USGS Open-File Report 94-588
Warm Pliocene high sea-level records from Arctic Alaska and possible implications for Antarctic ice volume 2.8-2.2 Ma
- J. Brigham-Grette
- Department of Geology & Geography, University of Massachusetts
- L. D. Carter
- U.S. Geological Survey, Anchorage, AK
- L. Marincovich
- U.S. Geological Survey, Menlo Park, CA
- E. Brouwers
- U.S. Geological Survey, Denver, CO
- D. M. Hopkins
- Alaska Quaternary Center, University of Alaska
The Gubik Formation of Arctic Alaska contains deposits that record at
least three eustatic high sea-level stands during the mid- to late
Pliocene when perennial sea ice was likely absent, permafrost was less
widespread, and treeline extended to the coast of the Arctic Ocean (
Brigham-Grette and Carter, 1992, for review). The geochronology of these
deposits is based upon amino acid geochemistry, paleomagnetic evidence,
vertebrate and invertebrate paleontology, and strontium age estimates.
The Colvillian transgression (Nulavik member) reached at least 40 m asl
and occurred long after the submergence of the Bering Strait (ca. 4 Ma,
Gladenkov et al., 1992) but before 2.6 Ma, at a time when boreal forest or
spruce/birch woodland, including rare pine, fir, and hemlock, reached the
coast (Nelson and Carter, 1992). The Bigbendian transgression (Killi
Creek member) reached at least 20 m asl and occurred about 2.6 Ma based
on paleomagnetic evidence recording the transition from normal to reversed
polarity. While some marine faunas are richer than those of the
Colvillian (Brouwers, 1994), pollen evidence suggests forests reaching the
coast were more open in character (Nelson and Carter, 1985). The
Fishcreekian transgression (Tuapaktushak member) reached at least 25 m
asl, but may have reached much higher based on correlative shell material
found inland at higher altitudes. This high sea-stand took place sometime
between 2.2 Ma and 2.6 Ma and is also characterized by warm marine faunas,
but pollen data in regressive deposits suggest conditions on the coastal
plain supported herb tundra with larch (Repenning et al., 1987; Nelson,
1994).
All of these transgressions post-date the mid-Pliocene (3.1-3.0 Ma)
warming recorded elsewhere in the world, and require that the Arctic Basin
remained relatively warm until nearly 2.2 Ma. The Pliocene marine
deposits of the Arctic Coastal plain, occur at altitudes of up to 70 m.
This area has been tectonically stable for at least the past 125 ka,
because shorelines formed during the last interglacial have not been
uplifted. We have found no evidence for uplift of the Pliocene marine
beds, and so we believe that eustatic sea-level during the Pliocene must
have been intermittently higher than present sea-level. Such high sea-
levels would seem to require at least periodic reductions in the size of
the Antarctic ice sheet accompanied by complete removal of the Greenland
ice sheet (cf. Funder et al., 1985; Bennike and Bocher, 1990 for the Kap
Kobenhaven Formation which is likely correlative with the Fishcreekian
transgression).
Erratics in all of these marine deposits suggest that during periods of
high sea-level, glaciers reached tidewater somewhere bordering the Arctic
Basin. Warm marine conditions and an ice-free Arctic Ocean may have been
conducive to glacierization of portions of the Arctic islands in a manner
unlike the late Pleistocene. Shell-bearing tills and extensive glaciation
postulated for the Ellesmere Island region may date from this time period
(Bell and England, 1992). Marine shells in the most extensive till sheet
are likely correlative with the Hvitland beds dated elsewhere on Ellesmere
Island to about 2.6 Ma and thought to be correlative with the Bigbendian
transgression. The limited amount of amino acid epimerization in shells
of this antiquity suggest that air and ground temperatures across the
Arctic have been low and severe since the time of the Fishcreekian
transgression.
Although the amount of regional uplift is not precisely known, the
elevation of the Gubik deposits requires that eustatic sea level was much
higher than at present during portions of the middle and late Pliocene.
These data, coupled with the warm conditions and lack of arctic sea ice,
argue in favor of models calling for a more dynamic Antarctic ice sheet
during this interval.
References Cited:
- Bell, T. and England, J., 1992, Extensive glaciations of Ellesmere Island--tentative age estimates based on amino acid ratios and paleoenvironmental implications: Byrd Polar Research Center Miscell Series M-322, p. 90-92.
- Bennike, O. and Bocher, J., 1990, Forest-tundra neighboring the North Pole--planet and insect remains from the Plio-Pleistocene Kap Kobenhavn Formation, North Greenland: Arctic, v. 43, no. 4, p. 331-338.
- Brigham-Grette, J. and Carter, L.D., 1992, Pliocene marine transgressions of North Alaska--circumarctic correlations and paleoclimatic interpretations: Arctic, v. 45, no. 1, p. 74-89.
- Brouwers, E.M., 1994, Late Pliocene paleoecological reconstructions based on ostracode assemblages from the Sagavanirktok and Gubik Formations, Alaskan North Slope: Arctic, v. 47, no. 1, p. 16-33.
- Funder, S., Abrahamsen, N., Bennike, O., Feyling-Hanssen, R.W., 1985, Forested Arctic--evidence from North Greenland: Geology, v. 13, p. 542-546.
- Gladenkov, Y., Barinov, K.B., Basilian, A.E., and Cronin, T.M., 1992, Stratigraphy and paleoceanography of Pliocene deposits of Karaginsky Island, Eastern Kamchatka, U.S.S.R.: Quaternary Science Reviews, v. 10, no. 2/3, p. 239-246.
- Nelson, R.E. and Carter, L.D., 1985, Pollen analysis of a late Pliocene and early Pleistocene section from the Gubik Formation of Arctic Alaska: Quaternary Research, v. 24, no. 3, p. 295-306.
- Nelson, R.E. and Carter, L.D., 1992, Preliminary interpretation of vegetation and paleoclimate in Northern Alaska during the Late Pliocene Colvillian marine transgression: U.S. Geological Survey Bulletin 1999, p. 219-222.
- Nelson, R.E., 1994, Pliocene marine palynology documents first appearance of lowland tundra in northern Alaska: Geological Society of America, Abstracts with Programs, v. 26, no. 7, p. 142.
- Repenning, C., Brouwers, E.M., Carter, L.D., Marincovich, L., Jr., and Ager, T.A., 1987, The Beringian ancestry of Phenacomys (Rodentia:Cricetidae) and the beginning of the modern Arctic Ocean borderland biota: U.S. Geological Survey Bulletin 1687, 31 p.
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