滇西昌宁-孟连带内石炭纪-二叠纪鲕粒灰岩的古地理意义

虽然在滇西昌宁-孟连带内发现了泥盆纪至中三叠世的放射虫硅质岩，但是目前对其构造古地理意义仍然有争议。对昌宁-孟连带晚石炭世至早二叠世碳酸盐岩地层内鲕粒灰岩进行了研究，结果表明，该套碳酸盐岩形成于动荡浅水沉积环境，其成因可能与古特提斯洋内碳酸盐岩洋岛海山有关，并且反映了温暖、较为干燥的古气候背景。根据地质背景资料分析，它们应该形成于南亚热带较干燥的气候环境。与东西两侧同期地层形成的古气候背景对比发现，在石炭纪-二叠纪时，昌宁-孟连带是分隔滨冈瓦纳地块群和华夏地块群的主支洋盆；在早二叠世时，该洋盆宽度约10°古纬距。

PALAEOGEOGRAPHIC IMPLICATIONS OF CARBONIFEROUS TO PERMIAN OOLITIC LIMESTONES IN THE CHANGNINGMENGLIAN BELT OF WEST YUNNAN

Although the radiolarian cherts of Devonian to Middle Triassic of deep water origin have been reported from the Changning Menglian belt (CMB) in west Yunnan Province, the tectono  palaeogeographic nature of the CMB is still in controversy. The confirmation of the oolitic limestones of the Late Carboniferous to the Early Permian Age in the CMB of west Yunnan Province implied the carbonate succession was accumulated in a shallow and agitating environment, possibly as the carbonate caps of oceanic islands. The formation of the carbonate ooids also indicated the ambient water of warm nature under the semi arid palaeoclimatic background. The analysis of geological context showed that the carbonate succession was formed in the southern subtropical semi arid paleo climate zone, in contrast to the time equivalents to the both sides of the CMB. The Changning Menglian ocean thus was the main branch of the Palaeo Tethyan ocean separated the blocks of Gondwana affinities from those of Cathaysian affinities, and situated in the southern subtropical semi arid palaeoclimatic zone and spanned about 10° in palaeolatitude in the Late Carboniferous to the Early Permian Age.