Print this pageStratigraphy of Deep-Water Turbidites, Part II: Variations and Controls on Geomorphological Elements
MORRIS, WILLIAM R., HENRY W. POSAMENTIER, STEVEN P. ROSS, and JAMES A. LORSONG
A geomorphologically-based tripartite system including: (I) a tributive canyon (or gully) province, (II) a turbidite valley province, and (III) a dis tributive channel complex province, commonly characterizes deep-marine turbidite complexes. The size and type of turbidite elements that characterize these provinces show considerable variation between different turbidite systems. This variability is controlled largely by feeder system type, sediment flux and caliber, tectonic activity, relative sea level, and basin margin physiography. The variation in the type and size of these turbidite elements significantly affects the distribution of reservoir facies in turbidite systems.
Province I serves primarily as a conduit for coarse grained sediment into the basin. Large sheff indenting submarine canyons are associated with the largest types of turbidite systems, have a well developed tripartite division, whereas juvenile submarine canyons or gullies feed small base of slope turbidite systems and slope aprons. Factors favoring the development of shelf-indenting canyons versus gullies include sheff margin maturity, confinement of feeder system and low sediment supply.
Province II, the turbidite valley, typically contains the thickest accumulation of coarse-grained sediment, primarily confined to narrow conduits. The dimensions of these turbidite valleys is largely controlled by sediment flux and caliber, and the type of slope conduit (in province I). The largest and longest of these turbidite valleys occur where sediment flux is high and sediment caliber low, whereas low sediment flux and high sediment caliber are characterized by smaller turbidite valley complexes.
The third turbidite province consists of a distributive complex of channels (described by others as unconfined-flow lobe deposits). This province lies at the basinward end of the turbidite valley where the levees are no longer capable of confining successive flows. The boundary between the turbidite valley and distributary channel complex migrates in response to avulsions and changes in sediment flux and caliber. This distributive complex of channels is broadly analogous to deltaic distributary mouth bars or crevasse splays in fluvial systems. The morphology of these distributary complexes ranges from broad braidplains in sand-rich systems to dendritic distributaries in mud-rich systems.