Geochemical characteristics of iron in sediments from the Sea of Marmara

Abstract

Two ~1000 cm long sediment cores were recovered from the Sea of Marmara, one with the occurrence of gas hydrates in the Western High, and the other without hydrates in the Cinarcik Basin. Differences in mineralogical and chemical compositions have been identified between the two sediment cores. Based on the results of the mineralogical and geochemical analyses, the main sources of the sediments are quite similar for both investigated areas, but the authigenic components are different, particularly iron sulfides and carbonates. Authigenic Fe(II) carbonate are much higher in Core MRS-CS-05 in the Western High, while crystalline Fe(III) phases are more abundant in Core MRS-CS-16 in the Cinarcik Basin. Notably, the enrichments of greigite (Fe3S4), a metastable ferromagnetic iron sulfide mineral and intermediate polysulfide, as well as iron carbonates are identified at 400 cmbsf with the maximum iron content in Core MRS-CS-05. These indicate the presence of a more reducing and acidic environment in the Western High, mainly due to higher organic matter content and seepage of heavy hydrocarbons in the sediments.

Fluids and processes at the seismically active fault zone in the Sea of Marmara

“…However, the high-resolution multi-proxy study carried out by Teichert et al (2018) provides a promising example of the use of authigenic carbonates as archives of past seismic activity. Iron has also been investigated as proxy for tracing the migration of fluids within the sedimentary column and their discharge at the seafloor (Yang et al, 2018). The presence of metastable ferromagnetic iron sulfide minerals on the Western High indicates a more reducing environment resulting from the degradation of heavy hydrocarbons and organic matter.…”

Time Integrated Metal Accumulation on Pellets in an Industrial Harbour “Durban Harbour”

“…This may be attributed to Cr being available only in trace amounts in the Durban Harbour sediments, thus leading to minimal accumulation in pellets. While iron is found in high background concentrations in sediments, it is also one of the key reactive elements in marine sediments and is highly subject to phase transformations by redox processes [26,27], which may impair its rate of accumulation on pellets. Holmes, Turner, and Thompson [13] similarly found metal concentration to be higher in pellets than in sediment.…”

Interpretation of Late‐Pleistocene/Holocene Transition in the Sea of Marmara From Geochemistry of Bulk Carbonates

“…Experimental studies have revealed that pH is a critical factor influencing the carbonate saturation state in sediments, with low pH leading to the dissolution of carbonates (Waldbusser et al, ). In the Western High, the sedimentary environment with low pH is created by anaerobic biodegradation of seeping petroleum, a phenomenon recognized by the occurrence of greigite (Yang et al, ). Greigite is formed in anoxic environments with a pH less than 5 (Roberts & Weaver, ), where carbonates, and primarily foraminifera, are dissolved.…”

“…The upper 0–79 cm below seafloor (cmbsf) part of the marine unit is dark green gray silty clay. This portion has a porous, brecciated structure resulting from gas hydrate dissociation and a strong smell of H 2 S. The lower part of the unit between 79 and 305 cmbsf is a sapropel containing up to 1.8 wt.% total organic carbon (TOC), which is clearly higher than that of 1.2 wt.% for the lacustrine unit below (Yang et al, ; Figure a). This sapropel layer (305–316 cmbsf) corresponds to the Holocene sapropel layer previously described in the SoM (Çağatay et al, ; Çağatay et al, ).…”

“…The sapropel is composed of dark olive green to greenish gray, laminated clay to silty clay. The TOC contents of the entire core, including the sapropel, is uniformly low with an average value of 1.2 wt.% (Yang et al, ). The low TOC values result from dilution of the organic carbon by a high detrital influx into the deep basin.…”