--> Abstract: Magnitude of Tectonic Uplift Events Along Passive Margins Estimated from Analysis of Base-Level Governed Erosion Surfaces, by Johan M. Bonow and Peter Japsen; #90082 (2008)

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Magnitude of Tectonic Uplift Events Along Passive Margins Estimated from Analysis of Base-Level Governed Erosion Surfaces

Johan M. Bonow and Peter Japsen
GEUS, Copenhagen, Denmark

The magnitude of recent tectonic uplift events along the passive margins in the Atlantic domain is evidenced by the high elevation of base-level governed erosion surfaces of regional extent and low relative relief. The difference in altitude between the present elevation of such a plateau and the base level to which it developed, reflects the amount of surface uplift since the surface was formed. The relief occasionally forms a series of steps resulting from multiple tectonic uplift events. Changes of the base level (uplift events) cause valleys to incise and the relief to rejuvenate. Consequently erosion surfaces will not survive for extended time in high-altitude positions. In West Greenland two erosion surfaces have been identified and the upper one cuts across basement and mid Eocene volcanics showing that this surface is significantly younger than the last, early Paleocene rift event in the area. The lower erosion surface is the evidence for a first phase of uplift, up to 1 km, prior to a later event, also up to 1 km, leading to the present stepped landscape. Scandinavia has two topographic domes with stepped surfaces. Uplift in the Neogene was 1 km for the Southern Scandes, while it was 0.5 km for the Northern Scandes. Northeast Brazil is dominated by two major erosion surfaces. The higher surface reaches elevations above 1 km and this altitude is probably due to Neogene uplift. The lower surface at c. 400 m a.s.l., is relatively well-preserved even where it cuts across strata prone to weathering. This indicates that it was affected by uplift and subsequent valley incision late, probably during the Plio-Pleistocene. These cases illustrate that geomorphological analysis of base-level governed erosion surfaces can be used to estimate the magnitude of uplift events.

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