Influence of inherited topography on gravitational slope failure: three‐dimensional numerical modelling of the La Clapière slope,Alpes‐Maritimes,France

Gravitational slope failure involves rock slopes at various scales. Nowadays, it is accepted that different factors influence slope destabilization, including topography. In many cases, slope failure occurs between tributary valleys cutting the slope. In this study, we ask what influence tributary valleys have on slope failure. To tackle this question, we developed a 3‐D numerical model of the La Clapière Slope and then examined a series of simplified 3‐D models with different geometries of tributary valleys (spacing and depth). Our results show that: (1) whatever considered in situ stresses are, including the third dimension reduces the destabilization threshold compared with 2‐D models; and (2) the spacing and the depth of tributary valleys influence slope failure. For shallow incisions, increasing the lateral spacing between tributary valleys does not affect failure localization but does increase slope damage (to a stable value from 2000 m). However, deeper incision does not affect slope damage but does contribute to failure localization. When the spacing is less than 1500 m, the part of the slope between tributary valleys is not involved in the failure process, but for spacings above 1500 m slope failure occurs between tributary valleys.     

Temporal and environmental significance of microbial lamination: Insights from Recent fluvial stromatolites in the River Piedra,Spain

Despite extensive research, the environmental and temporal significance of microbial lamination is still ambiguous because of the complexity of the parameters that control its development. A 13 year monitored record of modern fast‐accreting calcite stromatolites (mean 14 mm year^?1) from artificial substrates installed in rapid flow in the River Piedra (north‐east Spain) allows comparison of the sedimentological attributes of successive six‐month depositional packages with the known climatic, hydrophysical and hydrochemical parameters of the depositional system. The stromatolites are formed of dense, porous and macrocrystalline composite laminae. The dense and porous composite laminae, which are composed of two to eight laminae consisting largely of calcified cyanobacteria, are characterized by: (i) dense composite laminae, up to 15 mm thick, mostly with successive dense laminae and minor alternating dense and porous laminae; and (ii) porous composite laminae, up to 12 mm thick, consisting mainly of porous laminae alternating with thinner dense laminae. Most of the dense composite laminae formed during the warm periods (April to September), whereas most of the porous composite laminae developed in the cool periods (October to March). Each dense and porous composite lamina represents up to or slightly longer than six months. The alternation of these two types of composite laminae parallels seasonal changes in temperature. The dense and porous laminae result from shorter (for example, intraseasonal) variations in temperature, insolation and hydrological conditions. The macrocrystalline laminae, with crystals >100 μm long, occur isolated and grouped into composite laminae up to 1·7 mm thick. Their occurrence suggests the absence or poor development of microbial mats over periods of weeks to several months. Thus, stromatolite lamination can record different‐order, periodic and non‐periodic changes in the magnitude of environmental parameters over a single year. These results hold important implications for the temporal and environmental interpretation of lamination in microbial structures.     

Amazonsaurus maranhensis gen. et sp. nov. (Sauropoda, Diplodocoidea) from the Lower Cretaceous (Aptian–Albian) of Brazil

A new genus and species of an Aptian–Albian sauropod from the Itapecuru Formation, northern Brazil, Amazonsaurus maranhensis, is described. It is known from an incomplete, but diagnostic postcranial skeleton. The new taxon possesses several autapomorphies, such as the anterior caudal vertebrae with lateral laminae formed by the coalescence of the spinoprezygapophyseal and postzygodiapophyseal laminae and, to a lesser extent, of the postzygodiapophyseal laminae. It exhibits many synapomorphies supporting its inclusion in the Diplodocoidea. These include high caudal neural arches and anterior caudal neural arches with spinoprezygapophyseal laminae on the lateral aspect of the neural spine. This record is consistent with previous hypotheses on the existence of a community of Afro-South American dinosaurs.     

Cool water geyser travertine: Crystal Geyser,Utah, USA

A sloping travertine mound, approximately 85 m across and a few metres thick is actively forming from cool temperature waters issuing out of Crystal Geyser, east‐central Utah, USA. Older travertine deposits exist at the site, the waters having used the Little Grand Wash Fault system as conduits. In contrast, the present Crystal Geyser travertine mound forms from 18°C waters which have been erupting for the last 80 years from an abandoned oil well. The present Crystal Geyser travertine accumulation forms from a ‘man‐made’ cool temperature geyser system; nevertheless, the constituents are an analogue for ancient geyser‐fed carbonate deposits. The travertine primary fabric is composed of couplets of highly porous, thin micritic laminae intercalated with thicker iron oxide rich laminae. Low Mg‐calcite is the dominant mineralogy; however, aragonite is a major constituent in deposits proximal to the vent and decreases in abundance distally. Cements exhibit a variety of fabrics, isopachous being common. Constituents include micro‐stromatolites, clasts, pisoids and the common occurrence of Frutexites‐like iron oxide precipitates. Leptothrix, a common iron‐oxidizing bacterium, is believed to be responsible for the production of the dense iron‐rich laminae. Pisoids litter the ground around the vent and rapidly decrease distally in abundance and size.     

