Basinal Facies Research Articles

A predominantly ferruginous condition in the Ediacaran deep ocean: Geochemistry of black shales in the Ediacaran Doushantuo Formation, South China

The redox condition of the ocean played an important role in the evolution of the Ediacaran biota, but it remains largely unexplored, particularly for the deep ocean environment. In this study, we present a comprehensive study of Fe speciation and trace elements of the Doushantuo black shales from the Longe and Jinjiadong sections in South China, to investigate the redox condition of basinal environments in Ediacaran. In general, both sections show high FeHR/FeT ratios (>0.38), low FePy/FeHR ratios (<0.7), suggesting a predominately anoxic and ferruginous condition in the deep water of Nanhua basin during the Doushantuo period. A few high FePy/FeHR ratios (>0.7) in the Jinjiadong section indicating occasional euxinia in the basin facies. FePy/FeHR ratios show an increase in the middle part both in the Longe and Jinjiadong sections, indicating enhanced production of H2S via bacteria sulfate reduction (BSR) in the deep anoxic water, which was likely responsible to the upper Doushantuo negative carbon isotope excursion.The enrichment factors (EFs) of most redox sensitive trace elements in the sediments of both sections are low (≤1), while EF-Mo shows moderately enriched (∼3–60), which is similar to the modern Cariaco Basin. Because of paleogeographic restriction or persistent ocean stratification, the trace elements renewal would be mostly obstructed in the isolated deep water, and their inventory could become depleted, which cause the low EFs of most trace elements in sediments. However, for the non-euxinic deep ocean, a “particulate shuttle” would transport Mo from shallow water to deep water through adsorption-desorption on the Mn–Fe-oxyhydroxides, which maintained moderate Mo enrichment in seawater and related sediments.

Lithofacies and sedimentary sequence of the lower Cambrian Niutitang shale in the upper Yangtze platform, South China

The lower Cambrian Niutitang shale in the Upper Yangtze Platform is a hot target for shale gas exploration in China. In this paper, the lithofacies and sedimentary evolution characteristics about this shale formation are studied on the basis of outcrop investigation and experimental measurements. The variations on geochemistry, mineralogy, lithofacies and stratigraphic architecture of this shale are analyzed. This shale is rich in organic matter, with an average TOC content of 5.5%. Quartz and clay mineral dominate the mineral composition, with an average content of 57.3% and 29.8%, respectively. The TOC content correlates positively to quartz content, but negatively to clay mineral content. Trace element ratios of V/Cr, V/(V + Ni) and Ni/Co indicate anoxic to dysoxic conditions prevailed during the Niutitang shale deposition period in Early Cambrian, and moderate to weak degree of restriction are inferred by the covariation of Mo and TOC content. Five lithofacies are identified based on TOC content, mineral composition, texture and fabric: organic-rich siliceous shale, silty siliceous shale, calcareous siliceous shale, argillaceous shale, and silty mixed shale. Four lithofacies associations are interpreted to represent four different depositional facies from shelf margin to abyssal environments. The Niutitang Formation generally shows a shallowing-upward prograding depositional sequence and can be divided into two large shale cycles. From bottom to top, the organic matter content and anoxic degree decreases largely with the sea level fall. The average content of quartz deceases, but the average content of clay mineral increases. Stratigraphic correlation for this shale reveals an obviously decreasing trend of quartz content, but an increasing trend of organic matter and clay mineral contents from slope to basinal facies.

Geological characteristics and shale gas distribution of carboniferous mudstones in the Tarim Basin, China

