Strain analysis of a seismically imaged mass‐transport complex,offshore Uruguay     

Michael J. Steventon  Christopher A.‐L. Jackson  David M. Hodgson  Howard D. Johnson 《Basin Research》2019,31(3):600-620

Strain style, magnitude and distribution within mass‐transport complexes (MTCs) are important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally driven passive margins have been shown to approximately balance between updip extensional and downdip contractional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1,500 mbsf) and well‐imaged MTC, offshore Uruguay using a high‐resolution (12.5 m vertical and 15 × 12.5 m horizontal resolution) three‐dimensional seismic‐reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic‐attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub‐orthogonal shear zones, and fold‐thrust systems within the basal shear zone beneath rafted‐blocks. These features suggest multiple transport directions and phases of flow during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and contractional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra‐MTC rafted‐blocks due to their kinematic interactions with the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain difference between extension (1.6–1.9 km) and contraction (6.7–7.3 km) is calculated. We attribute this to a combination of distributed, sub‐seismic, ‘cryptic’ strain, likely related to de‐watering, grain‐scale deformation and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits.  相似文献   

Stratigraphy and internal structure of wind-dominated barrier islands (dune and machair) of the Outer Hebrides,Scotland     

J. Pile  J.A.G. Cooper  D.W.T. Jackson 《地球表面变化过程与地形》2019,44(7):1482-1493

The barrier islands that fringe the western shore of the Outer Hebrides are globally unusual in that they are developed on a planated bedrock (strandflat) surface. They also contain the most extensive area of machair (a distinctive vegetated sandy plain) in the British Isles. This paper presents the first investigation of the internal structure and morphology of these barrier islands and investigates the controls on their structure. The barriers form extensive (300-1000 metres wide) but thin (1.5-2 m) surficial deposits typically resting on bedrock. In areas where depressions exist in the bedrock, and where sediment supply permits, transgressive dunes underlie the machair. A distinctive machair facies of sub-horizontal, undulating reflections, which are laterally continuous over tens of metres is the dominant component of the barriers at each site. This reflects episodic deposition of windblown sand up to the level of the water table. Thereafter any additional sand is transported through the system to accumulate in topographic lows as lake fills, or on topographic highs as ‘high machair’. Eight radar facies were identified, the extent and presence of which vary between the study sites. Bedrock topography and sediment supply are interpreted as the dominant controls on variability in barrier structure. © 2019 John Wiley & Sons, Ltd.  相似文献   

Active Galactic Nuclei among Polar-Ring Galaxies     

Smirnov  D. V.  Reshetnikov  V. P. 《Astronomy Letters》2020,46(8):501-508

Astronomy Letters - Based on SDSS data, we consider the fraction of active galactic nuclei among polar-ring galaxies. We have found evidence for an excess of Seyfert galaxies and LINERS among...  相似文献   

The Dudica Epithermal Cu–Au Deposit (Republic of North Macedonia)     

Tasev  G.  Serafimovski  D.  Volkov  A. V.  Boev  B.  Djordjevic  T.  Kolitsch  U.  Serafimovski  T. 《Geology of Ore Deposits》2020,62(5):419-431

Geology of Ore Deposits - The Dudica deposit is located in the southern part of the Republic of North Macedonia (RNM), not far from the border with Greece in the Kozuf–Aridean volcanic...  相似文献   

The Structure of Potential Amur Tiger (Panthera tigris altaica) Habitats and Evaluation of Its Prey in Taipingou National Reserve (China) Based on Remote Sensing Data     

Shibing Zhu  Qu  Yi  Liu  Yingzhu  Dobrynin  D. V.  Sukhova  O. V.  Kotlov  I. P.  Sandlersky  R. B.  Yachmennikova  A. A.  Rozhnov  V. V. 《Izvestiya Atmospheric and Oceanic Physics》2020,56(9):1107-1126

Izvestiya, Atmospheric and Oceanic Physics - The population of the Amur tiger (Panthera tigris altaica) in the Russian Far East is currently being restored; young individuals are being spread...  相似文献   

Formation of Stellar Streams Due to the Decay of Star Clusters,OB Associations,and Galaxy Satellites     

Tutukov  A. V.  Sizova  M. D.  Vereshchagin  S. V. 《Astronomy Reports》2020,64(10):827-838

Astronomy Reports - This paper presents a scenario of the evolution of OB associations and star clusters from formation to decay, in the process of which they turn into stellar streams moving in...  相似文献   

Hydrothermal activity on the CV parent body: New perspectives from the giant Transantarctic Mountains minimeteorite TAM5.29     

J. Nava  M. D. Suttle  R. Spiess  L. Folco  J. Najorka  C. Carli  M. Massironi 《Meteoritics & planetary science》2020,55(1):164-183

