Quasi-Periodic Bedding in the Sedimentary Rock Record of Mars
Kevin W. Lewis,1*
Oded Aharonson,1
John P. Grotzinger,1
Randolph L. Kirk,2
Alfred S. McEwen,3
Terry-Ann Suer1
Widespread sedimentary rocks on Mars preserve evidence of surface
conditions different from the modern cold and dry environment,
although it is unknown how long conditions favorable to deposition
persisted. We used 1-meter stereo topographic maps to demonstrate
the presence of rhythmic bedding at several outcrops in the
Arabia Terra region. Repeating beds are
10 meters thick, and
one site contains hundreds of meters of strata bundled into
larger units at a
10:1 thickness ratio. This repetition likely
points to cyclicity in environmental conditions, possibly as
a result of astronomical forcing. If deposition were forced
by orbital variation, the rocks may have been deposited over
tens of millions of years.
2 U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86004, USA.
3 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
* To whom correspondence should be addressed. E-mail: klewis{at}gps.caltech.edu