Stratigraphy, sedimentology and bulk organic geochemistry of black shales from the Proterozoic Vindhyan Supergroup (central India)

Four organic-rich shale units of the Proterozoic Vindhyan sedimentary succession have been scanned to reveal their origin and hydrocarbon potential. The wavy-crinkly nature of the carbonaceous laminae is suggestive of a microbial mat origin of the shales. These shales are thus different from Phanerozoic black shales which typically exhibit planar laminae. The hydrocarbon potential of the black shale units has been evaluated by Rock-Eval pyrolysis. Total organic carbon content of many of the shales exceeds 1%. The meanT _max for the black shales translate to a vitrinite reflectance range of 2.05-2.40% Rm based on standard conversion techniques. These shales have reached the catagenetic stage near the beginning of anthracite formation.     

Cyanobacterially generated peloids in laminated,organic-matter rich,limestones: an unobtrusive presence

The late-Kimmeridgian Southern Jura (France) is a carbonate platform where laminated limestones accumulated locally (notably at Orbagnoux). The two types of laminations encountered result either from particle settling in a very quiet environment or from bacterial mat growth. In the latter case, as revealed by acid etching, the dark-coloured laminae result from filamentous cyanobacteria developments, whereas the light-coloured laminae appear, surprisingly, to comprise packed peloids. These peloids are interpreted as originating from the in vivo or shortly post mortem calcification of sheaths of coccoid cyanobacteria in an environment loaded by temporary excess alkalinity (and possible H₂S emissions). Thus, a simple etching treatment reveals the unsuspected, albeit prominent, role of cyanobacteria in the genesis of the limestones from Orbagnoux. As such facies are widespread in Late Jurassic records, the role of cyanobacteria in their formation deserves re-evaluation.     

广东省泥盆纪藻叠层石及其形成环境

一、引言自从Ginsburg(1955)及Logan等(1961,1964)研究了巴哈马、佛罗里达和西澳大利亚的现代藻叠层石以来,已经建立了用藻叠层石的形态和构造来解释现代或古代海洋沉积环境的基础。在我国,报道前寒武纪叠层石的文章较多,上古生代则不多见。作者自1980年以来对广东泥盆纪碳酸盐沉积中的藻叠层石做了一些研究,现根据所得资料进行报道。     

Deglacial seasonal and sub‐seasonal diatom record from Palmer Deep,Antarctica

The Antarctic Peninsula is one of the most sensitive regions of Antarctica to climate change. Here, ecological and cryospheric systems respond rapidly to climate fluctuations. A 4.4 m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core (ODP Site 1098) recovered from Basin I, Palmer Deep, western Antarctic Peninsula. This deglacial laminated interval was deposited directly over a glaciomarine diamict, hence during a globally recognised period of rapid climate change. The ultra‐high‐resolution deglacial record is analysed using SEM backscattered electron imagery and secondary electron imagery. Laminated to thinly bedded orange‐brown diatom ooze (near monogeneric Hyalochaete Chaetoceros spp. resting spores) alternates with blue‐grey terrigenous sediments (open water diatom species). These discrete laminae are interpreted as austral spring and summer signals respectively, with negligible winter deposition. Sub‐seasonal sub‐laminae are observed repeatedly through the summer laminae, suggesting variations in shelf waters throughout the summer. Tidal cycles, high storm intensities and/or intrusion of Circumpolar Deep Water onto the continental shelf introduced conditions which enhanced specific species productivity through the season. Copyright © 2005 John Wiley & Sons, Ltd.     

