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Eocene bryozoan assemblages from the La Meseta Formation of Seymour Island, Antarctica

Hara U., Mörs T., Hagström J., Requero M. A.

Geological Quarterly

2018

Vol. 62, No. 3

705--728

Early to Late Eocene bryozoans from the La Meseta Formation of Seymour Island were collected at two localities within the Cucullaea I Allomember (Telm4 and Telm5) on the northwestern side of the island and in two localities within the Submeseta Allomember (Telm6 and Telm7) on the northeastern side. This fauna is represented by cyclostomes of the suborders Tubuliporina and Cerioporina and suborders of Neocheilostomata, among which nine species have been recognized. The following new species are introduced: Micropora nordenskjoeldi sp. nov., Lunulites marambionis sp. nov., Otionellina antarctica sp. nov. and Otionellina eocenica sp. nov. Some other taxa recognized in the studied material, such as Reticrescis plicatus, Uharella seymourensis and Celleporaria mesetaensis, were previously described from the lowermost (Telm1) or uppermost parts (Telm6-7), thus their stratigraphical ranges within the La Meseta Formation are extended. The diverse growth-forms of the bryozoans include a sole ball-shaped celleporiform colony and reticulated and bilamellar-foliaceous colony, as well as rich encrusting and free-living forms (so-called sand faunas), indicating the existence of locally restricted shallow-marine environments. This is particularly true in the middle and upper parts of the La Meseta Formation (Telm4-7). Reticulated, spheroidal and robust, branched colonies, which thrived in the environmental conditions of the lower part (Telm1), are represented only by a sparse bryozoan biota in the upper part of the La Meseta Formation. Lunulitiforms, such as Lunulites and Otionellina which are warm water, free-living bryozoans, dominate in the siliciclastic sediments of Telm5, but erect folded sheets forming a shell bed composed of ?Goodonia occur in Telm6-7. These three genera are recognized in Antarctica for the first time. The austral genus Otionellina has its earliest fossil record here, showing close biogeographical links with the Late Eocene-Miocene faunas of Australia and New Zealand. The taxonomic composition of the studied fauna together with their growth forms is a very good tool for reconstructing palaeoenvironmental conditions in the middle and upper parts (Telm4-7) of the La Meseta Formation, deposited during the Late Ypresian-Priabonian.