Lower Greensand Research Articles

The stratigraphical distribution of mid-Cretaceous Foraminifera near Ventnor, Isle of Wight

Ventnor No. 2 Borehole, located near Ventnor, Isle of Wight, penetrated the basal part of the Chalk Group and the Selborne Group before terminating in the upper part of the Lower Greensand Group (Sandrock Formation). The borehole was examined for Foraminifera, and although they were not seen in the Sandrock Formation and Monks Bay Sandstone Formation, the remainder of the borehole yielded moderately low diversity assemblages dominated by agglutinated species. Foraminiferal zones 3–6 ( H dentatus to M. fallax/M. rostratum macrofaunal zones) were identified in the Gault Formation and zones 6 (lower) to 6a ( M. fallax/M. rostratum to A. briacensis macrofaunal zones) were identified in the Upper Greensand Formation. Assemblages from the overlying West Melbury Marly Chalk Formation were used to identify foraminiferal zones BGS1-BGS3 ( M. mantelli and M. dixoni macrofaunal zones).

A geological and hydrogeological assessment of the electrical conductivity information from the HiRES airborne geophysical survey of the Isle of Wight

A recent high resolution airborne geophysical survey across the Isle of Wight (IoW) and Lymington area has provided the first electromagnetic data across the relatively young geological formations characterising much of southern England. The multi-frequency data provide information on bulk electrical conductivity to depths of the order of 100 m. A GIS-based assessment of the electrical conductivity information in relation to bedrock geological classification has been conducted for the first time. The analysis uses over 104,000 measurements across onshore IoW and has established average and statistical properties as a function of bedrock geology. The average values are used to provide baseline maps of apparent electrical conductivity and the variation with depth (measured as a function of frequency). The average conductivity as a function of depth within the main aquifer units is summarised. The data indicate that the majority of the Palaeogene is characterised by values consistently in excess of 100 mS/m and with a surprisingly high degree of spatial heterogeneity. The youngest (Oligocene) Hamstead Member displays some strong edge effects and the largest localized values in conductivity. The central Upper Chalk is associated with the lowest observed conductivity values and mineral content and/or porosity appears to increase with increasing age. The large central outcrop of the Lower Greensand Group, Ferruginous Sand Formation provides persistently low (<30 mS/m) conductivity values which imply a relatively uniform distribution of clean sand content. Non-geological (e.g. environmental) responses are contained within the data set and examples of these in relation to a closed municipal landfill and an area of potential coastal saline intrusion are discussed. In the south, the Gault clay/mudstone of the Early Cretaceous appears as a distinctive conductive unit. Cross sectional modelling of the data has been undertaken across the aquifer units of the Southern Downs. The results indicate that the Gault Formation, acting as an aquitard, can be traced as a distinct unit under the more resistive Early Cretaceous Upper Greensand and Late Cretaceous Chalk formations. The conductivity modelling should therefore allow an estimation of the subsurface configuration of the aquifer and aquitard units.

The Lower Albian (Lower Cretaceous) Monk's Bay Sandstone Formation (formerly the Carstone) of the Isle of Wight: Its distribution, litho- and biostratigraphy

