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Provenance discrimination among foreshore, backshore, and dune environments in the black sand beaches along the Samandag/Hatay coasts, SE Turkey (E Mediterranean)

2018    Ergin, Mustafa; Karakas, Zehra S.; Tekin, Erdogan; Eser, Basak; Sozeri, Koray; Copuroglu, Ibrahim; Koc, Sukru; Simsek, Barbaros

The occurrence of beach placers, the chromite-rich black sand, and the factors controlling their distribution along the Samandag coasts, SE Turkey, was investigated. One hundred fifty-two surficial (upper 2 to 5 cm) samples of beach sediments from foreshore, backshore, and dune subenvironments; 24 river sediments; 25 samples from ophiolitic source rocks; and ore samples from 4 chromitite mines were collected between the years 2012 and 2015. In addition to hydrogeographic and geomorphological field observations, grain size analysis and total heavy mineral separation and conventional petrographic microscopy studies were carried out. Bimodal, well to moderately well sorted, fine to medium sands were predominant, and on the basis of grain size distribution, at least six sectors could be distinguished by their alongshore fining or coarsening tendencies. Obviously, spatial variations in drainage pattern of fluvial input, wave and current motions, and beach morphology played a crucial role in changing sediment texture. The total heavy mineral (THM) concentrations ranged from 1 to 92 wt% (avg. 40 wt%) in beach sediments and from 3 to 50 wt% in fluvial sediments whereby the bed load of the major and perennial Asi River contained lower THM (9-25 wt%) than its ephemeral tributaries (14-50 wt%) which are in much closer proximity to the source areas. Overall, the THM concentrations in foreshore, backshore, and dune subenvironments tend to decrease in southward direction, except for THM enrichment close to the Asi River mouth. This would reflect rather higher inputs from northerly ephemeral rivers draining the ophiolitic rocks with additionally net longshore sediment transport towards south. The coastal physical processes favoring heavy mineral enrichment such as spatial and temporal variations in swashzone wave dynamics with uprush, backwash, and infiltration effects on the beaches were also observed in the field. The opaque heavy mineral fractions are mostly found in grain size less than 0.25 mm and composed of chromite, magnetite, and ilmenite species with intergrowth textures. Non-opaque heavy mineral fractions were dominated by various species of pyroxenes and amphiboles with lesser amounts of serpentinized olivine. Formation of chromite-rich black sand placers along the Samandag beaches (SE Turkey) and also in river/stream beds resulted from the weathering of mafic-ultramafic rock complexes ("Hatay or Kizildag Ophiolites") and chromite-rich ores of the Amanos Mountains to define the provenance of placers and no considerable input was detected from the Asi River downstream from the Bassaer ophiolites of Syria.