记述产自西藏南部仲巴县的一个中国目前所知最年轻的菊石群 ,含 2科 4属 6种 ,其中 4新种。据菊石群面貌和它们所产出的层位可以划分出上、下两个组合带 :上部Pachydiscuscf.hidakaensis Libycoceraszhongbaense组合带 ;下部Manambolitescujiangdingensis M .pivaeteaui组合带。产菊石的曲贝亚组的下段和上段的中、下部(82F5 0及其以下层位 )为晚Campanian期 ,上段上部 (即 82F5 2及其以上层位 )为早Maastrichtian期。

This paper deals with an ammonoid fauna found in Zhongba County southern Xizang (Tibet), which is the youngest ammonoid fauna in age known in China at present. The fauna involves 2 families, 4 genera and 6 species (including 4 new species). Based on the features of ammonoid fauna and the vertical distribution, an upper and a lower assemblage zones have been distinguished: The upper assemblage Zone Pachydiscus cf. hidakaensis Libycoceras zhongbaense assemblage zone: only 2 genera, 2 species are found and the latter is a new species. Based on the fact that the former species was originally yielded in early Maastrichtian beds in Hokkaido, Japan, while the latter is similar to L.ismaelis , whose range is from late Campanian to late Maastrichtian, the age of this assemblage is referred to early Maastrichtian. The lower assemblage Zone Manambolites cujiangdingensis M. pivaeteauti assemblage zone: 3 genera, 5 species are found. In addition to the two marker species of the zone, the others are Coahuilites zhongbaensis sp.nov., Libycoceras tibetioum sp.nov. and L. zhongbaense sp.nov. Based on the occurrence of genus Manambolites being resticted to middle to late Campanian, especially the presence of M.pivaeteaui being only found in late Campanian both in Madagascar and Tunisia, it is appropriate to assign this assemblage zone to late Campanian. Ages of the beds yielding ammonoids are suggested as follows: Qubeiya Formation: The major part of the lower member, and lower and middle part of upper members (the beds below 82F50) can be assigned to late Campanian, while the upper part of the upper member (82F52 and the beds above) should be early Maastrichtian in age. As for the overlying Quxia Formation without ammonoids it is inferred that probably a part of the early Maastrichtian and late Maastrichtian are involved based on the findings of late Maastrichtian foraminifers and the boundary clay layer with iridium anomaly, which is commonly found at K T boundary in many places throughout the world. The considerable part of the upper Padana Formation underlying the Qubeiya Formation is also deducted and dated as early Campanian in age although no fossil evidence has been found.

Q915.818.4