Genesis and character of thin-bedded turbidites associated with submarine channels

• Published in: Marine and petroleum geology 2015-11, Vol.67, p.852-879
• Main Authors: Hansen, Larissa A.S., Callow, Richard H.T., Kane, Ian A., Gamberi, Fabiano, Rovere, Marzia, Cronin, Bryan T., Kneller, Benjamin C.
• Format: Article
• Language: English
• Subjects: Depositional terraces; External levees; Hydrocarbons; Ichnology; Internal levees; Levees; Reservoir; Submarine channels; Terraces; Thin-bedded turbidites
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2015.06.007

Submarine channel-related thin-bedded turbidites are deposited in environments such as external levees, internal levees, depositional terraces and at times of channel abandonment. Thin-bedded turbidites are defined as beds that are less than 10 cm thick, but the described environments can at times contain beds up to 100 cm thick which would be classified as medium- or thick-bedded. This paper addresses examples of these environments from the modern seafloor, outcrop and the subsurface to suggest criteria that assist in the differentiation of levees and terraces from an architectural, sedimentological, ichnological and hydrocarbon reservoir perspective. External levees confine channel belts and are elongate sedimentary deposits that are a product of over-spill of turbidity currents from the channel belt they confine. External levees often have predictable vertical, lateral and downstream changes in thickness and sand content but are commonly modified by collapse of the inner external levee into the channel, by collapse on the outer external levee, by sediment waves, and by interaction of external levees with topographic features such as other channels, other external levees, basin margins or previous slump/slide blocks, which can greatly modify the sand distribution within them. A combination of internal levees, depositional terraces and slide blocks of external levee sediment make up thin-bedded turbidites within channel belts. We differentiate between wedge-shaped internal levees and topographically flat or subdued depositional terraces, whose differing geometries and sand distribution reflect the fact that the flow processes involved in the formation of these deposits are different. The characteristic wedge shape of an internal levee requires sufficient space within the channel belt for the over-spilling current to spread, decelerate and deposit the majority of its silt and sand grade suspended sediment before reaching the bounding topography of the channel belt. In the case of depositional terraces the space available in the channel belt is insufficient for the current to decelerate and deposit the majority of its sediment before reaching the bounding topography of the channel belt, creating confined sheet-like deposits. External levees, internal levees and depositional terraces have distinct sedimentological characteristics such as sand bed thickness trends and sedimentary structures that can be used to distinguish them. Together with sedimentological