ABSTRACT BOOK Sandstone Landscapes ... - Sandstones.org

TRadek MikulášInstitute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Praha 6, CzechRepublic (mikulas@gli.cas.cz)Relief and its memory: Minute forms in sandstone surfacesRock surfaces of weakly lithified sandstone rock are a specific “memory register”: it is relatively easy toform a “record” (e.g., scratch, salt erosion feature, bioerosion feature, hardened body) but its durability maybe surprisingly high. Little attention has so far been paid to this aspect of the sandstone meso- andmicrorelief; however, the temporal analysis of the surfaces may help to date various events, e.g., fall ofrock block, deforestation, and soil degradation. Especially rich record can be obtained from honeycombsurfaces. Arcuate honeycomb pits usually show gravity-controlled orientation of their flat bottoms(probably because they function as “rock dishes” in specific situations). In result, surfaces of fallen blocksoften bear pits of double or triple shape. 1, symmetrical arcuate ones with oblique bottoms (i.e., the oldest,non-reconstructed generation). 2, “reconstructed” honeycombs, usually larger than the previous type; theirupper parts are inclined and somewhat asymmetrical, bottoms are flat. 3, symmetrical arcuate pits with flatbottoms (i.e., the youngest, post-event generation; cf. Mikuláš 2001a).Less frequent but well interpretable shapes of sandstone surfaces are oblique “ledges” formed throughrising of soil moisture in sidewalls of sandstone pillars. Therefore, an oblique ledge may mark long-lastingunchanged position of soil cover along the walls. In the area of historic settlement of Hradsko (KokořínNature Reserve), several ledges can be observed on the walls of sandstone coombs. In this case, thepossibility to correlate individual ledges and episodes of deforestation seems to be realistic (cf. Mikuláš2001b).Rock crusts, rock arches, abri, tree trunks, arcuate niches, tunnels and small precipitation forms (e.g.,spherical nodules) are other features of sandstone meso-and microrelief which may bear an interpretabletemporal record.References:Mikuláš, R. 2001a. Gravity and orientated pressure as factors controlling “honeycomb weathering” of theCretaceous castellated sandstones (northern Bohemia, Czech Republic). - Bull. Czech Geol. Survey, 76(4):217-226.Mikuláš R. 2001b. Poznámky ke vzniku některých prvků mikroreliéfu pískovcových skal. - Ochranapřírody, 56, 1, 19-21. Praha.The study is a part of the Research Programme of the Institute of Geology, AS CR, Praha (No. CEZ: 23-013-912).