Misplaced Pages

#761238

33-638: Historically, the Wessex Formation has been called alternately the " Variegated Marls and Sandstones ", a name used by W. J. Arkell in his 1947 map of the Isle of Purbeck as well as the " Wealden Marls " It was given its current formal name by Daley and Stewart in 1979. The Wessex Formation forms part of the Wealden Group within the Wessex Basin , an area of subsidence since Permo - Triassic times. The basin

66-504: A mygalomorph spider, Dungeyella gavini Libanodiamesa simpsoni , both chironomid midges, as well as Embolemopsis maryannae , a embolemid parasitic wasp. However a table of undescribed taxa has been given, and several images of some of the undescribed taxa have been released from various sources, including multiple chironomids, and a therevid dipteran . Cretamygale C. chasei Indeterminate Indeterminate Indeterminate Indeterminate Indeterminate Represented by

99-938: A boring in a gymnospermous seed. Polacanthoides ponderosus ? [REDACTED] [REDACTED] Hypsilophodon H. foxii Heterodontosauridae ? Indeterminate Iguanodon I. bernissartensis A hadrosauroid iguanodontian . Specimens classified as Iguanodon seelyi are referable to this species Mantellisaurus M. atherfieldensis Dollodon bampingi , Proplanicoxa ? Valdosaurus V. canaliculatus [REDACTED] Chondrosteosaurus C. gigas "Several cervical vertebrae." Eucamerotus E. foxi "Dorsal vertebra." Iuticosaurus I. valdensis "Several caudal vertebrae." Oplosaurus O. armatus "Tooth." Ornithopsis O. eucamerotus "Ischia and pubis.", regarded as an "undiagnostic titanosauriform of uncertain affinities." William Joscelyn Arkell William Joscelyn Arkell FGS , FRS (9 June 1904 – 18 April 1958)

132-566: A deep love of the English countryside from an early age, perhaps gained from long family summer holidays spent at Swanage , Dorset. He was later educated at Wellington College in Berkshire, where his ability in Natural History was recognised and he was able to devote significant time to develop his knowledge of this subject. He was a regular prize winner for his natural history essays, one of which

165-447: A defined majority is the fine-grained matrix as opposed to the clasts (in the case of a conglomerate) or allochems (in the case of a limestone). For a conglomerate , a rock is considered matrix-supported when clasts constitute less than 15% of its volume. Matrix support is considered characteristic of debris flow deposits, in which clasts are supported within a fabric of mud as they move downstream. Wackestones and mudstones under

198-411: A hundred complete and articulated skeletons of the dinosaur Hypsilophodon , sometimes even with preserved tail tendons. The bed is laterally extensive, being persistent for over a kilometre. It has been recently suggested that the accumulation of skeletons were a mass mortality event caused by a crevasse splay . Just above the " Hypsilophodon bed" the red mudstones of the Wessex Formation change to

231-448: A large house at Cumnor , near Oxford, before moving to Cambridge in 1949. They had three sons, born between 1932 and 1937. They also established a holiday home at Ringstead Bay in Dorset. Through his link with the family brewery business, Arkell was independently wealthy. Arkell had a large frame and height – he was 6 feet 4 inches (1.93 m) tall – but was never a well man. In

264-618: Is located along southern half of the Isle of Wight and Purbeck, extending offshore into the English Channel . The Wealden Group is also exposed significantly in the Weald Basin , which has a separate stratigraphic succession. The Wealden Group is not widely present elsewhere in Britain, as these areas were tectonic highs where little to no sediment deposition was taking place. The formation has limited exposure as it has been deeply buried beneath

297-614: Is obscured by a landslip. The Isle of Wight succession has two primary exposures, The major one being the several kilometre long section along the South West coastline around Brighstone Bay , and another smaller exposure on the South East coast near Yaverland . While the formation taken as a whole dates from the Berriasian to the Barremian, only the uppermost part of the formation is exposed on

330-839: The Mary Clark Thompson Medal from the United States National Academy of Sciences . He was elected a Fellow of the Royal Society (FRS) in 1947. Arkell was awarded the Lyell Medal by the Geological Society of London in 1949, and the Leopold von Buch medal of the German Geological Society in 1953. Matrix-supported rock In geology , a matrix-supported rock is a sedimentary rock of which

