Abstract

The Ellsworth Mountains, which contain some of the highest and most rugged peaks in the Antarctic, were discovered by Lincoln Ellsworth during his pioneering crosscontinent airplane flight made in 1935. The mountians were not explored on the ground until three successive University of Minnesota expeditions, under the direction of Professor Campbell Craddock of the university made a geological reconnaissance of them during the years 1961-1964.

These expeditions found approximately 40,000 feet of slightly metamorphosed sedimentary rocks, most of which are of marine origin. Only two good fossil sites were found, but these demonstrated that the youngest rock in the section is of Permian age (containing Glossopteris flora) and that a trilobite-bearing limestone unit in the middle of the section is of late Cambrian age. Consequently, there are at least 20,000 feet of Paleozoic sediments and 20,000 feet of Cambrian and probably older sediments which comprise nearly all of the outcrop area of the Ellsworth Mountains.

All rock units in the Ellsworth Mountains have suffered extreme structural deformation. The overall structural appearance is that of a northwestward plunging anticlinorium.

Low-grade regional metamorphism has altered nearly all of the rocks, with pronounced rock cleavage being common, as are authigenic sericite and chlorite minerals in the rock matrix material. The only igneous rocks observed in these mountains occur in the extreme southern and southeastern portions of the area and consist of a few basic dikes and sills, and one small intrusive gabbro body.