Red Claystone Research Articles

Impact of landslide on geoheritage: Opportunities through integration, geomorphological classification and machine learning

Landslides are widely understood to cause damage to the geological features and the surrounding environment. Our study focuses on the northern region of the Karangsambung-Karangbolong Geopark (KKNG), characterized by diverse lithology and multi-phase tectonics. This study aims to explore (i) landslide susceptibility assessment, (ii) geomorphological characteristics and distribution of landslide susceptibility, and (iii) identification of landslide impacts on geosites. We mapped morphogenesis, morphology, materials, and processes to understand the geomorphological context, identifying three primary landforms: structural, pediments, and fluvial. For landslide susceptibility mapping, we used the XGBoost algorithm with cross-validation and utilized the area under the receiver operating characteristic curve (AUROC) for model validation. The XGBoost model revealed a high susceptibility classification for 10 geosite points. Landslides have negative impacts, such as Olistoliths of coral limestones, Exotic-blocks of chert, and calcareous red claystone that change landforms and damage outcrops. Nevertheless, some landslides have positive impacts on the geosite, such as Exotic-blocks of phyllites, and Exotic-blocks of pillow lava and radiolarian chert, because landslides can reveal fresher outcrops and rock structures, and the outcrop area becomes larger. Landslide mapping has successfully identified geosites that are highly vulnerable and have adverse impacts, especially those with certain lithological characteristics. This research on viewing disaster as a harmful process has evolved into a more holistic view of the disaster. This view includes various positive aspects that involve understanding the complex interactions between geology and geomorphology towards the geosite. By understanding the relationship between geomorphologic features (morphology, material, process, morpho-arrangement) and landslide occurrence, effective management strategies can be implemented to develop geological heritage further.

STRATIGRAPHY, PETROLOGY AND FACIES ASSOCIATIONS OF THE QUATERNARY SPIN KAREZ GROUP, HANNA-SPIN KAREZ AREA, QUETTA DISTRICT, PAKISTAN

The Hanna-Spin Karez area which comprises the Quaternary succession of the Spin Karez Group is located adjacent to the junction of Sulaiman and Kirthar Fold-Thrust Belts (Quetta Syntaxes), southwest of the Zarghun Trough in the northwestern Balochistan, Pakistan. The area comprises over 800 m thick conformable succession of the Quaternary age, covering surface area of ~30 km2. The succession has been named as the Spin Karez Group, which are further subdivide from base to top into three distinct lithostratigraphic units as: Hanna Lake Conglomerate, Hanna Red Clays and Spin Karez Conglomerate. The Hanna Lake Conglomerate comprises 200 m thick succession of boulder-pebble conglomerate. The Hanna Red Clays comprise over 500 m thick succession of dominantly red claystone rarely interbedded with siltstone and very fine-grained sandstone. The Spin Karez Conglomerate is composed of over 100 m thick succession of well-stratified and moderately- to well-sorted cobble/pebble conglomerate with occasional sandstone/siltstone lenses. The Triassic to Pliocene age older successions from the region's north and west provided the polymictic conglomerate, boulder to pebble size limestone, sandstone, chert, and conglomerate fragments. The Spin Karez Group comprises 15 types of gravel, sandstone and mudstone facies, which were grouped into 5 facies associations. The facies associations include braided channel deposits (FA-1), sheet-flood deposits (FA-2), floodplain deposits (FA-3), marginal lacustrine deposits (FA-4) and open-water lacustrine deposits (FA-5). The Spin Karez group evolved in three phases: i) Deposition of the Hanna Lake conglomerate started with the proximal and distal braided channel systems in the northern and southern parts of the study area respectively; ii) Deposition of the Hanna Red clays deposited in shallow lake with episodic sub-aerial exposure, providing reddish colour to the mud-dominant facies; iii) The depositional basin, once again, transformed to braided channel system, of the Spin Karez conglomerate, which evolved over the shallow water lake deposits of the Hanna Red clays. The Spin Karez group was mainly controlled by continued subsidence and regional tectonics during the Quaternary period that accommodated the space for the small shallow basin (~30 km2) that stacked depositional systems.

