Annotated record of the detailed examination of Mn deposits from the Hirondelle Seamount, Eastern Equatorial Atlantic, supplement to: Jones, E J W; BouDagher-Fadel, M K; Thirlwall, Matthew F (2002): An investigation of seamount phosphorites in the Eastern Equatorial Atlantic. Marine Geology, 183(1-4), 143-162


Phosphorites with P2O5 contents up to 33% have been recovered from the eastern Atlantic between 6°N and 9°N. Formed from the replacement of shallow-water reef limestones of Middle Eocene age, the deposits are exposed on the crests of three subsided seamounts, Lighthill, Hirondelle and Carter, at depths of 794-1246, 1161-1176 and 552-1158 m, respectively. Phosphates exposed on the sea floor are associated with high levels of acoustic backscatter recorded using a ship's echo-sounder and a 10-kHz pinger towed ?30 m above the bottom. Seabed scintillometer measurements on Carter Seamount near 9°N, 21°W revealed high x-ray emission where phosphorites are known to crop out from photography and sampling. Uranium contents of the deposits lie in the range 9-46 ppm, values which are lower than those found in continental margin phosphates, but similar to concentrations in Pacific seamount phosphorites. 87Sr/86Sr ratios indicate that phosphatisation of the Middle Eocene reef limestones occurred in the Early-Middle Miocene (~16-23 Ma) on Carter and Hirondelle Seamounts and in the Late Miocene (~6 Ma) on Lighthill Seamount. Upwelling near the palaeo-equator probably played a vital role in diagenesis by promoting high biological productivity and a large flux of phosphorus to pore waters in the seamount limestones. Phosphorites are probably widespread on other sediment-capped seamounts and fracture-zone ridges in the Equatorial Atlantic.

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Metadata Access
Creator Jones, E J W; BouDagher-Fadel, M K; Thirlwall, Matthew F
Publisher PANGAEA - Data Publisher for Earth & Environmental Science
Publication Year 2002
Rights Creative Commons Attribution 3.0 Unported
OpenAccess true
Language English
Resource Type Supplementary Dataset
Format text/tab-separated-values
Size 10 data points
Discipline Earth System Research
Spatial Coverage (-20.294 LON, 9.015 LAT); Atlantic Ocean