Nannostratigraphy and palaeoecology of uppermost Mozduran Formation in the Kopeh-Dagh range (NE Iran)

The Mozduran Formation includes light-coloured, thick-bedded to massive limestone and porous dolomitic limestone and dolomite. In this study, 13 samples from the uppermost Mozduran Formation were taken from two localities and examined for calcareous nannofossils. A total of 19 species and 12 genera were identified in the Mozduran section and19 species and 13 genera for the Taherabad section. Based on these assemblages, the uppermost Mozduran Formation is assignable to Sissingh's (1977) biozone CC1 (Early Berriasian) at the Mozduran section and to biozone CC3 (Late Valanginian) at the Taherabad section. Thus, the formation is younger from east to west across the basin.     

A new amber deposit from the Cretaceous (uppermost Albian-lowermost Cenomanian) of southwestern France

A Cretaceous amber deposit has recently been discovered in a quarry of Charente-Maritime (southwestern France), at Cadeuil. This paper presents the sedimentary and palaeoenvironmental settings of the uppermost Albian-lowermost Cenomanian series including the amber deposit. A preliminary analysis of the amber samples reveals diverse fossil arthropods (a few mites and at least 20 insect families within 9 orders), as well as numerous micro-organisms, mainly algae and mycelia. A myceloid colony of bacteria, a flagellate algae and four especially well preserved insects are illustrated (Diptera Dolichopodidae, Diptera Chironomidae, Hymenoptera Parasitica, and Heteroptera Tingidae). The abundance of the limnic micro-organisms is discussed in terms of bloom events. Their relative scarcity in almost all the amber pieces containing fossil arthropods is attributed to differences in the origin of resin: production along trunk and branches for amber with arthropods; production by aquatic roots for amber rich in algae. The absence of pollen and spores in amber is attributed to differences in the respective periods of resin and palynomorph production, which may be related to a seasonal climate during the Albian-Cenomanian transition in Western Europe.     

The fossil record (calcareous nannofossils and foraminifers) in single intervals of the Upper Cretaceous flysch sequence of the West Carpathians, Czechoslovakia

Studies of calcareous nannofossils and microfossils and their distribution in different intervals of the flysch rhythms in the Kloko ník brook in the Bílé Karpaty Unit of the Magura Group of nappes in the West Carpathians gave the following results. The highest species diversity of calcareous nannofossils was found in the lower parts of the Bouma Te hemipelagic intervals. The Campanian marker species Ceratolithoides aculeus and Aspidolithus parcus were found in practically all layers studied. A stratigraphically important foraminiferal fauna was obtained from the upper parts of the Bouma Te intervals, including the Campanian-Maastrichtian planktic foraminifers Globotruncana arca and Globotruncanita stuartiformis. In the non-calcareous pelagites, agglutinated species with a range from the Late Cretaceous to the Paleogene dominate.     

Calcareous nannofossil biostratigraphy of Campanian strata (Abtalkh Formation) from the eastern Koppeh-Dagh Basin,NE Iran

The Campanian of the eastern Koppeh-Dagh Basin (NE Iran) is generally considered to be represented by the upper part of the Abderaz and the Abtalkh formations. The Abtalkh Formation, which is studied here, reaches thicknesses of up to 1750 m in the area. The formation is characterized by abundant, diverse, and poor to moderately well preserved calcareous nannofossil assemblages of Tethyan affinity. The assemblages were studied in detail in two sections in eastern Koppeh-Dagh, allowing construction of a precise biozonation for this stage. The Abtalkh Formation at sections in Abtalkh village and Padeha spans biozones CC20 to CC23a (UC15b^TP to UC16). The results of this study indicate a late early to late Campanian age for the formation in the area. The most complete Campanian sequence is in the southeast, where the Padeha section is located. Nannofossil abundance and diversity decreases upwards, showing a trend from the base to top of the formation. Dominance of warm water taxa, and low abundance of high latitude taxa, confirm placement of the basin in low to mid palaeolatitudes during deposition of the formation.     

