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New geologic maps for Alaska coming from USGS Revised North Slope nomenclature out; Umiat quadrangle map due soon Kristen Nelson Petroleum News Editor-in-Chief
The first thing any geologist new to Alaska’s North Slope has to do is get his mind around the geology. That has been made more difficult, Gil Mull told Petroleum News June 20, because the standard North Slope outcrop geology maps are decades old.
Mull, a petroleum geologist with the Alaska Division of Oil and Gas, has been working North Slope geology for 40 years. And the standard North Slope geologic maps, published by the U.S. Geological Survey in the late 1950s through the mid-1960s, are the same maps he used when he began doing North Slope field work in 1963.
Thanks to funding from the USGS, Mull is in the process of compiling geologic mapping he and others have done over the last 40 years into a new series of maps to be published by the USGS and the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys and Division of Oil and Gas.
The first map, the Umiat quadrangle, is in the final editing process and due out this summer.
The 40-year old USGS maps provided “an absolutely invaluable starting point … they really laid out the broad framework of stratigraphy, the rock strata and some of a general feel for the rock distribution… And a general idea of the structure,” Mull said.
Those original USGS maps were based on the first detailed mapping on the North Slope, work which began in the late 1940s, but were on different scales and by many different authors.
“So from one map area to the next, they didn’t necessarily match. The formation names were different sometimes,” he said. Revisions began in 1960s When Mull and Gar Pessel started mapping in 1963 for Richfield, they started at Umiat and worked eastward over into the Arctic National Wildlife Refuge. They used the existing USGS mapping, “done by a number of different people and to different scale. It had been done over a period of years, so when you went from one map to another, a lot of times the rock units didn’t match. Sometimes the stratigraphic names had changed,” Mull said.
So Mull and Pessel did their own independent mapping, “revised the existing USGS mapping and put it together with uniform coloring.”
The second year, 1964, the two worked from Umiat west to Point Hope. Both men worked on the geology, Mull said, and Pessel did the cartography.
Mull later worked for Exxon, and spent five field seasons working with Howard Sonoman doing the same quads in more detail. The Richfield maps were four miles to the inch, but those for Exxon were two miles to the inch.
“Again, we were building on the earlier mapping we’d done, plus the USGS mapping, but compiling it all at a uniform scale and a uniform sort of style of drafting,” Mull said.
After leaving Exxon in the mid-1970s, Mull spent the next 25 years first with the USGS and then the Alaska Division of Geological and Geophysical Surveys doing additional geological mapping and stratigraphic studies on the North Slope and northern Brooks Range, and further refining the earlier mapping. Hey, you should publish that Jump forward 30 years, to the mid-1990s, and Dave Houseknecht of the USGS was in Alaska working on an appraisal of ANWR and happened to see the series of maps laid out on a drafting table.
Houseknecht said he thought the maps should be published.
But it was “pretty much reconnaissance,” Mull said, “plus it was proprietary.” Even if the maps Houseknecht saw hadn’t been proprietary, Mull said, the data needed to be rechecked and revised and looked at with modern air photos.
Houseknecht got funding from USGS to digitize the maps so they could be revised, and Mull got permission from the companies to use the old maps as a starting point for revision.
The first of the revised quadrangles, Umiat, has now been through peer review and is in final editing at USGS.
Mull has digitized versions of the first five quadrangles, from Umiat to Point Lay, tacked to his office wall for corrections. The digitizing, and corrections sent in by Mull, are being done at the USGS in Reston, Va., by Chris Garrity, who works for Houseknecht. Early mapping When Mull and Pessel began doing North Slope field work they had an advantage not enjoyed by geologists who did the original USGS quad maps: helicopter transportation. Initially, it was an old Bell G-2 helicopter, Mull said, the kind that looks like a fish bowl with an open tail boom and carries a pilot and two passengers. But it allowed them to move quickly and to cover broad areas. In recent years much larger and faster helicopters have further simplified the process of regional mapping.
