Pub Date : 2022-01-02DOI: 10.1080/11035897.2021.2020333
T. Paiste, P. Männik, T. Meidla
ABSTRACT The boundaries of the Sandbian Stage are defined by graptolites. Because of their rare occurrence in the Estonian part of the Baltoscandian palaeobasin, other fossils, including conodonts, are used for biostratigraphy as good alternatives. Since the definition of Sandbian Stage/Age in 2002, information about conodonts from this time interval in Baltsocandia has improved considerably. In this paper, existing data on Sandbian conodont faunas from the Estonian part of the Baltoscandian palaeobasin, including the most recent information from the Velise V-97 core section (western part of mainland Estonia), is evaluated. Dating of these strata in the region is addressed and partly updated. Comparison of conodont successions from other regions of Baltoscandia with those from the Estonian sections is used to check consistency of known conodont zones. The rich conodont succession from the Velise V-97 drill core is considered a representative one for the Sandbian-age carbonate ramp environment in Baltoscandia. Most of the principal conodont zones within the Sandbian Stage were recognised whilst the lower and upper boundary intervals of the stage are poorly resolved. Despite the rich conodont faunas available, the boundaries of the Sandbian Stage are currently not clearly definable in the conodont succession. However, further detailed studies on the morphology and evolution of the earliest Amorphognathus (A. inaequalis and A. tvaerensis in particular), based on rich and well preserved material from different parts of Baltoscandia, might provide useful criteria for location of the Sandbian and Katian boundaries in non-graptolitiferous carbonate sections.
{"title":"Sandbian (Late Ordovician) conodonts in Estonia: distribution and biostratigraphy","authors":"T. Paiste, P. Männik, T. Meidla","doi":"10.1080/11035897.2021.2020333","DOIUrl":"https://doi.org/10.1080/11035897.2021.2020333","url":null,"abstract":"ABSTRACT The boundaries of the Sandbian Stage are defined by graptolites. Because of their rare occurrence in the Estonian part of the Baltoscandian palaeobasin, other fossils, including conodonts, are used for biostratigraphy as good alternatives. Since the definition of Sandbian Stage/Age in 2002, information about conodonts from this time interval in Baltsocandia has improved considerably. In this paper, existing data on Sandbian conodont faunas from the Estonian part of the Baltoscandian palaeobasin, including the most recent information from the Velise V-97 core section (western part of mainland Estonia), is evaluated. Dating of these strata in the region is addressed and partly updated. Comparison of conodont successions from other regions of Baltoscandia with those from the Estonian sections is used to check consistency of known conodont zones. The rich conodont succession from the Velise V-97 drill core is considered a representative one for the Sandbian-age carbonate ramp environment in Baltoscandia. Most of the principal conodont zones within the Sandbian Stage were recognised whilst the lower and upper boundary intervals of the stage are poorly resolved. Despite the rich conodont faunas available, the boundaries of the Sandbian Stage are currently not clearly definable in the conodont succession. However, further detailed studies on the morphology and evolution of the earliest Amorphognathus (A. inaequalis and A. tvaerensis in particular), based on rich and well preserved material from different parts of Baltoscandia, might provide useful criteria for location of the Sandbian and Katian boundaries in non-graptolitiferous carbonate sections.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44962392","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 : 2022-01-02DOI: 10.1080/11035897.2022.2032822
M. Streng, J. A. Rasmussen, J. R. Ebbestad, Thomas Weidner
ABSTRACT An Early Ordovician fauna of linguliform brachiopods and euconodonts is described from the Alum Shale Formation in northernmost Västerbotten County, northern Sweden. The fauna was recovered from a single carbonate concretion collected at an exposure near the northern shore of Lake Storvindeln. Despite of the fragmentary and tectonized preservation of the obtained fossils, at least eight different taxa of linguliform brachiopods and four species of euconodonts could be identified. Among the brachiopods, the ephippelasmatid Pomeraniotreta biernatae Bednarczyk, 1986 is most common; it is associated among others with the acrotretids Eurytreta cf. sabrinae (Callaway, 1877) and Ottenbyella sp., and a spinose specimen potentially representing the zhanatellid Thysanotos. Two of the brachiopod taxa appear to present new species, Pomeraniotreta n. sp. and Mytoella? n. sp., but additional material would be needed for a formal description. Euconodont specimens are rare and comprise coniform elements of Drepanodus arcuatus Pander, 1856, Drepanoistodus aff. amoenus (Lindström, 1955) sensu Löfgren (1994), Paroistodus numarcuatus (Lindström, 1955) and Rossodus aff. manitouensis Repetski & Ethington, 1983. Evaluation of the stratigraphic distribution of the different taxa of brachiopods and euconodonts under consideration of the local geology, suggests that the investigated sample represents a level in the upper part of the Tremadocian (Tr2) part of the Alum Shale Formation. The fauna represents the northernmost occurrence of age diagnostic Early Ordovician (Tremadocian) fossils in Sweden.
