SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Agić Heda) "

Sökning: WFRF:(Agić Heda)

  • Resultat 1-40 av 40
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Agić, Heda, 1989- (författare)
  • A new species of small acritarch with porous wall structure from the early Cambrian of Estonia, and implications for the fossil record of eukaryotic picoplankton
  • 2016
  • Ingår i: Palynology. - : Informa UK Limited. - 0191-6122 .- 1558-9188. ; 40:3, s. 343-356
  • Tidskriftsartikel (refereegranskat)abstract
    • The Proterozoic-Phanerozoic transition records a general trend of decrease in phytoplankton cell size, in contrast tothe earlier and much larger Ediacaran acritarchs. Particularly minute, unornamented but sculptured organic-walledmicrofossils have been recovered from the lower Cambrian Lükati Formation in northern Estonia. The lack of anysignificant thermal alteration in the formation allowed for excellent preservation of fine microstructures on thesemicrofossils. Among the rich palynomorph assemblage in Lükati, a new species of tiny, spheroidal eukaryoticmicrofossil is recorded: Reticella corrugata gen. et sp. nov. It is characterised by a corrugated and flexible vesicle wallthat is densely perforated by nano-scale pores. Despite its unique morphology, the new species shares diagnosticcharacters with fossil and extant prasinophyte algae. R. corrugata is among the smallest microfossils with typicaleukaryotic morphology (conspicuous wall sculpture) and contributes to the diversity of the size class of smallacritarchs. Size, abundance, inferred prasinophyte affinity and eukaryotic wall sculpture make this new taxon alikely member of the early eukaryotic picoplankton.
  •  
2.
  • Agić, Heda, 1989-, et al. (författare)
  • Affnity, life cycle, and intracellular complexity of organic-walled microfossils from the Mesoproterozoic of Shanxi, China
  • 2015
  • Ingår i: Journal of Paleontology. - : Cambridge Journals. - 0022-3360 .- 1937-2337. ; 89:1, s. 28-50
  • Tidskriftsartikel (refereegranskat)abstract
    • Light microscope and scanning electron microscope observations on new material of unicellularmicrofossils Dictyosphaera macroreticulata and Shuiyousphaeridium macroreticulatum, from the MesoproterozoicRuyang Group in China, provide insights into the microorganisms’ biological affinity, life cycle and cellularcomplexity. Gigantosphaeridium fibratum n. gen. et sp., is described and is one of the largest Mesoproterozoicmicrofossils recorded. Phenotypic characters of vesicle ornamentation and excystment structures, properties ofresistance and cell wall structure in Dictyosphaera and Shuiyousphaeridium are all diagnostic of microalgalcysts. The wide size ranges of the various morphotypes indicate growth phases compatible with the development ofreproductive cysts. Conspecific biologically, each morphotype represents an asexual (resting cyst) or sexual (zygotic cyst)stage in the life cycle, respectively. We reconstruct this hypothetical life cycle and infer that the organism demonstrates areproductive strategy of alternation of heteromorphic generations. Similarly in Gigantosphaeridium, a metabolicallyexpensive vesicle with processes suggests its protective role as a zygotic cyst. In combination with all these charactersand from the resemblance to extant green algae, we propose the placement of these ancient microorganisms in the stemgroup of Chloroplastida (Viridiplantae). A cell wall composed of primary and secondary layers in Dictyosphaera andShuiyouisphaeridium required a high cellular complexity for their synthesis and the presence of an endomembranesystem and the Golgi apparatus. The plastid was also present, accepting the organism was photosynthetic. The biotareveals a high degree of morphological and cell structural complexity, and provides an insight into ongoing eukaryoticevolution and the development of complex life cycles with sexual reproduction by 1200Ma.
  •  
3.
  • Agić, Heda, 1989-, et al. (författare)
  • Cyst and operculum formation in Cambrian-Ordovician galeate acritarchs from Estonia : implications for the algal phylogeny and blooms in the early Paleozoic
  • 2014
  • Ingår i: 4th International Palaeontological Congress Abstract Volume. ; , s. 913-
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Unicellular organic-walled microfossils have been recovered from the Cambrian Lükati Formation and the Tremadocian Varangu Formation exposed in northern Estonia. Due to a combination of main morphological and biochemical characters, mainly a) excystment opening, b) processes, c) acetolysis-  resistant vesicle wall, microfossils have been interpreted as reproductive cysts of green algae. Both microfossil assemblages reflect the evolutionary patterns though the early Palaeozoic: from the Cambrian radiation of morphologically innovative taxa to increase in diversity and more disparate Ordovician forms. Combined light transmitted and scanning electron microscopy on the Middle Cambrian to Tremadocian galeate plexus acritarchs Caldariola, Priscogalea and Stelliferidium, revealed exceptionally preserved morphological elements and rare structure among fossil and extant microbiota – an opening with operculum (lid) in reproductive cyst, in addition to lavish vesicle ornamentation and sculpture. Operculum formation model is reconstructed from fossils at different stages of operculum position and attachment. Comparative morphology shows strong similarity of galeates to the reproductive cysts of the extant algae of Dasycladales (Chlorophyta), where the lid covering the cyst opening is determined by an intrinsic lid-forming apparatus during the organism’s reproductive stage. Opercula in Cambro-Ordovician galeate acritarchs and Dasycladales may be considered a homologous character. Unique morphology of the operculum-bearing microbiota would have required a degree of intracellular sophistication for its development, suggesting advanced intracellular machinery present already in the early Palaeozoic phytoplankton. Additionally, a new species of minute, sphaeromorphic and aggregated eukaryotic microfossils is recorded. It possesses a vesicle wall with corrugated sculpture and perforated by nano-scale pores. These minute early Cambrian microfossils have diagnostic characters of prasinophyte algae.
  •  
4.
  • Agić, Heda, 1989-, et al. (författare)
  • Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton - a window into the early eukaryote evolution
  • 2017
  • Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; , s. 101-130
  • Tidskriftsartikel (refereegranskat)abstract
    • Mesoproterozoic Era was an important time for the initial diversification of eukaryotic groups and the appearance of the first complex morphologies. While eukaryotes evolved around 2.4 Ga, the first microfossils with ornamentation and sculpture occur in the 1.8-1.6 Ga successions worldwide. Shales and siltstones of the Ruyang Group, Shanxi Province, North China Craton, record a high diversity of such organic-walled microfossils. Recently, the depositional ages of this succession has been constrained to 1.75-1.40 Ga via   zircon U-Pb dating. This dating extends back the time of the first appearance of complex eukaryotic characters (e.g. processes, complex wall structure) in the fossil record. We have conducted a biostratigraphic investigation on of the samples throughout the fossiliferous Ruyang Group to provide an estimate of the early eukaryotic diversity in the Mesoproterozoic. Light- and scanning electron microscope studies have documented 26 species, including several that are reported for the first time, and some that were previously known only from younger, Neoproterozoic strata. Fossil diversity is high in the upper Baicaoping Formation, declines in the middle and reaches its peak in the upper Beidajian Formation. Novel morphologies among the unicellular Ruyang biota include a variety of processes, from tube-like extensions to hirsute spines, vesicles with velutinous outer membranes, as well as numerous specimens with internal bodies of varying sizes. We have also recorded the globally distributed Mesoproterozoic taxa Dictyosphaera, Shuiyousphaeridium, and Tappania. Key characters displayed by the Ruyang biota are consistent with reproductive structures (especially cysts among modern protists. These microfossils provide an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga.
  •  
5.
  • Agić, Heda, 1989- (författare)
  • Fossil Focus : Acritarchs
  • 2016
  • Ingår i: Palaeontology Online. ; 6:11, s. 1-13
  • Tidskriftsartikel (populärvet., debatt m.m.)
  •  
6.
  • Agić, Heda, 1989-, et al. (författare)
  • Is cyst formation in early eukaryotes a requirement for their preservation in the fossil record?
