Periodic anoxic shelf in the Early-Middle Ordovician transition:ichnosedimentologic evidence from west-central Utah,USA  

作　　者：龚一鸣 MaryL.Droser 

机构地区：[1]不详

出　　处：《Science China Earth Sciences》2001年第11期979-989,共11页中国科学（地球科学英文版）

基　　金：the National Natural Science Foundation of China (Grant Nos.40072041, 49472086), SSER project of Ministry of Science and Technology of China, and the National Science Foundation of USA.

摘　　要：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.Ichnosedimentologic evidence of periodic anoxic shelf in the Early-Middle Ordovician transition includes lower ichnodiversity, shallower bioturbation and burrowing depth (＜4 cm ), rare domichnia, tiny Chondrites 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.

关 键 词：anoxic shelf ICHNOFOSSILS event sedimentology Ordovician radiation UTAH USA 

分 类 号：P59[天文地球—地球化学]