Geological and Geomorphology Setting

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Entering the Sant' Andrea Valley, the Appia route track leans against a mountain ridge made by a Mesozoic carbonate rock sequence. More in detail, outcropping lithologies span over a time interval between the latemost Jurassic and the late Cretaceous. They include both detritic and micritic limestone, dolomitic limestone, dolomites and thin intercalations of marly-clayey intervals and red paleosoils (Figs.1,2).

In the southern zones of the study area, where the route climbs toward Itri, uppermost Jurassic-lower Cretaceous carbonates outcrop which are involved in a sequence of E-W oriented folds and thrusts; by these last, they tectonically overlie the upper Cretaceous carbonates. The geological setting is complicated by NNW-SSE oriented strike-slip faults generating sub-vertical rock cliffs where a transpressive kinematic prevailed (Figs.2,7,8). Generally, the southern zones are characterized by steep rock slopes (35°-45°).

In the northern zones, from the Sant'Andrea stronghold towards the Fondi Plain (Fig.2), the geological sequence is set in a regular monocline having dip angles of about 25°, this determining a less steep morphology. Several normal faults, having both an apenninc (NW-SE) and anti-apenninic (NE-SW) trend dissect the Lower Cretaceous (Aptian, figs. 3,4) part of the carbonate sequence and locally the youngest terms, Cenomanian-Turonian in age, outcrop (Figg. 5, 6). Nearby these tectonic elements, quarries used for rock material excavation gather.

Finally, continental Quaternary deposits unconformably lie over the Mesozoic carbonate sequence and are concentrated in the Sant' Andrea valley bottom; alluvial, colluvial and debris-fan deposits prevail in the northern zones, whereas debris and paleo-landslides deposits feature the southern zones (Fig.1).

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  Geological Map of the St. Andrea valley.
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  Panoramic view of the Mt. Aurunci carbonate ridges which delimit the SW edge of the Appia route track; the main geological and tectonic features are superimposed on it.
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  Regular monocline of Lower Cretaceous limestone dipping towards north-west with a mean inclination of 25 degree in the northern zone of the study area.
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  Focus on the Aptian (Lower Cretaceous) limestone and dolomites which are set in plurimetric beds and decimetric interlayers below the St. Andrea stronghold (quarry 4).
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  Outcrop of Cenomanian (Upper Crataceous) limestone observed south of the St. Andrea stronghold and set in plurimetric beds (quarry 8).
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  Outcrop of Turonian (Upper Cretaceous) detritic limestone with intercalations of red marly limestone (quarry 7).
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  Meso-scale fold with sub-horizontal axial surface observed in the southern sector of the St. Andrea valley, having trend compatible with the main thrust affecting the carbonate sequence.
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  Rocky escarpment of tectonic origin in the rock slope bounding the Appia route track and due to strike-slip faults having a transpressive kinematics.