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Why mountains matter

The mountains matter. Sure, everyone knows they are awesome. What geologist doesn’t love going to the mountains to visit outcrops or for recreation? What I’m talking about is how the mountains matter to people studying sedimentary basins. If you’re a petroleum geologist working in a foreland basin, I hope you already know that they are a major control on the geometry of the basin. Orogenic events such as continental collision, terrane accretion, and thrust faulting control lithospheric flexure and basin geometry. As petroleum geologists, we cannot ignore one of the major controls on accommodation space.

Accommodation space isn’t the only reason mountains matter to petroleum geologists. Basin-wide unconformities can be tied to orogenic events. Such unconformities are major sequence boundaries, but we should also ask what conditions led to the unconformity in the rock record.

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Take the Western Canada Sedimentary Basin, for example. The Jurassic sequence in the western part of the basin, which was a foreland basin at that time, is bounded by two major angular unconformities. Whatever tectonic event is causing this kind of basin-wide tilting may also be reactivating structures within the basin — structures that could be in your pool. Isn’t the orogeny worth at least a second thought?

It’s not just in foreland basins that regional tectonics matter. It’s not just syndepositional tectonics that matter either. Basement matters. Pre-existing structures control the orientation of new structures. They can be reactivated during extension or compression. Carbonate reef trends can be tied to basement lineaments. Facies transitions can be controlled by basement domains.

Let’s back this out one step further, and talk not just about sedimentary basins, but about all geology. It all matters. It’s all connected, and while a large majority of petroleum geologists are focused on sedimentary and/or structural geology, every other branch of earth science matters too. What insights could someone studying diamondoids in heavy oil give to someone studying diamond formation in kimberlites, or vice versa?

Introductory geology textbooks like to demonstrate concepts in neat cycles like the water cycle, the rock cycle, and the Wilson cycle. As geologists we know it is more complex than this, and yet we find ourselves discretizing the cycle, only concerning ourselves with the stage that contains our rocks. When we think of a temporal sequence we need to think about the processes involved as interconnected gears, like in a clock. In a foreland basin, the mountains are one of the big gears.


Acknowledgments

The photograph is licensed CC-BY by Flickr user Sam Beebe.

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