滇黔泥盆纪露头层序地层的初步研究

THE PRELIMINARY STUDY OF THE OUTCROP SEQUENCE STRATIGRAPHY DURING DEVONIAN IN EASTERN YUNNAN AND SOUTHWESTERN GUIZHOU

通过露头层序地层学研究,滇黔泥盆系中可识别出三个Ⅰ类和二个Ⅱ类层序界面,以及三个Ⅰ类和一个Ⅱ类层序:洛霍柯夫—布拉克期为碎屑岩Ⅰ类层序,由低水位、海侵和高水位三个体系域构成层序;爱姆新—爱菲尔期为碎屑岩—碳酸盐岩Ⅱ类层序,由陆棚边缘、海侵和高水位三个体系域构成层序;吉维特早期和吉维特晚期—法门期为两个相似的碳酸盐岩为主的Ⅰ类层序,都由低水位、海侵和高水位三个体系域构成层序。由沉积体系域演化作出的泥盆纪海平面变化曲线,不同于威尔的全球泥盆纪海平面变化Ⅱ级旋回,表明滇黔地区泥盆纪海水进退和上升、下降受局部构造控制。

The Devonian strata are of widespread occurrence in Eastern Yunnan and Southwestern Guizhou. The studies about stratigraphic division,correlation and sedimentary facies are carried out by the authors. The emphasis of this paper is concentrated in the sequence stratigraphy and sea level changes during Devonian in these areas. According to the outcrop sequence stratigraphy, two types of sequence boundaries have been distinguished in the strata. They are unconformity of correlative conformable boundies. There are three type I sequence boundaries including Silurian-Lochkovian,Eifelian-Givetian and early Givetian-late Givetian,and two type Ⅱ sequence boundaries including Pragian-Emsian and Famennian-Mississpian. The Lochkovian-Pragian is an involved type Ⅰ depositional sequence (belonging to clastic sedimentary cycle) and composed of lowstand systems tract,transgressive systems tract and highstand systems tract. The Emsian-Eifelian is a complex type Ⅱ depositional sequence (belonging to clast-carbonate sedimentary cycle) and is composed of shelf margin systems tract,transgressive systems tract and highstand systems tract. In the Givetian-Famennian, there are two type I depositional sequences.i. e. early Givetian and late Givetian-Famennian (all belonging to carbonate sedimentary cycle). They are composed of lowstand systems tract,transgressive systems tract and highstand systems tract. According to the relationship between these systems tracts and sea level changes, the curves showing the sea changes during Devonian in Eastern Yunnn and Southwestern Guizhou are different from the second order cycles of relative change of global sea level during Devonian (Vail et al, 1977b). Hence,it is controlled by the regional tectonism.