10.1 INTRODUCTION
10.1.1 Sediment Supply and Accommodation Space
This book has told the tale of how rock is broken down to sediment, how sediment is
transported and deposited, and then turned back to rock again. This, the concluding
chapter, describes the sedimentary basins within which the last acts of the great saga
unfold. This chapter attempts to answer these questions: Why should sedimentation occur in one place at a particular time? What is the spatial organization of large volumes
of sediment? What are the factors that control their facies? And how do petroleum and
mineralizing fluids move within basins?
Chapter 6 introduced the concepts of environments of erosion, equilibrium, and deposition. Recall that erosion normally occurs in mountainous regions. Equilibrial surfaces characterize many deserts and continental shelves. Depositional environments occur in both open marine basins and closed continental ones.
For sediment to accumulate in a marine basin there must be a vertical interval, termed
the accommodation space, between sea level and sea bed, the top of the accumulation
(Jervey, 1988). When examined closely, however, the concept of accommodation space
becomes complex. In marine environments, tide, wind, and wave-generated currents
may be so strong that sediment can never accumulate to sea level, but is constantly redistributed across the shelf or into deeper water. In a closed continental basin the concept of accommodation space becomes still more complicated. In lake basins the accommodation space may still be defined as the interval between the lake bed and the
surface. In continental environments, however, the accommodation space is defined as
the interval between the top of the accumulation and the equilibrial surface. In eolian
environments this may often be taken as the water table (Kocurek and Havholm, 1993).
This is because sand can only accumulate and be preserved below the water table. Dry
sand above this surface will be constantly reworked and transported. For enclosed fluvial basins the equilibrial surface is a plane level with the spill point of the basin (i.e.,
the lowest col through which sediment will be transported once accumulation reaches
the height of the col).
The rate at which the accommodation space is infilled is a function of several variables
in the basin and in the drainage catchment area. Variables within the basin include the
environment and its energy level, that is, the ability of wind, wave, and tidal currents to
transport, segregate, and deposit sediment. Other critical intra-basinal variables include
467
10.1.1 Sediment Supply and Accommodation Space
This book has told the tale of how rock is broken down to sediment, how sediment is
transported and deposited, and then turned back to rock again. This, the concluding
chapter, describes the sedimentary basins within which the last acts of the great saga
unfold. This chapter attempts to answer these questions: Why should sedimentation occur in one place at a particular time? What is the spatial organization of large volumes
of sediment? What are the factors that control their facies? And how do petroleum and
mineralizing fluids move within basins?
Chapter 6 introduced the concepts of environments of erosion, equilibrium, and deposition. Recall that erosion normally occurs in mountainous regions. Equilibrial surfaces characterize many deserts and continental shelves. Depositional environments occur in both open marine basins and closed continental ones.
For sediment to accumulate in a marine basin there must be a vertical interval, termed
the accommodation space, between sea level and sea bed, the top of the accumulation
(Jervey, 1988). When examined closely, however, the concept of accommodation space
becomes complex. In marine environments, tide, wind, and wave-generated currents
may be so strong that sediment can never accumulate to sea level, but is constantly redistributed across the shelf or into deeper water. In a closed continental basin the concept of accommodation space becomes still more complicated. In lake basins the accommodation space may still be defined as the interval between the lake bed and the
surface. In continental environments, however, the accommodation space is defined as
the interval between the top of the accumulation and the equilibrial surface. In eolian
environments this may often be taken as the water table (Kocurek and Havholm, 1993).
This is because sand can only accumulate and be preserved below the water table. Dry
sand above this surface will be constantly reworked and transported. For enclosed fluvial basins the equilibrial surface is a plane level with the spill point of the basin (i.e.,
the lowest col through which sediment will be transported once accumulation reaches
the height of the col).
The rate at which the accommodation space is infilled is a function of several variables
in the basin and in the drainage catchment area. Variables within the basin include the
environment and its energy level, that is, the ability of wind, wave, and tidal currents to
transport, segregate, and deposit sediment. Other critical intra-basinal variables include
467