Growth and Dolomitization of Silurian Reefs, St. Clair County, Michigan
Growth and Dolomitization of Silurian Reefs, St. Clair County, Michigan
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密歇根州圣克莱尔县志留纪珊瑚礁的生长和白云石化
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发表时间：
1969
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影响因子：
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通讯作者：
R. L. Jodry
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作者：
R. L. Jodry
密歇根东部的尖峰礁形成于尼亚加拉晚期-萨利南早期的碳酸盐岩-蒸发岩旋回沉积时期。礁层现在有盐层作为它们的横向等级物。然而，在沉积过程中将蒸发岩序列恢复到相对位置表明，这是碳酸盐层压实差异的结果，而不是礁岩和蒸发岩同时沉积的结果。碳酸盐岩泥浆在岩化过程中的压实作用，而不是胶结作用，也是该地区孔隙度损失的主要原因。在保留孔隙度的地方，存在抗压框架，并且孔隙度与框架的数量成正比。礁体及其周围的碳酸盐被白云化。白云化的模式、白云石的数量与层厚的关系、白云石的位置与蒸发岩层的关系以及白云化的时间表明，白云化是由大量原生水在沉积物中连续运动引起的。不能证明在蒸发岩沉积时期高浓度盐水的回流对白云化有很大贡献。碳酸盐岩泥体上的蒸发岩层序阻止了压实过程中水的垂直逸出。水被迫横向流向珊瑚礁，然后垂直流经珊瑚礁到达表面。大量的水被迫穿过相对较小体积的礁区岩石，为白云化提供镁。在强烈的蒸发旋回过程中，水流持续流出，改变了礁区蒸发岩的沉积，阻止了重盐水进入多孔礁体，破坏了孔隙度。
Pinnacle reefs in eastern Michigan were formed during a period of cyclic carbonate-evaporite deposition in latest Niagaran-early Salinan time. Reef sequences now have salt beds as their lateral equivalents. Restoration of evaporite sequences to their relative positions during deposition demonstrates, however, that this is the result of differential compaction of carbonate beds, rather than contemporaneous deposition of reef rock and evaporites. Compaction of carbonate mud during lithification, rather than cementation, also accounts for most porosity loss in the area. Where porosity is preserved, compaction-resistant framework is present, and the porosity is directly proportional to quantity of framework. The reef and surrounding carbonates are dolomitized. The pattern of dolomitization, quantity of dolomite in relation to bed thickness, position of the dolomite in relation to evaporite beds, and time of dolomitization suggest that dolomitization was caused by a continuous movement of large quantities of connate waters through the sediments. It cannot be shown that refluxion by highly concentrated brines during periods of evaporite deposition contributed substantially to dolomitization. Evaporite sequences overlying bodies of carbonate mud prevented the vertical escape of water during compaction. The water was forced to flow laterally to the reefs, and then vertically through them to the surface. This very large quantity of water was forced through a relatively small volume of rock in he reef area and supplied the magnesium for dolomitization. The outflow of water continued during intensely evaporitic cycles, altering evaporite deposition in the reef area, and preventing heavy brines from entering the porous reefs and destroying porosity.