early ...
Examination of the pre-adult morphology of planktonic foraminifera using the methods described above provides additional criteria for understanding their taxonomy and phylogenetic relationships. Although this study was concerned with a single time-slice in the Late Cretaceous, analysis of stratigraphic changes in the ontogenetic morphometry of particular taxonomic groups will certainly improve high-latitude biostratigraphy and provide further insight to paleoceanographic and paleoclimatic evolution. Samples provided by the Deep Sea Drilling Project (East Coast Repository, Lamont-Doherty Geological Observatory) are gratefully acknowledged. This research was partially funded by National Science Foundation grants DPP 85-17625 and Di p 84-20622. Jam grateful to the curators at the Scripps Institution of Oceanography for making the Deep Sea Drilling Project samples available to me. References
Arnold, A.J. 1982. Techniques for biometric analysis of foraminifera. Third North American Paleontological Convention, Proceedings, 1, 13-15.
Evidence from the Beardmore Glacier region for a late Paleozoic/early Mesozoic foreland basin
Huang, C. 1981. Observations on the interior of some late Neogene planktonic foraminifera. Journal of Foraminiferal Research, 1(3), 173-190.
Huber, B.T. In press. Upper Campanian-Paleocene foraminifera from the James Ross Island region (Antarctic Peninsula). In R.M. Feldmann and M.O. Woodburne (Eds.), Geology and Paleontology of Seymour Island, Antarctica. (Geological Society of America, Memoir Series 169.) Huber, B.T., D.M. Harwood, and P.N. Webb. 1983. Upper Cretaceous microfossil biostratigraphy of Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 18(5), 72-74.
Krasheninnikov, V.A., and I.A. Basov. 1983. Stratigraphy of Cretaceous sediments of the Falkland Plateau based on planktonic foraminifers, Deep Sea Drilling Project, Leg 71. In W.J. Ludwig, V.A. Krasheninnikov, et al. (Eds.), Initial Reports of the Deep Sea Drilling Project. Washington, D.C.: U.S. Government Printing Office. Sliter, W.V. 1976. Cretaceous foraminifera from the southwest Atlantic Ocean, Leg 36, Deep Sea Drilling Project. In P.F. Barker, I.W.D. Dalziel et al. (Eds.), Initial Reports of the Deep Sea Drilling Project.
Washington, D.C.: U.S. Government Printing Office.
• An Early Permian facies transition from terrestrial to marine toward the orogenic belt. • The existence of two major source areas, the east antarctic craton and calc-alkaline volcanics from a convergent paleo-
EAST ANTARCTIC £ Pensacola Mtns. CRATON /
JAMES W. CoI,uNsoN and JOHN L. ISBELI.
Byrd Polar Research Ccii hr
---------
and
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43220
New data and interpretations from our 1985-1986 field season in the Beardmore Glacier region lend support to the hypothesis that the Upper Paleozoic/Lower Mesozoic sedimentary sequence is part of a major foreland basin that paralleled the margin of the east antarctic craton. This foreland basin comprises at least four distinct stratigraphic basins (figure 1): Ellsworth Mountains (EM), Central Transantarctic Mountains (cTM), southern Victoria Land (svL), and northern Victoria Land (NvL). The stratigraphy of these basins has been summarized at length by Elliot (1975). Foreland basins are elongated depressions that develop on continental crust, typically near the edge of a craton, inboard of a fold/thrust belt. Lines of evidence supporting the foreland basin hypothesis include: • The widespread similarity of stratigraphic sequences from antarctic basins suggesting that they are genetically related. • Post-Early Permian to pre-Middle Jurassic folding in the Ellsworth and Pensacola mountains indicating the existence of an orogenic belt. • The thickening of time-equivalent sequences toward the orogenic belt. 1987 REVIEW
-1
EM BASIN lsrth Mtns
7
4' + South Pole
CTML BASIN
Shackle ton Beardmore GI. ROSS ICE SHELF
D Stratigraphic basins 500 igoo Kilometers
NVL
C6 ASIN
Rennick GI.
Figure 1. Location map showing extent of stratigraphic basins. ("EM" denotes "Ellsworth Mountains"; "CTM" denotes "central Transantarctic Mountains"; "SVL" denotes southern Victoria Land"; "NVL" denotes "northern Victoria Land?')