{"title":"First record of an Early Ordovician brachiopod and conodont fauna from Lapland, Sweden","authors":"M. Streng, J. A. Rasmussen, J. R. Ebbestad, Thomas Weidner","doi":"10.1080/11035897.2022.2032822","DOIUrl":"https://doi.org/10.1080/11035897.2022.2032822","url":null,"abstract":"ABSTRACT An Early Ordovician fauna of linguliform brachiopods and euconodonts is described from the Alum Shale Formation in northernmost Västerbotten County, northern Sweden. The fauna was recovered from a single carbonate concretion collected at an exposure near the northern shore of Lake Storvindeln. Despite of the fragmentary and tectonized preservation of the obtained fossils, at least eight different taxa of linguliform brachiopods and four species of euconodonts could be identified. Among the brachiopods, the ephippelasmatid Pomeraniotreta biernatae Bednarczyk, 1986 is most common; it is associated among others with the acrotretids Eurytreta cf. sabrinae (Callaway, 1877) and Ottenbyella sp., and a spinose specimen potentially representing the zhanatellid Thysanotos. Two of the brachiopod taxa appear to present new species, Pomeraniotreta n. sp. and Mytoella? n. sp., but additional material would be needed for a formal description. Euconodont specimens are rare and comprise coniform elements of Drepanodus arcuatus Pander, 1856, Drepanoistodus aff. amoenus (Lindström, 1955) sensu Löfgren (1994), Paroistodus numarcuatus (Lindström, 1955) and Rossodus aff. manitouensis Repetski & Ethington, 1983. Evaluation of the stratigraphic distribution of the different taxa of brachiopods and euconodonts under consideration of the local geology, suggests that the investigated sample represents a level in the upper part of the Tremadocian (Tr2) part of the Alum Shale Formation. The fauna represents the northernmost occurrence of age diagnostic Early Ordovician (Tremadocian) fossils in Sweden.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46027075","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 : 2022-01-02DOI: 10.1080/11035897.2021.1993453
A. Lindh
ABSTRACT Recent theories on the growth of continental crust stress its formation in pre-Archean and Archean times with minor additions at later times. The Earth has gone through a unidirectional evolution including surface changes, the genesis of life and an important loss of energy. The energy loss drives tectonic processes, but at a rate declining with available energy and thus with time. Semiquantitative modelling of energy-changes and transport indicates important differences between today’s Earth and the Paleoproterozoic Earth. Actualistic but non-uniformitarian arguments suggest that principal tectonic processes have changed over time. The Baltic Shield displays a fundamental difference in conditions between the c. 0.9 Ga high-pressure metamorphism including the occurrence of eclogite in the western Sveconorwegian Orogen and c. 2 Ga low-pressure metamorphism in the eastern Svecokarelian Orogen. This suggests that modern platetectonic processes were operative at c. 0.9 Ga but leaves the question whether it was active during the Svecokarelian orogeny open. The lack of eclogite in the Svecokarelian Orogen is explained with a change with time of the geotherm slope. The occurrence of two generations of granitic rocks of different compositions in the Svecokarelian is easily explained by an increased mantle heat flow in a stratified continental crust. In contrast to calc-alkaline platetectonic compositions, alkali-calcic rocks occur in a quarter-circle around the Svecokarelian core. The question arises whether modern plate-processes successively replaced proto-plate processes during Paleo- and Mesoproterozoic times.
