Sedimentology of proximal and distal deep-water deposits : syn-rift deposits of the burquan formation, Saudi Arabia and slurry-flow deposits of the wilcox formation, Gulf of Nexico and the Tyee formation, Oregon
Keywords: Geological and Environmental Sciences.

Gravity-driven sediment flows within deep-marine settings are responsible for transporting and ultimately redistributing immense volumes of sediment from the terrestrial realm into the deep sea. The sandy deposits of these flows, known as turbidites, form clastic reservoirs that are often host to vast hydrocarbon accumulations. Deep-water reservoirs are among the riskiest of exploration targets, yet their internal architectures and rock properties are among the least understood, largely because of the exceptional difficulty in observing active flows and the challenges associated with replicating them in the laboratory. Successfully identifying and penetrating a deep-water petroleum reservoir is in itself challenging, but it is equally and additionally challenging to find those that are economical in terms of their producibility. A rock's producibility is strongly linked to its textural properties, such as its grain size profile and mud content. These textural properties, in turn, are strongly controlled by the character of the depositing sediment flows, a first-order element of depositional analysis. This dissertation studies the deposits of three ancient deep-water systems, representing two contrasting basinal settings. Chapters 1 and 2 focus on ancient (Paleogene) fine-grained deposits from the distal parts of the Gulf of Mexico basin and the Tyee forearc basin of Oregon, respectively, while Chapter 3 focuses on proximal, coarse-grained syn-rift deposits associated with the opening of the Red Sea, NW Saudi Arabia (L. Miocene). Core taken from the Paleogene Wilcox Formation, deep-water Gulf of Mexico (Ch. 1), totaling some 360 meters of stratigraphy, was statistically analyzed in terms of facies types, bed thicknesses, and reservoir properties. The Wilcox Formation contains abundant slurry-flow deposits, a hybrid or transitional class of deposits commonly found in deep-water reservoirs that exhibits components of both good and poor reservoir quality. Slurry-flow deposits are characterized by a basal unit of clean, mud-poor sandstone and an upper unit of 'dirty, ' mud-rich sandstone. In addition to reducing producibility, this bipartite structuring of slurry-flow deposits makes them difficult to interpret because it seems they are deposited from two flow types during a single sedimentation event. This study demonstrates that in addition to distal lobe-fringe environments, a common interpretation ascribed to slurry-flow deposits, they also appear associated with splay-related avulsion events and autogenically-controlled lobes. In order to more closely explore how slurry-flow deposits are formed, Chapter 2 examined the fine-scale textural properties of individual slurry beds from the Tyee Formation, including grain size profiles, mud contents, and their associated upward trends, and compared them to those from more classical turbidites from the same formation. Finally, the Burqan Formation (Ch. 3), located on the Midyan Peninsula, Saudi Arabia, represents a world-class exposure of very coarse-grained and proximal syn-rift deposits. These deposits were evaluated in terms of their proximal to distal downslope changes and stratigraphic architecture. The results provide insight into the nature of conglomeratic deposition in deep-water environments, a relatively poorly understood phenomenon. Collectively, these findings have broader significance to the modeling of deep-marine petroleum reservoirs and should be appropriately considered in resource evaluations.