NUMERICAL-SIMULATION OF TURBIDITY-CURRENT FLOW AND SEDIMENTATION .2. RESULTS AND GEOLOGICAL APPLICATIONS

A process-based, forward computer model of turbidity current flow and sedimentation, termed the TCFS model, has been developed to trace the downslope evolution of individual turbidity flows. Details of the mode l itself have been presented in a preceding paper. We here outline a s eries of tests of the TCFS model. The sensitivity tests of the TCFS mo del to general geological controls reveal the quantitative relationshi p between these controls and the behaviour of turbidity flows and the geometry and textural features of the resulting turbidites. Experiment al turbidity currents on relatively steep slopes accelerate more rapid ly and reach higher velocities than those on gentle slopes. Flaws with larger initial volumes have higher initial velocities, travel further downslope, and form beds of greater thickness and downslope extent th an smaller flows. Experimental high-concentration flows with suspended -sediment concentrations of 25% accelerate more rapidly and reach high er downslope velocities than dilute flows with 5% suspended sediment. The higher velocities and enhanced hindered-settling effects of the hi gh-concentration flows lead to much greater transport distances and re duced vertical and lateral sediment size grading in the resulting turb idites. Beds formed by experimental high-concentration flows are massi ve or show coarse-tail grading whereas beds formed by low-concentratio n flows show distribution-grading. Experimental flows fed by coarse se diment sources tend to deposit the bulk of their suspended sediment lo ads on the proximal slope, resulting in more rapid flow deceleration a nd sedimentation than flows fed by silt-rich, fine-grained sediment so urces. Turbidites formed by coarse-sediment flows tend to have a wedge -shaped geometry, with low downslope extent and high surface relief, w hereas turbidites formed by fine-sediment flows tend to have a tabular geometry, with greater downslope extent and lower surface relief. A s pecific geological test of the TCFS model is based on studies of moder n turbidity currents in Bute Inlet, British Columbia, Canada. With the input initial and boundary conditions estimated from Bute Inlet, the model predicts the downslope velocity evolution of turbidity currents comparable to those of modern and ancient turbidity flows measured in Bute Inlet. Model-calculated vertical and downslope grain-size propert ies of turbidites are similar to those exhibited by surface and cared Bute Inlet turbidites. Model flows tend to decelerate more rapidly tha n some stronger turbidity currents in the Bute Inlet system, and model beds tend to decrease in grain-size downslope more rapidly than obser ved bottom sediments. This is probably because the TCFS model flows la cked clay, which is abundant in Bute Inlet; they do not fully simulate turbulent mixing of suspended sediments; and they better represent th e unsteady, depositional stage of turbidity-currents than the precedin g stage of more-or-less steady-flow conditions. These tests demonstrat e that the TCFS model provides a semi-quantitative method to study the growth patterns of submarine turbidite systems, It can serve as a pre dictive tool for analysing the facies architecture of ancient turbidit e systems through simulating multi-depositional events by improving it s erosion function, and the compatibility between its numerical compon ents.