Joint Argentine/American expedition to Seymour Island during austral ...
Joint Argentine/American expedition to Seymour Island during austral summer, 1988-1989
.t.
WILLIAM J . ZINSMEISTER 4, -
Department of Earth and Atmospheric Sciences Purdue University West Lafayette, Indiana 47907
During January, 1989, four U.S. scientists (William J . Zinsmeister, David H. Elliot, Philip Granchi, and Steven M. Hoff man) were invited to participate in Instituto Argentino Antartico expedition to Seymour Island. The specific objective of the field work during January was to continue our ongoing stratigraphic and paleontologic studies on the Cretaceous/Tertiary boundary and the Late Eocene sequence on Seymour Island. Although reconnaissance work on Seymour was initiated by an earlier joint Argentine/American expedition in 1974, the first major geological program on the Cretaceous/Tertiary boundary began in 1981 during the first American expedition to Seymour Island (Zinsmeister 1982), with subsequent field work during the austral summers of 1982-1983, 1984-1985, and 1986-1987. In addition to work on the Cretaceous/Tertiary boundary, extensive field work was also conducted on the late Eocene marine of the La Meseta Formation at the north end of the island. Results of these expeditions were summarized by Elliot et al. (1975) and Zinsmeister (1982, 1984, 1985, and 1987). It was recognized that the Cretaceous/Tertiary boundary on Seymour Island differed from other Cretaceous/Tertiary boundaries that have been studied. In contrast to the abrupt extinction of the biota encountered in Cretacous/Tertiary boundary sections from the mid and low latitudes, the Seymour Island section is characterized by a gradual transition in the faunas and floras across the boundary (Zinsmeister et al. 1989). The gradual nature reflects the greater degree of resolution obtained from Seymour Island section. The rate of deposition across the boundary was relatively rapid, in contrast to other sections which are characterized by greatly reduced rates of sedimentation, non-deposition, or the presence of a hiatus. The expanded nature of the Seymour Island section allows for a more detailed examination of the faunal changes that occurred during the latest Cretaceous and earliest Tertiary. Previous field work on the Cretaceous/Tertiary boundary on Seymour Island focused on sections that were either partly obscured on dip slopes with sampling spacing of a meter or greater. During the 1987 field season, an iridium anomaly was located, but precise stratigraphic relationships of the anomaly were insufficient and it was essential that the exact stratigraphic level be determined. One of the primary objectives was to re-sample this section at a 10-centimeter interval, to locate additional sections which were better exposed, and to sample these new sections at a 10-centimeter inverval. Three new exceptionally well exposed sections were discovered. One of these sections (figure) was sampled at a 10-centimeter in-
*
Well-exposed section across the Cretaceous/Tertiary boundary where samples were collected at 10-centimeter intervals.
terval and the other two at a 1-meter interval. These samples are now being studied at several institutions. Detailed surface collecting for macrofossils was also done in the Danian part of the Lopez de Bertodano Formation and in the lower part of the overlying Sobral Formation. A relatively diverse fauna of mollusks were recovered. These new fossils will provide new insight into the post-Cretaceous recovery of the marine biota of the high southern latitudes. A detailed biostratigraphic and mapping program was carried out by David Elliot of the Cape Wiman region at the northern tip of the island. Although some field work had been done in the past around Cape Wiman, the stratigraphic relationships were not clearly understood. (See Elliot and Hoffman, Antarctic Journal, this issue for summary of this work.) This work was supported by National Science Foundation grant DPP 84-16783 to William J. Zinsmeister.
References Elliot, D.H., and S.M. Hoffman. 1989. Geologic studies on Seymour Island. Antarctic Journal of the U.S., 24(5). Elliot, D.H., C. Rinaldi, W.J. Zinsmeister, T.A. Trautman, W.A. Bryant, and R. del Valle. 1975. Geological investigations on Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 10(1), 84-94. Zinsmeister, W.J. 1982. Summary of the first Seymour Island expedition to the James Ross Island area, Antarctic Peninsula. Antarctic Journal of the U.S., 17(5), 63-64. Zinsmeister, W.J. 1984. Geology and paleontology of Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 19(2), 1-5. Zinsmeister, W.J. 1985. 1985 Seymour Island expedition. Antarctic Journal of the U.S., 20(5), 41-42. Zinsmeister, W.J. 1987. Seymour Island expedition, 1986-1987. Antarctic Journal of the U.S., 22(5), 3-4. Zinsmeister, W.J., R.M. Feldmann, M.O. Woodburne, and D.H. Elliot. 1989. Latest Cretaceous/Earliest Tertiary Transition on Seymour Island, Antarctica. Journal of Paleontology, 63(6), 731-738.
