Carbonaceous Claystone Research Articles

The cranial and postcranial morphology of Hutchemys rememdium and its impact on the phylogenetic relationships of Plastomenidae (Testudinata, Trionychidae)

Hutchemys rememdium is a poorly understood softshell turtle (Trionychidae) from the mid Paleocene of the Williston Basin of North America previously known only from postcranial remains. A particularly rich collection of previously undescribed material from the Tiffanian 4 North American Land Mammal Age (NALMA) of North Dakota is here presented consisting of numerous shells that document new variation, some non-shell postcrania, and cranial remains, which are described based on 3D models extracted from micro-CT data. Although the observed shell variation weakens previously noted differences with the younger species Hutchemys arctochelys from the Clarkforkian NALMA, the two taxa are still recognized as distinct. Parsimony and Bayesian phylogenetic analyses reaffirm the previously challenged placement of Hutchemys rememdium within the clade Plastomenidae, mostly based on novel observations of cranial characters made possible by the new material and the micro-CT data. The new topology supports the notion that the well-ossified plastron of plastomenids originated twice in parallel near the Cretaceous/Paleogene boundary, once in the Hutchemys lineage and once in the Gilmoremys/Plastomenus lineage. Hutchemys rememdium is notable for being the only documented species of trionychid in the mid Paleocene of the Williston Basin. The presence of multiple individuals in a carbonaceous claystone indicates this taxon lived in swamps and lakes and its expanded triturating surface suggests it had a durophagous diet.

Origins of clay-rich strata in Cenozoic paleochannel deposits: an example from Suttor Formation, Queensland

Cenozoic sediments cover much of Queensland’s landscape and record changes in climate and flora that evolved in tandem with the tectonic evolution in eastern Australia, associated with uplift and erosion events arising from Late Cretaceous sea-floor spreading in the Coral Sea, leading to the passive margin we see today. In eastern Australia, incised and potentially fault-bounded valleys developed on the pre-Cenozoic landscape and were variably infilled at different times by siliciclastic sediments, carbonaceous muds and peat, and basaltic lava flows. This study examines a 100 m-deep drill core through one such siliciclastic-dominated paleochannel incised into upper Permian coal measures on the western limb of the Bowen Basin. Palynological analysis, core logging, hyperspectral logging of the core, X-ray diffraction (XRD), SEM–EDS and U–Pb zircon geochronology were used to investigate the age and origins of these clay-rich deposits. Palynological analysis confirmed that the strata belong to the upper Paleogene and Neogene Suttor Formation, a time when Australia’s climate has been interpreted to shift from wet and warm to a more arid setting. Core logging revealed that the sequence in the studied channel began as a breccia/alluvial fan with chaotic angular clasts of Permian laminated siltstone, tuff and coal floating in disturbed poorly lithified sand with evidence of soft sediment deformation, possibly initiated by localised faulting. These clasts were continually reworked and broken down into a clast supported pebble conglomerate capped by a series of claystone with intermittent carbonaceous claystone and lignite, interpreted to have formed in a lacustrine environment that could be localised on the floodplain (oxbow) or more regional in extent. Above this, and interpreted from palynology as corresponding to a climatic shift to more arid conditions, are well sorted but subrounded sugar sands and intermittent clays with abundant iron staining (?paleosols) interpreted to represent sandy ephemeral channels. These are overlain by extremely weathered undated basalts. The hyperspectral logging of the core and XRD studies of the white claystone samples indicate that they are kaolinite-rich, but observations under SEM–EDS noted that their honeycomb structure mimicked that of smectite. The presence of abundant zircon suggested the possibility of syndepositional volcaniclastics, but U–Pb zircon geochronology recorded an age of 272–254 Ma (middle to late Permian). Hence local recycling of the tuffaceous smectite-rich coal measures within the incised alluvial system, assisted by intense weathering under a warm and wet climate, and potentially acid leaching from the organic-rich layers was the origin of the kaolinite-rich clay strata. KEY POINTS Clay-rich Cenozoic paleochannels in the northern Bowen Basin belong to the upper Paleogene and Neogene Suttor Formation, based on palynological study. The clay-rich strata are developed by local recycling of middle to late Permian tuffaceous smectite-rich coal measures. The interpretation based on palynology and clay mineralogy confirm that Australia experienced a shift from wet and warm to a more arid climate during the upper Paleogene and Neogene.