363-500: The Nile valley of Egypt in association with the University of Chicago . Four notable monographs , authored jointly with Sandford and published by Chicago's Oriental Institute were the result of this work. Arkell was awarded a lectureship in geology at New College, Oxford in 1927, and was made a senior research fellow of that college in 1929. With few teaching or administrative duties, he

SECTION 10

#1732851651762

396-593: The University of Oxford after being awarded a Burdett-Coutts research scholarship . His research topic involved the taxonomy of the bivalves from the Upper Jurassic Corallian beds of England. For this and other papers on the Jurassic of Southern England he was awarded a D Phil in 1928. Whilst undertaking his doctoral research, Arkell spent four winter seasons (1926–1930) alongside K. S. Sandford , investigating evidence of Palaeolithic human remains in

429-511: The Isle of Wight. With less than 200 metres of exposed composite stratigraphic thickness, and which dates from Hauterivian to Barremian . A radiometric date has been obtained from the lower part of the succession, estimated to be 127.3 ± 2.7 million years ago. This makes the formation coeval with upper portion of the Weald Clay in the Weald Basin. The primary lithology of the exposed portion of

462-512: The Purbeck sections of the formation is the "Coarse Quartz Grit", an up to 6 metre thick sequence of conglomeratic ironstone , with many beds including numerous centimetre sized subangular to rounded pebbles predominantly of vein derived quartz , hence the name. This horizon is present throughout the Purbeck outcrops of the Wessex Formation. The transition to the Vectis Formation at Swanage

495-511: The Upper Jurassic reef deposits (the Coral Rag ) of England. He was an expert on the use of Jurassic limestones as building materials, and his research into the many different types of limestone used in the buildings of Oxford would result in publication of a book in 1947. The often obscure terminology used by miners and quarrymen was clarified by his dictionary of rock terms (1953). Arkell

528-551: The Wessex Formation are found as inclusions in amber. Amber can be found present as a rare component in plant debris beds in the Wessex formation both on the Isle of Wight and the Isle of Purbeck, however, the only significant concentration and where all of the inclusions have been found is a lag channel in the L6 plant debris horizon just south-east of Chilton Chine . Only four species from the amber have been formally described, Cretamygale chasei

561-447: The Wessex Formation. Freshwater bivalves can be found including unionids such as Margaritifera , Nippononaia , and Unio . These bivalves help reconstruct what the freshwater paleoenvironment may have been like during the formation's deposition. Specimens of Viviparus , a genus of freshwater snail , have also been found. While compression fossils of insects are found in the overlying Vectis Formation, all insect fossils in

594-503: The autumn of 1956 he suffered a severe stroke which left him partially paralysed and with double vision ; this was a detriment to his Sunday hobby of watercolour painting. Despite this his determination to continue his work and correspondence at the University of Cambridge continued. He suffered a second stroke on 18 April 1958 and died several hours later. Arkell received a D Sc from the University of Oxford in 1934. In 1944 he received

627-419: The base of the exposed portion of the formation includes calcitized conifer trunks up to metre in diameter and 2–3 metres long. A notable feature of the formation are the so-called "plant debris beds". These consist of a basal matrix supported conglomerate , grading upwards into grey mudstone with lignitic plant debris, including large trunk fragments of the extinct conifer Pseudofrenelopsis present in

660-582: The extent of Cornwall and Devon , with occasional large dropstones transported in tree roots being found in Wealden sediments over 100 kilometres from where they originated. The exposure in of the Wessex Formation in the Isle of Purbeck is largely confined to a thin belt on the south side of the Purbeck Ridge and is best exposed at Swanage , Lulworth Cove and Worbarrow Bay . One notable persistent horizon within

693-584: The extinct family Cheirolepidiaceae belonging to the genera Pseudofrenelopsis and Watsoniocladus , both of which have reduced xerophytic leaves adapted to arid conditions. Tree cover is thought to have been thin, and concentrated near waterways. The ground cover is thought to have consisted of xerophytic ferns . Wildfires were common occurrences, as evidenced by preserved charred vegetation. The Wessex Formation likely spans several million years of deposition, and not all taxa are likely to have been contemporaneous. Invertebrates are commonly preserved in

