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Studying relative sea level change and correlative adaptation of coastal structures on submerged Roman time ruins nearby Naples (southern Italy

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Relative sea level change Roman period Campi Flegrei (southern Italy) volcanic area a b s t r a c t The southwestern periphery of Naples is dominated by the Posillipo promontory, an elongated tuffaceous ridge belonging to Campi Flegrei active
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  Studying relative sea level change and correlative adaptation of coastal structures on submerged Roman time ruins nearby Naples(southern Italy) Pietro Aucelli  a , Aldo Cinque  b , Gaia Mattei  a ,  * , Gerardo Pappone  a , Angela Rizzo  a a Dipartimento di Scienze e Tecnologie, Universit   a Degli Studi di Napoli Parthenope, Naples, Italy b Dipartimento di Scienze Della Terra, dell ’   Ambiente e Delle Risorse, Universit   a di Napoli Federico II, Naples, Italy a r t i c l e i n f o  Article history: Received 11 October 2016Received in revised form16 August 2017Accepted 8 October 2017Available online xxx Keywords: Archaeological sea-level markersVertical ground movementsSubmerged geoarchaeological sitesRelative sea level changeRoman periodCampi Flegrei (southern Italy) volcanic area a b s t r a c t The southwesternperiphery of Naples is dominated by the Posillipo promontory, an elongatedtuffaceousridge belonging to Campi Flegrei active volcanic complex (CF). The central caldera of CF is well-known foroffering a rich geoarchaeological record of the vertical ground movements occurred since Roman times,as the case of the Portus Julius ruins (37 BC) presently found between 10 and 5 m bsl and the Middle AgesLithophaga perforations at about 7 m asl on the marble columns of the mecellum previously interpretedas Serapaeum (Morhange et al., 2006). In the last one hundred years, several unrest episodes have beenprecisely reconstructed in the same area (Del Gaudio et al., 2010; De Martino et al., 2014), but neverbefore, vertical ground movements have been presumed along the Posillipo hill, positioned over thecaldera rim. This paper deals with a research aimed to evaluate the vertical movements at Posillipo areaduring the last two millennia, by means of geomorphological and geophysical surveys in three sub-merged archaeological sites: Nisida Roman port, Marechiaro Roman port and ruins offshore VillaRosebery. By precisely measuring the present submersion of all remains found in those sites, two relativepaleo-sea levels have been detected: one for the 1st century BC at  4.4/-5 ± 0.5 m and another for the 1stcentury AD at  3 ± 0.5 m. Only seventeen centimetres of the difference between the two paleo-sea levelsis attributable to eustasy (Lambeck et al., 2011), while the rest (2 ± 0.5 m) has to be ascribed to a phase of accelerated subsidence which has still to be precisely dated and whose duration could have been as shortas few years or decades. The additional subsidence suffered by the area after the 1st century AD wascalculated to be 2.0  ±  0.5 m. Even though the ground deformations reconstructed in the Posillipo areaappear less strong than those recognized inside the CF caldera, they prove that vertical movements of volcanic srcin were not always con 󿬁 ned inside the caldera rim.In terms of human adaptation, the observed archaeological evidence narrates that Palazzo degli Spiritiwas restored closing the rooms submerged by sea, the breakwater of Marechiaro and the villa founda-tions at Rosebery were probably raised, in response to the relative sea level rise. ©  2017 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The Posillipo coastal sector, on the southwestern side of Naples(Italy),hostsremarkableunderwaterarchaeologicalevidencedated1st century BC  e  1st century AD, related to the expansion of Neapolis towards the Campi Flegrei area (CF). This promontory islocated on the southern periphery of the CF active volcaniccomplex.Especially the central caldera of CF is well known for