Green Shale Research Articles

Ichnological response to the Middle Eocene Climatic Optimum (MECO) in the Bartonian deposits of Kutch Basin, India

The Middle Eocene Climatic Optimum (MECO) represents a short-lived interval of global warming that disrupted the long-term cooling episode extending from the middle to late Eocene time. Biostratigraphically the MECO corresponds to the upper interval of planktic foraminiferal zones E11–E12 and the shallow benthic zone 17. Both the planktic and benthic foraminiferal zones are well-documented within the Bartonian mixed siliciclastic‑carbonate sequence of the Kutch Basin in western India. This case study aims to investigate the impact of MECO on the endobenthic community using ichnology as a proxy. The studied sequence comprises the underlying Harudi Formation, consisting of the marine green and grey shale and bioclastic limestone beds, and the overlying Fulra Limestone characterized by benthic foraminifera-rich limestones. The Harudi Formation is bereft of trace fossils except in one bioturbated firmground and two bioeroded hardground horizons. The MECO corresponds to the thin carbonate packstone, the middle green shale, and the Nummulites obtusus rudstone occurring at the middle to upper part of the Harudi succession, established earlier by a concurrent negative δ13Corg isotopic excursion. The shelly limestone or bivalve coquina bed deposited immediately prior to the beginning of the MECO consists of a monospecific firmground ichnofabric characterized by Balanoglossites triadicus. Out of two bioeroded beds, the lower one coincides with the earliest MECO interval and is marked by a brown carbonate hardground colonized with two ichnospecies of Gastrochaenolites. The upper bioeroded horizon corresponding to the end of the MECO is characterized by a series of top- and side-bioeroded (with Gastrochaenolites, Entobia, and Oichnus) carbonate nodules containing multigenerational septarian cracks. The upper hardground demarcates the top of the Nummulites obtusus coquina bed and the starkest basin-wide sediment starvation, making it a major condensed horizon that developed following a steady glacio-eustatic rise during the warming event. The MECO prompted the subsequent deposition of shallow-marine platform carbonates of the Fulra Limestone by accelerating a sharp rise in the sea-level and proliferation of diverse Larger Benthic Foraminifera in a warm oligotrophic seawater.

Biostratigraphy and Microfacies of the Mauddud Formation (Late Albian – Early Cenomanian) in Musaiyib Well No.1, Central Iraq

Upper Albian and Lower Cenomanian biostratigraphy and microfacies types of the Mauddud Formation from Musaiyib well No.1, Central Iraq are described and examined, which consists of thick to medium bedded limestone, marly limestone rich in argillaceous material, green shale, and dolomitic limestone beds. Thirty-six species from twenty-two genera of benthic foraminifera in addition to calcareous algae, coral, bivalves, gastropods, rudist fragments, brachiopods, bryozoan, and echinoid fragments are recognized from the Mauddud Formation of the studied well. On the basis of the recognized benthic foraminifera three biozones were determined: Mesorbitolina texana - Orbitolina qatarica Concurrent Range zone- Orbitolina sefini-Total R. Zone and Orbtolina concava Total R. Zone. Both suggest the Late Albian – Early Cenomanian age. The results of this study are compared with the work of others inside and outside Iraq. Based on the petrographical analyses, four major microfacies (Mudstone, wackestone, wackestone to packstone, and packstone), and nine sub-microfacies were identified. The Mauddud Formation was formed in a marine environment that was composed of the following three sub-environments: the inner ramp and the middle to the outer ramp.

On the coherence of the formation of containing and ore containing Precambrian formations Orikhovo-Pavlograd suture zone of the Ukrainian shield

This paper presents the results of detailed geological and structural surveys within the Orikhovo-Pavlograd suture zone of the Ukrainian shield. In the northern part of the Orikhovo-Pavlograd suture zone of the Ukrainian shield, dislocation structures of several generations are identified, which differ from each other in spatial placement and R-T values of material filling. The structures of the first five generations are formed by mineral parageneses from granulite to green shale facies of metamorphism; their age is connected to the time range of 3.6–1.8 billion years. Later dislocation structures are postmetamorphic. At the micro-meso levels of the organization, the selected structures are represented by striation, shale, linearity, cleft, cracks, etc.; at the macro level, they are represented by viscous and brittle faults. Systematized data on the structural and material organization of U-, Th-containing Pivnichno Tersyansk folded shape according to the principle of hierarchy of geological structures. It is shown that this U-, Th-perspective object is a highly ordered propulsion structure. That is, its formation was provoked by Paleoproterozoic displacements and occurred synchronously with the formation of containing geological bodies by turning up existing Precambrian formations with the creation of new structural and material parageneses. An idealized model of forming a single U-, Th-perspective structure is created, this will contribute to the search for uranium-thorium mineralization and the expansion of the mineral resource base of nuclear energy in Ukraine.

