Geologia CroaticaGeologia Croatica Geologia Croatica 66/3 205–218 6 Figs. 1 Tab. Zagreb 2013 The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves  Roberto Bizzarri1, Angela Baldanza1, Irene Luccioni2 and Alberto Recanatini2 1 Department of Earth Science, University of Perugia, P.za Università 1 I-06123 Perugia, Italy; (roberto.bizzarri@libero.it, angela.baldanza@unipg.it) 2 Via C. Colombo 18 I-60021, Camerano (AN), Italy; bvzm2002@yahoo.it doi: 10.4154/gc.2013.16 1. INTRODUCTION Around the Mt. Conero promontory of the Marches region (central Italy, Fig. 1), several hill towns, including Sirolo, Loreto, Castelfidardo, Osimo and Camerano, have man- made cave systems, originally intended for various uses e.g., water supply, housing, defence, granaries, escape routes, gatherings and rituals (RECANATINI, 1997, 2000). The ex- tensive Camerano “underground town” is composed of more than twenty complexes, formerly all connected. A local pop- ular saying attests that “...there is more of Camerano under- ground than above ground”. The entire cave system is local- ized under the historical centre, in the area of the first Piceno settlement of VII-VI century B.C. (as testified by the necrop- olis at the western side of the hill), subsequently occupied by the nucleus of the medieval fortress (Castelvecchio, 800 A.D.). Starting in pre-Roman times, the caverns were exca- vated in weakly cemented marine sands and clays. The orig- inal purpose of such wide and pervasive excavation is still unknown. The interpretation of sandstone quarries seems AB STRA CT The historical town of Camerano (Ancona, central Italy), built on a hill just west of the Mt. Conero promontory, is laced with a broad underground system of remarkable man-made caves. Thanks to the caves, we can view and de- scribe a composite sedimentological and stratigraphic section of Early Pleistocene (Calabrian) marine deposits, which lack subaerial outcrops. This study is aimed at a better definition of the sedimentological and palaeoenvironmental context of the Camerano area, and at improving the knowledge of the Camerano caves. Sediments are mainly cou- plets of massive- to- laminated, yellow-brown, bioclastic calcareous sand and massive, grey-green clay, of variable thickness. Each couplet shows an erosive basal surface and normal gradation, from sand to clay. Plane-parallel lam- ination, marked by recurring variations in grain size, is attributed to traction carpets and the sand horizons to resedi- mentation by sediment-gravity flows, with an eastern source (Mt. Conero). Conversely, clay reflects both western distal river-delta supply and a local contribution from marine productivity. Beds of matrix-supported gravel made of heterometric clay fragments dispersed in a bioclastic sand matrix also occur within the sedimentary section. These interpretations differ partially from earlier geological schemes and offer new insights into the palaeoenvironmental reconstruction of the Camerano area. The reconstruction involves a tectonically active Early Pleistocene basin, main- ly dominated by clay sedimentation, but periodically reached by storm- and seismic-induced carbonate gravity flows. The matrix-supported conglomerate of large clay fragments was probably derived from remobilization of partially lithified deposits along the basin’s eastern flank. Keywords: Sedimentology, Periadriatic Basin, Early Pleistocene, Marches, Central Italy Geologia Croatica 66/3Geologia Croatica 206 unsatisfactory, due to the richness of architectural motifs and ornaments testifying to a continuous human use through the centuries. Furthermore, the underground town has been uti- lized from the XI century A.D. to recent years for several different uses, often denoting a parallel evolution with the growth of the external town (RECANATINI, 1990, 1997). Thanks to the interest and competence of the Camerano Mu- nicipality and to the contribution of local amateurs, the his- torical and artistic features of the cave system have been well studied and the underground town is now largely accessible. Nevertheless, its geological features are still largely unknown. The recent building development superimposed on the medieval remains has totally obliterated the geological fea- tures and the outcrops all around the hill. Thus the exceptional underground town is the only avenue to reconstructing a com- posite sedimentological and stratigraphic section of the Early Pleistocene marine deposits (LUCCIONI, 2007), a component of the composite evolution of the Periadriatic Basin (a sector of the Plio-Pleistocene Adriatic foredeep sen su lato). In the whole Marches area (Fig. 1A), the surface structural configu- ration of the foredeep sediments, essential ly referable to as a gentle, easterly dipping growth monocline, largely obscures the complexity of the basin’s evolution. A series of buried deep-seated active thrusts and trans verse faults, strongly af- fected the basin physiography and guided the clastic fill pat- terns, imposing major control during much of the Plio–Pleis- tocene and dividing the basin into sectors with unique features and evolution (ORI & FRIEND, 1984; BIGI et al., 1997; CENTAMORE & NISIO, 2003; CANTALAMESSA & DI CEL MA, 2004). The basin is mainly filled by a Plio-Pleis- tocene clay-rich succession, and a general regressive trend is usually recognized, but the occurrence of several coarse clas- tic bodies, commonly underlain by major unconformities and intercalated at various stratigraphic levels, testifies to a com- plex sedimentary evolution (CANTALAMESSA et al., 2002; CANTALAMESSA & DI CELMA, 2004). Recent studies in- dicated the occurrence of submarine canyons in the south- western area, further complicating the sedimentological and palaeoenvironmental scenery (DI CEL MA et al., 2010; DI CELMA, 2011; DI CELMA & CAN TALAMESSA, 2012). This work provides description and interpretation of sedimen- tary features never previously described in the Ancona sector. In spite of their position in the uppermost part of the Plio- Pleistocene sedimentary sequen ce, within the general shal- lowing-upward trend, the studied deposits record outer-shelf resedimentation rather than beach and subaerial environments. The composite underground sec tion of Camerano puts a new light on sedimentary environments and processes and gives some insight into the evolution of the eastern margin of the basin, at least to the west of the Conero Mountain ‘island.’ 2. GEOLOGICAL SETTING Camerano is located 15 km SW of Ancona, in a hilly terri- tory on the western flank of Mt. Conero, and was built on top of a hill at about 231 m above s.l. (Fig. 1). Mt. Conero Figure 1: A) Geological sketch of the Ancona sector. The Marches area is also underlined (light gray in the insert). B) Comparison between lithostrati- graphic schemes proposed for the Pliocene-Pleistocene of the Periadriatic Basin. MNN=Mediterranean Neogene Nannofossil (according to RIO et al., 1990). Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 207 is an anticline of Umbria-Marches Meso-Cenozoic litho stra- ti graphic units. The hilly area west of Mt. Conero is cut by the present-day Aspio and Musone river valleys, both part of the wider Chienti Basin. It belongs geologically to the Neo gene-Quaternary Periadriatic Basin that developed dur- ing the late phases of the Apennine orogeny as the foredeep and foreland migrated eastward (BOCCALETTI et al., 1986, 1991; RICCI LUCCHI, 1986; CALAMITA et al., 1991; CEN T AMORE et al., 1991; ORI et al., 1991; CENTAMORE & NISIO, 2003). The main structure of the Periadritic Basin is the result of at least three different tectonic phases, that took place from the Miocene to recent times (CALAMITA et al., 1991; ORI et al., 1991; CELLO et al., 2009). On the basis of different tectono-sedimentary evolution, the Periadriatic Basin can be divided in the Ancona, Fermo, Teramo, and Chieti sectors (CANTALAMESSA et al., 1986; CENTAMORE & NISIO, 2003; CENTAMORE et al., 2009). Several authors inter- pret ed the Ancona sector (Fig. 1A), (which includes the Ca- merano territory), as a Pleistocene syn-tectonic basin (wedge- top basin: CENTAMORE et al., 1991; open piggy-back ba sin sensu ORI et al., 1991), related to evolution of the Mar- ches foredeep basin. The Ancona sector is bordered to the north and south by NE-SW oriented structural highs (faulted uplifts), while to the east and west it is bounded by com- pressio nal structures (anticlines, which are partially buried: CEN TAMORE et al., 2009). The entire Periadriatic Basin was submarine during most of the Pliocene and Pleistocene. The sedimentary deposits record the composite effects of tectonics and sea-level chan- ges. Several transgressive-regressive sedimentation cycles, delimited by major unconformities, are recognizable (Fig. 1B: COLALONGO et al., 1979; CANTALAMESSA et al., 1986; NANNI et al., 1986; CENTAMORE et al., 1991, 2009; ORI et al., 1991; CANTALAMESSA & DI CELMA, 2004; CELLO et al., 2009; MICARELLI et al., in press). Vertical and lateral facies variations suggest an intra-basin palaeoen- vironmental differentiation, induced by local tectonics and sea-level fluctuations (CANTALAMESSA & DI CELMA, 2004; CELLO et al., 2009; DI CELMA et al., 2010; DI CEL MA, 2011; DI CELMA & CANTALAMESSA, 2012). The Pliocene - Pleistocene marine succession (Fig. 1B) shows an overall transgressive-regressive trend, characterized, from base to top, by neritic- to- littoral sandstone and conglomer- ate deposits (Pliocene cycle), by pelitic deposits with inter- layered gravely sand/sandstone and sandy clay horizons (Mu tignano Formation), and finally by neritic- to- littoral and/or continental sand and gravel (Fermo Formation) (cf. CANTALAMESSA et al., 1986; CENTAMORE & MICA­ RELLI, 1991; CENTAMORE et al., 1991, 2009; CENTA­ MORE & NISIO, 2003). Recent geological mapping led to a partial stratigraphic revision (CELLO et al., 2009; SARTI et al., in press): deposits from both the Pliocene cycle and the Mutignano Formation are now grouped in the “Argille Azzurre” Formation (FAA - Formazione delle Argille Az- zurre: Early Pliocene - Early Pleistocene: Fig. 1B). The FAA is mainly pelitic and is subdivided into a Pliocene marly pelite with minor sandstones and a Pleistocene dominantly pelitic portion, characterized by four intercalated lithofacies: gravely sand/sandstone, sand/sandstone, clayey sand and san dy clay. Based on the sand/clay ratio and the distribution of lithofacies, several local members are also recognizable in the FAA (CANTALAMESSA et al., 2002; CANTALA- MES SA & DI CELMA, 2004; CELLO et al., 2009). This study deals only with the Pleistocene section. The Camerano sedimentary sequence is characterized by a lower part of mainly pelitic composition and by an upper part dom- inated by sand/sandstone intermingled with clay, formerly referred to as the Marne di Numana and Sabbie di Monte Gallo Formations, respectively, and as the Mutignano For- mation (Fig. 1B: FANCELLI & RADRIZZANI, 1964; CEN­ TAMORE et al., 1991; CENTAMORE & MICARELLI, 1991; CANTALAMESSA & DI CELMA, 2004). On the new geological maps (SARTI et al., in press), the Camerano sed- Figure 2: Map of the Camerano underground system (modified after RECANATINI, 1990): A) Planar view; B) Section view (same horizontal and vertical scale). 1=Grotta Ricotti; 2=Grotta Corraducci; 3=Grotta Gasparri-Trionfi; 4=Grotte del Torrone; 5=Grotta Mancinforte. Geologia Croatica 66/3Geologia Croatica 208 iments are entirely attributed to the FAA (Fig. 1B), in par- ticular to the pelitic lithofacies (lowermost part) and to the arenitic/pelitic and pelitic/arenitic lithofacies (uppermost part). The stratigraphic position and sedimentary features of the upper deposits place them in the Offida Member (Q1 phase sensu CELLO et al., 2009). 3. THE SUBTERRANEAN CAMERANO SECTION 3.1. Materials and methods Sedimentological and lithostratigraphic description has been carried out along and across the underground levels (Figs. 2, 3 and 4), and a composite sedimentological section has Figure 3: Views of the Camerano cave system: A, B, D, E) Grotta Corraducci: A) and B) show entirely the “Stairs” and “Trionfi room” sections of Figure 4, re- spectively; C) Grotta Ricotti; F) Grotta Gasparri-Trionfi; G) Grotta Mancinforte. Horizontal beds (A, D-G) and 5° westward inclined beds (B, C) are visible, as well as sand-clay couplets (SSC) and matrix-supported clay-clast conglomerate (arrows). Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 209 also provide a semi-quantitative grain-size analysis. With the same criteria, some clay fragments have been sampled and analysed (Fig. 4). Finally, nannoplankton biostratigraphy was carried out on all Grotta Mancinforte and Grotta Ricotti clay samples (Fig. 4). been reconstructed. In both the Grotta Mancinforte and Grotta Ricotti sections, close sampling (about 10 cm-spac- ing) for each sand-clay couplet (see below) was carried out, and 1 cm2 of washed residue has been counted to provide a quantitative analysis of foraminifers (Tab. 1). These samples Figure 4: Sedimentological and stratigraphic logs, drawn throughout the rooms, from west (left) to east (right), and along the three main cave levels. Horizontal distances are not to scale. Micropalaeontological and biostratigraphic samples (letters) and clay fragments samples (asterisks) are indicated. Nannofossil zones refer to RIO et al. (1990). Geologia Croatica 66/3Geologia Croatica 210 Ta bl e 1: F or am in ife ra a ss em bl ag es in th e lo w er m os t ( G ro tt a M an ci nf or te ) a nd u pp er m os t ( G ro tt a Ri co tt i) Ca m er an o se ct io n (m od ifi ed a ft er L U CC IO N I, 20 07 ). Pe rc en ta ge fo r e ac h ta xo n is c al cu la te d on th e to ta l o f b en - th ic a nd p la nk to ni c fo ra m in ife ra , r es pe ct iv el y. S =s an d le ve l; C= cl ay le ve l. Sa m pl es Li th ol og y Be nt hi c fo ra m in ife ra (n ) Pl an kt on ic fo ra m in ife ra (n ) To ta l s pe ci m en s/ cm 2 P/ B ra tio Pl an kt on ic fo ra m in ife ra (% ) Sp ec ie s D iv er si ty Benthic foraminifera Planktonic foraminifera Infaunal In fa un al / Ep ifa un al Epifaunal ot he r b en th ic fo ra m in ife ra % G lo bi ge rin a bu llo id es % G lo bi ge rin a qu in qu el ob a % G lo bi ge rin oi de s r ub er % G lo bi ge rin oi de s s ac cu lif er % G lo bi ge rin oi de s t ril ob us % G lo bo ro ta lia cr as sa fo rm is % G lo bo ro ta lia in fla ta % G lo bo ro ta lia c fr. g r. m en ar di i % H as tig er in a sip ho ni fe ra % N eo gl ob oq ua dr in a sp p. % O rb ul in a un iv er sa % Am m on ia g ro up % Bu lim in a gr ou p % Ca ss id ul in a sp . % M el on is sp . % Pu lle ni a sp . % U vi ge rin a gr ou p % Bo liv in a gr ou p % El ph id iu m g ro up % G yr oi di na a lti fo rm is % H ya lin ea b al th ic a % Le nt ic ul in a sp . % Lo ba tu la lo ba tu la % Pa te lli na co rr ug at a % Pl an ul in a ar im in en sis % Q ui nq ue lo cu lin a sp . % G ro tt a Ri co tt i R3 C 120 522 642 4 81 14 17 13 0 0 0 0 1 27 0 3 2 9 28 0 0 0 20 0 13 0 7 0 20 0 0 16 23 R2 C 42 336 378 8 89 12 5 0 0 0 0 0 0 24 0 5 0 36 24 0 0 7 18 0 27 0 0 0 33 0 0 0 23 R1 C 70 237 307 3 77 13 1 30 0 0 0 0 31 1 0 1 1 14 19 0 0 0 34 0 22 0 23 0 0 0 0 0 21 C4 S 129 119 248 1 48 25 6 7 0 2 0 3 0 8 2 2 8 5 32 0 8 19 24 0 11 0 38 0 18 0 7 0 3 C3 S 132 362 494 3 73 25 9 8 0 1 3 2 3 6 12 1 18 6 24 0 0 7 43 0 11 0 24 0 13 0 6 0 3 C8 C 187 607 794 3 76 25 10 5 0 3 3 4 4 3 17 1 