C.G. Mull1, Ellen E. Harris1, M.T. Whalen2, M.B. Mickey3, Arthur Banet4
(1) Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK
(2) University of Alaska, Fairbanks, Fairbanks, AK
(3) Micropaleo Consultants, Inc, Encinitas, CA
(4) Bureau of Land Management, Anchorage, AK
ABSTRACT: Organic-rich, Oil-prone Triassic-Lower Jurassic Source Rocks and a New Exploration Play Type in Southern Colville Basin and East-central Brooks Range Foothills, Northern Alaska
Mapping and geochemical studies in the east-central Brooks Range foothills suggest that organic-rich, oil-prone Triassic and Lower Jurassic source rocks are present in the southern Colville Basin in addition to dominantly gas-prone Cretaceous source rocks. Thrust sheets at the mountain front contain the Upper Triassic-Lower Jurassic Otuk Formation, which correlates partly with the Shublik Formation in the North Slope subsurface--a major source of Prudhoe Bay oil, and partly with the basal Kingak Formation-the source of the oil in the Alpine field. At the mountain front, the Otuk contains up to 6% total organic carbon (TOC) but is thermally overmature for generation of liquid hydrocarbons (>2.0%Ro). To the north, imbricate thrust sheets in a triangle zone beneath a passive roof thrust in Cretaceous cover rocks record progressively lower levels of thermal maturation. The northernmost thrust sheet in the triangle zone contains Upper Triassic and Lower Jurassic source rocks (6-10% TOC) that are thermally mature for oil generation (<1.2%Ro) and are more similar to the Shublik Formation of the North Slope subsurface than to the allochthonous Otuk Formation at the mountain front.
Thrust emplacement was coeval with mid-Cretaceous deposition of the Fortress Mountain and Torok Formations, which locally contain oil typed as Triassic by the U.S. Geological Survey. Similar relationships in the western Brooks Range suggest that the entire southern flank of the Colville Basin has potential for a variety of migration pathways associated with syndepositional structural emplacement of oil-prone Triassic and Jurassic source rocks into proximity with potential Cretaceous reservoirs.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado