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Thomas Servais - One of the best experts on this subject based on the ideXlab platform.
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palynomorphs of the fezouata shale lower ordovician morocco age and environmental constraints of the fezouata biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Thijs R.a. Vandenbroucke, Robert R Gaines, Bernard Pittet, Thomas ServaisAbstract:Abstract The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.
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Palynomorphs of the Fezouata Shale (Lower Ordovician, Morocco): Age and environmental constraints of the Fezouata Biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Robert R Gaines, Bernard Pittet, Thomas Servais, Thijs R.a. VandenbrouckeAbstract:The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1-2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision. (C) 2016 Elsevier B.V. All rights reserved.
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Belgium) : stratigraphy and palaeobiogeography
2015Co-Authors: Michel Vanguestaine, Thomas ServaisAbstract:Abstract. – The messaoudensis-trifidum Acritarch microflora is currently considered to be characteristic of latest Tremadocian-earliest Arenigian cold-water environments on the periphery of Gondwana, at high latitudes in the south-ern hemisphere. Integrated biostratigraphical studies on both Acritarchs and graptolites are available from two areas of peri-Gondwana, the Lake District (northwestern England) and the Sierra Morena (southwestern Spain). The assemblage was also recorded from other areas on the northern border of the Gondwana continent where macrofossils are generally not available: from southern Ireland, the Isle of Man, southern Wales, the island of Rügen in northern Germany, the Prague Basin in the Czech Republic, and southern Turkey. While it appears that the messaoudensis-trifidum Acritarch as-semblage is limited to cold-water environments in localities on the periphery of Gondwana, some of its elements can be found in other areas. Some taxa, but not the complete assemblage, have been identified in the eastern Cordillera of Ar-gentina, and some species of the assemblage are cited from continents which were situated at intermediate latitudes in warmer waters: some elements of the assemblage are described from localities of Baltica (from Norway, Estonia and the St. Petersburg area in northwestern Russia) and from the Yangzte Platform in southern China. In these regions, typi-cal representatives of the messaoudensis-trifidum assemblage co-occur with taxa typical of temperate and warm-water areas. The present paper reports the discovery of the messaoudensis-trifidum Acritarch assemblage in the Lierneu
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1 The Ordovician Acritarch genus Coryphidium
2015Co-Authors: Thomas Servais, Stewart G Molyneux, Marco VecoliAbstract:Abstract: The Acritarch genus Coryphidium Vavrdová 1972 is one of the most frequently recorded Acritarch taxa in the Ordovician. The original diagnoses, stratigraphical ranges and geographical distribution of all Coryphidium species are critically evaluated in a review of published literature supplemented by studies of material from the British Isles, Belgium, th
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an early middle ordovician Acritarch and prasinophyte assemblage from houping chongqing city south china biostratigraphical and palaeoenvironmental implications
Review of Palaeobotany and Palynology, 2013Co-Authors: Jun Li, Thomas ServaisAbstract:Abstract A moderately diverse Acritarch and prasinophyte assemblage is described from the Dacao and Yingpan formations of the Houping section, Chengkou, Chongqing, southwestern China (Upper Yangtze platform). The palynomorph assemblage consists of 41 species attributed to 25 genera (39 species and 23 genera of Acritarchs and two species and two genera of prasinophytes). It is dominated by Polygonium , Leiosphaeridia , Rhopaliophora , and Peteinosphaeridium . The first appearances of several taxa show a potential for stratigraphical correlation in the Floian (Early Ordovician). First appearance data (FADs) of Aureotesta , Petaloferidium , Striatotheca , the Veryhachium lairdii group and the V. trispinosum group indicate levels near the base of the Floian, whereas Ampullula , Arbusculidium filamentosum , Coryphidium bohemicum , Sacculidium and Tongzia first appear slightly higher. The Acritarch assemblages from ten localities in South China are analysed using principal component and cluster analysis for ecological discussion. Four Acritarch associations are distinguished from ten localities and related to different marine environments respectively.
Thijs R.a. Vandenbroucke - One of the best experts on this subject based on the ideXlab platform.
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palynomorphs of the fezouata shale lower ordovician morocco age and environmental constraints of the fezouata biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Thijs R.a. Vandenbroucke, Robert R Gaines, Bernard Pittet, Thomas ServaisAbstract:Abstract The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.
