Contribution a la tectonique du Bassin houiller de la Sarre: Recherche du tracé au sol de la Faille de la Sarre et de la Faille de la Rosselle (Faille Felsberg)

Zusammenfassung Es werden genauere Angaben gemacht über den Verlauf des Saarsprungs und des Felsbergsprunges an der Erdoberfläche. Der Saarsprung konnte von Bous bis Burbach verfolgt werden. Der Felsbergsprung verfolgt sich nach SE bis in den Rosselsprung.Das Vorkommen von Oberrotliegendem scheint an diese Verwerfungen gebunden zu sein. Es sind Zerrungsspalten, die während der Hauptfaltungsphase (saalische Phase nachStille) des Saar-Nahe-Beckens aufgebrochen sind. Es ist aber anzunehmen, daß sie während des Oberrotliegenden aktiv waren. Sie wurden nach Ablagerung der Trias neu belebt.     

Timing of vegetation changes at the end of the Holocene Humid Period in desert areas at the northern edge of the Atlantic and Indian monsoon systems

This article aims at discussing the ecological response of the terrestrial and fresh water dependant environments to the installation of arid conditions at the end of the Holocene Humid Period in the Atlantic and Indian monsoon domains. It is mainly focused on dry environments from Chad, Oman and Pakistan where new, high-resolution pollen sequences have been provided. Pollen data show that local hydrological conditions have played a major role in the destruction or survival of tropical tree populations at the end of the Holocene Humid Period, as well as partly explaining the asynchronous pattern of recorded environmental changes in most tropical regions. In desert areas, the response of the fresh water dependant systems to the shift from humid to arid climate conditions appears to have followed a threshold-like pattern. In contrast, terrestrial ecosystems have gradually adapted to increased drought, as shown by the progressive decrease of tropical tree species at Yoa or the gradual expansion in dry plant types in Oman and Pakistan from 6000 cal yrs BP to the present. A remarkable synchroneity in environmental change is recorded at the northern edge of the Atlantic and Indian monsoon systems, with the extreme end of the Holocene Humid Period corresponding to the last occurrence of tropical trees in the desert and the last record of prolonged SW monsoon rainfall over north-western Asia around 4700–4500 cal yrs BP.     

Simulating Head Recovery and Intermittent Discharge in Free Flowing Wells

Modeling of the head recovery (buildup) in and intermittent operation of flowing wells lacks rigorous analytical tools. Presently different methods are applied in discharging and recovery phases. The presented reliable approximate solution considers a continuous free flow process and time variant screen loss parameters. The latter are temporarily set to large value to prevent inflow into the well bore during the single recovery or in repeated shut down periods. This method is called as screen loss control or SLC technique and is verified by means of comparative analysis with the constant rate pumping‐recovery test simulated in leaky aquifer. The evaluation of the free flow and recovery test in the free flowing well 28 (Artesia Heights) concluded with calibrated parameters close to those obtained in the earlier analyses based on split well flow process. The simulation of intermittent flowing well operation also underwent successful validation resulting in reasonable values of the Q_w and s response functions.     

Late Devonian OIB alkaline gabbro in the Yarlung Zangbo Suture Zone: Remnants of the Paleo-Tethys?

The Yarlung Zangbo Suture Zone (YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys that occurred from early Mesozoic to early Cenozoic. We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a mélange zone of the western YZSZ. Single zircon U–Pb analyses from one representative gabbro sample by SIMS (Secondary Ion Mass Spectrometry) yielded a combined crystallization age of about 363.7 ± 1.7 Ma (1σ). In situ Hf isotopic analyses yielded ε_Hf(t) values of + 2.6 to + 5.5, suggesting an enriched mantle source. All of the gabbro samples show typical Ocean Island Basalt (OIB) affinity with little or no continental crust contamination. They also display strong geochemical similarities with the Hawaii basalts and the Xigaze seamount basalts suggestive of their intra-oceanic setting. These observations, in combination with the Early Carboniferous layered gabbros reported at Luobusa, indicate that these rocks could represent remnants of the Paleo-Tethys. We propose that a branch ocean separating the Western Qiangtang terrane and the Lhasa terrane from the Gondwana continent might have been present during the Late Devonian and the Early Carboniferous, providing new constrains on the configuration of Paleo-Tethys in Tibetan Plateau during early Late Paleozoic.     

Uncertainties in European summer precipitation changes: role of large scale circulation

Climate models suggest that anthropogenic emissions are likely to induce an important drying during summer over most of Europe in the late 21st century. However, the amplitude of the associated decrease in precipitation strongly varies among the different climate models. In order to reduce this spread, it is first necessary to identify its causes and the associated physical mechanisms. Consequently, the focus of this paper is to better estimate the role of large scale circulation (LSC) in precipitation changes over Europe using a multi-model framework and then to characterize the LSC changes using the weather regime paradigm. We show that LSC changes directly lead to a decrease of precipitation over northwestern Europe. This circulation-driven decrease in rainfall is mainly linked to an increase (decrease) of the occurrence of positive (negative) phase of the North Atlantic Oscillation regime. LSC is also responsible for a significant part of the models spread in precipitation changes over these regions. Over southern Europe, the role of LSC changes on multi-model mean precipitation changes is generally weak. We also show that the precipitation anomalies directly induced by LSC modifications seem to be further amplified through local feedbacks.     

Damages observed in locations of Oaxaca due to the Tehuantepec Mw8.2 earthquake,Mexico

On September 7, 2017, at 23:49 h (local time), a Mw8.2 intermediate-depth normal-fault earthquake occurred in the Gulf of Tehuantepec, 133 km away from Pijijiapan, Chiapas, and about 700 km away from Mexico City. This event caused 95 fatalities and severe damage to different types of structures located close to the epicenter. The main objective of this work is to present observed damages caused in the state of Oaxaca by this earthquake, which were mainly concentrated in self-built houses and historical and ancient buildings. The locations visited by the reconnaissance team of the Institute of Engineering from UNAM in Oaxaca included Salina Cruz, Tehuantepec, Ixtaltepec, Juchitán, Huatulco and La Ventosa.

     

Insects as zoogeomorphic agents: an extended review

Insects are the largest and most diverse group of living organisms on Earth, playing a critical but underestimated role as agents of geomorphic change. Burrowing insects create micro-scale landforms such as subterranean tunnels and surface mounds and, by this way, exert an influence on hydrology, soil erosion and sediment transfer at a wider landscape scale. However, social insects represented by ants and termites were the main taxa studied as geomorphic agents and ecosystem engineers. This article proposes an extended and critical literature review of insects as zoogeomorphic agents, with reference to various taxonomic orders and families of insects having a burrowing behaviour. It provides a large overview of their primary and secondary impacts on Earth surface systems, both supported by naturalistic evidence and available quantitative data. Some evolutionary insights are discussed based on fossil evidence of geomorphic work by insects and, at finer temporal scale, on recent advances in radiometric and luminescence dating of insect mounds. Finally, this article explores the fruitful links between geomorphology and entomology, and suggests several research perspectives in order to develop an integrated understanding of the importance of insects in Earth surface processes and landforms. © 2020 John Wiley & Sons, Ltd.     

External controls on the distribution,fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon,Cayo Coco (Cuba)

Active, carbonate‐mineralizing microbial mats flourish in a tropical, highly evaporative, marine‐fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea‐level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O₂ and HS^? profiles. High rates of O₂ production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate‐driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water‐level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind‐driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in‐depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.