Central Asian moisture modulated by proto-Paratethys Sea incursions since the early Eocene

Abstract

The establishment and evolution of the Asian monsoons and arid interior have been linked to uplift of the Tibetan Plateau, retreat of the inland proto-Paratethys Sea and global cooling during the Cenozoic. However, the respective role of these driving mechanisms remains poorly constrained. This is partly due to a lack of continental records covering the key Eocene epoch marked by the onset of Tibetan Plateau uplift, proto-Paratethys Sea incursions and long-term global cooling. In this study, we reconstruct paleoenvironments in the Xining Basin, NE Tibet, to show a long-term drying of the Asian continental interior from the early Eocene to the Oligocene. Superimposed on this trend are three alternations between arid mudflat and wetter saline lake intervals, which are interpreted to reflect atmospheric moisture fluctuations in the basin. We date these fluctuations using magnetostratigraphy and the radiometric age of an intercalated tuff layer. The first saline lake interval is tentatively constrained to the late Paleocene-early Eocene. The other two are firmly dated between ∼46 Ma (top magnetochron C21n) and ∼41 Ma (base C18r) and between ∼40 Ma (base C18n) and ∼37 Ma (top C17n). Remarkably, these phases correlate in time with highstands of the proto-Paratethys Sea. This strongly suggests that these sea incursions enhanced westerly moisture supply as far inland as the Xining Basin. We conclude that the proto-Paratethys Sea constituted a key driver of Asian climate and should be considered in model and proxy interpretations.

Paleogene evolution and demise of the proto‐Paratethys Sea in Central Asia (Tarim and Tajik basins): Role of intensified tectonic activity at ca. 41 Ma

“…In the Xining Basin further east, deposition of the late Palaeocene–early Eocene thick carbonaceous gypsum may coincide with the transgression of the 1st Paleogene sea incursion (ca. 59–57 Ma) in the SW Tarim Basin (Meijer et al, ). The subsequent sudden increase in lacustrine deposits at ca.…”

“…The short‐term change of depositional systems representing moisture shifts in the Qaidam and Xining Basin also do not correspond with global climate events (e.g. Meijer et al, ). Therefore, these findings of moisture fluctuations in the Xining and Qaidam basins coeval with sea transgressions and regressions in the Tarim Basin strengthen the hypothesis that the proto‐Paratethys Sea was an important mechanism influencing the westerly flux of moisture into Asia during the Paleogene.…”

“…The subsequent sudden increase in lacustrine deposits at ca. 45.7 Ma is closely linked with the transgression of the 2nd Paleogene sea incursion (Bosboom et al, 2014a;Meijer et al, 2018). An aridification step at ca.…”

“…At shorter time scales, Paleogene sea transgressions and regressions may have modulated moisture supply provided by the westerlies to Central and East Asia. To test this, we compared our results constraining the evolution of the proto-Paratethys Sea to the long-term and short-term humid and arid phases existing in the palaeoenvironmental records further east in the Tarim Basin (this study), Qaidam Basin (Bao et al, 2017;Song et al, 2013;Ye et al, 2016) and the Xining Basin (Meijer et al, 2018).…”

“…39.7 to 36.7 Ma but did not reach south Tarim where basin infilling was particularly strong (Figures 10 and 11c). The 3rd Paleogene sea incursion does not correspond in timing with the last Siberian F I G U R E 1 0 Simplified regional lithostratigraphic framework of the Paleogene sea incursions in the Tarim and Tajik basins, compared temporally with the regional tectonic events and related magmatism (Chapman et al, 2018 and references therein; slab break-off data from Negredo et al, 2007), palaeoenvironmental changes recorded in the Qaidam (Bao et al, 2017;Song et al, 2013;Ye et al, 2016) and Xining (Abels et al, 2011;Hoorn et al, 2012;Meijer et al, 2018) basins, global sea level curve (Kominz et al, 2018 andHaq et al, 1987) and global climate events (benthic δ 18 O record of Cramer et al, 2009). The approximate relative changes in sea level in the Tarim Basin are shown by thick solid lines.…”