  • 2015
  • Ingår i: Abstracts of the Astrobiology Science Conference 2015: Habitability, Habitable Worlds and Life.
  • Konferensbidrag (refereegranskat)abstract
    • Most of the Archaean-Proterozoic fossil record consists of non-biomineralizing microorganisms or their signatures. Body fossils of bacteria and early eukaryotes are preserved in siliciclastics, shales and carbonates, and are usually studied by preparation of thin sections or extraction from the rock matrix via acid maceration.The first eukaryotic organic-walled microfossils (OWM) appear at least by 1.8 Ga and undergo morphological diversification and evolutionary radiation in the Mesoproterozoic. There are no preserved eukaryotic-grade microfossils except OWM until the onset of biomineralization much later in the Neoproterozoic, evident in the record of testate amoebae (VSM) and microfossils with scaly elements.OWM are a less conspicuous component of the fos-sil record than taxa with skeletal or shelly elements. Organic matter decays quickly upon death of the organism, due to autolytic enzymes or degradation via het-erotrophy. However, species producing vegetative cells, resting cysts, zygotes, or spores, show considerable resistance to autolysis. Case studies on extractable carbonaceous OWM indicate they are preserved due to complex refractory molecules in the structure of their sturdy vesicle walls. Living analogues across protistan clades utilise such sporopollenin-like compounds for the cyst wall construction during reproductive phase. Algaenan-containing trilaminar sheath structure (TLS) is secreted during aplanospore formation in extant chlorophyte alga Haematococcus. TLS has also been documented in Leiosphaeridia acritarchs from the Cambrian Lükati Formation in Estonia. Leiosphaeridia is a long ranging morphotype, dating as far back as 1.8 Ga. Presence of TLS in these fossils suggests their function as reproductive cyst. Dictyosphaera-Shuiyousphaeridium plexus from the Mesoproterozoic Ruyang Group, China, also exhibits cyst-like morphology and unique elements of wall reinforcement: internally secreted organic platelets.In addition to these early OWM, many Meso-Neoproterozoic taxa such as Tappania, Trachyhystrychosphaera and Kildinella contain cyst-like characters: 1) reproductive openings, 2) ornamentation, 3) occa-sionally preserved internal bodies and 4) acetolysis-resistant vesicle walls – properties observed among extant encysting protists.Ornamented (process-bearing) microfossils in par-ticular bear strong similarities with zygotes of living unicellular algae. Property of acetolysis-resistant vesicle is a result of sporopollenin-like macromolecules in the wall, synthesized most commonly by the autotrophic eukaryotes. Presence of such recalcitrant organic walls requires significant metabolic investment by the microorganism, which suggests a protective and/or reproductive function. This also allows for easier, and more detailed preservation in the rock record.One of the concerns arising from the studies on the early eukaryotic fossils is the bias towards encysting organisms. The eventual search for the fossil record on other planetary bodies could face the same challenges as the Precambrian palaeobiology: fossilisation and eventual detection might be problematic for any unicellular eukaryotic-grade organisms if they have not evolved reproduction via encystment, or cyst formation as means of coping with adverse environmental conditions.
  •  
7.
  • Agic, Heda, et al. (författare)
  • Late Ediacaran occurrences of the organic-walled microfossils Granomarginata and flask-shaped Lagoenaforma collaris gen. et sp. nov.
  • 2022
  • Ingår i: Geological Magazine. - : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 159:7, s. 1071-1092
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 Stahpogieddi 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 Stahpogieddi 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.
  •  
8.
  • Agić, Heda, 1989-, et al. (författare)
  • Lateral growth of Late Pleistocene stromatolites from Walker Lake (Nevada) and proxy constraints on environmental change
  • 2014
  • Ingår i: 2014 GSA Annual Meeting in Vancouver. - : Geological Society of America. ; , s. 300-4-
  • Konferensbidrag (refereegranskat)abstract
    • Walker Lake, a terminal sodium bicarbonate lake in Western Nevada (Great Basin, USA) contains numerous carbonate structures, including stromatolites. The lake is a remnant of the larger Pleistocene Lake Lahontan system that has been isolated for the last ~12 ka. Stromatolites of unique macroscale morphology were collected at the ancient Lahontan shoreline during the 2014 International Geobiology Course.Initial observations of a stromatolite bed revealed a bowl-shaped carbonate framework composed of stacked, weakly laminated, vertical and horizontal petal-like structures with copious pore space. One laterally-oriented petal was taken off of the main structure and studied. Petrographical observations exhibit two types of alternating microfabrics and three transitions in microfabric. Both sparry crystal fans of calcite, and convex layers of fine micrite with occasional trapped crystals and fossils, were observed.Calibrated 14C ages (IntCal13) for the proximal and the distal end of the stromatolite are 35,540 YBP and 33,580 YBP, respectively. Clumped isotope (D47)-based estimates of temperature steadily increase throughout most of this interval, from the beginning of accretion, to the middle of the structure. By the distal end, values are at their peak, and at the tip temperatures decrease again. D47-temperatures correspond to microfabric, with textural changes associated with evidence for climatic fluctuations.We suggest the stromatolite formation may have been initiated during warmer intervals, induced by the chemical precipitation of calcite fans which served as a substrate for a biofilm growth. Microbial activity trapped the fine sediment and formed micrite. Colder conditions propagated fan precipitation. Microfabric alternation throughout the stromatolite records environmental change in the span of ca. 2000 years of Lake Lahontan history, likely in response to lake level fluctuations.
  •  
9.
  • Agic, Heda, et al. (författare)
  • Life through an Ediacaran glaciation : Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 635
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 St ' ahpogieddi 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, St ' ahpogieddi 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.
  •  
10.
  • Agic, Heda, et al. (författare)
  • Life through the 'Varanger ice ages' : microfossil record of late Neoproterozoic glacial-interglacial units from arctic Norway
  • 2018
  • Ingår i: Geological Society of America <em>Abstracts with Programs</em>. - : Geological Society of America.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The late Neoproterozoic strata in Finnmark (Arctic Norway) provide a good sedimentary record of Neoproterozoic glaciations on the Baltica paleocontinent. The lower Vestertana Group exposed on the Digermulen Peninsula contains two glaciogenic units, the Smalfjord and Mortensnes formations. Chemostratigraphic correlation dated the Smalfjord diamictite to the Marinoan glaciation (650-635 Ma), yet its age was also proposed to be older, per correlation to glacial units in central and southern Scandinavia. The diamictites are bracketing shales and siltstones of the interglacial Nyborg Formation. Stratigraphic, paleontological, and sedimentological data are presented from the interglacial-glacial succession, investigated by the Digermulen Early Life Research Group. Palynological analysis yielded well-preserved organic-walled microfossils (OWM) from the Nyborg Fm., and from fine-grained diamictite matrix in the Mortensnes Fm. via a modified extraction method.The interglacial Nyborg Fm. hosts a moderate diversity assemblage of prokaryotic and eukaryotic OWM, as well as acanthomorphic acritarchs such as Ceratosphaeridium, ?Cavaspina, and a novel process-bearing form. Organically preserved, enigmatic multicellular eukaryotic fossils occur in the upper Nyborg Fm. The Mortensens glacial assemblage is less diverse and contains bacterial filaments, leiosphaerids, toroidal forms, and Micrhystridium-type minute acanthomorphs.The presence of Doushantuo-Pertatataka type acritarchs in the Nyborg Fm., and small acanthomorphs in the Mortensnes diamictite corroborate an early Ediacaran age for the interglacial-glacial succession on Digermulen. In addition to the trace fossil and body-fossil record of Ediacara-biota in the overlying Stáhpogieddi Formation, the microfossil biostratigraphy suggests Marinoan and Gaskiers glaciation equivalent ages of the Varanger glaciations in Finnmark. Protistan diversity in the succession declined through and following the glaciation, until late Ediacaran.
