Geological Field Trips
Società Geologica Italiana
2011 Vol. 3 (2.1) ISPRA Istituto Superiore per la Protezione e la Ricerca Ambientale
SERVIZIO GEOLOGICO D’ITALIA Organo Cartografico dello Stato (legge N°68 del 2-2-1960) Dipartimento Difesa del Suolo
ISSN: 2038-4947
The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate 85° Congresso Nazionale della Società Geologica Italiana - Pisa, 2010
DOI: 10.3301/GFT.2011.02 The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate G. Zanchetta - I. Isola - L. Piccini - A. Dini GFT - Geological Field Trips geological fieldtrips2011-3(2.1) Periodico semestrale del Servizio Geologico d'Italia - ISPRA e della Società Geologica Italiana Geol.F.Trips, Vol.3 No.2.1 (2011), 55 pp., 19 figs. (DOI 10.3301/GFT.2011.02)
The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate 85° Congresso Nazionale della Società Geologica Italiana - Pisa, 2010
Giovanni Zanchetta(1), Ilaria Isola(2), Leonardo Piccini(3), Andrea Dini(4) with contributions of: Ilaria Baneschi(1), Massimo Guidi(1), Giancarlo Molli(4), Flavio Milazzo(4), Diego Pieruccioni(4), Eleonora Regattieri(4), Russell Drysdale(5) (1) Dipartimento di Scienze della Terra, Università di Pisa (2) Istituto Nazionale di Geofisica e Vulcanologia, sezione di Pisa (3) Dipartimento di Scienze della Terra, Università di Firenze (4) Istituto di Geoscienze e Georisorse, CNR Pisa (5) Department of Resource Management and Geography, University of Melbourne, Australia Corresponding author e-mail address: [email protected] - Cover photo: Giancarlo Molli Responsible Director Editorial Board Claudio Campobasso (ISPRA-Roma) M. Balini, G. Barrocu, C. Bartolini, 2 Editor in Chief D. Bernoulli, F. Calamita, B. Capaccioni, Gloria Ciarapica (SGI-Perugia) W. Cavazza, F.L. Chiocci, R. Compagnoni, D. Cosentino, Editorial Responsible S. Critelli, G.V. Dal Piaz, C. D'Ambrogi, Maria Letizia Pampaloni (ISPRA-Roma) P. Di Stefano, C. Doglioni, E. Erba, publishing group Editorial Manager R. Fantoni, P. Gianolla, L. Guerrieri, Mauro Roma (ISPRA-Roma) M. Mellini, S. Milli, M. Pantaloni, V. Pascucci, L. Passeri, A. Peccerillo, Convention Responsible L. Pomar, P. Ronchi (Eni), Anna Rosa Scalise (ISPRA-Roma) B.C. Schreiber, L. Simone, I. Spalla, Alessandro Zuccari (SGI-Roma) L.H. Tanner,C. Venturini, G. Zuffa. ISSN: 2038-4947 [online] http://www.isprambiente.it/site/it-IT/Pubblicazioni/Periodici_tecnici/Geological_Field_Trips
The Geological Survey of Italy, the Società Geologica Italiana and the Editorial group are not responsible for the ideas, opinions and contents of the guides published; the Authors of each paper are responsible for the ideas, opinions and contents published. Il Servizio Geologico d’Italia, la Società Geologica Italiana e il Gruppo editoriale non sono responsabili delle opinioni espresse e delle affermazioni pubblicate nella guida; l’Autore/i è/sono il/i solo/i responsabile/i. DOI: 10.3301/GFT.2011.02 The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate G. Zanchetta - I. Isola - L. Piccini - A. Dini geological fieldtrips2011-3(2.1)
INDEX
Information Paleoclimatology ...... 34 Paleoclimate studies on Alpi Apuane caves with Riassunto ...... 4 special reference on Monte Corchia ...... 36 Abstract ...... 5 The laghetto core: ca. 1,000000 years of continuous record of climatic changes ...... 37 The last interglacial (MIS5e) and its end ...... 38 Excursion notes The Holocene hydrological changes and Sapropel S1 deposition ...... 40 1. Introduction ...... 6 2. General geomorphological and geological 3 framework of the Alpi Apuane ...... 8 Itinerary Karst geomorphology ...... 9 Geology of the Alpi Apuane ...... 11 Corchia Cave Ore deposits: history and metallogeny ...... 12 Stop 1: Corchia Cave Tourist entrance ...... 42 3. The Monte Corchia ...... 15 Stop 2: Galleria Franosa ...... 42 Geological setting ...... 15 Stop 3: Galleria degli Inglesi ...... 43 The Levigliani Hg deposit ...... 17 Stop 4: Galleria del Venerdì ...... 44 The karst system ...... 24 Stop 5: Galleria delle Stalattiti ...... 44 General hydrology ...... 27 The Levigliani mercury mine The monitoring system, hypogean climate and Stop 6: Cava Romana ...... 45 water geochemistry ...... 28 Stop 7: Cavetta Tunnel ...... 47 index Hypogean climate ...... 28 Stop 8: Speranza ...... 49 Water geochemistry ...... 30 Drips ...... 30 Stable isotope water geochemistry ...... 32 References ...... 51
DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1)
4 information G. Zanchetta - I. Isola L. Piccini A. Dini Monte Corchia EVIGLIANI L The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Riassunto Il Monte Corchia è una delle località tipiche Alpi Apuane nella quale, nello spazio di pochi chilometri, pos- geomorfologia fino all’attività estrattiva, di problematiche relative sibile discutere di aspetti geologia strutturale, Quest’ultimo del basamento. aspetto è di ulteriore interesse poichè l’area stata ai processi di mineralizzazione noto che all’interno recenti. È peraltro anche in tempi relativamente oggetto di ricerche e sfruttamenti minerari della successione dei marmi della sinclinale del Monte Corchia si sviluppa la più carsica d’Italia lunga cavità del Corchia) con (l’Antro ben 52 km di gallerie e pozzi. Studi recenti stanno decodificando l’immenso del clima archivio naturale all’in- passato preservato terno delle concrezioni car- del bonatiche dell’Antro Corchia e stanno rico- struendo con estremo det- climatica taglio l’evoluzione ed ambientale delle ultime centinaia di migliaia anni di questa parte del bacino Mediterraneo. chiave: Parole Geologia, Mineralogia, Paleoclima, Alpi Apuane geological field trips 2011 - 3(2.1)
5 information G. Zanchetta - I. Isola L. Piccini A. Dini Field Stops The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Abstract Monte Corchia is one of the most typical geological structure Alpi Apuane but this not only peculiar marble geology, small area it is possible to combine structural Within a very aspect of this territory. exploitation, geomorphology and ore deposits. The last point is of worth interest because the area has been the subject of ore exploitation until the recent past. Within the marble succession of the Corchia synclinal core the longest Italian cave develops with 52 km of passages and galleries. Ongoing researches are exploring the huge paleoclimatic within the preserved archives carbonate concretion of the cave and are reconstructing, with extreme detail the climatic and of this evolution environmental sector of the Mediterranean basin. words: Key Geology, Mineralogy, Paleoclimate, Apuan Alps geological field trips 2011 - 3(2.1)
6 excursion notes G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate century, but systematic century, th century. In 1934, speleologists from Florence century. Fig. 1.1 - Sketch geological map of Alpi Apuane. The Fig. 1.1 - Sketch th is also shown. distribution of ore deposits inside the metamorphic units DOI: 10.3301/GFT.2011.02 explorations began only during the first half of explorations 20 1. Introduction Fig. 1.1) is Italy, Monte Corchia (Northern Tuscany, one of the most emblematic geological structure the Alpi Apuane but this is not only peculiar aspect of this territory. small area it is possible to combine Within a very geomorphology and mineralogy, geology, and friendly paleoclimatology with a warm welcome from the typical Apuan village of carbonate Levigliani. Within the Mesozoic succession (marble and dolostone) of the Corchia develops synclinal core, the longest Italian cave with 52 km of pits and galleries (Fig. 1.2). the 11 October 1840 by Emilio Simi, a Discovered system has the Monte Corchia cave local naturalist, of Italy. long been one of the most famous caves dates to the second of the cave Initial surveying half of the 19 attained the depth of about 540 m below reach in the the greatest depth ever entrance, geological field trips 2011 - 3(2.1)
7 excursion notes G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 world at that time. In the second half of the last century the Monte Corchia system attracted hundreds of world at that time. In the second half of last century Monte Corchia system attracted and some time the competition, among speleologists from Italy and abroad. In the 1980s collaboration, passages with the depth of more than 50 km cave groups allowed the exploration Italian caving several reaching 1185 m. district of the Alpi Apuane, Monte Corchia massif is a site historical and modern Being part of the vast sources of local income. In the recent past marble exploitation, which represents one of the most traditional and in the 2001 part of Park (1985), the area of Monte Corchia has been included in Alpi Apuane Regional opened to the public. system was the cave has shown that local economic benefits can arise from a more correct use of The opening of the tourist cave Sviluppo (Cooperativa the landscape and by additional incoming produced tourism. A local cooperative tourism joining promoted important activity in the area for attracting e Futuro Levigliani) has, in the last years, the different peculiarities of this land. understood the new scientific Speleologica Toscana) (Federazione Speleological Federation The Tuscan and has logistically economically supported (since the 1998) researchers of potential of the cave, concretions including stalagmites and of Pisa, INGV and CNR for using speleothems (cave University the Monte Corchia in recent years, for reconstructing past climate conditions. So, stalactites) as an archive for reconstructing the paleoclimate and system has turned out to be one of the most promising archives Cave et al. 2007), basin (Drysdale et al. 2004, 2005, 2007, 2009; Zanchetta in the Mediterranean paleoenvironment at the global scale (Drysdale et al. 2007, 2009). Owing with implications for the chronology of climatic events seen as a locality where different aspects to this new field of research, the Monte Corchia karst is not anymore but it is now studied as an unique system in which the of local geology and geomorphology can be observed, and the history of deformation mineralization of the cave geological structure conditioned the development the radiometric from which speleothems precipitate. Moreover, influenced the chemistry of drip waters have passages formation and then unique information on the timing of cave measurement of the concretions gives the recent uplift history of this sector Apennine. This field trip is an update synthesis work which are points of view, system from several conducted by specialists who are currently working on this cave producing a new and fresh holistic view of this environment. geological field trips 2011 - 3(2.1)
