DSC07984 (2)

142

CL Nitdrka/htmska

was ałready stated by earłier workers (e.g. Pettijohn et al. 1972: ICostnei^, 1975; Kaniccki 1975; Ttshcbenko 1986K

Chanod deposits come into dusters of Wb around 600—1000 (Fig. 1 5Al Such deposits laki down by the brakłcd rivers dunng the Ołdcr and Younger Pleni głacial arc characterized by the largest rangę of Ho yalues. The ’•>. of channd dcposits of the lategladal meandering river is less varied. and tka: of channel dcposits aocumulated by both the Wisłoka and the upper Yistula m upper Subatlantic times is kast varied. The present author ascribes tbe successive periods of inciease in grain abrasion dunng both the Yistulian and the Hołocene to the reworking of the deposits by the river. A similar phenomenon has been observed by E. Mydełska-Dowgjałło (19781 in the Yistula deposits within the Sandomierz Basin. Further evidence is suppiied by the fact that the younger the deposit, the greater is its homogeneity.

The Wo values (530— 930) of overbank deposits occurring in both valleys examined appear to be the lowest for all of the fossil sediments quoted above Overbank deposits are less homogeneous (Fig. 15B1

Differences in ąuartz grain abrasion due to yarious sedimentation eon-ditions of the channel fili deposits are cłearly visible. Palaeomeander fills b which accumulated under quiet condidons from suspension during yarious periods of the Vistulian and of the Hołocene in both vallevs show Iow Wo values (700—930). Like the channel deposits, sediments laid down by running water in the oxbows (Fig. 15C) are marked by better abraded grains (Wo = 800—1040).

Alluvial fan deposits contain well abraded quartz grains (Wo = 770—1085)l Their Hb values are less varied. Abrasion analysis madę of the different fan profiles indicates that morphoselection of grains took place on the fan surface during transport. The less well abraded grains (Fig. 15D) tended to be trans po rted over greater distances. This fact has previously been obsened by A. Kaniecki (1975) and by Z. Młynarczyk (1985).

The modem flood-formed deposits in the Vistula valley are marked by ven Iow Wo values which vary from 360 to 715 (Fig. 15Ek whereas those in the Wisłoka valley show higher Wo yalues ranging from 650 to 900. For deposits overlying the gravel bars reverse is true. Bar deposits of the Wisłoka are pooriy abraded {Wo = 480—700), whereas those of the Yistula are better rounded (Wo — 690 — 780) (Fig. 15F). The present author explains the above differences by Yarious conditions of transport and sedimentation prevailing during peak flows and Iow flows in the non-regulated Wisłoka channel and in the corrected channel of the upper Vistula. Sam pies taken from the sandy-gra\elly bar a show well rounded grains (Wo = 860 — 975) which display characteristks of channel deposits (Fig. 15F).

SUM M ARY

This work considers deposits accumulated in the mountain fordami, where the reduction of both gradients and river energy takes place. Table l ckariy shows that different types of deposits prevailed in the yarious periods of Kotli the Yistulian and the Hołocene. Because of the smali a moimi of profiks examined. especially in the upper Yistula valley. it is impossible to draw frr