Petrophysical core-based zonation of OW oilfield in the Bredasdorp Basin South Africa

This study aims to generate rock units based on core permeability and porosity of OW oilfield in the Bredasdorp Basin offshore South Africa. In this study, we identified and classified lithofacies based on sedimentology reports in conjunction with well logs. Lucia's petrophysical classification method is used to classify rocks into three classes. Results revealed three lithofacies as A (sandstone, coarse to medium-grained), B (fine to medium-grained sandstone), and C (carbonaceous claystone, finely laminated with siltstone). Lithofacies A is the best reservoir quality and corresponds to class 1, while lithofacies B and C correspond to class 2 and 3, which are good and poor reservoir quality rock, respectively. An integrated reservoir zonation for the rocks is based on four different zonation methods (Flow Zone indicator (FZI), Winland r35, Hydraulic conductivity (HC), and Stratigraphy modified Lorenz plot (SMLP)). Four flow zones Reservoir rock types (RRTs) were identified as RRT1, RRT3, RRT4, and RRT5, respectively. The RRT5 is the best reservoir quality composed of a megaporous rock unit, with an average FZI value between 5 and 10 µm, and HC from 40 to 120 mD/v3, ranked as very good. The most prolific flow units (RRT5 and RRT4 zones) form more than 75% of each well's flow capacities are supplied by two flow units (FU1 and FU3). The RRT1 is the most reduced rock quality composed of impervious and nanoporous rock. Quartz is the dominant framework grain, and siderite is the dominant cement that affects flow zones. This study has demonstrated a robust approach to delineate flow units in the OW oilfield. We have developed a useful regional petrophysical reservoir rock flow zonation model for clastic reservoir sediments. This study has produced, for the first time, insights into the petrophysical properties of the OW oilfield from the Bredasdorp Basin South Africa, based on integration of core and mineralogy data. A novel sandstone reservoir zonation classification criteria developed from this study can be applied to other datasets of sandstone reservoirs with confidence.

Petrographic and diagenetic study of siliciclastic Jurassic sediments from the northeastern margin of Africa: Implication for reservoir quality

Northeastern Egypt is one of the most important exposures in the Middle East and North Africa to study Jurassic facies. The present study analyzes 130 thin sections from a subsurface well (Well X) in the northern Gulf of Suez, and from two surface sections at Gebel Maghara (north Sinai) and Khashm Elgalala (North Eastern Desert), Egypt for petrographic and lithofacies analyses. In the present study, detailed petrographic analysis is used as a tool to better understand the diagenetic history of the Early to Late Jurassic siliciclastic sediments; the identified diagenetic elements are inferred concerning the reservoir quality. For this, sidewall cores, scanning electron microscopy and thin sections are used to detail detrital and authigenic mineralogy; these are then used to infer the depositional framework, factors controlling reservoir characteristics, and the operating diagenetic processes. The inferred depositional paleoenvironment is a prograding and retrograding linear siliciclastic shoreline within a shallow marine carbonate platform with coal swamps and occasional cross-cutting rivers. Diagenesis, petrographical characteristics and depositional conditions are the main factors controlling continental and marine reservoir architecture. The diagenetic processes affecting siliciclastic sedimentation are near the surface, shallow to intermediate burial, and deep burial cycles with different pore fluid filling at each stage. The siliciclastic sediments have been categorized into seven depositional lithofacies - calcareous claystone (S1a), carbonaceous claystone (S1b), siltstone (S2), planar and trough cross-bedded sandstone (S3), coarse, well rounded, large scale trough cross-bedded sandstone (S4), ooid sandstone (S5) and coal (C). Grain compaction, various phases of syntaxial quartz overgrowth, carbonate cementation and replacement, creation of dissolution porosity, and clay authigenesis are the most important diagenetic processes that have affected the siliciclastic continental and marine sediments. Many different diagenetic events, both destructive and constructive, have modified porosity. The destructive events include compaction and cementation (of silica, kaolinite, ferroan dolomite, Illite, and anhydride). The constructive events include silica cementation, feldspar dissolution, and ferroan dolomite dissolution. Additionally, present data also suggest that the continental sandstones have excellent reservoir quality whereas the marine sandstones have good to very good reservoir potential. Despite the excellent reservoir quality of the continental sandstone lithofacies, the effective stratigraphic seal is leaking. The interbedded calcareous and carbonaceous claystone lithofacies may provide an excellent stratigraphic seal for these siliciclastic reservoirs. Based on these analyses, a model is proposed that can be used as a template for subsurface Jurassic reservoir characterization and reservoir discrimination.

