Confined Flow in Deep-Water Settings from Slope to Basin Floor: Contrasting Architecture and Morphologies between Deposits Associated with Fully- and Partially-Contained Channelized Flow

Posamentier, Henry W.¹ (1) Anadarko Petroleum Corporation, The Woodlands, TX

Total to partial flow Confinement occurs in a variety of deep-water settings from slope to basin floor. Total confinement can occur within underfit systems or in cases where sediment gravity flows opportunistically use channels formed by other processes such as mass failure. In underfit channels, levee within master-bounding levee architecture is common. This situation can arise where flow discharge has diminished significantly between early and late phases of channel evolution. Sand-to-mud ratios within underfit flows as they travel basinward remain relatively constant because little mud-prone sediment from the upper parts of the turbidity currents is able to escape the confines of the master channel. No overbanking of master levees occurs and external levees are not constructed. Without the accelerated loss of fine-grained sediments associated with overbanking, fully-confined flows are capable of traveling greater distances before transitioning from leveed channel to frontal splay than similar flows only partially confined. Similarly, where flows occupy channels formed by mass failure, such as canyons and large slump scars, external levees do not form and sand-to-mud ratios remain relatively constant as flows travel basinward.

In those instances where only partial confinement occurs, overspill and flow-stripping processes can rapidly decrease the mud content in a flow, resulting in an accelerated increase in sand-to-mud ratio as turbidity currents travel basinward. Compared with similar flows that are fully confined, partially confined flows are characterized by transitions from leveed channel to frontal splay that lie markedly landward.

Sand habitats associated with fully confined flows are largely restricted to channel fills and minimal levee deposits. In contrast, sand habitats associated with partially confined flows are more varied and widespread, including not only channel fills but also crevasse splays, overbank sediment waves, and more widespread thin-bedded sands in levees.