Planation Surfaces in Basement Terrains

Godard, Alain; Simon‐Coinçon, Régine; Lagasquie, Jean-Jacques

doi:10.1007/978-3-642-56821-3_2

Cited by 5 publications

(3 citation statements)

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“…Low-relief landscapes hundreds of kilometres in extent at both high and low elevations are common fea-tures on the Earth's continents (e.g. King 1962King , 1967King , 1976Bird 1959;Ollier 1981;Hall 1991;de Brum Ferreira 1991;Lidmar-Bergström 1996;Gunnell 1998;Johansson 1999;Godard et al 2001b;Lageat & Gunnell 2001;Casa-Sainz & Cortés-Gracia 2002;Demoulin 2003;Bonow et al 2003Bonow et al , 2006a. They were labelled peneplains and used at the beginning of the 20th century to constrain base-level changes and uplift (e.g.…”

Section: Geomorphological Concepts Related To the Evolution Of Elevatmentioning

confidence: 99%

Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins

Green¹,

Lidmar‐Bergström

Japsen

et al. 2013

GEUS Bulletin

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The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1–2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes.

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Section: Geomorphological Concepts Related To the Evolution Of Elevatmentioning

confidence: 99%

Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins

Green¹,

Lidmar‐Bergström

Japsen

et al. 2013

GEUS Bulletin

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“…Deeply weathered crystalline basement rocks are common features of the geological record and are currently actively developing in warm and temperate climates. When weathering is effective for long periods in tectonically stable regions, it will affect the local geomorphology through pervasive saprolitization, relief reduction and possible development of planation surfaces 1 2 . In repeatedly glaciated areas such as Scandinavia, however, where glaciers and ice sheets have recently stripped large volumes of rocks, saprolites are only sparsely found.…”

mentioning

confidence: 99%

The inheritance of a Mesozoic landscape in western Scandinavia

et al. 2017

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In-situ weathered bedrock, saprolite, is locally found in Scandinavia, where it is commonly thought to represent pre-Pleistocene weathering possibly associated with landscape formation. The age of weathering, however, remains loosely constrained, which has an impact on existing geological and landscape evolution models and morphotectonic correlations. Here we provide new geochronological evidence that some of the low-altitude basement landforms on- and offshore southwestern Scandinavia are a rejuvenated geomorphological relic from Mesozoic times. K-Ar dating of authigenic, syn-weathering illite from saprolitic remnants constrains original basement exposure in the Late Triassic (221.3±7.0–206.2±4.2 Ma) through deep weathering in a warm climate and subsequent partial mobilization of the saprolitic mantle into the overlying sediment cascade system. The data support the bulk geomorphological development of west Scandinavia coastal basement rocks during the Mesozoic and later, long-lasting relative tectonic stability. Pleistocene glaciations played an additional geomorphological role, selectively stripping the landscape from the Mesozoic overburden and carving glacial landforms down to Plio–Pleistocene times. Saprolite K-Ar dating offers unprecedented possibilities to study past weathering and landscape evolution processes.

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“…Stratigraphic landscape analysis is thus a further development of a long tradition in geomorphology focussed on the study of large-scale landforms that contain information about long-term erosional processes and tectonic events (Davis 1899;Reusch 1901;Ahlmann 1919Ahlmann , 1941Penck 1924;Baulig 1935;Jessen 1943;King 1967;Brunsden 1993;Ahnert 1998;Godard et al 2001;Benito-Calvo & Pérez-González 2007;Peulvast et al 2009Peulvast et al , 2011Hetzel Fig. 2 Conceptual diagram illustrating the formation of peneplains through time: A: Initial topography.…”

Section: Stratigraphic Landscape Analysis For Mapping Erosion Surfaces In East Greenlandmentioning

confidence: 99%

Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic

Bonow

Japsen

2021

GEUS Bulletin

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Elevated plateaus with deeply incised valleys characterise elevated, passive continental margins (EPCMs) in all climate zones. These features are, however, a topic of debate regarding when and how the large-scale landscapes formed. We have investigated and mapped the partly glaciated landscape of North-East Greenland (70–78°N). The area consists of crystalline basement and Palaeozoic–Mesozoic rift basins, capped by Palaeogene basalts that erupted during the northeast Atlantic break-up. Our stratigraphic landscape analysis reveals a typical EPCM dominated by two elevated erosion surfaces, extending 200 km east–west and 900 km north–south. The low-relief Upper Planation Surface (UPS; c. 2 km above sea level) cuts across basement and Palaeogene basalts, indicating that it was graded to base level defined by the Atlantic Ocean in post-basalt times and subsequently uplifted. The UPS formed prior to the deposition of mid-Miocene lavas that rest on it, south of the study area. In the interior basement terrains, the Lower Planation Surface (LPS) forms fluvial valley benches at c. 1 km above sea level, incised below the UPS. The LPS is thus younger than the UPS, which implies that it formed post mid-Miocene. Towards the coast, the valley benches merge to form a coherent surface that defines flat-topped mountains. This shows that the LPS was graded to near sea level and was subsequently uplifted. Hence, both the UPS and the LPS formed as peneplains – erosion surfaces graded to base level. The fluvial valley benches associated with the LPS further indicates that full glacial conditions were only established after the uplift of the LPS in the early Pliocene (c. 5 Ma). The uplift of the LPS led to re-exposure of a Mesozoic etch surface. We conclude that episodes of late Neogene tectonic uplift shaped the stepped landscape and elevated topography in North-East Greenland.

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Planation Surfaces in Basement Terrains

Cited by 5 publications

References 0 publications

Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins

Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins

The inheritance of a Mesozoic landscape in western Scandinavia

Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic

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