Salinity reflux and dolomitization of southern Australian slope sediments: the importance of low carbonate saturation levels
Salinity reflux and dolomitization of southern Australian slope sediments: the importance of low carbonate saturation levels
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DOI：
10.1111/j.1365-3091.2011.01260.x
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发表时间：
2012-02
期刊：
影响因子：
3.5
通讯作者：
J. Rivers;T. Kurt Kyser;N. James
中科院分区：
文献类型：
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作者：
J. Rivers;T. Kurt Kyser;N. James
大洋钻探计划1127、1129、1130、1131和1132孔的异常咸水和南澳大利亚陆架沉积物中大型底栖有孔虫的同位素分析表明，澳大利亚南部边缘正在发生更新世-全新世中盐度反流。在与通常超过50‰盐度的海水有关的斜坡沉积物中观察到持续的白云石形成。在所有孔的顶部有一个冲洗良好的带，含有正常的海洋微量元素含量、碱度和pH值的孔隙水。白云石的沉淀分两个阶段发生在充分冲刷带的正下方。第一阶段是成核阶段，与相对较低的pH值(约7)的水有关，这是由于硫化氢的氧化从下向上扩散造成的。该白云石沉积在海底80m以下的沉积物中，二期白云石生长在第一期沉积的白云石岩芯上。二期白云岩的δ13C值与周围块体碳酸盐相似，而相对一期白云岩的锶值较高，这与在受文石和方解石溶解影响的水域中形成的白云石一致。该模型中的成核阶段(阶段1)挑战了更普遍接受的范式，即通过有效地提高白云石在海水中的饱和状态来克服海水对白云岩作用的抑制。
Anomalously saline waters in Ocean Drilling Program Holes 1127, 1129, 1130, 1131 and 1132, which penetrate southern Australian slope sediments, and isotopic analyses of large benthic foraminifera from southern Australian continental shelf sediments, indicate that Pleistocene–Holocene meso‐haline salinity reflux is occurring along the southern Australian margin. Ongoing dolomite formation is observed in slope sediments associated with marine waters commonly exceeding 50‰ salinity. A well‐flushed zone at the top of all holes contains pore waters with normal marine trace element contents, alkalinities and pH values. Dolomite precipitation occurs directly below the well‐flushed zone in two phases. Phase 1 is a nucleation stage associated with waters of relatively low pH (ca 7) caused by oxidation of H2S diffusing upward from below. This dolomite precipitates in sediments 80 m below the sea floor, Phase 2 dolomite grows on dolomite cores precipitated during Phase 1. Phase 2 dolomite has δ13C values similar to those of the surrounding bulk carbonate and high Sr values relative to Phase 1 dolomite, consistent with having formed in waters affected by aragonite and calcite dissolution. The nucleation stage in this model (Phase 1) challenges the more commonly accepted paradigm that inhibition of dolomitization by sea water is overcome by effectively increasing the saturation state of dolomite in sea water.