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Geology

In the area occupied by the Nature Reserve Val Rosandra - Dolina Glinščice, the most recent (40-45 million years ago) Karst stratigraphic successions (rock strata) are to be found, Palaeocene and Eocene limestones, which testify to the last days of carbonate sedimentation in the Tethys Sea, and Eocene flysch sandstones and marls, turbiditic sediments that signify the drowning of the marine shelf and it being covered by materials from the continents. In the alternation of Alpine and Dinaric tectonic phases that characterise the crustal evolution of the Periadriatic region (which today is part of Europe), the area of the Rosandra Valley - Dolina Glinščice became a key zone, whereby the limestone succession, at first constricted in folds, later broke into several overlapping sections. The result is an area that is also unique in terms of its geological features, which give the valley a very special natural charm.

From a structural point of view, the area of Val Rosandra - Dolina Glinščice belongs to the north-western end of the "Čičarija embriciate structure", an extensive geological formation characterised by a succession of reverse faults and overthrusts with a SE-NW orientation, located between the "Karst Platform" and the "Istrian Platform", two other geological structures located one to the north and one to the south. An excellent overview of the tectonics of the area can be obtained from the lookout point of San Lorenzo-Jezero, from where the layered structure can be seen, with the apparently sinclinalic course of the Valley and the anticlinalic course of Karst Mountain.

A series of compressive forces, the result of the collision between the Eurasian and African plates, has given rise to weak folds and three main overthrusts between the rigid limestone masses and the plastic flysch deposits: the folds on the southern slope of Mount Castellaro, the system of reverse faults on the slopes of Mount Stena and in the Draga Valley, the Val Rosandra - Dolina Glinščice syncline, the Crinale fault, the anticline with the knee fold of Mount Karst, and the overthrust of Mount Karst and the Little Karst of the San Servolo-Socerb Plateau. In the case of Mount Stena, this is a system of small overthrusts that generally bring Palaeocene-Eocene limestones into contact with Eocene fucoid marls. The degradation and intense weathering make this tectonic contact particularly evident along the path from Hervati-Hrvati to Bottazzo-Botač, where flysch sandstones embedded in the underlying marls can also be found.

The geological section revealed by the Karst Mountain is very educational: the broad anticlinal fold that begins to the left of the stream is complicated by the 'Ridge Fault', which dislocates an overlying limestone layer on the northern flank of the anticlinal marls. To the south there is a low-angle overthrust, the 'Monte Carso overthrust', which carries the limestone banks on the turbiditic flysch from Bagnoli to Prebeneg - San Servolo-Socerb and generates an underlying knee fold that determines the verticalization of the limestone layers, marls and flysch at the Antro di Bagnoli.

(Taken from the book "La Val Rosandra e l'ambiente circostante " chapter by Franco Cucchi - Cenni geologici)