Seismic modelling and paleoceanography at DSDP Site 574
Seismic modelling and paleoceanography at DSDP Site 574
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DSDP Site 574 的地震建模和古海洋学
DOI：
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
E. Winterer
中科院分区：
文献类型：
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作者：
L. Mayer;T. Shipley;F. Theyer;R. Wilkens;E. Winterer
为支持DSDP Leg 85钻井而收集的高分辨率水枪地震剖面分析显示，在赤道太平洋中部超过36万公里的范围内，有几个主要的、区域可追踪的反射器可以相互关联。由DSDP 574站点的船上物理性质测量（经过仔细校正为现场值）生成的合成地震图与现场记录非常吻合；该协议表明，旅行时间到深度的转换是准确的，并且允许在取心段精确（±5米）定位反射器。反射器的年代（±0.5 Ma）如下：橙色，21.5至22.5 Ma；黄色，20.5 ~ 21.5 Ma；薰衣草，16到17 Ma；红色，13.5 ~ 14.5 Ma；紫色，11到12毫安；布朗，7至8马；格林是3到4毫安。在其他85号法律规定的地点进行的类似分析得出了相同的年龄。因此，反射器是时间表面；本章将它们与主要的古海洋事件和相对海平面曲线的变化联系起来。橙色和黄色反射体与δ 13 C的显著升高、浮游有孔虫组合的重大变化、深环南极洋流的发展以及热带和极地之间陡峭的热梯度的建立有关。这种海洋环流系统的重组可能是对德雷克海峡打开的反应，它导致了热带太平洋水域的化学变化，导致了与这些反射物相关的硬结（因此阻抗对比）。拉文德反射器与一个巨大的碳酸盐最小值、“Chron 16碳位移”、广泛的中断（NH2）、主要的海平面上升波动和太平洋二氧化硅沉积的显著增加有关。它与氧富集或气候变冷无关。我们的结论是，这一事件代表了北大西洋深水（NADW）的引入对古水深和构造事件的响应，导致南极底水（AABW）环流的增强和大西洋和太平洋之间二氧化硅的分裂。红色反射器与较弱的碳酸盐最小值、广泛的冰隙（NH3）、海平面下降、微化石组合的显著变化以及与南极冰的积累有关的δ 18 θ的大幅增加有关。详细的同位素分析表明，这种同位素变化发生在3万年的间隔内，并且恰好发生在红色反射器的深处。紫色反射镜与极大的碳酸盐极小期、太平洋碳酸盐沉积方式的变化、主要的岩性界线、广泛的NH4断裂带、所有浮游微化石组合中低纬度和高纬度之间的省域性的增加、海平面上升的明显下降、δ 18 θ的富集以及北大西洋主要反射镜有关，被解释为北大西洋底水环流的增强。Brown反射镜与碳酸盐极小期、δ 18 θ富集、晚中新世δ 1 C衰竭、相对海平面曲线下降和主要的区系变化大致相关。Green反射体与大型碳酸盐极小期、δ 18 θ富集、北大西洋西部主要侵蚀事件和广泛分布的东大西洋地震反射体有关。大部分证据支持与北半球冰期开始的相关性，但详细的同位素分析表明，这一同位素事件可能与没有主要冰盖发育的较冷底部水域的建立有关。已经确定了几种类型的反射器。老剖面的反射作用是成岩作用的结果；区域可校正反射器与全球事件有关。在较年轻的（18 Ma后）剖面，局部反射体的特征是速度对比，而区域反射体的特征是由碳酸盐极小期引起的密度对比。跨越赤道太平洋的碳酸盐岩极小期（以及反射物）的两种产生模式是：(1)AABW的增强，而没有NADW的同时增强，因此大西洋和太平洋之间没有二氧化硅的分选；这种模式导致了不太极端的碳酸盐岩极小期；(2) AABW随NADW的增强而增强；这种模式导致极端碳酸盐极小期和赤道太平洋反射与北大西洋事件的相关性。Mayer， L., Theyer, F .等人。报告。DSDP， 85：华盛顿（美国政府印刷局）。这项工作得到了ONR合同N00014-82-K-0625和加拿大自然科学与工程委员会的支持。F.T.他的研究得到了美国国家科学基金会OCE 81-17997和OCE 85-04146的资助。T.S.由N00014-81-K-0728支持。2地址：（Mayer） Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1；（希普利）德克萨斯大学地球物理研究所，德克萨斯州奥斯汀78712；（现任地址）南加州大学地质科学系，洛杉矶大学公园分校，CA 90089；（Wilkens）麻省理工学院地球、大气与行星科学系，马萨诸塞州剑桥02139；（冬季）加州大学圣地亚哥分校斯克里普斯海洋研究所，La Jolla, CA 92093。赤道太平洋中部肥沃的水域产生了厚厚的生物沉积物，这是构造作用、环流作用、生产力和成岩作用之间相互作用的一个极其敏感的指标。赤道太平洋活塞岩心研究(如Arrhenius, 1952; Berger, 1973； CLIMAP, 1976; Hays et al., 1969；
The analysis of high-resolution watergun seismic profiles collected in support of DSDP Leg 85 drilling reveals several major, regionally traceable reflectors that can be correlated over more than 360,000 km in the central equatorial Pacific. Synthetic seismograms generated from shipboard physical property measurements (carefully corrected to in situ values) for DSDP Site 574 show excellent agreement with the field records; the agreement suggests that the traveltimeto-depth conversion is accurate and permits the precise (± 5 m) location of reflectors in the cored section. The reflectors can be dated (±0.5 Ma) as follows: Orange, 21.5 to 22.5 Ma; Yellow, 20.5 to 21.5 Ma; Lavender, 16 to 17 Ma; Red, 13.5 to 14.5 Ma; Purple, 11 to 12 Ma; Brown, 7 to 8 Ma; and Green, 3 to 4 Ma. Similar analyses at the other Leg 85 sites result in identical ages. The reflectors are thus time surfaces; this chapter relates them to major paleoceanographic events and changes in the relative sea-level curve. The Orange and Yellow reflectors are associated with a marked increase in δ 1 3 C, a major change in planktonic foraminiferal assemblages, the development of the deep Circum-Antarctic Current, and the establishment of steep thermal gradients between tropical and polar regions. This reorganization of the oceanic circulation system was probably a response to the opening of the Drake Passage, and it resulted in changes in the chemistry of tropical Pacific waters that caused the induration (and thus impedance contrasts) associated with these reflectors. The Lavender reflector is associated with a large carbonate minimum, the "Chron 16 carbon shift," a widespread hiatus (NH2), major eustatic sea-level fluctuations, and a significant