Stratigraphy of the Lower Cretaceous Sediments from the Carpathian Bend Area, Romania

The Lower Cretaceous sediments of the Ceahl?u Nappe (from the bend region of the Romanian Carpathians) were investigated from lithological and micropaleontological (calcareous nannoplankton) points of view. Our investigations revealed that the studied deposits were sedimented within the latest Tithonian-Albian interval. The calcareous nannofossil assemblages of the turbidite calcareous successions (the Sinaia Formation) were assigned to the NJK-?NC5 calcareous nannofossil zones, which cover the Late Tithonian-Early Barremian interval. The sandy-shaly turbidites, which followed the calcareous turbidites of the Sinaia Formation, are Early Barremian-Early Albian in age (interval covered by the ?NC5-NC8 calcareous nannofossil zones). Because the studied deposited are mainly turbidites, many reworked nannofossils from older deposits are present in the calcareous nannofloras. Thus, some biozones (i.e., NC5), defined based on the last occurrences of nannofossils, could not be identified. The calcareous nannofossil assemblages are composed of Tethyan taxa (which dominate the nannofloras) and cosmopolitan taxa. During two intervals (the Late Valanginian and across the Barremian/Aptian boundary), Tethyan and cosmopolitan nannofossils, together with Boreal ones, were observed. This type of mixed calcareous nannoplankton assemblage is indicative for sea-level high-stand, which allows the nannofloral exchange between the Tethyan and Boreal realms, within the two-above mentioned intervals.     

Calcareous phytoplankton from the Barremian/Aptian boundary interval in NW Germany

Two cored boreholes in the central part of the North West German Basin recovered a unique section of Upper Barremian to Lower Aptian strata. Calcareous nannofossils show a distinctive shift from boreal endemic assemblages in the Barremian to cosmopolitan ones in the Aptian. This onset of new cosmopolitan species (e.g., Chiastozygus litterarius, Flabellites oblongus, Rhagodiscus angustus, Braarudosphaera sp., Eprolithus sp.) is spread over an interval of 25m, starting well below the early Aptian "Fischschiefer", a dark laminated shale rich in organic matter. These changes in the composition of calcareous nannofossils indicate that major palaeoceanographic changes occurred before the deposition of the Fischschiefer.The distribution pattern of calcispheres allows the differentiation of two sedimentary successions, separated by the Fischschiefer. The lower succession, which includes the sediments below the base of the Fischschiefer, indicates a boreal-pelagic environment. The lower part of the upper successions which includes the Fischschiefer, represents warmer inner shelf conditions. This corresponds to the presence of rich Tethyan-derived nannoconid assemblages and the presence of the planktonic foraminifera Hedbergella in the Fischschiefer. The topmost part of the upper succession (middle Aptian, Hedbergella marl) suggests a change to a pelagic warmer water environment. Two new taxa are introduced: the calcareous dinoflagellate cyst Obliquipithonella laqueata n. sp. and the foraminiferan Choanaella fortunate n. gen. n. sp.     

The palynology and geology of the Lower Cretaceous (Aptian–Albian) of Munday’s Hill Quarry,Bedfordshire, UK

Early Cretaceous sediments of Aptian–Albian age outcrop at Munday’s Hill Quarry, Bedfordshire, England. Previous papers describing the section have resulted in different terminologies being applied. The Lower Cretaceous in Bedfordshire is represented by sediments belonging to the Lower Greensand Group and the Gault Clay Formation. Within the Lower Greensand Group in the study area the Woburn Sands Formation, are of Aptian–Albian age. Selected samples have been analysed for palynology. The analysis reveals diverse palynomorph assemblages, including well-preserved dinoflagellate cysts and sporomorphs. Comparison of the assemblages with published records indicates that the lower samples are of Late Aptian age. Forms recorded include common Kiokansium unituberculatum, Cerbia tabulata, Aptea polymorpha and Cyclonephelium inconspicuum. An Early Albian age is indicated for the uppermost sample.     

