Proceedings of the Geologists Association最新文献

{"title":"Do REEs in mudstones record bottom-water redox?: The Pliensbachian–Toarcian record (Lower Jurassic) and T-OAE in the Cleveland Basin, England","authors":"Ian Jarvis ,&nbsp;Elizabeth Atar ,&nbsp;Darren R. Gröcke ,&nbsp;João P. Trabucho-Alexandre","doi":"10.1016/j.pgeola.2025.101114","DOIUrl":"10.1016/j.pgeola.2025.101114","url":null,"abstract":"<div><div>The Pliensbachian–Toarcian of the Cleveland Basin provides a global reference for the interval incorporating the Toarcian Oceanic Anoxic Event (T-OAE ~<!--> <!-->183 Ma). Palaeoredox proxies show a progressive shift from oxic bottom waters in the late Pliensbachian through dysoxic–anoxic conditions in the earliest Toarcian to euxinia during the T-OAE. Anoxia–dysoxia persisted into the middle Toarcian. Laminated black shales with TOC contents &gt;<!--> <!-->2.5 % characterise the anoxic–euxinic intervals. The rare-earth element (REE) geochemistry of the succession sampled in the Dove's Nest core is described and compared to data from nearby Yorkshire coastal outcrops. Interpretation is based on a review of REE behaviour in modern marine water columns, pore waters and sediments. Mud(stone) REE patterns are insensitive to bottom-water redox conditions. The REEs are principally located in the siliciclastic clay fraction of modern marine muds and ancient mudstones. Bulk mud(stone)s generally exhibit relatively flat REE patterns when normalised to average shale. Cerium anomalies are largely absent. Stratigraphical trends in the Yorkshire succession are related principally to sediment grain size. Authigenic and biogenic phosphates, principally carbonate fluorapatite, when present, dominate the whole-rock REE inventory leading to convex-upward patterns and large positive middle REE (MREE/MREE*) anomalies. These occur sporadically throughout the oxic–euxinic intervals, showing no correlation to bottom-water redox. The REE geochemistry of marine mudstones presents a combination of primary mineralogical and grain-size controls related to sediment provenance combined with the impact of authigenic mineral formation. Bulk mudstone REE patterns do not provide a viable bottom-water redox proxy.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101114"},"PeriodicalIF":1.2,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microvertebrates from a Rhaetian neptunian dyke at Holwell, Somerset: Dating the fissures","authors":"Oliver J. Weeks ,&nbsp;Rebecca B. Cooper ,&nbsp;David I. Whiteside ,&nbsp;Christopher J. Duffin ,&nbsp;Charles Copp ,&nbsp;Claudia Hildebrandt ,&nbsp;Deborah Hutchinson ,&nbsp;Michael J. Benton","doi":"10.1016/j.pgeola.2025.101112","DOIUrl":"10.1016/j.pgeola.2025.101112","url":null,"abstract":"<div><div>Dating the Mesozoic-aged fissure deposits around Bristol and South Wales has been problematic, with ages of the older examples disputed as either Carnian or Rhaetian, a 30-million-year difference. The deposits filling fissures at Holwell, Somerset offer a chance to establish a date for at least one system of fissures because they are on the coast of the Mendip Palaeoisland, close to bedded Rhaetian marine deposits. The Holwell fissures have been known since the 1850s when they yielded some of the first ever reported Mesozoic mammals, and they are the type locality for several fossil shark species, <em>Duffinselache holwellensis</em>, <em>Pseudocetorhinus pickfordi</em> and <em>Palaeobates reticulatus</em>. Bone-rich fissure fills from a neptunian dyke at Holwell yielded over 3000 identifiable specimens, comprising mainly marine fishes but also coastal-dwelling placodonts and terrestrially derived lepidosaurs that lived on the palaeoisland. Over 95 % of the fauna comprises four fish taxa that are typical of the bedded Westbury Formation. The less common <em>Rhomphaiodon minor</em> associated with abundant <em>Synechodus rhaeticus</em> indicates that the deposits are likely not basal but are within the upper half of the Westbury Formation. We hereby confirm that these Holwell fissure fill faunas, including the mammals, are of Rhaetian age.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101112"},"PeriodicalIF":1.2,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322890","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A ctenochasmatid pterosaur from the Portland Limestone Formation (Late Jurassic, Tithonian) of southern England","authors":"Roy E. Smith,&nbsp;David M. Martill","doi":"10.1016/j.pgeola.2025.101100","DOIUrl":"10.1016/j.pgeola.2025.101100","url":null,"abstract":"<div><div>A new specimen of pterosaurian mandible from the Late Jurassic (Tithonian) Portland Limestone Group of southern England is described. Morphological considerations permit assignment to Pterodactyloidea. The elongate slender mandible and numerous closely spaced alveoli suggest it is a member of the Ctenochasmatidae. A faint median ridge on the occlusal surface between two grooves, converging into a median groove anteriorly, and the lack of a distinct premaxilla suggest the specimen is part of the symphysis of the mandible. This is the first documented record of a pterodactyloid from the Portland Group of England.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101100"},"PeriodicalIF":1.2,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New insights into Neogene to Pleistocene tectono-sedimentary major events in northeastern Tunisia from surface and subsurface data","authors":"Sofien Alyahyaoui,&nbsp;Hedi Zouari","doi":"10.1016/j.pgeola.2025.101099","DOIUrl":"10.1016/j.pgeola.2025.101099","url":null,"abstract":"<div><div>The main objective of this study is to analyse the structure of the Neogene to Recent rocks in the surface and subsurface of northeastern Tunisia, in order to identify unconformities in outcrops and detect these tectonic and sedimentary events in the subsurface data.</div><div>An integrated study of multi-data supported by the compilation of new outcrop data, seismic reflection profiles, and data from petroleum wells has been carried out in order to determine the structural evolution in the study area. This study has resulted in an improved understanding of the geological evolution of NE Tunisia during the Neogene to Pleistocene. Four major unconformities have been identified in this area, the Tortonian unconformity, the Messinian unconformity, the Pliocene unconformity and the mid-Pleistocene unconformity.</div><div>The mapping of unconformities indicates their association with a major inversion event that occurred from the Late Miocene to the present, resulting in the development of stratigraphy controlled by structural factors. The analysis of nineteen seismic sections has confirmed the existence of several features associated with compressive and transpressive tectonic events.</div><div>These include reverse faults, folds, and unconformities. The structural mapping of these unconformities reveals the presence of a dominant fault system bounding a large number of moderate sized basins.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101099"},"PeriodicalIF":1.2,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Culham Brickworks, Oxfordshire, England: New insights from 1852 on a puzzling Jurassic–Cretaceous section","authors":"Nigel Banks","doi":"10.1016/j.pgeola.2025.101098","DOIUrl":"10.1016/j.pgeola.2025.101098","url":null,"abstract":"<div><div>The Culham Brickworks was active from before 1850 for about 100 years and during its existence provided the only good exposure of the Early Cretaceous sub-Gault Formation unconformity in the Oxfordshire area of England. Six descriptions date from 1852 to 1926 detailing different sections as they were exposed in the <em>ca.</em> 350 m length of the excavations which moved gradually eastwards along the Thames riverbank. Over most of the excavated length the Gault Formation lies unconformably on the Late Jurassic Kimmeridge Clay Formation, but to the west the Aptian Lower Greensand Group intervenes and thickens to at least 4 m. A section described by John Phillips in 1860 has proved controversial, particularly for the claimed presence of 9 ft (2.7 m) of Kimmeridge Clay sands that were not seen by others. The earliest description is an unpublished manuscript from <em>ca.</em> 1852 by Daniel Sharpe containing previously unmentioned information, including a cross-section. This defines the Lower Greensand geometry more precisely and also throws additional doubt on Phillips' description. Using Sharpe's sections rather than Phillips', a cross-section has been drawn covering the entire length of the excavations. This illustrates significant relief at both the top of the Kimmeridge Clay Formation and the base of the Gault Formation. This reconstruction provides an essential starting point for any wider study of the Lower Greensand sandbody geometry and the nature of the sub-Gault Formation unconformity. The zonation of the Gault at the Brickworks continues to be reinterpreted, but the results are ambiguous.