Abstract: The dates reported by Smith et al. in 1995 are the first 40 Ar- 39 Ar ages for the Jehol Group in western Liaoning, Northeast China, which provide a considerably improved age calibration of the lowermost Yixian Formation of the Jehol Group, and indicate that the whole group was deposited entirely within the Early Cretaceous time. However, because Smith et al.' s report mistook the dates of three epigenetic igneous rock samples as the ages of the upper and lower parts of the Yixian Formation, respectively (samples 5, 10, 4), the isotopic dating results, as a whole, are perplexing and have been greatly misunderstood since they were published in 1995. In fact, those dates for the Jehol Group by Smith et al. represent the 40 Ar- 39 Ar ages of at least four horizons: 122.9 ± 0.3Ma (volcanics underlying the Daxinfangzi Bed of the Yixian Formation), 122.1 ± 0.2— 122.5 ± 0.3Ma (Ershilipu Bed of the Yixian Formation), 121.5 ± 0.9— 121.6 ± 0.5Ma (volcanic breccias above the Jingangshan Bed of the Yixian Formation), 120.8 ± 0.4— 121.4 ± 0.7Ma (epigenetic igneous rocks overlying or intruding into the Yixian Formation).

摘要： 对Smith等1995年热河群40Ar-39Ar 同位素测年工作的背景以及各样品的采样地点、层位与测年目的等作了补充介绍。由于Smith等的论文中将3组后期火山岩的测年结果分别误解为义县组下部与上部地层的同位素年龄，因而整体上混淆了义县组不同层位的测年结果。Smith等1995年发表的6组样品的测年数据实际上至少代表了4个与热河群义县组相关层位的40Ar-39Ar 同位素年龄:122.9±0.3Ma(凌源大新房子沉积层下伏火山岩),122.1±0.2~122.5±0.3Ma(凌源二十里堡沉积层),121.