Pub Date : 2023-06-07DOI: 10.37570/bgsd-2023-72-03
J. S. Peel
The upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of southern Lauge Koch Land and Løndal, south-western Peary Land, North Greenland (Laurentia) yields diverse assemblages of phosphatised Small Shelly Fossils after treatment with weak acetic acid. The occurrence merits description as a fossil Lagerstätte on account of the exceptional preservation of soft parts in some specimens, although the phosphatisation itself is generally rather coarse. Bradoriid and phosphatocopid arthropods are common and display substantial variation in their preservational history. Some specimens retain traces of internal morphology, although details are generally obscured by indifferent preservation. Rare specimens extend the range of stem-group pentastomid arthropods back by more than 10 million years. A unique hatching larva demonstrates the same early developmental stage of a stem-group priapulan worm to that described in some present-day priapulans. The preservation of an in place operculum has demonstrated that the widespread, supposed mollusc Protowenella is actually an unusual, strongly coiled hyolith. Abundant coprolites and cololites provide additional evidence of early phosphatisation. In terms of morphology, Cambrocoryne lagenamorpha gen. et sp. nov. superficially resembles wiwaxiid and some annelid sclerites, thelodont scales and the foraminiferan Lagena, but its true identity is obscure.
{"title":"A phosphatised fossil Lagerstätte from the middle Cambrian (Wuliuan Stage) of North Greenland (Laurentia)","authors":"J. S. Peel","doi":"10.37570/bgsd-2023-72-03","DOIUrl":"https://doi.org/10.37570/bgsd-2023-72-03","url":null,"abstract":"The upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of southern Lauge Koch Land and Løndal, south-western Peary Land, North Greenland (Laurentia) yields diverse assemblages of phosphatised Small Shelly Fossils after treatment with weak acetic acid. The occurrence merits description as a fossil Lagerstätte on account of the exceptional preservation of soft parts in some specimens, although the phosphatisation itself is generally rather coarse. Bradoriid and phosphatocopid arthropods are common and display substantial variation in their preservational history. Some specimens retain traces of internal morphology, although details are generally obscured by indifferent preservation. Rare specimens extend the range of stem-group pentastomid arthropods back by more than 10 million years. A unique hatching larva demonstrates the same early developmental stage of a stem-group priapulan worm to that described in some present-day priapulans. The preservation of an in place operculum has demonstrated that the widespread, supposed mollusc Protowenella is actually an unusual, strongly coiled hyolith. Abundant coprolites and cololites provide additional evidence of early phosphatisation. In terms of morphology, Cambrocoryne lagenamorpha gen. et sp. nov. superficially resembles wiwaxiid and some annelid sclerites, thelodont scales and the foraminiferan Lagena, but its true identity is obscure.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49393524","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}
Pub Date : 2023-06-07DOI: 10.37570/bgsd-2023-72-04
O. Bennike, B. Nilsson
We retrieved a sediment core from Vasby Mose, a calcareous fen on eastern Sjælland, Denmark. The record spans the period from c. 14 700 to 6800 cal. years BP. During the Lateglacial, Vasby Mose was a lake where minerogenic sandy and clayey sediments accumulated. In the early Lateglacial, from c. 14 700 to 13 200 cal. years BP, a tundralike open, treeless vegetation with Betula nana and Dryas octopetala was found in the region. During the Younger Dryas, a rich flora of aquatic plants was found in the lake. In the Early to Mid-Holocene, Vasby Mose was a spring-fed calcareous fen, with deposition of peat and tufa. The flora included the sedges Carex rostrata and Carex paniculata, the aquatic plant Menyathes trifoliata, the calciphilous reed plant Cladium mariscus and the today nationally extinct bryophyte Meesia triquetra. The fauna included aquatic mollusc taxa such as Pisidium sp., Valvata spp. And Bithynia tentaculate and terrestrial or semi-terrestrial species such as Galba truncatula, Euconolus cf. alderi, Succinea/Oxyloma, Zonitoides nitidus and Vallonia pulchella. The Preboreal oscillation and other Early Holocene climate events are seen as short-lived, wet intervals.
{"title":"Lateglacial to Mid-Holocene history of Vasby Mose, eastern Sjælland, Denmark","authors":"O. Bennike, B. Nilsson","doi":"10.37570/bgsd-2023-72-04","DOIUrl":"https://doi.org/10.37570/bgsd-2023-72-04","url":null,"abstract":"We retrieved a sediment core from Vasby Mose, a calcareous fen on eastern Sjælland, Denmark. The record spans the period from c. 14 700 to 6800 cal. years BP. During the Lateglacial, Vasby Mose was a lake where minerogenic sandy and clayey sediments accumulated. In the early Lateglacial, from c. 14 700 to 13 200 cal. years BP, a tundralike open, treeless vegetation with Betula nana and Dryas octopetala was found in the region. During the Younger Dryas, a rich flora of aquatic plants was found in the lake. In the Early to Mid-Holocene, Vasby Mose was a spring-fed calcareous fen, with deposition of peat and tufa. The flora included the sedges Carex rostrata and Carex paniculata, the aquatic plant Menyathes trifoliata, the calciphilous reed plant Cladium mariscus and the today nationally extinct bryophyte Meesia triquetra. The fauna included aquatic mollusc taxa such as Pisidium sp., Valvata spp. And Bithynia tentaculate and terrestrial or semi-terrestrial species such as Galba truncatula, Euconolus cf. alderi, Succinea/Oxyloma, Zonitoides nitidus and Vallonia pulchella. The Preboreal oscillation and other Early Holocene climate events are seen as short-lived, wet intervals.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45881935","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}
Pub Date : 2023-02-23DOI: 10.37570/bgsd-2023-72-02
O. Humlum, Hanne H. Cristiansen, Lis E. Mortensen, F. Stuart, J. Stone
This paper presents a new complete field mapping of glacial landscapes, landforms and sediments in the Faroe Islands, supplemented by observations from bathymetric maps of the Faroe Shelf. In addition, previous investigations of Quaternary and espe-cially the Weichselian glaciation of the archipelago are reviewed. New cosmogenic nuclide exposure ages indicate that the last extensive glaciation of the Faroe Islands occurred during the Late Weichselian, most likely during the Last Glacial Maximum (LGM; c. 26.5–19.0 cal. ka BP), although a Younger Dryas (c. 12.9–11.7 cal. ka BP) age cannot be entirely excluded. Geomorphological mapping provides a background for reconstructing the extent and type of the glaciation of the Faroe Islands. The reconstructed Weichselian glaciation appears to have had the character of an exten-sive valley glaciation, with several marine glacier termini. The present glaciation of southern Spitsbergen, Svalbard, represents a modern analogue of the reconstructed Weichselian glaciation in the Faroe Islands. The lack of raised coastal features in the Faroe Islands, also at protected sites, suggests that postglacial isostatic uplift was smaller than post-LGM eustatic sea level rise. Numerical glacier reconstructions carried out for different extents of the last extensive Faroese glaciation suggest that such limited postglacial isostatic crustal uplift requires that the Faroe Shelf was not extensively glaciated during the Late Weichselian, but it doubtless was so during at least one of the previous Quaternary glaciations.
{"title":"Weichselian Glaciation of the Faroe Islands","authors":"O. Humlum, Hanne H. Cristiansen, Lis E. Mortensen, F. Stuart, J. Stone","doi":"10.37570/bgsd-2023-72-02","DOIUrl":"https://doi.org/10.37570/bgsd-2023-72-02","url":null,"abstract":"This paper presents a new complete field mapping of glacial landscapes, landforms and sediments in the Faroe Islands, supplemented by observations from bathymetric maps of the Faroe Shelf. In addition, previous investigations of Quaternary and espe-cially the Weichselian glaciation of the archipelago are reviewed. New cosmogenic nuclide exposure ages indicate that the last extensive glaciation of the Faroe Islands occurred during the Late Weichselian, most likely during the Last Glacial Maximum (LGM; c. 26.5–19.0 cal. ka BP), although a Younger Dryas (c. 12.9–11.7 cal. ka BP) age cannot be entirely excluded. Geomorphological mapping provides a background for reconstructing the extent and type of the glaciation of the Faroe Islands. The reconstructed Weichselian glaciation appears to have had the character of an exten-sive valley glaciation, with several marine glacier termini. The present glaciation of southern Spitsbergen, Svalbard, represents a modern analogue of the reconstructed Weichselian glaciation in the Faroe Islands. The lack of raised coastal features in the Faroe Islands, also at protected sites, suggests that postglacial isostatic uplift was smaller than post-LGM eustatic sea level rise. Numerical glacier reconstructions carried out for different extents of the last extensive Faroese glaciation suggest that such limited postglacial isostatic crustal uplift requires that the Faroe Shelf was not extensively glaciated during the Late Weichselian, but it doubtless was so during at least one of the previous Quaternary glaciations.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43066673","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}
