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Particle sorting during sediment redistribution processes and the effect on 230 Th‐normalized mass accumulation rates
Author(s) -
Marcantonio Franco,
Lyle Mitchell,
Ibrahim Rami
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl060477
Subject(s) - geology , radiocarbon dating , mars exploration program , sediment , carbonate , mineralogy , geomorphology , paleontology , astrobiology , chemistry , physics , organic chemistry
The 230 Th method of determining mass accumulation rates (MARs) assumes that little to no fractionation occurs during sediment redistribution processes at the seafloor. We examine 230 Th inventories in radiocarbon‐dated multicore sediments from paired winnowed and focused sites at Cocos and Carnegie Ridges, Panama Basin. Radiocarbon‐derived sand MARs, which likely represent the vertical rain of particles poorly transported by bottom currents, are similar at each of the paired sites but are different using 230 Th normalization. 230 Th‐normalized MARs are about 60% lower at focused sites and likely underestimate vertical MARs, while the reverse is true for winnowed sites. We hypothesize that size fractionation occurs most frequently at lower current velocities, resulting in the coarse fraction being left behind and primarily the fine 230 Th‐rich grains being transported downslope. 230 Th‐normalization works well for recording fine‐grained (detrital and opal), but not coarse‐grained (carbonate), fluxes in regions that have undergone sediment redistribution.