Pre-late Quaternary glaciation of the Beardmore Glacier region ...
ton, B.C. Andersen, H.B. Conway, T.E. Lowell, M. Prentice, R. Weed, and E. Vrba. This project was supported by National Science Foundation grant DPP 83-19477. References Bockheim, J.G. 1982. Properties of a chronosequence of ultraxerous soils in the Trans-Antarctic Mountains. Geoderma, 28, 239-255. Bockheim, J.G. 1979. Relative age and origin of soils in eastern Wright Valley, Antarctica. Soil Science, 128, 142-152. Bockheim, J. G., and S.C. Wilson. 1979. Pedology of the Darwin Glacier area. Antarctic Journal of the U.S., 14(5), 58-59. Buntley, G.J., and F.C. Westin. 1965. A comparative study of developmental color in a chestnut-chernozem-brunizem climosequence. Soil Science Society of America Proceedings, 29, 579-582.
Pre-late Quaternary glaciation of the Beardmore Glacier region, Antarctica M. L. PRENTICE Institute for Quaternary Studies University of Maine Orono, Maine 04469
and Department of Geological Sciences Brown University Providence, Rhode island 02912
G.H. DENTON
Campbell, lB., and G.G.C. Claridge. 1975. Morphology and age relationships of Antarctic soils. In R.P. Suggate and M.M. Cresswell (Eds.), Quaternary studies. New Zealand Royal Society Bulletin, 13, 83-88. Denton, G.H., J.G. Bockheim, R.H. Rutford, and B.G. Andersen. In press. Glacial history of the Ellsworth Mountains, West Antarctica. In C. Craddock, J . Splettstoesser, and G.E Webers (Eds.) Geology of the Ellsworth Mountains, West Antarctica. Geological Society of America Memoir. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the TransAntarctic Mountains, Antarctica. (Institute of Polar Studies Report No.
56.) Columbus: Ohio State University Press. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget.
(Denton et al. 1984; Webb et al. 1984). This mode of glaciation contrasts markedly with relatively minor late Quaternary fluctuations (Denton, Prentice, and Burckle in press). Such a change in ice sheet behavior presents a major opportunity to understand the controls of antarctic ice volume, an important component of the global climate system. During the 1985-1986 austral field season, we conducted studies in the Beardmore Glacier region (figure 1) to test hypotheses for pre-late Quaternary glaciation. Here we report some preliminary results. We examined exposed highlands from the Dominion Range north to the Queen Elizabeth Range (figure 1). Topographic relief here is at least equal to the heights of the numerous 4,000meter peaks (figure 2). We found a variety of mud-rich glacial deposits, unconsolidated to consolidated, in addition to those previously described (Mercer 1972). We informally refer to all these deposits, which include the Sirius Formation, as "Sirius drift" because we consider formal stratigraphic subdivision premature.
Institute for Quaternary Studies
and Department of Geological Sciences University of Maine Orono, Maine 04469 T.V. LOWELL
Department of Geology University of Cincinnati Cincinnati, Ohio 45221
H.C. CONWAY Department of Chemical and Process Engineering University of Canterbury, Private Bag Christchurch, New Zealand
L.E. HEUSSER Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
Massive fluctuations of the antarctic ice sheet have been inferred for pre-late Quaternary time from continental evidence 1986 REVIEW
Sirius Drift Basal till patches. Thin patches of Sirius basal till are scattered throughout the region between elevations of 150 and 4,115 meters. Till patches were found at eleven localities above 3,000 meters. High-elevation till outcrops between 3,490 and 3,825 meters on Mount Falla; at 3,170, 3,215, 3,230, 3,370, and 4,015 meters on Mount Kirkpatrick; at 4,115 meters on Mount Mackellar; from 3,140 to 3,292 meters on Markham Plateau; and at 3,538 and 3,660 meters on Flat Top (figure 2). The till is yellow to gray, massive, and full of striated gravel. Consolidation is variable. Sirius basal till on Mount Falla and on the highest surface in the northern Dominion Range contains far-traveled erratics of Shackleton Limestone. Basal till on Markham Plateau contains far-traveled erratics of granite and gneiss as well as Shackleton Limestone. Bedrock beneath many till patches exhibits striations uniformly suggesting ice flow toward the northeast. High-elevation bedrock surfaces without till cover also exhibit well-preserved striations. Fifteen separate localities were found above 3,000 meters. Examples occur on Mount Miller between 3,215 and 4,220 meters; on Grindley Plateau between 3,380 and 4,220 meters; and on Flat Top between 3,000 and 3,660 meters (figure 2). These striations likewise indicate northeasterly ice flow. High-elevation terrain lacks a dominant topographic grain
95
/
IR Dominion
4o
PLATEAU
Range "Z
.1^^ ImW (,. /
411*
..