Carbonate tidal rhythmites from the Middle Jurassic of Britain

Newly discovered carbonate laminites are described from the Lincolnshire Limestone Formation (Middle Jurassic, Britain). These occur in the upper peloidal unit of fining-upward rhythms which comprise much of the lagoonal lower Lincolnshire Limestone in south Lincolnshire. The flat, millimetre-scale laminations are of three types: (1) alternating peloid-rich, peloid-poor laminae; (2) alternating bioclastic and peloidal laminae; (3) alternating bioclastic and micritic laminae. In all three types, small-scale cross-laminated sets (usually < 40 mm thick) also occur. The laminite horizons are usually < 150 mm thick and have, in some cases, been traced laterally for ～100 m. The close analogy of these carbonate laminites with siliciclastic counterparts favours their interpretation as tidal rhythmites, mechanically deposited in a low intertidal/shallow subtidal setting. The associated sedimentary features and overall stratigraphic-sedimentologic position of the deposits support this conclusion. According to the literature, mechanically deposited as opposed to algally induced carbonate laminites are rare outside the supratidal realm. Possible reasons for the real or imagined scarcity of intertidal/ subtidal carbonate laminites in ancient sedimentary regimes are discussed.     

Cuticular ultrastructure of a Cretaceous decapod crustacean

The cuticie of the lobster Hoploparia longimana (Sowerby) from the Cambridge Greensand (Upper Cretaceous), when etched in E.D.T.A. and examined with the scanning electron microscope, reveals detail of ultrastructure not previously described from any fossil arthropod cuticle. The fibre patterns of laminae and inter-laminae are described and interpreted by comparison with those in modern crustacean cuticles. Horizontal tubules at the laminae may represent a lamina membrane. The pore canals are round with fibrous walls and are surrounded by elliptical voids, possibly originally occupied by vertical fibres. Wider canals, around 15 μm in diameter, are probably setal ducts. The cuticle is now largely composed of an apatite.     

The influence of the Three Gorges Reservoir regulation on a typical tributary heat budget

Reservoir regulation and local climate both affect the heat budget of tributary bay. It is difficult for traditional methods to identify the influence of different factors on heat budget quantitatively. In this paper, for analysis of the control mechanisms of the heat budget of a large reservoir tributary, the water temperature distribution, and heat budget processes of the Meixi River, a typical tributary to the Three Gorges Reservoir was measured, and a new method was used to calculate the heat content composition of the tributary bay and identify the key factor of the heat balance. The result shows significant variation in the spatial and temporal distributions of water temperatures in the Meixi River, ranging from 12.4 to 28.9 °C on the surface and 12.0 to 24.4 °C at the bottom. The total heat exchange across the air–water interface that ranges from 0.1 to 6% of the budget is not the primary control factor of the annual tributary heat budget. Rather, the change in water depth produced by regulation of the Three Gorges Reservoir is the primary control factor of the tributary heat budget in the whole year, which ranges from 72 to 99% of the budget. The water temperature difference between the main stream and tributary is the not key factor of the heat budget, which ranges from 0.1 to 28% of the heat budget.     

Magnetic mineral variations of South Caspian Sea sediments at laminae scale

The 998-cm long sediment core was collected from the South basin of the Caspian Sea. Sediments from the lower, Late Pleistocene part of the core (998-90 cm) are marked by laminations, which rapidly disappear under oxidising conditions. TEM/EDS analyses of magnetic extracts, done at laminae scale, show the presence of iron monosulphide (greigite Fe₃S₄) in grey and black laminae. There are also small amounts of magnetite. Magnetic hysteresis parameters Mrs/Ms and Bcr/Bc, presented on a Day plot, cluster near SD/PSD boundary, with smaller particles for black laminae. This tendency is due to a higher content of greigite, relative to coarser grained detrital magnetite in black laminae, and to a lower relative content of greigite in grey laminae. Analyses of Ca/Mg carbonates, grain size of the bulk sediment, feldspars/quartz ratios and water content show that these parameters do not vary at laminae scale. These results suggest that the laminae are of early diagenetic rather than detrital origin, reflecting rhythmic, subtle variations in the geochemical environment during laminae formation.     

The growth mechanism of the aragonitic stalagmite laminae from Yunnan Xianren Cave,SW China revealed by cave monitoring