8 excursion notes G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 2. General geomorphological and geological framework of the Alpi Apuane Monte Corchia is located in the southwestern part of Alpi Apuane, a mainly calcareous mountain range, (Fig. 1.1). The alpine-like about 50 km long, 20 wide and up to 1947 m high, in the NW of Tuscany a relevant setting plays factors, among which the complex structural landscape of this region is due to several steep beddings and the tectonic repetition of different rocks (mainly limestones the very role. In particular, enhanced the role of differential erosion processes. have and phyllites) tectonic fluvial erosion accompanied by rapid is presumed to be the result of heavy The present topography 2007). Glacial and periglacial et al., 2003b; Bartolini, 2003; Fellin uplift during early Pleistocene (Piccini et al., features of the processes reshaped the landscape during last glacial stages, emphasizing “alpine-like” 1986). et al., Alpi Apuane (Braschi In this respect it is interesting to remember that the first Quaternary glacial remain of whole Apennine was interesting very in the Alpi Apuane (Cocchi,1872; Stoppani, 1872). The Apuan glacial remains have discovered in fact, the Apuan chain contains lowest glacial deposits of whole Italian peninsula. In characteristics: the Equilibrium Line Altitude of glaciers has been calculated for phase of development the most extensive 1986); this is the lowest recorded in Apennine et al., the internal areas at ca. 1200-1300 a.s.l. (Braschi reported the presence of at least 9 2005 for a recent review) have studies (e.g. see Federici, chain. Several glaciers on the northern side of Alpi Apuane with estimated fronts located in an extraordinarily valley low position (down to 600 m a.s.l.). divide of the Alpi Apuane, and it is located between Monte Corchia forms part of the main surface drainage this reason, local climate is For the coastline of Mar Ligure and inner basin Serchio River. and distance from the sea. This mountain as a function of elevation by strong spatial variations characterized a large part of the 2500 mm over exceeds parts in Europe. Mean annual rainfall ridge is one of the rainiest 1999). and Vittorini, 1994; Piccini et al., ridges it is more than 3000 mm/yr (Rapetti chain and on the central close to Monte Corchia, has a mean annual precipitation of 3055 mm, one the Campagrina station, very in Italy. highest values geological field trips 2011 - 3(2.1)
9 excursion notes G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Karst geomorphology in the Apuane because high relief and regional climatic Surface karst landforms are not well developed up to 3500 mm/yr) enhance mechanical-denudation and rainfall excursions conditions (i.e. high temperature during the last glacial and postglacial active been very mechanical erosion must have processes. In particular, areas are most of the previous surface karst landforms. Only in some restricted low-relief phases, destroying represent one of the most important karst caves small to medium-scale karst landforms. On the contrary, are longer than are deeper than 1000 m and 21 caves morphological features of the Alpi Apuane: nine caves The development. in origin with a predominance of vertical are percolation-vadose 3000 m. Most of the caves between 350 and 550 m a.s.l. surfaces at elevations reach local piezometric deepest caves three major generations distribution of the phreatic and epiphreatic passages in caves, Based on the vertical system, the Monte Corchia Complex (Fig. can be identified (Piccini, 1997). In the largest cave caves of base-level (Piccini, caves by a succession of percolation (vadose) each cut vertically are preserved, 1.2), at least four levels at an altitude of 1600-1700 m a.s.l., is preserved the uppermost level part of the massif, 1997). In the central occurs between 750 m to 1000 a.s.l. In the Corchia generation whilst the second and most widely developed and the second at 1450 m a.s.l., lying above Complex, the situation is slightly different, with first generation subsequently affected between 1000 and 1200 m a.s.l.. The latter form a wide anastomosing network that was are located on the seaward entrenchment. Below 1000 m, most of the Apuan caves by a major phase of vadose is of phreatic caves Most of the third generation the SW. towards side, and possess phreatic passages that drain caves, located at an altitude of 500 to 650 m. Phreatic tubes are also present the bottom major vertical on the NE side of Apuane, whilst are still active Spring caves level. adjacent to the modern piezometric is of epiphreatic caves downcutting. Here, a new generation been abandoned by valley side they have seaward between 250 and 350 m a.s.l. There are few chronological elements by which to mark now forming at elevations in the Alpi Apuane. the age of different stages karst development were formed of Corchia cave, including the upper level we can assume that the oldest relict caves, However, a dating provides during the early denudation stage of metamorphic carbonate rock. Apatite fission-track 1988; Abbate et of exhumation timing. According to thermochronological data (Bigazzi et al., first constraint 2007), the metamorphic rocks were still buried some km depth at ~4.5-5.0 Ma. A et al., 1994; Fellin al., is the age of alluvial-fan deposits in basins surrounding Apuane, second chronological constraint geological field trips 2011 - 3(2.1) excursion notes 10 Fig. 1.2 - AIMA 2001. Corchia cave map Corchia cave plotted on orthophoto G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) excursion notes 11 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 where pebbles belonging to the metamorphic core rest on Late Pliocene – Early Pleistocene lacustrine deposits and Puccinelli, 1988). The metamorphic core Avanzi 1985; Bertoldi, 1988; D’Amato (Calistri, 1974; Raggi, 3.0-2.5 Ma as a reasonable age estimate been exhumed by this stage. On basis, we can take must have for the initial karstification of metamorphic carbonate rock. This is agreement with oldest U/Pb and 2006; Woodhead et al., U/U ages obtained from speleothems comprised between 1.5 and 2.0 Ma (Woodhead unpublished data). et al., Geology of the Alpi Apuane Metamorphic (Tuscan The Alpi Apuane represents a tectonic window that shows the deepest exposed levels Units) of the Northern Apennines (Fig. 1.1). The is formed by a pile tectonic units “oceanic” Domain) lying below the westerly-derived from the Adriatic continental margin (Tuscan derived 1975; Carmignani and Kligfield, 1990; Molli Ligurian and sub-Ligurian accretionary wedge units (e.g. Elter, 2006 and references therein). Vaselli, major tectono-metamorphic units are distinguished in the Alpi Apuane region: Massa unit and Two peak metamorphic succession with the higher-grade basement and a Middle Triassic Apuane unit. A Paleozoic the Massa 2006) characterize in metapelites (references Molli and Vaselli, assemblages, kyanite+chlorithoid unit, which is well exposed in the westernmost part of Alpi Apuane. basement (mainly sequence made up of a Paleozoic the Apuane unit shows a lithostratigraphic On the contrary, 1994)- & Passeri, (Ciarapica Upper Triassic by a well-developed unconformably overlain and metavolcanics) phyllites continental to shallow water include thin Triassic cover-rocks Oligocene metasedimentary succession. The Mesozoic carbonate platform metasediments deposits followed by Upper Triassic-Liassic Verrucano-like comprising dolostones marbles”), which are followed by Middle Liassic- Fm), dolomitic marbles and (the famous “Carrara (Grezzoni Lower Cretaceous cherty metalimestones, cherts and calcschists. to Oligocene sericitic sedimentation during drowning of the are related to deep-water and calcschists, with marble interlayers, phyllites former carbonate platform. The Oligocene-Early Miocene(?) sedimentation of turbiditic metasandstones (Pseudomacigno fm.) closes the sedimentary history of domain. The Alpi Apuane deformation structures are interpreted as formed during two main tectono-metamorphic (D1 and D2 phases of Carmignani Kligfield, 1990),regional events which are regarded as a progressive geological field trips 2011 - 3(2.1) excursion notes 12 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 deformation of the inner Northern Apennine continental margin during collision and late to post-collision 2006). During D1, SW to NE directed overthrusts (e.g. Molli and Meccheri, 2000; Vaselli, evolution axial surfaces were produced during deformation and NE-facing tight to isoclinal recumbent folds with flat-lying in mid-crustal conditions. In the following D2 history previously formed structures were refolded and achieved. geometry of the tectonic units and structures was present-day crenulation axial planar foliation were formed, In the early stage of D2, folds associated with sub-horizontal associated with semi-brittle and brittle structures, represented by kink whereas later deformation was 2010). faults (Molli and Meccheri, 2000; Ottria Molli, Molli et al., and high-angle open folds, low- 2006 and references therein), peak metamorphism data (Molli and Vaselli, P-T According to available at and early deformation D1 were realized around 350-450 °C and pressure of 0.6-0.8 GPa) (temperature at T higher than 250 °C, predated 11 1986), while early stages of D2, developed 27-20 Ma (Kligfield et al., et al. (2007). Latest stages data of Balestrieri et al. (2003) and Fellin Ma according to the zircon fission track in the last 5 Ma as 4 km, are achieved locally exceeding movements of deformation, accommodating vertical at 100-120 °C between which suggests the transition thermochronometry, by low-temperature constrained 2007 and et al., 1994; Fellin 4 and 5 Ma in most of the metamorphic tectonic window (Abbate et al., references therein). Ore deposits: history and metallogeny styles and of of mineralization a variety deposits displaying The Alpi Apuane host a number of mineral (1858) “romantic” 1994). According to Simonin’s assemblages (Fig. 1.1; Lattanzi et al., elemental and mineral of Lucca and the port Luna (now Luni, close to town Carrara) ideas, the Etruscans founded colony deposits of Alpi Apuane. The same author suggests that run out from the Pb-Ag the silver to exploit and trade since this is the “planet” support this hypothesis, to which the the name itself of Luna (meaning “Moon”) may Although the presence of Etruscans in Luna area is reported some silver. Etruscans consecrated mining activity in the Alpi historical documents, there are no definite archaeological proofs that they practiced coast, in Caesarean age the Alpi 1985). Thanks to the definite “romanization” of Tuscan Apuane (Tanelli, elegant town, and became a famous, very Apuane became the site of intense marble exploitation. Luna rapidly basin. the “marmor Luneense” one of most appreciated marbles in entire Mediterranean geological field trips 2011 - 3(2.1) excursion notes 13 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 After the fall of the Roman Empire, marbles and ore deposits of the Alpi Apuane (and all over Tuscany) fell in Tuscany) Empire, marbles and ore deposits of the Alpi Apuane (and all over After the fall of Roman time that mining only in Middle Age and especially during late Renaissance total oblivion for centuries. It was mines) 1777), where Ag-Pb (Bottino and Argentiera Tozzetti, activity flourished again in Alpi Apuane (Targioni exploited by the local mines) were actively Monte Arsiccio and Fornovolasco deposits (Buca della Vena, and Fe mining activities (Medici family). After the “Medicean climax”, of Tuscany Dukes noble families and the Grand only in the second half of XIX century completely abandoned. It was reduced, or eventually were drastically started again reaching a new climax in the period oxides, and, subsequently Fe that mining for Ag-Pb minerals II, economical interest mainly focused onto barite and mixed War After the World Wars. between the two World muds for oil drilling, and concrete in building nuclear power plants ores utilised as heavy oxide barite-Fe mines). Monte Arsiccio and Pollone (Buca della Vena, respectively the two small mercury ore deposits of Levigliani and Ripa were discontinuously exploited from Middle Finally, to the larger Hg mines of Monte Amiata area (Southern giving productions comparable Age to 1970, never collectors and scientists for the the Levigliani mine is renown in Italy among mineral However, Tuscany). Levigliani Hg deposit also hosts mercury in large droplets occurring quartz veins. common presence of native mercurian sphalerite), and is the type- zincian metacinnabar, sulfide association (cinnabar, a peculiar Hg-Zn-Fe sulphosalt grumiplucite. locality for the mercury-bismuth the mining industry in Alpi Apuane is facing typical problems of most European regions, and Today, is currently limited to ornamental stones (marble) and building materials. extraction Apart from the economic aspects, Apuan metallogenic district remains of prime scientific importance due deposits associated with a peculiar metamorphic environment. hydrothermal to the occurrence of diverse contribute to the understanding of fluid circulation and element Therefore ore deposit studies in this area may of this portion the Tuscan evolution mobilization occurred during the collisional and late to post-collisional 2001). 