TAM5.29 is an extraterrestrial dust grain, collected on the Transantarctic Mountains (TAM). Its mineralogy is dominated by an Fe‐rich matrix composed of platy fayalitic olivines and clasts of andradite surrounded by diopside‐jarosite mantles; chondrules are absent. TAM5.29 records a complex geological history with evidence of extensive thermal metamorphism in the presence of fluids at T < 300 °C. Alteration was terminated by an impact, resulting in shock melt veins and compaction‐orientated foliation of olivine. A second episode of alteration at lower temperatures (<100 °C) occurred postimpact and is either parent body or terrestrial in origin and resulted in the formation of iddingsite. The lack of chondrules is explained by random subsampling of the parent body, with TAM5.29 representing a matrix‐only fragment. On the basis of bulk chemical composition, mineralogy, and geological history TAM5.29 demonstrates affinities to the CV_ox group with a mineralogical assemblage in between the Allende‐like and Bali‐like subgroups (CV_oxA and TAM5.29 are rich in andradite, magnetite, and FeNiS, but CV_oxA lacks hydrated minerals, common in TAM5.29; conversely, CV_oxB are rich in hydrated phyllosilicates but contain almost pure fayalite, not found in TAM5.29). In addition, TAM5.29 has a slightly different metasomatic history, in between the oxidized and reduced CV metamorphic grades while also recording higher oxidizing conditions as compared to the known CV chondrites. This study represents the third CV‐like cosmic dust particle, containing a unique composition, mineralogy, and fabric, demonstrating variation in the thermal metamorphic history of the CV parent body(‐ies).  相似文献   

Ionosphere Disturbances Preceding Earthquakes according to the Data of Ground Based Station of the Vertical Ionospheric Sounding Wakkanai   总被引：1，自引：0，他引：1  

S. A. Pulinets  A. D. Legen’ka  V. V. Hegai  V. P. Kim  L. P. Korsunova 《Geomagnetism and Aeronomy》2018,58(5):686-692

The paper analyzes the data of manual ionograms processing of hourly measurements of the critical frequency foF2 of the F2 ionospheric layer at the Wakkanai ionospheric vertical sounding station (Japan) in a geomagnetically quiet environment before a series of earthquakes with magnitude M > 6.0, for which the station entered the earthquake preparation zone, in order to detect possible Ionospheric Disturbances Preceding Earthquakes (IDPE), and to determine their quantitative characteristics. Detected IDPE, in the opinion of the authors, can be related to the processes of preparation of the corresponding earthquakes, i.e., to be Ionospheric Precursors of Earthquakes (IPE).  相似文献   

Estimating external magnetic field differences at high geomagnetic latitudes from a single station          下载免费PDF全文

Ciarán D. Beggan  Laurence Billingham  Ellen Clarke 《Geophysical Prospecting》2018,66(6):1227-1240

Providing an accurate estimate of the magnetic field on the Earth's surface at a location distant from an observatory has useful scientific and commercial applications, such as in repeat station data reduction, space weather nowcasting or aeromagnetic surveying. While the correlation of measurements between nearby magnetic observatories at low and mid‐latitudes is good, at high geomagnetic latitudes () the external field differences between observatories increase rapidly with distance, even during relatively low magnetic activity. Thus, it is of interest to describe how the differences (or errors) in external magnetic field extrapolation from a single observatory grow with distance from its location. These differences are modulated by local time, seasonal and solar cycle variations, as well as geomagnetic activity, giving a complex temporal and spatial relationship. A straightforward way to describe the differences are via confidence intervals for the extrapolated values with respect to distance. To compute the confidence intervals associated with extrapolation of the external field at varying distances from an observatory, we used 695 station‐years of overlapping minute‐mean data from 37 observatories and variometers at high latitudes from which we removed the main and crustal fields to isolate unmodelled signals. From this data set, the pairwise differences were analysed to quantify the variation during a range of time epochs and separation distances. We estimate the 68.3%, 95.4% and 99.7% confidence levels (equivalent to the 1σ, 2σ and 3σ Gaussian error bounds) from these differences for all components. We find that there is always a small non‐zero bias that we ascribe to instrumentation and local crustal field induction effects. The computed confidence intervals are typically twice as large in the north–south direction compared to the east‐west direction and smaller during the solstice months compared to the equinoxes.  相似文献   

Iron and Manganese in Groundwater: Using Kriging and GIS to Locate High Concentrations in Buncombe County,North Carolina          下载免费PDF全文

Crystal D. Johnson  Arpita Nandi  T. Andrew Joyner  Ingrid Luffman 《Ground water》2018,56(1):87-95

For health, economic, and aesthetic reasons, allowable concentrations (as suggested by the United States Environmental Protection Agency) of the secondary contaminants iron (Fe) and manganese (Mn) found present in drinking water are 0.3 and 0.05 mg/L, respectively. Water samples taken from private drinking wells in rural communities within Buncombe County, North Carolina contain concentrations of these metals that exceed secondary water quality criteria. This study predicted the spatial distribution of Fe and Mn in the county, and evaluated the effect of site environmental factors (bedrock geology, ground elevation, saprolite thickness, and drinking water well depth) in controlling the variability of Fe and Mn in groundwater. A statistically significant correlation between Fe and Mn concentrations, attributable to bedrock geology, was identified. Prediction models were created using ordinary kriging and cokriging interpolation techniques to estimate the presence of Fe and Mn in groundwater where direct measurements are not possible. This same procedure can be used to estimate the trend of other contaminants in the groundwater in different areas with similar hydrogeological settings.  相似文献