Age and origin of the lowlands of Mars

One of the many significant findings of the Mars Global Surveyor mission is the presence of hundreds of quasi-circular depressions (QCDs) observed from high-resolution MOLA topography data. Their presence has recently been interpreted to reflect a northern lowlands that archive some of the earliest recorded rocks on Mars, mostly below a veneer of Hesperian and Amazonian materials. Here we analyze these data, coupled with a recent synthesis of geologic, geophysical, geomorphic, topographic, and magnetic information. Such analysis allows us to suggest a potential plate tectonic phase during the recorded Early into Middle Noachian martian history that transitioned into a monoplate world with episodic magmatic-driven activity persisting to present. This working hypothesis is based on: (1) the observation that the basement of the northern plains is younger than the basement of the southern highlands, but older than the material exposures of the cratered highlands, suggesting different formational ages for each one of the three geologic-time units; (2) the observation that parts of the very ancient highland's crust are highly magnetized, thus suggesting that most if not all of the formation of the lowlands basement postdates the shut off of the martian dynamo, some 4 Gyr ago, and so allowing hundreds of millions of years for the shaping of the buried lowlands. Consequently, the role of endogenic processes in the earliest geological evolution of Mars (Early perhaps into Middle Noachian) requires reconsideration, since MOLA topographic and MGS magnetic data afford a temporal window sufficient for very early, non-primordial shaping of the northern lowlands' basement.     

The Auger Observatory in Argentina

The Auger Project studies the highest energies known in nature with an emphasis on energies ≥5 × 10¹⁹ eV, which are cosmic rays coming from the outer space reaching the Earth's surface with a very low flux. The questions to be elucidated are what are the origin, energy, production mechanism, and chemical composition of these cosmic rays. Auger aims at building two observatories in both the hemispheres and in 2000 the construction of the austral observatory started. Auger's two distinctive features are its exceptional size and its hybrid nature. It spans over an area of 3000 km² and is constituted by 24 fluorescence detector telescopes and 1600 surface detectors. As such, it will provide a large number of events with less systematic detection uncertainties. The construction of the Southern Observatory in Argentina is quite advanced and the buildings at the Central Station in Malargüe city are already operational. So are the telescope buildings at Cerros Los Leones and Coihueco (two prototype telescopes were operational at Los Leones, which have now been dismantled), 32 surface detectors, and the telecommunication and data acquisition systems. About 20-hybrid events/months were detected and currently two events/hours are registered with the surface detector array. The detection of hybrid events is the most important issue since it shows that the equipment operates within the design parameters.     

Meadow fragmentation and reproductive output of the SE Asian seagrass Enhalus acoroides

Flower and fruit production of the abundant, tall, long-lived, dioecious, surface-pollinating seagrass species Enhalus acoroides (L.) Royle were estimated at seven sites in the reef flats off Bolinao (NW Luzon, The Philippines) featuring different fragmentation of the seagrass meadows. Fragmentation of the seagrass meadow was quantified as cover of E. acoroides and all seagrass species present in 20×20 m plots. E. acoroides and overall seagrass cover were correlated positively. The proportion of female flowers of E. acoroides that developed a fruit increased sharply as overall seagrass cover was around 50%. Apparent sex ratio bore no relationship with overall seagrass cover. This threshold-type of relationship suggests that fragmentation of seagrass meadows can have a major effect on the reproductive output of this species. A possible mechanism underlying these results would be a non-linear increase of the efficiency of trapping the surface-dispersed pollen with increasing seagrass canopy density. This provides the first evidence based on real data that fragmentation can affect the population dynamics of seagrass species.     

