Depositional setting,provenance, and tectonic-volcanic setting of Eocene–Recent deep-sea sediments of the oceanic Izu–Bonin forearc,northwest Pacific (IODP Expedition 352)     

Alastair H. F. Robertson  Steffen Kutterolf  Aaron Avery  Alan T. Baxter  Katerina Petronotis  Gary D. Acton 《International Geology Review》2018,60(15):1816-1854

New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.  相似文献   

Origins and evolution of rhyolitic magmas in the central Snake River Plain: insights from coupled high-precision geochronology,oxygen isotope,and hafnium isotope analyses of zircon     

Dylan?P.?ColónEmail author  Ilya?N.?Bindeman  J?rn-Frederik?Wotzlaw  Eric?H.?Christiansen  Richard?A.?Stern 《Contributions to Mineralogy and Petrology》2018,173(2):11

We present new high-precision CA-ID-TIMS and in situ U–Pb ages together with Hf and O isotopic analyses (analyses performed all on the same grains) from four tuffs from the 15?10 Ma Bruneau–Jarbidge center of the Snake River Plain and from three rhyolitic units from the Kimberly borehole in the neighboring 10?6 Ma Twin Falls volcanic center. We find significant intrasample diversity in zircon ages (ranges of up to 3 Myr) and in δ¹⁸O (ranges of up to 6‰) and ε_Hf (ranges of up to 24 ε units) values. Zircon rims are also more homogeneous than the associated cores, and we show that zircon rim growth occurs faster than the resolution of in situ dating techniques. CA-ID-TIMS dating of a subset of zircon grains from the Twin Falls samples reveals complex crystallization histories spanning 10⁴–10⁶ years prior to some eruptions, suggesting that magma genesis was characterized by the cyclic remelting of buried volcanic rocks and intrusions associated with previous magmatic episodes. Age-dependent trends in zircon isotopic compositions show that rhyolite production in the Yellowstone hotspot track is driven by the mixing of mantle-derived melts (normal δ¹⁸O and ε_Hf) and a combination of Precambrian basement rock (normal δ¹⁸O and ε_Hf down to ??60) and shallow Mesozoic and Cenozoic age rocks, some of which are hydrothermally altered (to low δ¹⁸O values) by earlier stages of Snake River Plain magmatism. These crustal melts hybridize with juvenile basalts and rhyolites to produce the erupted rhyolites. We also observe that the Precambrian basement rock is only an important component in the erupted magmas in the first eruption at each caldera center, suggesting that the accumulation of new intrusions quickly builds an upper crustal intrusive body which is isolated from the Precambrian basement and evolves towards more isotopically juvenile and lower-δ¹⁸O compositions over time.  相似文献   

A Rhaetian microvertebrate fauna from Stowey Quarry,Somerset, U.K.     

Iacopo Cavicchini  H. Cecilia Heyworth  Christopher J. Duffin  Claudia Hildebrandt  Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):144-158

Rhaetian bone beds have been described from many locations in south-west England, around Bristol. One site that has never been reported is Stowey Quarry, some 13?km south of Bristol. This quarry yielded Lias, and revealed thin Rhaetian units in the quarry floor, including two bone beds, the basal Rhaetian bone bed, and a second, higher bone bed, also within the Westbury Formation. The fossil fauna of both includes elements typical of Rhaetian bone beds elsewhere, but showing differences in faunal composition between the two. The basal bone bed yielded more specimens and more species, with three taxa (Sargodon tomicus, Rhomphaiodon minor and Hybodus cloacinus) exclusive to this bed and eleven identified in total. Severnichthys acuminatus accounts for more than 50% of the countable teeth from the basal bone bed, followed by Gyrolepis albertii with 20%, Lissodus minimus with 14% and Rhomphaiodon minor with 9%. The basal bone bed, as ever, is dominated by chondrichthyans, whereas the upper bone bed is dominated by osteichthyans, which form 90% of the non-dental remains. The only unique taxon is Dapedium, and Gyrolepis albertii is the most abundant species with 45% of countable teeth, followed by Severnichthys acuminatus with 38% and Duffinselache holwellensis with 11%. These faunal differences, and the equally good condition of specimens between both samples confirms that the upper bone bed is independent of the basal bone bed, and is not a reworked subsample.  相似文献   

School vulnerability to disaster: examination of school closure,demographic, and exposure factors in Hurricane Ike’s wind swath     

