The assessment of chronological evolution of the channel functional units is an imperative aspect to understand the channel avulsion nature and planform change. In this study, the channel functional units (channel, aggradational and abandoned) and their distinct micro-morphologies have been assessed through the landuse and landcover classification, terrain analysis, lithostratigraphic records and fluctuating flow regimes in the ancient delta fan of the Subarnarekha basin. The distinct micro-morphological features of the functional units have been formed and evolved under the dominance of fluvial environment coupled with the fluctuating strength of Indian summer monsoon (ISM) and regression phase of sea-level since 6000 years before present (YBP). However, the borehole lithostratigraphic records reveal that the ancient delta fan was formed under the different fluvio-marine depositional environments of the marine transgression, regression and stillstand phases since 32,200 YBP. The riverbed of the recent course is ascended than the palaeo-courses due to declining trends of water discharge and sediment load in the last four decades as well as during the late Holocene mega-drought event. The channel unit and abandoned unit have been transformed into the aggradational unit with micro-morphologies of point bar, fill-terrace, and natural levee under the influence of channel avulsion and bulk of sediment deposition related to the fluctuating flow regime and base level of erosion. The micro-morphological features (marshes, oxbow lakes and meander neck-cuts) of the abandoned unit have been modified from the channel unit after diversion of the recent course from the palaeo-course owing to extreme discharge and valley drowning during lowstand.

中文翻译：

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印度Subarnarekha盆地三角洲扇古河道与古水文地貌环境相关的年代学演化

评估渠道功能单元的时间演变是了解渠道破坏性质和平面变化的必要方面。在这项研究中，通过Subarnarekha盆地古代三角扇的土地利用和土地覆盖分类，地形分析，岩石地层记录和波动的流型，评估了河道功能单元（河道，聚集的和废弃的）及其独特的微观形态。自从6000年前（YBP）以来，在河流环境的主导下，加上印度夏季风的波动强度（ISM）和海平面的回归阶段，已经形成并演化了功能单元的独特微观形态特征。然而，钻孔岩相地层记录表明，自从32,200 YBP以来，古代三角洲扇形构造是在海侵，回归和静止期的不同潮汐-海洋沉积环境下形成的。由于最近四十年以及全新世晚期特大干旱事件中水和沉积物负荷的下降趋势，最近河道的河床比古河道上升。在与水流波动和侵蚀基本水平有关的河道侵蚀和沉积物堆积的影响下，河道单元和废弃单元已转变成具有点状条形，充填层和天然堤防微观形态的聚集单元。 。微观形态特征（沼泽，