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":" ","pages":""},"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":" ","pages":""},"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":" ","pages":""},"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":" ","pages":""},"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":" ","pages":""},"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}
Pub Date : 2022-05-17DOI: 10.37570/bgsd-2022-71-02
B. Lauridsen, Stefanie Lode, E. Sheldon, P. Frykman, K. Anderskouv, J. Ineson
Understanding of the shallow shelf system in the Danish Basin during the Early Cretaceous has benefitted significantly from studying the previously overlooked Hauterivian–Aptian section of the Vedsted Formation of the Vinding-1 drill core. The presence of chalks in this section demonstrates that carbonate-rich pelagic sediment accumulated locally in the siliciclastic-dominated Danish Basin and that benthic carbonate production was insignificant. The area was not a carbonate platform in the Early Cretaceous and does not indicate any reworked carbonate supply from platform environments in the vicinity. The scarcity of benthic macrofossils in the cored section is due to the lack of a specialised boreal chalk fauna at that time, and the adjacent nearshore environment apparently did not support any substantial benthic carbonate production. A revised biostratigraphy of the cored section is presented based primarily on calcareous nannofossils, supported by foraminifera, ostracods, and belemnites. Four lithofacies describe the spectrum from marlstone to slightly marly chalk, and the facies succession characterises four depositional units recording two discrete transgressive–regressive cycles. The study provides a depositional record that permits sequence stratigraphic correlation to the Valdemar and Adda Fields in the Central Graben.
{"title":"Lower Cretaceous (Hauterivian–Aptian) pelagic carbonates in the Danish Basin: new data from the Vinding-1 well, central Jylland, Denmark.","authors":"B. Lauridsen, Stefanie Lode, E. Sheldon, P. Frykman, K. Anderskouv, J. Ineson","doi":"10.37570/bgsd-2022-71-02","DOIUrl":"https://doi.org/10.37570/bgsd-2022-71-02","url":null,"abstract":"Understanding of the shallow shelf system in the Danish Basin during the Early Cretaceous has benefitted significantly from studying the previously overlooked Hauterivian–Aptian section of the Vedsted Formation of the Vinding-1 drill core. The presence of chalks in this section demonstrates that carbonate-rich pelagic sediment accumulated locally in the siliciclastic-dominated Danish Basin and that benthic carbonate production was insignificant. The area was not a carbonate platform in the Early Cretaceous and does not indicate any reworked carbonate supply from platform environments in the vicinity. The scarcity of benthic macrofossils in the cored section is due to the lack of a specialised boreal chalk fauna at that time, and the adjacent nearshore environment apparently did not support any substantial benthic carbonate production. A revised biostratigraphy of the cored section is presented based primarily on calcareous nannofossils, supported by foraminifera, ostracods, and belemnites. Four lithofacies describe the spectrum from marlstone to slightly marly chalk, and the facies succession characterises four depositional units recording two discrete transgressive–regressive cycles. The study provides a depositional record that permits sequence stratigraphic correlation to the Valdemar and Adda Fields in the Central Graben.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2022-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48887042","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 : 2022-05-11DOI: 10.37570/bgsd-2022-70-07
O. Bennike, P. Astrup, B. Odgaard, C. Pearce, P. Wiberg‐Larsen
The Brabrand Sø area west of Aarhus in eastern Jylland, Denmark, was deglaciated about 18 000 to 17 000 years ago. Coring in the present-day lake area revealed Early Holocene stream deposits overlain by marine deposits. The area was transgressed by the sea at c. 8500 cal. years BP and a 12 km long, narrow fjord was formed. In the beginning, the fjord housed a species-poor marine or brackish-water fauna with molluscs Hydrobia sp. (mudsnail), Littorina littorea (winkle), Mytilus edulis (blue mussel) and Cerastoderma sp. (cockle). This phase was followed by a phase during which the fjord housed a species-rich fauna that included Ostrea edulis (European flat oyster) and Ruditapes decussatus (palourde clam). During this phase the salinity and summer water temperatures were higher than in present day Aarhus Bugt and we also see evidence for strong bottom currents. This phase was probably characterised by a fairly large tidal amplitude. Two radiocarbon ages of O. edulis shells of c. 6250 and 6700 cal. years BP indicate that such conditions peaked during the period of the Ertebølle culture. The high-salinity phase was followed by a phase with a more species-poor fauna, this phase was also characterised by a high sedimentation rate – a feature seen in other fjords in the region. We suggest that the shift could be due to a decrease in tidal amplitude. Brabrand Fjord was eventually transformed into a lake due to land uplift and closure of the connection to Aarhus Bugt due to longshore sediment transport but the timing of the transition from fjord to lake is still unknown.
