Palaeonvironmental reconstructions of the Dalichai Formation at the Balu section, northern Semnan, based on palynomorphs

The Dalichai Formation at Balu section in Payambaran area, northern Semnan, was studied by using palynomorphs and organic matter contents in order to determine its Palaeonvironmental conditions. A total of 55 samples were collected and treated for palynological studies. The formation at this section consists mainly of shale, calcareous shale and limestone. Palynologically, productive samples contain spore, pollen grains, dinoflagellate cysts, foraminiferal linings, acritarchs, wood debris (plant tissue) and Amorphous Organic Matters (AOM). The high amount of the AOM indicates a shallow, low oxygen levels and relatively quiet environment. Based on palynofacies data, such as proportion of blade-shape to equal dimensional opaque palynomacerals, the percentage of AOM to marine palynomorphs was determined. This indicates deposition of Dalichai Formation in a shallow, low oxygenated condition with a slow rate of sedimentation. However, occurrence of marine elements testifies intermittent marine incursions. The sharp increases in abundance of chorate dinoflagellate cysts in two parts of the section indicate short-term marine incursions in these parts.