Extant research on Paleozoic mudstone is well developed in the Tarim Basin, while the research on Carboniferous mudstone is relatively weak. Through systematic study of lithology, geochemical characteristics, reservoir characteristics and gas–bearing properties of Carboniferous mudstone in the Tarim Basin, this study aims to provide a geological basis for the Paleozoic shale gas exploration and development, favorable zone optimization, and resource potential evaluation in the Tarim Basin. The results show that the sedimentary environments of organic-rich mudstone in the study area were mainly basin facies and slope facies. Lithology is dominated by black carbonaceous mudstone, followed by calcareous mudstone, siliceous mudstone, and siliceous rocks. Mudstone is mainly developed in the Kalashayi Formation, which is located in the Bachu and Markit slope belt, with the cumulative thickness of 30–200 m. The organic carbon content is commonly more than 0.4%, and the organic matter types are type II and type III. Thermal evolution degree is widely distributed from a low mature to over mature stage, and different tectonic units have a greater difference. The contents of quartz plus feldspar are between 12% and 82.5%, with an average of 45.8%. The content distribution of clay mineral is from 12% to 57%, with an average of 38.2%. Carbonate minerals (mainly siderite) content is below 50%. The brittle mineral content of the mudstone is approximately 65%, with a strong compressibility, and the mudstone has the material basis of forming crack and natural fracture. Microscopic pores in micro–nanometer level are well developed in the mudstone, including micro bedding joint, microcrack, interbedded pores of clay mineral, nanoscale intragranular or edge pores in the massive organic matter, bioclastic micropores, and mineral dissolution pores, etc. According to the standards provided by the Ministry of Land and Resources in China, the Kalashayi Formation in Bamai Area is a favorable area for shale gas development.

Petrography and Geochemical Features of the Coastal Plain Sands Facies (Benin Formation) Around Nekede and Azara Egbelu Areas, Niger Delta Basin Southeast Nigeria

The Coastal Plain Sands Facies (Benin Formation) of the Niger Delta Basin consists of 99.8% thick accumulation of massive, loose, friable sandstone and 0.2% mud rock. It also consists of pebble imbrications and conglomeratic horizons. Petrographic studies revealed quartz as the dominant mineral (97%) which places the sandstone as quartz arenite. Other minerals include feldspar, limonite, zircon, opaque and minor clay matrix consisting 3%. Geochemical results shows high concentration of Silica (SiO₂) and Aluminum (Al₂O₃) in the sandstone which makes it mineralogical matured. Heavy minerals include Hematite (Fe₂O₃) and Zircon (Zr) while rare earth elements include La, Ce, Nd, Gd and Tb. Trace elements are Cu, Pb, Zn, Ag, Sr, V and Nb which has pronounced enrichment in clay than the sandstones. The color variation of white, yellow and pink are indicative of fully aerated environment and has no effect on the geochemistry of the sandstones.

Earliest Mississippian rugose corals of eastern Australia: post-disaster fauna across the Devonian-Carboniferous Boundary?

The most earliest Mississippian rugose corals are post-disaster taxa occurring in a biosphere strongly modified by the crises associated with the Devonian-Carboniferous Boundary. In Western Europe, basal Tournaisian rugose corals belong to the genera Conilophyllum, Hebukophyllum and Kizilia. Conilophyllum and Hebukophyllum are either homeomorphs or close relatives of each other and are likely post-disaster fauna showing wide morphological plasticity but with an unknown origin. Kizilia is a Lazzarus taxon, known also from basal Tournaisian strata of China, that suddenly reappeared at the Devonian-Carboniferous Boundary being related to the mid-Devonian stringophyllids. The deeper basinal facies of Western Europe (Montagne Noire, Rhenish Mts, Thuringia, Upper Franconia) yield mostly small non-dissepimented solitary rugose corals, together with some dissempimented ones, amongst which are mostly long-ranging taxa. In N America, Vesiculophyllum, a genus very similar, and probably related, to Kizilia occurs together with non-dissepimented long-ranging corals. Like most of the basal Tournaisian dissepimented rugose corals, Cystodactylon orbum gen. et sp. nov. and Gudmania darumbalae gen. et sp. nov. from the basal Tournaisian of eastern Australia are interpreted as post-disaster fauna. Their origin is not understood to date and they seemingly left no descent in the Carboniferous. Their stratigraphic range is extremely limited as they so far are known only in small reefs at the base of the lower Tournaisian Gudman Formation in the type area.

Sedimentology of the Early Jurassic limestone beds of the Kota Formation: record of carbonate wetlands in a continental rift basin of India

