Facies analysis of the Middle and Late Quaternary sediment infill of the northern Weihe Basin, Central China

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Abstract

ABSTRACT A detailed study of the uppermost 221 m of drill core LYH‐1 – located in the northern part of the Weihe Basin – reveals considerable environmental variety over the past 1 Myr. Studied parameters include lithofacies, sedimentological properties and micropalaeontological content of selected core‐samples. Present‐day environments in the research area have been used as analogues for past conditions. The palaeoenvironments documented in the sedimentary record are interpreted as shallow lakes, fluvial settings, soils and aeolian environments. The temporal variation of the environments indicates a rapid alternation between climate‐driven wet and dry phases, suggesting that these fluctuations are related to changes in monsoon intensity. However, on a larger temporal scale, the sedimentation and accumulation of water is also affected by local tectonics. End‐member modelling shows that the siliciclastic grain‐size distributions can be ascribed to the mixing of six distinct end‐members. Most of the sediments in core LYH‐1 have similar characteristics to the loess deposits from the Central Loess Plateau. However, the much higher sedimentation rates and sedimentary structures suggest that these sediments consist for a large part of fluvially reworked loess. A broad subdivision of the core into three main intervals can be made, tentatively dated by magnetostratigraphy. From 162 to 221 m (690–1000 ka), brackish wetland conditions with a regular influence from fluvial and/or distal alluvial fan systems prevailed. The interval 90–162 m (330–690 ka) shows more terrestrial settings with occasional hypersaline lakes. From 0 to 90 m (0–330 ka), the environment was a shallow wetland, albeit with a relatively low diversity of aquatic and terrestrial microfossils compared to the lower interval.

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