Authigenic Fe Mineralization in Shallow to Marginal Marine Environments: A Case Study from the Late Paleocene—Early Eocene Cambay Shale Formation

The late Paleocene–early Eocene warm greenhouse conditions, characterized by elevated pCO2 levels in the atmosphere and a dramatic increase in sea surface temperature, prompted abundant authigenic glauconite formation within the shallow marine sediments worldwide by lowering the net sedimentation rate, increasing organic productivity and expanding the oxygen minimum zones to shallow oceans. The early Eocene marginal marine Cambay Shale Formation experienced episodes of marine inundation represented by limestone–green shale alternations. The shales host abundant authigenic light-green, dark-green, and brown pellets. A detailed characterization of the pellets of the Valia and Vastan lignite mines, integrating the sedimentological, petrographical, mineralogical, and mineral geochemical data, suggests two distinct varieties of Fe–silicate formation, viz. glauconite and chamosite. While the glauconitic green pellets are ubiquitous to Valia and Vastan mines, brown chamosite pellets are confined within the basal part of the green shale facies alternating with fossiliferous limestone in the Vastan mine. The glauconites of the Valia mine manifest a ‘nascent’ to ‘slightly evolved’ maturation stage of glauconitization, whereas the glauconites of the Vastan mine represent the ‘evolved’ type. The limestone–green shale alternation in the Valia mine is overlain by a ~4 m-thick spherulitic mudstone facies comprising monomineralic sideritic spherulites, reflecting a pure FeCO3 composition. The glauconites in the Cambay Shale Formation transformed from kaolinite-rich clay pellets under dys-oxic depositional conditions. The increasing anoxicity within the microenvironment, possibly amplified by the rapid oxidation of continent-derived organic matter, facilitated chamosite formation instead of glauconite. The increased freshwater influx into the marginal marine depositional environment resulted in immature, K-poor glauconites of the Valia mine. The formation of siderite spherulites overlying the limestone–green shale alternation relates to the beginning of the regressive phase of sedimentation.

Inventory Of Landslides Triggered By Hurricane Matthews In Guantánamo, Cuba

Hurricane Matthew affected the eastern region of Cuba from October 4th to 5th causing large damages and numerous landslides. This research presents an inventory of landslides triggered by the hurricane. Visual interpretation of satellite images of moderate resolution from Sentinel 2A instrument and localized higher resolution satellite images provided by PlanetScope, as well as field research were the main sources of information. The resulting landslide inventory was compared with other landslide factors such as slope, geology, and soil deep and composition from maps at a scale of 1:100 000. Data recorded by 1-hour rain gauges and 24-hour rain gauge was also analyzed in order to identify rainfall thresholds for the occurrence of landslides during the Hurricane Matthew influence in the study region. A total of 619 landslides were identified and classified as rockslide, rockfall or debris flows. The research found the slope was not as important factor as the type of rock. Most of landslides were located in areas of green shale of volcanic and vulcanoclastic rocks and rocks of the ophiolitic complex formed by ancient remnants of oceanic crust. The accumulate rainfall threshold estimated for the event was between 178-407 mm/day.

The Upper Cretaceous variegated shales in the Ropianka Formation of the Magura Nappe (Outer Carpathians) – age and lithostratigraphic position

The lithological characteristics and age analysis of the variegated Farony Shale are presented for the first time. The Farony Shale occurs in the Lubomierz and Rabka areas in the Bystrica Subunit. It is located within medium- and thin-bedded sandy dominated turbidites of the Campanian–Paleocene Ropianka Formation. It is comprised of red shales laminated or interlayered with strongly bioturbated green shales. Exposures of the Farony Shale are observed along a distance of ~25 km, in the form of a narrow belt. The age of the variegated deposits is estimated based on agglutinated foraminifera to late Campanian–earliest Maastrichtian. Their deposition was associated with low-energy conditions and a temporary limitation of the supply of sandy material to the inner part of the Magura Basin.

