Evolution of sedimentary environment in the Eastern Henan Basin since the Late Pliocene

The Eastern Henan Basin is situated within the downstream alluvial plain of the Yellow River, harboring an impressive accumulation of over 500 m of fluviolacustrine strata since the Pliocene. However, the evolutionary characteristics and driving factors of the sedimentary environment in this region remain unclear due to a lack of reliable chronological constraints on the sedimentary sequence. Here, two cores were retrieved from Hangkonggang (HKG, 303.5 m) and Baisha (BS, 320.2 m) in the Eastern Henan Basin for comprehensive analyses of chronology and sedimentology. A combination of paleomagnetism, electron spin resonance (ESR), and optically stimulated luminescence (OSL) dating results indicates that sediments of two boreholes were accumulated spanning the last 3.48 Ma. Grain size distributions (GSDs) of typical sedimentary facies show that the boreholes predominantly encompass three types of sedimentary facies: riverbed, levee, and floodplain. Downcore variations of mean grain size (MGS) reveal that the sedimentary environment in this basin evolved from a dominant riverbed setting during the late Pliocene (3.48-2.72 Ma) to alternations between the floodplain and levee facies during the early Pleistocene (2.72-1.25 Ma) and subsequently between the riverbed, levee, and floodplain after 1.25 Ma. It was closely associated with the decrease in East Asian monsoon precipitation at 2.72 Ma and the increase at 1.25 Ma. Notably, the abrupt coarsening of MGS after 1.25 Ma was synchronized with the formation of the Sanmenxia terraces, implying the significant influence of the evolution of the Yellow River. Our results suggest that the sedimentary environment of the Eastern Henan Basin was predominantly affected by the stepwise evolution of the East Asian monsoon since 3.48 Ma and complementary landform transformation of the Yellow River since at least 1.25 Ma.