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Victoria University Antarctic Research Expedition Science and Logistics Reports 1968-69: VUWAE 13

Deltas

page 28

Deltas

A series of deltaic deposits along the southern margin of Lake Fryxell was also examined in some detail.

Several workers have described these features as deltaic deposits formed at the time of higher lake levels. Evidence that these features are in fact deltas, includes: fairly horizontal fine bedding, presence of beds of finely laminated silts, general surface morphology, etc. All these criteria are, however, also consistent with fan formation and in my view it is not yet possible to determine whether these features formed inside or outside the lake margin, although there is little doubt that most are “graded” to old lake levels. Similar comments are applicable to the deltaic deposits formed on the margin of ancestral Lake Vanda.

The slopes connecting one deltaic surface to another (the riser) are of interest. Whilst these deposits are very unstable, the slope deposits only veneer the original deltaic/fan deposition. This suggests that, either the delta/fans are very young or that downslope movement, even on very unstable slopes, is extremely slow. Slopes on deltas above meltwater channels, where the channel has trenched through the deposits, also have only a veneer of slope deposits parallel with the present slope, lying unconformably on truncated horizontal sediments. While these slopes may be actively undercut by meltwater, they are similar to those which have been unaffected (except by downslope movement and wind) since the lake level fell. Furthermore, the importance of snow drifting and wind has not yet been ascertained.