The Monk's Bay Sandstone Formation (MBSF) is the new name for the Lower Albian ferruginous sandstone that was formerly known as the Carstone of the Isle of Wight. The new term was proposed to remove any confusion with the Carstone, of similar age and lithology, described from the separate Lower Cretaceous sedimentary basin of Eastern England. This paper formalises the nomenclatural change outlined in the Lower Cretaceous Framework Report, ratified by the Geological Society Stratigraphy Commission. The MBSF, representing a major mid-Albian transgressive event, is described from a series of boreholes drilled by the British Geological Survey across the Isle of Wight, and from additional coastal exposures, together with reinterpretations of sections described in earlier works. The age range of the MBSF is determined in relation to recent biostratigraphical schemes supported with new data from the previously unknown presence of foraminifera. Deposits, belonging to the Leymeriella regularis Subzone, were previously considered to be absent from the succession and represent the stratigraphical gap separating the formation from the underlying Sandrock Formation. However a first occurrence of tubular foraminifera resembling Hyperammina/‘ Rhizammina cf dichotomata’ suggest that the oldest part of the formation in the northeast of the island may be of regularis Subzone age. This unconformity is correlated with the sequence boundary LG4 of Hesselbo and the presence of the Sonneratia kitchini Subzone at the base of the MBSF on the Isle of Wight suggests that this boundary should be placed at the lower of two candidate horizons within the successions of the Weald. The formation is restricted to the Isle of Wight but is coeval with similar coarse-grained sediments, e.g. the Carstone and ‘JunctionBeds’ to the north. The palaeogeography of the formation and the relationship with these similar deposits and the implications for the timing of mid-Albian structural events is briefly discussed. The identification of older Lower Greensand Group sediments beneath the MBSF in boreholes north of the Isle of Wight structure, together with new survey data indicating north–south orientated faulting affecting the early Cretaceous implies a tectonic element to the distribution the Lower Greensand Group sediments. Taken together these imply a complex interaction of tectonics and transgressive events throughout the Aptian and Albian over this structural high.

A review of hydrogeology and water resources on the Isle of Wight

Abstract The Isle of Wight is a small, heavily populated island, where complex and careful management is required to ensure sustainable use of water resources. Much of the island is underlain by permeable strata and groundwater is an important source of supply. Many groundwater studies were undertaken by the water provider and regulatory authority from the 1970s onwards, but this work is not publicly available. This paper reviews these previous studies and provides an overview of the hydrogeology of the island with particular focus on the Lower Greensand Group and the Chalk–Upper Greensand aquifer. As one of the areas in the UK to experience water shortages during the 1976 drought, the Isle of Wight became the focus for new strategies for the sustainable development of water, which included the exploitation of more marginal aquifers, water metering and an engineering solution to provide water from the mainland. Ensuring future water demand is managed sustainably in an area where aquifers are fully exploited is likely to rely on the twin-track approach of both further demand-management and unconventional water resource development, such as wastewater reuse or desalination.

Wavelet analysis of the correlations between soil properties and potential nitrous oxide emission at farm and landscape scales

We analysed data on nitrous oxide emission rate and some other properties of soil cores collected on a 7.5‐km transect across contrasting land uses and parent materials in eastern England. The variation on this landscape‐scale transect was compared with that of a comparable set of measurements made in a previous study on within‐farm spatial scales in the same region. We used the wavelet transform to analyse the scale dependence and spatial uniformity of the correlations between soil properties and emission rates from farm to landscape scale. The analysis revealed a complex pattern of scale dependence. Soil organic carbon was correlated with emission rates at within‐field scales only. There was a pronounced correlation between emission rates and a process‐specific function of the water‐filled pore space, seen only at landscape scales. Emission rates were strongly correlated with soil nitrate content at intermediate and coarsest scales (and significantly, although weakly, at the finest within‐field scales), and with pH at the intermediate scales. The wavelet analysis showed that these correlations were not spatially uniform. The correlation between nitrate concentration and emission rates at the finest landscape scale (between approximately 60 and 120 m) was not significant in the northern part of the transect corresponding primarily to soils over the Lower Greensand, but these variables were significantly correlated at this scale over other parent materials. These findings have implications for modelling and inventory of nitrous oxide emissions from soil. They indicate that, at the landscape scale, nitrate content and water‐filled pore space are key soil properties for predicting nitrous oxide emissions and should therefore be incorporated into process models and emission factors for inventory calculations.

