Abrupt cooling and surface uplift at 3.6 Ma in the Northeastern Tibetan Plateau and changes in dust source region to the Chinese Loess Plateau
Abstract
The topographic growth of a region may alter circulation and potential vorticity of air masses crossing elevated terrain, which may change weathering rates, increase aridification and availability of sediments for wind to entrain. It is hypothesized that these processes may have occurred in the Qilian Shan-Nan Shan thrust belt (QS belt) region, located in the northeastern Tibetan Plateau (NETP), where deformation and aridification increased since the Miocene. However, the NETP paleoelevation history is not well-constrained. Here we investigate the NETP Plio-Pleistocene paleoelevation and paleoclimate history using oxygen and carbon stable isotopes (δ13Cc, δ18Oc) and clumped-isotope thermometry (Δ47T) of carbonates from the Yilang sediment core (YLC), retrieved from the Qinghai Lake (QL) basin. The lake core shows changes in depositional environments and abrupt northward migration of the QL basin depocenter at 3.6 Ma, when normal faulting occurred. Using Δ47T of carbonates, we used transfer functions to calculate corresponding MAAT according to the depositional environment in which they formed. From 4.59-3.74 Ma, the YLC consists of lacustrine and palustrine environments with mean δ13Cc=-3.6‰, δ18Oc=-5.0‰, Δ47T=19.7˚C, and MAAT=7.6 to 11.9˚C. From 3.7-3.6 Ma, it records lacustrine deposits with mean δ13Cc=-1.2‰, δ18Oc=-3.8‰, Δ47T=22.6˚C, and MAAT=11.4 to 15.8˚C. From 3.6-3.3 Ma, it records palustrine deposits with mean δ13Cc=-3.4‰, δ18Oc=-7.5‰, Δ47T=12.5˚C, and MAAT=-6.7 to 3.4˚C. From 3.29-2.00 Ma, it records palustrine (ponds) and loess-paleosol environments with δ13Cc=-4.1‰, δ18Oc=-6.7‰, Δ47T=15.5˚C, and MAAT=-3.1 to 7.1˚C. These results suggest MAAT of 9.5 to 13.8˚C have decreased abruptly to values of -4.9 to 5.5˚C after 3.6 Ma, when tectonic events took place not only in the QL basin, but also on the margins of the NETP, which we infer to reflect regional surface uplift of the QS belt. Using a T-elevation gradient ("lapse-rate") of -5.5˚C/km, surface uplift on the order of 2.1±1.3 km is inferred. Surface uplift of the QS belt may have reorganized atmospheric circulation and regional climate patterns, promoting the shift in desert dust source region to low elevation east Asia sources as ~3.6 Ma, observed in the Chinese Loess Plateau.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC51I0938R
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL