COBISS: 1.01 ASPECTS OF THE EVOLUTION OF AN IMPORTANT GEO-ECOSySTEM IN THE LESSINIAN MOUNTAIN (VENETIAN PREALPS, ITALy) POGLEDI NA RAZVOJ POMEMBNEGA GEO-EKOSISTEMA V GORAH LESSINI (BENEŠKE PREDALPE, ITALIJA) Leonardo LATELLA1 & Ugo SAURO2 Abstract UDC 551.442:574.4 (234.323.4) Leonardo Latella & Ugo Sauro: Aspects of the evolution of an important geo-ecosystem in the Lessinian Mountain (Venetian Prealps, Italy) Te Grotta dell’Arena (476 V/VR), located in the Lessinian Mountain, at the elevation of 1512 m a.s.l., is a very important underground karst system. Although it is only 74 m long, sev-eral of the geological, geomorphological and environmental features of the High Lessinian underground karst are present in this cave. Te Grotta dell’Arena shares some common geological and faunistic characters with other important and well known karst systems. Tis cave has also one of the highest number of troglobitic species in all Venetian Prealps and some of them possibly originated in the pre-quaternary. From the geological point of view the cave is the expression of a contact karst, where diferent limestone types come in contact both stratigraphically and along tectonic structures. Te Grotta dell’Arena is located at the stratigraphic contact between the “Calcari del Gruppo di San Vigilio” and the “Rosso Ammonitico” and it is very close to a fault plane putting in vertical contact the two above formations with the “Biancone”, a kind of limestone closely stratifed and densely fractured, very sensible to frost weathering. It is interesting to note the presence of a good number of species of Tertiary, or more generally pre-quaternary, originate in the Grotta dell’Arena. Tis presence is possibly related to the geol-ogy of caves. In this paper the diferent kinds of underground karst systems in the Grottta dell’Arena and Lessinian Mountain, are analyzed and the relation with the cave fauna distribution are taken in consideration. Key words: karst evolution, geomorphology, biospeleology, faunistic invasions, Venetian Prealps, Italy. Izvleček UDK 551.442:574.4 (234.323.4) Leonardo Latella & Ugo Sauro: Pogledi na razvoj pomembnega geo-ekosistema v gorah Lessini (Beneške Predalpe, Italija) Jama Grotta dell’Arena (476 V/VR) v gorah Lessini, 1512 m n.m., je zelo pomemben podzemeljski kraški sistem. Čeprav je dolga le 74 m, vsebuje geološke, geomorfološke in okoljske elemente, značilne za kraško podzemlje Visokih Lessini. Grot-ta dell’Arena ima nekaj geoloških in favnističnih značilnosti skupnih z drugimi pomembnimi in znanimi kraškimi sistemi. Jama je med tistimi z največjim številom troglobiontskih vrst v vseh Beneških Predalpah, od katerih nekatere verjetno izvirajo izpred kvartarja. Z geološkega vidika predstavlja jama kontaktni kras, kjer so vzdolž stratigrafskega in tektonskega stika različni apnenci. Grotta dell’Arena je na stratigrafskem stiku med apnenci “Calcari del Gruppo di San Vigilio” in “Rosso Ammonitico” in je zelo blizu prelomne ploskve, vzdolž katere se vertikalno stikata omenjeni formaciji s formacijo “Bianco-ne”, to je vrsta drobnoplastovitega in gosto prepokanega, slabo odpornega apnenca. Zanimiva je prisotnost precejšnjega števila terciarnih oziroma splošneje predkvartarnih vrst. To je verjetno v zvezi z jamsko geologijo. V prispevku so podrobneje obravnavane različne vrste podzemskih kraških sistemov v sami jami Grottta dell’Arena kot tudi v gorah Lessini in tudi njihovi odnosi z razporeditvijo jamskega živalstva. Ključne besede: razvoj krasa, geomorfologija, biospeleologija, invazija favne, Beneške Predalpe, Italija. 