Facies analysis of the Asmari Formation in central and north-central Zagros basin, southwest Iran: Biostratigraphy, paleoecology and diagenesis

Abstract

Three sections of the Oligocene-Miocene Asmari Formation, crossing central and north-central Zagros foreland basin in SW Iran, were measured and studied in order to interpret the biostratigraphy, paleoecology (based on distribution of benthic foraminifera) and diagenesis. Forty-three foraminifer genera and species were encountered in the studied areas and the following assemblage zones have been defined: 1) Nummulites vascus-Nummulites fichteli, 2) Lepidocyclina-Operculina-Ditrupa, 3) Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus, 4) Miogypsina-Elphidium sp. 14 - Peneroplis farsenensis, and 5) Borelis melo curdica-Borelis melo melo. According to this study, deposition of the Asmari Formation with association of hyaline, lamellar, perforate large and flat foraminifera first started in the basin and slope environments during the Rupelian in Dehdez and Tufe-Sefid areas. Lagoon depositional environment colonized by sea-grass epiphytic foraminifera was encountered during Chattian and Aquitanian in Bagh-e Malek and Dehdez areas and mostly lagoon and slope environments prevailed during Burdigalian in Bagh-e Malek and Dehdez areas, respectively. The main diagenetic processes that affected the Asmari Formation were dolomitization (replacement and cementation), compaction (stylolitization) and dissolution. The extent of these diagenetic overprinting seems to be mainly facies controlled.