May 31, 2012

Physical Erosion Or Chemical Weathering?

The June GSA TODAY science article is now online and open access at In this issue, Gregory Retallack and Joshua Roering of the University of Oregon enter the long-standing debate as to whether rock platforms along coasts and rivers are the product of physical erosion or chemical weathering above the water table.

Although the notion of wave-cut or stream-cut platforms is firmly entrenched in the literature, Retallack and Roering present the case that a more important role is played by subaerial chemical weathering. Using data from intertidal and riverside rock platforms in southwest Oregon, they show that the platforms correspond to the saprock-bedrock boundary and remain within the zone of modern water table and intertidal fluctuation despite continuing tectonic uplift. Above this zone of frequent wet/dry cycling, the rock is weakened by subaerial weathering, producing a sharp decrease in rock strength. Hence, in this case, waves and floods do not cut rock but remove clasts already weakened by weathering to expose the local water table as a bedrock surface.

GSA Today articles are open access online; for a print copy, please contact Kea Giles at the e-mail address. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA Today in articles published.


On the Net: