عنوان مقاله [English]
Diverse and reasonably well preserved palynofloras including 148 species, dominated by microphytoplankton cysts (acritarchs and prasinophyte phycomata) and spore assemblages, occur in most of surface samples of the Geirud Formation at the Dehmolla section; scolecodonts and chitinozoans are also represented as subordinate components. Co-occurrence of marine and terrestrial palynomorphs clearly indicates deposition in a marginal marine setting. Vertical distribution pattern of spores permits erection of two local assemblage zones in the material studied (here informally termed assemblage zones I and II). Occurrence in assemblage zone I of such distinctive spores as Grandispora inculta, Cymbosporites catillus, Geminospora lemurata, Teichertospora iberica, Laevigatosporites ovatus, Densosporites spitsbergensis, Punctatisporites labiatus, Retusotriletes rugulatus, R. pychovii, R. dubiosus, Dictyotriletes australis, Diducites mucronatus, Archaeoperisaccus sp., Stenozonotriletes conformis, and Ancyrospora ancyrea collectively denotes an early Late Devonian (Frasnian) age; the assemblage appears to be compatible with the ovalis-bulliferus and parts of the optivus-triangulatus and torquata-gracilis Assembalge Zones of the Old Red Sandstone Continent (ORSC). The succeeding assemblage II embracing Retispora lepidophyta, Vallatisporites hystricosus, V. vallatus, Verruciretusispora loboziakii, Punctatisporites planus, Densosporites rarispinosus, and Grandisporafacilis correlates with the pusillites-lepidophyta, flexuosa-cornuta, and torquata-gracilis (partial) Assemblage Zones of the ORSC and is ascribed to late Late Devonian (Famennian). Additionally, a barren interval (20 m thick) devoid of any palynomorphs can also be identified in the basal, mostly red conglomerates and coarse-grained sandstones of the section studied. Co-occurrence of spore assemblages with such globally index microphytoplankton cysts as Cymatiosphaera perimembrana, Daillydium pentaster, Unellium lunatum, U. piriforme, Chomotriletes vedugensis, Crassiangulina sp. cf. C. tesselita corroborates the Late Devonian (Frasnian-Famennian) age assignment which is in general agreement with the faunal evidence. Affinity, diversity, and abundance of spores in the palynofloras investigated imply that contemporaneous coastal vegetation was probably diverse and likely dominated by lycopsids, filicopsids, and archaeopterid progymnosperms.