Exploration and development in the Zhaotong national shale gas demonstration area: Progress and prospects

The Zhaotong national shale gas demonstration area in Yunnan (hereinafter referred to as demonstration area) is China's third largest national shale gas production base after Changning–Weiyuan in Sichuan and Fuling in Chongqing. And after more than ten years of deep and careful cultivation, a series of important achievements have been obtained in the exploration and development. From the perspective of exploration and development history, theory and technology, this paper systematically summarizes the exploration discovery process and productivity construction progress of shale gas in the demonstration area, expounds the geological exploration theories and key technologies of mountain shale gas, and predicts their development prospect and direction. And the following research results are obtained. First, the exploration and development in the demonstration area has gone through five development stages, and so far, three major productivity construction zones have been formed, including Huangjinba and Zijinba middle–deep shale gas zones and Taiyang shallow shale gas zone, with cumulative proved geological reserves more than 3100 × 108 m3 and cumulative gas production more than 72 × 108 m3. It has been constructed into the third largest green shale gas demonstration base in China. Second, the “multi-field coordination and multi-element coupling” mountain shale gas enrichment, accumulation and occurrence theory of “sedimentary background controlling source rock and reservoir, reworking intensity controlling preservation, and three-dimensional sealing controlling enrichment” is put forward innovatively, and the “three-dimensional sealing system” accumulation model of extrabasinal shallow shale gas is established. Third, a series of zone selection and evaluation technologies for mountain shale gas in strongly reworked complex structural areas have been developed, and the concept of geology–engineering integration has first been adopted to create transparent shale gas reservoirs and cultivate high-yield wells. A major exploration breakthrough has been achieved from marginal basin medium deep shale gas layers to extrabasin ultra shallow to medium shallow ones, and domestic first large-scale monoblock shallow shale gas field with reserves over 2570 × 108 m3 has been discovered. Fourth, a landmark technological achievement and efficient development model with geology–engineering integration and shale geomechanical evaluation as the core has been formed, which leads the clean, green and efficient exploration and development of mountain shale gas. In conclusion, it is necessary to implement the exploration strategic idea of “two outgoing” in the demonstration area, i.e., “walking out of the stable area of the basin and marching into the complex structure areas in the Dianqianbei Depression” and “walking out of the Wufeng–Longmaxi Formation and exploring other layers for breakthrough”. What's more, it is recommended to carry out the double-layer stereoscopic horizontal well pattern deployment of “Leping Formation CBM (coal measure gas) + Longmaxi Formation shale gas” appropriately in a large scale, so as to establish a new integrated development model for the three-dimensional efficient development of mountain shale gas and CBM.

Conditions of formation and sources of fluids of the birthplace of barren residential quartz of hydrothermal-metamorphogenic-metasomatic and hydrothermal-metamorphogenic genesis (Middle and South Urals)

The paper considers the conditions of quartz formation of hydrothermal-metamorphogenic-metasomatic and hydrothermal-metamorphogenic genesis of deposits and manifestations of the Middle and Southern Urals based on the study of fluid inclusions by methods of thermobarogeochemistry, ion and gas chromatography. It is established that the studied quartz objects are formed in a wide temperature range, against the background of insignificant differences in pressure values. It is shown that the temperatures of mineral formation in deposits of hydrothermal-metamorphogenic-metasomatic genesis vary from 440-230 ° C at a pressure of 1.2-1.4 kbar. The formation of these veins occurred with the participation of K-Mg-Fe-chloride fluid with a salinity of 1.2-8.7 wt. % NaCl-eq., depleted Mg and Fe due to the deposition of magnesia-ferruginous carbonates. A typomorphic feature of hydrothermal-metamorphogenic-metasomatic quartz is the high values of boron associated with the placement of quartz veins among pegmatoids and the presence of boron-containing mineral inclusions on quartz-vein objects. Veins of hydrothermal-metamorphogenic genesis were formed when the crack system was filled with quartz with the participation of a substantially K-Na chloride fluid (0.2-15.5 wt. % NaCl-eq.), at homogenization temperatures of 435-335 ° C and a pressure of 1.3-2.3 kbar. In the composition of fluid inclusions of hydrothermal-metamorphogenic-metasomatic quartz, the sum of "harmful" components (H2O, CO2, CH4, Cl, B, Na, K, Mg and Li) is less than in hydrothermal-metamorphogenic quartz. The studied quartz deposits and veins were formed in the range of temperatures and pressures not higher than the green shale stage during several successive stages: the formation of quartz veins – in a more high-temperature hydrothermal stage, while subsequent changes in quartz veins occurred under the influence of metamorphism processes, with a decrease in temperature. Subsequent changes are associated with the appearance of fracturing, cataclysm and recrystallization of quartz bodies with a decrease in grain size.