17
Pacific margin, the latter becoming increasingly important with time. • A Late Permian reversal in fluvial paleocurrent directions in the CTM basin concomitant with the introduction of volcanic detritus. • The fluvial architecture of Upper Permian and Triassic deposits in the CTM basin, suggesting both deposition in large lowgradient alluvial fans derived from the orogenic belt and rapid subsidence in the basin. Figure 2 shows a cross-section of our reconstruction of the hypothetical foreland basin. Orientation of the basin was oblique to the present trend of the Transantarctic Mountains. The various stratigraphic basins are regarded as representing segments of the foreland basin from the orogenic belt toward the craton in the following order: EM CTM - SVL - NVL. Equivalent time-stratigraphic intervals thin progressively inboard. Permian and Lower Triassic strata wedge out in northern Victoria Land where very thin Upper Triassic fluvial deposits rest directly on crystalline basement (Collinson, Pennington, and Kemp 1987). The most compelling evidence for a foreland basin is the bimodal provenance of quartzitic and arkosic sands from cratonic basement, and volcaniclastic sands from a caic-alkaline paleo-Pacific margin source. The occurrence of volcanic tuffs in the Lower Permian in the EM basin and throughout the Triassic in the CTM basin indicates contemporaneous volcanism rather than erosion of older volcanics. The introduction of volcanic detritus was diachronous from basin to basin. The oldest volcaniclastic sediments occur in the EM basin in Lower Permian; they appear in the CTM basin in Upper Permian, and in the SVL and NVL basins in Triassic. Major drainage was longitudinal to the axis of the foreland basin and sandstone composition was controlled by location with respect to the axis of deposition. Barrett and Kohn (1975) identified a Permian drainage divide between the CTM and SVL basins across which paleocurrent data indicated dispersal in opposite directions. Drainage reversal supposedly occurred with uplift in the CTM basin at the transition from Permian to Triassic after which time all drainage flowed toward NVL. However, new paleocurrent data in the CTM basin indicate that the drainage reversal occurred in mid-Permian concurrently with the introduction into the basin of volcaniclastic sand from the paleo-Pacific margin. Uplift within the CTM basin seems unlikely as a cause for drainage reversal, because no evidence of major erosion or rejuvenation exists for that time. However, Late Permian folding and uplift in the
EM CTM SVL NVL
Triassic fluvial deposits X
E'I L-U Permian fluvial deposits L Permian inland sea deposits x x °T I u Carboniferous glacial deposits
Devonian shelf deposits 2000m X EIX1I U Palaeozoic-Precambrian basement
Figure 2. Generalized cross-section of foreland basin. ("m" denotes "meter:' "L" denotes "lower:' "U" denotes "upper:')
18
orogenic belt may have produced large alluvial fans that prograded into the CTM basin causing the drainage reversal. The Upper Permian Buckley Formation and Lower Triassic Fremouw Formation in the CTM basin were deposited by braided streams. These deposits are unusual in that a high percentage of flood-plain sediment is preserved. The concept of flood-plain destruction by erosion and lateral migration of braided channels is approached as a universal axiom; however, emphasis in the literature on Holocene streams has been on confined non-aggrading systems. Unconfined braided streams have been described from humid, low-gradient, alluvial fans in the Himalayan foreland (Brahmaputra River, Coleman 1969; Kosi River, Wells and Dorr 1987). Lateral migration of streams across Himalayan fans is by avulsion. During floods, much of the fan surface, including flood plains, is inundated. For lowgradient, humid, alluvial fans, thick flood-plain deposits can be preserved under conditions of rapid subsidence relative to avulsion periodicity (c.f., Allen 1978; Bridge and Leeder 