MIOCENE PELECYPODA IN THE WESTERN FOOTHILLS OF NORTHERN TAIWAN (PART I: STRATIGRAPHY, FAUNAL OCCURRENCES AND PALEOCEANOGRAPHIC SIGNIFICANCES)

臺灣西部麓山帶北段中新世斧足類化石研究（I：地層學、化石產狀及古海洋學意義）

黃奇瑜(CHI-YUE HUANG) ； 增田孝一郎(KOICHIRO MASUDA) ； 吳樂群(LEH-CHYUN WU)

《Collection and Research》 2期 (1990/12) Pp. 119-139

摘要

Miocene and latest Oligocene pelecypods were studied for Kuohsing-Nantou, Pitou, Mawutu, and Hsintien areas of the western foothills in northern and central Taiwan. Among them 34 species (39070) occur restrictly in the late Miocene Kueichulin Formation, 19 species (22%) are commonly found in both the late and early-middle Miocene formations, while 34 species (39%) are observed only in the early-middle Miocene sequences. The studied pelecypods all occur in an inner neritic environment. The early Miocene pelecypod fauna is very different from the late Oligocene fauna, but it is similar to those from the middle Miocene strata. A distinct faunal turnover of pelecypods is observed between middleMiocene and late Miocene assemblages. Geographic parallelism of the molluscan faunal change occurs between Taiwan and southwestern Japan. In Taiwan, temporal parallelism of faunal turnovers is recognized in pelecypods and benthic foraminifers. The Taiwan late/middle Miocene turnover event of pelecypods is equivalent to the post-Lushanian faunal change of benthic foraminifers, and is correlatable with the faunal change event from the Kadonosawa fauna (middle Miocene) to the Sagara fauna (late Miocene) in southwestern Japan. This faunal turnover in mollusks and benthic foraminifers might represent a paleoceanographic event of an intensification of the Kuroshio current in the Western Pacific. The pelecypod faunal turnover at the Miocene/Oligocene boundary is also recognizedin a change of foraminiferal compositions from the Shihtsaoan fauna to the Kuohsinian fauna. This event at the Miocene/Oligocene boundary might be attributed to a global paleoclimatic change from the cool Oligocene to the warm Miocene.

關鍵字

Miocene ； Pelecypods ； Stratigraphy ； Taiwan

並列摘要

本文研究臺灣北部西部麓山帶國姓－南投、鼻頭、馬武督及新店地區中新世及晚漸新世斧足類化石。於所採得之中新世化石中，34種(約佔39% ) 化石僅見於晚中新世桂竹林層， 19種(22 % ) 常見於晚期及早期一中期中新世地層，34種( 39% ) 則局限於早一中中新世地層。所有研究標本均產於內陸棚環境。早中新世斧足類化石群與晚漸新世化石群差異極大，但與中中新世化石群極為類似。在晚中新世與中中新世地層之間有一明顯之斧足類化石群變異。在臺灣與西南日本間可以發現軟體動物化石群的地理性平行變異現象。而在臺灣可以發現斧足類與底棲性有孔蟲化石間的時間性平行化石群變異關係。在臺灣晚中新世／中中新世間的斧足類化石群變異相當於同一時間的後廬山階底棲有孔蟲化石群變異，並可對比於西南日本門，澤化石群（中中新世）與晚中新世相良化石群間的變異。這個顯示在軟體動物與底棲孔蟲化石群的變異代表著在西太平洋的一個黑潮強化古海洋事件。斧足動物化石群於中新世／漸新世間的變異現象亦可見於底棲性有孔蟲化石群由石(石曹)階進入國姓階間的變異。此事件可能是由寒冷的漸新世進入溫暖的中新世古氣候變化所導致。

並列關鍵字

台灣 ； 中新世 ； 斧足類 ； 地層學 ； 化石產狀 ； 古海洋