Cryogenic brines as diagenetic fluids: Reconstructing the diagenetic history of the Victoria Land Basin using clumped isotopes
Cryogenic brines as diagenetic fluids: Reconstructing the diagenetic history of the Victoria Land Basin using clumped isotopes
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DOI：
10.1016/j.gca.2018.01.002
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发表时间：
2018-03
影响因子：
5
通讯作者：
P. Staudigel;S. Murray;D. Dunham;T. Frank;C. Fielding;P. Swart
中科院分区：
文献类型：
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作者：
P. Staudigel;S. Murray;D. Dunham;T. Frank;C. Fielding;P. Swart
南极地质钻探(ANDRILL-2A)从麦克默多海峡岩心中回收的碳酸盐相同位素分析(δ13C、δ18O和Δ47)表明，大多数次生碳酸盐矿物的形成温度低于现代埋藏温度，并且存在δ180水值在−11和−6‰VSmow之间的流体。这些流体被解释为来自海水冻结过程中形成的低温卤水。利用本文提出的内部校准方法，将Δ470值转换为温度。对水泥中Δ470值的测量表明，随着深度的增加，结晶温度越来越高，虽然与观测到的地温梯度大致平行，但始终转化为比当前埋藏温度更低的温度。这种温差表明，胶结物形成于∼260 ± 100 m时，比现在浅。这一深度范围对应于从3到11 myr的最小泥沙堆积时期，因此可以解释为大多数胶结物形成于此期间。通过对该地点胶结作用的时间积分模拟，也可以预测这种行为。如果这种胶结作用是在这些流体存在的情况下发生的，那么低温卤水一直是维多利亚陆地盆地的一个长期特征。在许多现代高纬度环境中都描述了类似于该地点的卤水，类似的流体可能在整个地质历史中冰川时期的其他冰缘沉积物和盆地的成岩历史中发挥了作用。计算的δ18O水值与孔隙流体中的实测值之间的一致性表明，Δ470替代物可用于确定碳酸盐岩中负δ18O值的来源，并且极端负值不一定是大气流体或高温反应的影响的结果。
The isotopic analyses (δ13C, δ18O, and Δ47) of carbonate phases recovered from a core in McMurdo Sound by ANtarctic geologic DRILLing (ANDRILL-2A) indicate that the majority of secondary carbonate mineral formation occurred at cooler temperatures than the modern burial temperature, and in the presence of fluids with δ18Owatervalues ranging between −11 and −6‰ VSMOW. These fluids are interpreted as being derived from a cryogenic brine formed during the freezing of seawater. The Δ47values were converted to temperature using an in-house calibration presented in this paper. Measurements of the Δ47values in the cements indicate increasingly warmer crystallization temperatures with depth and, while roughly parallel to the observed geothermal gradient, consistently translate to temperatures that are cooler than the current burial temperature. The difference in temperature suggests that cements formed when they were ∼260 ± 100 m shallower than at the present day. This depth range corresponds to a period of minimal sediment accumulation from 3 to 11 Myr; it is therefore interpreted that the majority of cements formed during this time. This behavior is also predicted by time-integrated modeling of cementation at this site. If this cementation had occurred in the presence of these fluids, then the cryogenic brines have been a longstanding feature in the Victoria Land Basin. Brines such as those found at this site have been described in numerous modern high-latitude settings, and analogous fluids could have played a role in the diagenetic history of other ice-proximal sediments and basins during glacial intervals throughout geologic history. The agreement between the calculated δ18Owatervalue and the measured values in the pore fluids shows how the Δ47proxy can be used to identify the origin of negative δ18O values in carbonate rocks and that extremely negative values do not necessarily need to be a result of the influence of meteoric fluids or reaction at high temperature.