摘要
测定的样品采自天津蓟县和北京门头沟青白口两地铁岭组碳酸盐,测得152对δ^(13)C和δ^(18)O数据,发现碳、氧同位素在两地铁岭组具有相同的变化趋势,并对它们的成因机制和地质意义进行了对比及探讨。
More than 150 samples were collected systematically from the Precambrian Tieling For-mation (about 1050--1220 Ma) in the Yanshar region. Two typical sections were selected. Oneis located in the Mentougou district, Beijing, and the other in Jixian County, Tianjin. Theδ^(13)C values of 152 carbonate samples show that changes in carbon isotopic composition of oceanwater were very low during the period in which the Tieling Formation was formed, probablydue to constant distribution ratio of total carbon between organic and inorganic carbon reser-volrs. Though the overall extent of variation is small, the δ^(13)C values of carbonates in the lo-wer parts of both sections are consistently and relatively more negative and instable thanthose of the upper parts. The δ^(13)C values of the upper parts represent the carbon isotopic com-position of ocean water in that geological time, while those of the lower parts reflect the en-vironmental change and influence of other factors. The δ^(18)O values of 152 carbonate samples vary dramatically with the maximum --2.2, theminimum --18.8 and the average --7.0‰. It is difficult to assume that the effects of meteoricwaters to the oxygen isotope compositions of the carbonates were the same in the different placesafter diagenesis, therefore the similar trends. Th similar trends in these two sections imply thatthe changes in δ^(18)O are primary. We attribute these primary changes to the influence of an-cient latitudes and depositional environments.
出处
《地球化学》
CAS
CSCD
北大核心
1993年第1期10-17,共8页
Geochimica
