南雄盆地红层岩石地层划分

LITHOSTRATIGRAPHIC SUBDIVISION OF RED BEDS IN NANXIONG BASIN,GUANGDONG,CHINA

南雄盆地白垩纪-古近纪红色地层累计厚达2525～7250m，依据沉积物从粗到细的变化，将南雄盆地红层划分为4个沉积旋回和2群9组8段，即南雄群（长坝组、江头组、园圃组、大风组、主田组、浈水组），罗佛寨群（上湖组、浓山组、古城村组），重新厘定了大风组、园圃组的涵义，新建江头组，取消松山组、黄坑组、坪岭组和丹霞组，简述各岩组的分布、岩性特征及生物化石。所划分的9个岩组，除长坝组与江头组之间有沉积间断为假整合接触外，其余各组均属连续沉积整合接触。长坝组一段、江头组、大凤组、浈水组以粗碎屑岩发育为主要特征，而长坝组二段、园圃组、主田组和罗佛寨群主要是一套细碎屑岩，由于岩石的物质成份、粗细、软硬不同，抗风化能力差异明显，反映在地貌形态和植被面貌上都有显著区别，依据岩性、地貌和植被特征各组之间的分界线标志明显容易划分，也便于野外地质填图。依此划分编绘了新的大比例尺（1／5万）南雄盆地地质图。

The Cretaceous-Palaeogene red beds of the Nanxiong Basin （2525-7250 m thick） have been subdivided into four sedimentary cycles and two lithostratigraphic groups containing nine formations （eight members）, i.e. in ascending order, the Nanxiong Group （including, in ascending order, the Changba, Jiangtou, Yuanpu, Dafeng, Zhutian, Zhenshui Formations） and Luofozai Group （including, in ascending order, the Shanghu, Nongshan and Guchengcun Formations）. We have revised the definition of the Dafeng Formation and the Yuanpu Formation, and have erected the Jiangtou Formation. We propose to abolish the Songshan, Huangkeng, Pingling and Danxia formations. At the same time we have also de- scribed the lithology, the fossil contents and field distribution for each lithological formation. There is a parallel unconformity between lowest two formations, i.e. between the Changba and Jiangtou Formations, while the conformable contact among other formations is recognized. The lower member of the Changba Formation, the Jiangtou Formation, the Dafeng Formation and the Zhenshui Formation are characterized by course clastic sediments, such as conglomerate, pebble bearing coarse sandstone. The Upper Member of the Jiangtou Formation, the Yuanpu Formation, the Zhutian Formation and the Luofozhai Group are mainly composed of fine grained sediments, i.e. mudstone and siltstone. Because of the variation in com- ponent, granularity and rock hardness, each formation has different weathering resistance that has been clearly reflected in the topography and vegetation. In the field the formation boundaries are clearly indicated by the topography and vegetation, which helps our large scale （1：50000） geological mapping.