Green Mudstone Research Articles

Origin of ferruginous coated grains in the Lower Jurassic palustrine limestones of the Pranhita–Godavari Basin, India

AbstractThe formation of calcareous coated grains like ooids and oncoids have been extensively researched. In contrast, the origin and genesis of ferruginous coated grains are less clear. Radically different processes like surficial weathering, hydrothermal exhalation and microbial activity have been advocated for the source of iron and the development of coatings. Modern examples are sparse and from marine environments affected by igneous activity. This study presents the features of ferruginous coated grains found in freshwater lacustrine–palustrine deposits of the Lower Jurassic syn‐rift strata of the Pranhita–Godavari Basin, India. The coated grains occur in metre‐thick lenticular bodies of nodular limestones enclosed in black mudstones containing plant debris and sulphates (gypsum and baryte). In the nodular limestones, sand‐size coated grains, along with chert and quartz grains, float in a micritic groundmass. Angular quartz grains embedded in dark, amorphous haematite–goethite constitute the nuclei of the coated grains. Cortices comprise numerous, thin, wavy laminae of goethite with trapped detrital grains. These coated grains are typically devoid of carbonates, although the outermost part of the cortex is replaced by calcite spars to varying extent. The black mudstone‐nodular limestone association occurs in between siliciclastic lacustrine deposits (laminated red and green mudstones) below, and the palustrine limestones‐green shale association above. The palustrine limestones contain remains of aquatic organisms, evidence of desiccation, paedogenesis, microbial‐mat formation, chert, baryte and gypsum layers. A few decimetre‐scale, wedge‐shaped, flood‐derived cross‐bedded sandstones occur locally. Due to the proximity of the depositional area to the marginal fault system of the rift basin and association of the limestones containing coated grains with sub‐aerially weathered microbialites, these ferruginous coated grains are ideally poised for a comparative assessment of various hypotheses of solute supply and precipitation. Based on field, microscopic and chemical characteristics, it is possible to conclude that microbially mediated precipitation in hydrothermal (hot spring)‐influenced pools is the most probable origin for these ferruginous coated grains.

Integrated simulation and monitoring to analyze failure mechanism of the anti-dip layered slope with soft and hard rock interbedding

The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding. In order to reveal the landslide mechanism, taking the north slope of Fushun West Open-pit Mine as an example, this paper analyzed the failure mechanism of different landslides with monitoring and field surveys, and simulated the evolution of landslides. The study indicated that when the green mudstone (hard rock) of the anti-dip slope contains siltized intercalations (soft rock), the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip, but also causes the shear failure of anti-dip layered slope with stable low dip. The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope. Its failure depth and failure time were far less than that of toppling failure. In terms of the development characteristics of deformation, toppling deformation has the long-term and progressive characteristics, but shear failure deformation has the abrupt and transient characteristics. This study has deepened the understanding of such slope landslide mechanism, and can provide reference for similar engineering.

Maceral and calcareous nannofossil assemblages as proxies of late Rupelian (Oligocene) environmental changes in the Paratethys: An example from a section of the Menilite Formation in the northern Outer Carpathians

