LAWRENCE A. FRAKES Department of Geology, Florida State University, Tallahassee, Florida 32306 JERRY L. MATTHEWS Department of Oceanography, University of California, San Diego, California 9203 7 JOHN C. CROWELL Department of Geological Sciences, University of California. Santa Barbara, California 93106

Late Paleozoic Glaciation: Part III,

ABSTRACT netic poles for the reconstructed Gondwana- Like other Gondwanaland fragments, An- land fragments of South America, Africa, and tarctica was glaciated during the late Paleozoic, Antarctica, the late Paleozoic segments of as demonstrated by striated floors and boulder which cross Antarctica from the Weddell Sea to pavements and by glacially striated clasts in Victoria land. diamictites and associated varvelike strata. Til- lites are known throughout the Transantarctic INTRODUCTION Mountains from the vicinity of Ross Island to Late Paleozoic glacial rocks were discovered the Pensacola Mountains, as well as in the Ells- in Antarctica in I960 (Long, 1962) and are worth Mountains in West Antarctica. These now known to occur throughout a wide stretch strata apparently were laid down in three basins of the , as well as in (Ellsworth-Pensacola basin, Horlick-Queen the Ellsworth Mountains of West Antarctica Maud basin, and Beardmore basin). (Craddock and others, 1964). Their recogni- Ice flowed into the Ellsworth-Pensacola basin tion in Antarctica is of particular significance from a major center located in the region of the because of the often expressed view that An- eastern Weddell Sea, possibly beginning in the tarctica is a drifted fragment of the ancient early Carboniferous. The Thiel salient, separat- supercontinent, Gondwanaland, and hence, ing the Ellsworth-Pensacola and Horlick- should contain its own counterparts of the Queen Maud basins, yielded some debris Paleozoic-Mesozoic Gondwana sedimentary se- northward into the former basin but served quence. The glacial strata of Antarctica occupy primarily as a major gathering ground for ice the same statigraphic positions as do glacial which flowed westward into the Horlick- rocks in the Gondwana sequences of southern Queen Maud basin. Similarly, the western Africa and South America, although ages over , where tillites are thin the southern hemisphere range from at least or absent, was a local center for ice flowing middle Carboniferous to Permian. eastward into the Horlick-Queen Maud basin Detailed studies have been carried out at and probably westward into the Beardmore ba- many Antarctic localities, so that regional syn- sin, although the latter direction is not yet thesis is now possible. Determination of proven by striae patterns. A major center of ice paleogeographic trends in Antarctica (Frakes accumulation also seems to have existed in and Crowell, 1968a) is also of significance in northern Victoria Land, whence flow was to- establishing the relative position of the polar ward the southeast. The Ellsworth-Pensacola continent in the Gondwanaland framework. basin was a continuously depressed Paleozoic Because major breakup of Gondwanaland did downwarp of major proportions, whereas the not occur until after glaciation took place, the Permian Horlick-Queen Maud and Beard- distribution of continental ice, and especially more basins were shallow depressions and poss- the directions of flow as recorded in the glacial ibly connected. deposits, can be used as an aid in matching The center of late Paleozoic glaciation may Antarctica with the other Gondwanaland frag- have migrated across Antarctica from the Wed- ments. For Antarctica, however, conclusions dell Sea region (early Carboniferous) to north- are less certain than for the other continents, ern Victoria Land (Permian), judging from the because so much of the continent is covered meager paleontological data and stratigraphic with ice, and so much of it has not yet been fully considerations. This would be in keeping with explored. the relative-motion curves of the paleomag- In the Transantarctic Mountains, late Paleo-

Geological Society of America Bulletin, vol. 82, p. 1581-1604, 16 figs., June 1971 1581

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zoic glacial rocks are exposed along the rim of Ross Island, they are very thin; farther north in the Antarctic Plateau, between the glaciers Victoria Land, their position is occupied by a which flow down to the Ross Ice Shelf from the disconformity between Devonian(P) and Per- interior (Fig. 1). Isolated outcrops are known mian strata. They also appear to be thin or miss- from west of Ross Island in Victoria Land ing from the segment of the central through the Horlick Mountains to the Pen- Transantarctic Mountains between the Queen sacola Mountains, two-thirds of the way across Maud Range and the Beardmore Glacier. the continent. The glacial strata constitute a In West Antarctica, an 1100-m-thick glacial lower part of the flat-lying Beacon "Group" section occurs in the Sentinel Range of the Ells- (equated by many workers with the Gondwana worth Mountains, lying high above limestones sequence of other southern continents; see Har- dated as Cambrian and below Permian elastics rington, 1965), and through this broad region in an apparently conformable sequence of de- they lie disconformably on still lower Beacon formed strata. Late Paleozoic glacials are not sedimentary rocks (Devonian), or unconforma- known from the largely Precambrian shield bly on the basement complex (Precambrian to area of East Antarctica; diamictites of Queen lower Paleozoic). They are followed, either Maud Land are probably Precambrian in age conformably or disconformably, by dominantly (Neethling, 1964). fluvial strata which locally bear Permian floras. There are obvious differences in the stratig- The glacial rocks display varying thicknesses raphy of late Paleozoic glacial rocks when ranging from a few meters to almost 400 m. viewed on a regional scale, and these will be The thickest known sections in this region oc- discussed in detail below. For the moment, we cur locally near the Beardmore Glacier. Near can point out the considerable differences be-

Figure 1. General localities in Antarctica.

