Lower Greensand Research Articles

Field Meeting, 24–5 April, 1993: the Lower Cretaceous of the Isle of Wight

A general field introduction to the stratigraphy and palaeontology of the Lower Cretaceous Wealden and Lower Greensand Groups was provided, with special emphasis on Wealden vertebrate localities. Recently discovered material from these localities was made available at the Museum of Isle of Wight Geology. An unrecorded insect fauna was recovered from the Vectis Formation of the Wealden Group during the field meeting and is briefly documented.

Influence of soil-extractable aluminium and pH on the uptake of aluminium from soil into the soybean plant (Glycine max)

The effects of soil pH and other soil properties on the uptake of AI by soybean plants have been investigated in a greenhouse experiment. Six soils were compared that were developed over six contrasting bedrock types ranging widely in their AI content and other chemical and physical characteristics, namely Oxford Clay, Chalk, Lower Lias Clay, Devonian Shale, Granite and Lower Greensand. Soil pH varied naturally between soil types and each soil was also amended to give two other pH levels using elemental sulphur and/or calcium carbonate. AI concentrations in various parts of the soybean plants were determined by ICP-AES after acid digestion. The AI solubility in the soils and hence its availability to the plants was estimated using a number of different reagents designed to extract different forms of AI.The AI concentration measured in the soybean leaves was found to be predicted most accurately by the 'available' AI extracted from soils by 0.02 M CaCl2. The relationship appears to the linear, with a correlation coefficient of 0.97 (p <0.01). The AI content of the leaves increases with decreasing soil pH. The relationship is non-linear with a marked increase in leaf AI for soils with pH <4.4. The amounts of 'plant-available' AI in the soils extracted with 0.02 M CaCl2 was much less than that extracted with 0.05 M EDTA, although both increased markedly with decreasing soil pH. The amount of AI measured in the soybean plants was directly related to both the 'available' forms of AI in the soils, and also to the pH of the soils. Soil pH was identified as a major factor that controls the uptake of Al from soil into the soybean plant.

Beryllium in river baseflow, shallow groundwaters and major aquifers of the U.K.

Beryllium is potentially a highly toxic element which may be mobilised especially under acidic conditions in natural waters. Results from major aquifers, the unsaturated zone, from shallow groundwaters and river baseflow were used to establish the naturally occurring, baseline concentrations in U.K. waters. Out of 924 samples from 13 aquifer units Be was detected in only 12 samples. In carbonate aquifers no Be was found above the detection limit of 0.05 μ g/l. The occurrence of Be >0.05 μ g/l was restricted to arenaceous aquifers where concentrations up to 1 μ g/l Be were found mainly in the Carboniferous Millstone Grit and Lower Cretaceous Lower Greensand aquifers. Interstitial water profiles from the unsaturated zones of the Lower Greensand (Surrey) and Triassic sandstone (West Midlands) contain Be concentrations in excess of 10 μ g/l within the top 10 m which may persist to the water table at concentrations near to 1 μ g/l Be. The only major anomaly to be found in river baseflow was from the Mourne Mountains of Northern Ireland where Be concentrations of up to 4.7 μ g/l were found associated with the outcrop of the Tertiary granite intrusion. Elsewhere, Be (0.22 μ g/l) was found in neutral groundwaters derived from granite feeding the acid Loch Fleet (southern Scotland) in which concentrations of 0.09 μ g/l were maintained. Beryllium occurrence therefore depends strongly on geology. The predominant aqueous species below pH 5.5 is Be 2+ and above this Be(OH) + dominates. The presence of high Al in most waters sampled greatly suppresses the formation of BeF complex ions. Beryllium shows close geochemical behaviour with Mg across a range of pH which may have environmental consequences, if Be substitution for Mg takes place.

