Palaeozoic acritarchs mostly represent organic-walled cysts of marine phytoplankton, and therefore, as primary producers, played an important role in the evolution of marine ecosystems. In this study, we use a selection of the most abundant acritarch taxa from the Cambrian and Ordovician of China to understand the evolution of the palaeoecological patterns of the phytoplankton over the period. The taxa are attributed to 40 easily distinguishable morphotypes, of which the precise palaeoenvironmental distribution from 60 localities is available. By placing the 40 morphotypes on inshore–offshore transects it can be concluded that acritarch microfloras were limited to inshore environments during the early Cambrian, and progressively extended from inshore environments to offshore marine habitats during the later parts of the Cambrian and towards the Early Ordovician, with a prominent shift near the Cambrian–Ordovician boundary, confirming the onset of the ‘Ordovician plankton revolution’. In addition, the acritarch morphotypes evolved from low-diversity assemblages in the early Cambrian, dominated by simple spherical forms with limited ornamentation and simple process structures, to highly diverse assemblages with very complex morphologies in the Early and Middle Ordovician. During the Ordovician, the complex acritarch assemblages occupied most marine habitats, with palaeoecological distribution patterns similar to modern dinoflagellates. This article is part of the theme issue ‘The impact of Chinese palaeontology on evolutionary research’.
Research Article| March 01, 1998 Estimation of slip rates in the southern Tien Shan using cosmic ray exposure dates of abandoned alluvial fans Erik Thorson Brown; Erik Thorson Brown 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Search for other works by this author on: GSW Google Scholar Didier L. Bourlés; Didier L. Bourlés 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Search for other works by this author on: GSW Google Scholar Grant M. Raisbeck; Grant M. Raisbeck 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Search for other works by this author on: GSW Google Scholar Françoise Yiou; Françoise Yiou 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Search for other works by this author on: GSW Google Scholar B. Clark Burchfiel; B. Clark Burchfiel 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Peter Molnar; Peter Molnar 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Deng Qidong; Deng Qidong 3Institute of Geology, State Seismology Bureau, Beijing, China Search for other works by this author on: GSW Google Scholar Li Jun Li Jun 4Provincial Bureau of Seismology, State Seismology Bureau, Urumqi, Xinjiang, China Search for other works by this author on: GSW Google Scholar Author and Article Information Erik Thorson Brown 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Didier L. Bourlés 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Grant M. Raisbeck 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France Françoise Yiou 1Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bâtiment 108, F-91405 Campus Orsay, France B. Clark Burchfiel 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Peter Molnar 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Deng Qidong 3Institute of Geology, State Seismology Bureau, Beijing, China Li Jun 4Provincial Bureau of Seismology, State Seismology Bureau, Urumqi, Xinjiang, China Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1998) 110 (3): 377–386. https://doi.org/10.1130/0016-7606(1998)110<0377:EOSRIT>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Erik Thorson Brown, Didier L. Bourlés, Grant M. Raisbeck, Françoise Yiou, B. Clark Burchfiel, Peter Molnar, Deng Qidong, Li Jun; Estimation of slip rates in the southern Tien Shan using cosmic ray exposure dates of abandoned alluvial fans. GSA Bulletin 1998;; 110 (3): 377–386. doi: https://doi.org/10.1130/0016-7606(1998)110<0377:EOSRIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Cosmic ray exposure dates (based on in situ–produced 10Be), in combination with measured heights of fault scarps that cut three abandoned fans, imply a slip rate of less than ∼2 mm/yr on the bounding thrust fault along a segment of the southern flank of the Tien Shan of central Asia. This rate, somewhat lower than those for the segment farther west and for the northern margin of the belt, implies that the distribution of shortening across the Tien Shan must change markedly along the belt. The date of abandonment of the smallest of the three fans is consistent with fan formation since the last glacial maximum, but the other two fans appear to have been formed and abandoned prior to that time. These and other results suggest that advances and retreats of alpine glaciers may not be synchronized with continental ice sheets and that not all prominent geomorphological features in arid Asian regions have formed since the last glacial maximum.In this study we have assessed the relationship between cosmogenic nuclide content of individual clasts and the time since their deposition on a surface. Cosmogenic nuclide accumulation represents the integrated total