Cretaceous-Tertiary (K-T) boundary evaporites in the Malatya Basin, eastern Turkey

Abstract

The Malatya basin is situated on the Anatolid-Torid plate of the Neo-Tethys Sea. Evaporites were deposited in the northwestern part of the Malatya basin, which is referred to as the Hekimhan sub-basin. Although the Gunduzbey sub-basin in the southeastern Malatya basin has coeval deposits, it contains no evaporate deposits. The evaporite is most likely the result of the last transgressive–regressive cycle of the Late Cretaceous Sea. The pre-evaporitic unit is represented by the carbonate platform deposit of the Loftusia banks, which partly underwent dolomitization and overlies the deep marine sediments. Celestite-bearing algal limestone was deposited directly below the gypsum-dominated evaporate unit in association with the organic-rich mudstone. Evaporite sedimentation took place in various types of environments, such as marginal shallow subaqueous with the association of sabkha–coastal lagoon and deeper subaqueous. It is assumed that the tectonic evolution of the basin margin, which occurred during the latest stage of the Cretaceous regression, was responsible for the environmental restriction leading to evaporate sedimentation under arid/semiarid climatic conditions. The 87Sr/86Sr ratios obtained from 38 samples of the gypsum and celestite-bearing limestones (11 samples) range between 0.707817 and 0.707980 and between 0.707783 and 0.707864, respectively. The δ34S values range from +19.5 to +22.4 ‰, and the δ18O values range from +9.6 to +12.7 ‰. These isotopic signatures correspond to that of Late Cretaceous/Early Paleocene (Cretaceous-Tertiary boundary) marine water. However, celestite exhibit(s) relatively higher δ34S and 87Sr/86Sr values than expected marine values, which could be a result of contribution of diagenetic fluid into the celestite-precipitated environment.