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Dr. Brad Goodfellow - Reinterpreting the Subcambrian peneplain - an investigation of bedrock structural controls on glacial erosion

Föreläsning

Biography:
Brad is a process geomorphologist originally from Australia where he studied physical geography at the University of Melbourne as a mature age student. He then completed his PhD at Stockholm University (with Arjen Stroeven) on weathering processes and landscape development in the mountains of northern Sweden. After graduating in 2008 he spent 4 years on a postdoc with George Hilley, a tectonic geomorphologist at Stanford University, investigating climatic and lithological controls on chemical weathering of rock. Since late 2012 he has been a researcher at Stockholm University and a guest researcher at Lund University. He is presently working on a glacial erosion project funded by the Swedish Nuclear Fuel and Waste Management Company and in dating tectonic faulting in carbonate rocks using 36Cl and U-Pb.

Abstract:
Fractures exert a key control on spatial patterns and rates of glacial erosion of bedrock. Across parts of central and southern Sweden, the Subcambrian peneplain (SCP), which is generally developed in granitic-gneiss basement, provides an initial boundary condition for Quaternary glacial erosion. From remnants adjacent to, or beneath, Cambrian sedimentary rocks, and from locations where only slight glacial erosion has been inferred, we see that the SCP is characterized by low amplitude (often meters-scale) convex ¿bumps¿, is often chemically weathered to depths of some meters or more, and displays abundant fractures. In some locations, such as in the Trollhättan area, exceptionally flat ¿billiard table¿ bedrock surfaces are also interpreted as SCP remnants, essentially unmodified by glacial erosion. In this talk, we will explore how topography perturbs near-surface gravitational (vertical) and tectonic (horizontal) stresses to create new, or open existing, bedrock fractures. This perturbation is significant, even in low-relief terrain. Generally, sub-vertical fractures open in valleys whereas sub-horizontal fractures open beneath hills. This spatial variation in fracturing controls rates (inferred from cosmogenic nuclides) and patterns of glacial erosion and subsequent relief development from the SCP. Landscape relief may increase by glacial excavation along sub-vertical fractures in valleys but conversely decrease by flattening of hilltops through glacial plucking of bedrock slabs along sub-horizontal fractures. Positive and negative feedbacks exist between topography, bedrock fracturing and glacial erosion, and qualitatively inferring the extent of glacial modification from local relief magnitudes and indications of streamlining and/or original SCP from landscape characteristics, such as ¿flatness¿, may be highly misleading.

Föreläsare: Dr. Brad Goodfellow

Datum: 2017-11-24

Tid: 15:00 - 16:00

Kategorier: Naturvetenskap

Arrangör: Jakob Heyman

Plats: Geovetarcentrum, Guldhedsgatan 5 A
Nimbus

Kontaktperson: Jakob Heyman

Sidansvarig: Henrik Thelin|Sidan uppdaterades: 2014-10-13
Dela:

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