Stratigraphic framework and calcareous nannofossil productivity of the Essaouira-Agadir Basin (Morocco) during the Aptian–Early Albian: Comparison with the north-Tethyan margin

In the southern Tethyan margin, the Essaouira-Agadir Basin (EAB), south of Morocco, exhibits well-exposed and fossiliferous sections of Aptian–Albian age. Biostratigraphy by ammonoids and sedimentological analysis have been realized for five sections located along an E-W transect in the EAB. The studied successions were dated from the latest Early Aptian to the Early Albian and are characterized by five major sedimentary discontinuities defining at least four main sedimentary sequences. The Late Aptian–Early Albian succession can be considered a gently westward-dipping ramp, marked by a deepening upward evolution. A quantitative study of calcareous nannofossils and calcium carbonate content has been performed on three of these sections. At this time, the EAB was located in the tropical-equatorial hot arid belt. The decrease in both calcium carbonate content and Nannoconus abundances at the Aptian–Albian transition could be the result of cooler climatic conditions recognized in the EAB, and/or of the associated increasing terrigenous input and nutrients, which hindered carbonate production. In the EAB, the nannofossil productivity is higher below the deposition of dark levels, which are coeval with the Niveau Paquier, recognized as the expression in southern France of the OAE 1b (Early Albian). During the Early Albian, the EAB was characterized by nannofossil fluxes two times lower than the upwelling-influenced Mazagan Plateau (southern Tethyan margin) and eight times lower than the Vocontian Basin (northern Tethyan margin). These results show that, with respect to the northern Tethyan margin, trophic conditions in sea surface waters of the pelagic realm of the southern Tethyan margin were lower. Comparable results obtained by Heldt et al. in the neritic realm of the southern Tethyan margin have been ascribed to more arid climatic conditions.     

鸡西群城子河组时代的进一步探讨

近年来 ,古生物工作者在鸡西群城子河组及其相当地层的生物化石研究方面取得了巨大的进展。在总结这些新的材料的基础上 ,通过与国外的化石组合进行对比 ,从海相双壳类、植物、孢粉及海相沟鞭藻化石等多方面的证据 ,尤其是根据 Thracia rotundata、Vectianella、Pseudaphrodina ricordeana等欧洲 Aptian阶重要的双壳类化石、被子植物及三沟类被子植物花粉的出现 ,城子河组的时代应为 Aptian期 - Albian期早期     

Transgressive-regressive cycles in Lower Cretaceous strata,Mississippi Interior Salt Basin area of the northeastern Gulf of Mexico,USA

Four transgressive-regressive (T-R) cycles and five T-R subcycles have been recognized in Lower Cretaceous strata of the northeastern Gulf of Mexico. These T-R cycles are the LKEGR-TR 1 (Lower Cretaceous, Eastern Gulf Region) (upper Valanginian–upper Aptian), the LKEGR-TR 2 (upper Aptian–middle Albian), the LKEGR-TR 3 (middle–upper Albian), and the LKEGR-TR 4 (upper Albian–lower Cenomanian) cycles. The LKEGR-TR 1 Cycle consists of three subcycles: LKEGR-TR 1–1 (upper Valanginian–lower Aptian), LKEGR-TR 1–2 (lower Aptian) and LKEGR-TR 1–3 (upper Aptian) subcycles. The LKEGR-TR 2–1 (upper Aptian–lower Albian) and the LKEGR-TR 2–2 (lower–middle Albian) subcycles constitute the LKEGR-TR 2 Cycle. The LKEGR-TR 3 and the LKEGR-TR 4 cycles consist of a single T-R cycle.Recognition of these T-R cycles is based upon stratal geometries, nature of cycle boundaries, facies stacking patterns within cycles, and large-scale shifts in major facies belts. The T-R subcycles are characterized by shifts in major facies belts that are not of the magnitude of a T-R cycle. The cycle boundary may be marked by a subaerial unconformity, ravinement surface, transgressive surface or surface of maximum regression. A single T-R cycle consists of an upward-deepening event (transgressive aggrading and backstepping phases) and an upward-shallowing event (regressive infilling phase). These events are separated by a surface of maximum transgression. The aggrading phase marks the change from base-level fall and erosion to base-level rise and sediment accumulation; this phase signals the initiation of the creation of shelf-accommodation space. The marine transgressive and flooding events of the backstepping phase are widespread and provide regional correlation datums. Therefore, these T-R cycles and subcycles can be identified, mapped, and correlated in the northeastern Gulf of Mexico area. The progradational events associated with the regressive infilling phase represent a major influx of siliciclastic sediments into the basin, the development of major reef build-ups at the shelf margin, and a significant loss of shelf-accommodation space. These T-R cycles are interpreted to be the result of the amount of and change in shelf-accommodation due to a combination of post-rift tectonics, loading subsidence, variations in siliciclastic sediment supply and dispersal systems, carbonate productivity and eustasy associated with a passive continental margin. The T-R cycles, where integrated with biostratigraphic data, can be correlated throughout the northern Gulf of Mexico region and have the potential for global correlation of Lower Cretaceous strata.     

