Palynomorphs - based palaeoecological implications of the Shemshak Formation, at the Khoshyeilagh section, northeastern Shahrud

Palaeoecology of the Shemshak Formation (Rhaetian–Middle Jurassic) at the Khoshyeilagh section north of Ghoznavi Village was studied by using palynomorphs and organic matter contents. This section with a thickness of 1280m consists of shale, sandatone and coal layers. A total of 67 samples contain diverse and well-preserved palynomorphs such as spores, pollen grains, opaque and transparent AOM, opaque phytoclasts, phytoplankton (dinofelagellate cysts), woody debris (plant tissue) were collected. Seventy three species of spores (47 genera) and 17 species of pollen (12 genera) are identified. Inferred natural relationships of the miospores imply derivation from a diverse parental flora of Filicopsida, Bryopsida, Lycopsida, Coniferopsida, Cycadopsida and Sphenopsida growing under warm humid conditions during the Rhaetian – Middle Jurassic. The abundance of Ricciisporites tuberculatus testifies a wet and moist condition when the Shemshak Formation was deposited. The high abundance of equi-dimensional and sorted phytoclasts (up to %98) accompanied with well-preserved terrestrial palynomorphs (spore and pollen) indicates accumulation in a moderate or high level of energy with an aerobic deltaic condition. However, occurrence of rare marine palynomorphs testifies intermittent marine incursions.