1998; Dini et al., 1992,1994; Costagliola et al., 1989; Lattanzi et al., et al., Domain (e.g. Benvenuti portions of the tectonic As shown in Figure 1.1, Apuan ore deposits are preferentially located the peripheral within the lower plate metamorphic units. to tectonic contacts, and almost exclusively in proximity window, where the largest outcrops of in the southern part of mountain massif, They are especially concentrated appear at a picture, two main empirical controls of mineralization From the above formations occur. Paleozoic siliciclastic and volcanic and Middle Triassic association, i.e. Paleozoic regional scale: (i) lithostratigraphic the outcrop scale At formations of the metamorphic units; (ii) tectonic structures Apenninic orogeny. geological field trips 2011 - 3(2.1) excursion notes 14 ) and 1 G. Zanchetta - I. Isola L. Piccini A. Dini ) mineralising episode. Taking into episode. Taking ) mineralising 2 ) to late-tectonic (syn D 1 The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate ) structures (Carmignani et al., 1978; Benvenuti et al., 1992; Costagliola et al., 1998; Dini et 1992; Costagliola et al., et al., 1978; Benvenuti ) structures (Carmignani et al., 2 DOI: 10.3301/GFT.2011.02 late tectonic (D account geochemistry, stable isotope and fluid inclusion data, the Apenninic metallogeny of the Alpi Apuane is stable isotope and fluid inclusion data, the Apenninic metallogeny account geochemistry, under conditions that, at least in the initial stages, were not far from peak the result of a synmetamorphic event (part of) metamorphic fluids derived metamorphic conditions, and there is evidence that the involved the elements from remobilization of pre-existing (proto-)ores. and down to the microscopic scale, mineralization is largely controlled by Apenninic early tectonic (D and down to the microscopic scale, mineralization al., 2001). Conversely, field and textural evidence suggests that a number of ore bodies or pre-concentrations field and textural 2001). Conversely, al., Pb- 2001), in agreement with the Paleozoic 1992; Dini et al., et al., (Benvenuti predate the Apenninic orogeny 1992). Pb model age of ore lead (Lattanzi et al., bimodal The first established metallogenic epoch in Alpi Apuane is apparently related to lower Paleozoic presumably affinity, and metabasites of sub-alkaline (“Porfiroidi”) represented by metarhyolites volcanism associated with this Metal concentrations (Middle-Late Ordovician). associated with the Caledonian cycle metal-enriched tourmalinites associated with magmatism should be represented by originally stratiform, 1989), and by et al., Benvenuti area (Pb-Ag-Zn; in the Bottino-Gallena-Argentiera-Valdicastello metarhyolites 2001). Due associated with metabasites and metatufites in the Levigliani area (Dini et al., Hg mineralization are difficult to establish. of these concentrations the original characteristics to the strong Apenninic overprint, is still a matter and Alpine cycles between the Variscan The existence in the Apuan area of a metallogenic event aborted associated with a pre-Tethyan is conceivably metallogeny 1994). A Permo-Triassic of debate (Lattanzi et al., initiated. In such a context, mineralization Fm) was rift during which deposition of Norian dolostones (Grezzoni paleogeographic be related to the concurrent alkaline mafic magmatism and/or specific favorable may 1985). The main expression of this inferred metallogenic 1985; Cortecci et al., et al., (e.g. Ciarapica environments deposits in the Valdicastello- diagenetic Ba-Fe is considered the formation of sedimentary-(hydrothermal?) event mines). and Fornovolasco Buca della Vena Calcaferro, Monte Arsiccio, belt (Pollone, Fornovolasco the main factor that accounts for present setting of deposits in Alpi was The Apenninic orogeny deposits at Bottino-Gallena-Argentiera-Pollone systems (most notably the Pb-Ag-Zn vein Apuane area. Several deposit at and the Cu-Fe deposit at Buca dell’Angina, area, the Hg deposits of Ripa and Levigliani, Cu-Au-Ag 2001). The 1998; Dini et al., 1992; Costagliola et al., et al., Benvenuti Frigido) were emplaced at this time (cf. evidence by isotopic dating; as previously stated, structural has not been established yet age of mineralization (syn D been early- have suggests that there may geological field trips 2011 - 3(2.1) excursion notes 15 Fig. 3.1a - Geological map of Monte Corchia area. G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 3. The Monte Corchia Geological setting since the late 1800s (Lotti, 1881; Zaccagna, The geology of this area has been the subject investigations exposures of the Valle rocks between the Paleozoic Mesozoic that time, the presence of east-dipping 1932). At overturned related with a west-facing del Giardino in the west and of Mosceta east (see Fig. 3.1a, b) was geological field trips 2011 - 3(2.1) excursion notes 16 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.1b - Cross profile of Monte Corchia. DOI: 10.3301/GFT.2011.02 syncline. A similar interpretation was followed later by Maxwell (1956). However, more recent structural studies more recent structural followed later by Maxwell (1956). However, syncline. A similar interpretation was 2000). According to the new rejected this simplified view (Carmignani and Giglia, 1983; Carmignani et al., have interpretation, the Corchia structure is result of polyphase deformation during which an originally non- refolded up to the present geometry showing syncline (D1) was facing overturned cylindrical eastward directed sense of younging. downward geological field trips 2011 - 3(2.1) excursion notes 17 G. Zanchetta - I. Isola L. Piccini A. Dini blastic phengite, chlorite, Fe–Mg–(Ca) carbonates, quartz, albite, blastic phengite, chlorite, Fe–Mg–(Ca) 1 The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate ; its abundance sharply decreases toward the contacts with the MQP. the contacts with MQP. ; its abundance sharply decreases toward 1 DOI: 10.3301/GFT.2011.02 and rare ilmenite as inclusions in the cores of carbonate crystals (Fig. 3.4). Rutile commonly occurs as small ilmenite as inclusions in the cores of carbonate crystals (Fig. 3.4). Rutile and rare prismatic crystals oriented along S The geological map (Fig. 3.1a) and cross-section 3.1b) enlighten some major features of the geology termination of the D1 syncline is well exposed in northern part the Monte Corchia area. A lateral of the D1 Corchia syncline is where the hinge zone map between the Monte Corchia peak and Fociomboli, M-structures and the related axial plane green schist foliation minor cartographic-scale exposed. In this zone, The crenulation cleavage. D2 folds associated with a sub-horizontal are refolded by open to tight east-facing cherty metalimestone in the northern part and rocks in the core of syncline are Late Jurassic youngest chloritic marbles and Oligocene metasandstones in to Cretaceous calcschists, metaradiolarites, Late Jurassic the southernmost part of map. Fm) and 40% in Jurassic dolostones (Grezzoni in the Triassic is developed About the 55% of Corchia Cave Calcari Selciferi, - Middle Jurassic in the Upper Triassic passages are carved marbles. About the 5% of cave or dolomitic marble. The boundary between dolostones and marbles does not seem to “Brecce di Seravezza” Only in the north-eastern sector some for the origin of cave. represent an important geological horizon passages follow the contact between marble and dolostone. is more influenced by passage orientations shows that the highest and oldest level An analysis of cave patterns. This can are controlled mainly by fracture levels lithological planes, whereas the lower and youngest not so occurred when the relief was development be explained assuming that the first stage of cave reduced by lithostatic load. was accentuated and the permeability of fracture The Levigliani Hg deposit The Levigliani deposit is located 2 km south of Monte Corchia (Figs. 1.1 and 3.2), hosted within the basement of the Apuane Unit cropping out below carbonate core Corchia syncline (Dini et Paleozoic metasandstones, the ore bodies occur within lowermost part of Late Ordovician 2001). Specifically, al., and in strict association with pale-green (MQP), near the contact with metarhyolites, quartzites and phyllites metabasites (Fig. 3.2 and 3.3). The (“metatufites”?) and calc-alkaline of carbonate-chloritic phyllites layers metatufites are mainly constituted by syn-D geological field trips 2011 - 3(2.1) excursion notes 18 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.2 - Detailed geological map and cross section of Levigliani Hg deposit. DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) excursion notes 19 deformation 1 ). Relics of a pre- ). Relics 2 Quartz-carbonate Cinnabar a quartz-carbonate- polished slab of typical Fig. 3.3 - Examples Cavetta Tunnel. Cavetta of Hg ores at Levigliani. a) disseminations and an isoclinally folded quartz- into a cinnabar veinlet at metatufite layer adit; Speranza b) hosted by cinnabar vein adit; metatufite, Speranza c) Levigliani metatufite showing two pyrite cubic with porphyroblasts pressure quartz-cinnabar shadows; also note some cinnabar disseminations (Ca) and Fe-Mg carbonate veinlets, adit; Speranza d) containing native veins mercury and other Hg sulfides hosted by the of the grey phyllites G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate ), representing the main foliation in field, while second 1 ) produced open folds and locally an evident crenulation cleavage (S ) produced open folds and locally an evident crenulation cleavage 2 DOI: 10.3301/GFT.2011.02 produced an axial plane schistosity (S deformation episode (D tectono-metamorphic event. attributed to a Variscan been tentatively existing foliation have In the Levigliani area, MQP are implicated in a very complex tectonic structure, produced by the interference In the Levigliani area, MQP are implicated in a very 1991). Syn-D structures (Conti et al., Apenninic deformation on earlier Variscan of Tertiary geological field trips 2011 - 3(2.1) excursion notes 20 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate . In the disseminated ore, pressure shadows of cinnabar and quartz, 1 extension lineation observed in the Levigliani area (Carmignani and Giglia, extension lineation observed 1 ratios (0.029–0.037) indicating an andesite-dacite composition and a subalkaline ratios , leading to repetition of the ore at various elevations (Fig. 3.2). elevations , leading to repetition of the ore at various 2 1 DOI: 10.3301/GFT.2011.02 affinity (Dini et al., 2001). Because of their stratigraphic position, close to the Ordovician metarhyolites, and metarhyolites, position, close to the Ordovician 2001). Because of their stratigraphic affinity (Dini et al., their compositional affinity with metabasites from different outcrops in the Alpi Apuane, that are considered 1993), a common age (Conti et al., compressional episode of Middle Ordovician to represent a calc-alkaline origin is suggested. 