{"title":"Has the tectonic regime of the Baltic Shield always remained the same?","authors":"A. Lindh","doi":"10.1080/11035897.2021.1993453","DOIUrl":"https://doi.org/10.1080/11035897.2021.1993453","url":null,"abstract":"ABSTRACT Recent theories on the growth of continental crust stress its formation in pre-Archean and Archean times with minor additions at later times. The Earth has gone through a unidirectional evolution including surface changes, the genesis of life and an important loss of energy. The energy loss drives tectonic processes, but at a rate declining with available energy and thus with time. Semiquantitative modelling of energy-changes and transport indicates important differences between today’s Earth and the Paleoproterozoic Earth. Actualistic but non-uniformitarian arguments suggest that principal tectonic processes have changed over time. The Baltic Shield displays a fundamental difference in conditions between the c. 0.9 Ga high-pressure metamorphism including the occurrence of eclogite in the western Sveconorwegian Orogen and c. 2 Ga low-pressure metamorphism in the eastern Svecokarelian Orogen. This suggests that modern platetectonic processes were operative at c. 0.9 Ga but leaves the question whether it was active during the Svecokarelian orogeny open. The lack of eclogite in the Svecokarelian Orogen is explained with a change with time of the geotherm slope. The occurrence of two generations of granitic rocks of different compositions in the Svecokarelian is easily explained by an increased mantle heat flow in a stratified continental crust. In contrast to calc-alkaline platetectonic compositions, alkali-calcic rocks occur in a quarter-circle around the Svecokarelian core. The question arises whether modern plate-processes successively replaced proto-plate processes during Paleo- and Mesoproterozoic times.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45224345","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 : 2021-11-17DOI: 10.1080/11035897.2021.1989716
A. Ernst, H. A. Nakrem
ABSTRACT Rhombotrypella superangustata and Dyscritellina fuglensis (Bryozoa, Trepostomata) were found for the first time in the Assistance Formation of Ellesmere Island, Canada. Both species correlate the Roadian age of the Assistance Formation with contemporary deposits in Northern Russia and Bjørnøya, Norway. They possess robust erect colonies adapted for shallow shelf conditions with moderate energy depositional environment with low sedimentation rate and hard substrate.
{"title":"Two trepostome bryozoans from the Assistance Formation (Permian, Roadian) near Lake Hazen, Ellesmere Island, Canada","authors":"A. Ernst, H. A. Nakrem","doi":"10.1080/11035897.2021.1989716","DOIUrl":"https://doi.org/10.1080/11035897.2021.1989716","url":null,"abstract":"ABSTRACT Rhombotrypella superangustata and Dyscritellina fuglensis (Bryozoa, Trepostomata) were found for the first time in the Assistance Formation of Ellesmere Island, Canada. Both species correlate the Roadian age of the Assistance Formation with contemporary deposits in Northern Russia and Bjørnøya, Norway. They possess robust erect colonies adapted for shallow shelf conditions with moderate energy depositional environment with low sedimentation rate and hard substrate.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47181605","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 : 2021-10-02DOI: 10.1080/11035897.2021.1979642
J. S. Peel
ABSTRACT Well-preserved holdfasts and early growth stages of the tubular cnidarian Sphenothallus are described from the early Silurian (Llandovery Series) of Washington Land, North Greenland. The diameter of the holdfast is determined by the formation of a basal disc attached to the substrate, upon which the initially conical, but subsequently tubular shell is formed. The characteristic opposing longitudinal thickenings are developed at each angular margin as the initially circular tube acquires an elliptical form.
