4.1 INTRODUCTION
The transportation and deposition of sediments are governed by the laws of physics.
The behavior of granular solids in fluids has been extensively studied by physicists and
by engineers of various types. Much of this work has been documented and will be found
in texts on hydraulics and fluid dynamics (Dailey and Harleman, 1966; Henderson, 1966;
Leliavsky, 1959). Accounts of the physical processes of sedimentation seen from a geological standpoint have been given by Bagnold (1966,1979), J. R. L. Allen (1970, 1985a),
P. A. Allen (1997), and Pye (1994).
This chapter introduces some of the fundamental concepts of sedimentation as a
means to understanding the fabric and structures of the deposits which they generate.
Sedimentation is, literally, the settling out of solid matter in a liquid. To the geologist,
however, sedimentary processes are generally understood as those which both transport
and deposit sediment. They include the work of water, wind, ice, and gravity. The physics of granular solids in fluids is described here. This is followed by accounts of sediment
transport and deposition by these four processes.
Matter occurs in three phases: solid, liquid, and gaseous. The physicist considers gases
and liquids together as fluids, on the grounds that, unlike solids, they both lack shear
strength. The behavior of granular solids in liquids and gases is comparable. The similarity of the bed forms and structures of windblown and water-laid deposits are the root
problem of differentiating them in sedimentary rocks.The starting point of an analysis
of sediment transport and deposition is Stokes' law. This was introduced when discussing the use of settling velocity as a way of measuring grain size (Chapter 3). Recall that
Stokes' law states:
W= I (P1- P)g ld2 '
18/x
where W is the settling velocity, (P1 - P) is the density difference between the particle
and the fluid, g is the acceleration due to gravity,/z is the fluid viscosity, and d is the particle diameter. A derivation of Stokes' law is found in Allen (1985a). Stokes' law states
that the settling velocity of a particle is related to its diameter, and to the difference
between the particle density and the density of the ambient fluid. Considered at its
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The transportation and deposition of sediments are governed by the laws of physics.
The behavior of granular solids in fluids has been extensively studied by physicists and
by engineers of various types. Much of this work has been documented and will be found
in texts on hydraulics and fluid dynamics (Dailey and Harleman, 1966; Henderson, 1966;
Leliavsky, 1959). Accounts of the physical processes of sedimentation seen from a geological standpoint have been given by Bagnold (1966,1979), J. R. L. Allen (1970, 1985a),
P. A. Allen (1997), and Pye (1994).
This chapter introduces some of the fundamental concepts of sedimentation as a
means to understanding the fabric and structures of the deposits which they generate.
Sedimentation is, literally, the settling out of solid matter in a liquid. To the geologist,
however, sedimentary processes are generally understood as those which both transport
and deposit sediment. They include the work of water, wind, ice, and gravity. The physics of granular solids in fluids is described here. This is followed by accounts of sediment
transport and deposition by these four processes.
Matter occurs in three phases: solid, liquid, and gaseous. The physicist considers gases
and liquids together as fluids, on the grounds that, unlike solids, they both lack shear
strength. The behavior of granular solids in liquids and gases is comparable. The similarity of the bed forms and structures of windblown and water-laid deposits are the root
problem of differentiating them in sedimentary rocks.The starting point of an analysis
of sediment transport and deposition is Stokes' law. This was introduced when discussing the use of settling velocity as a way of measuring grain size (Chapter 3). Recall that
Stokes' law states:
W= I (P1- P)g ld2 '
18/x
where W is the settling velocity, (P1 - P) is the density difference between the particle
and the fluid, g is the acceleration due to gravity,/z is the fluid viscosity, and d is the particle diameter. A derivation of Stokes' law is found in Allen (1985a). Stokes' law states
that the settling velocity of a particle is related to its diameter, and to the difference
between the particle density and the density of the ambient fluid. Considered at its
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