The Menilite Formation (Oligocene) of the Skole Nappe in the Polish Carpathians was deposited in the Paratethys. Deep-sea unbioturbated fine-grained carbonates of the Dynów Marl Member contain cold-water calcareous nannoplankton from Zone NP23 (Rupelian), including Reticulofenestra ornata and Pontosphaera fibula, which are typical of brackish waters in the Paratethys. It is likely that the water column was brackish in the upper part and fully marine and anoxic in the lower part. The Dynów Marl Member records the maximum isolation of the Paratethys from the oceanic circulation (the Upper Solenovian Event). The overlying green mudstones (probably the Krępak Member) are shallowly bioturbated. They contain fully marine, warm-water calcareous nannoplankton from Zone NP24. The environmental change (marine/brackish) is reflected in the quantity and type of organic matter. The abundance and preservation of organic matter are very high (TOC varies from 2.7 wt % to 26 wt %; HI values are >300 mg HC/g TOC) in brown, laminated shales, which were accumulated in saline anoxic conditions. The macerals in the shales are predominantly composed of the liptinite group, including lamalginite, telalginite, liptodetrinite, and bituminite. These macerals are primarily derived from planktonic and benthic algae as well as bacteria. The percentages of vitrinite and inertinite, originating from terrestrial sources, range up to 10% and 0.5%, respectively. The macerals are much less abundant in marls of the Dynów Marl Member because of dispersion in the carbonate groundmass during the calcareous nannoplankton blooms in brackish surface waters. The overall liptinite (mainly liptodetrinite and lamalginite) contribution is 77%–99.7%. Vitrinite and inertinite contents are in average 4.6% and 0.3%, respectively. Macerals are also infrequent in the overlying green mudstones, likely because of oxidation and consumption by organisms in warmer waters.

Effect of water on the rock strength and creep behavior of green mudstone

The weakening of rock mass after immersion substantially affects slope stability. Considering the mudstone in the north slope of the Fushun West Open pit as the research object, we investigated the failure and creep characteristics of mudstone under different immersion times and confining pressures. For this, we used a self-developed experimental apparatus that applies biaxial compression loading in a water immersion environment. Water significantly changed the strength and failure mode of the mudstone. The increase in confining pressure limits the expansion of the crack aperture, reduces the rock strength-weakening coefficient, and delays the rock weakening time. The change in cohesion is primarily responsible for the weakening of shear strength during immersion. Based on the creep test results, the creep curve of the soaking specimen was identical to that of the dry specimen in the initial phase. The weakening effect of water on the specimen increased as the soaking duration increased, due to which the creep curve of the soaking specimen gradually approached that of the saturated specimen. Water entered the microcracks and reacted with the rock interior, accelerating rock failure. Consequently, the soaking specimen had the lowest stress level for creep failure and the shortest failure time. The results of this experiment provide a reference for the long-term stability of the flooded slope.

Study on Phosphorus Adsorption Performance of Inorganic Modified Green Mudstone

Inorganic modified green mudstone (MGM) was prepared from the green mudstone (GM) residue of Fushun West Open Pit Mine and characterized by XRF, XRD, FTIR, and SEM of GM and MGM. According to the calculation of pore size and the BET equation, the pore size and specific surface area of the MGM were larger. The results of adsorption kinetics and isothermal adsorption experiments showed that the adsorption capacity of MGM for phosphate increased from 0.1 mg/g to 0.71 mg/g, which was obviously better than that of GM. The GM and MGM accorded with the quasi-second-order kinetic model. The isothermal adsorption data of GM accorded with the Freundlich model, and the isothermal data of MGM accorded with the Langmuir model, which indicated that the model of GM and MGM was an adsorption process from a double layer to a single layer. Thermodynamic data showed that the increase in temperature was beneficial to the adsorption of MGM. The internal diffusion model showed that due to the change of pore size structure after modification, the number of adsorption sites that could provide phosphate was increased, and at the same time, the change of internal elements led to the extension of the chemical reaction time by 700 min. Because of the ligand exchange and electrostatic interaction between phosphate, GM, and MGM, the adsorption results showed that acidity was better than alkalinity. To improve the recycling ability of MGM, hydrochloric acid with a concentration of 0.1 mol/L was determined as the best phosphorus resolving agent, and the resolving rate was still close to 80% after five cycles. The results showed that the MGM could be a promising adsorbent for the removal of phosphorus, providing a new way for resource utilization of mining waste residue.

Orbital eccentricity and inclination metronomes in Middle Miocene lacustrine mudstones of Jiuxi Basin, Tibet: Closing an astrochronology time gap and calibrating global cooling events

Reconstructing Cenozoic lacustrine astrochronology is essential for understanding climatic and environmental change around northeastern Tibetan Plateau. Existing models attribute the driving mechanism of regional precipitation and aridification to the Tibetan Plateau uplift and global climate change. However, in northeastern Tibet lacustrine astrochronology has a gap from 17 Ma to 14 Ma. To bridge this gap, we investigate Milankovitch-forced cyclicity of green-red mudstone rhythms deposited during the early Middle Miocene Epoch in Jiuxi Basin. We construct color rank stratigraphic series from lacustrine sedimentary successions, and develop a 3.6 Myr-long astrochronology from 16.0 Ma to 12.4 Ma that partly covers the gap. Time series analysis reveals dominant 405-kyr cycles associated with the long orbital eccentricity cycle, and 173-kyr and 1.2-Myr cycles associated with amplitude modulations of the obliquity cycle. We propose that orbital eccentricity (405-kyr cycle) and inclination (173-kyr cycle) metronomes were recorded as climate-sedimentary threshold responses in the lacustrine setting. The maxima of 173-kyr and 405-kyr cycles correspond to green mudstones during lake expansions, and their minima to red mudstones during lake contractions. Anchoring the astrochronology to modeled orbital eccentricity and inclination metronomes further reveals that the recorded astronomical cycles are in phase with those of the marine archives, and suggests that lake evolution in Jiuxi Basin was paced with Middle Miocene cooling events.

Rare clutch of Cretaceous turtle eggs preserved in the Kaiparowits Formation of southern Utah

Although turtles are common Mesozoic fossils, their eggs and nests are rare. Here, we describe an in-situ clutch of turtle eggs from the Campanian (Upper Cretaceous) Kaiparowits Formation of southern Utah. The clutch is preserved in a green mudstone associated with aquatic terrestrial gastropods. Eggshell is broadly distributed across an area of 3.75 m2 with three nearly complete, spherical eggs ∼2.9 cm in diameter, and another three partial eggs identified. The aragonitic eggshell is 0.7–1.2 mm thick and consists of closely packed, slightly domed shell units with a height to width ratio of 3.7:1 and nodular ornamentation 53–71 μm in diameter. Eggshell orientation (concave up/concave down) of 54:46 is consistent with in-situ preservation. An eggshell porosity of 42.5 mm correlates to a humid nesting environment. Extrapolating from egg size, the producing adult carapace length is estimated at 24.45 cm with an average clutch size of 9.91 eggs. The unique attributes of the eggshell warrant naming of a new oospecies, Testudoolithus tuberi. This fossil occurrence is another example of exceptional preservation in the Western Interior Basin associated with the Campanian “taphozone.”

Factors controlling the distribution of oil shale layers in the Eocene Fushun Basin, NE China

The Fushun Basin is a typical continental basin filled with organic-rich fine-grained sedimentary rocks, such as coal, oil shale and greyish green mudstone. Currently, research on this basin predominantly focuses on the enrichment mechanisms of organic matter in coal and oil shale and the controlling factors of coal seam transformation to oil shale. However, during the transformation stage, the deposition of oil shale ceased and was converted to interbeds of grey green mudstone and thin oil shale layers. The control mechanism of this type of sedimentary succession is still not clear. In this study, the thick oil shale in the upper part of the Jijuntun Formation (Unit I) and the high-frequency interbedded mudstone and thin oil shale in the Xiloutian Formation (Units II and III) were analysed as key strata. Organic and inorganic geochemical data were analysed to reconstruct the transformation of the various types and sources of organic matter and controlling factors including the palaeoclimate, palaeoweathering, bioproductivity, terrigenous clastic input, palaeosalinity, and redox conditions. Among these, Unit I was affected by humid climate conditions predominantly. The water depth and volume were large, and the input of terrigenous debris was low. Freshwater algae blooms and anoxic conditions led to a supply of organic matter and that was well preserved. This further resulted in a high abundance of organic matter in the sedimentary rocks. Unit II was affected by semihumid-semiarid and arid climate conditions. The lake became shallower while terrigenous clastic input and lake palaeosalinity increased; these changes represented the transition stage from freshwater to brackish water. The lake still exhibited suboxic/anoxic conditions, but the biological living space decreased, resulting in a limited organic matter supply and a low abundance of organic matter in the sediment. Unit III was affected by semihumid-semiarid climate conditions, and the palaeosalinity continued to increase. The lake had brackish water, with a high bioproductivity, a decreased water volume and a limited supply of organic matter. However, brackish water stratification occurred in the lake, which created a strongly anoxic environment and good preservation conditions, resulting in a secondary high abundance of organic matter. A comprehensive analysis indicates that the environmental change caused by the palaeoclimate was the main factor driving the oil shale deposition to cease and the onset to deposit grey green mudstone and thin oil shale in the Fushun Basin, Northeast Asia.

Soft-sediment deformation structures (SSDS) in the Ediacaran and lower Cambrian succession of the Aksu area, NW Tarim Basin, and their implications

The Tarim Basin, the largest continental and marine superimposed basin in the northwestern part of China, is typically viewed as a stable and uninterrupted sequence during the Ediacaran-Cambrian transition. Undeformed strata, thick shallow marine sediments and thin deep marine sediments characterize the basin. In this study, we identify various types of soft-sediment deformation structures (SSDS) and an unconformity at four localities in the Aksu area, NW Tarim Basin. SSDSs include large-scale load structures, plastic intrusions and extrusions, load casts and pillow structures, liquefied breccias, ground fissures and lateral liquefaction, boudinage-like SSDSs, mound and sag structures, slumps, and small syn-sedimentary faults. The deformed layers are sandwiched between undeformed sedimentary rocks. Deformation features are found in the (a) lower Cambrian Yuertusi Formation consisting of interbedded thin black shale and phosphorite chert layers, thick-bedded shallow gray dolomite and silicate layers; (b) upper Ediacaran Qigebulak Formation composed of dark gray to gray dolomite and grayish green mudstone layers; (c) in the brown sandstone layers of the lower Ediacaran Sugaitebulak Formation. These units contain fluvial-lacustrine, nearshore, carbonate platform, shelf, and bathyal sedimentary environments. The SSDSs and more detailed stratigraphy indicate a dynamic setting that includes the heretofore unrecognized unconformities, a sub-stratigraphic sequence interface and high magnitude seismic events. The SSDS were produced during rifting, short sub-aerial exposure and frequent seismic disturbances. Combined on the carbon and oxygen isotope records, gamma radiations and the concentrations of main and trace elements, the differences between the SSDS layers and the undeformed layers are preliminary analyzed. We propose that this sequence not reflect a stable tectonic-sedimentary environment during the Ediacaran-Cambrian transition. Therefore, these units provide a unique glimpse into paleo-tectonic activity and paleo-ecological-environmental variation in the Tarim Basin during the late period of Rodinia breakup and the assembly of Gondwana.

Analysis of microbial community structure and diversity in surrounding rock soil of different waste dump sites in fushun western opencast mine

It is importance to understand the correlation between the physicochemical properties of different surrounding rock soil and microbial communities in Fushun western opencast mining for the ecological restoration of land after mine closure. In this study, two layers of soil samples were collected from four different areas in Fushun western opencast mining: coal gangue area (CGA), green mudstone area (GMA), oil shale area (OSA) and mixed area (MA). Then, the effects of different surrounding rock soil physicochemical properties on the microbial communities were explored using the High-throughput sequencing technique. A wide diversity of taxonomical groups were present in four soil cores, and many were correlated with soil physicochemical properties. The obvious differences in microbial communities between different areas showed the influence of different surrounding rock soil on the microbial communities were significant. Redundancy analysis and the network diagram confirmed that soil physicochemical properties pH (Pondus Hydrogenii)-AN (Available Nitrogen)-EC (Electronic Conductivity)-WC (Water Content)-TK (Total Nitrogen), Cd (Cadmium)-Ni (Nickel) had great influence on the microbial communities. Therefore, this study can provide scientific judgments for the different surrounding rock soil physicochemical properties in coal mining, microbial-mediated rock mineralization and biogeochemical cycles.