1–3 m thick and 100–150 long, with an average The ore bodies exploited at Levigliani comprise two main horizons, Hg metal contained is estimated somewhere between 2000 and 5000 tonnes. of 0.3-0.5 wt.% Hg. Total grade where it occurs is strictly associated with pale-green metatufite layers, As previously said, Hg mineralization veins (Fig. 3.3). Some quartz-carbonate veins both as disseminations, and quartz–carbonate-sulfide mercury and minor Hg sulfides propagate from metatufites into the MQP (e.g. at “Cavetta” containing native where cinnabar (and adit). The disseminated ore is made up of millimetric clots and patches, forming levels metacinnabar) is flattened along S coherently oriented with the D Metabasites were observed either as irregular green masses inside the metatufites, or as dyke-like bodies into either as irregular green masses inside the metatufites, or dyke-like Metabasites were observed caused a complete recrystallization of these metamorphic events the MQP (Fig. 3.2). Alpine (and Variscan?) plagioclase phenocrysts, apatite Albitized rocks, with only minor iso-orientation of the lepidoblastic minerals. some phases in some samples; by contrast, ilmenite represent the few relict mineral and leucoxene-rimmed and magmatic textures are often present, leading to the distinction between blastoporphyric well preserved 1993; Fig. 3.4). The mafic phases are completely replaced by syn- Conti et al., types (cf. blastophytic The breakdown of the original magmatic minerals carbonates, and oxides. metamorphic chlorite, Fe–Mg–(Ca) of mobile elements does not reflect the original geochemical and petrologic implies that the concentration be cautiously attempted using of these rocks may a characterization features of the metabasites. However, HFS elements, which are considered to be immobile during greenschist facies metamorphism (Winchester and (0.38–0.59), low Nb/Y ratios 1977 and references therein). The Levigliani metabasites show relatively Floyd, high Zr/TiO and relatively 1983), commonly develop around euhedral pyrite crystals (Fig. 3.3 and 3.4). The mineralized metatufite layers pyrite crystals (Fig. 3.3 and 3.4). The mineralized around euhedral 1983), commonly develop are isoclinally folded by D geological field trips 2011 - 3(2.1) excursion notes 21 l polars. G. Zanchetta - I. Isola L. Piccini A. Dini detail of a cinnabar dissemination in the metatufites at c) detail of a Fe-Mg (Ca) carbonate porphyroblast (Cb) with inclusions of (Ca) carbonate porphyroblast detail of a Fe-Mg The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate d) Cinnabar Albitized DOI: 10.3301/GFT.2011.02 ilmenite (Ilm); note the microcrystals of rutile (Rt) oriented along the S1 foliation, Speranza adit; reflected light - paralle ilmenite (Ilm); note the microcrystals of rutile (Rt) oriented along S1 foliation, Speranza Speranza adit; transmitted light - crossed polars; adit; transmitted Speranza disseminations (Cn) coherently flattened and elongated with the (Ca) carbonate metatufite S1 foliation; note the oriented Fe-Mg light - crossed polars. adit; transmitted (Cb), Speranza porphyroblasts Fig. 3.4 - Microphotographs of rocks and ores from Levigliani mine. a) plagioclase from a metabasite lens sampled along the Galleria Lunga tunnel, light - transmitted crossed polars; b) geological field trips 2011 - 3(2.1) excursion notes 22 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate detail of Type B assemblage replacing zincian metacinnabar, Speranza adit; reflected light - Speranza B assemblage replacing zincian metacinnabar, detail of Type g) trail of small inclusions of native mercury in quartz from Cavetta adit; transmitted light - parallel polars. light - parallel adit; transmitted mercury in quartz from Cavetta of small inclusions native trail h) a cubic pyrite a crystal of zincian metacinnabar (Mcn; Type A assemblage) a crystal of zincian metacinnabar (Mcn; Type DOI: 10.3301/GFT.2011.02 replaced by cinnabar II, mercurian sphalerite and chalcopyrite adit; reflected from the rim into core, Speranza the grain penetrating B assemblage) as off-shoots (Cn+Sph+Cpy; Type light - crossed polars; Fig. 3.4 - Microphotographs of rocks and ores from Levigliani mine. e) porphyroblast with pressure shadows of quartz and cinnabar, adit; Speranza light transmitted - crossed polars; f) planar polars; geological field trips 2011 - 3(2.1) excursion notes 23 ) 2 G. Zanchetta - I. Isola L. Piccini A. Dini century some very large cavities century some very ore assemblage overprinted and ore assemblage overprinted th B-type assemblage is present almost exclusively B-type , constituted by cinnabar I, zincian metacinnabarite and A-type The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate assemblage during the retrograde stages of the Alpi Apuane assemblage during the retrograde structures. It is particularly well developed at “La Cavetta” adit. Here at “La Cavetta” structures. It is particularly well developed 2 226-280 °C; wt.% NaCl equiv. 1.4-5.9; small amounts of low density CO 226-280 °C; wt.% NaCl equiv. A-type h tot phase. According to the same authors, 1 , made up of cinnabar II + mercurian sphalerite + pyrite ± native mercury ± chalcopyrite , made up of cinnabar II + mercurian sphalerite pyrite ± native B-type ore equilibrated at P–T conditions (P = 0.3–0.4 GPa; T = 385–350 °C) close to those established during conditions (P = 0.3–0.4 GPa; at P–T ore equilibrated DOI: 10.3301/GFT.2011.02 in the late stage veins controlled by D in the late stage veins partially replaced the earlier metamorphism, at temperatures not exceeding 250 °C. To the late retrograde stage should be ascribed the the late retrograde 250 °C. To not exceeding metamorphism, at temperatures 1998). The grumiplucite (a Hg–Bi sulphosalt described by Orlandi et al., occurrence of the new mineral features of the fluid inclusions (T (containing about 1 tonne of native mercury) were found. (containing about 1 tonne of native suggested that chemistry, Dini et al. (1995, 2001), based on a detailed analysis of ore textures and mineral A-type the late evolution of the D the late evolution According to Dini et al. (1995), in both disseminated and vein mineralization two distinct Hg-bearing mineral mineralization According to Dini et al. (1995), in both disseminated and vein (Fig. 3.4): assemblages can be recognized pyrite; such as quartz, Mg-rich amounts of gangue minerals, galena ± pyrrhotite. Both assemblages include variable and albite. The dolomite, calcite, muscovite, siderite, Fe-rich fall within the field previously established for fluids that circulated during metamorphism in Apuane 1994), suggesting a syn-metamorphic nature of hydrothermal metamorphic complex (Lattanzi et al., circulation at Levigliani. metatufite In conclusion, at Levigliani, a strict spatial association between the Hg ore, and Ordovician a possible be merely accidental; however, This association may and metabasites can be observed. layers must be considered, in view of the genetic relationship between the metabasites and Hg mineralization Hg deposits of the European Variscan stratabound analogies existing between Levigliani and the early Paleozoic context large deposit of Almaden (Spain), which is hosted in a lithostratigraphic including the very terrains, Saupè, 1990). somewhat similar to Levigliani (Early Late Silurian siliciclastic formations and mafic volcanics; the Hg proto-ore (cinnabar metallogenic event, Admitting the existence, at Levigliani, of a Paleozoic lost by and, in part, conceivably (in quartz carbonate veins) locally reorganized/mobilized disseminations) was of the the system during subsequent Apenninic metamorphism. The peculiar geochemical character the Hg-filled cavities, that in other stopes usually do not exceed few millimetres, may reach a relevant size; reach a relevant few millimetres, may that in other stopes usually do not exceed the Hg-filled cavities, (1777), during exploitation in the 18 Tozzetti in fact, as reported by Targioni geological field trips 2011 - 3(2.1) excursion notes 24 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Levigliani Hg ore (presence of Zn, Fe, and Bi), coupled with the peculiar temperature-pressure conditions and Bi), coupled with the peculiar temperature-pressure Levigliani Hg ore (presence of Zn, Fe, association described above produced the complex mineral reached during the Apenninic metamorphic event part mercurian sphalerite, grumiplucite) helping us to unravel zincian metacinnabar, mercury, native (cinnabar, of the metallogenic puzzle region, and contributing to shed new light on tectonometamorphic- belt. of the Southern European Variscan of this fragment magmatic evolution The karst system inside the carbonate core of Corchia syncline, almost completely enclosed The karst system is developed system occupies the by the non-karstifiable, low permeability basement (Fig. 3.1b). The presently known cave which corresponds to the northern part of this geological structure, while in the southern and lower sector, explored caves. Monte Alto ridge, there are no relevant The whole system occupies a by a high morphologic complexity. system is characterised The Corchia cave the SE. The system now of rock about 2 km long, 1 wide and high, gently dipping towards volume just below the summit of Monte Corchia. the highest of which opens at 1637 m a.s.l., has 15 entrances, which is roughly elongated according to the The geological structure strongly controls the pattern of cave, This is true for of lithological beds and main cleavage. along the strike main fold axial surface, that is to say are mostly the major conduits, which represent main collectors, whereas secondary branches oriented ca. N-S. along fractures developed passages are originated under phreatic or epiphreatic conditions, in places strongly About half of the cave as complex 3D networks incision or by local breakdown. These conduits are organized modified by vadose and with a mainly the shape of regular tubes or canyons having distributed from 450 to 1550 m a.s.l., pattern (Fig. 3.5). horizontal passages intersect the epiphreatic networks along high-gradient flows, several Due to percolation or vadose which show the typical features of deep alpine karst and are common caves, These vertical the main fractures. system from surface to the main drainage features in the other areas of Alpi Apuane, are present active intercepted by surface erosion and modified is part of a steep canyon The upper entrance collector level. collapses. several geological field trips 2011 - 3(2.1) excursion notes 25 ages. G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.5 - Sketch profile of Monte Corchia cave system. 