Outcrop Sections Research Articles

Hydrocarbon source rock potential and paleoecological studies of the Surma sediments of Manipur region, India: Insights from palynology and organic geochemistry

The palynological assemblages, organic content, Rock-Eval analysis and stable isotope ratios of three outcrop sections were studied of the Miocene Surma Group in Indo-Myanmar Range to characterize the lithology, and assess kerogen types. The well-preserved palynological assemblages from the ATF, AAN and AAS sections indicate a tropical-subtropical climate with humid conditions. The δ13C values of the organic matter in these sections ranges from −19.92 to −26.08 ‰, indicative of C3 vegetation. Among these sections, our data indicates ATF has the driest and AAN wettest climate. Results from Rock-Eval analysis suggests that all the rock samples have poor organic richness (TOC < 0.5 %) and poor hydrocarbon generation potential (S2 < 0.5 mgHC/g). The organic matter of these samples is mixture of Type III and Type IV. The Tmax and Productive Index values support the results of visual kerogen analysis suggesting immature with mature and contaminant zones. The Surma sediments are poor source of gaseous hydrocarbons based on the results of this work.

Mineralogical and petrographic characteristics of the Ordovician-Silurian Wufeng-Longmaxi Shale in the Sichuan Basin and implications for depositional conditions and diagenesis of black shales

Depositional and diagenetic processes play important roles in controlling the fabric and petrophysical properties of black shales. In this study, an outcrop section of the Wufeng-Longmaxi Shale was studied through sedimentologic facies analysis, petrographic observations (both transmitted- and reflected-light microscopy and scanning electron microscopy), and X-ray diffraction analysis to investigate how depositional and diagenetic processes controlled the accumulation and evolution of organic-rich black shales. The studied Wufeng-Longmaxi Shale consists of over-mature black shales, with an equivalent vitrinite reflectance of 3.07%. Organic matter is dominated by pyrobitumen and graptolite, the former of which hosts abundant organic pores. Minerals mainly consist of quartz (average 42 wt %), carbonates (average 37.4 wt %), and clay minerals (average 15 wt %). Eighty percent of quartz is of biogenic origin, which occurs as siliceous fossils and microcrystalline quartz. Microcrystalline quartz forms a rigid framework and preserves organic pores from compaction. Clay minerals comprise dominantly (95 wt %) illite and mixed-layer illite/smectite. The vertical variations in lithofacies and quartz and carbonate mineral content exhibit three cycles, likely corresponding to three transgressive-regressive cycles. Within each cycle, quartz content first increases to reach a maximum at the maximum flooding surface, and then decreases. Although long being considered as deposited under quiescent and anoxic conditions, sedimentologic and petrographic analyses in this study indicate that the deposition of the Wufeng Formation and lower Longmaxi Formation was subject to intermittent reworking by bottom currents and bottom-water dysoxia. Meiofauna capable of tolerating low oxygen content could have lived in surficial sediments and disrupted the original fabric of sediments formed by bottom currents. Mineralogical and petrographic analyses in this study provide new insights into the accumulation mechanism of the organic-rich black shales of the Wufeng-Longmaxi Formations, calling for a critical reappraisal of other black shales that have conventionally been considered as deposited under mostly quiet and anoxic conditions. • Mineralogical and petrographic characteristics were studied. • Three stratigraphic cycles were identified. • Depositional conditions were not persistently quiescent and anoxic. • Intermittent reworking by bottom currents and bottom-water dysoxia existed.

Characteristics and primary mineralogy of fibrous marine dolomite cements in the end-Ediacaran Dengying Formation, South China: Implications for aragonite–dolomite seas

Fibrous marine cements are widely distributed in the terminal Ediacaran Dengying Formation of South China and are an important record for reconstructing paleoseawater chemistry. However, the morphological characteristics and filling sequence of these cements, and their formation mechanism and paleoceanographic significance, are poorly understood. Our investigation of five outcrop sections in the northern upper Yangtze region allows four types of fibrous dolomite cement to be identified: fascicular fast dolomite (FFD), radial fast dolomite (RFD), radial slow dolomite (RSD), and fascicular slow dolomite (FSD), where “fast” and “slow” refer to the optical character of cement crystals. FFD cements possess original aragonitic mineralogy, whereas RFD cements had high-Mg calcitic precursors that subsequently underwent mimetic dolomitization via syntaxial replacement. RSDs and FSDs are primary marine precipitates, whereas fibrous dolomite cements with length-fast optical characteristics (FFDs and RFDs) are of secondary origin. These fibrous cements are widely distributed laterally in the Dengying Formation, although the RSDs and FSDs occur only in the second member of this formation. Therefore, the seawater chemistry of the terminal Ediacaran period in the upper Yangtze area was dominated by an aragonite sea, with a regional short-lived “dolomite sea” during the late depositional stage of the second member of the Dengying Formation, from which dolomite may have directly precipitated.

