Consideration upon the River system in the north of the Suceava tableland

Abstract

The paleoevolution of the river system in the Moldavian Tableland has undergone at a theoretical level two successive hypothetical directions. The former direction, formulated in the first half of the XXth century, alleges the existence of a river system, with a transverse character, that prolonged to the east the Carpathian river systems. Specialists of this theory, Tufescu V. (1932), M. David (1933, quoted by V. Bacauanu - 1973) and Gheorghe Nastase (1946, quoted by V. Bacauanu - 1973) based their design on the presence of horizons of gravels with Carpathian elements on some interfluves to the east of the Siret valley, and the existence of some saddles, Loznica, Bucecea and Ruginoasa, located on the left side of the same river. The latter direction, diametrically opposite, supports the idea of evolution of the river system consecutively with the Sarmato-Pliocene Sea pulling back to the south. The hypothesis is supported and substantiated by I. Sîrcu (1955), C. Martiniuc and V. Bacauanu (1960), V. Bacauanu (1968, 1973). In this context it is considered that the Prut and Siret rivers carved the oldest valleys in the tableland. The authors explain the erosional genesis of the saddles arguing their inability to create transversal rivers on the basis of continuity upstream and downstream the saddles of terrace levels with relatively high altitudes, which proves the flow continuity on consequent valleys. The research carried out along the Suceava river valley and the immediate interstream area in order to create a scenario of the valley paleoevolution highlighted the presence of crystalline lithotopes in the petrographic structure of the accumulation deposits. The presence of such petrographic elements contradicts the present-day alluvia sources of the rivers that could have transported them:  Suceava or its tributaries Solonet, Ilisasca, Scheia. The rivers spring either from the Carpathian flysch or from the former area of platform sedimentation. We consider that the current Solonet, Ilisasca, Scheia streams and valleys and, through generalization, Sucevita and Solca, have nothing in common with the Carpathian Sarmatian paleosystem that built the Suceava Piedmont. The superior flows on the eastern slope of the Obcina Mare can be accounted through a normal regressive evolution, and the current saddles are the consequence of selective erosion. The old Carpathian system changed probably because of the Wallachian movements, only Moldova and Suceava maintained their former Carpathian flows. The current system didn’t go beyond the Suceava Valley in the east, therefore we can appreciate that the river with the same name installed itself previously. The relative altitude of the oldest terrace is of 180 – 190 m, which is attributed, according to the same morphochronological scheme, to the Superior Pleistocene. By comparing the absolute altitudes of the Suceava terraces to those of the hills which preserve piedmont deposits and also to the average altitude of the latter as compared to the adjacent valleys we cannot but wonder upon the age of the landforms in the north of the Tableland. We continue to be very much interested in the evolution of the river system as a whole in the north of the Moldovenesc Tableland, especially taking into account the interesting remarks made by professor Tufescu (1985) on some deposits situated east of Bucecea saddle, where he identified elements of Mesozoic sediments.