{"title":"Holocene development of Brabrand Fjord, eastern Jylland, Denmark.","authors":"O. Bennike, P. Astrup, B. Odgaard, C. Pearce, P. Wiberg‐Larsen","doi":"10.37570/bgsd-2022-70-07","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-07","url":null,"abstract":"The Brabrand Sø area west of Aarhus in eastern Jylland, Denmark, was deglaciated about 18 000 to 17 000 years ago. Coring in the present-day lake area revealed Early Holocene stream deposits overlain by marine deposits. The area was transgressed by the sea at c. 8500 cal. years BP and a 12 km long, narrow fjord was formed. In the beginning, the fjord housed a species-poor marine or brackish-water fauna with molluscs Hydrobia sp. (mudsnail), Littorina littorea (winkle), Mytilus edulis (blue mussel) and Cerastoderma sp. (cockle). This phase was followed by a phase during which the fjord housed a species-rich fauna that included Ostrea edulis (European flat oyster) and Ruditapes decussatus (palourde clam). During this phase the salinity and summer water temperatures were higher than in present day Aarhus Bugt and we also see evidence for strong bottom currents. This phase was probably characterised by a fairly large tidal amplitude. Two radiocarbon ages of O. edulis shells of c. 6250 and 6700 cal. years BP indicate that such conditions peaked during the period of the Ertebølle culture. The high-salinity phase was followed by a phase with a more species-poor fauna, this phase was also characterised by a high sedimentation rate – a feature seen in other fjords in the region. We suggest that the shift could be due to a decrease in tidal amplitude. Brabrand Fjord was eventually transformed into a lake due to land uplift and closure of the connection to Aarhus Bugt due to longshore sediment transport but the timing of the transition from fjord to lake is still unknown.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2022-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49431827","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 : 2022-04-22DOI: 10.37570/bgsd-2022-70-06
J. S. Peel, Artem V. Kouchinsky
Diverse assemblages of helcionelloid molluscs and mollusc-like microfossils are described from the upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of Lauge Koch Land and western Peary Land, North Greenland (Laurentia). The fauna compares closely to an assemblage of similar age from the Coonigan Formation of Australia, although the latter is preserved as silica replicas while the North Greenland fossils are dominantly preserved as phosphatized internal moulds. These internal moulds often retain a detailed impression of the inner surface of the shell, with a fine pitted texture typically present. Prominent deep grooves on the sub-apical surface in the erect helcionellids Dorispira and Erugoconus, corresponding to ridges on the shell interior, seem to be associated with control of water flow through the mantle cavity. Well-developed shell pores, preserved as tubercles on the internal mould, are common in species of the laterally compressed Mellopegma. New taxa: Dorispira avannga sp. nov., Dorispira septentrionalis sp. nov., Dorispira tavsenensis sp. nov., Dorispira tippik sp. nov., Erugoconus acuminatus gen. et sp. nov., Scenella? siku sp. nov., Sermeqiconus gen. nov., Tavseniconus erectus gen. et sp. nov., Vendrascospira troelseni gen. et sp. nov., Vendrascospira frykmani gen. et sp. nov.
