DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY

2800 —

2700 4

LACKEY RIDGE

2200

BUCKEYE TABLE

Second spur west of

Projected from Discovery Ridge

Schulthess Buttress

Canyon Peak

METERS ABOVE SEA LEVEL

2100

2000 —

E

Mount Giossopteris F

— 2000 m — Og

Og

5 10 KILOMETERS
|

oe

T
3 6 MILES
VERTICAL EXAGGERATION x 10
FIGURE 3.—Schematic cross section A-F through the Ohio Range.

116°00"

2500

}- 2400

- 2300

t 2200

2100

2000

1900

1800

115°00’

Prepared by the
UNITED STATES GEOLOGICAL SURVEY
under the auspices of the
NATIONAL SCIENCE FOUNDATION

114°00"

é

Bennett Nunataks

@

Vann Peak

Eldridge Peak

T

(0) Tuning Nunatak

Base from U.S. Geological Survey, 1959
Revised by authors

INTRODUCTION

The Ohio range is a north-facing, east-trending escarpment at the edge of the Polar Plateau
(fig. 1). The range is about 45 km long, and the highest point is on Mt. Schopf (2990 m above
sea level). Southward, ice overriding most of the Ohio Range merges with that of the Polar
Plateau; large ice falls occur along the southeastern side of Mount Schopf. Northward, ice of the
extensive Buckeye Table falls an average of 400 m through wide canyons along the escarpment
to merge with the ice of southern Marie Byrd Land. Summer air temperatures are always below
freezing, although dark rock surfaces occasionally rise above freezing. Winter temperatures have
not been recorded.

This map is derived in part from Long’s (1965) geologic map of the Ohio Range but also
includes field work done in the austral summer of 1979-1980 by a four-person expedition
sponsored by the New Zealand Antarctic Research Programme and the National Science
Foundation. The main purpose of the 1979-1980 project was to study the paleoecology and
sedimentology of the Horlick Formation (Bradshaw and McCartan, 1983; McCartan and
Bradshaw, in press), but the contacts and character of other formations were examined briefly.
The base map (U.S.G.S., 1963) and contacts were revised in the field using a Brunton Pocket
Transit and vertical and oblique aerial photographs (fig. 2). Previously measured sections (Long,
1965) were found to be as much as several hundred meters too thick when compared with the
most reliable topographic reference points on the base map (U.S.G.S., 1963). Schematic
stratigraphic columns presented herein (fig. 3) lack many details contained in Long’s (1965)
publication but probably reflect the thickness of units more accurately. The datum for the cross
section (fig. 3) is the top of basement, which appears to be an almost flat surface tilted less than
1° downward toward the east.

GEOLOGIC HISTORY

Little is known about the geologic history of the Ohio Range prior to the emplacement of a
granitic batholith in Middle Ordovician time. The granitic basement was eroded to a flat peneplain
before deposition of the overlying Horlick Formation. The granitic basement forms sheer cliffs as
much as 300 m high that extend the length of the Ohio Range (fig. 4), and wind-scoured
pavements that are especially well exposed on Discovery Ridge and Darling Ridge. The eroded
surface of the basement is about 100 m higher on the west end of the range than on the east end.
Clasts of basement rock in the Horlick Formation are all granitic, and so provide no clues about
rocks in the area older than the granite batholith.

The Horlick Formation is considered to be of Early Devonian age based on the presence of
stratigraphically diagnostic marine fossils (Boucout and others, 1963; Doumani and others, 1965).
Marine fossils were present at all of the sections studied, except at one unfossiliferous section on
the west spur of Schulthess Buttress. That section is composed of coarse arkosic sandstone with
festoon and antidune crossbeds and very rare mudstone beds; textures and structures suggest that
this unit was formed by fluvial deposition. The distribution of lithologies and fossils suggests
deposition in 2 to 30 m of water on a broad, unbarred coast that experienced low to moderate
tides (1-2.5 m), such as occur at German Bay in the North Sea (Dérjes and others, 1970;
Wunderlich, 1970). A Lower Devonian landmass lay to the north, and sediment transport was
predominantly towards the west, probably reflecting a longshore current (Long, 1965; McCartan
and Bradshaw, in press). The sequence at west Schulthess Buttress probably was deposited by a
river that supplied sediment to the coast.

116°00'

After deposition and consolidation of the Horlick Formation, gentle eastward tilting created a
western highland. Both Long (1965) and Frakes and others (1966) concluded that the Buckeye
Tillite, which overlies the Horlick Formation, is primarily of glacial origin with minor intercalated
waterlaid deposits. From studies of the striations on faceted boulders and pavements, as well as
crossbedding at several levels in the formation, Long (1965) interpreted ice movements as toward
the northeast and east; however, Frakes and others (1966) came to the opposite conclusion—that
ice and water currents had moved toward the southwest and west. Later in the Permian, the
sandstones and shales of the Discovery Ridge and Mt. Glossopteris Formations were deposited by
east-flowing streams and in large lakes.

A period of extension and injection of dolerite sills (Ferrar Dolerite) during Jurassic time
characterizes much of the Transantarctic Mountains (McDougall, 1963; Long, 1965; Treves, 1965).
In the Ohio Range, a thick dolerite sill intruded the rocks of the Mt. Glossopteris Formation. The
thermal effect of the sill is evident in the alteration of sandstone to quartz-sericite hornfels
immediately below the sill, and in the change of coal rank in the Mt. Glossopteris Formation. The
rank ranges from semianthracite near the base of the formation through anthracite to coke just
below the sill at the top of the formation (Schapiro and Gray, 1966). Estimates of coal rank by
vitrinite reflectance from coal samples collected on Discovery Ridge suggest that these samples
were also within the thermal aureole of an igneous intrusion (R. W. Stanton, U.S. Geological
Survey, personal communication, 1983).

High angle faults, possibly related to Jurassic rifting, partly controlled subsequent glacial
erosion.

Sedimentary rocks of the Ohio Range dip less than 1° to the east. Paleozoic rocks in Victoria
Land are also relatively undeformed (Allen, 1962), although the Paleozoic rocks of the Pensacola
Mountains, east of the Ohio Range, record multiple orogenic episodes (Schmidt, 1963).

The maximum temperature and depth of burial attained in the Horlick Formation on Darling
and Lackey Ridges have been estimated by analyzing the color of phosphatic fish plates, or
ichthyoliths (A. G. Harris, U.S.G.S., written communication, 1983; see also Epstein and others,
1977). Assuming that a 200-m-thick Jurassic sill was about 500 m stratigraphically above the Hor-
lick Formation on Darling and Lackey Ridges (a realistic projection from the large sill on Mt. Glos-
sopteris), a maximum temperature as high as 150°-200° C would have been reached during a
short-term (less than 1000 years) thermal pulse. If the sill did not extend as far as the area of Darl-
ing and Lackey Ridges, and the subtle alteration of fish plates from the Horlick Formation is due
entirely to long-term burial, then the maximum temperature attained did not exceed about 100°.
This latter temperature can be used to estimate the maximum amount of overburden by compari-
son with a realistic geothermal gradient (Hacquebard, 1975); a value of 4000 to 5000 m of over-
burden is thus obtained. Most likely, a combination of thermal and burial metamorphism affected
the rocks of the Horlick Formation.

ACKNOWLEDGEMENTS
This project was generously supported by the Antarctic Division of the New Zealand Division
of Scientific and Industrial Research, the Canterbury Museum Trust Board, the National Science
Foundation, and the U.S. Geological Survey.

oO L A R

Higgins Canyon

P L A T E A U

60°

120°

150° WEST 180° EAST 150°

FIGURE 1.—Location diagram. E,
East Antarctica; W, West Antarctica;
V, Victoria Land; Transantarctic
Mountains.

a = ——L a — — —L -
115°00" 114°00"
SCALE APPROXIMATELY 1:50,000 AT 84°45°
1 5 0 1 2 5 4 5 6 7 8 9 10 KILOMETERS
1 5 0 1 i 3 4 5 § MILES
CONTOUR INTERVAL 200 METERS
DATUM IS MEAN SEA LEVEL
NATIONAL GEODETIC VERTICAL DATUM OF 1929
LOCATION DIAGRAM
30° WEST 0° EAST 30°
Vertical aerial
60° photographs
90°
Oblique aerial photographs
120°

FIGURE 2.—Aerial photographs used in revision of base map.

Photograph by U S. Goolegical Survey

113°00'

{ earas
Th ‘\
4 ~ )/|
a signer Pk /
|
|
—{ e450"

Pigs

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FIGURE 4.—Oblique aerial photograph of the west end of the Ohio Range, looking south.

RECONNAISSANCE GEOLOGIC MAP OF THE OHIO RANGE, TRANSANTARCTIC MOUNTAINS, ANTARCTICA

By
Lucy McCartan, U.S. Geological Survey, Reston, Va.
Margaret A. Bradshaw, Canterbury Museum, Christchurch, New Zealand

Karl S. Kellogg, U.S. Geological Survey, Denver, Co.
1986

INTERIOR—-GEOLOGICAL SURVEY, RESTON, VA—1986—G84274

Geology mapped in 1979-80

U.S. ANTARCTIC RESEARCH PROGRAM
ANTARCTIC GEOLOGIC MAP A-13

CORRELATION OF MAP UNITS

Igneous Rocks Sediments Sedimentary Rocks
Qsc | Qm } QUATERNARY
Unconformity
Le | } JURASSIC
PERMIAN AND
Unconformity CARBONIFEROUS?
Unconformity
} DEVONIAN
Unconformity
} ORDOVICIAN

DESCRIPTION OF MAP UNITS

Qsc Scree—Rock debris with minor snow and ice matrix; only one deposit
mapped, on Discovery Ridge.

Qm Moraine—Rock debris entrained in moving ice masses; occurs mainly west
of Darling Ridge.

a] Ferrar Dolerite—The rock is a dark-gray to black, subophitic tholeiitic
basalt that shows a slight upward increase in plagioclase (labradorite
and calicic andesine) and granophyre, and an upward decrease in
pyroxene (pigeonite, augite, and minor hypersthene) (Treves, 1965). It
occurs as a sill, at least 150 m thick, with an eroded upper contact,
capping Mt. Schopf, and crops out over an area of about 2km by 10
km (Long, 1965).

| Mount Glossopteris Formation—The Mt. Glossopteris Formation (Long,
1965) consists of two members. The upper half of the formation is
dark-gray carbonaceous shale and mudstone with well-preserved fossil
Glossopteris and Gangamopteris leaves, grading to coal in some
places. Cridland (1962) has dated the leaves as Permian. A few
beds contain fresh-water pelecypods (Bradshaw, 1984) and bivalved
crustaceans (conchostracans; Doumani and Tasch, 1965). The lower
half of the formation consists of light tan, fine- to medium-grained
arkosic sandstone, with plant fragments in some beds.
The Mount Glossopteris Formation crops out east of Canyon
Peak. It's lower contact is gradational with the underlying Discovery
Ridge Formation; the contact has been placed arbitrarily at the base of
the first massive sandstone above the black, fissile shales of the
Discovery Ridge Formation (Long, 1965). The formation reaches a
maximum thickness of about 350 m on Mt. Glossopteris. On Mt.
Schopf, the top of the Mt. Glossopteris Formation has been intruded by
a dolerite sill.

P| Discovery Ridge Formation—Two members of the Discovery Ridge

Formation were defined by Long (1965). The lower member, which
includes the lowest quarter of the formation, is gray, platy shale, with
up to 30 percent silt-size quartz. The upper member is also shale, but
is darker, more fissile, and very carbonaceous. Lenses of impure, iron-
bearing limestone up to 10 cm thick and 4.5 m across are present in
the upper member. No body fossils are known from ‘the Discovery
Ridge Formation, but vertical and horizontal trace fossils made by
mobile invertebrates are abundant in the lower member, and burrows
are also present within a few meters of the contact with the overlying
Mt. Glossopteris Formation. The Discovery Ridge Formation
unconformably overlies the Buckeye Tillite and is exposed east of
Canyon Peak. The formation is best exposed in broad steps on
Discovery Ridge.

Buckeye Tillite—The Buckeye Tillite (Long, 1965; Frakes and others,
1966) consists mainly of massive diamictite with a few beds of water-
laid conglomerate, sandstone, and shale. The clasts are granite, gray
siltstone and sandstone, schist, gneiss, metavolcanics, and marble. The
matrix of the Buckeye Tillite is muddy even though there are many
clasts up to 6 m long. More than 90% of the coarse clasts in the
diamictite are subrounded to angular. Sparse pollen present in the
Buckeye is Early Permian to latest Carboniferous age (Kemp and
others, 1977).

The Buckeye Tillite unconformably overlies either the Horlick
Formation or the granitic basement. Broad channels up to several
hundred meters wide and 50 m deep mark the base of the Buckeye
Tillite, completely cutting out the Horlick Formation in places. The
Buckeye is more than 250 m thick at the east end of the range, and it
is the uppermost exposed unit everywhere west of Canyon Peak.

Ter | Horlick Formation—The Horlick Formation rests unconformably on the
granitic basement (Long, 1965), and consists of interbedded arkosic
and quartzose sandstone, chloritic mudstone and shale, and minor
limestone. Alll clasts other than fossil fragments and intraformational
mud chips could have been derived from the basement rocks.
Contorted beds in the top 50 cm of the Horlick Formation on Lackey
Ridge (McCartan and Bradshaw, in press), may be the result of ice
override associated with Permian glaciers that deposited the Buckeye
Tillite.

The formation is essentially flat-lying and because of post-
Horlick erosion it thins from a maximum of about 50 m on Discovery
Ridge to less than a meter on Lackey Ridge, and is absent on the first
spur west of Discovery Ridge.

Granitic Basement—Most rocks of the granitic basement are medium-
grained, massive to prophyritic granodiorites to monzogranites. Treves
(1965) reported K-Ar (biotite) and Rb-Sr (feldspar) ages of about 470
m.y. (Middle Ordovician) from a pink quartz monzonite that intrudes
gray granodiorite of unknown age. Rock samples from the second spur
west of Discovery Ridge are biotite monzogranite’ with roughly equal
proportions of plagioclase, potassium feldspar, and quartz. Samples
form Discovery Ridge have about 44 percent quartz and 20 percent
potassium feldspar, and plagioclase ranges from andesine (An35) to
oligoclase (An27) (McCartan and Bradshaw, in press).

EXPLANATION OF MAP SYMBOLS
Contact

Fault—Displacement shown where known. U, upthrown side; D, downthrown
side

eS Crevasse

REFERENCES CITED

Allen, A. D., 1962, Geological investigations in southern Victoria Land, Antarctica, Part 7—Forma-
tions of the Beacon Group in the Victoria Valley region: New Zealand Journal of Geology and
Geophysics, v. 5, p. 278.

Boucout, A. J., Coster, K. E., Ives, D., and Talent, J. A., 1963, Relationships of a new Lower De-
vonian Terebratuloid (Brachiopoda) from Antarctica: Bulletin of American Paleontology, v. 46
(207), p. 77-151.

Bradshaw, M. A., 1984, Permian nonmarine bivalves from the Ohio Range, Antarctica: Alcheringa,
v. 8, p. 305-309.

Bradshaw, M. A., and McCartan, Lucy, 1983, The depositional environment of the Lower
Devonian Horlick Formation, Ohio Range, in Oliver, R. L., James, P. R., and Jago, J. B., eds.,
Antarctic Earth Science: Canberra, Australian Academy of Science, p. 238-241.

Cridland, A. A., 1963, A Glossopteris flora from the Ohio Range, Antarctica: American Journal
of Botany, v. 50, p. 186-195.

