78 research outputs found
New information on the Ediacaran-Cambrian transition in the Vestertana Group, Finnmark, northern Norway, from trace fossils and organic-walled microfossils
Journal home page at https://njg.geologi.no/.The Vestertana Group on the Digermul Peninsula, Finnmark, northern Norway, presents one of the few, potentially continuous Ediacaran– Cambrian sections in Scandinavia. Trace fossils provide the main age constraint, with the boundary traditionally placed at the base of the Breidvika Formation. Here, we provide trace-fossil evidence to show that this boundary is at least as low as the third cycle of the Manndraperelva Member, Stáhpogieddi Formation, where Treptichnus pedum is associated with trilobed trace fossils. Organic-walled microfossils from the same stratigraphic interval include Granomarginata prima and the first report from Scandinavia of Cochleatina. The second cycle of the Manndraperelva Member contains trace fossils, including treptichnids and ?Cochlichnus isp. tentatively interpreted as latest Ediacaran. Reports of palaeopascichnids suggest a late Ediacaran age for the first cycle. The age of lower parts of the Stáhpogieddi Formation is poorly constrained but discoidal Ediacara-type fossils, vendotaenids, and possible simple trace fossils, suggest that the middle part of the Innerelva Member is younger than c. 560 Ma
Late Ordovician molluscs of the central and eastern Anti-Atlas, Morocco
More than 30 species of tergomyan, gastropod, bivalve and cephalopod molluscs are described from the Late Ordovician of central and eastern Anti-Atlas, Morocco. For the cephalopods this represents the first systematically known taxa of the region. Tergomyans and gastropods are most common in the more shaly part of the Lower Ktaoua Formation, while bivalves are more frequent in the sandy part of the Lower Second Bani Formation. A southern Gondwana aspect is evident for the tergomyan, gastropod and bivalve assemblages, sharing many taxa with Bohemia, while no clear signal is present for the cephalopods. The latter reflects insufficient knowledge of the fauna of large parts of these areas. The widely recognized Holopea? antiquata is transferred to the genus Radvanospira gen. nov.; other new gastropod taxa include Allossospira gen. nov., Tritonophon grandis sp. nov., Radvanospira baniensis sp. nov. and Lophospira latilabra sp. nov. Most of the diverse bivalve fauna and the few cephalopods are left in open nomenclature but new taxa include the bivalve Praenucula pojetai sp. nov. and the cephalopods Wadema tattai sp. nov. and Tafadnatoceras tiouririnense gen. et. sp. nov. The Late Ordovician bivalves from Morocco are dominated by pteriomorphs and protobranchs, inhabiting infaunal, semi-infaunal and epifaunal niches.Peer reviewe
First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance
Accepted manuscript version, licensed CC BY-NC-ND 4.0. We report for the first time carbonates from the upper Ediacaran sedimentary succession of Finnmark, Arctic Norway. Carbonates occur as calcareous siliciclastic beds, lenses, and concretions, some with calcite spherulites and cone-in-cone (CIC) calcite, in a mudrock to fine-grained sandstone succession from approximately 3 m to 26 m above the base of the 2nd cycle of the Manndrapselva Member of the Stáhpogieddi Formation (Vestertana Group). They occur c. 40 m below the Ediacaran–Cambrian boundary, which is well defined by trace fossils. Thin-section petrography and scanning micro X-ray fluorescence elemental mapping reveal a layered composition of the calcareous sedimentary rocks. In some of those, well-developed nested cones of CIC calcite form the outer layer. Thin clay coatings outline individual cones. The inner layers are composed of (1) carbonate with calcite spherulites (grainstone) and (2) thinly laminated fine-grained calcareous siliciclastics (mudstone and wackestone) indicated by elevated concentrations of Al, Si, Fe, and Ti. The inner siliciclastic layers contain framboidal pyrite and probably organic matter. Formation of calcite spherulites took place probably at the sediment–water interface either in a coastal littoral environment or in situ in the sublittoral zone under high alkaline conditions whereas CIC calcite formed during burial diagenesis and clearly in pre-Caledonian time before metamorphism and cleavage formation. This new record of carbonates with calcite spherulites and CIC structures from the Ediacaran of Arctic Norway adds to their rare occurrences in the geological record
