CD Type Section of the 1C PHI 3 Beacon Sandstone of Antarctica GEOLOGICAL SURVEY PROFESSIONAL PAPER 456-A Prepared on behalf of the National Science Foundation CQ g ^ CQ PQ EH CQ Type Section of the Beacon Sandstone of Antarctica By WARREN HAMILTON and PHILIP T. HAYES CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA GEOLOGICAL SURVEY PROFESSIONAL PAPER 456-A Prepared on behalf of the National Science Foundation UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 CONTENTS Page Diabase sheets Continued Page Abstract_____-____________________________________ Al Petrology__-___________________________________ A12 Introduction_______________ _ ______________________ 1 Metamorphism of the Beacon Sandstone___________ 12 Type section_______________________________________ 4 Age of diabase-__-__----------___-__--_-___---__ 12 Lower part-___________________________________ 4 Age of the Beacon Sandstone_____-_-----__-__-_______ 12 Middle part.___________________________________ 6 Fossils near type section_____-___________________ 12 Upper part---------------_____-----_-___-_-___- 7 Fossils from the Beacon Sandstone of other areas. __ 14 Correlations between sections------_____-____-___- Age of rocks beneath the Beacon Sandstone ________ 14 Nomenclature._____________________________________ Age of the Beacon Sandstane_-__--___--__-_______ 14 Past nomenclature._____________________________ Conditions of deposition___----______________________ 16 Proposed nomenclature and stratigraphic summary- 9 Crossbedding_ __________________________________ 16 Diabase sheets. ____________________________________ 12 Paleoclimate_ __________________________________ 17 Form________________________________________ 12 References cited_____-_--_._.-_-______.____________ 17 ILLUSTRATIONS Page FIGURE 1. Index map of Antarctica_________________________ Al 2. Index map of west coast of McMurdo Sound_________ 2 3. Geologic map of Beacon Heights__________________ 3 4. New Mountain from the north_____________________ 4 5. Columnar sections of Beacon Sandstone _____________ 5 6. West Beacon Heights from the northeast-___________ 6 7. West wall of Beacon Dry Valley___-_-__________--__ 8 8. West part of Finger Mountain from the north_______. 9 9. Pyramid Mountain from the northeast ______________ 10 10. East end of Finger Mountain from the south_________ 11 11. Molds of burrows.-_-___--____-____-___-_-_______- 13 12. Outcrop of upper part of sandstone of New Mountain- 15 13. Crossbedded strata----__-_____-------_____-__--_- 16 ni CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA TYPE SECTION OF THE BEACON SANDSTONE OF ANTARCTICA By WARREN HAMILTON and PHILIP T. HATES ABSTRACT "Gondwana" landmasses of Australia, India, South The Beacon Sandstone of Carboniferous(?), Permian, and Africa (Karroo System), and South America. early Mesozoic(?) age is widely distributed in East Antarctica. The formation was named by Ferrar in 1907 for exposures The Beacon Sandstone was named by Ferrar (1907) in Beacon Heights, near Taylor Glacier west of McMurdo Sound, for exposures on West Beacon Heights on the south but no type section has previously been described. This paper side of upper Taylor Glacier (figs. 2 and 3), South presents a composite section in the type area, assembled from Victoria Land. He estimated that about 2,500 feet of a published description of the basal strata by Zeller and others sandstone are present there but did not describe a type (1961), a previously unpublished description of the middle part by the present authors, and a published description of the section. McKelvey and Webb (1959) presented a de­ upper part by McKelvey and Webb (1959). tailed section of the upper part of the formation in the The Beacon Sandstone in its type area consists largely of type area, and Zeller and others (1961) described the light-colored medium- to coarse-grained sandstone, much of it basal part. These partial sections are here tied to the crossbedded. Beds of fine-grained sandstone and siltstone are section studied by us in the middle part of the forma­ subordinate. 1 Carbonaceous strata bearing constituents of the Glossopteris flora occur high in the formation. The middle tion on West Beacon Heights to give, for the first time, part of the formation consists of cliff-forming sandstone, easily a reasonably accurate type section of the Beacon Sand­ recognizable throughout the region, and is separated from the stone. ledge-forming section beneath by a disconformity. Total thick­ The Ross Sea coast of East Antarctica is bounded by a ness of the Beacon is about 4,000 feet. Intrusive into the range of high mountains, which forms a dam against the Beacon are huge sills and inclined sheets of quartz diabase (the Ferrar Dolerites) of Mesozoic age, which have an aggre­ vast inland ice plateau. Valley outlet glaciers, one of gate thickness of about the same amount. The three major units of the Beacon Sandstone in its type area are here referred to as