Dérjes, J., Gadow, S., Reineck, H-E., and Singh, I. B., 1970, Sedimentologie und makrobenthos
der Nordergriinde und der Assenjade (Nordsee): Senckenbergiana Maritima, v. 2, p. 31-59.

Doumani, G. A., and Tasch, P., 1965, A leaiid Conchostracan Zone (Permian) in the Ohio Range,
Horlick Mountains, Antarctica, in Hadley, J. B., ed., Geology and paleontology of the Antarc-
tic, Antarctic Research Series, VOLUME 6: Baltimore, American Geophysical Union (and
Garamond/Pridemark), p. 229-240.

Doumani, G. A., Boardman, R. S., Rowell, A. T., Boucout, A. J., Johnson, J. G., McAlester, A.
L., Saul, J., Fisher, D. W., and Miles, R. S., 1965, Lower Devonian fauna of the Horlick
Formation, Ohio Range, Antrctica, in Hadley, J. B., ed., Geology and paleontology of the
Antarctic, Antarctic Research Series, VOLUME 6: Baltimore, American Geophysical Union
(and Garamond/Pridemark), p. 241-281.

Epstein, A. G., Epstein, J. B., and Harris, L. D., 1977, Conodont color alteration—an index to
organic metamorphism: U.S. Geological Survey Professional Paper 995, 27 p.

Frakes, L. A., Matthews, J. L., Neder, I. R., Crowell, J. C., 1966, Movement directions in Late
Paleozoic glacial rocks of the Horlick and Pensacola Mountains, Antarctica: Science, v. 153,
p. 746-749,

Hacquebard, P. A., 1975, Pre-and postdeformational coalification and its significance for oil and
gas exploration, in Alpern,B., ed., Pétrographie de la matiete organique des sédiments, rela-
tions avec la paléotempérature et le potential pétrolier, Colloque International, Paris, 1973,
published by Centre National de la Recherche Scientifique, Paris, p. 225-241.

Kemp, E. M., Balme, B. E., Helby, R. J., Kyle, R. A., Playford, G., and Price, P. L., 1977, Car-
boniferous palynostratigraphy in Australia and Antarctica: a review: Bureau of Mineral Re-
sources Jour. of Australian Geol. and Geophysics, v. 2, p. 177-208.

Long, W. E., 1965, Stratigraphy of the Ohio Range, Antarctica, in Hadley, J. B., ed., Geology and
paleontology of the Antarctic, Antarctic Research Series, VOLUME 6: Baltimore, American
Geophysical Union (and Garamond/Pridemark), p. 71-116.

McCartan, Lucy, and Bradshaw, M. A., Petrology and sedimentology of the Horlick Formation
(Lower Devonian), Ohio Range, Transantarctic Mountains, Antarctica, in press

McDougall, |., 1963, Potassium-argon age measurements on dolerites from Antarctica and South
Africa: Journal Geophysical Research, v. 68, p. 1535-1545.

Schapiro, N., and Gray, R. J., 1966, Physical variations in highly metamorphosed Antarctic coals,
in P. H. Given, ed., Coal science: The American Conference on Coal Science proceeding,
1964, University Park, Pa., p. 196-210.

Schmidt, D. L., 1983, Proterozoic to Mesozoic mobile-belt geology, Pensacola Mountains, Antarc-
tica: U.S. Geological Survey Circular 911, p. 12 and 13.

Treves, S. B., 1965, Igneous and Metamorphic Rocks of the Ohio Range, Horlick Mountains,
Antarctica, in Hadley, J. B., ed., Geology and paleontology of the Antarctic, Antarctic
Research Series, VOLUME 6: Baltimore, American Geophysical Union (and Garamond/
Pridemark), p. 117-126.

United States Geological Survey, 1963, Topographic map of the Ohio Range, 1:250,000.

Wunderlich, Friedrich, 1970, Genesis and environment of the ‘“Nellenképfchenschichten” (Lower
Emsian, Rheinian Devon) at Locus Typicus in comparison with modern coastal environmentof
“the German Bay: Journal of Sedimentary Petrology, v. 40, p. 102-130.

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