1. SULFUR AND IRON ACCUMULATION IN NEOLITHIC ASH WOOD SAMPLE FROM YENIKAPI EXAVATION SITE
Nural Yilgor1, D.Dogu2, T. Kuster3
Introduction:
During the excavations of the Marmaray Rail Tube Tunnel Project in Yenikapi, Istanbul, Turkey, a great number of Neolithic period tree remnants were unearthed along with countless Byzantine and Ottoman period archaeological remains. Those trees were found at 8.5 m below the sea level during the excavations of the swamp and it was observed that the tree remnants were in an upright position. Firstly, the wood samples were examined anatomically to identify the species and after that one wood sample was chosen among the identified trees for the determination of chemical properties and further anatomical investigations. The tree remnants which were chosen for this study have been identified as Fraxinus spp. (ash wood). SEM observations and EDX map results show that ancient ash wood contains high amount of sulfur and iron elements which are typical for the marine-archaeological wood that is found in an anoxic conditions like seawater or swamp.
This result strengthens the possibility that the area where the trees were found had a connection with the sea.
Figure 2. The view of spongy and yellowish colour of wet unearthed ash wood
Fig.1. The excavation site of neolithic trees
Material and Method:
After wood samples were unearthed, they were subjected to anatomical examination to identify the species under light and photomicroscopes. The sample choosen for this study was identified as Fraxinus which is known as Ash.
The ancient sample was examined with scanning electron microscope (SEM) Carl Zeiss EVO 40, equipped with energy dispersive X-ray analyser to get a map of elements distributions on the surface and in cell walls.
Results and conclusion:
The map was obtained on the surface by the help of EDX spectrum analyser and according to EDX spectrum analyser S and Fe have the highest values following C and O elements in ancient buried ash wood. While elemental Fe is changing in the range of %7.2to %10.1, elemental S is changing %7 to %11.4 in ancient ash wood sample surface. SEM investigations demonstrate that there are many images that do not belong to the fungi or bacteria as seen in Fig.5 (a,b,c). SEM and EDX spectrum results show that iron and sulfur are present in a variety of particles of different sizes in contrast the fungi remains.
It is assumed that sulfate reducing bacteria are responsible from the formation of fraboidal pyrite which occurs under oxic conditions. It is suggested that in anoxic conditions like seabed or sediments, sulphate reducing bacteria produce hydrogen sulphide, H2S, which transforms to different reduced sulphur compounds in the waterlogged wood (1). On the other hand, bacterial attack facilitate the penetration of Fe2+ ions and H2S throughout the inner part of waterlogged wood. This result strengthens the possibility that the area where the trees were found had a connection with the sea.
References:
1.Yvonne Fors, Magnus Sandström. “Sulfur and iron in shipwrecks cause conservation concerns” Vol.35, Chemical Society Reviews, (2006)
Fig.3. The excavation site of neolithic trees (a) Cross section of ancient ash wood (b) Cross section of recent ash wood a  a b b
Figure 4 (a &b). EDX Spectrum of ancient wood of Fraxinus c
Table 1. Distribution of the elements in the ancient wood samples according to EDX Analyser.
Figure 5. SEM Images of ancient Fraxinus wood
(a) A view from cross section (b) Pyrite clusters (c) Pyrite framboids
1 Department of Forest Products Chemistry and Technology, Forestry Faculty, Istanbul University, 34473, Istanbul, TURKEY
2 Department of Forest Biology and Wood Protection Technology, Forestry Faculty, Istanbul University, 34473, Istanbul, TURKEY
3 USDA Forest Service, Forest Products Laboratory, Madison, WI, 53726, USA