在Lauge Koch Land和北格陵兰岛(Laurentia)西部Peary Land的上Henson Gletscher组(寒武系，妙岭系，五流期)中描述了不同的helcionelloid软体动物和类软体动物微化石组合。这些动物群与澳大利亚库尼根组的相似年龄的组合非常接近，尽管后者被保存为硅复制品，而北格陵兰的化石主要被保存为磷化的内部霉菌。这些内部模具通常保留了外壳内表面的详细印象，通常具有精细的麻点纹理。直立helcionellids Dorispira和Erugoconus的亚顶端表面上有突出的深沟槽，与壳内部的脊相对应，似乎与通过地幔腔的水流控制有关。发育良好的壳孔，在内部霉菌上以结节的形式保存，在侧向压缩的千层赘生物中很常见。新分类群:avannga Dorispira sp. nov.、septentrionalis sp. nov.、tavsenensis sp. nov.、tippik sp. nov.、Erugoconus acuminatus gen. et sp. nov.、Scenella?siku sp. nov, Sermeqiconus gen. nov, Tavseniconus erectus gen. et nov, Vendrascospira troelseni gen. et nov, Vendrascospira frykmani gen. et nov。
{"title":"Middle Cambrian (Miaolingian Series, Wuliuan Stage) molluscs and mollusc-like microfossils from North Greenland (Laurentia).","authors":"J. S. Peel, Artem V. Kouchinsky","doi":"10.37570/bgsd-2022-70-06","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-06","url":null,"abstract":"Diverse assemblages of helcionelloid molluscs and mollusc-like microfossils are described from the upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of Lauge Koch Land and western Peary Land, North Greenland (Laurentia). The fauna compares closely to an assemblage of similar age from the Coonigan Formation of Australia, although the latter is preserved as silica replicas while the North Greenland fossils are dominantly preserved as phosphatized internal moulds. These internal moulds often retain a detailed impression of the inner surface of the shell, with a fine pitted texture typically present. Prominent deep grooves on the sub-apical surface in the erect helcionellids Dorispira and Erugoconus, corresponding to ridges on the shell interior, seem to be associated with control of water flow through the mantle cavity. Well-developed shell pores, preserved as tubercles on the internal mould, are common in species of the laterally compressed Mellopegma. New taxa: Dorispira avannga sp. nov., Dorispira septentrionalis sp. nov., Dorispira tavsenensis sp. nov., Dorispira tippik sp. nov., Erugoconus acuminatus gen. et sp. nov., Scenella? siku sp. nov., Sermeqiconus gen. nov., Tavseniconus erectus gen. et sp. nov., Vendrascospira troelseni gen. et sp. nov., Vendrascospira frykmani gen. et sp. nov.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2022-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46810629","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 : 2022-04-08DOI: 10.37570/bgsd-2022-70-05
G. Carnevale, W. Schwarzhans, A. Schrøder, B. Lindow
A conger eel (Anguilliformes, Congridae) is described from the lower Lutetian concretionary nodules of the Lillebælt Clay Formation exposed at Trelde Næs, eastern Jutland, based on two partially complete articulated cranial skeletons. One of the cranial specimens exhibits an otolith void from which a cast was taken, used by Schwarzhans (2007) to describe the extinct Pseudoxenomystax treldeensis, which is placed herein within the new genus Smithconger gen. nov. Smithconger treldeensis (Schwarzhans, 2007) is characterized by well-developed lateral processes on the frontals, supraoccipital crest absent, sphenotic spine rather large, anteriorly pointed and exposed on the flattened surface of the skull roof, otic bullae considerably reduced, maxilla almost straight and distally pointed, maxillary and dentary teeth numerous and arranged in multiple rows, dentary with slightly convex ventral profile, opercle with smooth posterior margin and subopercle short. The otoliths of Smithconger treldeensis show high dorsal rim, broad and deep dorsal depression, no ventral furrow, sulcus straight, shallow, centrally positioned with anteriorly reduced colliculum, and ostial channel at anterior tip of colliculum short, not reaching the predorsal rim. The otolith-based species Bathycongrus waihaoensis Schwarzhans, 2019 from the Kaiatan (Bartonian/Priabonian) of New Zealand is also assigned to the genus Smithconger. Smithconger is tentatively referred to the congrid subfamily Congrinae due to the lack of hypohyals in the hyoid bar. This new Eocene genus of conger eel shows a certain degree of similarity with the extant Bassanago. The diversity and relationships of other Eocene congrids is also briefly discussed.
