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Geogr. Fis. Dinam. Quat. 30 (2007), 43-53, 10 figg., 2 tabb. TOMMASO DE PIPPO (*), CARLO DONADIO (*), PAOLO MIELE (*) &ALESSIO VALENTE (**) MORPHOLOGICAL EVIDENCE FOR LATE QUATERNARY TECTONIC ACTIVITY ALONG THE COAST OF GAETA (CENTRAL ITALY) ABSTRACT: DE PIPPO T, DONADIO C., MIELE P. & VALENTE A., Mor- condo quello che in questo lavoro è definito “modello ad ascensore” della phological evidence for Late Quaternary tectonic activity along the coast of costa. In particolare, sono state distinte una fase di sollevamento generaliz- Gaeta (central Italy). (IT ISSN 1724-4757, 2007). zato del settore costiero tra lo stadio isotopico 11 ed il substadio 5.5, se- guita da una fase di abbassamento più o meno continuo tra il substadio The study of morphological evidence for palaeo sea-levels observed 5.5 e lo stadio 3, interrotta da un debole sollevamento con tassi differen- along the southern Lazio coastline NW of Gaeta showed the occurrence ziali tra i substadi 5.3 e 5.1. Il modello dinamico proposto, che differisce of tectonic movements in the time interval between Marine Isotope da quanto sinora ipotizzato in letteratura, si basa sull’analisi di tutte le for- Stages (MIS) 11 and 3. On the basis of the heights, location and age of me osservate lungo la costa di Gaeta, sia quelle ben note in letteratura che marine terraces and wave cut notches, both above and below current sea quelle per la prima volta indicate nel presente lavoro. levels, examined in the various contiguous coastal zones, some conside- rations were made regarding the rates of differential rises and falls oc- TERMINI CHIAVE: Geomorfologia costiera, Neotettonica, Variazioni curring at structural discontinuities in the past 400,000 years, especially del livello marino, Pleistocene, Gaeta, Italia. between 150,000 years BP and the present-day. In particular, we distin- guished a phase of generalised uplift in the coastal sector between MIS 11 and 5.5, followed by a more or less continuous fall phase between ma- rine isotope substage 5.5 and stage 3, interrupted by a weak uplift with INTRODUCTION different rates between MIS 5.3 and 5.1. The dynamic model proposed, which differs from what has so far been hypothesised in the literature, is based on analysing all the forms observed along the coast north of Gaeta The Tyrrhenian coastline northwest of Gaeta in central (Lazio, central Italy), whether those known from the literature or those Italy is characterised by a succession of rocky calcareous indicated for the first time in this study. headlands and sandy pocket beaches. The latter develop in KEY WORDS: Coastal geomorphology, Neotectonics, Sea-level change, embayments connected to structural lines, transversal to Pleistocene, Gaeta, Italy. the coastline. Along the cliffs, both active and fossil, many features of palaeo sea-levels are preserved: notches, ter- RIASSUNTO: DE PIPPO T, DONADIO C., MIELE P. & VALENTE A., Evi- races and fringes of Lithophaga sp. burrows. denze morfologiche di attività tettonica tardo-quaternaria lungo la costa di The different heights of these forms, each assigned to a Gaeta (Lazio, Italia centrale). (IT ISSN 1724-4757, 2007). certain palaeo sea-level, could be explained by non-homo- Lo studio delle morfologie indicanti paleostazionamenti del livello geneous movements of blocks. These movements are relat- marino, presenti lungo il tratto di costa del Lazio meridionale a NW di ed to tectonic activity, which could have periodically af- Gaeta, ha permesso d’individuare l’esistenza di movimenti tettonici pro- fected one or more sectors between the Middle Pleis- trattisi durante l’intervallo di tempo compreso tra gli stadi isotopici marini (MIS) 11 e 3. Sulla base delle quote, dell’ubicazione e dell’età di terrazzi tocene and Holocene. Evaluation of their rates and extent, marini e solchi di battente, sia emersi che sommersi, esaminati nelle varie as well as the direction of movement (downlift or uplift) of zone costiere contigue, sono state fatte alcune considerazioni di carattere the different sectors, is connected to the position of sea quantitativo circa i tassi dei movimenti differenziali di sollevamento ed levels estimated from eustatic curves, available in the liter- abbassamento occorsi in corrispondenza di discontinuità strutturali negli ultimi 400.000 anni ed in dettaglio tra 150.000 anni fa ed il presente, se- ature, for the last 400 kyr. The aim of this work is to report the results of a de- tailed geomorphological survey, which focused on various palaeo sea-level traces along this coastal stretch, some of (*) Dipartimento di Scienze della Terra, University of Napoli Federico them observed for the first time. Moreover, comparison of II, Italy - [email protected]. (**) Dipartimento di Studi Geologici e Ambientali, University of the collected data with a recent eustatic curve confirmed Sannio, Benevento, Italy. the various