  •  
11.
  •  
12.
  • Agić, Heda, 1989-, et al. (författare)
  • Morphology of the Proterozoic eukaryotic microfossils as a reflection of their intracellular complexity
  • 2014
  • Ingår i: 4th International Palaeontological Congress Abstract Volume. ; , s. 256-
  • Konferensbidrag (refereegranskat)abstract
    • Mesoproterozoic is a time of increasing diversity of microscopic life and appearance of intricate new cell morphologies. First eukaryotes may have evolved around 2.4 Ga, but the first microbiota with intricate sculpture and ornamentation are found in the younger, 1.8.-1.6 Ga successions worldwide. Such microfossils were uncovered from the Ruyang Formation in Shanxi, China and Roper Group, Northern Territories, Australia, dating back to 1.6-1.0 Ga ago. Some of these unicellular organic-walled fossils share characters with Ediacaran and Phanerozoic fossils, as well as extant green microalgae. Key characters among some Precambrian acritarchs are acetolysis-resistant vesicle with multi-layered walls; vesicle ornamentation by diverse processes that are produced during cyst formation; and excystment openings for the release of gametes or daughter-cells. Combination of these morphological elements, also present in extant phytoplankton, reflects the fossils’ protective function as reproductive cysts, indicating that complex life cycles and reproduction were well under way in Mesoproterozoic. Several case studies of microfossil morphology likely induced by intrinsic eukaryotic mechanisms are presented.Distinctive vesicle wall composed of the primary layer reinforced by polygonal platelets in Mesoproterozoic taxa Dictyosphaera and Shuiyouisphaeridium, as well as the sophisticated vesicle-wall patterning on the fossil sphaeromorphs Valeria and younger Cerebrosphaera would have required a certain degree of complexity for their formation, as observed in the present day analogues among eukaryotic protists. This suggests the activity of the key eukaryotic organelles and cellular mechanisms and signalling for the cyst formation. Considering that Golgi apparatus and the endoplasmatic reticulum are the organelles regulating eukaryotic secretory pathway and synthesis of biopolymers used in cell-wall construction, they would have been required for the complex morphology observed in these Precambrian taxa. Therefore, the presence of GA and ER in the eukaryotic cell is inferred at the minimum age of 1.6-1.4 Ga. Similarly, morphology of acritarchs of the Cambrian galeate plexus, namely openings with opercula, is likely induced by the activity of the LFA organelle (lid-forming apparatus) as in the extant dasycladalean alga Acetabularia.Additionally, several new morphotypes from the Ruyang Formation are presented. These unicellular fossils bear a velutinous outer membrane surrounding an internal sphere, which suggests a protective function of a reproductive or a resting cyst.Cyst-like morphology varies in disparity, but its key features are consistent through Mesoproterozoic, Neoproterozoic and early Palaeozoic.
  •  
13.
  • Agić, Heda, 1989-, et al. (författare)
  • Organically-preserved multicellular eukaryote from the early Ediacaran Nyborg Formation, Arctic Norway
  • 2019
  • Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
  • Tidskriftsartikel (refereegranskat)abstract
    • Eukaryotic multicellularity originated in the Mesoproterozoic Era and evolved multiple times since, yet early multicellular fossils are scarce until the terminal Neoproterozoic and often restricted to cases of exceptional preservation. Here we describe unusual organically-preserved fossils from mudrocks, that provide support for the presence of organisms with differentiated cells (potentially an epithelial layer) in the late Neoproterozoic. Cyathinema digermulense gen. et sp. nov. from the Nyborg Formation, Vestertana Group, Digermulen Peninsula in Arctic Norway, is a new carbonaceous organ-taxon which consists of stacked tubes with cup-shaped ends. It represents parts of a larger organism (multicellular eukaryote or a colony), likely with greater preservation potential than its other elements. Arrangement of open-ended tubes invites comparison with cells of an epithelial layer present in a variety of eukaryotic clades. This tissue may have benefitted the organism in: avoiding overgrowth, limiting fouling, reproduction, or water filtration. C. digermulense shares characteristics with extant and fossil groups including red algae and their fossils, demosponge larvae and putative sponge fossils, colonial protists, and nematophytes. Regardless of its precise affinity, C. digermulense was a complex and likely benthic marine eukaryote exhibiting cellular differentiation, and a rare occurrence of early multicellularity outside of Konservat-Lagerstatten.
  •  
14.
  • Agić, Heda, 1989- (författare)
  • Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position.
  •  
15.
  • Agić, Heda, 1989-, et al. (författare)
  • Raman spectra analysis and comparison of Neoproterozoic organic-walled mesofossils
  • 2012
  • Ingår i: The 2012 Fermor Meeting of the Geological Society. - London. ; , s. 86-
  • Konferensbidrag (refereegranskat)abstract
    • Skeletal material first appears in the rock record in the terminal Ediacaran, leaving most of the Earth’s history only to minute organic fossils. Aside from abundant acritarchs (unicellular organic-walled phytoplankton) present from at least ~2.5 Ga, other Proterozoic organic fossils of complex (eukaryotic) organisms include fungi and macroscopic algae of still debated taxonomy. Often preserved as flattened carbonaceous filaments in several morphologies: (1) rounded, (2) stick-like elongate and (3) branching, these Neoproterozoic fossils, including Chuaria, Morania, Beltanelloides, Vendotaenia, possess limited characters and differ little in gross morphology. As a result, other methods are needed to elucidate their biological affinities and, ultimately, phylogeny.Here we present the comparison of the Raman spectra analysis of different macroalgal genera from Yakutia, Siberia, as well as that of a putative polychaete Sabellidites from the East European Platform, dated to the early Cryogenian (840-700 Ma) and lowermost Cambrian respectively.Data from the vibrational modes of organic molecules from the wall of unmineralised organisms reveal their chemistry and partially wall ultrastructure, presumably an indication of their relationships. Polyaromatic chain hydrocarbons and n-aliphatic pyrolysates suggest algal affinity for some of the Neoproterozoic organic problematica, yet most of the Raman spectra results are still difficult to fully identify, partially owing to the thermal maturity of the host rocks. However, there are clear differences between various groups, differentiating between parts of a single plexus (cf previous studies of Chuaria-Tawuia suggesting them to be components of a multicellular plant) and elements from other taxa. Additionally, the distinct organic matter spectra of Chuaria and Sabellidites indicate that Raman spectroscopy could be a useful method in identifying different branches of the early eukaryotes.As they are usually shallow-water and dependant on sunlight, the record of sturdy photosynthetic macroorganisms in the  Neoproterozoic strengthens the evidence that limits the extent of the harsh environmental conditions during the Cryogenian period, at least during the Kaigas and Sturtian glaciations.
  •  
16.
  • Agić, Heda, 1989-, et al. (författare)
  • Raman spectroscopy and microstructural comparison of carbonaceous compression and body fossils from the Neoproterozoic of Siberian and Eastern European platforms
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Macroscopic, organic-walled fossils preserved as carbonaceous compressions and body fossils are commonly occurring in the Neoproterozoic-Cambrian successions worldwide. Most of these fossils, including studied here Chuaria, Tawuia, and Beltemelliformis, have been accepted as algae, and Sabellidites as an early metazoan. They possess limited characters for biological identification and differ in gross morphology of spherodial vs. tubular millimetre-sized specimens. Consequently, other methods than morphologic observations are needed to elucidate their affinities and, ultimately, phylogeny. Here we present a comparison of the Raman spectrographic signatures and new scanning electron microscope (SEM) observations on different carbonaceous compression and body fossils from the Khajpakh Formation (Siberian Platform), and Nekrasovo Formation (East European Platform), referred to the Tonian-Cryogenian transitional interval (c. 840-700 Ma) and the lowermost Cambrian stage, respectively. Data from the Raman spectroscopy of the walls of non-mineralised organisms reveal their chemical properties, and, in additions to microstructural characters, may be used to resolve the fossils’ phylogenetic affinities. To test the basic recognition of organic matter in studied photosynthetic organisms vs. animals, we have examined algal compression fossils and organically-preserved body-fossil. Differences in the Raman spectroscopic signature between various taxa have been observed. Vibrational absorption bands similar to those characteristic of α-chitin signature have been detected in the organic wall of Sabellidites, consistent with its metazoan identity. Distinct organic matter spectra of the macroalgae Chuaria, Tawuia and Beltanelliformis, and the possible early annelid Sabellidites indicate that Raman spectroscopy could be a useful method in identifying different branches of the early eukaryotes. Additionally, the recognition of the earliest metazoans among un-diagnostic tubular fossils by biochemical signatures and wall ultrastructure, could provide the minimum age of their origins.
