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Currently mechanisms for the onset of the widespread aeolian dust accumulation in the Chinese Loess Plateau since 8–7 Ma remain elusive. In this study, we compile 11 records of climate (14–7 Ma) and tectonic activity of the Tibetan Plateau and its adjacent areas (15–6 Ma). The results suggest that strong tectonic activity in the northeastern Tibetan Plateau has produced massive debris and dust, which was deposited in the piedmont basins and reworked by weathering and fluviolacustrine erosion. At the same time, global cooling and uplift of the Tibetan Plateau over the period of 14–7 Ma intensified the East Asian winter monsoon and westerly winds (westerlies) while weakening the Asian summer monsoon, which led to the spread of dry land vegetation and aridification in interior China. Sediments in the piedmont basins were then exposed in the aridity and transported by the westerlies to the Chinese Loess Plateau and the North Pacific. We suggest that tectonic activity in the northeastern Tibetan Plateau and shifting global climate together triggered the widespread aeolian dust accumulation in the Chinese Loess Plateau and the North Pacific since 8–7 Ma. [ABSTRACT FROM PUBLISHER]

Abstract: Over the past decade, palynoflora investigation of Palaeogene and Neogene red beds and Pleistocene loess has been the focus of an increasing number of studies. Pollen extraction from sediments is a prerequisite for palynoflora investigation. This study explored a new pollen processing method and successfully extracted a large number of pollen grains from the Palaeogene red beds in the Liguanqiao Basin, Hubei Province and the Pleistocene loess from the southern Chinese Loess Plateau. There are several key steps in this new method. (1) Samples from arid to semi-arid regions are usually well cemented and should be gently crushed and sieved with 30-mesh screen for pollen analysis to maximize the number of pollen grains recovered from sediments. (2) In order to remove organic matter most effectively, samples should be heated until just boiling in ∼3% NaOH solution for not more than 5 min (3) The residue after acid–alkali treatment should be dried at 85 °C for 7–9 h to ensure that density of the heavy liquid is not diluted during the next step. (4) KI heavy liquid, with a density of 1.74–1.76, should be used to concentrate the pollen. (5) Sieving with a 7-μm stainless steel mesh resulted in the loss of few pollen grains. In contrast, sieving with a 10-μm nylon mesh resulted in loss of many small pollen grains. Importantly, this study extended the first appearance of Artemisia in China back to the Late Palaeocene, and is significant for vegetation reconstruction in the arid to semi-arid regions during the Cenozoic Era. [Copyright &y& Elsevier]

Abstract: Intense tectonic movement occurred along the northeastern margin of the Tibetan Plateau 3–4Ma. During the same time period, global climate changed from a period of stability to a period of frequent and abrupt changes, which prevented fluvial and glacial systems from establishing a state of equilibrium. Thus, it is difficult to directly attribute the 3–4Ma coarse-grained sediment accumulation in East Asia to climate change or tectonic activity. This study compares Late Cenozoic multi-proxy records from the Chinese Loess Plateau (CLP) to the low-latitude grain size, sea level and benthic δ 18O records from the South China Sea (SCS) and the high latitude grain-size record from Lake Baikal. All records suggest a steady and persistent cooling since ~4Ma, which correlates well with those cooling records from other regions around the world. This coincided in timing with the modeling results that the closure of the Central American Seaway (CAS) initiated strengthening of Atlantic meridional overturning circulation between 4.8 and 4.0Ma which led to both warming of the Northern Hemisphere (NH) and cooling of the Southern Hemisphere (SH). Cooling of the SH would induce a marked development of the Antarctic ice sheets at ~4Ma, pushing the Intertropical Convergence Zone (ITCZ) northward. This was superimposed on warming of the NH and brought more precipitation to the middle latitudes of the NH, resulting in increases in coarse-grained sediments in the Sikouzi section from the western CLP since 4.2Ma. Notably, the absence of coarse-grained sedimentation in the Sikouzi section during 3.0-2.1Ma and the gradual decrease in coarse-grained peaks since 2.1Ma reflected by the Sikouzi grain-size record probably resulted from stepwise increase in the NH ice volume pushing the ITCZ southward. On the other hand, development of the Antarctic ice sheets would induce global cooling and enhancement of physical weathering, initiating increases in sedimentation rates as well as increases in grain size from Lake Baikal to the CLP to the SCS. Therefore the closure of the CAS during 4.8–4.0Ma and its influence on ocean heat transport was possibly the major forcing factor for global cooling since 4Ma. A persistent and steady cooling during 4–3Ma probably made a significant contribution to the establishment of the NH ice sheets at 2.75Ma ago. [Copyright &y& Elsevier]