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101098"},"PeriodicalIF":1.2,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Orogenic and fluvio-tectonic insights into the formation of the Middle Atlas Caves in the Jurassic dolomites (Morocco)","authors":"Iliass Naouadir ,&nbsp;Samira Adil ,&nbsp;El Hassane Chellai ,&nbsp;Abdallah Elaaraj ,&nbsp;Abdennabi Alitane ,&nbsp;Mohammed Ettaki ,&nbsp;Márton Veress ,&nbsp;Ismail Naouadir","doi":"10.1016/j.pgeola.2025.101097","DOIUrl":"10.1016/j.pgeola.2025.101097","url":null,"abstract":"<div><div>This article examines the caves of the Moroccan Middle Atlas using a multi-scale approach, both at the regional and outcrop levels. Our study employs a dual approach, combining numerical analysis and field observation, to investigate the formation of karst features. The results reveal a notable diversity in cave morphology, shaped by regional geological structures, tectonic activity, karstifiable carbonate substrate, pluvial climatic phases, and fluvial dynamics. Over 80 cave entrances have been identified and analysed in the El Menzel Causse, showing a correlation between their development and the main tectonic features of the region, including the North Middle Atlas Fault, the Median Middle Atlas Fault, and the fluvial network of the Sebou River. We suggest that the presence of these tectonic structures, along with allochthonous units linked to the uplift of the Middle Atlas, combined with Quaternary fluvial dynamics, played a central role in the karstogenesis of the El Menzel Causse caves. For the first time, a comparative study has been conducted between the karst processes of the Moroccan Atlas Mountains and those of the Dinaric Alps. This comparison highlights similarities between the karst phenomena of these two mountain ranges. Our comparative study deepens the understanding of karst processes in this specific region of Morocco, whilst providing valuable insights in comparison with other global karst systems, thereby contributing to the advancement of knowledge in karstology on an international scale.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101097"},"PeriodicalIF":1.2,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sites of Special Scientific Interest: Their role and importance in conserving England's geoheritage","authors":"Colin D. Prosser,&nbsp;Hannah C. Townley","doi":"10.1016/j.pgeola.2025.101095","DOIUrl":"10.1016/j.pgeola.2025.101095","url":null,"abstract":"<div><div>The National Parks and Access to the Countryside Act (1949), the first national nature conservation legislation in Great Britain, included provision to designate, for the purpose of nature conservation, Sites of Special Scientific Interest (SSSIs) on account of their flora, fauna, geological or physiographical (geomorphological) features. Although often incorrectly perceived only as a means of conserving flora and fauna, SSSIs remain the primary mechanism for conserving and managing nationally and internationally important geological and geomorphological features in Great Britain. Seventy-five years on, and with questions being raised about how well they conserve flora and fauna given current threats and pressures, the role and effectiveness of SSSIs in conserving the highlights of England's geoheritage are explored. The importance of geological/geomorphological SSSIs, their origin, character, and workings, and the threats and pressures they face are described. The condition of the 1221 existing geological/geomorphological SSSIs in England is described and the strengths and weaknesses of existing SSSI legislation and policy are discussed, leading us to conclude that SSSIs have been, and remain, extremely effective in conserving England's geoheritage. Any future SSSI reform should recognise, build upon and celebrate the success of geological/geomorphological SSSIs, and would provide an opportunity to raise the profile of geoconservation in government policy and to futureproof the SSSI series. For example, simplifying the process for updating SSSI descriptions and site boundaries would make it easier to accommodate advances in scientific understanding and respond to the physical repositioning of geological/geomorphological features resulting from natural processes.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 3","pages":"Article 101095"},"PeriodicalIF":1.2,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143947895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microbial mound origin for enigmatic, sea-floor, circular structures? Purbeck Limestone Group, offshore Dorset, U.K.","authors":"Dan Bosence ,&nbsp;Jenny Collier ,&nbsp;Arnaud Gallois ,&nbsp;Ian Watkinson ,&nbsp;Chris Dunkerley ,&nbsp;Simon Fleckner","doi":"10.1016/j.pgeola.2025.01.002","DOIUrl":"10.1016/j.pgeola.2025.01.002","url":null,"abstract":"<div><div>This paper describes and interprets diver-collected, offshore samples to establish the origin of enigmatic large (100–200 m across) circular, dome-shaped features imaged using Multibeam Echo-Sounding (MBES) on the sea-floor of Weymouth Bay, Dorset, U.K. The structures occur within the Durlston Formation of the Purbeck Limestone Group (Late Jurassic–Early Cretaceous) that accumulated in a lagoon of variable salinity. A previous morphological study using MBES images alone led to four possible hypotheses for their origin; as isolated erosional remnants, as evaporite-related diapiric structures, as periclinal folds, or as eroded carbonate mounds that grew within the Purbeck lagoon. The petrographic study of seafloor samples taken from the centre of these structures results in their classification into nine sedimentary facies; eight limestones and one chert. The most abundant of these facies are similar to the well-known Purbeck limestones outcropping in nearby cliff sections, however four out of the nine facies have previously unrecorded microbialite components (intraclasts of travertine, stromatolites, laminated filamentous mudstones, and post-depositional, cavity-lining endostromatolites).