Paleoecology and paleoenvironment of the Middle–Upper Jurassic sedimentary succession,central Saudi Arabia

Four Middle–Upper Jurassic sections from central Saudi Arabia have been investigated to evaluate microfacies types and macro-invertebrate paleocommunities and to interpret their paleoecology and paleoenvironments. The studied Jurassic successions are part of the Middle–Upper Callovian Tuwaiq Mountain Limestone and the Middle–Upper Oxfordian Hanifa Formation. Three main facies were recorded, including mud-supported microfacies, grain-supported microfacies and boundstones. A data matrix comprising 48 macrobenthic species in 35 samples collected from four sections were grouped into fifteen assemblages and one poorly fossiliferous interval by means of a Q-mode cluster analysis. The recorded macrofaunal assemblages have been subdivided into low-stress and high-stress on the basis of hydrodynamic conditions, substrate type, nutrient supply and hypoxia. The low-stress assemblages occur in (a) high-energy paleoenvironments with firm substrates; (b) high-energy shoals with unstable substrates of low cohesion and in (c) low-energy open marine environments with soft-substrates. The moderate- to high-stress assemblages occur in (a) oligotrophic environments with reduced terrigenous input in shelf lagoonal or in restricted inner ramp settings; (b) low-energy, soft substrate environments with hypoxia below the sediment–water interface; and, in (c) high-energy shoals and shelf lagoonal environments. The temporal distribution patterns of epifaunal and infaunal bivalve taxa are controlled by variations in water energy, substrate characteristics and productivity level. The reported litho- and biofacies confirmed that the Callovian Tuwaiq Mountain Limestone and the Oxfordian Hanifa Formation were deposited across wide spectrum of depositional environments, ranging from restricted lagoon to moderately deeper open marine basin, and providing the perfect conditions for macrofossils.     

Late Mesozoic bivalve faunas from the Tetori Group,Japan

The Tetori Group of Japan ranks amongst the more important Upper Mesozoic strata in East Asia, with common animal and plant fossils throughout and is well suited for analyses of the links between environmental changes and the various animal and plant fossil assemblages. Three marine transgressions (i. e., Bathonian–Oxfordian, Tithonian–Berriasian and Hauterivian–Barremian in age) have been recognized in the Tetori Group, based on ammonite index taxa. These pulses are also reflected in bivalve faunas which comprise, 81 species in 65 genera (marine taxa) and 16 species in 13 genera (non-marine taxa). Many of these are considered as endemic species to the Tetori Group. In view of the fact that the occurrence of non-marine taxa was primarily controlled by environmental conditions, these do not constitute chronological indices. The faunal composition of the first marine transgressive phase is similar to that found elsewhere in southeast Asia, while that of the second one resembles both that of southeast Asia and of northeast China and Far East Russia. Assemblages of the third phase are similar to those of Heilongjiang, northeast China. Currents from the equator and high-latitudes explain these similarities.     

Jurassic foraminifera from Jajiya Member,Jaisalmer Formation,Western Rajasthan

The Jajiya Member of Jaisalmer Formation yielded a foraminiferal assemblage comprising twenty-three species dominated by the family Vaginulinidae. An Oxfordian age is assigned to the foraminiferal assemblage based on the record of some characteristic Oxfordian species reported from different parts of the world. The foraminiferal assemblage suggests an open marine shelf environment of deposition.     

Refinement of stratigraphy according to the first finds of planktonic species of <Emphasis Type="Italic">Orbulina</Emphasis> and <Emphasis Type="Italic">Praeorbulina</Emphasis> from the Guri Limestone of the Mishan Formation in northwest of Bandar Abbas,South Iran

The Zagros Basin is one of the most universal oil and gas basins that is located in the west to south of Iran and in north of the Arabian Plate. The Guri Member at the bottom of the Mishan Formation, in some areas such as Bandar Abbas hinterland, contains a significant amount of gas. The Bandar Abbas hinterland is located in the southeast of Zagros. The Guri Limestone is the youngest hydrocarbon reservoirs of the Zagros Sedimentary Basin. In this study, a total of 178 samples from the Guri Limestone in the Handun section are investigated for foraminiferal biostratigraphy. The study of foraminifers led to a recognition of 43 genera and 57 species of benthic and planktonic foraminifera. For the first time, planktonic foraminiferal species including Praeorbulina glomerosa, Praeorbulina transitoria, Orbulina suturalis, and Orbulina universa are reported, and based on the identified benthic and planktonic foraminifera taxa, the age of the Guri Member at Handun section is estimated as late Burdigalian to Langhian.     

