Contrasting sediment types from oxic and anoxic sites of the modern Black Sea:

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" Contrasting sediment types from oxic and anoxic sites of the modern Black Sea: "
T. W. Lyons R. A. Berner

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112709
Doc. No	:	TLpq304039565
Main Entry	:	R. A. Berner
	:	T. W. Lyons
Title & Author	:	Contrasting sediment types from oxic and anoxic sites of the modern Black Sea:\ T. W. LyonsR. A. Berner
College	:	Yale University
Date	:	1992
student score	:	1992
Degree	:	Ph.D.
Page No	:	396
Abstract	:	Box cores collected during Leg 4 of the 1988 R/V Knorr Black Sea Oceanographic Expedition revealed a wide range of uppermost Holocene sediment types sampled over a broad region of the southern basin. Box cores recovered from deep-water regions of the basin were dominated by coccolith-rich, microlaminated (Unit 1) sediments and muddy, gray turbidite layers. Unit 1 is not enriched in pyrite sulfur relative to typical Holocene marine sediments with comparable organic carbon (OC) concentrations accumulating under oxygenated bottom waters. Carbon-sulfur relationships (evaluated on a calcium-carbonate-free basis) demonstrate that OC and pyrite sulfur are essentially decoupled. These observations, combined with the persistence of elevated pore-water sulfide to depth and a strong correlation between pyrite sulfur and the detrital iron component argue strongly for iron-limited pyrite formation in Unit 1. Degree-of-pyritization (DOP) profiles (a measure of the extent to which the original potentially reactive iron has been transformed to pyrite) further indicate limitations in the availability of reactive iron in Unit 1 and suggest that the majority of the pyrite is formed in the sulfidic water column and/or very close to the sediment/water interface. Sulfur isotopic values and down-core trends observed for Unit 1 pyrite are compatible with predominantly water-column pyrite formation. The turbidite muds of the deep basin have been characterized in detail, including the observed high degrees of textural and chemical homogeneity. Oxic zone sediments were collected during two box-coring transects (Bosporus region and Bay of Sinop) on the Turkish outer shelf. Suboxic diagenetic conditions characterized by intense bioturbation, undetectable interstitial dissolved sulfide, low degrees of sulfate reduction and elevated levels of interstitial dissolved iron are typical of the sediments at each locality. Despite the existing pore-water conditions, subsurface enrichments in reduced sulfur, reactive iron and manganese, as well as high extents of Fe sulfidation were detected at the Bosporus coring sites. These observations are believed to record the intersection of the water column Fe-Mn redox-boundary particle maximum with the outer-shelf bottom during a past oxycline shoaling event to a depth usd\leusd85 m followed by a further rise and concomitant sulfidation of the Fe oxides by anoxic-sulfidic bottom waters.
Subject	:	Earth sciences
	:	Geochemistry