Pub Date : 2023-02-01DOI: 10.37570/bgsd-2023-72-01
A. Schrøder, G. Carnevale
Bony fishes are among the best represented macrofossils from the earliest Eocene Fur Formation, northern Denmark. The most abundant fish of the formation has never been formally described, in spite of its abundance throughout the formation, and only referred to as an ‘argentinoid’. This work provides a taxonomic study of this argentinoid taxon, which is described herein as Surlykus longigracilis gen. et sp. nov. The caudal skeleton shows separated first preural and first ural centra, a unique condition within the Argentiniformes. In addition, it is characterised by having a large mouth and a single supramaxilla, which suggest that Surlykus gen. nov. occupies a basal position within the Argentiniformes, representing the sister-group to all the other lineages of this clade ([Argentinidae + Opisthoproctidae] + [Bathylagidae + Microstomatidae]), and, consequently, a stem-group Argentiniformes. Mass-mortality assemblages may indicate that Surlykus longigracilis gen. et sp. nov. formed large schools in the ancient North Sea Basin, where it probably represented the trophic nucleus of the fish communities.
硬骨鱼是丹麦北部始新世早期Fur组中最具代表性的大型化石之一。该地层中最丰富的鱼类从未被正式描述过，尽管它在整个地层中都很丰富，只被称为“阿根廷类”。本文对该阿根廷类分类群进行了分类研究，并将其命名为Surlykus longigracilis gen. et sp. 11 .尾骨显示出第一脊膜中央和第一脊膜中央的分离，这在阿根廷目中是独一无二的。此外，它的特点是有一个大嘴和一个上腋窝，这表明Surlykus gen. nov.在阿根廷亚纲中处于基部位置，代表了该分支的所有其他谱系([阿根廷亚纲科+ Opisthoproctidae] + [Bathylagidae + Microstomatidae])的姐妹群，因此，它是阿根廷亚纲的茎群。大量死亡组合可能表明，长形苏利库斯(Surlykus longigracilis gen. et sp. 11)在古北海盆地形成了大型鱼群，它可能代表了古北海盆地鱼类群落的营养核。
{"title":"The argentiniform Surlykus longigracilis gen. et sp. nov., the most abundant fish from the Eocene Fur Formation of Denmark.","authors":"A. Schrøder, G. Carnevale","doi":"10.37570/bgsd-2023-72-01","DOIUrl":"https://doi.org/10.37570/bgsd-2023-72-01","url":null,"abstract":"Bony fishes are among the best represented macrofossils from the earliest Eocene Fur Formation, northern Denmark. The most abundant fish of the formation has never been formally described, in spite of its abundance throughout the formation, and only referred to as an ‘argentinoid’. This work provides a taxonomic study of this argentinoid taxon, which is described herein as Surlykus longigracilis gen. et sp. nov. The caudal skeleton shows separated first preural and first ural centra, a unique condition within the Argentiniformes. In addition, it is characterised by having a large mouth and a single supramaxilla, which suggest that Surlykus gen. nov. occupies a basal position within the Argentiniformes, representing the sister-group to all the other lineages of this clade ([Argentinidae + Opisthoproctidae] + [Bathylagidae + Microstomatidae]), and, consequently, a stem-group Argentiniformes. Mass-mortality assemblages may indicate that Surlykus longigracilis gen. et sp. nov. formed large schools in the ancient North Sea Basin, where it probably represented the trophic nucleus of the fish communities.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45260197","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}
Pub Date : 2022-11-30DOI: 10.37570/bgsd-2022-70-10
C. Duffin, J. Milán
Oblidens bornholmensis, known from isolated upper posterior (palatine) and lower posterior (mandibular) tooth plates, was the first myriacanthid holocephalian to be described from the Hasle Formation (Pliensbachian, Early Jurassic) of Bornholm (Denmark). Further collecting in the Hasle Formation has yielded seven more specimens of myriacanthid tooth plates. Two mandibular tooth plates are assigned to Myriacanthus paradoxus, thereby extending both the geographical and stratigraphic range of the genus. In addition to new material of Oblidens bornholmensis, some distinctive myriacanthid palatine and mandibular tooth plates are described and left in open nomenclature. The Early Pliensbachian deposits of Bornholm preserve the most diverse myriacanthid fauna known to date.
{"title":"Further holocephalian remains from the Hasle Formation (Early Jurassic) of Denmark.","authors":"C. Duffin, J. Milán","doi":"10.37570/bgsd-2022-70-10","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-10","url":null,"abstract":"Oblidens bornholmensis, known from isolated upper posterior (palatine) and lower posterior (mandibular) tooth plates, was the first myriacanthid holocephalian to be described from the Hasle Formation (Pliensbachian, Early Jurassic) of Bornholm (Denmark). Further collecting in the Hasle Formation has yielded seven more specimens of myriacanthid tooth plates. Two mandibular tooth plates are assigned to Myriacanthus paradoxus, thereby extending both the geographical and stratigraphic range of the genus. In addition to new material of Oblidens bornholmensis, some distinctive myriacanthid palatine and mandibular tooth plates are described and left in open nomenclature. The Early Pliensbachian deposits of Bornholm preserve the most diverse myriacanthid fauna known to date.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41718761","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}
Pub Date : 2022-09-26DOI: 10.37570/bgsd-2022-71-05
J. Ineson, H. Petersen, C. Andersen, M. Bjerager, F. Jakobsen, L. Kristensen, F. Mørk, E. Sheldon
An integrated seismic–stratigraphic study of the Lower Cretaceous Cromer Knoll Group was undertaken as part of a recent comprehensive analysis of the Upper Jurassic – lowermost Cretaceous petroleum system in the Danish Central Graben. This study of the basal group of the post-rift package yielded an updated regional assessment of the distribution of the Valhall, Tuxen, Sola and Rødby Formations. This is documented by four high resolution isochore maps (presented here) that record temporal shifts in subsidence patterns from the latest Ryazanian to the earliest Cenomanian. The distribution and thickness variation of the mud-dominated Valhall Formation (latest Ryazanian – early Hauterivian) at the base of the group attests to the progressive fill of inherited syn-rift morphology. The dominant depositional theme is thus ponding in, and onlap from, the main inherited depocentres, although growth faults and incipient inversion locally controlled stratigraphic architecture, and new depocentres were initiated in the east of the graben (Ål and Outer Rough Basins). The isochores for the succeeding, increasingly chalk-rich Tuxen, Sola and Rødby Formations (Hauterivian – earliest Cenomanian) document the regional weakening of syn-rift patterns but emphasize the shift in sedimentation patterns controlled by accelerating inversion activity in the east (Adda–Tyra area, Søgne Basin) and increased local subsidence. The latter sometimes coincided with syn-rift depocentres, such as the Roar Basin and the Arne-Elin Graben, but was also significant in the new Early Cretaceous depocentres in the west of the graben, particularly the Outer Rough Basin. The evolution of the Early Cretaceous basin recorded by this dataset reveals significant shifts in the subsidence pattern in the late Valanginian – early Hauterivian, in large part due to early inversion in the east, and during the late Aptian – early Albian when subsidence was focussed in central and western sub-basins, probably locally due to salt withdrawal. These events, in combination with sea-level change, had implications for the accumulation and preservation of Barremian and early Aptian reservoir chalks.
