Chalk Of England Research Articles

Development of spatial permeability variations in English Chalk aquifers

Abstract The Cretaceous Chalk in England forms dual-porosity aquifers, with low-permeability matrix and high-permeability networks of fissures, which are predominantly stress-relief fractures that have been enlarged by dissolution. This enlargement is a function of the volume of water that has passed along a fracture (the flowrate effect) and its degree of chemical undersaturation. Feedback effects result in the development of a distinctive permeability structure, with four particular characteristics: (i) troughs in the water table with high transmissivity and convergent groundwater flow; (ii) substantial increases in transmissivities in a downgradient direction; (iii) downgradient decreases in hydraulic gradient; and (iv) discharge from the high-transmissivity zones to the surface commonly at substantial springs. This distinctive self-organized permeability structure occurs throughout unconfined chalk aquifers. Early enlargement of fissures at a depth of 50–100 m below the water table is slow, but is much more rapid close to the water table and in the uppermost bedrock due to non-linear dissolution kinetics. A modelled dissolution profile shows that more than 95% of dissolution takes place in the top 1 m of bedrock, and that enlargement of fissures in the saturated zone results from progressive dissolution occurring over a period of a million years or more.

Self‐Potential as a Predictor of Seawater Intrusion in Coastal Groundwater Boreholes

AbstractMonitoring of self‐potentials (SPs) in the Chalk of England has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion (SI) and that this gradient is absent in boreholes further inland. Furthermore, a small but characteristic reduction in this gradient was observed several days prior to SI occurring. We present results from a combined hydrodynamic and electrodynamic model, which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of SP. The model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials, the exclusion efficiency, in different rock strata. Geoelectric heterogeneity, largely due to marls and hardgrounds with a relatively high exclusion efficiency, was the key factor in controlling the magnitude of the modeled SP gradient ahead of the saline front and its evolution prior to breakthrough. The model results suggest that, where sufficient geoelectric heterogeneity exists, borehole SP may be used as an early warning mechanism for SI.

Christopher John Wood (18 August 1939–27 January 2016): Palaeontologist and ‘owl’ of the Cretaceous

Chris Wood enhanced the world of Cretaceous research for more than 50 years. His British Geological Survey work helped develop the lithostratigraphy and biostratigraphy used to build the framework for investigating and then remapping the Chalk in England and Northern Ireland. In recognition of his work on the English Northern Province Chalk of the Lincolnshire and Yorkshire Wolds, the Yorkshire Geological Society presented him their most prestigious award, the John Phillips Medal, in 2015. His knowledge of the Chalk was also sought and applied to many engineering projects including the Channel Tunnel. In the international arena his palaeontological studies, in conjunction with the many European colleagues he corresponded with, contributed greatly to defining Cretaceous Stage and Substage concepts using a wide range of faunal indices which he also applied to the British successions. Having taught himself German he developed a lifelong working relationship with German colleagues, especially Gundolf Ernst and his research students in Berlin. Latterly, his special focus was on inoceramid bivalve fossils, working closely with Polish colleagues, in recognition of their abundance in the Upper Cretaceous and potential use as substage indices. His final years were marked by reviewing and editing papers for the journals Acta Geologica Polonica and Cretaceous Research.

Problems with determining the particle size distribution of chalk soil and some of their implications