A radiometric airborne geophysical survey of the Isle of Wight

A high resolution airborne geophysical survey across the Isle of Wight and Lymington area conducted in 2008 provided the first modern radiometric survey across the geological formations that characterise much of southern England. The basic radiometric data are presented and it is evident that bedrock geology exerts a controlling influence on the broad response characteristics of the naturally occurring radioelements. A GIS-based geological classification of the data provides a quantitative assessment and reveals that a relatively high percentage of the variability of the data is explained by the Cretaceous bedrock geology but this is much reduced in the Palaeogene. The three traditional Chalk units (Lower, Middle and Upper Chalk depicted on the currently available Geological Map) provide the lowest and most distinct behaviour within the Cretaceous sequence. Mineral content within the Chalk appears to increase with increasing age. A new method of representing the baseline radiometric information from the survey in terms of the mean values of the geological classification is presented. The variation of radioelement geochemistry within individual formations is examined in two case studies from the Cretaceous Lower Greensand Group and the Palaeogene Hamstead Member (Bouldnor Formation). The Cretaceous sequences provide the higher levels of discrimination of localised variations in radioelement distributions. A more detailed case study examines the potential influences from the degree of water saturation in the soil and superficial deposits.

Tidal Modeling of an Ancient Tide-Dominated Seaway, Part 2: The Aptian Lower Greensand Seaway of Northwest Europe

Abstract The Cretaceous Lower Greensand deposits of southeastern England and northern France contain abundant evidence of diurnal (once-daily) paleotides, with tidal influence increasing into the late Aptian. The Imperial College Ocean Model (ICOM) is used herein to determine the amplitude, origin (astronomical or co-oscillating), and characteristics (diurnal or semidiurnal) of the tides in the shallow marine “Lower Greensand Seaway” where these sediments were deposited. A global ocean paleotidal model of the Aptian predicts very low tidal ranges (microtidal) in the proto–Central Atlantic Ocean and Boreal Ocean, with higher tidal amplitudes, especially of the diurnal constituents, predicted in the northwestern Neotethys Ocean. This suggests that the Neotethys Ocean was the only significant source of oceanic tides to the Lower Greensand Seaway. Herein, the results of the global ocean paleotidal model are used to supply boundary conditions to a higher-resolution regional paleotidal model of the Lower Greensand Seaway. The regional paleotidal model shows that the tidal range of the Lower Greensand Seaway is largely controlled by the width of the connections to the open ocean. As sea levels rose during the Aptian, the oceanic connections widened, resulting in reduced frictional damping of the oceanic tidal wave. Coupled with funneling, shoaling, and Coriolis effects, this led to tidal amplification. Sensitivity tests using a variety of paleogeography and paleobathymetry scenarios suggest that the model predictions are robust. The global- to regional-scale paleotidal modeling presented here strongly suggests that there was a connection through France (in the Aube region of the Paris Basin) from the Neotethys Ocean to southeastern England. However, there are no time-equivalent deposits in this region to validate this suggestion. It is herein argued that that this is due either to postdepositional erosion or to low sediment supply coupled with strong tidal currents sweeping the seafloor to exposed bedrock.

Tidal Modeling of an Ancient Tide-Dominated Seaway, Part 1: Model Validation and Application to Global Early Cretaceous (Aptian) Tides

Abstract The utility of deep-time global paleotidal modeling is evaluated with a series of modeling experiments focused on the Early Cretaceous (Aptian). The results from a series of paleobathymetry sensitivity experiments indicate that, despite paleogeographic and paleobathymetric uncertainty, appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods. Before being applied to global paleotidal modeling, the Imperial College Ocean Model (ICOM) is validated for the computation of modern global tides. The ICOM results only deviate slightly from a “state-of-the-art” published model and were achieved with considerably less computational expense and without data assimilation. The results from global paleotidal modeling of the Early Cretaceous (Aptian) were assessed by comparison with the published geological record. ICOM predicts high mesotidal to macrotidal ranges on the Arabian Platform, around India (especially to the north and west), along the Pacific coast between North and South America, northeast of Australia, and around Southeast Asia. The model predicts low microtidal ranges in the proto-South Atlantic Ocean and Weddell Sea. A further validation test assessed the ability of the model to predict the dominant tidal constituents (diurnal or semidiurnal) in the Aptian “Lower Greensand Seaway” of southeastern England and Northern France. During the Aptian this region was connected to the Boreal, Proto-Atlantic, and Neotethys oceans and now preserves superbly documented tidal deposits. The model predicts low microtidal ranges in the proto-Central Atlantic Ocean and Boreal Ocean, suggesting that they had little impact on tides in the Lower Greensand Seaway. Higher tidal amplitudes, especially of diurnal (once-daily) tides, are predicted in the northwestern Neotethys Ocean, suggesting that this ocean was an important source of tidal energy to the Lower Greensand Seaway. Sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust. The prediction of predominantly diurnal tides is supported by published analyses of large dune-scale deposits in the Lower Greensand of southeast England.

