High resolution sequence stratigraphy and geochemistry of middle and upper Triassic sedimentary rocks, northeast and central Brooks Range, Alaska

• Main Author: Kelly, Landon Neal
• Format: Thesis
• Language: English
• Published: 2004
• Subjects: Fairbanks; Brooks Range; north slope; Prudhoe Bay; Alaska
• Online Access: http://hdl.handle.net/11122/6013

Thesis (M.S.) University of Alaska Fairbanks, 2004 Triassic age rocks constitute an important sedimentary interval on the North Slope of Alaska, because they include organic-rich source rocks that generated much of the oil that accumulated in the Prudhoe Bay field. Three detailed measured sections in the northeast and north-central Brooks Range are characterized using sequence stratigraphy, chemostratigraphy, biostratigraphy and ichnofabric, allowing interpretations about the evolution of the depositional environment and general paleogeographic setting through the Middle and Upper Triassic. High resolution correlation provides insight into the timing and pattern of source rock accumulation in the Shublik and Otuk Formations. Sequence and chemo-stratigraphic analyses suggest that deposition took place on a broad, low-angle shelf under fluctuating paleoceanographic conditions. Recorded are three third order sequences, each containing a sea level rise and highstand. Glauconitic, phosphatic, and organic-rich rocks of the Shublik and Otuk Formations indicate deposition in an environment characterized by oceanic upwelling. Organic and inorganic geochemical data support interpretations concerning paleoxygenation gradients. The cerium anomaly, manganese, phosphorus, vanadium, total organic carbon, and calcium-manganese ratio indicate dominantly oxic bottom waters during the Middle Triassic, dominantly low oxygen or anoxic conditions during much of the Upper Triassic, and a return to more oxic conditions in the late Upper Triassic. Ch. 1. Introduction -- ch. 2. Facies descriptions and formation subdivisions -- ch. 3. Facies associations and interpretations -- ch. 4. Sequence stratigraphy -- ch. 5. Geochemistry -- ch. 6. Results and conclusions -- Appendix 1 -- Appendix 2 -- References cited.