Sedimentary system characteristics and depositional filling model of Upper Permian–Lower Triassic in South Yellow Sea Basin

Abstract

In the South Yellow Sea Basin, Mesozoic–Paleozoic marine strata are generally well developed with large thickness, and no substantial breakthroughs have been made in hydrocarbon exploration. Through research, it is believed that the Upper Permian–Lower Triassic can be regarded as a long-term base-level cycle. Based on drilling data, characteristics of the lithology–electric property combination cyclicity, and the special lithology, the long-term base-level cycle was divided into five medium-term base-level cycles (MC₁–MC₅). On this basis, the Permian–Triassic sedimentary systems and their filling model were analyzed in accordance with the change of base-level cycle and transition of sedimentary environment, as well as characteristics of the drilling sedimentary facies and seismic facies. The results show that there were six sedimentary systems (fluvial, delta, tidal flat, open platform, restricted platform, and continental shelf) developed in the Upper Permian–Lower Triassic, the sedimentary systems were distributed such that the water was deep in the northwest and shallow in the southeast, and there were two base-level cycle filling models (a relatively stable tidal flat facies and a rapidly transgressive continental shelf facies to stable platform facies) developed in the Upper Permian–Lower Triassic. These models can provide a basis for evaluation of the Mesozoic–Paleozoic hydrocarbon geology in the South Yellow Sea Basin.

摘要

南黄海盆地中—古生代海相地层发育齐全且厚度较大,一直未获得实质性的油气勘探突破。研 究认为,南黄海盆地上二叠统—下三叠统可作为1 个长期基准面旋回。基于南黄海盆地钻井资料,以 岩电组合旋回性特征及特殊岩性为依据,将长期基准面旋回划分为5 个中期基准面旋回(MC1-MC5)。 在此基础上,依据基准面旋回变化和沉积环境的变迁,结合钻井沉积相及地震相特征,对南黄海盆地 二叠系—三叠系的沉积体系及充填模式进行了分析。结果表明:南黄海盆地二叠系龙潭组、大隆组和 三叠系青龙组发育6 大沉积体系—河流沉积体系、三角洲沉积体系、潮坪沉积体系、开阔台地沉积体 系、局限台地沉积体系、陆棚沉积体系;龙潭组、大隆组和青龙组沉积体系具有水体西北深、东南浅 的分布特征;上二叠统—下三叠统发育两种基准面旋回充填模式,即上二叠统龙潭组相对稳定的潮坪 相和上二叠统大隆组—下三叠统青龙组快速海侵的陆棚相至稳定的台地相,这些模式可为南黄海盆地 中—古生界油气地质评价提供基础依据。