美国怀俄明州拉那依段岩相及碳氧同位素地球化学特征

1980年6月,本文作者之一的K. Kelts曾去美国参加由经济古生物学者和矿物学者协会组织的地质旅行。该行主要是观察和研究怀俄明州西南始新统绿河组的沉积环境。对此次旅行中带回瑞士苏黎世联邦理工学院地质研究所的样品,曾作了切片、X-射线衍射和碳氧同位素分析。

PRELIMINARY STUDY ON LITHOFACIES AND STABLE ISTOPE GEOCHEMISTRY OF LANEY MEMBER OF EOCENE GREEN RIVER FORMATION, WYOMING, USA

Basing on a brief introduction of the depositional environments (facies) of the-Eocene Green River Formation, Wyoming, IUSA, the stable isotope geochemistry of carbon and oxygen for this formation has been discussed mainly in terms of experimental data. The δ¹⁸O values (PDB standard) of calcite are between -15 and -3‰, suggesting a generation of this mineral in a considerably wide range of salinity. The dolomites have δ¹⁸O values of -4 to +2.5‰ and might be referred to the products in saline to supersaline water media. The two minerals in the same specimen are quite different in their 6 values. These have proved the previous assumption that the calcite had been formed in a relatively fresh water lake, however, dolomite formed on a marginal mud flat and then transported into the lake by sheet flood. The variation trend of δ¹⁸O and δ¹³C value for the cyclic lacustrine sediments might be interpreted by climatic change and organic productivity. The carbonate sediments in the lake rim have the most negative δ¹⁸O values, the nearer to the lake center, the less negative values they have. This might be induced by the supplying of river and ground water into the lake, such an influence is decreasing towards the lake center. The sediments of marginal facies have negative δ¹³C values, and the nearer to the lake center, the more positive values they have. This could be explained by organic (algae) productivity.. The sedi-mentological and geochemical features described in the paper might serve as a reference to the study of many Mesozoic and Cenozoie lacustrine deposits in China (like the Jurassic Andin Formation in Ordos Basin and some Bogene Sequences in Eastern China).