Paleosols in clastic sedimentary rocks: their geologic applications

56( )M.J. KrausrEarth-Science ReÕiews 47 1999 41–70Fig. 8. Schematic diagram showing a paleocatena, which developed because of changes in grain size and topography away from the ancientchannel. A moderately or well-drained soil generally forms on the levee, although subsurface horizons can be gleyed Ž Bg horizon.becauseof proximity to the ground water table. Poorly to very poorly drained soils are more typical of the floodbasin Žmodified from Kraus andAslan, 1999 ..sparse organic matter. Grey soil colors are moreabundant lower in the profile ŽBg and Cg horizons,which are gleyed B and C horizons.because it iscloser to the ground water table and more prone toreduced conditions Ž e.g., Duchaufour, 1982 .. Awayfrom the channel, the soils become progressivelymore poorly drained because the topographic positionis lower and the sediment is finer-grained andless permeable. Waterlogged, reduced conditions favorthe accumulation and preservation of organicmatter in an Ag Ž gleyed A.horizon and the developmentof a thick, grey Bg horizon with many redoximorphicfeatures. Fluctuations of the water table alsoproduce intersecting slickensides in the clayey sediments.Ancient catenas have been described from Paleogenefluvial rocks Že.g., Fastovsky and McSweeney,1987. and from Jurassic deltaic plain deposits Že.g.,Arndorff, 1993 .. Those catenary relationships havebeen used to reconstruct the ancient floodplain landscape.Arndorff, for example, found that the distributionof different paleosols reflected their position onthe deltaic plain. Relatively well drained, light brownpaleosols with a yellowish to orange subsurface horizonformed on sandy natural levees and crevassesplays. In contrast, dark-colored silty claystones interpretedas gleyed alluvial soils formed in the backswamps.Pedofacies focus on lateral changes in the degreeof pedogenic development with increased distance