(Table 1) Pore-water chemistry, mineralogy and stable isotope ratios for ODP Leg 133 holes@en

The occurrence of dolomite in young Pleistocene sediments off the northeastern coast of Australia offers a special opportunity to examine dolomite formation relative to the original mineralogy and the remineralization of organic material through the processes of sulfate reduction and methanogenesis. The four cores examined in this study form a transect from shallow to deep water (Sites 821, 820, 819, and 822). At all sites, dolomite occurs in sediments of Pleistocene age and is more abundant closer to the continental margin (Site 821) than in sediments found in deeper water (Sites 819 and 822). In spite of the fact that the classic diagenetic zones of sulfate reduction and methanogenesis were all well developed at Sites 819, 820, 821, and 822, the d13C of the interstitial dissolved inorganic carbon (DIC) showed no evidence of these diagenetic processes. The dolomites retrieved from sediments showed d13C values similar to that of the DIC. The isotopic composition of the dolomite revealed no evidence of having been formed in either the sulfate reduction zone or the zone of methanogenesis. The Leg 133 sites differ from other anoxic hemipelagic areas in which extensive sulfate reduction and methanogenesis have been documented in that the sediments are dominated by CaCO3. Recrystallization of calcium carbonate apparently buffers the isotopic composition of the system, masking large isotopic changes that might be induced by additions of isotopically light or heavy CO2 derived from the processes of sulfate reduction and methanogenesis. The dolomite does not appear to be preferentially located in the portion of the cores in which sulfate is absent. Based on the association between the abundance of high-Mg calcite (HMC) and dolomite, it is thought that dolomites formed in response to the dissolution of HMC.澳大利亚东北海域更新世（Pleistocene）沉积物中白云石（dolomite）的产出，为探究白云石形成与原始矿物学特征、以及硫酸盐还原（sulfate reduction）和甲烷生成（methanogenesis）过程中有机质再矿化作用的关联提供了绝佳研究契机。本研究涉及的四个岩芯构成了一条从浅海到深海的断面站位（821、820、819及822号站位）。所有站位的更新世沉积物中均有白云石产出，且靠近大陆边缘的821号站位的白云石丰度，高于深海区域的819与822号站位。尽管819、820、821、822号站位均发育典型的硫酸盐还原与甲烷生成成岩带，但间隙水溶解无机碳（interstitial dissolved inorganic carbon, DIC）的碳同位素比值（δ¹³C）并未显示出这些成岩作用的痕迹。从沉积物中提取的白云石，其碳同位素比值与DIC的比值相近。白云石的同位素组成并未显示其形成于硫酸盐还原带或甲烷生成带的证据。与已有大量文献报道硫酸盐还原与甲烷生成作用的缺氧半远洋沉积区不同，本研究的Leg 133航次站位沉积物以碳酸钙（CaCO₃）为主。碳酸钙的重结晶作用显然对体系的同位素组成起到了缓冲作用，掩盖了硫酸盐还原与甲烷生成过程产生的轻、重同位素CO₂输入可能引发的显著同位素变化。白云石并未优先富集于岩芯中硫酸盐缺失的层位。基于高镁方解石（high-Mg calcite, HMC）丰度与白云石丰度之间的关联，研究认为白云石的形成是高镁方解石溶蚀作用的结果。