THE MODEL OF RESTRICTIVE PLANATION - AN A PPROACH TOWARDS UNDERSTANDING THE RULES OF LANDFORM DEVELOPMENT IN SEDIMENTARY-ROCKS OF VARIABLE RESISTANCE

Taking the Lower Franconian scarplands (Main River region of southern Germany) as an example, the compatibility of the formation of stepped planation surfaces with the structural governing of landform developme nt is explained and confirmed in a world-wide comparison for regions o f sedimentary rocks of varying resistance. Many structure-adapted land scapes evolved by spatially restricted lowering of planation surfaces as the decisive process and the etching of lower planation levels from an initial erosion surface. Paleoclimate, uplift and sea-level fluctu ations were the basic factors of landform differentiation, which mainl y expressed itself in an adaptation to the structural inventory by: th e formation of landforms, developing in dependence on structurally fav ored resistant rocks, rising above planation surfaces as uplands delim ited by escarpments or as hogbacks and swells, the adjustment of plana tion surface lowering to structurally weak terrain (due to facies, inc lination of strata, fracturing) and thus to the formation of largely s tructurally predetermined planation surfaces grading to the base level of erosion. The largely structurally determined lowering and local ex pansion of planation surfaces were the decisive characteristics of thi s type of landscape development and are termed ''restrictive planation ''. The concept of restrictive planation, in the context of later diss ection of the planation surfaces, helps explain the development of old er landforms. Its importance for present landform development cannot y et be fully assessed. The model of restrictive planation presented her e comprises common traits of the origin of structure-adapted landscape s in sedimentary rocks of variable resistance.