Preservation of Permian–Triassic boundary section in the Jurassic accretionary complex of the Lake Hamana, Central Japan

We examined the lithostratigraphy and deformation structures of the accreted pelagic rocks in Lake Hamana area, Central Japan, based on a detailed field mapping and the radiolarian ages. The constructed lithostratigraphy is composed of Lopingian (Upper Permian) grey chert, black chert, black claystone with a high carbon content of 4.85–6.78 wt%, siliceous claystone, black chert, and Anisian (Middle Triassic) grey chert, in the ascending order. The symmetry in the lithostratigraphy and the change in the radiolarian ages with respect to black carbonaceous claystone are presumed to represent a deep‐sea anoxic event that occurred across the Permian–Triassic (P–Tr) boundary. The P–Tr boundary black carbonaceous claystone suffered from an intense shear, resulting in blocks of siliceous claystone in the scaly black claystone matrix. In places, the sheared terrigenous rocks composed of sandstone blocks in the mudstone matrix are intercalated into the pelagic rocks, possibly representing complex mélange forming processes during the development of the Jurassic accretionary complex.

Paleoecological and paleoenvironmental interpretation of three successive macrofloras and palynofloras from the Kola Switch locality, lower Permian (Archer City Formation, Bowie Group) of Clay County, Texas, USA

Fossil floras have been recovered from a unique deposit of early Permian age in North-Central Texas. The site, Kola Switch, preserves three distinct floras in different lithofacies, in a succession from a single outcrop. The sedimentary environment appears to be a floodplain channel fill of primarily siltstones and claystones. The lowermost flora, preserved in a kaolinitic siltstone, indicates active water flow. It is dominated by plants typical of well-drained substrates, dominated by Sphenopteris germanica, and contains no wetland elements. The middle flora is from a finely laminated carbonaceous claystone and is dominated by marattialean tree ferns, with no elements from habitats typical of seasonal moisture availability. It contains no roots and appears to have formed as a floating peat mat. The upper flora is a mixed assemblage of wetland taxa and those typical of well-drained soil environments or a seasonal rainfall regime. Unlike the two lower floras, it has a relatively even distribution of dominance and is the most diverse of the three assemblages. Palynofloras also were recovered from each of these beds. The palynofloras, although varying between and even within the beds, indicate a common background species pool during the time interval sampled, suggesting that these distinct floras reflect local changes in microhabitat conditions under a constant climatic background. The palynoflora from each bed has characteristics in common with the macroflora of that bed, but also distinct differences. Together, the macroflora and microflora provide an unusually broad picture of this site through time. Kola Switch compares favorably with the recently described flora from the nearby Sanzenbacher Ranch site of approximately the same age and also with floras of Rotliegend age from Central Europe.

Major and rare earth element contents in sedimentary rocks of the Haymana formation, Ankara, Turkey

ABSTRACTThe study area is located 4 km east of Haymana, Ankara, Turkey. Major and rare earth element (REE) contents in samples collected from siltstone, carbonaceous claystone, and marl of the Haymana formation in the studied region and their distribution with respect to lithology and correlation relations yield important data on the evaluation of forming conditions of basin. Regarding the abundance of elements in various lithologies, the first and second group elements (SiO2, Al2O3, Na2O, TiO2, P2O5 and Fe2O3, K2O, REE) are more abundant in carbonaceous claystone and siltstone than that in marl, indicating that they are of detrital origin and controlled by clays. The abundance of CaO and TOT/C is lesser in siltstone than that in carbonaceous claystone and marl, implying that they are in marine origin. This is also supported by the correlation of elements. Based on REE abundances, lithologies are ranked in the order of claystone > siltstone > marl, which indicates that clays play an important role in REE enrichment. Correlation of REEs with major elements is indicative of detrital source and association with clay minerals. All the samples are represented by slightly negative Ce anomaly and positive Eu anomaly. Negative Ce and positive Eu anomalies are mostly typically of high oxygenated environments. Since negative Ce anomaly restricts oxygen enrichment to some extent, deposition environment might reflect oxic-anoxic conditions.

