Abstract:

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.

Key words: sedimentary numerical simulation, sedimentary architecture, hydrodynamic mechanism of deposition, nearshore bar, marine beach-bar, modern sediments