First record of Late Pennsylvanian fusulinids from the North Tianshan belt, NW China

A noteworthy late Pennsylvanian fusulinid fauna is for the first time reported from the Qi'eshan Formation in the Eastern Tianshan, NW China. From three main outcrop sections, 19 species of six genera are identified and illustrated, among which several index taxa are described in detail. The present fusulinids are assigned to the middle Kasimovian to early Gzhelian in age, representing the youngest fusulinid fauna in northern Xinjiang up to now, which constrains the age of the Qi'eshan Formation up to the early Gzhelian. Palaeobiogeographically, the fusulinid fauna in the Eastern Tianshan was closely related to the populations from Central Asia (e.g., southern Fergana, the Alay Mountains and Darvaz) of the western Palaeotethyan Subprovince, and kept exchanging with those from the Eastern European Platform of Ural Province, given the common, particularly endemic species. The characteristic species include Montiparus ex gr. sinuosus alaicus, Rauserites rossicus, Schwageriniformis fusiformis, Triticites acutus, Triticites arcticus, and Triticites arcticus cybaeus. This palaeobiogeographic affinity suggests that the close of timing of the North Tianshan Ocean was later than the Early Gzhelian, and that the southern Urals and western Palaeotethys shared a common fusulinid fauna during this period.

Abundant conodont faunas from the Olenekian (Early Triassic) of subsurface British Columbia, Canada and diversification of the Neogondolellinae around the Smithian–Spathian boundary

Abundant conodont faunas from the subsurface of British Columbia, Canada, allow the correlation of Lower and Middle Triassic strata with outcrop sections in British Columbia, the Canadian Arctic and the western USA, as well as recording the previously recognized radiation of neogondolellin conodonts in the early Spathian. Twenty-eight samples collected from the Progress Hz Caribou D-040-H/094-G-07 and Progress Hz Laprise A-082-I/094-G-01 wells yielded more than 1100 conodont specimens, representing twenty-nine pectiniform species belonging to fourteen genera. These faunas enable the recognition of the Dienerian–Smithian, Smithian–Spathian, and Spathian–Anisian boundaries in these wells. Five of the conodont species recognized in the Smithian and Spathian samples are new: Neogondolella n. sp. A, Borinella n. sp. A, Magnigondolella. n. sp. A, Columbitella n. sp. A, and Co. talpa sp. nov. Together with these new segminiplanate species, several other neogondolellin conodonts occur. These faunas are the manifestation in British Columbia of the previously recognized increase in abundance of neogondolellin conodonts in the early Spathian, and they are consistent with hypotheses in which the earliest species of Magnigondolella evolved from Borinella by a progressive fusion of the denticles of the carina. These conodonts help to characterize the events around the globally significant Smithian–Spathian boundary, and to correlate this boundary in North America.

An Early Jurassic (Sinemurian–Toarcian) stratigraphic framework for the occurrence of Organic Matter Preservation Intervals (OMPIs)

Lower Jurassic sedimentary successions in the Atlantic margin basins include several organic-rich intervals, some with source rock potential; time-equivalent units are also identified in on- and offshore areas worldwide. Despite decades of research, it is still unclear which mechanisms lead to the deposition of organic-rich sediments during the Early Jurassic. The objectives of this study are to construct a detailed temporal and geographical framework of Sinemurian–Toarcian organic matter preservation intervals (OMPIs; subdivided into local, regional, and superregional) and roughly constrain the relationship of OMPIs with the Lower Jurassic δ 13 C record. This survey combines an in-depth analysis of literature on the distribution of organic-rich facies in the Sinemurian–Toarcian with new geochemical studies [total organic carbon (TOC) and organic matter pyrolysis] from selected outcrop sections from Portugal, Spain, and Morocco. Strong local control on OMPIs during most of the Sinemurian is suggested. Regionally widespread organic-rich facies are associated with the most negative δ 13 C values of the broad Sinemurian–Pliensbachian negative carbon isotopic trend recorded in organic matter (including the Sinemurian–Pliensbachian Boundary Event). Pliensbachian OMPIs are expressive in the areas bordering the proto-Atlantic Ocean and are often linked with positive δ 13 C excursions and short-lived warm intervals, but OMPIs are also defined for the Late Pliensbachian cool interval. Early Toarcian superregional OMPIs are associated with some of the most pronounced δ 13 C excursions of the Mesozoic. Toarcian maximum TOC content occurs with the positive δ 13 C (recovery) trend following the δ 13 C negative shift typically linked with the Early Toarcian Oceanic Anoxic Event (T-OAE), supporting the notion that peak carbon sequestration/ocean anoxia post-dated the main phase of carbon input into the atmosphere, as also suggested by recent modelling efforts. However, additional superregional OMPIs predate and postdate the T-OAE, indicating that conditions favouring preservation of organic matter (increased productivity and/or enhanced preservation) during the Early Toarcian were not restricted to the T-OAE interval. The compilation of Sinemurian–Toarcian OMPIs presented in this paper demonstrates that organic-rich intervals of regional and superregional expression in the Lower Jurassic sedimentary record are ubiquitous and may even be more numerous than in the Cretaceous. Considering the association of some of the Sinemurian, Pliensbachian, and Toarcian (not taking into account the T-OAE related OMPIs) regional and superregional OMPIs with well-defined carbon isotopic excursions, it is here suggested that these hold the same relevance as the secondary OAEs of the Cretaceous, such as the Valanginian OAE (Weissert Event), Hauterivian OAE (Faraoni Event), and Late Aptian–Early Albian OAE (OAE 1b cluster).

Life at the continental–marine interface: palaeoenvironments and biota of the Alcobaça Formation (Late Jurassic, Central Portugal), with a formal definition of the unit appended

The Kimmeridgian Alcobaça Formation of the Lusitanian Basin forms a mixed carbonate–siliciclastic unit between basinal deposits of the Abadia Formation, and fluvial–terrestrial strata of the Lourinhã Formation. This study presents >2.5 km of detailed logs of nine outcrop sections of the Alcobaça Formation in its type region. Eight of these sections encircle the Caldas da Rainha Diapir, which was a prominent, emergent, passive salt diapir during the time of deposition. Palaeoenvironments of the unit form a complex mosaic of low- to high-energy, carbonate- or siliciclastic-dominated shallow shelf settings; coastal embayments and lagoons; and coastal plains with rivers, lakes and playas. In the strata, abundant microfauna is often joined by a rich macrofauna, usually dominated by bivalves. Locally, corals, calcareous sponges or oysters form meadows or patch reefs. These autochthonous to parautochthonous remnants of former communities are assigned to 35 benthic macrofaunal associations. The integration of palaeoecological analysis of these associations with microfaunal and sedimentological data provides constraint on their salinity ranges, which range from slightly hypersaline to freshwater. Frequent temporal and spatial salinity fluctuations are attributed to variations in relative sea-level, salt tectonics or climate. The NNE-trending Caldas da Rainha Diapir induced pronounced facies differentiation. Predominantly, non-marine siliciclastic facies in the northwest and carbonate to siliciclastic, marine to brackish facies in the southwest are contrasted by shallow-marine carbonate facies east of the diapir. Comprehensive exposure and well-preserved fossils make the Alcobaça Formation an excellent showcase to demonstrate how biofacies analysis can help to disentangle the interplay of climate changes, sea-level fluctuations and salt tectonics. Based on the improved characterisation of the unit, the Alcobaça Formation is formally defined, and seven members are established.

