Publication Date:
2023-08-28
Description:
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.
Keywords:
Atlantic Ocean; CD7; CD7-S50; Charles Darwin; Comment; Deposit type; DEPTH, sediment/rock; Description; File name; Identification; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; Photo/Video; Position; PV; Quantity of deposit; Sediment type; Substrate type; Uniform resource locator/link to image; Visual description
Type:
Dataset
Format:
text/tab-separated-values, 10 data points
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