Geothermal reservoir rocks of the Büyük Menderes Graben (Turkey): stratigraphic correlation by a multiproxy approach

Abstract

This paper focuses on the correlation of two different marble units from an approximately 3,900 m deep geothermal exploration well (GP-1) in western Turkey by petrographical and geochemical data. Future geothermal exploration drilling in that area will benefit from a better (tectono) stratigraphic correlation and a better definition of the reservoir geometry in the basin. It is an innovative approximation in many settings to correctly correlate marble units without clear stratigraphic markers or fossil record, in particular, when sample material is restricted to cuttings. The most distinctive petrographical and geochemical properties in this study are colour, light transmission along with rare-earth element + yttrium (REY) geochemistry, and stable carbon and oxygen isotope data. Two stratigraphic correlations can be maintained for two different marble horizons of the GP-1 well to different stratigraphic horizons outcropping in the study area. Additional Rb-Sr geochronology yields an age of the last metamorphic overprint of the marbles of approximately 30 Ma. This study shows that a multiproxy approach is required to yield a reliable stratigraphic correlation as an important component of geothermal exploration, which supports the conceptual geological model prior to further geothermal drilling.