环境敏感粒度组分在识别三角洲朵叶期次中的应用

Application of environmentally sensitive grain-size populations in identification of formation orders of delta lobes

以内蒙古黄旗海属内陆断陷型湖盆中面积最大且朵叶期次明显的大河湾三角洲为研究对象,通过野外采集的109个样品粒度特征分析,结合近200 a来该地区的水文资料,提取并对比环境敏感粒度组分,分析大河湾三角洲不同朵叶形成的水动力条件和沉积相带的异同,确定不同朵叶之间的叠置关系,从而识别出大河湾三角洲的发育期次。在此基础上,通过对比分析野外探槽岩相沉积特征、粒度特征,结合地形坡度变化,研究不同期次朵叶顺物源方向上的沉积构型变化特征。研究结果表明:大河湾三角洲经历了3次显著不同的水运力环境,形成了3期不同的朵叶,各朵叶在平面形态及沉积序列上有着明显的区别,其中以第1期水动力最稳定,形成的朵叶分布范围最广,面积最大;第2期水动力不稳定,朵叶最不发育;第3期水动力渐弱,以发育多个摆动强烈向前叠置的朵叶为特征。

The grain-size populations with environmentally sensitive components extracted from 109 samples in Dahewan delta which has the largest area and the most obvious stages combined with hydrologic data in 200 a were applied to distinguish the hydrodynamic condition and depositional environment from different lobes, and the superposition relationship and development period were confirmed, the sedimentary configuration in downstream direction of different lobes was studied through sedimentary characteristics and grain-size characteristics in filed trenches.The results show that hydrodynamic environment of Dahewan delta has changed three times, caused three different periods of lobes with different morphologies and sedimentary sequences. In the first period, the lobes have the most extensive distribution and the largest area under the stable hydrodynamic condition. In the second period, the lobes are weakly developed for the unstable hydrodynamic condition. In the last period, the lobes grow forward with frequent lateral sway under the decrescendo hydrodynamic condition.