{"title":"Early Cretaceous stratigraphic and basinal evolution of the Danish Central Graben: a review","authors":"J. Ineson, H. Petersen, C. Andersen, M. Bjerager, F. Jakobsen, L. Kristensen, F. Mørk, E. Sheldon","doi":"10.37570/bgsd-2022-71-05","DOIUrl":"https://doi.org/10.37570/bgsd-2022-71-05","url":null,"abstract":"An integrated seismic–stratigraphic study of the Lower Cretaceous Cromer Knoll Group was undertaken as part of a recent comprehensive analysis of the Upper Jurassic – lowermost Cretaceous petroleum system in the Danish Central Graben. This study of the basal group of the post-rift package yielded an updated regional assessment of the distribution of the Valhall, Tuxen, Sola and Rødby Formations. This is documented by four high resolution isochore maps (presented here) that record temporal shifts in subsidence patterns from the latest Ryazanian to the earliest Cenomanian. The distribution and thickness variation of the mud-dominated Valhall Formation (latest Ryazanian – early Hauterivian) at the base of the group attests to the progressive fill of inherited syn-rift morphology. The dominant depositional theme is thus ponding in, and onlap from, the main inherited depocentres, although growth faults and incipient inversion locally controlled stratigraphic architecture, and new depocentres were initiated in the east of the graben (Ål and Outer Rough Basins). The isochores for the succeeding, increasingly chalk-rich Tuxen, Sola and Rødby Formations (Hauterivian – earliest Cenomanian) document the regional weakening of syn-rift patterns but emphasize the shift in sedimentation patterns controlled by accelerating inversion activity in the east (Adda–Tyra area, Søgne Basin) and increased local subsidence. The latter sometimes coincided with syn-rift depocentres, such as the Roar Basin and the Arne-Elin Graben, but was also significant in the new Early Cretaceous depocentres in the west of the graben, particularly the Outer Rough Basin. The evolution of the Early Cretaceous basin recorded by this dataset reveals significant shifts in the subsidence pattern in the late Valanginian – early Hauterivian, in large part due to early inversion in the east, and during the late Aptian – early Albian when subsidence was focussed in central and western sub-basins, probably locally due to salt withdrawal. These events, in combination with sea-level change, had implications for the accumulation and preservation of Barremian and early Aptian reservoir chalks.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44892269","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}
Pub Date : 2022-08-26DOI: 10.37570/bgsd-2022-71-04
M. E. Jelby, J. Ineson, N. Thibault, S. Bodin, C. Blok, Niklas Edvardsen, Tatjana S. Clemmensen, T. Buls, K. Anderskouv
The Lower Cretaceous Tuxen (lower Hauterivian – upper Barremian) and Sola (upper Barremian – Albian) Formations in the Danish Central Graben (North Sea) constitute one of the oldest chalk successions recorded globally, but have received little attention with regards to sedimentary facies and depositional processes. This study presents the first comprehensive carbonate facies analysis of the succession, retrieved from seven drill cores from the Valdemar and Adda Fields. A total of 50 facies are identified, based on a continuum of six lithologies ranging from chalk to marlstone and tuffaceous siltstone to sandstone that display eight different sedimentary structures or fabrics, and two redox-associated lithological color variations (green and red) in the Adda Field. The eight sedimentary structures record: (i) comprehensive bioturbation of homogeneous sediment during fully oxygenated benthic conditions and low sedimentation rates; (ii) a similar bioturbation process but in heterogeneous sediment with lithological contrasts permitting visible burrows to form, perhaps due to rhythmic alternation between pelagic (clay-poor) and hemipelagic (clay-rich) sedimentation; (iii) pelagic to hemipelagic suspension settling in dysoxic to anoxic bottom-water conditions; (iv) patchy cementation of the shallow sea bed during incipient hardground formation; (v) reworking of bioclasts and chalk intraclasts by bottom or wave-induced currents and cohesive debris flows; (vi) pressure solution during late burial diagenesis; (vii) shear deformation by intense plastic deformation of unlithified sediment from limited lateral displacement; and (viii) silicification during burial diagenesis. The facies distribution indicates that active tectonism took place prior to the onset of anoxia that resulted in deposition of the Munk Marl Bed, which in the Valdemar Field was followed by tectonic waning and repeated anoxia. The Valdemar Field constituted a basinal depocenter and was flanked to the east by an early inversion high in the Adda Field characterized by condensation and bypass. The Fischschiefer Member represents a return to prevailing anoxia, consistent with global records of the early Aptian Oceanic Anoxic Event 1a (OAE-1a).
