Microplankton provide 9 Ma age for sediment in the Macquarie Island ophiolite complex
Macquarie Island in the southwest Pacific Ocean (558S) is unique as an exposed location for studyingoceanic crust generated by slow seafloor spreadingregions where rocks are difficult to date usingradiometric methods. Bolboforms, an extinct group of poorly known microplankton, in sedimentintercalate...
| Published in: | Australian Journal of Earth Sciences |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Blackwell Publishing Asia
2008
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| Subjects: | |
| Online Access: | https://doi.org/10.1080/08120090802266584 http://ecite.utas.edu.au/94850 |
| Summary: | Macquarie Island in the southwest Pacific Ocean (558S) is unique as an exposed location for studyingoceanic crust generated by slow seafloor spreadingregions where rocks are difficult to date usingradiometric methods. Bolboforms, an extinct group of poorly known microplankton, in sedimentintercalated with pillow lavas yield tight constraints (9.018.78 Ma) on the age of formation of thedominantly seafloor volcanic sequence constituting the south of the island. The occurrence of Bolboforma metzmacheri extends the known geographic range of this Late Miocene zonal markerspecies in the southwest Pacific. A monospecific calcareous nannoplankton flora ( Reticulofenestraperplexa ) accompanied by the foraminifer Neogloboquadrina pachyderma in sediment from thenorth part of the island indicates a slightly older age (9.59.3 Ma), consistent with a radiometric date(9.2+0.4 Ma) from nearby volcanics. The new age data indicate that the ocean floor volcanicsequence formed early in the Late Miocene, possibly along short segments of a slow-spreading midoceanridge. Bolboforms have potential to provide fine-scale dating in other similarly complex ridgesystems that are difficult to date by other means. |
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