Origin of blocky aragonite cement in Cenozoic glaciomarine sediments, McMurdo Sound, Antarctica
Origin of blocky aragonite cement in Cenozoic glaciomarine sediments, McMurdo Sound, Antarctica
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DOI：
10.1111/sed.12690
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发表时间：
2019-12
期刊：
影响因子：
3.5
通讯作者：
Mingyu Yang;T. Frank;C. Fielding;M. Smith;P. Swart
中科院分区：
文献类型：
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作者：
Mingyu Yang;T. Frank;C. Fielding;M. Smith;P. Swart
无机文石赋存于广泛的沉积环境中，其沉淀受复杂的物理化学因素控制。本研究探讨了南极洲麦克默多海峡新生代冰晶矿床中导致文石胶结物沉淀的成岩条件。从位于费勒冰川末端附近的Ciros-1岩芯中收集到了42块砂岩，其中含有晶间水泥。标准岩石学、拉曼光谱和电子探针分析表明，岩芯中有显著的文石水泥相，呈孔洞填充的块状组构。文石胶结物测定的氧同位素组成(δ18O=−30·0~−8·6‰维也纳Pee-Dee贝伦石)和聚集的同位素温度(TΔ47=13·1~31·5℃)对母流体的同位素组成(δ18Ow)提供了精确的约束，其范围主要在−10·8至−7·2‰维也纳标准平均海水之间。流体δ180w的值与孔隙水的值一致，以前在附近的AND-2A岩心中识别为低温卤水。岩石学和地球化学数据表明，Ciros-1岩芯中的文石水泥来自类似的卤水。在中中新世气候转换期间，卤水可能在麦克默多海峡西缘被洪水淹没的冰川山谷中形成并渗透沉积，随后在次表层向盆地流动。因此，卤水形成了一种长期的地下流体，至少从中新世中期开始，它就已经饱和了麦克默多海峡南部以下的新生代沉积物。Ciros-1岩心中的文石胶结作用被解释为反映了其靠近卤水形成地点的位置，以及更有可能经历持续高碳酸盐饱和度和镁/钙比的卤水。这一不寻常的发现扩大了已知文石水泥天然存在的范围。考虑到冰川岩环境中形成低温卤水的可能性，块状文石作为文石胶结物形态光谱的最终成员，可能比目前认为的更广泛地存在于冰川岩沉积物中。
Inorganic aragonite occurs in a wide spectrum of depositional environments and its precipitation is controlled by complex physio‐chemical factors. This study investigates diagenetic conditions that led to aragonite cement precipitation in Cenozoic glaciomarine deposits of McMurdo Sound, Antarctica. A total of 42 sandstones that host intergranular cement were collected from the CIROS‐1 core, located proximal to the terminus of Ferrar Glacier. Standard petrography, Raman spectroscopy and electron microprobe analysis reveal a prominent aragonite cement phase that occurs as a pore‐filling blocky fabric throughout the core. Oxygen isotope compositions (δ18O = −30·0 to −8·6‰ Vienna Pee‐Dee Belemnite) and clumped isotope temperatures (TΔ47 = 13·1 to 31·5°C) determined from the aragonite cements provide precise constraints on isotopic compositions (δ18Ow) of the parent fluid, which mostly range from −10·8 to −7·2‰ Vienna Standard Mean Ocean Water. The fluid δ18Ow values are consistent with those of pore water, previously identified as cryogenic brine in the nearby AND‐2A core. Petrographic and geochemical data suggest that aragonite cement in the CIROS‐1 core precipitated from a similar brine. The brine likely formed and infiltrated sediments in flooded glacial valleys along the western margin of McMurdo Sound during the middle Miocene Climatic Transition, and subsequently flowed basinward in the subsurface. Consequently, the brine forms as a longstanding subsurface fluid that has saturated Cenozoic sediments below southern McMurdo Sound since at least the middle Miocene. Aragonite cementation in the CIROS‐1 core is interpreted to reflect its proximal position to sites of brine formation and greater likelihood of experiencing brines with sustained high carbonate saturation states and Mg/Ca ratios. This unusual occurrence expands the range of known natural occurrences of aragonite cement. Given the potential for cryogenic brine formation in glaciomarine settings, blocky aragonite, as the end member of the spectrum of aragonite cement morphology, may be more widespread in glaciomarine sediments than currently thought.