{"title":"An Eocene conger eel (Teleostei, Anguilliformes) from the Lillebælt Clay Formation, Denmark","authors":"G. Carnevale, W. Schwarzhans, A. Schrøder, B. Lindow","doi":"10.37570/bgsd-2022-70-05","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-05","url":null,"abstract":"A conger eel (Anguilliformes, Congridae) is described from the lower Lutetian concretionary nodules of the Lillebælt Clay Formation exposed at Trelde Næs, eastern Jutland, based on two partially complete articulated cranial skeletons. One of the cranial specimens exhibits an otolith void from which a cast was taken, used by Schwarzhans (2007) to describe the extinct Pseudoxenomystax treldeensis, which is placed herein within the new genus Smithconger gen. nov. Smithconger treldeensis (Schwarzhans, 2007) is characterized by well-developed lateral processes on the frontals, supraoccipital crest absent, sphenotic spine rather large, anteriorly pointed and exposed on the flattened surface of the skull roof, otic bullae considerably reduced, maxilla almost straight and distally pointed, maxillary and dentary teeth numerous and arranged in multiple rows, dentary with slightly convex ventral profile, opercle with smooth posterior margin and subopercle short. The otoliths of Smithconger treldeensis show high dorsal rim, broad and deep dorsal depression, no ventral furrow, sulcus straight, shallow, centrally positioned with anteriorly reduced colliculum, and ostial channel at anterior tip of colliculum short, not reaching the predorsal rim. The otolith-based species Bathycongrus waihaoensis Schwarzhans, 2019 from the Kaiatan (Bartonian/Priabonian) of New Zealand is also assigned to the genus Smithconger. Smithconger is tentatively referred to the congrid subfamily Congrinae due to the lack of hypohyals in the hyoid bar. This new Eocene genus of conger eel shows a certain degree of similarity with the extant Bassanago. The diversity and relationships of other Eocene congrids is also briefly discussed.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2022-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46897128","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 : 2022-03-30DOI: 10.37570/bgsd-2022-70-04
O. Bennike, Lone Claudi-Hansen, Betina Magnussen, P. Wiberg‐Larsen
Studies of macrofossils indicate that the vegetation near Regstrup in north-west Sjælland, Denmark, from c. 13 600 to 13 500 cal. years BP was dominated by dwarf-shrub heaths. Betula pubescens (downy birch) arrived at c. 13 500 cal. years BP and became common after c. 13 200 cal. years BP. Open forests with B. pubescens and Populus tremula (aspen) dominated until c. 12 500 cal. years BP, indicating that an Allerød-type environment persisted for c. 350 years after the cooling at the onset of the Younger Dryas, which is dated to c. 12 850 years BP in ice cores from Green-land. Betula nana was common after c. 12 500 cal. years BP, indicating a return to a tundra-like landscape with dwarf-shrub heaths. The fauna included Rangifer taran-dus (reindeer), Castor fiber (Eurasian beaver) and possibly Lemmus lemmus (Norway lemming). The lake deposits contain remains of many species of aquatic plants and animals, including three species of fish. The flora and fauna indicate that the lake water was fairly nutrient-rich and alkaline.
{"title":"Macrofossil studies of Lateglacial sediments from Regstrup, north-west Sjælland, Denmark","authors":"O. Bennike, Lone Claudi-Hansen, Betina Magnussen, P. Wiberg‐Larsen","doi":"10.37570/bgsd-2022-70-04","DOIUrl":"https://doi.org/10.37570/bgsd-2022-70-04","url":null,"abstract":"Studies of macrofossils indicate that the vegetation near Regstrup in north-west Sjælland, Denmark, from c. 13 600 to 13 500 cal. years BP was dominated by dwarf-shrub heaths. Betula pubescens (downy birch) arrived at c. 13 500 cal. years BP and became common after c. 13 200 cal. years BP. Open forests with B. pubescens and Populus tremula (aspen) dominated until c. 12 500 cal. years BP, indicating that an Allerød-type environment persisted for c. 350 years after the cooling at the onset of the Younger Dryas, which is dated to c. 12 850 years BP in ice cores from Green-land. Betula nana was common after c. 12 500 cal. years BP, indicating a return to a tundra-like landscape with dwarf-shrub heaths. The fauna included Rangifer taran-dus (reindeer), Castor fiber (Eurasian beaver) and possibly Lemmus lemmus (Norway lemming). The lake deposits contain remains of many species of aquatic plants and animals, including three species of fish. The flora and fauna indicate that the lake water was fairly nutrient-rich and alkaline.","PeriodicalId":55310,"journal":{"name":"Bulletin of the Geological Society of Denmark","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2022-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43468161","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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