Possible Late Pleistocene volcanic activity on Nightingale Island, South Atlantic Ocean, based on geoelectrical resistivity measurements, sediment corings and ¹⁴C dating

Abstract

Tristan da Cunha is a volcanic island group situated in the central South Atlantic. The oldest of these islands, Nightingale Island, has an age of about 18 Ma. In the interior of the island, there are several wetlands situated in topographic depressions. The ages of these basins have been unknown, and their genesis has been debated. Aiming towards the reconstruction of the geomorphological history of these basins, we conducted geoelectrical resistivity measurements to map the subsurface topography, extracted peat and sediment cores and dated the onset of sedimentation applying the radiocarbon method. The irregular shapes of the basins and the lack of clear erosional features indicate that they are not eruption craters and were not formed by erosion. Instead, we regard them as morphological depressions formed between ridges of trachytic lava flows and domes at a late stage of the formation of the volcanic edifice. The onset of sedimentation within these basins appears to have occurred between 24 and 37 ka with the highest situated wetland yielding the highest ages. These ages are very young compared to the timing of the main phase of the formation of the island, implying volcanic activity on the island during the Late Pleistocene.

Keywords:

• South Atlantic
• Nightingale Island
• peat bogs
• subsurface topography
• ¹⁴C dating
• young volcanism

Acknowledgements

This study was financed by the Swedish Research Council (VR) to the project “The Last Termination in the central South Atlantic” granted to SB. Parts of the logistics were financed by a grant to SB from the Crafoord Foundation. We are very thankful for this support. We would also like to acknowledge fieldwork assistance from Martin Björck (Uppsala), the logistic support from the Tristan islanders and especially the help from Warren Glass and Donny Green during our stay on the island. We also appreciate the very detailed comments from one of the reviewers, whose obvious interest in the topic increased the quality of the manuscript.