A review of Macoma balthica (L) as a stratigraphic marker in the Pleistocene sediments of the southern North Sea Basin

The first occurrence and presence of the bivalve Macoma balthica in the Pleistocene shallow marine sediments (Crags) of East Anglia has long been used to characterise the youngest “Weybourne” or “Wroxham” Crag Formation of Early to early Middle Pleistocene age. A review of recent work on the morphological variation and genetic lineages of living populations of the species and of work on fossil discoveries in East Greenland suggests that the current palaeontological species definition is too narrow, that the species arrived in the Atlantic about 2.4 Ma and much earlier than is envisaged from the studies of the North Sea Basin, and that there were several trans-Arctic migrations of the species during the Pleistocene. This paper reviews these findings and concludes that: (i) detailed morphometric analyses of fossil Macoma species from the Crag need to be undertaken and the species definitions comprehensively reviewed to take account of the morphological and genetic variation seen in modern populations; (ii) detailed morphometric analysis of modern M. balthica should be undertaken and tied to the different genetic lineages, and (iii) the current palaeontological definition of Macoma balthica should not be relied on as the basis for a First Appearance Datum (FAD) in the Southern North Sea basin.     

Differential productions of rural gentrification: illustrations from North and South Norfolk

This paper focuses attention on the making of space for rural gentrification, both discursively and materially. The paper emphasises the differential constructions of gentrification within urban and rural studies. Connections are drawn between production-side theories of gentrification, notions of the ‘post-productivist countryside’ and studies that have related rural demographic change and gentrification with planning and property relations. Drawing on these three sets of ideas, the paper explores gentrification in rural Norfolk. It is argued that the contemporary geography of rural gentrification may in part reflect historic structures of landownership as well as settlement classifications associated with the land-use planning system. Country and District level analysis is followed up by detailed study of gentrification of two villages in Norfolk, which highlights how gentrified rural spaces may be produced in rather different way and through different agencies, and as a result takes different forms.     

Sources of suspended and deposited sediment in a broadland river

Increasing rates of bank erosion and sediment deposition have been reported from the Norfolk Broads since the early 19th century. The major sources of both suspended and deposited sediment in the rivers and Broads is quantified using sediment mineralogy, identified by X-ray diffraction. This indicates that higher proportions of bank derived sediment are present in suspension in the waterway during the summer months, due primarily to bank erosion by motor craft. Dated sediment cores show how the sources of inorganic sediment have changed over time. Whilst in the past upland catchment sources dominated, at present material is mainly derived from river bank material.     

Anatomy of a continent-backarc transform — The Vening Meinesz Fracture Zone northwest of New Zealand

The northwestern continental margin of New Zealand offers one of the finest examples of a continent-backarc transform. This transform, part of the Vening Meinesz Fracture Zone (VMFZ), accommodated about 170 km of sea-floor spreading in the Norfolk backare basin together with eastward migration of a volcanic arc, the Three Kings Ridge, in the Mid- to Late Miocene. Before the onset of spreading, strain along the VMFZ may have been linked to a major Early Miocene obduction event — the emplacement of the Northland Allochthon. The transform is manifested by a belt up to 50 km wide of left-stepping, linear fault scarps up to 2000 m high within an approximately 100 km-wide deformed zone. A marginal ridge, the Reinga Ridge, which includes a faulted, folded and uplifted Miocene sedimentary basin, occurs within the high-standing continental side of the deformed zone, whereas a narrow strip of linear detached blocks occupies the deep backarc oceanic side. Prespreading uplift and erosion of crust in the proto-backarc region, are volcanism, and obduction of the allochthon, supplied clastic sediments to the basin on the continental side. This basin was complexly deformed as the transform evolved. The transform was initiated as a dextral strike-slip fault zone, which developed right-branching splays and left-steps along its length, uplifting and cutting the continental margin into left-hand, en echelon blocks and relays. Folds formed locally within relay blocks and at the distal ends of the splays. Only the high continental side of this zone (the Reinga Ridge) remains, the formerly adjacent crust (the Three Kings Ridge) having been displaced towards the southeast. As the Three Kings block moved and the Norfolk Basin opened, opposing rift margins of the backarc basin foundered to form terraces. The oceanic side of the transform also subsided to produce the belt of detached blocks (some laterally displaced by strike slip) and linear troughs along the main escarpment system.     