Pranhita–Godavari is one of the major rift basins of peninsular India that was actively filled when the Indian landmass was a part of Gondwanaland, the southern supercontinent. The basin-fill succession of this continental rift basin is characterized mainly by fluvial sandstones and mudstones. In the Early Jurassic this basin hosted a freshwater carbonate deposit characterized by a 20–30 m thick alternation of laminated and massive limestones. The remains and traces of land vertebrates, invertebrates and plants suggest that this limestone serves as one of the rare examples of freshwater carbonate depositing environment within a continental rift basin. The limestone interval is characterized by repeatedly stacked meter-thick laminated and massive carbonate-rich sediments. These sediments are classified into two facies associations representing two main depositional domains of a rift-bound, large, freshwater wetland system: a shallow lacustrine palaeoenvironment and a palustrine paleoenvironment. The former palaeoenvironment is characterized by laminated carbonate facies and the later one is by mottled, nodular and bioturbated limestone. Repeated influx of siliclastics by surface flow into ca-rich water bodies produced the laminated carbonates. Whereas, subaerial modifications and reworking of primary deposits resulted in palustrine carbonates. Vertebrate tracks, evidences of rooting, and the absence of deep basinal facies in this succession along with repetitive stacking of sediments formed in subaqueous and subaerial conditions indicates that the depositional environment was more akin to a modern wetland. This Jurassic carbonate wetland developed in the rift basin when the watershed on the adjacent rift shoulder exposed Proterozoic carbonate rocks that provided the ions necessary for carbonate accumulation. The repeated stacking of meter-scale lacustrine and palustrine carbonates in this limestone reflect long-periodicity fluctuations in water level possibly related to subsidence events of the rift valley.

Geochemistry of host rocks in the Howards Pass district, Yukon-Northwest Territories, Canada: implications for sedimentary environments of Zn-Pb and phosphate mineralization

Detailed lithogeochemical data are reported here on early Paleozoic sedimentary rocks that host the large Howards Pass stratiform Zn-Pb deposits in Yukon-Northwest Territories. Redox-sensitive trace elements (Mo, Re, V, U) and Ce anomalies in members of the Duo Lake Formation record significant environmental changes. During the deposition of lower footwall units (Pyritic siliceous and Calcareous mudstone members), bottom waters were anoxic and sulphidic, respectively; these members formed in a marginal basin that may have become increasingly restricted with time. Relative to lower members, a major environmental change is proposed for deposition of the overlying Lower cherty mudstone member, which contains phosphorite beds up to ∼0.8 m thick in the upper part, near the base of the Zn-Pb deposits. The presence of these beds, together with models for modern phosphorite formation, suggests P input from an upwelling system and phosphorite deposition in an upper slope or outer shelf setting. The overlying Active mudstone member contains stratabound to stratiform Zn-Pb deposits within black mudstone and gray calcareous mudstone. Data for unmineralized black mudstone in this member indicate deposition under diverse redox conditions from suboxic to sulphidic. Especially distinctive in this member are uniformly low ratios of light to heavy rare earth elements that are unique within the Duo Lake Formation, attributed here to the dissolution of sedimentary apatite by downward-percolating acidic metalliferous brines. Strata that overlie the Active member (Upper siliceous mudstone member) consist mainly of black mudstone with thin (0.5–1.5 cm) laminae of fine-grained apatite, recording continued deposition on an upper slope or outer shelf under predominantly suboxic bottom waters. Results of this study suggest that exploration for similar stratiform sediment-hosted Zn-Pb deposits should include the outer parts of ancient continental margins, especially at and near stratigraphic transitions from marginal basin facies to overlying slope or shelf facies.

Facies development and paleoenvironment of the Hajajah Limestone Member, Aruma Formation, central Saudi Arabia

The Campanian Hajajah Limestone Member of the Aruma Formation was formed during two regressive episodes. Each of them formed of three depositional facies, from base to top: 1) intra-shelf basin facies, made up of fossiliferous green shale and mudstone with ostracods and badly preserved foraminifers. 2) fore-reef facies, consists of hard, massive, marly coralline limestone. The upper part is rich with low divers, badly to moderate preserved, solitary and colonial corals, and, 3) back reef and near-shore facies, consists of fossiliferous sandy dolomitized, bioturbated limestone with abundant reworked corals, bivalves, gastropods, and aggregate grains. On the basis of field observations, micro-and macrofossils and microfacies analysis, the Hajajah Limestone Member was deposited in distal marine settings below storm wave base in a low-energy environment changed upward to fore-reef framework in an open marine environment with moderate to high energy conditions and terminated with shallow marine facies with accumulation of skeletal grains by storms during regression.

Upper Ordovician – Upper Silurian conodont biostratigraphy, Devon Island and southern Ellesmere Island, Canadian Arctic Islands, with implications for regional stratigraphy, eustasy, and thermal maturation

The conodont biostratigraphy for the Upper Ordovician – Upper Silurian carbonate shelf (Irene Bay and Allen Bay formations) and interfingering basinal (Cape Phillips Formation) facies is established for parts of Devon and Ellesmere islands, central Canadian Arctic Islands. Revisions to the interpreted regional stratigraphic relationships and correlations are based on the stratigraphic distribution of the 51 conodont species representing 32 genera, identified from over 5000 well-preserved conodonts recovered from 101 productive samples in nine stratigraphic sections. The six zones recognized are, in ascending order, Amorphognathus ordovicicus Local-Range Zone, Aspelundia fluegeli Interval Zone, Pterospathodus celloni Local-Range Zone, Pt. pennatus procerus Local-Range Zone, Kockelella patula Local-Range Zone, and K. variabilis variabilis – Ozarkodina confluens Concurrent-Range Zone. These provided a more precise dating of the members and formations and, in particular, the range of hiatuses within this stratigraphic succession. The pattern of regional stratigraphy, facies changes, and hiatuses is interpreted as primarily related to the effects of glacioeustasy associated with the terminal Ordovician glaciation and smaller Early Silurian glacial phases, the backstepping of the Silurian shelf margin, and the geodynamic effects of the collision with Laurentia by Baltica to the east and Pearya to the north. Conodont colour alteration index values (CAI 1–6.5) from the nine sections complement earlier graptolite reflectance data in providing regional thermal maturation data of value in hydrocarbon exploration assessments.

Basin evolution model during cretaceous in the northeastern of Arabian plate in Kurdistan region

The research area concentrates in a part of the main Zagros fold and thrust belt in the Kurdistan region (Northern Iraq). From study tectono-stratigraphy we constrain the story of the basin evolution of Kurdistan during Cretaceous. However we mainly investigated the evolution of the pre-Subduction and Pre-collision periods, focusing on the relationship between tectonics and sedimentation. For this purposes we developed (1) a biostratigraphic approach using nannofossil analysis, (2) a fault tectonic analysis, and (3) a stratigraphic study. The Zagros fold belt in Kurdistan exhibits many lateral and vertical environmental and facies changes, especially during the Cretaceous times. During the Jurassic period the Kurdistan is occupied by the restricted Gotnia Basin. This basin disappeared and the Kurdistan area changed to open marine of a southwest Kermanshah Basin during the Cretaceous. During the Berriasian to Barremian the Kurdistan was covered by the carbonates of the Balambo and Sarmord formations. In the east and southeast the neritic Sarmord Formation gradationally and laterally passes to the basinal facies of the Balambo Formation. In the Aptian to Cenomanian period shallow massive reefal limestone of the Qamchuqa Formation deposited. The normal faulting that initiates during the Aptian is associated with an abrupt lateral change of the reefal Qamchuqa Formation to the Aptian-Cenomanian part of the Balambo Formation. During the Cenomanian-Early Turonian periods the graben formed in the Dokan Lake in eastern Kurdistan, where developed a deeper restricted environment (Dokan and Gulneri formations) surrounded by a shallow marine platform. During the Turonian the marine pelagic micritic cherty limestones of Kometan Formation covered northeast of Kurdistan, whereas in the Safeen, Shakrok and Harir anticlines the formation was totally, or partially, weathered during the Coniacian-Early Campanian period. The deposition during the Late Cretaceous is very heterogeneous with a gap in the Coniacian-Santonian times probably related to a non-deposition. Associated with extensive tectonics a basin developed during the Campanian with the deposition of shales, marls and marly limestones of the Shiranish Formation. The first appearance is the Kurdistan of the flysch facies of the Tanjero Formation was precisely dated of the Upper Campanian in northeastern Kurdistan. The Tanjero Formation conformably overlaying the Shiranish Formation and was deposited in the foredeep basin associated with the obduction of Tethyan ophiolites onto the Arabian Platform. The Early to Late Campanian period is a time of non-deposition in Central Kurdistan (Safeen, Shakrok and Harir anticlines). During the Late Campanian the Bekhme carbonate platform in the north disappeared when the marly limestones of the Shiranish Formation transgressed over the Bekmeh Platform. In the Aqra area the Maastrichtian Tanjero Formation laterally changed to the thick reefal sequence of the Aqra Formation that unconformably overlies by the Late Paleocene-Early Eocene lagoonal carbonate of the Khurmala Formation. The Campanian sedimentation is mainly controlled by NE- oriented normal faults forming Grabens in Dokan, Spilk and Soran areas. During the Maastrichtian in the extreme northeastern Kurdistan the NE-SW and NNW-SSE normal faults developed in the foredeep basin and originated horsts and grabens.