{"title":"Holdfasts of Sphenothallus (Cnidaria) from the early Silurian of western North Greenland (Laurentia)","authors":"J. S. Peel","doi":"10.1080/11035897.2021.1979642","DOIUrl":"https://doi.org/10.1080/11035897.2021.1979642","url":null,"abstract":"ABSTRACT Well-preserved holdfasts and early growth stages of the tubular cnidarian Sphenothallus are described from the early Silurian (Llandovery Series) of Washington Land, North Greenland. The diameter of the holdfast is determined by the formation of a basal disc attached to the substrate, upon which the initially conical, but subsequently tubular shell is formed. The characteristic opposing longitudinal thickenings are developed at each angular margin as the initially circular tube acquires an elliptical form.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42120529","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 : 2021-10-02DOI: 10.1080/11035897.2021.1939777
Å. Johansson
ABSTRACT Ten samples of felsic plutonic rocks from the Eastern Segment of the Sveconorwegian Orogen in southern Sweden, previously dated by ID-TIMS on zircon, have been dated anew using SIMS spot analysis of individual zircon grains, leading to more reliable and in most cases also more precise revised magmatic crystallization ages. A gneissic monzonite within the Protogine Zone in Småland yields a revised U-Pb age of ca. 1725 Ma, four samples of orthogneiss from Skåne all yield revised ages between 1700 and 1690 Ma, while two samples of coarse-grained granitic gneiss in the same region yield ages between 1690 and 1680 Ma. These revised ages are between 15 and 250 m.y. older than previously obtained TIMS ages. Two samples of the Gumlösa-Glimåkra granite along the Protogine Zone in northern Skåne and one sample of related syenite yield ages around 1220 Ma, similar but more precise compared to the previous ages. The U-Pb zircon data have been complemented by Hf isotope analysis by LA-ICP-MS on the same grains, and previously obtained initial Sr and Nd whole-rock isotope data have been recalculated to the revised crystallization ages. The Sr isotope data scatter, while the revised initial εNd values fall between +1 and +2 for the older rocks, and close to 0 for the younger intrusives along the Protogine Zone. Initial εHf in magmatic undisturbed zircons shows relatively little spread within each sample, between 2 and 4 Epsilon units, disregarding a few outliers, with average values for the 1725 to 1680 Ma rocks between +3 and +5.5 and for the 1220 Ma rocks at ca. +1.5. Covariation between initial εNd and initial εHf in the older rocks suggests either mixing between two isotopically distinct magma sources or one magma source which was isotopically heterogeneous. The isotopic signatures of the 1220 Ma intrusive rocks along the Protogine Zone are indicative of juvenile mantle input to their magmas, rather than pure crustal melting.
{"title":"Cleaning up the record – revised U-Pb zircon ages and new Hf isotope data from southern Sweden","authors":"Å. Johansson","doi":"10.1080/11035897.2021.1939777","DOIUrl":"https://doi.org/10.1080/11035897.2021.1939777","url":null,"abstract":"ABSTRACT Ten samples of felsic plutonic rocks from the Eastern Segment of the Sveconorwegian Orogen in southern Sweden, previously dated by ID-TIMS on zircon, have been dated anew using SIMS spot analysis of individual zircon grains, leading to more reliable and in most cases also more precise revised magmatic crystallization ages. A gneissic monzonite within the Protogine Zone in Småland yields a revised U-Pb age of ca. 1725 Ma, four samples of orthogneiss from Skåne all yield revised ages between 1700 and 1690 Ma, while two samples of coarse-grained granitic gneiss in the same region yield ages between 1690 and 1680 Ma. These revised ages are between 15 and 250 m.y. older than previously obtained TIMS ages. Two samples of the Gumlösa-Glimåkra granite along the Protogine Zone in northern Skåne and one sample of related syenite yield ages around 1220 Ma, similar but more precise compared to the previous ages. The U-Pb zircon data have been complemented by Hf isotope analysis by LA-ICP-MS on the same grains, and previously obtained initial Sr and Nd whole-rock isotope data have been recalculated to the revised crystallization ages. The Sr isotope data scatter, while the revised initial εNd values fall between +1 and +2 for the older rocks, and close to 0 for the younger intrusives along the Protogine Zone. Initial εHf in magmatic undisturbed zircons shows relatively little spread within each sample, between 2 and 4 Epsilon units, disregarding a few outliers, with average values for the 1725 to 1680 Ma rocks between +3 and +5.5 and for the 1220 Ma rocks at ca. +1.5. Covariation between initial εNd and initial εHf in the older rocks suggests either mixing between two isotopically distinct magma sources or one magma source which was isotopically heterogeneous. The isotopic signatures of the 1220 Ma intrusive rocks along the Protogine Zone are indicative of juvenile mantle input to their magmas, rather than pure crustal melting.