Paleoenvironmental controls on the morphology and abundance of the coccolith Watznaueria britannica (Late Jurassic,southern Germany) |
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| Institution: | 1. National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK;2. Centre for Biological Sciences, University of Southampton, Life Sciences Building 85, Highfield Campus, Southampton SO17 1BJ, UK;1. Center for Advanced Marine Core Research, Kochi University, 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan;2. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu Nankoku, Kochi 783-8502, Japan;3. Dept. of Earth Sciences, University College London, Gower St., London WC1E 6BT, UK;4. Institute for East China Sea Research, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan;5. National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa, Yokohama 236-8648, Japan;6. Department of Natural History Sciences, Graduate School of Science, Hokkaido University, N10W8, Sapporo 060-0810, Japan;7. Department of Biological Sciences, Faculty of Science, Hokkaido University, N10W8, Sapporo 060-0810, Japan;1. Institute for Study of the Earth''s Interior, Okayama University, Yamada, Misasa, Tottori 682-0193, Japan;2. Research and Education Faculty, Natural Sciences Cluster, Sciences Unit, Kochi University, Akebono-cho 2-5-1, Kochi 780-8520, Japan;3. Dept. of Earth Sciences, University College London, Gower St., London WC1E 6BT, United Kingdom;4. Centre for Marine Research, Ru?er Bo?kovi? Institute, 52210 Rovinj, Croatia;5. International Ocean Discovery Program, Texas A&M University, College Station, TX 77845, USA;6. Department of Natural History Sciences, Faculty of Science, Hokkaido University, N10W8, Sapporo 060-0810, Japan;1. Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Cx. P. 15001, 91501-970, Porto Alegre, RS, Brazil;2. Ústav geologie a paleontologie, P?írodovědecká fakulta, Univerzita Karlova, Albertov 6, Praha, Czech Republic;3. ITT FOSSIL - Instituto Tecnológico de Micropaleontologia, Universidade do Vale do Rio dos Sinos, Av. UNISINOS, 950, 93022-750, São Leopoldo, RS, Brazil;4. Institut für Geologie & Mineralogie, Universität zu Köln, Zülpicher Strasse 49a, 50674 Köln, Germany;5. MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, 28359 Bremen, Germany;6. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Cx. P. 15001, 91501-970, Porto Alegre, RS, Brazil;1. Department of Geosciences, Universität Bremen, PO Box 33 04 40, 28334 Bremen, Germany;2. School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia;3. Institute of Science and Engineering, Kanazawa University, Kakumamachi, Kanazawa, Ishikawa 920-1192, Japan;4. Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan |
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| Abstract: | The coccolithophore species Watznaueria britannica is dominant in Middle-Upper Jurassic calcareous nannofossil assemblages and presents morphological variation, including different coccolith size, shape and length of the central area and of the bridge. Six morphotypes can be recognized in the polarizing light microscope. The aim of this work is to better understand the morphological variability of W. britannica and determine if this variability is controlled by paleoecological factors. In order to investigate the potential paleoecological controls on W. britannica morphology and abundance, we carried out a biometric study on a restricted temporal interval: the Late Oxfordian, in the Swabian Alb (southern Germany), characterized by increasing carbonate production linked to climatic changes. The Balingen–Tieringen section, where previous works on sedimentology, nannofossil assemblage composition, and δ18O and δ13C analyses were performed, was selected for this study. The variations in morphology and abundances of W. britannica were studied on 40 samples of the Balingen–Tieringen section, presenting variable lithologies and calcium carbonate contents. For each level, seven biometric parameters (coccolith length, width and ellipticity, central area length, width and ellipticity and central area proportion with respect to the coccolith) were measured or calculated on digitally captured images of the first 100 W. britannica coccoliths observed in the light microscope. The relationships between the different biometric variables were described using bivariate and Principal Component Analyses. Biometric parameters and Principal Component factors extracted from nannofossil assemblages as well as other paleoenvironmental proxies, were investigated using regression, and their stratigraphic trends were compared. Principal component analysis of the six biometric variables (3938 measurements) on W. britannica coccoliths shows a reduced morphological variability compared to a significant size gradient. An allometric trend recognized on the total placolith and on the central area within the W. britannica assemblages suggests that the different morphotypes may represent intra-specific variability rather than different species. The general trend through Late Oxfordian shows an increase in size of W. britannica coccoliths, mainly driven by an increase in the contribution of the large morphotypes. Increasing placolith size is associated with drier and warmer climatic conditions during the latest Oxfordian. |
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