I/ L.\ I
44
IAlc
le
C
Gordon Is"
-
,..4"
/
,
C
C.
akin
ClarkNak M
/ (
4160
if
kt S
p )
CE
Ice and Snow
* Mountain Peak
Scale 1:1,000,000 0 20 40 60 $0 1O0m 0
We
Ice-free Terrain
4021 Elevation
in Meters
SHELF
20
40
eo
Miles
Source: Antarctic Map Folio S.ri.a - Foho 1 2
Figure 1. Sketch map of the Beardmore Glacier region. ("Km" denotes "kilometer.')
as occurs in the ice-free valleys region (Denton et al. 1984) and glacial trimlines like those that occur in the Ellsworth Mountains and northern Victoria Land (Denton et al. in press). Striated bedrock surfaces were found as low as 150 meters. The character of this Sirius till strongly suggests deposition from ice with a thawed bed. We infer that some patches, particularly those at high elevations, were deposited beneath thick continental ice that completely overrode the mountains. This inference is based on the high elevation of the till patches, the consistency of striation direction across a high-relief region, the far-traveled erratics within Sirius till in the Dominion Range and on Mount Falla and Markham Plateau, as well as the lack of high-elevation trimlines. Ice-marginal drift. Sirius drift also occurs as thick wedges alongside and at the confluence of major glacial troughs. Drift wedges are commonly associated with bedrock cliffs. The wedges are thickest directly adjacent to bedrock cliffs and pinch out away from the cliffs. Wedge crests parallel bedrock cliffs. Examples occur on the north wall of the Beardmore trough at The Cloudmaker and Willey Point as well as atop Mount Sirius (figure 2). In the Dominion Range, several wedges, up to 150 meters thick, parallel Mill Glacier for 25 kilometers. The lithostratigraphy of Sirius drift wedges is complex. The bottom portions are commonly rich in striated gravel and are basal till. Above this, many sedimentary units contain angular gravel with no glacial marks. These upper units are supra- and en-glacial drift as well a colluvium. Waterlaid deposits from well-stratified sandy gravel to horizontally laminated sandy mud are also common in the wedges. We infer from their form, distribution, and internal character that Sirius drift wedges were deposited subaerially by marginal 96
accretion at the margin of temperate ice below the coeval equilibrium line. Wedge elevations indicate that this paleoequilibrium line occurs today as high as 2,500 meters. Sirius waterlaid units suggest extensive summer melting. If our interpretations are correct, Sirius drift wedges represent a glacier system that was far short of overriding the mountains. Mayewski (1975), on the other hand, inferred complete overriding of the Transantarctic Mountains from such deposits. We generally agree with Mercer (1972) except for his proposal for considerable post-depositional glacial erosion of our ice-marginal drift. Rather, we interpret their wedge form as a primary feature reflecting deposition as lateral moraine. Organic material was found at nine different localities within Sirius ice-marginal drift exposed in the northern Dominion Range (Oliver Bluffs; Oliver 1964) (figure 2). The first locality was discovered on 3 December 1985. Wood fragments, amorphous plant debris, and Nothofagus pollen, a temperate forest genus of the Southern Hemisphere, are abundant. The excellent preservation and high concentration of the pollen as well as the absence of recycled palynomorphs as described by Truswell and Drewry (1984) preclude significant reworking. These plant macro- and microfossils corroborate the inference for warmerthan-present climate based on the form and lithologic character of Sirius drift. Dominion Drift Small boulder belts parallel to modern ice margins overlie Sirius drift throughout the Beardmore region. In the northern Dominion Range, these lateral moraines are well developed and stretch in unbroken sequence from the Beardmore Glacier at ANTARCTIC JOURNAL
meters thick here (figure 2). This would require the surface of the east antarctic ice sheet to have been much higher than today (figure 3). The high elevations of Sirius ice-marginal deposits indicate that even minimum ice cover during this period of temperate glaciation may have been greater than today (figure 3). Age control on Beardmore region glacial deposits is poor. Webb et al. (1984) reported late Oligocene diatoms in a sample of Sirius drift from Mount Sirius and rare Plio-Pleistocene diatoms in a Sirius sample from the northern Dominion Range. However, on the basis of diatoms in Sirius drift well outside the Beardmore region, Harwood (1985) proposed a late Pliocene age for Sirius drift throughout the Transantarctic Mountains. Poor understanding of the uplift history of the Transantarctic Mountains coupled with these chronologic problems precludes estimation of Sirius ice sheet surface elevations. Subsequent to Sirius temperate ice-sheet glaciation, Antarctica cooled and its ice cover assumed a polar character which it has retained to today. Mercer (1972) recognized a similar
1,800 meters up to 2,500 meters in elevation (figure 2). This is significantly higher than such drift had previously been found in this area (Mercer 1972; Mayewski 1975). These high moraines uniformly exhibit much more soil development than those lower down (Denton, Anderson, and Conway Antarctic Journal, this issue; Bockheim, Wilson, and Leide, Antarctic Journal, this issue) and are named "Dominion drift." Similar moraines mantle Sirius drift off the Walcott Névé near Gordon Valley. These Moraines consist of gravel, primarily boulders, and pods of silty till. We suggest that Dominion drift was deposited by ice with a frozen bed under a polar climate similar to today's. We infer from Sirius drift a long interval of temperate glaciation during which thick continental ice with a thawed bed completely overrode the mountains of the Beardmore region. Sirius glacial features were found from elevations of 150 to 4,220 meters. There are no trimlines above this to suggest that the highest peaks (4,550 meters) projected through the ice sheet at maximum volume. If they reflect contemporaneous glaciation, Sirius glacial features suggest that Sirius ice was at least 4,000 AS
QUEEN ALEXANDRA RANGE Kirkpatrick Grindley Plateau Flat Top Donaldson
DOMINION RANGE
Si
'St Meyer Buckley Island D Desert
Wiley Point
Si'f\
L1 LI1 Striated bedrock
0
fl
R St St/R
Lizard Point
w
ii
M
R
ZA 0 3Z
St'R
Z3 0 I—
Li
E St Falla \ St
FE-1
BEARDMORE
Striated erratics
[1] Sirius basal till []Il Sirius ice-marginal drift
Sirius Si/StIR
Cloudmaker
/ [I Dominion drift
GLACIER
[] Meyer drift
L2 ._L° 20
[HI] Beardmore drift
KM SCALE
L1 Plunket drift
I
0
QUEEN ALEXANDRA RANGE Elizabeth Mackellar 4 St
QUEEN ELIZABETH RANGE r 5A" Miller R
Markham 4m
'tR
Z
Rab/N
71
3
0
I-
w2 -J Li
. .
BOWDEN Kathleen R'-. 'S
0
R Clarkson Peak
Markham Plateau /
—I I o
St/
- I I NEVE BB 4"
GLACIER 1
rç.