Controls on event runoff coefficients in the eastern Italian Alps

Analyses of event runoff coefficients provide essential insight on catchment response, particularly if a range of catchments and a range of events are compared by a single indicator. In this study we examine the effect of climate, geology, land use, flood types and initial soil moisture conditions on the distribution functions of the event runoff coefficients for a set of 14 mountainous catchments located in the eastern Italian Alps, ranging in size from 7.3 to 608.4 km². Runoff coefficients were computed from hourly precipitation, runoff data and estimates of snowmelt. A total of 535 events were analysed over the period 1989–2004. We classified each basin using a “permeability index” which was inferred from a geologic map and ranged from “low” to “high permeability”. A continuous soil moisture accounting model was applied to each catchment to classify ‘wet’ and ‘dry’ initial soil moisture conditions. The results indicate that the spatial distribution of runoff coefficients is highly correlated with mean annual precipitation, with the mean runoff coefficient increasing with mean annual precipitation. Geology, through the ‘permeability index’, is another important control on runoff coefficients for catchments with mean annual precipitation less than 1200 mm. Land use, as indexed by the SCS curve number, influences runoff coefficient distribution to a lesser degree. An analysis of the runoff coefficients by flood type indicates that runoff coefficients increase with event snowmelt. Results show that there exists an intermediate region of subsurface water storage capacity, as indexed by a flow–duration curve-based index, which maximises the impact of initial wetness conditions on the runoff coefficient. This means that the difference between runoff coefficients characterised by wet and dry initial conditions is negligible both for basins with very large storage capacity and for basins with small storage capacity. For basins with intermediate storage capacities, the impact of the initial wetness conditions may be relatively large.     

The use of radon as tracer in environmental sciences

Radon can be used as a naturally occurring tracer for environmental processes. By means of grab-sampling or continuous monitoring of radon concentration, it is possible to assess several types of dynamic phenomena in air and water. We present a review of the use of radon and its progeny at the University of Cantabria. Radon can be an atmospheric dynamics indicator related with air mass interchange near land-sea discontinuities as well as for the study of vertical variations of air parameters (average values of different types of stability: 131–580 Bq m^?3). Concerning indoor gas, we present some results obtained at Altamira Cave (Spain): from 222 to 6549 Bq m^?3 (Hall) and from 999 to 6697 Bq m^?3 (Paintings Room). Finally, variations of radon concentration in soil (0.3 to 9.1 kBq m^?3) and underground water (values up to 500 Bq l^?1) provide relevant information about different geophysical phenomena.     

喀麦隆西南部Mamelles条带状铁建造元素地球化学特征

Mamelles铁矿床位于喀麦隆南部刚果克拉通西北缘,距离克里比地区东南方向约20km。该矿床由大规模、高品位磁铁矿矿体组成,赋存于Nyong杂岩体的条带状铁建造(BIF)中。该矿床中的BIF与角闪岩和片麻岩相伴生。在详细的野外调查基础上,我们获取了BIF的全岩地球化学数据,并用以约束它们的物质来源和沉积环境。弱正铕(Eu)异常(δEu=2.14～3.55)表明高温热液流体对MamellesBIF的贡献是通过海底火山岩蚀变作用的方式,并有少量碎屑物质输入。正铈(Ce)异常的缺失表明,这些BIF可能沉积在缺氧的深海环境中,如火山弧或弧后盆地深水区。     

Assessment of calanchi and rill–interrill erosion susceptibilities using terrain analysis and geostochastics: A case study in the Oltrepo Pavese,Northern Apennines,Italy

Soil erosion is one of the most important environmental problems distributed worldwide. In the last decades, numerous studies have been published on the assessment of soil erosion and the related processes and forms using empirical, conceptual and physically based models. For the prediction of the spatial distribution, more and more sophisticated stochastic modelling approaches have been proposed – especially on smaller spatial scales such as river basins. In this work, we apply a maximum entropy model (MaxEnt) to evaluate badlands (calanchi) and rill–interrill (sheet erosion) areas in the Oltrepo Pavese (Northern Apennines, Italy). The aim of the work is to assess the important environmental predictors that influence calanchi and rill–interrill erosion at the regional scale. We used 13 topographic parameters derived from a 12 m digital elevation model (TanDEM-X) and data on the lithology and land use. Additional information about the vegetation is introduced through the normalized difference vegetation index based on remotely sensed data (ASTER images). The results are presented in the form of susceptibility maps showing the spatial distribution of the occurrence probability for calanchi and rill–interrill erosion. For the validation of the MaxEnt model results, a support vector machine approach was applied. The models show reliable results and highlight several locations of the study area that are potentially prone to future soil erosion. Thus, coping and mitigation strategies may be developed to prevent or fight the soil erosion phenomenon under consideration. © 2020 John Wiley & Sons, Ltd.