Isotopic and chemical signatures of sedimentary smectite and diagenetic clinoptilolite of a lacustrine Neogene basin near Bigadic, western Turkey

The major element chemistry and the rare earth element (REE) distribution of sedimentary smectite and diagenetic clinoptilolite from the lacustrine volcanic-sedimentary succession near Bigadic in northwestern Anatolia, Turkey, suggest a constant influx of volcanogenic material into the basin with, especially, a systematic negative Eu anomaly. This is supported by the Sr isotope chemistry which shows slight differences in the 87 Sr/ 86 Sr of the sedimentary phases (carbonates and smectites) with values between 0.70835±7and0.70859±9 and the diagenetic clinoptilolite with values between0.70861±8and0.70893±17. This lacustrine volcanic-sedimentary succession is Early to Middle Miocene in age, with K Ar values for the biotite and hornblende of the basal volcanic rocks showing an average age of ∼22 Ma. The K Ar data of the clinoptilolite are strongly dependent on the permeability of the tuffaceous host rocks. They suggest an age of ∼14 Ma for the end of the diagenetic recrystallization of the clinoptilolite in impermeable rocks, and further chemical exchange with the interstitial fluids in the permeable rocks. This latter process induced a loss of radiogenic 40 Ar and REE out of the zeolites from the permeable tuffs, and might have had an influence on their chemical composition.