Late Miocene High-resolution Magnetostratigraphy And Climate Cycles In The Qaidam Basin

Lack of high-resolution long paleoclimate records, limits our understanding of the climate history of the Qaidam Basin. Although there are many paleomagnetic studies of Cenozoic strata in the Qaidam Basin, previous sampling resolution (3-5 meters) is generally low, resulting in some polarity reversal event missing and thus, uncertainties of the depositional ages. Here we present a high-resolution magnetostratigraphy and rock magnetic study of the fluvio-lacustrine sediments (Shizigou formation and Shangyoushashan formation) of the Late Miocene from the Huaitoutala section in the northeastern of Qaidam Basin, China. In addition, we compare color indicators, frequency magnetic susceptibility (χfd), isolation forcing, and the deep sea oxygen isotope records, obtained the following conclusions:(1) This set of sediments spans between ～9.9 to 5.9 Ma. Potential geomagnetic excursions were identified especially at 349 m and 359-361 m within C4r.2r, which can be well correlated to the counterparted in marine magnetic anomalies. This demonstrates that the Tibetan basin sediments have high potentials in recording high-resolution geomagnetic field signals.(2) The main magnetic signal carriers are magnetite and hematite. The type and size of the magnetic mineral particles are further clarified by the unmixing of backfield IRM(Isothermal Remanent Magnetization) curve and FORC diagram. Three magnetic components isolated by the unmixing of backfield IRM curve have peaks at 26 mT,88 mT and 330 mT, respectively, corresponding to superparamagnetic-single-domain ferrimagnetic minerals, slightly oxidized coarse ferrimagnetic minerals and hematite, respectively.(3) Spectrum results of magnetic parameters (xfd) showed that this set of sediment was deposited continuously at least on the orbital timescale. And the significant difference spectrum results of the various climate indicators nearby 8Ma;χfd was sensitivite to the strong 41kyr signal since 8 Ma, especially. The elevation caused by the uplift of the Tibetan Plateau and the increase of the latitudinal gradients are the main reason for this climate signal change.