基于磁性地层的渭河盆地灞河组研究

渭河盆地东南缘蓝田-渭南一带发育较连续完整的新生代地层，其中包含丰富的哺乳动物化石，特别是灞河组中产
出典型的三趾马化石，并曾据此建立了灞河期标准生物地层。鉴于灞河组及灞河期沉积地层在中国北方环境变化及古生物
研究中的重要意义，对陕西蓝田灞河南岸厚约246 m的段家坡灞河组典型剖面进行了详细古地磁年代学研究。磁性地层分
析确定的极性序列可与标准古地磁年表（GPTS） 较好对比，结果表明段家坡剖面灞河组年龄为11~7 Ma，属于晚中新世。
本研究支持灞河期单独作为一个地层年代单位，为哺乳动物化石的区域对比提供了相对准确的年代界定，同时结合与其它
盆地同时期沉积的对比探讨了灞河组的沉积环境和古气候，认为当时为半干旱型草原气候，沉积环境和气候与上覆的蓝田
组有很大不同。

Study on the Bahe Formation in the Weihe Basin Based on Magnetostratigraphy

There is a continuous Cenozoic sedimentary sequence in the Lantian-Weinan area in the southeastern Weihe Basin, which contains a large number of mammal fossils. The Bahe Formation is especially famous for the three-toed equid “Hipparion ” and the other mammal fossils, and it has been accordingly established as a standard of Bahe stage. However, there are still debates about the age of the Bahe Formation. In order to investigate the importance of the Bahe Formation and its sedimentary environmental changes and paleontological characteristics in the Late Neogene period in Northern China, we carried out a detailed magnetostratigraphic study of the type Bahe Formation called the Duanjiapo section (246 m thick), which is located on the southern bank of the Ba River, Lantian County, Shaanxi Province. The magnetic polarity sequence can be clearly calibrated to the Geomagnetic Polarity Time Scale (GPTS). The result shows that the age of the Bahe Formation is 11~7 Ma, corresponding to the Late Miocene. This study believes that the Bahe Age should be a separate stratigraphic unit that is different from the Baode Age. It could provide a more precise age for the regional mammal fossils comparison. Meanwhile, the Bahe Age is also different from the Lantian Age, according to the comparison of sedimentary environment and paleoclimate with other basins, i.e. the Linxia Basin and the Tianshui Basin. The Bahe Age is characterized by a much drier semiarid steppe climate whereas the Lantian Age is humid forest climate.