Extreme climate changes influenced early life evolution at ∼ 1.4 Ga: Implications from shales of the Xiamaling Formation, northern North China Craton

The Mesoproterozoic Era (ca.1.6–1.0 Ga) witnessed a long-term evolution stasis of eukaryote, which is usually ascribed to the persistent low atmospheric oxygen levels. However, several oxygenation processes were identified on different continents during the Mesoproterozoic Era, implying that the oxygen levels may not be the only factor influencing the evolution of early-life during the early Mesoproterozoic Era. Here, we report the molybdenum isotopes, redox sensitive elements, nutrient elements and total organic carbon (TOC) content of black and green shales from the ∼ 1.4 Ga Xiamaling Formation in the northern part of the North China Craton (NCC), which has been affected by Milankovitch-style cycle, orbital forcing of extreme change of climate ∼ 1.4 billion years ago. The highest δ98Mo of the green shale reaches 1.56 ± 0.04 ‰ (modern ocean: 2.34 ‰), which may also confirm that it was in an oxygenation state at that time. In contrast, the black shale has lower δ98Mo values (1.02 ± 0.07 ‰) than that of green shale, indicating a less oxidized environment. Moreover, the TOC and nutrient elements (e.g., P, Cu, Ni) contents of the black shale are higher than those of green shale, which results from an increased nutrient input caused by stronger weathering and river runoff during a wet period. We conclude that the marine environment was persistently oxidative during the deposition of the black and green shales, while the TOC contents of the black and green shales are mainly controlled by the concentration of the nutrient elements that are constrained by the climatic conditions. Even though in oxic aquatic environment, the unstable nutrient supply would hinder the early life evolution, our findings imply vice versa. Hence, these results imply that the extreme climate change leading to unsustainable supply of nutrients, may have largely influenced emergence and diversification of animals in the Mesoproterozoic Era.

Integrated palynology and sedimentology of the Mississippian of the Tisdafine Basin (Eastern Anti-Atlas, Morocco)

The Mississippian (Tournaisian–Visean) of the Jbel Asdaf area in the Tisdafine Basin (Eastern Anti-Atlas, Morocco) has been, for the first time, the subject of a palynological study. This work aims first to describe the lithological and the paleontological composition of the Aït Yalla and Tinerhir Formations, then to refine the age, reconstruct the paleoenvironment and assess the thermal maturity of the organic matter. The studied section is subdivided, from oldest to youngest, into three intervals, according to their lithological and paleontological compositions. Lithologically, the lower interval (lower part of the Aït Yalla Formation) and middle interval (upper part of the Aït Yalla Formation and basal part of the Tinerhir Formation) consist mostly of clay shales and green shales, respectively, both alternating with limestone or sandstone beds. The upper interval (upper part of the Tinerhir Formation) is dominated by sandstones, also alternating with pelitic-sandstone or limestone beds. The kerogen delivered by the analyzed samples is mostly of continental origin, composed mainly of opaque phytoclasts, while translucent phytoclasts and miospores are less represented. Marine fraction, consisting mainly of granular amorphous organic matter and some phytoplankton, are rare. Biostratigraphically, the late Visean Tripartites vetustus–Rotaspora fracta (VF) miospore Zone of the Western Europe biozonal scheme is recognized with some regards in the Tinerhir Formation, based on the first occurrence of the miospore Rotaspora cf. knoxi. Vallatisporites aff. ciliaris is another biostratigraphic marker taxon of the assemblage, whose the last occurrence marks the end of the VF Biozone at the top of the analyzed section. Qualitative and quantitative parameters of the different palynofacies constituents (e.g., shape, size, % of opaque and translucent phytoclasts) show, from the base to the top of the section, a gradual transition from a distal marine environment generally recognized in the Aït Yalla Formation towards an intermediate marine environment in the Tinerhir Formation, suggesting a sea-level fall. Optical analyses performed on the color of palynomorphs, mainly spores, suggest a thermal maturity, ranging from late mature to early post-mature stage for most of the analysed samples, with a burial depth and a temperature of at least 3300 m and 90 °C, respectively.