offering arich geoarchaeological record of the vertical ground movements,which have been affecting this sector since Roman times. In thearea, the ruins of Portus Julius (built in 37 BC) presently foundbetween  10 and  5 m bsl (Passaro et al., 2013) and the mecellumpreviously interpreted as Serapaeumwith Middle Ages Lithophagaperforations at about 7 m asl on the marble columns have beenstudied for this purpose (Morhange et al., 2006 and referencestherein).The archaeological data related to underwater structures of theancient Puteoli harbor and Baianus Lacus built during 1st century *  Corresponding author. E-mail address:  gaia.mattei@uniparthenope.it (G. Mattei). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint https://doi.org/10.1016/j.quaint.2017.10.0111040-6182/ ©  2017 Elsevier Ltd and INQUA. All rights reserved. Quaternary International xxx (2017) 1 e 21 Please cite this article in press as: Aucelli, P., et al., Studying relative sea level change and correlative adaptation of coastal structures onsubmerged Roman time ruins nearby Naples (southern Italy), Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.10.011  BC, show that the coastal sector of the CF caldera has subsided inthe last 2200 years. According to Passaro et al. (2013), the subsi-dence affecting this sector is up than 5 m on average and seems tobe not uniform. More in detail, the Eastern sector is characterizedby 5/5.2  ±  1 m subsidence while the Western from 5.7  ±  1 msubsidence on average. We can saythat the overall subsidence rate,which derives from the sum of the effects of spot uplifting crisesand of the overall downlifting of the Campi Flegrei, results in asubsidencecharacterizedbyanaveragerateof2.55( ± 0.5)mm/yforthe Eastern sector and 2.90 ( ± 0.5) mm/y for the western.After this period, Morhange et al. (2006) demonstrated that thesubsidence in Pozzuoli (measured at the macellum) acceleratedbetween the 5th and 15th centuries AD, including three maximumthreshold oscillations. During the  󿬁 rst phase, a marine trans-gression ended ca. 400 e 530 AD after its last restoration in 394 AD.No eruptive activity followed this phase.An early Middle Ages oscillation occurred ca. 700 e 900 AD, withno post-deformation volcanic eruption. A late Middle Ages sub-mersion, followed by a well-documented period of land uplift,culminated in the 1538 eruption of Monte Nuovo, ending morethan 3000 years of eruptive quiescence.FromthesubmergedremnantofPortusJuliusandthemacellumlocated along this coastal sector, a 13 m range of vertical groundmovements during the last 2000 years was reconstructed: a periodthat included at least two major cycles of uplift and lowering(Todesco et al., 2014).Geodetic measurements of ground elevation collected in thepresent Port of Pozzuoli between 1905 and 2009 (Del Gaudio et al.,2010) indicate episodes of ground uplift in 1953, 1969, and 1982,totaling about of 4 m of vertical displacement. After this period, asubsidencephasestartedbetween1985and2005,onlyinterruptedbycentimeter's episodes of uplift. Since 2006, the caldera has beenin 󿬂 ating again, at a slow but steady rate (D'Auria et al., 2011Todesco et al., 2014).In the extreme periphery of the CF volcanic area, the ancientlandscape of the Chiaia coastal plain (Naples) during the middleand late Holocene was reconstructed from geoarchaeological ex-cavations associated with public transport works. In this sector, asubsiding trend has been compensated by a progressive shorelineprogradation due to pyroclastic aggradation (Carsana et al., 2009;Cinque et al., 2011; Romano et al., 2013).Inthispaper,wepresenttheresultsofageoarchaeologicalstudyof the Posillipo promontory to the west of Chiaia plain (Fig. 1A),never studied before now, in order to better constrain the verticalmovements suffered by the eastern periphery of CF over the last2000 years, never measured before now. For this purpose, threecoastal sites of geoarchaeological value (Nisida Roman port, Mar-echiaro Roman port and the remains off Villa Rosebery) werestudied by means of both geomorphological observations andmarine geophysical surveys (Side Scan Sonar and Single Beamechosounder) (Mattei, 2016). 