钙质超微化石在第四纪年代地层学中的应用

钙质超微化石是海洋沉积中最重要的微体化石之一,一直是海相地层划分与对比、进行年代地层学研究的重要手段,在第四纪地层及其年代学研究中发挥着重要作用。第四纪钙质超微化石记录中共存在10个主要生物事件和10个次要生物事件,据此可划分为6个化石带和7个亚带。通过与有孔虫稳定氧同位素地层学与磁性地层学对比,可以获得每个钙质超微化石生物事件的绝对年龄,从而提高生物地层学的年代分辨率。除了生物事件外,钙质超微化石定量分析也可为年代地层学的建立提供依据,如全新世的Emiliania huxleyi高峰带和晚更新世中布容期的Gephyrocapsa caribbeanica高峰带,等等。钙质超微化石的稳定同位素与有孔虫稳定同位素一样,可用来进行地层划分与对比,还可以用于古海洋、古气候研究。

     

藏南江孜地区早白垩世甲不拉组钙质超微化石的特征及其地层意义

藏南江孜一带的侏罗纪—白垩纪海相地层被划分为维美组和甲不拉组。通过偏光显微镜和扫描电镜观察和分析,发现甲不拉组黑色页岩中含有保存较为完好的钙质超微化石。研究区的生物丰度和分异度偏低,经鉴定以椭圆球石科(Ellip-sagelosphaeraceae)生物群为主,数量相对丰富,但属种比较单调。超微化石指示甲不拉组为早白垩世沉积的产物。结合菊石和双壳类化石,认为甲不拉组地层时代属于早白垩世贝利阿斯期至凡兰吟期(Berriasian-Valanginian)。这一发现标志着西藏特提斯东部早白垩世地层中钙质超微化石的存在。甲不拉组早白垩世钙质超微化石的发现,为该地区海相地层的时代划分、对比提供了新的资料,也为寻找海相侏罗纪—白垩纪地层界线指示了目标。     

藏南江孜地区早白垩世甲不拉组钙质超微化石的特征及其地层意义

藏南江孜一带的侏罗纪—白垩纪海相地层被划分为维美组和甲不拉组。通过偏光显微镜和扫描电镜观察和分析,发现甲不拉组黑色页岩中含有保存较为完好的钙质超微化石。研究区的生物丰度和分异度偏低,经鉴定以椭圆球石科（Ellip-sagelosphaeraceae）生物群为主,数量相对丰富,但属种比较单调。超微化石指示甲不拉组为早白垩世沉积的产物。结合菊石和双壳类化石,认为甲不拉组地层时代属于早白垩世贝利阿斯期至凡兰吟期（Berriasian-Valanginian）。这一发现标志着西藏特提斯东部早白垩世地层中钙质超微化石的存在。甲不拉组早白垩世钙质超微化石的发现,为该地区海相地层的时代划分、对比提供了新的资料,也为寻找海相侏罗纪—白垩纪地层界线指示了目标。     

藏南江孜地区早白垩世甲不拉组钙质超微化石的特征及其地层意义

藏南江孜一带的侏罗纪—白垩纪海相地层被划分为维美组和甲不拉组。通过偏光显微镜和扫描电镜观察和分析,发现甲不拉组黑色页岩中含有保存较为完好的钙质超微化石。研究区的生物丰度和分异度偏低,经鉴定以椭圆球石科(Ellipsagelosphaeraceae)生物群为主,数量相对丰富,但属种比较单调。超微化石指示甲不拉组为早白垩世沉积的产物。结合菊石和双壳类化石,认为甲不拉组地层时代属于早白垩世贝利阿斯期至凡兰吟期 (Berriasian-Valanginian)。这一发现标志着西藏特提斯东部早白垩世地层中钙质超微化石的存在。甲不拉组早白垩世钙质超微化石的发现,为该地区海相地层的时代划分、对比提供了新的资料,也为寻找海相侏罗纪—白垩纪地层界线指示了目标。     

Calibration of Early Cretaceous dinoflagellate zones from the NWS of Australia to the global time scale through calcareous nannofossils

Palynomorphs and nannofossils were examined from the Lower Cretaceous interval of the well North Scarborough-1, drilled on the Exmouth Plateau, North West Shelf of Australia. Integration of the chronostratigraphic information from both fossil groups revealed discrepancies in the age information with the nannofossils suggesting a younger age than dinoflagellate cysts. The nannofossil events have a stronger tie to the global time scale than the dinoflagellate zones which are mainly local. The direct comparison of nannofossil and dinoflagellate events in the same section allows for improved stratigraphic precision and a revised correlation of Australian dinoflagellate zonal ages to the global time scale, GTS12. Global nannofossil ages confirm a Barremian–late Hauterivian age for the Muderongia australis Zone, but the Systematophora areolata to Dissimulidinium lobispinosum Zones appear to be 1–2 my younger than previously estimated.     