5'
rm0 0
Figure 2. Schematic topographic profile with surf icial geology across the Beardmore Glacier region from the Dominion Range north to the Queen Elizabeth Range. Figure 1 shows the line of section. Selected nearby features were projected into this section. ("Km" denotes "kilometer:" "M x 10" indicates that the elevation measurements are expressed in thousands of meters.)
1986 REVIEW
97
TRANSANTARCTIC MTNS.
0 100 250 •
Kirkpatrick
500 KM
Markham
4
Falls
I I
3
Elev. M2 (x103) 1 0
V
Scale: 1 6000,000
Titan
\iominion D Range
-1
'cart,urtsevL3 I Mtna Elev.
st
44'
Sirius I
Cloudmaker ..-
ROSS ICE SHELF 3
Ice Dome
A
2M
EAST ANTARCTIC ICE
FSTI
Sirius basal till
Dominion drift
El
Sirius ice-marginal drift
Striated bedrock surface
SHEET
H1
Wood
ki
Figure 3. Schematic topographic profile with surf icial geology through the Beardmore Glacier trough from the Ross Ice Shelf to interior East Antarctica. Figure 1 shows the line of section. Selected nearby features were projected into section. Ice and bedrock profiles are from Drewry (1983). The dashed line depicts the highest surface of the Beardmore Glacier during deposition of the Beardmore Drift, probably in late 1031, indicates that the elevation measurements are Wisconsin time (Denton et al., Antarctic Journal, this issue). "Km denotes "kilometer."'M x expressed in thousands of meters.)
change in glaciation style. The Dominion drift represents early polar glaciation. During Dominion glaciation, ice with a frozen bed reached at least the 2,500-meter level in the northern Dominion Range. Polar glaciation above this limit is not precluded because cold ice commonly leaves no record of its passage. The Beardmore region provides the strongest evidence to date supporting the hypothesis (Denton et al. 1984) for complete overriding of the Transantarctic Mountains by thick continental ice in pre-Late Quaternary time. Further, the Beardmore data suggest that antarctic ice attained this massive volume under remarkably temperate conditions. The Beardmore record also indicates that younger polar ice reached higher elevations than previously thought. We thank B. G. Andersen, J. G. Bockheim, J. E. Leide, and S. C. Wilson for their collaboration. D.H. Elliot and J.W. Collinson alerted us to important Sirius deposits. We are indebted to VXE-6 for their very-high-altitude helicopter support. This work was supported by National Science Foundation grants DPP 83-18808 and DPP 83-19477. References Bockheim, J.G., S.W. Wilson, and J.E. Leide. 1986. Soil development in the Beardmore Glacier region, Antarctica. Antarctic Journal of the U. S., 21(5). Bushnell, V. C. 1975. Antarctic map and folio series. New York: American Geographical Society.
98
Denton, G. H., M. Prentice, and L.H. Burckle. In press. Late Cenozoic history of the Antarctic Ice Sheet. In R.J. Tingey (Ed.), The geology of Antarctica. Cambridge: Oxford University Press. Denton, G.H., B.G. Andersen, and H.B. Conway. 1986. Late Quaternary surface fluctuations of the Beardmore Glacier, Antarctica. Antarctic Journal of the U.S., 21(5). Denton, G. H., M. Prentice, D. E. Kellogg, and T. B. Kellogg. 1984. Late Tertiary history of the Antarctic Ice Sheet: Evidence from the Dry Valleys. Geology, 12, 263-267. Drewry, D.J. (Ed.) 1983. Antarctica: Glaciological and geophysical folio. Cambridge: Scott Polar Research Institute. Harwood, D.M. 1985. Late Neogene climatic fluctuations in the southern high-latitudes: Implications of a warm Pliocene and deglaciated Antarctic continent. South African Journal of Science, 81, 239-241. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the Transantarctic Mountains, Antarctica. (Institute of Polar Studies, Report No.