ОБОСНОВАНИЕ ПОЗДНЕМЕЛОВОГО ВОЗРАСТА АНДРИАНОВСКОЙ СВИТЫ (СРЕДИННЫЙ ХРЕБЕТ, КАМЧАТКА)

The Andrianovka Formation exposed in the Sredinny Ridge (Kamchatka) is represented by green shales, quartzites, and amphibolites. Conclusions about the age of the deposits of the Andrianovka Formation were made on the basis of data on the ages of the underlying and/or overlying strata, and correlations with other structural units. For the first time, radiolarians of the Santonian-Early Campanian age were extracted from the least metamorphosed siliceous rocks of the Andrianovka Formation. The rocks of the Andrianovka Formation can be considered as a metamorphic analogue of the deposits of the Iruney Formation, which Santonian-Early Campanian radiolarians were also isolated from.

New chronological and paleontological evidence for Paleoproterozoic eukaryote distribution and stratigraphic correlation between the Yanliao and Xiong’er basins, North China Craton

North China Craton is one of the old cratons preserved continues recording of the early evolution of eukaryotes. Organic wall microfossils (OWMs) of eukaryotic affinity have been found in the late Paleoproterozoic sediments from the Yanliao and Xiong’er basins that located in the northern and southern margins of the North China Craton. However, accurate Paleoproterozoic stratigraphic correlation of these two basins still lacks precise chronological and convincing paleontological evidence. Here, we report a SIMS zircon U-Pb age (1647.8 ± 4.3 Ma) from a tuffite layer at the bottom of the Cuizhuang Formation of the Xiong’er Basin, which provides direct chronological evidence for its isochronous deposition with the Chuanlinggou Formation in the Yanliao Basin. Besides, abundant OWMs were recovered from red shales of the Chuanlinggou Formation from the present Taihang Mountains, which is located in the southern branch of the Yanliao Basin and close to the Xiong’er Basin. They are primarily spheroidal microfossils and contain at least one unambiguous unicellular eukaryotic taxa (Valeria lophostriata) and three probable eukaryotic taxa (Schizofusa sinica, Dongyesphaera tenuispina?, large Leiosphaeridia spp.). Our finding further confirms the appearance of unicellular eukaryotes in the Paleoproterozoic ocean and the expanding of their living scopes from the cratonic marginal basin to the intracratonic basin. However, the absence of eukaryotic OWMs in black shales and green shales with more hypoxic depositional waters than those of red shales, indicates that the oxygenated water is probably a key factor to the survival of eukaryotes and even their preservation as OWMs.

ГЕОЛОГІЯ СУБСІЛЕЗЬКОГО ПОКРИВУ В БАСЕЙНІ Р. РІКА (УКРАЇНСЬКІ ЗОВНІШНІ КАРПАТИ, ГОЛЯТИНСЬКА СТРУКТУРА)