1979). Under conditions of slow subsidence, only channel deposits are preserved; overbank sediments are reworked and flushed from the system. With rapid subsidence, flood-plain deposits are removed from the "zone of reworking" and preserved. Preservation of flood plain deposits in the CTM basin is consistent with rapid subsidence and deposition in an unconfined braided fluvial system on a humid, low-gradient alluvial fan. Further evidence for the fan model is found in the Lower Triassic between the Shackleton and Beardmore glaciers. In Early Triassic a large trunk stream that flowed along the axis of the foreland basin in CTM was fed quartzose sands from the east antarctic craton on one side and volcaniclastic sands from the paleo-Pacific margin on the other (Collinson, Kemp, and Eggert 1987). Paleocurrent vectors west of the Beardmore Glacier are generally northwestward toward SVL, but to the east, particularly around the Shackleton Glacier, they appear to shift southwestward from the direction of the paleo-Pacific margin. Concomitantly, Lower Triassic sandstones are increasingly volcaniclastic eastward toward the Shackleton Glacier area and the calc-alkaline volcanic source along the paleo-Pacific margin (Vavra 1984). This work was supported by National Science Foundation grant DPP 84-18354. References
Allen, J.R.L. 1978. Studies in fluvial sedimentation: An exploratory quantitative model for the architecture of avulsion-controlled alluvial suites. Sedimentary geology, 21, 129-147. Barrett, P.J., and B.P. Kohn. 1975. Changing sediment transport directions from Devonian to Triassic in the Beacon Supergroup of south Victoria Land, Antarctica. In K.S.W. Campbell (Ed.), Gondwana geology. Canberra: Australian National University Press. Bridge, J.S., and M.R. Leeder. 1979. A simulation model of alluvial stratigraphy. Sedinentology, 26, 617-644. Coleman, J.M. 1969. Brahmaputra River: Channel processes and sedimentation. Sedinientary geology, 3, 129-239. Collinson, J.W., N.R. Kemp, and J.T. Eggert. 1987. Comparison of the Triassic Gondwana sequences in the Transantarctic Mountains and Tasmania. In G.D. McKenzie (Ed.), Gondwana Six: Stratigraphy, sediinentology and paleontology. (Geophysical Monograph Series, Vol. 41.) Washington, D.C.: American Geophysical Union. Collinson, J.W., D.C. Pennington, and N.R. Kemp. 1987. Stratigraphy and petrology of Permian and Triassic fluvial deposits in northern Victoria Land, Antarctica. In E. Stump (Ed.), Geological investigations in northern Victoria Land. (Antarctic Research Series, Vol. 41.) Washington, D.C.: American Geophysical Union. ANTARCTIC JOURNAL
Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell (Ed.), Gondwana geology. Canberra: Australia, National University Press. Vavra, C.L. 1984. Triassic Fremouw and Falla Formations, central Transan-
Paleotectonic implications of the Permo-Carboniferous Pagoda Formation, Beardmore Glacier area M.G. MILLER and BARBARA J.
JULIA
WAUGH
Department of Geology Vanderbilt University
Nashville, Tennessee
MP
37235
MC
tarctic Mountains, Antarctica. (Institute of Polar Studies Report 87.) Columbus: Ohio State University. Wells, N.A., and J.A. Dorr, Jr. 1987. Shifting of the Kosi River, northern India. Geology, 15, 204-207.
Sedimentologic aspects of the glaciogenic Pagoda Formation place constraints upon the paleotectonic setting of the Beardmore Glacier area during Permo-Carboniferous time and pertain in particular to the proximity of this region to the paleoPacific margin of Gondwana. Glaciogenic beds form the base of the Victoria Group. Rare palynomorphs from the uppermost Pagoda Formation show that these rocks are of Permo-Carboniferous age (Askin personal communication). In the central Transantarctic Mountains, Permo-Triassic units of the upper Victoria Group were deposited on the cratonic side of a back-arc
200
ME
MH
9 A
A
A
A
A A a
A
^
A
A A A
.150
AAA AAA A
AA A
4 '-A A A A A
A A A A A
9
8'- 4 - AA A
9
A A
A
A A A
A
100 A8 A A A
.4
7
A A A
k -;. .
4.AA.
