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

2013 ◽  
Vol 30 ◽  
pp. 1-150 ◽  
Author(s):  
Paul F. Green ◽  
Karna Lidmar-Bergström ◽  
Peter Japsen ◽  
Johan M. Bonow ◽  
James A. Chalmers
Keyword(s):  
Sea Level ◽  
Sedimentary Basins ◽  
Landscape Analysis ◽  
Direct Result ◽  
Continental Margins ◽  
West Greenland ◽  
Base Level ◽  
Break Up ◽  
Geological Constraints ◽  
High Topography

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.

The origin of elevated plateaus along passive continental margins

2020 ◽  
Author(s):  
Johan M. Bonow ◽  
Peter Japsen ◽  
Paul F. Green ◽  
James A. Chalmers
Keyword(s):  
Sea Level ◽  
Continental Margins ◽  
East Greenland ◽  
Passive Margins ◽  
Base Level ◽  
Wide Range ◽  
The World ◽  
Incised Valleys ◽  
Break Up ◽  
High Level

<p>Many passive continental margins around the world are characterised by elevated plateaus at 1 to 2 km or more above sea level cut by deeply incised valleys and commonly separated from an adjacent coastal plain by one or more escarpments. Mesozoic–Cenozoic rift systems parallel to the coast are commonly present offshore with a transition from continental to oceanic crust further offshore. These landscapes occur in arctic, temperate and tropical climate and in different geological settings independent of the time span since break-up (e.g. along the Atlantic from south to north).</p><p>The plateaux are typically more than 100 km wide, much larger in some cases, and extend hundreds of kilometres along the margin, cutting across bedrock of different ages and resistances. The key to understanding the formation of regional, low-relief erosion surfaces is the base-level, as this is the level to which fluvial systems grade the landscape. The most likely base level is sea level, particularly for locations along continental margins during the post-rift development of passive margins.</p><p>It is commonly assumed that the characteristic, large-scale morphology of elevated, passive continental margins with  high-level plateaux and deeply incised valleys persisted since rifting and crustal separation Further, it is assumed that the absence of post-rift sediments is evidence of non-deposition, despite continental-stretching theory predicting deposition of a thick post-rift sequence overlying both the rift and its margins.</p><p>However, our studies of the passive continental margins of West and East Greenland, Norway, NE Brazil and southern Africa provide evidence of km-scale, post-rift subsidence and that the plateau surfaces were graded to sea level long after break-up and subsequently lifted to their present elevations. In some of these cases, the presence of post-rift marine sediments at high elevation provide direct proof of this interpretation. Since elevated plateaux cut by deeply incised valleys are a characteristic feature of these and other margins, this similarity suggests that such topography elsewhere in the world may also be unrelated to the processes of rifting and continental separation. We present a wide range of evidence from passive margins around the world in support of this hypothesis,</p><p> </p><p>Bonow et al. 2014: High-level landscapes along the margin of East Greenland – a record of tectonic uplift and incision after breakup in the NE Atlantic. Global and Planetary Change.</p><p>Green et al. 2018: Post-breakup burial and exhumation of passive continental margins: Seven propositions to inform geodynamic models. Gondwana Research.</p><p>Japsen et al. 2019: Elevated passive continental margins: Numerical modeling vs observations. A comment on Braun (2018). Gondwana Research.</p>

How syn-rift sedimentation promotes the formation of hyper-extended margins

2020 ◽  
Author(s):  
Susanne Buiter
Keyword(s):  
Sedimentary Basins ◽  
Surface Processes ◽  
Tectonic Activity ◽  
Tectonic Deformation ◽  
Continental Margins ◽  
Rifted Margins ◽  
Continental Rifts ◽  
Break Up ◽  
Mountain Belts ◽  
Sediment Layers

<p>Seismic observations show that some rifted continental margins may have substantial amounts of offshore sediments. For example, sediment layers of several kilometres thick are found on the margins of Mid Norway, Namibia and Angola. Intriguingly, these margins are wide, being characterised by distances of several hundreds of kilometres from typical continental crustal thicknesses of 30-40 km to clearly identifiable oceanic crust. On the other hand, some margins that are sediment-starved, such as Goban Spur, Flemish Cap and Northern Norway, have short onshore-to-offshore transitions. Variations in the amount of sediments not only impact the development of offshore sedimentary basins, but the changes in mass balance by erosion and sedimentation can also interact with extensional tectonic processes. In convergent settings, such feedback relationships between erosion and tectonic deformation have long been highlighted: Erosion reduces the elevation and width of mountain belts and in turn tectonic activity and exhumation are focused at regions of enhanced erosion. But what is the role played by surface processes during formation of rifted continental margins?</p><p>I use geodynamic finite-element experiments to explore the response of continental rifts to erosion and sedimentation from initial rifting to continental break-up. The experiments predict that rifted margins with thick syn-rift sedimentary packages are more likely to form hyper-extended crust and require more stretching to achieve continental break-up than sediment-starved margins. These findings imply that surface processes can control the style of continental break-up and that the role of sedimentation in rifted margin evolution goes far beyond the simple exertion of a passive weight.</p>

