南华北地区及其北部邻区上石炭统—中二叠统高分辨率层序地层

南华北地区石炭系—二叠系烃源岩广泛发育,是未来页岩气勘探的重要目标;然而,其研究程度低,区域地质构造复杂,岩性地层对比关系不清。基于高分辨率层序地层学及沉积学的相关理论,以区内12口井的钻测井资料和两口井的岩心资料为依据,开展了南华北地区及北部邻区上石炭统—中二叠统层序地层划分。结果显示,研究区内太原组、山西组和下石盒子组属于一个不完整的超长期旋回,内部可划分为5个长期旋回和14个中期旋回。中期基准面旋回结构样式可分为3类:(1)以上升半旋回为主的不完全对称类型,多发育在近岸三角洲背景下;(2)以下降半旋回为主的不完全对称类型,多发育在深水的潮间-潮下/潟湖环境;(3)上升半旋回与下降半旋回近于相等的近完全-完全相等的对称类型,在三角洲和潮坪相浅水区域均有发育。从南北向与东西向层序地层年代格架剖面分析可以发现,研究区内不存在大型的或者区域性的沉积间断与不整合面,但研究区因后期构造作用,南部与北部产生“翘板式”转换抬升,局部出现剥蚀间断,形成与上、下地层假整合接触。

High-resolution Stratigraphy of Upper Carboniferous-Middle Permian in Southern North China and Its Northern Surroundings

Permo-Carboniferous source rocks in southern North China are widely developed and become an important target for shale-gas exploration. However, regional study on the Carboniferous-Permian sequences is still inadequate due to the complex structure and unclear stratigraphic correlation. Based on high-resolution stratigraphy, sedimentology, core-logging, and seismic data from twelve wells, we first establish the stratigraphic sequence of the region. The results show that the Taiyuan, Shanxi and Xiashihezi formations belong to an incomplete super-long cycle, which could be divided into five long-term cycles and 14 medium-term cycles. The medium-term base-level circle structure patterns can be divided into three types:A and B, incomplete symmetrical type dominated by (A) ascending hemicycle and (B) descending semicircular gyrus; C, nearly half ascending and half descending with the same type of symmetry. A-type patterns are mostly developed in the nearshore delta sedimentary environment, whilst B-type patterns are mostly developed in the intertidal to subtidal/lagoon environment. Meanwhile, C-type patterns are common in shallow-water (deltaic or tidal) environments. Geostatistical analysis of the stratigraphic sequences (from north to south and from east to west) has found no regional discontinuities or unconformities.Due to local late-tectonic influence, the seesaw-style uplift may have generated local discontinuities, which formed the pseudo-unconformity between the upper and lower parts of the sequence.