  •  
17.
  • Agić, Heda, 1989-, et al. (författare)
  • Reproductive cyst and operculum formation in the Cambrian-Ordovician galeate-plexus microfossils
  • 2016
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:2, s. 278-294
  • Tidskriftsartikel (refereegranskat)abstract
    • Unicellular organic-walled microfossils from the Cambrian-Ordovician transition in Estonia (ca. 490-480 million years ago) exhibit rare characters reflecting their function as reproductive algal cysts. The studied assemblages record the evolutionary history of phytoplankton in the early Paleozoic Era: novel morphologies appearing through the Cambrian and subsequently diversifying in the Ordovician. Well preserved specimens were extracted following a standard palynological method and studied by light transmitted microscopy. The galeate plexus acritarchs Caldariola, Priscogalea and Stelliferidium have revealed exceptionally preserved morphological elements and a rare structure among both fossil and extant protists – an opening with operculum (lid) in reproductive cysts, in addition to lavish vesicle ornamentation and sculpture. Analogous morphology is observed in the living dasycladalean alga Acetabularia (Chlorophyta), which possesses an intrinsic lid-forming apparatus used during organism’s reproductive stage. Based on the observations on the fossil material and studies on the Acetabularia lid-formation, we propose a model of operculum formation in the galeate plexus microorganisms. Due to strong morphological and ecological similarities between galeate fossils and dasycladalean cysts, and the antiquity of this algal order, galeates may be positioned within green algae, more specifically Dasycladales. Unique morphology of the operculum-bearing microbiota would have required a high degree of intracellular complexity for its development, suggesting that advanced intracellular machinery was present already in the early Paleozoic phytoplankton. Additionally, minute prasinophyte microfossils Reticella corrugata  are reported for the first time in the Upper Cambrian strata. 
  •  
18.
  • Agic, Heda, et al. (författare)
  • Unusual organic-walled microfossil from the late Neoproterozoic Nyborg Formation, Digermulen Peninsula, Arctic Norway
  • 2017
  • Ingår i: ISECT 2017.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The late Neoproterozoic Nyborg Formation is exposed in the Tanafjord area, Finnmark, Arctic Norway, on Digermulen and Varanger Peninsulas. The succession is composed of ~400 m of interbedded shales, siltstone and purple to grey sandstone, deposited between Neoproterozoic low latitude glacial deposits. The Nyborg Fm. lies on top of the Smalfjord diamictite, and is overlain by the Mortensnes diamictite (the latter was attributed to both Marinoan (650-635 Ma) and Gaskiers (579 Ma) glaciations) and the Ediacaran-Cambrian Stáhpogieddi Formation. Thus, the Nyborg Fm. represents late Neoproterozoic, probably the last Cryogenian interglacial interval. Presented material was collected in 2014 by members of Digermulen Early Life Research Group, from organic-rich, grey-green shales and siltstones of the Nyborg Mbr. D, uppermost Nyborg Fm. between Árasulluokta and Guvssájohka valleys. Organic-walled microfossils were extracted from shale via standard palynological acetolysis in hydrofluoric acid, and studied via light and scanning electron microscopy. Microfossils from the Nyborg Fm. include Synsphaeridium-type aggregated cells, unbranched bacterial filaments (Polythrichoides and Siphonophycus), sphaeromorph and envelope-bearing acritarchs (leiosphaerids, Stictosphaeridium, Simia), and previously unrecognized aggregated tubular microfossils. These taxa are long-ranging, but common in glacial-interglacial units worldwide, and thus broadly corroborate the Cryogenian age of the Nyborg sediments. The novel fossil, up to 300 μm in size, is a parenchymatous meshwork of interconnected organic-walled tubes that terminate in cup-shaped apices 4-11 µm in diameter. Irregular tube clusters are truncated both in macerates and in thin sections, suggesting post mortem transport. Elemental EDXS analysis indicates that extracted meshwork microfossils are predominantly composed of carbonaceous material and also associated with small amounts of titanium and vanadium. Considering the branching and adjoined body plan of carbonaceous fossil, it was likely multicellular and of eukaryotic affinity. As such, it may represent an important step in the evolution of complex multicellularity and morphological complexity several million years before the appearance of Ediacaran organisms.
  •  
19.
  • Butler, Aodhan, et al. (författare)
  • Recent palaeobiological and stratigraphical advances from the Cambrian of Estonia
  • 2011
  • Ingår i: The 2nd Wiman Meeting. - Uppsala. ; , s. 5-5
  • Konferensbidrag (refereegranskat)abstract
    • The unique Cambrian sediments of Estonia represent an important and understudied component of the Baltic system. Here we present an overview of recent field studies conducted by Uppsala University in association with colleagues from the Baltic Geotourism project, that have revealed a number of exciting discoveries in terms of Cambrian palaeontology and stratigraphy of Estonia. These include new purported stem lophotrochozoans with bizarre shell structure. Current efforts to describe and systematically appraise this material are outlined. The presence of unusual shell structure and whether this is the result of taphonomic alteration or indeed represents a novel shell structure type is examined. We propose herein affinities to the inarticulate stem-brachiopod Mickwitzia based upon the presence of an umbo and the overall gross morphology.  Possible new records of Estoniadiscus discinoides (Schmidt 1888), an extremely rare enigmatic organism with postulated affinities to eldonioids or other stem-group lophophorates are also described from the type section at Kakumägi, within the Kakumägi member Member of the lower Cambrian Tiskre formationFormation. The discovery of Dictyonema Rhabdinopora sp. graptolites, which have until now demarcated the Cambrian-Ordovician boundary, in-situ approximately 3 m below the previous reported occurrence from the Pakri cape section of the Kallavere formation Formation is also significant. Our findings highlight the need for both a stratigraphical and palaeobiological reapprasal of these important sequences, and their correlative implications for the Swedish and broader Baltoscandian regions.
  •  
20.
  • Ebbestad, Jan Ove R., 1967-, et al. (författare)
  • Biostratigraphy and palaeontology of the lower Cambrian Duolbagáisá Formation on the Digermulen Peninsula, Arctic Norway
  • 2018
  • Ingår i: International Conference on Arctic Margins.
  • Konferensbidrag (refereegranskat)abstract
    • The lower Cambrian sequence on the Digermulen Peninsula (Finnmark, Arctic Norway) is the northernmost extension of the Cambrian deposits along the Caledonian front. It is exceedingly thick compared to cratonal successions typical of most of Baltica. The Duolbagáisá Formation represents the youngest lower Cambrian unit on the peninsula with the first trilobite-bearing strata, a plethora of trace fossils including diverse arthropod traces and Plagiogmus arcuatus, and abundant and wellpreserved organic walled microfossils (OWM). Extensive field work by the Digermulen Early Life Research Group allows for the first time a detailed appreciation of the age and faunal composition of the unit. The lower member is ~250 m thick with thin-bedded siltstone, sandstone and mudstone. A single unidentifiable holmiid thorax region occurs alongside arthropod trace fossils. OWM indicate the S. ornata-F. membranacea Zone. The upper member is ~390 m thick and consist of several upward shallowing parasequences with fine-grained sandstone, siltstone and mudstone followed by thick mature quartzite. The trace fossil Syringomorpha occurs throughout the upper member and Cruziana and Rusophycus are especially abundant in the upper parts. The first identifiable olenellid trilobites occur in a thick mudstone/siltstone interval at the middle of the member, along with an elliptocephalid trilobite and other arthropods. Abundant OWM indicate the H. dissimilare-S. ciliosa Zone with the higher levels belonging to the Volkovia-Liepaina Zone. The entire sequence thus span the Cambrian Series 2, stages 3–5.
