Plant Communities and Ecostratigraphy of the Lower and Middle Jurassic of Northern Iran

Abstract

The Early and Middle Jurassic plant communities of northern Iran were studied. It was observed that they both bore strong similarities. Communities with arthrophyte dominance were located in lowlands. The arborescent layer of the upper parts of the slopes and near-valley surfaces (flat interfluve?) was represented by Pityophyllum; the arborescent layer of the humid lower parts of the slopes was represented by Podozamites. Only communities of herbaceous cover differed considerably. Marattia intermedia and ?Pseudotorellia were common for the Early and Middle Jurassic. Czekanowskia ex gr. rigida, Cladophlebis denticulata, and Nilssonia obtusa, which dominated and codominated in the Early Jurassic, were replaced by N. vittaeformis, N. simplex, and Ptilophyllum pectin in the Middle Jurassic. High occurrence of the slope arborescent layer communities (in the Early Jurassic especially) suggests a prominent ruggedness of relief of near-basin parts of the land. Low occurrence of lowland herbaceous cover (especially in the Middle Jurassic) indicates underdevelopment of the valleys. The small number of stable dominants suggests that floras of the Early and Middle Jurassic of northern Iran belong to two ecoseries: Pityophyllum longifolium–Phymatoceras and Pityophyllum longifolium–Ludwigia (Ludwigella) rudis. The size of each of them is the same as a series of the general scale. The ecoseries are characterized.