Sedimentology and Geochemical Evaluation of Lignite-Argillite Sequences in a Named Basin in Bali Nyonga, Northwest, Cameroon

The sedimentology and geochemistry (major and trace element compositions) of lignite and argillite (carbonaceous shale and claystone) sequences in a Basin in Bali Nyonga, west of the Bamenda Mountain have been investigated to determine their sequences and the prevailing environmental conditions which control their formation. Ten representative samples were obtained fromtrenches, pits, and river and stream valleys in the study area. These samples and their ashes were subsequently examined using X-ray fluorescence spectrometry (XRF), inductively coupled plasma spectrometry (ICP), and X-ray diffraction analysis (XRD). The geochemical results revealed that thelithophile, chalcophile and siderophile elements were dominantly epigenetic in origin, mainly from detrital sources supported by high silica and alumina concentrations in all the samples. The mineral phases identified were quartz, kaolinite, illite, pyrite, hematite, and minor phases of feldspars,pseudorutile. The relatively high silica (54.10 wt%) and alumina contents (27.77 wt%) in these samples can be explained by high detrital input during peat formation. The low contents of MgO and CaO in the analysed samples agree very much with the continental setting of the peat formating basin. A clayey microband derived from alkaline volcanic ashes was identified in the lignite and the dominant composition of these clayey microbands was mixed-layer clay minerals of illite and kaolinte, which were interlayered with organic bands. The modes of occurrence of ash bands indicated that the volcanic activities were characterized by multiple eruptions, short time interval and small scale for each eruption during peat accumulation. The ratios of redox-sensitive traceelement (V/Cr versus Ni/Co and V/V + Ni versus Ni/Co), Sr/Ba, and major oxides ratio (CaO + MgO + Fe2O3)/(SiO2 + Al2O3) from the analysed samples from Bali Nyonga indicate a terrestrial, reductive (oxic), littoral to brackish water environmental conditions which are characteristics of paludal-lacustrine basin that is filled by Tertiary volcanic materials.

Volcanism, sedimentation, K/Ar and palynology studies, Yayu and Delbi-Moye Basins, Southwestern Plateau of Ethiopia

Major element, K/Ar, sedimentation and palynology data are reported on Tertiary volcanic and sedimentary rocks from the Yayu and Delbi-Moye Basins, SW Ethiopia. In the Yayu and Delbi-Moye Basins, pre-rift volcanic (basalts) and post-rift volcanic (basalts) are separated by coal and oil shale-bearing sedimentary rocks. The basalts are tholeiitic in composition. The K/Ar data on the volcanic rocks range from 10.98±0.55Ma (Lower Miocene i.e. Tortonian) to 111.19±2.83Ma (Early Cretaceous i.e. Aptian). Inter-Trappean coal and oil shale-bearing sedimentary rocks are widely distributed in the Yayu and Delbi-Moye Basins. The NNW–SSE fault system developed grabens and half-grabens for the deposition of coal and oil shale-bearing sedimentary rocks. The sedimentary successions are dominated by fine to medium-grained sandstones, siltstones, mudstones, carbonaceous shales, carbonaceous claystones, coal and oil shale seams, and are characterized by meandering river and lacustrine depositional environments. Fresh water algae Botryococcus brauni, Pediastrum sp., Polypodii sporites favus and Polypodii sporites afavus and Pachydermites diederixi, are common palynomorphs in the studied coal and oil shales, and are indicators of lacustrine environment. The presence of Peregrinipollis nigericus is consistent with Oligocene to Miocene. The presence of Euphorbiaceae, Papilionacae, Melastomtaceae sp., Dodonaea, Martretia quadricornis, Rubiaceae sp. (pollen derived from tropical shrubs), Sapotaceae spp. and Meliaceae spp. are indicative of humid, tropical rainforest conditions. Extensive bio-assemblages confirm that the age of coal and oil shale-bearing sedimentary rocks to be Oligocene to Miocene.

