Middle Jurassic biostratigraphy of plant macro and microfossils in Soltanieh Mountains, south of Zanjan, NW Iran

Abstract

Jurassic deposits a section in south of Zanjan contain various taxa of macro and microfloras. Six plant macrofossil species belonging to five genera of various orders such as Equisetales, Cycadales, Bennettitales, and Pinales (Coniferales) are identified. This section contains seventeen species of palynomorphs in which six spore species allocated to six genera, eight pollen species allocated to five genera, and three dinocyst species allocated to two genera are present. Based on the occurrence of Index fossils such as <em>Ptilophyllum harrisianum, Nilssonia</em> sp. cf. <em>N. bozorga</em>, and <em>Equisetites </em>sp. cf.<em> E. beanii</em>, an early Middle Jurassic (Aalenian-Bajocian) age suggested for these sediments. Therefore, these deposits considered to belong to the Dansirit Formation. Moreover, based on the stratigraphic distribution of index fossils of plant macrofossils, miospores, and dinocysts, three assemblage biozones recognized. These biozones are <em>Nilssonia</em> sp. cf. <em>N. bozorga-Ptilophyllum harrisianum, Klukisporites variegatus-Cycadopites crassimarginis</em>,and <em>Pareodinia ceratophora-Nannoceratopsis triceras </em>Assemblage Zone, respectively. All these biozones are comparable to the other Known Iranian biozones. Therefore, it is concluded that uniform environmental conditions are dominant through North, Central, and East Central of Iran during this interval. Furthermore, because of the occurrence of dinoflagellates, this area was located at the margin of Tethys Ocean.