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Mapping the North Slope
ALAN BAILEY & KAY CASHMAN - Reprint from Oct. 28, 2001, PN Petroleum News
Surprisingly, for an area as geologically significant as Alaska’s North Slope, the only readily available, color, geologic rendition of the entire area is a statewide map made in the 1970s by the U.S. Geological Survey at a scale of 1 inch per 40 miles. Although there are more recent and precise maps of various portions of the North Slope, some are private maps not available to the public and those that are available are a hodgepodge of different scales, styles and geologic interpretations.
Trying to make sense of the North Slope’s geology is a difficult exercise, especially for anyone new to the region. In an attempt to bring order from a certain amount of chaos, a team of specialists from the USGS and the Alaska Division of Oil and Gas is compiling an up-to-date set of geologic maps for the North Slope.
By early 2004, the team expects to have completed maps of a swathe of 15 quadrangles stretching south to north from the northern part of the Brooks Range to the edge of the Arctic coastal plain. From east to west, the project begins at the western edge of the Arctic National Wildlife Refuge and runs across the entire North Slope to the coast of the Chukchi Sea.
According to Gil Mull, veteran Alaska petroleum geologist working for the division on the project, the northern tier of quadrangles from Umiat to the west coast will be released at 1 inch per 4 miles. “The southern tier of quadrangles will be released at 1:125,000 — 1 inch equals 2 miles — because back close to the
mountain front, in what is informally called the disturbed belt, the geology is so chopped up and so complicated that it is really hard to portray at 1 inch per 4 miles,” Mull said.
The team’s 15 quadrangle maps will eventually be combined with USGS’s contemporary Arctic coastal plain (home
to Prudhoe Bay and other producing fields) and ANWR maps to make up an overall map of the North Slope.
Published at a scale of 1 inch per 16 miles, this map will include everything north of the Brooks Range from the western to the eastern borders of Alaska.
The USGS is providing most of the funding for the effort. The division is contributing Mull’s time. Mapping has a long history The USGS first started mapping on the North Slope at the end of the 19th century. However, the establishment of the Naval Petroleum Reserve stimulated particularly intense mapping activity in the 1920s, as well as a flurry of mapping projects from the mid-1940s to 1970s.
“This mapping was carried out by numerous geologists, and thus was published at a variety of scales using evolving stratigraphic nomenclature that changed over time,” Mull said.
Between 1963 and 1966 Mull participated in an ARCO project to reconnaissance map a line of quadrangles extending east to west across the middle of the North Slope. He took part in a similar, but more detailed, mapping exercise for Exxon between 1968 and 1972. “We …(concentrated) mostly on the southern tier of quads and up in ANWR,” Mull said.
Beginning in 1975, Mull began participating in USGS mapping projects across the North Slope. He is currently with the state Division of Oil and Gas and the state Division of Geological and Geophysical Surveys.
The older mapping The older maps are an excellent basis for a new set of maps,” Mull said.
Consequently, the USGS is digitizing many of the older maps as a starting point for its current project.
“We don’t want to use the older maps as is because since they were done there have been a lot of changes to the stratigraphy, nomenclature and geologic interpretation,” Mull said. “I’m sort of lucky by virtue of the fact that working for these various organizations at one time or another I’ve seen most of the (geology) from the east end to the west end (of the Slope),” Mull said.
In addition to incorporating new geological work and interpretations, the team is also using maps contributed by a number of sources, including companies working on the North Slope.
“The intent is to produce a modern suite of maps that will have consistent style, consistent nomenclature, consistent structural interpretation and consistent overall interpretation of the geology,” Mull said.
Working with Mull are USGS geologists Dave Houseknecht, who spearheaded the project by obtaining the funding, Ken Bird and Tom Moore.
“What makes this project inexpensive is Gil’s (Mull) 35-plus years mapping. There’s no question that he is one of the few active geologists who have mapped, from one side of the state to the other, the Brooks Range foothills for 50 to 60 miles north of the range,” Houseknecht said. USGS is digitizing maps Philip Freeman of the USGS is in charge of the digitization. Having the maps on computer in digital form enables the team to make updates and modifications with relative ease. The maps can be revised electronically, so that whole maps don’t have to be redrafted, Mull said.
Publication of the maps will occur progressively, a quadrangle at a time.
The team has already revised the Umiat quadrangle. It and the Killik River quadrangle are scheduled for publication sometime this winter.
All quadrangles should be published by the spring of 2003. The more generalized map of the entire North Slope is tentatively slated for completion in early 2004.
The maps will be available to the public both in digital and paper form. “The big benefit will be particularly to new organizations coming in; where they’ll have a consistent nomenclature and maps to start off with,” Mull said.
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