Shallow-Water Origin of a Devonian Black Shale, Cleveland Shale Member (Ohio Shale), Northeastern Ohio, USA

Black shales are usually interpreted to require anoxic bottom waters and deeper water sedimentation. There has long been a debate about whether the Devonian Cleveland Shale Member of the Ohio Shale (CSM) was deposited in shallow- or deep-water depositional environments. This study looked at the CSM at 3 stratigraphic sections and 5 well cores in northeastern Ohio. The CSM mostly consists of sapropelite (interbedded carbonaceous black mudstones and gray calcareous claystones). The black and gray “shales” are rhythmically bedded at micro- ( ≥35 km, while hyperpycnites are too thin ( ≤50 m depth).

Petrology, Geochemistry, and Fluid Inclusion Microthermometry of Sphalerite from the Laloki and Federal Flag Strata‐Bound Massive Sulfide Deposits, Papua New Guinea: Implications for Gold Mineralization

AbstractThe Laloki and Federal Flag deposits are two of the many (over 45) polymetallic massive sulfide deposits that occur in the Astrolabe Mineral Field, Papua New Guinea. New data of the mineralogical compositions, mineral textures, and fluid inclusion studies on sphalerite from Laloki and Federal Flag deposits were investigated to clarify physiochemical conditions of the mineralization at both deposits. The two deposits are located about 2 km apart and they are stratigraphically hosted by siliceous to carbonaceous claystone and rare gray chert of Paleocene–Eocene age. Massive sulfide ore and host rock samples were collected from each deposit for mineralogical, geochemical, and fluid inclusion studies. Mineralization at the Laloki deposit consists of early‐stage massive sulfide mineralization (sphalerite‐barite, chalcopyrite, and pyrite–marcasite) and late‐stage brecciation and remobilization of early‐stage massive sulfides that was accompanied by late‐stage sphalerite mineralization. Occurrence of native gold blebs in early‐stage massive pyrite–marcasite‐chalcopyrite ore with the association of pyrrhotite‐hematite and abundant planktonic foraminifera remnants was due to reduction of hydrothermal fluids by the reaction with organic‐rich sediments and seawater mixing. Precipitation of fine‐grained gold blebs in late‐stage Fe‐rich sphalerite resulted from low temperature and higher salinity ore fluids in sulfur reducing conditions. In contrast, the massive sulfide ores from the Federal Flag deposit contain Fe‐rich sphalerite and subordinate sulfarsenides. Native gold blebs occur as inclusions in Fe‐rich sphalerite, along sphalerite grain boundaries, and in the siliceous‐hematitic matrix. Such occurrences of native gold suggest that gold was initially precipitated from high‐temperature, moderate to highly reduced, low‐sulfur ore fluids. Concentrations of Au and Ag from both Laloki and Federal Flag deposits were within the range (<10 ppm Au and <100 ppm Ag) of massive sulfides at a mid‐ocean ridge setting rather than typical arc‐type massive sulfides. The complex relationship between FeS contents in sphalerite and gold grades of both deposits is probably due to the initial deposition of gold on the seafloor that may have been controlled by factors such as Au complexes, pH, and fO2 in combination with temperature and sulfur fugacity.

Fabric variability within layered Fe-oxide deposits in Mid-Late Miocene sedimentary formations, NW Borneo: Impact on facies architectural interpretations

Iron (Fe) can accumulate in various forms in sedimentary environments that experience alternating moisture conditions, hydration and dehydration processes and redox processes. It has been pointed out that there is a major gap in the understanding of the composition of mixed solid-phase minerals, their size, morphology and arrangement in the matrix and possible interactions with pore solutions and the environment of deposition. Variations in the fabric within concretions in some Mid-Late Miocene beds in NW Borneo suggest that there were more changes in the energy levels and processes involved than what has been perceived from routine fabric analyses of the sedimentary rocks. The sedimentary rocks are essentially carbonaceous claystones containing varying amounts of highly restricted marginal-marine fauna. The fauna probably accumulated in brackish waters, and comprise in-situ buried turritellid snails, fish teeth and bone tissue, fragments of crabs, very few forams and possibly ostracod shells. Evidence exists to support the concept of reworked cobble or pebble-sized fossiliferous mudstone clasts picking up contemporaneous shell fragments in these restricted conditions. Iron oxide content is seen as (i) micrite-size primary components forming part of a muddy matrix and (ii) diagenetic coatings. Coatings occur in a non-rhythmical pattern after the formation of mudstones, and the reworking of the material and subsequent coatings by iron. Iron coated pebbles/cobbles may experience re-cementing into large sheets giving the appearance of red beds. These occur under some very special redox conditions. These iron-concretion rich horizons appear then to represent extreme (climatic, etc) facies developments that were restricted to coastal areas during Mid-Late Miocene. Present-day iron deposition processes might be a key to understanding past processes. This study forms the basis for an enhanced understanding on facies architectural interpretations.

