Jökull - 01.01.2016, Page 60

Paweł Molewski and Leon Andrzejewski
Figure 7. Morphology of the southern study area (profiles A and B, see Figure 8). – Setlög og landform á syðra
rannsóknarsvæðinu, við sethjallasnið A og B.
lithofacies of ripple cross-lamination and climbing
ripple cross-lamination which record a south-west
to south-southwest palaeoflow direction. Macroscop-
ically, part of the silty-sandy lithofacies are rhyth-
mically laminated (horizontal and wavy lamination)
comprising alternating silty and silty-sandy laminae
of thickness 1 to 30 mm. In this unit, the cyclical
nature of sedimentation was also observed. Each of
the cycles is of varied coarseness, and can be sub-
divided into mainly silty (Fh, Fw) and silty-sandy
(FSh, FSr, FSrc,) or less commonly sandy-silty (SFm,
SFh) sections. Individual cycles have varying thick-
ness, ranging from 25 to 90 cm. Their silt parts are
usually more thick. These cycles are confirmed by
the Markov chain analysis of the probability of oc-
currence of lithofacies. In unit A1 the greatest proba-
bility of transition (6.08, 4.40, 4.24) is between silty
lithofacies and silty-sandy or sandy-silty. An alternat-
ing fine–coarsening upward sequence is observed in
the silty deposits of the upper part of unit A1 (the last
three cycles) whereas the bottom of the unit contains
silty and silty-sandy sediments with wavy lamination,
including a cobble 15-cm in diameter.
The characteristics of unit A1 indicate sediment
deposition in standing water (Fh, Fw, FSh, FSw) with
episodes of lower flow regime conditions (FSrc, FSr).
The deposition velocities of the currents, estimated on
the basis of the Koster formula (1978), range from
60 JÖKULL No. 66, 2016