Life through an Ediacaran glaciation: Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway
New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and Stáhpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, Stáhpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite
Distribution and correlation of Sabellidites cambriensis (Annelida?) in the basal Cambrian on Baltica
Sabellidites cambriensis is a tubular non-mineralized metazoan that appears as compressed ribbon-shaped imprints with transverse wrinkling, thick walls and an even tube diameter of up to 3 mm. The distribution of Sabellidites is investigated in three Ediacaran–Cambrian sections on the Digermulen Peninsula in Arctic Norway, spanning the Manndrapselva Member of the Stáhpogieddi Formation and the lower member of the Breidvika Formation. Here, the Ediacaran–Cambrian boundary is located in the lower part of the upper parasequence (third cycle) of the Manndrapselva Member. Specimens of Sabellidites are rare but consistently present close to the lowest level of Treptichnus pedum and upsection, whereas the taxon is common and abundant in the lower part of the lower member of the Breidvika Formation, with an upper record at c. 55 m above the base. The range is comparable with that of the GSSP section in Newfoundland, Canada, establishing Sabellidites as an index fossil for the lowermost Cambrian. In the Manndrapselva Member, Sabellidites co-occurs with the acritarch Granomarginata, indicative of the lowermost Cambrian Granomarginata Zone, whereas in the Breidvika Formation it co-occurs with Asteridium. Sabellidites is widely distributed in Baltica, through the Rovnian and Lontovan regional stages but confined to the Fortunian global stage. In its lower range, Sabellidites is associated with a Treptichnus pedum trace fossil association and a depauperate leiosphaerid acritarch assemblage, followed by a Granomarginata assemblage. In its upper range, Sabellidites co-occurs with acritarchs of the Asteridium–Comasphaeridium Zone and the tubular foraminiferan Platysolenites. In Baltica, Sabellidites is a useful index fossil
A late Caledonian tectono-thermal event in the Gaissa Nappe Complex, Arctic Norway: evidence from fine-fraction K‒Ar dating and illite crystallinity from the Digermulen Peninsula
This is an Accepted Manuscript of an article published by Taylor & Francis in GFF on 03 Oct 2019, available online: http://www.tandfonline.com/https://doi.org/10.1080/11035897.2019.1583685.Fine-fraction K‒Ar dating and illite crystallinity determination were applied on a peculiar pale olive green shale sample from the upper Ediacaran Indreelva Member (Stáhpogieddi Formation, Vestertana Group, Gaissa Nappe Complex) of the Digermulen Peninsula in Finnmark, Arctic Norway, to constrain the age and metamorphic conditions of tectono-thermal overprint. The <2 and <0.2 µm grain-size fractions are almost purely illite and yielded an illite crystallinity (expressed as the Kübler index) of 0.215 Δ° 2θ and 0.228 ∆° 2θ and K‒Ar ages of 403.9 ± 4.2 and 391.5 ± 4.0 Ma, respectively. The K‒Ar ages are interpreted to present late-stage thermal overprint under low epizonal conditions along a localised shear zone, likely post-dating the peak of metamorphism and cleavage generation on the Digermulen Peninsula. Thus, a later tectono-metamorphic event related to the late stage of the Scandian orogeny is locally recorded in the Gaissa Nappe Complex of the Caledonides of Finnmark. This late Scandian event was probably caused by orogenic extensional collapse and appears to have extended at least into Mid-Devonian time
Rare earth elements and neodymium and strontium isotopic constraints on provenance switch and post-depositional alteration of fossiliferous Ediacaran and lowermost Cambrian strata from Arctic Norway.
