Fill And Spill Model And Sand Distribution For Deep-water Mini-basins

Study area, Mad Dog, is located in the lower slope of the northern Gulf of Mexico, runs along the Sigsbee Escarpment and lies along the western edge of Atwater deep water fold belt. The prominent characters are numerous minibasins lying continental slope with partially or completely isolated from neighboring minibasins by salt ridges. The complicated topography and related accommodation can significantly affect the dynamics and deposition of turbidity currents. The model of minibasin filling and spilling and the discipline of sand distributions in minibasin still remains poorly understood, and these are also the aim of the study.From old to young, the evolution of minibasins in Mad Dog area can be divided into four phase, wedged phase, ponded phase, bypass phase and drape phase. During wedge stage, turbidity current tends to strip the upper mud-rich portions downstream across the sill and arouses the sills broadly eroded in entry and exit due to sill as a low bathymetric obstacle. Whereas, there is not dramatic channel shape incision detected on sill. Several small high sinuosity, variable directions channels and a large channel can be detected; however, most of these channels exhibit distinct deflection to parallel the trend of sill when they encounter the salt ridge. The onlap phenomenon still can be identified especially in early of this stage in despite of most strata extending over the positive relief. During ponded period, the downstream sill uplift created an enclosed depression causing sediments entirely trapped in minibasin. The most obviously phenomenon in this stage is strata onlap to the stoss slope of downstream salt ridge. The mass-transport deposits occurred on the reversal slope of salt ridge in downstream; whereas, in proximal of minibasin, abrupt reduction in sea-floor gradient setting didn’t engender submarine fan due to absent the feeding channel. During bypass stage, the multi-phase large, extending out the whole study area canyons in minibasin area exhibits low sinuosity absent-levee in early period and high sinuosity with cut-off loops and levees in the late stage. During drape stage, various mass-transport deposits pulse disturbed the hemipelagic equable deposits after the minibasin is entirely filled.According to aforementioned observations, during salt ridge relative low wedge period, large-scale flow-stripping processes can occur and cause some of the suspended sediment (including slit and clay) to surmount the crest of the barrier, resulting in initial fine-grained fill basinward of the mini-basin sill and possible coarser-grained material with sheet distribution blocked in the reversal sill. Furthermore, the progressive flow stripping of the fine-grained component of the turbidity currents will cause the upward increase in the sandstone/mudstone ratio and grain size into the very sandstone-rich portion. The flow filling and spilling pattern also determines to lack of submarine fan in proximal of minibasin. Ultimately, the minibasin filling and spilling model was established to forecast the location and distribution of sandstone in complicated submarine settings.