Disentangling interglacial sea level and global dynamic topography: Analysis of Madagascar

• Published in: Earth and planetary science letters 2019-08, Vol.519, p.61-69
• Main Authors: Stephenson, Simon N., White, Nicky J., Li, Tao, Robinson, Laura F.
• Format: Article
• Language: English
• Subjects: dynamic topography; geodynamics; glacial isostatic adjustment; last interglacial period; MIS 5e; sea level
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2019.04.029

Global inventories of stable sea-level markers for the peak of the last interglacial period, Marine Isotopic Stage (MIS) 5e, play a pivotal role in determining sea-level changes and in testing models of glacial isostatic adjustment. Here, we present surveying and radiometric dating results for emergent terraces from northern Madagascar, which is generally regarded as a stable equatorial site. Fossil coral specimens were dated using conventional and open-system corrected uranium series methods. Elevation of the upper (undated) terrace decreases from 33.8 m to 29.5 m over a distance of 35 km. An intermediate terrace has an average radiometric age of 130.7±13.2 ka (i.e. MIS 5e). Its elevation decreases from 9.3 m to 2.8 m over a distance of 80 km. The record of the lowest terrace is fragmentary and consists of beach rock containing rare corals with ages of 1.6–3.8 ka. The spatial gradient of the MIS 5e marker is inconsistent with glacio-isostatic adjustment calculations. Instead, we propose that variable elevations of this marker around Madagascar, and possibly throughout the Indian Ocean, at least partly reflect spatial patterns of dynamic topography generated by sub-plate mantle convection. •Flight of three coral reef terraces in northern Madagascar correspond to Holocene, last and previous interglacial periods.•Upper terrace tilted from 33.8 m to 29.5 m over 35 km. Intermediate terrace tilted from 9.3 m to 2.8 m over 80 km.•Tilting cannot be generated by glacial isostatic adjustment alone.•Tilting likely to be generated in part by growth of a sub-plate thermal anomaly within the asthenosphere.