西湖凹陷是东海陆架盆地中极具油气勘探价值的富烃凹陷，其始新统平湖组在近年来的勘探工作中持续取得突破，已成为油气勘探开发的重要层位。由于以往研究多基于宏观区域开展且资料分散，致使学术界对平湖组沉积体系的认识存在诸多争议，严重影响后续勘探开发的精准度与效率。研究以西湖凹陷平北地区平湖组早期沉积为切入点，综合运用岩心、测录井、地震等多种资料，深入开展了沉积体系研究，旨在明晰其沉积特征并建立沉积模式。经研究，平湖组下段可划分为层序一、层序二共2个三级层序，二者均展现出显著的潮汐沉积特征，标志性沉积构造包括双向交错层理、再作用面、双黏土层以及脉状—波状—透镜状潮汐复合层理等。其中，层序一时期，研究区呈现典型的障壁滨岸沉积环境。北东—南西走向的障壁砂坝将区域一分为二，西侧形成潟湖—潮坪体系，发育潮道、三角洲前缘等沉积微相；东侧为开阔滨岸体系，发育与障壁岛平行的条带状沿岸砂坝。而在层序二时期，受区域海侵作用的影响，障壁岛—潟湖体系发育受到抑制，沉积环境转变为潮汐主导的开阔潮坪沉积，完整发育砂坪—混合坪—泥坪沉积序列。受潮汐作用影响，潮间带—潮下带发育北西—南东向潮道，潮下带也发育潮汐砂坝和砂坪。进一步通过对砂体类型、形态、展布规律的详细剖析，并结合沉积环境与经典沉积模式，建立了障壁滨岸—潮坪复合沉积模式。模式的建立不仅为理解西湖凹陷沉积演化过程提供了依据，而且对指导西湖凹陷自斜坡带至凹陷区的油气勘探开发具有指导意义。

The Xihu Sag is a hydrocarbon-rich sag with high oil and gas exploration value in East China Sea Shelf Basin. In recent years, continuous breakthroughs have been achieved in the exploration efforts of the Eocene Pinghu Formation of Xihu Sag, making it an important target for oil and gas exploration and development. However, previous studies were mostly carried out on a macroscopic regional scale with scattered data, resulting in many controversies in the academic community regarding the depositional system of the Pinghu Formation, which seriously affects the accuracy and efficiency of subsequent exploration and development. Focusing on the early deposition of the Pinghu Formation in the Pingbei area of Xihu Sag, this study comprehensively utilized data including core, well logging, and seismic data to conduct an in-depth investigation of the depositional system, aiming to clarify depositional characteristics and establish a depositional model. This study divided the lower Pinghu Formation into two third-order sequences: Sequence 1 (SQ1) and Sequence 2 (SQ2). Both exhibited significant tidal depositional characteristics, with diagnostic depositional structures including bidirectional cross-bedding, reactivation surfaces, double mud layers, and flaser-wavy-lenticular tidal composite bedding. During the SQ1 period, the study area exhibited a typical barrier coastal depositional environment. The NE-SW-trending barrier sand bars divided the area into two parts. A lagoon-tidal flat system was formed on the west side, where depositional microfacies such as tidal channels and delta fronts developed. On the east side, there was an open coastal system, where strip-shaped longshore sand bars developed parallel to the barrier island. During the SQ2 period, affected by regional transgression, the development of the barrier island-lagoon system was suppressed, and the depositional environment transformed to a tide-dominated open tidal flat, completely developing depositional sequence of sand flat-mixed flat-mud flat. Affected by tidal action, NW-SE trending tidal channels developed in the intertidal and subtidal zones, and tidal sand bars and sand flats also developed in the subtidal zone. Furthermore, through a detailed analysis of sand body types, shapes, and distribution patterns, combined with the depositional environment and classic depositional models, a barrier coastal-tidal flat composite depositional model was established. The establishment of this model not only provides a basis for understanding the depositional evolution process of the Xihu Sag, but also offers guidance for oil and gas exploration and development from the slope zone to the sag area in Xihu Sag.