1) Main entrances, 2) phreatic and epiphreatic passages, 3) vadose pass 2) phreatic and epiphreatic passages, 3) vadose system. 1) Main entrances, profile of Monte Corchia cave Fig. 3.5 - Sketch DOI: 10.3301/GFT.2011.02 The canyon is a relict form, probably fed by a surface basin now completely destroyed by erosion (Piccini, is a relict form, probably fed by surface basin now completely destroyed The canyon of relict phreatic tubes, locally level encounters a well-developed 1400 m a.s.l. the canyon 1991, 1994). At direction of main cleavage. from NW to SE following the structural modified by rock falls, which develops oriented, phreatic morphologies became dominant of SW-NE to the SE after a long and deep canyon Trending sections of elliptical tubes. well-preserved and the galleries display geological field trips 2011 - 3(2.1) excursion notes 26 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate /s, flows in conduits partially water-filled. This circumstance is due to /s, flows in conduits partially water-filled. 3 DOI: 10.3301/GFT.2011.02 The morphology of these galleries suggests a relevant recharge of allogenic waters, which deposited conglomerates recharge of allogenic waters, The morphology of these galleries suggests a relevant pebbles. These pebbles consist of non-metamorphic sandstones coming from the Tuscan with well-rounded exotic catchment, which thus implies a cave or Ligurian nappes, lithologies which do not outcrop in the present day closes with a the SE, level different from the present one (Piccini, 1991, 1998). To morphologic setting very some ancient calcite deposits, now rockfall. In the last part, conduit system preserves large non-penetrable wall. collapse of cave because of the gravitational altered and mostly broken heavily and of which are still active many cut this paleo-phreatic level, caves of high-gradient different generations Several level almost horizontal More than one connection reaches a lower, water. of local infiltration are the present pathways has a most irregular plane pattern of phreatic tubes, which is located at an altitude ca. 1300-1350 m. This level in the marble rock. is completely carved system described above All the part of cave without significant diversion. and reaches a entrenchments descends northward one of the vadose part of the cave, In the north-western of phreatic and epiphreatic conduits at 1150-1200 m a.s.l.. Most these level second and more developed Fm). The pattern is complex, and it often difficult to recognize in dolostone (Grezzoni galleries are carved the main conduits from secondary ones. down along large In the SE sector upper system of phreatic conduits (1300-1450 m a.s.l.) trends gradually intersects the This large canyon modified and incised by free flow of a large quantity water. galleries heavily probably connected with the was of the karst complex at 1100-1200 m a.s.l. This level major phreatic level entrench some of these system of phreatic galleries. Deep canyons NW section to form a single and ramified Some vadose base level. incision close to the hydrological phreatic tubes, indicating a long phase of vadose between 900 and 800 m. The of phreatic conduits located about 200 m below, lead to a further level pathways in the inner part of system, where an underground stream, whose mean is still active level third cave discharge is presently around 0.15 m the occurrence of a structural dam that consists of low-permeability rocks (“Brecce di Serravezza” and “Scisti rocks (“Brecce di Serravezza” dam that consists of low-permeability the occurrence of a structural stream deepens with a long active obstacle the subterranean a Cloritoide”). Downstream of this structural an altitude of 600 m, the stream encounters a up to 40 m high. At stepped by a series of waterfalls canyon level. phreatic conduits, which indicates another local perched piezometric of water-filled further level at 600 m a.s.l. in the last section of cave The stream flows along an unknown path, and then re-appears morphology until it with a step-and-pool canyon the SE along a vadose stream deeps towards The cave at 450 m a.s.l. reaches the present bottom of cave, geological field trips 2011 - 3(2.1) excursion notes 27 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate /s (Piccini, 2002). 3 DOI: 10.3301/GFT.2011.02 General hydrology of the carbonate core structure of the Corchia karst system consists almost exclusively The hydrological No significant allogenic recharge Vezza. Monte Corchia-Monte Alto syncline, which is cut by the Torrente that in restricted areas on the east side of Monte Alto and lower part hydrological occurs, except system. Dolomite and marbles are the main karst aquifers. tests performed by the Federazione dye The catchment area is well depicted on the basis of several Corchia are located in 2002 and references therein). The springs that drain (Roncioni, Speleologica Toscana rises at 176 m a.s.l. Water Stazzemese, a few hundred meters upstream of Ponte Vezza, of Torrente the valley stream channel, that is the opposite side with respect to points in the left side of Vezza from several springs mantled by slope rock-fall, Here there are several the riverbed. Corchia system, a few meters above or “Cardoso” springs. which together are named “Le Fontanacce” some perennial and occasionally active, of this group springs, which are A precise measure of discharge is difficult due to the characteristics On the basis of few measures, mean discharge is though to be about distributed along the riverbed. 0.12 m The feeding karst area is well defined, being bordered by a belt of Paleozoic basement. The cave stream basement. The cave The feeding karst area is well defined, being bordered by a belt of Paleozoic under a rock collapse, at an altitude of 450 m a.s.l. and about 3 km disappears at the bottom of cave, from Cardoso spring. geological field trips 2011 - 3(2.1) excursion notes 28 G. Zanchetta - I. Isola L. Piccini A. Dini The monitoring system, hypogean climate and water geochemistry Hypogean climate meteorological monitoring Corchia Cave, At since 1998 by ARPAT has been in operation per la Protezione (Agenzia Regionale Further monitoring Toscana). dell’Ambiente, (URB-1 and URB-2) stations for temperature of Urbino were installed by the University of the project supported by within the frame M. Menichetti since 2005. Three the Prof. been installed meteorological stations have along the tourist path (Fig. 3.6). Station is at the intersection of tourist ARPAT-1 path (870 m artificial tunnel and the natural is located at “Galleria a.s.l.); station ARPAT-2 about 1.4 km from the entrance del Venerdì”, is located at at 830 m a.s.l.; station ARPAT-3 “Galleria delle Stalattiti” near URB-2, at 840 m a.s.l. and about 2 km from the artificial meteorological stations (MT-1 Two entrance. wind rain, measuring temperature, and MT-2), been speed and atmospheric pressure, have installed on the Monte Corchia slopes at two different elevations. The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.6 - stations. Location map of the monitoring DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) excursion notes 29 G. Zanchetta - I. Isola L. Piccini A. Dini Fig. 3.7 - Temperature measured in different stations the Corchia cave Fig. 3.7 - Temperature Galleria delle Stalattiti. (see figure 3.6 for station locations). Note the significant stability of The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Figure 3.7 shows the temperature fluctuations of the two external stations and three inner stations and MT-2) (MT-1 2 and URB-2) during the year (ARPAT-1, the fluctuations emphasize 2005. Typical and extreme stability of stations ARPAT-2 as expected URB-2 compared to ARPAT-1, for the deepest sectors of cave. has a mean annual Station ARPAT-1 significantly lower than the temperature due to the fact that it is located other two, through which near two lower entrances while ARPAT- cold air enters during winter, 2, which is more than 1 km from the is only marginally influenced entrances, In fact, the by external temperature. for maximum fluctuation in temperature is 4 °C, corresponding to station ARPAT-1 to 9.3 the minimum external temperature ranges the temperature ARPAT-2, °C. For from 7.6 °C to 9.0 °C. of the air coming from and both the stations record temperature the air flows downward During summer, clearly shows The graph walls. which here is already in thermal equilibrium with the cave upper entrances, the two stations temperature, the mean cave rises systematically above than when the external temperature indicating that the airflow changes direction. reach soon almost the same temperature, in agreement with stable in terms of temperature, The station URB-2 at the Galleria delle Stalattiti is relatively from a minimum of 7.3 °C ranges Temperature entrances. its position, nearly 2 km from the nearest natural (in March) to a maximum of 8.1 °C October and November). geological field trips 2011 - 3(2.1) excursion notes 30 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Water geochemistry been performed. Most have waters surface and cave chemical analyses of rain, several In the last ten years, been obtained from sites along the tourist path, although some samples have analyses have water of the cave been extensively been collected in the upper and less known sector of karst system. These data have has been started and waters discussed recently by Piccini et al. (2008). Since April 2009 a monitoring program month at the station CNR1 and CNR2 (Fig. 3.6) are collected every lake from 2 selected drip and one hypogean waters chemical features of the cave the most relevant for chemical and isotopic analysis. Here we summarize useful for paleoclimatological interpretations in particular form the data obtained from two stations. Drips (especially in the area of tourist different parts of the cave been collected over samples have Drip water of the feeding path) but only for CNR1 and CNR2 there are enough data a meaningful characterization The longest sampling period is for CNR2 station. waters. (Figure 3.8a). The CNR1 drip is are Ca-Mg bicarbonate waters of the two drips and lake The waters (figure 3.8b). The latter ones by a higher percentage of bicarbonate than CNR2 and the lake characterized show a higher content of the CNR2 and lake major content of sulphate. Moreover, a relatively have magnesium (Figure 3.8c). These chemical differences could reflect the different bedrocks along path of including an impermeable at the two stations. In fact, CNR 2 is underlain by a thick layer waters rain infiltrating Instead at CNR1, the rock dolomite with the presence of “Grezzoni”. and metavolcanics, basement of phyllite by is a well karstified marble. Furthermore, the chemistry of CNR2 drip extremely stable and characterised (Fig. an enrichment of Mg in relation to the calcium content if compared CNR1 drip and rainwater solid and the by higher content of dissolved is characterized 3.8d). This, with the fact that CNR2 waters in the of long residence time the waters condition, supported the hypothesis mentioned structural above are feeding the system compared to CNR1. Some tritium measurements confirmed that CNR2 dripwaters 2008). “older” than CNR1 ones (Piccini et al., geological field trips 2011 - 3(2.1) excursion notes 31 HCO3-SO4-Cl Mg/Ca molar Langelier- SO4 vs. Mg Fig. 3.8 - and lake waters. and lake Water geochemistry of Corchia waters: a) Ludwig classification that diagram identifies one water that is family, carbonatic waters; b) for ternary diagram and drip waters that waters, lake highlights the higher relative content on bicarbonate for CNR 1 drip and on sulphate for CNR 2 drip and lake waters; c) for diagram and lake dripwater waters; d) vs. Mg ratio for drip diagram rainwaters, waters, superficial external G. Zanchetta - I. Isola L. Piccini A. Dini b d The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate c a DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) excursion notes 32 H2O O 18 d - H2O H 2 d Fig. 3.9 - G. Zanchetta - I. Isola L. Piccini A. Dini Water Line. Water diagram fro CNR1 and CNR2 diagram stations (after Piccini et al., 2008). CMMWL: Central Line; Water Mediterranean GMWL: Global Meteoric -30 -35 -40 -45 -50 -55 -60
