Jaco H. Baas¹, James L. Best¹

(1) University of Leeds, Leeds, United Kingdom

ABSTRACT: Can Sedimentological Flows With Small Amounts Of Clay Particles Form Massive Sandstone Beds?

The boundaries of Newtonian and non-Newtonian flow were established through flume experiments investigating turbulence modulation in kaolin-laden flows using ultrasonic Doppler velocity profiling. In steady, uniform flows with a maximum downstream velocity of 39 cm/s and kaolin concentrations ranging up to 13%, three flow types were distinguished based on vertical profiles of horizontal velocity and the degree of turbulence suppression: (1) turbulent flow, with logarithmic velocity profile, at low volumetric sediment concentrations (C~1-2 %); (2) laminar plug flow at C > 4-5 %, with no turbulence and a plug zone moving on top of a laminar shear layer that possesses a steep velocity gradient, and (3) transitional flow at intermediate concentrations, in which most turbulence is generated by a basal shear layer, with quasi-laminar flow, and a weak velocity gradient characterising the upper region.

In transitional flows the basal shear layer had a lower velocity and higher turbulence intensity than in turbulent flow. Furthermore, downward directed flow accelerations were dominant at the base of the basal shear layer, and upward directed flow decelerations prevailed at the base of transitional-flow plugs.

The above threshold concentrations for turbulence suppression are common in many natural flows. The supportive strength of laminar plug flows (due to cohesion) and transitional-flow plugs (due to remaining turbulence and cohesion) may be insufficient to suspend non-cohesive particles. This has important implications for the sedimentary products of such flows: the deposits of sandy flows with small amounts of suspended clay may be massive, as often found in deep-marine successions.

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