Carbonate Turbidity Currents: Examining the Effects of Grain Density
Carbonate turbidity currents can transport particles of a wide range of size, shape, surface texture and density dependent on the spatio-temporal evolution of the source carbonate platform. Variation in grain properties potentially generates spatially and temporally complex flows. Facies character and distribution may vary from traditional siliciclastic models. To investigate one control on this potential variation, experimental gravity flows were generated to assess the influence of particle density on flow and sedimentation processes. Each experimental run used sediment of the same grain size but different densities. Results from experiments using 100% silicon carbide (ρ = 3214 kg m-3), 100% glass ballotini (ρ = 2650 kg m-3) and 50% particle mixtures will be presented. In runs with the same (1%) initial suspended sediment volume concentration, density currents with a mixed particle composition appear to transport more mass downstream and maintain greater head velocity than either of the single-particle-composition flows. In experiments with the same initial bulk density, and thus differing initial volume concentration, deposit distribution and head velocity of the mixed flow more closely match those of the flow with only low density particles. Mixtures of different particle densities cause flow behavior to differ from mono-density particle currents. Maintenance of flow propagation velocity in mixed flows results from high initial velocity provided by the denser particles and current buoyancy maintained by the prolonged presence of less dense particles. Carbonate turbidity currents, with mixed density particles, may more efficiently transport sands. Flow stratification resulting from grain density effects has implications for the development of vertical and downstream facies patterns. In a submarine channel setting, channel over-spilling has the potential to create coarse, low density sand levees. Examples of carbonate submarine channel levees commonly contain coarser sands than their siliciclastic counterparts. Therefore they might be attractive reservoir targets and/or increase effective reservoir size.