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tween the Paleozoic sections of the Ellsworth tively named the Ellsworth-Pensacola basin. and Pensacola Mountains on the one hand, and Two additional basins can be distinguished; all other known occurrences on the continent these are the Horlick-Queen Maud basin to the on the other. In the Ellsworths and Pensacolas, east, and the Beardmore basin to the west of a the glacial strata are part of a thick, largely clas- regional high located between the Axel Hei- tic sequence which was deposited throughout berg and Beardmore Glaciers. most, if not all, of the Paleozoic. These de- formed and metamorphosed sections (probably ELLSWORTH-PENSACOLA BASIN more than 10,000 m thick) might properly be termed geosynclinal in origin. For contrast, gla- General cial sequences elsewhere are basal or nearly so The Ellsworth-Pensacola basin contains ex- in the Beacon "Group" and consist of flat-lying, posures of Paleozoic and Mesozoic strata in the cratonic strata; granitic basement rocks are at Atlantic sector of Antarctica (Fig. 2). At pre- most a few tens of meters below the glacial beds sent, known exposures are limited to the re- in all places. gions for which the basin is named, but others Such markedly different sequences must eventually may be discovered in the Shackleton have formed in entirely different basins, par- Range and elsewhere. The basin lies adjacent to ticularly since the Ellsworth-Pensacola region is the Antarctic craton and partially in the far removed from the others, and transitional younger West Antarctic mobile belt. It is char- sequences are not known. The basin which is in acterized by a thick sequence (at least 10,000 part represented by the glacial deposits of the m) of conformable Paleozoic and Mesozoic Ellsworth and Pensacola Mountains is tenta- rocks, mostly clastic and slightly metamor-

TRANSPORT DIRECTION OF LATE PALEOZOIC °»

Figure 2. Regional locality map of the Ellsworth-Pensacola basin.

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phosed but locally strongly deformed. They are fragments and "heavy" minerals occur in all thus in marked contrast with rocks of the same thin sections. Sand-sized grains commonly have age elsewhere on the continent. angular boundaries etched by chemical solution In both Ellsworth and the Pensacola Moun- and penetrated by secondary growth of sericite tains, the glacial rocks overlie a thick sequence and other clay minerals. of quartz arenites and underlie plant-bearing The most striking feature of the Whiteout sandstone and shale. The glacial strata are dis- Conglomerate is its general lack of an environ- tinctive in that they are very thick (at least 300 mentally significant feature, bedding. How- m) and consist almost entirely of thick units of ever, an 11-m-thick section of alternating shale poorly bedded diamictite. These unusual rocks and siltstone interbeds occurs on the northwest closely resemble late Paleozoic strata of the slope of Mount Lymburner, near the top of the Falkland Islands, the Sierra de la Ventana in section. Also, a 5-m-thick unit of siltstone and Buenos Aires Province of Argentina, and the shale crops out northwest of Mount Earp and Cape Ranges of South Africa (Frakes and Cro- irregularly crumpled sandstone masses, as well, 1968b). much as 8 m long, occur on the northwest slope of Mount Lymburner, on the southern slope of Ellsworth Mountains Mount Holmboe and at Mount Warren. Wavey Glacial rocks of the Whiteout Conglomerate laminae which are indistinct occur at several in the Sentinel Range (Craddock and others, levels in the Whiteout, and two prominent ben- 1964) rest conformably on the Crashsite ches parallel to the top and bottom of the Quartzite and are followed conformably by the Whiteout Conglomerate can be traced through- Polarstar Formation. The Whiteout lacks fos- out the Sentinel Range. The combined thick- sils, but a late Paleozoic age is suggested by ness of these scattered interbeds makes up less Early Cambrian fossils well below the Whiteout than 6 percent of the total thickness of the and by a Glossopteris flora in the immediately Whiteout Conglomerate. overlying Polarstar Formation. At Mount Lym- On Mount Lymburner, the stratified section burner (Fig. 3), Craddock and others (1964) is composed of dark-gray alternating siltstone measured a 910-m-thick section of the White- and shale beds, generally less than 25 cm thick. out; at Mount Warren, we measured what is Most of the beds lack lamination; however, sev- probably a complete section, 1122 m. eral of the coarser siltstone beds are normally Diamictite, generally without any trace of graded. Rounded clasts ranging to 15 cm in bedding, comprises more than 95 percent of diameter are scattered throughout the unit as the Whiteout Conglomerate in the Sentinel "dropstones" (Fig. 5). They are not sorted as to Range of the Ellsworth Mountains (Fig. 4). It size, and they do not occur along specific bed- is pervaded by strong cleavage and jointing, ding planes. The surfaces of many of the beds and in many places pebbles have been stretched are irregularly warped and several of the thin- and rotated, so that studies of sedimentary fab- ner beds are folded and overturned. Axial ric are of little value. This monotonous se- planes dip to the west. Both the warping and quence consists of a silty matrix in which are set folding affected later sedimentation, indicating rounded to subrounded stones as much as 1 m that deformation took place before lithification. in diameter, but commonly less than 10 cm. The deformed sandstone fragments or intra- Less than 5 percent of the stones show stria- clasts, which are generally restricted to the up- tions. The general absence of striations proba- per quarter of the stradgraphic section, display bly results from the high proportion (up to 75 contorted cross-bedding and wispy, irregularly percent) of rocks with textures which are gen- mixed and gradational boundaries, also sug- erally too coarse to show any but the largest and gesting soft-sediment deformation. most deeply etched striations—granite, quartz- Directional-current and ice-flow indicators ite, and gneiss. Clast counts near Mount Earp have not been observed in the Whiteout Con- show approximately 45 percent quartzite of glomerate. However, a few ripple marks and various kinds, 20 percent granite, 10 percent cross-bedding occur in the underlying Crashsite gneiss, 10 percent limestone, 5 percent quartz, Quartzite and the overlying Polarstar Forma- and 5 percent miscellaneous kinds (including tion, which in both units indicate paleocurrent schist, phyllite, and chert). Striated surfaces flow toward the north-northwest (Matthews were not observed within or below the White- and others, 1967). A similar trend is therefore out. inferred for transportational processes during The matrix of the diamictite (material less deposition of the Whiteout Conglomerate.

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Figure 3. Locality map of the Sentinel Range.

than 2 mm in diameter) shows 26 to 62 percent Pensacola Mountains of submicroscopic material, 18 to 32 percent In the Pensacola Mountains, the Gale Mud- quartz, 5 to 21 percent plagioclase and micro- stone (Schmidt and Ford, 1969; Schmidt and cline feldspar, and from a trace to 17 percent Williams, 1970) consists predominantly of carbonate fragments. Lesser amounts of rock diamictite. The Gale is here assigned a Car-

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SENTINEL PENSACOLA OHIO MT. COUNTS MT. RABOT DARWIN RANGE MTS. RANGE (MINSHEW, 1970) (LINDSAY, 1969) ( LI NDSAY, 1969 ) GLACIER

METERS rrr-^ rv^^- p__1 H"=^T -. ^-^ DI SCON FOR MITY ~ ~ = 0 _ ?t? (J fit 7:7 ?f^ ::

* * t: J_ STRIATED BOULDER It! a a 0° * 1 PAVEMENT a o^

•J 1 tl I20~ t t HE t t • ' P7?