increase in silica deposition in the Pacific. It is not associated with 1 O enrichment or climatic cooling. We conclude that this event represents an intensification in Antarctic Bottom Water (AABW) circulation and the partitioning of silica between the Atlantic and the Pacific, caused by the introduction of North Atlantic Deep Water (NADW) in response to paleobathymetric and tectonic events. The Red reflector is associated with a subdued carbonate minimum, a widespread hiatus (NH3), a sea-level drop, significant changes in microfossil assemblages, and a major increase in δ 1 8 θ that has been linked with the buildup of Antarctic ice. Detailed isotopic analyses reveal that this isotopic shift occurred within an interval of 30,000 yr. and precisely at the depth of the Red reflector. The Purple reflector is associated with an extremely large carbonate minimum, a change in the style of carbonate deposition in the Pacific, a major lithologic boundary, a widespread hiatus (NH4), an increase in the provincialism between low and high latitudes in all planktonic microfossil assemblages, an apparent fall in eustatic sea level, an enrichment in δ 1 8 θ , and a major North Atlantic reflector interpreted as representing an intensification of North Atlantic bottom-water circulation. The Brown reflector is roughly associated with a small carbonate minimum, an enrichment in δ 1 8 θ , the late Miocene δ 1 C depletion, a drop in the relative sea-level curve, and major faunal changes. The Green reflector is associated with a large carbonate minimum, an enrichment in δ 1 8 θ , a major western North Atlantic erosional event, and a widespread eastern Atlantic seismic reflector. The bulk of evidence supports correlation with the onset of Northern Hemisphere glaciation, but detailed isotopic analyses indicate that this isotopic event may be linked to the establishment of colder bottom waters without major ice-sheet development. Several types of reflectors have been identified. The reflectors in the older section result from diagenetic effects; the regionally correctable reflectors are associated with global events. In the younger (post-18 Ma) section, local reflectors are characterized by velocity contrasts, whereas regional reflectors are associated with density contrasts caused by carbonate minima. Two modes of generation of carbonate minima (and thus of reflectors) spanning the equatorial Pacific are (1) the intensification of AABW without the concurrent intensification of NADW and so without fractionation of silica between the Atlantic and the Pacific; this mode results in the less extreme carbonate minima; and (2) the intensification of AABW in response to the intensification of NADW; this mode results in extreme carbonate minima and a correlation of equatorial Pacific reflectors with North Atlantic events. Mayer, L., Theyer, F , et al., Init. Repts. DSDP, 85: Washington (U.S. Govt. Printing Office). This work was supported by ONR contract N00014-82-K-0625 to L.M. and by the Natural Sciences and Engineering Council of Canada. F.T.'s research was supported by NSF grants OCE 81-17997 and OCE 85-04146. T.S. was supported by N00014-81-K-0728. 2 Addresses: (Mayer) Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1; (Shipley) University of Texas, Institute of Geophysics, Austin, TX 78712; (Theyer, present address) Department of Geological Sciences, University of Southern California, University Park, Los Angeles, CA 90089; (Wilkens) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139; (Winterer) Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093. INTRODUCTION The fertile waters of the central equatorial Pacific have produced a thick section of biogenic sediment that is an extremely sensitive indicator of the interplay among tectonism, circulation, productivity, and diagenesis. Studies of equatorial Pacific piston cores (e.g., Arrhenius, 1952; Berger, 1973; CLIMAP, 1976; Hays et al., 1969;