Late paleozoic phytogeographic provinces in China and its adjacent regions

Abstract

China's tectonic history is complex. The country consists of a number of amalgamated plates, microcontinents, and terranes, and consequently contains a wide diversity of floras representing all of the major biogeographic provinces of the late Paleozoic-the Angaran, Cathaysian, Gondwanan, and Euramerican. The boundaries of the late Paleozoic phytogeographic provinces are mostly coincident with the fold belts and deep fault zones that mark the sutures between the four major tectonic blocks within the country. These areas are known as the Junggar-Hinggan Region (a part of the Angaran Realm), the Sino-Korean-Tarim (North China) Block (in the North China Cathaysian Subrealm), the South China Block (in the South China Cathaysian Subrealm), and the Southern Xizang (Tibet)-Western Yunnan Region (in the Gondwanan Realm). The occurrence of Chacassopteris in northern Xinjiang and Angaridium in the eastern part of the Junggar-Hinggan region suggests that the floras in the Junggar-Hinggan region were on the southern fringe of the Angaran Floral Province on the Siberian plate and that the Angaran floras began to differentiate from their Late Devonian ancestors earlier (by the Visean) than the surrounding Euramerican and Cathaysian floras. Intermixing of Angaran and Cathaysian floras beginning in the early Late Permian is interpreted as evidence that collision between the Siberian and the Sino-Korean-Tarim Blocks began at this time and that the floras began to spread north and south across the suture. Climates are interpreted to range between temperate and subtropical. The Cathaysian Floral province consists of two major tectonic blocks (the Sino-Korean-Tarim (North China) Block and the South China Block) and several floral subzones. The lack of provincial differentiation between the Visean floras on the two blocks suggests that collision between them occurred during the Devonian. North and South China were vegetated by Euramerican floras until the Late Carboniferous when Cathaysian elements first began to differentiate in response to differences in the paleogeographic position of the blocks and possibly to tectonic factors. Differentiation did not proceed uniformly across all of the Cathaysian landmass. Rather it began as early as the early Westphalian in some subregions and as late as the Stephanian in others. The two major Cathaysian provinces were established by the Permian. The Cathaysian flora is interpreted to have developed in a tropical, probably ever-wet climatic zone. Tropical conditions persisted in South China throughout the Permian, but in North China, by early Late Permian, climatic conditions alternated between wet and dry, and by late Late Permian most of the Northern Hemisphere was experiencing extreme arid conditions. Large leaved forms like Taeniopteris are more common in North China compared to South China and the genus Gigantopteris is almost completely restricted to South China. South China also contains an abundance of Psaronius tree ferns and Gleicheniaceous ferns. Though arborescent lycopods were in a general state of decline, some species like Lepidodendron oculus-felis were still widespread in the Late Permian of South China. In the southern Xizang (Tibet)-western Yunnan Regions, floras from the Devonian to the Early Carboniferous, though somewhat endemic in nature, closely resembled the Eurasian floras. After the Early Carboniferous, two floral sub-provinces developed in Tibet. The sub-province south of the Yarlung-Zangbu Suture characteristically contains sediments with diamictites, a cold-water Stephanoviella fuana during the Late Carboniferous and a Gondwana flora during the Early Permian. This region is accepted to be part of the Indian Plate and is unquestionably part of the Gondwana Floral Province. The sub-province between the Yarlung-Zangbu Suture and the Bangongco-Dengqen Suture (known also as the Gangdis-Nyainqentanglha tectonic region) also contains diamictites and a Stephanoviella fauna, but contains none of the elements typical of the Glossopteris flora. This subprovince occasionally contains a few faunal elements typical of South China. The tectonic characteristics and the distribution of marine invertebrates and diamictite deposits suggest that the Chinese Gondwana province was a coherent landmass, the Median Plate, located on the northern fringe of Gondwanaland.