Petrologic and geochemical constraints on the origin of subsurface dolomite, Enewetak Atoll: An example of dolomitization by normal seawater
Petrologic and geochemical constraints on the origin of subsurface dolomite, Enewetak Atoll: An example of dolomitization by normal seawater
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埃尼韦塔克环礁地下白云石起源的岩石学和地球化学限制：正常海水白云石化的一个例子
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发表时间：
1984
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通讯作者：
A. Saller
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作者：
A. Saller
白云石存在于埃尼韦塔克环礁始新世地层海平面以下 1,250–1,400 米处。从岩相学上看，埃尼韦塔克深处的白云岩晚于始新世地层中刚性颗粒的脆性压实作用。这些白云岩的 87 Sr/ 86 Sr 比值 (0.70865–0.70901) 表明它们在中新世中期和现在之间形成过一次或多次。由于下中新世的顶部高于深白云岩层段 900 m 以上，因此白云岩必定是在最小埋藏深度 900 m 处形成的。稳定氧同位素测定表明白云石从冷海水中沉淀出来。环礁上的下中新世和始新世碳酸盐岩地层显然与寒冷的现代海水开放，这表明这些地层在白云石化过程中与海水开放。在大约 1,000 m 的深度，现代太平洋水的方解石变得不饱和，但白云石仍然过饱和。因此，有人认为，Enewetak 深层白云石是从埋藏深度超过 900 m 的寒冷深海水（方解石不饱和）中沉淀出来的。
Dolomite is present 1,250–1,400 m below sea level in Eocene strata of Enewetak Atoll. Petrographically, the deep Enewetak dolomite postdates brittle compaction of rigid grains in the host Eocene strata. The 87 Sr/ 86 Sr ratio of these dolomites (0.70865–0.70901) indicates that they formed at one or more times between the middle Miocene and the present. Since the top of the lower Miocene is more than 900 m above the deep dolomitic interval, the dolomite must have formed at a minimum burial depth of 900 m. Stable-oxygen-isotope determinations suggest dolomite precipitation from cold marine water. Lower Miocene and Eocene carbonate strata on the atoll are apparently in open communication with cold, modern ocean water, suggesting that those same strata were in open communication with ocean water during dolomitization. At a depth of about 1,000 m, modern Pacific Ocean water becomes undersaturated with respect to calcite but is still supersaturated with respect to dolomite. Therefore, it is proposed that the deep Enewetak dolomite precipitated from cold, deep ocean water (undersaturated with respect to calcite) at a burial depth of more than 900 m.