_ 1 0 ^ PLANT FOSSILS > t: W it •1'. :: l.::i:.:l SANDSTONE I6O- °a 0~I ..°^_ — i-.;"- \CZ. ; ; _ i^ ^ 'i ':A PAVEMENT S? 200- lit (S3 GRANITE 44 _ ;t ; :: •H Ifffl MARBLE it H '"' It "I DIAM CTITE "a^ — i 240 - a t * STRIATED BOULDER PAVEMENT 1; t f- l:-'i| CONGLOMERATE " 1 t : :: irf \-~.-',\ PEBBLY SHALE *° 280- :t |j|- ::t

VMVH UNCONFORMITY iti ^iVi^. it:

olt UNCONFORMITY S^t SOFT SEDIMENT FIT 32O - DRAG MARKS l-ww trt •J^J GLACIALSECTIONSINTHE QUEEN ALEXANDRA RANGE S ABOUT 175m - it °

36O- ^ iUNCONFORMITY ^ Figure 4. Columnar sections of late Paleozoic glacial rocks in Antarctica.

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the time of emplacement, but extend irregular apophyses into the surrounding mass, suggest- ing that they deformed plastically. Stratification in these sandstone intraclasts is chaotic, but at the margins, it tends to parallel the boundaries of the body. Other sandstone and conglomer- ate bodies appear to be similar to load casts and convolute bedding of sand in diamictite; in- place load casts are common and some attain gigantic proportions, as in the Cordiner Peaks (Fig. 7). Similarly, convolute bedding was ob- served in pockets 2 m deep (Fig. 8), below a striated boulder pavement. These structures in- dicate rapid deposition of sand on a highly mo- Figure 5. "Dropstone" in stratified diamictite, bile substratum. Whiteout Conglomerate, Sentinel Range (scale in cm). Structures which indicate ice-flow direction are abundant in and at the base of the Gale boniferous-Permian(?) age on the basis of its Mudstone. At Mt. Torbert, soft-sediment apparently conformable relationship to the un- grooves resembling drag marks occur on the derlying Dover Sandstone of Devonian(?) age. top of the highest Dover sandstones (Fig. 9), Thickness of the Gale is probably considerably and striated boulder pavements occur at three more than the 316 m (Fig. 4) as measured in a higher levels. Pavements also were found in topless section at Mt. Torbert (Frakes and other nunataks, but their relative stratigraphic others, 1966). Glossopteris-btating strata (Per- positions are unknown. From associated struc- mian) of the nearby Forrestal Range ap- tures on the pavements, the direction of ice parently overlie the Gale Mudstone. flow is deduced to have been generally toward The Gale Mudstone of the Pensacola Moun- the south-southwest, and this coincides with tains is exposed in many nunataks and isolated southwestwardly transport by paleoccurrents as ridges of the Neptune Range, in the Cordiner indicated by sedimentary structures such as rip- Peaks, and in the Forrestal Range (Fig. 6). The ple marks, sole marks, and cross-stratification dominant lithology of the unit is massive, lo- (Frakes and others, 1966). Some paleoccurrent cally faintly bedded diamictite, consisting of a flow toward the northeast is also indicated for sandy mudstone matrix and a disrupted frame- units high in the Gale Mudstone. work of clasts ranging to as much as 3 m in diameter. Petrography has been described by Williams (1969). Diamictite constitutes about HORLICK-QUEEN MAUD BASIN 90 percent of the unit and the remainder is made up of lenticular and disrupted bodies of General sandstone and conglomerate, with subsidiary Late Paleozoic glacial strata of the Horlick- amounts of pebbly shale. On the basis of counts, Queen Maud basin are exposed in the Ohio and clasts consist of about 28 percent granitic rocks, Wisconsin Ranges (Horlick Mountains) and in 20 percent quartzite, 14 percent each of sand- the Queen Maud Mountains as far west as the stone and vein quartz, and lesser amounts of Axel Heiberg Glacier (Fig. 10). Ice completely schist, volcanic rocks, gneiss, and chert. Striated covers a broad region to the east of the Ohio clasts are common. Range, making delineation of the basin margin Sandstone bodies in the Gale are tabular near difficult in that direction. The nearest outcrops the base, where they are associated with thin to the east consist of rocks of the basement conglomerate beds and lenses. Sandstone is complex in the Thiel Mountains, about 300 km dominantly fine- to medium-grained, poorly away. West from Mount Fridjof Nansen, glacial sorted, lithic arenite which displays poorly strata at the base of the conformable Beacon developed cross-bedding and local calcareous section are lacking or poorly developed (Bar- concretionary zones. Disrupted masses of sand- rett, 1965); this is taken to delimit the western stone occur throughout the Gale, are enclosed basin margin. Extent of the basin toward the and injected by diamictite, and attain a max- north is not known because of ice cover near imum dimension of 5 m. They are in sharp the head of the Ross Ice Shelf; to the south, the contact with diamictite, indicating cohesion at glacial rocks and their sedimentary cover dive

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H-

Figure 6. Locality map of the Pensacola Mountains.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/6/1581/3428332/i0016-7606-82-6-1581.pdf by guest on 23 September 2021 Figure 7. Enormous load-casts of conglomerate in diamictite. Hammer at middle right for scale. Gale Mudstone, Cordiner Peaks, Pensacola Mountains.

Figure 8. Enormous convolute bedding of sandstone and conglomerate in diamictite. White boulder at right is 4 m long. Gale Mudstone, Seay Nunatak, Pensacola Mountains.

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Figure 9. Drag marks on upper surface of Dover Sandstone, overlain by Gale Mudstone (scale in cm). Gale Mudstone, Mt. Torbert, Pensacola Mountains.

beneath the thick ice of the Antarctic Plateau. (Long, 1965), Weaver Formation Maximum thickness of the glacial strata, at Mount Weaver and the Wisconsin Range termed the Buckeye Formation, occurs at the (Doumani and Minshew, 1965; Minshew, type locality in the Ohio Range, where the unit 1966)—which appears to be conformable with measures 252 to 308 m thick (Long, 1962, the glacials except possibly in the Ohio Range. 1965). A detailed section, 303 m thick, was measured on Discovery Ridge (Frakes and oth- Ohio Range ers, 1966) and is shown in Figure 4 along with In the flat-lying Paleozoic-Mesozoic se- a section from the Wisconsin Range. West- quence of the Ohio Range, diamictite is the ward, thickness of equivalent strata decreases most common rock type in the Buckeye Forma- progressively, 56 to 140 m in the Wisconsin tion, accounting for about 82 percent of the Range (Frakes and others, 1966; Minshew, unit on Discovery Ridge. In all, 22 units of 1966) and an average of about 15 m in the diamictite ranging from less than 1 m to as broad region from the Watson Escarpment much as 55 m in thickness alternate with units through the Thorvald Nilsen Mountains (Min- of shale, sandstone, or conglomerate (Fig. 4). shew, 1967) to the Axel Heiberg Glacier. Bar- Sandstone beds, generally less than 1 m thick, rett (1965) reports thin, basal conglomerate constitute about 9 percent of the total thickness; limited to local depressions at Mount Fridjof conglomerate beds, also generally less than 1 m Nansen. thick, about 3 percent; and shale and siltstone Except for the Ohio Range, where the Buck- beds, usually less than 10m thick, about 6 per- eye in places lies disconformably on Devonian cent of the total. Sandstone layers and elongate marine sediments (Horlick Formation), the gla- bodies resembling eskers occur throughout the cials everywhere lie depositionally on rocks of formation, but shale and siltstone beds are re- the Precambrian to lower Paleozoic basement stricted to the upper half, and conglomerate to of granitic, volcanic, and metamorphic types. the lower half. Few beds can be traced farther They are followed by a sequence of shale and than about 1 km, although one unit of varvelike siltstone—Discovery Ridge Formation in the sandstone and shale in the middle part of the

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Figure 10. Locality map of the Horlick-Queen Maud basin.

Buckeye persist throughout the range, a dis- grained and only moderately sorted; cross-bed- tance greater than 24 km (Long, 1965). ding is rare. High in the section, sandstone Clasts in the diamictite, generally less than 20 tends to be finer grained and better sorted, and cm but in places up to 5 m in diameter, rest in asymmetrical ripple marks are common. Max- a gray to dark-green sandy matrix. Clasts rarely imum thickness of the sandstone beds is about exceed 10 percent of the rock; some are well 2 m; many are contorted owing to prelithifica- rounded but most are subangular to sub- tion deformation. The uppermost sandstones rounded; approximately 50 percent are faceted commonly are intensely contorted, with soft- on at least one side and striations occur on 10 sediment fold amplitudes ranging from 3 m to to 15 percent of the boulders. Striations are 10 m. Some of the sandstones and conglomer- found on stones of all lithologies but are most ates fill well-developed channels 10 to 20 m numerous and best developed on the faceted wide, but most are more extensive and can be surfaces of dark-gray, siltstone clasts. Coarse- traced to 1 to 2 km along the ridge. The sand- grained stones such as gneiss or granite, al- stone bed which extends throughout the range though polished or faceted, commonly lack is very fine grained, moderately well sorted, striations. Counts of 100 stones at two horizons and apparently massive. yielded the following mean percentages: gran- Shale beds, restricted to the upper half of the ite, 36 percent (most of which apparently was section, either lack stones or contain scattered derived from local basement rocks); dark-gray clasts that generally are less than 10 cm in diam- siltstone or metasiltstone, 41 percent; rhyolite, eter. Clasts displaying subparallel striae pat- 13 percent; quartzite of various kinds, 6 per- terns are not uncommon, and striae orientation cent; and miscellaneous types including chert, on them is random with respect to bedding. quartz, and gneiss, 3 percent. Clasts are concen- Sideritic concretions occur in a siltstone-shale trated in pavements at four separate horizons sequence which also includes varvelike beds (Fig. 11). (Fig. 12) and which lies near the middle of the Sandstone and conglomerate beds are coarse section in the Ohio Range.

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Wisconsin Range crops examined. The tops of some sandstone beds bear grooves apparently resulting from In the Wisconsin Range, nonstratified diam- motion of overriding ice; in places, they are ictite predominates in the Buckeye Formation. over 2 cm deep and 3 cm wide. Masses of sand- The only rocks that break the monotonous se- stone near the top of the Buckeye measure quence of diamictite are a few sandstone beds about 3 to 4 m in diameter, are composed of at the base and varvelike beds and several well-sorted sand that is stained by iron oxides, masses of contorted sandstone that occur in the and show contorted cross-bedding. These upper half (Fig. 4). Diamictite of the Wisconsin highly contorted beds undoubtedly were de- Range is similar to that of the Ohio Range, in formed before lithification, and they occur at that the gray to green matrix is sandy and sur- the same approximate horizon over an area of rounds boulders as much as 2 m in diameter. several km2. Sandstone that fills depressions in Granite clasts, most of which have a composi- the basement rock is never thicker than several tion similar to that of local granitic basement meters and is composed of horizontally lami- rocks, comprise 40 percent of all clasts; dense nated fine- to medium-grained sandstone inter- gray siltstone is the next most common stone calated with pebble conglomerate. Units encountered, forming 27 percent; quartzite is measure less than 30 cm thick, are highly con- next in importance with 19 percent, followed torted, and incorporate boulders up to 25 cm in by metamorphic rocks (10 percent) and vein diameter. quartz (5 percent). Limey spherical concretions ranging up to 30 cm in diameter occur through- Queen Maud Mountains out the unit, but are most numerous along a Minshew (1967) reports thin diamictite horizon approximately in the middle of the depositionally above rocks of the basement unit. complex in the Long Hills, and west of the Striated and faceted boulders are common in Wisconsin Range through much of the Queen diamictites of the Wisconsin Range, but boul- Maud Mountains to the region of the Axel Hei- der pavements were not observed in the out- berg Glacier. In the Queen Mauds, thickness

Figure 11. Striated boulder pavement within Buckeye Formation (scale in cm). Buckeye Formation, Discovery Ridge, Ohio Range.

