Red Mudstone Research Articles

Carboniferous Foraminifers of the Lower Part of the Ichinotani Formation, Hida Marginal Terrane, Japan

The Ichinotani Formation distributed in the Fukuji area, Hida Marginal Terrane, central Japan, consists of fossiliferous bedded limestone intercalating reddish mudstone and sharpstone conglomerate with a continental margin affinity. The lower part of the formation in the studied area is subdivided into five fusuline zones from lower to upper, Eostaffella kanmerai, Pseudostaffella antiqua, Pseudostaffella kanumai, Profusulinella fukujiensis, and Profusulinella dagmarae. These five zones are probably correlated to the Visean/Serpukhovian (Venevian/Tarusian), middle part of the Bashkirian (Akavasian), middle to upper part of the Bashkirian (Askynbashian to Tashatinian), upper part of the Bashkirian (Tashatinian to Asatausian), and uppermost Bashkirian (Asatausian), respectively, of the stratotypes of the Russian Platform and the South Urals based on the biostratigraphy, faunal composition and correlation of foraminifers. There are remarkable faunal transitions between the Eostaffella kanmerai and Pseudostaffella antiqua zones. Almost coeval Pseudostaffella–Profusulinella assemblages are recognized between the upper part of the Lower Member and the lower part of the Middle Member in the type section of the Ichinotani Formation. Thirty-three species of foraminifers are paleontologically noted and compared to those mainly of the type materials and the taxa to have been described from the Ichinotani Formation.

Alluvial fans in the latest phase of the Messinian Salinity Crisis: An example from the Chaabet Et Tabbela Formation, northern Tunisia, Central Mediterranean

Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km.The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions.

Influence of pH on moisture-absorbing swelling cracks of red layer in central Sichuan and its micro-mechanism

In this study, the influence of pH on the moisture-absorbing swelling cracks of red mudstone in southwest China was studied and its microscopic mechanism was revealed. A self-designed water absorption device combined with digital speckle correlation (DSCM), scanning electron microscope, XRD diffraction experiment, mercury injection experiment and other means were used. The results indicated that compared with an alkaline environment, an acidic environment resulted in the self-absorption and cracking of mudstone. The maximum water absorption rate of mudstone and crack rate in a pH of 3 were determined as 15.77 and 18.91%, respectively; whereas for pH = 11, they were 11.71 and 7.11%, respectively. In the acidic environment, the maximum combined displacement value and maximum principal strain value of mudstone self-priming and swelling evolution were both greater than in an alkaline environment. Simultaneously, in the former, the moisture absorption failure characteristics of mudstone exhibited increased swelling strain zones and swelling cores. The three possible mechanisms by which pH affects the expansion of mudstone hygroscopic cracks were proposed: hydration-expansion softening, adsorption-wedge failure, and humidity stress field. However, it was found that the solutions with different pH values may affect these three microscopic mechanisms through the following four physical or chemical processes: mineral dissolution, ion absorption and exchange, particle association, and pore change. The results of this study are expected to be of significance and aid in roadbed design, tunnel support, slope treatment, and other projects in the southwest region.

The collapse of the protoprecordillera and unification of the Paganzo and Calingasta-uspallata basins: Retamito Formation a key in the integrative biostratigraphic and palaeoenvironmental model

The Retamito Formation is located at the southernmost of Oriental Precordillera, San Juan, Argentina. This contribution defines eight facies associations: FA1 (breccias and conglomerates) linked to initial valley fills by a chaotic basal colluvium fan and/or karst collapse. FA2 (sandstones and gravelly sandstones) is interpreted as deposits of coastal shoreface systems. The FA3 (coal and coaly mudstones) could be attributed to a paralic environment and represent the first record of plant remains of Argentina (NBG Biozone). FA4 (gravel-bed) is interpreted as a proximal alluvial system. FA5 (shales) contains the first record of brachiopods and a new taxa Komiellanetes cesariae sp. nov, probably representing an eastward extension of the TS fauna in a brief marine incursion. FA6 (mudstones and sandstones) is deposited in a delta front system. The FA7 (red mudstones) are linked to lagoons deposits, where they preserved a floristic assemblage of megaflora remains (Ferugliocladus Superbiozone) composed of seeds, stems, and leaves that are most likely of Permian age. Finally, the FA8 (interbedded sandstones and mudstones) is interpreted as deposited by an anastomosed fluvial system. We present paleoenvironmental and paleontological data of the Retamito Formation correlated with the neighboring Andapaico and Ansilta formations in an east-west transect. This correlation parsimoniously linked the Paganzo and Calingasta-Uspallata Basins in seven filling scenarios (temporal stages Ts). From Ts1 to Ts5, both basins were separated by the Protoprecordillera. Common paleoenvironments on both basins suggest unification of them in Ts6 and Ts7. These temporal stages are paleontologically controlled by two new fossil levels and the corresponding sedimentary paleoenvironments that contain them. Thus, it could be demonstrated that the positive element of the Protoprecordillera was active until the Upper Carboniferous and collapsed towards Early Permian, unifying both basins in this sector of Gondwana.

