Discussion on ‘A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications’
Discussion on ‘A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications’
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关于“Rhynie Chert Konservat-Lagerstätte 的高精度 U-Pb 年龄限制：时间尺度和其他影响”的讨论
DOI：
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发表时间：
2013
影响因子：
2.7
通讯作者：
N. Trewin
中科院分区：
文献类型：
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作者：
Darren F. Mark;C. M. Rice;N. Trewin
我们欢迎Parry等人的贡献。（2011）关于全球重要的Rhynie温泉系统的年龄，阿伯丁郡，苏格兰。然而，虽然我们接受，他们提供了一个有价值的和强大的U-Pb年龄限制的米尔顿的诺斯安山岩和Rhynie离群地层序列，我们不接受，他们限制了温泉活动的时间，建议。
北安山岩未暴露的米尔顿的地球物理痕迹表明，它紧邻Rhynie断层带，并与之平行约2 km。它甚至可能位于Rhynie断层带内（参见Rice & Ashcroft 2004的讨论）。因此，它的地层位置是不确定的。Parry等人（2011年）指出，确切的地层位置并不重要，因为它们的首选地层位置位于Tillybrachty砂岩组和德莱登旗组内，这两个组都一直产出属于Al-emsiensis孢子组合生物带的孢子。这种说法是站不住脚的。的Mallis-emsiensis孢子组合生物带可能已经持续了几百万年，因此，潜在的，可能有一个显着的安山岩喷发和温泉活动的开始之间的间隙。
他们进一步假设安山岩与深部的安山岩岩浆房相连，为热液系统提供动力。这仍然是猜测。接受地层位置的不确定性，并通过主张安山岩和Rhynie燧石之间的最大沉积厚度和保守的沉积速率，Parry等人。（2011年）试图通过计算中间沉积物所代表的时间间隔，在时间上将安山岩与硅质岩联系起来。时间的估计取决于不整合面、不整合面和断层的存在，这种假设和不确定性使人对中间沉积物的厚度产生怀疑。
We welcome the contribution of Parry et al . (2011) concerning the age of the globally important Rhynie hot-spring system, Aberdeenshire, Scotland. However, although we accept that they have provided a valuable and robust U–Pb age constraint for the Milton of Noth Andesite and the Rhynie outlier stratigraphic succession, we do not accept that they have constrained the timing of hot-spring activity, as suggested.
The geophysical trace of the unexposed Milton of Noth Andesite indicates that it lies immediately adjacent to the Rhynie Fault Zone and runs parallel to it for some 2 km. It may even lie within the Rhynie Fault Zone (see discussion by Rice & Ashcroft 2004). Its stratigraphic position is therefore uncertain. Parry et al . (2011) stated that the exact stratigraphic position is not important because their preferred stratigraphic locations lie within the Tillybrachty Sandstone and Dryden Flags Formations, both of which have consistently yielded spores belonging to the polygonalis–emsiensis Spore Assemblage Biozone. This assertion is not valid. The polygonalis–emsiensis Spore Assemblage Biozone may have lasted several million years and thus, potentially, there could be a significant hiatus between eruption of the andesite and the onset of hot-spring activity.
They further assume that the andesite was linked to an andesitic magma chamber at depth, which powered the hydrothermal system. This remains speculation. Accepting the uncertainty in the stratigraphic position and by asserting a maximum thickness of sediment between the andesite and the Rhynie Cherts and a conservative deposition rate, Parry et al . (2011) attempted to temporally link the andesite to the cherts by calculating the time interval represented by the intervening sediment. The estimation of time depends on the absence of unconformities, disconformities and faulting, with such assumptions and uncertainties casting doubt on the thickness of the intervening sediments …