Particle size distribution (psd) is one of the most important features of the soil because it affects many of its other properties, and it determines how soil should be managed. To understand the properties of chalk soil, psd analyses should be based on the original material (including carbonates), and not just the acid-resistant fraction. Laser-based methods rather than traditional sedimentation methods are being used increasingly to determine particle size to reduce the cost of analysis. We give an overview of both approaches and the problems associated with them for analyzing the psd of chalk soil. In particular, we show that it is not appropriate to use the widely adopted 8 µm boundary between the clay and silt size fractions for samples determined by laser to estimate proportions of these size fractions that are equivalent to those based on sedimentation. We present data from field and national-scale surveys of soil derived from chalk in England. Results from both types of survey showed that laser methods tend to over-estimate the clay-size fraction compared to sedimentation for the 8 µm clay/silt boundary, and we suggest reasons for this. For soil derived from chalk, either the sedimentation methods need to be modified or it would be more appropriate to use a 4 µm threshold as an interim solution for laser methods. Correlations between the proportions of sand- and clay-sized fractions, and other properties such as organic matter and volumetric water content, were the opposite of what one would expect for soil dominated by silicate minerals. For water content, this appeared to be due to the predominance of porous, chalk fragments in the sand-sized fraction rather than quartz grains, and the abundance of fine (< 2 µm) calcite crystals rather than phyllosilicates in the clay-sized fraction. This was confirmed by scanning electron microscope (SEM) analyses. “Of all the rocks with which I am acquainted, there is none whose formation seems to tax the ingenuity of theorists so severely, as the chalk, in whatever respect we may think fit to consider it”. Thomas Allan, FRS Edinburgh 1823, Transactions of the Royal Society of Edinburgh.

Fluid flow in the Chalk of England

Summary The Chalk aquifer of England can be thought of as a multi-porosity medium. The matrix is a fine-grained limestone which generally has high porosity but small pore throats, so that its permeability is typically only 0.1 to 10 millidarcys (10 −4 to 10 −2 m day −1 ). A fairly uniform fracture system imparts a secondary permeability, which appears to be about 100 to 1000 mD (0.1 to 1 m day −1 ). Where the Chalk forms a major aquifer, most of the transmissivity results from the enlargement of fractures, by solution, to form a few highly permeable zones. Over much of the outcrop, weathering leads to the development of shallow permeable layers to form an additional component. Each of these permeability systems influences some aspect of subsurface water movement, with implications for resources, quality and construction.

Cretaceous chalk ichnofacies in Northern Europe

The Upper Cretaceous chalk of northern Europe is a pure calcitic, pelagic deposit which appears to be totally bioturbated in almost all cases. Trace fossils are abundant but there is no single association of trace fossils that can characterize all chalk. In the Maastrichtian chalk sequences of Denmark alone there are at least four ichnofacies (trace fossil associations): (A) a Zoophycos-dominated ichnofacies in fine-grained white chalk; (B) a Thalassinoides-dominated ichnofacies in white or gray chalk with a higher content of macrofaunal bioclasts; (C) a Planolites-dominated ichnofacies in slightly marly chalk, which seems to indicate a thixotropic substrate; (D) a hardground ichnofacies dominated by Entobia, Gastrochaenolites, and Trypanites. Several additional ichnofacies occur in the chalks of England, France, Belgium and the Netherlands that cannot be observed in Denmark: (E) nodular chalks, developed by numerous generations of Thalassinoides; (F) phosphatic chalks, characterized by pelletfilled Teichichnus and « Thalassinoides; (G) chalk marls, containing extremely abundant Chondrites; (H) calcarenitic tuffeau, containing locally abundant Ophiomorpha.

Influence of diagenesis on some index properties of chalk in England : Clayton, C R I Geotechnique, V33, N3, Sept 1983, P225–241

Influence of diagenesis on some index properties of chalk in England : Clayton, C R I Geotechnique, V33, N3, Sept 1983, P225–241

The influence of diagenesis on some index properties of chalk in England

The chalk in England is a highly variable material, and much of its variability stems from the wide variety of diagenetic processes which have been identified from lithological studies. This Paper reviews those processes, and presents results of laboratory index tests to determine their significance. The variability of the unweathered chalk is judged on the basis of approximately 600 tests to determine dry density, and 200 Atterberg Limit tests. The influence and extent of a number of diagenetic processes are examined. The degree to which the index properties are predictable (both stratigraphically and geographically) is discussed. En Angleterre la craie est un matériau qui varie beaucoup. Cette variabilité est le résultat d'une grande variété de phénomènes diagénétiques qui ont été identifiés à partir des études lithologiques. Cet article passe en revue ces phénomènes et puis présente les résultats des essais des propriétés caractéristiques faits dans le laboratoire avec le but de déterminer leur signification. La variabilité de la craie non délitée est évaluée à partir d'environ 600 essais de densité sèche et de 200 essais de limites d'Atterberg. L'influence et la valeur de quelques phénomènes diagénétiques sont examinées. L'article discute aussi comment on peut prédire les propriétés caractéristiques (par les méthodes stratigraphique et géographique).

