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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Energy Dissipation: Origin of Structure and Organization in Siliciclastic Sedimentary Systems
By
Siliciclastic strata are nested bundles of sedimentary bodies
classified and named according to depositional environment,
geometry, and scale. Our analysis
of 482 sedimentary bodies
formed by unidirectional, fully turbulent flows, ranging in length
scales from <10 cm to thousands of kilometers,
from most depositional environments, reveals
that the shapes of these bodies are statistically
similar, scale invariant, and independent of
depositional environment. This similarity
suggests that these bodies were deposited by
a common global physics. We postulate that
this fundamental physics is non-equilibrium
thermodynamics, in particular, energy dissipation
and dissipative structures.
Geologically significant flows are far-from-equilibrium
open systems with large energy gradients.
The Second Law of Thermodynamics requires that these gradients
be minimized. Far-from-equilibrium flows do this through
the formation of dissipative structures. The primary dissipative
structure in flows in all environments of deposition is
the jet/plume pair linked through a hydraulic jump. Such flow
structure is self
-similar and scale invariant, from the scale of the
entire flow down to the viscous sublayer. For this reason, the
bodies produced by this type of decelerating flow are also scale
invariant.
The jet/plume pair dissipates kinetic energy though entrainment in the jet portion of the flow causing flow deceleration. In the process, deposition occurs if the flow is carrying particles. As the resulting sedimentary body grows and interacts with the flow, it also becomes a dissipative structure. We believe that all sedimentary bodies, from current ripples to submarine fans, are dissipative structures. That is, a sedimentary body is the framework to optimally deliver kinetic energy through channels or flow pathways to new dissipation sites where jets are active.
As a result of deposition and consequent vertical growth of the sedimentary body, flows are superelevated by being locally forced up and over the deposit. This creates the energy dissipation paradox: in the process of dissipating kinetic energy, potential energy is created. Potential energy gradients are minimized by another dissipative mechanism, avulsion.
This evolution of sedimentary bodies from the
initial jet deposits to complex avulsive bodies
such as deltas and submarine fans follows a
specific pathway from jet deposit nonavulsive or
leaf deposit avulsive or tree deposit. We call this
the energy dissipation pathway. It is the scale
invariant pathway along which all sedimentary
bodies evolve. We believe that current ripples,
bars in rivers, deltas, and submarine fans all form and evolve
along this pathway. If correct, this hypothesis of energy
dissipation and the energy dissipation pathway provides a
new, unifying context for the analysis
and interpretation of
sedimentary systems.
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