Sedimentary formations of the Cretaceous Sakhalin Basin (Far East Asia)

The marine sedimentary formations of the Middle Albian to Maastrichtian in the Cretaceous Sakhalin Basin (CSB) were investigated. These successions of strata consist of interbedded sandy, clayey and calcareous rocks which are underlain by heterogeneous metamorphosed (up to greenschist facies) Paleozoic to Mesozoic (pre-Aptian) rocks. The studied sections display several different facies reflecting geological settings ranging from an inner shelf to a continental slope. Three depositional complexes bound by regional subaerial unconformities are recognized within the marine successions. Since the Albian, the CSB has been a rapidly subsiding marginal part of the Okhotsk Sea plate. The Naiba Valley succession, corresponding to a sublittoral zone, shows extremely high sedimentation rates up to 190 m/Ma. The stratigraphic distribution of lithofacies indicates that the CSB became shallower from the Middle Albian to the Maastrichtian.     

Ascription of the island of Ibiza to the Prebetic of Alicante (Betic Range,Spain) after correlation of Lower Cretaceous sedimentary successions

The lithostratigraphic succession of the Tithonian – Albian interval of the island of Ibiza shows a great similarity with that of the Internal Prebetic Zone in the Alicante area (Betic Range), with only slight differences in age and stratigraphic distribution. This similarities are based on the correlation of the following units: i) the Punta Jondal Formation of Ibiza with the Sierra del Pozo Formation of Alicante (Tithonian – early Valanginian); ii) the Port Sant Miquel Formation (Aptian) with the Arroyo de los Anchos Formation; iii) the Torre des Molar (early Aptian), Penyal de s’Águila (late Aptian) and Cala d'en Sardina (late Aptian) members of the Port Sant Miquel Formation with the Llopis, Almadich and Seguilí formations in Alicante; and iv) the Es Cubells Formation (Tithonian – earliest Cenomanian) with several marly units of the Prebetic of Alicante.The Ibiza Tithonian – Albian sedimentary succession was deposited within a NNW–SSE trending basin related to the Tethyan domain of SE Iberia. It is organized in three sedimentary successions (named Aubarca, San José and Ibiza successions, from NNW to SSE), which were tectonically stacked towards the NNW during the Alpine inversion of the basin. These sedimentary successions were deposited within the distal regions of a carbonate platform opened towards the southeast. In the SE sector of the island, the Ibiza succession is characterized by a thick and rhythmic alternation of basinal marls and marly limestones. Northwestwards, the San José succession is characterized by the presence of inner platform carbonate deposits at the base of the succession (Tithonian – early Valanginian). Finally, the presence of shallow-water rudist-bearing limestones (Aptian) in the northwestern sector, defines the Aubarca succession. The NNW–SSE evolution of the stratigraphic architecture from the Aubarca – San José – Ibiza successions is clearly similar to the tectonostratigraphic and palaeogeographic N–S zoning previously recognized from the Sierra de Mariola – Cabezón de Oro – Fontcalent successions in the Prebetic of Alicante, respectively.Stratigraphical sequence analysis of the sedimentary successions of the island of Ibiza allows recognizing a depositional stacking pattern defined by four long-term depositional megasequences, which can also be correlated with equivalent megasequences in the Prebetic of Alicante. The three lower megasequences (Tithonian – Albian) show a transgressive–regressive evolution, revealed by the deposition of transgressive hemipelagic facies in the lower part and the development of prograding shallow-water carbonate platforms during regressions. The fourth megasequence (Albian) is not as well developed as the previous megasequences, showing siliciclastic levels instead of the shallow-water carbonate platform facies, thus suggesting a development during major sea-level fall. Nevertheless, in the Ibizan successions, high resolution sequence stratigraphy and accurate biostratigraphic scales have not yet been established; consequently, the chronostratigraphy of megasequence boundaries and the maximum flooding surfaces are less accurate than in their Prebetic counterparts.     

