Upper Windermere Supergroup and the transition from rifting to continent-margin sedimentation, Nadaleen River area, northern Canadian Cordillera
Upper Windermere Supergroup and the transition from rifting to continent-margin sedimentation, Nadaleen River area, northern Canadian Cordillera
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DOI：
10.1130/b32039.1
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发表时间：
2019-09
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影响因子：
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通讯作者：
D. P. Moynihan;J. Strauss;L. Nelson;C. Padget
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文献类型：
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作者：
D. P. Moynihan;J. Strauss;L. Nelson;C. Padget
温德米尔超群和上覆单元的新元古代-寒武纪岩石记录了Rodinia的分裂和劳伦特西北部祖先大陆边缘的形成。理解这种转变的性质和时间一直受到阻碍，难以从中生代构造的对比沉积环境中关联日期不佳的沉积序列。在这里，我们提出了新的岩石和化学地层的数据，从中东部育空地区（加拿大）的Cryogenian-lower寒武纪继承，建立近端和远端的上部温德米尔超群和相关地层在北方加拿大科迪勒拉之间的相关性，并考虑西北劳伦边缘的形成的影响。新定义的Nadaleen组是埃迪卡拉纪宏体化石的首次出现，而上覆的Gametrail组具有大的负碳同位素异常，δ 13 Ccarb值低至-13‰，与全球发育的Shuram-Wonoka异常相关。我们还定义了拉克拉群，其中包括北方科迪勒拉温德米尔超群最年轻的（埃迪卡拉）部分。温德米尔超群的顶部以Risky Formation上方的不整合面为标志，该不整合面在Nadaleen River区域进入相关整合面。这个表面已被解释为标志着顶部的裂谷相关的继承，但我们提请注意通过早中寒武世的构造不稳定的证据，并认为从裂谷到裂谷后热沉降的过渡是由广泛的不整合下的上寒武纪碳酸盐岩的标志。这是年轻的解释年龄的裂谷后裂谷过渡沿着其他地方的祖先西劳伦大陆边缘。
Neoproterozoic–Cambrian rocks of the Windermere Supergroup and overlying units record the breakup of Rodinia and formation of the northwestern Laurentian ancestral continental margin. Understanding the nature and timing of this transition has been hampered by difficulty correlating poorly dated sedimentary successions from contrasting depositional settings across Mesozoic structures. Here we present new litho- and chemo-stratigraphic data from a Cryogenian–lower Cambrian succession in east-central Yukon (Canada), establish correlations between proximal and distal parts of the upper Windermere Supergroup and related strata in the northern Canadian Cordillera, and consider implications for the formation of the northwestern Laurentian margin. The newly defined Nadaleen Formation hosts the first appearance of Ediacaran macrofossils, while the overlying Gametrail Formation features a large negative carbon isotope anomaly with δ13Ccarb values as low as –13‰ that correlates with the globally developed Shuram-Wonoka anomaly. We also define the Rackla Group, which includes the youngest (Ediacaran) portions of the Windermere Supergroup in the northern Cordillera. The top of the Windermere Supergroup is marked by an unconformity above the Risky Formation that passes into a correlative conformity in the Nadaleen River area. This surface has been interpreted to mark the top of the rift-related succession, but we draw attention to evidence for tectonic instability through the early-middle Cambrian and argue that the transition from rifting to post-rift thermal subsidence is marked by a widespread unconformity that underlies upper Cambrian carbonate rocks. This is younger than the interpreted age of the rift to post-rift transition elsewhere along the ancestral western Laurentian continental margin.