Application of Hierarchical Clustering Endmember Modeling Analysis for Identification of Sedimentary Environment in the Houtao Section of the Upper Yellow River

The unmixing of grain-size distribution (GSD) with multivariate statistical analysis provides insight into sediment provenance, transport processes and environment conditions. In this article, we performed hierarchical clustering endmember modeling analysis (CEMMA) to identify the sedimentary environment of fluvial deposits at core HDZ04 drilled in the paleofloodplain on the north bank of the upper Yellow River. The CEMMA results show that four end members can effectively explain the variance in the dataset. End-Member 1 and End-Member 2 are polymodal and dominated by silty clay, and they are associated with the suspended load. End-Member 3 is composed of fine sand and silt, and medium-coarse sand makes up the majority of End-Member 4, corresponding to a mixed saltation load and bed load, respectively. Combined with the end-member scores, we constructed energy values to further divide the core samples into different depositional environments. Unit 2 and unit 5 have a high proportion of coarser end-member components, presenting a shallow channel and a high-energy channel environment, respectively. Unit 1 and unit 3 are composed of fine-grained silt and clay and are dominated by finer end-member components, which can be interpreted as a floodplain situation. Unit 4 is characterized by frequent fluctuations in grain-size composition and energy values, indicating the transition from a high-energy river channel to floodplain deposits. For the channel sedimentary environment, the accumulation rate was relatively low (0.32 mm/yr) due to the frequency migration of the channel. A high accumulation rate of the fluvial deposits had occurred in unit 1 during 1.6 Ka (4.35 mm/yr), which was a response to the influence of increased fluvial instability and human activity during the late Holocene.