LATE MIOCENE GEOHISTORY OF THE MUT AND ADANA BASINS (SOUTHERN TURKEY): INSIGHT FOR UPLIFT OF THE SOUTHERN MARGIN OF THE CENTRAL ANATOLIA PLATEAU

The Mut and the Adana basins developed on top of the Tauride units as late Oligocene-Miocene wedge-top basins. Their upper Oligocene-lowermost Miocene continental deposits recorded the last compressional phases associated with the Tauride orogeny in the area. Starting from the Burdigalian, a general increase in the subsidence rate provided enough accommodation space for sedimenting thick lower Miocene-Pleistocene successions. These deposits, which are mainly marine, sedimented across the present day southern margin of the Central Anatolian Plateau (CAP). This margin separates the uplifted area (CAP, Mut Basin) from downthrown and more subsiding sectors (Adana Basin).

The magnitude and timing of uplift of the southern margin of the CAP helps to define a critical phase of plateau development. Along the southern margin of the CAP, late Miocene marine deposits of the Mut Basin capping the basement rocks of the Taurides are almost undeformed. These deposits, which crop out at elevations higher than 2,000 m, are useful to define the age for plateau margin uplift. In the adjacent Adana Basin, located SE of the uplifted area of the CAP, a quite similar Middle-Late Miocene stratigraphy shows a general connection between these two basins. Recent field work carried out on these two basins allowed us to better constrain the major stratigraphical changes that occurred in those sedimentary basins starting from their onset, and consequently to reconstruct a more detailed geohistory for both basins.

Our new data from the Adana Basin better constrain the Tortonian-Pliocene interval. The stratigraphy of the Adana Basin recorded the Messinian salinity crisis (MSC) of the Mediterranean Sea in a marginal setting. We recognized two major unconformities (Messinian Erosional Surfaces; MES 1 and MES 2), which distinguish different phases of the MSC of the Mediterranean area (evaporitic, early post-evaporitic, and late post-evaporitic phases). The evaporitic phase was recorded by the cyclical deposition of anhydrite/sapropel couplets (Lower Evaporites), resting conformably on pre-evaporitic Messinian marls. Above the MES 1, which affects the Lower Evaporites and the Messinian pre-evaporitic deposits, resedimented gypsum beds, mainly due to debris-flows processes, with thick intercalations of marls, define the early post-evaporitic (p-ev1) phase of the MSC. The MES 2 separates the p-ev1 from the late post-evaporitic sediments (p-ev2), which in the Adana Basin are mainly characterized by coarse-grained deposits (fluvial conglomerates of the Handere Fm). According to the Messinian stratigraphy from other sites in the Mediterranean area (i.e. northern and central Apennines, Italy), these unconformities are well dated: MES 1 = 5.6 Ma; MES 2 = 5.45 Ma.

Using surface and subsurface data, we determined the geohistory of these two basins through a reconstruction of their subsidence curves. The Early-Middle Miocene geohistory is quite similar for both basins. Some differences are recognizable at the Middle Miocene/Late Mocene transition, likely due to the different position of the two areas with respect to the Arabia/Eurasia collision zone. At that time (late Serravallian, 12 Ma), the Adana Basin was uplifted and an erosional surface developed in the area cutting down to the deep marine marls of the Güvenç Fm (mainly Serravallian). Lower Tortonian continental sediments were deposited just above this erosional surface. In contrast, the Mut Basin was not so clearly affected by uplift, and sedimentation continued in a fully marine environment.

Our biostratigraphical and Sr-isotope analysis carried out on the highest marine deposits of the Mut Basin capping the southern margin point to a late Tortonian age, suggesting that uplift of that region is younger than late Tortonian. More precise indications about the uplift of the southern margin come from the stratigraphy of the Adana Basin. The subsidence curve for the Tortonian-Messinian interval of the Adana Basin shows an increase in the subsidence rate of the basin at about 5.6 Ma, corresponding to a period of increasing in the sedimentation rate (debris flows of resedimented gypsum deposits) just after the draw down of the Mediterranean base level (MES 1). However, a major increase in the subsidence rate is recorded at about 5.45 Ma, with the sedimentation of more than 1,000 m of fluvial deposits (conglomerates and marls of the Handere Fm) pertaining to the p-ev2 stage of the MSC of the Mediterranean (5.45-5.33 Ma), and containing late Messinian Lago-Mare fauna with Paratethyan immigrants (Loxocorniculina djafarovi Zone). In the Adana Basin, this event corresponds to a rapid deposition of clastics coming mainly from crystalline and sedimentary rocks of the Taurides. We interpret this as denoting a rapid uplift of the northwestern margin of the basin (southern margin of the CAP).