Porewater reactions in the unsaturated zone with special reference to groundwater quality in England

Summary Porewater composition is an important control on the reactions leading to the formation of residual deposits. Although the mobility of porewater means it is not retained in ancient residual deposits, porewater movement through the unsaturated zone is a key factor in aquifer recharge. Porewater composition provides a sensitive means of monitoring reactions, and if infiltration has been operative over sufficient period of time whole rock changes may also be detected. Reactions involving different sedimentary fractions (resistate, hydrolysate and precipitate) are considered for infiltration into the Permo-Triassic sandstones and the Chalk of England. Externally derived elements may be identified and their behaviour in the unsaturated zone described. The examples considered are rainwater Na and Cl, fertilizer NO 3 and sewage effluent Cu, Zn and Ni.

A Coniacian ammonite from the ‘Top Rock’ in the Chalk of Kent

SummaryThe occurrence of Barroisiceras within the top bed of the Zone of Holaster planus near Dover in Kent provides the first ammonite evidence for the position of the base of the Coniacian in the Chalk of England. Inoceramus cf. rotundatus occurs ½ m above the ‘Top Rock’.

The zonal value of foraminifera in the Chalk of England

The zonal value of foraminifera in the Chalk of England

A Surface Site in S.E. Devon

This lies about 2½ miles S.W. of Seaton, on Beer Head, which is an isolated and the most westerly mass of chalk in England, at a height of approximately 450-ft. O.D., at the extreme top and S.W. edge of the catchment basin of the Axe.Up to the present, all artifacts found have been picked up in 4 or 5 large ploughed fields on a plateau immediately behind the part of Beer Head known as South Down. These fields are divided from the cliff-edge by a strip of undisturbed turf only a few hundred yards in width. An aerial photograph shows this apparently level turf to be a network of small divisions and boundaries of various shapes, and several parallel curved lines or rows, all of which continue to where the cliff breaks away and which are untraceable from ground level.

V.—On the Recognition of Two Stages in the Upper Chalk

When writing a general account of the Upper Chalk of England for vol. iii of the Cretaceous Rocks of Britain (Mem. Geol. Survey, 1904), I stated the belief of Mr. W. Hill and myself that the British Tipper Chalk comprised more than one division of the value of a stage. We grouped the zones then recognized into two divisions, pointing out that the lower zones were essentially the Chalk with Micrasters and the upper zones the Chalk with Belemnites; but we did not systematically adopt these divisions as stages with definite names.

III.—Upper Cretaceous Terebelloids from England

The tubes formed of fish-debris, found throughout the Chalk of England, described by Mantell (1822) as Murœna(?) lewesiensis, referred by L. Agassiz (1844) to Dercetis elongatus, and placed among Annelida Tubicola as Terebella lewesiensis by William Davies (1879), are here described with more precise detail and retained in the position assigned to them by Davies. A diagnosis is provided and a holotype selected.A specimen from the Gault, of similar nature but larger, is made the type of a new species, ‘Terebella’ lutensis (Fig. 6).Similar tubes from the Cenomanian, built of Conifer debris and Echinoderm debris, are described, and the question whether these differences of composition indicate a difference of species is discussed, but left open for the evidence of further material. Such tubes may for the present be known as ‘Terebella’ cf. lewesiensis (Figs. 7, 8).Tubes without extraneous building material and with a cancellar ornament are also found in the Cretaceous rocks of England, and some were referred to Terebella lewesiensis by Davies. All those from the Chalk are here separated as ‘Terebella’ cancellata, n.sp. (Figs. 3–5).Two tubes made of mud bricks are discussed. One, apparently of Lower Cenomanian age, is referred to the rather doubtful genus Keckia (Fig. 1). The other, from the Gault, is referred to Granularia (Fig. 2). Both these genera are held to be of Annelid origin.