First finds of Late Tithonian and middle-late Albian radiolarian assemblages in volcanogenic-siliceous rocks of the Amur River right lower reaches and their tectonic significance

The lithological-stratigraphic study of volcanogenic-siliceous rocks developed on the left side of the Machtovaya River, a right tributary of the Amur River, yielded the first radiolarian assemblages of the late Late Tithonian, the late Late Tithonian-early Valanginian, and the middle-late Albian age. It is established that the stratigraphic succession of volcanogenic-siliceous rocks in this area is composed of upper Tithonian-Valanginian dark red to red-brown cherts with basalts in the lower part of the section and Albian dark gray clayey cherts, olive-gray siliceous-tuffaceous argillites, and tufaceous siltstones in its upper part. The replacement of cherts by their clayey varieties likely occurred in the Aptian. The composition, structure, and age of these strata and the rocks constituting the Kiselevka-Manoma accretionary complex are different, which indicates their different tectonic origin.     

Coastal sediments from the Algarve: low-latitude climate archive for the Aptian-Albian

The Late Aptian to Early Albian transition has previously been identified as a possible example of substantial climate cooling within the mid-Cretaceous greenhouse period. To study the response of continental weathering and terrestrial vegetation to this cooling episode at low- to mid-latitudes, marine nearshore deposits from the Algarve Basin (SW Portugal) have been investigated with a combined approach including palynology, clay mineralogy and bulk-rock geochemistry. In the Lower Aptian part of the succession, quartz-rich sandstone facies is accompanied by high abundances of early diagenetic kaolinite, which is interpreted to reflect episodes of enhanced humidity and high meteoric flow-through. In contrast, the Late Aptian to Early Albian deposits are characterized by high abundances of detrital clay minerals (mica and chlorite) indicating the dominance of physical weathering processes in the source area, most probably related to low precipitation rates in conjunction with tectonically enhanced erosion. Palynological data show a strong dominance of Classopollis pollen associated with low pteridophyte spore abundances, suggesting warm semi-arid to arid palaeoenvironments. Changes in sedimentation patterns from varicoloured lagoonal marls to thick-bedded shallow-water carbonates are neither expressed in the spore-pollen assemblages nor in the distributions of clay minerals which both remain essentially stable throughout the Late Aptian to Early Albian. These relatively stable patterns are in contrast with various lines of evidence, predominantly from high-latitude areas, that suggest a significant cooling during this time interval. Our study demonstrates that terrestrial environments of low- to mid-latitude regions were not significantly affected by the Late Aptian - Early Albian “cold snap”.     

Aptian and Albian atmospheric CO2 changes during oceanic anoxic events: Evidence from fossil Ginkgo cuticles in Jilin Province,Northeast China

The Early Cretaceous was a time with super-greenhouse conditions and episodic global oceanic anoxic events. However, relative timing of atmospheric CO₂ emissions and oceanic anoxic events, and their causal relationships remain matters of debate. Using the stomatal index approach, well-preserved fossil cuticles of Ginkgo from the Lower Cretaceous Changcai Formation, eastern Jilin, and from the Lower Cretaceous Yingcheng Formation, central Jilin, Northeast China, were investigated to reconstruct atmospheric CO₂ concentrations during the Aptian and earliest Albian (Early Cretaceous). The results indicate that the CO₂ concentrations reached 1098–1142 ppmv (Carboniferous standardization) or 970–1305 ppmv (regression function) during the Aptian and earliest Albian. Our estimates of palaeoatmospheric CO₂ concentrations during the earliest Albian (OAE 1b) are slightly higher than the data between the early Aptian Selli (OAE 1a) and the middle Aptian Fallot OAEs; this may indicate the absence of any great emissions of CO₂ during the latest Aptian and earliest Albian.     

