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渭河盆地渭南—蓝田地区堆积着连续的始新世以来的地层序列,是揭示新生代亚洲季风气候演化和环境变迁的良好材料。文章对陕西蓝田支家沟厚约330 m的红河组典型剖面进行了沉积学和环境替代指标的初步分析。结果表明,红河组发育时间属于中、晚始新世,是在较为稳定的沉积环境下的河湖相堆积。古流水方向为从南到北,且整个地层沉积环境稳定,从红河组上部到下部古水流方向未发生改变。赤铁矿是红河组的主要载磁矿物,可能含极少量磁铁矿。基于地层序列、岩性、哺乳动物化石和沉积物特性分析,渭河盆地地区在中、晚始新世时气候相对暖湿,植被覆盖度高,有湖泊、沼泽分布,东亚季风气候雏形可能已经出现;到早渐新世,气候趋向相对冷干,与全球范围内始新世—渐新世之交的气候转型相一致。研究为认识始新世中国中部古气候变化提供了新材料。
The continuous sequence of Eocene accumulations in the Weinan-Lantian area in the Weihe Basin is a good material to reveal the climate evolution and environmental changes of the monsoon Asia in the Cenozoic. In this paper, sedimentology and environmental replacement indicators of the typical profile of the Honghe Formation with a thickness of 330 m in Zhijiagou, Lantian, Shaanxi Province are analyzed. The results show that the developmental period of the Honghe Formation belongs to the middle and late Eocene, which is a facies accumulation of rivers and lakes in a relatively stable depositional environment. The ancient flow direction is from south to north, and the sedimentary environment is stable throughout the strata. The direction of paleo-water flow from the upper part to the lower part of the Honghe Formation has not changed. Hematite is the main magnetite in the Honghe Formation and may contain very small amounts of magnetite. Based on the analysis of stratigraphic sequences, lithology, mammalian fossils and sediment characteristics, the climate in the Weihe Basin is relatively warm and humid in the late Eocene with high vegetation coverage and lakes and swamps, and the embryonic form of the East Asian monsoon may have emerged. By the Early Oligocene, the climate tended to be relatively cold-dry, consistent with the global climate transition from the Eocene to Oligocene. The study provides new material for understanding the paleoclimate change in the middle of Eocene in central China.