I calanchi di Atri (Abruzzo): Caratteri mineralogici, geotecnici e geomorfologici

Abstract

Badlands morphology of Atri surroundings was studied on the basis of grain size analyses, mineralogical composition and geotechnical characters, and of observations on various badland types and diffusion. The areal distribution of badlands indicates that gullies prevail on southward-facing slopes. From the lithological point of view the materials showing a badland morphology are clay marls; from the grain size point of view, they belong to the field of clayey-silts in the Shepard diagram. According to the Passega diagram, the materials can be ascribed to a mixed (turbiditic/calm-water) sedimentary environment. From the mineralogical point of view, inactive minerals prevail, clay minerals being subordinate in amount. Among inactive minerals calcite prevails, with values around 30%; quartz and dolomite are secondary; feldspars and heavy minerals are subordinate; gypsum may be found in traces. Among clay minerals, micaceous clay prevails: illite is more abundant than smectite; clorite and kaolinite are occasionally present. Higher amounts of smectite have been found in the samples collected from "type B" badlands (smooth-shaped gullies, rounded divides). From a geotechnical point of view, the examined materials are classified as a stiff low-plasticity, inactive clayey silt.