Early Cretaceous migmatitic mafic granulites from the Sabzevar range (NE Iran): implications for the closure of the Mesozoic peri-Tethyan oceans in central Iran

The ophiolitic mélange of the Sabzevar Range (northern Iran) is a remnant of the Mesozoic oceanic basins on the northern margin of the Neotethys that were consumed during the Arabia–Eurasia convergence history. Occurrence of km-scale, dismembered mafic HP granulitic slices is reported in this study. Granulites record an episode of amphibole-dehydratation melting and felsic (tonalite/throndhjemite) melt segregation at c. 1.1 GPa and 800 °C. In situ U(-Th)–Pb geochronology of zircon and titanite grains hosted in melt segregations points to an Early Cretaceous (Albian) age for the metamorphic climax. Results of this study (i) impose reconsideration of the current palaeotectonic models of the Neothetyan convergent margin during the Early Cretaceous and (ii) argue that punctuated events of subduction of short-lived back-arc oceanic basins accompanied the long-lasting history of the Neotethyan subduction in the region.     

Aptian (Lower Cretaceous) biostratigraphy and cephalopods from north central Tunisia

Thick Aptian deposits in north central Tunisia comprise hemipelagic lower Aptian, reflecting the sea-level rise of OAE 1a, and an upper Aptian shallow marine environment characterized by the establishment of a carbonate platform facies. Carbon stable isotope data permit recognition of the OAE 1a event in the Djebel Serdj section. Cephalopods are rare throughout these successions, but occurrences are sufficient to date the facies changes and the position of the OAE1a event. Ammonite genera include lower Aptian Deshayesites, Dufrenoyia, Pseudohaploceras, Toxoceratoides and ?Ancyloceras; and upper Aptian Zuercherella, Riedelites and Parahoplites. Correlation of carbon isotope data with those of other Tethyan sections is undertaken together with the integration of planktonic foraminiferal data.     

Calcareous nannofossils from chalky limestone of upper Abderaz Formation and lower part of Abtalkh Formation in the Kopet-Dogh range NE Iran

For the first time, the calcareous nannofossils of the chalky limestone of upper Abderaz Formation and lower part of Abtalkh Formation have been studied. In this study, 83 nannoplanktonic species of 45 genera were identified and presented. A biostratigraphic study of calcareous nannofossils from this section has allowed the recognition of five calcareous nannofossil biozones of Sissingh (Geol Mijnbouw 56:37–65, 1977) CC17–CC21. On the obtained calcareous nannofossils, the age of this section is Late Santonian/Early Campanian–Early Late Campanian.     

南海东北部表层沉积中钙质超微化石的分布特征

对南海东北部188个表层沉积样品进行了钙质超微化石分析.结果表明,除2个样品外,其他样品均含有超微化石,但丰度相差悬殊,在(9～1 684)个/10视域范围内变化.钙质超微化石相对丰度在平面上的分布可划分为3个区.共鉴定出钙质超微化石17属27种,以Florishaera profunda,Gephyrocapsa oceanica,G.spp.(small)和Emiliania huxleyi为优势种.调查区钙质超微化石的分布受多种因素的综合影响.重点讨论了水深、陆源物质的输入、碳酸盐溶解作用等因素对超微化石丰度及优势种分布的影响.     

The first findings of fusulinids in the sections of the Sabzevar tectonic block (Iran)

The first fusulinids have been recorded from the eastern part of the Sabzevar tectonic block (Kuh-e-Ahuban Mountains, to the north of the town of Kashmar). The fusulinids have been grouped into two complexes. The first complex is represented by several species of the genus Rauserites, of probable Gzhelian age. The second complex is represented by numerous representatives of the Asselian genera Sphaeroschwagerina and Pseudoschwagerina, as well as species of the genera Schubertella, Rugosofusulina, Rugosochusenella and Praepseudofusulina. The age of these complexes is similar to that of complexes previously described from sections of Anarak (the Yazd block) and Zaladou (the Tabas block), but differ in the species composition. Many of the species present in these complexes are similar or identical to species from standard sections of Gzhelian and Asselian Stages of the Moskovian syncline and the Urals, which indicates that there were free connections between the East European and Iranian basins in Gzhelian and Asselian Stages.     

Dinocyst biostratigraphy of the Lower Cretaceous in North Siberia

The described scheme of the Lower Cretaceous (Berriasian-Barremian) stratigraphic subdivisions is elaborated based on palynological study of sections in the Khatanga depression, Ust-Yenisei region, Pur-Taz interfluve, and around the Ob River latitudinal segment, the North Siberia. Stratigraphic distribution of microphytoplankton studied in detail is used to distinguish 10 biostratigraphic units in the rank of dinocysts zones. Stratigraphic position of the zones is determined with confidence using data on the Lower Cretaceous reference sections in the Khatanga depression, which were principal ones by constructing the Boreal standard zonation. In majority, boundaries of the dinocysts beds are of a high correlation potential and can be regarded as reliable stratigraphic markers, as they are recognizable not only in Siberia, but also in northern Europe and America.     

