372
ing center extended and underwent various changes
in configuration. Important events, such as the ini�
tiation of spreading in the Labrador Sea, the extension of spreading between Greenland and Europe,
and various jumps in ridge position, brought about
significant changes in plate trajectories, which
would have been accompanied by changes in the
direction and intensity of intraplate stresses.
Detailed studies of sea-floor spreading patterns in
the north and central Atlantic Ocean by Srivastava
and Tapscott (1986) and Klitgord and Schouten
(1986) have yielded a detailed history of plate
motions. Their reconstruction of a continuous succession of matched plate margins as the Atlantic
Ocean opened indicates that the rotation poles of the
North American plate relative to Europe and Africa
changed at intervals of about 2-16 million years.
This episodicity is comparable in magnitude to the
duration of third-order stratigraphic cycles, a fact
that is highly suggestive. Furthermore, some of the
changes in rotation pole can be correlated in time
with changes in the position of depocenters in the
Mesozoic-Ceriozoic stratigraphic record of the US
Atlantic continental margin. Poag and Sevon (1989)
compiled detailed isopach maps of the post-rift sedimentary record, and interpreted these in terms of
the shifting pattern of denudation in and sediment
transport from the Appalachian and Adirondack
Mountains. It seems likely that many of the major
existing rivers that presently carry sediment into this
region have been in existence since the Mesozoic.
Poag and Sevon (1989) were able to show many
changes with time in the relative importance of these
various sediment sources, and it is suggestive that
several of these changes occurred at times of change
in Atlantic plate kinematics. The sea�floor spreading
record reveals at least 14 changes in plate configura�
tion in the central Atlantic since the Mid-Jurassic
(Klitgord and Schouten 1986). Seven of these
changes, at 2.5, 10, 17, 50, 59, 67, and 150 Ma, correspond to times when the major sediment dispersal
routes from the Appalachian Mountains to the continental shelf underwent a major shift (data from
Poag and Sevon 1989).
Tectonism is diachronous and, in the case of the
intraplate stresses discussed by Cloetingh (1988), the
effe cts vary across the plate. Adjacent plates may be
expected to have dissimilar tectonic histories, except
where major extensional or collisional events affect
adjoining plates. However, no such tectonic controls
would be expected to be global in scope.
Tectonic Control of Fluvial Sedimentation
11.3.6 Quantitative Models of Sediment Supply,
Transfer, and Accumulation
The purpose of this chapter is to address the question of allogenic controls on sedimentation. How
do fa ctors of tectonism (uplift, subsidence) and climate change affect sediment supply, sediment caliber, sediment transfer, and sediment accumulation?
What does the large-scale architecture of the nonmarine stratigraphic record tell us about the working of these controls, and is it possible to relate the
rates and magnitudes of the controlling processes to
any quantitative, measurable attributes of the sedimentary product? As stated by Paola (1988, p. 231),
"The transition of basin analysis from a descriptive to an
analytical science requires the development of well�
founded theoretical models for basin development. including both the formation of basins and their infilling
with sediments."
Models for basin fo rmation, based on analysis of
the thermal and mechanical behavior of the crust,
have now reached a sophisticated level of development (see summaries by Miall 1990; Allen and Allen
1990). Models ··Of basin filling have been slower to
develop. Much work has been carried out on the
physics of sediment transport (e.g., Middleton and
Southard 1977), but the quantitative relationships
that have been developed from such work relate only
to instantaneous sedimentary conditions and cannot be used for the analysis oflong-term (geological)
sediment transfer and accumulation. The alluvial
stratigraphy models summarized in Sect. 10.4.3 deal
only with autogenic sedimentary processes. It is only
in the past few years that successful approaches to
this problem have begun to evolve.
The major developments in this area have been
made by C. Paola, P.L. Heller, and their colleagues in
a series of papers (Paola 1988, 1990; Paola et al. 1992;
Heller and Paola 1992). This work addresses the
question of mass balance of gravel in nonmarine
basins - the transfer, sorting, and accumulation of
geologically significant gravel deposits over geologically meaningful time periods. There are several independent fa ctors to consider. Among the major
controls are the rate of input of sediment and water,
the rate of sediment transport and basin subsidence,
the grain�size distribution and composition of the
gravel, and its downstream reduction in grain size
through abrasion and selective sorting. As noted by
Paola (1988, p. 233):
ing center extended and underwent various changes
in configuration. Important events, such as the ini�
tiation of spreading in the Labrador Sea, the extension of spreading between Greenland and Europe,
and various jumps in ridge position, brought about
significant changes in plate trajectories, which
would have been accompanied by changes in the
direction and intensity of intraplate stresses.