1 Museo Civico di Storia Naturale di Verona. Lungadige Porta Vittoria, 9, 37129 Verona, Italy. E-mail: leonardo.latella@comune.verona.it 2 Universita degli Studi di Padova, Dipartimento di Geografa. Via del Santo 26, 35123 Padova, Italy. E-mail: ugo.sauro@unipd.it Received/Prejeto: 21.12.2006 TIME in KARST, POSTOJNA 2007, 69–75 LEONARDO LATELLA & UGO SAURO INTRODUCTION Te Grotta dell’ Arena is registered with the number 476 in the Cadastre of the Caves of Veneto Region (the cave has been surveyed by A. Pasa in 1942, and GAS USV in 1972); the karst area is ML03 (Monti Lessini 03). Te cave is 74 m long with a diference in elevation of - 22 m. It is located in the Lessinian Mountain district of Bosco Chiesanuova, in Malga Bagorno area. G.C: 11° 06’ 02’’ E 45° 39’ 56” N, elevation 1512 m a.s.l. Te Grotta dell’Arena is a signifcant kind of underground karst system in Lessinian Mountain in fact: – it is a type of speleogenetic style in the morpho-dynamic context of the High Lessinians, – several of the geological, geomorphological and environmental features of the High Lessinian underground karst are present in this cave and played a signif-cant role in karst evolution, – some of the best known karst systems in the Les-sinian Mountain (Mietto & Sauro, 2000; Rossi & Sauro, 1977), such as the Abisso della Preta, the Covolo di Cam-posilvano, the Abisso del Giacinto, the Abisso dei Lesi, the Ponte di Veja, share some common characters with the Grotta dell’Arena, – from the biospeleological point of view, this cave has one of the highest number of troglobitic species in all Venetian Prealps, – several troglobitic species are endemic for the Grotta dell’Arena or the Lessinian Mountains and some of them possibly originated in the pre-quaternary. Te Grotta dell’Arena is a large chamber, roughly el-liptical in plane section, with a main diameter of about 50 m. Te roof coincides mostly with bedding planes. Te southern part of the foor is characterized by a large, asymmetrical, funnel-shaped depression, a kind of sub-terranean doline developed in the collapse debris. Te chamber is situated a few meters below the top-ographical surface; it is connected to the surface through Gastropoda Opiliones Diplopoda Orthoptera Zospeum sp. Ischyropsalis strandi Lessinosoma paolettii Troglophilus sp. Anellida Copepoda Collembola Coleoptera Marionina n.sp. Speocyclops cfr. infernus Onychiurus hauseri Orotrechus vicentinus juccii Araneae Lessinocamptus caoduroi Pseudosinella concii Orotrechus pominii Troglohyphantes sp. Moraria n. sp. Sincarida Italaphaenops dimaioi Pseudoscorpiones Elaphoidella n. sp. Bathynella sp. Lessinodytes pivai Chthonius lessiniensis Isopoda Amphipoda Laemostenus schreibersi Neobisium torrei Androniscus degener Niphargus galvagnii similis Halberrria zorzii Balkanoroncus boldorii tab. 1: List of the cave-dwelling species in the Grotta dell’Arena. Fig. 1: Te collapse depression called Arena. 70 TIME in KARST – 2007 Fig. 2: Te large chamber in the Arena cave. In the foreground the debris blocks, in the background the inner “doline”. ASPECTS OF THE EVOLUTION OF AN IMPORTANT GEO-ECOSySTEM IN THE LESSINIAN MOUNTAIN some narrow passages which start from an open collapse depression located on a slope, which resembles a Roman theatre (i.e. an “Arena”, hence the name of the cave) (Fig.1, Fig. 2). Te depression is the result of the collapse of part of the subterranean room. To understand the signifcance of this cave it is nec-essary to: – delineate the geological, geomorphological, and, in general, environmental characteristics of this cave, – reconstruct the framework of the spatial and temporal evolution of the High Lessini karst, – taking into account the climatic and environmen-tal changes of the external environment surrounding the cave that occurred during the Pleistocene. – analyse the phyilogeographical and taxonomical afnities of the troglobitic elements of its fauna. THE ENVIRONMENTAL CONTExT Te Grotta dell’Arena had been previously defned not as a distinct structure, but as a window on a subterranean space, that allows us to see only some features of a karst system (Castiglioni & Sauro, 2002). In fact, the subter-ranean environment is a much more complex system, mostly hidden to the human perception. From the geological point of view the cave is expression of a contact karst, where diferent limestone types come in contact both stratigraphically and along tectonic structures (Capello et al. 1954; Pasa, 1954; Sauro, 1973, 1974, 2001). In particular, the limestone formations pres-ent here are: – “Calcari del Gruppo di San Vigilio” of lower-middle Jurassic, about 60 m in depth, pure both oolitic and bio-sparitic/–ruditic, or