On the Kimmeridgian (Jurassic) succession of the Normandy coast, northern France

Kimmeridgian rocks crop out on the Normandy coast north and south of the Seine Estuary at Le Havre in a series of small foreshore and cliff exposures separated by beach deposits and landslips. A total thickness of about 45 m of richly fossiliferous strata is exposed, ranging from the base of the Baylei Zone to the middle part of the Eudoxus Zone. The sections are mostly unprotected by sea-defence works and are subject to rapid marine erosion and renewal. Taken together, the Normandy exposures currently provide a more complete section through the low and middle parts of the Kimmeridgian Stage than any natural English section, including those of the Dorset type area. Descriptions and a stratigraphical interpretation of the Normandy sections are presented that enable the faunal collections to be placed in their regional chronostratigraphical context. The Kimmeridgian succession at outcrop on the Normandy coast contains numerous sedimentary breaks marked by erosion, hardground and omission surfaces. Some of these are disconformities that give rise to rapid lateral variations in the succession: biostratigraphical studies need, therefore, to be carried out with particular care

The distribution of the ammonite Gravesia (Salfeld, 1913) in the Kimmeridge Clay Formation (Late Jurassic) in Britain

Species of the ammonite Gravesia (Salfeld, 1913) have a widespread distribution in Europe over a relatively narrow stratigraphical range in the late Kimmeridgian and early Tithonian stages. The genus is a warm-water form that reaches its maximum stratigraphical range in the Submediterranean faunal province in central France and south Germany where six species have been recognised. Four of these, G. gigas (Zieten, 1830), G. gravesiana (d’Orbigny, 1850), G. irius (d’Orbigny, 1850) and G. lafauriana Hantzpergue, 1987 have been recorded in the Kimmeridge Clay Formation. A few examples have been found in cored boreholes, but most have come from the cliff and foreshore outcrops at Brandy Bay and Kimmeridge Bay in Dorset. The distribution of Gravesia in Britain is mostly restricted to the more calcareous parts of the succession where they represent migrations of a warmer water fauna into a region in which the ammonite assemblages were dominated by Subboreal forms of Aulacostephanus and Pectinatites. The palaeogeography of the late Jurassic in central and North West Europe comprised relatively small land areas separated by seaways that became progressively more restricted with time. In late Kimmeridgian and early Tithonian/Volgian times, migrations of warmer- and cooler-water ammonites through these seaways gave rise to mixed assemblages that enable correlations to be made between the local zonal schemes in the Submediterranean and Subboreal faunal provinces. Gravesia is one of the few ammonites that has a stratigraphical range that crosses the Kimmeridgian-Tithonian and Kimmeridgian-Volgian boundaries, and which has a large geographical distribution which includes much of North West and Central Europe and as far east as the Subarctic Urals. The known distribution of the genus in Britain is summarised herein, along with the first detailed account of its occurrence in the Kimmeridge Clay Formation in the Dorset type section

The stratigraphy of the Mercia Mudstone Group succession (mid to late Triassic) proved in the Wiscombe Park boreholes, Devon

The type section of the Mercia Mudstone Group is the almost complete exposure in the cliffs between Sidmouth and Axmouth on the south Devon coast. The group comprises four formations, in ascending order the Sidmouth Mudstone, Dunscombe Mudstone, Branscombe Mudstone and the Blue Anchor Formation. The type sections of the three oldest of these are at this locality. The partially cored Wiscombe Park No.1 and No.2 mineral-exploration boreholes, drilled by British Gypsum Ltd (now part of BPB UK Ltd) in 1982, were sited about 5.8 and 4.7km north of the cliff sections respectively. The deeper of these penetrated almost the whole of the Sidmouth Mudstone, the whole of the Dunscombe Mudstone and the lowest part of the Branscombe Mudstone. The lithological succession proved in the cored parts of the boreholes can be correlated in detail with that exposed in the cliffs. This has enabled geophysical logs made through the full length of the boreholes to be correlated with the cliff sections for the cored and uncored parts of the boreholes. The availability of a suite of geophysical logs that has been calibrated against the coastal exposures provides a key correlational link between the outcrop succession and a large number of uncored but geophysically logged hydrocarbon-exploration boreholes throughout the Wessex Basin. Eastwards from Wiscombe Park and the coastal exposures, beneath much of south Dorset, the Dunscombe Mudstone expands from 35m in thickness to over 180m by the addition of thick beds of halite (Gallois, 2003; Harvey and Stewart, 1998)

The stratigraphy of and well-completion reports for the Swanworth Quarry No. 1 and No. 2 and Metherhills No 1 boreholes (RGGE Project), Dorset

