| Author's Name: CUI Shiti1, ZHANG Shaowei1, CHENG Zhao1, ZHU Mao2,3,4, ZHENG Jianfeng2,3,4,
DUAN Junmao2,3,4, SHAO Guanming2,3,4 |
| This study addresses the core issues of unclear sequence architecture and sedimentary evolution patterns of the
bioclastic limestone member of the Carboniferous Bachu Formation in eastern Tazhong area, Tarim Basin. Based on a
wealth of data, including core, thin section, logging, and geochemical data, we conduct an in-depth analysis of the
petrological characteristics of the bioclastic limestone member, construct the sequence stratigraphic framework for this
member, and explore its control on sedimentation and reservoir formation. The research findings demonstrate that: (1) The
bioclastic limestone member in the eastern Tazhong area represents a mixed siliciclastic-carbonate sedimentation within a
marine-terrestrial transitional setting, mainly composed of micritic to peloidal limestone/dolomite, calcarenite/doloarenite
to calcirudite/doloyunrudite, mixed rocks, and transitional lithologies, with a relatively high content of terrigenous
clastics. The distribution of lithologies exhibits distinct vertical segmentation and lateral zonation patterns. (2) Based on
variations in lithology and sedimentary facies, the bioclastic limestone member, along with the underlying Donghe
sandstone member, the lower mudstone member, and the overlying middle mudstone member, forms a complete threeorder sequence. The bioclastic limestone member itself represents a complete transgressive-regressive sequence, with the
middle submember recording the relatively deepest marine flooding conditions during deposition. (3) The eustatic cycles
exert a decisive influence on the evolution of sedimentary microfacies and diagenetic processes. The lower and upper
submembers, deposited in shallow waters, are dominated by supratidal dolomicrite (dolomudstone) facies within
evaporitic tidal flats. During relative sea-level rise in the middle submember, high-energy grain shoal complexes
developed within intertidal settings, where superimposed high-frequency exposure events drove meteoric dissolution and
penecontemporaneous dolomitization, thereby generating high-quality reservoirs with superior storage capacity. These
dolomitized grain shoal and dolomicrite flats with pinprick vugs together constitute the most favorable reservoir facies of
the bioclastic limestone member in the eastern Tazhong area, Tarim Basin, and represent the primary targets for future
exploration and development |