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apparently does not exceed about 45 m, and the rent transport was generally to the southwest as glacial rocks locally are missing. Diamictite of judged from the orientation of primary sedi- glacial origin is the predominant rock type, but mentary structures. Our conclusion is that the sandstone, pebbly claystone, and siltstone are late Paleozoic ice flowed toward the west in the locally developed (Minshew, 1967). Clasts in Ohio Range (Frakes and others, 1966). diamictite consist predominantly of local base- Striated surfaces throughout the remainder ment types—granite, metasediments, and meta- of the Horlick-Queen Maud basin indicate gla- volcanics—and many display striae and facets. cial flow in the opposite sense; that is, generally toward the east. Minshew (1967) determined Transport Directions eastward flow, with some deflection toward the Transport directions of late Paleozoic ice in northeast, from striated surfaces below the the Horlick-Queen Maud basin are deduced Buckeye in the Wisconsin Range. Directional- from abundant striated floors beneath the gla- current indicators measured by Minshew show cial rocks, and from striated boulder-pave- that paleocurrents had a similar sense of flow, ments and grooved sandstone beds within the and Frakes and others (1966) indicated some glacial sequence. On the basis of clast imbrica- paleoccurent flow toward the south in the Wis- tion and fragment trains from parent clasts in consin Range. Striated floors in the eastern pavements of the Ohio Range, Long (1964) Queen Maud Mountains indicate ice transport inferred that ice flow was generally from west toward the east-northeast (Minshew, 1967), to east. Reexamination of these exposures re- and those in the Thorvald Nilsen Mountains vealed crescentic gouges on underlying suggest movement toward the segment be- Devonian rocks (Fig. 13) which indicate east- tween 120° and 165°, that is, toward the to-west flow of the ice (Frakes and others, southeast (W. E. Long, cited in Minshew, 1967). 1966). Additionally, individual striated boul- ders in pavements display evidence of east-to- BEARDMORE BASIN west flow in that only eastern (up-glacier) General margins are striated, whereas only western The Beardmore basin comprises the norther- (down-glacier) ends are plucked. Paleoccur- most occurrences of late Paleozoic glacial rocks

Figure 12. Varvelike siltstone and shale with "dropstones." Hammer for scale. Buckeye Formation, Ohio Range.

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in the Ross Sea sector of Antarctica (Fig. 14). west of the Beardmore Glacier where Grindley It is separated from the Horlick-Queen Maud (1963) discovered the Pagoda Tillite (here basin by the broad segment of the Transantarc- termed Formation) lying disconformably on tic Mountains between the Axel Heiberg Gla- Devonian(P) sandstone (Alexandra Formation) cier and the east side of the Beardmore Glacier, and followed conformably by rhythmites of the which displays little firm evidence of ancient Mackellar Formation. The Pagoda has been glaciation. Glacial strata of the Beardmore ba- studied by Matthews and others (1967) and sin are known from the mountain ranges fring- Barrett and others (1967, 1968a, 1968b). The ing the west side of the Beardmore Glacier most extensive work here is that of Lindsay westward to the vicinity of the Nimrod Glacier, (1969, 1970 ) who notes that the Pagoda For- and from the Darwin Glacier region. Farther to mation ranges in thickness from about 126 to the north and west, late Paleozic glacials have 395 m and averages about 175 m (Fig. 4). not been recognized except in the dry valley Diamictite constitutes 45 to 91 percent of the region west of Ross Island (Matz and Hayes, section, the thicker sections containing rela- 1966) where they may be represented by thin tively greater amounts of the associated rock lenticular bodies and as sizeable xenoliths in types, channel sandstone and tabular siltstone Jurassic Ferrar Dolerite. Generally, in central and limestone beds (Matthews and others, and northern Victoria Land, nonglacial Per- 1967; Lindsay, 1969). Diamictite is predomi- mian clastic rocks lie disconformably on nantly nonstratified and contains striated and Devonian strata, and this region is considered faceted clasts up to about 1 m diameter, set in to represent the northwestern margin of the a chloritic matrix. Dominant clast types in a Beardmore basin. large sample measured by Lindsay (1969) are as follows: graywacke (31 percent), gneiss (16 Queen Alexandra Range percent), granite (15 percent), limestone (9 The best-developed sequences of glacial percent), and chert (8 percent). rocks in the Beardmore basin lie closely to the In the Tillite Glacier region of the Queen

Figure 13 Crescentic gouges carved in Devonian Horlick Formation. Hammer for scale. Discovery Ridge, Ohio Range. Ice flowed toward upper right.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/6/1581/3428332/i0016-7606-82-6-1581.pdf by guest on 23 September 2021 Figure 14. Locality map of the Beardmore basin.

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Alexandra Range, diamictite occurs as three Glacier region (M. G. Laird, March 13, 1970, distinct units separated by shale, sandstone, or personal commun.) but have not been found in siltstone interbeds; nearby, Lindsay (1969) the broad region northwest of the Queen Alex- noted as many as 13 separate diamictites. andra Range. Cumulative thickness of the sandstone beds In the vicinity of the Nimrod Glacier, the generally is approximately equal to that of the Pagoda Tillite (Grindley, 1963) varies in thick- siltstone beds; but sandstone beds are inter- nesses from thin patches to more than 100 m calated as units less than 9 m thick throughout (M. G. Laird, March 13, 1970, personal com- the section; whereas siltstone occurs in units as mun.) The unit is composed predominantly of much as 25 m thick. Siltstone is restricted to the diamictite and sandstone; striated clasts occur, upper half of the section. Fissile shale is a minor but striated floors have not been observed. component which is recognized only near the Diamictites, which attain individual thicknesses base of the section. The thickness of any bed, of 12 m, are assigned a glacial origin and sand- regardless of lithology, is not uniform for any stones are termed fluvioglacial. appreciable distance, indicating that facies Four units of diamictite have been recog- changes are rapid. nized in a 65-m-thick section of the Darwin At Tillite Glacier, the basal dimictite is Tillite near the Darwin Glacier (Frakes and oth- poorly exposed and attains a maximum known ers, 1968). They are of variable lithology, the thickness of about 2.5 m. It contains sandstone lowest three being very sandy and containing masses showing internal contorted bedding. deformed sandstone masses, and the uppermost The second highest diamictite is nonstratified, being more like typical diamictites seen else- encloses sandstone lenses, and measures about where (Fig. 4). The latter, 17 m thick, contains 59 m thick. A well-sorted black shale, 3 m thick striated clasts as much as 40 cm in diameter in and lacking clasts, separates the two diamictites. a fine-grained matrix of recrystallized micas. The youngest diamictite lies above a 38-m-thick Clast types are of local granitic rocks (50 per- unit of siltstone and sandstone and measures cent), various sedimentary rocks (45 percent) about 20 m. Numerous limestone stringers and and other igneous and metamorphic types (5 lenses 20 to 50 cm thick occur in the lower part percent). Striated floors and pavements are of this diamictite, but otherwise statification is lacking, but sedimentary structures indicate poorly developed. that paleocurrents flowed generally toward the Most sandstone beds show evidence of defor- southeast, and a tillite fabric suggests ice flow mation prior to lithification that is manifested as toward the east-southeast (Frakes and others, a slight warping of laminae. Some beds as thick 1968). as 3 m are folded and overturned. At the type Ice-transport directions in the Beardmore ba- section of the Pagoda Formation, a sandstone sin are predominantly toward the southeast bed about 15m thick is cut by a steeply dipping with local deflections, as deduced from study of fault that shows approximately 50 m of vertical striated boulder pavements and soft-sediment separation. Near the fault plane, the sandstone striations (Matthews and others, 1967; Barrett bed is highly contorted, and stringers of the and others, 1967, 1968a, 1968b; Frakes and sandstone are mixed complexly with the diam- others, 1968; Lindsay, 1969, 1970). Paleocur- ictite. Beds of the overlying MacKellar Forma- rents seem to have flowed somewhat more to- tion are not displaced by the fault; therefore, ward the south, judging from the orientation of faulting probably took place before deposition sedimentary structures. of the MacKellar Formation. Because of the soft-sediment nature of the mixing, faulting is AGE AND CORRELATION judged to have occurred prior to lithification of the sandstone. Dating of Antarctic glacial deposits is difficult because of a paucity of fossil material. The only Darwin and Nimrod Glaciers date assigned at present by paleontological means is one based on spores (possibly Per- In the Darwin Glacier region (Haskell and mian) from the Buckeye Formation in the Ohio others, 1965), the Darwin Tillite lies discon- Range (J. M. Schopf, cited in Long, 1965). Else- formably on Devonian(P) Hatherton Sand- where, age determinations are made with refer- stone and is in turn followed disconformably by ence to stratigraphic relationships, most of the Misthound Coal Measures (Permian). Gla- which allow broad ranges. For example, in the cial strata have been reported from the Nimrod Ellsworth Mountains, the glacial Whiteout

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Conglomerate may be of any age between Cam- glaciation or from mass-movement processes; brian and Permian, but is probably Permian or we base our interpretations on field methods Carboniferous because of stratigraphic prox- (outlined /'« Frakes and Crowell, 1970a). Here, imity to overlying Permian rocks. It seems a diamicitite is considered glacial if it is as- likely that in much of the continent, the glacials sociated with glacial floors or pavements or are no older than early Carboniferous and that with other typically glacial strata, or if it con- none is younger than Permian. In each of the tains glacially striated stones. Such diamictites, three basins described above, glacial strata lo- like tills, are commonly massive or poorly bed- cally lie disconformably on Late Devonian ded and lack large sandstone intraclasts (that is, rocks and are followed conformably by plant- transported cohesive sediment). Lacking more bearing Permian units. diagnostic evidence, a decision on genesis can The glacial Gale Mudstone of the Pensacola be made on the presence or absence of the Mountains displays interesting contact relation- latter two characteristics. In the late Paleozoic, ships with underlying rocks in the Mt. Torbert processes of mass movement apparently were area. In this region, no evidence of unconform- widely associated with glaciation (Frakes and ity is discernible between the Gale and underly- Crowell, 1967, 1969, 1970a; Crowell and ing sandstone which is assigned to the Dover Frakes, 1968); where glacial debris underwent Sandstone (Schmidt and Ford, 1969). The con- mass movement, it is difficult to interpret mode tact is abrupt and visible for several kilometers of origin. of exposure. Moreover, the uppermost Dover In Antarctica, striated floors or pavements bed bears grooves strongly reminiscent of soft- occur in all three basins and in almost every sediment drag marks (Fig. 9). This is particu- major section which has been studied. More- larly significant in that plant debris of Late over, diamictites are widely associated with Devonian age occurs in the Dover of the south- varvelike shales bearing isolated, glacially ern Pensacolas (Schmidt and Ford, 1969), al- scribed stones and with fluvial strata which though long-range correlation of the Dover on resemble outwash deposits. There is thus little lithologic grounds is extremely tenuous. A doubt that Antarctica was glaciated during the possible Late Devonian or slightly younger age late Paleozoic, and the wide extent and great is thus possible for the basal Gale Mudstone. thickness of some of the glacial deposits suggest This is the only Antarctic locality where Paleo- that refrigeration was intense and long lasting. zoic glacial strata might be as old as early Car- As in other continents, glacial debris apparently boniferous. was involved in mudflows, landslides, and simi- A late Devonian or, more reasonably, early lar types of retransportation. Carboniferous age for glacial strata in the Pen- sacola Mountains would suggest a similar age PALEOGEOGRAPHY for the Whiteout Conglomerate of the Ells- worths, and leads to the speculation that Paleo- The geographic variations within diamictite zoic glaciation of Antarctica began first in the sequences reveal much about the history of late Ellsworth-Pensacola basin. It is of course possi- Paleozoic glaciation of Antarctica. We will ex- ble that the oldest portion of the Gale Mud- amine these variations with three aims in mind: stone is as young as Permian, although this (1) to determine as accurately as possible the would require a highly variable age for the distribution of environments of deposition, (2) Dover Sandstone. Another possibility exists— to ascertain how paleogeographic trends varied that throughout the continent, glacial strata are with time in the late Paleozoic, and (3) to exam- contemporaneous and range from early Car- ine the implications of Antarctic glaciation as boniferous to Permian in age—but this also is they relate to continental drift. not directly supportable. On the basis of the available evidence, we tentatively suggest that glaciation began in the Weddell Sea sector in Environments of Deposition the early Carboniferous (?), spread over the In the Ellsworth-Pensacola basin, only one continent in Permian time, and terminated be- major diamictite facies is known. The thick, fore the end of the Permian. massive diamictite here has been interpreted as of glacial-marine origin (Craddock and others, MODE OF ORIGIN 1964; Matthews and others, 1967), in view of Several techniques are known for determin- the fact that the great thicknesses probably re- ing whether diamictites have originated from quired a deep basin which was continuously