Evaluation of palaeo-oxygenation of the ocean bottom across the Permian–Triassic boundary

The ‘long-lasted anoxia’ of a deep ocean bottom which may be related to the Permian–Triassic (PT) mass extinction event has been accepted without critical evidence. The degree of bioturbation is examined for radiolarian chert successions in central Japan with the reassessment of geochemical proxies to evaluate the degree of palaeo-oxygenation of a pelagic oceanic bottom. No evidence for anoxia is found from Wuchiapingian and lower Changhsingian chert by the reassessment of geochemical proxies. Anoxia started from the late Changhsingian stage that was interrupted by an oxygenation event at the supposed PT boundary. Griesbachian to the earliest Smithian, being characterised by the occurrence of black carbonaceous claystone, is an anoxic interval with rare bioturbation in the early part and is oxygenated in the later part. Succeeding grey siliceous claystone of early Smithian represents largely an anoxic interval, but it is oxygenated in the later part of this stage. Grey siliceous claystone with black carbonaceous claystone interbeds of Spathian was suboxic to oxic, and temporal anoxia being caused mainly by high productivity intermittently was established within a short time interval. Red chert is rather common in Anisian, but unusual sedimentation of organic matter still continued until the latest Anisian.

Minimum and Terminal Velocities in Fluidization of Particulate Ceramsite at Ambient and Elevated Temperature

Ceramsite is an inert, heat-resistant, porous material that is made via the calcination of carbonaceous claystone in an oxidizing environment. Its basic mineral constituents are mullite, hematite, quartz, and kaolinite. Ceramsite particles have been proven to be a very practical and convenient bed material for performing various chemical reactions in high-temperature fluidized beds. Experimental measurements were performed to determine minimum fluidization velocities and the terminal (entrainment) velocities of beds of ceramsite at ambient and superambient temperature. Using air, experiments were conducted in a column with an inner diameter (ID) of 9.4 cm, with very narrow fractions of ceramsite particles spanning a wide range of 0.13−2.25 mm. The minimum fluidizing velocity was determined to decrease as the operating temperature increased for the beds of all the particles, except for the largest ones (2.25 mm). The bed of these particles exhibited an extremal (nonmonotonic) dependence of the minimum fluidizing velocity on temperature. Novel explicit equations have been developed that enable the direct estimation of the particle size corresponding to chosen minimum fluidizing and/or terminal velocities. Those formulas can be applied in engineering considerations and design calculations of fluidizing ceramsite and similar materials.

Alluvial and lacustrine facies in an extensional basin: The Miocene of Malatya basin, eastern Turkey