Ocean oxidation during the deposition of basal Ediacaran Doushantuo cap carbonates in the Yangtze Platform, South China

Precipitation of cap carbonate lithologies is a key feature of Cryogenian global glaciations. Negative carbonate carbon isotopic compositions (δ13Ccarb) of these cap carbonates have been variably interpreted as massive drawdown of atmospheric CO2 via extensive continental chemical weathering, methane oxidation, or postglacial upwelling. Each of these interpretations argues a non-steady state of carbon cycle in the aftermath of Marinoan global glaciation. To further explore the postglacial marine carbon cycle, we measured δ13Ccarb of cap carbonates from six localities in the Yangtze Platform, South China. The studied cap carbonates were deposited in a variety of sedimentary environments, ranging from the open shelf, slope, to basin facies. Cap carbonates deposited in different environments show distinct stratigraphic trends of δ13Ccarb. In the open shelf, δ13Ccarb profile of the Songlin section remains almost constant (−3 to −4‰), while the δ13Ccarb of the Jiulongwan section records a negative excursion, decreasing from −3.5‰ to −7‰. δ13Ccarb of cap carbonates deposited in the slope environment does not show stable stratigraphic trend. In the basin environment, δ13Ccarb demonstrates a sharp decline in the middle part of cap carbonates to the nadir value of ∼−11‰. The negative δ13Ccarb excursion is best interpreted in terms of oxidation of dissolved organic carbon (DOC), thus recording a pulse of ocean oxidation during cap carbonate precipitation. Clearly absence of negative δ13Ccarb excursion in all slope and most open shelf sections may imply that such oxidation event was not ubiquitous in the Yangtze Platform. We speculate that the renewed thermohaline circulation during deglaciation brought oxic surface water into ocean interior, which oxidized the basin environment of the Yangtze Platform. However, the deglacial thermohaline circulation was not strong enough to cause complete oxidation of the ocean. The sporadic oxidation in the open shelf, on the other hand, might result from the terrestrial influx of oxidant from postglacial continental weathering. Our study suggests that ocean oxidation, though sporadic, might have occurred during cap carbonate precipitation, and predated the first appearance of putative animal embryos.

Age and distribution of the Late Devonian brachiopod genus Dzieduszyckia Siemiradzki, 1909 in southern China

Conodont biostratigraphical work was done at four sections recently found with occurrence of the rhynchonellide brachiopod genus, Dzieduszyckia Siemiradzki, in southern Guangxi and in the border area between Dushan County of Guizhou and Nandan County of Guangxi, South China. These sections represent two different types of facies, i.e., carbonate platform and intraplatform basin. The conodont analysis reveals that this genus occurs in the Upper triangularis Zone and the Middle crepida Zone at the Dazhai Section, through the Lower to Upper crepida zones at Dalong, and is restricted within the Upper rhomboidea Zone at the two intraplatform basin sections (Changtang and Duli). This result demonstrates that the occurrence of these peculiar rhynchonellide brachiopods in South China, regardless of the depositional environments, is within the Lower Famennian instead of the previously suggested Upper Famennian. Furthermore, this brachiopod genus in South China began to inhabit on the carbonate platform almost since the beginning of the Famennian and did not extend to the intraplatform basin facies until the late Early Famennian.Available biostratigraphic data indicate that during the Early and Middle Famennian, Dzieduszyckia is widely distributed not only in South China, but also throughout the world, such as Morocco and southern Ural.Observation on the new collections from the four studied sections reveals that the peculiar rhynchonellide brachiopods have a great morphological variation within each section. Significant differences existed among the collections from different sedimentary settings and localities, probably reflecting the environmental and geographic constraint on the morphology of Dzieduszyckia. Samples from different layers in the same section have nearly identical morphological variation, suggesting the temporal inheritance in morphology of the rhynchonellide brachiopod.

