Initiation of the Mekong River Delta and paleo-environments of lowlands in Cambodia during the Holocene

为了阐明湄公河三角洲的起源和柬埔寨全新世低地的古环境，在柬埔寨三个地点进行了钻探调查和地震调查。低地第四纪地层至少由两个海相层序组成：全新世和晚更新世沉积，以不整合为界。全新世沉积物由河流沉积、潮汐-河流沉积和潮间带-潮下滩沉积组成。位于越南边境附近的PSG岩心含有沉积于潮间带-潮下滩环境的海洋沉积物，年龄为8000-8300卡尔BP，这意味着当时柬埔寨的海岸线更偏向陆地。这次海侵发生在8500-8400卡BP之间，海平面急剧上升，与8.4-8.5ka的融水脉动相对应。洪水过后，湄公河三角洲在8.3ka左右启动，并随着广泛分布在金边周围的5m厚泥炭沉积物的堆积而不断进积。从6.7ka至今，在人类活动的影响下，潮汐为主的环境转变为河流为主的环境。

Drilling survey at three sites and seismic survey in the Mekong River in Cambodia were conducted to clarify the initiation of the Mekong River Delta and paleo-environments of lowlands in Cambodia during the Holocene. Quaternary strata in the lowlands consists of at least two marine successions: Holocene and late Pleistocene sediments, bounded by an unconformity. Holocene sediments consist of fluvial sediment, tidal-fluvial sediment, and intertidal to subtidal flat sediment. PSG core located near the border of Vietnam contains marine sediments deposited at inter-to sub-tidal flat environment with ages of 8000-8300 cal BP, meaning that the shoreline was located more landward in Cambodia at that time. This marine inundation was occurred by a rapid sea-level rise during 8500-8400 cal BP abruptly, which will be correlated with 8.4-8.5 ka meltwater pulse. Just after the inundation, the Mekong River Delta was initiated at about 8.3 ka and has prograded with aggradational accumulation of 5m-thick peaty sediments distributed widely around Phnom Penh. Tide-dominated environment was changed into more fluvial dominated environment since 6.7 ka to the present with influences of human activities for the last 2 ka.