Alternative Resources

It all started in 2002, when Unocal revealed that its Trident-1 well had found 400 meters of 70-percent net Lower Wilcox Formation sand in the deepwater Gulf of Mexico, about 400 kilometers beyond the contemporaneous shelf break offshore south Texas. Art Berman and I gazed at a GOM activity map and pondered how that amount of sand could have been deposited so far out into the basin. Our working hypothesis was that this sand deposit was due to a drop in base level, but we also knew that the worldwide sea level was not in decline at that time. A log of the nearby Shell Great White well shows that this sand deposition began suddenly and ended suddenly. This was also puzzling, since we were trained to expect gradational coarsening-upward bedding during regression and fining-upward during transgression, rather than the sharp contacts we were seeing. Sudden avulsion of a major river in a deltaic environment could produce something like this, but how could it happen far beyond the shelf edge?