Page 73 - Sedimentology and Stratigraphy

Processes of Transport and Sedimentary Structures
60 Nichols/Sedimentology and Stratigraphy 9781405193795_4_004 Final Proof page 60 26.2.2009 8:16pm Compositor Name: ARaju

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Fig. 4.22 Forms of wave ripple: rolling
1 1 grain ripples produced when the oscilla-
tory motion is capable only of moving the
grains on the bed surface and vortex rip-
ples are formed by higher energy waves
relative to the grain size of the sediment.

Fig. 4.25 Wave ripple cross-lamination in sandstone (pen is
Fig. 4.23 Wave ripples in sand seen in plan view: note the
18 cm long).
symmetrical form, straight crests and bifurcating crest lines.
being climbing ripples which have distinctly asym-
metric dipping laminae.
In addition to the wave and current bedforms and
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sedimentary structures described in this chapter there

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are also features called ‘hummocky and swaley cross-
stratification’. These features are thought to be char-
acteristic of storm activity on continental shelves and
are considered separately in the chapter on this
depositional setting (14.2.1).

4.5 MASS FLOWS
Fig. 4.24 Internal stratification in wave ripples showing
cross-lamination in opposite directions within the same
layer. The wavelength may vary from a few centimetres to Mixtures of detritus and fluid that move under
tens of centimetres. gravity are known collectively as mass flows,