Hidden for one hundred years: a diverse theropod ichnoassemblage and cross-sectional tracks from the historic Early Jurassic Tsikoane ichnosite (Clarens Formation, northern Lesotho, southern Africa)

ABSTRACT The upper Stormberg Group of Lesotho has an abundant and diverse ichnological record that dates to the Early Jurassic. Herein, we re-evaluate a known ichnosite in the lowermost Clarens Formation (Karoo Supergroup) at Tsikoane in northern Lesotho. The site was reported to preserve tridactyl tracks as natural casts in the ceiling of overhangs and true track impressions on a fallen sandstone block. At least three track-bearing palaeosurfaces, associated with horizontally laminated sandstones and desiccated green mudstones, can be traced over a distance of 250 m. Associated with one of the track-bearing palaeosurfaces, discrete, U-shaped, cross-sectional structures are interpreted as a series of natural casts, surface tracks, true tracks and undertracks. Although the Tsikoane tracks were historically assigned to a single ichnogenus, later synonymised with Grallator, our findings show a higher diversity of tridactyl ichnites, with tracks that have Kayentapus-like and Eubrontes-like features in addition to previously recognised Grallator-like features. These new findings, within their high-resolution sedimentological context, improve the understanding of theropod palaeodiversity and palaeoecology in southern Africa during a crucial period in dinosaur history marked by increases in both abundance and diversity.

An unusually diverse northern biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming

The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate fauna in the Morrison Formation (Upper Jurassic) north of Como Bluff and the second-most diverse in the entire formation, after Reed’s Quarry 9. The deposit was an occasionally reactivated abandoned river channel, in interbedded green mudstone and laminated green-gray siltstone above a channel sandstone. The dinosaur material is densely distributed and is disarticulated to articulated, with several associated skeletons. The biota contains charophytes, horsetails, a possible seed fern, possible conifers, gastropods, two types of unionoid bivalves, diplostracans (“conchostracans”), a malacostracan, ray-finned fish, lungfish, a frog, salamanders, two types of turtles, rhynchocephalians, a lizard, choristoderes, two types of crocodyliforms, a pterosaur, Allosaurus and several types of small theropods including Tanycolagreus? and probable dromaeosaurids, numerous Camarasaurus and a diplodocine sauropod, a stegosaur, the neornithischian Nanosaurus, and the mammals Docodon, Amblotherium, and a multituberculate. Among these taxa, one of the unionoid bivalves, an atoposaurid crocodyliform, and the species of Amblotherium, which appear to be new and unique to the locality so far. The Docodon material may represent the first occurrence of D. apoxys outside of its type area in Colorado. Additionally, small, unusual theropod tooth types reported here may represent the first Late Jurassic occurrence of cf. Richardoestesia in North America and a possible abelisauroid, respectively.

Depositional model for a salinized lacustrine basin: The Permian Lucaogou Formation, Jimsar Sag, Junggar Basin, NW China