Biostratigraphic characterization by means of ammonoids of the lower Aptian Oceanic Anoxic Event (OAE 1a) in the eastern Iberian Chain (Maestrat Basin, eastern Spain)

It is now generally accepted that the Oceanic Anoxic Event 1a [OAE 1a] correlates with the lower part of the Leupoldina cabri planktonic foraminiferal Zone. Its calibration against the standard ammonite scale, however, seems to be more problematic. This is due, in part, to the fact that ammonites are scarce and/or of little diagnostic value from a biochronological viewpoint in the lower Aptian pelagic successions where the black shale horizons are better developed. We have been able to characterize OAE 1a geochemically in the relatively shallow water deposits of the eastern Iberian Chain (Maestrat Basin, eastern Spain), where ammonite faunas are rich. The interval corresponding to this event is dominated by the genera Roloboceras and Megatyloceras, accompanied by Deshayesites forbesi and Deshayesites gr. euglyphus/spathi. This assemblage is characteristic of the middle/upper part of the Deshayesites weissi Zone. The first occurrence of the species Deshayesites deshayesi (d'Orbigny), which marks the base of the overlying zone, takes place in our sections some metres above the OAE 1a interval. In the historical stratotype region of Cassis-La Bédoule (southern Provence Basin, southeastern France), the OAE 1a interval is also characterized by the presence of Roloboceras and Megatyloceras. Nevertheless, it has usually been correlated with the D. deshayesi Zone. In our opinion, this discrepancy is due to divergences in the taxonomic assignments of the deshayesitids present in these beds. In fact, the specimens attributed by French authors [Ropolo, P., Conte, G., Gonnet, R., Masse, J.P., Moullade, M., 2000. Les faunes d'Ammonites du Barrémien supérieur/Aptien inférieur (Bédoulien) dans la région stratotypique de Cassis-La Bédoule (SE France): état des connaissances et propositions pour une zonation par Ammonites du Bédoulien-type. Géologie Méditerranéenne 25, 167–175; Ropolo, P., Moullade, M., Gonnet, R., Conte, G., Tronchetti, G., 2006. The Deshayesitidae Stoyanov, 1949 (Ammonoidea) of the Aptian historical stratotype region at Cassis-La Bédoule (SE France), Carnets de Géologie / Notebooks on Geology Memoir 2006/01, 1–46.] to D. deshayesi and D. dechyi can be reinterpreted as belonging to D. forbesi. Following this reinterpretation, the Roloboceras beds (equivalent of OAE 1a) of Cassis-La Bédoule would also correspond to the D. weissi Zone. This age is additionally corroborated by data from southern England [Casey, R., 1961a. The stratigraphical palaeontology of the Lower Greensand. Palaeontology 3, 487–621; Casey, R., 1961b. A Monograph of the Ammonoidea of the Lower Greensand, part III. Palaeontographical Society, London, pp. 119–216], and by our recent observations in Le Teil (Ardèche Platform, southeastern France), where the Roloboceras faunas are also associated with Deshayesites consobrinus and Deshayesites gr. euglyphus, taxa that are characteristic of the D. weissi Zone.

