MESOZOIC RADIOLARIAN BIOSTRATIGRAPHY FROM MASIRAH OPHIOLITE, SULTANATE OF OMAN PART I: MIDDLE TRIASSIC, UPPERMOST JURASSIC AND LOWER CRETACEOUS SPUMELLARIANS AND MULTISEGMENTED NASSELLARIANS

阿曼馬瑟拉蛇綠岩體中生代放射蟲生物地層研究（I）中部三疊統、最上部侏羅統及下部白堊統之泡沫放射蟲類及多節織紋放射蟲類

P. DUMITRICA ； A. IMMENHAUSER ； R. DUMITRICA-JUD

《Collection and Research》 9期 (1997/06) Pp. 1-106

摘要

The Masirah Ophiolite of the SE Oman margin represents a fragment of a ＂lost ocean＂ formed in the Late Jurassic at latitude 40°S during the breakup of Gondwanaland. This ocean was subsequently subducted under Eurasia, when Greater India, including the present-day Masirah Ophiolite, its long journey towards the north. Masirah was emplaced onto the passive margin of SE Oman at about 65 Ma before India finally collided with Eurasia in the Paleogene. The autochthonous sedimentary record of the Masirah Ophiolite provides key evidence for a complex geologic history of its oceanic basement covering 150 Ma to the Present. Dating of samples has partly been performed on the basis of radiolarian assemblages, and partly on the basis of foraminifers and nannoplankton. Besides the expected Late Jurassic and Cretaceous radiolarian faunas, Mid-Triassic assemblages were also found in olistostromes shed during the latemost Maastrichtian. Triassic radiolarians are relatively poorly preserved. The Spongosilicarmiger italicus Zone (Oertlispongus inaequispinosus Subzone), Muelleritortis cochleata Zone and Tritortis kretaensis Zone have been recognized, proving the presence of the lower Fassanian, Longobardian, and lower Carnian. Jurassic radiolarians are only represented by upper Tithonian assemblages which are difficult to distinguish from lower Berriasian ones. Cretaceous radiolarians are represented by poorly to well-preserved Berriasian-Barremian, poorly preserved upper Aptian- upper Albian, and very well preserved Coniacian assemblages. Upper Tithonian-Barremian spumellarian and multisegmented nassellarian radiolarians are systematically studied in this first part of the paper. Nassellarians outnumber spumellarians: 70 spumellarian species, of which 10 are new, and more than 200 nassellarian species among which some 130 are multisegmented, of which 43 are new, have so far been recognized. Five new nassellarian genera are also described. Biostratigraphically the Aurisaturnalis carinatus Zone is divided into two new subzones: A carinatus carinatus Subzone (lower-lower upper Barremian) and A. carinatus perforatus Subzone (upper upper Barremian-lower Aptian).

關鍵字

Masirah Ophiolite ； Mesozoic ； Radiolaria ； stratigraphy ； systematics

並列摘要

位於阿曼東南邊疆的馬瑟拉蛇綠岩體是一個失落海洋的殘遺。晚侏羅世期間岡瓦納古陸分裂之際，在當時的南緯40°一帶曾經有一個古海洋，但當印度板塊及現今的馬瑟拉蛇綠岩體經過漫漫長途向歐亞大陸逼近、最後撞擊隱沒之後，這個古海洋也跟著消失了。至於馬瑟拉地塊則在六千五百萬年前，亦即印度板塊即將撞到歐亞板塊的早第三紀時期，被留置於阿曼的東南。馬瑟拉岩體中原地沈積的紀錄爲此種推論提供了關鍵性的證據雄完整地保存了這個海洋一億五千萬年來的歷史資料。地層的定年一部份依賴有孔蟲及超微化石，而放射蟲則是重要的依據，在晚白堊世（latemost Maastrichtian）形成的混同層中，我們發現了晚侏羅世、白堊紀以及中三疊世的放射蟲族群。其中三疊紀放射蟲的保存較差，可以辨識的放射蟲生物地層帶則有Spongosilicarmiger italicus帶（Oertlispongus inaequispinosus亞帶），Muellertortis cochleata帶及Toritortis kretaensis帶，證明該岩層分別屬於中三疊統（lower Fassanan及Longobardian）及上三疊統（lower Carnian）。唯一發現的侏羅紀放射蟲只有最上部的upper Tithonian族群，其與下部白堊統（lower Berriasian）族群極難分辨。白堊紀族群的年代和保存情形分別爲1）早白堊世早期（Berriasian- Barremian，保存不良至良好）；2）早白堊世晚期（late Aptian-late Alban保存不良）以及3）晚白堊世中期（Coniacian，保存良好）在本報告的系統分類部份只包括上部侏羅統至下部白堊統（upper Tithonian-Barremian）的泡沫蟲（spumellarians）和多節織紋蟲（nassellarians），其中織紋蟲（共有200餘種，約130種爲多節，已知43種爲新種）遠多於泡沫蟲（約有70種，其中有10個新種）。文中界訂了五個織紋蟲的新屬。另外在本研究中Aurisaturnalis carinatus帶被劃分成兩個新的亞帶，即A. carinatus carinatus亞帶（lower-lower upper Barremian）及A. carinatus peroratus亞帶（upper upper Barremian-lower Aptian）。

並列關鍵字

馬瑟拉蛇綠岩 ； 中生代 ； 放射蟲 ； 地層 ； 分類系統