Investigation of origin, sedimentary environment and preservation of organic matter: A case study in Garau Formation

Knowing the characteristics of suitable environments for precipitation of oil prone source rocks facilitates oil explorations and leads to development of oil fields. The current study investigates the organic matter properties and sedimentary environment conditions of the Garau Formation in various outcrop sections in Lurestan province from south-west of Iran (High Zagros) with using elemental analysis, visual kerogen analysis and Rock-Eval pyrolysis data. The geochemistry parameters indicate that the Garau Formation is an excellent oil prone source rock and composed of kerogen type I and II. The oxygen index (OI) is very low which reveals that organic matter deposited in an anoxic sedimentary environment and suitable for the preservation of organic matter and hydrocarbon generation. The visual analysis of isolated kerogens from source rock samples indicates the abundance of dark amorphous organic matter (AOM) with small amounts of phytoclasts and pyrite with no palynomorphs. Sedimentation seems to have occurred in deep and reduced parts of a carbonate basin during a rapid transgression. In addition, due to the effect of thermal maturation, the color of amorphous organic matter has darkened. The elemental analysis and Van-Krevelen diagram was shown that the type of organic matter and reveals the thermal maturity of the oil window. Moreover, amount of pyritic sulfur (Sp) and organic sulfur (So) contents have been calculated, and it was reveals that the high content of organic sulfur is a key element in the structure of organic matter.

Variations in microbial ecology during the Toarcian Oceanic Anoxic Event (Early Jurassic) in the Qiangtang Basin, Tibet: Evidence from biomarker and carbon isotopes

Reduced animal diversity during mass extinctions is commonly associated with resurgence of microbial abundances. The Toarcian Oceanic Anoxic Event (T-OAE) was a critical interval characterized by dramatic perturbations to the environment and life in the oceans and on land. A comprehensive organic geochemical study was performed on 19 samples from the upper Pliensbachian-lower Toarcian interval of the Quse Formation across the T-OAE at the Bilong Co outcrop section (also known as Biluo Co) in the Qiangtang Basin. Bulk geochemical analysis [total organic carbon contents (TOC): 2.0–8.0% wt., S2: 11–37 mg hydrocarbon/g bulk rock, Tmax: 435–441 °C] consistently suggests a narrow thermal maturity range of the Quse shale samples. The δ13C of maltene (δ13Cmaltene) and kerogen (δ13Ckerogen) fractions generally agree with the previously published δ13Corg curves, demonstrating the global T-OAE negative carbon isotope excursion (N-CIE). The elemental composition suggests a predominance of Type II kerogen, indicating the kerogen composition casts minimal effect on carbon isotopic signals. Petrographic examination demonstrated that the kerogens are mainly composed of alginate and amorphous organic matter, suggesting that a dominant source of kerogen originated from primary producers such as marine photosynthetic species that recorded the carbon fixation isotopic signature, whereas the bulk maltene represents a mixture of diversified organisms. By comparing the offset between δ13Corg, δ13Cmaltene and δ13Ckerogen in the T-OAE interval, two phases separated by the nadir of δ13C were recognized: early N-CIE and late N-CIE. In general, Phanerozoic δ13C values for preserved maltene and bulk organic matter in sediments are equal to or more negative than syngenetic kerogen; in the early N-CIE, however, δ13Ckerogen is more negative than δ13Cmaltene. Such isotopic inversions were previously attributed to the proliferation of 13C-enriched cyanobacteria and heterotrophic bacteria, which have been reported in Precambrian and Permo-Triassic transitional records. Moreover, the corresponding low sterane/hopane values in early N-CIE indicate an ecological shift reflecting microbial response to catastrophic environmental change that caused the extinction and initiated ecosystem changes during the early stage of T-OAE.

Controlling Factors for Organic Carbon Burial in the Late Cretaceous Nenjiang Formation of the Songliao Basin, NE China

The Songliao Basin (SLB) is a large terrestrial petroliferous basin located in northeastern China. The Nenjiang Formation represents excellent hydrocarbon source rocks for the Daqing oil field. Previous studies have indicated that the oil shale intervals from the first (K2n1) and second (K2n2) members of the Nenjiang Formation were formed in different depositional settings. In this study, we provide a new high-resolution (1 m interval) record from SK-1s core and compile three sets of published datasets from two drilling holes (Zk3389 and LY-1) and a composite outcrop section. According to the total organic carbon (TOC) chemostratigraphy, we have divided three variation cycles spanning from K2n1 to K2n2 and detected three potential oil shale intervals in the Nenjiang Formation. Combined with the productivity, salinity, and oxygenation proxies, we discuss the paleolimnological environmental changes during deposition of the Nenjiang Formation. Our new and compiled records support the model that excellent preservation conditions were associated with the formation of organic-rich sediments in the K2n1, while the productivity was the major controlling factor for organic matter enrichment in the K2n2.