</div><div>This petrographic analysis suggests a microbial carbonate mound origin for these structures that is also supported by their morphology, their restricted occurrence palaeogeographically and stratigraphically to within the Purbeck Limestone, and the occurrence of microbialites at this level in onshore outcrops. Carbonate mounds of this size, in a lagoonal setting, are previously unknown from the Wessex Basin but show some similarities with Early Cretaceous lacustrine build-ups in South Atlantic offshore basins. The work demonstrates how the interpretation of even an extremely well-known stratigraphy such as that of the Purbeck Group can be limited when only part of the marginal environment is exposed for study.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101093"},"PeriodicalIF":1.2,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Discovery of a phosphatic helical-looking microstructure in Sphenothallus (Cnidaria) from the Late Ordovician of Estonia: Implications for phosphatic biomineralization","authors":"Olev Vinn ,&nbsp;Anna Madison","doi":"10.1016/j.pgeola.2025.101096","DOIUrl":"10.1016/j.pgeola.2025.101096","url":null,"abstract":"<div><div>The tube of <em>Sphenothallus</em> cf. <em>longissimus</em> from the Late Ordovician of Estonia features a phosphatic, broadly laminar structure. It consists of four to five major laminae; each of the laminae is homogenous exteriorly and shows remains of fibres at the bottom. The fibres in most external tube parts exhibit a plywood structure akin to that of Carboniferous <em>Sphenothallus</em> specimens from Russia, whilst the microstructure of a fibrous lamella in the internal part of the tube resembles the aragonitic helical structure found in molluscs. The reinterpretation of the plywood structure as an original biomineral structure of <em>Sphenothallus</em> and the discovery of a phosphatic structure resembling the aragonitic helical structure of molluscs suggest that the biomineralization capabilities of <em>Sphenothallus</em> may have been exceptional among Cnidaria. It now appears possible that phosphatic biomineralization was significantly more advanced than carbonate biomineralization within Cnidaria. This enhanced phosphatic biomineralization could have provided <em>Sphenothallus</em> with evolutionary advantages over similar encrusting tubicolous organisms with less developed biomineralization during the Paleozoic era.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101096"},"PeriodicalIF":1.2,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Cretaceous-Paleocene ostracods and foraminifera assemblages from the Fguira Salah section (Fahs region, northern Tunisia): Biostratigraphy and palaeogeography","authors":"Ahlem Amri,&nbsp;Nesrine Ouchir,&nbsp;Sofien Alyahyaoui","doi":"10.1016/j.pgeola.2025.01.003","DOIUrl":"10.1016/j.pgeola.2025.01.003","url":null,"abstract":"<div><div>The biostratigraphical study of planktic and benthic foraminifera, and ostracod assemblages in the Fguira Salah section (Fahs area, Zaghouan region, NE Tunisia) aims to determine the age of these series for the first time. The vertical distribution of the ostracod species allows to distinguish five successive ostracod assemblages spanning the Santonian, Campanian and Paleocene intervals; with the Maastrichtian interval remaining unrecognised. These assemblages correspond to favourable environments for the ostracods diversity considering their adaptability to various environments. The studied assemblages that support the usefulness of ostracods are precious tools for biostratigraphical correlation and palaeoecological reconstructions. In the Fguira Salah section they contribute to highlighting particular palaeoecological factors, including changes in salinity, water depth, temperature, and hydrodynamism towards the whole palaeoenvironmental evolution in the region and its broader implications.</div></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"136 4","pages":"Article 101094"},"PeriodicalIF":1.2,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}