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Rob Westaway - One of the best experts on this subject based on the ideXlab platform.
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the pleistocene terrace staircase of the river thame central southern england and its significance for regional stratigraphic correlation drainage development and vertical crustal motions
Proceedings of the Geologists' Association, 2011Co-Authors: Rob WestawayAbstract:The Thame is one of the principal left-bank affluents of the Thames, the largest river in southern England; it joins the Upper Thames at Dorchester, ∼20 km downstream of Oxford. Its terraces include a younger group of four, which date from the late Middle Pleistocene and Late Pleistocene, are disposed subparallel to the modern river, and represent drainage within the modern catchment. At higher levels there are three older terraces, the Three Pigeons, Tiddington and Chilworth terraces, which are assigned to MIS 16, 14 and 12. With much gentler downstream gradients, these are fragmentary remnants of much more substantial fluvial deposits, indicating a much larger river that was disrupted by the Anglian (MIS 12) glaciation. This interpretation supersedes an earlier view that the glacigenic deposits in the Thame headwaters correlate with the Blackditch terrace, the highest of the younger group, which has hitherto provided an argument that the glaciation in this region occurred in MIS 10. It is suggested that the headwaters of the pre-Anglian ‘Greater Thame’ river were located near Northampton and that the Milton Sands of that area represent an upstream counterpart of the Chilworth terrace deposits. It is envisaged that this early Middle Pleistocene drainage geometry, located between the Jurassic limestone and Chalk escarpments, developed as a result of the increase in uplift rates that followed the Mid-Pleistocene Revolution (MPR). It is suggested that before this time, including during the Early Pleistocene, the modern Thame catchment and adjacent regions drained southeastward through the Chalk escarpment, but these small rivers lacked the erosional power to cut through the Chalk in pace with the faster uplift occurring in the early Middle Pleistocene, and so became diverted to the southwest, subparallel to the Chalk escarpment, to form the pre-Anglian ‘Greater Thame’ tributary of the Upper Thames. The post-MPR uplift is estimated to decrease northwestward from 90 m in the Middle Thames to 75 m near the Thame–Thames confluence and to 65 m upstream of Oxford. The post-Anglian (post-450 ka) component of uplift decreases northward from 33 m near the Thame–Thames confluence to an estimated ∼20 m in the Northampton area; the relative stability of the latter area makes feasible the proposed correlation between the Milton Sands and the pre-Anglian River Thame. Limited post-Anglian uplift in the Northampton area is also inferred from the upstream convergence of the terraces of the modern rivers Nene and Great Ouse. These observed lateral variations in vertical crustal motions reflect lateral variations in crustal properties (including heat flow, crustal thickness, and thickness of underplating at the base of the crust) that are known independently. This study thus provides, for the first time, an integrated explanation of the Pleistocene drainage development across a large region of central-southern England.
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quaternary vertical crustal motion and drainage evolution in east anglia and adjoining parts of southern england chronology of the ingham river terrace deposits
Boreas, 2009Co-Authors: Rob WestawayAbstract:Prior to its disruption during the Anglian glaciation (MIS 12), the Ingham or Bytham River used to flow eastwards across central England and East Anglia into the southern North Sea. It thus had a much larger catchment than any extant river system in Britain; its headwaters may well have been as far away as North Wales and/or NW England. Terrace deposits of this former river system crop out across East Anglia and, as for any other river, can be used to investigate uplift, landscape evolution and the physical properties of the underlying continental crust. However, such an investigation has hitherto been hampered by inconsistencies between different authors' terrace schemes; furthermore, and controversially, one such scheme has formed the basis for the inference that the region was affected by a pre-Anglian (MIS 16) glaciation. By re-examining the raw data, the Ingham River deposits are shown to be disposed in three terraces, inferred to date from MIS 16, 14 and 12. The evidence previously attributed to pre-Anglian glaciation is associated with the youngest of these terraces, and thus marks the MIS 12 (i.e. Anglian) glaciation; the argument for glaciation of the region in MIS 16 is thus an artefact of previous miscorrelation of the terrace deposits. It is inferred that development of the very large Ingham River was synchronous with decapitation of the former ‘Greater Thames’, or ‘High-level Kesgrave Thames’ river, some time between MIS 18 and MIS 16. Uplift histories at representative localities across East Anglia have been modelled using composite data sets, combining the terrace deposits of the Ingham River and of the post-Anglian rivers Lark and Waveney. The sites modelled are typefied by much faster uplift in the early Middle Pleistocene than in the late Middle Pleistocene; this effect is shown to be a consequence of the relative thinness (no more than ∼7–8 km thick) of the mobile lower-crustal layer, itself a consequence of the low surface heat flow in the London Platform crustal province. The post-Early Pleistocene uplift tapers eastward, consistent with the observed downstream convergence of the Ingham and Waveney terraces, and is close to zero near the modern coastline around Lowestoft and Great Yarmouth. Stratigraphic relationships between the Ingham terrace deposits and temperate-stage marine and terrestrial deposits in this coastal area allow sites to be dated; thus, Pakefield and Corton date from MIS 15, whereas Norton Subcourse dates from MIS 17. The oldest known Lower Palaeolithic sites in the region, characterized by flake artefacts, are Pakefield (MIS 15) and Hengrave (?MIS 14); younger pre-Anglian sites that have yielded handaxes and/or fossil material of the water vole Arvicola cantiana date from MIS 13. The minimal vertical crustal motion in this coastal area, where temperate-stage deposits from different climate cycles crop out close to present-day sea level, does not imply high crustal stability; instead, it indicates a ‘hinge zone’ between the uplifting hinterland and the subsiding depocentre in the southern North Sea.