Correlation of late Cretaceous calcareous nannofossil zones with ammonite zones and planktonic Foraminifera: the Austrian Gosau sections

The late Turonian to early Campanian calcareous nannofossil biostratigraphy of the Austrian Gosau Group is correlated with ammonite and planktonic foraminiferal zones. The standard Tethyan zonations for nannofossils and planktonic foraminifers are applied with only minor modifications. The basal marine sediments of the Gosau Group, bearing late Turonian-early Coniacian macrofossils, belong to the Marthasterites furcatus nannofossil Zone (CC13). The Micula decussata Zone (middle Coniacian to early Santonian) is combined with the Reinhardtites anthophorus Zone because of the rare occurrence of Renhardtites cf. R. anthophorus already in the Coniacian and taxonomic problems concerning the correct identification of this species. The Santonian-Campanian boundary lies within the Calculites obscures Zone (CCl7).     

Tschermak fractionation in calc-alkaline magmas: the Eocene Sabzevar volcanism (NE Iran)

Calc-alkaline arc magmatism at convergent plate margins is volumetrically dominated by metaluminous andesites. Many studies highlighted the importance of differentiation via fractionation processes of arc magmas, but only in the last decades, it has been demonstrated that not all rock-forming minerals may affect the evolution of calc-alkaline suites. In particular, a major role exerted by Al-rich hornblende amphibole as fractionating mineral phase has been documented in many volcanic arc settings. The aim of this work is to understand the role of the Tschermak molecule (CaAlAlSiO₆) hosted in the hornblende and plagioclase fractionation assemblage in driving magma differentiation in calc-alkaline magmatic suites. We explore this issue by applying replenishment–fractional crystallization (RFC) and rare earth element–Rayleigh fractional crystallization (REE-FC) modeling to the Sabzevar Eocene (ca. 45–47 Ma) calc-alkaline volcanism of NE Central Iran, where hornblende-controlled fractionation has been demonstrated. Major element mass balance modeling indicates RFC dominated by a fractionating assemblage made of Hbl_52.0–52.5 + Pl_44.1–44.2 + Ttn_3.3–3.9 (phases are expressed on total crystallized assemblage). REE-FC modeling shows, instead, a lower degree of fractionation with respect to RFC models that is interpreted as due to hornblende and plagioclase resorption by the residual melt. Calculations demonstrate that fractionation of the Tschermak molecule can readily produce dacite and rhyolite magmas starting from a calc-alkaline andesite source (FC = ca. 30 %). In particular, the Tschermak molecule controls both the heavy rare earth elements (HREE) and light rare earth element (LREE) budgets in calc-alkaline differentiation trends.     

Mineral chemistry of hydrothermal biotite from the Kahang porphyry copper deposit (NE Isfahan), Central Province of Iran

The Kahang porphyry Cu deposit, located northeast of Isfahan city in central of Iran, is associated with a composite Miocene stock and ranges in composition from diorite through granodiorite to quartz-monzonite. Field observations and petrographic studies show that the emplacement of the Kahang stock occurred in several pulses, each associated with its related hydrothermal activity. Early hydrothermal alteration started with a potassic style in the central part of the system and produced a secondary biotite–K-feldspar–magnetite assemblage accompanied by chalcopyrite and pyrite mineralization. Propylitic alteration that took place at the same time as the potassic alteration occurred in the peripheral portions of the stock. Subsequent phyllic alteration overprinted earlier potassic and propylitic alterations. Biotite grains from the potassic and phyllic zones show distinct chemical compositions. The FeO, TiO₂, MnO, K₂O, and Na₂O concentrations in biotite from the phyllic alteration zone are lower than those from the potassic alteration zone. The F and Cl contents of biotite from the potassic alteration zone display relatively high positive correlation with the X_Mg. The fluorine intercept values [IV(F)] from the potassic and phyllic alteration zones are strongly correlated with the fluorine/chlorine intercept values [IV(F/Cl)]. Biotite geothermometry for the potassic and phyllic alteration zones, based on the biotite geothermometer of Beane (1974), yields a temperature range of 422° to 437 °C (mean = 430 °C) and 329° to 336 °C (mean = 333 °C), respectively. The position of data in log (X_F/X_OH) ratio vs. X_Mg and X_Fe diagram suggests that biotite formed under dissimilar composition and temperature conditions in the potassic and phyllic alteration zones. Calculated log fugacity ratios of (fH₂O/fHF), (fH₂O/fHCl), and (fHF/fHCl) show that hydrothermal fluids associated with the potassic alteration were distinctively different from those fluids associated with the phyllic alteration zone at Kahang porphyry Cu deposit. The results of this research indicate that the chemistry of biotite is related to the chemical composition of the magma and the prevailing physical conditions during crystallization.