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Palynomorphs of the Fezouata Shale (Lower Ordovician, Morocco): Age and environmental constraints of the Fezouata Biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Robert R Gaines, Bernard Pittet, Thomas Servais, Thijs R.a. VandenbrouckeAbstract:The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1-2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision. (C) 2016 Elsevier B.V. All rights reserved.
Marco Vecoli - One of the best experts on this subject based on the ideXlab platform.
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middle ordovician Acritarchs and problematic organic walled microfossils from the saq hanadir transitional beds in the qsim 801 well saudi arabia
Revue de Micropaléontologie, 2017Co-Authors: Alain Le Herisse, Marco Vecoli, Pierre Breuer, Claudia Guidat, Charles H Wellman, Philippe SteemansAbstract:Abstract Core samples from the QSIM-801 water well, drilled in central Saudi Arabia, cover a 93-foot interval spanning the transition between the Sajir Member of the Saq Formation, that consists mainly of sandstones of tidal sand flat environments, and the Hanadir Member of the Qasim Formation, characterized by argillaceous graptolitic mudstones, corresponding to a tidal delta front. The samples contain abundant, exceptionally well-preserved and diverse palynomorphs, which include cryptospores, Acritarchs and chitinozoans, other problematic organic-walled microfossils as well as other organic particles such as cuticle-like fragments. The studied interval is biostratigraphically well constrained by the presence of chitinozoans of the formosa and pissotensis Zones of late-early to late Darriwilian age (Middle Ordovician) in the uppermost Saq Formation and Hanadir Member. The biostratigraphic age of the Sajir Member considered to span the Dapingian–Darriwilian boundary, is re-discussed based on the results herein. The uppermost part of the Sajir Member yielded the ichnofossil, Phycodes fusiforme . Acritarch assemblages from the Sajir Member of the Saq Formation are poorly diversified and dominated by sphaeromorphs. More diverse assemblages of Acritarchs, associated with enigmatic forms, occur in the Hanadir Member of the Qasim Formation. The contact between the two formations and the transition between the palynomorph assemblages are sharp, suggesting a stratigraphic hiatus. A quantitative analysis allows us to discuss the paleoenvironmental changes and possibly climatic changes associated with an hypothesis of ice house conditions during this period. Among the diagnostic Acritarch taxa observed are Frankea breviuscula, F. longiuscula , Baltisphaeridium ternatum , Dasydorus cirritus , Dicrodiacrodium ancoriforme, Poikilofusa ciliaris, Pterospermopsis colbathii and Uncinisphaera fusticula. These are associated with other typical forms known to range across the Lower–Middle Ordovician boundary, such as Aremoricanium rigaudae , Aureotesta clathrata , Barakella fortunata , B. rara, Baltisphaeridium klabavense, Glaucotesta latiramosa and Striatotheca spp. Galeate and peteinoid Acritarchs are also well represented, as well as tiny forms of ultraplanctonic size. Three new species of Acritarchs are proposed: Frankea longiuscula var . darriwilense var. nov, Micrhystridium regulum sp. nov, and Tyrannus proteus sp. nov. Repeated occurrences throughout the section of cryptospores, problematic microfossils such as organic filaments, cuticle-like tissues, striated and pigmented leiospheres frequently in clusters, are interpreted to reflect recurrent terrestrial and freshwater inputs in the depositional environment. Single-specimen, high-resolution analyses using Confocal Laser Scanning Microscopy on the enigmatic form Tyrannus proteus sp. nov. show fluorescence emission spectra and microstructural properties significantly different from those of typical marine Acritarchs from the same levels.
