Biostratigraphy of the Upper Devonian Khoshyeilagh Formation in NE Iran based on conodonts and other faunas

The Khoshyeilagh Formation located in the northeast of Iran yielded seven conodont species and sub-species and 19 macro- and microfossil taxa that allow recognition of two conodont biozones and one biozone based on calcareous microfossils. The latest Frasnian age (the Upper rhenana to linguiformis zones) is attributed to the topmost strata with Icriodus alternatus. Its replacement with I. cornutus indicates the Famennian (Lower triangularis to Lower crepida zones) corresponding to the Umbellina Zone. The fossil assemblages identified in the Khoshyeilagh Formation represent a shallow marine environment with a tropical climate at the time of deposition. The fossil species from the Khoshyeilagh Formation and the sedimentary basins in Algeria, Libya, Morocco, Poland, and Russia reveal a close connection between the Iranian plateau and the northern parts of Gondwana in the Late Devonian. The biofacies and lithofacies analyses show a sea level decline at the end of Frasnian, followed by a considerable sea level drop, as in other regions of the world. After a short time, in the Famennian, the deepening occurred in some parts of the area and the open marine facies (bioclast spicule wackestone-packstone) were deposited. This study is the first attempt to determine Frasnian-Famennian boundary based on conodont assemblages and other fossil species such as umbellulids, tentaculites, and ostracods. The distribution of these species is interpreted in sedimentological, stratigraphic, sequence stratigraphy, and the global eustatic context. Keywords: biofacies, conodont, Frasnian-Famennian boundary, Late Devonian, NE Iran. RESUMO – A Formacao Khoshyeilagh, localizada no nordeste do Ira, produziu sete especies de conodontes e subespecies e 19 taxons de macro- e microfosseis, o que permite o reconhecimento de duas biozonas de conodontes e uma biozona baseada nos microfosseis calcareos. A idade Frasniana mais superior (as zonas superiores rhenana a linguiformis) e atribuida ao estrato mais superior com Icriodus alternatus. A sua substituicao por I. cornutus indica o Famenniano (zonas iniciais triangularis superior a crepida superior), correspondendo a Zona de Umbellina. Os fosseis identificados na Formacao Khoshyeilagh representam um ambiente marinho raso, com um clima tropical, no momento de deposicao. As especies fosseis da Formacao Khoshyeilagh e as bacias sedimentares na Argelia, Libia, Marrocos, Polonia e Russia revelam uma conexao intima entre o plato iraniano e as partes norte do Gondwana no Neodevoniano. As biofacies e litofacies analisadas mostram um declinio do nivel do mar no final do Frasniano, seguido por uma consideravel queda do nivel do mar, como em outras regioes do mundo. Apos um curto tempo, no Famenniano, o aprofundamento ocorreu em algumas partes da area, e a facies marinha aberta (bioclast spicule wackestone-packstone) foi depositada. Este estudo e a primeira tentativa de determinar o limite Frasniano-Famenniano com base em associacoes de conodontes e outras especies fosseis, como umbellulideos, tentaculites e ostracodes. A distribuicao dessas especies e interpretada nos contextos sedimentologico, estratigrafico, de estratigrafia de sequencias e de eustasia global. Palavras-chave: biofacies, conodonte, limite Frasniano-Famenniano, Neodevoniano, NE Ira.