摘要
The Yah＇an Formation of the Ordos Basin is a sequence of four members, consisting of si- liciclastic sediments deposited in alluvial, lacustrine and mire settings during the Middle Jurassic. Samples collected from Members Two and Four contain abundant blackened plant material identified through standard analytical techniques as fusain （fossil charcoal）. The occurrence of fusain in fluvial sandstones at multiple horizons in the outcrops, combined with the previously reported high concentra- tion of inertinite in the coals of Member One, indicates that paleowildfire was a common occurrence in the Ordos Basin during Yan＇an deposition. Sedimentary evidence from Yan＇an outcrops suggests that the paleoclimate was seasonal during deposition of Members Two through Four, which may have contributed to the wildfire frequency. The presence of fusain in the Yah＇an Formation indicates that atmospheric oxygen levels were clearly above the minimum required for sustained combustion during the Middle Jurassic. This conclusion contradicts previous geochemical models for paleoatmospheric composition, but supports more recent studies.
The Yah＇an Formation of the Ordos Basin is a sequence of four members, consisting of si- liciclastic sediments deposited in alluvial, lacustrine and mire settings during the Middle Jurassic. Samples collected from Members Two and Four contain abundant blackened plant material identified through standard analytical techniques as fusain （fossil charcoal）. The occurrence of fusain in fluvial sandstones at multiple horizons in the outcrops, combined with the previously reported high concentra- tion of inertinite in the coals of Member One, indicates that paleowildfire was a common occurrence in the Ordos Basin during Yan＇an deposition. Sedimentary evidence from Yan＇an outcrops suggests that the paleoclimate was seasonal during deposition of Members Two through Four, which may have contributed to the wildfire frequency. The presence of fusain in the Yah＇an Formation indicates that atmospheric oxygen levels were clearly above the minimum required for sustained combustion during the Middle Jurassic. This conclusion contradicts previous geochemical models for paleoatmospheric composition, but supports more recent studies.
基金
supported by the National Basic Research Program of China(973 Program 2012CB821901)
National Natural Science Foundation of China(40772006)
the State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology Programs(20102108,20101104)
