Jet-Plume Depositional Bodies: The Primary Building Blocks of Wax Lake Delta, Louisiana
Robert W. Wellner1, Rick T. Beaubouef2, John C. Van Wagoner1, Harry R. Roberts3, and Tao Sun1
1 ExxonMobil Upstream Research Company, Houston, TX
2 ExxonMobil Exploration Company, Houston, TX
3 Louisiana State University, Baton Rouge, LA
Wax Lake delta is comprised of morphologically similar sedimentary bodies with predictable and statistically similar rock property trends. This relationship is thought to occur because each body is interpreted to have been deposited by expanding flows or wall jets.
Interpretation of aerial photographs indicates WLD formed by progradation and compensational stacking of jet deposits. In general, each body has a teardrop shape. The head of a body is characterized by thick, trough cross bedded sands that fill a scour. Vertical grain-size trends at any one location are typically uniform. The transition from the relatively confined scoured region to a conformable surface occurs over ~100 m and marks the transition from bedload to suspended load deposition. The suspended load deposits form a radial apron seaward of the scour pool. This suspended load region fines and thins away from the terminal end of the scour and is characterized by bedsets that exhibit partial or complete Bouma Sequences.
Abandonment of a body begins when the deposit reachs an elevation near mean low sea level. As this occurs, flow from the mouth of the distributary channel is forced into the topographic lows on either side of the stranded body. New bodies then develop adjacent to, and slightly seaward of, their stranded counterparts. In general, the readily available accommodation between bodies, not channel incision, is the dominant control on the development of new depocenters.
WLD is interpreted using a jet model, which departs from the model of distributary channel, stream-mouth bar, delta front, and prodelta.