南盘江坳陷泥盆系层序地层格架及古地理环境

FRAMEWORK OF SEQUENCE STRATIGRAPHY AND PALAEOGEOGRAPHIC ENVIRONMENT IN DEVONIAN, NANPANJIANG SAG

南盘江坳陷泥盆系划分为18个三级层序,下、中、上泥盆统分别包括7、5、6个三级层序,平均每个层序延续时限为2.87 Ma.按界面性质可将三级层序划分为10个Ⅰ型层序,8个Ⅱ型层序.上述18个三级层序构成二个超层序(二级层序).盆地腹部泥盆系层序发育齐全,而靠近继承性古陆边缘或沉积高地的浅水区则通常缺失下部1～4层序或顶部17～18层序,并具有自南部钦防海槽向中部右江地区和北部扬子古陆南缘,底部缺失层序增多的趋势.SSl低水位时期形成六盘水-南丹、曲靖-开远两个次级陆源碎屑浅海盆地,滇东曲靖一宜良一带为河-湖环境,而钦防海槽则为次深海海槽环境.海进时期,南盘江坳陷初步形成台-盆相间格局.高水位时期,盆地古地理环境分异较大,边缘形成三角洲环境、滨浅海环境及碳酸盐岩潮坪-泻湖环境;内部发育混积台地、盆地环境.台-盆相间的古地理格局进一步明显.SS2沉积时期,滇东北及黔中南地区形成碳酸盐岩台地;广西地区呈现出台一盆相间格局,常见生物礁及礁前塌积;钦防海槽则演化成统一的陆内裂谷盆地.在SS2沉积未期,滇东北、黔中南地区演化为广泛分布的局限台地.

The Devonian is divided into 18 third-order sequences, in which D_1, D_2, and D_3 include 7, 5 and 6 third-order sequences, respectively, each having the average 2.87 MPa duration, in Nanpanjiang Sag. According to boundary characteristic, these third-order sequences, which are composed of 2 supersequences (second-order sequence), are classified into 10 (I-type) and 8 II-type sequences. Although the Devonian being all in basin interior, lower 1st-4th or upper 17th-18th sequences were eroded near the edge of successive ancient land or on the depositional high with shallow water. The erosion number increases from the Qinfang trough in the south to Youjiang in the middle and the southern margin of the upper Yangtze land in the north. Two neritic marine subbasins included terrigenous clastic were developed on Liupanshui-Nandan and Qujing-Kaiyuan areas, fluvial-lake environment along Qujing-Yiliang, bathymetric trough on Qinfang in LST during SS1.The Nanpanjiang Sag became alternated platform and basin during TST. It was delta environment, seashore and neritic environment, carbonate tide flat-lagoon environment on the edge and mixed platform, basin environment in the interior with more differential palaeogeographic environment during HST. It developed carbonate platform on Diandongbei and Qianzhongnan area, alternated platform and basin with reef and fore-reef talus on Guangxi, intracontinental rift basin in Qingfang during SS2. In the late SS2, it became more extensive restricted platform on Diandongbei and Qianzhongnan areas.