A new scale shoal-forming model and natural gas exploration implications in Feixianguan Formation, northwestern Sichuan Basin, China

As an important exploration target in the Sichuan Basin, the Lower Triassic Feixianguan Formation has been previously interpreted to be deposited in the trough-platform margin system according to the genetic model of classic lithofacies paleogeography. However, this model does not apply to the northwestern Sichuan Basin. Accordingly, this study proposed a new genetic model that highlighted the carbonate ramp based on the outcrop sections, drilling and logging data, and seismic sections. A large-scale regional regression was found to occur in Sichuan Basin at the end of the Late Permian, leading to the evolution of the original Kaijiang-Liangping Trough into a very shallow tidal flat/lagoon environment at the beginning of the Early Triassic. The sedimentary pattern during the Early Triassic was different from that during the Late Permian. A total of six long-term cycles (LSC1-LSC6) were identified within the Feixianguan Formation. The deposition of LSC1-LSC3 witnessed the filling of the trough to a large extent, and the depositional periods of LSC4 and LSC5 were the main shoal-forming periods. The Feixianguan Formation in the study area was speculated to be deposited in the continuous continental carbonate ramp. With the intensified uplifting of the Longmenshan island chain and the Kangdian ancient land on the northwestern margin of the Upper Yangtze Platform, a large number of terrigenous materials were input into the study area from west to east, leading to the continuous eastward migration of the carbonate facies belt during the deposition of the Fei 1 and Fei 2 Members. Meanwhile, large-area inner-ramp shoal bodies were formed during the deposition of LSC5. It became possible to find a giant gas reservoir belt in the Feixianguan Formation of the northwestern Sichuan Basin and the results of this study provide a new complement to the existing classic trough-platform margin shoal-forming model.

Carbon and Nitrogen Cycle Dynamic in Continental Late-Carboniferous to Early Permian Basins of Eastern Pangea (Northeastern Massif Central, France)

Late Carboniferous to early Permian organic-rich sedimentary successions of late-orogenic continental basins from the northeastern Massif Central (France) coincide with both the Variscan mountain dismantling and the acme of the long-lasting Late Paleozoic Ice Age. Here, we investigate the carbon and nitrogen cycles in the newly dated sedimentary successions of the Decize–La Machine and Autun basins during these geodynamic and climate upheavals. The sedimentary organic matter has been analyzed through Rock-Eval pyrolysis, palynofacies and elemental and isotope geochemistry along cored-wells and outcropping sections, previously accurately defined in terms of paleo-depositional environments. Rock-Eval and palynofacies data have evidenced two origins of organic matter: a phytoplanktonic/bacterial lacustrine origin (Type I organic matter, organic δ13C values around −23.5‰), and a terrestrial origin (vascular land plants, Type III organic matter, organic δ13C values around −20‰), mixed in the deltaic-lacustrine sediments during background sedimentation (mean organic δ13C values around −22‰). Episodes of high organic matter storage, reflected by black shales and coal-bearing deposits (total organic carbon up to 20 and 70%, respectively) are also recognized in the successions, and are characterized by large negative organic carbon isotope excursions down to −29‰. We suggest that these negative isotope excursions reflect secondary processes, such as organic matter remineralization and/or secondary productivity varying under strict local controls, or possibly larger scale climate controls. At times, these negative δ13C excursions are paired with positive δ15N excursions up to +10‰, reflecting water column denitrification and anammox during lake-water stratification episodes. Together, these isotopic signals (i.e., low sedimentary organic δ13C associated with high bulk δ15N values) indicate periods of high primary productivity of surface waters, where nitrogen and carbon cycles are spatially decoupled. These local processes on the sedimentary isotope archives may partially blur our ability to directly reconstruct paleoclimate variations in such continental settings using only C and N isotopes. At last, we explore an organic δ13C-based mixing model to propose ways to disentangle autochthonous versus allochthonous origin of organic matter in lacustrine continental settings.

