Tournaisian (Mississippian) brachiopods from the Mobarak Formation, North Iran

Following detailed stratigraphic work on the Mississippian marlstone and bioclastic limestone of the Mobarak Formation of the Alborz Mountains in North Iran, forty-eight of the most important brachiopod taxa are here systematically described and illustrated. The ranges of the taxa are given along the Abrendan and Simeh Kuh stratigraphic sections, located north of Damgham. The examined brachiopod species date the base of the Mobarak Formation to the Tournaisian, in absence of age-diagnostic foraminifers. Change in brachiopod settling preferences indicates a shift from high energy, shallow-water settings with high nutrient supply in the lower part of the formation to quieter, soft, but not soppy substrates, with lower nutrient supply in the middle part of the Mobarak Formation. Brachiopod occurrence is instead scanty at its top. The palaeobiogeographic affinity of the Tournaisian brachiopods from North Iran indicates a closer relationship to North America, Western Europe and the Russian Platform than to cold-water Australian faunas, confirming the affinity of the other biota of the Alborz Mountains. This can be explained by the occurrence of warm surface-current gyres widely distributing brachiopod larvae across the Palaeotethys Ocean, where North Iran as other peri-Gondwanan blocks acted as staging-posts

Early Jurassic (latest Toarcian) brachiopods from the northeastern margin of the Western Tethys (Central Iran) and their paleobiogeographical significance

Brachiopod fauna from central Iran, recorded in the upper part of the Shemshak Group and attributed to the upper Toarcian (Pseudoradiosa-Aalensis zones), are reported for the first time in Iran. The assemblage recognized includes six different taxa: Homoeorhynchia sepahanensis nov. sp., formally described in this paper, Globirhynchia subobsoleta, Pseudogibbirhynchia sp., Tetrarhynchiidae sp. indet., Monsardithyris? aff. haresfieldensis, and Zeilleria cf. leckenbyi. Analysis of faunal affinities with other paleobiogeographical regions shows a free connection the central Iranian brachiopod fauna with wide areas of the northern shelf margin of the Tethys Ocean. This is due to an apparent disruption of bioprovinciality inferred for the late Toarcian-earliest Aalenian, congruent with a connection through the northern seaway across the peri-Laurasian epicontinental platforms.The present research is partially supported by Research Group VIGROB-167 (University of Alicante)

NANNOFOSSIL EVENTS AND STRATIGRAPHY OF THE ILAM FORMATION IN ZAGROS (SW IRAN)

Exploration studies of Cretaceous system in the Zagros region are very important due to the presence large hydrocarbon fields like the Ab-Teymur oilfield. The first data on the distribution of calcareous nannofossils in the Ilam Formation, belonging to the Bangestan Group in the Zagros Basin, are presented here. According to the distribution of calcareous nannofossils, the Upper Cretaceous deposits of the section are subdivided into three complete biostratigraphic units, namely: the Micula decussata (CC14-Late Coniacian), Reinhardtites anthophorus (CC15-late Early Santonian), Lucianorhabdus cayeuxii (CC16-Late Santonian) and base of CC17 zones. This record confirms the existence of biozone CC14 to basal CC17 of the zonation of Sissingh (1977), which suggests an age from Late Coniacian to Late Santonian for the studied sediments. Besides biostratigraphy, the presence of abundant calcareous nannofossils typical of warm climate and low latitude conditions in Ab-Teymur oilfield allows paleoenvironmental interpretations

Refinements in biostratigraphy, chronostratigraphy, and paleogeography of the Mississippian (Lower Carboniferous) Mobarak Formation, Alborz Mountains, Iran

ABSTRACT Detailed sampling of limestones from the Mobarak Formation at the Abrendan and Abnak measured sections in the eastern and central Alborz Mountains, northern Iran, yielded a diverse assemblage of Tournaisian – Lower Visean (Mississippian/Lower Carboniferous) calcareous microfossils (foraminifers, algae, incertae sedis). The Abrendan locality contains Tournaisian foraminifers in the upper part of the formation that correlate to the Ivorian and upper Courceyan – lower Chadian substages of western Europe and the Kosvinsky Horizon of the Russian Platform. Brachiopods confirm a Tournaisian age for the lower part of the Mobarak, which lacks age-diagnostic calcareous microfossils. Lower Visean foraminifers at Abnak provide good correlation to the western European Moliniacian and Arundian substages and the Russian Bobrikovsky Horizon. Synthesis of foraminiferal data from this and other published reports indicates that the top of the Mobarak Formation becomes increasingly older across the Alborz to the southeast, caused most likely by Pennsylvanian (Upper Carboniferous) exposure and erosion in the south followed by a latest Pennsylvanian – Early Permian transgression from the north. The microbiota at both sections and the macrofossils at Abrendan show close affinity to the warm-water Paleo-Tethyan Ocean, seemingly contradicting Early Mississippian paleomagnetic reconstructions placing the Alborz region at 45–50° South latitude. The discrepancy is not resolvable at this time, but the answer may lie in the circulation of Paleo-Tethyan currents to the south along the Gondwanan shelf, rather than to repositioning the Alborz region to the northern side of the Paleo-Tethyan Ocean.</jats:p