Detailed studies of sea-floor spreading patterns in
the north and central Atlantic Ocean by Srivastava
and Tapscott (1986) and Klitgord and Schouten
(1986) have yielded a detailed history of plate
motions. Their reconstruction of a continuous succession of matched plate margins as the Atlantic
Ocean opened indicates that the rotation poles of the
North American plate relative to Europe and Africa
changed at intervals of about 2-16 million years.
This episodicity is comparable in magnitude to the
duration of third-order stratigraphic cycles, a fact
that is highly suggestive. Furthermore, some of the
changes in rotation pole can be correlated in time
with changes in the position of depocenters in the
Mesozoic-Ceriozoic stratigraphic record of the US
Atlantic continental margin. Poag and Sevon (1989)
compiled detailed isopach maps of the post-rift sedimentary record, and interpreted these in terms of
the shifting pattern of denudation in and sediment
transport from the Appalachian and Adirondack
Mountains. It seems likely that many of the major
existing rivers that presently carry sediment into this
region have been in existence since the Mesozoic.
Poag and Sevon (1989) were able to show many
changes with time in the relative importance of these
various sediment sources, and it is suggestive that
several of these changes occurred at times of change
in Atlantic plate kinematics. The sea�floor spreading
record reveals at least 14 changes in plate configura�
tion in the central Atlantic since the Mid-Jurassic
(Klitgord and Schouten 1986). Seven of these
changes, at 2.5, 10, 17, 50, 59, 67, and 150 Ma, correspond to times when the major sediment dispersal
routes from the Appalachian Mountains to the continental shelf underwent a major shift (data from
Poag and Sevon 1989).
Tectonism is diachronous and, in the case of the
intraplate stresses discussed by Cloetingh (1988), the
effe cts vary across the plate. Adjacent plates may be
expected to have dissimilar tectonic histories, except
where major extensional or collisional events affect
adjoining plates. However, no such tectonic controls
would be expected to be global in scope.
Tectonic Control of Fluvial Sedimentation
11.3.6 Quantitative Models of Sediment Supply,
Transfer, and Accumulation
The purpose of this chapter is to address the question of allogenic controls on sedimentation. How
do fa ctors of tectonism (uplift, subsidence) and climate change affect sediment supply, sediment caliber, sediment transfer, and sediment accumulation?
What does the large-scale architecture of the nonmarine stratigraphic record tell us about the working of these controls, and is it possible to relate the
rates and magnitudes of the controlling processes to
any quantitative, measurable attributes of the sedimentary product? As stated by Paola (1988, p. 231),
"The transition of basin analysis from a descriptive to an
analytical science requires the development of well�
founded theoretical models for basin development. including both the formation of basins and their infilling
with sediments."
Models for basin fo rmation, based on analysis of
the thermal and mechanical behavior of the crust,
have now reached a sophisticated level of development (see summaries by Miall 1990; Allen and Allen
1990). Models ··Of basin filling have been slower to
develop. Much work has been carried out on the
physics of sediment transport (e.g., Middleton and
Southard 1977), but the quantitative relationships
that have been developed from such work relate only
to instantaneous sedimentary conditions and cannot be used for the analysis oflong-term (geological)
sediment transfer and accumulation. The alluvial
stratigraphy models summarized in Sect. 10.4.3 deal
only with autogenic sedimentary processes. It is only
in the past few years that successful approaches to
this problem have begun to evolve.
The major developments in this area have been
made by C. Paola, P.L. Heller, and their colleagues in
a series of papers (Paola 1988, 1990; Paola et al. 1992;
Heller and Paola 1992). This work addresses the
question of mass balance of gravel in nonmarine
basins - the transfer, sorting, and accumulation of
geologically significant gravel deposits over geologically meaningful time periods. There are several independent fa ctors to consider. Among the major
controls are the rate of input of sediment and water,
the rate of sediment transport and basin subsidence,
the grain�size distribution and composition of the
gravel, and its downstream reduction in grain size
through abrasion and selective sorting. As noted by
Paola (1988, p. 233):