{"title":"Unsupervised classification applications in enhancing lithological mapping and geological understanding – A case study from Northern Ireland","authors":"Z. Smillie, V. Demyanov, J. McKinley, M. Cooper","doi":"10.1144/jgs2022-136","DOIUrl":"https://doi.org/10.1144/jgs2022-136","url":null,"abstract":"Using pattern classification algorithms can help recognise and predict patterns in large and complex multivariate datasets. Utilising competitive learning, self-organising maps (SOMs) are known unsupervised classification tools that are considered very useful in pattern classification and recognition. This technique is based on the principles of vector quantification of similarities and clustering in a high-dimensional space, where the method can handle the analysis and visualization of high-dimensional data. The tool is ideal for analysing a complex combination of categorical and continuous spatial variables, with particular applications to geological features.\u0000 In this paper, we employ the tool to predict geological features based on airborne geophysical data acquired through the Tellus project in Northern Ireland. SOMs are applied through 8 experiments (iterations), incorporating the radiometric data in combination with geological features, including elevation, slope angle, terrain ruggedness (TRI), and geochronology. The SOMs proved successful in differentiating contrasting bedrock geology, such as acidic versus mafic igneous rocks, while data clustering over intermediate rocks was not as apparent. The presence of a thick cover of glacial deposits in most of the study area presented a challenge in the data clustering, particularly over the intermediate igneous and sedimentary bedrock types.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6603098\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44780356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Magnetostratigraphy of the Mercia Mudstone Group (Devon, UK): implications for regional relationships and chronostratigraphy in the Middle to Late Triassic of western Europe","authors":"M. Hounslow, R. Gallois","doi":"10.1144/jgs2022-173","DOIUrl":"https://doi.org/10.1144/jgs2022-173","url":null,"abstract":"Global synchronisation of environmental change in terrestrial successions in deep-time is challenging due to the paucity of dating methods, a case also applicable to the Middle to Upper Triassic Mercia Mudstone Group in Britain. Using coastal cliff sections, magnetostratigraphy was evaluated at 263 horizons, defining 53 magnetozones. Magnetozones from the lower 140 m of the group demonstrate correspondence to those from the mid Ladinian to early Carnian polarity timescale, dating which is compatible with magnetostratigraphy from the underlying Sherwood Sandstone Group. Magnetostratigraphy of the Dunscombe Mudstone Formation, and associated palynological data, suggest a late Carnian to earliest Norian age, and a dramatically lower accumulation rate than adjacent formations. The polarity record demonstrates coeval flooding events, evaporite deposits and intervals of sand supply between the Wessex Basin and the Central European Basin in the Carnian. This is the result of linked climatic and eustatic changes between these separate basins, related to aeolian dust supply and the shrinkage of hyper-arid source regions for the fines. Magnetostratigraphy from the Branscombe Mudstone and Blue Anchor formations demonstrates their Norian and early Rhaetian age. These and other data suggest an alternative synchronization of marine and non-marine polarity records for the Norian polarity timescale. 198 words\u0000 \u0000 Supplementary material:\u0000 Section details and detailed logs of the sampled sections and inferred sequence boundaries, magnetic mineralogy data, demagnetisation behaviour and mean directions, summary of virtual geomagnetic pole data and a comparison to other European poles, construction of other composite reference sections and revised polarity scales. Excel sheet of magnetic data statistically evaluated correlation models, and age models.\u0000 \u0000 \u0000 https://doi.org/10.6084/m9.figshare.c.6613788\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49256591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Structural configuration and tectonics of the Flemish Cap, offshore Newfoundland, from newly acquired seismic reflection data","authors":"P. Yang, J. Welford","doi":"10.1144/jgs2022-115","DOIUrl":"https://doi.org/10.1144/jgs2022-115","url":null,"abstract":"While the Flemish Cap played a pivotal role in the opening of the North Atlantic, the tectonic history of this continental ribbon has been poorly constrained due to insufficient seismic coverage. In this study, we present thirteen newly acquired seismic reflection profiles over the Flemish Cap, on which seismic reflectors show highly variable seismic facies both on and beneath the top acoustic basement, with exceptional imaging of layered crustal structure. The upper crust is primarily characterized by transparent, chaotic amplitude reflectivity. The lower crust, particularly on the flanks of the cap, exhibits relatively bright and coherent reflection packages interpreted as Appalachian orogenic fabrics based on onshore-offshore correlations from pre-rift plate reconstructions. Extensional systems within the continental crust of the Flemish Cap record a transitional stage between Paleozoic orogenic collapse and pre-Jurassic rifting. The crustal architecture associated with Mesozoic rifting of the Flemish Cap is also mapped and the interpreted distinct rift domains display along-strike variations. Overall, the complex tectonic history of the Flemish Cap involved dominantly ductile deformation during the Paleozoic orogenic stage, multiple deformation styles (primarily ductile and brittle-ductile) during the orogen-to-rift transitional stage, and brittle deformation during the major Jurassic-Cretaceous rifting stage.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"321 ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41274427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Phillips, E. Matchan, A. Gleadow, F. Brown, I. Mcdougall, T. Cerling, M. Leakey, J. Hergt, Louise N. Leakey
{"title":"40\u0000 Ar/\u0000 39\u0000 Ar eruption ages of Turkana Basin tuffs: millennial scale resolution constrains paleoclimate proxy tuning models and hominin fossil ages","authors":"D. Phillips, E. Matchan, A. Gleadow, F. Brown, I. Mcdougall, T. Cerling, M. Leakey, J. Hergt, Louise N. Leakey","doi":"10.1144/jgs2022-171","DOIUrl":"https://doi.org/10.1144/jgs2022-171","url":null,"abstract":"\u0000 The Turkana Basin in Kenya/Ethiopia hosts remarkable fossil-rich sediments that are central to our understanding of early hominin evolution, with interbedded volcanic tuffs providing critical time markers. However, the resolution of existing Early Pleistocene/Pliocene ages is limited to ∼20-60 kyr, inhibiting evaluation of climatic/environmental drivers of evolution. Here, we present high precision, single-feldspar\u0000 40\u0000 Ar/\u0000 39\u0000 Ar age and elemental data for four stratigraphically significant tuffs. These samples exhibit variably dispersed age distributions correlated with feldspar compositional trends, interpreted to indicate partial retention of inherited argon, related to crustal ‘cold storage’ and rapid melt infiltration preceding eruption. We evaluated various statistical methods and calculate astronomically calibrated, Bayesian age estimates of 1879.1 ± 0.6 ka (± 2.4 ka including external errors) for the KBS/H2 Tuff, 1837.4 ± 0.9 ka (± 2.4 ka) for the Malbe/H4 Tuff, 1357.5 ± 1.8 ka (± 2.5 ka) for the Chari/L Tuff and 1315.4 ± 1.9 ka (± 2.5 ka) for the Gele Tuff. Our results permit refined age constraints for important early\u0000 Homo\u0000 fossils, including the cranium KNM-ER1813 (\u0000 Homo habilis\u0000 ) and various\u0000 Homo erectus\u0000 fossils. The KBS Tuff age also provides an important calibration locus for orbital tuning of paleoclimate proxy records, revealing complex interplay between paleoclimate and geological drivers of sedimentation.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.6602994\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45014060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}