HISTORY OF BROOKS RANGE EXPLORATION AND DISCOVERY: A PERSONAL PERSPECTIVE
MULL, C.G., P.O. Box 117, Santa Fe, NM 87504, [email protected]
Geological exploration of the central and western Brooks Range began in 1901
and was exclusively by the U.S. Geological Survey (USGS) until the late 1950's.
In the northeastern Brooks Range the results of privately funded exploration by
Ernest Leffingwell were published by the USGS in 1919. In the mid-1920's and
mid-1940's to 1950's, the USGS conducted extensive mapping and stratigraphic
studies throughout the North Slope and into the mountains. These pioneering
geologists mapped the bedrock distribution of large portions of the Brooks Range
and North Slope, established the
stratigraphic
framework, and began to
understand the
structural
style. They recognized the asymmetric Colville
foreland basin north of the mountains, the contrast in stratigraphy and
structural
styles of the northeastern and central Brooks Range, the crustal
shortening in the frontal portion of the central and western parts of the
mountain belt, and thrust juxtaposition of contrasting far-travelled
stratigraphic
packages now termed allochthons. Beginning in the late 1950's and
into the 1960's and 1970's, oil industry geologists began regional mapping,
building on the USGS framework, filling gaps in the map coverage, and
interpreting or reinterpreting the
structural
style and tectonic evolution of
the range. Significant geological discoveries during this period included the
Lower Cretaceous unconformity (LCU) in the northeastern Brooks Range,
olistostromes and ophiolites in the western Brooks Range, and the Doonerak
fenster in the central Brooks Range, but because of industry proprietary
concerns, most of the new discoveries were published by the USGS. The
recognition of the Doonerak fenster deep within the range showed that the
frontal parts of the central and western Brooks Range are allochthonous on a
scale of many tens of miles and contrast with parautochthonous rocks of the
northeastern Brooks Range. The advent of plate tectonic concepts in the late
1960's resulted in
interpretation
of the Brooks Range as an alpine orogenic belt
formed by Jurassic to Cretaceous obduction of a Pacific oceanic arc over North
American continental crust of the Arctic Alaska microplate, with several hundred
miles of crustal shortening followed by mid- to Late Cretaceous rotation of
Arctic Alaska away from the Canadian Arctic Islands.