--> Mechanical Equilibrium in Sequence Stratigraphy, by S. Naofumi and M. Yosinori; #90986 (1994).

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Abstract: Mechanical Equilibrium in Sequence Stratigraphy

Sakuyama Naofumi, Matsuda Yosinori

In Sequence Stratigraphy "Regime Equation" is used to quantify morpho-dynamic interaction between sediment supply and accommodation. And the equation should satisfy equilibrium profile. This concept enable to describe Sequence Stratigraphy quantitatively, however there is no explanation of equilibrium itself and its origin except the shape of profile.

The sedimentary processes has both of dynamic and static characteristics. Fluid-sediment interaction with current and wave is a typical example of dynamic character. Static characteristics can be called as sediment stability, and is controlled by its shear strength, this strength can maintain not only slope angle but also facies distribution as a result.

Based on the Coulomb's law, Shear strength (^tgr) of the sediments is described with sediment's mechanical parameters of cohesion (c), vertical stress (^sgr1) and shear angle (^THgr) as:

[EQUATION]

In the real world, mechanical parameters are varying upon diagenetic stages, lithologies and surrounding conditions. However, to simply apply Coulomb's law for sedimentation, following relationships are assumed: (1) cohesion is function of porosity; (2) vertical stress is weight of above layer; (3) shear angle is function of porosity.

Sediment stability is described as an interaction of gravitational force (G) and external force (F):

F plus G > ^tgr: unstable

F plus G <= ^tgr: stable

This mechanism enable to understand static (or large scale) sediment movement and basin scale lithological distribution. The result of the simulation shows potentiality of this model for better understandings of the basin fill processes.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994