Proceedings of the Geologists Association最新文献

{"title":"Soft-sediment deformation and glacitectonite formation during the deglaciation of the Allt Cuaich catchment, Grampian Highlands, Scotland","authors":"Emrys Phillips,&nbsp;Jon W. Merritt","doi":"10.1016/j.pgeola.2024.06.003","DOIUrl":"10.1016/j.pgeola.2024.06.003","url":null,"abstract":"<div><p>This paper presents the results of a detailed study of a deformed sequence of Late Devensian<span><span> glacifluvial sands, gravels and diamictons exposed within river cliff sections cut by the Allt (river) Cuaich, northeast of Dalwhinnie in the Grampian Highlands of Scotland. Macroscale sedimentological and structural field observations are combined with micromorphological and microstructural analysis to investigate the ice-marginal processes which led to the deposition and subsequent deformation of these glacifluvial to glacilacustrine deposits. Sedimentological evidence indicates that water-lain deposits in the area are capped by till and record the eastward </span>progradation<span> of ice-proximal fans into water ponded by an ice margin that advanced up valley from the west/southwest. These glacifluvial/ice-marginal fan sequences were deformed and subsequently overridden by ice that advanced (at least 6 km) into the Cuaich catchment. A suite of similar, but undeformed ice-marginal fans and laminated glacilacustrine deposits were laid down during the subsequent withdrawal of ice down-valley. Microstructures present within the variably glacitectonised (folded, faulted) laminated sands, silts and clays reveal a complex history of local glacial readjustments in a dynamic ice-marginal aqueous setting. Brittle–ductile shearing, liquefaction<span> and remobilisation<span>, and extensional brittle faulting accompanied the deposition of an overlying till. A detailed model of brittle–ductile shearing and glacitectonite formation during the overriding of water-rich ice-marginal deposits involves initial proglacial thrusting and folding, followed by continued submarginal to subglacial brittle–ductile shearing and extensional faulting. The study supports growing evidence that in Scotland the British Ice Sheet underwent localised expansion towards the end of the main Late Devensian glaciation (Dimlington Stadial, 26–13 ka radiocarbon years BP). In addition, it clearly demonstrates that the complex polyphase deformation recorded by glacitectonised sequences may not simply be a product of intense subglacial deformation, but a result of progressive proglacial to submarginal deformation, followed by subglacial shear as the ice progressively overrides a preexisting sedimentary sequence.</span></span></span></span></p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 4","pages":"Pages 438-457"},"PeriodicalIF":1.2,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141707195","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 new record of coleoid arm hooks from the lowermost Jurassic of Lilstock, Somerset","authors":"Simon Penn ,&nbsp;Malcolm B. Hart ,&nbsp;Gregory D. Price","doi":"10.1016/j.pgeola.2024.05.006","DOIUrl":"10.1016/j.pgeola.2024.05.006","url":null,"abstract":"<div><p>We report on a new assemblage of coleoid arm hooks found in the Blue Lias (Lower Jurassic) succession near Lilstock (Somerset, UK). As there are no soft tissues or other materials (ink sac, phragmocone, <em>etc.</em>) preserved in the vicinity of the hooks, the genus and species cannot be accurately identified. Unlike the hooks of <em>Clarkeiteuthis</em>, which have distinctive inflated, bilobate bases, the hooks discussed herein are delicate, with a gently curved apex, which makes them quite similar to the arm hooks of <em>Belemnotheutis</em> or <em>Acanthoteuthis</em><span>. The assemblage of hooks shows a distinct organisation and, in some places, the hooks are clearly aligned as they would have been in life position. Comparable material of late Jurassic age from the Etches Collection (Kimmeridge, Dorset) is compared to the new arm hook assemblage.</span></p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 4","pages":"Pages 486-491"},"PeriodicalIF":1.2,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141700166","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 dinosaur tracks from the Middle Jurassic red beds of the Middle Atlas (Morocco): Application of photogrammetry to ichnology and conservation of geological heritage","authors":"Mustapha Amzil ,&nbsp;Mostafa Oukassou ,&nbsp;Jens N. Lallensack ,&nbsp;Hendrik Klein ,&nbsp;Omar Zafaty ,&nbsp;Hafid Saber ,&nbsp;André Charrière ,&nbsp;Christian Meyer ,&nbsp;Gerard D. Gierliński","doi":"10.1016/j.pgeola.2024.06.004","DOIUrl":"10.1016/j.pgeola.2024.06.004","url":null,"abstract":"<div><p><span>The El Mers I and II formations (Middle Jurassic, Bathonian) are geological units outcropping in the folded Middle Atlas of Morocco rich in body and trace fossils of dinosaurs. The numerous tracksites of these units have been little studied and are severely affected by ongoing erosion (</span><em>e.g.</em>, seasonal flooding) and, to a lesser degree, human activities (<em>e.g.</em><span>, urbanisation). The aim of this project is to fully document and interpret the dinosaur tracks of two historic sites and four new sites discovered in the El Mers area using digital photogrammetry<span>. The ichnofauna comprises abundant tracks and trackways of theropod and sauropod dinosaurs as well as of probable crocodylomorph tracks. The theropod tracks include several footprints of high anatomical fidelity, but the majority of the discovered tracks are identified to be penetrative tracks, with one site preserving abundant swim tracks. The sites preserve both small and enormous sauropod tracks. The enormous sauropod tracks are among the largest known worldwide, with a pes track length of up to 130 cm. The obtained 3D models are compared with site maps created by analogue mapping performed more than 15 years ago of the historical sites, revealing how erosion has both destructed surfaces and exposed new ones. The application of photogrammetry allows for the rapid collection of accurate high-resolution data with sustainable costs. The resulting 3D models can be used in research to digitally conserve threatened sites, and as a basis for knowledge transfer to the public. The present contribution encourages the intellectual, logistical, and social involvement of the local population to collaborate with scientists for the conservation of the rich geological heritage. Furthermore, scientific investigations in this area could shift from academic-only research to research focused on conservation and geotourism initiatives that involve local communities.</span></span></p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 4","pages":"Pages 458-480"},"PeriodicalIF":1.2,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141716081","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":"Carboniferous wildfire revisited: Wildfire, post-fire erosion and deposition in a Mississippian crater lake","authors":"Andrew C. Scott","doi":"10.1016/j.pgeola.2024.06.002","DOIUrl":"10.1016/j.pgeola.2024.06.002","url":null,"abstract":"<div><p>Fires have been shown to have been common in many Carboniferous ecosystems worldwide yet we still have little understanding of the detail of what, where and how such fires occur or indeed their effects both on the local ecosystem as well as on the Earth System as a whole. The Kingswood Limestone, of late Viséan (Mississippian age) found near Pettycur in Fife, Scotland, is interpreted as being deposited within a crater lake. The limestone contains a range of volcanic clasts together with charcoalified and uncharred plants. Two distinctive communities existed. One dominated by the small scrambling lycopsid <em>Oxroadia</em> that is permineralised and a second dominated by a range of pteridosperms and other gymnosperms preserved as charcoal. Fires surrounding a crater lake charred the plants that were then washed into the lake by post-fire erosion. All plant organs are found as charcoal including woody axes, leaves, pollen organs and ovules. <em>Oxroadia</em> that was living close to the lake was not affected by fire. Rising lake and sea levels allowed saline water to be introduced to the lake and connection to the sea was established. Many new charcoalified plants have still to be formally described. The Kingswood flora, together with the nearby Pettycur flora represents two of the most important Mississippian plant sites globally.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 4","pages":"Pages 416-437"},"PeriodicalIF":1.2,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016787824000300/pdfft?md5=5ab3868c0d6f462cf1ea3a5daf205517&pid=1-s2.0-S0016787824000300-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141692577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A thin-skinned thrust model for ice-marginal glacitectonic detachment and emplacement of Carboniferous bedrock rafts at Kilcummin Head, NW Ireland","authors":"David P. Vaughan ,&nbsp;Emrys Phillips ,&nbsp;Jonathan R. Lee ,&nbsp;Jane K. Hart","doi":"10.1016/j.pgeola.2024.04.001","DOIUrl":"10.1016/j.pgeola.2024.04.001","url":null,"abstract":"<div><p>This paper presents the results of a detailed macro- and microscale structural study of the glacitectonised sequence at Kilcummin Head on the western side of Killala Bay, County Mayo, northwest Ireland. The sequence comprises two laterally extensive, thrust-stacked rafts of Carboniferous limestone and mudstone emplaced upon the <em>in situ</em> bedrock of the Ballina Limestone Formation. Restored cross-sections reveal that the glacitectonised sequence has undergone extensive deformation and shortening of 61 %. This accompanied the formation of a prominent thrust-moraine associated with a northward ice advance across Killala Bay during the Midlandian (Devensian). A five-stage model is proposed to describe the deformation. Stage 1 comprises detachment of the rafts, and the majority of the sequence shortening. North-directed transport of the rafts occurred on a major décollement surface located at the base of the rafted sequence, marked by a mudstone-rich glacitectonite. Stage 2 accommodated further shortening <em>via</em> a series of imbricate thrusts leading to the stacking of the bedrock rafts (Stages 3 and 4). Stage 5 saw final stacking of rafts within a prominent thrust-block moraine, followed by the deposition of a sequence of coarse-grained, ice-marginal glacigenic deposits.