2. Geological and geomorphological setting  Posillipo hill, on the southeast border of CF volcanic area (Orsiet al., 1996), is an asymmetrical and homoclinal structure mainlymade of Neapolitan Yellow Tuff (NYT) (Fig.1B).The CF area is one of the active volcanic systems of the Medi-terranean region (Di Vito et al.,1999; Orsi et al., 2009; Smith et al.,2011) that started his activity more than 60 ky BP (Cinque et al.,1997; Scandone et al.,1991; Aucelli et al., 2017a).The structural depression of CF is interpreted as a caldera sys-tem, including a subaerial and a submerged part, which cover atotal area of about 230 km 2 . Within this depression, numerousQuaternaryventssuggestrecurrentunrest(Orsietal.,1996).TheCFcaldera is the largest feature of the Phlegraean Volcanic District(Orsietal.,2004;Berrinoetal.,2008),whichincludestheislandsof Procida and Ischia, as well as submarine vents in the northwesternGulf of Naples (Fig.1C).Thetwolargestcaldera-collapseeventsofCampiFlegreivolcanowere(Fig.1C):theCampanianIgnimbritesuper-eruption(CI;37ky;Fedele et al., 2003 and references therein) and the NYT (15 ky;Deino et al., 2004). Both eruptions emitted large volumes of magma, in fact, CI tephra was found as visible ash layer in thesouthernRussia(Pyleetal.,2006),instead,ashfromNYTwasfoundin Vela Spila, Croatia (Radic et al., 2008).Volcanic rocks older than the CI are the product of both effusiveand explosive eruptions. They are exposed only along the scarpsthat border the CF caldera and are mostly alkalitrachytic incomposition (Pappalardo et al.,1999).The CI eruption and caldera-collapse (Fig. 1C) was the earliestevent profoundly in 󿬂 uencing the present geological setting of thearea. During this eruption, at least 200 km 3 of trachytic-to-phonotrachytic magma (Fedele et al., 2003) were emplaced aspyroclastic-fall and 󿬂 ow deposits.An areaof about 30,000 km 2 wascovered by these highly mobile ignimbrites (Fisher et al.,1993).Volcanism between the CI and the NYT was con 󿬁 ned within thecaldera and characterized by explosive, mainly phreatomagmaticeruptions(Pappalardoetal.,1999).Theyoccurinscatteredoutcropsacross the central part of the city of Napoli and along the scarps of thePosillipohill(Orsietal.,1996;Pappalardoetal.,1999).Alongthesouthwestern scarps, in particular, the remnant of a tuff cone isexposedatTrentaremiandCoroglio sections.Thisconeis underlainby a pyroclastic sequence (Trentaremi tuff, 22.3 ky BP, Fedele et al.,2015) and in turn by the NYT (Pappalardo et al.,1999). The NYTeruption and caldera-collapse (Fig.1C) was the secondmore recent cataclysmic event in the history of the CF caldera. Itrepresents the largest known trachytic phreatoplinian eruption(Orsi et al.,1992). It emitted at least 40 km 3 (Deino et al., 2004) of latitic-to-trachytic magma emplaced as pyroclastic fall and  󿬂 owdeposits(Orsietal.,1992,1996).Thelatterdepositscoveredanareaof more than 1000 km 2 (Orsi et al., 1992). The resulting calderacovered an area of about 90 km 2 and was nested within the CIcaldera (Orsi et al., 1996).After the NYT eruption, an explosive volcanic activity anddeformationcan berecordedalongthestructuralboundariesof thecaldera, and faults within the caldera, between 15 and 9.5 ky(Gauro, Agnano and Archiaverno eruptions) followed by minorexplosive episodes (Fondi di Baia) between 8.6 and 8.4 ky (Di Vitoet al., 1999; Isaia et al., 2009). An alternation of gray - greenishand yellowish ashes separated by paleosoils related to the Agnanoeruption carpets the NYT deposit of the Posillipo hill (Fedele et al.,2015).Most of the well-preserved morphology, can be ascribed to thelast phase of eruption that occurred between 4.2 and 3.7 ky BP,when the Astroni (4.1 e 3.8 ky BP), Averno (3.7 ky BP) and Solfatara(4.1 e 3.8 ky BP) craters formed (Di Vitoet al.,1999; Orsi et al., 2009;Isaia et al., 2009). Along the Posillipo coastal sector the well-preserved Nisida tuff cone, entirely composed of strati 󿬁 ed yellowtuffs (3.9 ky BP, Fedele et al., 2015), is