Middle Miocene dinoflagellate cyst assemblages and changes in marine productivity in western Colombia

Changes in dinoflagellate assemblages indicate regional paleoceanographic events affecting western Colombia. Integration of palynomorph, planktonic foraminifera, and calcareous nannoplankton data from a 616 m thick outcrop section in the Ladrilleros-Juan Chaco region allows the construction of a detailed and reliable chronological framework and identification of marine high-productivity intervals. Results indicate marine deposition from middle (~15 Ma) to late (~10 Ma) Miocene. Dinoflagellate cyst assemblages are consistent with known regional assemblages and include more warm water taxa than cold ones. Correlation of the palynomorphs with the other microfossils studied allows calibration of the biostratigraphic ranges of seven species of dinoflagellate cysts commonly reported from tropical zones. The ratio between autotrophic and heterotrophic dinoflagellate cysts indicates an overall increase of paleoproductivity at ~13.8 Ma. Gonyaulacoid taxa dominate the lower interval (15–13.8 Ma), while peridinioid taxa dominate the upper segment (~13.8–10.5 Ma). This change coincides with the global cooling related to the growth of the Antarctic ice sheet (~14 Ma) and presumably increased the recurrence of events like La Niña in the equatorial Pacific. These conditions increased the primary productivity in the Pacific coastal region of northwestern Colombia, and four high-productivity intervals are tentatively correlated to the Mi3a, Mi-3b, Mi-4, and Mi-5 isotope events.

NEW GEOCHEMICAL INSIGHTS INTO CENOZOIC SOURCE ROCKS IN AZERBAIJAN: IMPLICATIONS FOR PETROLEUM SYSTEMS IN THE SOUTH CASPIAN REGION

The Maikop Group and the Diatom Formation constitute the two main source rocks in the South Caspian Basin and onshore Azerbaijan where large‐scale oil production began more than 150 years ago. However, the stratigraphic distribution of the source rocks and the vertical variation of source‐rock parameters are still poorly understood. The aim of the present paper is therefore to investigate in high resolution the source‐rock distribution in the Perekishkyul and Islamdag outcrop sections, located 25 km NW of Baku, which provide nearly complete middle Eocene and lower Oligocene to upper Miocene successions. Bulk geochemical parameters of 376 samples together with maceral, biomarker and isotope data were analysed. In addition, new Re/Os data provide independent age dating for the base of the Upper Maikop Formation (30.0 ± 1.0 Ma) and the paper shale within the Diatom Formation (7.2 ± 2.6 Ma). The presence of steradienes in high concentrations demonstrates the thermal immaturity of the studied successions, limiting the application of some biomarker ratios.Intervals with high TOC contents and containing kerogen Type II occur near the top of the middle Eocene succession. However, because of the low net thickness, these sediments are not considered to constitute significant hydrocarbon (HC) source rocks. The Maikop Group in the Islamdag section is 364 m thick and represents lower Oligocene (upper Solenovian) to middle Miocene (Kozakhurian) levels. Samples are characterized by moderately high TOC contents (∼1.8 wt.%) but low hydrogen index (HI) values (average ∼120 mgHC/gTOC) despite a dominance of aquatic organic matter (diatoms, methanotrophic archaea and sulphate‐reducing bacteria). Rhenium‐osmium chronology suggests low sedimentation rates (∼25 m/Ma), which may have had a negative impact on organic matter preservation. Terrigenous organic matter occurs in variable but typically low amounts. If mature, the Maikop Group sediments at Islamdag could generate about 2.5 tHC/m2.The Diatom Formation includes a 60 m thick paper shale interval with high TOC contents (average 4.35 wt.%) of kerogen Type II‐I (HI up to 770 mgHC/gTOC). The source potential is higher (∼3 tHC/m2) than that of the Maikop Group. The organic matter is dominated by algal material including diatoms. High TOC/S ratios suggest deposition under reduced salinity conditions. Strictly anoxic conditions are indicated by the presence of biomarkers for archaea involved in methane cycling.For oil‐source correlations and a better understanding of the petroleum system, it will be necessary to distinguish oil generated by the Maikop Group from that generated by the Diatom Formation. This study shows that these oils can be distinguished based on the distribution of specific biomarkers e.g. C30 steranes, C25 highly branched isoprenoids (HBIs), and the C25 isoprenoid pentamethylicosane (PMI).