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 260-281"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141055406","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 re-evaluation of Scelidosaurus remains from Ireland and the importance of apomorphy-based identifications","authors":"Kieran G. Satchell","doi":"10.1016/j.pgeola.2024.03.002","DOIUrl":"10.1016/j.pgeola.2024.03.002","url":null,"abstract":"<div><p><em>Scelidosaurus</em> is a herbivorous dinosaur belonging to the ornithischian clade Thyreophora. Until recently, its distribution was limited to the cliffs of Charmouth, on the south coast of Dorset, United Kingdom. In 2021, a fragmentary specimen from Lower Jurassic strata in Northern Ireland (BELUM K3998) was referred tentatively to <em>Scelidosaurus</em>. This bone, the proximal end of a femur, was suggested to be an ornithischian based on several characteristics, including gross morphology and osteohistology. This study reassesses these characteristics, and finds no evidence to support their use for identifying this specimen as either an ornithischian or <em>Scelidosaurus</em>. With the most comprehensive studies on <em>Scelidosaurus</em> finding no autapomorphies of the proximal femur, this study regards BELUM K3998 as Dinosauria indet. Additionally, this study highlights the importance of apomorphy-based approaches in taxonomy and the benefits of such methodologies.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 349-351"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140272329","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 first Protosiren remains preserved in ornamental limestones, Middle Eocene, North Eastern Desert, Egypt","authors":"Ahmed Mamdouh ,&nbsp;Ramadan M. El-Kahawy ,&nbsp;Mohamed AbdelGawad ,&nbsp;Gebely Abu El-Kheir","doi":"10.1016/j.pgeola.2024.04.005","DOIUrl":"10.1016/j.pgeola.2024.04.005","url":null,"abstract":"<div><p>A recent revelation has come to our attention, revealing the remarkably well-preserved post-cranial remains belonging to <em>Protosiren</em>. These remains include vertebrae, ribs, and fragmentary bones, and were discovered from two different horizons located in the Mokattam Formation of El-Galala Plateau, North Eastern Desert of Egypt. The first specimen, GCU0101, is identified as <em>Protosiren</em> sp., whereas the GCU0201 specimen is recognised as <em>Protosiren</em> cf. <em>P. fraasi</em> due to certain distinguishing features. These include vertebrae with wide keyhole-shaped neural canals, reduced tuberculum on the ribs, lack of pachyostotic ribs, and the possession of rugose articular rib head. This discovery is remarkable, as it offers a unique opportunity to study the ancient marine mammal's morphology and osteology, shedding light on its evolutionary history and ecological niche. The study documents the first occurrence of <em>Protosiren</em> from an ornamental limestone of the Middle Eocene (Bartonian) Observatory Formation from El-Galala Plateau, Northeastern Desert, Egypt.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 310-320"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140756193","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 Miocene (Tortonian, Menorca, Spain) benthic macrofauna preserved in a phosphatic hardground: A difficult but invaluable record of upwelling palaeoenvironments","authors":"Robin I. Knight","doi":"10.1016/j.pgeola.2024.04.002","DOIUrl":"10.1016/j.pgeola.2024.04.002","url":null,"abstract":"<div><p>This field study records that the Tortonian phosphatic hardground at S'Algar, Menorca has a diverse fossil macrobenthic fauna dominated by bivalves. These faunal elements occur in four preservational forms (A–D). Each taphonomic form within the hardground is characterised by different concentrations of <em>Entobia</em> isp. (clionaid sponge boring) and encrustation. The preservational forms have specific fossil macrofaunas associated with them, and the hardground represents a melange of bioclasts derived from different environments on the Menorcan Miocene shelf. These habitats are influenced by the upwelling event that provides the conditions for hardground mineralisation.</p><p>A <em>Glycymeris</em>-<em>Crassatella</em>-<em>Clypeaster</em> association (A) records part of a fauna that lived on the upper ramp slope that was periodically affected by high energy and low oxygen conditions due to upwelling waters. The smaller sized fauna (B), characterised by an arcid-carditid-venerid association is derived from the middle ramp that was affected by storms and a more persistent westward flowing current that intermittently drove upwelling. The fragmentary and disarticulated nature of both faunas indicates that they were mixed within the hardground <em>via</em> reworking processes driven by these seafloor energy regimes.