There has been increasing international awareness and concern in recent years about possible global climatic changes and their effects on local environments. In many of those parts of the world where detailed records have been kept for the last 50 to 100 years there is clear evidence of higher average summer temperatures, rising sea levels and a greater incidence of storms. The mechanisms behind these changes are not yet fully understood, and are likely to be complex. Increased emissions of carbon, nitrogen and sulphur oxides and hydrocarbon gases from transport and industrial processes are thought to have induced global climatic changes, but these changes are superimposed on natural changes that occur over time-scales that are too long for direct observation. For example, climatic changes related to variations in the radiant heat received from the sun are thought to occur as 2 1,000-year to 250,000-year cycles. The presence of such long-term climatic cycles can only be inferred from a detailed examination of the geological record. It was for this reason that the Natural Environment Research Council (NERC) decided in 1995 to allocate E900,OOO over 3 years to a special research topic, the Rapid Global Geological Events (RGGE) special topic, designed to examine in as great a detail as practicable a selected interval of the geological column. The aim is to apply to ancient sediments, analytical techniques used successfully to identify the effects of climatic changes in modem sediments. The Kimmeridge Clay was chosen by the RGGE Steering Committee (Chaired by Professor D J Vaughan, Manchester University) because it consists of an apparently unbroken sequence of highly fossiliferous marine mudstones, about 150 million years old, that represent about 3 million years of Earth history. The mudstones contain rhythmic variations in clay mineralogy, fauna and organic content that reflect climatic and sea-level changes. The aim of the project is to apply as many state-of-the art analytical methods as possible to a continuous core taken through the full thickness of the Kimmeridge Clay to enable these changes to be documented and the processes that cause them to be understood

Natural and artificial influences on coastal erosion at Sidmouth, Devon, UK

Like many small coastal towns in the UK, Sidmouth in Devon was founded on the valley sides adjacent to a river outfall that provided a natural harbour. Subsequent expansion of the town in the late 18th and early 19th centuries, when living by or visiting the sea became popular for health reasons, involved the entrainment of the river and building on land that was subject to marine flooding. Engineering works in the 19th and 20th centuries that were designed to protect the low-lying parts of the town included the construction of sea walls, and groynes and offshore bunds to protect a ridge of storm-beach gravels that acts as a natural sea defence. These works have collectively had an effect on erosion rates in the cliffs of Triassic sandstone and mudstone on the east side of the town. Natural landslide mechanisms in the cliffs adjacent to Sidmouth include rock-block and toppling failures induced by marine undercutting, and hydraulic stoping along faults and major joints at the foot of the cliffs. The principal landslide mechanism is the collapse of unconsolidated Head deposits and deeply weathered mudstones in the highest (mostly 3 to 5 m) part of the cliff. The falling material commonly destabilises the underlying well-jointed sandstones and mudstones. Artificial factors that have influenced erosion rates in the cliffs east of the River Sid outfall in the last 100 years have included the refraction of waves adjacent to the end of the river wall, and interference with the easterly longshore drift of the beach gravels. A secondary factor has been the destabilising influence of a Victorian railway tunnel that was dug parallel to and up to 25 m from the cliff face on the east side of the town. In the absence of quantitative monitoring data, published estimates of the rates of cliff erosion are significantly higher than those obtained in the present study from a comparison of maps made between 1802 and 2006

The development and origin of karst in the Upper Greensand Formation (Cretaceous) of south-west England

The Upper Greensand of south-west England can be divided on bulk lithology into two roughly equal parts, each 25 to 30 m thick. The lower part, the Foxmould Member, consists of weakly cemented glauconitic sandstones with low carbonate contents. The member weathers, largely by oxidation, to soft, loose, yellow and foxy brown sands. In contrast, the overlying Whitecliff Chert and Bindon Sandstone members consist of calcareous sandstones and sandy calcarenites with numerous chert-rich horizons. Dissolution, particularly during the warm humid climates of the Eocene and the periglacial climates of the late Pleistocene, has been the dominant weathering process in these two members. Karstic features observed on the east Devon and west Dorset outcrops include widespread pervasive dissolution that has locally reduced the in situ thickness of the Whitecliff Chert and Bindon Sandstone members to less than half their original thickness, along with deep solution pipes, and at one locality, caves. These discrete solution features occur beneath a thick capping of Chalk that is not markedly affected by dissolution. Over much of east Devon and west Dorset, the residual loose sands and chert blocks derived from the dissolution of the Upper Greensand were remobilised during the late Pleistocene to form extensive Head deposits