Fine-grained sedimentary rocks are well developed in a salinized lacustrine basin in the Junggar Basin, China. Understanding the sedimentary characteristics and process of these fine-grained sediments is essential to find the exploration target for tight oil. In this study, the sedimentary characteristics and forming mechanism of fine-grained sediments in the Permian Lucaogou Formation within the Jimsar Sag were investigated based on core and thin section observation, SEM combined with XRD and geochemical data, and eleven lithofacies were identified, including (1) brecciated dolomitic mudstone, (2) intraclastic conglomerate, (3) mixed siliciclastic and intraclastic grainstone, (4) dolomitic siltstone, (5) Carbonate packstone and grainstone, (6) dolomitic mudstone, (7) laminated algae-bearing tuffaceous mudstone, (8) massive tuffaceous mudstone, (9) turbidite dolomitic mudstone to siltstone, (10) pebbled sandstone, and (11) green mudstone and siltstone. The organic constituents in the fine-grained sedimentary rocks include sapropelic, exinite, vitrinite, inertinite and secondary macerals, which are dominated by unstructured algae and asphaltene. The fine-grained sedimentary rocks are characterized by high-frequency cycles composed of three successive facies associations: profundal, littoral–sublittoral and palustrine, which recorded distinct lacustrine expansion and contraction. Developed mud cracks, paleosols and vertical dissolution fractures in the fine-grained sedimentary rocks indicate that these facies recorded the depositional process in an ephemeral to perennial lake in an arid climate. Fluvio-deltaic and aeolian transport were main modes for transporting the siliciclastic component that ultimately accumulated in a subaqueous and subaerial environment. The dolomite in the littoral zone might develop with the evaporitic concentration of the lake water during the early diagenetic stage. The depositional processes in the profundal zone included suspension and turbidity currents. Multiphase volcanic activities affected the lithofacies and prompted the accumulation of organic matter. Understating the depositional process of the fine-grained sedimentary rocks in the Lucaogou Formation in the Jimsar Sag is helpful to understand the depositional environment in the salinized lacustrine basin in the Junggar Basin.

Thrust duplex deformation in the volcaniclastic sequence of the Fatima fold-and-thrust belt in the west-central Arabian Shield

In this study, we present a field-based structural analysis of the unmetamorphosed Precambrian volcaniclastic sequences of the west-central Arabian Shield. The study area is known as the Fatima fold-and-thrust belt, which is an overturned synclinorium that developed during the Neoproterozoic era. This belt is composed primarily of green mudstone, green sandstone, an andesite flow, limestone, red mudstone and pyroclastic units. This stratigraphic succession, which presents different rheological multilayers, offers significant mesoscale folding and thrust-related structures. Mechanical anisotropy and thickness contrasts have played significant roles in controlling the style of the deformation. Deformed hinge zones, a simple duplex, a domino-style duplex, and imbricated and antiformal stacks are among the thrust-related structures presented and analyzed. The domino-style duplex observed on the backlimbs of the overturned anticlines formed a unique pattern that developed during thrust propagation. The results of this study indicate that the thrust duplex developed according to a thick-skinned model, and it represents a newly recognized tectonic regime in the Arabian Shield. Comprehensive field mapping and structural analyses revealed that the zone under study area was affected by four phases of deformation (D1–D4). The D1 and D2 phases present ductile deformation that developed during the final cratonization and assembly of the Arabian Shield, and they can be recognized at both the map and outcrop scales. The D1 phase represents a progressive regime and is indicated by a NW-SE stress orientation and the formation of a series of coaxial symmetrical NE-SW-plunging folds. NNW-directed thrust-related structures progressively developed during the D2 phase. An approximately fifty-three percent tectonic shortening can be calculated based on the restored structures. D3 and D4 have a brittle nature and are indicated by shearing and normal faulting, respectively.

Petrographic Characterization of the Different Types of Basalts of Harrat Al Fatih, Ablah Area, West Central Arabian Shield, Saudi Arabia

Harrat Al Fatih is located southwest of Ablah area, Assir terrain, southwestern Arabian Shield. It is present as black laterally extended horizontal basaltic sheet just overlying folded strata of the volcano-sedimentary succession of Ablah Formation (green mudstones, dolostones and green and red volcaniclastic red beds). These basalts are rift-related and represent part of the Oligo-Miocene basic volcanics of the western part of Saudi Arabia. The detailed field and microscopic description of these basalts enable the author to classify it into two main types: 1) Grey tuffaceous glassy basalts that present overlying the Ablah Formation. This basalt type is generally soft, bedded and intercalated with grey, green and red tuffaceous mudstones. Microscopically it composed of minute lath-like plagioclase and pyroxene crystals embedded in glassy groundmass. 2) Black olivine-rich basalts which are present in the topmost part of harrat Al Fatih are generally black, hard and contain remarkable reddish brown oxidized olivine spots and some calcite and amorphous quartz domains. Under the microscope, this basalt type is microcrystalline and composed mainly of lamellar twined Ca-plagioclase and colored olivines and pyroxenes. The olivines show different stages of oxidation and formation of amorphous blood red iron-oxyhydroxides and black hematite. The present study revealed the formation of the grey basalts at the initial stages of the volcanic eruption in ephemeral lakes and the second type of basalt was during the consolidation of proper basic magmas at the final stages of the volcanic eruption.

