藏南舌羊齿植物群的发现和其在地质学及古地理学上的意义

喜马拉雅地区一直被传统地质学认为是一个典型的古地槽区,属于劳亚和冈瓦纳两古大陆之间的古地中海的一部分,具有很厚的古生代到老第三纪的海相沉积。本世纪上叶,魏格纳就提出大陆漂移的假说,设想陆块之间曾有过大规模的水平移动,可是大陆固定和海洋永存的传统观念在人们脑海中根深蒂固。

ON THE DISCOVERY OF A GLOSSOPTERIS FLORA IN SOUTHERN XIZANG AND ITS SIGNIFICANCE IN GEOLOGY AND PALAEOGEOGRAPHY

The present paper deals with a Glossopteris flora newly found by the Scientific Expedition Party of Academia Sinica in southern Xizang. Fossils were collected from the grey shales of the Qubu Formation in the localities Qubu of the Pazhuo Region of district Dingjia. Glossopteris communis is by far the most predominant element, Others are G. angustifolia, G. indica, Sphenophyllum speciosum, Raniganjia qubuensis sp. nov., Dizeugotheca qubuensis sp. nov., Dichotomopteris qubuensis sp. nov. and an un named fern. The Qubu Formation is considered equivalent to the Raniganj series of the Damuda Division of the Lower Gondwana System of India. The age of this flora is, therefore, assigned to early Late Permian.The diagnoses of the three new species are given as follows: Ramiganjia qubuensis: stem 1-2 cm in diameter. Nodes and internodes distinct. Internodes 3-6 cm in length, longitudinally ribbed. Ribs 16-24 in number, continuous over the nodes. Whorled-leaves disc-like, united at the base for about 1/3?2/3 of their length. Leaf segments 14-22 in number, all equal in size, 3-4 cm long and 3-4 mm wide, straight and broadly pointed in apex, entire in margin, smooth in surface, and uninerved.Dizeugotheca qubuensis: Frond bipinnate, rigid, with strong rachis of 2 mm in diameter. Ultimate pinna sword-shaped, 3.4 cm long and 9 mm wide, alternate and contiguous. Rachilla also strong, 0.8 mm across. Pinnules about 16-17 on either side of the rachilla, borne at broad acute angle, about 70-80° to the rachilla, contiguous, oblong or tongue-shaped, 3.5×1.5 to 3×2 mm, alternate, connected near the base, round apex and entire in margin. Midvein distinct up to the apex and giving off secondary veins at acute angle; secondary veins 6-7 on either side of the midvein, opposite to subopposite, slightly curved towards the apex and never forked. First pair of secondary veins arising at 40-50°, strongly curved forward, other pairs at 30-40°, slightly curved-nearly straight, parallel to each other. Distance between the 1st and 2nd pairs of the secondary veins greater than that of others.Dichotomopteris qubuensis: Frond a least bipinnate, ultimate pinna broadly elongate and lanceolate, contiguous or overlapping. Rachilla strong, 1-2mm broad, pinnules alternate, borne at broad acute angle about 50-60° to the rachilla, linear-oblong-falcate, 2cm long, 0.5-1cm wide, entire, connected near the base, and obtusely rounded apex. Midrib distinct and strong about 0.4 mm wide, arising at an acute angle about 45° from the rachilla, curved at the base, and dissolved near the apex. Secondary veins 10-12 on either side of the mid-vein, alternately arranged. First pair of secondary veins, arising at the base of the midvein, equally dichotomising twice; second to ninth pairs of the secondary veins sympodially forked 3 times, curved towards the margin of pinnule.The Qubu Formation is widely distributed in a belt about 50 km north to the main Himalayas, from Longda, Selong, Tulong, Qubu to Quzong, that indicates that the Himalayan region was then the interior part of the Gondwanaland. Thus, it disproves the so-called "Himalayan Geosyncline" and the geosuture line between the Indian Plate and the Eurasia Plate.The author further suggests that the Cathayian flora had almost nothing to do with the Glossopteris-flora of India during Late Permian. The plants Schizoneura manchuriensis and Bhipidopsis ginkgoides appeared somewhere in the Cathayian flora must have migrated from the Angaraland rather than from the Gondwanaland claimed by Konno (1964, 1965) and Sheng and Lee (1970). The so-called "Glossopteris angustifolia and G. guizhouensis" found in Tailand and Guizhou (China) respectively are too fragmentary to be identified as Glossopteris.