Early to mid-Cretaceous tectonics and unconformities of the Wessex Basin (southern England)

Sediment distribution patterns, time-subsidence plots, seismic data and outcrop analysis of the Lower Cretaceous (?Ryazanian-Albian) of the Wessex Basin, southern England, suggest that a number of unconformable horizons exist and that there is no single ‘late Cimmerian unconformity’ surface. A tectonic change, from areally restricted deposition in the Weald and Channel sub-basins to extensive sedimentation across the whole of southern England, began in the mid-Aptian. This change ended with transgression of basement ‘highs’ in the early Albian of the Dorset area, and later Albian of the Devon and London Platform basin margin areas: its onset can be linked to the Austrian tectonic phase of Europe. The onset of marine deposition in the Aptian is coincident with periodic transgression of the margins of the Wessex Basin throughout the Aptian-Albian. Mid-late Aptian and early/mid-AIbian transgressions were preceded by periods of erosion. The Aptian-Albian Lower Greensand is characterized by transgressive-regressive phases, suggesting a short-term controlling process (third-order eustatic changes or intra-plate mechanisms). Tectonic changes in the mid-Aptian include uplift followed by widespread subsidence. This change coincides with a time of plate reorganization in the European and North Atlantic areas.

Trace metals in interstitial waters from sandstones: acidic inputs to shallow groundwaters

There is some evidence from southern Britain that shallow groundwaters in non-carbonate lithologies may be affected by acidic deposition. To investigate this, interstitial water profiles down to 12 m have been obtained from unsaturated sands or semi-consolidated sandstones from the Folkestone Beds (Lower Greensand) of Surrey and the Sherwood Sandstone of the West Midlands. The pH of the interstitial waters generally increased with depth and reflected an increase in the base saturation of the exchange complex. Beneath the highly acidic surface soil horizons (pH 3·0–3·5), interstitial waters with a pH of 4·0–4·5 were found down to depths of several metres. The pH progressively increased to around pH 5·5 because of base cation desorption and the weathering of silicate minerals. High concentrations of aluminium (10–20 mg litre −1) and other metals (Fe, Mn, Cu, Ni, Co, Zn, Be) were found in the interstitial water in the upper unsaturated zone. Most metal concentrations were strongly pH-dependent but also reflected the geochemical characteristics of the parent sands or sandstones. H + and trace element concentrations were slightly higher beneath areas of afforestation than beneath heathland. The downward fluxes of solutes have been estimated using rainfall-derived chloride as a non-reactive solute. The profiles retain a record of 10–20 years input allowing the past inputs from SO 4 and other species to be estimated using solute/chloride ratios. Cation exchange sites are probably depleted over a period of decades and there can be a significant decrease in the unsaturated zone pH as a result of increased or sustained acidic deposition. The shallow groundwater environment (0–15 m) in non-carbonate terrains is therefore a sensitive environment where high metal concentrations may be generated and may ultimately lead to water quality problems in shallow water supplies.

Correlation of the Hythe Beds Formation (Lower Greensand Group: early-mid-Aptian), southern England

The outcrop and sub-surface stratigraphy of the Hythe Beds Formation shows a coarsening-up cyclicity in the arenaceous successions of the western Weald Basin (Hants. & Surrey), and in the glauconitic/argillaceous deposits of Sussex/Kent. Correlation can be achieved through the identification of hiatus surfaces, the most distinctive of which are dark, smectite-enriched clays with belemnites and phosphate nodule beds. These beds are interpreted to be the product of transgressive conditions. Correlation may be difficult in clastic shelf successions: the use of distinctive transgressive event beds provides a model for other successions displaying similar facies.

The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment

The Gault-Lower Greensand Junction Beds at representative sections from Bentley, Hampshire in the west, to Folkestone in the east, in southern England, and at Wissant on the opposite French coast are described, some in detail for the first time, others revised from earlier accounts. The nature of the deposits reflects the occurrence of periods of sediment deposition followed by intervals of submarine current scour and phosphatic pebble bed formation. This is associated with the basic transgressive change from shallow water conditions of the late Lower Greensand sea ( Leymeriella acuticostata Subzone), to the deeper and less turbulent water environment in which clay-grade sediments of the Gault were able to be deposited over the region of southern England and northern France. The sediments are dated by ammonites and range in age from the Leymeriella regularis Subzone ( Leymeriella tardefurcata Zone), through the Superzone of Douvilleiceras mammillatum (both Lower Albian) into the early Middle Albian Lyelliceras lyelli Subzone ( Hoplites dentatus Zone), but at no single locality is a continuous sediment sequence preserved. The only evidence of tectonic activity is a folding phase at the end of the acuticostata Subzone followed by planation, which separates the sandwave and lagoonal environment of the bulk of the Folkestone Beds and Woburn Sands from that of the relatively flat-bedded Gault-Lower Greensand Junction Beds.

