Gravity anomaly and interpretation map of the Chignik and Sutwik Island quadrangles, Alaska

The gravity field of the Chignik and Sutwik Island
quadrangles near the center of the Alaska Peninsula represents
a complex series of transitions between probable
continental crust on the north, probable oceanic crust on the
south, sedimentary basins on each side of the peninsula, and a
central structural high and volcanic arc. The resulting
gravity field may be generalized as a central southwest- to
northeast-trending gravity high bordered on both sides by
flanking gravity lows over sedimentary basins underlying the
lowlands and continental shelf. All three gravitational
features show discontinuities and magnitude variations that
reflect the complex geologic setting.

Data concerning this complex gravity field have accumulated
slowly and intermittently since an initial measurement
was made at Port Heiden more than 25 years go (Thiel
and others, 1958, 1959). A few reconnaissance measurements
by R. V. Allen and an offshore traverse conducted by the U.S.
Coast and Geodetic Survey R/V Surveyor were made in the
early 1960's (Barnes and others, 1966; Barnes, 1967). At
about the same time, Gulf Oil Corp. contracted for a
relatively detailed survey of the lowlands on the north shore
of the peninsula; the map prepared from this survey is now
available (Gulf Oil Corp., Port Moller Development Contract
Report, available at U.S. Geological Survey, Anchorage,
Alaska). In the early 1970's, a few new land measurements
were made by P. L. Dobey, of the Alaska Division of
Geological and Geophysical Surveys, and an offshore traverse
was completed by the R/V C. Greene on contract to the U.S.
Geological Survey (Fisher, 1979, and M. A. Fisher, written
commun., 1977). The most recent measurements, the basis
for this map, were made by M. E. Yount, D. L. Detra, D. R.
Jefferis, and J. E. Case during the mineral assessment of the
two quadrangles. D. F. Barnes, R. L. Morin, D. R. Jefferis,
and R. F. Sikora have shared in the data compilation.
Geologic background for the text was provided by R. L.
Detterman, T. P. Miller, E. Young, and F. H. Wilson (1979,
1981).