Geochemistry of an exotic sediment layer above sapropel S-1: mud expulsion from the Urania Basin, eastern Mediterranean?

Abstract

In a gravity core from the eastern Mediterranean Sea, a chemically and mineralogically distinct, 5.5-cmthick layer is present above sapropel S-1 and overlain by hemipelagic marls. Calcite is completely absent in this exotic layer, dolomite is present only in small amounts, and the Cr concentrations are significantly enhanced. The layer was deposited primarily under reducing conditions, but the distributions of redoxsensitive elements show that a large part of the exotic layer is now oxidised by a downward-progressing oxidation front. Sediments from within the nearby anoxic, hypersaline Urania Basin are similar to those from the exotic layer, in particular in S-, C-, and O-isotope distributions of pyrite and dolomite, as well as increased Cr concentrations. Mud expulsion due to expansion of gas-rich mud is proposed to explain the presence of the exotic layer outside the Urania Basin. The deposition of an anoxic layer above S-1 shielded the sapropel from oxidation which resulted in the rare occurrence of a complete preservation of S-1 and provides the first minimum age for the start of anoxic mud accumulation in the Urania Basin.

Microbial Community of a Hydrothermal Mud Vent Underneath the Deep-Sea Anoxic Brine Lake Urania (Eastern Mediterranean)

“…In spite of the fact that the Urania mud fluids are hotter and less saline than overlying brine (10% salinity, 45°C and 27% salinity, 16°C, respectively), the mixing of these two compartments does not occur due to the higher clay content and higher density of the former, and stable formation of a thin interface was detected (Corselli et al 1998; Charlou et al 2003). The occasional upward expulsion of brine basin sediments due to extreme gas pressure in the mud fluids has also been documented (Hübner et al 2003).…”

Temporal stability and origin of chemoclines in the deep hypersaline anoxic Urania basin

“…The characteristic Mediterranean sapropel S‐1 beneath this layer has been dated to 6675 ± 35 years B.P. [ Hübner et al ., ]. However, this finding is not withstanding that the Urania basin as encountered today is indeed younger.…”

“…Since its discovery, numerous expeditions have returned to Urania basin and investigated its stratification [Corselli et al, 1998;Sass et al, 2001;Hübner et al, 2003;Ferrer et al, 2005;Yakimov et al, 2007;Borin et al, 2009]. All have consistently reported a confined interface between seawater and brine of 2-3 m thickness-suggesting that strong chemical gradients have persisted for at least two decades.…”

“…There is also a pronounced temperature anomaly of up to 45°C in a basal, deep pit in the western limb [Fusi et al, 1996] where a mud vent enters the basin [Corselli et al, 1996]. Nearby, sediment layers have been interpreted as ejected material [Hübner et al, 2003;Aloisi et al, 2006;Yakimov et al, 2007]. It has therefore been concluded that the mud volcano is injecting fluidized sediments into Urania basin and supports physical mixing by advection and/or thermal convection [Aloisi et al, 2006].…”

Contamination trends of trace metals and coupling with algal productivity in sediment cores in Pearl River Delta, South China

“…The plot for ZT suggests a combined role of AOM and Fe/Mn oxides to the trace metals during the deposition (Fig. 3a) (Förstner et al, 1979;Hübner et al, 2003). The AOM and Fe/Al/Mn oxides have an important effect on the association and release of trace metals in aquatic environment (Lopez et al, 2006).…”