内蒙古锡林浩特盆地早侏罗世晚期植物群:兼论中国早侏罗世晚期气候

首次报道了产于内蒙古锡林浩特盆地侏罗系红旗组的植物群,共计21属37种。该植物群由木贼目、真蕨纲、苏铁纲、银杏纲、松柏纲和少量分散保存的种子等组成,以真蕨类丰富、蚌壳蕨科Coniopteris和Eboracia出现以及南方型分子较多等为特征。该植物群的时代为早侏罗世晚期,反映研究区红旗组主体的沉积时代为早侏罗世晚期,上部沉积可能形成于中侏罗世早期。气候敏感植物,特别是南方型分子的出现,指示锡林浩特盆地早侏罗世晚期属于暖温带—亚热带气候区,气候较热或短期有一定程度的偏干旱;其气温较早侏罗世早期和中侏罗世早期更高,说明早侏罗世晚期发生过1次升温气候事件。对早、中侏罗世植物群和沉积特征的综合分析表明,中国在早侏罗世晚期可划分出黑龙江东部温凉气候区、北方暖温带温暖潮湿气候区、中部热带—亚热带半干旱—半潮湿气候区、中南热带—亚热带干旱气候区和西藏—滇西热带干旱气候区共5个气候区,其中北方暖温带温暖潮湿气候区与中部热带—亚热带半干旱—半潮湿气候区的界线较早侏罗世早期和中侏罗世早期偏北4°～8°(纬度),亦说明早侏罗世晚期发生了升温事件。此升温事件与中亚和西伯利亚的图阿尔期升温事件相当,其很可能是早侏罗世晚期图阿尔期大洋缺氧事件(T-OAE)在陆地生态系统中的响应。

A late Early Jurassic flora from Xilinhot Basin of Inner Mongolia,with discussions on coeval climate in China

The flora from the Jurassic Hongqi Formation of the Xilinhot Basin,Inner Mongolia,North China,is composed of 37 species in 21 genera:Equisetites sp. and Neocalamites sp. of Equisetales;Hausmannia ussuriensis Kryshtofovich,H. leeiana Sze,Coniopteris bella Harris,C. sp.,Eboracia lobifolia(Phillips)Thomas,Todites williamsonia(Bronign.)Seward,Cladophlebis angutula (Heer)Fontaine,Cl. asiatica Chow et Yeh,Cl. cf. asiatica Chow et Yeh,Cl. haiburnensis(L. et H.)Bronigniart,Cl. hsiehiana Sze, Cl. lobifolia(Phillips)Bronigniart, Cl.ingens Harris,Cl.pseudoraciborskii Srebrodolskaja,Cl. shansiensis,Cl. scariosa Harris Sze and Cl. sp. nov. of Filicopsida;Anomozamites turkmenicus Burakova,Nilssoniopteris angustifolia Wang,Ptilophyllum contiguum Sze,Pterophyllum sp.,Nilssonia sp. nov. and Ctenis sp. of Cycadopsida;Ginkgoites ferganensis Brick,Ginkgoites hottonii (Sternb.)Heer, Phoenicopsis angustifolia Heer,Czekanowskia setacea Heer, Cz. latifolia Turutanova-Ketova and Sphenobaiera sp. of Ginkgopsida;Elatocladus sp.1, Elatocladus sp.2,Podozamites eichwaldi Schimper,Pityophyllum longifolium(Nath.)Moeller and Pityophyllum sp. of Coniferopsida and seed Carpolithus sp. The flora is characterized by abundant ferns and appearance of Coniopteris and Eboracia of the Dicksoniacea and some thermophilous elements. The thermophilous plants include dipteridaceous fern Hausmannia and Ptilophyllum of Bennettitales. The age of the flora is late Early Jurassic and most possibly the Toarcian. The age of the Hongqi Formation is chiefly late Early Jurassic and its upper part is possibly the early Middle Jurassic. The appearance of the climate sensitive plants,particularly the south-type(thermophilous)elements,indicates that the Xilinhot Basin was located in the warm temperate zone-subtropic zone during the late Early Jurassic. It was warmer than that of the early Early Jurassic and early Middle Jurassic,indicating a temperature raising event in the late Early Jurassic. Based on the palaeontological and sedimentary data, there existed 5 palaeoclimatic regions during the late Early Jurassic in China,namely the eastern Heilongjiang warm-cool climatic region,North China warm-temperate and warm-humid climatic region,central China tropic-subtropical semi-arid and semi-humid climatic region,central-southern China tropic-subtropical arid climatic region and the Tibet-western Yunnan tropical arid climatic region. The boundary between the warm-temperate warm-humid climatic region and the tropic-subtropical semi-arid and semi-humid climatic region was about 4-8 degrees of latitude northwards than both in the early Early Jurassic and early Middle Jurassic,also indicating a temperature arising event occurred in the late Early Jurassic. This climatic event most possibly happened in the Toarcian of Early Jurassic and is likely the response of the terrestrial ecological system to the Toarcian Oceanic Anoxic Event(T-OAE).