Abstract: Neocomian Source and Reservoir Rocks in the Western Brooks Range and Arctic Slope, Alaska

C. G. (Gil) Mull, R. R. Reifenstuhl, E. E. Harris, R. K. Crowder

Detailed (1:63,360) mapping of the Tingmerkpuk sandstone and associated rocks in the Misheguk Mountain and DeLong Mountains quadrangles of the western Brooks Range thrust belt documents potential hydrocarbon source and reservoir rocks in the northern foothills of the western DeLong Mountains and adjacent Colville basin of northwest Alaska. The Neocomian Tingmerkpuk sandstone has been mapped in a nearly continuous 50 mile belt in the northern foothills, and mapped discontinuously with the related "coquinoid limestone" facies for another 40 miles toward the Lisburne Peninsula in the western part of the DeLong Mountains quadrangle. Two facies belts juxtaposed by thrusting are mapped. A northern belt has a succession of up to 400 feet of fine-grained quartzarenite with charac eristics of turbidity current deposition. A parallel southern belt contains similar but much finer grained and more thinly bedded sandstone that apparently is a more distal Tingmerkpuk facies. The distribution of the facies belts is compatible with a northern source for the Tingmerkpuk and represents a model for interpretation of Neocomian depositional environments in the Colville basin to the north. Neocomian(?) to Albian micaceous shale, litharenite, and graywacke that overlies the Tingmerkpuk represents the onset of deposition of orogenic sediments derived from the Brooks Range to the south, and the merging of northern and southern sediment sources in the Colville basin.

Both the proximal and distal Tingmerkpuk facies contain clay shale interbeds and overlie the Upper Jurassic to Neocomian Kingak Shale. Preliminary geochemical data show that in the thrust belt, these shales are thermally overmature (Ro 1.4-1.6), but are good source rocks with total organic content (TOC) that ranges from 1.2 to 1.8%. Organic extracts show that the shale contains mixed organic material that has generated some waxy oil and gas. Shale in the overlying Brookian rocks is also thermally overmature (Ro 1.2-1.5%), but contains up to 1.8% TOC from a dominantly terrigenous source, and has generated gas.

In outcrops at Surprise Creek, in the foothills north of the thrust belt, the Kingak (1.9% TOC) and underlying Triassic Shublik Formation (4.6% TOC) are excellent oil source rocks with thermal maturity close to peak oil generation stage (Ro 0.75-0.9%). These rocks have lower thermal maturity values than expected for their stratigraphic position within the deeper parts of the Colville basin and indicate anomalous burial and uplift history in parts of the basin. Preliminary apatite fission-track (AFTA) data from the thrust belt indicate a stage of rapid uplift and cooling at about 53-61 Ma.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California