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古地磁测年表明,甘肃董湾晚新近纪剖面代表了7.3～3.5 Ma间的连续风成古土壤堆积。在74.8 m厚的剖面上,发现了小哺乳动物化石层位40个,共产出小哺乳动物39种。根据小哺乳动物组合特点,董湾剖面可以划分出4个生物地层带,Ⅰ+Ⅱ带为晚中新世晚期,相当于保德期;Ⅲ+Ⅳ带为上新世早期,相当于榆社期早期。中新统/上新统界线(5.33 Ma)位于剖面距顶部35.5 m处,比以鼢鼠Mesosiphneus最早出现为标志的生物地层Ⅲ带的底界低2 m。由于榆社阶底界直接对应于中新统/上新统界线,该剖面因其良好的地层和生物条件可被推荐为榆社阶界线层型的候选剖面。
Paleomagnetism dating shows that the late Neogene section of Dongwan, Gansu, represented a continuous wind accumulation between 7.3 and 3.5 Ma. On a section of 74.8 m thick, 40 small mammalian fossil beds were found and 39 small mammals were co-produced. According to the characteristics of small mammal assemblages, four biogenic stratigraphic zones can be distinguished in Dongwan section. Late stage of Late Iliocene is Belt Ⅰ + Ⅱ, which is equivalent to Baode Period. Ⅲ + Ⅳ belt is early Pliocene, which is equivalent to Yushe Early period. The Miocene / Pliocene boundary line (5.33 Ma) is located at a distance of 35.5 m from the top of the profile, 2 m below the bottom boundary of the biozone Ⅲ zone marked by the earliest appearance of Mesosiphneus. Because the bottom boundary of Yushe directly corresponds to the Miocene / Pliocene boundary, the profile can be recommended as a candidate profile of Yushe boundary line stratification due to its favorable stratigraphic and biological conditions.