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1 The Ordovician Acritarch genus Coryphidium
2015Co-Authors: Thomas Servais, Stewart G Molyneux, Marco VecoliAbstract:Abstract: The Acritarch genus Coryphidium Vavrdová 1972 is one of the most frequently recorded Acritarch taxa in the Ordovician. The original diagnoses, stratigraphical ranges and geographical distribution of all Coryphidium species are critically evaluated in a review of published literature supplemented by studies of material from the British Isles, Belgium, th
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palynology and isotope geochronology of the upper ordovician silurian successions ghelli and soltan maidan formations in the khoshyeilagh area eastern alborz range northern iran stratigraphic and palaeogeographic implications
Review of Palaeobotany and Palynology, 2011Co-Authors: Mohammad Ghavidelsyooki, Jamshid Hassanzadeh, Marco VecoliAbstract:Surface samples from the Ghelli and Soltan Maidan Formations in the Khoshyeilagh area of the eastern Alborz Range, northern Iran, were analyzed to determine the age and the stratigraphic relationship of these two units. The samples contained rich palynomorph assemblages, dominated by Acritarchs (36 species recognized, distributed among 28 genera) and chitinozoans (nine species identified, distributed among seven genera). Cryptospores and scolecodonts as well as a few graptolite remains were also observed, although not studied in detail. Based on the restricted stratigraphic range of chitinozoan and Acritarch species, a Late Ordovician (late Katian–Hirnantian) age is assigned to the Ghelli Formation. Palynological samples from the Soltan Maidan Formation yielded Acritarch assemblages characterized by species commonly found in Upper Ordovician sediments together with typical middle Silurian forms. Considering reworking of the Upper Ordovician species, the age of the investigated part of the Soltan Maidan Formation is not younger than Gorstian (early Ludlow, early late Silurian). U–Pb zircon ages of 434.4 ± 6.4 Ma (Telychian, late Llandovery, late early Silurian) obtained for granitic clasts collected at the base of the Soltan Maidan Formation, are consistent with the inferred palynological age and indicate that granite emplacement, cooling, exhumation, erosion, transportation and deposition of its clasts took place in a time interval estimated to be 5 to 10 million year long. Based on the presence of diagnostic chitinozoan taxa, the Ghelli Formation can be assigned to the Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones. Chitinozoan assemblages reflect a clear palaeobiogeographic affinity with the previously defined ‘North Gondwana Domain’. The composition of Acritarch assemblages also appears to be consistent with newly proposed hypotheses of a Late Ordovician phytoplanktonic biogeographical differentiation between a Laurentian/Baltica realm, and a Gondwanan realm to which the present assemblages belong. The presence of cryptospores together with taxonomically diverse chitinozoan, Acritarch, and scolecodont assemblages, suggest a relatively shallow marine, platformal depositional environment for the Ghelli Formation.
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environmental changes reflected by palynomorphs in the early middle ordovician hanadir member of the qasim formation saudi arabia
Revue de Micropaléontologie, 2007Co-Authors: Alain Le Herisse, Mansour Alruwaili, Merrell A Miller, Marco VecoliAbstract:Abstract Core samples from the QASIM-801 (QSIM-801) water well in the Qasim Region of central Saudi Arabia were investigated palynologically. The interval studied contains the transgressive succession from the Sajir Member of the Saq Formation to the Hanadir Member of the Qasim Formation, and yields well-preserved and abundant cryptospores, microphytoplankton (Acritarchs and chlorophycean algae), and chitinozoans, indicative of a Darriwilian (Llanvirn) age. The lowermost portion of the cored interval from the upper Sajir Member consists of fine-grained sandstones deposited in tidal flat, and shallow-marine settings. It is characterized by abundant and diverse cryptospores (permanent tetrads, dyads, monads), cuticle-like phytoclasts, and a low diversity assemblage of marine palynomorphs. The upper part of the cored interval from the Hanadir Member is composed of hemipelagic to pelagic, organic-rich, graptolitic shales, and micaceous shales, of middle- to outer-shelf depositional settings, which yield abundant marine palynomorphs (Acritarchs and chitinozoans). Cryptospore-bearing horizons are interspersed in the succession. Changes in the composition of palynomorph assemblages reflect higher frequency environmental changes within an overall transgressive succession. Four new Acritarch species are described in open nomenclature, Tyrannus sp. A, Clypeolus sp. A,? Pulvinosphaeridium sp. A, and? Tinacula sp. A.
