The key to much of our understanding of stratigraphy relies heavily on Walther’s Law. The vertical juxtaposition of deposits that represent various depositional environments allows us to pick surfaces, correlate wide-spread geological processes, and determine time-rock and time-surface relationships; in other words, it’s kind of important to the whole sedimentology and stratigraphy thing.
While Walther’s Law works pretty well for shallow marine successions (for instance, the shoreface succession), we start to get into hazy territory in nonmarine environments (and deep marine, too). What is a Waltherian succession in an evaporative lake? How about in fluvial/alluvial successions? More to the point, when do we pick a surface that delineates a non-waltherian succession?
Once again, I present some pretty pictures gleaned from NASA World Wind! ENJOY!
This first picture is an overhead view of a lake basin north of the Ordos basin; a river, sourced from nearby mountains, feeds a large lacustrine delta, with distributary network, near a pretty good-sized dune field in the lower left. Alluvial fans make an apperance as well. If the lake levels drop, how will the migration of these disparate features be recorded, and how would we interpret them? Could get kinda complicated.
This second image is an oblique view (at 10x VE).
This last picture is a pretty nifty image of some Kelvin-Helmholtz instabilities developing on the edge of a hypopycnal plume.