The Middle to Upper Jurassic stable isotope record of Madagascar: Linking temperature changes with plate tectonics during the break-up of Gondwana

Stable isotope (δ¹⁸O, δ¹³C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3 °C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9 °C) and a minimum in the Early Kimmeridgian (12.3 °C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0 °C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6 °C around averages between 14.4 and 14.7 °C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5 °C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.     

Biostratigraphy and ammonites of the Middle Oxfordian to lowermost Upper Kimmeridgian in northern Central Siberia

The Middle Oxfordian to lowermost Upper Kimmeridgian ammonite faunas from northern Central Siberia (Nordvik, Chernokhrebetnaya, and Levaya Boyarka sections) are discussed, giving the basis for distinguishing the ammonite zones based on cardioceratid ammonites of the genus Amoeboceras (Boreal zonation), and, within the Kimmeridgian Stage, faunas–for distinguishing zones based on the aulacostephanid ammonites (Subboreal zonation). The succession of Boreal ammonites is essentially the same as in other areas of the Arctic and NW Europe, but the Subboreal ammonites differ somewhat from those known from NW Europe and Greenland. The Siberian aulacostephanid zones—the Involuta Zone and the Evoluta Zone—are correlated with the Baylei Zone (without its lowermost portion), and the Cymodoce Zone/lowermost part of the Mutabilis Zone (the Askepta Subzone) from NW Europe. The uniform character of the Boreal ammonite faunas in the Arctic makes possible a discussion on their phylogeny during the Late Oxfordian and Kimmeridgian: the succession of particular groups of Amoeboceras species referred to successive subgenera is revealed by the occurrence of well differentiated assemblages of typical normal-sized macro and microconchs, intermittently marked by the occurrence of assemblages of paedomorphic “small-sized microconchs” appearing at some levels preceeding marked evolutionary modifications. Some comments on the paleontology of separate groups of ammonites are also given. These include a discussion on the occurrence of Middle Oxfordian ammonites of the genus Cardioceras in the Nordvik section in relation to the critical review of the paper of Rogov and Wierzbowski (2009) by Nikitenko et al. (2011). The discussion shows that the oldest deposits in the section belong to the Middle Oxfordian, which results in the necessity for some changes in the foraminiferal zonal scheme of Nikitenko et al. (2011). The ammonites of the Pictonia involuta group are distinguished as the new subgenus Mesezhnikovia Wierzbowski and Rogov.     

Upper Campanian-lower Maastrichtian planktonic foraminifers from Govorov Guyot (Magellan Seamounts,Pacific Ocean)

The planktonic foraminiferal assemblage from foraminiferal limestone (ooze) dredged from the summit of one of guyots in the Magellan Seamount system of the Pacific is dominated by one-keeled species belonging to the genus Globotruncanita. The taxonomic composition of the assemblage correlates host rocks with the upper Campanian-lower Maastrichtian. One species and one subspecies are described as new taxa.     

Sedimentary Cladocera as indicators of past water-level changes in shallow northern lakes

The usability of subfossil Cladocera assemblages in reconstructing long-term changes in lake level was examined by testing the relationship between Cladocera-based planktonic/littoral (P/L) ratio and water-level inference model in a surface-sediment dataset and in a 2000-yr sediment record in Finland. The relationships between measured and inferred water levels and P/L ratios were significant in the dataset, implying that littoral taxa are primarily deposited in shallow littoral areas, while planktonic cladocerans accumulate abundantly mainly in deepwater locations. The 2000-yr water-level reconstructions based on the water-level inference model and P/L ratio corresponded closely with each other and with a previously available midge-inferred water-level reconstruction from the same core, showing a period of lower water level around AD 300–1000 and suggesting that the methods are valid for paleolimnological and -climatological use.     

The Alan-Kyr Coniacian–Campanian section (Crimean Mountains): Biostratigraphy and paleobiogeography aspects

This investigation continues the study of the Alan-Kyr reference section (Central Crimea, Belogorsk Region). The zoned age difference in the stratigraphic scheme of the Upper Cretaceous in the Eastern European Platform is considered according to benthic and planktonic foraminifers, as well as radiolarians in the Alan-Kyr section. This fact can be explained based on the suggestion that stratigraphically important taxa could have appeared in Crimea several million years earlier than on the platform, where they could migrate under the great global eustatic transgression in the Early Campanian. We also considered the influence of paleobiogeographic conditions on the taxonomic composition of the zoned foraminifer complexes, both benthic and planktonic.     