Shakedown behavior of saturated weathered red mudstone

Red mudstone is widely distributed in the southwest part of China, and it has been used as the fill material in the construction of railway embankment. Shakedown behavior of saturated red mudstone fill material(SRMF) was characterized via a series of drained cyclic triaxial tests. Three types of deformation response were recorded in this study. Strong correlation was observed between deformation response and stress state (confining pressure, cyclic amplitude and cyclic stress ratio). In order to determine the shakedown limit and the creep limit, responses of axial strain, axial strain rate and dissipated energy were used. Especially for the determination of the creep limit, correlation between dissipated energy and cyclic stress ratio was used to overcoming the difficulty encountered in conventional method. Tests results showed that the cyclic stress ratios corresponding to the shakedown and creep limits were lower than the monotonic compression strength. A clear power function was identified to correlate the limits with confining pressure.

Palaeoclimatic and diagenetic controls based on clay mineralogy and organic matter distribution: The continental rift Cuyo Basin (Triassic), west‐central Argentina

AbstractThe Triassic Cuyo rift Basin is one of the renowned petroleum systems in South America that records distinctive alluvial, lacustrine and fluvial settings with volcanic input. The present study focuses on the clay mineral assemblages that represent the syn‐rift to post‐rift fills. Four clay mineral assemblages are defined based on X‐ray diffraction, optical and electron microscopy analyses. The illite/mica‐dominated assemblage is documented in the syn‐rift I (Cerro de las Cabras Formation). Such mineral phases are inherited and derived from the erosion of pre‐rift units, suggesting that physical weathering associated with a warm and semi‐arid climate played a leading role in their occurrence. Authigenic smectite clays are diagnostic in organic‐lean mudstones of the syn‐rift II (lower Potrerillos Formation) which point to alteration of pyroclastic material under a warm and semi‐arid to humid climate. A warm and humid climate prevailed during the deposition of lacustrine hydrocarbon source rocks (upper Potrerillos and Cacheuta formations). Organic‐rich mudstones show the illite/mica–kaolinite–smectite assemblage in conjunction with amorphous organic matter and restricted terrigenous elements. Diagenetic kaolinite booklets and bipyramidal quartz are attributed to the acidification of pore‐water related to kerogen transformation during burial diagenesis. Vitrinite reflectance values (ca 0.63%) confirm that organic‐rich sediments reached the earliest oil window; however, smectite is devoid of illite layers throughout the Triassic succession, probably related to the absence of potassium in the system and the high crystallinity of the smectite, which delayed the transformation of smectite into mixed layers illite–smectite. Red mudstones of the post‐rift II (the fluvial‐lacustrine Rio Blanco Formation) show the kaolinite‐dominated assemblage where the authigenic kaolinite is interpreted to be derived from the alteration of volcaniclastic detritus and indicative of warm climate with markedly wet periods.

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.

The pottery from the Bronze Age settlement at Podsmreka in the Dolenjska region


 
 
 Excavations at Podsmreka near Višnja Gora unearthed a Bronze Age settlement and associated five burials of children or juvenile individuals. They brought to light a wealth of finds that include accumulations of red mudstone, yellow siltstone and bauxite cobbles, the collecting and processing of which was an important activity of the settlement’s inhabitants, but also quantities of pottery that is the topic of this contribution discussing, more particularly, its typological and chronological attribution. Together with the pottery from Oloris, it defines the phenomenon that is the Oloris-Podsmreka horizon, which covers the Middle and transition to the Late Bronze Age in the south-eastern Alpine area.
 