the sandstone of New Mountain (the lower ledge-forming unit), the sandstone of Pyramid Mountain (the middle cliff-forming unit), and the sandstone of Finger Mountain (the upper ledge-forming fossiliferous unit). A thin sequence of diverse rocks, described by Zeller and others (1961), beneath the sandstone of New Mountain may not prop­ erly belong to the Beacon Sandstone. Although several authors have proposed recently that the Beacon be elevated to group status, they have not established mappable formations within the Beacon; consequently, their proposals are premature. Because geologic fieldwork is' likely to be of reconnaissance character and in widely separated areas for some time to come, it seems preferable for the present to maintain formation status for the Beacon Sandstone and to subdivide it into local formal members only when the utility of these is demonstrated by detailed work. INTRODUCTION The Beacon Sandstone of Carboniferous(?), Per­ mian, and early Mesozoic( ?) age forms a discontinuous cover upon much of East Antarctica, the large part of the continent lying mainly in east longitudes (fig. 1). FIGURE 1. Index map of Antarctica. Asterisk indicates location of The sandstone carries a Glossopteris flora and shares Beacon Sandstone type locality. Localities mentioned in text are many features with correlative rocks of the other Priestley Glacier, P; Mount Gran, M; Beardmore Glacier, B ; Mount Weaver, W; Horlick Mountains, H; and Amery locality, A. Al A2 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA 160" 161* 162" 163* 164° 165° 78° 10 MILES 20 KILOMETERS FIGURE 2. Index map of mountains west of McMurdo Sound. Hatched line outlines area of geologic map (fig. 3). which is Taylor Glacier, flow across these mountains which we were flown by a U.S. Navy ski-equipped air­ from the plateau toward the sea through the major plane, as part of our study of the Taylor Glacier-Taylor transverse valleys. Pre-Devonian granitic and meta- Dry Valley region (Hamilton and Hayes, 1960). morphic rocks form the coastal foothills and lower areas We are much indebted to L. H. Daugherty, S. H. in the central part of the range. Above these basement Mamay, J. J. Mulligan, and J. M. Schopf for permitting rocks in the central part of the range, and forming us to cite some of their unpublished data on the pale- nearly all the exposed rock of the western part of the obotany of the Beacon Sandstone. To Schopf in partic­ range, is the almost undef ormed Beacon Sandstone and ular must also go much of the credit for the discussion the diabase sheets intruded into it. of paleobotany and age of the Beacon. Our fieldwork on the type section was done during This work was carried out on behalf of the National November 1958, from a camp on Taylor Glacier, to Science Foundation. TYPE SECTION OF BEACON SANDSTONE OF ANTARCTICA A3 EXPLANATION Plutonic basement complex Fault Mountain peak 3 MILES 4 KILOMETERS FIGCEE 3. Geologic map -of Beacon Heights and vicinity. Map prepared by photogrammetric methods from vertical aerial photographs, sup­ plemented by field observations and by ground and oblique aerial photographs. Dashed contacts modified from McKelvey and Webb (1959). Arrows show direction of ice flow. A4 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA TYPE SECTION the northwest. McKelvey and Webb (1959) described The Beacon Sandstone of the type area (fig. 3) is the upper part of the sandstone 3 miles farther west. about 4,000 feet thick and dips 2°-4° westward. The All but the basal strata of the Beacon are divisible few faults are short and of small displacement. Injec­ into three easily recognized units in the type area and ted into the sandstone are huge sills and inclined sheets the surrounding region. The lower unit, here referred of quartz diabase with an aggregate thickness of about to as the sandstone of New Mountain, is ledge-forming 4,000 feet, so that the total thickness of sandstone and sandstone. The middle unit, the sandstone of Pyramid diabase is about 8,000 feet. The local relief is but 4,000 Mountain, is thick bedded and cliff forming. The upper feet, and it is necessary to define a composite type section unit, the sandstone of Finger Mountain, is ledge forming from separate traverses. and includes much siltstone and carbonaceous strata. The base of the Beacon Sandstone crops out at the These units are defined more fully on page 10. southeast end of the mountain mass of the type area, and here Zeller and others (1961) described the lower LOWER PART part of the formation. We measured the middle part The base and lower part of the Beacon Sandstone of the formation at West Beacon Heights, 7 miles to were examined by Zeller and others (1961) on the FIGURE 4. New Mountain, seen from the north, showing the lower part of the Beacon Sandstone. Pre-Devonian basement rocks crop out at base of bluffs by Windy Gully. A thick diabase sill lies near the base of the Beacon, and another is at the top of New Mountain.