The author's detailed geological mapping works suggest that the Holyatyn Structure (located near the villages of Holyatyn and Maidan in the Rika River basin, Ukrainian Carpathians, Transcarpathian administrative region) is a destructured fragment of the Sub-Silesian Nappe located in the Outer Carpathians between the Silesian and Skyba nappes. Within this structure, Lower Cretaceous–Oligocene deposits are developed among the Oligocene flysch of neighboring tectonic units. The stratigraphic succession of these deposits is represented by: dark to black flysch (Shypot Formation, Barremian–Albian); green shales with cherts; red and green shales and marls (Holyatyn Beds, Upper Cretaceous–Paleocene); greenish and dark to black flysch (Soimy Formation, Eocene); black shales, cherts and sandstones (Menilite Formation, Oligocene) and gray flysch with layers of black shales (Verets or Transitional Formation, Oligocene). The limestone blocks (unknown age) is developed in front of the thrust-sheet. According to sedimentological features (typical hemipelagites), age and microfauna content, the Holyatyn Beds correspond to the Weglowka Marls of the Subsilesian Unit in the Polish Carpathians, while the Weglowka Marls are a “diagnostic lithofacies” for the Subsilesian Unit. The Holyatyn Structure is probably an “extruded lens”, the anticline core of which is composed of deformed Lower Cretaceous flysch and ductile Upper Cretaceous clay-marly Holyatyn Beds. This extrusion apparently occurred after nappe structure forming and was caused by transpressive movements. In result, the relatively thin and ductile Subsilesian Nappe was stretched into separate tectonic lenses (large boudins ?) placed between the rigid flysch of neighboring tectonic nappes. One such lens is the Holyatyn Structure, which is similar to the transpressive “flower structure”. A ductile-type melange is exposed in the thrust zone of the Silesian/Sub-Silesian nappes. It suggests that the initial thrust stage occured in poorly consolidated water-saturated sediments.

Paleoenvironmental Conditions during the Paleocene–Eocene Transition Imprinted within the Glauconitic Giral Member of the Barmer Basin, India

The roughly 6 m thick limestone–green shale alternation within the lignite-bearing Giral Member of the Barmer Basin corresponds to a marine flooding event immediately after the Paleocene–Eocene transition. A detailed characterization of the glauconite using Electron Probe Micro Analyzer (EPMA), X-Ray Diffraction (XRD), Mössbauer and Field Emission Gun-Scanning Electron Microscope (FEG-SEM) reveals its origin in the backdrop of prevailing warm climatic conditions. The glauconite pellets vary from fine silt-sized to coarse sand-sized pellets, often reaching ~60% of the rock by volume. Mineralogical investigation reveals a ‘nascent’ to ‘slightly evolved’ character of the marginal marine-originated glauconite showing considerable interstratification. The chemical composition of the glauconite is unusual with a high Al2O3 (>10 wt%) and moderately high Fe2O3(total) contents (>15 wt%). While the K2O content of these glauconites is low, the interlayer sites are atypically rich in Na2O, frequently occupying ~33% of the total interlayer sites. The Mössbauer spectrum indicates 10% of the total iron is in ferrous form. High tetrahedral Al3+ of these glauconites suggests a high-alumina substrate that transformed to glauconite by octahedral Al-for-Fe substitution followed by the addition of K into the interlayer structure. The unusually high Na2O suggests the possibility of a soda-rich pore water formed by the dissolution of alkaline volcanic minerals. The Giral glauconite formation could have been a part of the major contributors in the Fe-sequestration cycle in the Early Eocene shelves. Warm climate during the Early Eocene time favored the glauconitization because of the enhanced supply of Fe, Al, and Si and proliferation of an oxygen-depleted depositional environment.

Biostratigraphy of Baghamshah Formation based on calcareous nannofossils in the Southwest Tabas, Iran

The Tabas Block is part of the Central Iran microcontinent, located between the Lut Block in the East and the Yazd Block in the West. The Baghamshah Formation is the second lithostratigraphic unit from the sedimentary cycle of the Magu Group and the Baghamshah Subgroup in the Jurassic of Tabas Block. This formation is conformably underlaid with the grey pisoidal limestones of the Parvadeh Formation and overlaid with the Pectinid limestones of the Kamar-e-Mehdi Formation (Esfandiar Subgroup). In this research, the biostratigraphy of the Baghamshah Formation in the Rizu and Kamar-e-Mehdi sections, based on calcareous nannofossils, is examined. The thickness of the Baghamshah Formation in the Rizu section is 270 m (mostly including marl and green shales with intercalation of limestones and calcareous sandstones), and in the Kamar-e- Mehdi section is 236 m (composed of gypsiferous marly shales, marl, marly shales and alternation of marl-shale with limestones and calcareous sandstones). According to the taxonomic studies in the Rizu section, 52 species belong to 24 genera, and in the Kamar-e-Mehdi section, 45 species belong to 23 genera of calcareous nannofossils. Based on index calcareous nannofossils, the CC1, CC2, CC3, and CC4 biozones established by Sissinghh in both sections were determined. It is mentioned that CC5 biozone only occur in Kamar-e-Mehdi section. According to the identified biozones, the suggested age of the Baghamshah Formation is early Berriasian–early Hauterivian in the Rizu section, and early Berriasian–late Hauterivian in the Kamar-e-Mehdi section. Keywords: biostratigraphy, Baghamshah, calcareous nannofossils,Tabas, Iran.

