Conceptualization and characterization of a coastal multi-layered aquifer system in the Taranto Gulf (southern Italy)     

Giovanna De Filippis  Mauro Giudici  Stefano Margiotta  Sergio Negri 《Environmental Earth Sciences》2016,75(8):686

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Bioerosion and encrustation rates in recent mollusk death assemblages on a supratidal siliciclastic setting,Playa Norte,Veracruz State,Mexico     

Catalina Gómez-Espinosa  F. Raúl Gío-Argáez  Ester A. Farinati  Salvador Aliotta  Sergio Adrian Salgado-Souto 《Arabian Journal of Geosciences》2018,11(8):188

This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.  相似文献   

Built environment and agricultural value at risk from Hurricane Irma flooding in Florida (USA)     

Miller  Alexander J.  Arias  Mauricio E.  Alvarez  Sergio 《Natural Hazards》2021,109(2):1327-1348

Natural Hazards - Flooding is the most costly type of natural disaster, as well as the most frequent. To provide risk-based flood insurance, providers must be able to accurately determine an...  相似文献   

Modelling size effect on rock aggregates strength using a DEM bonded-cell model     

Huillca  Yoshiro  Silva  Matías  Ovalle  Carlos  Quezada  Juan Carlos  Carrasco  Sergio  Villavicencio  Gabriel Eduardo 《Acta Geotechnica》2021,16(3):699-709

Empirical evidence has shown that particle breakage affects the mechanical behaviour of granular materials. The source of this mechanism takes place at the particle scale, and the main consequence on the macromechanical behaviour is increasing compressibility. Due to the inverse correlation between particle size and particle crushing strength, coarse rockfill materials are particularly vulnerable to mechanical degradation due to particle breakage. However, such coarse materials do not fit in standard laboratory devices, and the alternative of large sample testing is usually unavailable or too expensive. Alternatively, recent works have proposed multi-scale approaches using the discrete element method (DEM) to carry out numerical testing of coarse crushable materials, although few studies have focused on size effects. This article presents the application of a DEM bonded-cell model to study particle size-strength correlation on angular rock aggregates. Each particle is modelled by a cluster of perfectly rigid polyhedral cells with Mohr–Coulomb contact law. Constant cell density within particles implies that the presence of potential fragmentation planes increases with size. Therefore, particle strength decreases with size. A comprehensive sensitivity analysis was carried out through 1477 particle crushing simulations in a given particle size. Based on published experimental data on calcareous rock aggregates, part of the simulations were used for calibration, and 97 additional simulations of a coarser size fraction were performed for validation. The results show a good agreement with the empirical data in terms of size effect and data scatter through Weibull statistics.

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Palaeoenvironments of the Mediterranean Basin at the Messinian hypersaline/hyposaline transition: evidence from natural radioactivity and microfacies of post‐evaporitic successions of the Adriatic sub‐basin     

Gianluca Sampalmieri  Annalisa Iadanza  Paola Cipollari  Domenico Cosentino  Sergio Lo Mastro 《地学学报》2010,22(4):239-250

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Introduction     

Nemesio M. Pérez  Sergio Gurrieri  Chi-Yu King  Yuri Taran 《Pure and Applied Geophysics》2007,164(12):2373-2375

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Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change     

Patrick A. Hesp  Sergio Rebello Dillenburg  Eduardo Guimaraes Barboza  Luiz C. P. Clerot  Luiz J. Tomazelli  Ricardo Norberto Ayup Zouain 《地球表面变化过程与地形》2007,32(3):407-414

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Enhanced data and methods for improving open and free global population grids: putting ‘leaving no one behind’ into practice     

Sergio Freire  Marcello Schiavina  Aneta J. Florczyk  Kytt MacManus  Martino Pesaresi  Christina Corbane 《International Journal of Digital Earth》2020,13(1):61-77

ABSTRACT

Data on global population distribution are a strategic resource currently in high demand in an age of new Development Agendas that call for universal inclusiveness of people. However, quality, detail, and age of census data varies significantly by country and suffers from shortcomings that propagate to derived population grids and their applications. In this work, the improved capabilities of recent remote sensing-derived global settlement data to detect and mitigate major discrepancies with census data is explored. Open layers mapping built-up presence were used to revise census units deemed as ‘unpopulated’ and to harmonize population distribution along coastlines. Automated procedures to detect and mitigate these anomalies, while minimizing changes to census geometry, preserving the regional distribution of population, and the overall counts were developed, tested, and applied. The two procedures employed for the detection of deficiencies in global census data obtained high rates of true positives, after verification and validation. Results also show that the targeted anomalies were significantly mitigated and are encouraging for further uses of free and open geospatial data derived from remote sensing in complementing and improving conventional sources of fundamental population statistics.  相似文献   