  •  
21.
  • Ebbestad, Jan Ove R., 1967-, et al. (författare)
  • Distribution and correlation of Sabellidites cambriensis (Annelida?) in the basal Cambrian on Baltica
  • 2022
  • Ingår i: Geological Magazine. - : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 159:7, s. 1262-1283
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 Stahpogieddi 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.
  •  
22.
  • Ebbestad, Jan Ove R., et al. (författare)
  • Distribution and correlation of Sabellidites cambriensis (Annelida?) in the basal Cambrian on Baltica
  • 2021
  • Ingår i: Geological Magazine. - Cambridge : Cambridge University Press (CUP). - 0016-7568 .- 1469-5081. ; 159:7, s. 1262-1283
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
23.
  •  
24.
  • Högström, Anette, et al. (författare)
  • New occurrences and extension of the stratigraphical range of discoidal Ediacara‑type fossils on the Digermul Peninsula, northern Norway
  • 2014
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • In Scandinavia the evolutionary events across the Ediacaran–Cambrian transition can only be studied in continuous section on the Digermul Peninsula, northern Norway, in the siliciclastic Stáhpogiedde Formation. This roughly 500 m-thick unit comprises, in ascending order, the Lillevannet, Innerelva and Manndraperelva members. Trace fossils, including Treptichnus pedum, and organic-walled microfossils, including Granomarginata prima, position the base of the Cambrian in the upper part of the Manndraperelva Member. Some 20 years ago discoidal Ediacara-type fossils were found in the middle part of Innerelva Member. Recent field seasons have provided abundant new material of Aspidella-type fossils and extended their stratigraphical range to within about 15 m above the Lillevannet Member. The exclusive presence of discoidal forms may reflect a taphonomic bias and/or be evidence of a greater age than that of the more diverse Ediacaran assemblages. That the latter may be the case is indicated by the stratigraphic proximity of the lowest occurrences of Aspidella to the Mortensnes diamictite, recently tentatively considered a Gaskiers glaciation equivalent (c.580 Ma). This raises the question of hitherto unrecognised breaks in sedimentation in the Stáhpogiedde Formation. In order to explore this question we have sampled the succession for organic-walled microfossils, detrital mineral geochronology and sediment geochemistry.
  •  
25.
  • Högström, Anette, et al. (författare)
  • Palaeopascichnus from the Ediacaran of the Digermulen Peninsula, Arctic Norway and the age of the Varanger Ice Age
  • 2018
  • Ingår i: 5th International Palaeontological Conference. ; , s. 292-
  • Konferensbidrag (refereegranskat)abstract
    • Palaeopascichnids are possibly the longest-ranging macroscopic Ediacaran fossils (ca. 565-542 Ma).They are bedding plane-parallel modular fossils composed of series of closely spaced millimeter sizedcircular, sausage- or kidney- shaped units. Earlier regarded as trace fossils, they are now seen as bodyfossils: possible xenophyophoran protists or protists of uncertain affinities. The Cryogenian to lower Cambrian succession (Vestertana group) exposed on the Digermulen Peninsula starts with the glacial Smalfjorden, interglacial Nyborg and glacial Mortensnes fms, collectively known as the Varanger Ice Age.Together with the succeeding Stáhpogieddi Fm. they reflect changes from global icehouse to greenhouse conditions. The Stáhpogieddi Fm. starts with the Lillevannet Mbr. followed by the Indreelva Mbr., yielding Ediacara-type fossils. The highest member in the Stáhpogieddi Fm, the Manndrapselva Mbr, contains the Ediacaran- Cambrian boundary. Palaeopascichnus is found at three horizons within the Stáhpogieddi Fm. The youngest, within the Manndrapselva Mbr., is latest Ediacaran, based on associated trace fossils, as well as occurring below trace fossils from the Treptichnus pedum ichnozone. Palaeopascichnus is also present near the base of the Manndrapselva Mbr. The oldest occurrence is from a horizon transitional between the Lillevannet and Indreelva Mbrs. Age constraints on the Varangerian glacial deposits are poor and their relationship to Neoproterozoic glacial events is equivocal. Studies over the last several decades have placed the Smalfjorden Fm. within the globally developed Marinoan glaciation (ca. 645–635 Ma) based on the presence of cap dolostones. The Mortensnes Fm. has been aligned within the Ediacaran Gaskiers glaciation(ca. 580 Ma) on the basis of carbon isotope stratigraphy. However, alternative interpretations exist,including that of a Marinoan affinity for all of the Varanger ice age. Palaeopascichnus at the Lillevannet Mbr. to Indreelva Mbr. transition indicates that this part of the succession is younger than 565 Ma. Because the transition between the Mortensnes Fm. and the succeeding Stáhpogieddi Fm. is seemingly without major breaks in sedimentation, this is consistent with a Gaskiers, or younger age for the Mortensnes Fm. An older age (Marinoan) requires the discovery of major breaks in the sedimentary record.
  •  
26.
  • Jensen, Soren, et al. (författare)
  • New occurrences of Palaeopascichnus from the Stahpogieddi Formation, Arctic Norway, and their bearing on the age of the Varanger Ice Age
  • 2018
  • Ingår i: Canadian journal of earth sciences (Print). - : CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS. - 0008-4077 .- 1480-3313. ; 55:11, s. 1253-1261
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on new occurrences of the late Ediacaran problematicum Palaeopascichnus (Protista?) from the Stahpogieddi Formation, Arctic Norway. The stratigraphically lowest occurrences are in beds transitional between the Lillevannet and Indreelva members: the highest in the second cycle of the Manndrapselva Member, stratigraphically close to the lowest occurrences of Cambrian-type trace fossils. This establishes a long stratigraphical range of Palaeopascichnus on the Digermulen Peninsula, as has been previously documented from Newfoundland, South Australia, and elsewhere in Baltica. The age range of Palaeopascichnus in Avalonia and Baltica is from similar to 565 to 541 Ma. Since the transition from the Mortensnes Formation to the Stahpogieddi Formation is without a major break in sedimentation, this supports the inference that the underlying glacigenic Mortensnes Formation is ca. 580 Ma, and therefore Gaskiers-equivalent, or younger.
  •  
27.
  • Jensen, Soren, et al. (författare)
  • Scratch circles from the Ediacaran and Cambrian of Arctic Norway and southern Africa, with a review of scratch circle occurrences
  • 2018
  • Ingår i: Bulletin of Geosciences. - : CZECH GEOLOGICAL SURVEY. - 1214-1119 .- 1802-8225. ; 93:3, s. 287-304
  • Forskningsöversikt (refereegranskat)abstract
    • Scratch circles - bedding plane parallel sedimentary structures formed by the passive rotation of a tethered organism into the surrounding sediment - are relatively rare in the geological record. Here new occurrences of scratch circles are described from the Ediacaran-Cambrian Stahpogieddi Formation, Digermulen Peninsula, Arctic Norway, and from the Ediacaran Nudaus and Urusis formations, Nama Group, of southern Africa. A literature survey confirms a previously noted concentration of scratch circles reported from shallow marine upper Ediacaran-lower Cambrian and paralic Carboniferous rocks. Scratch circle identification and nomenclature are discussed. The stratigraphical range of the trace fossils Treptichnus pedum and Gyrolithes isp. in the Stahpogieddi Formation are extended downward. Combined with earlier reports of Harlaniella podolica this adds new precision to the placement of the Ediacaran-Cambrian boundary on the Digermulen Peninsula.
