Page 194 - Sedimentology and Stratigraphy

Types of Delta 181

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Fig. 12.3 Classification of deltas taking

grain size, and hence sediment supply
mechanisms, into account. (Modified
from Orton & Reading 1993.)

& $

%

Fig. 12.4 Controls on delta environ-

ments and facies. (Adapted from Elliott
1986a.)
only a few tens to hundreds of metres across, while formed by multiple channels (e.g. the Ganges Delta,
the largest deltas cover areas of thousands of square Bangladesh). The overall form is found to be related to
kilometres. The ‘original’ delta is at the mouth of the the relative importance of three main processes: the
River Nile (Egypt), an area of flat land with river current in the river, the action of waves and the
channels that had the triangular shape of the action of tides. The sediments deposited by the Mis-
fourth letter of the Greek alphabet, D (Fig. 12.2). sissippi and Ganges deltas are mainly mud and silt,
This shape, however, is not shared by many other but others, such as the Rhone Delta (France) are
deltas (Fig. 12.2) and the morphologies range from much sandier, and deltas fed by pebbly streams
elongate ‘fingers’ building out into the sea (such as can be made up of a high proportion of gravel
the Mississippi Delta, USA) to highly indented shapes (e.g. Skeidarsandur, Iceland). Gravelly deltas are not