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Debated: Wave-Cut or Weathering or Both?

June 2012 GSA Today science article

Geological Society of America


IMAGE: This is a saprock-bedrock boundary at water table in coastal rock platform at Sunset Bay (A) and alluvial rock platform at Days Creek (B), Ore. view more

Credit: G. Retallack and J. Roering.

Boulder, Colorado, USA - 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 address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA Today in articles published.

Wave-cut or water-table platforms of rocky coasts and rivers?
Gregory J. Retallack and Joshua J. Roering, Dept. of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA. Pages 4󈝶 doi: 10.1130/GSATG144A.1.

GSA Today is The Geological Society of America's science and news magazine for members and other earth scientists. Refereed lead science articles present exciting new research or synthesize important issues in a format understandable to all in the earth science community. GSA Today also often features a refereed "Groundwork" article -- tightly focused papers on issues of import to earth science policy, planning, funding, or education. All GSA Today articles are open access at

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