Paleoecological reconstruction by subsurface faunal assemblages of the quaternary deposits in lower Mesopotamia, southern Iraq

Khor Abdullah is a strategically important marine area located between Iraq and Kuwait. Reconstructing the region's paleoenvironments and coastal evolution during the Quaternary period relies heavily on sea-level fluctuations, climatic conditions and neotectonics. This study examined two subbottom sediment cores (Cores 4 and 8), which were recovered from a depth of 40 m within the Grand Al-Faw Port region. Four primary faunal groups were identified foraminifera, ostracoda, mollusca and bryozoa—alongside notable sterile intervals lacking microfauna at multiple core depths. Benthic foraminifera were represented by six species, with the family Milliolidae dominating Core 4, which indicates turbid environments across supratidal, intertidal, and subtidal zones. Twelve ostracod species were identified, mostly corresponding to freshwater habitats. Furthermore, ten pelecypod and five gastropod species were documented, reflecting turbid and lagoonal environments. Bryozoa, meanwhile, occurred sporadically with low diversity. A distinct marine horizon at a depth of 28–30 m in Core 4 marks an Early Holocene marine transgression, which is interlayered with marsh deposits and evidence of subsequent marine regression. Textural analysis revealed that the core sediments predominantly consist of silt, muddy sand and sandy silt. According to the hydrodynamic conditions diagram, most sediment samples fall within the quietest environment. This explains the absence of fauna at most depths, as the soil texture at these depths is unsuitable for habitation by fauna.