10.2 SEDIMENTARY BASINS CLASSIFIED AND DESCRIBED
475
tion of petroleum source beds, the heat flow to which they are subjected, and the migration pathways and loci of entrapment of petroleum fluids (McKenzie, 1981).
Basins formed as a result of crustal thinning and rifting are of particular interest to
the petroleum industry because they are an important habitat for petroleum. Many theories have been advanced to explain their formation. Of the many models proposed,
three are particularly significant. Salveson (1976, 1979) proposed a model of passive
crustal separation in which the continental crust was deemed to deform by brittle failure, while the subcrustal lithosphere is thinned by ductile necking. This model was
largely based on studies of the Red Sea and Gulf of Suez rift system.
McKenzie (1978) proposed a model that assumed that both the crust and subcrustal
lithosphere deformed by brittle failure. This model was largely based on studies of the
North Sea basin.
Wernicke (1981, 1985) proposed a model for crustal thinning by means of simple
shear, in which a low-angle fault extends from the surface right through the lithosphere.
This model was largely based on studies of the basin and range tectonic province of
North America.
These three models are illustrated in Fig. 10.9, left. The McKenzie model has received
particular interest in the oil industry because it offers a means of predicting the history
of heat flow in a sedimentary basin. This is a prerequisite to the accurate modeling of
petroleum generation and sediment diagenesis. Basin formation commences after a prerift idyll phase, during which the crust is in isostatic balance and a state of thermal equilibrium. As rifting develops, the crust thins, heat flux increases, and the temperature of
the shallow rocks rises. After rifting has ceased, the crust cools, shrinks, and collapses.
Sedimentation continues, but now infills a gently subsiding basin. Faults die out at the
top of the syn-rift sediments. The crust returns to thermal equilibrium and a postrift
idyll phase. The resultant basin is colloquially referred to as a "steer's head" basin, because it is reminiscent of a Texas Longhorn or Highland Cattle (Fig. 10.9, right).
McKenzie demonstrated mathematically that the heat flow within a basin was related to the amount of crustal stretching, termed the/3 value. The higher the rate of
stretching, the higher the heat flux during the initial phase of rifting (Fig. 10.10, upper).
The/3 value for a basin may be discovered by constructing a burial history curve for
the basin and comparing it with known curves calculated for given/3 factors (Fig. 10.10,
lower). The accurate prediction of the history of heat flow in a sedimentary basin is a
prerequisite to the accurate modeling of petroleum generation (Dore et al., 1991; Helbig, 1994).
10.2 SEDIMENTARY BASINS CLASSIFIED AND DESCRIBED
10.2.1 Classification of Sedimentary Basins
Attempts to classify the various types of sedimentary basins have been made by many
geologists, notably Weeks (1958), Halbouty et al. (1970), Perrodon (1971), Klemme
(1980), and Allen and Allen (1990). These classifications vary according to the defining
parameters which have been chosen, and according to the purpose for which a scheme
475
tion of petroleum source beds, the heat flow to which they are subjected, and the migration pathways and loci of entrapment of petroleum fluids (McKenzie, 1981).
Basins formed as a result of crustal thinning and rifting are of particular interest to
the petroleum industry because they are an important habitat for petroleum. Many theories have been advanced to explain their formation. Of the many models proposed,
three are particularly significant. Salveson (1976, 1979) proposed a model of passive
crustal separation in which the continental crust was deemed to deform by brittle failure, while the subcrustal lithosphere is thinned by ductile necking. This model was
largely based on studies of the Red Sea and Gulf of Suez rift system.
McKenzie (1978) proposed a model that assumed that both the crust and subcrustal
lithosphere deformed by brittle failure. This model was largely based on studies of the
North Sea basin.
Wernicke (1981, 1985) proposed a model for crustal thinning by means of simple
shear, in which a low-angle fault extends from the surface right through the lithosphere.
This model was largely based on studies of the basin and range tectonic province of
North America.
These three models are illustrated in Fig. 10.9, left. The McKenzie model has received
particular interest in the oil industry because it offers a means of predicting the history
of heat flow in a sedimentary basin. This is a prerequisite to the accurate modeling of
petroleum generation and sediment diagenesis. Basin formation commences after a prerift idyll phase, during which the crust is in isostatic balance and a state of thermal equilibrium. As rifting develops, the crust thins, heat flux increases, and the temperature of
the shallow rocks rises. After rifting has ceased, the crust cools, shrinks, and collapses.
Sedimentation continues, but now infills a gently subsiding basin. Faults die out at the
top of the syn-rift sediments. The crust returns to thermal equilibrium and a postrift
idyll phase. The resultant basin is colloquially referred to as a "steer's head" basin, because it is reminiscent of a Texas Longhorn or Highland Cattle (Fig. 10.9, right).
McKenzie demonstrated mathematically that the heat flow within a basin was related to the amount of crustal stretching, termed the/3 value. The higher the rate of
stretching, the higher the heat flux during the initial phase of rifting (Fig. 10.10, upper).
The/3 value for a basin may be discovered by constructing a burial history curve for
the basin and comparing it with known curves calculated for given/3 factors (Fig. 10.10,
lower). The accurate prediction of the history of heat flow in a sedimentary basin is a
prerequisite to the accurate modeling of petroleum generation (Dore et al., 1991; Helbig, 1994).
10.2 SEDIMENTARY BASINS CLASSIFIED AND DESCRIBED
10.2.1 Classification of Sedimentary Basins
Attempts to classify the various types of sedimentary basins have been made by many
geologists, notably Weeks (1958), Halbouty et al. (1970), Perrodon (1971), Klemme
(1980), and Allen and Allen (1990). These classifications vary according to the defining
parameters which have been chosen, and according to the purpose for which a scheme