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The Plio-Pleistocene evaporitic lacustrine succession in the Qaidam Basin, which was recovered by drill core SG-1, provides the material for understanding the maturation of dolomite since dolomite is present in the core from 7.6 to 870 m depth, spanning a time interval of 0.1–2.8 Ma. Twenty-two samples were collected at different burial depths. The samples were examined by thin-section petrography and SEM for textures, and analyzed for mineralogy (XRD), trace elements and carbon and oxygen isotopes. The main mineral compositions of each sample are dolomite, quartz, halite and gypsum. Dolomite is mostly scattered with spheroidal to ellipsoidal shapes, several microns in diameter, partially encapsulated in gypsum. Microbial micropores and calcified microorganisms are observed on and within the dolomite crystals and in the thin sections. The degree of ordering of the dolomite gradually increases with burial depth, which basically conforms to the first-order reaction function. The crystal constants of dolomite decrease with burial depth, indicating recrystallisation with increasing overburden. The trace elements of the dolomites are significantly different from those of hydrothermal dolomites, but close to lacustrine microbial carbonate. It is concluded that the dolomites in core SG-1 are mainly authigenic, with microbial processes a likely facilitator of dolomite precipitation. The dolomite formed and then evolved in crystal structure during burial, gradually approaching ordered stochiometric dolomite. This study gives clues to link microbial dolomite to the massive ideal dolomite rock encountered in the geological record. • The Plio-Pleistocene dolomite in the core SG-1 is authigenic in the Qaidam paleo lake. • The formation of dolomite crystals in the core SG-1 was associated with microbially mediation process. • The microbial dolomite crystals continued to mature toward ideal state during burial. [ABSTRACT FROM AUTHOR]

Different from the ITCZ-driven global tropical monsoon, the development of a monsoon-dominated climate within previously subtropical arid Asia has conventionally been regarded as marking the onset of a modern-like monsoon over East Asia. This monsoon has increasingly been reported as having appeared in the Eocene or older and linking with different forcings. Here we present robust climatic records from well-dated fluviolacustrine sediments from the eastern central Tibetan Plateau which demonstrate that such a monsoon was not established in the northern subtropical area (∼32-33oN) until at least ∼35 Ma, rather a Mediterranean-type-like climate toward drier prevailed. Numerical modelling supports that neither the existence of an Andes-like Gangdese Mts. along Tibet southern margin, nor an elevated south-central Tibet, nor an increased atmospheric CO 2 concentration, were sufficient to drive the expansion of the Asian tropical monsoon northward to ∼32oN in Asia in the Eocene. • The Paleogene succession on the eastern central Tibetan Plateau was determined at ∼53–35 Ma. • Asian monsoon did not expand to northern subtropical East Asia before 35 Ma. • Forcing factor for late Eocene monsoon could not enhance monsoon to expand to northern subtropics. [ABSTRACT FROM AUTHOR]