Early Cambrian (Stage 4) brachiopods from the Shipai Formation in the Three Gorges area of South China

Yue Liang,Lars E Holmer,Xiaolin Duan,Marissa J Betts,Fan Liu,Zhifei Zhang,Yanlong Chen

doi:10.1017/jpa.2020.117

Yue Liang, Lars E Holmer + Show 5 more

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https://doi.org/10.1017/jpa.2020.117

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Abstract

AbstractDiverse and abundant fossil taxa have been described in the lower Cambrian Shipai Formation in the Three Gorges area of Hubei Province, South China, but the taxonomy and diversity of the co-occurring brachiopod fauna are still far from clear. Here we describe the brachiopod fauna recovered from the Shipai Formation in the Three Gorges area of South China, including representatives of the subphylum Linguliformea: linguloids (Lingulellotreta ergalievi,Eoobolus malongensis, and Neobolidae gen. indet. sp. indet.), and an acrotretoid (Linnarssonia sapushanensis); and representatives from the subphylum Rhynchonelliformea: the calcareous-shelled Kutorginates (Kutorgina sinensis,Kutorginasp., andNisusia liantuoensis). This brachiopod assemblage and the first occurrence ofLinnarssonia sapushanensisshell beds permit correlation of the Shipai Formation in the Three Gorges area of Hubei Province with the Stage 4 Wulongqing Formation in the Wuding area of eastern Yunnan. This correlation is further strengthened by the first appearance datum (FAD) of the rhynchonelliform brachiopodNisusiain the upper silty mudstone of both the Shipai and Wulongqing formations. The new well-preserved material, derived from siliciclastic rocks, also gives critical new insights into the fine shell structure ofL.sapushanensis. Microstructural studies on micromorphic acrotretoids (likeLinnarssonia) have previously been restricted to fossils that were acid-etched from limestones. This is the first study to carry out detailed comparative ultrastructural studies on acrotretoid shells preserved in siliciclastic rocks. This work reveals a hollow tube and solid column microstructure in the acrotretoid shells from the Shipai Formation, which is likely to be equivalent of traditional column and central canal observed in shells dissolved from limestones.

Highlights

Brachiopods are among the most important faunal components of Palaeozoic marine communities, and have a long geological history dating back to the early Cambrian (Terreneuvian, Stage 2) (Sepkoski et al, 1981; Holmer et al, 1996; Bassett et al, 1999; Carlson, 2016; Z.F. Zhang et al, 2016; Harper et al, 2017)
The recovered brachiopod fauna comprises six families, including Acrotretidae, Lingulellotretidae, Eoobolidae, Neobolidae, Nisusiidae, and Kutorginidae. This brachiopod fauna displays close similarity to the Guanshan fauna previously described from the Wulongqing Formation (Stage 4), eastern Yunnan (Hu et al, 2013; Zhang et al, 2020a, b)
>4500 individual valves have been collected from the Shipai Formation at Yichang by the work-team of the Early Life Institute (ELI), and all specimens are deposited in the Northwest University Early Life Institute, Xi’an, China

Summary

Introduction

Brachiopods are among the most important faunal components of Palaeozoic marine communities, and have a long geological history dating back to the early Cambrian (Terreneuvian, Stage 2) (Sepkoski et al, 1981; Holmer et al, 1996; Bassett et al, 1999; Carlson, 2016; Z.F. Zhang et al, 2016; Harper et al, 2017). The recovered brachiopod fauna comprises six families, including Acrotretidae, Lingulellotretidae, Eoobolidae, Neobolidae, Nisusiidae, and Kutorginidae This brachiopod fauna displays close similarity to the Guanshan fauna previously described from the Wulongqing Formation (Stage 4), eastern Yunnan (Hu et al, 2013; Zhang et al, 2020a, b). The Shuijingtuo Formation (black shale and limestone) disconformably overlies the Yanjiahe Formation, and has yielded abundant and diverse shelly fossils, including brachiopods, in addition to the oldest eodiscoid trilobites in South China The upper boundary of the Shipai Formation is marked by the contact with the argillaceous striped and oolitic limestone of the Tianheban Formation, which is itself conformably overlain by the dolomitic Shilongdong Formation (Fig. 1.3)

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