The Kulm Facies of the Montagne Noire (Mississippian, southern France)

1. Introduction With the beginning of geological and stratigraphical research in Western Europe in the early 19th century, two main marine facies realms have been identified in the lower Carboniferous (Mississippian) strata based on specific lithologies and organic content. The Carboniferous Limestone or Kohlenkalk represents the shallow-water platform facies and was first identified in the British Isles and Southern Belgium. The Kulm is equivalent of the deeper water, basinal facies of the German Rhenohercynian Basin (Fig. 1). Both names are still widely in use and especially the Kulm has been exported outside its regional and stratigraphical context. Figure 1. Localisation of the main outcrops of Kulm Facies in the framework of Variscan Europe. The attribution of the regions 5-6 in the southern Variscides is disputable. Kulm deposits in Variscan massifs included in Alpine mountain chains (e.g. Betic Cordillera) have been omitted except for the Pyrenees. The division into large tectonic units is from Franke (2014). One of these examples is found in southwest France. Here, south of the Massif Central, the remnants of a Mississippian foreland basin are exposed in the Montagne Noire, the Mouthoumet Massif and the Pyrenees (Fig. 1). The best-exposed and most complete succession is found in the Montagne Noire (Figs 1, 2). It is the aim of the paper to summarize the currently available data on the Kulm Facies of that region, to discuss a depositional model, to place the successio

A tight-gas reservoir in the basinal facies of the Upper Permian Ca1 in the southwestern Zechstein Basin, Poland

The Ca1 basinal deposits of the Werra cycle in the southwestern Zechstein Basin, Poland, are similar to those in other parts of the basin, although a high porosity (15 %) dolomite reservoir unit in the middle part near the Rudna Copper Mine (KGHM Polska Miedź S.A.) has a gas accumulation comprised mainly of nitrogen. The reservoir horizon is developed within dolomitic grainstone and occurs in the upper part of the second regressive cycle of the Zechstein Limestone as a result of redeposition of unconsolidated sediment from the carbonate platform margin to the basin floor. Early dissolution of the aragonite components of the grainstone and early dolomitization created moldic and minor intercrystalline porosity. The most important process that formed the porosity was deep burial release of carbon dioxide from the thermal decomposition of organic matter within over- and underlying deposits. The acidic porewater resulted in the dissolution of the rock fabric, which increased the porosity, and on the other hand caused the formation of a Mn-rich dolomite cement that precipitated in the intercrystalline space surrounding the newly formed pores. The created isolated pores were partially filled by euhedral dolomite crystals with Mn-rims. Later dissolution and cementation had a significant influence on the isotopic results. The δ18O values show a clear decrease in the grainstone section from −2 to −5 ‰. The δ13C values (from −3.84 to −5.40 ‰) are typical for the Polish Zechstein Basin; however, there is no significant increase in the δ13C values up-section as is the case for the coeval platform facies. This may indicate that the basinal facies was deposited in more uniform conditions than the platform facies.

Paleogeographical reorganization of the Moscow Syneclise during the Severodvinian (Capitanian–Wuchiapingian) time based on isotopic (δ13C and δ18O) and paleontological data, Permian Period, East European Platform

Detailed studies of the isotope composition of carbon and oxygen (δ13C and δ18O) in sedimentary and pedogenic carbonates from the stratotype of the Severodvinian Stage of the Permian System (Sukhona River, Vologda Region) are provided. In these deposits, the value of δ13C is the greatest for the Upper Permian and Lower Triassic of European Russia. This level is correlated with the Kamura isotopic geochemical event in the marine sections of Panthalassa and the Tethyan Region, which was connected with a fall in temperature during the Early–Middle Capitanian. Variations of δ18O in the Severodvinian Stage also support the concept of general fall in temperature. The lower part of the Severodvinian Stage is characterized by carbonates with a very heavy oxygen isotope composition, about 32–34‰ SMOW, which accumulated during evaporitization of a large basin. In the upper part of the Severodvinian Stage, the value of δ18O rhythmically changes from 22–24‰ SMOW to 34‰, naturally following the cyclicity established based on sedimentological features. The minimal values of δ18O are episodes of a significant decrease in salinity as a result of decreased temperature and humidification. The highest values of the isotope content of oxygen correspond to the episodes of short warming and evaporitization of shallow lakes. A general decrease in average annual temperature in the middle of the Severodvinian Age was associated with activation of rivers and intensification of terrigenous sedimentation, which resulted in replacement of the basin facies by alluvial facies and to wide occurrence of aerial and subaerial conditions. Simultaneously, in the latter half of the Severodvinian Age on the East European Platform, there was essential renewal of assemblages of tetrapods, fishes, ostracodes, mollusks, and plants.