ANTARCTIC JOURNAL
.t.
WILLIAM J . ZINSMEISTER 4, -
Department of Earth and Atmospheric Sciences Purdue University West Lafayette, Indiana 47907
During January, 1989, four U.S. scientists (William J . Zinsmeister, David H. Elliot, Philip Granchi, and Steven M. Hoff man) were invited to participate in Instituto Argentino Antartico expedition to Seymour Island. The specific objective of the field work during January was to continue our ongoing stratigraphic and paleontologic studies on the Cretaceous/Tertiary boundary and the Late Eocene sequence on Seymour Island. Although reconnaissance work on Seymour was initiated by an earlier joint Argentine/American expedition in 1974, the first major geological program on the Cretaceous/Tertiary boundary began in 1981 during the first American expedition to Seymour Island (Zinsmeister 1982), with subsequent field work during the austral summers of 1982-1983, 1984-1985, and 1986-1987. In addition to work on the Cretaceous/Tertiary boundary, extensive field work was also conducted on the late Eocene marine of the La Meseta Formation at the north end of the island. Results of these expeditions were summarized by Elliot et al. (1975) and Zinsmeister (1982, 1984, 1985, and 1987). It was recognized that the Cretaceous/Tertiary boundary on Seymour Island differed from other Cretaceous/Tertiary boundaries that have been studied. In contrast to the abrupt extinction of the biota encountered in Cretacous/Tertiary boundary sections from the mid and low latitudes, the Seymour Island section is characterized by a gradual transition in the faunas and floras across the boundary (Zinsmeister et al. 1989). The gradual nature reflects the greater degree of resolution obtained from Seymour Island section. The rate of deposition across the boundary was relatively rapid, in contrast to other sections which are characterized by greatly reduced rates of sedimentation, non-deposition, or the presence of a hiatus. The expanded nature of the Seymour Island section allows for a more detailed examination of the faunal changes that occurred during the latest Cretaceous and earliest Tertiary. Previous field work on the Cretaceous/Tertiary boundary on Seymour Island focused on sections that were either partly obscured on dip slopes with sampling spacing of a meter or greater. During the 1987 field season, an iridium anomaly was located, but precise stratigraphic relationships of the anomaly were insufficient and it was essential that the exact stratigraphic level be determined. One of the primary objectives was to re-sample this section at a 10-centimeter interval, to locate additional sections which were better exposed, and to sample these new sections at a 10-centimeter inverval. Three new exceptionally well exposed sections were discovered. One of these sections (figure) was sampled at a 10-centimeter in-
*
Well-exposed section across the Cretaceous/Tertiary boundary where samples were collected at 10-centimeter intervals.
terval and the other two at a 1-meter interval. These samples are now being studied at several institutions. Detailed surface collecting for macrofossils was also done in the Danian part of the Lopez de Bertodano Formation and in the lower part of the overlying Sobral Formation. A relatively diverse fauna of mollusks were recovered. These new fossils will provide new insight into the post-Cretaceous recovery of the marine biota of the high southern latitudes. A detailed biostratigraphic and mapping program was carried out by David Elliot of the Cape Wiman region at the northern tip of the island. Although some field work had been done in the past around Cape Wiman, the stratigraphic relationships were not clearly understood. (See Elliot and Hoffman, Antarctic Journal, this issue for summary of this work.) This work was supported by National Science Foundation grant DPP 84-16783 to William J. Zinsmeister.
References Elliot, D.H., and S.M. Hoffman. 1989. Geologic studies on Seymour Island. Antarctic Journal of the U.S., 24(5). Elliot, D.H., C. Rinaldi, W.J. Zinsmeister, T.A. Trautman, W.A. Bryant, and R. del Valle. 1975. Geological investigations on Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 10(1), 84-94. Zinsmeister, W.J. 1982. Summary of the first Seymour Island expedition to the James Ross Island area, Antarctic Peninsula. Antarctic Journal of the U.S., 17(5), 63-64. Zinsmeister, W.J. 1984. Geology and paleontology of Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 19(2), 1-5. Zinsmeister, W.J. 1985. 1985 Seymour Island expedition. Antarctic Journal of the U.S., 20(5), 41-42. Zinsmeister, W.J. 1987. Seymour Island expedition, 1986-1987. Antarctic Journal of the U.S., 22(5), 3-4. Zinsmeister, W.J., R.M. Feldmann, M.O. Woodburne, and D.H. Elliot. 1989. Latest Cretaceous/Earliest Tertiary Transition on Seymour Island, Antarctica. Journal of Paleontology, 63(6), 731-738.
ANTARCTIC JOURNAL