 

Research on Internal Structure and Mechanism of Landslide Based on Hydrogeophysical Investigation (Quan’an Landslide, Southwest China)

The survey area is located in the planning area of Longquan national urban park, with frequent human activities, numerous water conservancy, transportation projects, and frequent geological disasters such as landslides. The Red Mudstone has low strength and easy to soften in the case of water, and it is very prone to landslide in rainy season. At present, there are many studies on Red Mudstone Landslides, but most of them are analyzed by geological means, and the monitoring process is also dominated by surface deformation and settlement; there is less analysis with hydrogeological that is caused by rainfall and human activities. For Red Mudstone Landslides, to effectively reveal and analyze the process of the Slip Mechanism, we need to carry out the characteristics of hydrogeological structure and underground physical structure, and compare with surface monitoring and point geological structure. In this study, a one-year field survey and hydrogeophysical survey were carried out. Combined with the characteristics of environmental geology, the geophysical forward modeling problem based on finite element method was used to verify the influence of rainfall on the electrical characteristics of underground media. The smoothness constrained least square method and three-dimensional unstructured grid method are used to interpret the ERT data, analyze the abnormal patterns of electrical structure of landslide in different seasons, and correspond well with the GPR data. According to the characteristics of surface vegetation and weathering, as well as the displacement and settlement monitoring after landslide, the spatial characteristics of red bed landslide are revealed, and the relationship between landslide, rainfall, and human activities is clarified.

Mesoscopic representative elementary area of red mudstone based on U-Net segmentation

Mesoscopic representative elementary area of red mudstone based on U-Net segmentation

The synthesis of soft rocks based on physical and mechanical properties of red mudstone

Although similarity simulation experiments have been widely used in geotechnical engineering, their application in soft rock mechanics is still limited due to the complex water–rock interaction of such rocks. The purpose of this study was to synthesise red mudstone–like materials by the method of mineral composition and proportion are completely similar to that of natural rock samples, using sodium silicate content, compression time and vertical stress to investigate the mechanical properties and composition of soft rocks. The physical and mechanical properties of the synthetic red mudstone–like materials were compared with those of natural red mudstone by the density, acoustic characteristics, and microstructure investigation as well as uniaxial and triaxial compression tests. The results show that the synthetic red mudstone–like materials can reproduce the physical and mechanical properties of natural red mudstone. They show that sodium silicate content is one of the most important factors governing mechanical properties, such as internal friction angle, of the synthetic red mudstone–like materials. Importantly, the synthesis method developed in this study could potentially be widely implemented in rock mechanics and engineering.

Shallow marine glauconitization during the Proterozoic in response to intrabasinal tectonics: A study from the Proterozoic Lower Bhander Sandstone, Central India

Glauconite forms authigenically by the replacement of quartz and feldspar substrates within the Precambrian Lower Bhander Sandstone (LBS) of the Vindhyan Basin. The glauconite exhibits consistently high K2O (7.08–8.62 wt%) and low to moderate TFe2O3 (6.20–18.5 wt%). The X-Ray Diffraction study reveals an evolved to highly evolved glauconitic mica structure. The deposition of mudstone-dominated LBS took place in a shallow marginal marine environment within a low gradient epeiric sea. The overall fining upward succession of the LBS comprises multi-storied, meter scale progradational cycles defined by red mudstone and sandstone–siltstone alternation in ascending order. The repetitive cycles indicate recurrent low-magnitude basin subsidence of the epeiric seafloor. Slump folds and slide planes, associated with the wedge-shaped mud pebble conglomerate, mark each episodes of basin subsidence. The glauconite occurs within sandstone and the sandy matrix of a wedge-shaped conglomerate at the base of a shallowing upward cycle which starts with a grey colored mudstone. The enrichment factors of redox-sensitive elements elucidate sub-oxic depositional condition during the glauconitization. The redox-sensitive element ratios (V/Cr, V/Sc) corroborates the sub-oxic depositional condition for the glauconitic interval and oxic environment for the encasing sediments. The formation of glauconite in the LBS corresponds to the deepening of the basin in response to the tectonic subsidence. The meter scale progradational cycles, recording the transition from suboxic to oxic conditions, corresponds to tectonically-induced deepening and subsequent filling. This study recognizes the significance of intrabasinal tectonics in facilitating suitable redox conditions for the glauconitization process within Proterozoic shallow epeiric sea deposit.

