Capture Basins Research Articles

L'evoluzione geologica e lo spazio geografico delle Alpi Occidentali

B/OGEOGHAPHIA - vol. XVI - 1992 {Pubblicato il 31 dicembre 1992) ll popolamento delle Alpi Occidentali L’evoluzione geologica e lo spazio geografico delle Alpi Occidentali AUGUSTO BIANCOTTI, ROBERTO MALARODA e GIULIO PAVIA Dz'pmqzfz'/7ze/zto dz‘ Scienze della Terra zlel[’U/zz‘z2er5z'tti e Ce/ztro St;/511' /llpi Oct‘z't/6/zta[z' def C.N.R. — V221 Acczzt/e/72121 delle Scie/zze, 5 — 10123 Tori/20 SUMMARY Palaeobiogeographical characterization of the western sector of the Alps must take account of a long series of substantial geodynamic, geological, palaeogeographical and palaeoclimatic changes that tool: place from the Mesozoic onwards (about 200 Ma). The main stages began with the Jurassic expansion (Fig. 1), and continued through the Upper Cretaceous - Palaeogene compressive dynamics (45-35 Ma) due to the collision between the Eurasiatic and African plates to build the Alpine system, whose reliefs emerged to acquire a fully European biogeographic pertinence. New lines of comrntinication between Europe, Africa and Asia opened up during the Miocene as a result of post-collisional crustal settlements. Today’s palaeogeographical configuration may be supposed to have been reached after the tectonic events at the end of the Miocene and beginning of the Pliocene (6.7-5.3 Ma). A series of glacial-interglacial alternation during the Quaternary has led to the present heterogeneous biogeographical picture with a variety of taxa pointing to contrasting climatic conditions. lt must not be thought, however, that the climate alone has been inllticntial since the beginning of the Quaternary. The geological and lithological setting has never ceased to exert an effect on individual regions of the Alps (Figs. 2 and 3). Furthermore, neotectonic movements continue to alter altitudes, capture basins and runoff directions under our very feet, as it were. Geomorphological analysis is rarely able to provide evidence of these changes (Figs. 4 and 5 ). None the less, one must accept the notion that they have been at work, on an average, everywhere, and take them, therefore, into clue account (Table 1). Human settlement of the Alps proceeded apace from the time of the interglacial periods and has left abundant evidence of its various stages. It was from AD. 800 onwards, however, owing to a general rise in temperature after the cold period of Roman times, that the Western Alps were the scene of economic development at the expense of the flatlands, which became marshy and were regarded as of marginal importance. In the second half of the 16th century, on the other hand, the beginning of a «Little Ice Age» meant that the mountains no longer held the centre of the stage. Their ensuring depopulation was soon the cause of adverse effects, starting with disturbances of the hydrogeological setting. Today, however, the tide is beginning to turn. A typical example is the Aosta Valley, where an increase in the population of the main valley floor, in fact, has recently been accompanied by resettlement of the high terraces and heads of the side Valleys. Le Alpi Occidentali, piccola parte del sistema orogenetico alpino-himalayano, hanno tratti che sono comuni con questo ma anche caratteri particolari (Malaro— da, 1987). Comune e l’eta, cretaceo—terziaria e la netta differenziazione della loro storia in una fase preparatoria distensiva triassic0—giurassica, quella che un tempo si definiva fase di geosinclinale, una fase compressiva che ha avuto inizio nel Cre- taceo e sviluppo parossistico nell’Oligocene inferiore—Miocene inferiore, ed infi- ne una fase definita postorogenetica, essenzialmente di sollevamento, che ha ca- ratterizzato i ternpi dal Miocene superiore in poi. Peculiare delle Alpi Occidentali e pero l’entita della compressione che in 25

Applied Functional Analysis

The Projection Theorem. Theorems on Extension and Separation. Dual Spaces and Transposed Operators. The Banach Theorem and the Banach-Steinhaus Theorem. Construction of Hilbert Spaces. L ~ 2 Spaces and Convolution Operators. Sobolev Spaces of Functions of One Variable. Some Approximation Procedures in Spaces of Functions. Sobolev Spaces of Functions of Several Variables and the Fourier Transform. Introduction to Set-Valued Analysis and Convex Analysis. Elementary Spectral Theory. Hilbert-Schmidt Operators and Tensor Products. Boundary Value Problems. Differential-Operational Equations and Semigroups of Operators. Viability Kernels and Capture Basins. First-Order Partial Differential Equations. Selection of Results. Exercises. Bibliography. Index.