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辽西凌源地区张家口组是否存在及其与义县组之间关系的问题一直存在争议。笔者研究表明,凌源地区不仅存在张家口组,而且其与义县组之间为角度不整合接触,它们是不同构造层的产物;义县组的底部层位即为大王杖子层(尖山沟层)。激光ICPMS锆石U-Pb测年得出该地区张家口组火山岩顶界年龄为132.4～130.2Ma,前人得出该地区义县组底部层位(即大王杖子层)的形成时代为126～123Ma,反映该地区张家口组顶部与义县组底界之间存在约6Ma的时间间隔。此时间间隔内研究区不仅发生了构造格架的转换,也是辽西北票—义县地区幔源高镁火山岩的主体喷发期,中国东部中生代岩浆作用也在此时期达到高潮,翼北—辽西地区该时期之后发生了热河生物群大爆发,说明该时期也是一个重要的生物界限。
There is controversy over the existence of the Zhangjiakou formation in the Lingyuan area of western Liaoning and its relationship with the Yixian formation. The author’s research shows that not only the Zhangjiakou Formation but also the unconformity contact with the Yixian Formation exist in the Lingyuan area, which are the products of different tectonic layers. The bottom layer of the Yixian Formation is the Wangzhangzi Formation ). The ICP-MS zircon U-Pb dating of the volcanic rocks in the Zhangjiakou Formation in the area from 132.4 to 130.2 Ma indicates that the formation age of the lowermost member of the Yixian Formation in this area (ie, Wangzhangzi Formation) is 126-123 Ma , Reflecting a time interval of about 6 Ma between the top of Zhangjiakou Formation and the bottom of Yixian Formation in this area. During this interval, not only tectonic framework transformation but also the main eruption of mantle-derived magnesia volcanic rocks in the ticket-Yixian area of western Liaoning Province and the Mesozoic magmatism in eastern China peaked at this period. The Jehol Biota explosion occurred after this period, indicating that this period is also an important biological boundary.