Zhang Huizhi

Origins and simulated thermal alteration of sterols and keto-alcohols in deep-sea marine sediments of the Okinawa Trough

Abstract Compositional data on the sterol and alcohol fractions isolated from deep-sea marine sediments from the Okinawa Trough were obtained to determine the relative contribution from marine and terrestrial inputs. Following extraction, the total saponified neutral fraction was derivatized witn BSTFA and then analysed by capillary GC and GC-MS. A suite of C26–C29 stenols and stanols and C30–C32 keto-alcohols were identified in the sediments. Major sterols included 27-nor-24-methylcholesta-5,22E-dien-3s-ol and cholest-5-en-3s-ol, which are most likely from marine fauna, and the C28 sterols 24-methylcholesta-5,22E-dien-3s-ol and 24-methylcholesta-5,24(28)-dien-3s-ol, both of which are common in diatoms. C29 sterols were dominated by sterols with 24-ethyl substitution of higher plant origin, but 23,24-dimethyl sterols which are found in some marine phytoplankton were also quite abundant. The major 4-methyl sterol was 4α,23,24-trimethyl-5α-cholest-22E-en-3s-ol which is considered a common indicator of dinoflagellates. Each sterol co-occurred with the corresponding 5α-stanol. Other indicators of terrestrial input such as α- and s-amyrin were also identified. The sediments also contained significant amounts of the C30 keto-alcohol triacontan-15-one-1-ol, as well as smaller amounts of C31 and C32 keto-alcohols. These unusual lipids are found in many marine sediments, and they may be formed by the oxidation of the corresponding C30–C32 alkyl diols found in some marine microalgae. The thermal stability of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 h at temperatures ranging from 100°C to 200°C. The C27 stanol/stenol ratio increased with increasing temperatures up to 140°C, as did the corresponding C28 and C29 stanol/stenol ratios. The keto-alcohols were more stable than sterols under these conditions.

Assessment of water-recharging based on ecological features of riparian forest in the lower reaches of Tarim River

The occurrence and development of riparian forests which are mainly dominated by mesophytes species relate closely with surface water. Since there is no water discharge to the lower reaches of Tarim River in past 5 decade years, the riparian forests degrade severely. Based on the analyses of the monitored data of Yingsu, Argan and Luobuzhuang in 2002 and 2003, the effect of water-recharging is discussed. The water-recharging project neglects the fact that that it is flooding that controls the process of Populus euphratica colonizing on the bare surface, but focuses on groundwater influence on vegetation. The flooding control deviates inherent laws of riparian forests development, so the natural regeneration of riparian forests is checked. The response scope of riparian plants on groundwater uplift is extremely narrow, and most riparian communities have not been optimized. No seedlings of dominant species are found in flooding areas because their physio-ecological characteristics are ignored. The vegetation changes in vicinities of stream only reflect the demand of mesophytes species on the shallow groundwater, however, the water-recharging fails to provide suitable habitats for the seedlings establishment of riparian plants. The present water-recharging scheme is difficult to realize vegetation restoration.

ORGANIC GEOCHEMISTRY OF ARTIFICIALLY HEATED SPHAGNUM COAL CONSIDERED AS POSSIBLE SOURCE ROCK FOR OIL AND GAS

A preliminary study of simulated thermal maturity has been conducted to evaluate the oil, gas and hydrocarbon generation potential of sphagnum coal in the Jinsuo brown coal basin, Yunnan Province and to understand the characteristics of the element composition and biomarkers in the course of thermal alteration. The experimental result was compared with that of xylitic coal, a kind of lithotype of soft brown coal. It is considered that sphagnum coal possesses the potential of forming economic accumulation of oil and gas. Its highest proportion of oil and hydrocarbon generation is 510 mg/g Corg. and 232.1 mg/g Corg. respectively. At an R_(ran)~° value of 2.51%, the ratio of gas generation from sphagnum coal attains to 620.5 ml/g Corg. In view of sphagnum coal being different from the conventional soft brown coal in various respects such as coal forming raw materials and enviroments as well as physico-chemical properties, it is Suggested as a special kind of source rock for coal-generated oil and gas.