皖南地区二叠纪层序地层研究

STUDY ON THE PERMIAN SEQUENCE STRATIGRAPHY OF SOUTHERN ANHUI

以层序地层学理论为基础 ,根据皖南地区二叠系钻孔、测井和露头剖面等资料 ,详细研究了该区二叠纪层序地层及海平面变化 ,划分了沉积层序和沉积体系域 ,探讨了界面性质、层序类型及层序特征。本区二叠系可划分出 2个 级和 4个 级层序。2个 级层序的时限分别对应早二叠世和晚二叠世 ,这与中国南方二叠纪构造旋回盆地变更时限相一致。 4个 级层序分别对应于栖霞阶、茅口阶、龙潭阶和长兴阶。栖霞阶和龙潭阶为 类沉积层序 ,其层序底界为类型 界线不整合 ;茅口阶和长兴阶为 类层序 ,其底界为类型 界线不整合。区内低水位体系域不发育 ,沉积层序基本上由海侵体系域和高水位体系域组成。二叠纪存在四次三级海平面变化周期和二次二级海平面变化周期 ,后者可能与全球海平面升降有关。早二叠世早期的海侵及晚期的海退可能代表大区域性的海平面升降。

Based on the theory of sequence stratigraphy and the data from drilling well cores, well logs, and outcropping sections etc., the Permian sequence strata and sea level changes in the study area are detailedly studied in this paper. Division of the depositional sequences and system tracts are made. The nature of the boundary, type and characteristics of sequence are discussed. The Permian strata can be divided into two grade Ⅱ sequences and four grade Ⅲ sequences. The time limits of two grade Ⅱ sequences correspond to Early Permian and Late Permian and they are consistent with tectonic cycle and time limits of basin changing in southern China. The four grade Ⅲ sequences correspond respectively to the Early Permian Qixia (Chihsia) and Maokou Formations and Late Permian Longtan and Changxing (Changhsing) Formations. The Qixia (Chihsia) and Longtan Sequences represent type Ⅰ sequence, the lower boundary of which is referred to as type Ⅰ unconformity; The Maokou and Changxing (Changhsing) Sequences represent type Ⅱ sequence, the lower boundary of which is referred to as type Ⅱ unconformity. The sedimentary sequences in the study area are composed generally of transgression sedimentary system and high water level sedimenyary system, lacking of low water level sedimentary system. There were four periods of grade Ⅲ and two grade Ⅱ sea level changes during the Permian Period. The latter may be related to the eustatic change of sea level. The early Qixia (Chihsia) trangression and late Maokou regression may represent a large regional sea level changes.