The effect of chlorite interlayering on <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar biotite dating: an <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar laser-probe and TEM investigations of variably chloritised biotites     

Gianfranco?Di VincenzoEmail author  Cecilia?Viti  Sergio?Rocchi 《Contributions to Mineralogy and Petrology》2003,145(6):643-658

Biotite is one of the most common minerals dated by the ⁴⁰Ar–³⁹Ar method. It frequently shows K contents below the expected stoichiometric value, suggesting the presence of low-K impurities. The most common low-K alteration product of biotite is chlorite. Therefore, it is important to understand the effects of chlorite interlayering on ⁴⁰Ar–³⁹Ar ages in order to correctly interpret ⁴⁰Ar–³⁹Ar data. This study examines the outcome of ⁴⁰Ar–³⁹Ar dating analyses on variably chloritised biotites from Ordovician intrusive rocks. The infrared (IR) laser-probe technique and different gas extraction methods were adopted. Incremental laser-heating data on bulk samples yielded hump-shaped age profiles with meaningless young and old age steps. Both the extent of anomalous old age steps and the degree of discordance of the age spectra were much more pronounced in the more chloritised biotite samples. In contrast, in situ data on rock chips and total-fusion ages on single biotite flakes yielded ages concordant with, or younger than, the inferred emplacement ages. Transmission electron microscopy (TEM) was used to texturally characterise biotite samples at the nanometre scale. It was also used to document the complex decomposition-transformation process affecting interlayered biotite–chlorite during in-vacuo IR-laser heating to temperatures ranging from ~600 to >1,000 °C. TEM results suggest that hump-shaped age profiles result from an interplay between ³⁹Ar_K redistribution by recoil during sample irradiation and differential release of argon isotopes hosted in three main reservoirs. These reservoirs are (from least to most retentive): extended defects, chlorite and biotite. The final descending age segment is attributed to the progressive release of argon with increasing temperature from large biotite domains for which ³⁹Ar_K recoil loss was less important. ⁴⁰Ar–³⁹Ar data support previous findings, which suggest that ⁴⁰Ar–³⁹Ar ages when recoil effects are minimised, provide minimum estimates that approach the true biotite age, when the pristine domains are analysed. The most effective approach for obtaining meaningful ⁴⁰Ar–³⁹Ar ages was using individual total-fusion analyses on carefully selected, single flakes previously split along the basal cleavage by wet-grinding and corresponding to a sample mass of a few micrograms.Editorial responsibility: I Parsons  相似文献   

Groundwater resource degradation in coastal plains: The example of the Cecina area (Tuscany – Central Italy)     

Sergio Grassi  Gianni CortecciPaolo Squarci 《Applied Geochemistry》2007

The paper describes the degradation of the groundwater resources in the Cecina area, where seawater intrusion, B contamination and NO₃ pollution are all affecting the heavily exploited Pleistocene aquifer. Over-pumping has brought water levels to about 0 m.a.s.l. as far as about 7 km from the shore line, thereby promoting the seawater intrusion. The intrusion, which is characterized by cation exchange phenomena and Ca–Cl type waters, enters the plain mostly through the shallower horizons. The saline front, which advanced from 0.5 to 1 km in 4 a, has by now reached the foot of the hills to the east of the town, where it is also affecting wells of the local aqueduct. Boron contamination, linked to past discharge of industrial waste transported downstream by the river, reached concentrations as high as 3.5 mg/L in the mid-1980s. Although a decreasing trend is now under way, B content is still close to 1 mg/L. The presence of high NO₃, which, together with the seawater intrusion, represents a major issue for groundwater management in the area, is linked to the widespread utilization of fertilizers. Nitrate concentration, which reaches a maximum of about 300 mg/L in the shallow aquifer horizons and then decreases rather regularly with depth, is strongly influenced by precipitation. However, irrigation also contributes significantly to transporting the NO₃ contamination to depth, as clearly shown by δ¹⁸O data. The severe decline in the quality of the groundwater resource in the Cecina area is further compounded by an overall decrease in water availability in the region of Tuscany, as evidenced by long-term monitoring of precipitation and fluvial discharge.  相似文献