Thick layers of dark lacustrine mudstone in the Nenjiang Forma- tion record the evolution of local depositional environments in the Songliao Basin. This evolution in lake water is accurately reflected in variations in trace element compositions in sedimentary rocks. In this study, element geo- chemistry and clay mineralogy in successive cores were investigated to have a closer insight into the paleolimnological environment and organic accumulation during the Nenjiang epoch. Analysis of the contents of Mn, Ca and Ti, as well as Rb/Sr and Sr/Cu revealed that paleoclimate cycled between warm and humid to semi-arid and hot. The study of Sr/Ba ratios, clay minerals and stable isotopes indicated that both high and low salinity existed in two stages, and that high salinity in Member 1 of the Nenjiang Formation is likely correlated with transgressive events. Analysis of the ratios of V/V + Ni, Ni/V and Th/U suggested that the paleolimnological environment was reducing. The investigation of paleotemperature demonstrated that the Nenjiang Formation was deposited in a warm water environment, analysis of carbon and oxygen isotopes revealed its deposition in open paleolake. High paleoproductivity and salinity as well as redox potentials represent the most favorable environment for oil shale enrichment.

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Paleolimnological environments and organic accumulation of the nenjiang formation in the southeastern songliao basin, china

AMS14C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 μm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ18O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300–6300 a BP, strong and unstable; 6300–3800 a BP, strong but stable; 3800–1400 a BP, weak and unstable; after 1400 a BP, weak but stable.

Records of the East Asian winter monsoon from the mud area on the inner shelf of the East China Sea since the mid-Holocene

Shanghai soft clay was deposited in the Yangtze River Delta in the Late Pleistocene and Holocene eras. The general engineering properties of this clay have been studied in the last few decades. However, limited research on its depositional history and impact on geotechnical properties is available. In this paper, the depositional history of Shanghai clay was reproduced based on sea level changes and other geological information. The unique depositional environment was compared with two other Asian clays, Ariake clay in Japan and Bangkok clay in Thailand. The physical, mineralogical and mechanical properties of different strata were investigated by a series of laboratory tests. It was found that silt-sized grain particles dominated the clay materials and illite is the major clay mineral, while clay-sized grains and smectite are predominant in Ariake and Bangkok clays. The liquid limit, plastic limit and activity are lower than the Ariake and Bangkok clays. Oedometer tests and undrained triaxial tests indicated a less sensitive structure. Stronger hydraulic conditions (faster stream velocity) and the origin of material in the middle and lower reaches of the Yangtze River account for the large amount of silt-sized particles and illite. A less saline depositional environment is the main reason for the weaker structure in Shanghai clay than the two other Asian clays.

Depositional environment and geotechnical properties of Shanghai clay: a comparison with Ariake and Bangkok clays.

Previously underused information from radiocarbon dates in well-characterised sedimentary sequences in the southern Yangtze Delta, China, is here utilised in reconstruction of patterns of ancient erosion. The southern Yangtze Delta was an important focus of food production in the early Neolithic. Anomalous radiocarbon dates in Holocene sediments from the southern part of the delta are unevenly distributed through time. Two clusters of dates – in sediments ca. 9000–7000 cal. BP and ca. 3000–1000 cal. BP – most likely indicate two periods of intensive erosion and redeposition of organic materials. The older of the two clusters may have been associated with a marked episode of marine transgression, whereas the younger cluster could reflect increasing levels of human disruption of soils and sediments in the catchment. A relatively late increase in anthropogenic soil erosion supports recent archaeological evidence that, following its early Neolithic origins, agricultural expansion and intensification occurred later on the southern Yangtze Delta than previously thought.

Radiocarbon anomalies suggest late onset of agricultural intensification in the catchment of the southern part of the Yangtze Delta, China

A preliminary study of a sediment core drilled from the mud area on the inner shelf of the East China Sea: Implications for paleoclimatic changes during the fast transgression period (13 ka B.P.-8 ka B.P.)

Clay minerals in 15 surficial samples and 5 profile samples from the Yangtze Delta plain were analyzed by X-ray diffraction. The result shows that clay mineral assemblage of the surfical sediments arc distinguished by the coastline 7 500 - 8 000 a BP, indicating different sediment sources and sedimentary environments. The change of content of illite vs. kaolinite in the profile sediments reflects the climate fluctuations since late Pleistocene.

Distribution of Clay Minerals in the Yangtze Delta Plain and Its Paleoenvironmental Implication(Chinese)

Let L be a subspace of F~n and P_l be the orthogonal projection of F~n onto L, where F=C or R. Let A be an n×n matrix. In this paper, we will give the perturbation analysis of the generalized Bott-Duffin inverse A_((L))~((+))=P_l(AP_l+I-P_l)~+ when A and L have small perturbation. Using this result, we establish a perturbation analysis to the least squares solution of the system Ax+B~*y=b, Bx=d under certain small perturbation of A and B.

Chen Zhongyuan

Papers

Distribution of Clay Minerals in the Yangtze Delta Plain and Its Paleoenvironmental Implication(Chinese)

Perturbation Analysis of the Generalized Bott-Duffin Inverse of L-zero Matrices(II)(English)