Geochemical and Geological Features of the Calcrete Formations in Konya (Central Turkey) and Their Relationship With the Konya Fault Zone

Abstract

The Konya Closed Basin (Quaternary, Central Turkey) is a graben basin which expands toward the east-west and it is controlled by faults on three sides: The Konya fault zone in the west, the Divanlar fault zone in the east and the Karaömerler fault zone in the north. Calcretes developed in relation to fault systems in the Konya region are concentrated in areas where faults cut Quaternary aged terrestrial deposits. 
 In this study, it is aimed to elucidate the deposition conditions, geochemistry and age (with ESR method) of the calcareous deposits associated with faults in the Konya Closed Basin.
 Calcretes in the region existing as coatings, dust, nodules and layers are in the form of dolocrete and clayey calcrete. Dolocretes were deposited in the Quaternary terrestrial sediments on the ophiolitic rocks and geochemical data point to an ultramafic source. Bacterial community, clay, quartz minerals and calcite cement are observed in the calcretes formed in areas with limestone basement.
 According to the results of ICP-MS analysis of samples taken from Konya calcretes, the %MgO contents are between 0.99 and 7.7; CaO%: between 34.71 and 50.71; %SiO2 between 3.22 and 20.59. %MgO in dolocretes are between 11.65 and 21.01; %CaO between 8.44 and 29.57; %SiO2 values between 4.48 and 9.17
 The δ13C and δ18O isotope values of calcretes range from -3.87 to -7.62 and from -3.62 to -7.45 respectfully. Average δ13C values indicate that calcrete formation took place under pedogenic condition or in shallow groundwater.
 The calcretes deposited in 3 locations around the city of Konya (on the Konya fault zone) were dated by using the Electron Spin Resonance (ESR) method and ages between 217.47 and 389.85 ky were obtained. The calcrete samples taken from the fault planes (dip-slip normal fault bordering the Upper Cretaceous Ophiolitic Mélange and the Quaternary Karahüyük Formation) gave a relative age for faulting as being 292.86 ky. This first dating study conducted in the Konya Fault Zone has provided important clues to elucidate the formation history of Konya Closed Basin (KCB) and the paleo-seismological past of Konya.