Clay mineralogy of the Cretaceous strata of the British Isles

AbstractThe clay mineralogy of the Cretaceous strata of the British Isles is described and discussed within its lithostratigraphical and biostratigraphical framework using published and unpublished sources as well as 1400 new clay mineral analyses. The regional clay mineral variation is described systematically for the following strata:(1)Southern England — Purbeck Limestone Group (Berriasian/Ryazanian; Lulworth and Durlston formations), Wealden Group (Valanginian—Barremian/Aptian; Ashdown, Wadhurst Clay, Tunbridge Wells Sands, Grinstead Clay Member, Wealden Clay, Wessex and Vectis formations), Lower Greensand (Aptian—Lower Albian; Atherfield Clay, Hythe, Sandgate, Folkestone Sands, Ferruginous Sands, Woburn Sands and Faringdon Sponge Gravels formations), Selborne Group (Middle—Upper Albian; Gault Clay and Upper Greensand formations) and the Chalk Group (Cenomanian—Lower Maastrichtian).(2)Eastern England — Cromer Knoll Group (Ryazanian—Upper Albian; Speeton Clay, Spilsby Sandstone, Sandringham Sands, Claxby Ironstone, Tealby, Roach Ironstone, Dersingham, Carstone and Red Chalk (or Hunstanton Red Limestone) formations).(3)Scotland — Inner Hebrides Group (Cenomanian—Campanian; Morvern Greensand, Gribun Chalk, Coire Riabhach Phosphatic Hibernian Greensands formations).(4)Northern Ireland — Hibernian Greensands (Cenomanian—Santonian) and Ulster White Limestone formations (Santonian—Lower Maastrichtian).The stratigraphical patterns of clay mineral variation divide naturally into two types; firstly, the more complex pattern of the Lower Cretaceous strata and secondly, the simple pattern of the Upper Cretaceous. Clay mineral variations in the non-marine and marine Lower Cretaceous strata of England are best explained by the interplay of two main clay mineral assemblages between which all gradations occur. The assemblage which dominates the main clay formations consists of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals, and sometimes includes vermiculite and traces of chlorite. It is dominantly of detrital origin and detailed evidence indicates it is derived largely from the reworking of Mesozoic sediments although ultimately from weathered Palaeozoic sediments and metasediments. Although mainly of detrital origin, this assemblage contains a persistent component that formed coevally with the approximate depositional age of its host sediment. Whether this component is of soil origin or was neoformed in the sediment shortly after deposition is unclear. There is little firm evidence indicating the sources of this clay mineral detritus. However, in the strata of the Wealden Group of southern England, mineral trends suggest three sources; one of these was to the west (Cornubian Massif), another must have been the Anglo- Brabant landmass. In the Selborne Group (Middle—Upper Albian) and in the overlying Lower Chalk (Cenomanian) where this assemblage makes its last appearance in the Cretaceous of England, there is good evidence of easterly and south-easterly sources.The second main assemblage tends to be largely monominerallic, and usually dominated by smectite with or without small amounts of mica; less frequently, kaolin, berthierine or glauconite sensu lato is the sole or dominant component. It is considered to be of volcanogenic origin, derived from the argillization of volcanic ash under different conditions of deposition and diagenesis. The source of the ash in Berriasian—Aptian times seems to have been an extensive volcanic field in the southern part of the North Sea and in the Netherlands, whereas in the Albian (and extending into the Cenomanian) a westerly source dominated. The current controversy about the role of climate or pattern of volcanic activity controlling the clay mineral stratigraphy of the Lower Cretaceous is reviewed.In the lower part of the Upper Cretaceous strata of England, Scotland and Ireland, sand-grade glauconite is particularly abundant. Much of it represents the glauconitization of pene- contemporanous volcanic ash, possibly of basaltic origin, associated with continental breakup and the opening up of the Atlantic Ocean and the earliest stages in the development of the Hebridean Tertiary Igneous Province. The Upper Cretaceous Chalk facies of England and Ireland is dominated by a smectite-rich clay assemblage containing mica, and the various hypotheses for its origin (detrital, neoformation, volcanogenic) are reviewed in the light of available mineralogical, chemical and geological data.

