Mass Delivery and Frequency of Submarine Fan-Building Turbidity Currents

Submarine fans are the largest sediment accumulations on Earth and represent the ultimate sink for clastic detritus. The sediment budget and frequency of turbidity currents that construct submarine fans are poorly understood due to lack of modern flow measurements. Only in the past few years have reliable flow measurements been made in submarine canyons, while no sand-carrying flow has been measured on a submarine fan. However, core and seismic data from modern submarine fan systems can be used to reconstruct sediment budgets and flow frequencies. Using a simple formulation that uses only three measurements (sediment mass of the fan, duration of deposition, and the flow recurrence interval), this study calculates event mass delivery and event frequency for an intraslope submarine fan on the western Niger Delta continental margin. Ranges of each measurement enable a probabilistic uncertainty analysis of the event mass-frequency parameter space. Results indicate that the mass delivered to the fan by a single turbidity current is on the order of 0.8 to 3 megatons (Mt) and the frequency of these events ranges from 85 to 195 yr-1. The total mass of the youngest lobe element on the intraslope submarine fan is 60 Mt and the total duration of deposition is 4,000 years, indicating that between 20 and 30 event beds compose this lobe element. Using data from other well-characterized modern submarine fan systems, we compare turbidity current mass delivery and frequency in different tectonic and physiographic settings. Preliminary results suggest that terminal submarine fans have larger event volumes than intraslope fans, suggesting significant sediment bypass in intraslope settings. Furthermore, different submarine lobe/fan hierarchical levels (e.g., lobe elements vs. lobes) occupy separate regions of the mass-frequency parameter space. This study demonstrates that valuable information about sediment budgets and event frequencies can be derived using simple mass-balance formulations. The ranges of mass delivery and event frequency presented here can be used as a tool for predicting geometric and age constraints in ancient (subsurface or outcropping) submarine fan successions.