保德阶层型剖面磁性地层学研究

MAGNETOSTRATIGRAPHY OF STRATOTYPE SECTION OF THE BAODE STAGE

古地磁测量表明 ,中国新近系保德阶界线层型 ,山西保德冀家沟剖面记录了 12个正极性段与 11个负极性段。上部黄土显示了正极性与负极性 ,记录了松山负反极性带的一部分 ;红色黏土与砂砾岩层记录了 Cande95古地磁极性年表中的 C2 An.1n,C2 An.2 n,C2 An.3n,C3n.1n,C3n.2 n,C3n.3n,C3n.4 n,C3An.1n,C3An.2 n,C3Bn,C4 n.1n,C4 n.2 n及其间负极性带。剖面红色黏土的地质年龄为 8.0 Ma— 3.0 Ma,包括了榆社期的早期和保德期的中、晚期。冀家沟保德阶剖面含有二层哺乳动物化石层 ,上化石层以含丰富的鹿科化石为特点 ,相当于含 4 9地点动物群的层位 ,年龄约 5 .5 0 Ma;下化石层相当于含 30地点动物群层位 ,古地磁年龄应当在 6 .5 Ma— 7.0 Ma之间。

Paleomagnetic measurements demonstrate that the Jijiagou section which is the stratotype one of Baode Stage of the Neogene in China records 12 normal and 11 reversed polarity zones. In the section the upper loess layers include normal and reversed polarity zones, recording parts of Matuyama reversed polarity zone; the lower layers of red clay and sandy gravel record normal polarity zones including C2An.1n, C2An.2n, C2An.3n, C3n.1n, C3n.2n, C3n.3n, C3n.4n, C3An.1n, C3An.2n, C3Bn, C4n.1n, C4n.2n and interbedded reversed zones corresponded to Cande 95 Time Scale. The geological age of the Jijiagou section located at Baode County, Shaanxi Province is 8.0—3.0 Ma, comprising the early stage of Yushe Stage and middle, late stage of the Baode Stage. Some sections of the Baode Stage contain two fossil mammal layers. The upper one characterized by containing sufficient fossils of deer family which can be corresponded to the location of the 49th site fauna has age of about 5.50Ma. The lower one can be corresponded to the location of the 30th site fauna, paleomagnetic age of which is between 6.5 Ma and 7.0Ma.