formed by highly lithi 󿬁 edbeds of ashes and pumices (Rosi and Sbrana, 1987).ThemostrecenteruptionofCFwasthatofMonteNuovoat1538AD (Di Vito et al.,1987; Guidoboni and Ciuccarelli, 2011).The CF area is currently characterized by high geothermalgradient, fumarolic activities and bradyseism, ancient Greek termsmeaning slow movementof the landmass. This termwas coined byArturIssel,an importantItalian geologistof the19th century AD,todesignate the vertical ground movements occurring in volcanicareas. The cause of negative (i.e. rising) and positive (i.e. descend-ing) bradyseism can be either the intrusion of new magma and its P. Aucelli et al. / Quaternary International xxx (2017) 1 e  21 2 Please cite this article in press as: Aucelli, P., et al., Studying relative sea level change and correlative adaptation of coastal structures onsubmerged Roman time ruins nearby Naples (southern Italy), Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.10.011  Fig.1.  A) Coastal landscape of Naples; B) Geological sketch of study area, with the position of the three archaeological sites studied in red (NI1 e Nisida; MA1-5 Marechiaro; RO1-5Rosebery) and the position of Pausilypon villa in blue (Lambeck et al., 2011); C) Campi Flegrei caldera limits (after Smith et al., 2011). (For interpretation of the references to colour in this  󿬁 gure legend, the reader is referred to the web version of this article.) P. Aucelli et al. / Quaternary International xxx (2017) 1 e  21  3 Please cite this article in press as: Aucelli, P., et al., Studying relative sea level change and correlative adaptation of coastal structures onsubmerged Roman time ruins nearby Naples (southern Italy), Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.10.011  degassing or  󿬂 uctuations of hydrothermal activity causing expan-sion and contraction of rocks and sediments due to variations of pore pressure in relation with heat  󿬂 ux variations.AncientbradyseismicmovementsalongtheCFcoastalsectoraretesti 󿬁 ed by relative sea level oscillations archaeologically docu-mented, as in the case of Portus Julius and the macellum (previ-ously interpreted as Serapaeum, Cinque et al., 1997; Morhangeet al., 2006; Todesco et al., 2014). Instead, in the surrounding areaof the Port of Pozzuoli, two lowering episodes followed by twouplifts have been documented by recent geodetic measurements,between 1905 and 1985 (Del Gaudio et al., 2010). A seismic activityaccompanied even the small uplifts.Afterthisperiod, asubsidence phase affectedthis area, between1985 and 2005 (D'Auria et al., 2011; Todesco et al., 2014). The GPStime series at CF caldera from 2000 to 2013 demonstrate that thecaldericareanowadaysisinaconstantmotionbothinupliftingandin downlifting, and the geometry of the movements has a circularpattern centered in Pozzuoli, that involve Posillipo hill, even if themeasured vertical displacement is a few centimeters (De Martinoet al., 2014).The eastern periphery of CF volcanic area is the Naples coastalsector (Fig. 1A), primarily characterized by landforms due toendogenousdynamics,suchaspositiveandnegativevolcanicformsand fault scarps (Romano et al., 2013; Aucelli et al., 2017b).The superimposed torrential dissections and the wave actionhave generated a coastal landscape made of alternating small bayssometimes hosting narrow coastal plains, and cliffed promontoriessuch as that of Posillipo (Fig. 1A).Almost everywhere in Naples, the dominant bedrock is (at leastin the  󿬁 rst tens of meters underground) the NYT (Deino et al.,2004).This formation is normally mantled by pyroclastic fall depositsbelongingtoeruptionsfromthemanymonogeniccraters(tuffconeand ring) appeared inside the CF caldera between 10 and 3.8 ky BP(Di Vito et al.,1999; Cinque et al., 2011; Ermolli et al., 2014). In thesectors with steep gradients as the Posillipo sea cliff (Fig. 1B), theNYT is outcropping (Fedele et al., 2015; Putignano et al., 2014).ThePosillipohillismainlymadebythelithi 󿬁 edfaciesoftheNYT(Fedele et al., 2015, Fig. 1B). Two different members (LM and UM from bottom to top) of this formation have