鄂尔多斯盆地东缘石炭-二叠纪煤系层序-古地理与聚煤作用

为了揭示克拉通陆表海盆地层序界面形成机制及等时地层格架内古地理背景下煤层聚集特征，以鄂尔多斯盆地东缘为例开展了本溪组-山西组层序地层和聚煤作用研究.识别出区域不整合面、盆地基底沉降差异形成的海侵方向转换面（BTR）、正常海退形成的冲刷面（NSS）和暴露面（NES）及其对应的整合面（NCC）、强制性海退形成的河流侵蚀面（FEU）和暴露面（FES）及对应的整合面（FCC）4种层序界面类型，将研究煤系划分为3个三级层序、6个四级层序.认为基准面周期性变化控制了沉积体系的演化、废弃和聚煤作用的发生，而聚煤基底沉积环境和聚煤期盆地基底沉降速率控制了煤层厚度及其平面上的稳定性，提出了等时地层格架内古地理背景下的综合聚煤模式.结果表明：区域广泛分布的厚煤层形成于Ⅱ型层序界面及Ⅰ型层序最大海退面（初始海泛面）附近；澙湖-潮坪为主的沉积背景下有利聚煤中心位于剩余可容空间相对较低的潮坪环境，潮坪-三角洲-澙湖为主的沉积背景下有利聚煤中心位于基底沉降速率快、剩余可容空间中等的潮坪环境，浅水河流三角洲沉积背景下有利聚煤中心位于基底沉降速率快、剩余可容空间相对较高的三角洲平原间湾湖泊和局限海环境。

Sequence-paleogeography and coal accumulation of Carboniferous-Permian coal measures in the Eastern Ordos Basin

In order to reveal sequence boundary formation mechanism of large scale craton epicontinental basin and coal accumulation characteristics under paleogeographic setting of isochronous sequence stratigraphic framework,sequence stratigraphic framework and coal accumulation were analyzed for the Permo-Carboniferous of Benxi-Shanxi Formation in the eastern Ordos Basin.A total of four types of sequence boundary are identified,which are regional unconformity surface,transgressive direction turnaround surface(BTR) resulted from settlement difference of basin basement,and normal regressive erosion surface(NSS),exposed surface(NES),corresponding conformity surface(NCC),and river erosion surface(FEU) resulted from compulsory regression,exposed surface(FES),corresponding conformity surface(FCC).Coal-bearing strata is divided into three third-order sequences and six fourth-order sequences.Authores find that cyclical changes of base level controls the occurrence of coal accumulation,coal-base depositional environment and basin basement subsidence rate during coal accumulation period controls seam thickness and continuity.Paleogeographic comprehensive coal accumulation model within isochronous stratigraphic framework is proposed.The results show that widely distributed thick coal seams form around Ⅱ-type sequence interface and the largest regression surface(initial flooding surface) of Ⅰ-type sequence;under the lagoon-tidal flat context,coal-center is located in the tidal flat depositional environment,whose remaining accommodation space is small;under the lagoon-delta-tidal flat context,coal-center is located in the tidal flat depositional environment,whose remaining accommodation space is moderate and basement subsidence rate is large;under the shallow river delta context,coal-center is located in the restricted sea and lakes and bays of the delta plain depositional environment,whose remaining accommodation space is large and basement subsidence rate is large.