-0 DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEOLOGIC MAP OF THE DAVIS VALLEY QUADRANGLE AND PART OF THE CORDINER PEAKS QUADRANGLE, PENSACOLA MOUNTAINS, ANTARCTICA By Arthur B. Ford, Dwight L. Schmidt, and Walter W. Boyd, Jr. Prepared by the U.S. GEOLOGICAL SURVEY under the auspices of the NATIONAL SCIENCE FOUNDATION -N V'l 0 0 0 0 U.S. ANTARCTIC RESEARCH PROGRAM MAP Published by the U.S. Geological Survey, 1978 G GEOLOGIC MAP SYMBOLS COMMONLY USED ON MAPS OF THE UNITED STATES GEOLOGICAL SURVEY (Special symbols are shown in explanation) Contact-Dashed where approximately Strike and dip of beds-Ball indicates located; short dashed where inferred; top of beds known from sedimentary dotted where concealed structures _1!_ Inclined EB Horizontal Contact-Showing dip; well exposed at -+- Vertical Overturned triangle -..J!. Strike and dip of foliation Fault-Dashed where approximately located; short dashed where inferred; ~ Inclined -+·Vertical +Horizontal dotted where concealed Strike and dip of cleavage Fault, showing dip-Ball and bar on ~ Inclined ~Vertical +Horizontal downthrown side Bearing and plunge of lineation Normal fault-Hachured on down­ '~Inclined • Vertical - Horizontal thrown side Strike and dip of joints Fault-Showing relative horizontal -~ Inclined --Vertical +Horizontal movement Note: Planar symbols (strike and dip + + + + + + Thrust fault-Sawteeth on upper plate of beds, foliation or schistosity, and cleav­ age) may be combined with linear symbols to record data observed at ~ Anticline-Showing direction of plunge; same locality by superimposed symbols dashed where approximately located; at point of observation. Coexisting dotted where concealed planar symbols are shown intersecting at point of observation. Asymmetric anticline-Short arrow indicates steeper limb Shafts Overturned anticline-Showing direction of dip of limbs · ~ Vertical ~ Inclined Syncline-Showing direction of plunge; Adit, tunnel, or slope dashed where approximately located; >-Accessible >+-Inaccessible dotted where concealed X Prospect Asymmetric syncline-Short arrow indicates steeper limb Quarry X' Active )(' Abandoned Overturned syncline-Showing direction of dip of limbs Gravel pit X Active X Abandoned Monocline-Showing direction of plunge of axis Oil wells o Drilling ¢ Shut-in -<r Dry hole, ~20 Minor anticline-Showing plunge of axi~ *Gas ~ Show of gas abandoned ---E--+60 Minor syncline-Showing plunge of axis • Oil ~ Show of oil DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP A-10 UNITED STATES GEOLOGICAL SURVEY GEOLOGY OF THE DAVIS VALLEY QUADRANGLE AND PART OF THE CORDINER PEAKS QUADRANGLE, PENSACOLA MOUNTAINS, ANTARCTICA By Arthur B. Ford, Dwight L. Schmidt, and Walter W. Boyd, Jr. l INTRODUCTION Dufek Massif. Our 1965-66 studies showed that the intrusion makes up all of Dufek Massif and virtually The area that includes the Davis Valley quadrangle all of the Forresta1 Range (Ford and others, 1978). and part of the Cordiner Peaks quadrangle in the Geophysical surveys show that most of the body is Pensacola Mountains was first seen and photographed covered by ice sheets adjoining the ranges and that on January 13, 1956, on a U.S. Navy transpolar its areal size is of the order of half that of the flight from McMurdo Sound. An International Bushveld intrusion of South Africa (Behrendt and Geophysical Year (IGY) oversnow traverse party others, 1974 ). from Ellsworth Station reached Cairn Ridge, near Dufek Massif, December 9, 19 57, during the first Access to this remote part of the continent is dif­ exploration of the inner margins of the Filchner and ficult except by ski-equipped aircraft. Although the Ronne Ice Shelves (Neuburg and others, 1959). ice terrain near Dufek Massif is suitable for ski-plane Trimetrogon aerial mapping photography was landings, aircraft operations are commonly hindered obtained by the U.S. Air Force in January 1958, by adverse weather conditions. Our two seasons' at which time nearly the full extent of the Pensacola experience in the area indicates that, at least in the Mountains was first seen.2 summer months, the likelihood of poor visibility from fog and low clouds is the major factor limiting Geological, geophysical, and geodetic surveys of aircraft activity. Winds are generally slight along the the entire map area, as well as over many other parts northern escarpment of Dufek Massif. Summer of the Pensacola Mountains, were made by the U.S. temperatures during our work near Dufek Massif Geological Survey during the 1965-66 field season generally ranged from about -16°C (4°F) to -3°C (Huffman and Schmidt, 1966). The surveys used (26°F) and averaged about -8° C (18°F). close support of U.S. Army UH-lB turbine heli­ Work on the Dufek intrusion in 1965-66 was copters operating from a base camp in the central chiefly by A. B. Ford and W. W. Boyd, Jr. Study of Neptune Range, where the field party was placed the sedimentary country rocks in the Cordiner Peaks by U.S. Navy LC-130F (Hercules) aircraft from and Spanley Rocks was mainly by D. L. Schmidt and McMurdo