Rock formation and deformation - Fundamentals of the Physical Environment - page 268

Plate 12.8 A sequence of waterlain muds, silts and fine
sands (Glan-y-mor Member of the Eryri Formation) deposited
in a glacier-margin environment at Glan-y-mor-isaf, west of
Conwy, North Wales. Texture and colour changes between
each successive (younger) layer from the base indicate
changes in sediment source and water velocity, with internal
syngenetic, downslope slump and collapse structures.
Photo: Ken Addison

Plate 12.7 Angular unconformity between near-horizontal
Carboniferous Limestone deposited directly on steeply
dipping eroded Ordovician turbidites, exposed in the Ingleton
Falls, western Yorkshire Dales. The time interval between
deposition of the two strata is at least 110 Ma.
Photo: Ken Addison

(a) (b) (c)

Flow

20

Depth decreases
Velocity increases

Plane bed (upper)

2

Dunes and sandwaves

Linguoid

Plane bed
(lower)

Straight Sinuous Catenary Lunate

0.2 Ripples

No sediment motion

0.02

Depth increases
Velocity decreases

0.1 0.5

Particle size (mm)

1.0

Figure 12.13 Relations between stream power, particle size and bed forms: (a) the effect of increasing stream power on
bedform; (b) upper plane bedform (top), dune (middle) and ripple bedforms (bottom); (c) the form and depth/velocity relationship
of ripples.
Source: Partly after Allen (1968)