川东北新元古代克拉通裂陷的厘定及其深层油气意义

Reconfirmation of Neoproterozoic intra-cratonic rift in northeast Sichuan Basin and its significance of deep oil and gas

关键词:  四川盆地  Rodinia裂解  新元古代  川东北克拉通裂陷  沉积序列  构造古地理  深层油气

Key words:  Sichuan Basin  Rodinia rifting  Neoproterozoic  intra-cratonic lift in northeast Sichuan  sedimentary sequence  tectonic paleogeography  deep oil and gas

摘要:

四川盆地安岳震旦-寒武系特大型气田的发现，极大地鼓舞了相关学者对四川盆地深层油气勘探新领域的探索热情，然而，对于川东北地区深层古地理格局的认识尚存在不少争议。本文通过对四川盆地北缘、东北缘新元古代-寒武纪地层剖面的综合调查与区域对比研究，基于关键事件序列的系统厘定，重建了川东北及邻区的新元古代-寒武纪原型盆地地层格架；同时，结合盆内最新实施的深层钻井和地球物理资料解析，基本厘定了川东北克拉通裂陷的演化时限、发育范围、充填序列、区域古地理格局及其演化过程。研究显示川东北克拉通裂陷的演化经历了三个阶段：（1）新元古代板溪期-震旦纪早期为伸展断陷期，与南华裂谷系开启同步，表现为快速充填，区域沉积分异显著；（2）震旦纪陡山沱晚期-寒武纪筇竹寺期为伸展沉降期，沉积厚度小，但烃源岩相对发育；（3）寒武纪沧浪铺期至寒武纪末为挤压扰曲与充填期，发育局限台地-潟湖相含膏岩系。不同于绵阳-长宁克拉通裂陷，川东北克拉通裂陷开启早，其早期为补偿性裂谷充填、中晚期则为欠补偿的碳质泥页岩和碳酸盐岩沉积组合。由此可见，这一新认识或将对川东北深层油气勘探方向预测具有重要意义。

Abstract:

The discovery of Anyue Sinian-Cambrian giant gas field in Sichuan Basin has greatly encouraged relevant scholars to explore new fields of deep oil and gas in Sichuan Basin. However, there are still many controversies about the understanding of deep paleogeographic pattern in Northeast Sichuan. In this paper, the Neoproterozoic-Cambrian stratigraphic profiles in the north and northeast margin of Sichuan Basin are investigated and correlated, and stratigraphic framework of the Neoproterozoic-Cambrian prototype basin is reconstructed based on the key event records of sedimentary sequence.At the same time, combined with the latest deep drillings and geophysical data analyses in the basin, the evolution time, development range, filling sequence, paleogeographic pattern and evolution process of the intra-craton rift in Northeast Sichuan have been determined preliminarily. The study displays that the formation and evolution of the intra-craton rift in Northeast Sichuan can be divided into three stages:(1) The extensional faulting during Banxi period to early Sinian of Neoproterozoic, which coincides with the opening of the South China rift system, showing rapid filling, large sedimentary thickness and significant regional sedimentary differentiation; (2) The extensional settlement from the late Doushantuo period of Sinian to Qiongzhusi period of Cambrian, whose strata thickness is small, but the source rock is relatively developed; (3) The compression disturbance and depression from Canglangpu period to the end of Cambrian, in which the facies of limited platform and lagoon are developed with thick layer argillaceous rocks, argillaceous dolomite and gypsum-bearing rock series. Different from the short evolution of Mianyang-Changning intra-craton rift, the northeast Sichuan intra-craton rift occurs earlier, its early stage is compensatory rift filling, and the middle and late stages are composed of undercompensated fine clastic rocks and carbonate rocks. This new discovery may be of great significance to the prediction and exploration of deep oil and gas in Northeast Sichuan.