TRACE AND RARE EARTH ELEMENT GEOCHEMISTRY OF THE UPPER MIOCENE-PLIOCENE LACUSTRINE EVAPORITES OF THE BOR-ULUKISLA BASIN (NIGDE, TURKEY)

11th International Multidisciplinary Scientific GeoConference SGEM2011, www.sgem.org, SGEM2011 Conference Proceedings/ ISSN 1314-2704, June 20-25, 2011, Vol. 1, 1031-1038 pp

ABSTRACT

The Bor-Ulukışla Basin situated in the south-eastern part of the Tuz Gölü Basin, Central
Anatolia, provide prominent example of lacustrine basins and varying assemblages of
evaporite and detrital minerals. The evaporatic sedimentation formed in the central part
of the basin as a shallow, saline lake system, where abundant halite and Ca-Na sulfate
deposits. Sodium sulfates and also halite deposits have been exploited from the recent
salt-playa lakes in the basin. The evaporites were deposited by related to the Messinian
salinity crisis (MSC) in the Mediterranean region. Samples collected from field and
from six deep cores in the basin. Evaporite minerals are dominated by halite, Na-Casulfate
minerals (anhydrite, gypsum, glauberite, thenardite and mirabilite), Mg-sulfate
minerals (bloedite, epsomite), dolomite, magnesite and calcite. Generally quartz,
feldspar, mica and detrital clay minerals are present at the margin of the basin.

Trace and rare earth element geochemistry and some of the elemental ratios show clear
associations with detrital (clastic) and evaporite (chemical) phases of deposits. The RE
and some trace element (V, Sc, Cr, Co, Ni, As, Ba, Rb, Th) contents are higher in the
clay-rich samples than the evaporite-rich samples. The carbonate-rich samples have an intermediate REE abundance. Clay and carbonate rich samples show homogeneous REE patterns, can be explained by the higher chemical weathering. Evaporite samples exhibit a variable REE pattern. In the evaporate sediments, the Eu anomaly is slightly to
moderately positive (1.38-2.51). The positive anomaly shows a volcanic origin. In the Ca-sulfate, Mg-sulfate and chloride samples have low La/Yb ratios (LREE). And also evaporate sediments have negative slight-moderate Ce anomaly (0.4-0.99). Negative Ce anomaly of evaporites suggests marine influence in the basin.

Geochemical considerations such as Mg/Ca, Na/Ca, Sr/Ca ratios and Sr contents have
been integrated to interpret evaporation and salinity ranges (fresh and high salinity
conditions) in the basin. The high differences (17.2-5438.5ppm) in the strontium
contents among the carbonate and sulfate levels of the Bor-Ulukışla evaporites could
reflect deposition under hydrologically unstable conditions and shallow waters.

Keywords: REE, geochemistry, halite, sodium sulfate, Central Anatolia.