{"title":"Facies and depositional processes of Lower Cretaceous carbonates, Danish Central Graben.","authors":"M. E. Jelby, J. Ineson, N. Thibault, S. Bodin, C. Blok, Niklas Edvardsen, Tatjana S. Clemmensen, T. Buls, K. Anderskouv","doi":"10.37570/bgsd-2022-71-04","DOIUrl":"https://doi.org/10.37570/bgsd-2022-71-04","url":null,"abstract":"The Lower Cretaceous Tuxen (lower Hauterivian – upper Barremian) and Sola (upper Barremian – Albian) Formations in the Danish Central Graben (North Sea) constitute one of the oldest chalk successions recorded globally, but have received little attention with regards to sedimentary facies and depositional processes. This study presents the first comprehensive carbonate facies analysis of the succession, retrieved from seven drill cores from the Valdemar and Adda Fields. A total of 50 facies are identified, based on a continuum of six lithologies ranging from chalk to marlstone and tuffaceous siltstone to sandstone that display eight different sedimentary structures or fabrics, and two redox-associated lithological color variations (green and red) in the Adda Field. The eight sedimentary structures record: (i) comprehensive bioturbation of homogeneous sediment during fully oxygenated benthic conditions and low sedimentation rates; (ii) a similar bioturbation process but in heterogeneous sediment with lithological contrasts permitting visible burrows to form, perhaps due to rhythmic alternation between pelagic (clay-poor) and hemipelagic (clay-rich) sedimentation; (iii) pelagic to hemipelagic suspension settling in dysoxic to anoxic bottom-water conditions; (iv) patchy cementation of the shallow sea bed during incipient hardground formation; (v) reworking of bioclasts and chalk intraclasts by bottom or wave-induced currents and cohesive debris flows; (vi) pressure solution during late burial diagenesis; (vii) shear deformation by intense plastic deformation of unlithified sediment from limited lateral displacement; and (viii) silicification during burial diagenesis. The facies distribution indicates that active tectonism took place prior to the onset of anoxia that resulted in deposition of the Munk Marl Bed, which in the Valdemar Field was followed by tectonic waning and repeated anoxia. The Valdemar Field constituted a basinal depocenter and was flanked to the east by an early inversion high in the Adda Field characterized by condensation and bypass. The Fischschiefer Member represents a return to prevailing anoxia, consistent with global records of the early Aptian Oceanic Anoxic Event 1a (OAE-1a).","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45931107","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}
Pub Date : 2022-08-24DOI: 10.37570/bgsd-2022-70-08
Valerian J. P. Jésus, O. Mateus, J. Milán, L. Clemmensen
During the Triassic, Batrachia diverged into ancestors of frogs (Salientia) and salamanders (Caudata). Fossils of Triassic batrachians are rare and found only in a few outcrops, such as the Middle Sakamena Formation of Madagascar (Induan). Only three Triassic taxa have been described, the two early frogs Triadobatrachus and Czatkiobatrachus and the early salamander Triassurus. Here we describe a right ilium, collected in 1991, attributed to the first batrachian from the Late Triassic Carlsberg Fjord Member (Ørsted Dal Formation, Fleming Fjord Group) in the Jameson Land Basin, located in central East Greenland. The fossil specimen only displays the proximal part of a right ilium, missing its shaft. After a thorough comparison with several clades (lizards, temnospondyls, salamanders and frogs), we consider the specimen as a lissamphibian sharing feature with salientians and anurans: squarish acetabular region, deeply concave acetabular surface, laterally projecting acetabular rim, flat mesial surface. It is the youngest Triassic specimen of Batrachia to date and one of the northernmost of the Late Triassic.
{"title":"First occurrence of a frog-like batrachian (Amphibia) in the Late Triassic Fleming Fjord Group, central East Greenland","authors":"Valerian J. P. Jésus, O. Mateus, J. Milán, L. Clemmensen","doi":"10.37570/bgsd-2022-70-08","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-08","url":null,"abstract":"During the Triassic, Batrachia diverged into ancestors of frogs (Salientia) and salamanders (Caudata). Fossils of Triassic batrachians are rare and found only in a few outcrops, such as the Middle Sakamena Formation of Madagascar (Induan). Only three Triassic taxa have been described, the two early frogs Triadobatrachus and Czatkiobatrachus and the early salamander Triassurus. Here we describe a right ilium, collected in 1991, attributed to the first batrachian from the Late Triassic Carlsberg Fjord Member (Ørsted Dal Formation, Fleming Fjord Group) in the Jameson Land Basin, located in central East Greenland. The fossil specimen only displays the proximal part of a right ilium, missing its shaft. After a thorough comparison with several clades (lizards, temnospondyls, salamanders and frogs), we consider the specimen as a lissamphibian sharing feature with salientians and anurans: squarish acetabular region, deeply concave acetabular surface, laterally projecting acetabular rim, flat mesial surface. It is the youngest Triassic specimen of Batrachia to date and one of the northernmost of the Late Triassic.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46259983","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}
Pub Date : 2022-08-24DOI: 10.37570/bgsd-2022-70-09
Lothar H. Vallon, A. Rindsberg
A new trace fossil, Koptichnus rasmussenae, was recently reported from the Cretaceous of Denmark. This burrow is thickly lined with cuboids that the tracemaker cut from siliceous sponges. A newly discovered specimen from the lower Selandian Kerteminde Marl, found in a loose boulder in the Gundstrup gravel pit (Fyn, Denmark), extends the stratigraphical range of this ichnotaxon from the previously known Coniacian to the middle Paleocene and demonstrates that this distinct behaviour of harvesting and shaping building material survived the K-Pg extinction event.