reef limestones, relatively densely fractured, – “Rosso Ammonitico”, a condensed rock unit of middle- upper Jurassic age, about 30 m in depth, made up by nodular micritic limestone very resistant to erosion, crossed by widely spaced fractures, – “Biancone”, a chalk type unit, from the lower and middle Cretaceous, 100-200 meters in depth, made up by whitish marly limestone closely stratifed and densely fractured, very sensible to frost weathering. Te Scaglia Rossa formation of the upper Creta-ceous, and the Eocene limestone, which lie above the Bi-ancone in the western and southern part of the plateau are not present in the studied area because they have been completely eroded. Below the “Calcari del Gruppo di San Vigilio” there is the formation “Calcari Grigi di Noriglio”, of lower Jurassic, which is about 300 m in depth and out-crops in the slopes of the main valleys, a kind of fuvio-karstic canyons. Te Grotta dell’Arena is located at the stratigraphic contact between the “Calcari del Gruppo di San Vigilio” and the “Rosso Ammonitico” and it is very close to a fault plane putting in vertical contact the two above formations with the Biancone (Fig. 3). Te cover rocks of the cave are made mostly by the massive beds of lower Rosso Ammonitico, whereas the inner cave is mostly developed inside the Calcari del Gruppo di San Vigilio. At the topo-graphical surface, the line of the normal fault runs along Fig. 3: Sketches of the Arena cave system: I – Plan of the system; the grey corresponds to the biancone rock unit. II – vertical model of the karst system. Legend: 1) biancone formation, 2) Rosso Ammonitico, 3) Calcari del Gruppo di San vigilio and Calcari Grigi, 4) debris pipe in the cave, 5) bedding plane karst zone at the contact Rosso Ammonitico- Calcari del Gruppo di San vigilio, 6) fault plane karst zone, a) at the biancone side, b) at the Rosso Ammonitico side, 7) lateral fow inside and from the biancone aquifer, 8) vertical karst fow. TIME in KARST – 2007 71 LEONARDO LATELLA & UGO SAURO a small valley, a few meters to the east of the cave; the displacement of the fault is about 100 m. From the geomorphological point of view, Biancone is dissected by a network of dry valleys, whereas Rosso Ammonitico generates a rocky landscape with large fat karren separated by corridors, or rock cities of large blocks. From the hydrological viewpoint, the water circu-lates difusely inside the dense network of discontinuities SPATIAL AND TEMPORAL EVO It is easy to understand that the Grotta dell’Arena results of diferent spatial and temporal processes which oc-curred as a consequence of several predisposing factors. In fact, the cave is at the same time, an example of litho-logical contact karst, of intra-stratal karst, of fault zone karst and of a subterranean hydrological transition from a dispersed and sub-horizontal water fow to a more con-centrated and sub-vertical one. Te Grotta dell’Arena system is fed by a lateral water fow coming from the Biancone aquifer and crossing the fault zone, facilitated by the westward dipping of the stra-ta. Te speleogenesis of the cave has taken place in the lithological, tectonic and hydrological transition zone. Each cave we visit represents a moment of a long history, it is like the picture of a movie. Surely the present aspect of this cave and of its collapsed part are the result of relatively recent processes, occurred mostly during the middle and upper Pleistocene. But the karst system of which the cave is expression has surely begun to develop much earlier. Some caves, located in middle of the Lessinian plateau and in the Berici hills, are the result of the re-activa-tion of old paleokarstic nets developed during the Paleo-gene (Rossi & Zorzin, 1989, 1991; Dal Molin et al. 2000); other caves with fllings from the early middle Pleisto-cene developed mostly during the lower Pleistocene. Te Grotta dell’Arena chamber seems to be related with the second group. Te fault to the east side of the cave is a paleotec-tonic feature of Jurassic age, reactivated during the Cre-taceous and later by the Alpine orogenesis during the Paleogene and the