Eocene Mollusca from the vicinity of McCulloch’s Bridge, Waihao River, South Canterbury, New Zealand: Paleoecology and systematics

Publication Type:Journal Article
Year of Publication:1992
Authors:Maxwell, P. A.
Journal:Geological Survey Paleontological Bulletin
Keywords:Eocene (New Zealand)

A total of 250 species of molluscs are recorded from the Bortonian to Kaiatan (Middle - Late Eocene) Waihao Greensand and Ashley Mudstone exposed in the Waihao River near McCulloch's Bridge. Of these, 212 species are recorded from a 2m thick bed (here named the Tahu Member) of early Kaiatan age, and 77 from a tuff bed (Kapua Tuff - also Kaiatan) from higher in the section. The two faunules differ considerably both qualitatively and quantitatively from each other and neither greatly resembles other Arnold Series faunules. The greatest similarity is between the Tahu Member faunule and that from the Hampden Formation (Bortonian) of Hampden Beach, North Otago. A genus-by-genus autecological analysis of the Tahu Member and Kapua Tuff faunules indicates deposition of these units at depths in the range 150-250 m, with the Kapua Tuff probably being deposited at greater depths than the Tahu Member. Taxonomic structure analysis of these faunules gives results reasonably consistent with this conclusion. The Tahu Member molluscan faunule suggests that sea temperatures during the early Kaiatan were much higher than those prevailing in South Canterbury at the present day and probably considerably higher than those in northernmost New Zealand. Evidence from molluscs and to some extent, other fossil groups and from oxygen isotope analyses indicates a sharp drop in temperature at or near the end of the Bortonian, leading to the extinction of several distinctive molluscan genera. Temperatures apparently rose from early Kaiatan to Late Kaiatan - Runangan. (auth)

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