Organic geochemistry of Oxfordian carbon-rich sedimentary rocks of the Russian plate

The lithology and geochemistry of upper Oxfordian sedimentary rocks enriched in marine organic matter (OM) have been studied. These rocks occur as a persistent unit of Upper Jurassic rocks exposed on the right bank of the Unzha River in the Kostroma district. The OM was investigated in detail in both the carbon-rich rocks and their hosts. It was established that the OMs from the Oxfordian rocks are characterized by a low degree of thermal (catagenetic) maturity and their geochemical signature reflects specific features of synsedimentary and early diagenetic processes. Kerogen in the carbon-rich sedimentary rocks is markedly enriched in S_org, and its formation was related to the early diagenetic sulfate reduction (sulfurization of the lipid fraction of the initial OM). The composition of kerogen from the host clay is sharply distinct in many parameters. No derivatives of isorenieratene were revealed in the aromatic fraction of bitumen in the carbon-rich rocks. The Oxfordian carbonaceous rocks are distinguished by slightly enriched in S, Mo, V, and Ni. Anoxic conditions were unstable in the water column during the deposition of carbon-rich sediments (such conditions were probably episodic). The C_org-rich unit formed due to a short-term abrupt increase in the productivity of phytoplankton related to eutrophication of water, probably, as a result of the recycling and redistribution of biophile elements.     

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin,Tibetan Plateau

Global climate during the Jurassic has been commonly described as a uniform greenhouse climate for a long time. However, the climate scenario of a cool episode during the Callovian–Oxfordian transition following by a warming trend during the Oxfordian (163.53 to 157.4 Ma) is documented in many localities of the western Tethys. It is still unclear if a correlatable climate scenario also occurred in the eastern Tethys during the same time interval. In this study, a detailed geochemical analysis on the 1060 m thick successions (the Xiali and Suowa formations) from the Yanshiping section of the Qiangtang Basin, located in the eastern Tethys margin during the Callovian–Oxfordian periods, was performed. To reveal the climate evolution of the basin, carbonate content and soluble salt concentrations (SO₄²⁻, Cl⁻) were chosen as climatic indices. The results show that the overall climate patterns during the deposition of the Xiali and Suowa formations can be divided into three stages: relatively humid (~ 164.0 to 160.9 Ma), dry (~ 160.9 to 159.6 Ma), semi-dry (~ 159.6 to 156.8 Ma). A similar warming climate scenario also occurred in eastern Tethys during the Callovian–Oxfordian transition (~ 160.9 to 159.6 Ma). Besides, we clarify that the Jurassic True polar wander (TPW), the motion of the lithosphere and mantle with respect to Earth’s spin axis, inducing climatic shifts were responsible for the aridification of the Qiangtang Basin during the Callovian–Oxfordian transition with a review of the paleolatitude of the Xiali formation (19.7 + 2.8/−2.6° N) and the Suowa formation (20.7 + 4.1/−3.7° N). It is because the TPW rotations shifted the East Asia blocks (the North and South China, Qiangtang, and Qaidam blocks) from the humid zone to the tropical/subtropical arid zone and triggered the remarkable aridification during the Middle-Late Jurassic (ca. 165–155 Ma).

     

dC Variations in Late Jurassic Carbonates, Jaisalmer Formation, Western India

The carbon isotope measurements, carried out on subsurface carbonate samples from Oxfordian Jaisalmer Formation, western India, yield positive d¹³C values up to +3.17%. The most positive Oxfordian C-isotope value corresponds to the carbon isotope excursion measured in samples from from other late Jurassic basins of world. The latest Oxfordian C-isotope values of Jaisalmer Basin fluctuate around 2% while the C-isotope values of 1.50% mark the base of Kimmeridgian. The Oxfordian C-isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level.     

