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Abstract
Palynomorphs are used for palynostratigraphy, and to derive paleoecological and paleobiogeographical inferences from the Middle Jurassic Shemshak Formation, Alborz Ranges, northwestern Iran. The rock unit contains diverse, reasonably preserved palynofloras dominated by miospores and dinoflagellate cysts. Vertical distribution of miospores allows for the introduction of Klukisporites variegatus -Striatella spp.- Contignisporites burgeri assemblage zone in the host strata. The presence of such key miospore species as Striatella jurassica, S. patenii, S. seebergensis, and Contignisporites burgeri indicates a Middle Jurassic (late Bajocian–Bathonian) age. Based on the stratigraphic distribution of dinoflagellate cysts, encountered Cribroperidinium crispum Total Range Biozone (late Bajocian); Dichadogonyaulax sellwoodii Interval Biozone (Bathonian–early Callovian), and Subzone “a” of the D. sellwoodii Zone (early–middle Bathonian) are identified. Miospores dominating the examined assemblages are assigned, in ascending order of abundance, to Pterophyta, Coniferophyta, Pteridospermophyta, Lycophyta, Ginkgophyta, Cycadophyta, and Sphenophyta. Such parental vegetation apparently flourished under a wet, warm-to-warm-temperate climate. The co-occurrence of such index warm-moderate water dinoflagellate cysts as Pareodinia halosa, Ctenidodinium continuum, and Pareodinia ceratophora supports this overview. The assemblages though contain both Eurasian and Gondwanan elements but bear closer similarity to those from the former, thus suggesting paleoproximity to the northeastern margin of the Neotethys Ocean during the Middle Jurassic.
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