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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Formation, uplift and dissection of planation surfaces at passive continental margins - a new approach
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Formation, uplift and dissection of planation surfaces at passive continental margins - a new approach

机译：被动大陆边缘平坦面的形成，隆起和剥离-一种新方法

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The usefulness of large-scale, low-relief, high-level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists. We argue that the formation of low-relief Surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels. In the absence of other options the most likely base level is sea level. We have analysed West Greenland landscapes in a recent study by combining the cooling history front apatite fission-track analysis (AFTA) data with the denudation history from landscape analysis and the stratigraphic record. An important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed. The present-day high-level plateau in West Greenland is the remnant of a planation surface that was formed by denudation that lasted c. 20 million years during which up to I km of cover was removed after maximum burial at the Eocene-Oligocene transition. Here we present additional AFTA data to show that the planation Surface is the end-product of Cenozoic denudation even in basement areas and argue that Phanerozoic sediments - most likely of Cretaceous-Palaeogene age - must have been present prior to denudation. The planation surface was offset by reactivated faults and uplifted to present-clay altitudes of up to 2 km. The uplift occurred in two late Neogene phases that caused incision of valleys below the planation surface and their subsequent uplift. We therefore find that the elevated and deeply dissected plateau is evidence of episodic post-rift uplift that took place millions of years after cessation of sea-floor spreading west of Greenland. We suggest that other margins with similar morphology may also be characterized by episodic post-rift uplift unrelated to the processes of rifting and continental separation, rather than being permanently uplifted since the time of rifting, as is commonly assumed.
机译：大规模，低起伏，高水平的景观作为隆升事件标志的有用性已成为地貌学家意见分歧的主题。我们认为，在较大范围内低起伏地表的形成以及跨越不同年龄和抵抗力的基岩的切割必须由不同的基础水平来指导。在没有其他选择的情况下，最有可能的基准面是海平面。我们在最近的一项研究中通过将冷却历史前磷灰石裂变径迹分析（AFTA）数据与景观分析和地层记录的剥蚀历史相结合，分析了西格陵兰岛的景观。我们的方法与经典地貌方法之间的重要区别在于，我们现在能够记录何时沉积厚厚的岩石，然后将其去除。如今，西格陵兰岛的高海拔高原是平坦的表面的残留物，该平坦的表面是由持续了c的剥蚀作用形成的。 2000万年以来，始新世-渐新世过渡期的最大埋葬时间后，移除了长达1 km的覆盖层。在这里，我们提供了更多的AFTA数据，以显示平坦的地表甚至是在基底区域的新生代剥蚀的最终产物，并认为剥脱之前必须存在生代沉积物-最有可能是白垩纪-古近纪时代的沉积物。平坦的地面被重新激活的断层所抵消，并被抬升至目前的粘土高度，达2 km。隆起发生在新近纪的两个晚期，导致切开平整表面以下的山谷并随后隆起。因此，我们发现高原和深层解剖的高原是断续的裂谷后隆升的证据，该裂谷后格陵兰向西扩散的海底停止了数百万年。我们建议，具有相似形态的其他边缘也可能以与裂谷作用和大陆分离过程无关的间歇性裂谷后隆升为特征，而不是像通常认为的那样自裂谷以来一直呈永久性隆升。

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