Mid-Cretaceous pCO2 based on stomata of the extinct conifer Pseudofrenelopsis (Cheirolepidiaceae)

Stomatal characteristics of an extinct Cretaceous conifer, Pseudofrenelopsis parceramosa (Fontaine) Watson, are used to reconstruct atmospheric carbon dioxide ( p CO 2 ) over a time previously inferred to exhibit major fluctuations in this greenhouse gas. Samples are from nonmarine to marine strata of the Wealden and Lower Greensand Groups of England and the Potomac Group of the eastern United States, of Hauterivian to Albian age (136–100 Ma). Atmospheric p CO 2 is estimated from the ratios between stomatal indices of fossil cuticles and those from four modern analogs (nearest living equivalent plants). Using this approach, and two calibration methods to explore ranges, results show relatively low and only slightly varying p CO 2 over the Hauterivian–Albian interval: a low of ∼560–960 ppm in the early Barremian and a high of ∼620–1200 ppm in the Albian. Data from the Barremian Wealden Group yield p CO 2 values indistinguishable from a soil-carbonate–based estimate from the same beds. The new p CO 2 estimates are compatible with sedimentological and oxygen-isotope evidence for relatively cool mid-Cretaceous climates.

Transgressive changes from tidal estuarine to marine embayment depositional systems: The Lower Cretaceous Woburn Sands of southern England and comparison with Holocene analogs

The Lower Cretaceous Woburn Sands (Lower Greensand Group) in southern England constitutes one of the most intensively studied tidal sandstone outcrops for sedimentological and reservoir analog studies. Most recent workers have interpreted the whole 30–60-m (100–200-ft)-thick succession around Leighton Buzzard as representing an ancient tide-dominated estuary. However, unequivocal estuary characteristics are limited to the lowermost part (about 15–20 m [50–66 ft]). We suggest that a significant portion of the Woburn Sands, and most of the middle part, was formed in a tide-dominated marine embayment. Hence, the vertical facies change from the lower to middle part of the Woburn Sands is interpreted as a change from (1) a narrow estuary to (2) a broad marine embayment. The Wash embayment in eastern England is a striking modern analog; it receives most of its sediments and waters from marine sources and is largely filled with nondiluted seawater. Moreover, the Holocene transgressive history of The Wash is remarkably similar to the transgressive evolution of the Woburn Sands. Early estuarine sequence models predict landward translation of facies zones along the valley thalweg during transgression, but eventual facies translation in the strike direction has not been fully documented or discussed. An embayment facies that is not commonly confined in the early incised valley can occur vertically between the estuarine valley fill and marine shelf deposits and is probably underrepresented in current models. However, this segment of the transgression, comprising along-strike bay expansion and the development of a broad marine embayment, may be more important than previously thought.

The potential for methane emissions from groundwaters of the UK

Methane (CH 4) is only a trace constituent of the atmosphere but an important greenhouse gas. Although groundwater is unlikely to be a major source of atmospheric CH 4, its contribution to the CH 4 budget of the UK has up to now been poorly characterised. Groundwater CH 4 concentrations have been measured on 85 samples from water-supply boreholes and a further eight from other miscellaneous water sources. Concentrations in abstracted groundwaters ranged from <0.05–42.9 μg/l for Chalk, <0.05–22 μg/l for the Lower Greensand, 0.05–21.2 μg/l for the Lincolnshire Limestone and from <0.05–465 μg/l for the Triassic sandstone. Having the largest abstraction volume, the Chalk is likely to be the main UK groundwater contributor to global CH 4 emissions. A calculation to estimate the total emissions of CH 4 from water-supply groundwater sources based on the median and the maximum CH 4 concentrations gave values of 2.2×10 −6 and 3.3×10 −4 Tg/year. Estimates show groundwater contributes a maximum of 0.05% of all UK CH 4 emissions and a further two orders of magnitude less in terms of the global CH 4 budget. Other groundwater sources such as inflows to tunnels may have significantly higher CH 4 concentrations, but the volume of water discharged is much lower and the overall amount of CH 4 outgassed is likely to be of the same order as the aquifer release. The generally low concentrations of CH 4 in groundwater supplies suggest no threat of explosion, although groundwater released by excavations remains a hazard.

