大连石河地区坡洪积物粒度特征与沉积环境分析

Grain-Size Characteristics and Sedimentary Environment Analysis of Slope-Pluvial Deposits in Shihe Area, Dalian

摘要: 坡洪积物作为坡积和洪积作用下的沉积类型，是分析第四纪环境变化的良好载体。本文基于大连石河地区坡洪积剖面16个样品的粒度分析，探讨其沉积环境，结论如下：(1) 剖面除砾石外，以粉砂为主，均值为55.30%。第①~③黏土含量略高，指示水动力减弱、气候略干。第④层粗颗粒富集，含大砾石，黏土含量最低，反映环境湿润，洪水突发、水动力强劲。第⑤~⑦层平均粒径变细，粗砂含量升高，属稳定低能环境叠加片流。第⑧层粗砂含量最高，粉砂低且含砾石，为季节性洪水期粗粒快速堆积产物。(2) 平均粒径(4.14~6.98 Φ)垂向波动显著，水动力多变。分选系数均值5.36，分选极差，与野外观察的颗粒混杂、砾石磨圆度低且多呈棱角状、分选差的特征高度一致，为典型近源快速堆积。偏度以正偏、近对称为主，指示洪水粗颗粒沉积与后期细颗粒填充共存。第⑧层低峰态，粗粒富集且分选差，反映极端强降水事件。(3) 粒度波动指示气候变化控制沉积动力，频率曲线多峰，反映沉积动力充足且复杂，为坡面重力、片流作用与区域突发性洪水沉积事件的叠加。

Abstract: Slope-pluvial deposits, as a transitional deposit resulting from the combined action of slope processes and fluvial processes, serve as an excellent indicator for analyzing Quaternary environmental changes. Based on a granulometric analysis of 16 samples from a slope-pluvial profile in the Shihe area of Dalian, this study investigates its depositional environment. The conclusions are as follows: (1) The profile is dominated by silt (mean: 55.30%), excluding gravel. Layers 1 - 3 exhibit slightly higher clay content, indicating weakened hydrodynamics and a slightly drier climate. Layer 4 is characterized by coarse-particle enrichment, including large gravels, and the lowest clay content, reflecting a wetter environment with sudden flooding events and strong hydrodynamics. Layers 5 - 7 show a finer average grain size yet elevated coarse sand content, interpreted as a stable, low-energy environment overprinted by sheetwash. Layer 8 contains the highest coarse sand content, low silt content, and includes gravels, representing rapid deposition of coarse material during seasonal flood events. (2) Mean grain size (4.14~6.98 Φ) shows significant vertical fluctuation, indicating highly variable hydrodynamics. The mean sorting coefficient (5.36) indicates extremely poor sorting, consistent with field observations of poorly sorted, angular to subangular gravels with low roundness-characteristic of typical proximal rapid deposition. Skewness is primarily positive to near-symmetrical, signifying the coexistence of flood-deposited coarse particles and later fine-particle infiltration. Layer 8 exhibits low kurtosis, coarse-particle enrichment, and poor sorting, reflecting an extreme high-precipitation event. (3) Grain-size fluctuations indicate sedimentary dynamics controlled by climatic changes. Multimodal frequency distribution curves reflect abundant and complex sediment transport dynamics, resulting from the superimposition of slope gravitational processes, sheetwash, and regional episodic flood deposition events.