By contrast, the first USGS North Slope map work was done by canoe, in 1899-1900. That field party was a single traverse, Mull said. They went up the John River to Anaktuvuk Pass in the winter by dog team and waited for spring breakup. They floated down the Anaktuvuk River to the Colville River to the coast and then canoed around to Barrow. In the 1920s there were expeditions after the establishment of the Naval Petroleum Reserve No. 4 (now the National Petroleum Reserve-Alaska). These were similar sorts of traverses, Mull said, coming up in the winter, waiting for breakup and floating the rivers in canoes. That work provided the beginning framework geology for the North Slope, he said, and a generalized map was published in the late 1930s.
Detailed mapping started in the 1940s when active exploration and the first drilling was done in NPR-4 by the Navy, and formation and rock names were more established. That work was done with boat traverses, on ‘weasels’ — small tracked amphibious vessels — and on foot. The results were published in the late 1950s into the mid-1960s as a series of USGS professional papers and maps. Trying to follow the maps When Mull and Pessel began working in the early 1960s, they were flying out of Umiat, “and we were trying to follow the published maps and we were having trouble,” Mull said.
The maps were done on different scales, by different authors and sometimes with different nomenclature.
“Some of the formation names that had been described just didn’t jibe with modern stratigraphic concepts,” Mull said. And those early geologists were “working on foot, working limited areas and some of the nomenclature that had grown up was really involved.”
What we wanted, he said, was regional mapping.
What they sometimes found on the earlier maps was mapping limited to small areas: “if you’re working on foot in an area,” Mull said, “you’re working in a very different scale.” Some of the earlier mapping was the equivalent of describing individual trees on a hillside, rather than describing patches of spruce here and birch there, he said.
Because the work for the earlier maps was done by foot, without the advantage of helicopter transportation, the stratigraphic nomenclature was involved and while it worked fine for a small area, it didn’t work well for an area 20 miles away.
“Well the obstacle for everyone coming up onto the North Slope cold is getting a handle around all the names. There was just a proliferation of stratigraphic names,” Mull said. Some names abandoned Part of the project is revising stratigraphic nomenclature. And that part of the project had to be completed before the maps could be published, because the maps are edited against formally established nomenclature.
That paper titled “Revised Cretaceous and Tertiary Stratigraphic Nomenclature in the Colville Basin,” by Gil Mull, Dave Houseknecht and Ken Bird, has been completed and is available on the net: http://pubs.usgs.gov/pp/p1673/
“We’re lumping and redefining some of the names and changing some of the formation boundaries,” Mull said.
Some of the nomenclature problems were evident in the 1960s, and developed because formations were named by a number of different people in an era when transportation was difficult. Flying around from one area to the next, Mull said, they’d find, for example, that the Grandstand formation looked just like the Chandler formation.
“We’re simply abandoning some of the names … because there are just way too many of them and some of them are meaningless on a regional basis,” he said.
Naming is also being simplified where possible. For example, the Schrader Bluff formation used to be described as having three members: Sentinel Hill, Barrow Trail and Rogers Creek. These names have been changed to simplify, Mull said, and are now: Upper Schrader Bluff, Middle Schrader Bluff and Lower Schrader Bluff.
The changes, Mull said, are based on “modern stratigraphic terminology and also more modern geologic concepts.” There is also the advantage of modern high-resolution air photos, taken from the U-2 spy plane at 60,000 feet in the late 1970s to mid-1980s. These aerial photographs show much more detailed structure than the earlier low resolution black and white air photos taken in the 1940s, he said, and also help to better identify rock outcrops to be studied.
The advantages now available include much more modern and faster helicopters which let you cover large amounts of ground in a short time, modern aerial photography, new geologic concepts and “the advantage of the … framework that was done mostly by the USGS. … We’re making changes in it, but you shouldn’t criticize the original work they did,” Mull said.
And, he said, people will certainly do additional detailed work and find things they disagree with in the new maps:
“No geologic map is ever completed,” Mull said.
“It’s always a work in progress. Somebody next year will go in and start poking around in more detail here and there and say, ‘what the heck was Gil thinking there?”
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