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Supplements of Geografia Fisica e Dinamica Quaternaria
Volume I - 1988

 

Proceedings of the meeting:
The Morphotectonics in Italy

BIANCOTTI A. & MOTTA M.

Morfotettonica dell’altopiano delle Manie e zone circostanti (Liguria occidentale) – Morphoneotectonics of the High of Plain Mànie and sorroundigs (Western Liguria, ltaly)

Pages 45-68

Abstract

The High Plain of Mànie (in the Finale arca, Western Liguria) is mainly constituted by carbonate lithotype, subject to a considerable karst processo While the karst m;crolalldlonm can be rcferred to the dynamics of thc present slope, the karst macroltmd/onm are sirnilar to those are typical of the tropical karst landscapc. Thanks to a quantitative geornorphologic survey, it has been found out that thc morphogenesis of the top surface of the High Plain dates back to a hotter and welter period than the present ane, responsibI e for thc cockpit shape of the biggest karst sags whieh is still recognizable in spite of re-modclling al lacer times. This marphogenetic scagc has been formed framed in the reconstruction of the post-serravallian evolution of the whole area. Such reconstruction has been achieved through the examination of the hypogeous karst phenomena, the analysis of the 73 karst pits (most of which have been surveyed far the first time), the discovery in some places of Quaternary flora and fauna, the study of the hydrographic grid (thanks to it the apparent contraddietions betwcen thc indicative parameters of thc maturity degree of the basins and thc hydrographic not have been explained), the study of a «surface of peaks» extended to most of thc surveyed area and of the morphologic steps at the edge of the high plains. The results can be synthetized as follows: aher the settling of the «Pietra di Finale» (Serravalliano) the zone definitely emerges forming a structural high, also emergent during the pliocenic transgression. As in many circummediterranean regions, also in this zone, probably during the Plio·Pleistocene, there was the formaticn of an erosion glacis, proof of which is the existence of a «sudace of peaks». FoUowing the raising movements in that area, the glacies is erodcd and a karst high plain forms in the zone of carbonate rocks. Later, once or more than once, the zone bccomes hotter and wetter than it is in the present day with the ensuing formation of cockpits which latcr are partly dismantled by an erosive phase. TItis erosive phase transforms the high plain in smaUer units such as the Mànie High plain. During a pcriod of standstill of the relative raising movements of the region, the formation of Jarge valley bottoms (the one of the Rio Ponci is still wcU preserved) takes pIace together with a series of morphological steps, 100-145 meters above t!le present sea-Ievel, such as the alluvial deposits of the Ponei. The re-occurence of relative raising movements brings to the prescnt situation and to the dismantling of most of the old valley bottoms through a new erosion which has resulted in a rejuvenation of the whole region. At present this erosive phase is at its final stage. The present erosion process, mostly in the zone formed by metamorphic or quartztitic rocks, is mainly due to antropic causes. The raising of the region has been accompanied by quaternary eustatic oscillations. Proof of twc of them, which may be referred to the Uppcr Pleistocene, is the existence of fossil deposits at Capo Noli.

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