The Geochemistry of 1 ky Old Euxinic Sediments of the Western Black Sea

Octavian G Duliu,Gheorghe Oaie,Emil Constantinescu,Marina V Frontasyeva,Ana-Voica Bojar,Carmen I Cristache,Otilia-Ana Culicov

doi:10.3390/geosciences9110455

Abstract

To get more data on the geochemistry of Black Sea euxinic sediments, a 50-cm core was collected at a depth of 600 m on a Western Black Sea Continental Platform slope. The core contained unconsolidated sediments rich in cocoolithic ooze and mud. Epithermal Neutron and Prompt Gamma Activation Analysis were used to determine the content of nine major (Na, Mg, Al, Si, K, Ca, Ti, Mn, and Fe as oxides) and 32 trace elements (Cl, Sc, V, Cr, Co, Ni, Zn, As, Se, Br, Rb, Sr, Zr, Mo, Sn, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Yb, Hf, Ta, W, Th, and U) with a precision varying between 3 and 9%. The core contained unconsolidated sediment rich in coccolithic ooze and mud. Previous 210 Pb geochronology suggests an age of ∼1 ky of considered sediments. Major components distribution showed that, except for Cl and Ca, the contents of all other elements are similar to Upper Continental Crust (UCC) and North American Shale Composite (NASC). The distribution of the 32 trace elements showed similarities to the UCC, except for redox-sensitive metals Fe, Se, Mo, and U, of which the significantly higher content reflects the presence of euxinic conditions during deposition. A chondrite normalized plot of nine rare earth elements indicated a similarity to UCC and NASC, suggesting a continental origin of sedimentary material.

Highlights

The Black Sea, an inland sea with a surface area of 422,000 km2 and a maximum depth of m [1], is the largest meromictic basin in the world
The Total Organic Carbon (TOC) content varied between 3% and 6%, in good concordance with previous data reported in Reference [28]
The final experimental data regarding the content of the nine major oxides and 31 trace elements as determined by Epithermal Neutron Activation Analysis (ENAA) and PGAA can be freely accessed at http://dx.doi.org/

Summary

Introduction

The Black Sea, an inland sea with a surface area of 422,000 km and a maximum depth of m [1], is the largest meromictic basin in the world. Geosciences 2019, 9, 455 a much thicker layer below the oxygenated one, filling the rest of the basin. The lower layer, devoid of oxygen and saturated with hydrogen sulfide, forms an euxinic environment, populated only by extremophile bacteria that produce hydrogen sulfide and carbon dioxide [2,3]. As the euxinc zone is completely devoid of bioturbating organisms, it represents an ideal environment to preserve sedimentary structure for long periods of time, allowing a systematic reconstruction of past processes. The Black Sea catchment basin extends over Europe and the Anatolian Peninsula and covers an area of 1,874,904 km. The Danube itself contributes annually with about 3.0–3.5 × 107 tons of sediments, which are discharged and spread over the western continental platform [5,6] as well as within the euxinic zone

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Conclusion