一个露头层序地层划分模型——以桂中北泥盆纪盆地为例

AN OUTCROP SEQUENCE DIVISION MODEL: EXAMPLES FROM THE DEVONIAN BASIN IN NORTHERN AND CENTRAL GUANGXI

关键词:  层序  泥盆纪  桂中北

Key words:  sequence  Devonian  northern and central Guangxi

摘要:

以海蚀面(下界)与沟蚀面或陆蚀面(上界)所限之滨相地层厘定为海退体系域(FSST)为依据,建立以海退体系域之上的沟蚀面为底界所构成的Ⅲ型层序边界面类型,即区别于Ⅰ型层序,又不同于Ⅱ型层序,并能更客观地反映桂中北泥盆纪沉积盆地露头层序地层特征。这一露头层序地层模型研究的关键在于识别与判断层序中一些具特殊成因意义的界面,这些界面包括陆蚀面、海蚀面、沟蚀面、暴露面等;其次是研究露头剖面相序,不同的沉积体系域具不同的加积、进积或退积叠置样式;最后是沉积结构构造的分析研究,它是露头层序地层研究的基础。桂中北泥盆纪沉积盆地依据上述新模型划分出7个Vail级旋回层序,其中包括2个Ⅲ类层序,这些层序叠置的地史延续时间在1Ma至几十个Ma之间。

Abstract:

In terms of the falling stage systems tract (FSST) which developed between the regressive surface of marine erosion and the ravinement surface or regressive surface of subaerial erosion,the present paper defines a ravinement surface above the FSST as the type Ⅲ sequence boundary.This new type of sequence boundary is different from both the type Ⅰ and type Ⅱ sequence boundaries,and can be more gearned to actural circumstances of the Devonican outcrop sequence stratigraphic features in northern and central Guangxi. The key to understand the new type of sequence model,on one hand,is to distinguish some special genetic boundary surfaces,which include regressive surface of subaerial erosion,regressive surface of marine erosion,ravinement surface,exposure surface and palaeokarsti-fication surface and so on.On the other hand,the facies sequence analysis of the outcrop sections is much more important.Different sedimentary systems tracts may display distinctive aggradational,progradational and/or retrogradational association patterns.At last,the basic work of outcrop sequence stratigraphic research is to recognize sedimentary textures and structures.According to the model and method mentioned above,the Devonian strata in northern and central Guangxi can be divided into seven Vail-scale sequences,of which two are type Ⅲ sequences,with a time duration of about one to tens of Ma.