Hydro-Damage Properties of Red-Bed Mudstone Failures Induced by Nonlinear Seepage and Diffusion Effect

Nonlinear catastrophes caused by geological fluids are a fundamental issue in rock mechanics and the geoengineering hazard field. For the consideration of hydrodynamic force on red-bed mudstone softening damage, X-ray visualization tests on the fissure flow in mudstone block failure under hydrodynamic force was performed in this study based on block scale, and the physical phenomena of fissure seepage and nonlinear diffusion were further explored. A new method for evaluating the hydro-damage degrees of rocks using an X-ray image analysis was proposed, and the quantitative relation of diffusion coefficients of hydro-damage and seepage was established. The research results revealed that the hydrodynamic force promoted the fluid-filled fissure behavior in mudstone specimen failure. Furthermore, the seepage and diffusion phenomena of fluid in rocks during failures were indicated using X-ray imaging. A dual mechanical behavior was presented in the nonlinear seepage and abnormal diffusion of a red mudstone geological body under hydrodynamic conditions. The damaged degree of mudstone was aggravated by the effect of hydrodynamic force, and the initial seepage–diffusion coefficient with respect to lower hydro-damage was larger than the final seepage–diffusion coefficient with respect to higher hydro-damage of rocks with a decreasing nonlinear trend.

Early Pliocene marine transgression into the lower Colorado River valley, southwestern USA, by re-flooding of a former tidal strait

Abstract Marine straits and seaways are known to host a wide range of sedimentary processes and products, but the role of marine connections in the development of large river systems remains little studied. This study explores a hypothesis that shallow-marine waters flooded the lower Colorado River valley at c. 5 Ma along a fault-controlled former tidal strait, soon after the river was first integrated into the northern Gulf of California. The upper bioclastic member of the southern Bouse Formation provides a critical test of this hypothesis. The upper bioclastic member contains wave ripple-laminated bioclastic grainstone with minor red mudstone, pebbly grainstone with hummocky cross-stratification (HCS)-like stratification and symmetrical gravelly ripples, and calcareous-matrix conglomerate. Fossils include upward-branching segmented coralline-like red algae with no known modern relatives but confirmed as marine calcareous algae, echinoid spines, barnacles, shallow-marine foraminifers, clams, and serpulid worm tubes. These results provide evidence for deposition in a shallow-marine bay or estuary seaward of the transgressive backstepping Colorado River delta. Tsunamis generated by seismic and meteorological sources likely produced the HCS-like and wave-ripple cross-bedding in poorly-sorted gravelly grainstone. Marine waters inundated a former tidal strait within a fault-bounded tectonic lowland that connected the lower Colorado River to the Gulf of California. Delta backstepping and transgression resulted from a decrease in sediment output due to sediment trapping in upstream basins and relative sea-level rise produced by regional tectonic subsidence.

Vertical variations of minerals in clayey sedimentary rocks in the cores of two-deep exploration wells from the Kozlu coalfield (Zonguldak, NW Türkiye), with emphasis on tonstein (schieferton) formation

The majority of Turkish bituminous coal resources are located in the Zonguldak Basin. The Carboniferous coal seams in the Alacaağzı, Kozlu, and Karadon formations have received interest. However, the detailed mineralogical compositions of clayey sedimentary rocks in coal-bearing sequences in the basin have been limited. This study aims to investigate vertical variations of mineralogical compositions of Carboniferous and Early Cretaceous clayey sedimentary rocks cored in the two-deep exploration wells (K20/K and K20/H) from the Kozlu coalfield using XRD and SEM-EDX analyses data. In addition, a special interest is also given to tonstein layers identified within the Kozlu and Karadon formations. The XRD analyses revealed that the quartz and clay minerals are the main components, and the latter is generally the dominant phase in all studied formations. Besides, clay fraction minerals (chlorite, illite/mica, and kaolinite) are common, while illite/smectite mixed-layer clay mineral is only identified in the two samples. The tonstein samples display similar mineralogical compositions to other samples, while several accessory minerals (e.g., apatite, baddeleyite, monazite, and zircon) are also present. Furthermore, calcite, dolomite, and hematite are mainly observed from the Early Cretaceous samples of the Zonguldak Formation. The vertical distributions of quartz and clay fraction minerals are variable throughout the studied two exploration wells. The vertical variations of clay fraction mineral illite/mica could be mainly related to changes in clastic influx from the basement, while kaolinite seems to be controlled by synchronous volcanic inputs during the Carboniferous. This could also be evident by the predominance of kaolinite and associated volcanogenic mineral grains in tonstein samples. The common presence of carbonate minerals in the Zonguldak Formation is clearly related to shallow marine depositional conditions, while hematite in the reddish mudstone and claystone samples of this formation could be related to short-term terrestrization during the Cretaceous or afterwards.

