中国南方中、新生代盆地对海相中、古生界的迭加、改造分析

SUPERPOSITION AND RECONSTRUCTION OF MARINE MESO-PALEOZOIC STRATA BY MESO-CENOZOIC BASINS IN SOUTHERN CHINA

本文主要论述了我国南方中、新生代四期构造变格发育的主要盆地原型及其在主要盆地的迭加特征,并根据中、新生代盆地原型的迭加方式和构造改造特点,将南方主要探区的海相中、古生界后期改造形式划分为五种类型,即:持续前渊*迭加型、渊-滑-断-拗迭加型、渊-滑/断迭加型、推覆构造及影子盆地型、残留改造型,进而分别探讨了它们的主要构造特点和在油气保存条件上的差异。分析认为,以四川盆地为代表的持续前渊迭加是海相天然气在中、新生代得到有效保存的最有利类型;其次应为中下扬子地区以江汉盆地、皖南-苏北盆地为代表的渊-滑-断-拗迭加型,它们在早期(T3-J2)前渊盆地迭加和晚期(K2以来)的断陷-拗陷迭加下曾先后为海相中、古生界构建了区域封盖条件,尽管在第二变格期(J3-K1)遭受到燕山运动强烈挤压-走滑作用的改造,但在晚期断-拗盆地迭加下可为海相中、古生界二次生烃油气提供有效保存;而以楚雄盆地、十万大山盆地为代表的渊-滑/断迭加型,尽管早期(T3-J2)前渊盆地迭加为海相中古生界构建了区域封盖条件,但自第二变格期以来由于受到冲断与走滑联合作用影响,使盆地整体形成高块断构造,对海相油气保存造成不利影响;同时指出,要注意推覆构造中的"影子盆地"尤其是区域滑脱层之下的油气保存条件,以及像南盘江拗陷这类残留改造型的弱变形带。

This paper focuses on the main basin prototypes developed in four tectonic evolution periods and their superposition in southern China during the Meso-Cenozoic. According to the superposition and tectonic reconstruction of basin prototype, five types of late reconstruction could be recognized for marine Meso-Paleozoie in southern China, namely the persistent foredeep superposition, foredeep-slide-fauh- depression superposition, foredeep-slide or fault superposition, nappe structure and shadow basin, and relict reconstruction. Moreover we discuss their main tectonic characteristics and difference in the condition for oil-gas preservation. The study indicates that the persistent foreland basin superposition, represented by the Sichuan Basin, is most favorable for preservation of marine Meso-Cenozoic natural gas. The second favorable type is the foredeep-shde-fauh-depression superposition, with its examples in Jiangsu Basin and Wannan-Subei Basin in middle-lower Yangtze. Under the early foreland basin superposition （Late Triassic to Middle Jurassic） and the late fault depression-depression superposition （since Middle Cretaceous）, it successively constituted a regional enclosed condition for marine Meso-Paleozoic, and offered a condition for preservation of the second oil-gas formation of marine Meso-Paleozoic although it had been deformed by the strong Yanshanian compression-strike-slip during Late Jurassic to Early Cretaceous. The foredeepslide or fault superposition, represented by the Chuxiong Basin and Shiwan Mountain Basin, set up a regional enclosed condition for marine Meso-Paleozoic in the early stage （Late Triassic to Middle Jurassic）, but then imposed an effect upon preservation of marine oil-gas, because it led the basins as a whole to form block structures under the effect of strike-slip and thrust since the second structure stage. In addition, it is pointed out that much attention should be drawn to the ＂shadow basin＂ in nappe structure, especially to oil-gas preservation condition below the regional decollement layer as well as the relict reeonstrneted weak deformation belt such as Nanpanjiang depression.