Deposition of sapropel S1 sediments in oxic pelagic and anoxic brine environments in the eastern Mediterranean: differences in diagenesis and preservation
A. Rutten et al., Deposition of sapropel S1 sediments in oxic pelagic and anoxic brine environments in the eastern Mediterranean: differences in diagenesis and preservation, MARINE GEOL, 153(1-4), 1999, pp. 319-335
Sediments from a boxcore in the previously anoxic brine-filled Poseidon Bas
in, eastern Mediterranean, have been studied and compared to sediments depo
sited in a 'normal' eastern Mediterranean environment. The boxcore can be d
ivided into three main sedimentary intervals based on AMS-radiocarbon ages,
foraminiferal and geochemical zonations. From the base of the core upwards
these are: (1) 12.3-31.2 cm, organic-rich sediments redeposited from withi
n the brine; (2) 6.6-12.3 cm, sediment containing a 'cold' foraminifera fau
na redeposited from above the brine into the basin while the brine was stil
l present; (3) 0-6.6 cm, oxic pelagic sediment accumulated since the reoxyg
enation of Poseidon Basin which occurred similar to 1800 yrs BP. Near the b
ase of the latter unit, a Mn-oxide peak has formed and it marks the present
boundary between oxic and suboxic environments. A progressive downward oxi
dation front, which is usually found in 'normal' sapropel S1 sediments, has
never formed in Poseidon Basin sediments. This has resulted in the preserv
ation of the relationship between organic carbon and organic-related trace
elements, e.g. Se, in the organic-rich sediments of Poseidon Basin, whereas
such a relationship has been obliterated in 'normal' sapropel S1 sediments
. On the basis of the carbonate content as well as the Sr/Ca ratio, preserv
ation of carbonates appears to be better in the brine sapropel sediments of
BC15 than it is in 'normal' sapropel S1 sediments. The high opal content o
f BC15 shows that biogenic opal is also much better preserved. The overall
lower C-org/Ba ratio in BC15 suggests a better preservation of barite relat
ive to that of organic carbon in shallow brine sediments, but is as yet inc
onclusive for the organic carbon preservation potential of brine relative t
o 'normal' unoxidised sediments. (C) 1999 Elsevier Science B.V. All rights
reserved.