{"title":"Cutting through sponge and time – a new record of Koptichnus rasmussenae (trace fossil) from the Kerteminde Marl (middle Paleocene), Denmark","authors":"Lothar H. Vallon, A. Rindsberg","doi":"10.37570/bgsd-2022-70-09","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-09","url":null,"abstract":"A new trace fossil, Koptichnus rasmussenae, was recently reported from the Cretaceous of Denmark. This burrow is thickly lined with cuboids that the tracemaker cut from siliceous sponges. A newly discovered specimen from the lower Selandian Kerteminde Marl, found in a loose boulder in the Gundstrup gravel pit (Fyn, Denmark), extends the stratigraphical range of this ichnotaxon from the previously known Coniacian to the middle Paleocene and demonstrates that this distinct behaviour of harvesting and shaping building material survived the K-Pg extinction event.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47386546","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}
Pub Date : 2022-08-15DOI: 10.37570/bgsd-2022-71-03
M. Lorentzen, K. Bredesen, F. Smit, T. Hansen, L. Nielsen, K. Mosegaard
The mapping of faults provides essential information on many aspects of seismic exploration, characterisation of reservoirs for compartmentalisation and cap-rock integrity. However, manual interpretation of faults from seismic data is time-consuming and challenging due to limited resolution and seismic noise. In this study, we apply a convolutional neural network trained on synthetic seismic data with planar fault shapes to improve fault mapping in the Lower and Upper Cretaceous sections of the Valdemar Field in the Danish North Sea. Our objective is to evaluate the performance of the neural network model on post-stack seismic data from the Valdemar Field. Comparison with variance and ant-tracking attributes and a manual fault interpretation shows that the neural network predicts faults with more details that may improve the overall geological and tectonic understanding of the study area and add information on potential compartmentalisation that was previously overlooked. However, the neural network is sensitive to seismic noise, which can distort the fault predictions. Therefore, the proposed model should be treated as an additional fault interpretation tool. Nonetheless, the method represents a state-of-the-art fault mapping tool that can be useful for hydrocarbon exploration and CO2 storage site evaluations.
{"title":"Mapping Cretaceous faults using a convolutional neural network – A field example from the Danish North Sea","authors":"M. Lorentzen, K. Bredesen, F. Smit, T. Hansen, L. Nielsen, K. Mosegaard","doi":"10.37570/bgsd-2022-71-03","DOIUrl":"https://doi.org/10.37570/bgsd-2022-71-03","url":null,"abstract":"The mapping of faults provides essential information on many aspects of seismic exploration, characterisation of reservoirs for compartmentalisation and cap-rock integrity. However, manual interpretation of faults from seismic data is time-consuming and challenging due to limited resolution and seismic noise. In this study, we apply a convolutional neural network trained on synthetic seismic data with planar fault shapes to improve fault mapping in the Lower and Upper Cretaceous sections of the Valdemar Field in the Danish North Sea. Our objective is to evaluate the performance of the neural network model on post-stack seismic data from the Valdemar Field. Comparison with variance and ant-tracking attributes and a manual fault interpretation shows that the neural network predicts faults with more details that may improve the overall geological and tectonic understanding of the study area and add information on potential compartmentalisation that was previously overlooked. However, the neural network is sensitive to seismic noise, which can distort the fault predictions. Therefore, the proposed model should be treated as an additional fault interpretation tool. Nonetheless, the method represents a state-of-the-art fault mapping tool that can be useful for hydrocarbon exploration and CO2 storage site evaluations.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45643546","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}
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