been distinguished byScarpati et al. (1993). The lower member (LM) ranging approx-imatively from 1 to 10 m thick is made of cineritic and pumiceouslapilli fall layers. The overlying member (UM) represents the mainpart of the succession (about 30 m thick) and is characterized bytwo distinctive facies: a proximal, lithi 󿬁 ed yellow one (tufo) and adistal, unlithi 󿬁 ed gray one (pozzolana) (Deino et al., 2004; Fedeleet al., 2015). The post-NYT soft cover is made of a sequence alter-natingreworkedandinsitupyroclastics(upto30mthick),withthefallout deposits of the Soccavo eruption (10.3 e 9.5 ky BP, Amatoet al., 2009; Cinque et al., 2011) at the base.The coastal sector of Posillipo is characterized by a tufa sea cliff mainly cut on NYT deposits (Fig.1B). Anyway, in the coastal stretchbetween Coroglio Mt. and Trentaremi bay, older volcanic depositsrelated to the Trentaremi eruption (22 ky BP, Fedele et al., 2015)crop out. These deposits, partially buried below the NYT depositsconstitute the border of a tuff ring partially destroyed by seawatererosion (Fedele et al., 2015). Moving from the bottom upward, theformation is made by a narrowly strati 󿬁 ed yellow tuff with recur-rent cross-bedding and dune structures and small erosional chan-nels. A succession of massive to crudely strati 󿬁 ed decimetric layerswith pumices and ballistic blocks is found above an erosional sur-face. The overlying deposits are represented by a strati 󿬁 edsequence of cineritic and pumiceous lapilli levels, lying above awell-developed paleosoil horizon (Fedele et al., 2015).In the case of Nisida island (Fig. 1B), the coast is sculptured onNisida tuff (3.9 ky BP), laying on the submerged NYT deposits(Fedele et al., 2015).The deposit of this formation is made of a succession of massiveyellow tuff layers with pumice lapilli and lava lithics dispersedwithin the abundant cineritic matrix and strati 󿬁 ed unlithi 󿬁 ed lightgray cineritic layers (pozzolana) (Fedele et al., 2015).The Posillipo sea cliff increases in height moving southward andis interrupted by small bays hosting pocket beaches.Since the Greek-Roman times, the evolution of this coastalsector was in 󿬂 uenced by NYT mining activity as well as by theerosive action of meteo-marine factors, testi 󿬁 ed by wide sub-merged abrasion platforms along the cliffs as the cases of thecoastal plains of Riva Fiorita (Fig. 2A) and Posillipo cape nowadayssubmerged.The incisions characterizing the Posillipo hill helps in locatingseveral faults and fractures belonging to the post-NYT tectonics(Cinqueetal.,2011).Themain 󿬂 uvialdissectionsalongthePosillipocoastal sector are the canyon east of Cenito bay bypassing Posillipostreet by means of a bridge (Fig. 2A) and the canyon of Gaiola(Fig. 2B).TheNE e SWtrendingsectorfromPosillipocapetoGaiolaislandhas a very valuable coastal landscape with a rugged coastlinecharacterized by the presence of bays. This coastal sector has hos-ted luxury villas since the Roman time, as the Pausilypon Romanvilla described in the following section and built at Gaiola island.This small island mainly made in NYT has a maximum height of 11m.Themaritimeconnectionstothevillawereguaranteedbytheport of Marechiaro, close to the homonym village.The coastal sector between the Gaiola and Nisida islands(Fig. 2C), SE  e  NW trending, increases signi 󿬁 cantly in height,reaching 150 m at Coroglio Mount. The morphology of this coastalstretch is articulated by the presence of bays (Cala Trentaremi, CalaBadessa) and small promontories (Punta del Cavallo and Puntad'Annone). This morphological pattern continues until Cala Tren-taremi, a beautiful bay bounded by a long spur, which extendsseaward, well known as the  “ Punta del Cavallo ” , a relic of theTrentaremi volcano (Fig. 2C). The tuff cone of Nisida island waspartially dismantled, leaving a passage inside the crater anddrawing a small bay used as a landing during the Roman period,well-known as Porto Paone (Fig. 2C). The most important Romanport of the area is the Nisida Port, directly linked to the Misenomilitary port (Gunther,1913).This coastalstretchis delimitedbyastructural highborderedbyNisida Island to the West and the seaward extending of the Gaiolapromontory to the Est. This morpho-structural structure favors theaccumulation of sandy and gravel sediments in this area. The hu-man activity along this sector, however, can be recognized in theconstruction of a Roman tunnel said Sejanus Gallery, crossingMount Coroglio and Posillipo hill (Gunther, 1913). 