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

2021 ◽  
Vol 45 (1) ◽  
Author(s):  
Johan M. Bonow ◽  
Peter Japsen
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Continental Margins ◽  
Rift Basins ◽  
East Greenland ◽  
Planation Surface ◽  
Base Level ◽  
North East ◽  
The North ◽  
Late Neogene

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.

A Suggested Origin of Continental Slopes and of Submarine Canyons

1950 ◽  
Vol 87 (2) ◽  
pp. 102-104 ◽  
Author(s):  
K. O. Emery
Keyword(s):  
Sea Level ◽  
Shear Plane ◽  
Continental Margins ◽  
Submarine Canyons ◽  
Continental Shelves ◽  
Continental Slopes

AbstractThrusting along a shear plane at the continental margins may result in a temporary up-bulging of the margins above sea-level. During the time of exposure erosion by streams should have incised canyons which now, after isostatic readjustment of the margins, constitute the widely distributed submarine canyons. Known downwarped peneplains below the surface of continental shelves may have been developed on the bulged margins by long continued erosion. The margins may, thus, have served as- sources of some sediments now found on land and believed to have been derived from a seaward direction.

Landscape development in western and central Dronning Maud Land, East Antarctica

2001 ◽  
Vol 13 (3) ◽  
pp. 302-311 ◽  
Author(s):  
Jens-Ove Näslund
Keyword(s):  
Large Scale ◽  
High Elevation ◽  
Continental Margins ◽  
Landscape Development ◽  
Ice Streams ◽  
The North ◽  
Ice Stream ◽  
Dronning Maud Land ◽  
Break Up

Large-scale bedrock morphology and relief of two key areas, the Jutulsessen Nunatak and the Jutulstraumen ice stream are used to discuss glascial history and landscape development in western and central Dronning Maud Land, Antarctica. Two main landform components were identified: well-defined summit plateau surfaces and a typical alpine glacial landscape. The flat, high-elevation plateau surfaces previously were part of one or several continuous regional planation surfaces. In western Dronning Maud Land, overlying cover rocks of late Palaeozoic age show that the planation surface(s) existed in the early Permian, prior to the break-up of Gondwana. A well-develoment escarpment, a mega landform typical for passive continental margins, bounds the palaeosurface remnants to the north for a distance of at least 700 km. The Cenozoic glacial landscape, incised in the palaeosurface and escarpment, is exemplified by Jutulsessen Nunatak, where a c. 1.2 km deep glacial valley system is developed. However, the prominent Penck-Jutul Trough represents some of the deepest dissection of the palaeosurface. This originally tectonic feature is today occupied by the Jutulstraumen ice stream. New topographic data show that the bed of the Penck-Jutul Trough is situated 1.9±1.1 km below sea level, and that the total landscape relief is at least 4.2 km. Today's relief is a result of several processes, including tectonic faulting, subaerial weathering, fluvial erosion, and glacial erosion. It is probable that erosion by ice streams has deepened the tectonic troughs of Dronning Maud Land since the onset of ice sheet glaciation in the Oligocene, and continues today. An attempt is made to identify major events in the long-term landscape development of Dronning Maud Land, since the break-up of the Gondwana continent.

scholarly journals Neoglacial change of ice cover and the related response of the Earth's crust in West Greenland

1993 ◽  
Vol 159 ◽  
pp. 121-126
Author(s):  
A Weidick
Keyword(s):  
Spatial Distribution ◽  
Sea Level ◽  
Early Holocene ◽  
Relative Sea Level ◽  
West Greenland ◽  
Exact Data ◽  
Present Information ◽  
Long Time ◽  
Related Response ◽  
Inland Ice

The cooling trends of Neoglacial time caused re-formation of minor local glaciers and expansion of the Inland Ice margin. A consequence of this glacial reactivation in West Greenland was the conversion of an early Holocene glacio-isostatic emergence to Neoglacial submergence. Although the major trends of fluctuations of ice margins and relative sea level have been studied over a long time, exact data on the spatial distribution of Neoglacial changes of glacier load and relative sea level are still sparse. Present information points to a major conversion from emergence to submergence between 1000 and 3000 B.P., depending on location and the effect of superimposed secondary oscillations.

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