滇缅马生物区系及其在古特提斯中的位置

SIBUMASU BIOTIC PROVINCE AND ITS POSITION IN PALEOTETHYS

本文从古生物地理学的角度,全面搜集并系统总结了滇缅马地块晚古生代的有关古生物资料,证明该地块石炭—二叠纪时既非冈瓦纳生物大区的组成部分,也非华夏生物区系的组成部分,而应作为1个独立的区系归入特提斯生物大区。滇缅马地块在古生代的大部分时间是1个游离于其它陆块之间的相对独立的微大陆,有着与古特提斯中其它地块不尽相同的演化历史。晚古生代的古特提斯可能不象某些作者想象的那么宽阔,但也并非仅由浅海区组成,这是1个由一系列宽窄不一,发育历史各有差异的较小洋盆及陆间海组成的横贯东西的海域,属于洋岛相间的岛海环境。

The origin of the physically barrier-limited provinces is by no means instantaneous, it is the daughter of Father Time. A province should be rather large with rather precise boundaries, be independent of environmental control (Ager, 1971), and be recognisable on the basis of a collection of communities associated in space and rime (Valentine, 1968) which possess distinctive features from the comparable communities belonging to other such provinces, including some endemic elements. In the present paper, the concept 'Tethys' is regarded as a broad seaway, partially of oceanic and transitional types, stretching from Mediterranean region to Timor and Irian Jaya between Gondwana and Laurasia (Tollmann et al., 1985). As a resuh of plate subduction and collision, coupled with rifting and sea-floor spreading, this seaway underwent a long process of complicated changes as time went on. For the sake of convenience, the present paper follows the usage that Paleotethys represented the Late Paleozoic seaway only (Huang and Chen, 1987). In the Permo-Carboniferous Paleotethys, two biotic realms can be distinguished: the Tethyan realm and the Gondwana realm occurring in the northern and southern domains respectively. The latter is further subdivided into the Andean, Partinan, Austrazean, Westralian, and Cimmerian (≈Peri-Gondwana) provinces (Archbold, 1983). Three provinces have been recognized in the Tethyan realm, namely, the Cathaysia province(Fang, 1985), the West Tethyah province (including Tunisia, Sicily, South Europe, Turkey, Crimea, Northern Iran, and Central Asia), and the America Tethys (Huang and Chen, 1987) or 'Exotic' province (Yancey, 1975). In this paper, the fourth province of the Tethyan realm, i.e. the Sibumasu province, is defined. A comprehensive study on the various fossil groups of the Sibumasu block suggests that the Permo-Carboniferous Sibumasu biotic province should be recognized as bordering on the Changning-Shuangjiang-Huoeisai-Lampang-Raub-Bentong Zone in the east, and on the Bijiang-Longling-Ruili-Mandalya-Sittang Valley Zone in the west (Text-fig. 1), and characterized by the following features: (1) No reliable Gondwana cold-water biota elements or authenticated glacial deposits are known from this block. The so-called Dingjiazhai pebble-bearing layer of glaciomarine facies, in fact, is a product of debris flow and those specimens identified as Eurydesrna should be included in the genus Schiziodus instead (Fang et al., 1990). The Early Permian cool-water fauna reported by Waterhouse (1982) is most likely of a temperate nature (Dickins, 1985). Overall, the temperate and warm water fauna occupies a dominant position in this province which is rich in carbonate sediments (such as the Shan Dolomite Group——i.e. the Plateau Limestone of Shan State, the Rat Buri Limestone of Thai-Malay Peninsula and the Permo-Carboniferous limestones of Gengma-Menglian district, Western Yunnan), especially in contemporaneous dolomite and o(?)litic limestone, indicating a warm and arid climate (Witzke, 1988). (2) No tropical Cathaysian biotas (Fang, 1985) and reef complex have been reported from the Sibumasu block. The taxonomic diversity (species richness) of the biotas in this block is lower than that in the Cathaysian Province. The absence of Late Paleozoic coal seams all over the block and the occurrence of the mixed Permian Cathaysian-Gondwana flora in Yongde-Gengma district of western Yunnan suggest the Sibumasu block lying between the equatorial coal swamp zone (Cathaysian flora) and the southern temperate coal swamp zone (Glossopteris flora). (3) The mixture of eurychoric elements from various provinces makes a unique association of the Sibumasu province which contains not only both Peri-Gondwana and Cathaysian elements but also European, Ural and Boreal elements. The occurrence could be explained by the position of the Sibumasu block in Paleotethys and its paleoclimatic conditions. (4) Quite a number of endemic genera and species are characteristic of the province. The paleogeographic features of the Sibumasu block are subject to conflicting opinions in spite of the abundant information acquired in recent years (Burton, 1970; Ridd, 1971, 1980; Stauffer et al., 1972; McElhinny et al., 1974; Kremp, 1977; Archbold et al., 1982; Metcalfe, 1984; Seng(?)r and Hsü, 1984; Nakazawa, 1985; Huang and Chen, 1987). As a microcontinent, the Sibumasu block might lie in an intermediate position in Paleotethysduring the Carboniferous and Early Permian time (Text-fig. 2) instead of being attached to the Gondwanaland because the differences in bioras and stratigraphical sequences between them are so obvious. It drifted away from the Gondwanaland (Northwest Australia) probably during the Ordovician time (Burrett and Stair, 1985, 1987), Since then the Sibumasu block had been wandering between Gondwana and Laurasia until it collided with the Lincang Arc Terrain, the Indo-China block, and the Manabor block during Late Permian and Early Triassic (Fang et al., 1990). It was the existence of a series of intermediate blocks in Paleotethys, such as the Sibumasu, Central Iran, Central Afghanistan, Lhasa, and Timor blocks, that formed the stepping stones for dispersal and migration of both terrestrial species and shallow-water marine species from one continent or continental margin to another.