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biostratigraphy taxonomic diversity and patterns of morphological evolution of ordovician Acritarchs organic walled microphytoplankton from the northern gondwana margin in relation to palaeoclimatic and palaeogeographic changes
Earth-Science Reviews, 2004Co-Authors: Marco Vecoli, Alain Le HerisseAbstract:Abstract Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organic-walled microfossils in the Palaeozoic. The majority of Acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organic-walled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms. Calculation of evolutionary rates and development of a detailed diversity curve at specific level, form the basis for discussing the influence of global palaeoenvironmental perturbations on the evolution of organic-walled microphytoplankton in northern Gondwana during latest Cambrian through Ordovician times. The potential of Acritarchs for biostratigraphic correlation at the regional scale (northern Gondwana domain) is much improved by our detailed revision of distributional patterns of 245 Acritarch taxa. The most important Cambro-Ordovician Acritarch bio-events are short periods of diversification, which also correspond to introduction of morphological innovations, observed in latest Cambrian and earliest Tremadoc, late Tremadoc, early Arenig, basal Llanvirn, and latest Ashgill, and an important extinction phase in the early Caradoc. Overall, Acritarch diversity increased from the basal Ordovician up to the middle Llanvirn, then declined in the early and middle Caradoc. During Ashgill times, the assemblages are poorly diversified at the generic level as a result of a combined effect of sea level drawdown and onset of glacial conditions, but no major extinction event is observed in connection with the end-Ordovician biotic crisis. The peak in Acritarch diversity during Middle Ordovician times appears to be correlated to maximum spread of palaeogeographical assembly. Acritarch dynamics appear largely uncorrelated to second order sea-level oscillations; the primary abiotic controls on Acritarch evolution were palaeogeographical and the associated palaeoceanographic changes (especially during Middle Ordovician), and the end-Ordovician palaeoclimatic shift. The Acritarch fossil record provides important information on the evolution of oceanic primary producers, however, the relationships between Acritarch diversity, oceanic productivity, and evolution of invertebrate animals are proving much more complex than previously thought. In particular, the hypothesis of a causal relationship between changes in Acritarch diversity and metazoan evolution in the Palaeozoic is not supported by our data.
Malcolm R Walter - One of the best experts on this subject based on the ideXlab platform.
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combined micro fourier transform infrared ftir spectroscopy and micro raman spectroscopy of proterozoic Acritarchs a new approach to palaeobiology
Precambrian Research, 2005Co-Authors: Craig P Marshall, Andrew H Knoll, Emmanuelle Javaux, Malcolm R WalterAbstract:Abstract Micro-scale analytical techniques permit correlation of chemistry with morphology of individual Proterozoic Acritarchs (organic-walled microfossils), and thus provide new approaches for elucidating their biological affinities. A combination of micro-Fourier transform infrared (FTIR) spectroscopy and laser micro-Raman spectroscopy was used to investigate the organic structure and composition of individual Acritarchs. Well preserved Neoproterozoic Acritarchs from the Tanana Formation, Australia (ca. 590–565 Ma), and Mesoproterozoic Acritarchs from the Roper Group (1.5–1.4 Ga), Australia, and Ruyang Group, China (1.4–1.3 Ga, age poorly resolved but certainly >1000 Ma and H stretching bands in the 2900 cm−1 region relative to the C C aromatic ring stretching band at 1600 cm−1. This FTIR spectrum is consistent with the FTIR spectra obtained from algaenans isolated from extant chlorophyte and eustigmatophyte microalgae. FTIR spectra of Leiosphaeridia sp. from the Tanana Formation contain a less intense aliphatic C H stretching band relative to the C C aromatic ring stretching band. By comparison, the spectra acquired from the Mesoproterozoic Acritarchs were dominated by C C aromatic ring stretching bands at 1600 cm−1 relative to moderate-weak CH3 terminal groups (1345 cm−1), C H aliphatic stretching (3000–2700 cm−1), and C O (1710 cm−1), although some differences in biopolymer composition occurred between species. Curve-fitting of the aliphatic C Hx stretching region provides greater insight into the aliphatic structures of the Acritarchs. The CH2/CH3 intensity ratio can be used to assess the relative chain length and degree of branching. Organic material in the Tanarium conoideum consists of straight long chain hydrocarbons, while the other Acritarchs contain hydrocarbons consisting of short chains that are highly branched. In this study it was found that Raman spectroscopy does not provide additional information about biopolymer composition of Proterozoic Acritarchs, but rather offers complementary data regarding the aromaticity and degree of saturation of the macromolecular structure of Acritarch cysts.
