鄂西奥陶系庙坡组海林檎Cheirocrinus penniger(Eichwald,1842)的发现

First record of Cheirocrinus penniger (Eichwald, 1842)(Cystoidea) from the Ordovician Miaopo Formation in western Hubei, China

鄂西地区中–晚奥陶世之交的庙坡组由数米厚的页岩夹少量薄层灰岩构成,沉积于扬子陆表海区凹陷带中,深度位于最大浪基面下,含有多样性、丰度高的化石组合。宜昌北部的陈家河剖面以及远安真金剖面庙坡组中–上部页岩属晚奥陶世桑比期Nemagraptus gracilis笔石带。笔者在该层位首次采获30余枚海林檎化石,经系统古生物学鉴定均为Cheirocrinus penniger (Eichwald, 1842)。远安真金剖面产出的C. penniger标本多以萼部区数个不同类型压扁的骨板形式保存, 1枚标本保存有完整的茎部;宜昌陈家河剖面的C. penniger标本均以单个萼部骨板形式保存。奥陶纪的Cheirocrinus广泛分布于多个板块,本文描记庙坡组的Cheirocrinus化石记录实例,扩展了该属在华南板块的时空分布,它可以从黔南三都早奥陶世斜坡相的同高组延续到晚奥陶世台内凹陷带的庙坡组。

The Miaopo Formation of the Middle–Upper Ordovician transition in western Hubei Province of China, is a few meters thick and composed of shales intercalated with thin-bedded bioclastic limestones. It was deposited in an intra–platform depression with marine–floor depth below major wave-base of the Yangtze Epicontinental Sea. The unit is high biodiversity and has an abundance of macrofossils. We report for the first time on Cystoidea fossils from the shales in the mid-upper part of the Miaopo Formation at Chenjiahe section of northern Yichang, and Zhenjin section of Yuan’an County. Based on the co-occurred graptolitic faunas, the units yielding more than 30 Cystoidea fossils are assigned to the Nemagraptus gracilis Biozone of the basal Sandbian, Upper Ordovician. Cystoidea fossils are morphologically identified and described as Cheirocrinus penniger(Eichwald, 1842). In taphonomic aspect, the C. penniger fossils from the Zhenjin section are dominated by aggregated and compressed calyx plates, including a complete specimen with column preserved. Same species from the equivalent horizon at the Chenjiahe section are single disarticulated calyx plates. The Cheirocrinus was a cosmopolitan genus in the Ordovician. Cheirocrinus of the present discovery expands the temporal and spatial distribution of the genus, i.e. from the Early Ordovician Tonggao Formation(slope facies) to the Late Ordovician Miaopo Formation(intra-platform depression) in the South China Block.