2 δ H (H O) 2 diagram. Almost all waters plot closely to Almost all waters diagram. H2O O 18 d - H2O Ο + 10 18 H δ 2 d = 8
Η 2 δ The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate lucchesi" "Risalita dei "Risalita " Vidal River" " Vidal "Gronda Stream""Gronda Ο + 15 18 δ CNR1 station Pools GMWL Stream water CMMWL CNR2 station "Artificial Entrance" = 8
Η 2 δ O) 2 (H O 18 δ DOI: 10.3301/GFT.2011.02 10 -9.5 -9 -8.5 -8 -7.5 -7 -6.5 -6 Stable isotope water geochemistry plotted in the Figure 3.9 shows the Corchia waters the Central Mediterranean Meteoric Water Line (CMMWL), with a deuterium excess (d) of 15 (Longinelli and Line (CMMWL), with a deuterium excess Meteoric Water Mediterranean the Central Line without reaching the Global Meteoric Water 2003). A few of the data points show lower d values Selmo, is mainly due to CNR1 station, the drips collected at entrance (GMWL, with a d = 10). The spread of values (the latter collected only once in March 2005). The lower isotopic in the artificial gallery and flowing waters from snow derived of water can be explained by infiltration in particular those of the flowing waters, values, from higher altitude derived 1998) and, possibly, (Mussi et al., by lower d values melting, usually characterised recharge areas. - geological field trips 2011 - 3(2.1) excursion notes 33 Fig. 3.10 - Oxygen al., 2008). al., isotopic composition of drip points CNR1 and CNR2 (after Piccini et
G. Zanchetta - I. Isola L. Piccini A. Dini 20/02/07 0.6 ±
H (TU)
3 4.0 28/12/06
CNR1 station CNR2 station
10/12/06
26/11/06
28/10/06 29/09/06 0.7 ±
H (TU)
3 5.5
22/09/06 16/04/05
The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate 16/03/05
Date of collection 24/09/04 (1week) 24/09/04 0.6 ±
H (TU)
2.7 3
17/09/04 (3 months) (3 17/09/04
04/01/2004 13/12/2003 0.4 ±
H (TU)
2.2 3
22/08/03 07/06/03
-8.0 -7.8 -7.6 -7.4 -7.2 -7.0 -6.8 -6.6 -6.4 -6.2 -8.4 -8.2
O‰ O‰ δ 18 DOI: 10.3301/GFT.2011.02 Figure 3.10 shows the oxygen isotope composition of the drip stations CNR1 and CNR2 along with four Figure 3.10 shows the oxygen determinations of tritium content. In detail, the data show substantial stability station CNR2 (mean: - for station CNR1 (mean: -7.3±0.4‰). The different 7.4±0.1‰) and a significantly higher variability that there is no mixing of of the two stations is replicated by tritium data. On hypothesis behaviour for CNR2, and values of different ages, the tritium data suggest residence times ca. 50 years waters do not support of sampling for CNR1. The data available consistent with precipitation occurring within the year between CNR1 and CNR2, which significant differences in the altitude of recharge (ca 0.1‰ on average any to be influenced by of CNR1 likely can locally represent less than 100 m (Mussi et al. 1998), with the values out in the case of CNR2. which is averaged isotopic variability, rainfall seasonal effects and year-to–year geological field trips 2011 - 3(2.1) excursion notes 34 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate -century climate change, but they can help us to better understand the nature of this challenge”. st DOI: 10.3301/GFT.2011.02 Therefore, quantitative paleoclimate data are of paramount importance for understanding the climate system paleoclimate data are of paramount Therefore, quantitative and offer past scenarios for testing climate models, which are at the base of our future projections. important resources seem certain to have and water predictions of future climate, changes in rainfall Given of region (Giorgi 2006). Understanding the variability socio-economic and political impacts in the Mediterranean different time scales is therefore an essential prerequisite for establishing predicted future over hydro-climate region is 2002). The Mediterranean climate change and its possible impact on human society (Mariotti et al., long and rich history of human use, including some the world’s and has an exceptionally both climate-sensitive information on climatic which preserve archives of natural most important past civilisations. The investigation importance to understand the is of paramount thousands of years changes in the last several and hydrological 2010). et al., causes and the potential impact of changes in next future for this area (Robert from the global to regional the climatic variability to understand which mechanisms transfer Moreover, chronology. records with precise and accurate detailed regional proxy scale it is necessary to have within the palaeoclimate community because of rich wealth marine- and ice-core records are celebrated Many non- we still lack the means by which to date them precisely or verify However, of information they preserve. questions about palaeoclimate, based age models. Precise control is vital for addressing many radiometrically Paleoclimatology and its about humanity facing at present the serious problem of global warming The increasing awareness potentiality to cause significant climatic changes, which are caused or amplified by anthropogenic activities, neither a political fields of science. Although, Earth scientists can provide poses important challenges for many nor an economical answer to this problem, they can contribute obtain a better knowledge of the climate a complete picture of considered not to be long enough give system. The instrumental record is generally of the era beyond It is crucial, therefore, to extend the record of climatic variability climatic variability. can be, how rapidly climatic variations instrumental measurements if we are to understand how large natural climatic changes on regional and global scales, what change, which internal mechanism drive climate may and C. Cox recently by P. this is well summarized external or internal forcing factors control them. Overall, data cannot tell us how to meet the challenge of Jones (2008) on Science where they stated: “Paleoclimatic managing 21 geological field trips 2011 - 3(2.1) excursion notes 35 C respond to climate 13 G. Zanchetta - I. Isola L. Piccini A. Dini d O and 18 d C offers important insights on change local amount 13 d O and 18 d The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate C) isotope ratios are amongst the most widely used climate proxies in are amongst the most widely used climate proxies C) isotope ratios 13 d O) and carbon ( 18 d DOI: 10.3301/GFT.2011.02 of precipitation (Bar-Mattehws et al. 2000), storm-track trajectory (especially when it is coupled with the study trajectory et al. 2000), storm-track of precipitation (Bar-Mattehws and biological activity of 2000) and change in typology of vegetation of fluid inclusions, e.g. Matthews et al., in speleothems has variation et al. 1998). The study of trace-element catchment (Dorale a cave the soil over of the new 2006), thanks to the development et al., (Fairchild in recent years dramatically accelerated to climatic change U and Na are responsive Ba, P, studies show that Mg, Sr, techniques of laser ablation. Many as with stable isotopes the relationships between climate and (e.g. Hellstrom and McCulloch, 2000). However, 2006). Fluorescence changes in et al., response appear to be location-specific (Fairchild trace-element soil (McGarry in the degree of humification organic matter overlying speleothems reflect variations amount and and rainfall 2000). The degree of humification is mainly controlled by temperature and Baker, So, for these climatic parameters. can act as proxy in fluorescence peak emission wavelength variations studies with high resolution, especially if accompanied by speleothems are suitable material for multiproxy coupled with meterological data collected at regional scale. environment of the cave monitoring programme like the timing, duration and inter-hemispheric phasing of terminations, the duration and structure of phasing of terminations, the duration and inter-hemispheric the timing, duration like interglacials, the timing and process by which Earth plunges back into a glacial stage so on. calcite precipitates, e.g. stalagmites, stalactites, flowstones) are highly regarded in the Speleothems (cave and paleoclimate. This relies from the of paleoenvironment international scientific community as archives to environmental highly sensitivity of speleothem properties (e.g. chemical composition, growth rate) the However, the cave). biological activity in the soil above amount of rainfall, (e.g. temperature, parameters of this success is the possibility to obtain a robust age control. Indeed, speleothems are arguably most key potential, preservation 2003) because of their excellent ideal material for U/Th dating (Richards and Dorale, the last 15 in analytical techniques and technologies over systems. Developments particularly in deep cave three orders of magnitude, to required for a U/Th date fall by over seen the amount of uranium have years age estimate can now be obtained from as little a few billionths of the point where a precise and accurate plasma-source mass spectrometric techniques (Hellstrom, 2003). using advanced of uranium gram Oxygen ( speleothems studies (e.g. McDermott et al., 2006). The way in which 2006). The way speleothems studies (e.g. McDermott et al., through time varies markedly for different region to the Earth, so it is essential to have knowledge of the for different region to the Earth, so it is essential have markedly through time varies site. However, controlling factors at a given geological field trips 2011 - 3(2.1) excursion notes 36 Th (e.g. 232 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Woodhead et al., 2006; Drysdale et al., 2009) 2006; Drysdale et al., et al., Woodhead (ca. 5 to U concentration by an elevated and are characterised the application of U/Th particularly successful and, recently this has allow to apply with 25 ppm). This