Duan, W., Cai, B., Tan, M., Liu, H. & Zhang, Y. 2012 (January): The growth mechanism of the aragonitic stalagmite laminae from Yunnan Xianren Cave, SW China revealed by cave monitoring. Boreas, Vol. 41, pp. 113–123. 10.1111/j.1502‐3885.2011.00226.x. ISSN 0300‐9483. Stalagmites from Xianren Cave in Yunnan Province, SW China have visible bands of alternating compact and porous sub‐layers, which have recently been demonstrated to be annual: the compact sub‐layer consists of elongated columnar aragonites with a general longitudinal orientation (parallel to the vertical growth axis), while the porous sub‐layer is composed mainly of needle aragonites forming radiating masses. In order to understand the growth mechanism of this type of stalagmite laminae, factors that could determine the growth rate and crystal structures of modern carbonates, such as cave‐air temperature, CO₂ concentration, drip rate and the hydrochemical parameters of drip water, have been monitored systematically. In this study, we selected five active drip sites to monitor for two years at a monthly frequency. Based on the monitoring results and the analyses of stalagmite laminae, we conclude that the compact sub‐layer forms in winter, when the drip rate is moderate and the degassing is slow, continuous and prolonged. The porous sub‐layer forms in early spring, when the drip rate is lower and Mg/Ca is higher than that during the formation of the compact sub‐layer. We also found exceptionally some calcite laminae. Furthermore, we discovered modern calcites precipitating at all study sites in the first hydrologic year when the rainfall was very abundant. Therefore, it is suggested that the occurrence of localized calcites in an aragonitic stalagmite indicates an interval of higher rainfall.     

Surface velocity monitoring of Skamri Glacier from 2018 to 2021 based on Landsat-8 images北大核心CSCD

Skamri Glacier is the largest glacier in China, and it is a surge-type glacier. The study on the charac⁃ teristics of glacial movement is of great significance for early warning of glacial disasters caused by glacier surge. In this paper, 20 pairs of Landsat-8 images from 2018 to 2021 were selected to extract the surface veloci⁃ ty of Skamri Glacier using optical image feature tracking method, analyze the uncertainty of velocity, and ana⁃ lyze the temporal and spatial changes characteristics of velocity of the glacier. The results show that there are ob⁃ vious spatial differences in the surface velocity of Skamri Glacier. During the period from January 2018 to June 2019, the velocity of the south tributary of Skamri Glacier is much greater than that of its north tributary（west）, while during the period from June 2019 to November 2021, it presents completely opposite spatial characteris⁃ tics, which is mainly due to the sudden increase of the velocity of the north tributary（west）in June 2019. Ac⁃ cording to the results of velocity changes from 2018 to 2021, it is found that the north tributary（west）surges in June 2019 and is still in the surge period until November 2021. The north tributary（west）glacier terminus will advance about 320 m towards the main glacier from August 2020 to September 2021;The velocity of the south tributary has been very large during the study period, and the maximum velocity reaches 441 m·a-1;The veloci⁃ ty of the north tributary（east）of Skamri Glacier increased sharply in July 2021, and the tributary may surge;The velocity of the main glacier of Skamri Glacier increased significantly after the confluence of the south tribu⁃ tary and the surge of the two north tributaries. In addition, there are temporal and spatial differences in the eleva⁃ tion distribution of the maximum velocity of the main glacier and its tributaries in this area. © 2022 Science Press (China). All rights reserved.     

River tributaries as sediment sinks: Processes operating where the Tapajós and Xingu rivers meet the Amazon tidal river

The Amazon River is the largest fluvial source of fresh water and sediment to the global ocean and has the longest tidally influenced reach in the world. Two major rivers, the Tapajós and Xingu, enter the Amazon along its tidal reach. However, unlike most fluvial confluences, these are not one‐way conduits through which water and sediment flow downstream towards the sea. The drowned‐river valleys (rias) at the confluences of the Tapajós and Xingu with the Amazon River experience water‐level fluctuations associated not only with the seasonal rise and fall of the river network, but also with semidiurnal tides that propagate as far as 800 km up the Amazon River. Superimposed seasonal and tidal forcing, distinct sediment and temperature signatures of Amazon and tributary waters, and antecedent geomorphology combine to create mainstem–tributary confluences that act as sediment traps rather than sources of sediment. Hydrodynamic measurements are combined with data from sediment cores to determine the distribution of tributary‐derived and Amazon‐derived sediment within the ria basins, characterize the sediment‐transport mechanisms within the confluence areas and estimate rates of sediment accumulation within both rias. The Tapajós and Xingu ria basins trap the majority of the sediment carried by the tributaries themselves in addition to ca 20 Mt year^?1 of sediment sourced from the Amazon River. These findings have implications for the interpretation of stratigraphy associated with incised‐valley systems, such as those that dominated the transfer of sediment to the oceans during lowstands in sea level.     

