MICROFACIES, SYSTEMATIC DESCRIPTION, TAXONOMY AND DEPOSITIONAL ENVIRONMENTS OF THE AZKAND FORMATION (LATE OLIGOCENE – EARLY MIOCENE) IN THE KIRKUK AREA OF THE ZAGROS BASIN, NORTHEASTERN IRAQ

DOI:10.5281/zenodo.18061281

Abstract

Backgrounds:The Azkand Formation represents an important carbonate succession whose age, depositional environments, and platform evolution remain critical for regional paleogeographic reconstruction. This study provides a systematic micropaleontological and sedimentological investigation to refine its stratigraphic framework and environmental interpretation.

Methods: The Azkand Formation was systematically described and taxonomically classified at two key reference sections: the Khabaz Well-3 subsurface section and the Qara Chaugh Dagh surface outcrop. A total of fifty subsurface samples from Khabaz Well-3 and twenty-six surface samples from Qara Chaugh Dagh were analyzed using micropaleontological identification and detailed microfacies analysis to establish a robust depositional and chronological framework.

Results: The formation is characterized by high diversity and abundance of larger benthic foraminifera, including Lepidocyclina, Amphistegina, Pararotalia, Neorotalia, Nummulitidae, Miogypsina, Miogypsinoides, Valvulina, Textularia, Operculina, Rotalia, Nephrolepidina, and various encrusting forms. These assemblages constrain the age of the Azkand Formation to the Late Oligocene–Early Miocene interval. Microfacies analysis identified four distinct facies types: (1) fine bioclastic packstone dominated by small benthic foraminifera; (2) fine to very coarse bioclastic packstone rich in larger benthic foraminifera; (3) very fine to coarse larger foraminiferal packstone to grainstone; and (4) fine to very coarse bioclastic packstone to boundstone with coral and encrusting organisms. These facies indicate deposition within an isolated carbonate platform and slope system, ranging from deeper slope-toe environments to shallow sublittoral settings. Vertical and lateral facies variations reflect persistent open-marine conditions, moderate energy regimes, and episodic bioclastic reworking.

Conclusions: Integrated micropaleontological and sedimentological data demonstrate that the Azkand Formation represents a well-developed Oligo–Miocene carbonate platform system. The stratigraphic record provides valuable insights into regional paleogeographic evolution and improves understanding of carbonate platform Top of Form Bottom of Form

Keywords : Azkand Formation, Oligocene-Miocene, Benthic foraminifera, Microfacies, Paleoenvironments, Iraq