High degrees of Fe mineral sulfidation are found in the euxinic sedime
nts of the Black Sea. With the short time scale of diagenesis (2000-30
00 yr or less) and the slow reaction kinetics between sulfide and Fe-c
ontainlng silicates, extensive sulfidation of silicate Fe cannot accou
nt for these results. Also, the extent of Fe sulfidation in Black Sea
sediments is much higher than sulfidic normal marine sediments encount
ering similar exposure times to sulfide. Sediment trap results indicat
e that sulfidized Pe is delivered to the sediment with depositing orga
nic matter and independently of lithogenic particles containing unreac
tive Fe silicate phases. We combine these observations and propose tha
t Fe mineral sulfidation in the euxinic Black Sea is driven by the dec
omposition, by sulfate reduction, of particulate organic matter settli
ng through the anoxic water-column as marine snow aggregates. Locally
rapid rates of sulfate reduction at the site of organic decomposition
produce elevated sulfide concentrations, encouraging dissolved Fe2+ pr
ecipitation as Fe sulfide minerals in the upper Fe-rich portion of the
anoxic zone. The high deposition rate of this sulfidized Fe, compared
to lithogenic particulates, generates the high extents of Fe sulfidat
ion. Sediments from some regions in the euxinic Black Sea have low ext
ents of Fe sulfidation, similar to those from sulfidic normal marine e
nvironments. In some instances these low extents of sulfidation are as
sociated with turbidites originating from the basin margins. In other
instances sedimentology Is poorly constrained so that an association b
etween turbidite deposition and extents of Fe mineral sulfidation cann
ot be certain. We note a seasonality in the extent of Fe mineral sulfi
dation from sediment trap results such that in the summer months highl
y sulfidized Fe deposits,whereas in the winter, the depositing Fe ess
sulfidized. Thus, variability in the proportion of winter-like and sum
mer-like particle deposition can provide a mechanism, in addition to t
urbidites, by which variable extents of Fe mineral sulfidation can be
generated in euxinic basin sediments.