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Supplements of Geografia Fisica e Dinamica Quaternaria
Volume I - 1988

 

Proceedings of the meeting:
The Morphotectonics in Italy

CASTIGLIONI G. B., MENEGHEL M. & SAURO U.

Elementi per una ricostruzione dell’evoluzione morfotettonica delle Prealpi Venete – Morphotectonic evolution of the Venetian Prealps: some elements

Pages 31-43

Abstract

From thc geological.structural and morphotectonic viewpoints, tbe Venetian Prealps show many similarities of forms parrly due to the prevalence of very thick carbonatic formations. However, they also show spcrific peculiarities, duc to their different tcctonic historics and to thc features and directions of the thrusts which caused their evolution during the most recent phases of Alpine orogenesis. The aim of this work is to re-exmninc and re-order thc facts and problcms characterizing the Venetian Prealps region, parrl)’ on the basis af llCWly acquired knowledges. l-iowever, it should be noted that only by rneans of specific researches, which this report wiU hopefully stimulate, will it be possible to provide exhaustive answers to some of the problems noted here. After a bricf presentation of the few c1emenrs of chronological significance regarding the Neogene and Lower and Middle Pleistocene, the geologic-stfucLUral features of the prealpine belt are illustrated. This belt is involvcd in at least tluee large-scale tcetonic systcms, aU with dif(crent dircctions. In rclation to the features of these systems, the following morphotectonic styles are found: a) style with monoclinaI blocks, prevailing in the western scctor; bl tabular style, prevailing in the centrai sector; c) complex style with faulted folds (north-east sector). One can find large tectonic scarps both limiting the monoclinal blocks and at the southern border connccted with f1exures or faultfolds. More particularl)’ smaller faulr scarps arc present at some edges and interior parts of thc mainly tabular structures (e.g. Lessini Moun· tains). Some of these are the expression of recent movements, of Pleistocene and in some cases Holocene age. ‘nlere is remarkable congruencc between large forms and structures, OOth in the tabular areas (plateaus) and in those with monoclinal blocks and fold areas, in the sense that OOth orographic trend and altitude reflect tectonics directly. The Vcnetian PreaIps show very good ex· amples of spccific tectonjc forms nnd derived strl1ctural forms modell· ed by crosional proccsscs, with results which are congruent with tectonjcs. Naturally, there are also exceptions, e.g., large-scale inversions of relicf mainly in the areas of maximum uplift, and minor but exemplary cases in single localitics. Large crosional forms which are signifi. cant in reconstructing the histor)’ of the Prealpine rclicfs are groupcd in the following way: a) I,inear stili active, erosional forms (Iarge valleys mainJy of canyon type): these express strong downcutting of the drainagc network and were caused by the most recent large uplifts; b) linear relict erosionai forms: thcse are represented by valley trunks isolatcd wirh rcspcct t’o the current drainage network, as a conscquence of deviations and sometimes captures. These trunks are generally c1carly hanging, and have less stecp slapcs than the active vaUeys; c) lcvelled forrns: these extensive sudaces are slightly undulate and are also mainly relict forms; they also preserve systems of relict valleys, indieating past evolutionary forrns which developed near the local or generai base level; their current altitude is the result of later uplift phenomena. Three types of relict surfaces are distinguished: a) olci planation surfaccs with strong structural control; b) old planation surfaccs slightly controllecl b)’ strueture; c) hilly areas deriving from the disseclion of hypothesized planation surfaces, of which some parts, prescrved near the sl1mmits of the hills, approximatcly at the same altitudcs, may stili be recognized. These three types of surface involvc OOth the plateaus aod the hilIy areas. Some plateaus, although being erosional surfaces with strong structural control, and in practice be.!onging to the category of substrueturai surfacçs, reveal the aneient erosional phases, as well as later modifications due lO karsric or pcriglacial processes. Other deepcr trunks of rclict valleys indicate significant variations in the drainage network occurring during later evolutionary phases, during which the mountainous rnassifs may have been further dismembercd and variously tilted, as an cffcct of tcctonic movements. These movements may also be demonstrated in some cases by anomalies in the trends of the older valleys.

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