Fang Nianqiao

Late Palaeozoic and Triassic deep-water deposits and tectonic evolution of the Palaeotethys in the Changning-Menglian and Lancangjiang belts, southwestern Yunnan

Abstract Discontinously exposed deep-water deposits in the Changning-Menglian belt, characterized by terrigenous turbidites, turbiditic marlstones, bedded radiolarian cherts, pelagic radiolarian shales, and some basaltic lavas and pyroclastic rocks, constitute a continous record of Palaeotethys evolution from early Devonian to middle Triassic, and strongly suggest that this belt is the main branch of the Palaeotethyan polyisland ocean in the Hercynian-Indosinian stage. According to the sedimentary history of the Changning-Menglian belt, the main basin of the Palaeotethys after opening for a long period narrowed markedly in the late permian but kept its typical oceanic environment until the end of middle Triassic. In the Lancangjiang belt, deep-water deposits occured mainly during the late Carboniferous to early Permian and are related to the island-arc volcanic activities. These deposits appear to be similar to those from the Petchabun belt of Thailand. Following the emergence of the Lincang magmatic arc in the studied area, which took place in mid-Permian times, the deep-water basin in the Lancangjiang belt between the Lincang and Simao massifs was closed, while the Palaeotethys main oceanic basin, represented by the Changning-Menglian belt to the west of the Lincang arc, hosted diverse pelagic sediments.

Palaeoenvironmental Evolution Deduced from Organic Carbon Stable Isotope Compositions of Napahai Lake Sediments, Northwestern Yunnan, China

The Napahai Lake, situated in the hinterland of the Hengduan Mountains, is a basin by the erosion of carbonate rocks. The lake levels have experienced great fluctuation between low stand and high stand stages. The lake level changes directly influences the amount and distribution of aquatic plant communities that used different sources of carbon for photosynthesis, thereby imprinting the organic sediments with a characteristic 13 C composition. Another reason influencing the 13 C composition for bulk organic sediment, in this case, is the change of reduction oxidation condition in the alternative stages. In addition with the strong dissolution of carbonate strata in humid cool conditions, the lake level fluctuations and climatic changes could be reconstructed using HI, TOC and δ 13 C. The results show that increase in total organic carbon and hydrogen index correlates in general, with decrease in δ 13 C values, which could be attributed to the flourishing of emerging and floating aquatic plants as well as a relative reduction environment in a low lake level associated with a warm dry or temperate dry climate. The decreases of TOC and HI often correlate well with δ 13 C value increasing in a high lake level stage accompanied with a cool humid climate, which might be attributed to low productivity of aquatic plants, oxidation that triggers decomposition of organic matters and strong dissolution of carbonate strata in humid cool conditions. The palaeo environmental reconstruction shows that major environmental changes took place at 32kaBP and 15kaBP respectively. The lake levels exhibited frequent fluctuations between ca.57-43kaBP, and then the lake level slightly rose from ca.43kaBP to ca.37kaBP. After then, the lake level dropped dramatically when the climate became warm and dry. From ca.32kaBP, the lake level had a distinct rise due to cool humid climate and kept high until the end of the Last Glacial Maximum. A warm dry climate returned to the areas again and the lake level remained lowering during the Holocene. After the lake level rose in a minor amplitude from ca.3-2kaBP., modern climate dominates the Napahai lake.

Paleoceanographical records under impact of the Indian monsoon from the Bengal Deep Sea Fan and Ninetyeast Ridge during the last 260 ka

