The 7^th International Symposium on Environmental Geochemistry, September 24-27, 2006, Beijing, China

Preface The International Symposium on Environmental Geochemistry, first held in London, Great Britain in 1985, has become a premier international forum for the presentation and discussion of advances in scientific understanding of environmental geochemistry. The 7^th International Symposium on Environmental Geochemistry is being held in Beijing, China. The symposium is sponsored by the State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences and the Chinese Society for Mineralogy, Petrology and Geochemistry.     

Sorption properties of 1, 3, 5-trichlorobenznene on kerogen

Kerogen is an important organic matter fraction widely spread in soils and sediments. It plays a major role in the sorption and sequestration of hydrophobic organic contaminants （HOCs） such as trichlorobenzene （TCB）. It is known that kerogen is geochemically heterogeneous due to the differences in source materials and diagenesis history. We hypothesized that kerogen derived from different source materials and diagenetic history exhibits different sorption properties for TCB. We employed two different kerogen materials （coals） as the original materials and two series of kerogen for a given series with an identical source material but different alteration history were yielded through thermal treatment at temperature ranging from 200 to 500℃. The original and treated materials were characterized for their physicochemical properties. Sorption experiments were conducted with batch reactor systems using 1, 3, 5-TCB as the HOCs sorbates and the original and treated materials as the sorbents.     

New data on age of ore-hosting sequence of the Saf’yanovka deposit, Central Urals, based on foraminifers

The Saf’yanovka copper massive sulfide deposit is situated 10 km northeast from the town of Rezh, on the eastern slope of the Central Urals. The ore-hosting plagiorhyolite-dacitic sequence consists of tephrites and tuffites with interlayers of dark gray siliceous-carboniferous pelites and psephytes from 0.1 to 1.5 m thick. The shells of the Parathurammina tamarae L. Petrovae, 1981 foraminifer were identified in one of the lightened interlayers in the siliceous-carboniferous sequence. The samples for study were taken from the southern part of the orebody in the open-pit between prospecting lines 2 and 3, horizons 170 and 157. The inner part of the shell is composed of quartz and apatite, and the wall, by apatite with rare calcite grains. One shell contains a tacking disk allowing us to refer these foraminifers to the attached benthos typical of the shallow marine basin (sublitoral). In the Urals, the Parathurammina tamarae L. Petrovae, 1981 foraminifer is known in limestones from the Eifel-Givetian (Langurskii and Vysotinskii Horizons); the siliceous-carboniferous rocks from the ore-hosting sequence from the Saf’yanovka deposit has the same age.     

Mineral Components, Texture, and Forming Conditions of Hydrothermal Chimney on the East Pacific Rise at 9°-10°N

To characterize the hydrothermal processes of East Pacific rise at 9o-10oN, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope, scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely: (i) anhydrite marcasite pyrite, (ii) pyrite sphalerite chalcopyrite, and (iii) chalcopyrite bornite digenite covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.     

The Late Palaeozoic Rifting on Hainan Island, China

There occurred rifting on Hainan Island in the Late Palaeozoic. Bimodal volcanic rocks composed ofbasalt and rhyolite developed in the Carboniferous. Widespread in the Late Palaeozoic formations are severallayers of fluvial intermontane conglomerates whose distribution is controlled by rift faults. The Late Palaeozoicdeposits dominaled by clastic rocks are, for a major part, of marine facies and of continental facies in the lowerand upper parts. Lithological and lithochemical studies indicate that the detrital rocks were formed in atectonic setting of continental rifting. The evolution of the rifting terminated at the stage of transition form anintra continental rift to an intercontinental one and the rift basin was a bay opening westward to the sea.     

Lu–Hf constraints on pre-, syn,and post-collision associations of the Gurupi Belt,Brazil: Insights on the Rhyacian crustal evolution

The Gurupi Belt (together with the São Luís cratonic fragment), in north-northeastern Brazil, has been described in previous studies that used extensive field geology, structural analysis, airborne geophysics, zircon U–Pb dating, and whole-rock Sm–Nd isotope and geochemical data as a polyphase orogenic belt, with the Rhyacian being the main period of crust formation. This was related to a 2240 Ma to 2140 Ma accretionary processes that produced juvenile crust, which has subsequently been reworked during a collisional event at 2100 ± 20 Ma, with little evidence of Archean crust. In this study, we use Lu–Hf isotopic data in zircon from granitoids (including gneiss) of variable magmatic series, and amphibolite to improve the knowledge of this scenario, and investigate additional evidence of recycling of Archean basement. Pre-collisional high Ba-Sr and ferroan granitoids and amphibolite formed in island arc (2180–2145 Ma), show only zircons with suprachondritic εHf values (ca. +1 to +8) indicating the large predominance of juvenile magmas. Only 10% of the data show slightly negative εHf values (0 to ?4), which have been observed in granodiorite-gneiss formed in continental arc (2170–2140 Ma), and in strongly peraluminous collisional granites (2125–2070 Ma), indicating the rework of older Paleoproterozoic to Archean components (Hf_TDM = 2.11–3.69 Ga). A two-component mixing model using both Hf and published Nd isotope data are in line with this interpretation and indicate more than 90% of juvenile material, and less influence of Archean materials. Comparing with other Rhyacian terranes that are interpreted to have been close to Gurupi in a pre-Columbia configuration (ca. 2.0 Ga), our results differ from those of SE-Guiana Shield, which show strong influence of Archean protoliths, and are very similar to those of the central-eastern portion of the Baoulé-Mossi Domain of the West African Craton, which has also been formed largely by juvenile magmas in an accretionary-collisional orogen.     

Effect of climatic oscillations on flood occurrence on Papaloapan River,México,during the 1550–2000 period

This study presents a chronology of historical and measured flood events in the Papaloapan River basin of Mexico during 450 years. Twenty-eight historical floods were recorded during the period 1550–1948 on this river and one flood event (1969) in the instrumental era (1949–2000), of which 14 were extraordinary floods and only 15 were catastrophic ones. There were several flood-rich decades during 1860–1870, 1880–1890, 1920–1930 and 1940–1950. Wavelet analysis found a significant flooding periodicity of 58 years. The wavelet coherence analysis found that flooding had an in-phase relationship with the Atlantic Multidecadal Oscillation and also with the Pacific Decadal Oscillation. Logistic regression corroborated that there exists a positive relationship between floods events and these two natural climatic oscillations. The logistic regression model predicted correctly 92% of flood events.     

Discussion on Induan—Olenekian Boundary in Chohu,Anhui Province, China

This paper proposes a scheme for the definition of the Lower Triassic Induan-Olenekian boundary(IOB) based on investigation of sections in Chaohu, Anhui Province, China as well as data accunulated from other studies elsewhere. The conodont Neospathodus waageni is suggested as the index fossil of the boundary. According to the FAD of N.waageni, the IOB is at the base of bed 25-2 of the West Pingdingshan Section in Chaohu,42.19 m above the Permian-Triassic boundary, and it is slightly higher than the base of the Flemingites-Euflemingites Ammonoid Zone at the section.