云南保山早石炭世头足类

EARLY CARBONIFEROUS CEPHALOPODS OF BAOSHAN, YUNNAN

一、前言滇西保山地区早石炭世沉积是以地台型碳酸盐岩为特征,分布广泛,化石较丰富,但本区石炭纪头足类尚未被报道.近年中国科学院横断山科考队及成都地质学院在保山地区进行地质调查时,先后于保山板桥东北蒋家湾清水沟早石炭世地层中采获一些头足类化石.经研究有鹦鹉螺: Michelinoceras, Mooreoccras, Pseudocyrtoceras, Aphelaeceras, Thrincoceras; 菊石: Merocanites(Michiganites), Imitoceras, Bollandites,Dzhaprakoceras, Girtyoceras. 这些头足类化石为早石炭世维宪期早期的产物,大多数种属在我国属首次报道。

The cephalopods dealt with here were collected from Qingshuigou, Baoshan County, western Yunnan by Hengduan Mountains Scientific Expedition Team and Chengdu College of Geology. After critical identification, 10 genera and 17 species including one new species are recognized, namely, Mickelinoceras sp., Mooreoceras nomale Miller, Dunbar et Condra, Pseudocyrtoceras sp., Aphelaeceras sp., Tkrincoceras sp., Merocanites (Mickigonites) bicarinatus Pareyn, M. (M.) sp., Imitoceras cf. xizangense Liang, Dzhaprakoceras deflexum Kusina, D. subtile Kusina, D. djaprakense (Librovitch), Bollandites bashatchensis Popov, B. cf. boreus Kusina. B. minusculus (Kusina), B. castletonensis (Bisat), B. baoshanensis sp. nov., Girtyoceras platyforme Moore and G. kazakhorum Ruzhencev. This faunule is recorded for the first time in Yunnan and is considered to be of the Early Visean age. The cephalopod-bearing strata may be correlated with the Merocanites-Ammonellipsites zone to lower Beyrichoceras-Goniatites zone in USSR (Ruzhentsev and Bogoslovckaya, 1971) or the upper Fascipericyclus-Amn?onellipsites zone to Beyrichoceras zone (Ramsbottom and Saunders, 1985). Description of new species Bollandites baoshanensis sp. nov. Shell moderate to large, thick-discoidal, semi-involute. Venter and ventrolateral zones well rounded; flanks rather wide and slightly convex. Umbilicus moderate-sized; umbilical shoulder subround. Surface ornamented with fine growth lines and shallow transverse constrictions. Ventral lobe long, strongly divergent forwards; prongs of the ventral lobe curved outwards; lateral lobe rather wide; external saddle round, Comparison: This species is distinguished from B. minusculus (Kusina) by having a thicker conch and. a broader umbilicus. In addition, the new species has more narrow ventral lobes which strongly diverge forwards.