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depressed during the Paleozoic. However, (1969) suggests that the Ellsworth Mountains Schmidt and Williams (1969) infer a nonma- were torn away from a position marginal to the rine origin for the Gale Mudstone on the basis Antarctic Plateau as part of a crustal tongue of geochemical analyses. Fossils are thus far which was pushing westward in the Mesozoic. lacking from the glacial sequences to support There may be other interpretations. Until these either idea, and it is possible that both fresh- major problems are solved, the configuration of water and marine environments were present. the Ellsworth-Pensacola basin and its relation- The deformed sandstone intraclasts which are ships to the source areas must be based on the abundant at certain horizons in the diamictite present distribution of the rocks. probably represent cohesive sandstone beds In the Horlick-Queen Maud basin, quite which were broken apart and transported from different conditions prevailed. Evidence of the basin margins by mass movement. The marked Paleozoic downsinking is lacking and diamictite enveloping these masses is accord- the remnants of the basin probably represent ingly assigned an origin from proximally posi- glacial deposition on the margin of the late tioned mass movement, but the presence of Paleozoic continent. The rocks reflect this in striated stones indicates that the transported that they in large part consist of morainal dia- material was first derived from a glaciated ter- mictite with abundant striated floors and pave- rain. ments, and are associated with eskerlike Basin-margin facies other than the proximal sandstone bodies and varvelike strata which mass-movement facies are not presently known bear plant fragments. Mudflow and fluvial fa- in the Ellsworth-Pensacola basin, and thus the cies also occur, suggesting periodic retranspor- original configuration must be inferred from the transport directions and other considera- tions (Frakes and others, 1966). The dominant north-to-south ice and paleocurrent flow for the Gale Mudstone in the Pensacola Mountains suggests a sizeable ice-center in the eastern Weddell Sea region. This is supported by the apparent concentration of striated pavements and large sandstone intraclasts in the northern Pensacolas and their relative scarcity else- where. These disrupted sandstone masses EARLY CARBONIFEROUS (proximal mudflow deposits) would be ex- pected to accumulate downslope from the basin margins. The less common structures indicating south-to-north paleocurrents, on the other hand, suggest another source area, possibly located in the region of the Thiel Mountains; this one might also have served as the center from which ice radiated northward toward the Ellsworths. It seems likely that ice occupied the entire rim of the present Antarctic Plateau LATE CARBONIFEROUS (Schmidt and Williams, 1970), but it may have been best developed in the two salients repre- sented by the eastern Weddell Sea and the Thiel Mountains (Fig. 15A). Between the sali- ents, a continuously subsiding basin extended to the north and may have bounded the conti- nent during the late Paleozoic. This picture is complicated by intense post- glacial tectonism. The tectonic strike of the Ells- PERMIAN worth Mountains is perpendicular to that of the Pensacolas, suggesting that their positions rela- Figure 1 5. Paleogeographic maps of Antarctica dur- ing the late Paleozoic. Stippled area = jtlacial center; tive to one another may have been changed heavy lines enclose the three basins of this study; arrows since the sediments were laid down. Schopf show directions of ice flow.

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tation of glacial debris by mass movement and In the Beardmore basin, diamictite facies meltwater streams. suggest moraine forming and mass-movement The Horlick-Queen Maud basin apparently processes, at least partially in a subaqueous en- received glacial debris from both the east and vironment (Matthews and others, 1967; Bar- west margins. The thickest glacials in this basin rett and others, 1967; Frakes and others, 1968; (Ohio Range) are also the most proximal to the Lindsay, 1968, 1969). Strata associated with eastern basin margin (Fig. 15C), whereas the the diamictite include slumped sandstone, small deposits in the Wisconsin Range and the Queen sandstone deltas, and dropstone shale; this com- Maud Mountains thin gradually over a deeply bination suggests deposition near the shoreline eroded base toward 'the western margin. Flow of a water body. Alternation of diamictite and directions deduced from primary structures in- sandy units may be indicative of at least four dicate that flow was predominantly from the glacial cycles (Fig. 4), but again the extent can- east in the Ohio Range but, for the most part, not be determined because of a lack of good from the west elsewhere. criteria for correlation. The thickest late Paleozoic glacial sections lie The varvelike strata suggest that ponding was near the Beardmore Glacier; however, this may common on the glaciated terrain, and some of not have been the original situation, in view of these lakes may have been geographically ex- the fact that north from the Darwin Glacier, the tensive, judging from the widespread con- flat-lying glacial rocks are cut and possibly com- tinuity of one varved unit near the top of the pletely removed by a major unconformity. The Buckeye in the Ohio and Wisconsin Ranges. thick sections, however, show no evidence of Although such strata may indicate at least two derivation from the ice center which separated major cycles of glaciation, the evidence is too the Beardmore basin from the Horlick-Queen scanty to allow correlation of cycles throughout Maud basin. Further work southeast of the the basin. Proximal mudflow facies follow Beardmore Glacier is needed here to delineate closely on lacustrine facies and the tops of some sedimentation trends and the basin margin. sandstone beds are striated, suggesting a Moreover, because the region north of the Dar- renewed influx of glacial material. win Glacier was subjected to deep erosion in The eastern basin-margin cannot be posi- the late Paleozoic, it seems unlikely that glacial tioned precisely but probably would lie be- strata there were deposited in a deep basin. We tween the Ohio Range and the Thiel conclude that the Beardmore basin was asym- Mountains. Ice flowed westwardly from this metrical, with a deep southern and a shallow margin as far as the Ohio Range but also north- northern margin. In this sense, it was similar to wardly into the Ellsworth-Pensacola basin. The the Horlick-Queen Maud basin. The two ba- Thiel salient thus seems to have been a center sins differ, however, in that transport seems at of radiating ice flow (Frakes and Crowell, this point to have been entirely from the north- 1968a). This hypothesis could be tested further ern margin in the Beardmore, whereas it was if we had better knowledge of the pre-glacial from both sides in the Horlick-Queen Maud geology of the intervening regions and if clast basin. types in diamictites were less variable. The westward thinning of glacial sections in Migration of Ice Centers the Queen Maud Mountains and their virtual absence farther west are taken to indicate a As noted above, there is some evidence that western ice center of lesser magnitude. This the glacial deposits differ in age from place to center probably was positioned between the place. They may be as old as Devonian but Horlick-Queen Maud and the Beardmore ba- more probably are early Carboniferous in the sins, that is, in the broad region from the Axel Pensacola Mountains, but spores indicate a Per- Heiberg Glacier to the Beardmore Glacier. mian age in the Ohio Range. This does not There is evidence in the considerable relief of necessarily mean that Permian glaciation was the floor (Lindsay, 1969; Minshew, 1967) that lacking entirely in the Pensacolas and that Car- this region was somewhat more elevated than boniferous ice did not occur in the Horlicks. other centers. Ice flow radiated toward the Rather, the position of the Ohio Range spores south and the southeast into the Horlick- in the middle of the glacial section suggests that Queen Maud basin and possibly toward the most glacial deposits there originated in the Beardmore basin to the northwest. Permian, whereas conformable relations of the

