OCCURRENCE OF RUFFORDIA AND NAGEIOPSIS FROM THE EARLY CRETACEOUS YIXIAN FORMATION OF WESTERN LIAONING AND ITS STRATIGRAPHIC SIGNIFICANCE
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Abstract:
The fossil plants collected by the author in the past fifteen years from the Yixian Formation of western Liao ning amount to about 20 genera, which are dominated by ginkgophytes (including such genera as Baiera, Sphenobaiera, Phoenicopsis, Czekanowskia, Solenites and Leptostrobus ) and conifers ( Pityolepis, Pityospermum, Schizolepis, Nageiopsis, Podozamites and Elatocladus ), with less abundant sphenopsida ( Equisetites ), ferns ( Ruffordia, Coniopteris, Acanthopteris?, Clado phlebis) and cycadophytes ( Tyrmia) , as well as some problematic angiosperms. This assemblage is very similar in general aspect to the Early Cretaceous flora of Mongolia (Krassilov, 1982), and also comparable in floristic composition to the Early Cretaceous floras of Siberia which are characterized especially by abundant Dicksoniaceae, besides ginkgophytes and conifers. The most significant for dating the strata is the presence of Ruffordia and Nageiopsis in the present collection. This paper is to describe Ruffordia goeppertii (Dunker) Seward and Nageiopsis ex gr. zamioides (Fontaine) Berry. The former is an important element of Early Cretaceous floras in Laurasia, while the latter was firstly recorded by Fontaine (1889) from the Lower Cretaceous Potomac Group of eastern America, and later on it also has been described by Seward (1895) from the Wealden flora, Oishi (1940) from the Lower Cretaceous Ryoseki Formation in Japan, Bell (1956) from the Lower Cretaceous Bairmore Group of western Canada and Kryshtofovich and Prynada (1932) from the Lower Cretaceous Nikan Group. The Yixian Formation of western Liaoning should, therefore, belong to Early Cretaceous on the evidence of fossil plants.