Neogene. Te area where the cave is located probably emerged from the sea during the Oli-gocene, as the southern part of the Lessinian plateau. Te erosion of the Eocene rock unit occurred during late Pa-leogene and early Neogene. Te Scaglia Rossa formation was probably eroded during middle to late Neogene. At the beginning of the quaternary these two formations of the Biancone unit; the preferential fows is sub-parallel to the topographical surface and occurs mostly below the dry valley bottoms, but is also infuenced by the structural setting; vertical losses occur along the fault and fracture zones. In contrast, water circulation is more concentrated and mostly vertical in the Rosso Ammonitico. TION OF THE KARST SySTEM disappeared completely in the area (remnants of Scaglia are still present in the western High Lessinian). A model showing the sequence of landscapes devel-oped in the diferent rocks by the erosion can be created, based on present-day landscapes of other parts of the Lessini Mountains, where the eroded geological formations are still present. Tus in the southwestern Lessinian Mountain (High Valpolicella) there is an active hydro-graphic network with gorges entrenched in both Eocene Limestones and in the Scaglia Rossa. Here, the early morphogenesis, afer the emersion and the uplif, has been mostly of the fuvial type, marked by the development of a network of valleys strongly con-trolled by the tectonic structure. So, a valley developed along the fault line. Following the incision of the Scaglia Rossa, the karst process begun to afect the fault zone. But, it is especially afer the erosion of the Scaglia Rossa that the aquifer hosted in the Biancone started to feed a new underground karst system located near to the fault zone of which the Grotta dell’Arena is the present day expression. From this simple model it is possible to infer that the evolution of the underground karst system started since Neogene, probably since middle- upper- Miocene. Te transition from the fuvial environment to the karst environment has been accompanied by the development of a fuviokarstic milieu in the Biancone. In this milieu, which is still present, there is not surface runof except during exceptional events, but there is a difuse circula-tion inside the rock, for some aspects similar to that oc-curring below the river beds, inside the alluvial deposits (Fig. 4). 72 TIME in KARST – 2007 ASPECTS OF THE EVOLUTION OF AN IMPORTANT GEO-ECOSySTEM IN THE LESSINIAN MOUNTAIN Fig. 4: Sketch of the morphological evolution of the alti Lessini according with the erosional stages reached by the relief (progressive erosion of the rock units). THE CLIMATE AND ENVIRONMENTAL CHANGES DURING THE PLEISTOCENE Te Lessinian Mountain plateau was afected by the cli-matic and environmental changes of the Pleistocene. In the cave area there is no evidence of past development of local glaciers (the nearest local glacier was more than 1 km to the northwest). However, traces of strong perigla-cial processes, such as remnants of small rock glaciers, nivation niches, etc. are present (Sauro, 2002). During the last würm sporadic permafrost was present in the area. Te material resulting from the collapse of the Are- na depression has been afected by cryoclastic processes, as shown by a large solifuction lobe located to the north side of the same hollow. Te climate and enviromental change occurred in the Pleistocene, afected the colonization of the subterra-nean environment by some actual troglobitic species and shaped the distribution of the species that colonized this environments before the Pleistocene. THE CAVE FAUNA AT PRESENT Te cave fauna of the Grotta dell’Arena is characterized by the presence of high number of troglobitic and en-demic species (Caoduro & Rufo, 1998). Colonization of the cave by the troglobitic elements occurred in difer- ent times. Ancient elements of this fauna colonized the subterranean environments before the Pleistocene, and other species invaded the cave in diferent periods along the quaternary. TIME in KARST – 2007 73 LEONARDO LATELLA & UGO SAURO Today, this cave has a high number