长江三峡西部自流井组植物化石和气候环境分析

FOSSIL PLANTS AND PALAEOCLIMATICENVIRONMENT FROM THE ZILIUJING FORMATION IN THEWESTERN YANGTZE GORGES AREA, CHINA

中侏罗世植物化石以往在华南记载很少.本文报道了产自三峡西部云阳县南溪自流井组东岳庙段的植物化石,共计10属15种,其中包括一个新种;详细论述了该植物组合的性质和时代,指出其重要分子基本上是从下伏珍珠冲组植物群延续发展而来的,并依据组合中含Co-niopteris cf.burejensis等分子,提出其时代属中侏罗世的意见;此外,从组合成分等来看,认为中侏罗世东岳庙期的气候环境具有亚热带半潮湿的特点,但从此期开始,三峡一带大陆性气候影响日益增强,干旱渐趋明显.

A plant assemblage has been found from the Dongyuemiao Member of the Middle Jurassic Ziliujing Formation in the western Yangtze Gorges area, which was rarely struck in previous re-searches. The assemblage comprises 10 gerena and 15 species, the main elements of which are: Eq-uisetites sp., Phlebopteris cf. polypodioides Brongniart, Dictyophyllum nathorsti Zeiller, Clathropteris meniscioides Brongniart, C. platyphylla (Goeppert), Stachypteris? anomala(sp. nov.), Coniopteris cf. burejensis (Zalessly), C. hymenophylloides Brongniart, C. murrayana (Brongniart), Cladophlebis sp., Otozamites mixomorphus Ye, O. hsiangchiensis Sze, O. nala-jingensis Tsao et Guo, Anomozanites cf. gracilis. Nathorst, Cycadites sp. (sp. nov.), etc. It is obvious that this assemblage is predominated by Filices, especially Dipteridaceae and Dicksoniaceae. The former includes Dictyophyllum nathorsti, Clathropteris meniscioides, C. platyphylla; the latter contains Coniopteris hymenophylloides, C. murrayana, C. cf. burejensis. The Cycado-phytes are also rather flourishing in the assemblage, all of which belong to Bennettitales, such as Anomozamites cf. gracilis, Cycadites sp. (sp. nov.), Otozamites mixomorphus, O. hsiangchiensis, O. nalajingensis, etc. The Sphenopsida is very scarce. Based on Coniopteris cf. burejensis etc., the present assemblage is designated to Middle Jurassic in age, and could be comparable with those assemblages from the Qianfuyan Formation in northern Sichuan Province, the Xietan Formation in western Hubei Province and the Yushanjian Formation in western Zhejiang Province. In addition, on the ground that the present assemblage contains more elements of Dipteridaceae and Bennettitales with rather simple composition, it is inferred that semi-humid climate conditions of subtropical zone was dominanted in the Yangtze Gorges area during the Dongyuemiao stage of Middle Jurassic, and starting from this stage, the influence of the continental climate was increasingly strong and the arid climate was gradually evident.