Sequence stratigraphic analysis of the Aptian-Albian Lower Greensand in southern England

Facies analysis and its use in sequence stratigraphy is described using the Lower Greensand of southern England as an example, and the resulting interpretations are outlined. This work forms an independent test of sequence stratigraphic techniques and the Exxon ‘cycle chart’. Sequence stratigraphy is a very powerful tool in the analysis of problematic successions, although some modification is made here in emphasizing the use of the transgressive surface. Changing palaeoenvironmental conditions, and the effect that palaeoceanography has on the recognition of sequence boundaries, are also discussed. Broad agreement is found between these results and the cycle chart, although changing tidal conditions alter the criteria available for analysis of the Aptian-Albian Lower Greensand succession. Comparison between this study and sequence stratigraphic analyses conducted in the more condensed type sections of England and France shows that further sequence boundaries are recognizable.

The influence of tectonics on early Cretaceous sedimentation in Bedfordshire, England

The Lower Cretaceous sediments of the Bedfordshire area are Aptian and Albian in age. During this time the area was situated within an extensional tectonic regime, and the pattern of sedimentation, in terms of lateral variation both in sediment type and thickness, reflects the influence of normal faulting. Jurassic topography, created by block faulting and erosion, controlled the distribution of later facies largely by continued tectonic processes, especially the reactivation of the Jurassic fault block system, which produced syn-sedimentary faulting of the overlying sequence. Thus the ‘traditional’ view of the infill of an erosional basin by the Lower Greensand is challenged.

Geophysical correlation of the Aptian and Albian formations in the Wessex Basin of southern England

AbstractUsing geophysical borehole log signatures and basic lithological information from sidewall cores and well-cuttings, division and correlation of the mid-Cretaceous sediments of the Wessex Basin can be achieved. A sub-Gault (early Albian) unconformity surface is mapped with some accuracy across the Hampshire–Dorset area, and the deposits of a previous, Aptian transgression are observed. The distinctive log signatures aid in facies reconstructions and sequence stratigraphical analysis: especially the onlap of basal Gault horizons onto and across basement ‘highs’. The highly variable thickness and lithological distributions characteristic of the Wealden pass upward into laterally extensive facies distributions in the Lower Greensand and Gault. Sequence boundaries are identified at the base of the Wealden; Lower Greensand; Gault; within the Gault (cristatumsubzone); and base Chalk.

Changes in the provenance of pebbly detritus in southern Britain and northern France associated with basin rifting

Abstract Stratigraphical and geographical variations in the composition of pebble suites in Upper Jurassic and Lower Cretaceous rocks in southern Britain and northern France provide a means for studying both local and regional changes in tectonic conditions associated with basin development. Local variations in pebble suites provide evidence of major fault-associated uplift and erosion of intrabasinal and basin-margin highs during earliest Cretaceous times, and the subsequent post-faulting subsidence and marine onlap in mid-Cretaceous times. Regional provenance studies have demonstrated that the Upper Jurassic and Lower Cretaceous pebble suites of southern Britain and Normandy are separable into six assemblages. Assemblage 1 is dominated by Carboniferous shelf chert, and is typical of Upper Jurassic pebble suites in Oxfordshire and Wiltshire, and Cretaceous pebble suites reworked from these older pebble beds. This detritus was probably derived from the western margin of the Anglo-Brabant Massif. Assemblage 2 which is quartz dominated, includes Carboniferous basinal chert and tourmalinite, and is restricted to the Cretaceous pebble beds of Dorset. This assemblage was sourced principally from the Cornubian Massif. Assemblage 3 contains subequal proportions of quartz and Carboniferous shelf chert and is present in the Lower Greensand pebble beds of the Isle of Wight, Hampshire, Wiltshire and Oxfordshire and Wealden pebble beds in the western and southern Weald. The distribution of this assemblage implies its derivation from the eastern margin of the Welsh Massif. Assemblage 4 is characterized by a high proportion of sandstone clasts and is restricted to the Cretaceous pebble suites of Kent and East Sussex. Material in this assemblage was derived principally from the southern margin of the Anglo-Brabant Massif. Assemblage 5 is compositionally akin to assemblage 3 but is restricted to the Albian pebble beds of the East Midlands Shelf. This material was derived from the northern margin of the Anglo Brabant Massif, with minor amounts of material from the Market Weighton High. Assemblage 6 is quartz dominated and includes clasts of deformed sandstone and vein rock. This assemblage is restricted to the Aptian and Albian pebble beds of Normandy which are derived from the northern margin of the Armorican Massif. In the Weald and Central Channel Basins, a change from chert-dominated assemblage 1 suites to quartz-rich pebble suites (assemblages 2 to 5) occurred at the beginning of the Cretaceous as a result of uplift and erosion of the marginal massifs adjacent to the rifting basin, accompanied by a regional fall in relative sea level. In contrast, on the East Midlands Shelf modifications to the detrital suite did not occur until the mid-Cretaceous, due to the Early Cretaceous reworking of Mesozoic detritus on the Shelf, probably from the uplift and erosion of the Sole Pit area. Subsequently, with the onset of subsidence in the Sole Pit area and a regional marine transgression during Albian times, the adjacent massifs were rejuvenated causing an input of fresh clastic material onto the Shelf.

