Periodic anoxic shelf in the Early-Middle Ordovician transition: ichnosedimentologic evidence from west-central Utah, USA |
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| Authors: | GONG Yiming Mary LDroser |
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| Institution: | 1. Faculty of Earth Science, China University of Geosciences, Wuhan 430074, China;Department of Earth Science, University of California, Riverside, CA 92521, USA
2. Department of Earth Science, University of California, Riverside, CA 92521, USA |
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| Abstract: | Ichnosedimentologic evidence of periodic anoxic shelf in the Early-Middle Ordovician transition includes lower ichnodiversity,
shallower bioturbation and burrowing depth (<4 cm), rare domichnia, tinyChondrites occupying shallower or shallowest tiering, widely distributed nodules of limonite pseudomorphs after pyrite, occurrence of
trace fossils being closely associated with the storm event layers, and stratigraphic successions with orbital cyclostratigraphic
architecture. It is suggested that lower atmospheric oxygen level during the Early Paleozoic, the Ordovician radiation, dramatic
transgression and warmer temperatures would result in the periodic anoxia in the Early-Middle Ordovician transition. This
episode began at the later Early Ordovician and lasted about 3.4 Ma on the basis of orbital cyclostratigraphy. |
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| Keywords: | anoxic shelf ichnofossils event sedimentology Ordovician radiation Utah USA |
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