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45581522","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 : 2021-09-13DOI: 10.1080/11035897.2021.1936156
J. Maletz, P. Ahlberg
ABSTRACT The Krapperup drill core from Scania (Skåne), southern Sweden, includes one of the most important graptolitic Darriwilian (upper Middle Ordovician) successions of Baltica. Only some intervals have been documented previously and especially the uppermost part of the succession has been completely unknown. A fairly complete succession of mid- to late Darriwilian age provides insight into the early evolution of the axonophoran (biserial) graptolites and demonstrates a distinct biogeographical faunal differentiation during this time. Graptolites from the mid-Darriwilian Holmograptus lentus and Nicholsonograptus fasciculatus biozones are discussed and important specimens and species from the Krapperup drill core are illustrated. Ekstroemograptus inexpectatus n. gen., n. sp. from the Holmograptus lentus Biozone is described as new.
瑞典南部Scania (sk ne)的Krapperup岩心包含了波罗的海最重要的笔石系Darriwilian(中奥陶统上)序列之一。以前只有一些间隔被记录下来，特别是演替的最上面部分是完全未知的。一个相当完整的中晚期达里威廉时代序列，提供了对轴索笔石(双序列)早期进化的深入了解，并证明了这一时期明显的生物地理区系分化。讨论了中darriwilian Holmograptus lentus和Nicholsonograptus fasciculatus生物带的笔石，并举例说明了Krapperup岩心的重要标本和种。来自lentus Holmograptus的Ekstroemograptus inexpectatus n. gen.， n. sp.被描述为新种。
{"title":"Upper Darriwilian (Middle Ordovician) graptolite biostratigraphy and correlation of the Krapperup drill core, Scania, Sweden","authors":"J. Maletz, P. Ahlberg","doi":"10.1080/11035897.2021.1936156","DOIUrl":"https://doi.org/10.1080/11035897.2021.1936156","url":null,"abstract":"ABSTRACT The Krapperup drill core from Scania (Skåne), southern Sweden, includes one of the most important graptolitic Darriwilian (upper Middle Ordovician) successions of Baltica. Only some intervals have been documented previously and especially the uppermost part of the succession has been completely unknown. A fairly complete succession of mid- to late Darriwilian age provides insight into the early evolution of the axonophoran (biserial) graptolites and demonstrates a distinct biogeographical faunal differentiation during this time. Graptolites from the mid-Darriwilian Holmograptus lentus and Nicholsonograptus fasciculatus biozones are discussed and important specimens and species from the Krapperup drill core are illustrated. Ekstroemograptus inexpectatus n. gen., n. sp. from the Holmograptus lentus Biozone is described as new.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41770110","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 : 2021-09-08DOI: 10.1080/11035897.2021.1941239
Aleksander Majchrzyk, W. Kozłowski, A. Żylińska
ABSTRACT The precipitation of both biotic and abiotic calcium carbonate is of great importance in modern and ancient global biogeochemical cycles. In the present-day oceans, the widespread precipitation of inorganic CaCO3 on the seafloor or in the water column is possible only under extraordinary circumstances. By contrast, in the geological record, authigenic seafloor carbonate cements were widespread in the supersaturated, anoxic oceans of the Precambrian. Widespread authigenic carbonate precipitation ceased by the end of the Neoproterozoic as a consequence of global oceanic oxygenation: in the Phanerozoic, it occurred only during major anoxic events (for example, at the Permian/Triassic boundary) or in restricted, stagnant basins. Here, we present an anomalous record of CaCO3 precipitation from the Cambrian Alum Shale Basin of the Baltica palaeocontinent with Precambrian-like authigenic, seafloor encrusting, crystalline carbonates. The depositional environment of this well-recognized, cool-water, stagnant anoxic basin favoured local carbonate precipitation via the surplus generation of alkalinity in anoxic bottom waters. However, the correlation of the acme of authigenic carbonate formation with the onset and peak of the Steptoean Positive Carbon Isotope Excursion (SPICE) suggests a driver−trigger relation between the two phenomena. On a smaller scale, carbonate authigenic precipitation is manifested by a cement-supported texture of the limestone intercalations in the Alum Shale facies. Instantaneous calcification of the faunal remains, termed here the Snedronningen phenomenon, must have been of great importance in the formation of Orsten-type Konservat Lagerstätten.