Controlling the Iron Migration Mechanism for the Cretaceous Sediment Color Variations in Sichuan Basin, China.

Cretaceous continental sediments in Sichuan Basin, China, have different colors, and the reasons for their formation are not determined. Based on mineralogical and geochemical characteristics, red beds and nonred beds in the Upper and Lower Cretaceous sedimentary strata in the western Sichuan Basin are described and tested in this study. The test and analysis of the mineral composition, element content, and iron speciation of mudstone samples with gray-green, gray, and red colors in Cangxi, Bailong, and Guankou formations found that the change in hematite content directly causes the color difference of samples. For red mudstone, the average chemical index of alteration, chemical index of weathering, weather eluviation index (Ba), Ca/(Mg*Al), and Al2O3/SiO2 index are 67.75, 79.94, 2.07, 0.26, and 0.26, respectively, indicating that chemical weathering is the most intense. The geochemical indexes corresponding to gray samples are 64.41, 74.91, 2.08, 0.19, and 0.24, respectively. Those corresponding to the gray-green samples are 62.30, 70.68, 2.17, 0.21, and 0.24, with the weakest chemical weathering. The ratio of Cu/Zn and the enrichment factor of V show that red and nonred bed samples are formed in weak oxidation and weak reduction environments, respectively. The red sample contains the highest content of hematite iron. The gray-green sample mainly represents paramagnetic ferrous in clay minerals. The geochemical contents of the gray sample’s three iron elements are slightly different, mainly trivalent iron. The change in iron speciation content in different color samples shows that the Fe element forming hematite in red bed samples may come from the weathering of source rock and clay minerals subjected to secondary weathering. At present, it is confirmed that different colors of samples are related to different weathering degrees of source rocks, which can be related to hot, dry/humid climates. It is necessary to distinguish the climate type in combination with other indicators.

Lithostratigraphy and microfacies analysis of Avanah Formation (Middle Eocene) in Gomaspan section northeast Erbil City, Kurdistan region, Iraq

Lithostratigraphy and microfacies analysis of the Avanah Formation (Middle Eocene) were studied in the Gomaspan section in the Bina Bawi anticline, northeast of Erbil city, Kurdistan Region, Iraq. The field observations refer that the formation attains 56 m of medium to thick bedded yellow limestone, grey dolomitic limestone and blue marly dolomitic limestone interbedded with thin beds of blue marl and dark grey shale with an interval of sandy limestone in the middle part and thin to medium bedded limestone interbedded with red mudstone. The petrographic study of 29 thin sections of Avanah carbonates revealed that the majority of the matrix is carbonate mud (micrite) with few microspar. The skeletal grains include benthic foraminifera, dasycladacean green algae, ostracods, calcispheres, pelecypods, rare planktonic foraminifera and bryozoa in addition to bioclasts. Non-skeletal grains encompass peloids, oncoids, intraclasts and extraclasts with common monocrystalline quartz. Based on the field observation and petrographic analysis, three different lithostratigraphic units were identified. They are in ascending order: A-Thick bedded dolomitic marly limestone interbedded with shale. B- Bedded interbedded with red mudstone. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and 12 submicrofacies are recognized. From the sum of all petrographic, facies, textural analyses, it is concluded that Avanah Formation in Gomaspan section, was deposited in shallow marine environment, semi restricted lagoon, in lower and upper parts and open lagoon environment in the middle part interval.

Lithostratigraphy and microfacies analysis of Avanah Formation (Middle Eocene) in Gomaspan section northeast Erbil City, Kurdistan region, Iraq