An overview of the Cretaceous oceanic anoxic events in Egypt, southern Tethys

Abstract The Cretaceous Period ( c. 143–66 Ma) attested to successive phases of regional tectonic activities and large-scale submarine volcanism resulting in increased atmospheric CO 2 concentrations, enhanced greenhouse climate and global warming, surface water bioproductivity and well-developed pore and bottom water anoxia, especially during the mid-Cretaceous (Aptian to Turonian). These conditions triggered widespread deposition of organic carbon (OC)-rich black shales during episodes of severe oxygen exhaustion, commonly known as oceanic anoxic events (OAEs). Oceanic anoxic events had many important consequences, including the widespread mass extinction of marine and terrestrial organisms. Several intervals of enhanced oxic ventilation and deposition of OC-poor pelagic–hemipelagic red carbonates and claystone interrupted Cretaceous OAEs, which are commonly known as Cretaceous oceanic red beds (CORBs). The mid-Cretaceous black shales from many parts of the world and the corresponding global carbon cycle changes indicated that OAE1 (Selli Level) and OAE2 (Bonarelli Event) are the most widespread and well-defined OAEs compared with the more regional OAE3 and Valanginian–Hauterivian black shales (Weissert Event). These appear to have been more restricted to the Atlantic and adjacent areas, a result of more regional conditions rather than being forced by global environmental perturbations. In the course of this review, the Egyptian territory in the southern Tethys shelf is taken as a case study area for the development, evolution and regional expression of mid-Cretaceous OAEs. The region is characterized by a thick Cretaceous sedimentary succession of OC-rich black shale and OC-poor carbonates and mudstone interbeds. The late Albian OAE1d was reported in the North Western Desert (upper Kharita Formation) based on a positive carbon isotope excursion and moderate total sulfur, total organic carbon and redox-sensitive elements. The end-Cenomanian OAE2 was reported in several regions of Egypt based on positive δ 13 C excursions. However, differential deposition between OC-rich and OC-poor facies took place, especially in marginal to shallow marine settings where black shales are absent, such as in the Eastern Desert and Sinai. During the Coniacian–Santonian, OC-poor limestone, calcareous shale and red claystone were deposited under enhanced water column respiration in Egypt. This indicates that enhanced oxygenated ocean circulation controlled organic matter decomposition during weak continental weathering and enhanced carbonate production, all of which led to the deposition of OC-poor CORBs in this region.

Explore the Constituents and Mechanism of Traditional Chinese Medicine Preparation Zhachong Shisan Pills Based on HPLC-QTOF-MS and Network Pharmacology

Introduction: Th study aims to establish the chromatographic fingerprint of Zhachong Shisan pills (ZSP), and to explore its active components and mechanism of analgesic and anti-inflammatory action. Method: First, the Personal Compound Database and Library (PCDL) of ZSP was constructed through literature mining, and then the chemical composition and fingerprint of methanol extractions from 8 batches of ZSP were studied using High-Performance Liquid Chromatography with Quadrupole Time-Of-Flight tandem Mass Spectrometry (HPLC-QTOF-MS) technology. Furthermore, network pharmacology was used to explore the active compounds, potential targets, and signal pathways of analgesic and anti-inflammatory activity of ZSP. A total of 102 compounds were detected in positive and negative ion mode. Results: Fifty-six characteristic peaks in positive ion mode and 78 characteristic peaks in negative ion mode were confirmed as common peaks in the fingerprint of ZSP. Through network pharmacology research, the effective components, key targets, and signal pathways of ZSP for the treatment of cerebral apoplexy by analgesic and anti-inflammatory effects were all analyzed. Conclusion: This study explained the substance basis of the analgesic and anti-inflammatory effects of Zhachong Shisan Pills, and explores its possible mechanisms, providing ideas for rational clinical medication and in-depth pharmacological research.

Calcareous-nannofossil biostratigraphy of the Miocene Fatha Formation at the Miryas section, Qaradagh Mountain Series, Sulaimaniyah, Kurdistan Region, Iraq

