Occurrence of phosphatic microfossils in an Ediacaran–Cambrian mid-oceanic paleo-atoll limestone of southern Siberia |
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Authors: | Yuko Uchio Yukio Isozaki Michael M. Buslov Shigenori Maruyama |
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Affiliation: | aDepartment of Earth and Planetary Sciences, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8550, Japan;bNational Museum of Nature and Science, Ueno Park, Taito, Tokyo 110-8718, Japan;cDepartment of Earth Science and Astronomy, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan;dInstitute of Geology and Mineralogy, Siberian Branch, Russian Academy of Science, Novosibirsk 6300900, Russia |
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Abstract: | New phosphatic microfossils were recently discovered in an Ediacaran–Cambrian mid-oceanic paleo-atoll limestone in the southern Gorny Altai Mountains in southern Siberia. Microfossils with calcium phosphate shells are abundant in the limestone that occurs as an exotic block within a Cambrian accretionary complex in the Kurai area. SEM observations confirm that the calcium phosphatic shells are ellipsoidal and equal-sized, about 200–300 μm in diameter. Shell walls are about 1 μm thick. As the absence of external and internal structures hinders a detailed comparison/identification, these microfossils are tentatively treated here as paleontological problematica. EPMA-analysis confirmed the concentration of elements P and Ca in microfossil shells and the absence in the matrix, suggesting the primary phosphatic composition of the shells. Because phosphatic microfossils are generally scarce in the Ediacaran but abundant from the Lower Cambrian, in particular within pre-trilobitic SSF assemblages, the phosphatic fossil-bearing limestone in the Kurai area possibly belongs to the Lower Cambrian. The present find proves that mid-oceanic paleo-seamounts as well as continental shelf domains had already been inhabited by diverse metazoans in the Ediacaran–Cambrian transitional interval. |
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Keywords: | Cambrian Ediacaran Phosphate Mid-ocean Atoll Altai |
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