Diagenesis of late Cenozoic diatomaceous deposits and formation of the bottom simulating reflector in the southern Bering Sea
Diagenesis of late Cenozoic diatomaceous deposits and formation of the bottom simulating reflector in the southern Bering Sea
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白令海南部晚新生代硅藻土沉积与海底模拟反射体的形成
DOI：
10.1111/j.1365-3091.1978.tb00307.x
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发表时间：
1978
期刊：
影响因子：
3.5
通讯作者：
Jacquelyn Miller
中科院分区：
文献类型：
--
作者：
J. Hein;D. Scholl;J. Barron;Marjorie G. Jones;Jacquelyn Miller
在第19航次深海钻探项目现场，硅藻泥和硅藻泥岩覆盖在陆源泥岩层之上。厚达300-725米，但最常见的厚度约为600米。硅藻硅藻壳的成岩作用遵循一系列可预测的物理和化学变化，这些变化主要与温度有关（埋藏深度和当地地热梯度）。在最初的300-400米埋藏期间，硅藻壳破碎并经历轻度溶解。到600米时，蛋白石A（生物硅）的溶解很普遍。在600至700米深的海底下，大量二氧化硅以无机蛋白石A的形式再沉淀。无机蛋白石-A通过晶体生长迅速转化为蛋白石-CT。其结果是形成硅质胶结泥岩和瓷岩层。
区域声反射（称为底部模拟反射，或BSR）发生在600米深度附近的部分。这种声波事件标志着硅化作用（胶结作用）活跃的上表面。在白令海沉积物中，蛋白石-A在35° C至50°C之间的温度下转化为蛋白石-CT。这一温度范围对应于约600米的海底深度，是硅化作用最活跃的区域。因此，BSR代表等温表面;它记录的温度是将蛋白石-A转化为蛋白石-CT所需的温度。在硅质岩段底部的温度适合（35°-50 ° C）发生硅质成岩作用之前，需要沉积至少500 m厚的硅质沉积物。因此，硅质成岩作用直到更新世才开始。一旦硅化开始，在第四纪沉积物的积累，成岩前锋（BSR）向上移动的步伐向上迁移的热边界。
X射线衍射图和SEM照片显示了三种二氧化硅相，生物蛋白石-A，无机蛋白石-A '和蛋白石-CT。它们的微晶尺寸分别为11-16 A、20-27 A和40-81 A，垂直于101。在DSDP 192站，蛋白石CT的d（101）反射随埋深的增加而减小。这是通过固态排序发生的，需要至少700米的埋藏。
第19航次岩心中的斜发沸石大多数是由硅质碎屑的成岩作用形成的，而不是通常报道的由火山碎屑的蚀变作用形成的。
Diatom ooze and diatomaceous mudstone overlie terrigenous mudstone beds at Leg 19 Deep Sea Drilling Project sites. The diatomaceous units are 300-725 m thick but most commonly are about 600 m. Diagenesis of diatom frustules follows a predictable series of physical and chemical changes that are related primarily to temperature (depth of burial and local geothermal gradient). During the first 300-400 m of burial frustules are fragmented and undergo mild dissolution. By 600 m dissolution of opal-A (biogenic silica) is widespread. Silica reprecipitates abundantly as inorganic opal-A between 600 and 700 m sub-bottom depth. Inorganic opal-A is rapidly transformed by crystal growth to opal-CT. The result is formation of silica cemented mudstone and porcelanite beds.
A regional acoustic reflector (called the bottom-simulating reflector, or BSR) occurs near 600 m depth in the sections. This acoustic event marks the upper surface where silicification (cementation) is active. In Bering Sea deposits, opal-A is transformed to opal-CT at temperatures between 35° and 50°C. This temperature range corresponds to a sub-bottom depth of about 600 m and is the area where silicification is most active. Thus, the BSR represents an isothermal surface; the temperature it records is that required to transform opal-A to opal-CT. Deposition of at least 500 m of diatomaceous sediment was required before the temperature at the base of the diatomaceous section was appropriate (35°-50°C) for silica diagenesis to occur. Accordingly, silica diagenesis did not begin until Pleistocene time. Once silicification began, in response to sediment accumulation during the Quaternary, the diagenetic front (the BSR) moved upsection in pace with the upward migrating thermal boundary.
X-ray diffractograms and SEM photographs show three silica phases, biogenic opal-A, inorganic opal-A’, and opal-CT. These have crystallite sizes of 11-16 A, 20-27 A, and 40-81 A, respectively, normal to 101. The d(101) reflection of opal-CT decreases with depth of burial at DSDP Site 192. This occurs by solid-state ordering and requires at least 700 m of burial.
Most clinoptilolite in Leg 19 cores forms from the diagenesis of siliceous debris rather than from the alteration of volcanic debris as is commonly reported.