藏北羌塘丁固—加措地区康托组的时代

Age of the Kangtog Formation in the Dinggo-Gyaco area, Qiangtang, northern Tibet, China.

自西藏区域地质调查大队创建康托组以来,康托组岩石地层单位广泛应用于羌塘地区,普遍认为其时代为新近纪。笔者于丁固—加措地区的康托组地层中采获古近纪轮藻化石Obtusocharasp.,O.lanpingensis,Gyrogonaqinajiangica和部分孢粉化石,并在康托组底部安山岩中获K-Ar年龄65.1～66.5Ma。上述轮藻组合与同位素年龄指示的地层时代为古新世—始新世,据此将测区康托组的时代确定为古近纪。由于测区康托组之上被唢纳湖组或鱼鳞山组角度不整合覆盖,因此康托组时代的确定不仅进一步完善了测区新生代地层系统,还指示测区在康托组与唢纳湖组或鱼鳞山组之间发生了一次强烈的构造运动。

Since the Regional Geological Survey Party of Tibet （1986） established the Kangtog Formation, the Kangtog Formation has been widely applied in the Qiangtang area. Its age is generally thought to be Neogene. The authors have obtained the Paleogene charophytes Obtusochara sp., O. lanpingensis and Gyrogona qinojiangica in the Kangtog Formation in the Dinggo-Gyaco area and K-Ar ages of 65.1-66.5 Ma for andesite at the base of the Kangtog Formation. The ages of the strata indicated by the above-mentioned charophyte assemblage and isotope ages are Paleocene-Eocene. On that basis, the age of the Kangtog Formation in the survey area is determined to be Paleogene. Because the Kangtog Formation in the area is unconformably overlain by the Suonahu or Yulinshan Formation, the determination of the age of the Kangtog Formation not only further improves the Cenozoic stratigraphic system in the area but also indicates the occurrence of a strong tectonic movement between the Kangtog Formation and the Suonahu or Yulinshan Formation in the area.