During the Neogene, both strike-slip and extensional regimes coexisted, giving rise to a number of fault-bounded basins in eastern Turkey. One of these basins, the Malatya basin, contains a thick sequence (up to 2000 m) of alluvial and lacustrine deposits. This paper focuses on the Miocene alluvial and lacustrine deposits in the northern part of the basin. Alluvial and lacustrine deposits in the study area, having a thickness over 1200 m, are divided into three units on the basis of their vertical sequential changes and lithologic characteristics. These are the lower alluvial unit, lacustrine unit, and upper alluvial unit. The lower alluvial unit is composed of stratified conglomerate (Gm), planar cross-stratified conglomerate (Gp), trough cross-stratified sandstone (St), planar cross-stratified sandstone (Sp), horizontally stratified sandstone (Sh), ripple cross-laminated sandstone (Sr), red mudstone (Fm), carbonaceous claystone (Fl1), and rarely limestone (Pf). Facies Gm, Gp, and Sh characterize alluvial fan to sheetflood deposits. Facies St, Sp, Sh, and Sr are interpreted as braided stream to sheetflood deposits. Facies Fm, Fl1 and siltstone are interpreted as deposits in an alluvial plain system with an ephemeral setting. Carbonaceous claystone (Fl1) and limestone (Pf) are interpreted as a shallow lake, situated as a distal environment in alluvial plain. The middle unit, interpreted as channel/crevasse-splay, swamp and lacustrine deposits, is composed of interbedded sandstone–siltstone–grey claystone (SF), low-angle cross-stratified sandstone (Sl), planar cross-stratified sandstone (Sp), limestone (Pf), carbonaceous claystone (Fl1), marl (Fl2), and coal (C). The upper alluvial unit is composed of Gm, Gp, St, Sp, Sh, Sr, and Fm characterizing a low sinuosity river. Most of the alluvial input into the basin was from the north, northeast, and east. Soft-sediment deformation structures (slump folds) which indicate seismically active areas were formed within the lacustrine facies. The sediment supply, lake level fluctuation, and facies architecture were mainly controlled by synsedimentary tectonism.

Geochemistry of Late Permian to Early Triassic pelagic cherts from southwest Japan: implications for an oceanic redox change

Major, trace, and rare earth element abundances were determined for the southwestern Japanese pelagic chert sequence from the early Late Permian to early Early Triassic to investigate a redox change in deep-sea pelagic environments before and at the Permo–Triassic boundary (PTB) (251 Ma). The sequence was primarily deposited in the deep-sea of the superocean Panthalassa, and then was accreted to Japan in the Middle Jurassic. A remarkable lithostratigraphic change from red chert to siliceous∼carbonaceous claystone through gray chert is observed in this sequence. Constituent elements for these sedimentary rocks are essentially derived from two sources: (1) an ancient seawater via biogenic (mainly radiolarian), hydrothermal, and authigenic materials and (2) an average shale-like terrigenous material. The present measurement demonstrates significant stratigraphic changes of the Ce/Ce non-ter* value (estimated Ce anomaly value of non-terrigenous component, recalculated by subtraction of terrigenous REEs from bulk REEs) and the (Mn/TE) sample/(Mn/TE) PAAS value (excess Mn component other than terrigenous one; TE=terrigenous elements including Ti, Al, Nb, Hf, Th; PAAS=Post-Archean Average Australian Shale) in the Permian chert. The Ce/Ce non-ter* values increase from <0.2 to 1 and the (Mn/TE) sample/(Mn/TE) PAAS values decrease up-section, suggesting that the redox condition of deep-sea open-ocean changed from oxic to suboxic in an interval of approximately 10 Myr. The (∑Fe/TE) sample/(∑Fe/TE) PAAS and (Mn/TE) sample/(Mn/TE) PAAS values of carbonaceous claystone near or at the PTB are less than unity, suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition. This supports the idea of the PTB oceanic anoxia in the superocean Panthalassa. The present data suggest that the anoxic condition prevailed in the deep-sea pelagic regions for an extremely long period, much more than 10 Myr, from the middle Late Permian to early Early Triassic. This long-term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the Phanerozoic.

Confirmation of the Permian/Triassic boundary in deep-sea sedimentary rocks; earliest Triassic condonts from black carbonaceous claystone of the Ubara section in the Tamba Belt, Southwest Japan.

We found earliest Triassic (Griesbachian) conodont, Hindeodus parvus, from the basal part of the black carbonaceous claystone of the Ubara Permian/Triassic boundary section in the Tamba Belt. We also obtained Late Permian (Changxingian) conodonts from the underlying gray siliceous claystone as already reported from other P/T boundary sections. The lithologic boundary between the gray siliceous claystone and the black carbonaceous claystone is confirmed to be the Permian/Triassic boundary in deep-sea sedimentary rocks.

