The Bow City structure,southern Alberta,Canada: The deep roots of a complex impact structure?     

Paul Glombick  Douglas R. Schmitt  Wei Xie  Todd Bown  Ben Hathway  Christopher Banks 《Meteoritics & planetary science》2014,49(5):872-895

Geological and geophysical evidence is presented for a newly discovered, probable remnant complex impact structure. The structure, located near Bow City, southern Alberta, has no obvious morphological expression at surface. The geometry of the structure in the shallow subsurface, mapped using downhole geophysical well logs, is a semicircular structural depression approximately 8 km in diameter with a semicircular uplifted central region. Detailed subsurface mapping revealed evidence of localized duplication of stratigraphic section in the central uplift area and omission of strata within the surrounding annular region. Field mapping of outcrop confirmed an inlier of older rocks present within the center of the structure. Evidence of deformation along the eastern margin of the central uplift includes thrust faulting, folding, and steeply dipping bedding. Normal faults were mapped along the northern margin of the annular region. Isopach maps reveal that structural thickening and thinning were accommodated primarily within the Belly River Group. Evidence from legacy 2‐D seismic data is consistent with the subsurface mapping and reveals additional insight into the geometry of the structure, including a series of listric normal faults in the annular region and complex faulting within the central uplift. The absence of any ejecta blanket, breccia, suevite, or melt sheet (based on available data) is consistent with the Bow City structure being the remnant of a deeply eroded, complex impact structure. Accordingly, the Bow City structure may provide rare access and insight into zones of deformation remaining beneath an excavated transient crater in stratified siliciclastic target rocks.  相似文献   

Probabilistic projections of transient climate change     

Glen R. Harris  David M. H. Sexton  Ben B. B. Booth  Mat Collins  James M. Murphy 《Climate Dynamics》2013,40(11-12):2937-2972

This paper describes a Bayesian methodology for prediction of multivariate probability distribution functions (PDFs) for transient regional climate change. The approach is based upon PDFs for the equilibrium response to doubled carbon dioxide, derived from a comprehensive sampling of uncertainties in modelling of surface and atmospheric processes, and constrained by multiannual mean observations of recent climate. These PDFs are sampled and scaled by global mean temperature predicted by a Simple Climate Model (SCM), in order to emulate corresponding transient responses. The sampled projections are then reweighted, based upon the likelihood that they correctly replicate observed historical changes in surface temperature, and combined to provide PDFs for 20 year averages of regional temperature and precipitation changes to the end of the twenty-first century, for the A1B emissions scenario. The PDFs also account for modelling uncertainties associated with aerosol forcing, ocean heat uptake and the terrestrial carbon cycle, sampled using SCM configurations calibrated to the response of perturbed physics ensembles generated using the Hadley Centre climate model HadCM3, and other international climate model simulations. Weighting the projections using observational metrics of recent mean climate is found to be as effective at constraining the future transient response as metrics based on historical trends. The spread in global temperature response due to modelling uncertainty in the carbon cycle feedbacks is determined to be about 65–80 % of the spread arising from uncertainties in modelling atmospheric, oceanic and aerosol processes of the climate system. Early twenty-first century aerosol forcing is found to be extremely unlikely to be less than ?1.7 W m^?2. Our technique provides a rigorous and formal method of combining several lines of evidence used in the previous IPCC expert assessment of the Transient Climate Response. The 10th, 50th and 90th percentiles of our observationally constrained PDF for the Transient Climate Response are 1.6, 2.0 and 2.4 °C respectively, compared with the 10–90 % range of 1.0–3.0 °C assessed by the IPCC.  相似文献   

近10a湖北省强降水时空分布特征与主要天气概念模型   总被引：2，自引：0，他引：2  

吴翠红  王晓玲  龙利民  牛奔  王珊珊  李银娥 《湖北气象》2013,(2):113-119

利用湖北省78个气象站逐小时雨量和地面风场资料、NCEP/NCAR再分析资料以及新一代天气雷达资料和卫星云图资料,对湖北省1999—2009年208例强降水过程的时空分布、雨团源地和路径、雨强特征、主要影响天气系统进行了普查分析。结果表明:湖北省强降水源地主要位于鄂西山区和江汉平原南部,在不同引导气流的作用下,强降水雨团主要有6条活动路径;强降水频发区主要位于孝感、黄冈北部和宜昌等地,孝感是全省强降水频发中心;影响强降水的天气系统主要有干线(又称露点锋,下同)、湿舌、暖切顶部辐合区、冷切尾部辐合区、气流汇合区、涌线、地面辐合线;根据干线的不同作用和影响方式,将湖北省180个干线类强降水分成干侵入型、干混合型、干锋生型和暖干型四种类型。基于对动力、水汽、不稳定三个条件以及强降水落区等显著特征的总结分析,归纳出四种干线类强降水的天气概念模型。  相似文献   

Climatic indices in the interpretation of the phenological phases of the olive in mediterranean areas during its biological cycle     

F. Orlandi  H. Garcia-Mozo  A. Ben Dhiab  C. Galán  M. Msallem  B. Romano  M. Abichou  E. Dominguez-Vilches  M. Fornaciari 《Climatic change》2013,116(2):263-284