EXPLANATION
4 A
Inferred Ice:
A
50 A A
Al
JA 4
Al
I AlI IA
Om
shale F: •1 fine sandstone :. coarse sandstone silty diamictite A A] sandy sandy diamictite sandstone lenses in diamictite LI crudely stratified diamictite A A
Z Retreat Advance
Figure 1. Selected stratigraphic columns through the Pagoda Formation in the Beardmore Glacier area showing interpretation of glacial advance and retreat. ["MP" denotes "Markham Plateau" (northwest). "MC" denotes "Mount Counts" (north face). "ME" denotes "Mount Elizabeth?' "Mu" denotes "Mount Hermanson?' "m" denotes "meter"] For more details see Miller (in preparation). 1987
REVIEW
19
Arnold, A.J. 1982. Techniques for biometric analysis of foraminifera. Third North American Paleontological Convention, Proceedings, 1, 13-15.
Evidence from the Beardmore Glacier region for a late Paleozoic/early Mesozoic foreland basin
Huang, C. 1981. Observations on the interior of some late Neogene planktonic foraminifera. Journal of Foraminiferal Research, 1(3), 173-190.
Huber, B.T. In press. Upper Campanian-Paleocene foraminifera from the James Ross Island region (Antarctic Peninsula). In R.M. Feldmann and M.O. Woodburne (Eds.), Geology and Paleontology of Seymour Island, Antarctica. (Geological Society of America, Memoir Series 169.) Huber, B.T., D.M. Harwood, and P.N. Webb. 1983. Upper Cretaceous microfossil biostratigraphy of Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 18(5), 72-74.
Krasheninnikov, V.A., and I.A. Basov. 1983. Stratigraphy of Cretaceous sediments of the Falkland Plateau based on planktonic foraminifers, Deep Sea Drilling Project, Leg 71. In W.J. Ludwig, V.A. Krasheninnikov, et al. (Eds.), Initial Reports of the Deep Sea Drilling Project. Washington, D.C.: U.S. Government Printing Office. Sliter, W.V. 1976. Cretaceous foraminifera from the southwest Atlantic Ocean, Leg 36, Deep Sea Drilling Project. In P.F. Barker, I.W.D. Dalziel et al. (Eds.), Initial Reports of the Deep Sea Drilling Project.
Washington, D.C.: U.S. Government Printing Office.
• An Early Permian facies transition from terrestrial to marine toward the orogenic belt. • The existence of two major source areas, the east antarctic craton and calc-alkaline volcanics from a convergent paleo-
EAST ANTARCTIC £ Pensacola Mtns. CRATON /
JAMES W. CoI,uNsoN and JOHN L. ISBELI.
Byrd Polar Research Ccii hr
---------
and
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43220
New data and interpretations from our 1985-1986 field season in the Beardmore Glacier region lend support to the hypothesis that the Upper Paleozoic/Lower Mesozoic sedimentary sequence is part of a major foreland basin that paralleled the margin of the east antarctic craton. This foreland basin comprises at least four distinct stratigraphic basins (figure 1): Ellsworth Mountains (EM), Central Transantarctic Mountains (cTM), southern Victoria Land (svL), and northern Victoria Land (NvL). The stratigraphy of these basins has been summarized at length by Elliot (1975). Foreland basins are elongated depressions that develop on continental crust, typically near the edge of a craton, inboard of a fold/thrust belt. Lines of evidence supporting the foreland basin hypothesis include: • The widespread similarity of stratigraphic sequences from antarctic basins suggesting that they are genetically related. • Post-Early Permian to pre-Middle Jurassic folding in the Ellsworth and Pensacola mountains indicating the existence of an orogenic belt. • The thickening of time-equivalent sequences toward the orogenic belt. 1987 REVIEW
-1
EM BASIN lsrth Mtns
7
4' + South Pole
CTML BASIN
Shackle ton Beardmore GI. ROSS ICE SHELF
D Stratigraphic basins 500 igoo Kilometers
NVL
C6 ASIN
Rennick GI.
Figure 1. Location map showing extent of stratigraphic basins. ("EM" denotes "Ellsworth Mountains"; "CTM" denotes "central Transantarctic Mountains"; "SVL" denotes southern Victoria Land"; "NVL" denotes "northern Victoria Land?')
17
Pacific margin, the latter becoming increasingly important with time. • A Late Permian reversal in fluvial paleocurrent directions in the CTM basin concomitant with the introduction of volcanic detritus. • The fluvial architecture of Upper Permian and Triassic deposits in the CTM basin, suggesting both deposition in large lowgradient alluvial fans derived from the orogenic belt and rapid subsidence in the basin. Figure 2 shows a cross-section of our reconstruction of the hypothetical foreland basin. Orientation of the basin was oblique to the present trend of the Transantarctic Mountains. The various stratigraphic basins are regarded as representing segments of the foreland basin from the orogenic belt toward the craton in the following order: EM CTM - SVL - NVL. Equivalent time-stratigraphic intervals thin progressively inboard. Permian and Lower Triassic strata wedge out in northern Victoria Land where very thin Upper Triassic fluvial deposits rest directly on crystalline basement (Collinson, Pennington, and Kemp 1987). The most compelling evidence for a foreland basin is the bimodal provenance of quartzitic and arkosic sands from cratonic basement, and volcaniclastic sands from a caic-alkaline paleo-Pacific margin source. The occurrence of volcanic tuffs in the Lower Permian in the EM basin and throughout the Triassic in the CTM basin indicates contemporaneous volcanism rather than erosion of older volcanics. The introduction of volcanic detritus was diachronous from basin to basin. The oldest volcaniclastic sediments occur in the EM basin in Lower Permian; they appear in the CTM basin in Upper Permian, and in the SVL and NVL basins in Triassic. Major drainage was longitudinal to the axis of the foreland basin and sandstone composition was controlled by location with respect to the axis of deposition. Barrett and Kohn (1975) identified a Permian drainage divide between the CTM and SVL basins across which paleocurrent data indicated dispersal in opposite directions. Drainage reversal supposedly occurred with uplift in the CTM basin at the transition from Permian to Triassic after which time all drainage flowed toward NVL. However, new paleocurrent data in the CTM basin indicate that the drainage reversal occurred in mid-Permian concurrently with the introduction into the basin of volcaniclastic sand from the paleo-Pacific margin. Uplift within the CTM basin seems unlikely as a cause for drainage reversal, because no evidence of major erosion or rejuvenation exists for that time. However, Late Permian folding and uplift in the
EM CTM SVL NVL
Triassic fluvial deposits X
E'I L-U Permian fluvial deposits L Permian inland sea deposits x x °T I u Carboniferous glacial deposits
Devonian shelf deposits 2000m X EIX1I U Palaeozoic-Precambrian basement
Figure 2. Generalized cross-section of foreland basin. ("m" denotes "meter:' "L" denotes "lower:' "U" denotes "upper:')
18
orogenic belt may have produced large alluvial fans that prograded into the CTM basin causing the drainage reversal. The Upper Permian Buckley Formation and Lower Triassic Fremouw Formation in the CTM basin were deposited by braided streams. These deposits are unusual in that a high percentage of flood-plain sediment is preserved. The concept of flood-plain destruction by erosion and lateral migration of braided channels is approached as a universal axiom; however, emphasis in the literature on Holocene streams has been on confined non-aggrading systems. Unconfined braided streams have been described from humid, low-gradient, alluvial fans in the Himalayan foreland (Brahmaputra River, Coleman 1969; Kosi River, Wells and Dorr 1987). Lateral migration of streams across Himalayan fans is by avulsion. During floods, much of the fan surface, including flood plains, is inundated. For lowgradient, humid, alluvial fans, thick flood-plain deposits can be preserved under conditions of rapid subsidence relative to avulsion periodicity (c.f., Allen 1978; Bridge and Leeder 1979). Under conditions of slow subsidence, only channel deposits are preserved; overbank sediments are reworked and flushed from the system. With rapid subsidence, flood-plain deposits are removed from the "zone of reworking" and preserved. Preservation of flood plain deposits in the CTM basin is consistent with rapid