Decline and recovery of the Aptian carbonate factory in the southern Apennine carbonate shelves (southern Italy): Climatic/oceanographic vs. local tectonic controls

In interpreting the inception and demise of different carbonate depositional systems, climatic-oceanographic variations together with sea-level oscillations are commonly considered key elements. However, local tectonic controls cannot be ruled out. In attempts to discriminate among the main factors controlling the evolution of the southern Apennine mid-Cretaceous carbonate system, detailed facies analyses have been performed on Aptian–Albian carbonate successions in the Matese Group (southern Apennines). Since the mid Aptian, the analysed successions testify to a tectonically-driven topography, replacing the previous large tropical shallow-water domain with subdomains characterised by diversified sedimentological trends. Nevertheless, around the middle part of the Aptian, the studied successions register palaeoecological signals that cannot be linked exclusively with tectonic disturbance because of the coeval appearance of analogous signals at a global scale, including a significant change in biological assemblages and an outbreak of organisms indicative of stressful conditions in the water mass.Upper Bedoulian strata clearly record open marine settings characterised by a significant richness of the benthic communities. The biota included rudists, gastropods and echinoids plus many different benthic foraminifers and green algae. Rudists considered to be typically “tropical” forms (the caprinid Offneria nicolinae (Mainelli) and Offneria murgensis Masse, the requieniid Lovetchenia Masse and the monopleurid Agriopleura Kühn) characterise thick subtidally deposited strata in which large coral colonies and mollusc shells contributed to occasional storm-related skeletal concentrations.The analysed Gargasian strata show impoverished biota: caprinids totally disappear, both as in situ and storm-related layer components, and hermatypic corals are drastically reduced. Muddy lithofacies prevail in intertidal metric cycles in which cyanobacterial consortia, both in the form of dense laminae and coalescent oncoids, orbitolinids and small gastropods (cerithiids) suggest restricted, nutrient-rich water. Large oncoids of Bacinella irregularis/Lithocodium aggregatum and mollusc (mostly chondrodontids and gastropods) shell fragments significantly contribute to storm-related coarse skeletal intercalations, in which oligotrophic condition-adapted forms (e.g., hermatypic corals) are reduced or absent. This pattern suggests generalised conditions of stress in the water mass and in more marginal open areas.During the mid-Aptian interval, characterised by the flourishing of assemblages adapted to mesotrophic–eutrophic conditions, the southern Apennines shallow-water domain shows a progressive reduction of the previous mainly aragonite-dominated chlorozoan assemblages and an increase of calcite-dominated skeletal components, including rudists with thickened calcitic outer shell layers. Cyanobacteria and polychaetes characteristically marked the first phases of recovery in the shallow-water domains, rapidly evolving into more complex and differentiated assemblages. The outbreak of nerineid and acteonid gastropods seems to be related to a flourishing of cyanobacterial mats and related microphytae and also to the presence of polychaetes tubes (Thartarella cocumeriformis (Wahlman)). Moreover, the grazing activity of the nerineids favoured the flourishing of oyster-like bivalves. Among the rudists, the persistence and radiation of species adapted to a wide range of temperatures, such as Requieniidae and Monopleuridae as well as the first elevator Radiolitidae suggests some kind of oceanographic change (e.g., seawater chemistry and/or temperature).On the basis of the features described above, we propose the existence of a complex environmental scenario in which cooler conditions, presumably coupled with meso/eutrophic and locally oligophotic conditions, related to climatic/oceanographic global changes, cooperated in modifying the carbonate factory characterisation in a tectonically controlled setting.     

