Topic: A Regional Look at Nanushuk Formation Facies in Outcrop, Brooks Range Foothills, Alaska
Speaker: Gregory C. Wilson, ConocoPhillips Alaska Inc.
The Albian-Cenomanian Nanushuk Formation, a largely regressive sequence of shelfal to nearshore marine, deltaic, and transitional to nonmarine rock strata crops out over a west-east belt of the Brooks Range Foothills of the western and central North Slope. Correlative rocks in the subsurface have garnered headlines in recent years with the Willow and Pikka-trend discoveries, but the Nanushuk Formation in outcrop has been a focus of work for decades by industry, the Alaska State DGGS, and the USGS. This presentation is focused on the less attention-grabbing outcrop distribution and facies of the Nanushuk Formation across the Brooks Range Foothills. The author has had the opportunity to work these rocks across the full extent of the outcrop belt from the east-central North Slope to the Chukchi Sea.
Studies over the last few decades can be lumped into regions of helicopter access. Outcrops within relatively easy range of camps along the Dalton Highway (“Haul Road”) and Umiat of the central to east-central North Slope have received the most attention in recent years, including detailed work by Dave Lepain and others with the State DGGS. Thick successions of marine and nonmarine are locally well exposed in foothills structures. These outcrops help establish a south-to-north loss of nonmarine facies, as well as several indications of relative sea level fall resulting in either forced regression or shelfal incision. The ultimate flooding event at the top of the Nanushuk Formation is exposed at several localities.
Outcrops of the west-central North Slope in the headwaters of the Meade River and upper Kigalik River are the most inaccessible from established camps and airstrips. A reconnaissance foray by ARCO in 1996 and a return for detailed stratigraphy by ConocoPhillips in 2006 revealed thick successions of lower coastal plain deposits readily tied to USGS seismic lines. One deep ravine succession unofficially named “Grand Canyon” was about 1000 feet of mostly inter-channel fill, but also contained channel and splay sands. Indications of marine facies were largely absent. A nearby outcrop (Lili Creek) with growth-position trees was the subject of a “Short notes on Alaska geology 1997” publication. South of this area marine facies of the Nanushuk are poorly exposed along continuous ridges.
Outcrops of the western foothills, accessible from airstrips at Deadfall, Akulik, and Eagle Creek, afford access to a wide range of environments. Mesas of the Eagle Creek area display thick successions of nearshore marine rocks (formerly “Kukpowruk Fm.”). Laterally continuous ridges of this marine facies reveal low-amplitude structures by the sweeping ridge designs on local topography. Outcrops of the Corwin Bluffs on the Chukchi Sea exhibit interdistributary flood plain deposits with coals, but also outcrops of multi-story channel complexes of sandstone as much as 100 feet thick. A short distance inland from the Corwin Bluffs are nonmarine gravel and cobble conglomerates with ridges as thick as 50 feet. Low country of the Utukok and Kukpowruk Rivers exposes flood plain deposits with localized distributary channels and interdistributary coal measures common. The Deadfall-Kukpowruk River area was drilled and explored for coal by BHP Billiton in 2008 while the author was present.
Greg Wilson is currently Manager of Exploration Operations and Technology for ConocoPhillips Alaska. He has 29 years of oil and gas exploration experience in Alaska with ConocoPhillips and heritage companies, ARCO and Phillips. His team assists Exploration and Development in Alaska, including drilling operations support, project evaluation, seismic acquisition, and seismic processing. Prior to his roles in management, Greg worked as project geologist for numerous exploration wells on the North Slope and conducted many seasons of field work in the Brooks Range foothills.
In years past Greg served various roles for the Alaska Geological Society, including President, Vice-President, and for eight years Newsletter Editor. In addition, he co-chaired the 2006 Joint AAPG-GSA-SPE Convention and the 2008 “Prudhoe at 40” Technical Conference. Greg currently serves on the State Mapping Board. He received a Distinguished Service Award from the Pacific Section of AAPG in 2011. Greg was an adjunct lecturer at Alaska Pacific University for five years. His PhD in Geology is from the University of Wisconsin-Madison.
Time: Doors open at 11:30 am, talk is from 12-1 pm