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

Abstract

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.

Magnitude of rift‐related burial and orogenic contraction in the Marrakech High Atlas revealed by zircon (U‐Th)/He thermochronology and thermal modeling

“…Rifting in the Atlantic margin is reported to end in the Early Jurassic [ Stets , ; Medina , ; Piqué and Laville , ; Le Roy and Piqué , ; Tari et al ., ; Hafid et al ., ; El Arabi , ; Tari and Jabour , ] in response to the onset of seafloor spreading and formation of Atlantic oceanic crust between 195 Ma and 170 Ma [ Medina , ; Sahabi et al ., ; Davison , ]. However, there are numerous cases along the rift flanks of the Atlantic and other oceans where uplift, peneplanation, and burial occurred during postrift times [e.g., Green et al ., , and references therein]. While the causes of these vertical movements are not fully understood, Green et al .…”

Evolution of the central West Greenland margin and the Nuussuaq Basin: Localised basin uplift along a stable continental margin proposed from thermochronological data

“…Moreover, the glacial history of both sections of the margin differ heavily, with the Nuussuaq Region experiencing significant widespread glacial erosion, while in the south much of the erosion is constrained by the topography. These variations in geology, structure and glacial history demonstrate the dichotomy between the Nuussuaq Region and the SW margin, suggesting the topography of both are likely sourced from separate sources, Mesozoic rifting in the south and Cenozoic volcanism and isostasy in the north Anell, Thybo, & Artemieva, 2009;Cloetingh, Gradstein, Kooi, Grant, & Kaminski, 1990;Eyles, 1996; Gołe z dowski, Nielsen, & Clausen, 2012; Green, Lidmar-Bergstr€ om, Japsen, Bonow, & Chalmers, 2013;Japsen & Chalmers, 2000;Japsen et al, 2010;McGregor et al, 2013;Nielsen et al, 2009). The results of this study suggest postrift uplift along the West Greenland Margin is only recorded within the Nuussuaq Basin during the Cenozoic and no evidence of any significant uplift is documented along the southern extent of the margin.…”

Contrasting Mesozoic evolution across the boundary between on and off craton regions of the South African plateau inferred from apatite fission track and (U‐Th‐Sm)/He thermochronology

“…Many of the early geomorphological studies are based on the concept of the formation of continent-wide planation surfaces formed by prolonged erosion that are subsequently dissected by later erosion events following regional uplift of lowering of base level, and therefore, their remnants can be extrapolated regionally. The occurrence and significance of continental erosion surfaces as geomorphic markers have been thoroughly discussed with frequent reference to the African case [e.g., Dixey, 1955;King, 1955;Ollier and Marker, 1985;Summerfield, 1985;Partridge and Maud, 1987;Van der Beek et al, 2002;Burke and Gunnell, 2008;Green et al, 2013].…”