西太平洋晚第三纪钙质超微化石及其古海洋学意义

本文研究了菲律宾海东部,北部“大洋钻探工程”125航次782A和786A二个钻孔晚第三纪的钙质超微化石。本区自下而上划分为13个带(或亚带),存在三个沉积间断:晚渐新世与中中新世之间;中中新世与晚中新世之间以及晚中新世与早上新世之间。据超微化石分析,本区晚第三纪存在4个相对暖水期和4个相对较凉期。根据菲律宾海东部,中部“深海钻探工程”58、59、60三个航次以及我国东海陆架、台湾东海岸及西部地区,南海北缘等地钙质超微化石分带的对比,晚渐新世与早中新世之间以及中、上新世之间的沉积间断在环西太平洋一侧具有普遍性,但形成原因不尽相同。

NEOCENE CALCAREOUS NANNOFOSSILS FROM THE WEST PACIFIC OCEAN AND THEIR SIGNIFICANCE FOR PALEO-OCEANOGRAGHY

The study area named Bonin basin was located in the north of the Philippine Sea. The area is a complex arc and basin series formed since the start ofwestward subduction of Pacific lithosphere in Eocene. This paper addresses the nannofossil stratigraphy of Miocene-Pliocene sediments, and these materials were collected from two holes, 782A and 786A, Ocean Drilling Program, Leg 125. Based on Okada and Bukry's zonation, there are 13 zones (or subzones), of them, Zones CN1-3, Zone CN8 and Subzone CNl0a are missing. The three hiatuses were detected as follows: between Upper Oligocene/Middle Miocene, within Late Miocene, and between Late Miocene/Early Pliocene. The relative abundance of Reticulofenestra pseudoumbilica and R.Haqii is very high and may make up 40 percent of the total content of calcareous nan-noplankton in Miocene. It indicates that the calcareous nannoplankton is a typical mid-latitude assemblage. In Neogene of this area we can identify four relative warmer stages, and four relative colder stages based on the relative abundance of Discoaster+Sphenolithus, the ratio of abundance of Discoaster/Coc-colithus, the ratio of abundance of Dsicoaster peniaradiatus+'D.brouweri/ D.intercalaris+D.surculus, the relative abundance of. Coccolithus pelagicus, and the change of complex diversity (D). The four relative warmer stages can basically coincide with the high abundance of calcium carbonate content. The warmest stage in the Neogene is middle Middle Miocene (Subzone CN5a) from the study area. The hiatus between Late Oligocene/Miocene is common in the Philippine basin everywhere, and it also can be found in the East China Sea, South China Sea and west or east of Taiwan. But the number of nannofossil zones which are-missing is different in different region. In the abyssal region the hiatus may be formed by the scouring of bottom currents, but the hiatuses in the continental shelf of China sea and sea area near Taiwan are definitely related to the regression of Northern Hemisphere in this time. The hiatus between Miocene/Pliocene is common in the West Pacific Ocean and the continental shelf of China sea.