The Digermulen Peninsula in northeastern Finnmark, Arctic Norway, comprises one of the most complete
Ediacaran–Cambrian transitions worldwide with a nearly continuous record of micro- and macrofossils from the
interval of the diversification of complex life. Here, we report on the provenance and post-depositional alteration
of argillaceous mudstones from the Digermulen Peninsula using rare earth elements and Sm–Nd and Rb–Sr
isotopic systematics to provide an environmental context and better understand this important transition in
Earth’s history. The studied sections comprise a mid-Ediacaran glacial–interglacial cycle, including the Nyborg
Formation (ca. 590 Ma) and Mortensnes Formation (related to the ca. 580 Ma-old Gaskiers glaciation), and the
Stahpogieddi ´ Formation (ca. 560–537 Ma), which yields Ediacara-type fossils in the Indreelva Member and
contains the Ediacaran–Cambrian boundary interval in the Manndrapselva Member and basal part of the
informal Lower Breidvika member (ca. 537–530 Ma). Three sample groups, (1) Nyborg and Mortensnes formations, (2) the lowermost five samples from the Indreelva Member and (3) the remaining samples from the
Indreelva as well as from the Manndrapselva and Lower Breidvika members, can be distinguished, belonging to
distinct depositional units. All samples have negative εNd(T) values (− 6.00 to − 21.04) indicating a dominant
input of terrigenous detritus with an old continental crust affinity. Significant shifts in Sm–Nd isotope values are
related to changes in the sediment source, i.e. Svecofennian province vs Karelian province vs Svecofennian
province plus in addition likely some juvenile (late Neoproterozoic volcanic) material, and probably reflect
palaeotectonic reorganisation along the Iapetus-facing margin of Baltica. The combined Rb–Sr isotopic data of all
samples yield an errorchron age of about 430 Ma reflecting the resetting of the Rb–Sr whole-rock isotope systems
of the mudstones during the Scandian tectono-metamorphic event in the Gaissa Nappe Complex of Finnmark.
Preservation of palaeopascichnids coincides with the sedimentation regimes of sample groups 2 and 3 while
other Ediacara-type fossils, e.g. Aspidella-type and frondose forms, are limited to the sample group 3. Our results
are similar to those of earlier studies from the East European Platform in suggesting oxic seafloor conditions
during the late Ediacaran
Marine redox conditions during deposition of Late Ordovician and Early Silurian organic-rich mudrocks in the Siljan ring district, central Sweden
The final publication is available at Elsevier via https://doi.org/10.1016/j.chemgeo.2017.03.015 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 licenseThe Late Ordovician Period witnessed the second largest mass extinction in the Phanerozoic Eon and the Hirnantian glaciation. To infer ocean redox conditions across the Ordovician-Silurian transition, we measured the U (as δ238U relative to standard CRM145 = 0‰) and Mo (as δ98Mo relative to standard NIST SRM 3134 = +0.25‰) isotope compositions of 26 organic-rich mudrock samples from the Late Ordovician (Katian) Fjäcka Shale and the Early Silurian (Aeronian-Telychian) Kallholn Formation (Siljan ring district, Sweden). The magnitude of Re,Mo, and U enrichments, ReEF/MoEF and UEF/MoEF ratios, and sedimentary Fe speciation point to locally euxinic bottom water conditions during deposition of the Fjäcka Shale. The same proxies suggest that black shales of the Kallholn Formation were deposited under transiently euxinic conditions with the chemocline situated near the sediment-water interface, whereas gray shales stratigraphically equivalent to the upper Kallholn Formation were deposited from oxygenated bottom waters. These observations are consistent with higher δ98Mo and δ238U in the Fjäcka Shale compared with the Kallholn Formation. Because the Fjäcka Shalewas deposited from persistently euxinic bottomwaters, theMo and U isotope compositions from these rocks can be used to estimate the extent of global ocean euxinia and ocean anoxia (euxinic plus ferruginous conditions), respectively. Elevated MoEF and Mo/TOC ratios in the euxinic Fjäcka Shale suggest no more than moderate basin restriction from the open ocean as well as non-quantitative removal ofMo from the euxinic bottom waters, thus pointing toMo isotope fractionation between seawater and the euxinic sediments. Hence, we infer that even the highest δ98Mo(+1.28‰) preserved in the Fjäcka Shale is only aminimum estimate for theMoisotope composition of coeval global seawater. Correcting for seawater-sediment Mo isotope fractionation, the δ98Mo of late
Katian seawater may have been +1.4–2.1‰, which corresponds to ~10–70% Mo removal into the euxinic sink. The
