中国白垩纪植物群与生物地层学

CRETACEOUS FLORAS AND BIOSTRATIGRAPHY OF CHINA

早白垩世时中国可划分出北方、南方和藏南3个植物地理区。北方植物地理区可归入瓦赫拉梅耶夫的西伯利亚加拿大植物地理区,发育有热河、阜新和大砬子3个植物群。热河植物群产于辽西义县组和九佛堂组及其他相当地层,时代为早白垩世早期,以苏铁纲和松柏纲占主导地位。阜新植物群赋存于辽西的沙海组和阜新组及相当地层,以真蕨纲、银杏纲和松柏纲共同繁盛,苏铁纲和木贼目较丰富为特点。由早而晚可以进一步划分为Acanthopteris-Ginkgoco riacea组合、Ruffordia goepperti-Dryopterites组合和Ctenis lyrata-Chilinia组合,分别产于辽西的沙海组、阜新组中下部和阜新组上部。大砬子植物群产于吉林延吉盆地的大砬子组和松辽盆地的泉头组,被子植物占优势且掌鳞杉科丰富。南方植物地理区属于瓦赫拉梅耶夫的欧洲中国植物地理区的范畴,苏铁纲、鳞叶或锥叶型松柏和小羽片小而叶膜厚的真蕨类(主要是Cladophlebis)占主导地位,缺少银杏纲、真蕨纲的蚌壳蕨科及单缝孢类型等,为热带、亚热带植物群,可进一步划分为东部、西藏北部和中部3个亚区。其中,东部亚区滨邻古太平洋,以浙江、福建和山东莱阳盆地等的植物为代表,以鳞叶和锥叶型松柏与本内苏铁Ptilophyllum占优势。该亚区植物群可以进一步划分为3或4个植物组合,自早至晚包括Cupressinocladus-Pagiophyllum组合、Cladophlebis-Ptilophyllum组合、Ruffordia-Zamiophyllum组合和Suturovagina-Frenelopsis组合。西藏北部亚区邻近古特提斯洋东北岸,植物群与东部亚区的基本特点一致,但真蕨类更为繁盛,特别是海金沙科Klukia属和里白科的Gleichenites相当丰富,并有海金沙科的Scleropteris属和马通蕨科存在,裸子植物以苏铁纲为主,松柏纲相对较少,可进一步划分为两个组合。中部亚区介于上述两个亚区之间,由于气候干旱,植物群不发育,以甘肃酒泉盆地、民和盆地所产化石为代表,特点是鳞叶、锥叶型松柏类为主,掌鳞杉科较发育,其他类型罕见。藏南植物地理区属于澳大利亚植物地理区的范畴,只发现于喜玛拉雅地区。晚白垩世植物群只发现于东北、华南、西藏等地的少数地点和少数层位,研究程度较低,还不能进一步划分出植物地理区系和组合。以植物化石为主要依据,结合其他生物和非生物证据,建立了中国不同植物地理区白垩纪含植物化石的地层及相关地层的对比关系。

In the Early Cretaceous, there existed three phytogeographical regions in China, namely the North China, South China and southern Tibet regions. The North China Phytogeographical Region, which belongs to Vakhrameev＇s Siberian-Canadian Phytogeographical Region, developed three floras, including the Jehol, Fuxin and Dalazi floras in ascending order. The Jehol flora, which occurs in the Yixian Formation and the Jiufotang Formation of western Liaoning and contemporaneous strata in other areas, is dominated by Cycadopsida and Coniferopsida. It is regared as early Early Cretaceous in age. The Fuxin flora, characterized by the dominanca of the Filicopsida, Ginkgopsida and Coniferopsida, with abundant Cycadopsida and Equisetales, occurs in the Shahai Formation and the Fuxin Formation of western Liaoning and other equivalent strata. The Filicopsida is represented by abundant Dicksoniaceae, Osmundaceae, Schizaeaceae and monolete spore elements in the flora. This flora can be subdivided into three assemblages, which are in ascending order the Acanthopteris-Ginkgo coriacea assemblage, Ruffordia goepperti-Dryopterites assemblage and Ctenis lyrata-Chilinia assemblage. These three assemblages occur, respectively, in the Shahai Formation, and the lower-middle and upper parts of the Fuxin Formation in western Liaoning Province. The Dalazi flora from the Dalazi Formation of the Yanji basin of Jilin Province and the Quantou Formation of the Songliao basin, northeastern China, is characterized by the dominance of angiosperms and abundant scale-like or awl-shaped leaf conifers including Pseudof- renelopsis, Frenelopsis and Suturovagina of the Cheirolepidiacae and the form genera Brachyphyllum and Pagiophyl- lumm. The South China Phytogeographical Region belongs to Vakhrameev＇s Euro-Sinian Phytogeographical Region, with the dominance of Cycadopsida, scale-like or awl-shaped leaf conifers, small and thick pinnule ferns （mainly Clado- phlebis）, and the absence of Ginkgopsida, dicksoniaceous and monolete spore ferns. It represents tropical-subtropical floras, and can be divided into three sub-regions, namely the Eastern sub-region, the North Tibet sub-region and the Center sub-region. The Eastern sub-region, near the ancient Pacific Ocean, is typically represented by plants from Zhejiang and Fujian Provinces and the Laiyang basin of Shandong Province, where the scale-like or awl-shaped leaf conifers and Ptilophyllum of Bennettitales dominated, and schizaeaceous fern Ruffordia commonly occurs. The schizaeaceous fern Klukia and gleieheniaceous fern Gleichenites appear but are not very abundant in the flora. The Early Cretaceous flora ot this sub-region can be divided into 3 or 4 assemblages, in ascending order, the Cupressinocla- dus-Pagiophyllum assemblage, Cladophlebis-Ptilophyllum assemblage, Ruffordia-Zamiophyllum assemblage and Su- turovagina-Frenelopsis assemblage. The flora of the Tibet sub-region shares the main characteristics with the Eastern sub-region, but the ferns are more abundant, particularly rich in Klukia and Gleichenites, and with the occurrence of Scleropteris （a schizaeaceous fern） and some matoniaceaous ferns; gynmosperms are rich in Cycadopsida and relatively poor in Coniferopsida. The flora of the North Tibet sub-region could be further subdivided into two assemblages. The Center sub-region between the two sub-regions discussed above is characterized by poorly-developed floras in arid en- vironments. The flora consists of a low diversity of species and low abundance of fossils, and is dominated by scaly or awl-shaped leaf conifers. The southern Tibet phytogeographical region, where fossils, including araucariaceous conifers and the seed fern Pachypteris specifica, have just been reported in the Himalaya area, belongs to the Austral Phytogeographical Region of Vakhrameev （1991）. The Late Cretaceous floras hitherto have only been found from a few horizons of some localities scattered in Northeast China, South China and Tibet. It can not be divided into phytogeographical regions or into assemblages due to the lack of sufficient data. Principally based on plant fossils and the intergration of biostratigraphical and other chionostratigraphic data, the correlations of the Cretaceous plant fossil-bearing strata and the relevant strata in different phytogeographical regions of China have been established in the present paper.