25 1 13 2 0 10 22 0 14 0 34 0 15 0 12 1 2 C6 C 8 756 764 95 99 11 0 13 0 0 0 0 0 0 0 13 13 50 13 0 0 0 19 0 16 0 16 0 15 0 0 16 17 C5 S 15 17 32 1 53 10 20 20 0 0 0 0 0 13 7 0 0 0 20 0 7 13 0 0 41 0 29 0 0 0 0 0 29 C4* C 111 247 358 2 69 25 20 5 0 5 0 3 1 5 3 2 19 2 25 1 5 6 19 0 13 0 38 0 17 0 10 0 2 C3* S 77 304 381 4 80 18 6 6 0 0 6 1 0 4 10 0 5 4 55 1 0 0 20 0 19 0 33 1 21 0 1 1 4 C2 C 97 384 481 4 80 20 10 9 0 0 0 6 7 7 29 1 4 1 18 0 0 7 23 0 9 0 30 2 22 2 11 0 2 C1 S 58 51 109 1 47 19 10 7 0 3 0 2 2 17 9 2 7 7 28 7 0 0 14 0 12 0 24 0 35 0 6 0 10 G ro tt a M an ci nf or te A8 S 57 39 96 1 41 16 4 16 0 0 0 0 0 7 2 4 12 2 9 0 42 4 5 0 3 0 54 0 3 0 8 0 28 A7 C 267 515 782 2 66 35 3 11 2 1 0 4 1 8 14 1 6 7 27 0 0 13 23 0 22 0 30 0 12 0 6 2 4 A6 S 71 73 144 1 51 23 6 4 0 1 0 4 1 13 1 1 21 1 24 0 0 21 23 0 15 0 55 0 0 0 3 4 0 A5 C 81 74 155 1 48 20 7 5 0 1 0 0 0 26 4 2 0 20 27 0 0 7 20 0 3 0 18 0 9 0 0 9 41 A4 S 72 32 104 0 31 20 13 10 0 0 0 0 0 11 6 0 17 3 21 1 10 10 3 0 9 0 38 0 6 0 0 3 41 A3 C 188 322 510 2 63 29 1 16 9 0 1 1 4 1 14 0 15 4 15 1 0 17 33 0 14 0 17 0 20 0 10 3 3 A2 S 46 61 107 1 57 19 2 13 4 0 0 2 0 11 4 0 24 2 13 0 13 11 11 0 13 0 52 0 11 0 2 0 10 A1 C 179 247 426 1 58 38 8 7 4 2 0 2 5 6 14 2 6 7 17 0 3 16 32 0 17 0 19 0 17 2 7 2 4 B14 S 37 264 301 7 88 11 0 0 0 0 0 0 0 30 3 0 0 0 54 0 11 3 23 0 23 0 23 0 27 0 0 0 5 B13 C 165 165 330 1 50 15 6 12 0 0 0 0 0 18 12 1 0 12 27 0 6 5 21 0 24 0 24 0 0 0 0 0 30 B12 S 9 - 9 - 0 3 0 0 0 0 0 0 0 44 0 0 0 0 0 11 44 0 0 0 0 0 0 0 0 0 0 0 0 B11 C 52 146 198 3 74 14 40 0 0 0 0 0 0 2 8 2 0 6 37 2 0 4 34 0 0 0 55 0 3 0 0 1 7 B10 S 99 54 153 1 35 23 10 7 4 1 0 2 0 3 10 1 18 3 26 2 3 9 20 0 19 0 37 0 11 4 0 0 9 B9 C 199 255 454 1 56 32 1 9 2 0 2 3 5 2 16 2 15 4 22 2 0 17 27 0 22 0 25 0 11 2 8 2 2 B8 S 54 52 106 1 49 22 26 6 0 0 0 2 2 0 6 4 7 0 26 4 4 15 10 0 19 0 46 0 4 0 2 0 19 B7 C 229 327 556 1 59 33 12 9 0 1 1 3 1 8 10 0 9 8 21 2 1 12 24 0 16 0 22 0 13 1 17 2 4 B6 S 38 80 118 2 68 22 11 5 0 3 0 0 0 0 5 0 21 3 16 8 8 21 18 0 16 0 38 3 11 1 4 3 8 B5 C 128 191 319 2 60 37 2 4 1 4 0 4 2 8 4 2 4 10 32 6 1 16 25 0 11 2 26 2 8 3 10 4 10 B4 S 42 40 82 1 49 21 12 5 0 0 0 5 0 36 7 0 0 2 14 2 5 12 18 0 8 0 20 0 15 0 5 18 18 B3 C 105 81 186 1 44 29 6 7 1 0 0 4 0 20 0 4 0 1 42 0 5 11 31 0 11 1 19 1 11 4 5 5 12 B2 S 65 95 160 2 59 26 2 14 0 0 0 0 0 20 0 0 2 8 34 8 2 12 23 2 5 4 32 0 11 2 5 1 15 B1 C 158 86 244 1 35 33 0 6 4 1 1 4 2 15 1 1 1 18 29 3 2 13 0 1 8 5 19 0 14 1 0 6 47 B0 S 66 42 108 1 39 31 5 3 0 2 0 5 2 12 6 0 2 3 15 9 6 32 17 0 10 7 24 0 10 2 2 2 26 Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 211 The superposition of three main accessible cave levels (Figs. 2, 3: RECANATINI, 1990, 1997), with their pattern of tunnels, allows one to describe a section about 30 m thick of Early Pleistocene marine deposits (Fig. 4), and provides a three-dimensional view of depositional geometries. The recent opening of the touristic route across the caves allows completion of the stratigraphic succession, and a one-metre- spaced sampling was carried out. A refinement of the pre- liminary micropalaeontological analyses (cf. LUCCIONI, 2007) is also provided. Sedimentary deposits are mainly lightly cemented, yel- low-brown sand and grey-green clay couplets, with variable thickness and sand/clay ratios. Sedimentary beds alterna- tively show a sub-horizontal attitude or an average 5° west- ward inclination (Fig. 3): this feature is extremely variable along the section, and also for the same beds throughout the rooms, while interposition of tectonic disturbances has not been documented. Although it may reflect the regional tec- tonics (main gentle south-westward dip of FAA in the An- cona sector), this local variability is considered here as a primary depositional feature reflecting the original gentle inclination and the irregularities of the slope. Unfortunately, the interposition of erosional scars and/or unconformity sur- faces has not yet been documented, and the 3D geometries of depositional bodies are hard to reconstruct. The uppermost (Grotta Ricotti) and intermediate cave levels are separated by about 30 m of deposits (Figs. 2b, 4), only partly visible through some ventilation pits, indicating that the sand-clay alternation is continuous throughout the section. In the up- permost Grotta Ricotti (n. 1 in Fig. 2) and in the middle- level cave system (Grotta Corraducci, Grotte del Torrone: ns. 2 and 4 in Fig. 2, respectively), two main matrix-supported gravel horizons occur, made of claystone fragments of vari- ous sizes (from 2–3 cm to 50–60 cm), dispersed in a bioclas- tic sandy matrix (hereafter: clay-clast conglomerate). Minor clay-clast horizons are locally visible in the Corraducci-Tri- onfi-Torrone complex (ns. 2, 3 and 4 in Fig. 2) as well as in the lowermost Grotta Mancinforte (n. 5 in Fig. 2). 3.2. Sedimentological analysis Sand-clay couplets - Sand-clay couplets are the main depositional feature visible in the caves. Each couplet is marked at the base by an erosional surface, locally with load casts. Most couplets are normally graded, from plane-paral- Figure 5: Main facies occurring in the studied deposits. A) Sand-clay couplets: alternation of plane-parallel laminated sand and massive clay horizons (Grotta Corraducci). NGc=normally graded couplet; SSCc= couplet with sharp sand-clay contact; rl=reverse-graded laminae; es=erosion surface; cc=clay chips. B) Detail of reverse-graded laminae in sand (Grotta Mancinforte). C, D) Matrix-supported conglomerate of clay clasts dispersed in yellow sand ma- trix: A-type (C, Grotta Ricotti) and B-type (D, Grotta Corraducci) clay-clast conglomerates are shown. Geologia Croatica 66/3Geologia Croatica 212 lel laminated sand to massive clay, or more rarely the sand- clay transition is sharp (Fig. 5A). However, the sand intervals are typically reverse graded at the base. A single couplet can vary from 10 cm to 1.5 m in thick- ness, and the sand/clay ratio is also variable: thickness var- ies from 5 cm to 1 m for sandy horizons, and from 5 to 50 cm, for clay beds. Average values are about 40–50 cm and 20 cm for sand and clay horizons, respectively. The sand/ clay ratio approximately varies from 1:1 to 4:1. Sand lithol- ogy is dominated by bioclastic fragments, with subordinate limestone clasts and rare quartz and chert clasts. Sand grains, varying from fine to coarse sand, are 50–90% bioclasts (main ly shell fragments and benthic foraminifera), 10–50% monogenic carbonate lithoclasts, with less than 5% other lithoclasts. Clay chips occur at the base of some sand hori- zons (Fig. 5A). In their lowermost portion, most sand hori- zons are characterized by reverse-graded, plane-parallel lam- inae (Figs. 5A, 5B); only rarely, do sands appear massive. Patchy pseudospar cement occurs, whereas a pelitic matrix is totally absent (“washed” look). Some sand horizons also show parallel cross-lamination (H ~5 cm) and/or symmetric ripple lamination in the uppermost part, but they are very rare along the section (less than 10% of the couplets). Grain size gradually decreases upward, passing to silt and clay, and it is still generally marked by a parallel lamination; sharp sand/clay contacts are also documented (Fig. 5A). The rare cross- to ripple laminated layers are confined to some of these sand beds with sharp tops. Among the mud fraction, clay largely dominates. Massive clay beds are characterized by high plasticity and by a fossil content of foraminifera and other very small bioclasts. Oxidation zones are present at the erosional base of many couplets, or marking sharp sand-clay transitions. Oxi- da tion partially extends into the overlying deposits, and thus appears to represent a post-depositional (diagenetic) feature. Clay-clast conglomerate – Matrix-supported conglom- erates are represented by claystone fragments, partially lithi- fied and dispersed into a bioclastic sandy matrix. Clay frag- ments are highly variable in size (from few centimetres up to 50 cm in diameter) and shape, sub-angular to sub-rounded. The claystone chips appear identical in colour, plasticity, and grain size to the interlayered clay horizons, and they are also comparable to the clay beds in terms of fossil content. The sandy matrix has the same grain size, composition, cemen- tation as the sand beds, and comparable microfossil assem- blages. Two different types of conglomerate are recognizable (Fig. 5): A – Type: block-size conglomerate, with erosion base surface, probably channelled (Figs. 3C, 5C). The size of clay clasts decreases upward, and a sort of normal gradation is documented; nonetheless, the contact with overlying sands is sharp. B – Type: cobble- to pebble-size conglomerate layers, localized within sand layers (Figs. 3E, 5D), with no recog- nizable erosion base surface. Clay clasts are interposed be- tween very coarse grained, massive sand and medium to fine grained, plane-parallel laminated sand. 3.3. Palaeontological record and stratigraphic data Malacofauna – The first naturalist studies of the Camer- ano caves (PROCACCINI RICCI, 1841; DE BOSIS, 1860) noted the abundance of fossil remains, mainly represented by marine molluscs. The major fossil horizons are observable along the cave vaults. A rich fossil collection has been gath- ered between 1970 and 1980, and is on display at the Camer- ano Town Hall (Collezione A. Ruzziconi). The fossil record includes Pecten jacobaeus (LINNAEUS), Callista (Callista) chione (LINNAEUS), Glossus humanus (LINNA EUS), Venus spp., Chlamys (Aequipecten) opercularis (LINNAEUS), Chlamys (Flexopecten) inaequicostalis (LA MARCK), Ostrea lamellosa BROCCHI, scaphopods and ser pulids. Although the fossil assemblage has no stratigra phic relevance, it is roughly homogeneous throughout the section and comparable to the one described by FANCELLI & RADRIZZANI (1964) for the “Sabbie di Monte Gallo” Unit. Foraminifera - Both sand and clay beds are rich in ben- thic and planktonic foraminifera. Preliminary stratigraphic and micropalaeontological data for Grotta Mancinforte and Grotta Ricotti deposits are reported by LUCCIONI (2007). The occurrence, from the base of the section, of frequent Globorotalia inflata and rare Globorotalia crassaformis con- strains the whole section to the Gelasian-Calabrian interval. An Early Pleistocene age is also indicated by the common occurrence throughout the section of Hyalinea balthica (BALDANZA et al., 2011). Calcareous nannofossils - The Calcareous nannofossil analysis has been carried out in clay deposits, as they are to- tally missing in sand horizons. The nannoflora, locally very abundant and in a good state of preservation, is dominated by small Gephyrocapsa, medium Gephyrocapsa, large Ge- phyrocapsa (sensu RAFFI, 2002), Coccolithus pelagicus, Helicosphaera sellii and Helicosphaera carteri, and could be referred to MNN 19c and MNN19d Nannofossil Subzones (RIO et al., 1990). Nannofossil analyses constrain the Camerano section to the Calabrian, thus better defining the age as Qm phase, as de- scribed in CENTAMORE et al. (1991) and CENTAMORE & MICARELLI (1991), or the Q1 phase (CELLO et al., 2009). These data also agree with the age proposed for the top of FAA in the recent CARG Project (SARTI et al., in press). 4. DISCUSSION 4.1. Palaeoecological inferences The whole malacofauna is indicative of clayey or sandy floor palaeoenvironments (PERES & PICARD, 1964); the occur- rence of the genera Glossus, Callista and Chlamys probably reflects a minimum depth of about 40 m. Furthermore, Glos- sus indicates cool conditions at the sea floor. We suppose the lack of gastropods in the assemblage is probably due to the instability of the sea-floor. The benthic and planktonic foraminifera assemblages (Tab. 1) show no remarkable differences between sand and clay horizons in the Camerano sedimentary sequence, except Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 213 for specimen abundances and species diversity, which are both higher in clay beds (LUCCIONI, 2007). The micropalaeon- tological content (Tab. 1) shows evidence of mixed planktonic foraminifera, shallow-water (20-50 m depth) (Ammonia spp., Elphidium spp. and Quinqueloculina spp.) and deeper water (50-100 m) benthic foraminifera (Bolivina spp., Bulimina spp., Cassidulina spp., Hyalinea balthica, Uvi gerina spp., Gy- roidina spp.). Percentages of shallow water specimens on to- tal benthic foraminifera (Tab. 1) vary from 21% to 55% in sandy beds and from 6% to 64% in clay horizons. As expected, the P/B ratio is significantly higher for clay beds: neverthe- less, in 60% of the sand beds, the P/B ratio is ≥1, evidencing an anomalous enrichment in the plank tonic component for sandy deposits (Tab. 1). Thus, sand -clay couplets reasonably document resedimentation/remobilization events, followed by the re-establishment of low-energy conditions, while clay ho- rizons document resedimentation, distal river supply and wa- ter-column productivity of biota. As a result of remobilization, a gradual transition is expected in clay beds, from a reworked microfauna assemblage at the base, to an assemblage at the top dominated by water-column productivity. Unfortunately, the avail able data do not allow documentation of this varia- tion; more detailed analyses are needed. Benthic foraminifera assemblages (average values of about 33% of shallow-water taxa and about 25% of deeper water taxa), as well as plankton/benthos ratios (Tab. 1), in- dicate a shallow-water sandy sea floor, distally connected to a deeper (up to 100 m) clayey floor (circa-littoral to upper bathyal zones). Cold-water planktonic foraminifera, such as Globorotalia inflata, Globigerina bulloides and Neoglobo- quadrina spp., consistently occur in the assemblage with temperate to warm water specimens (Globigerinoides spp., Orbulina universa) (Tab. 1). Through the deeper benthic fo- raminifer assemblages, the abundance of Bolivina spp., Bulimina spp., Cassidulina spp., Hyalinea balthica and Len- ticulina spp. also indicates that the basin-floor environment underwent low-oxygenated, cool-water conditions (BALD- ANZA et al., 2011). This situation is probably related to wa- ter-mass stratification and thermal isolation of the basin floor. 4.2. Sedimentological interpretation According to fossil content and sedimentary features, deposits are referred to an open marine environment, mainly below and only occasionally across the storm wave base, as testified by the extreme rarity of wave-induced structures; nonetheless, some clay should be discussed. Clay beds re- flect a suspension-dominated offshore marine environment. On the other hand, considering the micropaleontological as- semblages, sandy beds clearly show evidence of mixing of proximal (both epifaunal and infaunal) and distal benthic taxa. The clay source is distal river sedimentation and/or in- trabasinal remobilization rather than ancient Conero “Island” beach systems. Except for the argillaceous Oligocene Schlier Fm., the limestone/marly limestone units outcropping in the present-day M. Conero anticline, could not produce the large amount of clay in Pliocene to Pleistocene marine deposits. Moreover, in the Camerano deposits, Cretaceous to Miocene reworked microfossils are very rare. Sands are mainly reverse-graded, plane-parallel laminat ed. Plane-parallel lamination in sandy deposits may be indicative of various sedimentary environments; nevertheless, reverse grading more commonly occurs in sediment