Sedimentology, structural evolution and tectonic setting of the late Precambrian Longmyndian Supergroup of the Welsh Borderland, UK
Sedimentology, structural evolution and tectonic setting of the late Precambrian Longmyndian Supergroup of the Welsh Borderland, UK
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英国威尔士边境晚前寒武纪龙门超群的沉积学、构造演化和构造背景
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发表时间：
1990
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通讯作者：
J. Pauley
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作者：
J. Pauley
摘要龙民甸超群是一个厚约6500米的晚前寒武纪沉积序列。该层序内缺少主要的不整合面。龙目甸超群可划分为四个相组合：（1）浊积岩，（2）水下三角洲，（3）冲积平原，（4）辫状河冲积。这些被组织成一个单一的，广泛向上变粗，横向序列，与浊积岩协会在基地和辫状河冲积协会向顶部。这些沉积物被解释为沉积在一个弧前或可能是弧间盆地中，该盆地位于一个同生岩浆弧的北部，（现在相邻的）乌里柯尼亚火山杂岩被认为是其中的一部分。龙敏阶超群变形为一个紧密的北北东-南西西向向斜。断层模式和应变标志表明，它是在左旋平移挤压变形。邻近的庞茨福德-林利和丘奇-斯特雷顿断层系统被认为是主要的走滑断层系统，它们大约与朗明迪安超群的变形同时开始。走滑运动沿着这些断层系统导致并置的Uriconian火山杂岩与Longmyndian超群。晚前寒武纪/早寒武纪变形的一些地层和放射性测年证据表明。由于有证据表明断层系统在古生代遭受了走滑位移，因此很难确定晚前寒武纪/早寒武纪变形的规模和类型。然而，在威尔士西北部的晚前寒武纪/早寒武纪左旋扭压变形的认识表明，威尔士边境地区的前寒武纪在晚前寒武纪/早寒武纪期间也发生了类似的变形。
Abstract The Longmyndian Supergroup is an approximately 6500 m thick sedimentary sequence of late Precambrian age. Major unconformities within this sequence are lacking. The Longmyndian Supergroup can be divided into four facies associations: (1) turbidite, (2) subaqueous delta, (3) alluvial floodplain, and (4) braided alluvial. These are organized into a single, broadly upwards-coarsening, progradational sequence, with the turbidite association at the base and the braided alluvial association towards the top. The sediments are interpreted to have been deposited in a forearc, or possibly interarc, basin which lay to the north of a contemporaneous magmatic arc, of which the (now adjacent) Uriconian Volcanic Complex is considered to have been a part. The Longmyndian Supergroup has been deformed into a tight NNE-SSW trending syncline. Fault patterns and strain markers within the Longmyndian indicate that it was deformed during sinistral transpression. The adjacent Pontesford-Linley and Church Stretton fault systems are considered to be major strike-slip fault systems which were initiated at about the same time as the deformation of the Longmyndian Supergroup. Strike-slip movements along these fault systems resulted in the juxtaposition of the Uriconian Volcanic Complex with the Longmyndian Supergroup. Late Precambrian/early Cambrian deformation is indicated by some stratigraphic and radiometric age-dating evidence. Since there is evidence that the fault systems have suffered strike-slip displacements during the Palaeozoic it is difficult to be certain of the magnitude and style of the late Precambrian/early Cambrian deformation. However, the recognition of late Precambrian/early Cambrian sinistral transpressional deformation in northwest Wales suggests that the Precambrian of the Welsh Borderland was similarly deformed during the late Precambrian/early Cambrian.