Can We Recognize Tectonic Geomorphology from the Late Paleozoic? A Study of Three Half-Grabens Onshore the Northeast Atlantic Margin

In this study we investigate how landscapes are inherited from continental rifting on long timescales. Areas that are currently undergoing extension typically have topographical features and drainage patterns that are easy to recognize. How these topographical rift features evolve on long timescales, however, is poorly understood. Recent work from onshore parts of the northeast Atlantic margin suggests that some present-day landforms are inherited from late Paleozoic, Mesozoic and Early Cenozoic rifting and opening of the North Atlantic Ocean. These relict landscapes are difficult to recognize, as the topography is reworked by post-rift Cenozoic uplift and erosion, as well as repeated Quaternary glaciations. For that reason, interpretations of these landscapes vary considerably. However, some of these relict rift features are demonstrably preserved in half-grabens, as sedimentary basins with well-established ages. Our research studies the topography around three half-grabens in Norway and on Svalbard, and aims to quantify landscape inheritance from rifting and margin formation. To do so, we use structural and geomorphological field observations, and remote sensing such as digital elevation model analyses and seismic images. We classify landscapes in detail, systematically reviewing present-day landscape distributions in order to distinguish extensional tectonic landforms from other geomorphological features. Preliminary results find that certain present-day landforms along the northeast Atlantic Ocean are relics from rifting from as far back as the late Paleozoic. This is expressed by, among other things, major topographic contrasts between footwall and hanging wall in all three half-grabens. This means higher topographical elevations and deeper incision in the footwalls compared to the hanging walls. Additionally, the three study areas have very different landscapes, suggesting that their individual post-rift landscape evolutions were very different from each other. These differences seem to be influenced by the degree of glacial incision, the degree of erosional exploitation of pre-rift structures, and possible Late-Cretaceous or younger reactivation of basin-bounding normal faults.