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Geologitc Majp of the Saratoga Tajble Quadrangle, Pensacola Mountains, Antarctica

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Geologitc Majp of the Saratoga Tajble Quadrangle, Pensacola Mountains, Antarctica DEJP> A.R TMENT Of THE INTERIOR !UNHTJED STATES GEOLOGICAL SURVEY GEOLOGITC MAJP OF THE SARATOGA TAJBLE QUADRANGLE, PENSACOLA MOUNTAINS, ANTARCTICA By Arthur B. Forrd, Dwight L. Schmidt, Walter W. Boyd 9 Jrr., and Willis H. Nelson Prepared by the U.S. GEOLOGHCAL SURVEY under the auspices of the NATIONAL SCIENCE FOUNDATITON - t-J (.1\ 0 b 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 _!!!_ Inclined EB Horizontal Contact-Showing dip; well exposed at -t- Vertical -.;:.Overturned triangle Strike and dip of foliation Fault-Dashed where approximately located; short dashed where inferred; .31?_ Inclined --+- Vertical +Horizontal dotted where concealed Strike and dip of cleavage Fault, showing dip-Ball and bar on ~ Inclined 1--f Vertical +Horizontal downthrown side Bearing and plunge of lineation -,--..,....--.,.-~"""T"-...-- 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 'X' 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 -¢- Dry hole, Minor anticline-Showing plunge of axis ~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-9 UNITED STATES GEOLOGICAL SURVEY GEOLOGY OF THE SARATOGA TABLE QUADRANGLE PENSACOLA MOUNTAINS, ANTARCTICA by Arthur B. Ford, Dwight L. Schmidt, Walter W. Boyd, Jr.! and Willis H. Nelson INTRODUCTION weather conditions to be mostly fair, but strong winds The area that includes the Saratoga Table quadrangle were common near mountain escarpments. Summer tem­ in the Pensacola Mountains was first seen and photo­ peratures during our work in the area ranged from about graphed on January 13, 1956, on a U.S. Navy transpo­ -l9°C (-2°F) to -7°C (20°F) and averaged about -12°C lar flight from McMurdo Sound. Trimetrogon aerial (10°F). mapping photography of the quadrangle was obtained Work on the Dufek intrusion in 1965 - 66 was chiefly in January 1958 by the U.S. Air Force. 2 The area was by A.B. Ford and W.W. Boyd, Jr. and was continued in first visited by U.S. Geological Survey parties in the January 1974 by Ford. Study of the sedimentary country austral summer, 1965 - 66. rocks was mainly by D.L. Schmidt and W.H. Nelson. Geological, geophysical, and geodetic surveys of the This report briefly outlines geologic relations and reviews entire map area, as well as over many other parts of the work done in the quadrangle and adjacent regions. Pensacola Mountains, were made by the U.S. Geological Acknowledgments. -This work was part of the Survey during the 1965 - 66 field season (Huffman and U.S. Antarctic Research Program of the Office of Schmidt, 1966). The surveys used close support of Polar Programs, National Science Foundation. General U.S. Army UH - 1B turbine helicopters operating from a logistic and fixed-wing aircraft support was provided base camp in the central Neptune Range where the field by the U.S. Navy Air Development Squadron Six. party was placed by U.S. Navy LC- 130F (Hercules) air­ Helicopter support was provided by the U.S. Army craft from McMurdo Station. This work completed the Aviation Detachment. We gratefully acknowledge the geologic mapping of the entire 540-km-long chain of the help of all support personnel, of Jerry Huffman, National Pensacola Mountains, a project begun in 1962- 63 at Science Foundation, in coordinating the field logistical the south end of the mountains (Schmidt and Ford,l969). support, and the assistance by Steven W. Nelson in Additional geologic studies were made in January 1974 in laboratory studies related to this project. the vicinity of Mount Lechner (Cameron and Ford, 1974) SYNOPSIS OF GEOLOGIC STUDIES during investigations of possible ice-runway aircraft land­ The map area is near the north end of the Pensacola ing sites by the U.S. Army Cold Regions Research and Mountains, a mountain group that forms part of the Engineering Laboratory (Kovacs and Abele, 1974). transcontinental chain of the Transantarctic Mountains The major geologic feature of this quadrangle is the (fig. 1B). Principal ranges of the Pensacola Mountains south end of the Dufek intrusion (Ford and Boyd, 1968), are shown in figure lA. an immense differentiated stratiform mafic igneous body The principal rock exposures in the map area are