[X] My Assistant

[imipak]

Universe Today article on a new Science paper, "Quasi-Periodic Bedding in the Sedimentary Rock Record of Mars" (abstract. ) (UT just happened to be the first write-up I came across; there's plenty of coverage elsewhere.)

"One of the fun things about this project for me is that we were able to use techniques on Mars that are the bread and butter of studies of stratigraphy on Earth," says Aharonson. "We substituted a high-resolution camera in orbit around Mars and stereo processing for a geologist's Brunton Compass and mapboard, and were able to derive the same quantitative information on the same scale. This enabled conclusions that have qualitative meaning similar to those we chase on Earth."

It would be curious if the process that caused this terraced / stepped terrain would only show up in one location; are there any similar landforms? ISTR seeing many HiRISE images of layered terrain where the layers appeared, to my lay eyes, to be superficially similar, but I'm no geologist. How ubiquitous an effect is this in layered sedimentary rocks? Informed comment gratefully received

[tdemko]

This branch of geosciences is called cyclostratigraphy. Although cycles of sedimentation related to lunar, seasonal, and sunspot cycles had long been recognized, stable isotope analyses of fossil marine critters and sediments lead to the development of our current understanding of the relationships between incoming solar radiation (insolation) and the planetary orbital parameters of eccentricity, precession, and obliquity. The orbital-induced insolation effects are called Milankovitch cycles, after the Serbian mathematician and engineer Milutin Milanković who first quantitatively elucidated them. On earth, the most dramatic connection between orbitally-modulated insolation, climate, and sedimentary processes is the control of the growth and decay of continental ice sheets and the resulting sea level changes (as much as 100's m), the "pacemaker" of the Ice Ages. Of course, many more connections and teleconnections have been documented (strength of monsoons, ENSO cycles, etc.), thus the emergence of this branch of stratigraphy and related branches of geochemistry and paleoclimatology.

On modern (and geologically recent) Mars, it seems that orbitally-modulated insolation changes also must control the distribution and phase of volatiles on the surface and in the near-surface environments. As, on earth, other related climatic affects, including atmospheric circulation patterns, also vary in this beat-like fashion. We are just starting to glimpse the large-scale (here visible from orbit) physical stratigraphic evidence of these cycles. Regional and outcrop-scale mapping, along with facies and geochemical analyses will tell us much more...

[rlorenz]

......The orbital-induced insolation effects are called Milankovitch cycles, after the Serbian mathematician and engineer Milutin Milanković who first quantitatively elucidated them.

Err, a better term is Croll-Milankovic cycles. The Scot, James Croll, really figured the whole thing out earlier
(he studied the boulder clays and other geological evidence for glaciation, calculated how much heat the
gulf stream transports and thus how much colder northern europe would be without it, and estimated
the climatic effect of orbit/spin changes.). He laid out the big picture. Milankovic just redid the
mathematics a little better.....