Date

2015-11-08

Author

Ocakoğlu, Faruk
Yılmaz, İsmail Ömer

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100 km-long, NE-running Pınarbaşı basin (Central Anatolia, E Kayseri) comprises sporadic, km-scale tufa deposits at its uppermost stratigraphic levels in vicinity of basin margin. Tufa deposits are covered by well-dated, extensive Valibaba tepe ignimbrite (2.52 Ma) following several metres thick fluvial sediments. Sedimentological, stable isotopic, microscopic and magnetic susceptibility (MS) data from tufa outcrops in vicinity of Samağır village at the north of basin provide important constraints for the Late Pliocene terrestrial climate of Central Anatolia. The investigated 25 m thick carbonate succession which is interpreted as spring-fed tufa in a basin margin setting, consists of two architectural packages of laterally hundreds of meters persistence. First package is formed from phytoherm framestone, phytoherm boundstone and laterally and vertically interfingering minor coarse phytoclastic/intraclastic tufa. Phytoherm framestone facies consists of highly porous in situ carbonate-encrusted reeds and spherical aquatic plants. Phytoherm boundstone facies is whitish, laminated or massive and quite dense. Second building package consists of 80-100 cm thick yellow fine-grained phytoclastic tufa. It contains ellipsoidal oncoids and horizontal tubular remains, as well as cross bedding and reactivation surfaces all explaining an agitated environment. These two architectural elements abruptly overly each other forming couplets. Phytoherm boundstones display bacterial dendrites and filaments under microscope and in SEM studies. In between the filaments, silt/sand sized grains of similar texture and origin are observed. In phytoherm framestone facies, reeds and other aquatic elements are found within a pelletic and micritic matrix. Phytoclastic/intarclastic facies comprises abundant carbonate clasts as well as ostracod and Charophyte fragments in a pelletic and micritic matrix. Through the section, there is strong positive correlation between 18O and 13C stable isotopes. Based on changes in 18O concentrations, the section is divided into 3 larger cycles each with about 10 m thick. Magnitude of the cycles is about 2-2.5 %0. The lowermost larger cycle comprises nested smaller cycles of about 2 m thick whose magnitude in turn is in the order of 1-2 %0. More negative 18O concentrations generally match with detrital tufa facies. Additionally, MS measurements carried out at laboratory using highly sensitive MS2B Dual sensor display generally positive correlation with 13C concentrations. SEM investigations show that higher MS-value intervals have more probably airborn fine grains captured within algal/bacterial filaments. The findings show that the hierarchical cycles would correspond to Milankovitch bands of 100 ka and 21 ka respectively. The phytohermal facies that constitutes the bulk of the section is formed in hot periods while the phytoclastic/intraclastic intervals are developed in cool/dry periods when degradation/reworking of existing tufa facies dominate. Temperature estimates (4-10 0C) deduced from the magnitude of 18O curve implies that the glacial/deglacial cycles had been already under operation before late Pliocene in Central Anatolia.

Subject Keywords

Late Pliocene, Spring-fed tufa, Stable isotopes, Magnetic susceptibility, Paleoclimate, Geç Pliyosen, Kaynaktan beslenen tufa, Duraylı izotop, Manyetik susseptibilite, Paleo-iklim

URI

https://hdl.handle.net/11511/75725

Collections

Department of Geological Engineering, Conference / Seminar