四川西昌盆地下二叠统层序特征及充填模式

四川西昌盆地下二叠统的地层划分对比争议较大，油气勘探程度低。本文通过详细的露头层序地层学研究，结合层序地球化学方法和原理，对西昌盆地下二叠统进行了层序划分和对比，结果表明：西昌盆地下二叠统地层可划分为1 个二级层序、2 个层序组和6 个三级层序；P₁q 层序组构成下二叠统二级层序的LST 和TST，层序4 下部发育的（茅口组底部）凝缩层相当于二级层序的最大海泛面，而P₁m 中上部（包括层序4 中上部、层序5、6）则构成HST；西昌地区下二叠统层序发育形成过程，总体表现为海平面上升和盆地不断向古陆超覆；沉积序列、古氧相含量、锶含量、碳氧同位素和TOC 的变化旋回揭示西昌盆地早二叠世经历了六次三级海平面变化旋回（六个三级层序），在华南地区乃至全球范围内均可进行对比；建立的层序充填模式揭示出早Hessian 早期全球海平面上升，盆地不断向古陆超覆，奠定了早二叠世西昌海域盆地的轮廓，Roadian 早期海平面上升达到最高位，并沉积一套整个华南均可对比的眼球状灰岩或页状藻灰岩，Capitanian 晚期全球构造海平面下降，结束了西昌地区克拉通盆地的演化阶段。

Sequence stratigraphy of Lower Permian of Xichang Basin, Sichuan

The stratigraphic division and correlation of the Lower Permian from Xichang Basin of Sichuan are controversial. Guided by principle of sequence stratigraphic geochemistry, and combined with the detailed studying of outcrop, sequence stratigraphy of the Lower Permian in Xichang Basin was researched and contrasted. One second order sequence, two sequences group and six third order sequences was divided. The second order sequence was constituted with LST, TST, MFS (maximum flooding surface), and HST. LST and TST was Equivalent to P₁q . MFS is the condensed section which developed near the bottom of the 4th third order sequence. HST was Equivalent to the upper part of P₁m which included the upper part of the 4th third order sequence, the 5th and the 6th third order sequences. During the development of the sequence stratigraphy in Xichang Basin, the sea-level had been rising and the sediment always deposited up to the Ancient Land. So many aspects such as sedimentary succession, content of pale oxygenation, content of Strontium, the variations in carbon and oxygen isotopic values and TOC uncovered that Xichang Basin undergo six times sea level rising and falling during the middle Permian ,which means occur six third order sequence. It could correlate with southern China and evenwithin the scope of the world. The established filling model of sequence had revealed that global sea-level rising had taken place in early Hessian and basin continued overlapping the ancient land, and during this stage the outling of Xichang basin formed. In the early stage of Roadian, the sea-level rising reached the highest, and deposited a set of augen limestone or sheet algal limestone which can be founded in south China. In the late stage of Capitanian, the sea-level falled, and it ended the stage of evolution of cratonic basin in Xichang area.