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Orbital-scale East Asian summer monsoon (EASM) variability has been extensively investigated in Pliocene-Quaternary loess and marine sediments. In recent years, middle-late Miocene orbital-scale EASM variability has been depicted in lacustrine deposits from NE Tibetan basins, showing a dominant cyclicity of ∼100 kyr eccentricity. However, EASM variability during the early Miocene time remains poorly understood. Here, we investigate the sedimentary record of the early Miocene Xianshuihe Formation, Lanzhou Basin, in order to further constrain the NE Tibetan hydrological evolution and link it to orbital-scale monsoonal variability. By analyzing the lithology, magnetostratigraphy and cyclostratigraphic records of a 270-m section, we show that Lanzhou lake expansion cycles were consistently dominated by ∼100 kyr eccentricity forcing in early Miocene, except for the ∼20.8-19.8 Ma interval showing dominant obliquity control. These records are in agreement with deep-sea oxygen isotopic records, and are potentially linked to Antarctic ice sheet modulations related the precession amplitude modulation by eccentricity. A weakening of weathering intensity in Lanzhou Basin after 20.8 Ma may be attributed to orogenic barriers for westerly moisture and weakened surface temperature resulted from the rapid uplift of NE Tibet and surrounding mountains in the time interval of late Oligocene-early Miocene. • Eccentricity forcing Lanzhou lake evolution of ∼21.6-20.8 Ma and ∼17.2-19.8 Ma. • Obliquity forcing Lanzhou lake evolution between ∼19.8 and 20.8 Ma. • Weakening of the weathering intensity in Lanzhou Basin after 20.8 Ma. [ABSTRACT FROM AUTHOR]

The latest Paleocene to early Eocene was an interval of globally warm climate. However, the driving mechanisms regulating climate across this interval remain unclear due to the paucity of well-dated and stratigraphically continuous records from terrestrial basins. In this study, we present a continuous ∼430-m lacustrine core record from the QY-1 borehole spanning the late Paleocene-Early Eocene in the Subei Basin, East China. This unique record can be used to better elucidate the response of terrestrial sedimentation to astronomically forced climate change. A 4.54 Myr long astronomical time scale spanning 57.1 to 52.56 Ma is constructed for the second member of the Funing Formation (E f 2) based on magnetostratigraphy and cyclostratigraphy. Low-latitude summer insolation via eccentricity modulation of precession controlled paleolake evolution in the basin during the studied interval. At the same time, we show that the climate system during this greenhouse state was sensitive enough to respond to the small changes in insolation associated with 200-kyr eccentricity cycles. Evidence from gamma ray data suggests that the climate in the Subei Basin changed from warm and humid to arid at ∼54.1 Ma. • Establish an ATS with magnetostratigraphy and cyclostratigraphy for E f 2 in Subei Basin, East China. • A record of astronomically forced climate changes in the late Paleocene to early Eocene terrestrial succession in the Subei Basin was conformed. • The climate system during this greenhouse state was sensitive enough to respond to the small changes in insolation associated with 200-kyr eccentricity cycles. [ABSTRACT FROM AUTHOR]

The middle to late Eocene marked a key transition from greenhouse to coolhouse. However, a lack of high-resolution and temporally well-constrained continental records hinders our understanding of the driving mechanisms of climate change during this period. In this study, we combined magnetostratigraphy and cyclostratigraphy to establish a high-resolution astronomical time scale spanning the middle to late Eocene (∼42.4 Ma to ∼35.3 Ma) through a 214-m succession of the continental Honghe Formation in the Weihe Basin, North China. Our results show that variability in the hydroclimate of the Weihe Basin at this time was dominated by eccentricity (∼405 kyr and ∼100 kyr) and obliquity (∼1.15 Myr and ∼173 kyr) forcing. Meridional insolation gradient variations controlled by obliquity, and low-latitude summer insolation via eccentricity modulation of precession jointly controlled paleolake evolution in the basin during the ∼42.4 Ma to ∼35.3 Ma interval, rather than being controlled by eccentricity or obliquity as previously inferred. Our study provides new insights into the driving mechanisms of orbital-scale hydroclimate evolution in continental lake basins during the ice-free middle to late Eocene. • Astronomical time scale for the middle to lower Honghe Formation of the Weihe Basin, North China. • Obliquity and Eccentricity jointly controlled paleolake evolution in the Weihe basin during middle to late Eocene. [ABSTRACT FROM AUTHOR]