A seven-million-year hornblende mineral record from the central Chinese Loess Plateau

Abstract

Previous studies of the late Cenozoic erosion rate have yielded different views—long-term stable rates or a significant increase at climate transitions—leading to uncertainty concerning the hypothesized global erosion rate controlled by either tectonic uplift or climatic changes. Here, we present a seven-million-year hornblende mineral record along the Lingtai section of the Chinese Loess Plateau. By examining the spatial distribution of hornblende minerals in seven desert basins, which are potential loess source areas, we constructed a ratio of hornblende versus total heavy minerals to reflect past changes in physical/chemical weathering strength. Our results demonstrate that the ratio has generally increased since 7 Ma, with three significant shifts recorded at 2.6 Ma, 1.4 Ma and 0.5 Ma linked to the onset, continuation and expansion of the Northern Hemisphere glaciation, respectively. Given that chemical weathering during the diagenetic history produces a trend of smoothly increasing hornblende migrating upwards, the three shifts at these boundaries can be interpreted as changes in the bedrock erosion rate on the northern Tibetan Plateau, which may be related to tectonic uplift events and incision of the Yellow River. Evidence presented here supports the idea of coupling between climate change, tectonic uplift and regional erosion.

Glacial–interglacial change in chlorite concentration from the Lingtai section in the Chinese Loess Plateau over the past 1.2 Ma and its possible forcing mechanisms

“…Chlorite concentration in the fine versus coarse grain-size fractions in the Lingtai section, which is a proxy indicator for atmospheric circulation. Muscovite (this study) (b) and hornblende (c) (He et al, 2017) concentrations along the same section. (d) Magnetic susceptibility values (Chen et al, 2006).…”

“…Variations in hornblende and muscovite minerals in the same profile provide further evidence that chemical weathering during diagenesis played a minor role in shaping the glacial–interglacial chlorite pattern. Our previous studies have shown that hornblende concentrations are between 0 and 2.5% over the past 1.2 Ma in the Lingtai section (He et al, 2017), a range equivalent to that of the chlorite concentration. However, the hornblende concentrations do not display glacial–interglacial changes (Fig.…”

“…On the basis of a large data set of mineralogical assemblages, Nie and Peng (2014) have suggested that the dust provenance remained unchanged between glacial loess and interglacial paleosol at least for the past 400–500 ka. Further temporal-spatial dust studies using single-species plagioclase (He et al, 2016) and hornblende (He et al, 2017) have suggested that the deserts on the northeastern Tibetan Plateau dominated the dust material contribution to the CLP in the late Pleistocene. This highlights the significance of the dust route along the northeastern Tibetan Plateau.…”

“…Mineralogical studies provided another clue to the transport pathway of Asian dust from potential dust sources to the loess deposits (Nie et al, 2013; Nie and Peng, 2014; He et al, 2016, 2017). On the basis of a large data set of mineralogical assemblages, Nie and Peng (2014) have suggested that the dust provenance remained unchanged between glacial loess and interglacial paleosol at least for the past 400–500 ka.…”

Evolution of the Upper Yellow River as Revealed by Changes in Heavy-Mineral and Geochemical (REE) Signatures of Fluvial Terraces (Lanzhou, China)

“…The abundance of amphibole indicates prominent contributions from basement rocks [24,47], with the amphibole series forming in a wide range of temperature and pressure conditions in igneous and metamorphic rocks [48]. A ratio of amphibole versus total heavy minerals has been used to reflect past changes in the origin of loess from the central Chinese Loess Plateau [49]. Because more than 73% of the heavy-mineral fraction is composed of amphibole plus epidote in Yellow River terraces, we here use the ratio between these two dominant minerals as a tracer of provenance change.…”