56.) Columbus: Ohio State University Press. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie, (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Oliver, R.L. 1964. Geological observations at Plunket Point, Beardmore Glacier. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Holland Publishing. Truswell, E.M., and D.J. Drewry. 1984. Distribution and provenance of recycled palynomorphs in surficial sediments of the Ross Sea, Antarctica. Marine Geology, 59, 187-214. Webb, P.-N., D.H. Harwood, J.H. McKelvey, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291.
ANTARCTIC JOURNAL
Pre-late Quaternary glaciation of the Beardmore Glacier region, Antarctica M. L. PRENTICE Institute for Quaternary Studies University of Maine Orono, Maine 04469
and Department of Geological Sciences Brown University Providence, Rhode island 02912
G.H. DENTON
Campbell, lB., and G.G.C. Claridge. 1975. Morphology and age relationships of Antarctic soils. In R.P. Suggate and M.M. Cresswell (Eds.), Quaternary studies. New Zealand Royal Society Bulletin, 13, 83-88. Denton, G.H., J.G. Bockheim, R.H. Rutford, and B.G. Andersen. In press. Glacial history of the Ellsworth Mountains, West Antarctica. In C. Craddock, J . Splettstoesser, and G.E Webers (Eds.) Geology of the Ellsworth Mountains, West Antarctica. Geological Society of America Memoir. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the TransAntarctic Mountains, Antarctica. (Institute of Polar Studies Report No.
56.) Columbus: Ohio State University Press. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget.
(Denton et al. 1984; Webb et al. 1984). This mode of glaciation contrasts markedly with relatively minor late Quaternary fluctuations (Denton, Prentice, and Burckle in press). Such a change in ice sheet behavior presents a major opportunity to understand the controls of antarctic ice volume, an important component of the global climate system. During the 1985-1986 austral field season, we conducted studies in the Beardmore Glacier region (figure 1) to test hypotheses for pre-late Quaternary glaciation. Here we report some preliminary results. We examined exposed highlands from the Dominion Range north to the Queen Elizabeth Range (figure 1). Topographic relief here is at least equal to the heights of the numerous 4,000meter peaks (figure 2). We found a variety of mud-rich glacial deposits, unconsolidated to consolidated, in addition to those previously described (Mercer 1972). We informally refer to all these deposits, which include the Sirius Formation, as "Sirius drift" because we consider formal stratigraphic subdivision premature.
Institute for Quaternary Studies
and Department of Geological Sciences University of Maine Orono, Maine 04469 T.V. LOWELL
Department of Geology University of Cincinnati Cincinnati, Ohio 45221
H.C. CONWAY Department of Chemical and Process Engineering University of Canterbury, Private Bag Christchurch, New Zealand
L.E. HEUSSER Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
Massive fluctuations of the antarctic ice sheet have been inferred for pre-late Quaternary time from continental evidence 1986 REVIEW
Sirius Drift Basal till patches. Thin patches of Sirius basal till are scattered throughout the region between elevations of 150 and 4,115 meters. Till patches were found at eleven localities above 3,000 meters. High-elevation till outcrops between 3,490 and 3,825 meters on Mount Falla; at 3,170, 3,215, 3,230, 3,370, and 4,015 meters on Mount Kirkpatrick; at 4,115 meters on Mount Mackellar; from 3,140 to 3,292 meters on Markham Plateau; and at 3,538 and 3,660 meters on Flat Top (figure 2). The till is yellow to gray, massive, and full of striated gravel. Consolidation is variable. Sirius basal till on Mount Falla and on the highest surface in the northern Dominion Range contains far-traveled erratics of Shackleton Limestone. Basal till on Markham Plateau contains far-traveled erratics of granite and gneiss as well as Shackleton Limestone. Bedrock beneath many till patches exhibits striations uniformly suggesting ice flow toward the northeast. High-elevation bedrock surfaces without till cover also exhibit well-preserved striations. Fifteen separate localities were found above 3,000 meters. Examples occur on Mount Miller between 3,215 and 4,220 meters; on Grindley Plateau between 3,380 and 4,220 meters; and on Flat Top between 3,000 and 3,660 meters (figure 2). These striations likewise indicate northeasterly ice flow. High-elevation terrain lacks a dominant topographic grain
95
/
IR Dominion
4o
PLATEAU
Range "Z
.1^^ ImW (,. /
411*
..