The orbital and interior climatic cycles can be found both in the Bengal Deep Sea Fan and Ninetyeast Ridge, North Indian Ocean. The periodicity of the Quaternary glacio-eustacy by 100 ka gave a strong impact on the sedimentation in the fan area and the monsoon signals controlled by the obliquity and precession were easily picked up. This paper discusses the possible correlation between the environmental elements on the basis of the ETP phase wheels. A rapid change with short-periods develops during the past 60 ka in the region under study as well. The variability of paleoproductivity has a nonlinear response to the Indian summer monsoon. As contrasted to the Northwest Indian Ocean, here an abundance ofGlobigerina bulloides, a proxy to indicate upwelling current, does not imply so much a promotion of the summer monsoon as its decrease. The record from the ridge area shows in a longer-scale a climatic evolutionary feature corresponding to that of the fan area. A special and great event arising at around 165 kaBP and meaning a catastrophe for ecological environment is reported in this paper. It is also regarded as a result induced by the monsoon.The orbital and interior climatic cycles can be found both in the Bengal Deep Sea Fan and Ninetyeast Ridge, North Indian Ocean. The periodicity of the Quaternary glacio-eustacy by 100 ka gave a strong impact on the sedimentation in the fan area and the monsoon signals controlled by the obliquity and precession were easily picked up. This paper discusses the possible correlation between the environmental elements on the basis of the ETP phase wheels. A rapid change with short-periods develops during the past 60 ka in the region under study as well. The variability of paleoproductivity has a nonlinear response to the Indian summer monsoon. As contrasted to the Northwest Indian Ocean, here an abundance ofGlobigerina bulloides, a proxy to indicate upwelling current, does not imply so much a promotion of the summer monsoon as its decrease. The record from the ridge area shows in a longer-scale a climatic evolutionary feature corresponding to that of the fan area. A special and great event arising at around 165 kaBP and meaning a catastrophe for ecological environment is reported in this paper. It is also regarded as a result induced by the monsoon.

Climate history of the middle reach of the Yangtze river over the past 9000 years: A speleothem isotopic record from Za cave, Hubei, China

A stalagmite in Qingjiang, Hubei, has yielded the records of hydrogen and oxygen as well as carbon isotopic changes and provided a climate history of 9000 years. The hydrogen isotopic ratio in fluid inclusions and the oxygen isotopic ratio in stalagmite calcite are controlled by meteoric water, which is in response to ambient temperature or precipitation amount. The carbon isotopic ratio, sensitive to the nature of vegetation, also can be used to reconstruct the climate history. The carbon-14 and U-series dated stalagmite records reveal that climate oscillated in the middle reach of Yangtze river over the past 9000 years: (1) 9.0-6.5 kaBP, a cooler and more humid condition; (2) 6.5-4.0 kaBP, with warmer and drier weather; (3) 4.0-2.0 kaBP, cold weather with heavy precipitation, and (4) 2.0 kaBP to present, tendency to be warmer and drier.A stalagmite in Qingjiang, Hubei, has yielded the records of hydrogen and oxygen as well as carbon isotopic changes and provided a climate history of 9000 years. The hydrogen isotopic ratio in fluid inclusions and the oxygen isotopic ratio in stalagmite calcite are controlled by meteoric water, which is in response to ambient temperature or precipitation amount. The carbon isotopic ratio, sensitive to the nature of vegetation, also can be used to reconstruct the climate history. The carbon-14 and U-series dated stalagmite records reveal that climate oscillated in the middle reach of Yangtze river over the past 9000 years: (1) 9.0-6.5 kaBP, a cooler and more humid condition; (2) 6.5-4.0 kaBP, with warmer and drier weather; (3) 4.0-2.0 kaBP, cold weather with heavy precipitation, and (4) 2.0 kaBP to present, tendency to be warmer and drier.

Relative brightness index and it’s climatic significance from lacustrine sediment of napahai lake, northwestern yunnan plateau, china

Information on the palaeoenvironment from Late Pleistocene to Holocene in northwestern Yannan Plateau has been deduced from a study of a 28. 81m-long core taken from Napahai Lake. The results from Relative Brightness Index (RBI) as well as those from the lithological analyses of bulk sediments, total organic carbon and granulometric analyses have been used to reconstruct the environmental and climatic evolution of the area. The ages were provided by three 14C datings. The record suggested a climate fluctuation between warm-dry and cool-wet from ca. 57 to 32ka B. P., which led a shallowing and swamping of the lake. The water level again increased quickly at ca. 32ka B. P., reached it’s peak during LGM (Last Glacial Maximum, ca. 18–20ka B. P.) and remained relative high until ca. 15ka B. P. The high water level at LGM is attributed to cold-wet conditions. The area experienced an abrupt and unstable climatic changes during the transition period from 15 to 10ka B. P. with a dominated littoral environment. A warm-dry climate led to the contraction of the lake during the Holocene and reed-swamps beoame dominant. After a minor wet-cool pulse during the Late Holocene, the modern climate became to be established.