A recent large landslide at the Spittles, Lyme Regis, Dorset and its implications for the stability of the adjacent urban area

The Black Ven-Spittles landslide is an old, probably Pleistocene, complex of interacting coastal landslides that are in the process of being reactivated as a result of a combination of man-made works and marine erosion. The upper part of the complex is underlain by Cretaceous rocks and the lower part by the Jurassic Charmouth Mudstone Formation. Large-scale rotational and translational failures have occurred in the Cretaceous rocks at less than 10-year intervals during the past 60 years, almost always during or shortly after prolonged periods of rainfall. In contrast, large-scale failures have been infrequent in the Charmouth Mudstone and have been restricted to areas where a low (<1.5°) seaward dip has resulted in bedding-plane-initiated failures. Two such failures have been recorded, in 1908 and 2008, both in the same area at the western end of the landslide complex in the area closest to the Lyme Regis urban area. The first of these occurred at 1.15 pm on June 10th 1908 and involved the collapse, or partial collapse, of 450 m of cliff. It involved an estimated total of more than 300,000 tonnes of rock in what was probably the culmination of three separate failures that occurred in rapid succession. The second, involving an area of c. 40,000 m2 and c. 500,000 tonnes of material, occurred over a period of a few hours starting at 8 pm on May 6th 2008. In addition, the new landslide intersected part of the former (c. 1920-1973) town rubbish tip with the result that glass, metal, other wastes and possible pollutants were deposited on the beach. Before-and-after geological surveys of the area and the availability of pre- and post-failure photographs and LiDAR surveys have made it possible to determine how the 2008 failure was initiated, and how it progressed. Both the 1908 and 2008 failures appear to have started as relatively small rock-block collapses in a fracture zone associated with a minor fault. At its western end, the new landslide is <300 m from the Lyme Regis built-up area and separated from it by similar mudstones with small faults that may be equally prone to failure

Correlation of the Triassic and Jurassic successions proved in the Lyme Regis (1901) borehole with those exposed on the nearby Devon and Dorset coasts

The Lyme Regis (1901) Borehole was one of numerous coal-exploration boreholes drilled in southern England during the late 19th and early 20th centuries. It is one of the few deep boreholes (>200 m depth) in the east Devon-west Dorset area and, unlike more recent hydrocarbon-exploration boreholes, was continuously cored. The borehole was sited [NGR SY 3364 9297] on the floodplain of the River Lim on the outcrop of the Jurassic Blue Lias Formation, and was continuously cored to a final depth of 396.85 m within the Triassic Mercia Mudstone Group. Selected samples and some of the cores were examined by the Geological Survey geologists Jukes-Browne and Woodward who were working in the area at the time of drilling. The former published a description of the succession based on his and Woodward’s notes and the driller’s log, and correlated it with the succession of Triassic and Jurassic rocks that are almost wholly exposed in the cliffs between Sidmouth and Lyme Regis. A recent revision of the stratigraphy of the coastal successions has enabled that proved in the borehole to be reassessed and placed more accurately into its regional stratigraphical context

The origin of the Clay-with-Flints : the missing link

The Clay-with-flints has a patchy, but extensive, outcrop in southern England south of the limit of the Anglian ice sheets, and in northern France where it is referred to as the Argiles à silex. Since early Victorian times, when it was recognised that its principal components were clay and unworn flints, the deposit has been presumed to have been derived from the dissolution of large volumes of chalk. It was also recognised, however, that the clay contents of typical chalks were too low to have produced the clay-flint ratios of much of the Clay-with-flints. The additional clay, together with sand that could not have been derived from the Chalk Group, was therefore presumed to be of later origin. The solution hypothesis remained largely undisputed until the 20th Century, even though there is no published example of an intermediate stage in the process in the form of a layer of partially dissolved chalk. The age of formation of the Clay-with-flints has long been the subject of dispute, partly because of the absence of palaeontological evidence, and partly because the name has been applied to a wide variety of lithologies including reworked and remobilised materials. Suggested ages range from Palaeocene in parts of northern France to Pleistocene in the London Basin. In east Devon and west Dorset, beds of partially dissolved in situ Upper Greensand and Chalk tens of metres thick are overlain by Clay-with-flints. They confirm the importance of large-scale solution as a contributing factor in the formation of the deposit in south-west England. The partially dissolved layers and the Clay-with-flints were folded and faulted in the Miocene, and they can be seen to pre-date Pleistocene erosional features including hanging dry valleys and frost-wedge pipes. The principal phase of dissolution is presumed to have been in warm moist climates during the Palaeocene-Eocene Thermal Maximum