Comparative geology - the tale of two rivers

I recently went on a canoe trip along the Trinity River (our track is shown by the red snaky line in the picture below).  We spent the day looking at sedimentary features associated with modern river systems, and by doing so, thinking about processes at work in rivers, and the resulting rock architecture.  As geologists, we often study modern environments (like rivers, beaches, deltas etc) to gather clues that help us understand the rocks and the processes that formed them.

The trip to the Trinity (more details in this post) reminded me of the Arges River in Romania; if looked from above, both have a lot in common.

Note that the scale of the two satellite images are similar, so the size of the geomorphic features can be easily compared.  The width of the meander belt in the two images is similar.  Two abandoned meander loops (red arrows) have similar dimensions and shape.  Their paleo meander belts (active sometime in the recent past and still visible on the satellite image) have similar widths (black arrows).

The zoomed satellite photos show that the size of the active channels are similar.  The Arges shows better the point bars within the active channel, but this is only because the picture of the Trinity was taken at near bank-full stage, where most of the point-bars are submerged.
These two rivers, although in somewhat different settings, would most likely create a very similar rock succession.  I have to take a canoe trip along Arges sometime in the future, and at that point I will have on the ground pictures from the both locations.  Until then, wait for the next post on the Trinity, and enjoy the birds-eye view of the two rivers.

Comparative geology

I am starting a new series of posts on “comparative geology”, in which I will compare and contrast geological features, settings, processes, events mostly for … the fun of it. Comparison is used as an investigative tool in other sciences; comparative anatomy is one example. The closest to my background is the case of sedimentary geologists using the term “analogs” when they compare rocks formed in similar depositional settings. Often analogs are used to compare rocks in the subsurface, where information is sparse and often one-dimensional (or three-dimensional but low resolution), with outcrops where rocks may be often seen in three-dimensions, touched, smelled, even tasted (ok, you have to be a geologist to enjoy that aspect). Another example of comparative geology is from the Earth and Planetary Sciences, where geomorphic or geologic features or processes on Earth are compared to those observed on other planets, with the goal of understanding processes on distant places in the Universe. The “distributary fans on Mars” are one example of this comparative geology concept.

The idea came to me this past week, while on vacation in the Sierra Nevada, a paradise for geologists. Many places I've seen during this trip reminded me one way or another of geologic features or settings in Romania; hence the opportunity for comparative geology on Romania Rocks.

There are many advantages for using comparison as an investigative tool in geosciences: when you compare and contrast features or processes, you understand them better; and then, there is the opportunity to come up with that wacky idea that would turn into a big breakthrough because you looked at things in a different way, or from a different perspective.