Recognition and documentation of depositional sequences from outcrop: an example from the Aptian and Albian on the eastern margin of the Wessex Basin

Stratigraphic data relating to the Aptian and Albian sediments around Folkestone in southeast England, on the eastern margin of the Wessex Basin, are plotted graphically to illustrate biostratigraphic gaps and condensed intervals. These are then used to suggest candidate sequence boundaries, notated LG1-4 and Gl-3, which are named after the Lower Greensand and Gault. The biostratigraphic subzones apparently unrepresented in the area are: LG1 obsoletus and bodei; LG2 gracite and debile; LG3 schrammeni; Gl bulliensis. Candidate sequence boundaries G2 (cristatum Subzone) and G3 (auritus Subzone) are erosion surfaces correlating with probable biostratigraphic gaps elsewhere in the basin. The age of LG4 is uncertain but must lie within the mammillatum Superzone. All candidate sequence boundaries correspond closely to those predicted by recent global sea-level cycle charts, and additionally there is a close match between predicted maximum flooding surfaces and the occurrence of condensed intervals. Most of the candidate sequence boundaries could have been formed as a result of rapid, and at least regionally extensive, relative sea-level falls, but the sedimentological contexts of LG3 and Gl suggest that these may have been generated by transgression-related sediment condensation. The minor sequence boundary in the loricatus Zone (intermedius Subzone) illustrated in the cycle charts cannot be unambiguously recognized at outcrop in the Folkestone area. Additional sequence boundaries not shown in the cycle charts may also be present in the Wessex Basin.

Stratigraphic relations of the Lower Greensand (Lower Cretaceous) of the Calne area, Wiltshire

The Lower Greensand (Aptian-Albian) around Calne in Wiltshire, lies on Jurassic Lower Kimmeridge Clay (mid- Aulacostephanoides mutabilis Zone) and comprises a lower, relatively clean, fine to medium grained sand, overlain by iron-rich poorly-sorted, medium to coarse grained sandstone. The upper beds are identified as the Carstone, but the lower sands are lithologically different from the closely adjacent Lower Greensand occurrences on the margins of the Wessex Basin. They are here named the Calne Sands Formation of the England). The Calne Sands form an areally-restricted sequence with sand-grade sediment coarsening upwards and a concomitant increase in clay content. Palynological evidence indicates that they are referable to the Hypacanthoplites jacobi Zone. The age and sedimentary facies contrast with the nearby Seend Ironsand ( Parahoplites nutfieldiensis Zone). Both occurrences however are interpreted as transgressive deposits infilling NW-SE palaeovalleys cut into Jurassic basement. The Calne Sands may infill a topography created during a post- nutfieldiensis base-level fall. Palaeocurrent indicators in the Calne Sands show a dominant north-westerly transport direction which is the opposite to that for coeval strata in other parts of the Wessex Basin.

Depositional trends in the Upper Jurassic-Lower Cretaceous of the northern margin of the Wessex Basin

In the exposed Upper Jurassic and Lower Cretaceous sediments along the northern margin of the Wessex Basin (Buckinghamshire to Wiltshire), structural and minor depositional basin orientations are often aligned NW to SE. Local depocentres in the late Jurassic and earliest Cretaceous rarely coincide with those of the mid-Cretaceous Lower Greensand. The “inversion” of these sub-basins is commonly across major NW-SE orientated faults; this change in the position of basins subsidiary to the Wessex Basin occurred in the time gap now represented by the base Lower Greensand unconformity (?Berriasian-mid-Aptian). It was during this time that subtle (or long term) shifts in basement structure became amplified. In this case sub-basin inversion is adequately explained by a long sedimentary hiatus rather than short lived active tectonism.