Reuse of quarry fines in production of secondary aggregates

Large volumes of wastes are associated with the production of aggregates and dimension stone. Fine-grained wastes are particularly problematic and are deposited in settlement ponds or managed by stockpiling until backfill space becomes available. Although these fine materials have poor engineering properties, when they are mixed with hydraulic binders in a CO2-rich atmosphere, they can be bound together to form pellets suitable for use as aggregates. In the present work, a by-product called hassock, which originates from the quarrying of Kentish ragstone, is investigated for use as secondary aggregate. In excess of 200000 t of this poor-quality fine-grained material, originating from the Lower Greensand Formation of southern England, are disposed of each year. Hassock waste was blended with other solid waste products, namely cement kiln dust, ground granulated blast furnace slag and pulverised fuel ash, and was pelletised in a CO2-rich atmosphere. The pellets, produced by carbonate cementation; typically have a pH of 9–9·5 and aggregate impact values ranging from 14 to 19.

The bennettitalean trunk genera Cycadeoidea and Monanthesia in the Purbeck, Wealden and Lower Greensand of southern England: a reassessment

The history of the discovery of the Lower Purbeck dirt-beds on the Isle of Portland and the silicified bennettitalean trunks occurring within these fossil soils is reviewed and discussed. In the absence of the original type material, neotypes are selected for the two poorly-defined Purbeck species Cycadeoidea megalophylla Buckland and Cycadeoidea microphylla Buckland. A third cycadeoid trunk species, Cycadeoidea gigantea Seward, from higher in the Portland Purbeck sequence, is reassigned to the genus Monanthesia Wieland ex Delevoryas, the use of which is discussed in relation to the genus Cycadeoidea Buckland. Synonymies are presented for both genera and for all the more or less recognisable named species from the English Lower Cretaceous. Newly collected specimens from the Isle of Wight support the view that loose beach specimens of Cycadeoidea and Monanthesia trunks, formerly considered to be from the Wealden, are actually from the Lower Greensand. It is suggested that additions to our knowledge of English cycadeoid trunks can only be achieved by the use of invasive techniques, which are recommended for the further study of type specimens.

Fossil-wood carbon-isotope stratigraphy of the non-marine Wealden Group (Lower Cretaceous, southern England)

Fossil-wood carbon-isotope data are presented for the Wessex Formation, a non-marine unit within the Lower Cretaceous (Valanginian–Barremian) Wealden Group of the Isle of Wight and Dorset, southern England. The carbon-isotope values have a range (δ 13 C c . −26.6 to −19.8‰) that is consistent with that expected for Mesozoic C 3 plants. Consideration of the Isle of Wight fossil-wood carbon-isotope data together with data from Dorset allows construction of a composite fossil-wood carbon-isotope curve for almost the entire Wealden Group. The new carbon-isotope curve is in smooth continuity with data previously published from the overlying lagoonal Vectis Formation and marine Lower Greensand Group of Aptian age. A tentative correlation with a Tethyan reference carbon-isotope curve allows the provisional application of stage-level chronostratigraphy to the Wealden Group. Correlations suggest that the Wealden Group sediments are dominantly of Hauterivian and Barremian age and that the Valanginian is either condensed or partially missing. The carbon-isotope data presented indicate that even during times of relative carbon-cycle quiescence atmosphere CO 2 faithfully tracks the carbon-isotopic composition of the oceanic reservoir.

