Physical Models of Subaqueous Transitional Sediment-Gravity Flows: Stacked Flow Interaction and Remobilization

Abstract

Many of the deposits in deep-water depositional systems exhibit features that suggest deposition by a combination of turbulent and laminar flow, transitional between turbidites and debrites. We modeled the interaction of these transitional sediment-gravity flows by stacking two flows with similar sand-mud-water ratios. Flows and deposit remobilizations were analyzed using a combination of sonar acquisition during the flows, post-flow 3D sonar acquisition, laser scan bathymetry maps, and sediment freeze cores. For all runs a large part of the sand was deposited in the proximal end, and at the base of the deposit, but for the more debris flow-like runs there were increased amounts of sand mixed with mud farther down dip and higher up in the deposit. Deposit tops were generally mud-dominated. Overall, deposits from the second flows had a similar geometry to deposits from the initial flows, with sand dominating in the proximal at the base. However, the second flows remobilized the upper portion of the initial flow deposit. This resulted in complete erosion and incorporation of the muddy deposit cap and some sand from the initial flow deposit into the overriding flow. Locally, the second flow scoured the initial flow deposit, filling the scour pit with sand and mud, only then to be overtopped by remobilized sediment from the initial flow deposit. These experiments show that transitional flows can and probably should be expected to interact with and remobilize deposits from previous flows. This can include sweeping away late-stage muds, incorporating sand from older flow deposits into younger flows, or even full remobilization. This interaction results in a redistribution of lithofacies that do not match existing depositional models for sediment gravity flows. Identifying the controls on deposits patterns is especially important for reservoir prediction in areas with poor seismic imaging and limited well-control, a situation not uncommon in ultra-deep water settings.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017