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associated with significant uplift of the Tibetan Plateau in the Late Miocene Microbial lipid records of highly alkaline deposits and enhanced aridity

ABSTRACTSaline alkaline sediments and soils are widespread in arid and semiarid regions, but their occurrence in ancient dry periods remains unknown due to the lack of a suitable proxy. On the basis of investigations of modern Chinese soils with a wide pH range of 3.5–9.1, we sug-gest that the microbial lipid ratio R i/b , i.e., the abundance ratio of archaeal isoprenoid GDGTs (glycerol dialkyl glycerol tetraethers) to bacterial branched GDGTs, indicates the presence of drought-induced alkaline deposits in terrestrial settings. The R i/b is invariant in modern soils with pH 600 mm, but it increases sharply at higher pH values and lower mean annual precipitation (<600 mm). In contrast, the CBT index (the cyclization ratio of branched GDGTs), which has been proposed to reﬂ ect envi-ronmental pH in other contexts, appears to be relatively stable in the highly alkaline Chinese soils from semiarid and arid regions investigated. We further explore the R