Forcing
Mechanisms in Sequence Stratigraphy and the use of Simple Large-Scale Forward
Numerical Models
Geslin, Jeffrey1 (1)
ExxonMobil Exploration Company,
The interrelated forcing mechanisms of
climate, tectonics and eustasy control accommodation generation and sediment
supply rates that produce sequence stratigraphic architectures. The relative
dominance of one mechanism at a given location along a depositional profile
controls stratigraphic architectures at subregional to regional scales. Cyclic
changes in forcing mechanisms produce cyclic changes in accommodation
generation rate (A) and sediment supply rate (S). The ratio of rate of change
of accommodation generation rate (dA/dt) and rate of change of sediment supply
rate (dS/dt) controls generation of progradational, aggradational and
retrogradational stacking, as well as sequence boundaries and flooding
surfaces. Understand the distribution and cyclicity of dominant forcing
mechanisms along a depositional profile is crucial to successfully building
large-scale forward numerical models that predict lateral and vertical stratal
continuity and variability.
Simple large-scale forward numerical
models were used to investigate the effects of climatic and eustatic cyclicity
on a fluvial depositional profile where aggradation or degradation of the
landscape is controlled by changes in the equilibrium profile of the stream.
These finite difference pseudo-2D models demonstrate several sequence
stratigraphic concepts. 1) Eustatically generated sequence boundaries extend
only a relatively short distance updip of the shoreline (100-150 km) within the
models, dependent upon the degree to which dA/dt / dS/dt << 1. 2)
Sequence boundary formation in down-dip areas is dependent upon both baselevel
fall and stream power available to erode. 3) Climatic sequence boundaries that
form updip of areas affected by eustasy can be spatially and temporally
unrelated to down-dip eustatic sequence boundaries.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California