USGS Open-File Report 94-588
Recent progress in the investigation of late Neogene records adjacent to the east Antarctic craton-west Antarctic rift system lithosphere boundary
- P.N. Webb
- Byrd Polar Research Center and Department of Geological Sciences, The Ohio State University
- D.M. Harwood
- Department of Geology, University of Nebraska
- B.C. McKelvey
- Department of Geology & Geophysics, University of New England, Armidale, Australia
- M.G.C. Mabin
- Department of Geography, James Cook University, Queensland, Australia
Impressive strides have been made in the investigation of the Antarctic
late Neogene over the past decade, and the assault proceeds with pace and
vigor within a variety of fields and sub-fields. As might be expected,
attempts at integration of these data provide a full spectrum of
agreement and disagreement, highlight clashes of hypothesis and dogma,
and lead us to the realization that the total data base leaves much to be
desired.
Divergent interpretations of late Neogene terrestrial environments and
climate in the Transantarctic Mountains (Webb et al., 1994, Webb and
Harwood, 1991, Sugden et al., 1993) have overshadowed many positive
developments. The basic tenets of the Webb-Harwood hypothesis ice sheet
history and biotic accommodation are intact and even enhanced a decade
after presentation and provide, in our opinion, an equally convincing
alternative position to that promoted by George Denton, David Marchant,
Michael Prentice, David Sugden and their collaborators.
Investigations of seismic stratigraphy from parts of the West Antarctic
Rift System basins (Alonso et al., 1992) hold the promise that the
Pliocene terrestrial and littoral marine record in and adjacent to the
Transantarctic Mountains might eventually be integrated with that of the
Victoria Land and Eastern basins, and correlation with Southern Ocean
biochronology further reinforced (Harwood and Maruyama, 1992).
Antarctic-Northern Hemisphere Relationships
Recent publications on the late Neogene glacial record of the Yakataga
Formation on the northeastern Pacific Alaskan margin (Lagoe et al., 1993),
and offshore southeastern Greenland (Larsen et al., 1994) portray a
comparable array of marine and terrestrial environments and events to
those deduced for the Ross Embayment and invite closer comparisons of
timing and inter-hemisphere oceanographic and climatic interactions.
Tectonic History
The occurrence of in situ marine and terrestrial Pliocene fossil material,
including vascular plants, at elevations of between 1300 and 1700m above
present sea level is clearly anomalous and is explained by post-Sirius
tectonic uplift of between 350 and 548m/m.y. (Webb et al., 1994; in
preparation). The existence of tree taxa at 1700m might be explained by
periods of exceptional Pliocene warmth at high southern latitudes (85°).
However, the close association of plants and subjacent marine sediments
and the sea level datum this implies, makes an original setting near sea
level a more reasonable explanation.
Glacial History
The multi-package stratigraphy and intervening hiatuses apparent in both
marine and terrestrial successions, the variety of glacigene lithofacies,
and the in situ marine and terrestrial fossil material, all point to a
history of multiple advance and retreat by a dynamic glacier system within
Beardmore valley. Beardmore Fjord penetrated almost the complete
breadth (+165km) of the Transantarctic Mountains from its junction with
the southern Ross Sea, and was at times covered by a "surging" tidewater
glacier with a source at the inland end of the valley. It is clear, then,
that during this phase of the Pliocene the Beardmore area was not
enveloped by an overriding ice sheet.
Paleoceanography, Sea Level Oscillations And Glacial History
Alonso et al. (1992) recognized a suspected Pliocene-Pleistocene
succession in the Eastern Basin of the Ross Sea with a thickness of up to
600m. This succession was subdivided into seven seismic units, each
separated by distinctive and often widespread erosional boundaries. These
authors interpreted the seismic stratigraphy as indicative of multiple ice
sheet advance (grounding) and retreat (ungrounding/floating) events and
noted a possible association with sea level oscillations. Further, they
suggest (p.93), "These fluctuations in grounding line position indicate
extreme variations in the Antarctic climate and sea level", and "Ice sheet
grounding events do not require a polar climate; they could reflect
subpolar to temperate shifts in climate." As noted above, Beardmore Fjord
stratigraphy and glacier history also indicates a multiple-event history
of ice advance/grounding and retreat/floating, and it is important that a
possible glacial and eustatic event relationship between the two areas be
examined.
Concluding Comments
Our preliminary investigation of the Beardmore valley suggests that this
area has the potential to become a significant southern high latitude
Pliocene data point. Clearly, an active rift margin shoulder provides a
favorable structural setting for Pliocene studies. The value of the area
rests, to a large degree, on our ability to recognize the contribution of
glacial, tectonic, and eustatic events to the history of the area.
The most negative aspect of work in this region to date is that age
control of specific events is inadequate. The region is far removed from
a long-lived volcanic center and ash and flow dating seems unlikely. More
intense collecting for microfossils is likely to improve the data base
within the marine facies of the Sirius Group, allowing improved
correlation to other Trunk Valley fjord systems such as Taylor and Wright
valleys (Barrett et al. 1992; Ishman and Rieck, 1992) and with the Ross
Embayment rift basins (Alonso et al., 1992). Temporal control of
terrestrial facies and event history will prove much more challenging. A
serious magnetostratigraphy program should be contemplated.
We cannot escape the fact that our views on late Neogene climate and
glacial history are seriously at odds with the stabilist ice sheet
arguments of Sugden et al. (1993).
References Cited:
- Alonso, B., Anderson, J.L., Diaz, J. I., and Bartek, L.R., 1992, Pliocene-Pleistocene seismic stratigraphy of the Ross Sea--Evidence for multiple ice sheet grounding episodes, in D.H. Elliot, ed., Contributions to Antarctic Research III: American Geophysical Union, Antarctic Research Series, v. 57, p. 93-103.
- Barrett, P.J., Adams, C.J., McIntosh, W.C., Swisher, C.C. and Wilson, G.S., 1992, Geochronological evidence supporting Antarctic deglaciation three million years ago: Nature, v. 359, p. 816-818.
- Harwood, D.M. and Maruyama, T., 1992, Middle Eocene to Pleistocene diatom biostratigraphy of ODP Leg 120, Kerguelen Plateau: Proceedings of the Ocean Drilling Program, Scientific Results v. 120, p. 683-733.
- Ishman, S.E. and Rieck, H. J., 1992, A late Neogene Antarctic glacio-eustatic record, Victoria Land Basin , Antarctica, in J.P. Kennett and D.A. Warnke, editors, The Antarctic Paleoenvironment--A Perspective On Global Change, Part One: American Geophysical Union, Antarctic Research Series, v. 56, p. 327-347.
- Lagoe, M.B., Eyles, C.H., Eyles, N., Hale, C., 1993, Timing of Cenozoic tidewater glaciation in the far North Pacific: Geological Society Bulletin, v. 105, p. 1542-1560.
- Larsen, H.C., Saunders, A.D., Clift, P.D., Beget, J., Wei, W., Spezzaferri, S., et al., 1994, Seven million years of glaciation in Greenland: Science, v. 264, p. 952-955.
- Sugden, D.E., Marchant, D.R., and Denton, G.H., 1993, The case for a stable East Antarctic ice Sheet: Geografiska Annaler, v. 75A, 351p.
- Webb, P.N. and Harwood, D.M., 1991, Late Cenozoic glacial history of the Ross Embayment, Antarctica: Quaternary Science Reviews, v. 10, no. 2/3, p. 215-223.
- Webb, P.N., Harwood, D.M., M.G.C. and McKelvey, B.C., 1994, Late Neogene uplift of the Transantarctic Mountains in the Beardmore Glacier region: Terra Antarctica, v. 1, no. 2.
- Webb, P.N., Mabin, M.C.G., Harwood, D.M., and McKelvey, B.C., in prep., Cloudmaker Formation (Sirius Group): An uplifted late Cenozoic marine and terrestrial glacigene succession, middle Beardmore Glacier-Queen Alexandra region, Transantarctic Mountains.
This page is <https://pubs.usgs.gov/openfile/of94-588/21_Webb.html>
Maintained by Eastern Publications Group Web Team
Last modified 28-Feb-2001