Integrated planktonic stratigraphy and paleoenvironments of the Lower-Middle Miocene successions in the central and southern parts of the Gulf of Suez,Egypt

Lower to Middle Miocene successions in three offshore wells named GS 160-2, QQ-89, and Ras Elush-2 located in the central and southern parts of the Gulf of Suez were examined for their planktonic foraminifera, calcareous nannofossil assemblages, and paleoenvironments. These successions are subdivided from older to younger into Aquitanian Nukhul, Burdigalian-Langhian Rudeis, Langhian Kareem, and Serravallian Belayim formations. The identified foraminifera includes 54 benthic species belonging to 25 genera and 47 planktonic species belonging to 11 genera, in addition to 64 calcareous nannofossil species belonging to 21 genera. The stratigraphic distribution of these assemblages suggests classifying the studied successions into seven planktonic foraminiferal and six calcareous nannoplankton biozones. The planktonic foraminiferal and calcareous nannoplankton biozones are integrated. Different environments ranging from shallow inner to outer shelf are recognized. This is based on quantitative analyses of foraminifera including benthic biofacies, planktonic/benthonic ratio, and diversity. Syn-rift tectonics played an important role in configuration of the Miocene depositional history in the Gulf of Suez region.     

Carbon and oxygen-isotope stratigraphy of the Early Cretaceous carbonate platform of Pădurea Craiului (Apuseni Mountains,Romania): A chemostratigraphic correlation and paleoenvironmental tool

Stable C and O isotope records were obtained from carbonate rocks spanning the Hauterivian to Cenomanian interval collected in several sections from the carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania). In the absence of some key biostratigraphic marker species, stable isotopes were applied as a tool for stratigraphic correlation and dating. The composite δ¹³C and δ¹⁸O curves for the Early Cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes. The Hauterivian and the Barremian limestones (Blid Formation) display lower δ¹³C values (−2.8‰ to +2.9‰) relative to the Aptian–Albian deposits (−2.6‰ to +5.4‰) (Ecleja, Valea Măgurii and Vârciorog Formations). The red detrital formation (Albian–Cenomanian) is characterized by a highly variable distribution of the δ¹³C values (−3.5‰ to +3.9‰). Based on the similarities between the C-isotope curve established in Pădurea Craiului and from other sections in the Tethyan and the Pacific regions, two major oceanic anoxic events characterized by δ¹³C positive excursions were clearly recognized. The first is the OAE1a event (Early Aptian) in the upper part of the Ecleja Formation and the Valea Măgurii Formation. The second is the OAE1b event (Late Aptian–Albian) in the upper part of the Vârciorog Formation and in the Subpiatră Member. The position of the Aptian/Albian boundary is estimated to be at the upper part of the Vârciorog Formation, immediately after the beginning of the δ¹³C positive excursion. The δ¹³C data show major negative excursions during the Barremian (Blid Formation), Early Aptian (Ecleja Formation), and Late Aptian (Vârciorog Formation). The O isotope variation pattern (−10.2‰ to −2.1‰) is consistent with progressively warming temperatures during the Early Barremian followed by a cooling period. A subsequent warming period culminated in the Early Aptian. A significant cooling phase corresponds to the Late Aptian and Early Albian and the climate cooled again during the Late Albian and into the Early Cenomanian stage. The data provide a better understanding of the Early Cretaceous sedimentation cycles in Pădurea Craiului and create a more reliable framework for regional correlations.     

Microfacies and age of the Ceahlău Massif carbonate olistoliths (Eastern Carpathians,Romania): Remnants of a lowermost Cretaceous carbonate platform

We carried out a comprehensive facies/microfacies, micropalaeontological and biostratigraphical analysis of several carbonate olistoliths incorporated within a widely developed Albian conglomeratic sequence from the Eastern Carpathians of Romania. The majority of the sampled olistoliths contain a rich assemblage of benthic foraminifera and calcareous green algae. All of the described microfossils represent common lowermost Cretaceous taxa not previously reported from these carbonate elements or from this region. Based on benthic foraminifera assemblages the age of the studied olistoliths is upper Berriasian–lower Valanginian, contrary to the general belief that they are Barremian–Aptian in age. The dominant microfacies types mainly reflect deposition in shallow-water environments and show similarities with synchronous platform carbonates of the central-western Neotethys Ocean. The micropalaeontological and sedimentological data support new interpretations concerning the source area of these carbonate elements and provide new information concerning the evolution of the lowermost Cretaceous carbonate platforms of the Carpathians.     