surface exposure of rocks in source regions during transport and since deposition. Postdepositional processes (erosion, burial, bioturbation, and cryoturbation), all of which decrease the quantity of cosmogenic nuclides produced in a rock in a given time and hence the apparent exposure age, also cause significant scatter among apparent ages of samples from the surfaces. Very low 10Be concentrations in material from active streambeds and at depth below one of the fan surfaces indicate that exposure prior to deposition onto fan surfaces was minimal (<∼2000 yr); it follows that the dates for individual clasts are lower limits for the time since abandonment of the fans. Because such dates place lower bounds on the time since initiation of scarp preservation, the associated slip rates should represent upper limits. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract Veryhachium Deunff 1954, originally described from the Ordovician of western France, is one of the most frequently recorded acritarch genera. Over 250 species and subspecies, from the Cambrian to the Neogene, have been attributed to the genus. This genus has a simple morphology; it displays a triangular, rectangular, or polygonal central vesicle, with a few, simple processes drawn out from the angles of the vesicle in a single plane, and sometimes with supplementary or auxiliary processes arising from the vesicle body. Veryhachium has been emended and revised numerous times. The number of valid species is excessive: most are probably synonyms. To facilitate effective classification, only a few morphological categories should be retained. For the Lower Paleozoic, the use of two informal groups is proposed. These are the Veryhachium trispinosum group for triangular specimens, and the Veryhachium lairdii group for rectangular forms. Although generally abundant and widespread throughout the Phanerozoic, Veryhachium is of limited biostratigraphic, paleoecologic, or paleogeographic value. However, its First Appearance Datum (FAD) is of great importance for Ordovician stratigraphy; the first Veryhachium morphotypes appear in the Tremadocian Stage, making the genus an important biostratigraphic marker.
A well preserved acritarch assemblage is herein reported from the Azygograptus suecicus Biozone (“Arenigian”) of Meitan Formation at Huanghuachong section, Guizhou Province, South China. The following taxa have been identified: Acanthodiacrodium sp. Adorfia hoffmannensis Cramer, Allam et al. , 1974 Arbusculidium bicuspidatum (Burmann, 1968) Eisenack et al. , 1976 A.destrombesii Deunff,1968 A.filamentosum (Vavrdova,1965) Vavrdova,1972 Baltisphaeridium granosum Kjellstrom,1971 B. hirsutoides (Eisenack, 1951) Eisenack,1958 Coryphidium bohemicum Vavrdova,1972 Cymatiogalea granulata Vavrdova,1966 Leiofusa tumida Downie, 1959 Leiosphaeridia sp. Micrhystridium inconspicuum aremoricanum Paris et Deunff,1970 M.parinconspicuum Deflandre,1945 Peteinosphaeridium trifurcatum breviradiatum (Eisenack, 1959) Eisenack,1965 P.trifurcatum intermedium Eisenack,1976 P.trifurcatum trifurcatum (Eisenack,1959) Staplin et al. , 1965 Pirea ornata (Burmann, 1970) Eisenack et al. , 1973 Polygonium gracile Vavrdova,1966 Rhopaliophora impexa Tappan et Loeblich, 1971 R.membrana Li,1987 Stellechinatum brachyscolum Turner,1984 Striatotheca principalis parva Burmann,1970 Veryhachium trispinosum (Eisenack, 1938) Deunff,1954, ex Downie, 1959 Polygonium gracile it the commonest species among the assemblage, making up 55% of the total taxa. Cymatiogalea granulata is the second commnonest taxon, making up 12%, the other common genera are Peteinosphaeridium (8%), Rhopaliophora (6%), Arbusculidium and Baltisphaeridium (both 4%), Striatotheca (3%). The Huanghuachong assemblage is correlated with the assemblages from the equivalent strata of other localities from the Yangtze Platform, e.g. Tongzi of northern Guizhou, Sandu of southern Guizhou, Ningqiang of southern Shaanxi, Qijiang of southeastern Sichuan, Jishou of western Hunan, Yichang of western Hubei and Yushan of eastern Jiangxi. All of these assemblages are, to a certain extent, similar in composition and in the occurrence of diagnostic acritarch taxa. They are included in the Perigandwana acritarch Province. The assemblage of Yichang, however, yields many endemic and Baltic elements thought it shows a prevalent Perigondwana character. The difference of Yichang assemblage with those from other localities of the upper Yangtze region is rather environmental control than the provincial influence. Yushan is the only published acritarch locality of the lower Yangtze region. More data are needed for better understanding of acritarch flora from the lower Yangtze region. Stellechinatum is reported from Huanghuachong. That is not common in the Yangtze localities. The previous occurrence of this genus is from Yichang, Ningqiang and Xiushan. That extends the range of this genus from “Caradocian” downward to “Arenigian”. Acknowledgements This study is part of the PICS jointly sponsored by the Chinese Academy of Sciences and CNRS, and supported by NSFC(No.49972007) and MST (No.G2000077700).
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