Depositional environment and burial history of a Lower Cretaceous carbonaceous claystone, Bornholm, Denmark

A c. 1 m thick carbonaceous claystone from the type locality of the Lower Cretaceous Skyttegård Member (Rabekke Formation), Bornholm, has been investigated by organic pétrographie and organic geochemical methods in order to assess the depositional environment of the claystone and the thermal maturity of the organic matter. The claystone was deposited in a low-energy, anoxic lake which occasionally was marine influenced. The organic matter is terrestrial and can be classified as kerogen type III and lib. Detrital organic matter and cutinite are characteristic components. The organic matter is allochthonous but the transport distance was short, and the plant material was probably mainly derived from plants growing at the edge of, or nearto, the lake. Source-specific biomarkers such as norisopimarane suggest that the plant litter was derived from a gymnospermous, low-diversity vegetation. Evidence for early angiospermous plants cannot be demonstrated with any certainty. A huminite reflectance value of 0.24%Rm and several geochemical parameters indicate that the organic matter is highly immature. It has only experienced coalification corresponding to the peat stage. Estimates show that, prior to uplift, the claystone was buried to a maximum of approximately 260 m. Reflectance data further suggest that a maximum c. 550 m thick sediment package was removed by erosion prior to deposition of the ?uppermost Jurassic-Lower Cretaceous sediments on Lower Jurassic strata.

Depositional environments of coal and associated siliciclastic sediments in the Lower and Middle Jurassic of Denmark. The Øresund -5, -7, -13, -15 and -18 wells

Five cored wells located in the Fennoscandian Border Zone in the Øresund area, Denmark, encountered Lower or Middle Jurassic coal-bearing strata; the coal seams are Lignite to Sub-bituminous A/High Vol. Bituminous C in rank. A number of shallowing-upward units are recognized in the five wells. Each unit is capped by a coal seam. Correlation of these shallowing-upward units between wells is difficult on the basis of available biostratigraphy and log data. Seven of the coal seams result from establishment of peatforming conditions due to infilling of freshwater lakes, whereas the last two of the coal seams result from peat accumulation on top of restricted brackish lagoon or bay sediments. However, only one of the latter two seams accumulated in an environment influenced by saline water. Hence, the investigated coals represent almost entirely freshwater peat-forming environments. Three main types of environments are defined: 1) Type 1 is a sparsely vegetated open water swamp; it is represented by a limnic facies. The deposit is typically a carbonaceous claystone with a high content of allochthonous organic matter; 2) Type 2 is a densely vegetated rheotrophic, nutrient-rich and anoxic swamp; it is represented by a limnotelmatic to telmatic facies. The coal has a very high content of humified organic matter; 3) Type 3, subdivided into the types 3a and 3b, is the driest environment of the three types. Type 3a is a desiccated ombrotrophic raised bog represented by a terrestrial facies. It is strongly influenced by a fluctuating watertable. The coals contain a high content of inertinite that generally shows a low reflectance. Type 3b is a mesotrophic to ombrotrophic domed bog; the environment alternates between dry oxidizing conditions and wet conditions. It is represented by a telmatic to terrestrial facies. In general, the three types of environments form ecosystems characterized by the groundwater influence, nutrient supply, and vegetation. Successions representing the hydrological evolution towards drier conditions due to vertical peat accretion are recognized in some of the seams. The vegetation was small-statured and consisted of a prominent herbaceous type of flora, shrub-like plants, smaller arboreous plants and, to a lesser extent, larger plants.

A new Cretaceous-Tertiary boundary locality in the western powder River basin, Wyoming: biological and geological implications

A newly discovered Cretaceous-Tertiary (K-T) boundary locality in the western Powder River basin, Wyoming, is characterized by a palynologically defined extinction horizon, a fern-spore abundance anomaly, a strong iridium anomaly, and shock-metamorphosed quartz grains. Detailed microstratigraphic analyses show that about one third of the palynoflora (mostly angiosperm pollen) disappeared abruptly, placing the K-T boundary within a distinctive, 1- to 2-cm-thick claystone layer. Shocked quartz grains are concentrated at the top of this layer, and although fern-spore and iridium concentrations are high in this layer, they reach their maximum concentrations in a 2-cm-thick carbonaceous claystone that overlies the boundary claystone layer. The evidence supports the theory that the K-T boundary event was associated with the impact of an extraterrestrial body or bodies. Palynological analyses of samples from the K-T boundary interval document extensive changes in the flora that resulted from the boundary event. The palynologically and geochemically defined K-T boundary provides a unique time-line of use in regional basin analysis.