gravity flow de- posits than in current/wave deposits. Sandy storm deposits may be parallel-laminated in the basal portion (plane beds). As a storm subsides a decrease of energy, from erosive capac- ity to critical and subcritical flow, to the final recovering of fair-weather conditions, should produce a suite of sedimentary structures, from HCS to swaley-laminations, to wave ripples. Except for the rare occurrence of small scale cross-lamination and/or wave ripples, these structures are not documented through the Camerano section. The hypothesis that sand-clay couplets are shelf storm deposits seems unsatisfactory. Plane-parallel laminated, reverse-graded sands can be identified as facies F7 (MUTTI, 1992) or S1 (LOWE, 1982), both described from siliciclastic turbidites, and are compa- rable to the “traction carpets” described in sandstones (DZU­ LYNSKI & SANDERS, 1962; MIDDLETON, 1970, 1993; HISCOTT & MIDDLETON, 1979; LOWE, 1982; TODD, 1989; SOHN, 1997). On the other hand, the sands are largely bioclastic. A study on the hydraulic equivalence between bioclasts and lithoclasts of different lithology is beyond the scope of this work; nevertheless, bioclastic and lithoclastic sands should behave similarly during the formation of “trac- tion carpets”. Both facies S1 (LOWE, 1982) and F7 (MUTTI, 1992) in siliciclastic deposits are attributed to “High Density Turbidity Currents”. Sandy beds presumably represent basi- nal resedimentation of nearshore bioclastic sands, promoted by storm-induced turbidity currents. The lack of clay matrix in the sandy beds is probably due to the flow conditions during the event, and to a negligi- ble original amount of clay in nearshore remobilized depos- its, according to a mechanism resembling the one proposed for ‘carbonate turbidites’ (COLACICCHI & BALDAN ZA, 1986). Thus, the gradual to sharp transition to clay mainly represents the more or less gradual or rapid re-establishment of low-energy conditions. The physical characters (colour, plasticity, textural features) and the microfossil content (see below) are unvarying across clay beds, as well as in clay chips at the base of couplets. In each couplet, a clay content reasonably derives from erosion of clay-floor sediments, en- trapment of clay chips and resedimentation of fines during the turbiditic event (ENOS, 1969). Nevertheless, this “turbi- di te” clay fraction is indistinguishable from the true hemipe- la gite (Fig. 6A). This interpretation looks reasonable; however, some issues are to be considered. The carbonate tur bidites are typically fed by a carbonate platform system, which provides the biogenic component. The question is, if a submerged beach, in a siliciclastic context, may export basin-ward car- bonate sand with a relevant amount of bioclasts. The origin of sand is presumably local, and the most reasonable expla- nation is that M. Conero island and its Pliocene to Pleisto cene calcarenitic beaches were the main source area for san dy de- posits (Fig. 6). In fact, bioclastic calcarenitic beaches are documented in the area, at least during the Early Pliocene (“Trave horizon”: e.g. CANTALAMESSA et al., 1986; CEN- TAMORE & MICARELLI, 1991; SARTI et al., in press). Geologia Croatica 66/3Geologia Croatica 214 The lack of clay matrix in the sandy beds is a critical point in interpreting sand-clay couplets as turbidites. In fact, the suspended silt/clay fraction (or micrite in carbonate tur- bidites: COLACICCHI & BALDANZA, 1986) plays a sig- nificant role in the turbulent flow movement. The occurrence of beds showing gradation from sand to clay (NGc in Fig. 5A) seems to demonstrate that clay was initially present in the suspension together with sand. The sand/clay separation may derive from flow partition between a lower laminar layer (i.e., flowing grain layer) and an upper turbulent layer (i.e., turbidity current). In this case, sand layers may be better de- fined as grain flow deposits, while only the upper, very fine sand to clayey part of graded couplets can be considered a true turbidite (SANDERS, 1965; POSTMA et al., 1988; SAN DERS & FRIEDMAN, 1997; MULDER & ALEXAN- DER, 2001; SHANMUGAM, 2002). The occurrence of both graded and sharp sand-clay transition indicates that the orig- inal sediment gravity flow may or may not reach the condi- tions for internal stratification. Thus, not all the flows evolve as turbidity currents, and the sharp transition could represent the successive settlement of suspended clay above a grain flow deposit. B-type clay-clast conglomerates seem to be integral parts of the sand layers. Sedimentary features resemble those in the experiments of POSTMA et al. (1988) on high-density turbulent flows, except for the larger scale of clay clasts in Camerano deposits. According to that model, deposition ori- ginates in consequence of density stratification of the flow. B-type conglomerate might result from storm-induced, high- density turbidity currents. A-type clay-clast conglomerates are identifiable as deb- rites (sensu STOW, 1985), deriving from remobilization of semi-lithified clay beds and unlithified sands. Thus, they are interpreted as debris-flow deposits. Slope failure can produce debris flows directly, if internal cohesion is lost, even on gen- tle slopes (DOTT, 1963; RODINE & JOHNSON, 1976), or debris flows may derive from distal evolution of other mass- movements (LOWE, 1982; NEMEC & STEEL, 1984; STOW, 1985; MUTTI, 1992; MULDER & ALEXANDER, 2001; DASGUPTA, 2003). The original clay amount is prob- ably a leading factor in debris flows (HAMPTON, 1975). However, clay in the conglomerates of the Camerano section is confined to large clay clasts, and none is present within the sandy matrix. The lack of cohesion in unlithified sand beds should facilitate initiation of flows. Finally, some considerations about the relationship be- tween clay-clast conglomerates and sand-clay couplets are proposed. Grain flows/turbidites may be induced in sands both by down-current evolution of debris flows (HAMP- TON, 1972; MUTTI, 1992; ILSTAD et al., 2004a; ELVER- HØI et al., 2010) or promoted by storm events (WALKER, 1984). The amount of clay in the initial mixture is critical for debris-flow movement along a low-inclination slope (less than 2% of clay to maintain a fine-sand debris flow, up to 19% for coarse-sand debris flow, according to HAMPTON, 1975), as well as for the features of evolving flow caused by water intrusion (HAMPTON, 1972, 1975; POST MA et al., 1988; ILSTAD et al., 2004a; ELVERHØI et al., 2010). Thus, the clay-clast conglomerates may result from disturbance and mass failures of semi-lithified beds by overloading or earthquakes rather than storm-induced hydraulic pressures. In this scenario, sand-clay couplets and clay-clast con- glomerates result from different processes acting on a gentle, but unstable, slope (Fig. 6A). Figure 6: Basin and palaeoenvironmental reconstruction, according to the alternative proposed sedimentation models (see text). A) Gentle sloped out- er shelf, with alternate sediment gravity flows deposits (sands) and offshore clay deposits, and occurrence of seismic-induced debrites (conglomerates). B) Alternative interpretative model for A-type and B-type clay gravel. Seismic-induced slumps (not documented in the Camerano section) remobilizing bioclastic sand and cohesive clay horizons, evolving basin-ward to matrix-supported gravel. SWB = Storm wave base. Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 215 In an alternative interpretation, both A- and B-type con- glomerates, as well as sand-clay couplets, may originate from the distal modification of slumps (Fig. 6B). Slump deposits have not yet been found in the Camerano section or in the neighbouring areas, however. The two gravel types could be interpreted as more proximal (A) and distal (B) slump depos- its, respectively (Fig. 6B). Slumps were most likely induced by seismic activity, and clay beds acted as detachment levels along a gentle slope. Nevertheless, clay does not occur within the matrix, which is solely bioclastic sand. The seismic shock probably mobilized semi-lithified sand-clay couplets, which started moving as a unique body. Low-permeability clay lay- ers are responsible for the increase in fluid pressure as pore water is expelled from underlying sand beds under shear stress (STURM, 1971; HAMPTON, 1972; MALTMAN, 1994; HAMP TON et al., 1996; STRACHAN, 2002; ILSTAD et al., 2004b; SULTAN et al., 2004). Pore-water pressure causes slumps on very low slopes (FIELD et al., 1982; MCADOO et al., 2000; STRACHAN, 2002; GARCIA-TORTOSA et al., 2011; ALSOP & MARCO, in press). Slumps distally evolved to non-cohesive debris flows (sensu LOWE, 1982 and NE­ MEC & STEEL, 1984), mainly supported by buoyancy and dispersive pressure mechanisms, rather than by cohesion. Lar ge clay clasts were preserved during the motion, a very short transport. This slump model (Fig. 6B) is comparable to the one proposed by COLACICCHI & MONACO (1994) for the Cretaceous-Palaeogene Scag lia Basin. If the debris flow continues incorporating water, the dilution may promote a high -density turbidity current, with flow density stratification (SANDERS, 1965; HAMP TON, 1972, 1975; POSTMA et al., 1988; SANDERS & FRIEDMAN, 1997; SHANMUGAM, 2002; ILSTAD et al., 2004a; ELVERHØI et al., 2010). Dur- ing this evolution, the sand-clay couplets are probably sedi- mented, as turbidity currents and/or grain flows are succeeded by settlement of suspended clay. 4.3. Facies interpretation The alternating sand/clay beds, characteristic of the up- permost deposits of the Camerano hill sedimentary succes- sion, observable only in the subterranean outcrops, are very similar to the arenitic/pelitic or pelitic/arenitic lithofacies belonging to the FAA (SARTI et al., in press). There are, however, some important differences between the Camerano and typical FAA lithofacies. Compared to the FAA, massive sand beds in the Camerano sedimentary sequence are rare, large-scale cross-lamination and hummocky geometries are totally lacking, sand is dominantly plane-parallel laminated and reverse graded, and clay beds are massive rather than thin-laminated. On the other hand, the sand/clay ratio is the sedimentological feature most comparable with the ones ex- hibited by arenitic/pelitic lithofacies in deposits cropping out west of Camerano and by the Offida Member (CELLO et al., 2009; SARTI et al., in press). Sand lithology is dominated by bioclastic fragments, with subordinate lithics, indicating that sediments were locally derived. Deposits referable to slump evolution were formerly reported in deposits from the western flank of the Periadriatic Basin (CANTALAMESSA et al., 1986; DI CELMA et al., 2010; DI CELMA, 2011), but were never documented before in the eastern area and in Early Pleistocene deposits. Finally, according to our inter- pretation, both Sand-clay couplets and Clay-clast conglom- erate, cannot be related to the shoreface and/or offshore tran- sition deposits recognized by SARTI et al. (in press) in the Camerano area, and are most likely resedimented in a deeper basin environment (outer shelf). 4.4. Palaeoenvironmental reconstruction Sedimentological evidence indicates that the Camerano sedimentary sequence was deposited in a shallow outer shelf (Fig. 6A), positioned in close proximity to a partially emer- gent structural high, an island, today partially identifiable with Mt. Conero. This sandy shoreface to inner shelf envi- ronment represented the source of the carbonate sand. De- posits were moved offshore by storm waves, and resedi- mented to the outer shelf by storm-induced turbidity currents, debris flows and grain flows. Due to their carbonate compo- sition and the richness in bioclasts, a local origin for sandy deposits is presumed. The outer shelf/basin was character- ized by deposition of clay, presumably supplied by distant western river deltas, mixed with primary productivity within the water column. In addition, an integrated submarine-can- yon and basin system is documented in the southwestern Periadriatic basin, during the Early Pleistocene at least (DI CELMA et al., 2010; DI CELMA, 2011). A local contribu- tion to clay from this source cannot be excluded. The close variability of sub-horizontal and 5° westward inclination for sedimentary beds could reflect an original gently inclined, irregular slope. Irregularities may be the con- sequence of 3D geometries of larger sediment gravity flow deposits (debrites). The outer shelf periodically received shal- low-water carbonate near-shore sediments, remobilized from the eastern inner shelf by storm events and resedimented as carbonate turbidites of high density and/or grain flow depos- its. These sediment gravity flows also partially eroded clay beds, and clay was involved in the resedimentation events. From Miocene times onward the Marches area underwent a tectonic compressive regime and seismic activity; the occur- rence of seismic-induced debris flow deposits and/or slump deposits, recorded as conglomerates in the Camerano succes- sion (Fig. 6), documents sedimentation in a tectonically active context, continuing throughout the Early Pleistocene. 5. CONCLUSIONS Thanks to the exceptional underground town of Camerano it is possible to describe a composite sedimentological and stratigraphic section of Early Pleistocene marine deposits (MNN 19c and 19d Nannofossil subzones), that are lacking suitable subaerial outcrops. Additionally, superposition of different cave levels and the complex pattern of tunnels pro- vide a unique three-dimensional view of depositional geom- etries, facies heterogeneity, and succession. Relative to the usual FAA features, facies described through the Camerano section show some peculiarities; moreover, some contradic- tory characteristics have been described, and not all of them can be easily interpreted. Deposits are clearly marine, and Geologia Croatica 66/3Geologia Croatica 216 they are not referable to the alternation of foreshore/back- shore deposits and brackish deposits, recognized in the area by SARTI et al. (in press). Due to the dominance of plank- tonic foraminifera, deposition on a nearshore environment has been excluded, and an outer shelf environment is more probable. The lack of typical storm-related structures, such as HCS, swaley cross-lamination, etc., indicate the sand-clay couplets are not tempestites. Thus, deposits are interpreted herein as sediment gravity-flow deposits, mainly initiated by storm events, above storm-wave base. On the basis of facies analysis and sedimentological in- ferences, we constructed a sedimentation model and hypoth- esized the palaeoenvironmental context for the deposition of the Camerano sedimentary sequence (Fig. 6). Sand-clay cou- plets are described as storm-induced carbonate turbidites of high density and/or grain flow deposits, and matrix-sup- ported conglomerate of clay clasts are interpreted as debrites. If they were produced by debris flows or distal evolution of slumps, the conglomerates, particularly the A-type, suggest that sedimentation occurred in an unstable, probably tecton- ically active, outer-shelf environment. Palaeoecological data indicate a depth range from 40 to about 100 m, supporting the hypothesis of a shallow outer- shelf environment. Clay horizons were apparently supplied from distal river deltas to the west, enriched by planktonic pelagic sedimentation. Storm-induced