标题：THE CARBON AND OXYGEN ISOTOPE
CHARACTERISTICS AND PALEOENVIRONMENTAL
SIGNIFICANCE OF LOWER-MIDDLE CARBONIFEROUS
CARBONATE ROCKS OF THE EASTERN CASPIAN BASIN
摘要：Carboniferous carbonate rocks provide im- portant oil and gas reservoirs in the eastern Caspian Basin. Carbon and oxygen isotopes record the pale- oenvironment and diagenetic environment of reser- voir formation. Carbon and oxygen isotope analyses of 76 lower-middle Carboniferous carbonate rocks from the Zanarol area were combined with petro- graphic analysis to investigate the paleoenvironmentduring formation of the carbonate rocks. Most of the 1CPDB values are between-2%o and 6%, with an average of 0.67%o. Most of the 818OpR values are between-7%o and-4%o, with an average of-6.13%o. These values indicate that paleoenvironmental infor- mation is preserved in spite of some diagenetio changes. The values of Z are 120-134, consistent with formation of the carbonate rocks in normal to saline seawater salinities within a marine environ- ment. The paleotemperature was 200C-28C, which indicates a warm subtropical climate at the time of deposition. The carbon and oxygen isotope values indicate that the B layer underwent diagenesis in anear-surface environment, and that the G and D lay- ers underwent diagenesis in medium-deep burial en- vironments. The 1CPDe values of the B layer sam- ples are higher than those of the G and D layers, which is attributed to changes in the sedimentary en- vironment. The main facies represented by the G and D layers is an open platform facies, while the B layer formed on an open continental shelf. An abrupt change in carbon and oxygen isotope ratios at the top of the B layer is attributed to tectonic movement in the eastern part the study area associated with theUral orogeny during the late Carboniferous. At thistime, water in the sediments became and organic ac- tivity declined as the area of the open sea shrunk and the water stagnated, with a consequent increase in water salinity and an abrupt increase in the & lCppB and 818OpB isotopes.
关键词：Caspian Basin;Zanarol;Carboniferous System;Carbonate rocks;Carbon and oxygen isotopes
