Geologic map of the Umiat-Gubik area, central North Slope, Alaska

Report of Investigation 2018-6, Geologic map of the Umiat-Gubik area, central North Slope, Alaska, provides a 1:63,360-scale geologic map of the hydrocarbon-bearing Umiat-Gubik area of the central North Slope, Alaska, spans approximately 2,100 km2 at the northern extent of the Brooks Range foothills fold-and-thrust belt in the Colville foreland basin. This geologic map was prepared through assimilation of field observations, aerial and satellite imagery, seismic-reflection data, and well logs. Near-surface formation picks were available or derived for most of the area's 24 exploration wells, and two cross-sections were constructed along lines of section that are constrained at depth by our interpretations of publicly available two-dimensional seismic data. The mapped area hosts exposures of Upper Cretaceous strata in the Nanushuk, Seabee, Tuluvak, Schrader Bluff, and Prince Creek Formations, constituting an approximately 2-km-thick succession that crops out discontinuously in the low-relief, tundra-mantled region. This part of the siliciclastic Brookian megasequence stratigraphy comprises principally shallow-marine deposits. Our work benefits from and reflects recent sequence-stratigraphic advances that better constrain how this part of the Colville basin continued to fill by a northeastward prograding clastic wedge during Late Cretaceous time, with the exposed stratigraphy recognized as basin-scale topset units. A series of east- to east-southeast-trending, km-scale wavelength, gentle folds are mapped in the area. Anticlines are locally breached by thrusts and interpreted to be folded above faulted and penetratively deformed mid-Cretaceous Torok Formation. Undeveloped, sub-commercial (as of this writing) petroleum accumulations occur along doubly plunging anticlinal traps at three long-recognized fields in the map area: Umiat (mostly oil), Gubik (gas), and East Umiat (gas). The Umiat oil field structural culmination is modified by thrust faults that breach the surface, and the East Umiat gas field is associated with a north-dipping back-thrust that is evident in seismic data and cuts across the Upper Cretaceous stratigraphy; thrust faults near the Gubik gas field lie within and below the Torok Formation. Various interpretations have previously been published for some of the area's structures, with important implications for petroleum trap geometries in the gas-prone foothills region. We present new data and interpretations that support the inference of a principal, south-dipping thrust fault that breaches the north limb of Umiat anticline near Umiat. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/30099.

Tags: alluvial deposits, anaktuvuk river, barrow trail member, bearpaw creek, bentonite, brookian, brookian sequence, brooks range, campanian, cenomanian, chandler river, colville basin, colville river, coniacian, cretaceous, dggs, energy, folds, foreland basin, formations, fossil creek, fracture, gems, gems ncgmp09, geologic, geologic map, gubic gas field, henry creek, hydrocarbon, kakiagun lake, kikiakrorak river, kogosukruk river, kutchik river, maastrichtian, mudstone, nanushuk formation, north slope, oil and gas, outcrop samples, petroleum, prince creek, prince creek formation, quaternary, rainy creek, roger creek, rogers creek member, sandstone, santonian, schrader bluff formation, seabee creek, seabee formation, sedimentary rocks, seismic interpretation, sentinel hill member, sequence stratigraphy, shivugak bluff, siltstone, statemap project, surficial geology, tattitgak bluff, tuluvak formation, turonian, umiat, umiat lake, umiat mountain
Organization: State of Alaska