of cave-adapted animals. Of the 43 taxa known for the cave, 24 could be considered eucavernicolous species (sensu Rufo, 1955: eutroglophiles+troglobites). Te specialization index (eutroglobites/ eucavernicolous), has a value of 0.91, this means that 91% of the cave species in the Grotta dell’Arena are troglobionts. FINAL REMARKS Te subterranean karst of the alti Lessini is much more spatially developed than what is perceived by a speleolo-gist. It consists not only in large pits and chambers but in a network of smaller cavities and fssures. In the two horizontal dimensions it is a kind of net, even if aniso-tropic, better developed along the fault zones and some bedding planes. In the vertical dimension the anisotropy is even greater, and the thickness overpasses one thou-sand of meters. In the time dimension, this karst network has evolved progressively, even with diferent speeds infu-enced by the changes of the morphostructural setting and of the external environment. Te karst morphogen-esis occurred as result of the co-occurrence of various favourable conditions. Te hydro-geological condition of the alluvial de-posits of the water courses of the early erosional stage, during middle Neogene, are no present here nowadays, but there are situation for some aspects similar both be-low the valley bottoms of the Biancone and in the difuse net of karst fssures developed inside this rock unit. Tis difuse aquifer is in contact with the more typical karst aquifer of the limestone of the Jurassic rock units. Likewise, some of the larger karst pockets developed in the Eocene limestone, may have had some connections with the karst cavities in the Scaglia, and, along the main fault structures or volcanic structures, also with the karst voids in the Jurassic rock units. Here, sudden and sharp changes of conditions of the underground environments have not occurred dur-ing the late Neogene and the Pleistocene. Even the abrupt climatic changes of the Pleistocene have had a limited infuence on the underground environments, according with the large thickness reached by it before the end of Neogene. It is interesting to note the presence of a good num-ber of species of Terziary, or generally pre-quaternary, origin in the Grotta dell’Arena. Te most important relict species are: balkanoroncus boldorii (Beier, 1931), Lessino-camptus caoduroi Stoch, 1997, Italaphaenops dimaioi Ghi-dini, 1964 and Lessinodytes pivai Vigna Taglianti e Sciaky, 1988 (Casale & Vigna Taglianti, 1975; Vigna Taglianti & Sciaky, 1988; Gardini, 1991; Galassi pers. com.). Te presence and distribution of these species inside the caves of Lessinia (particularly the terrestrial species) has been usually related to certain environmental char-acteristic like temperature, humidity, air circulation etc. However, on the basis of the actual knowledge (Latella & Verdari, 2006), it appears that all these species are present in caves with a large range of temperatures, altitude and morphology. All these caves are developed inside, or in contact with, the Biancone or Scaglia (Cretaceous limestone) formations. It is likely that the geomorphology of the cave plays an important role not only in shaping the historical distribution, but also the actual presence, of cave animals in Lessinian area. ACKNOwLEDGMENTS we are grateful to Sandro Rufo for the helpful discus-sions and for the reading of the manuscript. we also thanks Augusto Vigna Taglianti for the informations re- garding Trechinae, Diana Galassi for the informations on Copepoda and Beatrice Sambugar for the Anellida. Tanks to Cristina Bruno for the linguistic review. 74 TIME in KARST – 2007 ASPECTS OF THE EVOLUTION OF AN IMPORTANT GEO-ECOSySTEM IN THE LESSINIAN MOUNTAIN REFERENCES Caoduro, G. & Rufo, S., 1998: La Grotta dell’Arena, un biotopo di eccezionale interesse negli alti Lessini. La Lessinia ieri oggi domani: quaderno culturale 1998, 39-44. Casale, A. & Vigna TAglianti, A., 1976: Note su Itala-phaenops dimaioi Ghidini (Coleoptera, Carabide). Bollettino del Museo Civico di Storia Naturale di Verona, 2 (1975): 293-314. 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