差异可容纳空间背景下湖相层序样式与三角洲形态响应: 鄱阳湖与岱海湖对比研究*

近年来随着层序地层学研究逐步走向定量化,将其标准化已成为沉积学界的共识。可容纳空间作为层序标准化中重要的参数之一,受到越来越多的关注。然而,不同可容纳空间背景下汇水盆地的坡度和沉积供给量均存在差异,其复杂的沉积过程造成当前研究难以准确刻画出对应层序参数演化与三角洲形态之间的耦合关系。本次研究选取中国2个典型的湖泊—三角洲进行对比研究,包括较为平缓的鄱阳湖赣江三角洲(地层倾角小于1°)与坡度相对较大的岱海湖周缘三角洲(地层倾角3°~10°)。通过对近30年不同水位期卫星照片解译,并将其与现代沉积剖面解释相结合,明确了: (1)可容纳空间快速增加背景下,湖岸线变化相对稳定,但平面影响范围较小; 三角洲在低位域(LST)时期主要发育帚状或朵状前积体,在湖侵域(TST)和高位域(HST)时期主要表现为朵叶状或鸟足状前积体。(2)缓坡低可容纳空间背景下,湖岸线变化较为剧烈,并且影响范围较大; 三角洲在低位进积域(RST)时期多以鸟足状前积体为主,内部发育指状沙坝,高位域(HST)时期表现为鸟足状前积体,同时沿岸沙坝较为发育。综合上述认识,结合沉积正演模拟结果,在经典层序和滨岸坡折岸线迁移模式的基础上,分别针对可容纳空间快速增加背景和低可容纳空间背景,建立了对应的层序—三角洲发育模式,并从长短周期尺度分析了不同可容纳空间背景下层序—沉积演化过程的控制因素。

Lacustrine sequence patterns under different accommodation space settings and the responding delta morphology: a comparison of Poyang Lake and Daihai Lake

Nowadays,stratigraphic stratigraphy has gradually moved toward quantification,and its standardization has become a consensus in the sedimentological community. As one of the essential parameters in stratigraphic standardization,it has received more and more attention in recent research. In this study,two typical lacustrine deltas in China were selected for comparative study,including the Ganjiang River delta of Poyang Lake with a relatively slope(dip angle<1°),and the deltas around Daihai lake with a relatively slope slope(dip angle 3°~10°). Based on the interpretation of satellite photographys of different water levels in the past 30 years and the interpretation of modern outcrop/trench profiles,this study examines their sedimentary evolution and points out their facies distribution pattern: (1)In the high accommodation space area,the changes of lake shoreline are relatively stable in a setting of rapid increase of accommodable space,but the planar influence range is limited. The responding delta mainly developed a broom-shaped or fan-shaped geometry during the low lake-level systems tract(LST),and lobate shape(high sedimentary supply rate)or bird-foot shape(low sedimentary supply rate)during the transgression systems tract(TST)and high lake level systems tract(HST). (2)The lake shoreline changes drastically in a low accommodation space area,and the influence range is more extensive. The responding deltas are observed to show a bird-foot shape in the low lake-level regression systems tract(RST),and are dominated by finger-sharped bars. In contrast,in the transgression systems tract(TST)period,the deltas are bird-foot-shaped and are dominated by offshore bars. Based on the above observations,the results of forward simulation,as well as insights from the classical stratigraphic sequence and shoreline migration process,this study establishes corresponding stratigraphic stacking pattern-deltaic development modes for high and low accommodation space settings,respectively. Furthermore,the controlling factors of sequence-sedimentary evolution in different accommodation settings are analyzed from the persepctive of long-term and short-term scales.