Development of a subglacial drainage system and its effect on glacitectonism within the polydeformed Middle Pleistocene (Anglian) glacigenic sequence of north Norfolk,Eastern England

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.     

New insights into the deformation of a Middle Pleistocene glaciotectonised sequence in Norfolk,England through magnetic and structural analysis

North Norfolk is a classic area for the study of glacial sediments with a complex glaciotectonic deformational history, but the processes leading to the formation of some structures can be ambiguous. Anisotropy of magnetic susceptibility (AMS) analyses, providing quantitative fabric data, have been combined with the analysis of visible structures and applied to the Bacton Green Till Member, exposed at Bacton, Norfolk. Thermomagnetic curves, low temperature susceptibility and acquisition of isothermal remanent magnetism (IRM) reveal that the magnetic mineralogy is dominated by paramagnetic phases. The magnetic foliation is parallel to fold axial planes and weakly inclined to bedding, whilst the magnetic lineation is orientated parallel to stretching, indicated by the presence of stretching lineations and the trend of sheath folds. Variations in the orientation of the magnetic lineation suggest that the Bacton section has been subject to polyphase deformation. After subaqueous deposition, the sequence was overridden by ice and glaciotectonically deformed which involved stretching initially north–south, then east–west. These results show that AMS can be used to detect strain in three dimensions through a glaciotectonite where paramagnetic mineralogy is dominant. This approach therefore provides further support to the use of AMS as a fast, objective and accurate method of examining strain within deformed glacial sediments.     

Marine Isotope Stage 7–6 transition age for beach sediments at Morston,north Norfolk,UK: implications for Pleistocene chronology,stratigraphy and tectonics

Optically stimulated luminescence age estimates for the Pleistocene beach at Morston, north Norfolk, UK, obtained by the single‐aliquot regenerative‐dose protocol, indicate a Marine Isotope Stage (MIS) 7–6 transition date. The view that the beach is of Ipswichian (MIS 5e) age, held virtually unanimously for the last 75 years, may now be discarded. The extant beach sequence lies up to ～5 m OD, yet global models suggest that MIS 7–6 sea levels were typically substantially below that of today. The explanation may lie with poorly understood regional tectonic movements. The MIS 7–6 date helps to constrain the ages of glacial deposits that bracket the beach sediments at Morston. The underlying Marly Drift till cannot be younger than MIS 8; this may also be true for the complex assemblage of glaciogenic landforms and sediments, including the Blakeney esker, in the adjacent lower Glaven valley. The well‐established Late Devensian (MIS 2) age of the Hunstanton Till is not compromised by the date of the Morston beach. There is no indication of a proposed Briton's Lane glaciation during MIS 6 times. Copyright © 2009 John Wiley & Sons, Ltd.     

Understanding and modelling spatial drain–aquifer interactions in a low‐lying coastal aquifer—the Thurne catchment,Norfolk, UK

Seawater intrusion into fresh groundwater formations generally results inadvertently from human activities, such as over‐abstraction from coastal aquifers. This article describes the data analysis to quantify drain–aquifer interactions in a low‐lying pump‐drained coastal aquifer, which is subject to saline intrusion due to widespread land drainage, and the resulting development and application of a numerical groundwater model to understand the spatial groundwater system behaviour (including groundwater salinity fluxes). Without measured flow data in this pump‐drained catchment, a novel groundwater head‐dependent approach to hydrograph separation is described. Time‐variant and time‐invariant MODFLOW analyses are utilised to examine the flow processes. A new approach to calculate drain coefficients, which represent the extensive network of drainage ditches in the regional model, using field information, is described; the sum of the drainage coefficients are close to the values independently estimated from the head‐dependent hydrograph separation. Results show that (1) the groundwater flows into the drainage systems are well reproduced using the new drain coefficients, (2) particle tracking of fresh and saline water can explain observed spatial salinity distribution within drainage networks and (3) the modelled flow of seawater across the coast is approximately 25% greater than that discharged by the pumps, demonstrating the need for drainage management to be aware of the slow response of groundwater systems to past drainage system changes. The article demonstrates that numerical groundwater modelling can produce the improved understanding needed to inform management decisions in such complex environments. Copyright © 2010 John Wiley & Sons, Ltd.