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glacials to Devonian(?) rocks in the Pensacolas Sea glacial center adjacent to and up-glacier point toward an early Carboniferous (?) initia- from Carboniferous Dwyka Tillite of South tion of glaciation. We tentatively suggest that Africa (Fig. 16). This helps to solve the prob- this apparent age difference can be explained lem of late Paleozoic glaciers flowing out of the by migration of glacial centers. Indian Ocean (du Toit, 1921) by providing a In the Pensacolas, primary structures in the seat for the ice. Similarly, glacial flow from out lower half of the section all indicate transport of the Southern Ocean south of Australia and toward the southern quadrant: the few struc- Tasmania (Sprigg, 1967; Banks, 1962) can be tures which document north-flowing paleocur- explained by placing Antarctica adjacent to the rents are limited to the upper half. The initial Great Australian Bight. In this case, the Ross ice center in the Weddell Sea region thus con- Sea ice center lies up-glacier from glacial depos- tributed the bulk of the early sediment in the its of southern Australia and Tasmania (Frakes Ellsworth-Pensacola basin; this was relatively and Crowell, 1970b). later supplemented by paleocurrents, and possi- Correspondence is also good in terms of age bly mudflows, streaming northward from the between the Carboniferous-Permian(P) Dwyka Thiel salient. There is evidence from direc- Tillite of Africa and the Gale Mudstone-White- tional structures in the Ellsworth Mountains out Conglomerate of the Ellsworth-Pensacola that the Thiel region was glaciated, but the ab- basin in Antarctica. The same is true for the solute timing is uncertain in both the Pen- Permian-Carboniferous glacials of the Aus- sacolas and the Ellsworths. tralian mainland and Tasmania and those of the The Thiel salient also contributed to Permian Antarctica Beardmore basin. In effect, the gla- glaciation in the Ohio Range, however, so that cial deposits of Antarctica fit temporally into the major flow from this ice center had a minimum general younging trend from the South Ameri- age of Permian. It probably first formed not can to the Australian sector of Gondwanaland. earlier than the late Carboniferous, unless the The trend possibly results in part from the high- Ohio Range section is greatly attenuated. latitude migration of Gondwanaland across the Age of the two other centers is probably Per- pole, as suggested by summarized paleomag- mian but greater accuracy and precision is not netic evidence (for Africa: McElhinny and oth- now possible. The ice center separating the ers, 1968; for Australia: Irving and Robertson, Horlick-Queen Maud and Beardmore basins, 1969; for South America and Antarctica: Creer, and the one north of the Beardmore basin can- 1965). The curves representing relative motion not now be dated because of a lack of fossils and between continents and pole are parallel and meaningful stratigraphic relations within the nearly coincident (Fig. 16), thus supporting the basins. The sum of the evidence is compatible view that Gondwanaland moved as a unit over with a model in which glaciation spread from an the pole during the later Paleozoic. early Carboniferous(P) center in the eastern The idea that the Weddell Sea region was Weddell Sea across the continent to the Ross glaciated prior to the glaciation of the Ross Sea Sea region in the Permian (Fig. 15). sector is based on a tenuous lithologic correla- tion of the Dover Sandstone in the Pensacola Relationships to Gondwanaland Mountains. However, it is interesting that the Glaciation hypothesis of migrating glacial centers con- forms so well with the paleomagnetic data; a Glaciation of the southern continents and great deal of additional work is clearly needed India can be explained by reassembling them to substantiate these views. into the parent supercontinent, Gondwanaland, and passing the assembly over the South Rota- ACKNOWLEDGMENTS tional Pole (see King, 1962; Holmes, 1965). This concept has been expanded in an attempt We express appreciation to the members of to explain most of the Paleozoic glacial deposits our field parties: Irving R. Neder, Courtney J. of the southern hemisphere (Crowell and Skinner, Donald A. Coates, T. W. Gevers,John Frakes, 1970). As a test, if glaciation occurred E. Marzolf, and Lloyd N. Edwards. We are on adjacent Gondwana continents, then the grateful to Dwight L. Schmidt for field guid- broad glacial patterns should show correspond- ance and critical comments on the manuscript. ence in age and trends. Matching of the 1000-m We also thank Wesley E. LeMasurier, Campbell isobaths for Antarctica and Africa (Smith and Craddock, and Malcolm G. Laird for critical Hallam, 1970) places the postulated Weddell comments, and numerous geologists who have

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/6/1581/3428332/i0016-7606-82-6-1581.pdf by guest on 23 September 2021 REFERENCES CITED 1601

P- PENSACOLA MTS. E - ELLSWORTH MTS.

0 POLAR MOTION PATH, ANTARCTIC DATA

A««4 POLAR MOTION PATH, AFRICAN DATA

• POLAR MOTION PATH, AUSTRALIAN DATA

LATE PALEOZOIC ICE FLOW

JURASSIC (ZIJDERVELD, 1968 )

Figure 16. Reconstructed Gondwanaland. Based on positions of late Paleozoic ice centers and polar-motion paths from paleomagnetic data.

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