Refinements in biostratigraphy, chronostratigraphy, and paleogeography of the Mississippian (Lower Carboniferous) Mobarak Formation, Alborz Mountains, Iran

Detailed sampling of limestones from the Mobarak Formation at the Abrendan and Abnak measured sections in the eastern and central Alborz Mountains, northern Iran, yielded a diverse assemblage of Tournaisian - Lower Visean (Mississippian/ Lower Carboniferous) calcareous microfossils (foraminifers, algae, incertae sedis). The Abrendan locality contains Tournaisian foraminifers in the upper part of the formation that correlate to the Ivorian and upper Courceyan - lower Chadian substages of western Europe and the Kosvinsky Horizon of the Russian Platform. Brachiopods confirm a Tournaisian age for the lower part of the Mobarak, which lacks age-diagnostic calcareous microfossils. Lower Visean foraminifers at Abnak provide good correlation to the western European Moliniacian and Arundian substages and the Russian Bobrikovsky Horizon. Synthesis of foraminiferal data from this and other published reports indicates that the top of the Mobarak Formation becomes increasingly older across the Alborz to the southeast, caused most likely by Pennsylvanian (Upper Carboniferous) exposure and erosion in the south followed by a latest Pennsylvanian - Early Permian transgression from the north. The microbiota at both sections and the macrofossils at Abrendan show close affinity to the warm-water Paleo-Tethyan Ocean, seemingly contradicting Early Mississippian paleomagnetic reconstructions placing the Alborz region at 45-50\ub0 South latitude. The discrepancy is not resolvable at this time, but the answer may lie in the circulation of Paleo-Tethyan currents to the south along the Gondwanan shelf, rather than to repositioning the Alborz region to the northern side of the Paleo-Tethyan Ocean

Tournaisian (Mississippian) brachiopods from the Mobarak Formation, North Iran

ABSTRACTFollowing detailed stratigraphic work on the Mississippian marlstone and bioclastic limestone of the Mobarak Formation of the Alborz Mountains in North Iran, forty-eight of the most important brachiopod taxa are here systematically described and illustrated. The ranges of the taxa are given along the Abrendan and Simeh Kuh stratigraphic sections, located north of Damgham. The examined brachiopod species date the base of the Mobarak Formation to the Tournaisian, in absence of age-diagnostic foraminifers. Change in brachiopod settling preferences indicates a shift from high energy, shallow-water settings with high nutrient supply in the lower part of the formation to quieter, soft, but not soppy substrates, with lower nutrient supply in the middle part of the Mobarak Formation. Brachiopod occurrence is instead scanty at its top. The palaeobiogeographic affinity of the Tournaisian brachiopods from North Iran indicates a closer relationship to North America, Western Europe and the Russian Platform than to cold-water Australian faunas, confirming the affinity of the other biota of the Alborz Mountains. This can be explained by the occurrence of warm surface-current gyres widely distributing brachiopod larvae across the Palaeotethys Ocean, where North Iran as other peri-Gondwanan blocks acted as staging-posts.</jats:p

Additional brachiopod findings from the Lopingian succession of the Ali Bashi Mountains, NW Iran

Aim of this note is to describe additional Endings of Lopingian brachiopods along the Main Valley section and at Localities 1, 3, and 4 of the Ali Bashi Mountains, NW Iran. Here we provide: 1) taxonomic descriptions of two newly recorded taxa, one of which is a new species, Meekella julfensis n. sp.; 2) more information on the stratigraphic range of brachiopods from the Ali Bashi Mountains, which show a greater abundance and diversity in the upper part of the Julfa Formation, in the Ali Bashi Formation, and in the Boundary Clay. The newly collected faunas are characterized by miniaturization which is considered to be a response to deep water conditions in well oxygenated, but trophic resource-limited settings, and not a Lilliput-effect related to the end-Permian crisis; 3) a discussion on the phylogenetic relationships between Araxathyris and Transcaucasathyris, proposing that the former may have evolved from the latter by the convergence of the dental plates to form a spondylium, that was probably a structure that functioned to optimize the muscle length in response to greater shell volumes