The present study implemented a regional phenological model that was derived through the growing season index and adapted to a widespread Mediterranean species, the olive (Olea europaea L.). This model considers not only individual phenological events, but also the main vegetative and reproductive phenological phases of the species, in an integrated biological approach. The regional model generally does not need to include specific meteorological variables calculated as weekly or monthly averages which could limit the extrapolation over large areas. The main climatic limitations of the olive cultivation areas in the south Mediterranean at latitudes around 10° (practically speaking, the geographical limits of the olive) are estimated here. This analysis uses information relating to local climatic changes over the last two decades (1990–1999, 2000–2009) to provide interpretations of the temperature, solar radiation rate, and evapotranspiration trends. This has allowed creation of a Mediterranean phenological model adapted to the olive, which presents the contemporary climate requirements during winter and the warm summer season. The climate analysis and comparisons of these two decades has allowed us to reveal a reduction in the index according to the minimum temperature, which has particular consequences in the northern monitoring areas. This phenomenon appears to present new positive scenarios for the future regarding a northward shift of olive cultivation areas, due to the potential enlargement of the growing season in winter. However, negative scenarios can also be foreseen in consideration of the failure to satisfy the minimum chilling requirements in the traditional southern cultivation areas of the olive.  相似文献   

Loss on ignition vs. thermogravimetric analysis: a comparative study to determine organic matter and carbonate content in sediments     

Bensharada  Mohammed  Telford  Richard  Stern  Ben  Gaffney  Vince 《Journal of Paleolimnology》2022,67(2):191-197

Journal of Paleolimnology - Mass loss at specified temperatures has been used widely to determine amounts of organic matter and carbonate in sediment samples. The loss on ignition (LOI) method is...  相似文献   

Straddling the tholeiitic/calc-alkaline transition: the effects of modest amounts of water on magmatic differentiation at Newberry Volcano,Oregon     

Ben?E.?MandlerEmail author  Julie?M.?Donnelly-Nolan  Timothy?L.?Grove 《Contributions to Mineralogy and Petrology》2014,168(4):1066

Melting experiments have been performed at 1 bar (anhydrous) and 1- and 2-kbar H₂O-saturated conditions to study the effect of water on the differentiation of a basaltic andesite. The starting material was a mafic pumice from the compositionally zoned tuff deposited during the ~75 ka caldera-forming eruption of Newberry Volcano, a rear-arc volcanic center in the central Oregon Cascades. Pumices in the tuff of Newberry caldera (TNC) span a continuous silica range from 53 to 74 wt% and feature an unusually high-Na₂O content of 6.5 wt% at 67 wt% SiO₂. This wide range of magmatic compositions erupted in a single event makes the TNC an excellent natural laboratory in which to study the conditions of magmatic differentiation. Our experimental results and mineral–melt hygrometers/thermometers yield similar estimates of pre-eruptive H₂O contents and temperatures of the TNC liquids. The most primitive (mafic) basaltic andesites record a pre-eruptive H₂O content of 1.5 wt% and a liquidus temperature of 1,060–1,070 °C at upper crustal pressure. This modest H₂O content produces a distinctive fractionation trend that is much more enriched in Na, Fe, and Ti than the calc-alkaline trend typical of wetter arc magmas, but slightly less enriched in Fe and Ti than the tholeiitic trend of dry magmas. Modest H₂O contents might be expected at Newberry Volcano given its location in the Cascade rear arc, and the same fractionation trend is also observed in the rim andesites of the rear-arc Medicine Lake volcano in the southern Cascades. However, the Na–Fe–Ti enrichment characteristic of modest H₂O (1–2 wt%) is also observed to the west of Newberry in magmas erupted from the arc axis, such as the Shevlin Park Tuff and several lava flows from the Three Sisters. This shows that modest-H₂O magmas are being generated directly beneath the arc axis as well as in the rear arc. Because liquid lines of descent are particularly sensitive to water content in the range of 0–3 wt% H₂O, they provide a quantitative and reliable tool for precisely determining pre-eruptive H₂O content using major-element data from pumices or lava flows. Coupled enrichment in Na, Fe, and Ti relative to the calc-alkaline trend is a general feature of fractional crystallization in the presence of modest amounts of H₂O, which may be used to look for “damp” fractionation sequences elsewhere.  相似文献   

First microbialites associated to organic-rich facies of the Oceanic Anoxic Event 2 (Northern Tunisia,Cenomanian–Turonian transition)     

Mohsen Layeb  Moez Ben Fadhel  Yosra Layeb-Tounsi  Mohamed Ben Youssef 《Arabian Journal of Geosciences》2014,7(8):3349-3363

