Carbon isotopic studies of individual lipids in organisms from the Nansha sea area, China

Carbon isotopes of individual lipids in typical organisms from the Nansha sea area were measured by the GC-IRMS analytical technique. δ13C values of saturated fatty acids in different organisms examined are from 25.6‰ to 29.7‰ with the average values ranging from 26.4‰ to 28.2‰ and the variance range of 1.8‰ between different organisms is also observed. Unsaturated fatty acids have heavy carbon isotopic compositions and the mean differences of 2.9‰–6.8‰ compared to the same carbon number saturated fatty acids. δ13C values of n-alkanes range from 27.5‰ to 29.7‰ and their mean values, ranging from 28.6‰ to 28.9‰, are very close in different organisms. The mean difference in δ13C between the saturated fatty acids and n-alkanes is only 1.5‰, indicating that they have similar biosynthetic pathways. The carbon isotopic variations between the different carbon-number lipids are mostly within ±2.0‰, reflecting that they experienced a biosynthetic process of the carbon chain elongation. At the same time, the carbon isotopic genetic relationships between the biological and sedimentary lipids are established by comparative studies of carbon isotopic compositions of individual lipids in organisms and sediments from the Nansha sea area, which provides scientific basis for carbon isotopic applied research of individual lipids.

Origin of Li-F-rich granite: Evidence from high P-T experiments

Though magmatic origin of Li-F-rich granite has been supported effectively by the existence of volcanic and subvolcanic rocks and melt inclusions trapped in them with similar chemical compositions, evidence from high T-P experiments is poor up to now. To simulate the evolution process of Li-F-rich granite and to interpret its forming mechanism, a series of melting-crystallization experiments were carried out. Under the conditions of 1×108 Pa and 570–700°C, a magmatic mineral association of quartz + alkali feldspar + lithium muscovite/ferromuscovite ± fluorite ± cassiterite is found in leucogranite-HF-H2O system. This indicates the following points: (i) Fluorite, light-colored muscovite and cassiterite can crystallize directly from the Li-F-rich granitic melt. (ii) The coexistence of dark-colored micas (e.g. biotite) and light-colored micas (e.g. lithium muscovite and ferromuscovite) suggests that the muscovite granite and two-mica granite can be formed under magmatic condition. The zonal texture of micas is not the sole feature for the micas of hydrothermal origin. (iii) As crystallization proceeds, the SiO2 concentration of the residual melt decreases, while the Al2O3 and F concentrations and A/CNK, NKA/Si ratios of the melt incerese, favoring the formation of Li-F-rich granites. Our experiment results are well consistent with the vertical zonation widely observed in rare metal bearing granites, and therefore provide strong experimental evidence for magmatic origin of Li-F-rich granite.

Extreme flood events and climate change around 3500 aBP in the Central Plains of China

The Xinzhai Period (35503400 aBP) belongs to Late Neolithic Culture, which bridges the Longshan Culture and the Xia Culture in the Central Plains of China. By studying the living environment of ancient human beings at the Xinzhai site, Henan Province, this paper pre-sents the discovery of extreme floods which threatened and destroyed the living environment of the ancient human beings during the Xinzhai Period. Pollen analysis and carbon-oxygen isotope measurement suggest that the climate was warm and wet during the Xinzhai Period, in contrast to the warm and arid climate during the Longshan Culture Period. The frequent flood events were the response of abrupt climate change during the Xinzhai Period. The conclusions drawn from this study not only help better understand the environmental change in the Central Plains of China around 3500 aBP, but also provide important clues to the environmental background for the origin of Chinese civilization.

Sequence stratigraphy of Jurassic-Cretaceous boundary strata in Luanping, Northern Hebei, China

A sediment-continuous section of Jurassic-Cretaceous (J-K) boundary strata was found in Zhangjiagou of Luanping, northern Hebei Province, China. The boundary strata were systematically divided into 5 sequences, 13 subsequences and 139 parasequences by sedimentary cyclicities and facies analysis. According to stable time-ranges of subsequences and parasequences, some boundary ages can be marked as 142.90 Ma of the SQ I (Dabeigou Fm) basal bound, 141.16 Ma of the SQ II basal bound, 140.00 Ma of the SQ III (Dadianzi Fm) basal bound, 138.24 Ma of the SQ VI (Zhangjiagou Fm) basal bound and 135.34 Ma of the SQ V (Zhangjiagou Fm) top-bound. A sequence-stratigraphic framework of the Dabeigou-Zhangjiagou Fms has been constructed by tracing sequence-bounds, marker-beds and fossil zones. The basin-development and tectonic activities are studied based on sequence-stratigraphic evidence. 5 sequences represent 5 tectonic cycles and all the 6 sequence-bounds reflect tectonic activities. Tectonic activities clearly influence the basin-development that can be divided into 3 stages in the J-K transitional period. Each stage consists of a down-faulting-rising process, i.e. from strongly rising of basin-bottom, then violently faulting down (with volcanic eruptions) and to gently rising. The development shows a pattern of bottom down-faulting with basin narrowing and rising with spreading. Keywords sequence - stratigraphy - terrestrial stratotype - Jurassic-Cretaceous bound DOI: 10.1360/03yd0451