The mineralogy and petrography of the Sulphur Band phosphates (Aptian-Albian), at Folkestone, Kent

A series of phosphate nodule horizons occur at the junction of the Lower Greensand (Folkestone Beds), and the Gault at Folkestone in Kent, each layer representing a hiatus in sedimentation. The most complex of these is the Sulphur Band, which has been subjected to a detailed petrographic and geochemical analysis in order to gain insights into methods of formation, as well as compare this phosphate deposit to those above and below. Some method of quantifying the relative time period represented by each phosphate nodule horizon is attempted, and a comparison with the Hythe Beds-Sandgate Beds junction is made.

The geology of some Middlesex churches

Most of the older churches of Middlesex (11th to 14th century) contain a building material which has not received serious attention until recent years, variously called ‘gravel-stone’, ‘rubblestone’ or ‘ironstone’. On analysis, and plotted in relationship to superficial deposits and solid geology across the area, this material can be demonstrated as reflecting the underlying subsoil and outcrop, locally consolidated by mineral cementation from groundwaters. Otherwise, Kentish Rag (from the Lower Greensand near Maidstone) and Reigate Stone (Upper Greensand) were widely used in Middlesex churches in such a way as to show that their differing resistance to weathering was clearly appreciated.

Goethite ooids: growth mechanism and sandwave transport in the Lower Greensand (early Cretaceous, southern England)

AbstractThe Woburn Sands (Lower Greensand Group, Aptian–Albian age), in Billington Crossing quarry, Leighton Buzzard, Bedfordshire, England, show, along bedding planes of tabular cross-stratification, foreset alternations of quartz grains and goethitic ooids. Field and petrographic evidence suggest that: (a) the goethite in the layers and cores is primary; (b) the ooids formed by mechanical accretion of original Fe-hydroxide gels around nuclei on the sea-floor in shallower nearshore adjacent environments; (c) goethite cores of some ooids represent an earlier stage of iron deposition within the sediment where silica adsorbed by the iron-gels segregated in inclusions; (d) short-term variations in current strength and iron supply are responsible for the different arrangements of goethite platelets (tangential to random to radial) in the ferruginous layers in connection with the degree of crystallization of the colloidal iron during the accretion stage; (e) the ooids were then swept away in deeper waters by tidal action where their segregation in the lower parts of each foreset lamina is believed to have been hydraulically controlled.

Palaeoecology and event stratigraphy of the Wealden-Lower Greensand transition in the Isle of Wight

Event stratigraphy combines sedimentological, trace fossil and palaeoecological criteria, in identifying six fades associations in the Vectis Formation (Weald Shales) of the Isle of Wight. This sequence suggests that prior to deposition of the marine Lower Greensand (Aptian-Albian), the Vectis Formation underwent a gradual increase in marine influence. Storm/flood event beds are common, and black shales with a lack of benthos are ascribed to limited oxygenation in the Vectis Formation lagoon. As far as eustatic models are concerned it is suggested that the Upper Barremian to Aptian sea-level rise was gradual, the Perna Beds (lowest Aptian) forming at the restricted to normal marine transition during a period of base-level rise.

The stratigraphy and palaeontology of the Lower Greensand of the Hoes Farm Borehole, near Petworth, Sussex

The Hoes Farm Borehole provides a cored sequence through the Atherfield Clay, Hythe Beds and the lowest part (Fittleworth Beds) of the Sandgate Beds. Macrofaunas and ostracods have been collected from many levels and, for the first time, the Ostracoda from the English Aptian have been examined over an extended sequence with good macropalaeontological control. A 0.7 m seam of fuller's earth, recorded near the base of the Hythe Beds, yielded an ostracod fauna of bowerbanki Zone age. A new stratal unit, the Hoes Farm Member, mainly of deshayesi Zone age, has been defined at the base of the Hythe Beds.

Thermal energy storage in the Lower Greensand aquifer in Cambridgeshire : Kitching, R; Adams, B Q J Engng Geol V19, N2, 1986, P143–154

Thermal energy storage in the Lower Greensand aquifer in Cambridgeshire : Kitching, R; Adams, B Q J Engng Geol V19, N2, 1986, P143–154