</p><p>Some of the large gastropod taxa, dentition-up <em>Glycymeris</em> and <em>Gastrochaena</em> suggest that the hardground had its own fauna. Preservation A fauna and other opportunistic taxa inhabited an environment where the hardground was exposed on the Miocene seafloor as ‘islands’ surrounded by thin layers of looser sediment. Phosphatic bioclasts in the underlying limestone indicate that similar mineralised beds were formed elsewhere on the shelf prior to the formation of the studied outcrop.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 282-300"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140792792","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":"Latest Jurassic–Early Cretaceous sedimentary cyclicity and events (Wessex Basin, southern England): A case of pulsed mantle convection?","authors":"Jonathan D. Radley ,&nbsp;Robert A. Coram","doi":"10.1016/j.pgeola.2024.02.002","DOIUrl":"10.1016/j.pgeola.2024.02.002","url":null,"abstract":"<div><p>A pulsed mantle convection model has been proposed for regional third-order cyclic sea level changes during time intervals for which robust evidence of extensive polar ice caps is lacking. One such interval, the Late Jurassic–Early Cretaceous, is represented in southern England's Wessex Basin by the marine to non-marine Portland and Purbeck Limestone groups and Wealden Group and Supergroup. Third-order cyclicity in this succession is reviewed against the mantle convection model, involving pulsed growth of a regional uplift centred on the Cornubian Massif, bordering the Wessex Basin. Supporting evidence for the model is forthcoming from cyclicities in the Upper Tithonian marine Portland Group and Hauterivian–Lower Aptian alluvial–lacustrine–lagoonal Weald Clay Group. Third-order cycles in the Berriasian–Valanginian alluvial–lacustrine Hastings Group reflect fault reactivation along the Anglo-Brabant Massif, conventionally linked to North Atlantic opening. Credible cyclicities on comparable scales have not been identified in the Upper Tithonian–Lower Valanginian lagoonal–lacustrine Purbeck Limestone Group or the Valanginian–Barremian fluvial–alluvial Wessex Formation. Purbeck lithofacies are defined largely by climatic and local tectonic signals; cyclicities were potentially masked in the Wessex Formation by dynamic fluvial processes in proximity to the massif. Certain biotic events in the Purbeck Limestone Group and fluvial events in the Wessex Formation possibly reflect vertical movements of the Cornubian uplift.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 237-246"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141277885","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":"Was there a low-altitude Younger Dryas Stadial glacier in south-east Wales? Re-interpretation of landforms and palaeo-climatic inferences","authors":"Richard A. Shakesby ,&nbsp;Stephen L. Cornford ,&nbsp;John F. Hiemstra","doi":"10.1016/j.pgeola.2024.04.003","DOIUrl":"10.1016/j.pgeola.2024.04.003","url":null,"abstract":"<div><p>A glacial origin for cirque-like hollows cut into the western escarpment of the Usk valley near Abergavenny, South Wales has become widely accepted. Associated supposed extensive moraine ‘festoons’ have been depicted merging and contemporaneous with Last Glacial Maximum (LGM) deposits formed by ice occupying the adjacent Usk valley. We re-interpret these festoons as the product mainly of rock slope failures (RSFs) emanating from the hollows. A cirque glacier origin is preferred to account for a compact double-ridge feature in one of the hollows. The equilibrium-line altitude (ELA) of the reconstructed glacier (357 m) is &gt;<!--> <!-->60 m lower than all similarly small, presumed Younger Dryas Stadial (YDS; <em>c.</em>, 12.9–11.7 ka) glaciers elsewhere in South Wales. To test whether this glacier nevertheless might date from the YDS, we apply three approaches to reconstruct annual palaeo-precipitation amounts at the ELA, two based on relationships between accumulation and ablation for modern glaciers and the third on a simple degree-day model (DDM) using likely climatic characteristics for this event. The DDM can be tailored to represent the recognised large-amplitude YDS annual temperature range rather than the much smaller one experienced by modern glaciers, making it our preferred approach. Although conditions along the Usk valley escarpment during the LGM would have been well suited to cirque glacier formation, the DDM approach, using the large-amplitude annual temperature ranges, suggests that a YDS age might also be possible. The results have implications for re-assessing the likely ages of some former small glaciers in South Wales.</p></div>","PeriodicalId":49672,"journal":{"name":"Proceedings of the Geologists Association","volume":"135 3","pages":"Pages 301-309"},"PeriodicalIF":1.2,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140755546","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}