Variation in Depositional Pattern of Experimental Turbidity Currents Going Through a Break-of-Slope as a Function of Their Efficiency

Abstract

In turbidity current systems break-of-slopes are often associated with a channel-lobe transition zone and occur at the transition from continental slope to abyssal plain, or perched on irregular or stepped slopes. Turbiditic deposits in break-of-slope settings can form reservoirs for hydrocarbons depending on their upslope termination. In high-efficiency system, where grains are transported far into the basin, the deposits are located on the basin floor detached from the slope forming a stratigraphic trap, while in low-efficiency system the deposits are connected onto the slope making the formation of a stratigraphic trap unlikely. Therefore, the better understanding of the control factors on the systems efficiency in a break-of-slope setting is of interest for hydrocarbon exploration. The change in flow properties of a turbidity current going through a break-of-slope are well described in several experimental studies and build a strong foundation for the work presented here. However, the link between the flow properties and the resulting depositional pattern remains poorly constrained. This study will use experiments that focus on the scaling of the depositional behavior of turbidity currents to illustrate which geometrical factors of a break-of-slope setting lead to slope-attached and slope-detached depositional patterns. The plain and the slope angle have a very distinct effect on the flow properties and the linked depositional pattern. These effects are clearly reflected in the velocity and turbulence profiles of the flows, making it possible to link the flow properties to the onset of deposition. With steeper slopes the flow velocity increases and the onset of deposition is shifted further into the basin (i.e. efficiency is increasing). Steeper plain angles will led to a downward shift on the elevation of the velocity maximum and reduce the amount of deposition in the plain. However, the onset of deposition will stay at the same position, since it is controlled only by the slope angle. The experimental results will be linked to outcrop studies of a comparable deep-marine turbidite system from the Karoo basin (South Africa).

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016