Morphometric comparison of weathering features on side by side carbonate rock surfaces with different exposure ages ― A case from the Croatian coast

Abstract

[EN]This study presents the comparison of morphometry of karren features developed on two rock surfaces located side by side having different exposure times. Cosmogenic 36Cl analyses were used to determine the age of a rock surface exposed after a rockslide that occurred ∼2400 years ago, whereas the rock surface not affected by the slide was exposed to weathering for a longer time period. Clint and grikes, trittkarren, rillenkarren, solution pits, and kamenitzas were measured. Comparatively less density of grikes on the surface affected by the slide made it having a fresh appearance. Most of the grikes were inherited from previous weathering stage and exposure time since the rockslide event has not been sufficient to homogenize these features between both rock surfaces. Tritkarren and rillenkarren were preferentially found on the rockslide surface indicating that their genesis is likely to occur at decadal to centennial timescale. Solution pits and kamenitzas were found on both surfaces and some of their size parameters were indistinguishable between the populations of both rock surfaces. Area and depth parameters of both forms were clearly correlated and we define a morphometric index: A/D ratio as the slope between these two parameters within each population. After an initial stage, preferential weathering occurs along the vertical axis in solution pits and laterally in kamenitzas. Thus, we suggest that the A/D ratio is related to the evolution/relative age of the karren features. Thus, under rock surfaces affected by the same weathering conditions, lower A/D ratios of solution pits and higher A/D ratios of kamenitzas indicate longer time exposed to weathering. Thus, although solution pits and kamenitzas are likely to be developed in decadal to centennial timescales, their morphology changes through time at millennial timescale and it can be tracked by morphometric analysis.