{"title":"Authigenic calcium carbonate precipitation in the “bathtub ring” around the anoxic Alum Shale Basin during the Furongian SPICE event (Baltic Basin, northern Poland)","authors":"Aleksander Majchrzyk, W. Kozłowski, A. Żylińska","doi":"10.1080/11035897.2021.1941239","DOIUrl":"https://doi.org/10.1080/11035897.2021.1941239","url":null,"abstract":"ABSTRACT The precipitation of both biotic and abiotic calcium carbonate is of great importance in modern and ancient global biogeochemical cycles. In the present-day oceans, the widespread precipitation of inorganic CaCO3 on the seafloor or in the water column is possible only under extraordinary circumstances. By contrast, in the geological record, authigenic seafloor carbonate cements were widespread in the supersaturated, anoxic oceans of the Precambrian. Widespread authigenic carbonate precipitation ceased by the end of the Neoproterozoic as a consequence of global oceanic oxygenation: in the Phanerozoic, it occurred only during major anoxic events (for example, at the Permian/Triassic boundary) or in restricted, stagnant basins. Here, we present an anomalous record of CaCO3 precipitation from the Cambrian Alum Shale Basin of the Baltica palaeocontinent with Precambrian-like authigenic, seafloor encrusting, crystalline carbonates. The depositional environment of this well-recognized, cool-water, stagnant anoxic basin favoured local carbonate precipitation via the surplus generation of alkalinity in anoxic bottom waters. However, the correlation of the acme of authigenic carbonate formation with the onset and peak of the Steptoean Positive Carbon Isotope Excursion (SPICE) suggests a driver−trigger relation between the two phenomena. On a smaller scale, carbonate authigenic precipitation is manifested by a cement-supported texture of the limestone intercalations in the Alum Shale facies. Instantaneous calcification of the faunal remains, termed here the Snedronningen phenomenon, must have been of great importance in the formation of Orsten-type Konservat Lagerstätten.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43721207","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 : 2021-07-15DOI: 10.1080/11035897.2021.1939776
M. Krabbendam, Romesh Palamakumbura, C. Arnhardt, A. Hall
ABSTRACT Dense networks of dilated fractures occur locally in the upper 5–15 m of bedrock in basement gneisses in eastern Sweden. Near Forsmark, pre-existing sub-horizontal fractures have been jacked open and filled with water-lain sediment, likely during the latest Weichselian glaciation. Despite extensive previous research, it is uncertain whether subglacial hydraulic jacking led to the generation of new fractures, in addition to reactivation of pre-existing ones. Re-analysis of historic photos from excavations near the Forsmark power plant indicates formation of two types of new fracture. Firstly, rock fragments were broken off the main fracture surfaces as existing fractures were jacked open. Secondly, fracture analysis shows that whilst few subvertical fractures occur above tight sub-horizontal fractures, a higher density of vertical fractures occurs above dilated sub-horizontal fractures, suggesting new formation. We apply a model of beam failure theory, borrowed from structural engineering, to constrain potential new fracture generation, using assumptions based on measured water pressure fluctuations from beneath the Greenland Ice Sheet. This modelling shows that beam failure is a plausible mechanism for the generation of new vertical fractures during a subglacial water fluctuation cycle under a range of realistic glaciological conditions. This implies that hydraulic jacking can result in further in situ disruption and brecciation of the shallow rock mass, decreasing the rock mass strength and increasing its hydraulic conductivity. Altogether, hydraulic jacking of existing fractures and the formation of new vertical fractures results in effective subglacial mechanical weathering of the shallow rock mass.