subsidence and deposition in an unconfined braided fluvial system on a humid, low-gradient alluvial fan. Further evidence for the fan model is found in the Lower Triassic between the Shackleton and Beardmore glaciers. In Early Triassic a large trunk stream that flowed along the axis of the foreland basin in CTM was fed quartzose sands from the east antarctic craton on one side and volcaniclastic sands from the paleo-Pacific margin on the other (Collinson, Kemp, and Eggert 1987). Paleocurrent vectors west of the Beardmore Glacier are generally northwestward toward SVL, but to the east, particularly around the Shackleton Glacier, they appear to shift southwestward from the direction of the paleo-Pacific margin. Concomitantly, Lower Triassic sandstones are increasingly volcaniclastic eastward toward the Shackleton Glacier area and the calc-alkaline volcanic source along the paleo-Pacific margin (Vavra 1984). This work was supported by National Science Foundation grant DPP 84-18354. References
Allen, J.R.L. 1978. Studies in fluvial sedimentation: An exploratory quantitative model for the architecture of avulsion-controlled alluvial suites. Sedimentary geology, 21, 129-147. Barrett, P.J., and B.P. Kohn. 1975. Changing sediment transport directions from Devonian to Triassic in the Beacon Supergroup of south Victoria Land, Antarctica. In K.S.W. Campbell (Ed.), Gondwana geology. Canberra: Australian National University Press. Bridge, J.S., and M.R. Leeder. 1979. A simulation model of alluvial stratigraphy. Sedinentology, 26, 617-644. Coleman, J.M. 1969. Brahmaputra River: Channel processes and sedimentation. Sedinientary geology, 3, 129-239. Collinson, J.W., N.R. Kemp, and J.T. Eggert. 1987. Comparison of the Triassic Gondwana sequences in the Transantarctic Mountains and Tasmania. In G.D. McKenzie (Ed.), Gondwana Six: Stratigraphy, sediinentology and paleontology. (Geophysical Monograph Series, Vol. 41.) Washington, D.C.: American Geophysical Union. Collinson, J.W., D.C. Pennington, and N.R. Kemp. 1987. Stratigraphy and petrology of Permian and Triassic fluvial deposits in northern Victoria Land, Antarctica. In E. Stump (Ed.), Geological investigations in northern Victoria Land. (Antarctic Research Series, Vol. 41.) Washington, D.C.: American Geophysical Union. ANTARCTIC JOURNAL
Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell (Ed.), Gondwana geology. Canberra: Australia, National University Press. Vavra, C.L. 1984. Triassic Fremouw and Falla Formations, central Transan-
Paleotectonic implications of the Permo-Carboniferous Pagoda Formation, Beardmore Glacier area M.G. MILLER and BARBARA J.
JULIA
WAUGH
Department of Geology Vanderbilt University
Nashville, Tennessee
MP
37235
MC
tarctic Mountains, Antarctica. (Institute of Polar Studies Report 87.) Columbus: Ohio State University. Wells, N.A., and J.A. Dorr, Jr. 1987. Shifting of the Kosi River, northern India. Geology, 15, 204-207.
Sedimentologic aspects of the glaciogenic Pagoda Formation place constraints upon the paleotectonic setting of the Beardmore Glacier area during Permo-Carboniferous time and pertain in particular to the proximity of this region to the paleoPacific margin of Gondwana. Glaciogenic beds form the base of the Victoria Group. Rare palynomorphs from the uppermost Pagoda Formation show that these rocks are of Permo-Carboniferous age (Askin personal communication). In the central Transantarctic Mountains, Permo-Triassic units of the upper Victoria Group were deposited on the cratonic side of a back-arc
200
ME
MH
9 A
A
A
A
A A a
A
^
A
A A A
.150
AAA AAA A
AA A
4 '-A A A A A
A A A A A
9
8'- 4 - AA A
9
A A
A
A A A
A
100 A8 A A A
.4
7
A A A
k -;. .
4.AA.
EXPLANATION
4 A
Inferred Ice:
A
50 A A
Al
JA 4
Al
I AlI IA
Om
shale F: •1 fine sandstone :. coarse sandstone silty diamictite A A] sandy sandy diamictite sandstone lenses in diamictite LI crudely stratified diamictite A A
Z Retreat Advance
Figure 1. Selected stratigraphic columns through the Pagoda Formation in the Beardmore Glacier area showing interpretation of glacial advance and retreat. ["MP" denotes "Markham Plateau" (northwest). "MC" denotes "Mount Counts" (north face). "ME" denotes "Mount Elizabeth?' "Mu" denotes "Mount Hermanson?' "m" denotes "meter"] For more details see Miller (in preparation). 1987
REVIEW
19
