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124 E. Niedzialktm ska

—    mcan diameter (Mz),

— iodusive graphic standard deviation

— inclusive graphic skewness (SkJ,

—    graphic kurtosis (K_c).

The degree of quartz grain abrasion has been described using Kryger;,',/ abrasion index Wo (1964). For the determination of the intcmal differenuatku of the sampies in respect of abrasion Rotnickfs equation (personaJ co*. munication) has been used. It defines the standard deviation for grouped data being described by the symbol a₀ and named the homogeneity index:

where:

/ = mean ąuantity of grains in a given class (Xf = 100), m = reference of the size class in the sample, c = interval (accepted c = 2).

The Sheppard correction (0.083) was adapted (Mills 1952). Lower valnes of the index indicate the greater homogeneity of the sample in respect of tbe abrasion degree. Higher values denote a greater differentiation.

According to J. R. L. ADen’s classification (1965) which has been modifbć (StarkeL Thomes 1981) and supplemented (Teisseyre 1985) the following typet of fossil deposits were identified:

1.    Channel deposits (di) induding channel-lag deposits (ch-lj and be deposits which were laid down in the river channel bel o w bankfull stages. Ba: deposits comprise central bar deposits and point bar deposits.

2.    Overbank deposits (ob) accumulated outside the channel to form tk floodplain; these include:

—    levee deposits (ob-1) consisting of bed materiał and the coarsest suspended sediment accumulated outside the channel,

—    floodbasin or backswamp deposits (ob-fb) composed of hne suspenósć sediment being accumulated beyond the natural levees during floods.

—    floodplain deposits (ob-fp) being accumulated outside the natural levtes b* flowing water.

3.    Transitory deposits include:

—    channel fili deposits (d) formed of minerał or organie matenals accumnUied in the abandoned or cut off channel,

—    alJimal fan deposits (tf) laid down by tributaries on the floor of the mai valley.

The ages of the matenals collected havc prccisely been determmed by mm radiocarbon datings (Ale.tandrowicz et ai 1981; Gilot et ai 1982: Niedziafco*-ska et al. 1985). The two valleys examined show distinct contrasts in bodi aga and types of deposits (Tab. 1) due to the diflerent types of sedimentation thot In the Wisłoka va!ley. the literał development of the yalley floor by wada-cutting of the eariier theets and by deposition of the suocessivd> yomęa sediment* was dominant (Alenandrowicz et al. 1981). Cofisequeotiy, grat ▼ańations in both ages and depositiona! environments do t\nx. The Vni