I/ L.\ I
44
IAlc
le
C
Gordon Is"
-
,..4"
/
,
C
C.
akin
ClarkNak M
/ (
4160
if
kt S
p )
CE
Ice and Snow
* Mountain Peak
Scale 1:1,000,000 0 20 40 60 $0 1O0m 0
We
Ice-free Terrain
4021 Elevation
in Meters
SHELF
20
40
eo
Miles
Source: Antarctic Map Folio S.ri.a - Foho 1 2
Figure 1. Sketch map of the Beardmore Glacier region. ("Km" denotes "kilometer.')
as occurs in the ice-free valleys region (Denton et al. 1984) and glacial trimlines like those that occur in the Ellsworth Mountains and northern Victoria Land (Denton et al. in press). Striated bedrock surfaces were found as low as 150 meters. The character of this Sirius till strongly suggests deposition from ice with a thawed bed. We infer that some patches, particularly those at high elevations, were deposited beneath thick continental ice that completely overrode the mountains. This inference is based on the high elevation of the till patches, the consistency of striation direction across a high-relief region, the far-traveled erratics within Sirius till in the Dominion Range and on Mount Falla and Markham Plateau, as well as the lack of high-elevation trimlines. Ice-marginal drift. Sirius drift also occurs as thick wedges alongside and at the confluence of major glacial troughs. Drift wedges are commonly associated with bedrock cliffs. The wedges are thickest directly adjacent to bedrock cliffs and pinch out away from the cliffs. Wedge crests parallel bedrock cliffs. Examples occur on the north wall of the Beardmore trough at The Cloudmaker and Willey Point as well as atop Mount Sirius (figure 2). In the Dominion Range, several wedges, up to 150 meters thick, parallel Mill Glacier for 25 kilometers. The lithostratigraphy of Sirius drift wedges is complex. The bottom portions are commonly rich in striated gravel and are basal till. Above this, many sedimentary units contain angular gravel with no glacial marks. These upper units are supra- and en-glacial drift as well a colluvium. Waterlaid deposits from well-stratified sandy gravel to horizontally laminated sandy mud are also common in the wedges. We infer from their form, distribution, and internal character that Sirius drift wedges were deposited subaerially by marginal 96
accretion at the margin of temperate ice below the coeval equilibrium line. Wedge elevations indicate that this paleoequilibrium line occurs today as high as 2,500 meters. Sirius waterlaid units suggest extensive summer melting. If our interpretations are correct, Sirius drift wedges represent a glacier system that was far short of overriding the mountains. Mayewski (1975), on the other hand, inferred complete overriding of the Transantarctic Mountains from such deposits. We generally agree with Mercer (1972) except for his proposal for considerable post-depositional glacial erosion of our ice-marginal drift. Rather, we interpret their wedge form as a primary feature reflecting deposition as lateral moraine. Organic material was found at nine different localities within Sirius ice-marginal drift exposed in the northern Dominion Range (Oliver Bluffs; Oliver 1964) (figure 2). The first locality was discovered on 3 December 1985. Wood fragments, amorphous plant debris, and Nothofagus pollen, a temperate forest genus of the Southern Hemisphere, are abundant. The excellent preservation and high concentration of the pollen as well as the absence of recycled palynomorphs as described by Truswell and Drewry (1984) preclude significant reworking. These plant macro- and microfossils corroborate the inference for warmerthan-present climate based on the form and lithologic character of Sirius drift. Dominion Drift Small boulder belts parallel to modern ice margins overlie Sirius drift throughout the Beardmore region. In the northern Dominion Range, these lateral moraines are well developed and stretch in unbroken sequence from the Beardmore Glacier at ANTARCTIC JOURNAL
