsolidated and contains well-preserved primary stratification. The wrapping of glacitectonic foliation around the intraclasts and the development of folds relating to mechanical instabilities indicate that the intraclasts acted as competent masses within a more easily deformable fine-grained till that accommodated the majority of the strain. Sharp contacts and distinctive heavy-mineral assemblages indicate little intermixing between the sand and till. Five hypotheses about the entrainment and evolution of the intraclasts are tested against sedimentological, structural and mineralogical observations. The most reasonable hypothesis attributes the intraclasts to glacitectonic deformation of “warm” permafrost. Initial ice advance caused large-scale thrusting of proglacial permafrost that led to the stacking of pre-glacial and ice-marginal sediments that were subsequently deformed sub-marginally to generate the intraclasts. Preservation of primary stratification within the intraclasts is attributed to deformation at temperatures slightly below the pressure-melting point, when pore ice cemented the intraclasts as rigid bodies. At the same time deformation was concentrated into the surrounding finer-grained till because of its significant liquid water content and ductile rheology. It is concluded that the intraclasts provide a criterion to identify past glacier–permafrost interactions and a potential means of differentiating between subglacial deformation under unfrozen and partially-frozen conditions. ► We examine the origin and significance of sand intraclasts within tills. ► Occur as competent masses within deformed tills in north Norfolk. ► Cohesion associated with the development of an ice cement. ► Rheological contrast within deformed tills consistent with sub-freezing temperatures. ► Intraclasts are potentially diagnostic of glacier–permafrost interactions.
    Keywords: Palaeoglaciology ; Glacial Sedimentology ; Glacitectonic Deformation ; Permafrost ; Sciences (General) ; Geology
    ISSN: 0277-3791
    E-ISSN: 1873-457X
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  • 9
    Language: English
    In: Quaternary Science Reviews, 01 February 2015, Vol.109, pp.88-110
    Description: Subglacial drainage systems exert a major control on basal-sliding rates and glacier dynamics. However, comparatively few studies have examined the sedimentary record of subglacial drainage. This is due to the paucity of modern analogues, the limited recognition and preservation of upper flow regime deposits within the geological record, and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments (e.g. glacier outburst flood deposits). Within this study, the sedimentological and structural evolution of a subglacial to subaerial (ice-marginal/proglacial) drainage system is examined. Particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context. Facies are attributed to subglacial meltwater activity and record sedimentation within a confined, but progressively enlargening, subglacial channel system produced under dune to upper flow regime conditions. Bedforms include rare large-scale sinusoidal bedding with syn-depositional deformation produced by current-induced traction and shearing within the channel margins. Subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel-abandonment or a seasonal drainage regime. Retreat of the ice margin, led to the establishment of subaerial drainage with phases of sheet-flow punctuated by channel incision and anastomosing channel development under diurnal, ablation-related, seasonal discharge. The presence of extensive hydrofracture networks demonstrate that proglacial groundwater-levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream.
    Keywords: Subglacial Drainage ; Upper Plane Bed ; Helicoidal Flow ; Sinusoidal Bedding ; Hydrofracturing ; Groundwater ; Sciences (General) ; Geology
    ISSN: 0277-3791
    E-ISSN: 1873-457X
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  • 10
    Language: English
    In: Proceedings of the Geologists' Association, September 2013, Vol.124(5), pp.802-817
    Description: The deformed metasedimentary bedrock and overlying diamictons in western Anglesey, NW Wales, record evidence of glacier-permafrost interactions during the Late Devensian (Weichselian). The locally highly brecciated New Harbour Group bedrock is directly overlain by a bedrock-rich diamicton which preserves evidence of having undergone both periglacial (brecciation, hydrofracturing) and glacitectonic deformation (thrusting, folding), and is therefore interpreted as periglacial head deposit. The diamicton locally posses a well-developed clast macrofabric which preserves the orientation of the pre-existing tectonic structures within underlying metasedimentary rocks. Both the diamicton and New Harbour Group were variably reworked during the deposition of the later Irish Sea diamicton, resulting in the detachment of bedrock rafts and formation of a pervasively deformed glacitectonite. These structural and stratigraphic relationships are used to demonstrate that a potentially extensive layer of permafrost developed across the island before it was overridden by the Irish Sea Ice Stream. These findings have important implications for the glacial history of Anglesey, indicating that the island remained relatively ice-free prior to its inundation by ice flowing southwards down the Irish Sea Basin. Palynological data obtained from the diamictons across Anglesey clearly demonstrates that they have an Irish Sea provenance. Importantly no Lower Palaeozoic palynomorphs were identified, indicating that it is unlikely that Anglesey was overridden by ice emanating from the Snowdon ice cap developed on the adjacent Welsh mainland. Permafrost was once again re-established across Anglesey after the Irish Sea Ice Stream had retreated, resulting in the formation of involutions which deform both the lower bedrock-rich and overlying Irish Sea diamictons.
    Keywords: Periglacial Deformation ; Glacially Tectonised Bedrock ; Anglesey ; Irish Sea Ice ; Geology
    ISSN: 0016-7878
    Source: ScienceDirect Journals (Elsevier)
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