VARIATIONS IN THE FINE-SCALE COMPOSITION OF A CENTRAL PACIFIC FERROMANGANESE CRUST: PALEOCEANOGRAPHIC IMPLICATIONS
VARIATIONS IN THE FINE-SCALE COMPOSITION OF A CENTRAL PACIFIC FERROMANGANESE CRUST: PALEOCEANOGRAPHIC IMPLICATIONS
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DOI：
10.1029/91pa02936
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发表时间：
1992-02-01
期刊：
影响因子：
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通讯作者：
Clague, David A.
中科院分区：
文献类型：
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作者：
Hein, James R.;Bohrson, Wendy A.;Clague, David A.
利用中太平洋Horizon Guyot(水深1800~1780m)的47~60 mm厚的Fe-Mn结壳，评价了结壳作为新近纪古海洋和古气候条件记录器的潜力。用显微探针法测定了抛光薄片中16种元素的化学成分。每毫米进行三次分析，并取其平均值，得出每毫米的成分。通过测量地壳的锶同位素组成，并与第三纪海水曲线进行比较，确定了地壳的年龄。地壳代表18.5英里。氢氧化铁和氢氧化锰的生长。地壳由交替的梨状层和层状层组成。梨状层形成的时间间隔与海底沉积物中广泛的新近纪深海休止期相同。梨状层代表了在深水水流增强时期的生长，而L沉积段代表了更平静的条件。梨状层和新近系休止期之间的对应关系是如此之强，以至于我们能够为地壳选择可变生长速率模型而不是恒定生长速率模型。地壳中的化学变化有两种形式。第一种是成分的广泛变化，主要由四次多项式来定义，与地壳中每种元素的化学剖面相适应。二是成分的高频变化。更广泛的变化主要发生在15 Ma、11.5 Ma、7.4 Ma、6.4 Ma、5.2 Ma和4.6 Ma左右，这可能与古海洋环流和两极冰盖发育的重大变化有关。高频变化的周期可能反映了轨道强迫引起的气候变化。这些高频变化可能对应于3.47、2.04和1.31m.y的高阶偏心周期。
A 47-to 60-mm-thick Fe-Mn crust from Horizon Guyot (water depth 1800-1780 m), central Pacific, was used to evaluate the potential of crusts as recorders of Neogene paleoceanographic and paleoclimatic conditions. The chemical composition was determined by microprobe for 16 elements from a polished thin section. Three analyse was made per millimeter and averaged to give the composition of each millimeter. T he age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the Tertiary seawater curve. The crust represents 18.5 m.y. of growth of Fe and Mn oxyhydroxides. The crust is composed of alternating botryoidal and laminated layers. T he botryoidal layers formed during the same time intervals that widespread Neogene deep-sea hiatuses were forming in bottom sediments. The botryoidal layers represent growth during times of intensified deepwater flow, whereas the l aminated intervals represent more quiescent conditions. T. he correspondence between the botryoidal layers and the Neogene hiatuses is so strong that we were able to choose a variable growth rate m del over a constant growth rate model for the crust. Chemical changes in the crust take two forms. The first is represented by broad changes in the composition defined chiefly by fourth-order polynomial fits to the chemical profiles of each element with depth in the crust. The second is high-frequency changes in composition. The broader changes occurred primarily at about 15, 11.5, 7.4, 6.4, 5.2, and 4.6 Ma, which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles. The periods of the high-frequency changes may reflect climatic changes that resulted from orbital forcing. These high-frequency changes may correspond to the high-order eccentricity periods of 3.47, 2.04, and 1.31 m.y.