Widespread Late Devonian marine anoxia in eastern North America: a case study of the Kettle Point Formation black shale, southwestern Ontario

The Kettle Point Formation of southwestern Ontario consists of intervals of organic-rich interlaminated black shale interbedded with organic-poor greyish green mudstones and rare red beds, separated by metre-scale sequences of non-interlaminated black shale. The formation shows a largely consistent background value for the black shales around −20‰ δ34S, punctuated by a substantial positive excursion of ∼32‰ (up to +12.87‰) that coincides with a significant interval of greyish green mudstone and red beds. Lithological and geochemical data indicate that the black shales were deposited during periods of anoxia, with thick intervals of non-interlaminated black shales recording the peak of anoxia, whereas the greyish green mudstones record deposition in more oxygenated environments. Relative water depth is interpreted as the key control on the vertical and lateral distribution of the Kettle Point lithofacies. Interbedded black shales and greyish green mudstones were deposited in relatively shallow waters, where minor, short-lived falls in relative sea level promoted dysoxic to oxic conditions and the deposition of organic-poor lithologies. Non-interlaminated black shales are indicative of substantial rises in relative sea level, resulting in widespread anoxia and the deposition of thicker and more laterally extensive packages of organic-rich sediment. The formation of black shales in relatively shallow waters in southwestern Ontario implies that the extensive deposition of organic-rich sediment across eastern North America during the Late Devonian was a product of widespread anoxia related to restricted circulation in intracratonic and foreland basin depositional centers.

An approach to paleoclimatic conditions for Devonian (upper Lochkovian and middle Givetian) ironstone formation, NW Anatolian carbonate platform

Lower-middle Devonian iron-bearing successions were studied along 2 measured stratigraphic sections in the Camdag region of NW Anatolia. Ironstones in the upper part of the Findikli Formation in Kabalakdere are characterized by alternating red and green mudstones and sandstones at the bottom, followed by a series of dolomite, dolomitic limestone with oolitic ironstones, and chamositic mudstones at the top. Conodonts from these carbonates indicate the delta-pesavis zones of the late Lochkovian. The 12- to 45-m-thick Ferizli Formation unconformably overlies the Findikli Formation with a quartz-arenite succession at the bottom. The formation comprises alternating red, iron-rich limestones and dolomitic limestones, where iron-rich bioclastic grainstones are more dominant than iron-rich oolitic grainstones. The dolomitic limestones in this succession mark the ensensis and hemiansatus zones of the middle Givetian age. Mineralogically, the carbonates are dominated by goethitized and chamositized fossil fragments and chamositic oolites. In the oolitic facies, the oolites are made up of iron-bearing carbonates/iron, the bioclast of micritized/ironized brachiopods, and crinoids, whereas the matrix includes goethite, brown iron-silicates, chamosite, sideritic oolites, quartz clasts, and brachiopods. Partial iron precipitation within microborings or precipitation along the spine holes on echinoid grains is observed in the bioclastic grainstone/biosparite facies. Iron peloids are also recognized in the grainstone facies. Iron precipitation could be explained as precipitation of transported and dissolved iron from a terrestrial environment under wet/subtropical climate conditions within oxidizing and increased pH conditions, or as dissolved iron transported by upwelling currents over the shelves and precipitated under an oxidizing environment. The cyclic occurrence of primary iron in a marine carbonate environment and its extensive distribution over large areas indicates that a controlling mechanism for iron-rich carbonates and mudstones could be related to the cooperation of climate, sea level, and oceanographic changes in the middle Givetian. During the late Lochkovian, the same or very similar controlling factors might have operated, where the alternation of red mudstones can be explained by lateral facies changes or changes in terrestrial/nutrient influx.

