Composition and formation of laminated sediments in Diss Mere, Norfolk, England

The chemical and biological composition of laminated lake-sediments deposited between about 2,500 and 5,500 years B.P. in Diss Mere, Norfolk, England is described. The distribution of Ca, Fe, S, and Si in pale and dark laminae is established by energy-dispersive X-ray microanalysis. The pale laminae consist primarily of calcium carbonate and the dark layers contain mainly Fe, S, Si, and dark organic material. The diatom composition of 16 individual light and dark laminae shows no consistent differences between light and dark layers. There are, however, higher frequencies of chrysophycean cysts in seven of the eight dark layers, suggesting these layers were deposited in late summer or fall. Pollen analyses of the pale and dark layers show that pollen percentages of early-flowering trees and shrubs are highest in the dark laminae and that pollen values of late-flowering plants are highest in the pale layers. The biological data indicate that the pale layers were formed in the late spring and early summer, whereas the dark laminae were deposited in late summer, fall, winter, and the early spring. Seasonal supply of CaCO₃ was the major variable responsible for couplet formation.     

Wind action and sand movement near Holkham Bay,North Norfolk Coast,England

In Holkham Bay, North Norfolk Coast, England, a wide beach and coastal dunes have formed as a result of wave action and wind activity. This article describes the experiments and field observations that were carried out to explore the nature of wind activity that is presently affecting the morphology of the beach and dunes.The experiments and field observations indicate: (1) Sand is blown off the beach surface very soon after it is exposed during the low tide if the wind velocity is above 3.0 m/sec. (2) Winds from the south, east, and west in Holkham Bay are offshore winds and do not exert much influence on dune formation in the area. (3) The dominant winds (those that exert most marked effect on the beach and dunes) are the northerly, northeasterly and the northwesterly winds. (4) The average annual accretion rate of sand by the wind on the beach is about 3,600 m³. (5) Knowing the annual accretion rate and the volume of aeolian dunes, it is possible to determine their relative ages.     

Early and Middle Pleistocene river systems in eastern England: evidence from Leet Hill,southern Norfolk,England

Pleistocene sediments at Leet Hill, southern Norfolk are examined in terms of their sedimentary structures, palaeocurrent indicators, clast and heavy mineral lithology and litho- and morphostratigraphic position. Colour of the quartzite and vein-quartz clasts is used to differentiate the Bytham and the Kesgrave sands and gravels, with the Bytham sands and gravels having a significantly higher proportion of coloured material. The Kirby Cane sands and gravels are the lower sedimentary unit and were deposited by the Bytham river, which drained a catchment extending into central England. At Leet Hill, erosion of the Kesgrave Sands and Gravels by the Bytham river has given the Kirby Cane sands and gravels a distinctive lithological assemblage. Trace clast lithologies suggest that the Kesgrave Sands and Gravels in the region of Leet Hill were deposited in a coastal location with an input from northern sources as well as southern and Welsh sources diagnostic of the Thames catchment. The glaciofluvial Leet Hill Sands and Gravels were deposited by outwash from the Anglian Scandinavian ice sheet. Initially the flow direction of the outwash was determined by the Bytham river valley, but this changed to a southerly direction once the valley had been infilled. This paper provides the first indication of the location of the boundary (Early Pleistocene coastline) between the fluvial Kesgrave Sands and Gravels and the marine equivalent reworked by coastal processes, and demonstrates the way the pre-glacial relief initially controlled patterns of glaciofluvial sedimentation during the early part of the Anglian glaciation. Copyright © 1999 John Wiley & Sons, Ltd.     

Formation of siderite-Mg-calcite-iron sulphide concretions in intertidal marsh and sandflat sediments, north Norfolk, England

Concretions cemented mainly by siderite, Mg-calcite and iron monosulphide are common in late Holocene marsh and sandflat sediments on parts of the north Norfolk coast. Field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate-reducing bacteria are active. δ¹³C values ranging from ?3 to ?11·8% (mean ?5·9%0) suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter. δ¹⁸O values ranged from ?6·4% to + 0·8% (mean ?1·0%) suggesting that carbonate precipitated in porewaters ranging from pure sea water to-sea water diluted with meteoric water. Chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation. Some concretions have formed around fragments of wood or metal, but others contain no apparent nucleus. In field experiments siderite, FeS and Mg-calcite were precipitated around several different nuclei within a period of six months. We suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction, such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron.     

