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Palaeogeography,
Palaeoclimatology, Palaeoecology 172,
297-312 (2001) Jerzy Dzik
& Andrzej Gaździcki Abstract.
A
short-term return of environmental conditions similar to those of the
end-Cretaceous is marked by the reappearance of nautiloid cephalopods in the
early-middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula.
Previous findings have been supplemented by a collections of 33 specimens. The
nautiloids come from several horizons, the oldest sample apparently being
located close to the base of the formation (Telm1), the most numerous coming
from the Cucullaea bed of Telm2-3. A
few specimens were collected from Telm4-6. The La Meseta Formation nautiloid
assemblages developed apparently in response to one of the Eocene warmings and
resulting transgression of a warm sea. The incursion of nautiloids into
southern high latitudes was roughly coeval with their expansion to the
northern European seas and the succession of faunas was parallel in both
regions. Based on the analogy with the early Eocene London Clay
nautiloid assemblages an estimate of bathymetric evolution of the environment
can be made by. The presence of a relatively shallow-water form similar to Cimomia imperialis close to the base of the early-middle Eocene La
Meseta Formation (Telm1) marks the beginning of the marine transgression. The
dominant La Meseta species, Euciphoceras
argentinae, was apparently an analogue of the English E. regale, the occurrence of which in the London Clay corresponds to
the highest sea level stand. The presence of Aturia in the higher part (Telm4-5) of the La Meseta Formation
suggests that cold oceanic waters possibly entered the area, accompanied by a
sea-level drop. The last nautiloid (Telm6) is an Euciphoceras sp. with less concave septa than in E.
argentinae, interpreted to be indicative of shallower habitat depth limits.
Both incursion of the nautiloids to, and their disappearance from the Eocene
high latitudes were connected with a fundamental rearrangement of the
geographic distribution of particular lineages. |