  •  
28.
  • Jensen, Sören, et al. (författare)
  • Trace fossils across the Ediacaran–Cambrian boundary on the Digermulen Peninsula, Arctic Norway
  • 2017
  • Ingår i: ISECT 2017. - : Memorial University, St. Johns.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The Digermulen Peninsula, Arctic Norway, contains one of the most complete Ediacaran–Cambrian sedimentary rock successions on Baltica. The boundary interval spans the Manndrapselva Mbr of the Stáhpogieddi Fm. and the Lower Mbr of the Breidvika Fm., consisting of several coarsening upward cycles, each less than 100 meters thick, dominated by mudstone and sandstone, and terminated by shallow-marine sandstone. Nigel Banks established the general succession of trace fossils in the 1970's, with additional information added more recently by Duncan McIlroy and members of the Digermulen Early Life Research Group.                      The second cycle of the Manndrapselva Mbr is late Ediacaran on the presence of the problematicum Harlaniella podolica. Trace fossils in this cycle include Planolites, Torrowangea rosei and, uniquely for the Digermulen succession, the horizontal cork-screw shaped Helicolithus. A report of treptichnids is here revised as vertically meandering trace fossils. The greatest trace fossil width in this sequence is 8 mm, although most are a few mm wide; recorded depth less than 10 mm. Close to the base of the third cycle of the Manndrapselva Mbr Treptichnus pedum and Gyrolithes appear. Harlaniella and the lowest occurrences of T. pedum and Gyrolithes are separated by some 30 metres of a sandstone-dominated interval from which trace fossils have not been recovered to date. Higher in the third cycle three-lobed trace fossils of the “Bure ichnocomplex” are found. Treptichnus pedum, Gyrolithes and trace fossils of the Bure ichnocomplex continue into the Lower Mbr of the Breidvika Fm., with T. pedum and Gyrolithes of larger size than found in the Manndrapselva Mbr. In addition there are Rusophycus and rare Teichichnus. The Treptichnus pedum Zone on the Digermulen Peninsula spans about 100 metres of section.                      The general validity of global Ediacaran–Cambrian trace fossil-based correlation has stood the test of time. The succession of trace fossils and problematica on the Digermulen Peninsula allows for particularly close comparison with that of the GSSP section on the Burin Peninsula, Newfoundland, as well as Podolia, Ukraine. Important future challenges include better control on the age of the base of the T. pedum Zone, as well as that of the base of the Rusophycus avalonensis Zone, and the identification of possible diachroneities of these zones, where this is not obviously the result of facies unsuited for trace fossil preservation.
  •  
29.
  • Meinhold, Guido, et al. (författare)
  • 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
  • 2019
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 141:4, s. 289-294
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 Δ° 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.
  •  
30.
  • Meinhold, Guido, et al. (författare)
  • Composition and provenance of upper Neoproterozoic and Cambrian sediments from Finnmark, Arctic Norway : Insights from a multi-method approach on the Digermulen Peninsula
  • 2018
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The remote Digermulen Peninsula by the Tanafjorden of north-eastern Finnmark, Arctic Norway, contains an almost complete sedimentary record across the Ediacaran–Cambrian transition as well as microfossils, macrofossils and trace fossils for studying the Ediacaran biota and the Cambrian radiation. It is one of the few localities worldwide and the only locality in Scandinavia where Ediacara-type fossils have been found. The site was located at the edge of Baltica during the Ediacaran–Cambrian transition, where potentially the dramatic climatic turnover from icehouse to greenhouse conditions can be deduced and tied to large-scale plate tectonics. The Digermulen Peninsula was first studied in the 1930s by Sven Føyn, who also published a geological map in 1937, emended by Harold G. Reading in 1959. In the following years, more detailed mapping was carried out by students from Oxford University. The exposed rocks on the Digermulen Peninsula belong to the Vestertana and Digermulen groups of the Lower Allochthon overlying the Baltic Shield. The succession consists mainly of quartz-rich sandstones and mudrocks. Deposition took place in various environments including fluvial, shallow marine and deeper marine settings. As shown by previous studies using palaeocurrent data, sediment supply was from the Baltic Shield toward the passive margin of Baltica in pre-Ediacaran time. At one point within the Ediacaran succession, it shifted by 180 degrees due to the newly formed Timanian orogen. This orogen formed in north-eastern Baltica during the late Neoproterozoic. It caused a change in source area due to the formation of the Timanian foreland basin to the east of Digermulen Peninsula. Extensive field and laboratory work by the Digermulen Early Life Research Group, with funding from the Research Council of Norway, allows for the first time a detailed analysis of sediment supply and to test current palaeotectonic models based on a multi-method provenance approach on Neoproterozoic and Cambrian mudrocks and sandstones of the Digermulen Peninsula. The methods include, amongst others, thin-section petrography, bulk-rock geochemistry (XRF, ICP-MS), bulk-rock mineralogy (XRD), conventional heavy mineral analysis, single-grain geochemistry (EMP) and zircon U-Pb geochronology. We present and discuss the first results to decipher the sediment sources and to track changes of sediment supply through this critical time interval of Earth’s history.
  •  
31.
  • Meinhold, Guido, et al. (författare)
  • First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance
  • 2019
  • Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 328, s. 99-110
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 Stahpogieddi 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.
  •  
32.
  • Meinhold, Guido, et al. (författare)
  • 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
  • 2022
  • Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 381
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 St & PRIME;ahpogieddi 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 for-mations, (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 epsilon(Nd)(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.
  •  
33.
  • Meinhold, Guido, et al. (författare)
  • 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
  • 2020
  • Ingår i: Geological Magazine. - : CAMBRIDGE UNIV PRESS. - 0016-7568 .- 1469-5081. ; 157:8, s. 1367-1372
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
34.
  • Moczydlowska, Malgorzata, 1951-, et al. (författare)
  • A Tonian age for the Visingsö Group in Sweden constrained by detrital zircon dating and biochronology : implications for evolutionary events
  • 2018
  • Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 155:5, s. 1175-1189
  • Tidskriftsartikel (refereegranskat)abstract
    • Detrital zircon U–Pb ages from samples of the Neoproterozoic Visingsö Group, Sweden, yield a maximum depositional age of ≤ 886±9 Ma (2σ). A minimum depositional age is established biochronologically using organic-walled and vase-shaped microfossils present in the upper formation of the Visingsö Group; the upper formation correlates with the Kwagunt Formation of the 780–740 Ma Chuar Group in Arizona, USA, and the lower Mount Harper Group, Yukon, Canada, that is older than 740 Ma. Mineralized scale microfossils of the type recorded from the upper Fifteenmile Group, Yukon, Canada, where they occur in a narrow stratigraphic range and are younger than 788 Ma, are recognized for the first time outside Laurentia. The mineralized scale microfossils in the upper formation of the Visingsö Group seem to have a wider stratigraphic range, and are older than c. 740 Ma. The inferred age range of mineralized scale microfossils is 788–740 Ma. This time interval coincides with the vase-shaped microfossil range because both microfossil groups co-occur. The combined isotopic and biochronologic ages constrain the Visingsö Group to between ≤ 886 and 740 Ma, thus Tonian in age. This is the first robust age determination for the Visingsö Group, which preserves a rich microfossil assemblage of worldwide distribution. The organic and mineralized microorganisms preserved in the Visingsö Group and coeval successions elsewhere document global evolutionary events of auto- and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the Neoproterozoic chronostratigraphic subdivision.
  •  
35.
