The effects of grain-density variation on turbidity currents and some implications for the deposition of carbonate turbidites

Sediment grains in carbonate turbidity currents vary greatly in size, shape, surface texture, and density depending on the evolution of the source carbonate platform in time and space. Facies character and distribution may vary from traditional siliciclastic turbidite models not only because of the difference in composition but also because variation in grain properties influences flow and depositional behavior. Experimental gravity flows were generated to investigate one control on this variation. The experiments used silicon carbide ( = 3214 kg m–3) and glass ballotini ( = 2650 kg m–3) with a similar grain-size distribution in varying proportions to assess the influence of particle density on flow and sedimentation processes. Mixed-particle density flows were more efficient than single-particle density flows. Flow propagation was faster in flows with greater initial bulk density determined by grain density and suspended-sediment concentration. With mixed-particle suspensions flow propagation velocity was maintained for longer due to the presence of low-settling-velocity particles. As a result mixed-particle density flows transported more sediment downstream compared to single-particle density flows of similar initial suspended-sediment volume concentration. Because of the wider range of grain types in carbonate turbidity currents they may more effectively transport coarse, sand-grade sediment to more distal sites in a marine basin compared to siliciclastic counterparts of equivalent initial volume. This results in differences in bed and facies geometry and distribution.