make to 2006). Therefore coupling different methods linked et al., results the U/Pb technique (Woodhead excellent the use of U-series, now it possible to affirm that Corchia (in particular Galleria delle Stallatiti) can preserve from extensive an almost continuous record of the climatic change during last ca. 1.5 Ma or more. Results showed that Corchia speleothems capture the last years and careful reconnaissance work conducted over marine sediments at least for the last 400 ka. major palaeoclimate changes recorded in North Atlantic isotopic composition significant is the oxygen Particularly Some outstanding examples are discussed below. the of speleothem calcite, which can be mainly related to changes in the amount precipitation over 2004). The amount of precipitation, in turn, seems to be related catchment area (e.g. Drysdale et al., masses released to this Circulation through the amount of vapour changes in the Meridional Overturning in calcite are related isotopic values 2009). So that higher oxygen (Drysdale et al., sector of Mediterranean are reduced. Whereas, lower oxygen from the Atlantic masses advection to colder condition when vapour from the masses advected and increase in vapour are usually related to climatic improvement isotopic values to this region. Atlantic Paleoclimate studies on Alpi Apuane caves with special reference Monte Corchia of particular interest for paleoclimatological purpose a high number of caves The Alpi Apuane area preserves triggered a high amount of rainfall 2006). They receive 2005; Drysdale et al., 2003a; Isola et al., (Piccini et al., moisture sourced from the Atlantic eastward-moving influence, which mainly traps orographic by the Apuane’s this area is close to the Gulf of Genoa, one most important Moreover, and the western Mediterranean this area particularly This concomitance of factors makes formation in the Mediterranean. area of cyclone circulation. the Mediterranean over suitable for studying past climatic changes and the role of North Atlantic with the Federazione of Pisa, in collaboration the Earth Science Department of University Today, of Florence, the IGG-CNR, the Earth Science Department of University INGV, Speleologica Toscana, in caves of Melbourne and the SUERC Glasgow is studying several of Newcastle, the University University Grotta del Vento. di Mosciano, che Urla, Tana Tana the area: Antro del Corchia, Grotta della Renella, been obtained from Antro del Corchia. Indisputably the most important scientific results have of the Corchia speleothems is that they are virtually free One of the special characteristics geological field trips 2011 - 3(2.1) excursion notes 37 G. Zanchetta - I. Isola L. Piccini A. Dini O stack’ (2005) (a standard 18 d reference series for global ice-volume changes) and ice-core palaeotemperatures from EPICA (Antarctica, e.g. community members, 2004) shows it b The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Drilling operation within the "Laghetto Drilling operation a) The CD3 just extracted: it contains ca. 1 Ma of The CD3 just extracted: m resolution stable isotope record has been compiled from a 23-cm thick core (CD3 core, Fig. 3.11b, b) m Fig. 3.11 - climate history. a basso"; DOI: 10.3301/GFT.2011.02 The laghetto core: ca. 1,000000 years of continuous record climatic changes drilled in 2007-2008 (fig. 3.11a). The “Laghetto basso” is a small pool within “Galleria delle Stalattiti” and was work for the setting explorations, of cavers if years even monitoring program This pool is now under an extensive chemistry and producing pollution. influenced the water the tourist path and frequentation have A 200- Drysdale et al. in progress). This record appears to be continuous and spans the period 0–0.960 Ma. Currently, ages and by tying sections of its isotope profile to other dated Corchia its chronology is based on 12 U-Th ‘LR04 benthic comparison with Lisiecki and Raymo’s stalagmites. Nevertheless, geological field trips 2011 - 3(2.1) excursion notes 38 D d G. Zanchetta - I. Isola L. Piccini A. Dini O stack (Lisiecki and Raymo, 2005). Note the O stack (Lisiecki and Raymo, 18 d Fig. 3.12 - The "Laghetto core" isotopic record impressive correlation. impressive (a proxy for paleotemperature, EPICA 2004) and LR04 for paleotemperature, (a proxy benthic compared with some of the most famous records: EPICA The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate continental As far as we are . O record indicate a 18 d radiometrically datable O stack’, but in this case must reflect O stack’, 18 d C, which show a very similar features of the LR04 C, which show a very 13 DOI: 10.3301/GFT.2011.02 more effect of climate on soil above the cave. more effect of climate on soil above The last interglacial (MIS5e) and its end The last interglacial is probably one of the most studied period of the Earth climate for its potential to represent higher than current a phase of climatic warming interglacial in absence of human perturbation. Evidence following the last of millennial-scale cold events in North interglacial optimum are well preserved marine cores, Greenland ice, and pollen records Atlantic et al., 1993; Kukla from Europe (e.g. Dansgaard et al., 2002 among others). benthic record of this duration and continuity exists. It is record of this duration interesting to note that the clearly preserves every glacial-interglacial transition every clearly preserves (Fig. 3.12) of the last million years no other aware, significant changes of the average values at ca 500 values significant changes of the average ka, which cannot seen so clearly in the marine record. of rearrangement indicate a general This may in this area (possibly reflecting cycle hydrological changes in at more regional scale, like some event from North advection the amount of vapour patter is maintained though the general Atlantic), is supported by the into the details. This observation d geological field trips 2011 - 3(2.1) excursion notes 39 O record 18 d G. Zanchetta - I. Isola L. Piccini A. Dini Fig. 3.13 - Comparison between the Eemian aridity pulse (Sirocko et al., 2005). et al., Eemian aridity pulse (Sirocko from Corchia Speleothems (different colour means record obtained from different stalagmites; after 2009 and unpublished data) Drysdale et al., 2007). Cold et al., Monticchio pollen record (Brauer 1994; 2006. LEAP: late- after McManus et al., event However, their timing was previously mostly their timing was However, dating. A composite undetermined by radiometric record formed by 4 different stalagmites has permitted to reconstruct a detailed paleoclimatic record between ca. 150 to 90 yr allowing capture in detail some important climatic changes (Fig. 3.13). Detailed correlation with north Atlantic marine core record shows that the penultimate II) commenced glacial termination (Termination before the present, too 141,000 ±2500 years early to be explained by Northern Hemisphere summer insolation but consistent with changes in 2009). This is obliquity (Drysdale et al., Earth’s in the particularly important because variations intensity of high-latitude Northern Hemisphere largely by precession of summer insolation, driven are widely thought to control the the equinoxes, timing of Late Pleistocene glacial terminations. The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) excursion notes 40 O values of the first O values 18 d G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate O record with the pollen record of Monticchio (Brauer et al., 2007), et al., O record with the pollen of Monticchio (Brauer 18 d DOI: 10.3301/GFT.2011.02 However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism obliquity may recently it has been suggested that changes in Earth’s However, (Hubert, 2006). Using these this last hypothesis and the data of Corchia substantially corroborated which dated important cooling events, speleothems Drysdale et al. (2007) were also able to radiometrically responsible for the demise of “Eemian forest” was in southern Europe and close the last Interglacial. Figure the comparison of this 3.13 illustrate which is considered one of the best dated record of the last 140 ka in the Mediterranean region. which is considered one of the best dated record last 140 ka in Mediterranean if some events even According to figure 3.13 there are evident differences between Corchia and Monticchio, appear chronologically consistent. From these figures (if the correlations proposed are correct) Monticchio chronology appears less robust than usually believed. The Holocene hydrological changes and Sapropel S1 deposition The small stalagmite CC26 has yielded one of the most remarkable and complete record Holocene for ca. the last 13 ka (so including late part of Late Glacial). The stable the Italian peninsula covering between ages, indicates enhanced regional rainfall isotope record from CC26 supported by 17 uranium-series 2007). Within this phase, et al., ca. 8.9 and 7.3 kyr cal. BP at the time of sapropel S1 deposition (Zanchetta occurred between 7.9 and 7.3 kyr cal. BP (Fig. 3.14). Comparison with different marine the highest rainfall 2000), suggests Matthews et al., Bar- record (Israel, records, and in particular with the Soreq Cave and lake basins. and Eastern Mediterranean between the Western substantial in-phase occurrence of enhanced rainfall are also recognizable. It is interesting to note that the average minor events However, part of the Holocene are systematically lower than the second half of the Holocene (Giraudi et al., 2010). This et al., part of the Holocene are systematically lower than second half (Giraudi in agreement with other from the North Atlantic, decreasing of moisture advection suggests a progressive region probably linked and in the Sahara in the Mediterranean evidence that report decrease amount of rainfall 2000). decrease in summer insolation (e.g. deMenocal et al., to progressive geological field trips 2011 - 3(2.1) excursion notes 41 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.14 - CC26 oxygen isotope record (after Zanchetta et al., 2007). Possible colder/drier events are colder/drier events 2007). Possible et al., isotope record (after Zanchetta Fig. 3.14 - CC26 oxygen highlighted (light grey box). Two wet phases during Holocene are also indicated. Two highlighted (light grey box). DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) itinerary 42 Fig. 3.15 - Corchia location of the stops. cave map showing the cave G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Field Stops DOI: 10.3301/GFT.2011.02 Corchia Cave Stop 1: Corchia Cave Tourist entrance to the introduction history of The first stop is devoted and its opening to the tourist of Corchia Cave the exploration view of the a general (Fig. 3.15). From the artificial entrance main structure of the Monte Corchia can be outlined and briefly discussed, as well geomorphological features. Stop 2: Galleria Franosa is the first passage we meet entering The Galleria Franosa through the artificial tunnel. In first and upper part it a descending tubular phreatic tunnel. looks like a large and deep canyon- Along the iron stair we observe high while the floor The ceiling is very gallery. like consists of a steep debris slope. If we carefully look at large rounded we can observe morphology of