REFLECTIONS ON THE NUKA FORMATION AND OTHER RELATED ROCKS IN THE WESTERN BROOKS RANGE, ALASKA

LEWIS, Christopher J., P.O. Box 924, 2 Berry Lane, Ross, CA 94957, [email protected]

These reflections are derived from four geological field surveys carried out by the author from 1964 to 1970 as part of various BP Exploration (Alaska)teams. In 1970, the entire field season was devoted to a study of the Nuka Formation area. This was not only directed at the stratigraphic and structural features of the formation itself but also to its stratigraphic and structural relationships to the surrounding rocks.

The main purpose of the survey work was to identify potential reservoirs in the Mountain Front area, attempt to ascertain their relationship to potential source rocks and seals and hope to develop a case for projecting them northwards into potential petroleum traps on lands that might become available for drilling on the Arctic Slope. This objective was not achieved but much time was devoted to studying the stratigraphy and structural relationships.

If one examines geological maps of the Western Brooks Range, for example: Plate 7.1 in USGS Professional Paper 1399 compiled by Mayfield from unpublished field mapping by Tailleur, one will find in the legend an abundance of allochthons, no less than seven. In our observations, we only identified one clearly defined nappe. We called it the Echo Mountain Nappe. This would probably include the Tailleur's Copter Peak, Ipnavik River and Misheguk Mountain allochthons. Although, structural relationships in the Mountain Front are very complex there is some evidence of facies changes, which might also explain away some of the other allochthons. The talk will be supported by a series of cross-sections attempting to reconstruct the evolution of the area through time.