The middle Miocene Fatha Formation is a prominent cap rock for hydrocarbon accumulations in Iraq’s oil fields. It is widely distributed in the Low Folded Zone but less common in the High Folded Zone of Iraq. For the first time, a nannostratigraphic study has been conducted on the formation at the Miryas locality in the High Folded Zone of the Qaradagh Mountain Series, southwest of Sulaimaniyah, Kurdistan Region, Iraq. The Fatha Formation consists of claystone, siltstone, marlstone, gypsum and few limestone beds. Ten samples were taken from marl-rich strata in the upper part of the formation between the red claystones of the Miryas. On the basis of the identified calcareous nannofossils, three biozones are recorded from the upper part of the Fatha Formation: the NN1, NN2 and NN3 zones. The combined stratigraphic ranges of the calcareous nannofossils identified here support the early Miocene–Aquitanian age; Discoaster druggii, Sphenolithus belemnos, S. cometa, S. procerus, S. tintinnabulum, S. delphix and S. capricornutus are marker species of the Aquitanian that have been identified inside the Miryas’s smear slides. These genera/species are also accompanied by the occurrences of Sphenolithus moriformis, Cyclicargolithus floridanus, Reticulofenestra minuta, R. bisecta, S. minuta, S. dictyoda, Coccolithus pelagicus, Helicosphaera carteri and Coronocyclus nitescens. The appearance of Discoaster saundersi at the top of the formation indicates the last occurrence of the NN2 zone of the Aquitanian and first occurrence of the NN3 zone of the Burdigalian. Through this study, for the first time, the early Miocene biozones determined within the Fatha Formation indicate that lower Miocene sediments (facies) were not deposited at some locations in the Qaradagh Mountain Series. Instead, the equivalent cap rock sediments of the Fatha Formation were deposited in the High Folded Zone; this clarifies why accumulation of hydrocarbons is rare within the late Oligocene–earliest Miocene succession in the High Folded Zone rather than the reservoir rocks of the same age in the Low Folded Zone (such as Kirkuk Oil Fields). KEY POINTS First study of nannostratigraphy of the Fatha Formation in the High Folded Zone of Iraq. First study of early Miocene nanno-biozones within the Fatha Formation. First record of NN1, NN2 and NN3 zones within the Fatha Formation.

Influence of the Meso-Cenozoic tectonics on groundwater and surface water flows in the Skoura hydrogeological basin (folded Middle Atlas, Morocco)

The Skoura hydrogeological basin, part of the Folded Middle Atlas Mountain range, is located 30 km NE of Boulemane city and 50 km SE of Sefrou city. It is limited to the North and North-East by the Aichoun reliefs, to the West by the North Middle Atlas Fault (NMAF) and to the South by the Tichoukt ridge. It corresponds to a collapsed area resulting from polyphase tectonics succeeding from the Upper Miocene to present day. Its location between two major structural lines favors the accumulation and runoff of all precipitated water. This work aims to identify the geological structures which guide groundwater and surface water flows. The geological mapping and the measurements of the water points capturing the water table, have allowed to reconstitute the geodynamic evolution of this basin on one hand, and to identify the various aquifers containing the water table on the other hand. The Skoura water table circulates within four aquifer systems represented by Liassic carbonates, Bathonian sandstones, Vallesian lacustrine limestone and the Plio-Quaternary fluvio-lacustrine deposits. The impermeable substratum of each reservoir layer is respectively represented from bottom to top by Triassic-Liassic red claystones, Bathonian versicolored marls, Vallesian lacustrine claystones and Upper Miocene marls. The superposition of the piezometric map with the fracturing map shows that the groundwater flow axis is multidirectional. Groundwater flows along faults and fracture, following two main directions converging towards the Mdaz River. A first flow from SW to NE characterizing the upstream part of the hydrogeological basin and a second flow from West to East which covers its central part. Concerning surface water flows, they are guided by the submeridian and transverse faults, as well as by the two major faults (NMAF and the Tichoukt Fault) which have played a major role in the genesis and evolution of the Oued Mdaz valley.

ANALISIS FASIES PADA FORMASI MENANGA, PEKON GUNUNGKASIH, TANGGAMUS DAN SUNGAI WAY SABU, PESAWARAN, LAMPUNG

The Menanga Formation is part of the Woyla terrane, the last large terrane amalgamated formed island of Sumatra. Woyla terrane consist of Cretaceous arc assemblage and relatively lack of research has been done on this formation in Lampung and surrounding areas. This study aims to identify the facies of the Menanga Formation. Research was carried out by making a measured stratigraphic and dividing it into facies and facies associations. The data were taken from two places, in Gunungkasih, Tanggamus and Way Sabu, Pesawaran, Lampung. The results showed that the Menanga Formation has eight facies, there are red claystone (F1), gray claystone (F2), bioturbated siltstone (F3), laminated siltstone (F4), laminated fine sandstone (F5), Parallel sandstone (F6), ripple sandstone (F7), loadcast sandstone (F8), and graded bedding sandstone (F9). The Menanga Formation facies were grouped into two facies associations, namely levee facies association (AF1) and channel facies association (AF2). AF1 consists of F1, F2, F3, F4, and F5 which shows the upper part of the turbidite sequence while AF2 consists of F5, F6, F7, F8, and F9 which shows the lower part of the turbidite sequence. The Menanga Formation shows siltstone dominance with sedimentary structure formed due to turbidit current and stacking pattern show fining upward-thinning upward indicate midfan lobe environment The Menanga Formation interpreted to be deposited in submarine fan environment whose sediment material originates from the Woyla volcanic arc.

KARAKTERISTIK DAN GANESA ENDAPAN POLIMETALIK DAERAH GUNUNG KASIH, PUGUNG, TANGGAMUS, PROVINSI LAMPUNG

Indonesia is a country that has economically valuable mineral deposits such as nickel, aluminum, cobalt and manganese. These economical metallic minerals have an important role in the sustainability of the battery industry's long-term plans required during the energy transition. Manganese (Mn) is the fourth most widely used metal in the world which can be used as an industrial alloy. This study aims to determine the type of manganese that can be found in the research area, determine the hostrock (carrying rock) of sediment, and determine the type of deposit in the study area. Research data collection was carried out at 13 different points centered on the Gunung Kasih area and its surroundings. The data taken in the form of rock samples. Processing of data using petrological analysis and taking microscopic photos in the laboratory. The results showed that there were three forms of manganese oxide minerals, namely acicular, botryoidal and dendritic. Manganese oxide minerals in this area were found filling the fractures in several types of rock, namely red clay, clay, andesite, and lapilli tuff. The type of manganese oxide deposits in the study area is included in the type of residual manganese deposits associated with hydrothermal deposits. Rocks carrying manganese oxide minerals can come from red claystones of the Menanga Formation or igneous rocks and pyroclastic rocks of the Hulusimpang Formation.

Identification of Land Movement Safety Factors on the Slope of Lolak Dam

North Arm Sulawesi is a triple junction between three convergent plates which results in development of geological structures at all scales, thereby triggering the potential for land motion. Lolak Dam is an infrastructure that functions as a water reservoir which is then channeled for domestic needs. This research aims to identify safety factors of the Lolak Dam slopes where land motion occurs several times. Field data in the form of lithology was carried out by geomechanical testing in the form of specific gravity, cohesion, and internal shear angle. The analysis was carried out on the slopes of the Lolak Dam on the left backrest which is a spillway area. The method used is Bishop with the help of the Slide v.6 Program. Lithological in the research area obtained gray claystone, red claystone, chert slate, sandstone, and basalt. Safety factors result which using the Slide program are 1.517 (Stable) in slope 1, 1,260 (Stable) in slope 2, and 0.745 (unstable) in slope 3.

MESOZOIC TETHYAN RADIOLARITE AGE DETERMINATION, ZAGROS SUTURE ZONE, KURDISTAN, NE IRAQ

A regional belt of Mesozoic Tethyan radiolarites extends along the northeastern Arabian plate's margin. Outcrops of this radiolarite were documented from Hawasina series in Oman, and northeastwards to Pichakun Series of southern Iran, to Kermanshah of northwest Iran passing onto the Qulqula Group of northeast Iraq up until the Kocali Series of Turkey. The age of most of these radiolarite suites was already constrained. It is the purpose of this work to investigate the age of the radiolarite Suites in northeast Iraq using Radiolarian microfossils chronostratigraphy. Patches of the Mesozoic radiolarite suites are exposed at the Zagros suture zone in Kurdistan Region of northeast Iraq and known as the Qulqula Group. It consists of complexly deformed and thick slices of pelagic radiolarian chert and siliceous limestone, radiolarian red claystone and siliceous mudstone, and reddish-green mudstone and limestone. These units were sampled from three areas (Naurabab, Penjween, and Hawraman) located to the south and east of Sulaimani city in Kurdistan, for radiolarian micropaleontological analysis. Radiolaria microfossils identification and age determination is done at specialized laboratories. Results of the radiolarian age constraint show that these sediments range from Bajocian to the end of the Cenomanian.

New Ideas and Critical review of Middle Eocene Gercus Formation, Kurdistan Region, NE-Iraq

In Iraq, Gercus Formation (Middle Eocene) crops out now near boundary between Low and High Folded Zone and generally consisted of red claystone and sandstone with occasionalbeds of conglomerate. Lithologically, it changes toward the southwest to carbonatesiliclastics of either Khurmala or Aliji Formations inside the Low Folded Zone. All previous studies have concluded that the environment of the formation was fluvial and deltaic of continental mollasse facies with possible some shallow marine sediments at its lower part. Conversely, the most recent two studies have assigned two different, opposite environments of the formation, which are deep marine (turbidite facies), and desert environments. The aim of the present study is critical and objective analysis of the previous studies in addition to introduction of new ideas that are opposite to deep marine and aeolian environments. The study gives many evidences and features for justification of the introduced new ideas, which are revealing the actual environment of the formation. This reveal is depended on the field and regional correlation in areas of boundary between High and Low Folded Zone (area of exposure of Gercus Formation) and area of Imbricated and Thrust Zone where its equivalent in age and facies (unit five of Red Bed Series) is exposed. The present study supports neither the deep marine turbidite nor the desert erg system of the previous studies. The present study proves that the Gercus Formation consists of the distal alluvial fan and its proximal part is unit five of Red Bed.

Palaeo‐environment in an ancient low‐latitude, arid lacustrine basin with loessite: The Smith Bank Formation (Early Triassic) in the Central North Sea, UK Continental Shelf

AbstractPredominantly fine‐grained strata were deposited in the Smith Bank Formation (Early Triassic) in the Central North Sea area of the Northern Permian Basin. Previously regarded as monotonous red claystone, examination of continuous core reveals abundant stratification, significant variation in colour, siltstone as the prevalent average grain size, and claystone is rare. Loessite occurs beyond the north‐western lacustrine margin, and aerosol dust has inundated clay pellets derived from aeolian reworking of the desiccated lake floor. The loessite has limited evidence of pluvial reworking but rare fossil roots testify to sufficient moisture to sustain plants. Loessite has not previously been differentiated successfully from other fine‐grained strata in the subsurface, but this study defines the presence of random grain‐fabric orientation as an intrinsic unequivocal characteristic of loessite that formed during air‐fall deposition of aerosol dust. Comparison with outcrop data verifies the utility of grain fabric to differentiate loessite. Tosudite, an aluminous di‐octahedral regularly ordered mixed‐layer chlorite/smectite, which is rare in sedimentary rock, forms a significant proportion (10 to 21%) of the clay mineral fraction of loessite along with a similar quantity of kaolinite. In all other samples, only illite and chlorite are identified, which is typical of fine‐grained Triassic strata. In a location, close to the southern lake margin, lacustrine strata are characterized by fining‐upward couplets of very fine‐grained sandstone into siltstone and mudstone, with occasional desiccated surfaces. Small sand injections and associated sand extrusions are common and indicate periodic fluidization of sand. Precise stratigraphic location of the Smith Bank Formation is problematic because of extremely sparse fossil preservation; however, there is no sedimentological evidence for a period of hyperaridity known from the early Olenekian in continental Europe, which may mean that the North Permian Basin was never hyperarid or that the Smith Bank Formation is restricted to the Induan.

Pullout resistance mechanism of bearing reinforcement embedded in residual clayey soils

A bearing reinforcement earth (BRE) wall was proposed as an alternative, temporary structure replacing a natural slope to enhance performance and slope stability. The pullout resistance mechanism of the bearing reinforcement embedded in the compacted residual soils (red clay and claystone), which is required for BRE wall design, is investigated in this paper. The pullout resistance predictive method is recommended for both soils. The pullout resistance of the bearing reinforcement comprises both friction and bearing components. The peak interface factor (αp) between the soil and the longitudinal member is found to be 0.66 and 0.40 for red clay and claystone, respectively, while the residual interface factor (αr) is 0.47 and 0.22 for red clay and claystone, respectively. Though the red clay has a higher αp and αr than the claystone, the friction pullout resistance is lower than that of the claystone due to a lower shear strength. The pullout bearing resistance of transverse members (Pbn) can be calculated ...

Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey–Lleyn, NW Wales, U.K.: MORB and OIB in the Iapetus Ocean

The Gwna Group in Anglesey–Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent mélanges that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group.Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey–Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.

Lithologic and rock magnetic evidence for the Mid-Miocene Climatic Optimum recorded in the sedimentary archive of the Xining Basin, NE Tibetan Plateau

Abstract Thick Cenozoic deposits in the Xining Basin provide great potential for understanding the tectonic and climatic evolution of the NE Tibetan Plateau. However, the Middle Miocene Climatic Optimum (MMCO) in this basin has not been reported up until now, due to the poor exposure of the uppermost strata covering this interval. In this study, a 194 m-deep core of flood–plain to channel–flood deposits was obtained from the Tashan flats above the Xiejia Section in the Xining Basin. Magnetostratigraphic dating of the core determines its age at ca. 18.5–13.5 Ma. Lithological and rock magnetic analyses demonstrate that the most prominent changes recorded in the present study occurred between ~ 17 and ~ 14 Ma. During this period, the sedimentary sequence mostly consists of gray-white or bluish-gray claystone and muddy siltstone, intercalated with some thin red claystone. The rock magnetic parameters show a large variability, with higher values in thin red claystone beds and lower values in gray-white or bluish-gray layers. These features demonstrate that, due to a warm and wet climate, extensive rivers had developed in the Mid-Miocene and that a reducing sedimentary environment prevailed. These “favorable” climatic conditions coincide with the MMCO as based on global deep-sea deposit records, indicating that this warm event exerted a major impact on regional climate change in the NE Tibetan Plateau during the Mid-Miocene.

Foundation of a Gravity Dam on Layered Soft Rock: Shear Strength of Bedding Planes in Laboratory and Large “In Situ” Tests

A 100 m high gravity dam (Castrovido dam, Burgos, Spain) is founded on a soft Weald red claystone with inter-bedded sandstone strata. Claystone weathering was identified in vertical and horizontal profiles of water content and dry density. Peak and residual strength of rock matrix is given in the paper. Clay and sandstone layers dip 15°–20° in the upstream direction. Dam stability is essentially controlled by the available shear strength at the sedimentation planes. Block samples were recovered for each of the contact types mentioned. They were tested in high capacity shear box machine (30 × 30 cm). In addition, large scale shear tests (80 × 80 cm) were performed in situ. The roughness of the sheared plane was determined after each one of the tests. Additional information includes some direct shear tests on joints recovered in borings and the results of residual strength tests performed on clay fillings on a ring shear apparatus. The results of all the tests performed are compared in the paper showing the effect of shearing surface roughness. In general, strength envelopes determined “in situ” exhibit a marked nonlinearity at the low range of confining stresses (0–0.2 MPa). Laboratory tests on smaller specimens show linear Mohr–Coulomb envelopes. Existing relationships between joint roughness and strength envelopes were also included in the comparison. The paper discusses the procedure followed to select an appropriate strength envelope for design purposes on the basis of all the available information. The case points out the difficulty to select unambiguously a suitable design strength for the critical sedimentation surfaces despite the efforts displayed in the field and in the laboratory.

Permian continental paleoenvironments in Southeastern Asia: New insights from the Luang Prabang Basin (Laos)

In Laos (Southeastern Asia), Late Paleozoic sediments were identified by early French explorations across Indochina during the late 19th century (Pavie missions), but little work was undertaken to characterize the sedimentological and stratigraphical context until now. From detailed sedimentological and paleontological studies, we propose an interpretation of the depositional environment and of the stratigraphic context of series located on the right bank of the Mekong River in the Luang Prabang Basin where three main formations were described. The silicoclastic Red Claystone Formation, attributed to alluvial plain environment, contains large fragments of unidentified dicynodonts. The Limestones and Sandstones Formation preserves a new macrofloral assemblage displaying affinities with Middle to Late Permian Cathaysian floras of South China. This assemblage occurs as an intercalation within marine calcareous sandstones that have yielded a marine fauna, including the ammonoid Pseudotirolites sp. which indicates a Late Permian (Changhsingian) age. The well-developed Purple Claystones Formation yielded an abundant and well preserved Late Permian fauna composed of a carnivorous amphibian and numerous Dicynodon cranial and postcranial elements. This formation shows a vertical evolution from braided river to alluvial plain with sheet-flood sand bed and bed-load rivers, with a constant supply of volcanic clasts. Results from the analysis of the paleontological associations in the Luang Prabang Basin suggest that a continental communication between Laurussia and the Indochina Block existed during the Permian, allowing for migration of the terrestrial Dicynodon fauna.