{"title":"Rock fracturing by subglacial hydraulic jacking in basement rocks, eastern Sweden: the role of beam failure","authors":"M. Krabbendam, Romesh Palamakumbura, C. Arnhardt, A. Hall","doi":"10.1080/11035897.2021.1939776","DOIUrl":"https://doi.org/10.1080/11035897.2021.1939776","url":null,"abstract":"ABSTRACT Dense networks of dilated fractures occur locally in the upper 5–15 m of bedrock in basement gneisses in eastern Sweden. Near Forsmark, pre-existing sub-horizontal fractures have been jacked open and filled with water-lain sediment, likely during the latest Weichselian glaciation. Despite extensive previous research, it is uncertain whether subglacial hydraulic jacking led to the generation of new fractures, in addition to reactivation of pre-existing ones. Re-analysis of historic photos from excavations near the Forsmark power plant indicates formation of two types of new fracture. Firstly, rock fragments were broken off the main fracture surfaces as existing fractures were jacked open. Secondly, fracture analysis shows that whilst few subvertical fractures occur above tight sub-horizontal fractures, a higher density of vertical fractures occurs above dilated sub-horizontal fractures, suggesting new formation. We apply a model of beam failure theory, borrowed from structural engineering, to constrain potential new fracture generation, using assumptions based on measured water pressure fluctuations from beneath the Greenland Ice Sheet. This modelling shows that beam failure is a plausible mechanism for the generation of new vertical fractures during a subglacial water fluctuation cycle under a range of realistic glaciological conditions. This implies that hydraulic jacking can result in further in situ disruption and brecciation of the shallow rock mass, decreasing the rock mass strength and increasing its hydraulic conductivity. Altogether, hydraulic jacking of existing fractures and the formation of new vertical fractures results in effective subglacial mechanical weathering of the shallow rock mass.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42344638","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 : 2021-07-03DOI: 10.1080/11035897.2021.1895304
M. Steinthorsdottir, C. Elliott‐Kingston, Mario Coiro, J. McElwain
ABSTRACT To understand Earth´s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO2, across the Triassic–Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO2-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO2. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO2 reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO2 response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO2, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO2 compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO2 reconstructions, for example through biogeochemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO2 can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO2 responders, such as Ginkgoales.
{"title":"Searching for a nearest living equivalent for Bennettitales: a promising extinct plant group for stomatal proxy reconstructions of Mesozoic pCO2","authors":"M. Steinthorsdottir, C. Elliott‐Kingston, Mario Coiro, J. McElwain","doi":"10.1080/11035897.2021.1895304","DOIUrl":"https://doi.org/10.1080/11035897.2021.1895304","url":null,"abstract":"ABSTRACT To understand Earth´s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO2, across the Triassic–Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO2-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO2. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO2 reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO2 response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO2, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO2 compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO2 reconstructions, for example through biogeochemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO2 can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO2 responders, such as Ginkgoales.","PeriodicalId":55094,"journal":{"name":"Gff","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/11035897.2021.1895304","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45296977","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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