the walls vadose niches (scallops) and no sign of a progressive that this tunnel is not can so realize entrenchment. We but a conduit formed under phreatic really a canyon were probably conditions, whose ceiling and walls In the last part a very flowing upward. reshaped by water peculiar deposit formed by small rounded pebbles This cemented by sparitic calcite mantles the left wall. sediment is probably due to in-site reworking of rock during floods. flowing water debris by upward geological field trips 2011 - 3(2.1) itinerary 43 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.16 - The cross profile of “Galleria degli Inglesi” showing the location stops 1-4. DOI: 10.3301/GFT.2011.02 Stop 3: Galleria degli Inglesi in the sixties by British cavers are at the beginning of Galleria degli Inglesi (Fig. 3.16), discovered We three different tunnels along a fracture Here we can observe of Buca d’Eolo. coming from the upper entrance oriented. The lower passage shows a downcutting phase and leads to the rim of 30 m deep about NNW-SSE pebbles of non- Suzanne). In this part we found an alluvial deposit containing rounded exotic pit (Pozzo the pebbles come from an upper is still problematic. Probably, metamorphic sandstone, whose provenance system, through an unknown path. In fact similar pebbles can be found in the highest part of the cave level during the first phase of of the Corchia complex (at 1450 m a.s.l.) and were probably deposited into cave different from the present one. very of the karst, when landscape Alpi Apuane was development geological field trips 2011 - 3(2.1) itinerary 44 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Stop 4: Galleria del Venerdì (first pool) flow directed to SE. is a large tunnel formed under phreatic condition by water The Galleria del Venerdì due to air bubbles or mixing corrosion testify the phreatic origin. Alluvial deposits consisting Ceiling pockets there are not clear forms due to incision under vadose of sand and pebbles testify a phase filling, anyway first almost completely filled with sediments. Almost certainly this condition, probably because the gallery was fed by the Galleria Firenze first than the Galleria degli Inglesi, which was deactivated was part of the cave sediments during a long epiphreatic phase. removed progressively Slow flowing waters branch. Stop 5: Galleria delle Stalattiti of the whole Corchia system. Here we are ca. 400 m below surface. In this This gallery is the most decorated clastic deposit. On this old flowstone a poorly preserved gallery a first flowstone (older than ca 1.5 Ma?) covers with the most phases of concretions represented by different stalagmite generations, there are several conspicuous phase seems to be related Middle Pleistocene, whereas fewer stalagmites active using cores. investigate which was during Holocene. Similar complexity is recorded in the flowstone stratigraphy, structure, which is due to phases of enhanced air flow in the cave Most of the stalagmites show a pop-corn like and extremely reduced drip supply (most are visible in the lower part of gallery). These structure can be 2004), been related to glacial conditions (e.g. Drysdale et al., found also in the stalagmite section and have tall gallery series, white part of the very In the central present outside the cave. when harsh climate was deposition not well understood. phase of aragonite stalagmites are present. These related to a generalised studied and dated as well more than stalagmites (plus a minor number collected in situ) was broken Several produced ages indicated the most important phase of concretion was 6 m of flowstone cores. Radiometric by some phase of partial interruption, probably between ca. 100 to 800-900 ka, although this seems marked cannot rule out that some particular due to local changes in the flow paths and/or climatic condition. We carbon isotope regulated phases of depositions. However, prominent phases of tectonic uplift can have did not change the cave composition from speleothems seems to suggest that the soil-epikarst system above much in the last million year. geological field trips 2011 - 3(2.1) itinerary 45 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Fig. 3.17 - Schematic map showing the underground works at Levigliani mine and the geological stops. DOI: 10.3301/GFT.2011.02 The Levigliani mercury mine The mining works of Levigliani (Fig. 3.17), abandoned in a touristic been recently transformed since 1970, have e Futuro Sviluppo mining park (managed by Cooperativa of The old mining plants and the entrance Levigliani a.r.l.). the underground works are now easily accessible and part of tunnels are safely and scenically lightened. The tourist visit of the Hg mine is part so-called “Corchia an interesting to provide underground” project, developed and artificial underground cavities. view of both natural in detail The outcrops of Hg orebodies can be observed and openings tunnels, ramps thanks to the several during the mining activity. excavated Stop 6: Cava Romana office near the entrance This adit come first after the ticket of the mining park. A short crosscut drift (ca. 25 m long; 518 m a.s.l.), almost orthogonal to the main scistosity, allows the access at base of an inclined excavation of the opening descending from the surface (entrance inclined room is at 535 m a.s.l.). An green (max. 1 meter thick; N20 45E) with metatufite layer exploited by room was cinnabar disseminations and veinlets (Fig. 3.18a). The large pillar sustaining and pillar operations geological field trips 2011 - 3(2.1) itinerary 46 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate the quartz-carbonate veins the quartz-carbonate The inclined an exploitation opening at Speranza adit (Stop 8). Speranza c) Cavetta adit (Stop 7); Cavetta containing native mercury at containing native b) adit (Stop 6); surface at Cava Romana surface at Cava descending from the excavation opening excavation a) at Levigliani mine. underground works Examples of Fig. 3.18 - DOI: 10.3301/GFT.2011.02 geological field trips 2011 - 3(2.1) itinerary 47 ) 3 G. Zanchetta - I. Isola L. Piccini A. Dini O and Hg. 2 The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate . The veins are hosted by grey phyllites placed at the hanging wall of a metatufite placed at the hanging wall are hosted by grey phyllites . The veins DOI: 10.3301/GFT.2011.02 Stop 7: Cavetta Tunnel and separation adit the path crosses remains of plants for mineral Romana of Cava After the entrance adit (530 m a.s.l.). The Cavetta mercury distillation. Then the path rise to main mining area: Cavetta used for drawing of the ore deposit. It was zone tunnel represented the access route to main productive air and (cinnabar) adits, as well for intake Hg) and Speranza (native off the ore from both Cavetta quartz-carbonate of sub-parallel into a swarm along strike driven tunnel was haulage. The Cavetta mercurian sphalerite, pyrite, chalcopyrite, etc. (Fig. 3.18b and cinnabar, mercury, with native veins/veinlets grey prismatic crystals of a new bismuth-mercury tiny ago were discovered 3.19a-b). Here, about ten years (1-10 mm small cavities display 1998). Quartz veins sulfosalt: the grumiplucite (Fig. 3.19d; Orlandi et al., the hanging-wall is made by metatufite showing its typical structure/texture with several generations of strongly generations is made by metatufite showing its typical structure/texture with several the hanging-wall mercury. native with cinnabar and rarely veins and quartz-carbonate veinlets deformed Fe-Mg-carbonate Coming a large hole now filled by clear water. leaving continued few meters under the drift level Exploitation was few meters below the lower contact with metatufites, it grey phyllites, back along the drift into hanging-wall mercury that crosscut the main with droplets of native veinlet a small quartz-carbonate is possible to observe by late-tectonic re-mobilization of represents the escaping path of Hg-rich fluids derived It may scistosity. small fluid inclusions made by H disseminated cinnabar ore. Quartz contains many variably filled by native mercury; opening of such cavities by digging sometimes produces a weeping of mercury; opening of such cavities filled by native variably (1776) wrote: Tozzetti were found. Targioni large cavities During exploitation in XVIII century very mercury. “one time, after blasting, mercury weepeed for six minutes and the miners had not enough flasks that also two helmets were half-filled” are well- adit). Hg-rich quartz veins Romana continuation of that exploited at Cava (the along strike layer after tens of meters inside. However, of the tunnel and can be followed for several exposed at the entrance suddenly decrease and the tunnel continue for about 130 m in barren about 70 m the number of Hg-rich veins metatufite layer adit. Here the tunnel enter a mineralized until it reach the base of Speranza grey phyllites parallel descending from the external outcrops placed on opposite side of hill (at ca. 573 m a.s.l.). Two zincian metacinnabar, of cinnabar, that explored/exploited disseminations and veins connect three levels ramps associated with many vein mercurian sphalerite and pyrite. A beautiful isoclinally folded quartz-cinnabar at the base of first ramp. flattened and elongated cinnabar disseminations can be observed geological field trips 2011 - 3(2.1) itinerary 48 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate a tiny tabular crystal of a tiny d) a crystal of zincian metacinnabar c) ) associated with cinnabar, mercurian sphalerite ) associated with cinnabar, 4 S 2 droplets of a prismatic DOI: 10.3301/GFT.2011.02 and native mercury; Cavetta adit (Stop 7). mercury; Cavetta and native grumiplucite (HgBi Fig. 3.19 - of Microphotographs found into minerals the vugs of quartz at Levigliani. veins a) exagonal cinnabar crystal modified by rombohedron faces; adit (Stop 7); Cavetta b) mercury native associated with quartz and creamy adit (Stop 7); dolomite; Cavetta adit (Stop 8); with quartz; Speranza geological field trips 2011 - 3(2.1) itinerary 49 G. Zanchetta - I. Isola L. Piccini A. Dini The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate DOI: 10.3301/GFT.2011.02 Stop 8: Speranza First the path leads to the upper mining adit (Speranza). tunnel, a small trail of Cavetta From the entrance excavation of the Speranza reaches the Galleria Lunga adit (535 m a.s.l.), then it rise up to entrance with cinnabar disseminations follow a green metatufite layer openings (ca. 573 m a.s.l.). The descending ramps steps digged into the rock and a rope (max. 1 meter thick; N45 30-45E). Several veins and quartz-cinnabar metatufites with (ca. 564 a.s.l.). Here are exposed outcrops of mineralized help the descent to first level mercurian sphalerite, etc. zincian metacinnabar, containing cinnabar, cinnabar disseminations and quartz veins of pyrite (up (Fig. 3.18c and 3.19c). A peculiar feature of this area is the presence large cubic porphyroblasts to 2 cm) with beautiful pressure shadows of quartz and cinnabar (Fig. 3.4c 3.4e). The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate G. Zanchetta - I. Isola - L. Piccini - A. Dini g e o l o g i c a l f f i e l d t t r i p s 2 2 0 1 1 -3 3 ( 2 . 1 )
50 m e m o r a n d u m
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