High-resolution stratigraphy of the Upper Jurassic section(Laptev Sea coast)

Jurassic strata are widespread through Arctic Siberia and host oil and gas fields. However, in most cases, the geology of such vast areas still remains unexplored, and study of the Jurassic stratigraphy and reconstructions of geologic history are possible only through analysis of sediment cores. In this connection, there is a clear need for detailed studies of microfaunas (foraminifera, ostracods) and palynomorphs (dinocysts, spores, and pollen). The studied reference section of the Upper Jurassic and Lower Cretaceous is located on the left side of Anabar Bay of the Laptev Sea (Nordvik Peninsula, Cape Urdyuk-Khaya). An uninterrupted and continuous section from the Upper Oxfordian to the Lower Valanginian is exposed in coastal cliffs and consists mainly of silty clay deposits with abundant macro- and microfossils. Integrated field studies (biostratigraphy, lithostratigraphy, sedimentology) allow a more detailed characterization of the regional geologic framework. A detailed subdivision of the section is based on the systematic composition of ammonites from Upper Oxfordian and Kimmeridgian deposits. Several foraminiferal zones of the Upper Oxfordian and Lower Volgian are defined, and some of them are denfined for the first time. The distribution of ostracods in the section is analyzed for the first time. The section is also studied using palynological analysis, that results in its detailed subdivision on palynological data and recognition of two sequences of palynostratigraphic units. The integrated stratigraphy is used to establish the precise position of stage and substage boundaries. The continuity of the section is defined based on micropaleontological and palynological data.     

New data on Maastrichtian-Paleocene foraminifers from the Sinegorsk Horizon of Southern Sakhalin

Data on planktonic foraminifers first found in the reference section of the Sinegorsk Horizon outcropping along the Naiba River are discussed. The lower part of this stratigraphic unit yields an assemblage of upper Maastrichtian low-latitude thermophilic species, while its upper layers contain upper Paleocene (Thanetian) taxa. Beds with different benthic foraminifers are also defined in the unit.     

The Jurassic orthopteran Allaboilus gigantus Ren and Meng, 2006 (Prophalangopsidae) from Beipiao,Northeast China and its biostratigraphical significance

The orthopteran Allaboilus gigantus Ren and Meng, 2006 (Prophalangopsidae) is reported based on a male forewing from the Middle-Upper Jurassic Haifanggou Formation of Beipiao, western Liaoning, China. This discovery greatly extends the distribution of the species from Daohugou in Inner Mongolia eastwards to Beipiao in western Liaoning. It further provides new evidence for correlation of the Daohugou Beds with the Haifanggou Formation indicating a Callovian-early Oxfordian age for the Daohugou Beds.     

La plate-forme carbonatée oxfordienne de Lorraine : arguments pour une ouverture vers la mer Germanique

The study of sedimentary facies in the quarry of Dompcevrin (Middle Oxfordian) located northwestward of St-Mihiel (Meuse department) provides evidences of high-energy depositional conditions. The occurrence of beaches associated with hurricane coral breccias containing megaclasts is characteristic of platform edge environments. The open sea was located northeastward, in the direction of Germany, as it is indicated by the direction of progradation of beaches. It is concluded that the Oxfordian carbonate platform of Lorraine was opened to the northeast toward the Germanic Sea during the Middle Oxfordian. To cite this article: C. Carpentier et al., C. R. Geoscience 336 (2004).     

Zonal stratigraphy and biogeography of the West Siberian Oxfordian based on ammonites

The Oxfordian Stage of West Siberia contains Boreal ammonites Cardioceratidae. The authors’ bank of paleontological data includes ~ 500 definitions of Cardioceratinae, permitting a considerable refinement of the official Oxfordian regional zonal scale. The lower substage is divided into the Cardioceras (Scarburgiceras) obliteratum, C. (S.) scarburgense, and C. (S.) gloriosum Zones instead of beds with C. (S.) spp., whereas the C. (Cardioceras) percaelatum and C. (C.) cordatum Zones are recognized instead of beds with C. (C.) spp. We have found new ammonites typical of the Middle Oxfordian C. (Subvertebriceras) densiplicatum and C. (Miticardioceras) tenuiserratum Zones. The first of these zones is divided into two subzones. The Upper Oxfordian includes the Amoeboceras glosense and A. serratum Zones instead of beds with A. spp., and the A. regulare Zone and beds with A. rosenkrantzi are recognized instead of the A. ex gr. regulare Zone. The genus Ringsteadia (Aulacostephanidae) is observed only in the northwestern part of the region, along the eastern slope of the North Urals; therefore, two upper units of the biostratigraphic scale correspond to beds with Ringsteadia marstonensis.In the Oxfordian, West Siberia and northern Siberia belonged to the North Siberian province of the Arctic realm. Only in the latest Oxfordian did the northwestern West Siberian basin become part of the Boreal-Atlantic realm, as evidenced by the distribution of Ringsteadia on the eastern slope of the Cis-Polar Urals.     