A.-M. Esnard  B. S. Lai  C. Wyczalkowski  N. Malmin  H. J. Shah 《Natural Hazards》2018,90(2):513-535

Damage and destruction to schools from climate-related disasters can have significant and lasting impacts on curriculum and educational programs, educational attainment, and future income-earning potential of affected students. As such, assessing the potential impact of hazards is crucial to the ability of individuals, households, and communities to respond to natural disasters, extreme events, and economic crises. Yet, few studies have focused on assessing the vulnerability of schools in coastal regions of the USA. Using Hurricane Ike’s tropical storm wind swath in the State of Texas as our study area, we: (1) assessed the spatial distribution patterns of school closures and (2) tested the relationship between school closure and vulnerability factors (namely physical exposure and school demographics) using zero-inflated negative binomial regression models. The regression results show that higher probabilities of hurricane strikes, more urbanized school districts, and school districts located in coastal counties on the right side of Ike’s path have significant positive associations with an increase in the number of school closure days. Socioeconomic characteristics were not significantly associated with the number of days closed, with the exception of proportion of Hispanic youth in schools, a result which is not supported by the social vulnerability literature. At a practical level, understanding how hurricanes may adversely impact schools is important for developing appropriate preparedness, mitigation, recovery, and adaptation strategies. For example, school districts on the right side of the hurricane track can plan in advance for potential damage and destruction. The ability of a community to respond to future natural disasters, extreme events, and economic crises depends in part on mitigating these adverse effects.  相似文献   

Age and Provenance Areas of Terrigenous Rocks of the Dzhida Terrane: Results of U—Th—Pb (LA-ICP-MS) Geochronological Study of Detrital Zircons     

L. Z. Reznitskii  V. P. Kovach  I. G. Barash  Yu. V. Plotkina  K. -L. Wang  H. -Y. Chiu 《Stratigraphy and Geological Correlation》2018,26(5):489-513

The results of U—Th—Pb (LA-ICP-MS) geochronological studies of detrital zircons from terrigenous rocks of the Dzhida terrane of the Central Asian Fold Belt (CAFB) are presented. The data obtained allow us to distinguish the following age maxima (Ma): 578 and 634 (Vendian); 720, 823, and 919 (Late Riphean); 1922, 2090, 2225, and 2321 (Early Proterozoic). A number of zircons have Late Archean age in the interval of 2670–2980 Ma. Taking into account Late Cambrian age (504–506 Ma) of intrusive rocks that intruded the Dzhida terrane, a possible sedimentation period of sequences of this terrane is estimated to be in the interval of 580–510 Ma (from Vendian to Late Cambrian). The possible provenance areas of terrigenous sediments are proposed and the previously proposed models of geodynamic evolution of the Dzhida terrane are correlated with new geochronological data.  相似文献   

Integration of stress testing with graph theory to assess the resilience of urban road networks under seismic hazards     

Nazli Yonca Aydin  H. Sebnem Duzgun  Friedemann Wenzel  Hans Rudolf Heinimann 《Natural Hazards》2018,91(1):37-68

Transportation networks daily provide accessibility and crucial services to societies. However, they must also maintain an acceptable level of service to critical infrastructures in the case of disruptions, especially during natural disasters. We have developed a method for assessing the resilience of transportation network topology when exposed to environmental hazards. This approach integrates graph theory with stress testing methodology and involves five basic steps: (1) establishment of a scenario set that covers a range of seismic damage potential in the network, (2) assessment of resilience using various graph-based metrics, (3) topology-based simulations, (4) evaluation of changes in graph-based metrics, and (5) examination of resilience in terms of spatial distribution of critical nodes and the entire network topology. Our case study was from the city of Kathmandu in Nepal, where the earthquake on April 25, 2015, followed by a major aftershock on May 12, 2015, led to numerous casualties and caused significant damage. Therefore, it is a good example for demonstrating and validating the developed methodology. The results presented here indicate that the proposed approach is quite efficient and accurate in assisting stakeholders when evaluating the resilience of transportation networks based on their topology.  相似文献   

The present-day active deformation in the central and northern parts of the Gulf of Suez area,Egypt, from earthquake focal mechanism data     