Neoichnology of Chalk cobbles from north Norfolk,England: implications for taphonomy and palaeoecology

The study of marine biota of the North Sea from the perspective of its relevance to palaeontology (Aktuopaläontologie) has enabled modern patterns and processes to be identified that can also be recognised in ancient communities. A collection of Chalk cobbles from the coast of north Norfolk, eastern England, preserves a limited ichnofauna: Gastrochaenolites ornatus Kelly and Bromley; Gastrochaenolites isp.; and Caulostrepsis isp. All cobbles show evidence of physical modification (corrasion) since they were bored; no Gastrochaenolites is complete and no clast has Caulostrepsis on all sides, therefore clasts have been corraded subsequent to boring. Only one producing organism in Gastrochaenolites, probably Barnea sp., is preserved in situ. Gastrochaenolites borings were infested by a range of encrusting organisms after the demise (and removal of shells) of the boring bivalves: thread-like algae; agglutinated worm tubes; cheilostome bryozoan Cryptosula pallasiana (Moll); and serpulids Hydroides norvegica Gunnerus and Pomatoceras triqueter (Linnaeus). Such a suite of encrusting organisms would be impossible to see in a fossil boring filled with lithified sedimentary rock unless it was released by dissolution of the substrate. Such cobbles, corraded since they were infested by borers, leave only portions of traces for identification, commonly only to ichnogenus.     

Changes in intertidal dunes during two spring-neap cycles, Lifeboat Station Bank, Wells-next-the-Sea, Norfolk (England)

Twice-daily observations over a fixed range were made covering three consecutive sets of spring tides. Some dune population dimensions (e.g. mean wavelength) show a long-lasting (at least weeks) alteration during the most vigorous springs, but a short-lived (tides or days only) change over the weaker ones. Other properties (e.g. mean height) experience merely short-lived alterations. The changes seem to be linked to the creation during spring tides of new dunes of an initially small size (minor dunes), which introduces new matured dunes into the populations if there is sufficient subsequent sediment transport, and to the limited ability of individual dunes to respond to changing hydraulic conditions during their life-spans. The dunes are active during only a very small proportion of each spring-neap cycle, but the bank is permanently covered by them, and cross-stratification caused by dune movement is the only internal structure. Without a knowledge of the history and dynamics of the dune populations, the quality of the environment at Lifeboat Station Bank cannot be satisfactorily assessed from the sedimentary products.     

Proglacial glaciotectonic deformation and the origin of the Cromer Ridge push moraine complex, North Norfolk, England

The landscape of northeast Norfolk is dominated by a high (>50 m) ridge which has been interpreted as an end moraine (Cromer Ridge). This feature is truncated by coastal erosion at Trimingham. Evidence of large- and small-scale compressive styles of deformation is found throughout the sequence, except at the very top, where late Anglian/early Hoxnian lake sediments are found within an undeformed kettle hole. The deformation consists of open folds (including chevron folds) and listric thrust faults. It is suggested that these are the result of a single compressive event, which was caused by proglacial glaciotectonic deformation. It is inferred that this deformation is due to a combination of frontal pushing and compressive stresses transmitted through a subglacial deforming wedge. It is also shown that strain increases towards the ice sheet margin, as reflected by the deformational styles (from open folding up-glacier to listric thrust faulting down-glacier). The Cromer Ridge is shown to be a push moraine complex related to an actively retreating ice margin.     

The history of Cu,Pb, and Zn inputs to Narragansett Bay,Rhode Island as recorded by salt-marsh sediments