阿姆河右岸B区中部卡洛夫-牛津阶高精度层序地层划分及层序发育模式

土库曼斯坦阿姆河盆地是世界上著名的大型含油气沉积盆地,然而目前盆地内卡洛夫—牛津阶的层序划分和地层对比依然存在争议。基于Vail经典层序地层学及沉积学相关理论,以阿姆河右岸B区29口井的岩心资料及50口井的测井资料为依据,结合地震、薄片、地球化学等手段,开展了阿姆河右岸B区卡洛夫-牛津阶的层序地层研究。将阿姆河右岸B区卡洛夫-牛津阶划分为5个三级层序和15个四级层序,其中卡洛夫阶包括2个三级层序(SQ1和SQ2),牛津阶分为3个三级层序(SQ3-SQ5)。在高精度层序划分的基础上,建立了研究区的层序地层格架,在垂向上,各级层序格架内部高位域生屑砂屑灰岩及礁滩体沉积更为发育;在平面上,根据不同层序沉积几何体和沉积相的分布,明确提出了卡洛夫期和牛津期发育两种不同的碳酸盐岩台地类型的观点：SQ1-SQ2时期(卡洛夫期)研究区应为缓坡型台地,初始具有西高东低的地貌,坡度较缓,沉积速率差别不大,主要发育缓坡台地层序地层模式;SQ3-SQ5时期(牛津期)则演化为镶边台地,研究区沉积速率远小于A区,随着海平面变化形成了差异巨大的西高东低沉积地貌。     

Problems of Oxfordian and Kimmeridgian stratigraphy in northern Central Siberia (Nordvik Peninsula section)

The Oxfordian–Lower Hauterivian section of the Nordvik Peninsula (northern Central Siberia) is a reference for developing zonal scales for various fossil groups and improving the Boreal zonal standard. In the middle 1950s–late 1980s, it was studied extensively by geologists, stratigraphers, lithologists, and experts on various fossil groups. These studies yielded rich fossil and microfossil collections and a set of parallel zonal scales for various faunal groups. Recently, a new detailed ammonite zonation of the Oxfordian and Kimmeridgian units of this section has been proposed. These results contradict the previous biostratigraphic data on ammonites, foraminifers, and palynomorphs. In the present paper, all the biostratigraphic data on the Oxfordian and Kimmeridgian units of the Nordvik Peninsula (Cape Urdyuk-Khaya) and northern Central Siberia undergo a comprehensive analysis and comparison with those on the Boreal Realm. The ammonite-constrained stratigraphic position of the lower Upper Jurassic in the Cape Urdyuk-Khaya section is interpreted as Upper Oxfordian or Middle Oxfordian. In our view, this difference in the understanding is due to the misidentification of some Oxfordian ammonite forms. The zones based on other fossil groups (foraminifers, dinocysts) which were distinguished in the Upper Oxfordian and Kimmeridgian sections of the Nordvik Peninsula are well traceable circumarctically. Their stratigraphic position in various regions of the Northern Hemisphere is constrained by ammonites and bivalves. However, if we use the last alternative ammonite zonation of this section part, hardly explicable contradictions will appear in interregional foraminiferal and dinocyst correlations.     

"Biostratigraphy and Paleoecology of Paleocene/Eocene (P/E) interval of some geological sections in Central Egypt"

The Paleocene/Eocene boundary intervals were studied in three outcrops along the Nile Valley: Gabal Taramsa, Gabal Qreiya, and Gabal Nag El Quda in Qena and Esna regions. The planktonic and benthic foraminifera have been examined. The qualitative study of planktonic foraminifera distinguishes eight planktonic biozones from (P4 and P5) Paleocene age to (E1, E2, E3, E4, E5, and E6) Early Eocene age. The analysis of quantitative distribution patterns of benthic foraminifera allows the reconstruction of the paleoenvironmental settings in the studied area. The disappearance or scarce appearance of deeper-water benthic foraminifera (Angulogavelinella avnimelechi and Gavelinella rubiginosus) and increasing dominance of shallow-marine taxa (Buliminides, Loxostomoides applinae) indicate deposition in shallow water environments. The benthic foraminiferal assemblages which dominated by Loxostomoides applinae, Buliminids, and Lenticulina indicate Dysoxic conditions and maximum food levels. The species of mid-way type fauna dominate the assemblages of the studied area; the species of Velasco-type fauna are very rare.