I. Abu El-Nader  H. M. Hussein 《Natural Hazards》2018,92(3):1355-1369

The average seismic strain rate is estimated for the seismotectonic zone of the northern/central parts of the Gulf of Suez. The principal strain rate tensor and velocity tensor were derived from a combination of earthquake focal mechanisms data and seismic moment of small-sized earthquakes covering a time span of 13 years (1992–2004). A total of 17 focal mechanism solutions have been used in the calculation of the moment tensor summation. The local magnitudes (MLs) of these events range from 2.8 to 4.7. The analysis indicates that the dominant mode of deformation in the central and northern parts of the Gulf of Suez is extension at a rate of 0.008 mm/year in N28°E direction and a small crustal thinning of 0.0034 mm/year. This low level of strain means that this zone experienced a little seismic deformation. There is also a right lateral shear motion along the ESE–WNW direction. This strain pattern is consistent with the predominant NW–SE normal faulting and ESE–WNW dextral transtensive faults in this zone. Comparing the results obtained from both stress and strain tensors, we find that the orientations of the principal axes of both tensors have the same direction with a small difference between them. Both tensors show a predominantly extensional domain. The nearly good correspondence between principal stress and strain orientations in the area suggests that the tectonic strength is relatively uniform for this crustal volume.  相似文献   

Pedotransfer functions to estimate soil water content at field capacity and permanent wilting point in hot Arid Western India   总被引：1，自引：0，他引：1  

Priyabrata Santra  Mahesh Kumar  R N Kumawat  D K Painuli  K M Hati  G B M Heuvelink  N H Batjes 《Journal of Earth System Science》2018,127(3):35

Characterization of soil water retention, e.g., water content at field capacity (FC) and permanent wilting point (PWP) over a landscape plays a key role in efficient utilization of available scarce water resources in dry land agriculture; however, direct measurement thereof for multiple locations in the field is not always feasible. Therefore, pedotransfer functions (PTFs) were developed to estimate soil water retention at FC and PWP for dryland soils of India. A soil database available for Arid Western India (N=370) was used to develop PTFs. The developed PTFs were tested in two independent datasets from arid regions of India (N=36) and an arid region of USA (N=1789). While testing these PTFs using independent data from India, root mean square error (RMSE) was found to be 2.65 and 1.08 for FC and PWP, respectively, whereas for most of the tested ‘established’ PTFs, the RMSE was >3.41 and >1.15, respectively. Performance of the developed PTFs from the independent dataset from USA was comparable with estimates derived from ‘established’ PTFs. For wide applicability of the developed PTFs, a user-friendly soil moisture calculator was developed. The PTFs developed in this study may be quite useful to farmers for scheduling irrigation water as per soil type.  相似文献   

What does the occurrence of Sporormiella (Preussia) spores mean in Australian fossil sequences?          下载免费PDF全文

John Dodson  Judith H. Field 《第四纪科学杂志》2018,33(4):380-392

Understanding the loss of the final few species of Australian megafauna is beset by a paucity of data on human arrival, well‐provenanced megafauna, human/megafauna population range and distribution (coexistence and interaction), and the range, scale and impact of environmental changes spanning the human–megafauna period. To overcome these shortcomings, the occurrence and decline of coprophilous fungal spores of Sporormiella in sediments have been used as a proxy for extinct megaherbivores. The Sporormiella evidence is presented as the key indicator of extinction timing and these reports are often from locations where there is no known archaeological record or megafauna remains. However, interpreting fungal spore occurrence is not straightforward, as demonstrated by studies investigating taphonomy, taxonomy and the types of animal dung where Sporormiella occurs. No detailed studies on these problems exist for Australia and no evidence supporting the use of Sporormiella as a valid proxy has been reported. Here we examine the occurrence of Sporormiella spores from Cuddie Springs in south‐eastern Australia. Despite a well‐preserved suite of megafauna fossils, Sporormiella occurrence is sporadic and frequencies are low. We conclude that using Sporormiella alone as an indicator for the presence of megafauna is premature for the Australian context.  相似文献   

Climatic Changes in the Dynamic Topography and Geostrophic Circulation of the Arctic Ocean     

Timokhov  L. A.  Ivanov  V. V.  Kassens  H.  Lebedev  N. V.  Frolov  I. Ye.  Hölemann  J. 《Doklady Earth Sciences》2018,480(1):685-688

Doklady Earth Sciences - According to historical oceanographic data, anomalies in the dynamic topography during the winter period were calculated and two climatic stages of dynamic condition of the...  相似文献