Biostratigraphical control of thrust models for the Southern Uplands of Scotland
Biostratigraphical control of thrust models for the Southern Uplands of Scotland
复制标题
苏格兰南部高地逆冲模型的生物地层控制
DOI：
10.1017/s0263593300002194
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
R. A. Hughes
中科院分区：
文献类型：
--
作者：
A. Rushton;P. Stone;R. A. Hughes
摘要 笔石生物地层学提供了一种稳健且相对准确的方法来关联奥陶纪和志留纪半白岩和浊积岩序列，并已用于确定苏格兰南部高地区域冲断带的结构发育。总体结构模式早已被认识到：单个冲断层内的杂砂岩在相对较短的时间间隔内沉积，向南逐渐变得更年轻；每一个都覆盖了沉积时间较长的基底莫法特页岩群。然而，最近对笔石生物带方案的改进使得能够更好地评估冲断带内的沿走向变化，这里用两条横断面来说明；一个是基于加洛韦莱因斯和柯库布里地区（南部高地西南）的工作，另一个是基于皮布尔斯-霍伊克地区（南部高地东北部）的工作。西南横断面最接近常规模式，其中向南传播的逆冲锋包含了顺序较年轻的杂砂岩单元。均匀的几何形状仅在冲断带南缘的局部被产生结构弹出的反向冲断系统打断。 NE 横断面偏离了这种规则模型：北部扇区显示了冲断带的有序起始，但向东南方向，冲断片年龄的分布更加不规则，这可以通过无序运动得到最好的解释。该样线还显示出相同生物地层间隔的重复叠瓦现象比西南更远的地方明显。在这两个横断面中，从兰多弗里时代中期开始，冲断带几何形状发生了根本性变化，并在文洛克河开始时恢复到向前破坏、顺序冲断。其原因尚待猜测，但可能与调节向前推力传播的障碍有关。然而，人们认识到逆冲几何形状的这种变化是大多数逆冲带的基本特征，并且不需要单一的区域显着原因。
Abstract Graptolite biostratigraphy affords a robust and relatively accurate means of correlating Ordovician and Silurian hemipelagite and turbidite sequences and has been used to establish the structural development of the regional thrust belt in the Southern Uplands of Scotland. The overall structural pattern has long been recognised: greywackes within individual thrust slices, deposited within a relatively short time-interval, become sequentially younger southwards; each overlies the basal Moffat Shale Group which was deposited over a longer time. However, recent refinement of the graptolite biozonal scheme has allowed the better assessment of along-strike variations within the thrust belt which are here illustrated by two transects; one, based on work in the Rhins of Galloway and the Kirkcudbright areas (SW Southern Uplands), and the other in the Peebles-Hawick area (NE Southern Uplands). The SW transect most closely approximates to the regular pattern wherein a southward-propagating thrust-front incorporated sequentially younger greywacke units. The uniform geometry is interrupted only locally, towards the southern margin of the thrust belt, by a system of back-thrusts producing structural pop-ups. The NE transect departs from this regular model: a northern sector shows the orderly initiation of the thrust belt, but towards the SE a more irregular distribution of the thrust-slice agescan be best explained by outof- sequence movement. This transect also shows more repetitive imbrication of the same biostratigraphic interval than is apparent farther SW. In both transects the fundamental changes in thrustbelt geometry took place from mid-Llandovery times onwards, with a reversion to forward-breaking, in-sequence thrusting at the beginning of the Wenlock. The cause is a matter for speculation, but may be linked withthe accommodation of an obstacle to forward-thrust propagation. However it is recognised that such variationsin thrust geometry are a fundamental feature of most thrust belts and do not require a single regionally significant cause.