Station. This work completed the geologic W. H. Nelson and was continued in the Cordiner mapping of the entire 540-km-long chain of the Peaks in January 1974 by Ford. Pensacola Mountains, a project begun in 1962-63 This report briefly outlines geologic relations and at the south end of the mountains (Schmidt and Ford, 1969). Additional geologic studies were made reviews work done in the area of the map sheet and in January 197 4 in the Cordiner Peaks (Cameron adjacent regions. and Ford, 1974) during investigations of possible Acknowledgments. - This work was part of the ice-runway aircraft landing sites by the U.S. Army U.S. Antarctic Research Program of the Office of Cold Regions Research and Engineering Laboratory Polar Programs, National Science Foundation. (Kovacs and Abele, 1974 ). General logistic and fixed-wing aircraft support was The major geologic feature of the area shown on provided by the U.S. Navy Air Development this map is the northern part of the Dufek intrusion Squadron Six. Helicopter support was provided by (Ford and Boyd, 1968), an immense differentiated the U.S. Army Aviation Detachment. We gratefully stratiform mafic igneous body that was discovered acknowledge the help of all support personnel, of in 1957 by an IGY traverse party visiting Dufek Jerry Huffman, National Science Foundation, in Massif, a northern range of the Pensacola Mountains coordinating the field logistical support, and the (Aughenbaugh, 1961; Walker, 1961; Neuburg and assistance by Steven W. Nelson in laboratory studies others, 19 59). Time limitations and the presence of related to this project. crevasse fields on the J a burg Glacier limited the IGY SYNOPSIS OF GEOLOGIC STUDIES studies to lower parts of the northern escarpment of The map area is near the north end of the Pensacola Mountains, a mountain group that 1 Present address, Geological Survey of Finland Helsinki 2Aerial photographs of the Pensacola Mountai~s can be forms part of the transcontinental chain of the ordered from the U.S. Geological Survey, National Center, Transantarctic Mountains (fig. 1B). Principal ranges Reston, Va 22092. of the Pensacola Mountains are shown in figure 1A. EXPLANATION Bedrock exposure Escarpment""""' Hachures on downslope side Direction of ice flow A B Figure I. - Index maps. A, Major ranges of the Pensacola Mountains and location of Camp Neptune. B, Location of Pensacola Mountains in Antarctica. The principal rock exposures in the mapped area Williams ( 1969). The summary below is drawn largely are units of the Dufek intrusion. This layered igneous from these sources. body, which is Jurassic in age, intruded moderately SEDIMENTARY ROCKS to highly deformed Precambrian to Permian sedimen­ The sedimentary units exposed in this area belong tary rocks during the time of emplacement of sills chiefly to the youngest of three depositional se­ of Ferrar Dolerite throughout the Transantarctic quences known to the south in the Neptune Range. Mountains (Grindley, 1963). The poorly exposed In the Neptune Range the sequences are clearly seen sedimentary country rocks are visible only in general­ to be separated by angular unconformities. Fossils ly small and isolated nunataks in the southern part of are scarce in or absent from most units, but available the map area. Relations between sedimentary forma­ paleontologic and radiometric age data suggest that tions are inferred to be the same as in the Neptune ages of the sequences are ( 1) Precambrian, (2) Middle Range, about 40 km south of Dufek Massif, where and Late(?) Cambrian, and (3) Ordovician(?) to the units are much better exposed (Schmidt and Permian. Rocks correlative with the oldest of these others, 1978). General geologic relations between sequences are exposed only on a few small nunataks ranges of the Pensacola Mountains are shown on the near the southwest corner of the map area but 1:1 ,000,000-scale map of Schmidt and Ford ( 1969). probably are much more extensive under the cover Formal rock-stratigraphic nomenclature for the of ice. Correlatives of the second sequence are not Dufek intrusion is presented by Ford (1976) and for exposed but could occur beneath the ice cover. sedimentary rocks is given by Schmidt and others Rocks of the third sequence form the principal ( 1964, 1965), Schmidt and Ford ( 1969), and nunataks south of the Dufek intrusion in this area. "';jl, 2 The Patuxent Formation, of late Precambrian 1968). Depositional environments ranged from high age (Schmidt and others, 1978), makes up the oldest energy in late orogenic to early postorogenic time sequence and consists in the Neptune Range of at (Ordovician? to Silurian?) during deposition in local least about 10,000 m of metasubgraywacke and basins of the basal part of the Neptune Group, to low slate locally interbedded with voluminous basaltic energy during Devonian to Permian deposition of and felsic volcanic materials. Radiometric dating later sediments, which probably took place on a (Eastin and Faure, 1972) suggests that some of slowly subsiding continental shelf or terrestrial plain.