Monday, August 29, 2011

Foreland basins in a nutshell: Part III - Retroarc and peripheral foreland basins

Part I
Part II

The Western Canada Foreland Basin (WCFB) is a retroarc foreland basin. There are two main types of foreland basins, retroarc and peripheral. Both form during collisional tectonics.

A peripheral foreland basin, also known as an Alpine-style foreland basin, forms on the subducting plate (usually during continent-continent collision).

A retroarc foreland basin, also known as an Andean-style foreland basin, forms on the upper plate (usually during continent-oceanic plate collision).

Note: nothing is implied in the scale of the two figures above: there is definitely some vertical exaggeration going on.

I've often wondered if there is a difference in the sediment deposition patterns in the two classes of foreland basins. A reading of Hugh Sinclair's 1997 paper, Tectonostratigraphic model for underfilled peripheral foreland basins: an Alpine perspective, in which he describes the "underfilled trinity," (a favourite term of mine, by the way) felt a lot like reading a description of the Jurassic succession in the WCFB, except that he was describing a peripheral foreland basin. I suspect, therefore, that the sedimentological record alone would not be enough to discriminate between these two types of foreland basin.

In fact, this is what has been found by other authors, such as Dickinson: "Designation of a given foreland basin as either a retroarc basin or a peripheral basin thus depends upon a knowledge of the sequence and timing of tectonic events in the adjacent orogen" (Dickinson, 1974, p21).

Why does this matter? Well, having an "underfilled trinity" in the WCFB means that the foreland basin depositional sequences began appearing sooner than everyone thought, and that fits with what I'm proposing with my research. It also means that although foreland basins contain a record of the adjacent orogeny, we cannot use the basin fill alone to say if it is a retroarc or a peripheral foreland basin. It may seem strange that we wouldn't know this, but recent, and controversial, hypotheses about the evolution of the western margin of North America imply that the western foreland basins are peripheral, not retroarc (and by mentioning this, I'm not saying that I agree with those hypotheses).

In part IV, I'll talk about foreland basin fill: flysche, molasse, backbulges, underfilling...


Dickinson, W. (1974). Plate Tectonics and Sedimentation. In W. Dickinson (Ed.), Tectonics and Sedimentation (pp. 1-27). Society of Economic Paleontologists and Mineralogists.
Sinclair, H. H. D. (1997). Tectonostratigraphic model for underfilled peripheral foreland basins : An Alpine perspective. Geological Society of America Bulletin, 109(3), 324-346. Geological Soc America.

1 comment:

  1. hi, what do you think of the arabian basin is? is it a retro or peripheral foreland basin?