|mhorn||Дата: Thursday, 25.06.2015, 12:24 | Сообщение # 1|
|Li G., Matsuoka A. (2015) Searching for a non-marine Jurassic/Cretaceous boundary in northeastern China // The Journal of the Geological Society of Japan. Vol.121. No. 3. P.109-122. |
The well-developed Jurassic and Cretaceous strata of northeastern China are mostly of non-marine origin. The definition of the non marine Jurassic/Cretaceous (J/K) boundary in northeastern China is based mainly on the age assignment of the well-known non-marine Jehol Biota of eastern Asia. Although the Eosestheria-Ephemeropsis-Lycoptera-bearing strata in China, Mongolia, and Transbaikalia (Russia) were originally assigned to the Early Cretaceous in the 1920s, the age of the entire Jehol Group of western Liaoning, northeastern China, which contains the Jehol Biota in the lower part and the Fuxin Biota in the upper part, was revised to Middle-Late Jurassic during the early 1960s. This age revision was further supported by the recovery of an apparent Bathonian (Middle Jurassic) Arctocephalites ammonite fauna and a Late Jurassic Buchia fauna from eastern Heilongjiang Province in the middle 1980s. During the early 1990s, through revisions of the ages of the above-mentioned marine faunas of eastern Heilongjiang from Jurassic to Early Cretaceous, the Jehol Biota was re-dated as Early Cretaceous by some authors. At the same time, the recovery of feathered dinosaurs, early birds, mammals, and angiosperms from the Yixian and Jiufotang formations encouraged precise radiometric dating of the Jehol Group and its underlying strata in western Liaoning and northern Hebei. The new radiometric dating indicates that the non-marine J/K boundary in northern China falls within the contemporaneous Houcheng Formation (northern Hebei) and Tuchengzi Formation (western Liaoning), which are stratigraphically much lower than the Jehol Group of western Liaoning.
Middle Jurassic - Lower Cretaceous ammonites & aptychi