meters thick here (figure 2). This would require the surface of the east antarctic ice sheet to have been much higher than today (figure 3). The high elevations of Sirius ice-marginal deposits indicate that even minimum ice cover during this period of temperate glaciation may have been greater than today (figure 3). Age control on Beardmore region glacial deposits is poor. Webb et al. (1984) reported late Oligocene diatoms in a sample of Sirius drift from Mount Sirius and rare Plio-Pleistocene diatoms in a Sirius sample from the northern Dominion Range. However, on the basis of diatoms in Sirius drift well outside the Beardmore region, Harwood (1985) proposed a late Pliocene age for Sirius drift throughout the Transantarctic Mountains. Poor understanding of the uplift history of the Transantarctic Mountains coupled with these chronologic problems precludes estimation of Sirius ice sheet surface elevations. Subsequent to Sirius temperate ice-sheet glaciation, Antarctica cooled and its ice cover assumed a polar character which it has retained to today. Mercer (1972) recognized a similar
1,800 meters up to 2,500 meters in elevation (figure 2). This is significantly higher than such drift had previously been found in this area (Mercer 1972; Mayewski 1975). These high moraines uniformly exhibit much more soil development than those lower down (Denton, Anderson, and Conway Antarctic Journal, this issue; Bockheim, Wilson, and Leide, Antarctic Journal, this issue) and are named "Dominion drift." Similar moraines mantle Sirius drift off the Walcott Névé near Gordon Valley. These Moraines consist of gravel, primarily boulders, and pods of silty till. We suggest that Dominion drift was deposited by ice with a frozen bed under a polar climate similar to today's. We infer from Sirius drift a long interval of temperate glaciation during which thick continental ice with a thawed bed completely overrode the mountains of the Beardmore region. Sirius glacial features were found from elevations of 150 to 4,220 meters. There are no trimlines above this to suggest that the highest peaks (4,550 meters) projected through the ice sheet at maximum volume. If they reflect contemporaneous glaciation, Sirius glacial features suggest that Sirius ice was at least 4,000 AS
QUEEN ALEXANDRA RANGE Kirkpatrick Grindley Plateau Flat Top Donaldson
DOMINION RANGE
Si
'St Meyer Buckley Island D Desert
Wiley Point
Si'f\
L1 LI1 Striated bedrock
0
fl
R St St/R
Lizard Point
w
ii
M
R
ZA 0 3Z
St'R
Z3 0 I—
Li
E St Falla \ St
FE-1
BEARDMORE
Striated erratics
[1] Sirius basal till []Il Sirius ice-marginal drift
Sirius Si/StIR
Cloudmaker
/ [I Dominion drift
GLACIER
[] Meyer drift
L2 ._L° 20
[HI] Beardmore drift
KM SCALE
L1 Plunket drift
I
0
QUEEN ALEXANDRA RANGE Elizabeth Mackellar 4 St
QUEEN ELIZABETH RANGE r 5A" Miller R
Markham 4m
'tR
Z
Rab/N
71
3
0
I-
w2 -J Li
. .
BOWDEN Kathleen R'-. 'S
0
R Clarkson Peak
Markham Plateau /
—I I o
St/
- I I NEVE BB 4"
GLACIER 1
rç.
5'
rm0 0
Figure 2. Schematic topographic profile with surf icial geology across the Beardmore Glacier region from the Dominion Range north to the Queen Elizabeth Range. Figure 1 shows the line of section. Selected nearby features were projected into this section. ("Km" denotes "kilometer:" "M x 10" indicates that the elevation measurements are expressed in thousands of meters.)
1986 REVIEW
97
TRANSANTARCTIC MTNS.
