用聚类分析方法探讨晚二叠世安加拉植物地理区的内部划分

ON SUBDIVISION OF ANGARA FLORAL PROVINCE IN LIGHT OF CLUSTER ANALYSIS

晚古生代末,全球明显地分为四大植物地理区系,在这四大植物地理区分别生长着欧美植物群、华夏植物群、冈瓦纳植物群和安加拉植物群。这些植物群面貌各异,彼此近于平行发展。安加拉植物地理区,西自乌拉尔山脉西北侧的伯绍拉盆地,东至海参崴,南达我国新疆准噶尔盆地、内蒙古北部与东北北部。此区安加拉植物群生存于石炭纪及二叠纪,尤其以晚二叠纪最具区域特色。该植物群的主要特征是:植物不很繁盛,植物体多较矮小,树干切面常具年轮,代表有季节分化的温暖潮湿环境。关于安加拉植物群及安加拉植物地理区的内部划分前人已做了一些工作(Meyen,1982,1987),

In their important attributions to the subdivision of the Angara province, Drs. S. V. Meyen and M. V. Durante pointed out that there are obvious differences between the inner areas and the south periphery of Angaraland. From the writer's study on the abundance of species or types of the representative genera found through Cluster Analysis, it is suggested that in Late Permian, the Angara flora was distributed in a semicircular pattern with a center at the Tunguska basin. From the Tunguska basin outwards, four floral zones can be recognized, i. e. Tunguska basin-Verhoyan (possibly including part of N. Mongolia) Zone; Kuznets basinWest Tajmyr(possibly including N. Mongolia and part of N. Premoria) Zone; Petchora basin N. Kazakhstan (?)-Turpan of Xinjiang-SE Mongolia-Xiaoxing'anling-Premoria Zone, and E. Margin of E. Europe-S. Ural-S. Kazakhstan (?)-N. margin of Tarim basin (?)-Nanshan of Gansu(possibly including the north part of N. China) Zone. In the first zone the Late Permian floras are featured by the rather monotonous types of cordairaleans, ferns and few articulataleans, and the lack of such typical Late Permian Angara pteridosperms as 'Callipteris', Comia and Psygmophyllum. In the second zone the Late Permian floras differ from those of the first zone in the much more luxuriance of the floras, which are composed of rich fossil plants such as pteridosperms, ferns, articulataleans and especially cordaitaleans. In the third zone, pteridospermous plants occupy a predominant position, espeeialy 'Callipteris' with pinnules in the form of alethopteroid and connected with each other at the base, and Comia with deep splits on the margin of pinnule, rather than 'Callipteris' with short and small pinnules and Comia with shallow splits on the margin of pinnule in the second zone, while ferns, cordaitaleans and articulataleans come next. One more important characteristic feature lies in these floras mixed with a few Euramerican elements in the Petchora basin and N. Kazakhstan, and with Cathaysian ones in the Turpan basin of Xinjiang, SE Mongolia, Xiaoxing'anling and especially in Premoria. In the fourth Zone the Late Permian floras consist of rather scarce typical Angara materials but rich Euramerican conifers as well as Subangara elements, e. g. Tatarina, Phylladoderma and Quadrocladus. Of importance is that this zone is beyond the Angara floral province. It has been taken for granted that vegetations in geological times were distributed in latitudinal zones from equator areas of low latitudes to polar areas of high latitudes as well as inmodern times. The semicircular zones of the Late Permian Angara flora might have corresponded to the latitudes of that time as proposed by Ustritsky in the light of pale0magnetism and palaeontology (based mainly on marine fossils). The second zone becomes unclear eastwards and much more Cathaysian elements are contained in Premoria than in other south peripheric areas of the third zone; such phenornena might have been influenced by the cold boreal ocean and warm Tethys ocean. The cold boteal ocean stretched to thenorth part of Mongolia in the form of gulf and thus brought forth the similarity of the Late Permian flora of N. Mongolia to those of the Tunguska basin and Verhoyan. Along the northwest coast of the Tethys ocean oc- curred north-flowing warm currents, which brought a humid-warm weather to Premoria just as those of N, China and hence made it possible for many Cathaysian plants to exist therein.