The association of poorly ordered graphite, coke and bitumens in greenschist facies rocks of the Poniklá Group, Lugicum, Czech Republic: the result of graphitization of various types of carbonaceous matter

Greenschist facies rocks of the Poniklá Group (Ordovician-Silurian), Czech Republic, contain several types of carbonaceous matter that differ in their morphology, texture, reflectance and Raman characteristics. The first type consists of large (up to 3 mm) irregularly bound particles of low reflectance (R_omin = 0.9%; R_omax = 5.6%). The area ratio of the 1585 cm^-1 to 1350 cm^-1 Raman peaks (1.08–1.17) indicates an intermediate degree of graphitization. The formation of this type of highly porous particle, displaying a texture reminiscent of regular or needle coke, is attributed to the thermal alteration of the amorphous (structureless) kerogen of the precursor sediments. The second type consists of lamellar particles up to 30 μm thick, which can be associated with the latter or can occur independently in white mica-rich laminae. This type is characterized by high bireflectance (R_omin = 0.6%; R_omax = 11.9%) and by lower ratios (0.70–0.82) of the Raman peak areas. These particles are interpreted as the product of solid-state, diffusion-controlled graphitization of a chemically homogeneous organic material, e.g. of graptolite periderms. The third type consists of isometric, up to 2 mm large, commonly fractured grains and fragments which mainly occur in quartz-rich laminae. In reflected light, the texture is either homogeneous or consists of various types of anisotropic mozaics. The Raman peak area ratios (0.75–1.14) indicate a highly variable degree of structural ordering. These particles are considered as the remains of metamorphosed bitumens, accumulated in the sandy laminae of the original sediments. The fourth type consists of small particles of carbonaceous matter (maximum length 25 μm, thickness 1-2 μm), which occur adjacent to crystal faces of white micas. This type is probably the product of epitaxial growth of graphite from the gaseous phase. The results of this work indicate that the differences in the degree of graphitization of the carbonaceous matter in low-grade metamorphosed rocks can be mainly related to the initial nature of the sedimentary organic matter and to its premetamorphic history.     

藻类勃发—湖相油源岩形成的一种重要机制

浮游藻类是重要的湖相生油母质，本文以渤海湾盆地济阳坳陷早第三纪湖相生油岩为例，研究了其中藻类（主要是颗石藻和沟鞭藻＿化石的分布特征，并通过与现代水体中藻类生产和沉积作用的比较，探讨了生油湖泊中藻类生产和沉积方式及其对油源岩形成所起的控制作用，结果显示，藻类勃发现象在早第三纪生油湖泊中相当普遍，而且贯穿于各类油源岩的形成过程，这类快速事件性沉积是湖相油源岩形成的一种重要机制。     

Brick-like texture and radial rays in Triassic pisolites of Lombardy,Italy: A clue to distinguish ancient aragonitic pisolites

Triassic pisolites from the Calcare Rosso, Lombardy, Italy, were formed in a hypersaline vadose environment and now show alternating dolomite and calcite laminae. The calcite consists either of microsparite laminae with a brick-like fabric, or of a mass of mosaic crystals with the external form of square-ended rays.These features suggest that the original laminae and rays were aragonitic, like those of the Holocene supratidal pisolites of the Persian Gulf, which consist of alternating laminae of unoriented nannomicrite with Mg-rich mucilaginous material, and aragonitic fibers with radial orientation separated by mucilaginous films. It is suggested that the transformation to brick-like and ray textures passed through the following diagenetic path: (1) original formation of fibrous aragonite laminae; (2) local aggrading recrystallization of aragonite fibers to large square-ended rays during hypersaline phases; (3) dolomitization of Mg-rich mucilaginous nannomicrite laminae during hyposaline phases; (4) inversion of the aragonite fibers and rays to calcite on a piece-by piece basis that preserved the original textural details, when the pH or Mg/Ca ratio dropped.The brick-like and ray fabrics have not been found in laminae of continental freshwater pisolites because these were deposited as equant and stable crystals of low-Mg calcite. These textures consequently make it possible to establish the chemistry of the depositional and early diagenetic milieu for some ancient pisolitic rocks.     

A New Sauropod Dinosaur from the Late Cretaceous Gaogou Formation of Nanyang,Henan Province

A new sauropod dinosaur Baotianmansaurus henanensis gen. et sp. nov. from the Cretaceous Gaogou Formation of Neixiang, Henan Province is erected. It is characterized by somphospondylous presacral vertebrae; a highly-developed lamina system on the dorsal vertebrae; transverse process supported by four laminae; and the dorsal portion of the anterior centroparapophyseal lamina is bifurcated, with a small branch extending to the ventral surface of the prezygapophysis. It represents a new titanosauriform sauropod.