0 100 250 •
Kirkpatrick
500 KM
Markham
4
Falls
I I
3
Elev. M2 (x103) 1 0
V
Scale: 1 6000,000
Titan
\iominion D Range
-1
'cart,urtsevL3 I Mtna Elev.
st
44'
Sirius I
Cloudmaker ..-
ROSS ICE SHELF 3
Ice Dome
A
2M
EAST ANTARCTIC ICE
FSTI
Sirius basal till
Dominion drift
El
Sirius ice-marginal drift
Striated bedrock surface
SHEET
H1
Wood
ki
Figure 3. Schematic topographic profile with surf icial geology through the Beardmore Glacier trough from the Ross Ice Shelf to interior East Antarctica. Figure 1 shows the line of section. Selected nearby features were projected into section. Ice and bedrock profiles are from Drewry (1983). The dashed line depicts the highest surface of the Beardmore Glacier during deposition of the Beardmore Drift, probably in late 1031, indicates that the elevation measurements are Wisconsin time (Denton et al., Antarctic Journal, this issue). "Km denotes "kilometer."'M x expressed in thousands of meters.)
change in glaciation style. The Dominion drift represents early polar glaciation. During Dominion glaciation, ice with a frozen bed reached at least the 2,500-meter level in the northern Dominion Range. Polar glaciation above this limit is not precluded because cold ice commonly leaves no record of its passage. The Beardmore region provides the strongest evidence to date supporting the hypothesis (Denton et al. 1984) for complete overriding of the Transantarctic Mountains by thick continental ice in pre-Late Quaternary time. Further, the Beardmore data suggest that antarctic ice attained this massive volume under remarkably temperate conditions. The Beardmore record also indicates that younger polar ice reached higher elevations than previously thought. We thank B. G. Andersen, J. G. Bockheim, J. E. Leide, and S. C. Wilson for their collaboration. D.H. Elliot and J.W. Collinson alerted us to important Sirius deposits. We are indebted to VXE-6 for their very-high-altitude helicopter support. This work was supported by National Science Foundation grants DPP 83-18808 and DPP 83-19477. References Bockheim, J.G., S.W. Wilson, and J.E. Leide. 1986. Soil development in the Beardmore Glacier region, Antarctica. Antarctic Journal of the U. S., 21(5). Bushnell, V. C. 1975. Antarctic map and folio series. New York: American Geographical Society.
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Denton, G. H., M. Prentice, and L.H. Burckle. In press. Late Cenozoic history of the Antarctic Ice Sheet. In R.J. Tingey (Ed.), The geology of Antarctica. Cambridge: Oxford University Press. Denton, G.H., B.G. Andersen, and H.B. Conway. 1986. Late Quaternary surface fluctuations of the Beardmore Glacier, Antarctica. Antarctic Journal of the U.S., 21(5). Denton, G. H., M. Prentice, D. E. Kellogg, and T. B. Kellogg. 1984. Late Tertiary history of the Antarctic Ice Sheet: Evidence from the Dry Valleys. Geology, 12, 263-267. Drewry, D.J. (Ed.) 1983. Antarctica: Glaciological and geophysical folio. Cambridge: Scott Polar Research Institute. Harwood, D.M. 1985. Late Neogene climatic fluctuations in the southern high-latitudes: Implications of a warm Pliocene and deglaciated Antarctic continent. South African Journal of Science, 81, 239-241. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the Transantarctic Mountains, Antarctica. (Institute of Polar Studies, Report No.
56.) Columbus: Ohio State University Press. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie, (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Oliver, R.L. 1964. Geological observations at Plunket Point, Beardmore Glacier. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Holland Publishing. Truswell, E.M., and D.J. Drewry. 1984. Distribution and provenance of recycled palynomorphs in surficial sediments of the Ross Sea, Antarctica. Marine Geology, 59, 187-214. Webb, P.-N., D.H. Harwood, J.H. McKelvey, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291.
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