The Late Devonian Frasnian–Famennian Event in South China — Patterns and causes of extinctions, sea level changes, and isotope variations

The Frasnian–Famennian (F–F) event may be recognized in various facies areas in South China. In the pelagic cherty basin facies, both Lower and Upper Kellwasser events can seemingly be recognized. In the deeper water carbonate facies, the F–F event level is well controlled in light of conodont biostratigraphy. In the shallow water carbonate and mixed carbonate-shale facies, the F–F boundary may be defined by clear taxonomic distinction in benthic fossils (articulate brachiopods and corals) as well as evidence from minor pelagic fossils. Post-extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups. In open shallow water platform to inter-platform depression areas, brachiopods seem to recover quickly, probably in the Middle Pa. triangularis Zone; benthic ostracodes seem to recover at a later stage; recovery of rugose corals did not happen until the uppermost Famennian. Three steps of the F–F mass extinction are postulated: 1) extinction of diverse brachiopods (including most atrypids); 2) extinction of pelagic conodonts; 3) extinction of both benthic faunas (very abundant and diverse rugose corals and ostracodes) and pelagic conodonts. Evidence of an end-Frasnian regression in South China is clear, particularly in shallow water settings. However, in deeper water settings, the picture is complicated, with evidence of both sea level rise and fall in the latest Frasnian. It may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic/hydrothermal activities may have mainly caused frequent and rapid climatically warming-cooling alterations and sea level changes as well as marine ecologic collapse (eutrophication, microbial blooming, seawater acidification, and anoxia), which may explain the F–F extinction pattern in South China.

Sedimentary evolution of overlapped sand bodies in terrestrial faulted lacustrine basin: Insights from 3D stratigraphic forward modeling

Terrestrial faulted lacustrine basins usually have large variabilities in structural subsidence and multiple river sources. The facies in such basins are thus characterised by frequently changed facies and complex relationship of overlapped sand bodies (e.g. Liaoxi Depression of Liaodong Bay, Bohai Sea, China). Therefore, it's a great challenge to quantitatively describe evolution of sand bodies and their overlap relationship. In this study a three-dimensional stratigraphic forward model is used to solve this problem, which is corrected according to well log data. After the parameter optimization was verified against borehole strata thickness and lithology, this model had a thickness error within 8%, and the lithology distribution agreed with the well data as a whole.Four evolution phases of the Shahejie 3 Formation were recognised through the modeling. In the first phase, the lake level rose, and the eastern fan delta sand developed. In the second phase, the fan delta sand scaled up, and the braided river delta front sand developed at a small scale. In the third phase, the lake level shifted from falling to rising, the fan delta sand further expanded the scale, and the braided river delta developed at a large scale. Sands on both sides overlapped at a large scale. In the fourth phase, the lake level rose, the lake basin expanded, and lake shale was the main lithology in the study area. From the sedimentary evolution of Es3 formation, sand overlapped in the third stage. In 39.75 Ma, two parts of the sand body began to overlap and reached largest scale in 39.6 Ma, which was approximately 10 km2. Both then retrograded to a separation in 39 Ma when the overlap ended.Coupling stratigraphic forward simulation with uncertainty quantification allowed us to estimate the influence of each stratigraphic parameter on sand overlap. Fluvial discharge appears to be the most influential parameter while the initial bathymetry and lake level variations exert a minor to moderate impact.

Climate changes during the Early–Middle Triassic transition in the E. Iberian plate and their palaeogeographic significance in the western Tethys continental domain