From northern Tunisia, small-scale well-preserved microbialites, contemporaneous to the global oceanic anoxic event 2 (OAE 2) are first reported on the southern Tethyan Margin. These microbialites are encased within the pelagic organic-rich black shales of the Bahloul Formation (Cenomanian–Turonian transition). Biostratigraphic, petrographic, and geochemical investigations carried out to constrain their biogenicity and genesis character led to consider them as thrombolites and stromatolites occurring in lenticular bioherms/biostromes and columnar bodies co-relatable to the global ‘filament event’ of the authors, close to the base of the Watinoceras ammonite zone. Abundant clotted micrite, cyanobacterial filaments, and algal tissues point to the key process of microbial carbonate precipitation and to a major role played by microbes in the stabilisation and subsequent lithification, which in turn favoured the preservation of the original structure of the microbialites. These microbially induced carbonate formations are considered as favoured by chemosynthetic fauna of bivalve molluscs and lithistid sponges which were able to host symbiotic microbial communities. The latter contributed to the precipitation of authigenic calcite and non-carbonate minerals (e.g. pyrite) fuelled by microbial activity under sulphate-reducing conditions. The carbonate body onset is considered to be initiated by seafloor instability due to syndepositional fault acting that induced the appraisal of uplifted tilted blocks within oxygenated waters but near the anoxic water masses. Generated depressions allowed the development of chemosynthetic-based communities. Deep faults related to Triassic salt domes acted as conducts for hydrocarbon and salt brine expulsion to the seafloor and the microbialite growth was enhanced by an abrupt uprising sea level under warmer conditions.  相似文献   

Hydrogeological and mixing process of waters in deep aquifers in arid regions: south east Tunisia   总被引：1，自引：0，他引：1  

Jalila Makni  Fatma Ben Brahim  Saoussan Hassine  Salem Bouri  Hamed Ben Dhia 《Arabian Journal of Geosciences》2014,7(2):799-809

This study addresses the hydrogeochemistry of thermal and cold waters from south east Tunisia. Temperature intervals are 38.5–68 °C and 22–27.8 °C for thermal water and cold water, respectively. Three distinct hydrogeological systems supply water either for irrigation or for drinking; they are: (1) the Continental Intercalaire geothermal aquifer (CI), (2) the Turonian aquifer and (3) the Senonian aquifer. A synthetic study including hydrochemical, hydrogeological and geothermal approaches have been applied in order to evaluate the inter-aquifers water transfer in south east of Tunisia. By using silica geothermometers and saturation indices for different solid phases, estimated thermal reservoir temperature varies between 52 and 87 °C and between 75 and 110 °C, respectively. Based on chemical and thermal data, mixing, which occurs between the ascending deep geothermal water and shallow cold water, is about 57 % cold water.  相似文献   

Evolution of Pleistocene travertine depositional system from terraced slope to fissure-ridge in a mixed travertine-alluvial succession (Jebel El Mida,Gafsa, southern Tunisia)     

Mohsen Henchiri  Walid Ben Ahmed  Andrea Brogi  Mehmet Cihat Alçiçek  Ramdhane Benassi 《Geodinamica Acta》2017,29(1):20-41

The Quaternary stratigraphic record of Jebel El Mida, composed of continental deposits, is a useful example of concomitant travertines and alluvial deposition in an extensional setting. Travertine deposition occurred in a faulted Pleistocene alluvial fan giving rise to seven (recognised) facies interfingering with five other alluvial ones. The travertine depositional events indicate a tectonically driven evolution from terraced slope (facies group FC1–FC6) to a travertine fissure ridge-type depositing phase (facies group of FC1–FC7). Interfingering between travertine and alluvial facies indicates the co-existence of adjacent and time-equivalent depositional environments. The travertine deposition resulted from deep origin hydrothermal fluids channelled along damaged rocks volumes associated to a regional fault system, named as the Gafsa Fault (GF). The travertine–terrigenous succession in Jebel El Mida highlights the major role played by the GF in controlling: (i) the hydrothermal fluid flow, still active as also indicated by the numerous thermal springs aligned along the fault zone; (ii) paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. The paleoclimatic correlation with adjacent localities reveals that, at that time, humid episodes could have contributed to the recharge of the hydrothermal system and to the deposition of alluvial sediments.  相似文献   

The possible source of the causal time arrow in geo-historical explanations     

Gadi Kravitz 《地学前缘(英文版)》2017,8(3):555-564

My argument in this article, will be that nature, in general, and human nature in particular, suggests that, in principle, it is possible to derive the causal time arrow from several physical time arrows existing in nature and appearing to be unidirectional and irreversible phenomena. A more concrete argument will be that the assumption of a causal time arrow to which geologists resort in all geo-historical explanations, apparently originates in geo-historical time arrows concealed in unidirectional and irreversible physical-geological processes. I will illustrate this claim with a few examples of geo-historical explanations in the theory of plate tectonics, most of which are based on irreversible geo-physical processes. My final argument is a broader, of an epistemological nature, according to which the causal time arrow assumption used in logical-causative explanations in everyday life and in science, apparently “derives” in a way from the geo-historical time arrow. I will base this argument on the causal relationship and mutual influence that occurs in nature between geo-historical and evolutionary processes in animals, including developmental processes of the human brain and mind. From this reductionist argument, nicely integrated in the framework of evolutionary epistemology (EEM), it is possible to derive a wider naturalistic argument according to which, on principle, the laws of geo-historical physics can be reduced to the laws of logic and causality.  相似文献