Mid-Cretaceous Tuor-Yuryakh Section of Kotelnyi Island,New Siberian Islands: How Does the Probable Basement of Sedimentary Cover of the Laptev Sea Look on Land?

The model of geological structure of sedimentary cover of the Laptev Sea accepted by most geologists suggests that the lower seismic complex of the cover begins by the Aptian–Albian sedimentary rocks. They can be studied in natural outcrops of Kotelnyi Island. The section of the Tuor-Yuryakh Trough, which exposes the lower part of the Cretaceous complex, is described in the paper. It is composed of continental coaliferous rocks ~100 m thick. The marking beds divide it into five members, which are traced along the western wall of the trough at the distance up to 3 km. The spore–pollen complexes and plant megafossils indicate that almost the entire visible section of the mid-Cretaceous is Albian. Only its lower part no more than 14 m thick can probably belong to the Aptian. Marine facies with Albian foraminifers were found 15 m above the bottom of the Cretaceous complex. The section of the Cretaceous rocks is underlain by the Lower Jurassic marine clays and siltstones. The foraminifer assemblages of this part of the section are typical of the upper Sinemurian–Pliensbachian and fossil bivalves indicate late Sinemurian age of the host rocks. The hiatus ~70 Ma duration has no expression in the section and this boundary can de facto be substantiated only by microfossils. This vague contact between the Lower Jurassic and mid-Cretaceous rocks does not correspond to geophysical characteristics of the bottom of the lower seismic complex of the cover of the eastern part of the Laptev Sea. The latter is described as the most evident seismic horizon of the section of the cover, suggesting unconformable occurrence of the lower seismic complex on a peneplenized surface of lithified and dislocated rocks. This is mostly similar to the bottom of the Eocene sediments, which were observed on Belkovsky and Kotelnyi islands. The paper discusses possible application of our land results for interpretation of the shelf seismic sections of the Laptev Sea. It is concluded that local reasons are responsible for a vague boundary between the Lower Jurassic and mid-Cretaceous sequences in the section studied. Our observations support ideas on possible Aptian–Albian age of the rocks of the basement of the lower seismic complex; however, it is proposed to use also the previously popular idea on the Eocene age of the lower seismic complex of sedimentary cover of the eastern part of the Laptev Sea as one of the possible working scenarios.     

Latitudinally different responses of Tethyan shoal‐water carbonate systems to the Early Aptian oceanic anoxic event (OAE 1a)

Ocean‐wide anoxic events represent intensively investigated anomalies in the global carbon cycle. Most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black‐shale deposition and carbon‐isotope excursions. The study of ocean‐wide anoxic events and coeval shallow‐water settings is now increasingly seen as an interesting complementary approach, but one that is not without problems. Whereas platform drowning characterizes the Early Aptian of the northern Tethyan margin, Lithocodium–Bacinella‐rich facies and ongoing shoal‐water sedimentation at the southern Tethyan margin (Oman) bears important information on potential causes of carbon‐cycle perturbations. The present paper seeks to test the supra‐regional relevance of the Oman data by investigating coeval central Tethyan limestones. Three Lower Aptian shoal‐water sections in Istria (Croatia), deposited on the isolated Adriatic Carbonate Platform, are investigated applying chemostratigraphy (carbon and strontium) and detailed sedimentological analysis. The focus is on peritidal to lagoonal facies characterized by mass occurrences of Lithocodium–Bacinella, an enigmatic microencruster community. Lithocodium–Bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness, with several layers merging to metre‐thick packages. Growth fabrics within the layers include oncoidal morphotypes, lumps, interconnected patches and columns, layers and rare nodular to massive bindstone facies. These growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart. This widespread distribution suggests that specific Lithocodium–Bacinella morphotypes might serve as regional stratigraphic markers. The high‐resolution carbon‐isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium‐isotope data obtained from screened rudist low‐Mg calcite. The chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of Early Aptian oceanic anoxic event 1a. Moreover, results indicate the near‐coeval nature of Lithocodium–Bacinella bloom facies in Istria and Oman. The outcomes of this study point to latitudinally different responses of Tethyan shoal‐water carbonate systems (platform drowning versus Lithocodium–Bacinella blooms) to the ocean‐wide anoxic event 1a.     

