Delle Rose M., Cacciatore G., Patianna M.,, 2007, The carbonate accretions of the Mannute Caves (Salento, southern Italy) and their paleoenvironmental significances., Epitome (Udine) 2 (2007): 287.,
URL: http://www.cnr.it/prodotto/i/118243

Physic-chemical and biological features exert primary control on the growth of carbonate continental deposits, and produce a far greater morphologic and petrologic range. Such deposits appear to be parts of a continuum genetically allied carbonate fabrics mediated by environmental factors. Karstic caves usually host conditions suitable to the growth of carbonate accretions. Among the abiotic hypogean accretions, vadose and phreatic speleothems are referred to carbon dioxide degassing of dripping water and saturation of water solution. Nevertheless, the karst environments can allow the development of composite accretions, showing a number of interbedded or coalescent macro-morphology, texture and fabric. In the Salento peninsula, the emerged southeastern portion of the Apulia Carbonatic Ridge (Auct.), inside the Mannute caves system, placed within lower Chattian - early Messinian clinostratified slope systems laterally disposed and grafted one upon the other, five main morphological types of accretions have been identified_ sub conical stalactites, bulky "elephant foot" stalactites, erratic pseudo-stalactites, (i.e. speleothems of abnormal shape grow downward from the cave roof) sub cylindrical stalagmites and sigmoidal composite accretions. Their morphological and petrological description and genetic interpretations are the issues of this note. The sub conical stalactites and the sub cylindrical stalagmites represent the usual speleothems growth through water dripping. Concerning the erratic accretions, biogenic structures was recognized by means of microscope observation. According to a current terminology, they can be refer to the calcareous tufa deposits. Noticeable is that also parts of the sigmoidal composite accretions are formed by similar biogenic building. A few erratic pseudo-stalactites and sigmoidal composite accretions are presently interested by water dripping and colonised by plants association which can actively enhance such accretions. In fact, this tufas are seen to be the results of both physic-chemical and biogenic precipitations associated with biofilm encrustations involuntarily product during the decaying vegetation metabolised from micro-organisms. Active tufa precipitation is severely limited by low temperatures as this restricts soil respiration and limestone dissolution. In the temperate regions tufa accretion normally coincides with the interglacial phases. About the bulky "elephant foot" stalactites, their morphological features let the attribution to the phreatic overgrowths. More in detail, these accretions should be developed around pre-existing stalactites situated at the range of paleo-sea level stands through aggregation of floating calcite rafts. Whose thickness corresponds to the water table fluctuations, which is in turn controlled by tides. This reconstruction need of freshwater - marine mixing zone inside the cave, probably a coastal spring, suitable to determine carbonates oversaturation of the brackish water. The above summarily described carbonate accretions offer different possibility to the paleoenvironmental and paleoclimatic reconstructions, and appear remarkable geological indicators. A detailed topographic survey have performed also tacking into account the neo-tectonic activity of the area, characterized by differential uplift and tilting. The accuracy of the draft of the cave performed allow to locate every component of the karst system with an high degree of detail. Accretions can be positioned in the 3D space with a precision of few millimetres and the virtual manipulation allow to bring both caves and accretions back into pre-tectonic uplift positions. Detailed morphological and petrological analyses will finish the research.

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