In this study, soil magnetic measurements (susceptibility and hysteretic parameters) and soil hydrocarbon analyses were conducted on samples from three profiles (profiles I and II run across, and profile III runs parallel to the trend of the Jingbian gas field in the Ordos basin, central China) to determine the relationship between themagnetic anomalies (e.g., volume-specific magnetic susceptibility k) and the hydrocarbon seepage environments. The results document a strong correlation between magnetic susceptibility and soil-gas hydrocarbon concentration. Furthermore, the spatial distribution of k and hydrocarbon anomalies correlate with those of the gas field. In addition, magnetic minerals in the soils with higher susceptibility are predominantly magnetite, with little or no substitution of titanium compared to that of samples with lower susceptibility (＜7×10-5 SI [International Unit of susceptibility]). These results provide strong evidences for the formation of highly magnetic minerals in close association with hydrocarbon seepage. Recognition of such seepageinduced magnetic anomalies can be used to facilitate the exploration for oil and gas in China and elsewhere.

The Tuoku region in northern Tarim Basin of China is a key area for studying oil/gas reservoir rocks. The magnetic and mineralogical parameters of well cuttings from two wells, well S7, situated on oil/gas field, and well S6, at an oil/water interface, were measured. The two wells are located in the same structure with similar strata and types of lithology, but well S6 is a showing well of oil and gas 5km northwest of well S7. The purpose of this paper is to evaluate the possibility and distribution of secondary magnetic alteration that may have occurred due to hydrocarbon migration above an oil/gas accumulation. It is concluded that the magnetism of well cuttings from major strata in well S7, including source rocks, oil reservoir rocks and cap rocks, and in Quaternary (Q) soil is higher than that from well S6. The Cambrian oil2bearing strata and cap rocks have even higher magnetism in well S7. The shape and parameters of magnetic hysteresis loops indicate that soft (Hc＜20mT, Hs＜0.3T) ferrimagnetic components dominate the magnetic carriers within the strongly magnetic strata of well S7, whereas a mixed paramagnetic and ferrimagnetic distribution occurs in well S6 (for example, low coecivity Hc and nonsaturating magnetized character). Analysis of heavy minerals shows that the contents of iron oxide (magnetite, maghemite and hematite) in well S7 are often higher than those in well S6. The magnetite content in samples of cuttings from Cambrian rocks can reach 9.7% in oil-bearing strata in well S7, and in strata Ekm and N1j are 1.215% and 1.498%, respectively. Typical spherical magnetite grains are found within the main source rocks and the soils in well S7. By analysis of surface microtexture and of trace element contents, we infer that the spherical magnetite is composed of aggregates of ultrafine particles that are probably authigenic magnetite formed in a hydrocarbon halo background.

通过对腾格里沙漠南缘红水河剖面的地层分析和年代序列建立，依据分辨率40～50a的TOC、TIC、元素和稳定同位素（δ180）分析及孢粉分析，重建了腾格里沙漠南缘过渡区全新世8000～3000aBP期间的古气候演变序列。结果显示，（7980）～6870aBP气候变化特点为具振荡性的升温期，且尤以7410～6870aBP最为明显；6870～4620aBP为高温期，并可分为6620～5770aBP温暖而湿润的第1高温期和5360～5130aBP以干热为特征的第2高温期。在5880～5360aBP，即两个高温期之间，气候曾发生持续干化，温度有3次波动降低。第1高温期可被视为本区全新世气候适宜期。5130～4620aBP温度有所降低，但湿度增加，并在4830～4790aBP存在一强降温事件，预示着全新世高温期的衰减；4620aBP开始为降温期并在4620～4320，4010～3590和3270～（3110）aBP出现3次分别与高山冰进相关的低温期。

Study of forming mechanism of "chimney-effect" (CE) has important significance for basic theory and applications of non-seismic geophysical and geochemical methods locating oil/gas reservoirs. The theoretical basis of comprehensive evaluation of mechanism of CE using principles of magnetism, geochemistry and mineralogy has been reviewed, with the problems to be solved: (i) study for the relationship between process of oil/gas migration and geochemical field; (ii) analysis of genesis of magnetic, geochemical and mineralogical anomaly; (iii) interpretation of surface soil magnetism and geochemical anomaly combined with seismic data.