Lower Miocene to Quaternary Diatom Biostratigraphy of Leg 57, off Northeastern Japan, Deep Sea Drilling Project
Lower Miocene to Quaternary Diatom Biostratigraphy of Leg 57, off Northeastern Japan, Deep Sea Drilling Project
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日本东北部海域深海钻探项目第 57 段下中新统至第四纪硅藻生物地层学
DOI：
10.2973/dsdp.proc.5657.117.1980
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发表时间：
1980
期刊：
影响因子：
--
通讯作者：
J. Barron
中科院分区：
文献类型：
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作者：
J. Barron
在第57航次期间回收的沉积物为西北太平洋的硅藻提供了一个几乎完整的中新世晚期至全新世的复合参考剖面。高纬度和中纬度硅藻占主导地位的组合，但由于暖水黑潮的影响，低纬度硅藻一直存在于低丰度。与赤道太平洋古地磁地层学相关的低纬度硅藻基准面显示，在第57航次地点北纬40°处，时间上几乎没有位移。高纬度和低纬度的硅藻带是可识别的上中新世到第四纪的网站438和440，从而允许这些地带的上中新世的第一个直接详细的相关性。提出了11个新的亚区，这提供了完善现有的北太平洋高纬度硅藻地带性。此外，还对Denticula lauta带的底界进行了界定，并提出了中新统上、下统的Actinocyclus ingens带。在438号和440号站点发现了一个中新世晚期的间断，时间跨度约为560万年至670万年。在北太平洋中高纬度地区，无论是在陆坡还是在海盆，都存在着相关的间断。在加州的海岸，这段时间对应于沉积物积累速率的增加，这与从层压泥岩到上覆的更大块的泥质泥岩的过渡有关。这些中新世最新的沉积事件显然与全球变冷事件有关。北太平洋新近纪硅藻生物地层学近年来进展迅速（Burckle和Opdyke，1977; Koizumi，1977）。在低纬度地区，Burckle（1972，1977）的硅藻分带已被广泛接受，而Koizumi（1973，1975 b）的分带可以很容易地应用于高纬度地区和日本。几个硅藻基准面（第一次和最后一次出现）与低纬度（Burckle，1972; 1978）和高纬度（Donahue，1970; Koizumi，1975 d）的古地磁地层学直接相关。Burckle和Opdyke（1977）和Koizumi（1977）提供了上新世和第四纪高纬度和低纬度硅藻带的相互对比;然而，由于缺乏合适和完整的地层剖面，无法详细对比中新世的带。在深海钻探项目的日本海沟断面（第56和57航段，1977年9月至12月）期间，沿着北纬40°左右横跨日本海沟的东西断面采集了一系列中新世至第四纪硅质参考剖面（图1）。第57航次在两个地点（地点438和440）恢复了一个几乎完整的新近纪硅质记录，作为一个复合物，在整个剖面中含有相当常见的、保存良好的硅藻。腿57网站附近的冷水Oyashio电流和暖水黑潮电流，和热带和高纬度硅藻组合的混合物，结果允许详细的相关性低和高纬度地带的中中新世通过全新世。此外，第57航段站点距离海岸足够近（约130至200 km），因此始终存在可用于日本和加州相关性的近海岸浮游硅藻。本章的硅藻分带与小泉（Koizumi，1973，1975 b）的高纬度北太平洋硅藻分带略有不同（图2）。提出了11个新的亚带和一个附加带，Actinocyclus ingens带，并定义了Denticula lauta带的基底。这种分带总结如下，生物地层学部分有其他评论。Denticulaericae Zone（Koizumi，1973）定义：从最后一次出现到现在的时间间隔。分区：无。备注：最后一次出现的海链藻nidulus var. nidulus与带的底部重合（Koizumi，1977）。
Sediments recovered during Leg 57 provide a nearly complete lower Miocene to Holocene composite reference section for diatoms in the northwestern Pacific. Highand middle-latitude diatoms dominate the assemblages; however, because of the influence of the warm-water Kuroshio Current, low-latitude diatoms are consistently present in low abundance. Low-latitude diatom datums tied to paleomagnetic stratigraphy in the equatorial Pacific show little or no displacement in time at the 40°N latitude of the Leg 57 sites. Both highand low-latitude diatom zones are recognizable in the upper Miocene to Quaternary of Sites 438 and 440 and thus allow the first direct detailed correlation of these zonations for the upper Miocene. Eleven new subzones, which offer refinement of the existing high-latitude diatom zonation of the North Pacific, are proposed. In addition, the base of the Denticula lauta Zone is defined, and a new zone, the Actinocyclus ingens Zone, is proposed for the upper lower Miocene. A late Miocene hiatus spanning the interval from about 5.6 to 6.7 m.y.B.P. is identified at Sites 438 and 440. Correlative hiatuses occur throughout the middleand high-latitude North Pacific both on the continental slopes and in the ocean basins. Onshore in California, this interval corresponds with an increase in the rate of sediment accumulation associated with the transition from laminated diatomites to overlying, more massive diatomaceous mudstones. These latest Miocene sedimentologic events apparently are related to a global cooling event. INTRODUCTION Neogene diatom biostratigraphy in the North Pacific has progressed rapidly in recent years (Burckle and Opdyke, 1977; Koizumi, 1977). In low latitudes the diatom zonation of Burckle (1972, 1977) has found wide acceptance, whereas Koizumi's (1973, 1975b) zonation can readily be applied in high latitudes and in Japan. Several diatom datum levels (first and last occurrences) have been correlated directly with paleomagnetic stratigraphy both in low latitudes (Burckle, 1972; 1978) and in high latitudes (Donahue, 1970; Koizumi, 1975d). Burckle and Opdyke (1977) and Koizumi (1977) have provided cross-correlations of the highand low-latitude diatom zonations for the Pliocene and Quaternary; however, the lack of suitable and complete stratigraphic sections has prevented detailed correlations of the zonations for the Miocene. During the Japan Trench Transect of the Deep Sea Drilling Project (Legs 56 and 57, September to December, 1977), a series of excellent Miocene to Quaternary siliceous reference sections were cored along an east to west transect at about 40°N latitude across the Japan Trench (Figure 1). Leg 57 recovered a nearly complete Neogene siliceous record as a composite at two sites (Sites 438 and 440) which contains fairly common, moderately well-preserved to well-preserved diatoms throughout the section. The Leg 57 sites lie near the present-day confluence of the cool-water Oyashio Current and the warm-water Kuroshio Current, and the mixture of tropical and highlatitude diatom assemblages that results allows detailed correlation of lowand high-latitude zonations for the middle Miocene through the Holocene. In addition, the Leg 57 sites are near enough to shore (about 130 to 200 km) that nearshore planktonic diatoms, which are useful in correlations in Japan and in California, are consistently present. ZONATION The diatom zonation of this chapter is modified slightly from the high-latitude North Pacific diatom zonation of Koizumi (1973, 1975b) (Figure 2). Eleven new subzones and one additional zone, the Actinocyclus ingens Zone, are proposed, and the base of the Denticula lauta Zone is defined. This zonation is summarized below, and additional comments appear in the biostratigraphy section. Denticula seminae Zone (Koizumi, 1973) Definition: The interval from the last occurrence of Rhizosolenia curvirostris to the present. Subzones: None. Remarks: The last occurrence of Thalassiosira nidulus var. nidulus coincides with the base of the zone (Koizumi, 1977).