Depositional Environment of the Upper Triassic Baluti Formation in Gara Anticline, Kurdistan Region, North Iraq: Insight from Microfacies and Biomarker Characteristics

The studied section is located in the core of the Gara Anticline, about 12 km southeast of Amedi Town. The Baluti Formation is generally composed of grey and green shale, calcareous, dolostone with intercalations of thinly bedded dolostones, dolomitic limestones, and silicified limestones which are occasionally brecciated. The petrographic study shows five main microfacies in the Baluti Formation namely; finely laminated dolomudstone, fossil-barren and lime mudstone, fenestral mudstone/packstone, peloids and ooids wackestone, and lithoclasts (intraclasts) grainstones. The mudstones facies with no fauna and radial-fibrous ooids can point to a protected and low energy environment. Moreover, fenestral structures are reliable criteria for identifying a tidal flat environment. The presence of the lithoclasts (intraclasts) with radial ooids and a few terrestrial fragments may represent a quiet environment, albeit one affected by infrequent storm deposits. As a supplementary to microfacies, the biomarker characterizations were used to deduce the depositional environment of the Baluti Formation. Biomarker parameters show that the Baluti Formation could be deposited in anoxic to suboxic environment, and organic matter input is more likely characterized by land plant organic matter. This study showed that the most likely paleoenvironments for the Baluti Formation were supratidal, intertidal, subtidal, and sand shoals setting. However, the lack and/or very low diversity of skeletal fauna, and the lack of subaerial exposure may indicate that some parts of the formation seem to be deposited in low energy and restricted environment (Lagoon).

Occurrence and characterization of tremolite asbestos from the Mid Atlantic Ridge

Tremolite is one of the most common amphibole species and, in the fibrous form (i.e., characterized by crystals/particles consisting of fibres with length > 5 µm, width < 3 µm and aspect ratio > 3), one of the six asbestos minerals. Until now the attention of crystallographers has focused only on samples from continental environment. Here we report the first chemical and structural data of a tremolite asbestos found along the Mid Atlantic Ridge (MAR) at the eastern intersection of the Romanche Transform Fault (Equatorial MAR). Tremolite is associated with chlorite and lizardite and was formed through the green shale facies lower than zeolite in a predominantly fluid system. MAR tremolite asbestos shows very slight deviations from the ideal crystal structure of tremolite. Differences in cation site partitioning were found with respect to tremolite asbestos from ophiolitic complexes, attributed to the different chemical–physical conditions during the mineral formation. In particular, oceanic tremolite asbestos is enriched in Al and Na, forming a trend clearly distinct from the continental tremolites.

The Bawang Member, a unique unit of Belaga Formation in the Miri Zone, Central Sarawak, NW Borneo Malaysia: Revised stratigraphic and sedimentological characteristics

Bawang Member (Unit 4) of Late Eocene age is the fifth and the youngest member of Belaga Formation. In general, the Late Cretaceous to Late Eocene turbidite sequence of Rajang Group in the lower Rajang area (Central Sarawak) is characterized by Belaga Formation. This member is unique and is only exposed in the vicinity of the Tatau area (Arip valley and Tatau High region) with limited exposures. In this research we present new evidence, to support its position on the stratigraphic column, based on field observations (stratigraphic and sedimentological characteristics) and lab analysis (TOC). Numerous recently exposed sections were visited in the study area. Four litho-facies were identified in the Bawang Member based on sedimentological observations; (1) Massive sandstone facies (SF1), (2) Medium to thick-bedded sandstone facies (SF2), (3) Thin bedded heterolithic facies (SF3), and (4) Mudstone or Shale facies (SF4). Reddish maroon and green shales exposed in Tatau High region are only exposed in another member of Belaga Formation i.e. Kapit Member. The Bawang Member sediments differ from the Tatau High region sediments in absence of cleavage and internal sedimentary features (rip-up clasts), the occurrence of bioturbation, and with lesser exposures of mud facies. On the contrary, the Tatau High sediments show higher ratios of mud facies, presence of cleavage in shales and even in few sandstones, and absence of major bioturbation of strata. The presence of internal sedimentary features (rip-up clasts) in Tatau High and in Kapit Member supports the idea that these are the parts of the same rock unit. Furthermore, contrasting TOC values between these two units (Bawang and Tatau High), and the similarity of TOC among Tatau High and Kapit Member are also in support of the same idea. Based on the differences of facies (rock) types, the effect of cleavage, absence of rip-up clasts, the occurrence of bioturbations and different TOC values, we confirm that the Tatau High rocks must be older than most of Bawang Member exposures and are actually the faulted blocks of Kapit Member.

