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,气候趋向相对冷于,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 fluvial-lacustrine deposits in Weinan-Lantian areas,Weihe Basin,central China,provides an excellent record for understanding Asian monsoon evolution and environmental changes in the Cenozoic era.A preliminary sedimentology and stratigraphic analysis of the typical Honghe Formation at Zhijiagou site (330 m thick),which is located between the Lishan mountain and Hengling tableland,Lantian County,Shaanxi Province,is carried out.Our results indicate that the Honghe Formation was formed in the middle and late Eocene,and/or early Oligocene,under a relatively continuous fluvial-lacustrine depositional environment,with sediments sourced from the Qinling orogen.The paleocurrent direction in the Honghe Formation is from south to north,lasting the entire depositional time from top to bottom.The dominant magnetic carrier of the Honghe Formation is hematite,perhaps contains a small part of magnetite.We conclude that the climate was more humid and warmer in the middle and late Eocene in Weihe Basin,central China,when there were abundant plants,lakes,and swamps in Lantian area,but it may turn to relatively cold and dry conditions in early Oligocene,which is consistent with the climate transition of Eocene-Oligocene around the world.Our preliminary results from the Honghe Formation suggest that the Asian monsoon-like circulation may exist by the middle Eocene,when central China was relatively humid.However,our preliminary finding needs to be further tested.
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