Latest Ordovician-early Silurian chitinozoans from the eastern Alborz Mountain Range, Kopet-Dagh region, northeastern Iran: biostratigraphy and palaeobiogeography

Chitinozoans were extracted from latest Ordovician to early Silurian strata in the Alborz Mountain Range, northeastern Iran; 24 species were identified and six local biozones established. Five new chitinozoan species are described: Ancyrochitina bqjnourdensis, AnciTochitinafatemae, Ancyrochitina longifilosa, Angochitina iranica, and Angoehitina multipodspina. Correlation with existing formal biozonations suggests that the uppermost part of the Ghelli Formation is of mid-Ashgill age and that Member I of the Niur Formation ranges from early Rhuddanian to late Telychian. The recovered chitinozoan fauna is dominated by species which are endemic to the study area. A significant proportion of taxa is shared with typical Baltican assemblages, suggesting palaeobiogeographical affinities between Iran and the Baltica palaeocontinent. Taxa shared with typical North Gondwanan assemblages are only a minor component of the Iranian chitinozoan fauna. The present results confirm previous observations that current appreciation of chitinozoan provincialism may be affected by sample-and (palaeo)geographic coverage biases, particularly for the Silurian. Similarly, the application of existing biostratigraphic schemes for the dating of the Iranian Silurian sediments proved problematical, confirrriing the need of incorporating more data from little known areas (such as Iran) in global databases. (c) 2006 Published by Elsevier B.V

Palynostratigraphy of Middle Cambrian to lowermost Ordovician stratal sequences in the High Zagros Mountains, southern Iran: Regional stratigraphic implications, and palaeobiogeographic significance

A palynological investigation of Cambro-Ordovician stratal sequences in the High Zagros Mountains of southern Iran permits the definition of a series of successive acritarch assemblage zones of chronostratigraphic significance, much improving the current knowledge of the Lower Palaeozoic stratigraphy of this important area for oil exploration. The five acritarch assemblage zones can be readily correlated with previously established palynostratigraphic schemes constrained by co-occurrence of independent age evidence, confirming the utility of organic-walled microfossils for the detailed biostratigraphic characterization of sedimentary units. The proposed biozonation will facilitate accurate dating of the southern Iranian Cambrian sequences during future drilling of deep test oil wells. Acritarch assemblage zone I (Middle Cambrian), occurs at the base of Member C of the Mila Formation; assemblages zone II (late Middle to earliest Late Cambrian) extends through the middle and upper part of the same lithostratigraphic unit; zone III (early Late Cambrian in age) characterizes the lower part of the Ilebeyk Formation; zone IV (middle Late Cambrian up to Cambrian/Ordovician transitional levels) occurs in the middle and upper part of the Ilebeyk Formation; finally, acritarch assemblage zone V ranges through the basal part of the Zardkuh Formation and proves an early Tremadocian age for the latter unit. The Mid-Late Cambrian acritarch associations show a marked Avalonian palaeobiogeographical affinity, also sharing a high proportion of taxa with typical Baltican and North Africa-Gondwanan assemblages; on the other hand, they are clearly different from known Laurentian (North America) fossil microphytoplankton suites. These results are in general agreement with current palaeogeographical models which place Avalonia, Baltica, and the North African part of Gondwana, all at relatively high southern palaeolatitudes, in contrast with the sub-equatorial position of Laurentia. However, the presence of many typical "Avalonian" taxa in the Iranian Mid-Late Cambrian assemblages would suggest a closer position of Iran to Avalonia than currently envisaged. The observed breakdown of acritarch biogeographic differentiation in earliest Ordovician times possibly represents a major disruption of oceanic current patterns and a lessened palace latitudinal thermal gradient. (c) 2008 Elsevier B.V. All rights reserved

Palynology and isotope geochronology of the Upper Ordovician-Silurian successions (Ghelli and Soltan Maidan Formations) in the Khoshyeilagh area, eastern Alborz Range, northern Iran; stratigraphic and palaeogeographic implications

