Early Holocene age and provenance of a mid-shelf delta lobe south of the Strait of Bosphorus, Turkey, and its link to vigorous Black Sea outflow

• Published in: Marine geology Vol. 380; pp. 113 - 137
• Main Authors: Aksu, A.E., Hiscott, R.N., Yaltırak, C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2016
• Subjects: Age; Black Sea outflow; Brackish; Deltas; Holocene delta; Lobes; Marine; Marine geology; Marmara Sea; Mineral liberation analysis; Outflow; Sand; Seismic surveys; Straits; MED, Black Sea; MED, Marmara Sea; MED, Turkey, Istanbul; MED, Turkey; Mineral liberation analysis; Marmara Sea; Black Sea outflow; Holocene delta
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2016.07.003

The chronology of an abandoned Holocene delta lobe (present water depth ~40–70m) on the northeastern shelf of the Marmara Sea south of the Strait of Bosphorus was revised from the early Holocene (~11.0–9.7calka) to the middle Holocene (6.65–3.75calka) by Eriş et al. (Eriş, K.K., Ryan, W.B.F., Çağatay, M.N., Sancar, Ü., Lericolais, G., Ménot, G., Bard, E., 2007. The timing and evolution of the post-glacial transgression across the Sea of Marmara shelf south of İstanbul. Marine Geology, 243, 57–76). Three independent seismic and multibeam surveys and replotting of navigational fixes for the 1992/1993-vintage survey lines which Eriş et al. correlated to their MD04-2750 giant piston core confirm that they misplotted the location of the MD04-2750 core site on seismic profiles by a minimum of ~200m. Because of rapid convergence of seismic reflections in this critical area, the assessment of the age of the Holocene delta proposed by Eriş et al. is incorrect. Instead, existing and new data allow the age of this delta lobe to be refined to ~11.1–10.2calka (±~200–300years each) using several dated cores and the MD04-2750 chronology itself. A dense grid of previously unpublished seismic data shows that the lobe emanates from the Strait of Bosphorus and not from any of the local small streams. Mineralogy of the very fine sand fraction of the delta excludes the Kurbağalıdere stream as a source of the detritus, as does the composition of detrital hornblendes. It is concluded that the early Holocene delta lobe indeed records a period of strong Black Sea outflow, as advocated by co-authors RNH and AEA in 2002. Re-examination of multibeam imagery from the strait itself provides support for strong southward flow that potentially coincided with accumulation of the delta lobe at the southern exit of the strait. •A delta lobe in NE Marmara Sea emanates from the Strait of Bosphorus and not from local streams.•Mineralogy of very fine deltaic sand excludes local streams as a source of detritus.•Delta age is ~11.1–10.2calka, from a time when Mediterranean water had not reached the Black Sea.•South-directed megaflutes in Strait of Bosphorus were possibly cut by megafloods from central Asia.