average authigenic δ238U of the Fjäcka Shale is −0.05‰ to +0.02‰ after correcting for a range of possible detrital
δ238U values, thus yielding an overall average of ~0‰. Taking into account isotope fractionation during U removal
to euxinic sediments, we infer that late Katian seawater δ238U was about−0.85‰to−0.60‰. A steady-state U isotope
mass balance model reveals that 46–63% of riverine U input was removed in anoxic settings. Based on the Mo
and U isotope data, we infer that euxinic and anoxic waters may have covered b1% and at least 5% (potentially
tens of percent) of the total seafloor area during the late Katian, respectively, based on previously publishedmodels
that relate themagnitude of Mo and U burial fluxes to the areal extent of euxinic and anoxic seafloor. By comparison,
only 0.21–0.35% and b1% of the total seafloor area was covered by anoxic waters today and during the Cenozoic, respectively. The difference between the estimated extent of ocean anoxia (euxinic plus ferruginous) and ocean euxinia
points to an appreciable extent of ferruginous water masses during the late Katian. Integration of our data with
previous studies thus supports the hypothesis that ocean oxygenation intensified during the subsequent Hirnantian
glaciation (when seawater δ98Motemporarily reached values similar to today). Hence, environmental stresses related
to glaciation, not an expansion of ocean anoxia,may have triggered the first phase of the Hirnantianmass extinction.NSERC Discovery grant || (RGPIN-435930)
Chinese 973 program || (grant No. 2013CB955704)
NSFC || (grant No. 41172030
Late Ediacaran occurrences of the organic-walled microfossils Granomarginata and flask-shaped Lagoenaforma collaris gen. et sp. nov.
New occurrences of flask-shaped and envelope-bearing microfossils, including the predominantly Cambrian taxon Granomarginata, are reported from new localities, as well as from earlier in time (Ediacaran) than previously known. The stratigraphic range of Granomarginata extends into the Cambrian System, where it had a cosmopolitan distribution. This newly reported Ediacaran record includes areas from Norway (Baltica), Newfoundland (Avalonia) and Namibia (adjacent to the Kalahari Craton), and puts the oldest global occurrence of Granomarginata in the Indreelva Member (< 563 Ma) of the Stáhpogieddi Formation on the Digermulen Peninsula, Arctic Norway. Although Granomarginata is rare within the assemblage, these new occurrences together with previously reported occurrences from India and Poland, suggest a potentially widespread palaeogeographic distribution of Granomarginata through the middle–late Ediacaran interval. A new flask-shaped microfossil Lagoenaforma collaris gen. et sp. nov. is also reported in horizons containing Granomarginata from the Stáhpogieddi Formation in Norway and the Dabis Formation in Namibia, and flask-shaped fossils are also found in the Gibbett Hill Formation in Newfoundland. The Granomarginata–Lagoenaforma association, in addition to a low-diversity organic-walled microfossil assemblage, occurs in the strata postdating the Shuram carbon isotope excursion, and may eventually be of use in terminal Ediacaran biostratigraphy. These older occurrences of Granomarginata add to a growing record of body fossil taxa spanning the Ediacaran–Cambrian boundary
U–Pb dating of calcite in ancient carbonates for age estimates of syn- to post-depositional processes: a case study from the upper Ediacaran strata of Finnmark, Arctic Norway
Results of in situ U–Pb dating of calcite spherulites, cone-in-cone (CIC) calcite and calcite fibres from a calcareous concretion of the upper Ediacaran of Finnmark, Arctic Norway, are reported. Calcite spherulites from the innermost layers of the concretion yielded a lower intercept age of 563 ± 70 Ma, which, although imprecise, is within uncertainty of the age of sedimentation based on fossil assemblages. Non-deformed CIC calcite from the bottom part of the concretion yielded an age of 475 ± 25 Ma, which is interpreted as the age of CIC calcite formation during a period of fluid overpressure induced during burial of the sediments. Deformed CIC calcite from the top part of the concretion yielded an age of 418 ± 23 Ma, which overlaps with a known Caledonian tectono-metamorphic event, and indicates a potential post-depositional overprint at this time. Calcite fibres that grew in small fissures along spherulite rims, which are interpreted as a recrystallization feature during deformation and formation of a cleavage, gave an imprecise age of 486 ± 161 Ma. Our results show that U–Pb dating of calcite can provide age constraints for ancient carbonates and syn- to post-depositional processes that operated during burial and metamorphic overprinting
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