西峡盆地含恐龙蛋化石剖面磁性地层学结果及其构造地质意义

Magnetostratigraphic study and its geological significance of the dinosaur egg-bearing section in Xixia Basin,Central China

通过对河南南阳西峡盆地含恐龙蛋化石的阳域一丹水剖面的岩石磁学与古地磁学研究表明,该陆相沉积地层的特征剩磁载体以赤铁矿与磁铁矿为主,特征剩磁通过了倒转检验,表明其很可能为岩石形成时期获得的原生剩磁.结合该剖面古生物资料,磁性地层学结果表明,剖面上部2973～3023 m处年代为83～79 Ma;该剖面蛋化石所在最高层位年龄不晚于83 Ma,暗示该地区大型爬行动物的绝灭可能与西峡地区当时的气候、环境变化有关.此外,自晚白垩世以来,该剖面所处位置相对华北和华南地块发生了约18°的顺时针旋转,可能由该地区的局部构造活动引起.

A paleomagnetic and rock magnetic investigation is reported from the dinosaur egg-bearing Yangcheng-Danshui section in the Xixia Basin （Henan province in central China）. Results indicate that hematite and magnetite are the main carriers of remanence in this terrigenous section. The primary nature of characteristic remanent magnetization （ChRM） is ascertained by positive reversal test, suggesting that the ChRM was probably acquired in or close to the period when the sedimentary rocks were formed. Together with biostratigraphical and biochronological data, magnetostratigraphic results in this section unravel that the upper section spanning from 2973 m to 3023 m was deposited between 83Ma and 79 Ma in the Late Cretaceous. It therefore appears that the highest dinosaur egg-bearing layer in the Xixia Basin was accumulated prior to 83 Ma. These results imply that the extinction of the large reptiles commonly occurred in the Late Cretaceous might be related to the sharply rapid climate and natural environment change in the Xixia Basin, central China. In addition, the terrane of the section located is suggested to have undergone some 18° clockwise rotation with respect to the North and South China blocks during the post-Late Cretaceous times, which was possibly triggered by the local tectonic activities.