A new Oligo-Miocene Mammal-Bearing site from a sedimentary intercalation in the trap basalts of Central Eritrea

We report the findings of two proboscideans from a sedimentary intercalation within the Central Eritrea Tertiary Trap basalt succession. These intertrappean sediments can be traced continuously between Tera’emni and Adi Quala in the Mendefera region, and are interbedded between the underlying Asmara/Aiba-Alaji basalts and the overlying Adi Ugri basalt. This intercalation is up to 50 m thick and consists of a predominant intensely pedogenized red, green and gray mudstone and siltstone with subordinate channelized pebbly sandstone. The newly discovered mammal remains come from the coarse-grained deposits in the Mai Gobro section. Available radiometric datings of the host volcanic rocks constrain the age of the fossils between 24.6 and 22.1 Ma, i.e. at the transition between the Oligocene and the Miocene. The fossil vertebrate remains from Mai Gobro represent two proboscidean families, Deinotheriidae and Gomphotheriidae. The morphological grade of the two Mai Gobro proboscideans would suggest a more derived stage than that of representatives of the same families known from other Oligocene African sited (e.g. Chilga, Ethiopia), suggesting a possible Oligo-Miocene age.

THE EFFECT OF SOME PHYSIOCHEMICAL FACTORS ON PEDOGENIC DISTRIBUTION OF MANGANESE IN SOME

Eight soil pedons were chosen. in Nineveh Province to determine the effect of physiochemical factors 0n pedogenic distribution of manganese extracted by DCB method. The results indicated that topography had a significant effect in all studied soils. the highest . manganese values in Al-Hamdania ranged between (40-47) mg.Kg-1. followed by Al-Fadhlia & Kara-Tapa regions ranged between (36-39). (11.6-35) mg.Kg-1 respectively. Soil depth had significant effect in Al-Fadhlia & Al-Hamdania regions with ratio effect of 30% . 50% respectively. CaCO3 had a significant effect in Al-Hamdania region only. Organic matter had a slight effect. Soil fine fraction (silt & clay) had unclear effect in which manganese ranged between 37.2-39.52 mg.Kg-1in Al-Hamdania region. Soil pH had non-significant effect on manganese pedogenic distribution in studied soils. DCB was effective extracting method for Mn-Fe concretions and thin black coatings on red and green mudstone.

Depositional and halokinetic-sequence stratigraphy of the Neoproterozoic Wonoka Formation adjacent to Patawarta allochthonous salt sheet, Central Flinders Ranges, South Australia

Abstract Parts of two third-order Neoproterozoic (Marinoan) depositional sequences are documented in the Wilpena Group (Wonoka Formation and Bonney Sandstone) at Patawarta diapir, located in the central Flinders Ranges, South Australia. These sequences represent an overall regressive succession transitioning upwards from outer to middle wave-dominated shelf deposits to a tidally dominated barrier bar to coastal plain. The lower, middle, upper limestone and green mudstone informal members of the Wonoka Formation comprise the Highstand Systems Tract of the lower sequence. The Sequence Boundary is at the top of the Wonoka green mudstone member and is overlain by the Lowstand Systems Tract of the upper sequence, which includes the lower dolomite, sandstone and upper dolomite beds of the Patsy Hill Member of the Bonney Sandstone. The upper sequence Transgressive Systems Tract comprises the Bonney Sandstone. These units comprise one complete tapered composite halokinetic sequence (CHS). The lower halokinetic-sequence boundary is associated with the Maximum Flooding Surface of the lower depositional sequence and the upper halokinetic-sequence boundary is interpreted as the Transgressive Surface of the overlying depositional sequence where an angular truncation of up to 90° is documented.