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DIAGENESIS OF THORIUM ISOTOPES IN DEEP‐SEA SEDIMENTS 1
Author(s) -
Antal Paul S.
Publication year - 1966
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1966.11.2.0278
Subject(s) - authigenic , thorium , diagenesis , geology , radionuclide , leaching (pedology) , uranium , sediment , mineralogy , dissolution , nitric acid , geochemistry , radiochemistry , environmental chemistry , chemistry , soil science , geomorphology , metallurgy , materials science , inorganic chemistry , physics , quantum mechanics , soil water
227 Th, 230 Th, and 232 Th were extracted from Caribbean Sea sediment samples of known age using 8 n HNO 3 or coned HCl. The yields were compared with the radionuclide content obtained by complete dissolution of the sample and with previously reported data on red clays in Pacific Ocean cores. These comparisons indicate that the internal consistency of dates and sedimentation rates is insufficient to prove the validity of leaching procedures. The nitric acid leaching yields of authigenic 230 Th decrease with depth in the core, that is, with sample age; whereas leaching of 232 Th is independent of depth. It is suggested that the initially soluble precipitate of 230 Th is transformed in the sediment to a more acid‐resistant state, the apparent half‐life of this transformation being 24,000 years at 3C. Therefore, in the solution obtained by partial extraction, the decrease of the ratio 230 TH : 232 Th with depth in the core is clue not only to radioactive decay but also to the decreased solubility of authigenic 230 Th. Thus, sedimentation rates calculated from ( 230 Th : 232 Th) solution may be too low by a factor of three.