Surface samples from the Ghelli and Soltan Maidan Formations in the Khoshyeilagh area of the eastern Alborz Range, northern Iran, were analyzed to determine the age and the stratigraphic relationship of these two units. The samples contained rich palynomorph assemblages, dominated by acritarchs (36 species recognized, distributed among 28 genera) and chitinozoans (nine species identified, distributed among seven genera). Cryptospores and scolecodonts as well as a few graptolite remains were also observed, although not studied in detail. Based on the restricted stratigraphic range of chitinozoan and acritarch species, a Late Ordovician (late Katian-Hirnantian) age is assigned to the Ghelli Formation. Palynological samples from the Soltan Maidan Formation yielded acritarch assemblages characterized by species commonly found in Upper Ordovician sediments together with typical middle Silurian forms. Considering reworking of the Upper Ordovician species, the age of the investigated part of the Soltan Maidan Formation is not younger than Gorstian (early Ludlow, early late Silurian). U-Pb zircon ages of 434.4 +/- 6.4 Ma (Telychian, late Llandovery, late early Silurian) obtained for granitic clasts collected at the base of the Soltan Maidan Formation, are consistent with the inferred palynological age and indicate that granite emplacement, cooling, exhumation, erosion, transportation and deposition of its clasts took place in a time interval estimated to be 5 to 10 million year long. Based on the presence of diagnostic chitinozoan taxa, the Ghelli Formation can be assigned to the Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones. Chitinozoan assemblages reflect a clear palaeobiogeographic affinity with the previously defined 'North Gondwana Domain'. The composition of acritarch assemblages also appears to be consistent with newly proposed hypotheses of a Late Ordovician phytoplanktonic biogeographical differentiation between a Laurentian/Baltica realm, and a Gondwanan realm to which the present assemblages belong. The presence of cryptospores together with taxonomically diverse chitinozoan, acritarch, and scolecodont assemblages, suggest a relatively shallow marine, platformal depositional environment for the Ghelli Formation. (C) 2011 Elsevier B.V. All rights reserved

Late Ordovician (Katian) spores in Sweden: oldest land plant remains from Baltica

A palynological study of the Ordovician–Silurian boundary (Katian–Rhuddanian) succession in the Röstaånga-1 drillcore, southern Sweden, has been performed. The lithology is dominated by mudstone and graptolitic shale, with subordinate limestone, formed in the deeper marine halo of southernBaltica. The palynological assemblages are dominated by marine microfossils, mainly chitinozoans and acritarchs. Sparse but well-preserved cryptospores, including Tetrahedraletes medinensis, Tetrahedraletes grayii and Pseudodyadospora sp., were encountered in the Lindegård Formation (late Katian–early Hirnantian), with the oldest record just above the first appearance of the graptolite species Dicellograptus complanatus. This represents the earliest record of early land plant spores from Sweden and possibly also from Baltica and implies that land plants had migrated to the palaeocontinent Baltica by at least the Late Ordovician

Burial History Reconstruction and Thermal Modelling at Kuh-E Mond, SW Iran.

At the Kuh-e Mond anticline (Fars Province, SW Iran) and in nearby offshore structures,large volumes of natural gas are reservoired in the Permian ? Early Triassic DehramGroup while heavy oil has been discovered in the Cretaceous Sarvak and Eocene JahrumFormations. In this paper, we use data from six exploration wells and from nearby surfaceexposures to reconstruct the burial history at Kuh-e Mond. Regional observations showthat the thick sedimentary fill in this part of the Zagros Basin was subjected to intensetectonism during the Zagros Orogeny, with a paroxysmal phase during the late Mioceneand Pliocene. Thermal modelling and geochemical data from Kuh-e Mond and adjacentfields allows possible hydrocarbon generation and migration mechanisms to be identified.Maturities predicted using Lopatin?s TTI model are in accordance with maturities obtainedfrom vitrinite reflectance measurements.We show that formations which have source potential in the nearby Dezful Embayment(including the Pabdeh, Gurpi, Gadvan and Kazhdumi Formations) have not reached theoil window in the Mond wells. Moreover, their organic carbon content is very low as theywere deposited in oxic, shallow-water settings. Underlying units (including the Ordovicianand Cambrian) could have reached the gas window but contain little organic matter.Silurian shales (Sarchahan Formation), which generate gas at Kuh-e Gahkum andKuh-e Faraghan (north of Bandar Abbas) and in Saudi Arabia and elsewhere in theMiddle East, are absent from the Mond structure.The absence of source rocks suggests that the gas and heavy oil accumulations at Kuh-eMond and at nearby fields have most probably undergone long-distance lateral migrationfrom distant source kitchens