Lake deposits of moderate salinity as sensitive indicators of lake level fluctuations: Example from the Upper Rotliegend saline lake (Middle–Late Permian, Northeast Germany)

The Rotliegend saline lake periodically covered wide areas of the Southern Permian Basin in Northwest Europe during the Permian. The sedimentology, mineralogy and geochemistry of lake deposits were studied to document very high frequency lake level fluctuations and to evaluate their triggers. Increased precipitation and marine ingressions into the basin resulted in lake extension. Increased run-off is documented by intercalated fluvial deposits in low-salinity deposits of the lake. Because lake deposits reflect mainly deposition in relatively wet climate phases, they are not correlatable to halite deposits in other basin areas. Decreased precipitation is followed by shrinkage of the lake, desiccation at its margins, and higher lake salinity due to concentration of the brine. Carbonate and anhydrite contents of lake deposits increased considerably before the areas fell dry, but halite is not preserved in the study area. Falling lake level is also reflected by the occurrence of wave ripples, reflecting decreased water depth and finally by desiccation and formation of evaporite crusts. Not only the mineralogical content, but also the colour of lake claystones changes with varying salinity. Anhydrite- and carbonate-free red claystones were replaced by violet to green and grey anhydritic and calcareous claystone or marls with increasing salinity. The amount of boron adsorbed on illite also corresponds to changes in salinity and can therefore be used as a palaeosalinity indicator. Rare earth element concentrations within lake deposits do not reflect variations in salinity but different palaeogeographical settings. Marine ingressions into the lake are neither reflected by the amount of boron adsorbed onto illite nor by rare earth element contents of the lake deposits. Highly saline deposits are partly characterised by intensive deformation, which can be interpreted as seismites or dissolution breccias.

An “Inverse Conglomerate” Paleomagnetic Test and Timing of In Situ Terra Rossa Formation at Bloomington, Indiana

Directions of remanent magnetism in an ∼2-m interval of terra rossa claystone at Bloomington, Indiana, cluster around the current Earth magnetic field direction, a fact consistent with authigenic formation of the terra rossa over the last 0.78 m.yr., the date of the latest earth’s magnetic field reversal, and suggesting a minimum terra rossa formation rate of ∼2: 5m =m:yr: Paleomagnetic directions in limestone “floaters” within the terra rossa are indistinguishable from directions of the bedrock Mississippian Harrodsburg Limestone, indicating that the floaters are in situ and perfectly preserve their original stratigraphic position. Thus, the red claystone containing the floaters is interpreted as an authigenic, isovolumetric replacement of the Harrodsburg—the replacement of which the floaters escaped—and precludes the possibility that the floaters and the surrounding claystone are a mudflow that had carried limestone blocks in it. The implication that the claystone is authigenic independently confirms the petrographic observations reported previously that the red clay grew in situ, replacing the underlying limestone at a moving metasomatic front. Rock magnetic studies of the terra rossa clays show evidence of both goethite and maghemite as main magnetic carriers of this remanence. Both minerals are independently known to occur in pisolites of the terra rossa. The ferric-ironbearing red clays also are weakly magnetic.

Cambrian paleosols and landscapes of South Australia*

Cambrian marine, grey shales are widespread, and so are Cambrian intertidal, redbeds with weakly developed marine-influenced paleosols. A broader view of Cambrian landscapes and soilscapes now comes from paleosols of alluvial coastal plains of the Cambrian (to Ordovician?) Parachilna, Billy Creek, Moodlatana, Balcoracana, Pantapinna and Grindstone Range Formations in the central Flinders Ranges of South Australia. Paleosols are recognised by soil structures such as calcareous nodules (caliche) and cracked ridges (mukkara). They also show gradational changes down-profile in minerals, grainsize and chemical composition comparable with soils. Some of these Cambrian paleosols are thick (>1 m) and well developed (large caliche nodules). They indicate stable alluvial and coastal landscapes of quartzo-feldspathic and locally tuffaceous sediments. Paleoclimates were generally semiarid, although several intervals of subhumid paleoclimate coincide with local marine transgression. Drab-haloed filaments in red claystones, and elephant-skin and carpet textures in sandstones of some of the paleosols may be evidence of biological soil crusts, and some waterlogged marginal marine and lacustrine paleosols had animal burrows. Cambrian paleosols of the Flinders Ranges are assignable to the modern soil orders Vertisol, Aridisol, Inceptisol and Entisol. Modern soils of the Flinders Ranges and central Australia are within the same orders as the Cambrian paleosols, supporting evidence from paleogeomorphology that some Australian landscapes and soilscapes are very ancient indeed.