The distribution of metals with depth in sediment cores sampled from industrialized estuaries can reveal long-term trends in loadings to the waterbody. Salt marsh cores were sampled from five locations from the head to the mouth of Narragansett Bay and from one location from a marsh inside a lagoon on the coast of Block Island Sound with the intent of reconstructing historical loadings of Pb, Cu, and Zn to this estuary. Concentrations of Fe and Mn were measured as indicators of redox conditions of the sediment column. Chronologies were developed using accretion rates determined previsly from²¹⁰Pb analyses of the same cores. Excess metal inventories and enrichment over pre-industrial concentrations were greater in upper bay cores reflecting the location of sources at the head of the estuary. The bay cores were similar with respect to the distributions of Cu, Pb, and Zn. Concentrations of all metals began to increase over background levels at depths corredponding approximately to the year 1900. Most of the cores showed peak concentrations of Cu and Pb in the early 1950s and 1970s. Distributions of Zn were more variable among cores, showing peaks in the early 1920s in some cores and in the 1950s and 1970s in others. In general, the observed distributions in the bay cores are consistent with estimated long-term trends in loadings from atmospheric and sewage sources. The metal distributions in the lagoon core appear to reflect atmospheric loadings. However, there are features in some cores that are not explainable using the estimated trends in source inputs. There also is not a 1∶1 correspondence between changes in sediment metal concentrations and changes in loadings. It is likely that this method of reconstruction would benefit from a more detailed characterization of sources, but comparison of sediment and historical records do show that attempts to reduce loadings to the bay have been successful.     

Implications of dissected drift at Stockdale Head,western Lake District,northern England

From mapping and consideration of prominent drift ridges at Stockdale Head, western Lake District, northern England it is inferred that the ridges are the products of dissection of a glacigenic or soliflual drift sheet rather than landforms constructed at the margins of a Loch Lomond Stade (LLS) valley‐head glacier. This proposal has implications for the recognition of LLS glacier limits and, possibly, understanding the dearth of moraine ridges associated with Dimlington ice in Lake District valleys. Copyright © 2004 John Wiley & Sons, Ltd.     

Palaeoenvironments of the Hoxnian Nar Valley Clay,Norfolk, England: Evidence from an integrated study of diatoms and ostracods

Diatoms and ostracods from the Nar Valley, west Norfolk, England are analysed with a view to establishing marine and freshwater palaeoenvironments of the Hoxnian interglacial Stage. No microfossils were recovered from the non-marine facies, but rich assemblages of both fossil groups were extracted from the marine Nar Valley Clay and these, together with associated sedimentological evidence, indicate that the environment of deposition changed from a relatively nearshore, muddy shelf setting, to one that was more littoral and subject to higher current regimes, with salinities remaining at normal marine levels through both depositional phases. It is suggested that this sequence may reflect a regressional phase towards the close of the Hoxnian Stage, with palaeotemperature evidence from at least one ostracod species suggesting a warmer climate than at present. Non-recovery of microfossils from some of the samples analysed is attributed to unfavourable palaeoenvironmental conditions and/or post-depositional ground-water percolation.     

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.     

Seasonal and environmental variations in sediment accretion in a Long Island salt marsh

Flax Pond is a small (0.5 km²) salt marsh on the north shore of Long Island, New York. Two 1 m² plots within each of the following environments were covered with a marker layer of either brick dust or aluminum glitter: 1) bare mud flats; 2) areas newly colonized by Spartina alterniflora; and 3) high intertidal. S. alterniflora peat surfaces. Monthly cores revealed the amount of sediment that accumulated since placement of the marker. Accretion rates from October, 1974 to February, 1976 were as follows: bare mud flats ?20.5 to 45.5 mm/yr; recently vegetated mud flats ?9.5 to 37.0 mm/yr; and high intertidal peat surfaces ?2.0 to 4.25 mm/yr. Sedimentation rates decrease with increasing elevation because of the reduced tidal submergence time and decreased height of the overlying water column. In areas of low elevation, ice and storms cause either erosion or a reduced rate of accretion during the winter months. The average mud accretion rate over the past 173 years is 3.4 mm/yr. Differences between the short-term rate and the long-term rate indicate substantial annual variation in the accumulation of mud in salt marshes. Short-term rates of peat accretion are similar to long-term estimates, indicating that rates of peat accretion are relatively constant over long intervals.     

A dated cave sediment record of Pleistocene transgressions on Berry Head,Southwest England

Berry Head, a limestone headland in Torbay, southwest England, exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m. Solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms, and developed in a marine/freshwater mixing zone whose position was controlled by high sea-level still-stands. Corbridge Cave in Berry Head Quarry lies below the raised beaches in Torbay, and contains evidence of three marine transgressions in the form of fine-grained marine ponding deposits with a marine microfauna. Uranium-series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5.8 m OD, while an earlier transgression (probably during stage 7) reached at least 7.2 m OD. These findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in Southwest Britain, and a correlation of the Unnamed Stage of Bowen, Sykes, Reeves, Miller, Andrews, Brew and Hare with oxygen isotope stage 5e is proposed.