广西南宁盆地早第三纪沉积相特征

本文论述了南宁盆地的地质构造背景和第三纪地层、沉积相、古地理演化特征,其中侧重对沉积相剖析认为:南宁盆地在中生代以来形成的NE、NW向两组断裂的“X”型构造背景条件下,受NEE、NNE向各两条断裂控制呈菱形状的第三纪陆相断陷盆地;沉积相以湖相为主,河流相、洪积相次之。前者可分为滨湖、浅湖、半深湖等3个亚相,尤以浅湖相发育,后二者仅在古新世至始新世早、中期发育并分布在湖盆边缘;盆地演化过程中始新世时曾一度上升遭受剥蚀,致使瓦窑村组与上覆地层呈不整合接触,由古新世→始新世末盆地中心由SW→NE迁移,盆地范围增大趋势。还指出南湖组与凤凰山组、古亭组是同期(始新世早、中期)异相产物,盆地内产褐煤、粘土与石英砂等矿产。

FEATURES OF THE PALAEOGENE SEDIMENTARY FACIES OF THE NANNING BASIN, GUANGXI

This paper deals with the structural setting , Tertiary stratigraphy, sedimentary facles, and evolution of paleogeography of the Nanning Basin with a stress on the sedimentary facies. The Nanning Basin is a rhombic-shaped Tertiary continental fault-subsidence basin controlled by the NE- and NW-trending faults on the background of two groups of X-shaped faults which trend NEE and NNE respectively and have developed since Mesozoic Era. The sedimentary fades of it is dominated by lacustrine fades with fluvial and plurial facies in subordinate position. Among them, the former can be divided into three subfacies: lakeshore, shallow and semi-deep lake, with the shallow lake facies being the most developed. The latters began to develop during Palaeocene to early and middle Eocene and were mainly distributed along the margins of the lacustrine basin. The Nanning Basin was once subjected to uplift and denudation in Eocene during its development , which accounts for the existance of the uncomformity between the Wayaocun Formation and its overlying sequences. The centre of the Basin was shifted from southwest to northeast between Palaeocene and the end of Eocene, with tine basin area being enlarged. This study also shows that the Nanhu, Fenghuangshan and Guting Formations were deposited contemporaneously (in early and middle Eoene) and belong to different facies of the Basin. Mineral resources such as lignite, day and quartz sand have been found in Nanning Basin.