SECTION 20

#1732851651762

726-404: The formation are associated with the debris beds. Vertebrate fossils are mostly disarticulated individual bones and teeth, suggesting a long subaerial exposure prior to burial, though the bones lack abrasion , suggesting that they had not been significantly transported. Partial skeletons also sometimes occur, but are uncommon. Autochthonous siderite nodules are also present, which encase some of

759-405: The formation on the Isle of Wight consists of featureless purple- red overbank mudstone, interbedded with sandstones. The environment of deposition was a floodplain within a narrow, east–west oriented valley. The climate at the time of deposition is considered to be semi-arid , based on the presence of pedogenic calcrete nodules within the mudstones. The "Pine Raft" horizon found near

792-460: The fossils. Plant debris beds also exist within the Swanage section, and one of these horizons has yielded microvertebrate remains. While most fossils are associated with the plant debris beds, a notable exception is the " Hypsilophodon bed" present near the top of the formation, an up to 1 metre thick bed of silty red-green mudstone, with two separate horizons that have produced almost exclusively over

825-579: The leading expert on this specialist area. He was inundated with fossils for identification, particularly from oil companies. As a consequence, he travelled widely in the Middle East, examining many Jurassic exposures from this area. Arkell then consolidated his knowledge of the Jurassic and published Jurassic Geology of the World in 1956. The large, detailed volume to this day remains a classic and influential text. Arkell married Ruby Percival in 1929 and bought

858-647: The subsequent Lower Greensand . Selbourne and Chalk Groups , as well as being very vulnerable to erosion. It has been exposed at the surface due to the creation of anticlinal structures as a distant effect of the formation of the Pyrenees as part of the Alpine Orogeny during the Paleogene . The major source rocks for the sediments were from the Cornubian Massif to the west, an upland region roughly equivalent to

891-440: The transitional light coloured sandstone "White rock" and overlying laminated grey mudstones of the Vectis Formation , caused by the changing of environmental conditions from that of a floodplain to coastal lagoon conditions. The palaeoenvironment of the Wessex Formation is considered to have been semi-arid, and has variously been compared to chaparral or macchia Mediterranean shrubland . The dominant trees were conifers of

924-506: The upper portion. These were formed by sheet flood deposits induced by storms that filled pre-existing topographic lows like oxbow lakes and abandoned channels in the floodplain depositional environment. The debris beds do not form a continuous horizon throughout the formation, but are laterally extensive over tens of metres. Many of the wood fragments in the debris beds are cemented together with large nodules of pyrite , suggesting depositional conditions were anoxic . Most fossils within

957-546: Was a British geologist and palaeontologist , regarded as the leading authority on the Jurassic Period during the middle part of the 20th century. Arkell was born in Highworth , Wiltshire, the youngest of a family of seven. His father, James Arkell was a partner in the prosperous family business Arkell's Brewery (which is still family owned today). His mother, Laura Jane Arkell, was an artist of noted ability. He developed

990-642: Was a treatise on the Dorset Robber Flies ( Asilidae ). He privately published a set of poems, Seven Poems , that reflected his love of nature and the outdoors. In October 1922, at the second attempt (after failing the Latin examination), Arkell was admitted to New College, Oxford . He had initially intended to read entomology but despite being tutored by the great Julian Huxley , he decided that his career lay in geology and palaeontology . In 1925 he graduated with First Class Honours in geology. He remained at

1023-444: Was able to devote almost all his time to research. This culminated with the publication in 1933 of The Jurassic System of Great Britain , a 681-page work which critically examined and consolidated all previous work on the Jurassic, including the formations described by the pioneer of British geology, William Smith , in the 19th century. It established Arkell (at age 29) as an authority on the Jurassic. He also published extensively on

Wessex Formation - Misplaced Pages Continue

1056-464: Was at its most intense. In 1943 he became seriously ill, spending five months in hospital after a pneumothorax operation. After demobilisation at the end of the war, Arkell accepted a senior research fellowship at Trinity College, Cambridge , holding an office at the Sedgwick Museum . In this time Arkell began to work on the use of ammonites as zone fossils in Jurassic stratigraphy and became

1089-579: Was interested in the tectonic history of Southern England, particularly with reference to the highly folded beds of the Isle of Purbeck . He contributed to reports published by the British Geological Survey , especially around the area of Weymouth and Portland . The Second World War interrupted his research in 1941, and Arkell worked for the Ministry of Transport in London while bombing of that city

#761238