武夷山南段前寒武纪浅变质岩系的划分与时代

武夷山南段前寒武纪地层分布较广。从下至上分为楼子坝群、丁屋岭组、南岩组和黄连组。过去因缺乏可靠的微古植物化石证据和同位素地质年龄资料,对其时代归属分歧颇大。为此,作者对该区的前寒武系进行了系统的微古植物取样、分析,参考最近的Nd同位素模式年龄资料,认为:楼子坝群为前震旦系,大致相当于蓟县系与青白口系;丁屋岭组为下震旦统;南岩组和黄连组为上震旦统;江西东南部的"下寒武统炭质板岩"应归入老虎塘组,属上震旦统。     

Aptian to Coniacian (Early–Late Cretaceous) palynostratigraphy of the Gustav Group, James Ross Basin, Antarctica

The Gustav Group of the James Ross Basin, Antarctic Peninsula, forms part of a major Southern Hemisphere Cretaceous reference section. Palynological data, chiefly from dinoflagellate cysts, integrated with macrofaunal evidence and strontium isotope stratigraphy, indicate that the Gustav Group, which is approximately 2.6 km thick, is Aptian–Coniacian in age. Aptian–Coniacian palynofloras in the James Ross Basin closely resemble coeval associations from Australia and New Zealand, and Australian palynological zonation schemes are applicable to the Gustav Group. The lowermost units, the coeval Pedersen and Lagrelius Point formations, have both yielded early Aptian dinoflagellate cysts. Because the overlying Kotick Point Formation is of early to mid Albian age, the Aptian/Albian boundary is placed, questionably, at the Lagrelius Point Formation–Kotick Point Formation boundary on James Ross Island, and this transition may be unconformable. Although the Kotick Point Formation is largely early Albian on dinoflagellate cyst evidence, the uppermost part of the formation appears to be of mid Albian age. This differentiation of the early and mid Albian has refined the age of the formation, previously considered to be Aptian–Albian, based on macrofaunal evidence. The Whisky Bay Formation is of late Albian to latest Turonian age on dinoflagellate cyst evidence and this supports the macrofaunal ages. Late Albian palynofloras have been recorded from the Gin Cove, lower Tumbledown Cliffs, Bibby Point and the lower–middle Lewis Hill members. However, the Cenomanian age of the upper Tumbledown Cliffs and Rum Cove members, based on molluscan evidence, is not supported by the dinoflagellate cyst floras and further work is required on this succession. The uppermost part of the Whisky Bay Formation in north-west James Ross Island is of mid to late Turonian age and this is confirmed by strontium isotope stratigraphy. The uppermost unit, the Hidden Lake Formation, is Coniacian in age on both palaeontological and strontium isotope evidence. The uppermost part of the formation appears to be early Santonian based on dinoflagellate cysts, but strontium isotope stratigraphy constrains this as being no younger than late Coniacian. This refined palynostratigraphy greatly improves the potential of the James Ross Basin as a major Cretaceous Southern Hemisphere reference section.     

甘肃酒泉盆地早白垩世植物化石及其古气候意义

首次较系统报道了产于甘肃酒泉盆地下白垩统的植物化石,分为两个植物组合。Athrotaxites-Solenites组合产于赤金堡组上段,有Solenites luanpingensis Wang,Pityocladus cf.i waianus(ishi)Chow,Pityocladus sp.,Athrotaxites berryi Bell等,时代大致为早白垩世早期,反映潮湿或半干旱半潮湿气候。Brachyphyllum-Pseudofrenelopsis组合见于中沟组上部,包括Sphenopterissp.,Pseudofrenelopsis dalatzensis(Chowet Tsao)Cao ex Zhou,Cupressinocladus elegans(Chow)Chow,Cupressinocladus sp.,Pagiophyllumyumenense sp.nov.,Pagiophyllumcompressum sp.nov.,Pagiophyllum sp.,Brachyphyllumningshiaense Chow et Tsao,Brachyphyllumobtusum Chow et Tsao,Elatocladus sp.,Podozamites sp.,Carpolithus sp.等12种,时代为Aptian-Albian期,反映干旱型气候。