Foramniferal morphogroups of the Qom Formation in the Natanz and Qom regions: implication for paleoenvironmental and paleoecological interpretations

Morphogroup analysis, due to independence of species level taxonomy, as wel as permit to comparison of assemblages of differing ages, is a useful tool for ecological and palaeoecological interpretation. Foramniferal study of the Qom Formation in the Natanz (with Rupelin-Chattian?-Aquitanian in age and 330 m thickness) and Khorabad (southeastern Qom; with Rupelin-Burdigalian in age and 260 m thickness) sections resulted in identification of 8 morphogroups. The morphogroups were distinguished according to test/shell morphology and architecture (general shape, mode of coiling, and arrangement and number of chambers), inferred life habitat either living on the surface of the sediments or within the sediments (epifaunal and infaunal), and feeding strategy. Generaly, epifaunal morphogroups were dominated in both study sections. The lower 200 m of the Natanz section, are dominated by calcareous porcelaneous morphogroups; while the upper layers are dominated by hyaline morphogroups, which indicates the lower and upper parts were deposited in inner ramp (lagoonal environments) and open sea, respectively. This significant change through time reffers to gradual increasing of the basin depth, decreasing the light intensity, reducing the salinity and decreacing the nutrient level. The distribution of morphogroups in the Khorabad section follows a reverse pattern; so that, despite the minor fluctuations, the lower 200 m of the Khorabad section, are dominated by hyaline morphogroups; while the upper layers are dominated by porcelaneous morphogroups, which indicates the lower and upper parts were deposited in open sea and inner ramp (lagoonal environments), respectively.