Until recently the climate of the Early–Middle Triassic at low latitudes was broadly considered as generally temperate-warm with no major climate oscillations. This work examines the climate of this period through a detailed study of the sedimentary, plant, soil and mineral records of continental rocks (Buntsandstein facies) in eastern Iberian basins. Our findings indicate temporal climate variations for these near equator (10°–14°N) regions and unveil the significance of such variations in the southern Laurasian domain.The climate of Iberia's Early Triassic was mainly dominated by alternating brief (<0.4ma) arid and semi-arid climate periods, with two main arid periods documented at the end of the Smithian and middle Spathian. However, an initial short subhumid to semi-arid period was also observed in the late Spathian. Remarkably, this latter period appears just after an unconformity related to the tectonically induced Hardegsen Event in western Europe. It is also of interest that this short subhumid climate period is concurrent with the beginning of faunal and floral recovery in the basins examined. The Early Triassic ended again with a short very arid period.Although the beginning of the Anisian (Aegean) was represented by alternating arid and semi-arid to subhumid intervals, during the Bithynian and Pelsonian clearly wetter climates are recorded by the succession consisting of alternating semi-arid to semi-humid intervals. This general tendency was interrupted by three short but marked intervals, two humid intervals in the late Bithynian, and one arid period near the Bithynian/Pelsonian boundary.Iberia was crossed by prominent irregular highs separating marked corridors or isolated areas. This palaeogeography, prevailing since Variscan tectonics, clearly conditioned dominant climates and their geographical distribution. No clear climate belts developed in these conditions. However, isolated internal climate zones separated by elevated areas are identified. This palaeogeographic configuration and the low latitudinal position of Iberia determined central Iberia highs in the southernmost border of Laurasia, beyond which more humid conditions clearly extended towards the equator reaching the present-day Moroccan Meseta and Argana Basin.

Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part III: The heteroconchs

The heteroconch bivalve fauna of the deep-water (&gt;200 m) Keasey Formation in northwestern Oregon records the Eocene–Oligocene climatic transition and replacement of tropical widely-distributed taxa by the cryophilic taxa that dominate modern high-latitude faunas of the North Pacific. Low-diversity assemblages occur in tuffaceous mudstone and siltstone facies of a deep nearshore basin at the onset of subduction on the Cascadia Margin. Six species of anomalodesmatan heteroconchs have been treated separately, and the remaining Keasey heteroconchs treated here include one basal archiheterodont and 13 imparidentian euheterodonts. The families represented are Carditidae, Thyasiridae, Lucinidae, Lasaeidae, Cardiidae, Tellinidae, Basterotiidae, Mactridae and Veneridae. New taxa include the genus Anechinocardium and seven new species: Cyclocardia moniligena, Conchocele bathyaulax, Conchocele taylori, Kellia saxiriva, Kellia vokesi, Moerella quasimacoma and Saxicavella burnsi. Three species lacking adequate material for formal description are treated in open nomenclature. New features useful for taxonomic discrimination include heretofore unrecognized differences in micro-spines and lamellae on the posterior slope in cardiid bivalve genera and presence of a faint subumbonal ridge in three genera of basterotiid bivalves. Four of the new species are in families in which thiotrophic and methanotrophic chemosymbioses have evolved. Specimens are typically articulated. Shell material is well preserved in the massive units but often chalky or highly altered at cold-seep sites. Fossils are never abundant except for local concentrations in carbonate mounds and associated carbonate lenses, blebs and nodules at cold-seep localities. Multiple lines of evidence of both diffuse and robust flow of fluids rich in reduced compounds are reviewed for three sites where the fauna includes an inner core of chemosymbiotic taxa and peripheral zone of taxa that are opportunistic and tolerant of hypoxia.

Calpionellid biostratigraphy across the Jurassic/Cretaceous boundary in San José de Iturbide, Nuevo León, northeastern Mexico

Detailed bed-by-bed sampling on an outcrop of the La Casita and Taraises formations in northeastern Mexico (San Jose de Iturbide, Nuevo Leon State) allows the delimitation of the Jurassic/Cretaceous boundary. The Late Tithonian was determined by the presence of the Crassicollaria Zone (Colomi Subzone). Underlying subzones (Remanei and Brevis) were not identified due to the scarcity and poor preservation of calpionellids. The Jurassic/Cretaceous boundary was defined by the acme of the small and spherical form of the species Calpionella alpina Lorenz in sample IT-120. The Berriasian was divided into two zones and five subzones: the Calpionella Zone (Alpina, Ferasini and Elliptica subzones) and the Calpionellopsis Zone (Simplex and Oblonga subzones). The facies studied indicate that deposition during the Tithonian occurred in a toe of slope environment with occasional deep shelf incursions. Near the Jurassic/Cretaceous boundary, a sea level drop is recorded and the facies indicate a slope environment with the occurrence of a breccia level. A general deepening of the environments recorded within the frame of the Elliptica Subzone where the deposits pass into basinal facies