David Vaughanhirsch - One of the best experts on this subject based on the ideXlab platform.
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the middle pleistocene glacial evolution of northern east anglia uk a dynamic tectonostratigraphic parasequence approach
Journal of Quaternary Science, 2017Co-Authors: Emrys Phillips, James Rose, David VaughanhirschAbstract: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. © 2016 British Geological Survey, NERC Journal of Quaternary Science © 2016 John Wiley & Sons Ltd
James Rose - One of the best experts on this subject based on the ideXlab platform.
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the middle pleistocene glacial evolution of northern east anglia uk a dynamic tectonostratigraphic parasequence approach
Journal of Quaternary Science, 2017Co-Authors: Emrys Phillips, James Rose, David VaughanhirschAbstract: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. © 2016 British Geological Survey, NERC Journal of Quaternary Science © 2016 John Wiley & Sons Ltd
Emrys Phillips - One of the best experts on this subject based on the ideXlab platform.
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the middle pleistocene glacial evolution of northern east anglia uk a dynamic tectonostratigraphic parasequence approach
Journal of Quaternary Science, 2017Co-Authors: Emrys Phillips, James Rose, David VaughanhirschAbstract: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. © 2016 British Geological Survey, NERC Journal of Quaternary Science © 2016 John Wiley & Sons Ltd
Philip L. Gibbard - One of the best experts on this subject based on the ideXlab platform.
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middle pleistocene ice marginal sedimentation in the transitional zone between the constrained and unconstrained ice sheet margin east anglia england
Boreas, 2017Co-Authors: Karolina Leszczynska, Steve Boreham, Philip L. GibbardAbstract:It is uncommon in the North Sea basin and northwestern Europe for the ice-marginal glacial successions of the Middle Pleistocene, Anglian (Elsterian) age to be well preserved and not overridden by subsequent glaciations. The existence of extensive and thick (˜20 m) Middle Pleistocene sand and gravel successions in East Anglia, England, provide a unique opportunity to reconstruct and understand the palaeoenvironmental conditions in the Anglian ice-marginal zone, and further across the North Sea basin. This paper uses data from 80 sections in two sand and gravel quarries in East Anglia to provide the first evidence concerning: (i) the character of the ice-marginal processes in the unique, transitional zone between the topographically constrained and unconstrained Anglian ice-sheet margin; (ii) the role of meltwater in the re-shaping of topographically driven preglacial drainage; and (iii) the position and the number of oscillations of the Anglian ice-sheet margin in the form of a sediment-landform assemblage. Moreover the current research adds to the discussion on the presence and extent of the proglacial lake in the North Sea Basin during the Anglian glaciation. The sand and gravel successions in the Anglian ice-marginal zone are primarily reworked proto-Thames sediments deposited by meltwater. At the beginning of the glaciation, the meltwater followed the preglacial (proto-Thames) river course. However, as the ice sheet advanced, it was re-routed, overwhelming and abandoning the old river course and depositing an extensive ice-marginal subaqueous fan. The succession includes evidence for at least two enhanced meltwater release events, as well as indications of glaciolacustrine sedimentation. The character of the described sedimentary settings is discussed in the wider context of the presence of the North Sea Lake.
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the Anglian hoxnian evolution of an ice marginal drainage system in suffolk england
Proceedings of the Geologists' Association, 1993Co-Authors: Steve Mathers, Jan Zalasiewicz, Philip L. Gibbard, S. M. PeglarAbstract:Deposits relating to the former Anglian ice-margin have been studied at two sites in southeast Suffolk: Rookery Farm, near Eyke; and at Shottisham. Their 3D geometry was established by a combination of ground conductivity mapping and augering/drilling. The deposits are predominantly clay-rich and commonly preserved in channels comparable with the ice-marginal channels described from adjacent parts of Suffolk. The early phase of sedimentation is characterized by till (boulder clay) and/or sand and gravel; subsequently lacustrine clay was deposited. These lacustrine clays are variably organic and were distinguished by their very high conductivity, enabling the thickest sequences to be pinpointed and drilled. Palynological investigation has shown that at both sites clays of mid-Hoxnian age are present. This indicates that the channelized Anglian ice-marginal drainage topography persisted until well into the succeeding warm Hoxnian Stage, with deposition of lacustrine clays commencing during a regional rise in water table in the mid-Hoxnian.