units that was discovered in 1957 by an International Geophysi­ of the Dufek intrusion. This layered igneous body, which cal Year (IGY) traverse party visiting Dufek Massif, a is Jurassic in age, intruded moderately to highly deformed northern range of the Pensacola Mountains (Aughenbaugh, Precambrian to Permian sedimentary rocks during the time 1961; Walker, 1961; Neuburg and others, 1959). Our of emplacement of sills of Ferrar Dolerite throughout the 1965 - 66 studies showed that the intrusion makes up all Transantarctic Mountains (Grindley, 1963). The poorly of Dufek Massif (Ford and others, 1978) and virtually all exposed sedimentary country rocks are visible only in of the Forrestal Range. Geophysical surveys show that small, isolated nunataks in the southern and southwestern most of the body is covered by ice sheets adjoining the parts of the Forrestal Range. Relations between sedimen­ ranges and that its area is of the order of half that of the tary formations are inferred to be the same as in the Nep­ Bushveld intrusion of South Africa (Behrendt and others, tune Range, about 60 km southwest of the Forrestal Range, 1974). where the units are much better exposed (Schmidt and Access to this remote part of the continent is difficult others, 1978). General geologic relations between ranges except by ski-equipped aircraft. The ice terrain near the of the Pensacola Mountains are shown on the 1: 1,000,000- Forrestal Range is gen~ally suitable for ski-plane landings scale map of Schmidt and Ford (1969). Formal rock­ n"r two seasons' experrence in the area showed summer stratigraphic nomenclature for the Dufek intrusion is pre­ sented by Ford (1976)"and for sedimentary rocks is given 1 Present address, Geological Survey of Finland, Helsinki 2 by Schmidt and others (1964, 1965), Schmidt and Ford Aerial photographs of the Pensacola Mountains can be ordered from the U.S. Geological Survey, National Center, ( 1969), and Williams ( 1969). The summary below is Reston, Virginia 22092 drawn largely from these sources. ~. EXPLANATION Bedrock exposure f1'rtf Escarpment Hachures on down slope side Direction of ice flow $~..... ,,, Crevasse zone 50 KILOMETERS I I A B Figure 1. -Index maps. A, Major ranges of the Pensacola Mountains and location of Camp Neptune. B, Location of Pensacola Mountains in Antarctica. SEDIMENTARY ROCKS 10,000 m of metasubgraywacke and slate locally inter­ The sedimentary units exposed in this quadrangle be­ bedded with voluminous basaltic and felsic volcanic ma­ long chiefly to the youngest of three depositional sequences terials. Radiometric dating (Eastin and Faure, 1972) sug­ known to the south and west in the Neptune Range. The gests that some of these volcanic units may be as old as sequences in the Neptune Range are clearly seen to be sep­ 1,210 m.y. Diabase sills locally intrude the formation. arated by angular unconformities. Fossils are scarce in or The igneous units of the formation are not known in the absent from most units, but available paleontologic and Saratoga Table quadrangle. The Patuxent sediments were radiometric age data suggest that ages of the sequences deposited in a high-energy environment, probably a vol­ are ( 1) Precambrian, (2) Middle and Late(?) Cambrian, and canically active eugeosyncline, as indicated by lithologies (3) Ordovician(?) to Permian. Rocks correlative with the and abundant sedimentary structures such as graded bed­ oldest of these sequences are exposed only on small nuna­ ding, channel features,and sole markings. The Patuxent taks in the westernmost part of the Saratoga Table quad­ was widely metamorphosed to the greenschist facies dur­ rangle but are probably much more extensive under the ing an orogeny near the end of the Precambrian. cover of ice. Correlatives of the second sequence are not The second sequence, which is not known to occur in known but could occur beneath the ice cover. Rocks of and may be absent from the Saratoga Table quadrangle, the third sequence form the principal nunataks south and consists of a fossilferous Middle Cambrian (Palmer and west of the Dufek intrusion in this area. Gatehouse, 1972) limestone and overlying silicic volcanic The Patuxent Formation, of late Precambrian age and clastic sedimentary units that have a composite thick­ (Schmidt and others, 1978), makes up the oldest sequence ness of at least 700 m.
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