Mouth-bar sand bodies serve as significant hydrocarbon reservoirs in the deltaic sedimentary system. However, due to the limitations of the dimensions, scales, and resolutions of data on outcrops, modern deposits, and underground reservoirs, the systematic characterization of both the internal sedimentary evolution processes and the architectural characteristics of the mouth-bar sand bodies remains challenging. By integrating sedimentary numerical simulations and modern sediment observations, we analyze the sedimentary evolution of typical mouth bars, reveal their internal architectural patterns, and thoroughly explore the hydrodynamic mathematical models and mechanisms in their development areas. The results indicate that the sedimentary evolution of typical mouth bars can be divided into five stages: vertical aggradation, progradation, lateral aggradation, stabilization, and the formation of composite mouth bars. These mouth bars exhibit varying morphological characteristics across these evolutionary stages, appearing small elongated tongue-shaped, nearly rhombus, triangular or V-shaped, mid-channel bar-shaped, and long ellipse-shaped sequentially. The sedimentary evolution of mouth bars is governed by hydrodynamic variations. The combined action of jets, basin-floor friction, and water buoyancy, results in the formation of varying aggradational styles and diverse planar morphologies of the existing mouth bars. Additionally, variations in hydrodynamic conditions lead to differentiation in the internal architectural patterns of mouth bars. Accordingly, their internal aggradational styles can be classified into vertical aggradation, progradation, and lateral aggradation. For an individual mouth bar, the developmental model of its internal architecture shows spatial differentiation, featuring vertical aggradation-predominated central part, progradation-dominated front end, and lateral draping and aggradation-prevalent side wings. This study provides a theoretical basis for the fine-scale characterization of the internal architectures of mouth bars in fluvial-dominated deltas while also serving as a guide for analyzing the subsurface architectures of mouth-bar reservoirs.

Beach-bar sandbodies are important hydrocarbon reservoirs formed under complex and varied hydrodynamic mechanisms. However, due to the limitations of data on outcrops and modern analogs, the understanding of their developmental processes, geometric morphologies, dynamic evolutionary patterns, and superposition within internal architectures remains unclear. Given this, we analyze the sedimentary evolution and hydrodynamic mechanisms of typical shore-normal, linearly distributed nearshore bars using sedimentary numerical simulations combined with modern analogs. Furthermore, we delineate the developmental and evolutionary patterns of these typical nearshore bars. The results show that a typical marine nearshore bar undergoes five stages of development: the formation of tapered bars, the development of crescentic bars, and the formation, expansion, and developmental termination of a banded compound bar. Modern analogs reveal bars at various developmental stages, which were formed under diverse coastal hydrodynamic conditions. Tapered bars and crescentic bars are a series of small-scale bars that are roughly equally spaced. The tapered bars evolve into crescentic bars due to the continuous erosion from uprush and longshore currents. In between the tapered and crescentic bars, there exhibit inter-bar rip channels and backflow trenches on the top. Both bar types represent typical topset deposits. Over time, the crescentic bars and their inter-bar rip channels receive deposits, forming a relatively uniform banded compound bar, demonstrated as typical lateral depositon This bar, after widening and thickening under the action of onshore and bottom currents, finally emerges above water and constitutes barrier shorelines. The internal architecture of a compound bar, which may comprise several tapered bars, crescentic bars and inter-bar channels, displays the tapered bar, interbar channel and tapered bar deposits superimposition or the crescentic bar, interbar channel and crescentic bar deposits superimposition that, corresponding to thick-thin-thick sequences on profiles.