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LANG, S. Ooo ost West Trading, C. GEZE, 8. NiCCO, J. EAHU, M.
RElFF, W. Italy is described. Its mode of origin and the transformation by minor morphological processes in the Holocene are discussed. He explained it as a result of stripping off the mantle of soil and weathered rocks by glacier action from a previously weathered and karstified limestone area. This type of karst is best developed in regions with horizontal or gently ooo ost West Trading limestone strata. The staircase karst is characterised by the absence of a sheet of moraine deposits.
According to B'dgli such moraines disappeared by solution after the glaciation. The area of Fanes Piccola is described in some detail in this paper. The processes which tend to modify and destroy the typical features of the staircase karst are discussed as well as the concomitant forms. Topography and geology of the Fanes Pieeal a area: The Fanes Piccola area is situated in ooo ost West Trading karstic headwater zone of a small creek: the Rio di San Vi gil i o in the Dolomi t es.
The staircase karst occupies the central part of the topographic and tectonic basin-like depression of Fanes Piccola, at an altitude of m. The beds show two predominant ranges of thickness: 35 50 cm and cm. The strata are horizontal or have ooo ost West Trading a dip of some degrees.
Further details on the geology and geomorphology of the Fanes region are presented by HutschlechnerMerlaBevilacquaand Engelen The genesis and forms of the staircase karst : The Fanes depression is part of an old fluviatile valley system. Its origin goes back at least to the Upper Tertiary.
The weathering processes in preglacial and interglacial periods disrupted the cohesion of the strata by solution along vertical joints and horizontal bedding planes. Proofs of such processes were found by the author in the comparable nearby Fosses area, loamy, red-coloured weathering residues are preserved there it deep fissures. During the subsequent stagesof glaciation of the area, the mantle of soil and the underlying zone of loose blocks were carried off by the ice.
The valley bottom and the slopes were stripped bare down to the fixed, non-weathered bedrock. The general topographic slope of the valley sides in the staircase karst was measured in many locations around the La Varella settlement.
The dints have attained a depth of 15 cm and a length up to 1 m Fig. Their occurrence is mainly restricted to the tiick beds, T. Those solutional features are found on the broad flat steps of the staircase karst as well as in the very steep rounded rims of the beds.
Small alpine shrubs, grasses and ferns grow at their bottom and they evidently caused the considerable local solution étude doptions the production of humic acids and carbon dioxyde. The preserved lower parts of dints along joints German: Kluftkarren; French: lapils S diaclases were not obliterated by glacial scour on account of their position in the fixed, non-weathered bedrock.
These dints or grikes are widened now by solution along the steep sides. The younger, vertical dints within the grikes have very sharp edges ooo ost West Trading are especially well developed along the upstream side of the comment fonctionnent les signaux de trading, where most of the surficial run-off that is ooo ost West Trading and caught by the grike flows in.
Frost shattering produces locally small, angular rock fragments on bare patches within the grass cover of fHe steps of the staircase. The fragments range in size from some centimeters to 15 cm. A remarkable notch of 5 15 cm heighi and 10 30 cm depth was observed along the lower side of many thick limestone beds, and along partings within thicker beds which crop out in the slopes Fig.
The formation of this feature may be explained in the following way: Rainwash concentrates water, soil par tides and tiny rock fragments in the angles of the steps of the staircase karst. Consequently a moisture reserve is created in an elongate strip at the base of the bed.
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This moisture attacks the lower side of the adjacent limestone bed along the bedding plane. As soon as a small notch has come into being, the solutioral process may continue more easily.
The rainwash-flowing over the steep side of the overlying stratum, turns into the ceiling of the notch and then the water drips or flows on the moist and shadowy bottom. Then flakes with an area of 2 3 square decimeters and a thickness of 1 2 cm get detached in the ceiling of the notch and fall down.
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This disintegration of the overlying bed takes place under the influence of gravity, sideward infiltration of wafer along minor bedding planes and vertical micro-joints within the thicker beds, and by frost action.
The rock fragments which fall info the moist weathering residue at the bottom of the notch gradually disappear by solution. The notch constitutes a favourable microcl imaiological zone for vegefation, which in turn promotes further solution by the production of humic acids and carbon dioxyde, 6. The veil of small-grained moraine deposits has gradually disappeared by solution and it has been washed away partly since the end of the glaciation.
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The liassic limestones in front of the stepped slope are dissected along joints. To the left of the La Varella settlement postglacial options et actualités and peaty deposits fill in the depressions of the topography.
The blocky talus cone above it was formed by a huge postglacial rockf al 1.
Note the upper rims of the beds which have been rounded by glacial abrasion. The solution notches along the lower side of the beds are visible. The glacially rounded upper rims of the beds, and the postglacial solution furrows are visible. Break away of three angular blocks of limestone along joints and the underlying bedding plane.
Note the increase in tilt of the successive blocks. Sapping of a limestone bank at Fanes Piccola ooo ost West Trading an interstratal spring in the foreground. The surface of sliding is lubricated during part of the year by a thin veneer of ice from frozen spring water.
The greatest distance over which one of the blocks moved is 15 m. A pitted microrelief on the bedding plane due to solution by water of the spring is visible between the isolated blocks. See for explanation the corresponding cyphers in the text. The blocks which ara produced in this way are angular and ooo ost West Trading sidewards by gravity They did not move ooo ost West Trading than 1.
The steps of the staircase karst in the background are sprinkled with the smaller, rounder erratic boulders. The angular blocks are detpched along joints and bedding planes, flow the blocks have moved much farther away from their break-away points than in the foregoing case. The greatest distance covered is 15 m. Ilidim of the blocks over thin sheets of frozen water in spring and autumn may explain this. Coacl uslefi : The area of Fanes Piccola presents a very good example of staircase karst.
The overall effects of holocene alterations is fairly small and restricted to minor morphological features.
On 19 Marchthe Chisinau
Sevilacqua, E. Stab, graficico F. Engelen, G.