V.—Some Cirripedes from the Chalk of Salisbury, Wilts

Although the remains of pedunculated Cirripedes are comparatively rare in the Chalk of England, especially in its lower zones, one can, by careful collecting extended over a number of years, get together a fair series of the detached valves of the capitulum. Thus a very fine series of Cirripede remains has been accumulated by Dr. H. P. Blackmore, F.G.S., from the upper zones of the Chalk near Salisbury. This collection, which, through the kindness of Dr. Blackmore, I have lately had the opportunity of examining, is especially rich in the valves of Scalpellum fossula, Darwin, and S. maximum (J. de C. Sowerby).

Description of the Fossil Remains of Mollusca Found in the Chalk of England. Cephalopoda - Index

Description of the Fossil Remains of Mollusca Found in the Chalk of England. Cephalopoda - Index

VI.—Remarks on the Irregular Echinoids of the White Chalk of England as exhibited in the British Museum (Natural History)

Having been asked by Dr. Smith Woodward and Dr. Bather to look over the collection of Irregular Echinoids from the English Chalk in the British Museum with a view to bringing the exhibition up to date, it appears a favourable opportunity to say a few words as to the nomenclature and distribution of these animals.

I.—Memoirs of the Geological Survey of the United Kingdom - The Cretaceous Rocks of Britain. Vol. III: The Upper Chalk of England. By A. J. Jukes-Browne, with Contributions by William Hill. Svo; pp. X, 566, Plate, illustrations. (London, 1904. Price 10s.)

I.—Memoirs of the Geological Survey of the United Kingdom - The Cretaceous Rocks of Britain. Vol. III: The Upper Chalk of England. By A. J. Jukes-Browne, with Contributions by William Hill. Svo; pp. X, 566, Plate, illustrations. (London, 1904. Price 10s.)

Memoirs of the geological survey of the United Kingdom.—The cretaceous rocks of Britain. Vol. III. The Upper Chalk of England. By A. J. Jukes-Browne. With contributions by William Hill, F.G.S. 8vo. Pp. x and 566. With 79 illustrations in the text and 1 plate. 1904. E. Stanford, London; J. Menzies, Edinburgh; and Hodges &amp; Co., Dublin. Price 10s.

<i>Memoirs of the geological survey of the United Kingdom.—The cretaceous rocks of Britain</i>. Vol. III. <i>The Upper Chalk of England</i>. By A. J. J<scp>ukes</scp>-B<scp>rowne</scp>. With contributions by W<scp>illiam</scp> H<scp>ill</scp>, F.G.S. 8vo. Pp. x and 566. With 79 illustrations in the text and 1 plate. 1904. E. Stanford, London; J. Menzies, Edinburgh; and Hodges &amp; Co., Dublin. Price 10<i>s.</i>

Memoirs of the Geological Survey of the United Kingdom.—The Cretaceous rocks of Britain. Vol. II. The lower and middle chalk of England. By A. J. Jukes-Browne, B.A., F.G.S. With contributions by William Hill, F.G.S. 8vo. Pages xiii and 568. With 93 illustrations, including one geological map, two plates from photographs, and four from micrographs. E. Stanford, London: J. Menzies, Edinburgh;

<i>Memoirs of the Geological Survey of the United Kingdom.—The Cretaceous rocks of Britain</i>. Vol. II. <i>The lower and middle chalk of England</i>. By A. J. J<scp>ukes</scp>-B<scp>rowne</scp>, B.A., F.G.S. With contributions by W<scp>illiam</scp> H<scp>ill</scp>, F.G.S. 8vo. Pages xiii and 568. With 93 illustrations, including one geological map, two plates from photographs, and four from micrographs. E. Stanford, London: J. Menzies, Edinburgh;