Geological history, Ichnofacies and Sequence Stratigraphy of the Eocene – Oligocene Boundary at Sinjar Area, Northwestern Iraq

Three outcrop sections for the Eocene- Oligocene boundary have been studied in Sinjar anticline northwestern Iraq. This study includes the lithostratigraphy, biostratigraphy and the identification of trace fossils and related ichnofacies in order to report the geological history of this boundary in the frame of sequence stratigraphy. Jaddala Formation, which is composed of marl and marly limestone, represents deep (outer shelf-upper bathyal) Eocene facies, Palani and Tarjil formations represent deposition in deep basinal environments during Early and Late Oligocene sequences. The Eocene- Oligocene boundary in Sinjar area represents a disconformity surface, where the deposition ceased in the Middle Eocene (Lutetian) at the end of Jaddala Formation, forming the firmground Glossifungites Ichnofacies which embrace Thalassinoides ichnotaxa in Jaddala section, and the hardground Trypanites Ichnofacies in Sharafiddin section, while at Sinjar section, a chalky limestone bed deposited at the Early Oligocene (Rupelian) Palani Formation representing Skolithos Ichnofacies. A rapid wide transgression took place at the end of Early Oligocene (Rupelian) leading to the deposition of Palani Formation, and continued through the Late Oligocene (Chattian) leading to the deposition of Tarjil Formation.

Wildfire events at the Triassic\u2013Jurassic boundary of the Tabas Basin, Central Iran

This paper presents organic geochemical evidence pointing to the occurrence of wildfire events at the Triassic–Jurassic boundary in Central Iran. The studied outcrop section (the Kamarmacheh Kuh section) is comprised of the Upper Triassic Nayband Formation which passes conformably into the Lower Jurassic Ab-e-Haji Formation with no sharp boundary. Organic petrographical studies reveal a higher concentration of semi-fusinite macerals and microscopic charcoal at the boundary between studied formations. This observation can be an evidence for widespread wildfire events at the Triassic–Jurassic boundary of the studied area. Following these fires, vast areas of land were exposed for erosion and large volumes of clastic sediments were provided due to increased run-off. This agrees well with previous sedimentological and stratigraphical studies suggesting a major change in the depositional conditions from marine to non-marine at the Triassic–Jurassic boundary of the Tabas Basin. These findings can have important implications about paleo-depositional settings of the studied formations and the nature of the associated organic matter.

Grid mapping revealed hidden geochemical lens and its chemostratigraphic bias in the middle‐upper Permian marine carbonate sequence in Laibin, South China

Deep‐time chemostratigraphy provides important data for stratigraphy and palaeoenvironmental reconstruction. Geochemical analysis for the same proxy from the same outcrop section, however, often results in different data among various researchers. The dispute was ascribed to inappropriate screening of samples weathering, pre‐treatment, and analytical methods. An outstanding example is that a great variation of 1–3‰ in δ13CVPDB values from the same horizons at Auxiliary Global Stratotype of Section and Point for the Guadalupian–Lopingian (G‐L) boundary in Tieqiao, Laibin, South China was obtained by various research groups. The Walther's Law of Facies suggests that such differences in analytical results may be due to the diachronism of samples measured in high‐resolution stratigraphy. Although lithology and broad sedimentary facies are the same in a lithostratigraphic unit, heterogeneous distribution of bioclastics, δ13Corg, provenances, trace elements, and age‐controlling geochemical signals might have printed on sediments within the same bed. Here, we verified the variations by grid mapping and sampling, a new method for high‐resolution chemostratigraphy, and this practice is applied to the auxiliary GSSP at the Tieqiao section. A total of nine parallel columnar sections from the upper Guadalupian to lowest Lopingian were measured and sampled. In addition, four lateral profiles along four beds were also sampled, and two of them are close to the lower part of the section (upper Guadalupian) and near the G‐L boundary, respectively. These analytical results are plotted along the coordinate of X–Y axis and form the grid mapping on the outcrop. Contour maps of various proxies (i.e., CaO%, total Fe%, and δ13Ccarb) based on the grid mapping were constructed on the outcrop, instead of single excursions of various geochemical proxies throughout the upper Guadalupian to lowest Lopingian. The results show different negative excursions of δ13Ccarb coinciding with biotic extinction near the G‐L boundary and answered the differences of proxy reported in previous studies. Grid mapping of various proxies shows general trends of the proxies on the outcrop; however, there are invisible beddings across lenses in dozens meters size of geochemical abnormal. Analytical data of the same proxy from the same horizons at different columnar sections may present different excursions if sampling on the abnormal lenses or not. This is why the data are different among various studies when different columnar sections were sampled. Various lenses of geochemical abnormal which may be linked tectonic controlled diagenesis, and microhabitat et al., and resulted in the bias from different columnar sections were sampled.

