S. Julio Friedmann¹, David C. Mohrig², Carlos Pirmez², Anthony R. Sprague², T. Kenneth Fowler²

(1) ExxonMobil Upstream Research Co, Houston, TX
(2) ExxonMobil Upstream Research Co

ABSTRACT: Deep-water depositional styles linked to regional controls: Phase diagrams and equilibrium profiles

Subaqueous sediment gravity flows, especially turbidity currents, change profoundly and rapidly between deposition and erosion. It has been long known that many factors affect this behavior, chiefly gradient, flow concentration, flow column height, and distribution of grain-sizes. These are chiefly the result, respectively, of slope tectonics and basin configuration, failure size and rate, degree of confinement, and regional provenance inputs (modulated by the shelf and hinterland effects). This paper presents an attempt to reduce the number of parameters into a few key variables, including independent ones like gradient and dependent ones like flow velocity. The discussion is confined to turbidity currents and their products.

One can construct phase diagrams that map the behavior of depositional units across a variety of static and changing slope and basin floor configurations. These diagrams plot key variables against each other (e.g., gradient vs. velocity) and each diagram contains an equilibrium line. This is the position in phase space where neither erosion nor deposition occurs for the given set of input parameters. The thinness of this line reflects the rarity of equilibrium, but helps to explain how systems evolve towards equilibrium conditions. Erosion, bypass, and reservoir architecture can be mapped out within such parameter space as well. This approach provides a quick conceptual method to check basin depositional models against the controlling regional inputs.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado