Inverted Paleochannels in Central Utah, Analogs for Mars
||Figure 1. Ross Irwin atop the central Utah deposits.
Dr. Ross Irwin
How often you do see a river valley or channel that is raised above the surrounding surface? This inversion of relief, called an inverted paleochannel, arises when the channel bed sediments are more resistant to erosion than are floodplain deposits on the adjacent valley floors1. Inverted paleochannels have been identified in many areas around the globe, but the ones in central Utah are outstanding examples (see Figure 1). Through studying terrestrial examples, geologists hope to resolve whether these Martian features are old fluvial channels, and if so, to determine the size of the rivers that formed them.
The paleochannels in central Utah were formed in the Late Jurassic1. During the Early Cretaceous sediment was deposited from the highlands, and later from western Sevier mountain belt1. The mid-Cretaceous was characterized by a global increase in sea level1. The newly formed oceanic basin flooded the original channel system and culminated in burying the channel sediments with ~900 m of marine sediment1. Only after ~75 million years of burial were the paleochannels exhumed during regional uplift in the middle to late Cenozoic1. The carbonate cementation of the channel sediments hardened them and enhanced their resistance to erosion. The less resistant surrounding valleys eroded away leading to the current inverted state of the Utah paleochannels1.
Did the features on Mars have a similar geologic history to the paleochannels in Utah? Whereas the inverted relief in Utah resulted from erosion by subsequent fluvial activity, the Martian examples would have been eroded by wind1. Were the Martian sinuous ridges cemented in a similar fashion to the Utah paleochannels and if so, by what if not carbonate1? By studying the terrestrial analogs in Utah both aerially and on the ground, scientists hope to better understand what we can say for certain about the similar features on Mars.
1. Williams et al. (2007), Exhumed Paleochannels in Central Utah – Analogues for Raised Curvilinear Features on Mars.
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