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Combined micro-Fourier transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy of Proterozoic Acritarchs: A new approach to Paleobiology
2005Co-Authors: Craig P Marshall, Andrew H Knoll, Emmanuelle Javaux, Malcolm R WalterAbstract:Abstract Micro-scale analytical techniques permit correlation of chemistry with morphology of individual Proterozoic Acritarchs (organic-walled microfossils), and thus provide new approaches for elucidating their biological affinities. A combination of micro-Fourier transform infrared (FTIR) spectroscopy and laser micro-Raman spectroscopy was used to investigate the organic structure and composition of individual Acritarchs. Well preserved Neoproterozoic Acritarchs from the Tanana Formation, Australia (ca. 590-565 Ma), and Mesoproterozoic Acritarchs from the Roper Group (1.5-1.4 Ga), Australia, and Ruyang Group, China (1.4-1.3 Ga, age poorly resolved but certainly >1000 Ma and <1625 Ma) have thermal maturities that range from immature to oil window. FTIR spectra of Tanarium conoideum from the Tanana Formation contain intense aliphatic C H stretching bands in the 2900 cm −1 region relative to the C C aromatic ring stretching band at 1600 cm −1 . This FTIR spectrum is consistent with the FTIR spectra obtained from algaenans isolated from extant chlorophyte and eustigmatophyte microalgae. FTIR spectra of Leiosphaeridia sp. from the Tanana Formation contain a less intense aliphatic C H stretching band relative to the C C aromatic ring stretching band. By comparison, the spectra acquired from the Mesoproterozoic Acritarchs were dominated by C C aromatic ring stretching bands at 1600 cm −1 relative to moderate-weak CH 3 terminal groups (1345 cm −1 ), C H aliphatic stretching (3000-2700 cm −1 ), and C O (1710 cm −1 ), although some differences in biopolymer composition occurred between species. Curve-fitting of the aliphatic C H x stretching region provides greater insight into the aliphatic structures of the Acritarchs. The CH 2 /CH 3 intensity ratio can be used to assess the relative chain length and degree of branching. Organic material in the Tanarium conoideum consists of straight long chain hydrocarbons, while the other Acritarchs contain hydrocarbons consisting of short chains that are highly branched. In this study it was found that Raman spectroscopy does not provide additional information about biopolymer composition of Proterozoic Acritarchs, but rather offers complementary data regarding the aromaticity and degree of saturation of the macromolecular structure of Acritarch cysts
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neoproterozoic biotic diversification snowball earth or aftermath of the acraman impact
Geology, 2003Co-Authors: Kathleen Grey, Malcolm R Walter, Clive R CalverAbstract:Biostratigraphic and chemostratigraphic studies of Australian late Neoproterozoic (Ediacarian) fossil plankton (Acritarch) successions reveal a striking relationship between a radical palynofloral change, a short-lived negative excursion in the carbon isotope composition of kerogen, and a debris layer from the ca. 580 Ma Acraman bolide impact event. Palynomorphs changed from an assemblage dominated by long-ranging, simple spheroids to a much more diverse assemblage characterized by short-ranging, large, complex, process-bearing (acanthomorph) Acritarchs, with the first appearance of 57 species. A marked negative carbon isotope excursion was followed by a steady rise coinciding with acanthomorph radiation. There are no apparent sedimentological controls on this radiation. Although the snowball Earth hypothesis predicts postglacial biotic change, radiation did not happen until long after the Marinoan glaciation and not until a second postglacial transgression. We propose that a global extinction and recovery event may have been associated with the Acraman bolide impact. Indications are that the Acraman event could rank with similar Phanerozoic major impact events.
Hendrik Nowak - One of the best experts on this subject based on the ideXlab platform.
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palynomorphs of the fezouata shale lower ordovician morocco age and environmental constraints of the fezouata biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Thijs R.a. Vandenbroucke, Robert R Gaines, Bernard Pittet, Thomas ServaisAbstract:Abstract The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.
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Palynomorphs of the Fezouata Shale (Lower Ordovician, Morocco): Age and environmental constraints of the Fezouata Biota
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Hendrik Nowak, Mustapha Akodad, Romain Vaucher, Robert R Gaines, Bernard Pittet, Thomas Servais, Thijs R.a. VandenbrouckeAbstract:The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstatte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded Acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The Acritarchs can be assigned to the diagnostic messaoudensis-trifidum Acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The Acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1-2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstatte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision. (C) 2016 Elsevier B.V. All rights reserved.