Triassic clam shrimps ("Conchostraca"; Branchiopoda: Diplostraca) from Mallorca: Taxonomic description and interregional comparisons.

We describe four upper Lower Triassic to lower Middle Triassic clam shrimp-bearing intervals from Mallorca, which include the clam shrimp species Hornestheria sp. aff. Hornestheria sollingensis and several other forms of carapace valve morphology: Hornestheria? Morphotype 1, Hornestheria? Morphotype 2, and other undetermined carapace valves. All of this material was obtained from red-bed units cropping out in the Serra de Tramuntana mountains of Mallorca (western Mediterranean). Except for a few morphologically similar carapace valves of Middle Triassic age from China, Hornestheria is known only from the type locality of its type species, Hornestheria sollingensis Kozur et Lepper, in the Solling Formation (Middle Buntsandstein Subgroup) in the German part of the Central European Basin. According to its original definition, the larval carapace valve of Hornestheria Kozur et Lepper is characterized by a radial sculpture, but this characteristic apparently is only variably developed. Due to both a limited number of previously known occurrences of Hornestheria and its poorly known carapace valve morphology, open nomenclature is applied to the taxonomy herein. The studied specimens were freshly collected from outcrop sections composed of greyish-green to greyish-red laminated claystones and siltstones that accumulated in a fluvial facies. The clam shrimp specimens are accompanied by remains of insects and fishes, invertebrate and tetrapod ichnofossils, and micro-/macroplant remains, all of which either have been described by previous workers or are currently part of a separate study.

Paleoecologic implications of foraminiferal assemblages in the Upper Cretaceous-Paleogene strata, eastern Dahomey (Benin) Basin, southwestern Nigeria

The paleoecologic conditions of eastern Dahomey (Benin) Basin during Late Campanian-Eocene were investigated using foraminifera as proxies. Twenty-four (24) samples obtained from four (4) exploration boreholes and three (3) exposed outcrop sections were subjected to conventional micropaleontological processing techniques. Thirty-one (31) species of foraminifera (25 benthic and 6 planktic species) were identified from the samples. The recovered assemblages consist predominantly of Paleocene calcareous benthic species such as Anomalinoides midwayensis, Anomalinoides umboniferus, Eponides pseudoelevatus, Gavellina guineana, and Cibicides succedens. Sparse occurrence of Late Cretaceous agglutinated benthic species comprising Ammobaculites coprolithiformis and Textularia hockleyensis was also recorded. The Upper Cretaceous strata are either devoid of microfauna or contain few agglutinated taxa suggestive of continental to brackish water settings. The development of calcareous benthic foraminiferal assemblages in Paleogene strata of the study area signaled the incursion of open marine neritic conditions. Influx of sandy sediments at some horizons in the studied boreholes resulted into increased pore-water oxygenation leading to poor preservation of benthic foraminifera at these horizons. Planktic/benthic (P/B) ratio analysis of the foraminiferal assemblages suggests paleo-water depth not exceeding 65 m.

Sequence stratigraphy, depositional setting and evolution of the Fahliyan carbonate platform (Zagros fold-thrust belt, SW Iran) in the Early Cretaceous

A regional sequence-stratigraphic framework is proposed for the Berriasian-Barremian shallow platform succession in the Zagros Fold-Thrust Belt (FTB), based on outcrop sections, in combination with subsurface data. The time framework is supported by new biostratigraphic results, using benthic foraminifera, dasycladalean algae and tintinnids, calibrated by Sr-isotope data. We identified and described four large-scale sequences and sixteen small-scale sequences throughout the studied succession. Large-scale sequences occur in the Berriasian-earliest Valanginian, Valanginian, Hauterivian and early to late Barremian. Based on facies associations, a relative water depth has been assigned to distinct depositional environments. Four successive architectures were observed in the platform growth: rimmed platform during the early-middle Berriasian, isolated rimmed platform in the middle Berriasian-earliest Valanginian, non-rimmed open platform to ramp in the Valanginian, and finally a mixed siliciclastic-carbonate platform to ramp in the Hauterivian-Barremian.