CHRONOSTRATIGRAPHY OF WESTERN ANATOLIAN SUPRADETACHMENT BASINS USING DETRITAL ZIRCON GEOCHRONOLOGY

Western Turkey underwent episodic N-S extension following a Late Cretaceous–Paleogene compressional regime. However, the timing of exhumation is debated, hampering development of geodynamic models or links to causal mechanisms. Cenozoic extension in the northern Menderes Massif may have begun as early as 36–28 Ma as indicated by Th-Pb ages of monazites, or as late as 22–20 Ma based on the age of synextensional plutons. Extension resulted in formation of the N-S oriented Selendi and Gӧrdes basins as well as the E-W trending Alaşehir Basin.

Previous research suggests onset sediment accumulation in the Gӧrdes Basin between 24.1 and 21.7 Ma . However the older age is based on K-Ar dating of dikes from that cross-cut the basement of the Gordes Basin, and which are lithologically correlated to clasts in the lower basin fill. The younger age is from the tuffaceous uppermost formation and therefore should represent a minimum age of the basin fill. K-Ar ages from volcanic domes that underlie the oldest stratigraphy in the center of the Gordes Basin range from 18.4 ± 0.8 Ma to 16.3 ± 0.5 Ma, implausibly implying that they erupted after the surrounding basin fill was deposited. This suggests that either the age of the basin fill or the conclusion that the igneous rocks are volcanic is incorrect.

We tackle the question of the age and sediment source of the Gӧrdes, Selendi and Alaşehir supradetachment basins using detrital zircon geochronology. This method allows us to determine sediment provenance and maximum depositional ages from a wide variety of zircon-containing lithologies. The result is a higher-resolution chronostratigraphic record and correlations than was previously possible.

Preliminary data from a sandstone in the lowermost formation in the Gördes Basin yield a maximum depositional age of 17.5 Ma, whereas a stratigraphically higher tuffaceous sample from the same formation yields an age of 16 Ma. In contrast to earlier conclusions that sedimentation in the Gördes Basin began in the latest Oligocene or early Miocene (Chattian–Aquitanian), these new data indicate a later (Burdigalian) onset of sedimentation. Furthermore, detrital zircon data indicate that the earliest basin-filling sediments were derived from a mixture of sources with affinities with the Tauride and Anatolide belts. Sediment provenance changes rapidly upsection and within 50 meters the Anatolide source is absent.