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Rates of development of tafoni in the Moenkopi and Kaibab formations in Meteor Crater and on the Colorado Plateau, northeastern Arizona
Author(s) -
Norwick Stephen A.,
Dexter Leland R.
Publication year - 2002
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.276
Subject(s) - geology , outcrop , lithology , plateau (mathematics) , impact crater , homogeneous , weathering , geomorphology , mineralogy , paleontology , thermodynamics , mathematical analysis , physics , mathematics , astronomy
Tafoni are pits formed by non‐uniform weathering in otherwise uniform rock. Two equations have been proposed for the rate of development of tafoni, both based on 2000‐year‐old outcrops from the coast of Japan. We have taken tafoni measurements from the Meteor Crater, Arizona, and vicinity that extend the equations back at least 50 000 years. As reported in earlier studies, we found pit depth to be the best tafone parameter to measure. The size of the pit decreases significantly with increasing inclination of the rock surface; however, the size of the pit can vary greatly for other reasons. In some cases the measurements are statistically significantly different between two stations taken from contiguous areas of similar inclination and aspect in an apparently homogeneous bed. It is clear, however, that over tens of thousands of years tafoni enlarge significantly. Our data are generally log‐normal and all are markedly heteroscedastic. The 1991 equation proposed by Matsukura and Matsuoka does not fit our data. The 1996 equation proposed by Sunamura provides a better fit. We propose a sigmoidal equation D = b 1 + e ( b 2+( b 3/ t )) where D is the depth, t is the age, and b 1, b 2 and b 3 vary with lithology. This new equation fits our data far better than the earlier published equations. Copyright © 2002 John Wiley & Sons, Ltd.