CHARACTERIZATION AND DIAGENESIS OF THE LA TE JURASSIC AGE ORGANIC-MATTER IN THE WESTERN TAURUS RANGE (SOUTHERN TURKEY) - PALEOENVIRONMENT AND TECTONIC CONSEQUENCES

The parautochthonous platform carbonates in the central part of wester n Taurus Mts (S Turkey) include a late Jurassic to early Cretaceous pe lagic epidose, known as the Akkuyu Formation and well dated by abundan t pelagic fauna. In the southwestern part of the basin, this formation consists of clear, thinly bedded micritic limestones and contains a b lack key-horizon (3 to 5 m thick) rich in organic matter. To the NE, t he Akkuyu Fm. Grades into shallow-marine dark limestones with a benthi c fauna, and black fetid dolomites. Rock-Eval pyrolyses of outcropping sample yielded up to 9% total organic carbon. The richest horizons co ntain a marine organic matter (HI > 650 mg HC/g TOC) derived from phyt oplankton (amorphous organic matter). The degree of maturation of orga nic matter strongly increases from SW to NE, perpendicularly to the th rust front of Beysehir-Hadim nappes. According to the geochemical, pa lynological, reflectometric and mineralogical parameters, two contrast ed areas can be distinguished : the first one, located SW of the thrus t front is characterized by a moderate maturity (beginning of oil-wind ow, Tmax = 429 to 438-degrees, TAI light brown, R0 = 0.32 to 0.52 %); the second area is situated 20 km behind the thrust front and shows a much greater thermal maturity (gas-window, Tmax = 475 to 545-degrees, TAI dark brown, R0 = 1.23 %). Illite cristallinity estimated by the 00 1 peak sharpness (width at half height) displays a mean value of 13/10 -degrees 2THETA) for the first area and 5/10-degrees 2THETA for the se cond one where the diagenetic impact is more important. This study dem onstrates the anoxic character of the Akkuyu Fm. during late Jurassic. We interpret the difference of maturation linked to a rise of tempera ture between the two areas as a consequence of the deeper burial of th e Mesozoic platform carbonate under the Beysehir-Hadim thrust sheets. The data presented here suggest that the present front of the nappes is close to the actual maximum extension of thrusting.