Tuesday, July 5, 2011

Foreland basins in a nutshell: Part I - Foreland Basin vs. Sedimentary Basin

I study foreland basins. Specifically, I'm looking at the initiation of the western Canada foreland basin and challenging the traditional view of when this initiation took place. In order to do this, I need to use a different definition/model for foreland basins than what has previously been used in western Canada.

Different model, you ask? As I have learned over the last two years, there are different types of foreland basins, and different models for explaining deposition within them. Because I want to have a clear picture of all these different models in my head for my thesis, I'm going to attempt to give an overview of them here.

Today, part I will focus on clearing up a common misconception, at least here in western Canada. The western Canada foreland basin (WCFB) is not the same as the western Canada sedimentary basin (WCSB). The WCSB is the entire sedimentary record in western Canada, beginning with the Belt-Purcell and Windermere deposits in the Proterozoic and continuing through to present times. The WCFB is the sediments deposited during the Cordilleran Orogeny through the Mesozoic and early Paleogene. In the following figure, from the Geological Atlas of Western Canada, you can see the extent of the WCSB. The WCFB is approximately coincident with what is labeled here as the Alberta Basin. However, the foreland basin deposits do actually extend into the Cordillera, like the WCSB does.

Many maps often erroneously depict the western edge of the WCSB and/or the WCFB as being coincident with the eastern edge of Cordilleran deformation (as is the case with the Alberta Basin shown here). Most of the fold-thrust belt contains sedimentary rocks, therefore they are deposited in the WCSB, and in the case of the Mesozoic and Paleogene rocks, the WCFB.

Image source: www.ags.gov.ab.ca/publications/wcsb_atlas/a_ch03/ch_03.html

In part II, I will look at the most basic definition of what a foreland basin is, and how plate tectonic theory influenced our understanding of foreland basins.

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