The Piedras de Afilar Formation (Neoproterozoic, Uruguay): Sedimentology and provenance of a key unit for SW-Gondwana paleogeography

The Piedras de Afilar Formation (PAFm) is a late Neoproterozoic sedimentary succession autochthonous to the Tandilia Terrane, part of the Río de la Plata Craton. It overlies with erosional unconformity a Paleoproterozoic igneous and metamorphic basement. According to facies analysis and lithostratigraphy, the PAFm is divided into three members for which detailed petrography, X-ray diffractometry and geochemistry studies were carried out: (1) the Cuchilla Alta Member, made up of yellowish-white quartz arenites and subarkoses with through, planar and hummocky cross-stratification, ripples, interference ripples and flute casts; (2) the Arroyo del Junquito Member, comprising dark grey, red and green shales and siltstones, with wavy lamination and wrinkle structures; and (3) the Arroyo de la Tuna Member, made up of grey limestones, grey to green marls, rhythmites and dark shales. Dolerite sills, up to 50 m thick, intrude the succession, and affect clay mineralogy and rare earth composition near the contact. A deepening, fining- and thining-upward sequence in a shallow marine paleoenvironment is evidenced by facies analysis. Ce anomalies are negative at the base of the Arroyo del Junquito Member and become positive up section, indicating increasingly anoxic conditions.Paleocurrents show a bimodal oblique pattern, with predominant paleocurrents to the north-east and subordinately to the east, suggesting a provenance from the west, which agree with detrital zircon interpretation. Sm–Nd analyses of shales yielded TDM model ages between 2.53 and 1.55 Ga, which indicate a mixed provenance from Paleoproterozoic units of the Río de la Plata Craton and from a proto-Andean, Mesoproterozoic belt at its western border, in accordance with available detrital zircon ages for sandstones of the PAFm. The influence of a recycled orogen as source area is also shown by sandstone petrography and trace element composition of shales. The correlation with other Ediacaran successions of the Río de la Plata Craton, such as the lower Arroyo del Soldado Group in Uruguay and lower Sierras Bayas Group in Argentina, is strengthened by the new data. All units were deposited on a stable shelf developed at the eastern margin of the Río de la Plata Craton.

Late Cretaceous palynomorphs from the Golfo San Jorge Basin, Argentina

A lithofacial and palynological study was carried out on the Cañadón Seco Formation in the La Frieda Oeste x-1 well (Golfo San Jorge Basin). According to sedimentological characteristics of the core four main litofacies lithofacies are defined: 1. Cross-bedded sandstones, 2. Interlaminated fine-grained sandstones and mudstones, 3. Shales, and 4. Muddy tuff. The cross-bedded sandstones correspond to channel deposits, which are interpreted as lateral bars (point bars) or attached bars. The interchannel area is dominated by interlaminated fine-grained sandstones and mudstones, together with shales. The former represents sedimentation occurred in proximal floodplain areas, while shales correspond to deposition in distal floodplains, where thin and scarce muddy tuff intercalations indicate ash fall events. The palynological assemblage here analyzed was recovered from the green shales corresponding to distal floodplains areas, probably surrounding temporary water bodies. The floristic assemblage contains abundant fern spores as a dominant group, followed by angiosperm and gymnosperm pollen grains. Bryophyte and lycophyte spores, along with fungal remains, are also present in lower proportions. Based on the taxonomic content of the palynoflora, a Turonian–Coniacian age is suggested for this assemblage. Additionally, some taxa present in the assemblage allow inferring temperate to warm and humid conditions. This new record represents a period of time little known for the evolution of angiosperms in the southern region of Gondwana.