Paleoenvironmental Evaluation Using an Integrated Microfacies Evidence and Triangle Model Diagram: A Case Study from Khurmala Formation, Northeastern Iraq

The sequence of the Khurmala Formation located in northeastern Iraq was measured and sampled to evaluate its paleoenvironmental features, including sedimentological and microfacies analyses. The studied formation was analyzed under an optical microscope and was dominated by three main types of microfacies: coralligenous–algal wackestone, foraminiferal–peloidal packstone, and foraminiferal–peloidal grainstone. These hosted microfacies in the Khurmala Formation rarely contain a non-geniculate algae that insufficient for complete reef-building as a crest, but among the common algae, there are calcareous geniculate and green algae associated with benthic foraminifera and a minor component of planktonic foraminifera in the basin due to high-energetic open shallow-water environmental conditions during the deposition of the Khurmala Formation. The relative percentages of foraminifera, including both benthic and planktonic, plotted on triangular diagrams revealed a graphic indicator of paleoenvironment analyses. Detailed examination and analyses for microfacies, new findings of calcareous green algae (<i>Acicularia</i> and <i>Clypeina</i>), and microfacies analyses based on the triangle method and standard facies zones, denote that the upper part of the Khurmala Formation was richer in fined grain and <i>Acicularia</i> green algae, reflecting lower energy conditions than during deposition in the lower part of the formation, which was represented by algal wackestone microfacies and dominated by <i>Clypeina</i> green algae. In summary, these fluctuations in facies/microfacies changes, the appearance of new green algae, and different percentages of foraminiferal content are linked to the global sea level fluctuation that occurred during the Paleocene–Eocene interval.