Junliang Ji

The early-Eocene climate optimum (EECO) event in the Qaidam basin, northwest China: clay evidence

Abstract Clay mineralogy and its palaeoclimatic interpretation of the early-Eocene (~53.3-49.70 Ma) sediments at Lulehe, Qaidam basin, northwest China, were investigated using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The interval of ~53.3–49.70 Ma, including the early-Eocene climate optimum (EECO) with isotopic events, was the transition period of ‘‘greenhouse’’ to ‘‘icehouse’’. Climate changes during the episode were documented in the sediments and were expressed by the proportion of clay species and clay indices, as well as by the proportion of non-clay minerals, gypsum, halite and calcite. Our results suggest that a warm and humid climate prevailed over the period ~53.3–52.90 Ma, followed by a warm and seasonally dry and humid climate in the period ~52.90–51.0 Ma and a subsequently warm and humid climate in the period ~51.0–49.70 Ma. Three warmer and more humid intervals were observed at 52.7, 51.0 and 50.5 Ma based on clay indices. The climate evolution in the Qaidam Basin during the period derived from the clay mineralogical study is in good agreement with the early Eocene global climate change, and the warm and seasonally dry and humid episode in the early Eocene in Qaidam basin is a regional response to the global early-Eocene climate optimum.

Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin.

The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ18O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time.

Palaeogene–Neogene Stratigraphic Sequences of the Tibetan Plateau and Their Response to Plateau Uplift

A total of 98 remnant basins and 5 stratigraphic domains with 13 stratigraphic subdomains have been recognized on the Tibetan Plateau. Through investigating the types of remnant basin, the tectonic setting, the stratigraphic sequences and sedimentary characteristics, and the evolution of the sediments, we divide the uplift process and sedimentary response for the Tibetan Plateau into three stages and eight substages. These are the subduction–collision uplift stage (65–34 Ma) with three substages, the intercontinental convergence and compressive uplift stage (34–13 Ma) with three substages, and the intercontinental isostatic adjustment uplift stage (since 13 Ma) with two substages.

Late Pleistocene sedimentary sequences and paleoclimate changes in Xunhua basin in the upper reach of Yellow River in China

The third terrace of the Yellow River was well developed in Xunhua basin in the north-east margin of the Tibetan Plateau. The terrace was formed at ca 75 ka as dated by the optically stimulated luminescence (OSL) method. On the basis of grain size, magnetic susceptibility and palynological data, six episodes of the climatic change were identified in Xunhua basin; they include very warm and humid period during 120–114 ka, cool and dry period during 114–105 ka, warm and humid period during 105–98 ka, gradually cooling period during 98–85 ka, warm and humid period during 85–75 ka, very cold and dry period during 75–63 ka. The six stages of climatic change recorded in Xunhua basin correspond to the marine oxygen isotope stages (MIS) of 5e, 5d, 5c, 5b, 5a and 4, respectively.