  • Moczydłowska, Małgorzata, et al. (författare)
  • Ecdysozoan-like sclerites among Ediacaran microfossils
  • 2015
  • Ingår i: Geological Magazine. - Cambridge : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 152:6, s. 1145-1148
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the occurrence of organically preserved microfossils from the subsurface Ediacaran strata overlying the East European Platform in Poland, in the form of sclerites and cuticle fragments of larger organisms. They are morphologically similar to those known from Cambrian strata and associated with various metazoan fossils of recognized phyla. The Ediacaran age of the microfossils is evident from the stratigraphic position below the base of the Cambrian System and above the isotopically dated tuff layers at c. 551±4Ma. Within this strata interval, other characteristic Ediacaran microorganisms co-occur such as cyanobacteria, vendotaenids, microalgae, Ceratophyton,Valkyria and macroscopic annelidan Sabellidites. The recent contributions of organic sclerites in revealing the scope of the Cambrian explosion are therefore also potentially extendable back to the Ediacaran Period when animals first appear in the fossil record.
  •  
36.
  • Moczydłowska, Małgorzata, et al. (författare)
  • Timing of the origin of plastid and evolutionary history of chlorophyta by microfossil record
  • 2014
  • Ingår i: Abstract Volume. ; , s. 258-258
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The origin of plastid in eukaryotes and the minimum age of this event based on microfossil recordare indirectly inferred by recognizing green algae among organically preserved, unicellularmicrofossils other than cyanobacteria. Single primary symbiosis of cyanobacterium establishedalgae and led to divergence of Archaeplastida, including Chlorophyta. The reproductive cystsof extant microalgae share characters derived from their early green algal ancestors. The geneticinheritance and eventually its phenotypic expression are universally shared. Similarly, the enzymesbinding specific compounds in photosynthesis evolved from cyanobacteria and are present in allphotosynthesising organisms since the Archean. Molecular clock analyses suggest that primaryplastid was established by c. 1.5 Ga, whereas by fossil record c. 1.8 Ga (Leiosphaeridia) or 2.1 Ga(Grypania). The fossil record of stem group eukaryotes without assignment to living groups isat 2.1 Ga by carbonaceous compressions (Grypania), however, the recognition as an alga is notexcluded, and it would provide the minimum age of the origin of plastid. Spheroidal microfossils(Leiosphaeridia) with multilayered cell-wall and trilaminar sheath structure that is the algal character ofChlorophyceae are documented throughout the Proterozoic into Cambrian. Because of the presenceof this character and interpreted as algal cysts, some leiosphaerids show record of chlorophyceanspersistently since 1.8 Ga. Microfossils with phycoma-like morphology suggesting prasinophyceanaffinity are known at minimum age of 1.4–1.2 Ga (Pterospermopsimorpha, Pterospermella, Simia,Tasmanites). Microfossils of the Proterozoic to Cambrian ages assessed by body plan, ornamentation,excystment structure, cell wall resistance and ultrastructure, and internal bodies defined by theirown walls, are recognized as algal zygotic cysts and phycomata by comparison with extant greenalgae. Internal bodies are a part of reproductive cysts, resembling those known in Chlorophyta.They are inferred to be endocysts containing zygote, if single, or offspring cells, if multiple, insexual and asexual generations of ancient taxa of the classes Chlorophyceae and Prasinophyceae.Based on the earliest occurrence of microfossils with morphologic characteristic of a zygoticcyst, multilayered cell-wall structure indicative of the primary and secondary wall, and with aninternal body in the Dictyosphaera-Shuiyousphaeridium plexus, the sexual reproduction is evident atc. 1.4-1.2 Ga. It became common in the Neoproterozoic (Cymatiosphaeroides, Trachyhystrichosphaera,Vandalosphaeridium, Tanarium, Asterocapsoides, Ancorosphaeridium, Densisphaera), and the Cambrian(Skiagia, Polygonium). The divergence of Chlorophyta from the lineage of Chloroplastida occurredat the minimum age of 1.8 Ga, and the origin of primary plastid prior to this time.
  •  
37.
  • Palacios, Teodoro, et al. (författare)
  • Acritarchs from the Duolbagaisa Formation (Cambrian Series 2, Miaolingian) on the Digermulen Peninsula, Finnmark, Arctic Norway : towards a high-resolution Cambrian chronostratigraphy
  • 2020
  • Ingår i: Geological Magazine. - : CAMBRIDGE UNIV PRESS. - 0016-7568 .- 1469-5081. ; 157:12, s. 2051-2066
  • Tidskriftsartikel (refereegranskat)abstract
    • New information on acritarchs from the Duolbagaisa Formation, Digermulen Peninsula, Arctic Norway, enable recognition of the three Cambrian Series 2 acritarch-based zones: the Skiagia ornata-Fimbriaglomerella membranacea, Heliosphaeridium dissimilare-Skiagia ciliosa and Volkovia dentifera-Liepaina plana Assemblage zones. Acritarchs of the Skiagia ornata-Fimbriaglomerella membranacea Zone (Cambrian Stage 3) appear near the base of the unit, close to an undetermined trilobite. In the Upper Member of the Duolbagaisa Formation, in levels with Kjerulfia n. sp. and Elliptocephala n. sp., appears an assemblage with abundant Skiagia ciliosa, indicative of the Heliosphaeridium dissimilare-Skiagia ciliosa Zone. A few metres higher appear Liepaina plana, Heliosphaeridium notatum and Retisphaeridium dichamerum, which indicate the Volkovia dentifera-Liepaina plana Zone (Cambrian Stage 4). The transition between the Duolbagaisa Formation and the overlying Kistedalen Formation is marked by the appearance of Comasphaeridium longispinosum, Multiplicisphaeridium llynense and Eliasum llaniscum, diagnostic of the Miaolingian Series. This coincides with the disappearance of Skiagia; occurrences of Skiagia in Miaolingian strata consist of reworked material related to the Hawke Bay regression at the Cambrian Stage 4-Wuliuan transition. The absence of Skiagia in higher levels of the Duolbagaisa Formation and Kistedalen Formation suggests that no unconformity formed during the Hawke Bay regression in this area. The chronostratigraphical significance of the Skiagia ornata-Fimbriaglomerella membranacea, Heliosphaeridium dissimilare-Skiagia ciliosa and Volkovia dentifera-Liepaina plana zones is critically analysed. Correlation of the Duolbagaisa Formation with peri-Gondwanan terrains of Avalonia and Iberia is established. The Digermulen Peninsula has great potential as a reference section for establishing a Cambrian chronostratigraphy based on acritarchs.
  •  
38.
  • Palacios, Teodor, et al. (författare)
  • Organic-walled microfossils and organic fossils across the Ediacaran–Cambrian boundary on the Digermulen Peninsula, Arctic Norway
  • 2017
  • Ingår i: ISECT 2017. - : Memorial University, St. Johns.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The Digermulen Peninsula, Arctic Norway, contains one of the most complete Ediacaran–Cambrian sedimentary rock successions on Baltica. The boundary interval spans the Manndrapselva Mbr of the Stáhpogieddi Fm. and the Lower Mbr of the Breidvika Fm.Abundant organic-walled microfossils (OWM) and organic fossils (OF) in the second and third cycles of Manndrapselva Mbr and the lower part of the Breidvika Fm., coupled with a rich record of trace fossils reinforces the potential of the area for detailed biostratigraphic studies of the Ediacaran–Cambrian transition.The second cycle of the Mandrapselva Mbr, with simple trace fossils and the Ediacaran- confined problematicum Harlaniella podolica, contains a low diversity of OWM represented by abundant filamentous cyanobacterial sheaths, thick-walled sphaeromorphs, Pterospermopsimorpha sp. and Leiosphaeridia spp. Organic fossils include abundant tussled masses of nano-scale filament interpreted as degraded sabelliditid tubular fossils. The third cycle, which yields the first occurrence of the trace fossil Treptichnus pedum, include a similar assemblage of OWM, and the first appearance of Granomarginata prima, a cosmopolitan acritarch with a first appearance in the Cambrian. Close to the base of the third cycle there is an increased diversity of OF, including the appearance of Ceratophyton at a level approximating the first T. pedum. In the upper part of the third cycle Cochleatina is found.The Lower Mbr of the Breidvika Fm. yields productive samples in levels below the lowest occurrence of the arthropod-type trace fossil Rusophycus. The association remains one of low diversity, with the continued presence of Ceratophyton and nano-scale filaments, the latter abundant in levels with rich occurrences of Sabellidites cambriensis but absent at levels close to the appearance of Rusophycus. Basal levels of the Breidvika Fm. yield the first process-bearing acritarchs, represented by rare specimens of the small and weakly ornamented Asteridium tornatum. There are also abundant clusters of Symplassosphaeridium sp. Compared to Manndrapselva Mbr there is a decrease in thick-walled sphaeromorphs.
  •  
39.
  • Petryshyn, Victoria, et al. (författare)
  • Stromatolites in Walker Lake (Nevada, Great Basin, USA) record climate and lake level changes ~ 35,000 years ago
  • 2016
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 451, s. 140-151
  • Tidskriftsartikel (refereegranskat)abstract
    • Walker Lake is a closed-basin remnant of the large Pleistocene glacial Lake Lahontan system that has experienced multiple high amplitude (100–200 m) changes in water level over the past ~ 40,000 years in response to changes in climate. A laminated carbonate stromatolite composed of varying proportions of calcite fans and micrite was collected from a paleoshoreline located at approximately 58 m above present lake level. Radiocarbon dating revealed that the stromatolite spans approximately 2000 years of growth, from 35,227 to 33,727 calibrated years before present (YBP), a time period during which paleolake-level is not well-constrained. Distinct laminae were drilled along the growth axis, and the resulting powders were collected for clumped isotope analyses to generate formation temperatures (lake water temperatures) during stromatolite formation from which δ18Owater was calculated.Results indicate that the stromatolite experienced an initial increase in temperature and water δ18O values followed by a decrease in both during the course of accretion. The resulting temperature and isotopic data were input into a Rayleigh distillation model for lakewater evaporation in order to estimate the magnitude of lake level and volume fluctuations over the course of accretion. Modeling results reveal a lake level decrease of between 8.1 and 15.6 m, followed by an increase of between 4.3 and 8.8 m during the course of stromatolite growth.The results of this study indicate that Walker Lake experienced significant lake volume change over the course of 2000 years, perhaps as a response to precipitation changes driven by fluctuations in the polar jet stream and accompanying changes in regional climate, and/or evaporation-induced changes in lake level. These results add to a growing body of research indicating that stromatolites and other lacustrine tufas represent a detailed and extensive terrestrial archive that can potentially be used to reconstruct the timing and magnitude of climate change.
  •  
40.
  • Taylor, Wendy L., et al. (författare)
  • Possible trilobozoans with internal structures from the Late Ediacaran Nama Group, Northern Cape, South Africa
  • 2017
  • Ingår i: ISECT 2017. - St Johns : Memorial University, St. Johns.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Sedimentary rocks of the classic Nama Group extend for over 1000 km from southern Namibia across the Orange River and into northwestern Republic of South Africa. We report on fossils from the Nama Group deposited in the southern part of the Witputs sub-basin exposed in the Northern Cape Province of the RSA between Vioolsdrif and Springbok. This succession begins with the shallow marine and fluvial siliciclastics and platform carbonates of the Dabis and Zaris formations. Carbonates of the Zaris Fm. yield the late Ediacaran skeletal fossils Cloudina and Namacalathus. The Nudaus Fm. begins with sandstone of the Niederhagen Mbr., followed by the shale-dominated Vingerbreek Mbr. The Vingerbreek Mbr. in southern Namibia has been interpreted as a muddy tidal deposit in places with strong microbial mat signature whereas the upper part of the member in the Springbok-Vioolsdrif area has been interpreted as storm-influenced shallow marine deposits. The Vingerbreek Mbr. near Springbok measures c.100 m and is constrained by radiometric ages in over- and underlying rocks elsewhere in the Nama Basin to between 547 and 545 Ma. The succession in the Vioolsdrif-Springbok area terminates with the Urusis Fm., comprising quartzarenites of the Nasep Mbr. and the carbonate-dominated Huns Mbr. In late 2016, four discoidal fossils were collected from a fine-grained silciclastic interval within the Vingerbreek Mbr. to the north of Springbok. The fossils occur in an assemblage with abundant vendotaenids, textured organic surfaces (TOS), scratch circles, various skeletal tubes, several types of small dimples and horizontal trace fossils. Micro-CT scans were made of all four discs, and in the case of the largest disc (diam. 4 cm), complex internal structures are visible. There are three distinct central “pouches” with no apparent connection to each other. Each central pouch appears to be connected by tubes to five smaller pouches. These clusters of five outer pouches form a peripheral ring of 15 circular chambers at the inferred “base” of the disc and become more irregular towards the “top”. The wrinkled outer surface, distinct margin and tripartite symmetry suggest a trilobozoan body plan with possible affinities with Rugoconites and Skinnera. Most trilobozoan taxa are known only from simple external moulds. The more complex mineralogy and taphonomy exhibited by these specimens, offers a unique taphonomic window that may help unravel the paleobiology of this enigmatic group.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-40 av 40
Typ av publikation
tidskriftsartikel (19)
konferensbidrag (17)
annan publikation (1)
doktorsavhandling (1)
forskningsöversikt (1)
licentiatavhandling (1)
visa fler...
visa färre...
Typ av innehåll
refereegranskat (27)
övrigt vetenskapligt/konstnärligt (12)
populärvet., debatt m.m. (1)
Författare/redaktör
Meinhold, Guido (22)
Taylor, Wendy L. (22)
Ebbestad, Jan Ove R. ... (21)
Agić, Heda, 1989- (20)
Agic, Heda (20)
Jensen, Sören (16)
visa fler...
Moczydłowska, Małgor ... (13)
Høyberget, Magne (12)
Högström, Anette (11)
Palacios, Teodor (11)
Palacios, Teodoro (10)
Hoyberget, Magne (8)
Hogstrom, Anette E. ... (6)
Jensen, Soren (6)
Högström, Anette E. ... (5)
Yin, Leiming (3)
Hybertsen, Frida (3)
Canfield, Donald (2)
Moczydlowska, Malgor ... (2)
Novis, Linn K. (2)
Arslan, Arzu (2)
McIlroy, Duncan (2)
Vickers-Rich, Patric ... (1)
Hall, Michael (1)
Matthews, Jack J. (1)
Ward, L. (1)
Juarez Rivera, M. (1)
Kerrigan, Z. (1)
Petryshyn, V.A. (1)
Corsetti, F.A. (1)
Tripati, A. (1)
Moczydlowska, Malgor ... (1)
Willman, Sebastian, ... (1)
Westall, Frances, Do ... (1)
Butterfield, Nichola ... (1)
Xiao, Shuhai, Profes ... (1)
Bauert, Heikki (1)
Wickström, Linda (1)
Streng, Michael (1)
Wemmer, Klaus (1)
Holmer, Lars (1)
Pease, Victoria (1)
Ebbestad, Jan Ove R. (1)
Budd, Graham (1)
Willman, Sebastian (1)
Butler, Aodhan (1)
Roberts, Nick M. W. (1)
Ou, Zhiji (1)
Tripati, Aradhna (1)
Almond, John (1)
visa färre...
Lärosäte
Uppsala universitet (39)
Stockholms universitet (1)
Naturhistoriska riksmuseet (1)
Språk
Engelska (39)
Svenska (1)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (40)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy