Lower Tertiary Deposition in Walker Ridge, Gulf of Mexico: An Example of Sedimentary Distribution in an Unrestricted Basin

Adam M. Seitchik and Timothy Powell
Devon Energy, Houston, TX

Prior to the Cascade discovery, the presence of a thick, aerially extensive Wilcox sand interval extending into the Walker Ridge Area was unknown. The Cascade #1 well, originally targeted as a Miocene test, penetrated a substantial section of hydrocarbon bearing sands in the Wilcox section. Further drilling in Walker Ridge and Keathley Canyon areas confirmed a pervasive depositional system of amalgamated sheet sands and opened a new exploration trend in a mature basin. Provenance studies and regional geologic interpretation indicate multiple sediment sources from the North and Northwest, specifically the Rockdale and Holly Springs deltas. These Deltas supplied sediments to the Walker Ridge fold belt from shelf margins located over 300 miles away. Deep water sedimentation may have occurred as a result of punctuated, catastrophic events, continuously sourced sand systems or a combination of the two. This sedimentation had minimal influence on underlying salt with paleo-reconstructions supporting Lower and Middle Miocene structural growth. Isopach maps of the Lower Tertiary section in the Walker Ridge fold belt show relatively minor thickness variations indicating subtle structures with low relief during Wilcox deposition. Thus the robust Walker Ridge fold belt present today caused little impediment to deposition at Wilcox time. In addition, mapping Lower Tertiary salt truncations in the Walker Ridge Area identifies no significant barriers that could obstruct sedimentation. As a result, deposition during Wilcox time occurred in an unrestricted basin, facilitating thick sheet sand accumulations across the Walker Ridge area.