Cenozoic Calcareous Nannofossil Biostratigraphy from the Northeastern Atlantic OceanDeep Sea Drilling Project Leg 81
Cenozoic Calcareous Nannofossil Biostratigraphy from the Northeastern Atlantic OceanDeep Sea Drilling Project Leg 81
复制标题
东北大西洋新生代钙质超微化石生物地层学深海钻探项目第 81 段
DOI：
10.2973/dsdp.proc.81.105.1984
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发表时间：
1984
影响因子：
5.3
通讯作者：
J. Backman
中科院分区：
文献类型：
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作者：
J. Backman
使用钙质超微化石，生物地层学分析的沉积序列在腿81钻探显示连续上新近纪沉积在所有网站，除了在网站555上新世是失踪。上新世的一系列灾难性事件的消失实际上与它们的低纬消失是同步的。一个例外是Discoaster surculus，它在冰筏沉积开始时消失，0.1百万年。在其灭绝年龄之前; D. pentaradiatus在冰筏漂流的第二低周期开始时消失，非常接近其灭绝年龄。冰筏漂流的开始是一个突然的事件，它反映了240万年前欧洲北方主要冰川作用的开始。前下中新统和中中新统层序的代表性较差，只有555号站点显示了一个扩展和连续的中中新统层序。554号站点显示了最长的渐新世层序，但它是浓缩的（11.5米），可能被间断破坏。锰的形成发生在渐新世早期（552A孔）和554号站点（被上始新世覆盖）始新世期间。上始新世和中始新世层段的代表性较差;例如，Chiasmolithus gigas亚区（CP13b亚区或NP15区）仅存在于单个2 cm厚的层位（552 A孔）中。552号站点显示了始新世NP11至NP14区的最完整记录，而NP10区在553和555号站点显著扩大。仅在555站点恢复了明确的上古新统（NP9区），该层序夹在两个玄武岩堆之间。引言8孔在4个地点钻在西南边缘的罗科尔高原在大西洋东北部的第81腿的深海钻探项目。研究中心位置见图1。所恢复的沉积物产生了更新世至上古新统的钙质超微化石，表1 - 8中列出了所选样品的分布。调查了大约1200个样本。上新近纪和下始新世反映了几乎连续的沉积，而只有片段的干预间隔保存。因此，将新近系和古近系层序分别提出并讨论。分类群的分布是通过定性估计的相对丰度。新近纪表显示了三个相对丰度水平：实心圆圈代表丰度超过总组合的10%;空心圆圈代表丰度在1%和10%之间;十字代表丰度小于总组合的1%。从始新世下部和古新世上部陆架沉积物中形成的碎屑岩通常含有极低丰度的颗石。在许多样本中，要找到足够的样本来估计相对丰度遇到了相当大的困难，而在许多其他样本中，这种估计结果完全没有意义。由于无法成功地获得相对丰度的一致估计，古近系丰度被显示为“罕见”（空心方块）或“更常见”（实心方块）。渐新世20 10 ° W Roberts，D. G.，Schnitker，D.，等]，init.共和党人DSDP，81：华盛顿（美国政府印刷局）。2地址：瑞典斯德哥尔摩S-106 91，斯德哥尔摩大学地质系。图1.第81航段（552 - 555号场地）、第48航段（403 - 404号场地）和第12航段（117号场地）期间钻探的场地位置。和中上始新世组合被纳入该系统，以保持表中的内部一致性，尽管表示新近纪样品丰度的方法可以应用于多个样品水平。以前对罗卡尔地区钙质超微化石生物地层学的研究包括PerchNielsen（1972）和Müller（1979）的研究。这些作者以及本作者主要依赖于Martini（1971）、Bukry（1973，1975）以及Okada和Bukry（1980）提出的生物地层分带。它们的分带方案主要反映了热带和亚热带地区物种进出的地层关系。因此，一些地层-
Using calcareous nannofossils, a biostratigraphic analysis of sedimentary sequences drilled during Leg 81 reveals continuous upper Neogene deposition at all sites, except at Site 555 where the Pliocene is missing. The series of Pliocene discoaster disappearances are practically synchronous with their low latitude extinctions. An exception is Discoaster surculus which disappears at the initiation of ice-rafted deposition, 0.1 m.y. prior to its extinction age; D. pentaradiatus disappears at the beginning of the second lowest cycle of ice rafting, very close to its extinction age. The onset of ice rafting is an abrupt event, which reflects the initiation of major northern European glaciation at 2.4 m.y. ago. The lower and middle Miocene sequences are poorly represented, except at Site 555 which shows an expanded and continuous middle Miocene sequence. Site 554 shows the longest Oligocene sequence, but it is condensed (11.5 m) and probably marred by hiatuses. Manganese formation took place during the early Oligocene (Hole 552A) and during the Eocene at Site 554 (overlain by upper Eocene). The upper and middle Eocene intervals are poorly represented; for example, the Chiasmolithus gigas subzone (Subzone CP13b or Zone NPl5) is only present in a single 2-cm thick horizon (Hole 552A). Site 552 shows the most complete record of the Eocene Zones NPl 1 through NP14, whereas Zone NP10 is considerably expanded at Sites 553 and 555. Definite upper Paleocene (Zone NP9) is only recovered at Site 555, where this sequence is interbedded between two basalt piles. INTRODUCTION Eight holes at four sites were drilled at the southwest margin of the Rockall Plateau in the northeast Atlantic Ocean during Leg 81 of the Deep Sea Drilling Project. Site locations are shown in Figure 1. The sediments recovered yielded Pleistocene through upper Paleocene calcareous nannofossils, and their distribution is presented from selected samples in Tables 1-8. Approximately 1200 samples were investigated. The upper Neogene and lower Eocene reflect virtually continuous deposition, whereas only fragments of the intervening intervals are preserved. Therefore the Neogene and Paleogene sequences are presented and discussed separately. The distribution of taxa is presented through qualitatively estimated relative abundances. The Neogene tables show three levels of relative abundance: filled circles represent an abundance in excess of 10% of the total assemblage; open circles represent an abundance between 1 and 10%; crosses represent an abundance less than 1% of the total assemblage. Smear slides made from the lower Eocene and upper Paleocene shelf sediments contain, as a rule, very low abundances of coccoliths. In many samples considerable difficulties were met in finding enough specimens to estimate relative abundances, and in many other samples this estimate turned out to be completely meaningless. Because consistent estimates of relative abundances could not be successfully achieved, Paleogene abundances are shown either as "rare" (open squares) or "more commonly occurring" (filled squares). Oligocene 20 10° W Roberts, D. G., Schnitker, D., et a]., Init. Repts. DSDP, 81: Washington (U.S. Govt. Printing Office). 2 Address: Department of Geology, University of Stockholm, S-106 91 Stockholm, Sweden. Figure 1. Locations of sites drilled during Leg 81 (Sites 552-555), Leg 48 (Sites 403-404), and Leg 12 (Site 117). and upper-middle Eocene assemblages are incorporated in this system for internal consistency in the tables, although the way of representing abundances in the Neogene samples could have been applied at several sample levels. ZONATION Previous studies of calcareous nannofossil biostratigraphy from the Rockall area include those of PerchNielsen (1972) and Müller (1979). These authors, as well as the present one, have predominantly relied on biostratigraphic zonations suggested by Martini (1971), Bukry (1973, 1975), and Okada and Bukry (1980). Their zonal schemes primarily reflect stratigraphic relationships of exits and entries of species in tropical and subtropical areas. As a consequence some stratigraphic in-