movements in this «unstable» area. 43 GEOLOGICAL AND GEOMORPHOLOGICAL by a series of hills often with a cone or truncated cone SETTING shape. Along the coast the alternation of large and small pock- The investigated coast is situated in southern Lazio, be- et beaches (fig. 2) is also related to the presence of faults, tween the coastal plains of Fondi and Formia-Garigliano, chiefly NE-SW oriented, as well as cliffs, whose develop- and extends some 14 km from the headland of Monte Or- ment was controlled by tectonics, as noted for the cliff of lando, in Gaeta, northwards to Torre Capovento (fig. 1). Monte Orlando and the fossil cliff of Monte Moneta, in- The coastal zone lies in a sector structurally limited to the land from the plain of Sant’Agostino (fig. 3). NE by an important, albeit local, tectonic line with a NW- Going from E to W the headland of Monte Orlando, SE Apenninic trend. This line, called «Gaeta-Itri-Monte the highest coastal relief, is encountered first. It is made of Calvo», sharply separates a northeastern area where Cre- cretaceous limestones with a prevalent eastward dip. The taceous limestone dominates from a southwestern area, western slopes are modelled with gentle forms covered where the coast in question is located and where Triassic- by clastic deposits, such as the red sands referable to the Jurassic dolomite outcrops prevail. Moving away from this lithologic unity of duna rossa antica (Blanc & alii, 1953; line and upwards in the succession more limestone, Juras- Bergomi & alii, 1969; Bono, 1985; Dai Pra, 1995) assigned sic in age, is found, as may be observed along the slope of to Middle-Upper Pleistocene and colluvial detritus (Va- Mts. Lisantro and Dragone (De Riso, 1964). Finally in the lente, 1999). The southern slopes, characterised by cliffs coastal outcrop, that forms the top of the succession, rep- some 80-100 m in height, are however extremely steep and resented by mainly Cretaceous limestones, Pleistocene and subject to active or quiescent rockfalls. Holocene deposits, chiefly continental in origin, in limited The cliff constituting the western side of the headland outcrops, complete the sedimentary succession (Accordi & bordering Serapo beach, is at present fossil in its inner sec- Carbone, 1988) in the investigated area. tor, whereas in the still active sector it continues under the The carbonatic succession heavily crossed by a net- sea down to –10 m with a monotonous sandy bottom. work of structural discontinuity with NW-SE and NE-SW The southern side, by contrast, consists of a cliff which trends (Ambrosetti & alii, 1987; Cerisola & Montone, 1992; reaches about +120 m and continues down to –15/–30 m Carrara, 1995a, 1995b Carrara & alii, 1995), have a pro- with a steeper bottom, characterised by terraced forms; at nounced influence on the local geomorphological setting. – 40/–50 m a sandy bottom gently slopes downwards. The Owing to the strict correlation between the tectonic NE-SW trend (Antonioli, 1991; 1995; Valente, 1999; Miele, structure and the morphological evolution of the area, 2003) of such morphologic elements feels the effects of the slopes of the reliefs consist of fault scarps or fault-line structural control by which the direction of the transversal scarps and separate valleys, developing along local tec- elements is influenced, such as the wide aperture which tonic lines, mainly with NW-SE and NE-SW trends (less tends to isolate stacks such as Montagna Spaccata. Inside frequently E-W). The landscape is therefore characterised the latter there are some caves, obviously reworked both FIG. 1 - Geological outline of the Gaeta coastal sector (Latium, central Italy); 1) altitude (m a.s.l.); 2) isobath (-m); 3) Mesozoic carbonatic outcrops; 4) Pleistocene-Holocene deposits; 5) fault; 6) uncertain or buried fault. 44 FIG. 2 - Features of ancient sea-level standings along the coastal zone of Gaeta; 1) altitude (m a.s.l.); 2) isobath (-m); ● Sant’Agostino; ▲ Arenauta; ★ Ariana; ■ Fontania - La Catena and Monte Orlando - Serapo. The arrows indicate the sections of Spiaggetta dei Ricci (fig. 5) and Arenauta (fig. 7). FIG. 3 - View of the little coastal plain of Sant’Agostino with Punta Cetarola. The coastal plain is in- land characterized by alluvial fan and talus deposits. by waves and karstic phenomena, that also continue below rocky headlands that separate these beaches. At their base sea level. a sandy bottom is usually present, which gently slopes Serapo beach, sited west of the Monte Orlando head- down to –18/–27 m. At such depths there are steep slopes land (fig. 4), is the relic of a tombolo joining the head- in a range between –20/–25 m and –44/–48 m at Cape land to the mainland. Further west a system of pocket Capovento and near Monte a Mare as well as at –30/–35 m beaches is visible: Fontania, Ariana, Arenauta, San Vito in the stretch between the beaches of Sant’Agostino and and Sant’Agostino, in this order.