3. Archaeological background  3.1. Pausilypon villa The construction of the gorgeous Pausilyponvilla can be relatedto the expansion of Neapolis towards the CF area during the lateRepublican period. This phenomenon is demonstrated by theconstruction of new roads, the opening of monumental galleriessuch as the Neapolitan Crypt and the Sejanus Gallery and by thestrengthening of existing roads.The  󿬁 rst owner of the Pausilypon villa was the rich Romanknight Publius Vedius Pollio, an important political  󿬁 gure of Augustus court. In 15 BC Publius Vedius Pollio died leaving toAugustus and his descendant his villa and other annexed pro-prieties as legacy. P. Aucelli et al. / Quaternary International xxx (2017) 1 e  21 4 Please cite this article in press as: Aucelli, P., et al., Studying relative sea level change and correlative adaptation of coastal structures onsubmerged Roman time ruins nearby Naples (southern Italy), Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.10.011  Augustus enlarged it, adapting it to the needs of an imperialresidence. The villa reached its greatest expansion in the 1st cen-tury AD, although in the 2nd century AD the villa was still part of the emperor's property, as evidenced by a leaden  󿬁 stula, with thename of Emperor Hadrian found in the so-called superior thermalbaths.The Pausilypon villa was built on various terraces sloping downtoward the sea, on both sides of the Gaiola valley. The housingcomplex, extending from west of Trentaremi bay to east of Mar-echiaro area, also included the so-called Palazzo degli Spiriti andextended in an area just behind the today's Istituto San Francesco(Gunther,1913; Varriale, 2007). The Nisida and Marechiaro harborswere annexed to the villa.Today numerous evidence of the imposing housing complex,covering an area of about 9 ha, are preserved and in part insertedinto private properties. 4. Methods Three coastal archaeological sites (Nisida Roman port,Marechiaro Roman port and the remains off Villa Rosebery) werestudied by means of direct and indirect methods, integrated into amulti-techniques approach (Aucelli et al., 2016b, 2017b). An inte-grated geoarchaeological survey, including geomorphological ob-servations and geophysical surveys, was executed at each site(Fig. 3A). The marine geophysical surveys were carried out bymeansofasidescansonarmorphologicalsystemandasinglebeamechosounder bathymetric system. In very shallow water areas, amorpho-bathymetric survey was carried out by using a marinedrone, engineered by our research group speci 󿬁 cally to carry outmeasurement until the shoreline (Giordano et al., 2016). Finally, ascuba-diver realized direct measurement of each underwaterarchaeo-marker by means of a level staff. The direct measurementwas essential in order to perform the data correction, and a correctinterpretationof thearchaeological markers(Lambecketal., 2004). 4.1. SSS surveys The integrated geoarchaeological surveys of the three coastalsites (Fig. 3A) were realized using marine geophysical techniques. Fig. 2.  A) Panoramic photo of the coastal stretch between Cenito bay and Posillipo cape; B) Panoramic photo of the coastal stretch between Posillipo cape and Gaiola island; C)Panoramic photo of the coastal stretch between Gaiola island and Nisida island. P. Aucelli et al. / Quaternary International xxx (2017) 1 e  21  5 Please cite this article in press as: Aucelli, P., et al., Studying relative sea level change and correlative adaptation of coastal structures onsubmerged Roman time ruins nearby Naples (southern Italy), Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.10.011
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