A Middle Jurassic (Upper Bajocian) Radiolarian Assemblage from Snowshoe Formation, East-Central Oregon

美國奧瑞岡中東地區中侏羅世（晚巴柔期）放射蟲族群

葉貴玉(Kuei-yu Yeh)

《Collection and Research》 24期 (2011/12) Pp. 1-77

https://doi.org/10.6693/CAR.2011.24.1

摘要

This is the second in a series of studies dealing with the whole fauna taxonomic studies of Middle Jurassic radiolarian assemblages from the Snowshoe Formation, east-central Oregon. All the studied specimens were obtained from a limestone nodule (with locality number OR549B). Totally 126 forms were identified and assigned respectively to 26 families and 46 genera. Among them 19 new species, one new genus (Barbuta Yeh) and one new family (Barbutidae Yeh) are described. The studied assemblage is moderately high in diversity. It is characterized by the abundant occurrence of Emiluvia brevispina Yeh, n. sp., Emiluvia meganodosa Yeh, n. sp., Emiluvia parvinodosa Yeh, n. sp., Hiscocapsa minuta Yeh, n. sp., Hsuum lupherium Pessagno and Whalen, Hsuum porasolense Pessagno and Whalen, Hsuum robustum Pessagno and Whalen, Leugeo parvispina Hull, Perispyridium facetum Pessagno and Blome, Perispyridium tamarackense Pessagno and Blome, Praeparvicingula burnsensis (Pessagno and Whalen), Praeparvicingula grantensis (Pessagno and Whalen) and Praeparvicingula sodaensis (Pessagno and Whalen). The forms with large size tests and muticyrtid nassellarians with skirt-like structure at final post-abdominal chamber are found completely absent in the studied fauna. The results of this study are not only helpful to understand the Middle Jurassic radiolarian faunas from North America, but also providing useful information to establish the Middle Jurassic biostratigraphic zonal scheme and to do future studies on global faunal comparison.

關鍵字

Radiolarian ； Bajocian ； Middle Jurassic ； Snowshoe Formation ； east-central Oregon

並列摘要

本文乃筆者自2009開始針對美國奧瑞岡中東地區之斯諾秀組（Snowshoe Formation）出土之一系列中侏羅世放射蟲完整族群（whole fauna）進行系統分類研究所完成的第二篇研究報告。本研究之放射蟲標本皆為培桑諾教授（Emile A. Pessagno, Jr.）贈與國立自然科學博物館、產地編號OR549 B的一塊鈣質結核標本，經筆者親自處理所得。本研究之放射蟲族群歧異度甚高，總共有126種，分別歸屬於26科41屬，包括本文新描述的19個新種、1個新屬（Barbuta Yeh）和1個新科（Barbutidae Yeh）。根據前人對菊石標本之定年資料，OR549 B之所屬年代為中侏羅世巴柔晚期（late Bajocian, Middle Jurassic）。本研究族群之主要特徵有三：包括（一）個體數量較多種有Emiluvia brevispina Yeh, 新種，Emiluvia meganodosa Yeh, 新種，Emiluvia parvinodosa Yeh, 新種，Hiscocapsa minuta Yeh, 新種，Hsuum lupherium Pessagno and Whalen，Hsuum parasolense Pessagno and Whalen，Hsuum robustum Pessagno and Whalen，Leugeo parvispina Hull，Perispyridium facetum Pessagno and Blome，Perispyridium tamarackense Pessagno and Blome，Praeparvicingula burnsensis（Pessagno and Whalen），Praeparvicingula grantensis（Pessagno and Whalen）以及Praeparvicingula sodaensis（Pessagno and Whalen）；（二）標本個體皆偏小（小於180μm），以及（三）帶有喇叭狀開口或最後一節附有裙擺狀延伸構造的罩籠蟲完全沒有出現；其古生態意義有待進一步研究。本報告不僅有助於吾人對北美中侏羅放射蟲族群之認識，亦對全球中侏羅世放射蟲生物地層帶之建立及比對提供重要資料。

並列關鍵字

放射蟲 ； 巴柔期 ； 中侏羅世 ； 斯諾秀組 ； 奧瑞岡中東地區