Morfometria di clasti calcarei appartenenti a detriti di falda ed a depositi glaciali

Morphometry of limestone clasts belonging to slope debris and glacial deposits

Abstract

Experimental tests were performed upon slope debris and moraine deposits in order to probe into morphometric features of environments having a low mobilization energy. Limestone facies were singled out for investigation, so that research returns could be compared with those obtained in previous laboratory and field investigations on fluvial and marine environments by CORTEMIGLIA (1985, 1989a, 1989b). Operating on dimensional populations of clasts whose lengths ranged between 40 and 60 mm, made up of 120 individuals for each sample, a number of parameters were measured by means of a «CDB Storm» electronic digital calibre, whose resolution power and accuracy fell within the 0,01 mm range. These parameters were: the aerodynamic lift index (0) by ROSFELDER (1961), the first order rounding index (E) by CAILEUX & TRICART (1963), the rounding index (R) by KUENEN (1956), the flattening index (AP) by CAILLEUX & TRICART (1963), the sphericity index (SF) by KRUMBEIN (1941), the OP index by DOBKINS & FORX (1970), the shape index (CFR) by WINKELMOLEN (1982) and the simplified shape index (CFS) by CORTEMIGLIA (1989 b). Data analysis has yielded, for slope debris, an overall trend of the median of rounding indices E and R towards rising values with decreasing height. This suggests therefore that it might be advisable to verify the working hypothesis whether the linear correlation between height and median values of rounding indices can be extended to the universe of limestone clasts from slope debris. As to the morphometric differences between slope debris and moraine deposits, the latter appear to be more worn out above the height of 1500 metres (43 ≤ E ≤ 85 for debris and 70 ≤ E ≤ 125 for moraines), have higher shape coefficients (CFR =3,75 and CFS = 11,2 for debris; CFR ≥3,99 and CFS ≥ 11,5 for moraines), and clast frequencies with Vg < Vg far higher than those of slope debris (> 97% for debris and < 85% for moraines).