Palaeoecology and systematics of Early Devonian bivalves from the Horlick Formation, Ohio Range, Antarctica
Title:
Palaeoecology and systematics of Early Devonian bivalves from the Horlick Formation, Ohio Range, Antarctica
Author:
Bradshaw, Margaret A. McCartan, Lucy
Appeared in:
Alcheringa
Paging:
Volume 15 (1991) nr. 1 pages 1-42
Year:
1991
Contents:
A fauna of bivalves, many of them large and thick-shelled, occurs in the 50-metre-thick, clastic, Early Devonian Horlick Formation of the Ohio Range, Antarctica. Together with the ecology of other fossils, the bivalves indicate a high-energy, near-shore environment, with deposition strongly influenced by storm activity. The distribution of bivalves and other fossils is related to nine lithofacies. Most of the fauna comprises death assemblages. Thick external bryozoan growths on parts of certain bivalves and brachiopods suggest partial burial of shells during life. Other evidence indicates that some shells were exhumed and reburied. In terms of bottom communities, most of the fauna falls within Benthic Assemblages 1 and 2, and was close to shore, but the Australospirifer and crinoid-dominated fauna of lithofacies 8 at the top of the sequence indicates Benthic Assemblage 4 or 5, and lay further offshore. The fauna shows strong Malvinokaffric affinities and lesser connections with the Devonian of Reefton, New Zealand. Shallow water phosphate deposits that are anomalous for the latitudes proposed for the Ohio Range (58° S) may be explained by either higher global temperatures during the Devonian, or by post-Devonian strike-slip movement of the region. The fauna is numerically dominated by brachiopods, but taxonomically, bivalves are more varied and form a strong component in assemblages. The bivalves include infaunal, epifaunal and semi-infaunal forms. A suggested mode of life for each bivalve is included in the systematic section of this paper. Re-collection, and the restudy of existing material, has resulted in the establishment of two new genera and eight new species. The genus Notonucula has been proposed for Nuculoidea-like palaeotaxodonts that lack marginal micropectenations of the shell, and Obrimia for a new, large, thick-shelled genus that has been tentatively placed in the family Edmondiidae. New bivalve species include: Notonucula cuspidis, Notonucula demissa, Nuculites frigidus, Modiomorpha herculi, Obrimia hadrosa, Obrimia ovalis, Palaeosolen algidus, and Prothyris (Prothyris) darlingensis. Recorded for the first time from the Horlick Formation are Phestia cf. P. viator, Gosseletia? sp., Pterinea? sp., Glossites sp., and Orthonota sp.; also hyolithids and crinoid holdfasts.
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