Barremian-Aptian Biostratigraphy in Yazd Block, Central Iran

Abstract

The Lower Cretaceous benthic Limestone in Yazd Block (Central Iran zone) is known as the Taft and Shahkuh Formations. In this study, the age of the Taft and Shahkuh Formation, is examined based on biostratigraphic and paleontological investigations of Taft Formation in sections of Herisht (NE Ardakan) and Abanbar (NE Ardakan) and Shahkuh Formation in Chahpalang section (North Ardakan). According to the lithostratigraphic investigations, the taft and Shahkuh Formation in these sections include of thin bedded to medium bedded and massive limestone. Micropaleontology study of the Taft and Shahkuh Formation has led to the recognition of numerous genus and species which belong to Orbitolinidae Families such as: Dictyoconus pachymarginalis, Montseciellaarabica, Mesorbitolina parva, Paleodictyoconus sp., Paleodictyoconusactinostoma, Palorbitolina sp., Palorbitolina lenticularis, Praeorbitolinacormyi, Praeorbitolina cf. wienandsi, Praeorbitolina claveli, Praeorbotolinasp., cf. Paleodictyoconus sp., Palorbitolina ultima. and Calcareous Algae such as: Acroporella sp., Acroporella cf. Radoicicae, Actinoporella sp., Arabicodiumsp., Arabicodium cf. elongates, Augioporella cf. fouryae, Bacinellairregularis, Bueina sp., Boueina cf. hochstetteri, Boueina minima, Bueina cf.pygmaea, Cayeuxia sp., Cayeuxia anae, Garwoodia sp., Garwoodia cf. maxima,Girvanella sp., Griphoporella aff. Cretacea, Halimeda sp., Kopedagaria sp.,Kopedagaria sphaerica, Lithocodium aggregatum, Marinella sp., Montiellaelitzae, Marinella lugeoni, Marinella cf. yogoslavica, Neomeris sp., Neomeriscf. cretacea, Neomeris cf. pfenderae, Parachaetetes asvapatii, Permocalculussp., Permocalculus dragastani, Permocalculus minutes, Pseudoactinoporella sp.,Pseudoactinoporella iranica, Pseudoactinoporella cf. iranica, Pycnoporidiumlobatum, Rivularia sp., Salpingoporella sp., Salpingoporella cf. patruliusi,Salpingoporella cf. johnsoni, Salpingoporella pygmaea, Salpingoporellamehlbergii, Salpingoporella aff. Turgida, Salpingoporella cf. dinarica,Suppiluliumaella cf. praebalkanica, Udotea flabellum. Based on the identified Microfossil, such as Orbitolinid fossil, the age of the Taft Formation in the Kuh-e Herisht is assigned to Upper Barremian-Middle Aptian, and in the Abanbar area is determined as Upper Barremian-Lower Aptian, at least the age of the Shahkuh Formation in the Chahpalang area is determined as Upper Barremian-Lower Aptian.