Paleosol and dolocrete associated clay mineral occurrences in siliciclastic red sediments of the Late Miocene Kömişini Formation of the Tuzgölü basin in central Turkey

Abstract

The Late Miocene was characterized by high global temperatures and partly to nearly complete desiccation of the Mediterranean Sea throughout the latter part of the Messinian age (the Messinian salinity crisis). The Late Miocene marine Mediterranean Sea area has been widely studied from different perspectives, but terrestrial paleoenvironmental and paleoclimatic records from the Mediterranean area are highly limited in their spatial range. To this end, the paleosols, dolocrete and fluvial sedimentary rocks of the Kömişini Formation in the northwestern part of the Tuzgölü basin are described in detail. Six lithofacies were identified as (A) clast-supported gravel, (B) massive (pebbly) sandstone, (C) massive mudstone, (D) disrupted mud, (E) disrupted conglomerate, and (F) disrupted matrix-supported conglomerate. The siliciclastic facies were interpreted as braidplain, and the distal part of braidplain deposits is associated with an ophiolitic area while the disrupted mud and disrupted conglomerate were identified as three types of paleosols: Inceptisols, Aridisol and Vertisols. The calcretes occur in the paleosols in nodular, powder, and massive forms. Clay minerals include smectite, chlorite, palygorskite, illite, and serpentine. Gypsum, smectite and chlorite are dominant minerals at the base and middle part of the section, whereas palygorskite and illite appear as the prevailing clay minerals in the upper sections. Smectite, illite and palygorskite precipitated in a vadose zone from strongly evaporated alkaline water rich in Si, Ca and Mg and poor in Al at increased temperatures and at an advanced stage of dolocrete and paleosol formation. K, Si, Mg, Al+Fe and Ca are required for smectite, illite, palygorskite and calcification. Given the increase in Ba, Cr, Ni and Co, these cations might have originated from ophiolite, carbonate and volcanic units. As a consequence, the vertical distribution of clay mineral types suggests the variations of paleoclimatic conditions during the deposition, and the relationships among the type of host rock, paleosol and dolocrete, which corresponds to nearly complete desiccation of the Mediterranean Sea.