Lithostratigraphy and microfacies analysis of the Avanah Formation (Middle Eocene) were studied in the Gomaspan section in the Bina Bawi anticline, northeast of Erbil city, Kurdistan Region, Iraq. The field observations refer that the formation attains 56 m of medium to thick bedded yellow limestone, grey dolomitic limestone and blue marly dolomitic limestone interbedded with thin beds of blue marl and dark grey shale with an interval of sandy limestone in the middle part and thin to medium bedded limestone interbedded with red mudstone. The petrographic study of 29 thin sections of Avanah carbonates revealed that the majority of the matrix is carbonate mud (micrite) with few microspar. The skeletal grains include benthic foraminifera, dasycladacean green algae, ostracods, calcispheres, pelecypods, rare planktonic foraminifera and bryozoa in addition to bioclasts. Non-skeletal grains encompass peloids, oncoids, intraclasts and extraclasts with common monocrystalline quartz. Based on the field observation and petrographic analysis, three different lithostratigraphic units were identified. They are in ascending order: A-Thick bedded dolomitic marly limestone interbedded with shale. B- Bedded dolomitic limestone interbedded with shale and marl. C- Thin to medium bedded limestone interbedded with red mudstone. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and 12 submicrofacies are recognized. From the sum of all petrographic, facies, textural analyses, it is concluded that Avanah Formation in Gomaspan section, was deposited in shallow marine environment, semi restricted lagoon, in lower and upper parts and open lagoon environment in the middle part interval.

Permo-Triassic aeolian red clay of southwestern England and its palaeoenvironmental implications

Late Permian and Triassic red mudstones are widely distributed and exposed in southwestern England. This homogenous, massive mudstone succession has been extensively studied for its palaeoenvironmental potential. However, its origin and palaeoenvironment remain under debate. The Triassic Mercia mudstone was early proposed to be aeolian loessic clay based on collapse nature when wetted or loaded and its similarities with aeolian clay in Quaternary Australia, but lacks experimental confirmation and is not generally accepted. In comparison with aeolian red clay in China, here we confirmed that the Triassic Mercia mudstone, together with the Upper Permian Aylesbeare mudstone, was dominated by aeolian clay. This was based on lines of evidence regarding sedimentary structure, particle grain size, geochemistry, micromorphology, and pedogenic features. The results showed that the Mercia mudstone and the Aylesbeare mudstone had sedimentary structures and grain size distributions that were similar to the aeolian red clay in the Chinese Loess Plateau. The major chemical elements correlated well with the aeolian red clay, with the exception of minor discrepancies in CaO and K2O. The similarity in the rare earth element (REE) distribution of the Mercia mudstone and the Aylesbeare mustone with aeolian red clay inferred their similar origin. Widespread pedogenic features indicated the universal development of palaeovertisols forming in alternating wet/dry climates. It was hypothesised that Permo-Triassic southwestern England was dominated by aeolian dust accumulation in a seasonal wet/dry climate, whereas perennial lakes or longstanding rivers across the study area might not exist.

An improved apparent polar wander path for southwest Japan: post-Cretaceous multiphase rotations with respect to the Asian continent

To construct the Mesozoic apparent polar wander path (APWP) for the inner arc of the southwestern Japanese islands (referred to as southwest Japan) and compare it to that of East Asia, a 110 Ma paleomagnetic pole for southwest Japan was determined. Mudstone and sandstone samples were collected from 16 sites for paleomagnetic analysis in the Lower Cretaceous Inakura Formation of the Inakura area in the central part of southwest Japan. A high-temperature magnetization component, with unblocking temperatures of 670–695 °C, was isolated from 12 sites of red mudstone. Of these, 11 sites revealed a primary remanent magnetization during the Early Cretaceous. The primary directions combined with the previously reported ones provide a new mean direction (D = 79.7°, I = 47.4°, α95 = 6.5°, N = 17), and a corresponding paleomagnetic pole that is representative of southwest Japan (24.6° N, 203.1° E, A95 = 6.8°). The Early Cretaceous paleomagnetic pole, together with the Late Cretaceous and Cenozoic poles, constitute a new APWP for southwest Japan. The new APWP illustrates a standstill polar position during 110–70 Ma, suggesting tectonic quiescence of this region. This standstill was followed by two large tracks during the Cenozoic. We interpret these tracks as clockwise tectonic rotations of southwest Japan that occurred twice during the Cenozoic. The earlier tectonic rotation occurred for a tectonic unit positioned below northeast China, the Liaodong and Korean Peninsulas, and southwest Japan (East Tan-Lu Block) during the Paleogene. The later rotation took place only under southwest Japan during the Neogene. Cenozoic multiphase rifting activity in the eastern margin of the Asian continent was responsible for the tectonic rotations that are observed from the paleomagnetic studies. Intermittent rifting may constitute a series of phenomena due to asthenospheric convection, induced by the growth of the Eurasian mega-continent in the Mesozoic.