上扬子奥陶纪层序岩相古地理重建及油气勘探启示

四川盆地奥陶系岩相古地理格局研究程度偏低、认识出入较大，沉积期古隆起分布有待进一步研究.运用最新的井震及野外资料，在层序地层划分与对比基础上，建立了上扬子地区奥陶纪三级层序地层格架，并重建了重点层位层序岩相古地理.研究揭示，二级层序结构控制了沉积充填结构，每个二级层序的下部地层厚度起伏明显，指示了古地貌明显起伏特征，古隆起区具有明显的三级层序超覆沉积缺失结构；二级层序晚期古隆起范围缩小，填平补齐作用使得三级层序地层厚度总体稳定.岩相古地理分析揭示，奥陶纪总体具有北部、西部和南部三面稳定古隆起环绕中部凹陷区特征，川中古隆起明显分隔中部凹陷区；认为川中古隆起及南北两侧古隆起具有间歇性扩大、川东地区SSQ2早期存在隆起区，而中部凹陷区总体具有持续性沉降及向东迁移的特征.研究表明，早奥陶世桐梓组沉积期继承了娄山关群的总体古地理格局结构，形成了2个膏岩区及古隆起周缘白云石化颗粒滩相带组合，而湄潭组可能存在西部来源的三角洲沉积. 

Ordovician Sequence and Lithofacies Paleogeography Reconstruction in Upper Yangtze Region and Its Implications for Oil and Gas Exploration

There are different understandings about lithofacies paleogeographic features of Ordovician in Sichuan Basin, and its synsedimentary paleo-uplifts need further research.Using the latest well, seismic data and field data, a study on the Ordovician lithofacies paleogeography on the basis of the sequence stratigraphic division and comparison is carried out.The Ordovician third-order sequence stratigraphic framework in the Upper Yangtze region was established, and the lithofacies palaeogeography of the key stratigraphic sequence was reconstructed.The study reveals that the sedimentary filling texture of Ordovician was controlled by second-order sequence stratigraphy.The strata thickness varies in the lower of each second-order sequence stratigraphy, indicating distinct fluctuant paleogeomorphology.Third-order sequence stratigraphy overlied toward the paleo-uplift region resulting in the loss of strata.The range of paleo-uplift was reduced at the late stage of second-order sequence, and the stratigraphic thickness of the third-order sequence was generally stable as the result of filling.The analysis of lithofacies paleogeography reveals that stable uplifts surrounded the central depressions from three sides, including the north, west, and south during Ordovician, and paleo-uplift in central Sichuan divided central depressions into two parts clearly.It is believed that the paleo-uplift in the central Sichuan and the paleo-uplift on both north and south sides are characterized by intermittent expansion.An uplift area exists during SSQ2 in the east of Sichuan.The central depression has the characteristics of continuous settlement and eastward migration.The study reveals that Early Ordovician Tongzi Formation had inherited the overall paleogeographic background of Loushanguan Group of Cambrian, forming two gypsum rock areas and dolomitization grain shoals distributed around paleo-uplift.In addition, delta depositions sourced from the west of study area maybe existed during Meitan period.