carbonate turbidites periodically carried proximal bioclastic material from the western coast of Mt. Conero “island” (Fig. 6). Large clay fragments from matrix-supported conglomerates, probably derived from seismic remobilization of partially lithified de- posits along the inner shelf, although their provenance is not clearly determinable. The microfossil record is consistent with the inferred palaeoenvironmental reconstruction. Never- theless, some uncertainty remains about some apparently con- flicting aspects (relatively shallow depth, low slope, lack of clay matrix in “turbidites”, source area, rare occurrence of symmetrical cross-lamination), and other studies are need ed. Overall, the data presented in this study greatly improve the geological knowledge of the Camerano caves and sur- rounding territory. ACKNOWLEDGEMENT The authors would like to thank the people of the Pro Loco “Carlo Maratti”, the Camerano tourist agency office (IAT) and the Camerano Municipality for their kindness and cooperation during this project. We are also indebted to Dr. Keegan E. ALAGNA for the friendly revision of the manuscript and the useful suggestions. Authors are also grateful to Prof. Paul ENOS for his useful critical reading of the manuscript, and to the two reviewers for their comments and suggestions. REFERENCES ALSOP, G.I. & MARCO, S. (in press): Seismogenic slump folds formed by gravity-driven tectonics down a negligible subaqueous slope.– Tectonophysics (2013), doi: 10.1016/j.tecto.2013.04.004 BALDANZA, A., BIZZARRI, R. & HEPACH, H. (2011): New biostrati- graphic data from the Early Pleistocene Tyrrhenian paleocoast (west- ern Umbria, Central Italy).– Geol. Croat., 64/2, 133–142, doi: 10.4154/gc.2011.11 BIGI, S., CANTALAMESSA, G., CENTAMORE, E., DIDASKALOU, P., MICARELLI, A., NISIO, S., PENNESI, T. & POTETTI, M. (1997): The Periadriatic Basin (Marche-Abruzzi sector, Central Italy) during the Plio–Pleistocene.– G. Geol., 59, 245– 259. BOCCALETTI, M., CALAMITA, F., CENTAMORE, E., CHIOCCHI­ NI, U., DEIANA, G., MICARELLI, A., MORATTI, G. & POTET­ TI, M. (1986): Evoluzione dell’Appennino tosco - umbro - marchi- giano durante il Neogene.– Gior. Geol., 48/1, 227–233. BOCCALETTI, M., CERRINA FARONI, A., MARTINELLI, P., MO­ RATTI, G., PLESI, G. & SANI, F. (1991): L’alternanza distensione- compressione nel quadro evolutivo dei bacini neogenici dell’Appen- nino Settentrionale.– Studi Geol. Cam., Vol. Spec. 91/1, 187–192. CALAMITA, F., CELLO, G., CENTAMORE, E., DEIANA, G., MICA­ RELLI, A., PALTRINIERI, W. & RIDOLFI, M. (1991): Stile defor- mativo e cronologia della deformazione lungo tre sezioni bilanciate dall’Appennino Umbro-Marchigiano alla costa Adriatica.– Studi Geol. Cam., Vol. Spec. 91/1, 295–314. CANTALAMESSA, G., CENTAMORE, E., CHIOCCHINI, U., COLA­ LONGO, M.L., MICARELLI, A., NANNI, T., PASINI, G., POTET­ TI, M. & RICCI LUCCHI, F. (1986): Il Plio-Pleistocene delle Mar- che.– In: CENTAMORE, E. & DEIANA, G. (eds.): La Geologia delle Marche. Studi Geol. Cam., Vol. Spec. 73� Congresso Soc. Ge-Studi Geol. Cam., Vol. Spec. 73� Congresso Soc. Ge- ol. It., 61–68. CANTALAMESSA G. & DI CELMA, C. (2004): Sequence response to syndepositional regional uplift: insights from high-resolution se- quen ce stratigraphy of late Early Pleistocene strata, Periadriatic Ba- sin, central Italy.– Sedimentary Geology, 164, 283–309. doi: 10.1016/j.sedgeo.2003.11.003 CANTALAMESSA, G., CENTAMORE, E., DIDASKALOU, P., MICA- RELLI, A., NAPOLEONE, G. & POTETTI, M. (2002): Elementi di correlazione nella successione marina plio-pleistocenica del Ba- cino Periadriatico Marchigiano.– Studi Geol. Cam. Nuova Ser., 1, 33–50. CELLO, G., COCCIONI, R., GAZZANI, D., NESCI, O., PENNACCHIO- NI, E., PICCINI, M., RICCIONI, M., SAMPAOLESI., S., TONDI, E., CRITELLI, S., LE PERA, E., NEGRI, A., DIDASKALOU, P., POTETTI, M., SAVELLI, D., FARABOLLINI, P., MAZZOLI, S. & D’ANGELI, T. (2009): Note illustrative della Carta Geologica d’Italia alla scala 1:50.000-Foglio 303 “Macerata”.– ISPRA, 90 p. CENTAMORE, E., CANTALAMESSA, G., MICARELLI, A., POTET­ TI, M., BERTI, D., BIGI, S., MORELLI, C. & RIDOLFI, M. (1991): Stratigrafia ed analisi di facies dei depositi del Miocene e del Plio- cene inferiore dell’Avanfossa Marchigiano-Abruzzese e delle zone limitrofe.– Studi Geol. Cam., Vol. Spec. 91/2, 125–131. CENTAMORE, E., FARABOLLINI, P. & ANGELINI, S. (2009): Guida all’escursione:”Geologia e geomorfologia del settore fermano nel bacino periadriatico marchigiano-abruzzese”.– Rend. Online Soc. Geol. It., 8, 162–168. CENTAMORE, E. & MICARELLI, A. (1991): Stratigrafia.– In: L’am- biente fisico delle Marche, Geologia, Geomorfologia, Idrogeologia. SELCA, Firenze, 1–66. CENTAMORE, E. & NISIO, S. (2003): Significative events in the Peri- adriatic foredeeps evolution (Abruzzo-Italy).– Studi Geol. Cam., Vol. Spec. 73� Congresso Soc. Geol. It., 39–48. COLACICCHI, R. & BALDANZA, A. (1986): Carbonate turbidites in a Mesozoic pelagic basin: Scaglia Formation, Apennines, Comparison with siliciclastic depositional models.– Sedim. Geol., 48, 81–105. doi: 10.1016/0037-0738 COLACICCHI, R. & MONACO, P. (1994): Pure carbonate gravity flow deposits of the Scaglia Basin compared with Central Apennine sili- ciclastics (Marnoso-Arenacea and Laga): analogies and differen- ces.– Mem. Sc. Geol., 46, 25–31. Bizzarri et al.: The geology of the Camerano area through the reconstruction of sedimentary sequences of the urban caves Geologia Croatica 217 COLALONGO, M.L., NANNI, T. & RICCI LUCCHI, F. (1979): Sedi- mentazione ciclica nel Pleistocene anconetano.– Geol. Romana, 18, 71–93. DASGUPTA, P. (2003): Sediment gravity flow - the conceptual problems.– Earth-Sci. Rev., 62, 265–281, doi: 10.1016/S0012-8252(02)00160-5 DE BOSIS, F. (1860): Ancona e dintorni. Cenni di storia naturale.– An- cona. DI CELMA, C. (2011): Sedimentology, architecture, and depositional evo lution of a coarse-grained submarine canyon fill from the Ge- lasian (early Pleistocene) of the Peri-Adriatic basin, Offida, central Italy.– Sediment. Geol., 238/3–4, 233–253. doi: 10.1016/j.sedg- eo.2011.05.003 DI CELMA, C. & CANTALAMESSA, G. (2012): Off-shelf sedimen- tary record of recurring global sea-level changes during the Plio- Pleistocene: evidence from the cyclic fills of exhumed slope systems in central Italy.– Journal of the Geological Society, 169/6, 630–643. doi: 10.1144/jgs2012-041 DI CELMA, C., CANTALAMESSA, G., DIDASKALOU, P. & LORI, P. (2010): Sedimentology, architecture, and sequence stratigraphy of coarse-grained, submarine canyon fills from the Pleistocene (Gela- sian-Calabrian) of the Peri-Adriatic basin, central Italy.– Marine and Petroleum Geology, 27/7, 1340–1365. doi: 10.1016/j.marpetgeo. 2010.05.011 DOTT, R.H. JR. (1963): Dynamics of subaqueous gravity depositional processes.– American Association of Petroleum Geologists Bull., 47/1, 104–128. DZULYNSKI, S. & SANDERS, J.E. (1962): Current marks on firm mud bottoms.– Trans Conn. Acad. Arts Set., 42, 57–96. ELVERHØI, A., BREIEN, H., DE BLASIO, F.V., HARBITZ, C.B. & PAGLIARDI, M. (2010): Submarine landslides and the importance of the initial sediment composition for run-out length and final deposit.– Ocean Dynamics, 60, 1027–1046, doi: 10.1007/s10236-010-0317-z ENOS, P. (1969): Anatomy of a flysch.– J. Sediment. Petrol., 39/2, 680–723. FANCELLI, R. & RADRIZZANI, S. (1964): Note illustrative della Carta Geologica d’Italia del foglio n�118 – Ancona.– Serv. Geol. It., Ro ma. FIELD, M.E., GARDNER, J.V., JENNINGS, A.E. & EDWARDS, B.D. (1982): Earthquake-induced sediment failures on a 0.25° slope, Kla- math River delta, California.– Geology, 10, 542–546. GARCIA-TORTOSA, F.J., ALFARO, P., GILBERT, L. & SCOTT, G. (2011): Seismically induced slump on an extremely gentle slope (<1�) of the Pleistocene Tecopa paleolake (California).– Geology, 39, 1055–1058. HAMPTON, M.A. (1972): The role of subaqueous debris flow in gener- ating turbidity currents.– J. Sediment. Petrol., 42/4, 775–793. HAMPTON, M.A. (1975): Competence of fine-grained debris flows.– J. Sediment. Petrol., 45/4, 834–844. HAMPTON, M.A., LEE, H.J. & LOCAT, J. (1996): Submarine landsli- des.– Rev. Geophys., 34/ 1, 33–59. HISCOTT, R.N. & MIDDLETON, G.V. (1979): Depositional mechanics of thick-bedded sandstones at the base of a submarine slope, Tourelle Formation (Lower Ordovician), Quebec, Canada.– In: DOYLE, R.J. & PILKEY, O.H. (eds.): Geology of Continental Slopes. SEPM Spec. Publ., 27, 307–326. doi: 10.2110/pec.79.27.0307 ILSTAD, T., ELVERHØI, A., ISSLERA, D. & MARR, J.G. (2004a): Sub- aqueous debris flow behaviour and its dependence on the sand/clay ratio: a laboratory study using particle tracking.– Mar. Geol., 213, 415–438. doi: 10.1016/j.margeo.2004.10.017 ILSTAD, T., MARR, J.G., ELVERHØI, A. & HARBITZ, C.B. (2004b): Laboratory studies of subaqueous debris flows by measurements of pore-fluid pressure and total stress.– Mar. Geol., 213, 403–414. doi: 10.1016/j.margeo.2004.10.016 LOWE, D.R. (1982): Sediment gravity flows II. Depositional models with special reference to the deposits of high-density turbidity currents.– J. Sedim. Petrol., 52/1, 279–297. doi:10.1306/212F7F31-2B24- 11D7-8648000102C1865D LUCCIONI, I. (2007): Geologia ipogea di Camerano – Storia della città sotto la città.– Collana: Quaderni di Storia cameranese, Castelfidar- do, 115 p. MALTMAN, A. (1994): Deformation structures preserved in rocks.– In: MALTMAN, A. (ed.): The geological deformation of sediments. London, Chapman & Hall, 261–307. MCADOO, B.G., PRATSON, L.F. & ORANGE, D.L. (2000): Subma- rine landslide geomorphology, US continental slope.– Mar. Geol., 169/1-2, 103–136. MICARELLI, A., CANTALAMESSA, G., DIDASKALOU, P., POTET­ TI, M., PAMBIANCHI, G., LE PERA, E., CRITELLI, S., PENNE- SI, T. & MAZZOLI, S. (in press): Carta Geologica d’Italia – Foglio 314 “Montegiorgio”. Note Illustrative – ISPRA, Roma, 90 p. MIDDLETON, G.V. (1970): Experimental studies related to problems of flysch sedimentation.– In: LAJOIE, J. (ed.): Flysch Sedimentology in North America. Geol. Assoc. Can. Spec. Pap., 7, 253–272. MIDDLETON, G.V. (1993): Sediment deposition from turbidity cur- rents.– Ann. Rev. Earth Planet. Sc., 21, 89–114. doi:10.1146/an- nurev.ea.21.050193.000513 MULDER, T. & ALEXANDER, J. (2001): The physical character of sub- aqueous sedimentary density flows and their deposits.– Sedimentol- ogy, 48/2, 269–299. doi: 10.1046/j.1365-3091.2001.00360.x MUTTI, E. (1992): Turbidite sandstones.– Agip, Milano, 275 p. NANNI, T., PENNACCHIONI, E. & RAINONE, M.L. (1986): Il bacino Pleistocenico marchigiano.– In: “Atti Riunione Gruppo Sedimento- logia CNR, Ancona, 5-7 Giugno 1986”, 13–43. NEMEC, W. & STEEL, R.J. (1984): Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass - flow deposit.– In: KOSTER, E.H. & STEEL, R.J. (eds.): Sedimentology of gravels and conglomerates. Canadian Society of Petroleum Ge- ologists Memoir, 10, 1–31. ORI, G.G & FRIEND, P.F. (1984): Sedimentary basins formed and car- ried piggyback in active thrust sheets.– Geology, 12, 475–478. doi: 10.1130/0091-7613(1984)12<475:SBFACP>2.0.CO;2 ORI, G.G., SERAFINI, G., VISENTIN, C., RICCI LUCCHI, F., CASN- EDI, R., COLALONGO, M.L. & MOSNA, S. (1991): The Pliocene - Pleistocene Adriatic foredeep (Marche and Abruzzo, Italy): an in- tegrated approach to surface and subsurface geology.– 3rd E.A.P.G. Conference, Adriatic Foredeep Field Trip Guide Book, 26-30/05/91, Firenze. PÉRÈS, J.M. & PICARD, J. (1964): Nouveau manuel de bionomie ben- thique de la mer Méditerranée.– Recueil des travaux de la Station marine d’Endoume, Marseille, 47/31, 3–137. POSTMA, G., NEMEC, W. & KLEINSPEHN, K.L. (1988): Large float- ing clasts in turbidites: a mechanism for their emplacement.– Sedi- ment. Geol., 58, 47–61. doi: 10.1016/0037-0738(88)90005-X PROCACCINI RICCI, V. (1841): Descrizione del Monte della Crescia e del Monte San Pietro. Senigallia. RAFFI, I. (2002): Revision of the early – middle Pleistocene calcareous nannofossil biochronology (1.75 – 0.85 Ma).– Mar. Micropal., 45, 25–55. doi: 10.1016/S0377-8398(01)00044-5 RECANATINI, A. (1990): Le grotte di Camerano.– Collana: Quaderni di Storia cameranese, Castelfidardo, 85 p. RECANATINI, A. (1997): Le grotte del Conero. Ricerche di speleologia archeologica nel Parco del Conero.– Collana: I Voli del Conero, 4, UTJ, Jesi, 254 p. RECANATINI, A. (2000): La città segreta, correlazioni tra sviluppo urba- no di superficie e rete ipogea nei centri storici alle falde del Conero. Il caso di Camerano e Osimo.– In: “Atti del Convegno: La memoria del sottosuolo. Camerano 17/18 luglio 1999. Cavità artificiali e siste- mi ipogei sotto i centri storici alle falde del Conero ed in area meso- adriatica.” Jesi, 169–202. RICCI LUCCHI, F. (1986): The Oligocene to Recent foreland basins of the Northern Apennines.– Spec. Publs. Int. Ass. Sediment., 8, 105–139. doi: 10.1002/9781444303810.ch6 Geologia Croatica 66/3Geologia Croatica 218 RIO, D., RAFFI, I. & VILLA, G. (1990): Pliocene-Pleistocene calcare- ous nannofossil distribution patterns in the Western Mediterranean.– In: KASTENS, K. & MASCLE, J. (eds.): Proc. ODP Sc. Res., 107, 513–533. doi:10.2973/odp.proc.sr.107.164.1990 RODINE, J.D. & JOHNSON, A.M. (1976): The ability of debris heavily freighted with coarse clastic materials, to flow on gentle slopes.– Sedimentology, 23/2, 213–234. doi: 10.1111/j.1365-3091.1976. tb00047.x SANDERS, J.E. (1965): Primary sedimentary structures formed by tur- bidity currents and related resedimentation mechanisms.– In: MID- DLETON, G.V. (ed.): Primary Sedimentary Structures and Their Hydrodynamic Interpretation.– SEPM Spec. Publ., 12, 192–219. SANDERS, J.E. & FRIEDMAN, G.M. (1997): History of petroleum ex- ploration in turbidites and related deep-water deposits.– Northeast- ern Geology and Environmental Sciences, 19/1–2, 67–102. SARTI, M., COLTORTI, M., BUDINI, A., MATTIONI, L., PIERUCCI- NI, P., ROSSINI, L., GIUNTA, S. & NEGRI, A. (in press): Carta Geologica d’Italia - Foglio 293 “Osimo”. Note Illustrative - ISPRA, Roma, 140 p. SHANMUGAM, G. (2002): Ten turbidite myths.– Earth-Sci. Rev., 58, 311– 341. doi: 10.1016/S0012-8252(02)00065-X SOHN, Y.K. (1997): On Traction-Carpet Sedimentation.– J. Se- dim. Res., 67, 502–509. doi:10.1306/D42685AE-2B26-11D7- 8648000102C1865D STOW, D.A.V. (1985): Deep-sea Clastic Sediments.– In: BRENCHLEY, P.J. & WILLIAMS, B.P. J. (eds.): Sedimentology, Recent Develop- ments and Applied Aspects. Blackwell, London, 67–93. STRACHAN, L.J. (2002): Slump-initiated and controlled syndeposition- al sandstone remobilization; an example from the Namurian of County Clare, Ireland.– Sedimentology, 49, 25–41. STURM, E. (1971): Subaqueous slump structures.– Geol. Soc. Am. Bull., 82/2, 481–484. doi: 10.1130/0016-7606(1971)82[481:SSS]2.0.CO;2 SULTAN, N., COCHONAT, P., CANALS, M., CATTANEO, A., DEN- NIELOU, B., HAFLIDASON, H., LABERG, J.S., LONG, D., MIENERT, J. &TRINCARDI, F. (2004): Triggering mechanisms of slope instability processes and sediment failures on continental mar- gins: a geotechnical approach.– Mar. Geol., 213/1–4, 291–321. TODD, S.P. (1989): Stream-driven, high-density gravelly traction carpets: possible deposits in the Trabeg Conglomerate Formation, SW Ireland and some theoretical considerations of their origin.– Sedi- mentology, 36, 513–530. doi: 10.1111/j.1365-3091.1989.tb02083.x WALKER, R.G. (1984): Facies Models.– Geosciences Canada, 317 p. Manuscript received August 11, 2012 Revised manuscript accepted July 29, 2013 Available online October 5, 2013