The geochemistry of boron and its isotopes in groundwaters from marine and non-marine sandstone aquifers

The geological evolution of B in two UK sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones. Measurements have been made of major element geochemistry, B concentrations and B isotopic ratios. The isotopic measurements were carried out using ICP/MS following a simple preconcentration step. Isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of Atlantic air over Britain and depleted signatures representative of continental air. In the marine Lower Greensand aquifer dissolution of glauconite results in the mobilisation of B and a correlation with SO4 suggests that this dissolution is related to the oxidation of pyrite which appears to be the SO4-forming reaction in the aquifer. In the non-marine Hastings beds isotopic ratios and a correlation with HCO3 suggest that B is associated with the dissolution of ferroan carbonates. In both aquifers the geochemical evolution of B is complex and more information is needed on the behaviour of B isotopes during evapotranspiration and groundwater recharge.

Palaeowaters in the aquifers of the coastal regions of southern and eastern England

Abstract The marked climatic changes that occurred during the Late Quaternary and Holocene have had a significant impact on the evolution of the groundwater systems at and near the English coastline. Lowered sea levels and the emergence of a much larger landmass over most of the past 100 ka have also ensured deeper groundwater circulation in the vicinity of the modern coastline. The impacts on the Chalk and Lower Greensand (Albian) aquifers along the English Channel and North Sea coasts are examined, using mainly geochemical and isotopic evidence, especially from borehole depth profiles and interstitial waters. Along the south coast, fresh groundwaters are found to depths of 250–300 m below OD (ordnance datum) in the Brighton-Worthing area, as well as beneath Poole Harbour, which are related to deeper circulation during lowered sea levels, controlled by the central palaeovalley of the English Channel. In contrast, pockets of saline groundwater are found, protected in east-west structures, which are considered to be little-modified Chalk formation waters. In the Albian sands, near Worthing, freshwaters dating to 7 ka are found at a depth of −450 m OD, suggesting that movement of groundwater towards the shoreline and possibly beyond is still occurring. The east-west structures also influence groundwater migration in north Kent, where fresh palaeowaters can be identified beneath saline water which invaded during the Holocene sea-level rise. In the East Midlands Sherwood Sandstone aquifer, freshwater is found to a depth of −500 m OD, showing continuous geochemical evolution probably over a period of 100 ka, although an ‘age gap’ of between c. 20 and 10 ka c. corresponds to permafrost cover. These palaeowaters in coastal and near-coastal areas remain effectively isolated from the active present-day meteoric flow system but represent high-value resources that may, in some cases, extend offshore.

Modelling the impact of predicted climate change on landslide frequency and magnitude in SE England

General circulation models (GCMs) predict an increase in rainfall and temperature for SE England as a consequence of the build up of greenhouse gases and sulphate aerosols in the global atmosphere. This paper uses a geographical information system (GIS)-based combined slope hydrology/stability model linked to downscaled GCM data to assess the likely impact of such a change on the frequency and magnitude of landslide activity. The model has been applied to a 4 km section of the Lower Greensand escarpment near Hythe, Kent, SE England which has a history of landslide activity, and is typical of many inland landslides in SE England. The results indicate that increases in rainfall will be matched by increases in evapotranspiration, leaving the frequency of large landslides unchanged. However, the modelling suggests an increased dynamism of shallow soil moisture stores which may lead to a reduction in frequency of smaller landslides over the next 80 years.

Anomalous cross-bedding directions in the late Aptian Lower Greensand of southern England and their possible correlative significance

Palaeocurrent data for the Lower Greensand indicate a preponderance of flow to the southeast but evidence for current flow to the northwest has been obtained from late Aptian Lower Greensand successions near Nutfield (Surrey), Caine (Wiltshire) and Leighton Buzzard (Bedfordshire). It is argued that these anomalous palaeocurrent directions represent current flow in relatively shallow water and that such conditions are likely to have existed during a specific period of relatively low sealevel stand in the late Late Aptian. On this basis the occurrence of anomalous cross-bedding directions may be used to establish a correlation between northern and southern Lower Greensand successions within an interval noted for its poor biostratigraphic record.