East Asian summer monsoon (EASM) and winter monsoon (EAWM) variability on orbital time scales during the late Miocene remains poorly constrained. Climate models reveal variable responses of the EASM and EAWM to astronomical forcing, but there is a lack of empirical evidence from the geological record to validate these results. In this study, we used time series analysis to reconstruct climatic changes and orbital forcing from eolian and lacustrine sediment archives from NE Tibet during the late Miocene. Analysis of magnetic susceptibility data demonstrates that lacustrine sediments in the Tianshui Basin (Yaodian section) show dominant ∼100 k.y. eccentricity forcing in the late Miocene (ca. 10.25−8 Ma). In contrast, eolian deposits in the Jianzha Basin (Jiarang section) show significant 405 k.y. eccentricity and 41 k.y. obliquity forcing over the same interval with weak evidence for ∼100 k.y. eccentricity cycles. Grain size data from the Yaodian section support a lacustrine origin of these sediments and also support previous work demonstrating aridification in NE Tibet after ca. 8.6 Ma. Taken together, our analyses highlight markedly different orbital forcing responses of lacustrine and eolian sedimentary systems during the late Miocene. We suggest that the dominant ∼100 k.y. lacustrine cycles in the Yaodian section, which were mainly controlled by EASM variability, may have been linked to Antarctic ice sheet and/or low-latitude insolation modulations related to precession amplitude modulation by eccentricity. In contrast, the orbital signature of eolian sediments in the Jiarang section was significantly influenced by the EAWM and can be linked to variability in meridional temperature/pressure gradients.

This content is PDF only. Please click on the PDF icon to access.
You do not currently have access to this article.