Interpreted Regional Seismic Reflection Lines, National Petroleum Reserve in Alaska

Interpretation of reprocessed data from a regional grid of 25 public-domain 2-D seismic profiles in the National Petroleum Reserve in Alaska has enabled an analysis of subsurface geologic relations throughout that region. Notable results include interpretations of the geometry of the Mississippian Umiat and Meade basins, and depositional patterns in the thick succession of younger strata that were influenced by major structural features such as the Barrow arch and the Brooks Range.

Pre-Mississippian low-grade metamorphic rocks and subordinate granites of the Franklinian sequence are the basement rocks of the region. The top of the Franklinian is imaged as one of the highest amplitude, most continuous reflections.

The sedimentary succession includes (1) the Mississippian to Triassic Ellesmerian sequence (consisting of the Endicott, Lisburne and Sadlerochit groups, and the Shublik Formation and Sag River Sandstone; (2) the Beaufortian sequence, comprising the Jurassic to Lower Cretaceous Kingak Shale and the overlying Lower Cretaceous pebble shale unit; and (3) the Cretaceous to Paleocene Brookian sequence, which includes the Hue Shale and the Torok, Nanushuk, Seabee, Tuluvak, Schrader Bluff, and Prince Creek formations.

Stratigraphic horizons that were mapped seismically include the tops of the Franklinian basement, the Endicott, Lisburne, and Sadlerochit groups, the Shublik Formation, the Sag River Sandstone, the Lower Cretaceous unconformity (LCU), and the gamma-ray zone of the Hue Shale. Distinguishing criteria were established for the seismic-reflection characteristics for each of these horizons, and the results were used in the correlation of units across the basins and onto the bordering margins.