辽西中上侏罗统土城子组植物化石的新发现

DISCOVERY OF FOSSIL PLANTS FROM MIDDLE—UPPER JURASSIC TUCHENGZI FORMATION IN WESTERN LIAONING,CHINA

报道产自辽宁北票三宝营土城子组 2种木化石及 10种植物化石 (包括 5新种 )。它们反映了干旱气候条件下沙漠绿洲型的植被特征 。

Western Liaoning is one of a few typical areas in China where continental Mesozoic deposits are well developed. The Tuchengzi Formation is widely distributed in the region in company with the Lanqi Formation, with the typical place located in Beipiao Basin. The Tuchengzi Formation may be subdivided into three parts based on lithology: the lower part is mainly composed of gray purple shales and clay siltsto nes, the middle part is predominated by purple red conglomerates and the upper part is represented by purple or gray green sandstones with large cross beddings. It is disconformably underlain by the Lanqi Formation and unconformably overlain by the Upper Jurassic Yixian Formation, with a total thickness of 870—2 900 m. Only a few fossils were found in the intericalated layers of the lower member, including estherians, spores pollen and dinosaur footprints in the middle member. However, here no plant megafossils have been reported from this formation. All material described in the paper was first obtained by the authors from the Upper Member of Tuchengzi Formation in 1997—1998. The fossil locality is in Liujiagou near Sanbaoying of Beipiao city(Text fig.1). They include the following taxa: Fossil woods Protophyllocladoxylon franconicum Vogellehner and Xenoxylon ellipticum Schultze Motel; and other fossil plants associated with them namely: Leptostrobus marginatus Samylyna, Pityolepis sphenoides Zheng sp. nov., P. pachyrachis Zheng sp. nov., P. laxiformis Wang, P. pingquanensis Wang, Schizolepis beipiaoensis Zheng sp. nov., S. shangyuanensis Zheng sp. nov., Podozamites sp., Elatides leptolepis Zheng sp. nov., and Carpolithus fabiformis Zheng et Zhang, etc. Only the five new species are described in this article. The discovery of these fossils not only adds some new members to the Middle—Upper Jurassic redbed floras in Northern China, but also provides new evidence for illustrating the outline (Text fig.6) of the evolutionary process of the terrestrial ecosystem across the Middle Upper Jurassic boundary linked with redbed floras. At present, owing to the scarcity of fossils, the geological age of the Tuchengzi Formation has been debated. Wang et al .(1987) considered this formation to be late Middle Jurassic based on the estherians; Pu et al .(1982) attributed the formation to early Late Jurassic according to the spore pollen assemblage, while the present authors suggest that the formation should be early Late Jurassic or late Middle Jurassic—early Late Jurassic in age.