Compositional trends through the Holocene mud succession of the southwestern Black Sea shelf, and implications for sedimentary provenance and water-level history

Lister, Christopher J. (2014) Compositional trends through the Holocene mud succession of the southwestern Black Sea shelf, and implications for sedimentary provenance and water-level history. Masters thesis, Memorial University of Newfoundland.

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Abstract

Piston core MAR02–45P and its trigger weight core (MAR02–45TWC) record sedimentation over the last 10.3 cal ka on the SW Black Sea shelf with only one hiatus (from 5.4–2.1 cal ka BP). Geochemical and mineralogical studies were undertaken on the fine fraction of these sediments in an attempt to better define lithologic units, and to search for evidence of changing provenance. Isopach maps were used to estimate the volume of sediments deposited on the shelf. This estimate of sediment volume was compared to expected deliverable volumes from local rivers, as calculated using a robust empirical equation for sediment flux, available from the literature. Four geochemical units (Units A, B, C1, C2) were identified, in agreement with previous studies. Correlation tables expose four groups of similarly behaving elements that govern the geochemical trends throughout MAR02–45. There is carbonate group composed of Ca, Mg, and Sr, and a mainly detrital group believed to reside in aluminosilicate minerals composed of Sc, Fe, Co, Ce, La, Th and Y. In contrast, As, Rb, Br, Mn and Sr are interpreted to have entered the sediment from the water column, or were mobile during early diagenesis and Cu, Pb, Ni, Zn, U and V are interpreted to indicate adsorption onto fine-grained phyllosilicates and/or organic matter during early diagenesis. A ~45 cm upward adjustment in the placement of the previously recognized α1 key seismic marker in the core is suggested by the new geochemical data. Unit C1 (10.3–8.4 cal ka BP) contains some detritus from local sources, especially marked by spikes in Cr abundance associated with sandy horizons. Unit C2 (8.4–7.5 cal ka BP) contains the familiar signatures of Unit C1 as well as a high TS concentration. This unit preserves the geochemical signature of a previously identified ‘first-pulse’ of Mediterranean water entering the Early Holocene Black Sea. Unit B (7.5–5.4 cal ka BP) records a well-oxygenated environment with abundant mollusk communities and infaunal burrows. Unit A (2.1–0 cal ka BP) chronicles the dysoxic conditions that continue to the present, and has higher than average abundances of the redox-sensitive elements Cu, Ni, Zn, Pb, U, and Th. Grain size analysis on nearby core MAR05–50 shows a bimodal texture similar to that of loess found within the Danube drainage basin. Geochemical comparisons between two loess profiles and core MAR02–45 show similar abundances for only one element. Mineralogically, Units A, B, and C are similar to one another except for a downcore increase in the abundance of calcite, some of which is likely detrital. Although specific sediment sources (provenance) could not be determined, it is concluded that the volume of sediment deposited in Unit C is too large to have been delivered from only local sources, indicating that the SW Black Sea shelf must have been in open communication with the larger Black Sea basin since ~10.3 cal ka BP. The geochemical and mineralogical data are consistent with this conclusion, although they cannot be used to quantify the contribution from the various potential sources in the western Black Sea.

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