滹沱河古河道晚第四纪高分辨率地层层序及沉积特征

HIGH RESOLUTION STRATIGRAPHIC SEQUENCE AND SEDIMENTARY CHARACTERISTICS IN LATE QUATERNARY OF HUTUO RIVER PALEOCHANNEL

高分辨率层序地层学摆脱了与海平面变化相联系的束缚,对于远离海洋的陆相地层尤其是河流相地层而言,具有明显的理论优势和实践意义,更适用于内陆流域第四纪地层的划分和对比。本文运用高分辨率层序地层学理论和分析方法,利用滹沱河冲洪积扇区典型钻孔的岩芯记录、粒度数据和光释光年龄建立了滹沱河古河道晚第四纪的高分辨率地层层序,为滹沱河流域晚第四纪河流相地层的划分和对比提供了重要基础。结果表明:滹沱河古河道晚第四纪沉积物为一套辫状河沉积,发育河道和泛滥平原两种沉积亚相,其粒度参数统计特征存在明显差异;滹沱河古河道晚第四纪地层可识别出4个超短期旋回和2个短期基准面旋回,2个短期旋回之间的层序界面处于短期基准面的最低值,具有地层对比意义。在该界面之上发育厚层叠置的辫状河道沉积,界面之下发育厚层、富含钙质结核的干旱冲积平原沉积。该界面特征明显、易识别,在整个古河道发育区可对比,其界面年龄约为76 ka。

High-resolution sequence stratigraphy has been freed from the constraints associated with sea-level change.It has the obvious theory superiority and the practice significance for the terrestrial formation far from the ocean,especially for the fluvial facies.In this research,high-resolution sequence stratigraphy theory and analytical methods are used to establish high resolution stratigraphic sequence of Late Quaternary of Hutuo River.It provides an important foundation for the Late Quaternary fluvial stratigraphic division and correlation in Hutuo River area.The results indicate that the Late Quaternary sediments of the Hutuo River are a set of braided river deposits,showing two sedimentary subfacies:river channel facies and flood plain facies.The sta・tistical characteristics of grain size parameters are obviously different between two subfacies.Four ultra-short cycles and two short-term base level cycles are identified.The sequence boundary between the two short-term cycles is at the lowest of the short・term base level,which has the significance for chronostratigraphic correla・tion.The age of the sequence boundary is about 76 ka.