Geological characteristics and spatial distribution of paleo-inlet channels beneath the outer banks barrier islands,North Carolina,USA     

David J. Mallinson  Curtis W. Smith  Stephen J. Culver  Stanley R. Riggs  Dorothea Ames 《Estuarine, Coastal and Shelf Science》2010

Nearly 200 km of high-resolution ground penetrating radar (GPR) data were acquired along the Outer Banks barrier island system of North Carolina, USA. GPR data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel, flood-tide delta, overwash, peat and inner shelf. Previously undocumented paleo-inlet channels constitute a significant portion of the shallow geologic framework between Oregon Inlet and Cape Hatteras. GPR data reveal the complex stratigraphy associated with multiple sequences of cut-and-fill within inlet channels. Two types of paleochannels (non-migrating and migrating) were classified based on geometry and fill-patterns. Sediments and foraminifera collected from vibracores were correlated to GPR data to define the regional shallow stratigraphic framework. Channel-fill facies are characterized by clinoform packages, sometimes bounded by erosional surfaces, indicating variable sediment transport directions from the ocean and sound sides. Channels are incised into older flood-tide delta deposits corresponding to older inlet activity when barriers existed further seaward. Flood-tide delta deposits are capped with marsh peat and overwash units. Migrating inlet facies occur under the widest portions of the island, whereas narrow portions of the island are underlain by the non-migrating inlet facies or flood-tide delta/overwash facies. This geologic/geomorphic relationship is attributed to the successional stage of island evolution during transgression, and sediment transport processes associated with the different inlet types. The radar facies, lithofacies, and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record.  相似文献   

53Mn and 60Fe in iron meteorites—New data,model calculations     

Ingo Leya  Jean‐Christophe David  Thomas Faestermann  Michaela Froehlich  Niko Kivel  Dominik Koll  Gunther Korschinek  Sarah McIntyre  Silke Merchel  Stefan Pavetich  Georg Rugel  Dorothea Schumann  Thomas Smith  Anton Wallner 《Meteoritics & planetary science》2020,55(4):818-831

We measured specific activities of the long‐lived cosmogenic radionuclides ⁶⁰Fe in 28 iron meteorites and ⁵³Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14 MV Heavy Ion Accelerator Facility at ANU Canberra for all samples except for two which were measured at the Maier‐Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG), we measured six samples for ⁵³Mn. This work doubles the number of existing individual ⁶⁰Fe data and quadruples the number of iron meteorites studied for ⁶⁰Fe. We also significantly extended the entire ⁵³Mn database for iron meteorites. The ⁵³Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of ⁶⁰Fe and ⁵³Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model. Predictions for the ⁶⁰Fe activity concentrations are about a factor of 2 higher, for ⁵³Mn, they are ~30% lower, compared to the earlier model, which gives now a better agreement with the experimental data.  相似文献   

Radionuclide activities in recent chondrite falls determined by gamma‐ray spectrometry: Implications for terrestrial age estimates     

ke V. Rosn  Beda A. Hofmann  Moritz von Sivers  Marc Schumann 《Meteoritics & planetary science》2020,55(1):149-163

Radionuclide activities were measured in the low‐background gamma‐ray spectrometry facility GeMSE in eight meteorite falls (Lost City, Tamdakht, Huaxi, Boumdeid, Xining, Kamargaon, Degtevo, and Ouidiyat Sbaa) and two finds (SaU 606 and Mürtschenstock) to evaluate the use of radionuclides for terrestrial age estimates. Results indicate that these meteorites were all derived from small‐ (r < 25 cm) to medium‐sized (r < 65 cm) meteoroids. Short‐lived ⁴⁸V (t_1/2 = 16.0 d) and ⁵¹Cr (t_1/2 = 27.7 d) were only detected in Oudiyat Sbaa (EH), while ⁷Be (t_1/2 = 53.1 d) was also detected in Degtevo (H) and Kamargaon (L), in agreement with reported fall dates. The ²²Na/²⁶Al activity ratio in Huaxi agrees with the previously reported short cosmic‐ray exposure age of this meteorite while ²²Na/²⁶Al in Kamargaon likely records a complex exposure history. Bayesian statistical analysis verifies the detection of very low activities of ⁴⁴Ti (t_1/2 = 60 a) in the relatively large H chondrites (>100 g) Degtevo, Huaxi, Tamdakht, Lost City, and SaU 606. Additionally, large samples from Oudiyat Sbaa (EH) and Kamargaon (L) gave positive detections. For H chondrite target compositions, detected ⁴⁴Ti(Fe+Ni)/²⁶Al averaged 0.055 ± 0.013. Activities of ²²Na and ⁵⁴Mn in SaU 606 show that this meteorite fell between July and September 2012, making SaU 606 the second recent fall from Oman identified using gamma‐ray spectrometry. The upper activity limit of ²²Na in the Mürtschenstock meteorite shows that it fell prior to 1999 and is not related to a bolide observation in 2015. Mürtschenstock shows ¹³⁷Cs ~10× higher than previously determined in Oman meteorites, likely due to Chernobyl fallout.  相似文献   

A Diagnostic Study of the Global Distribution of Contrails Part II: Future Air Traffic Scenarios     

K. Gierens  R. Sausen  U. Schumann 《Theoretical and Applied Climatology》1999,63(1-2):1-9

Summary  The global distribution of the contrail coverage is computed for several scenarios of aviation in the years 2015 and 2050 and compared to 1992 using meteorological analysis data representative of present temperature and humidity conditions and assuming 0.5% cover in a reference region 30° W–30° E, 35° N–75° N covering parts of western Europe and the North Atlantic. The mean contrail coverage of the Earth is computed to increase by a factor of about three compared to 1992 and to reach 0.25% in 2015. For three different scenarios of aviation and for constant climatic conditions, the global mean contrail coverage reaches values between 0.26% and 0.75% for 2050. Contrail coverage increases more strongly than total fuel burn mainly because of more traffic in the upper troposphere and because of more efficient engines with cooler exhaust. The overall efficiency of propulsion is expected to grow from about 0.3 in the fleet average of 1992, to 0.4 in 2015, and to 0.5 in 2050. The expansion of air traffic makes Canada, Alaska, the North Pacific route from North America to Japan and most of the Asian continent new regions where contrails are expected to cover more than 0.5% on average. Received September 7, 1998 Revised January 4, 1999  相似文献   

Machine learning based identification of dominant controls on runoff dynamics     

Henning Oppel  Andreas H. Schumann 《水文研究》2020,34(11):2450-2465

Hydrological models used for flood prediction in ungauged catchments are commonly fitted to regionally transferred data. The key issue of this procedure is to identify hydrologically similar catchments. Therefore, the dominant controls for the process of interest have to be known. In this study, we applied a new machine learning based approach to identify the catchment characteristics that can be used to identify the active processes controlling runoff dynamics. A random forest (RF) regressor has been trained to estimate the drainage velocity parameters of a geomorphologic instantaneous unit hydrograph (GIUH) in ungauged catchments, based on regionally available data. We analyzed the learning procedure of the algorithm and identified preferred donor catchments for each ungauged catchment. Based on the obtained machine learning results from catchment grouping, a classification scheme for drainage network characteristics has been derived. This classification scheme has been applied in a flood forecasting case study. The results demonstrate that the RF could be trained properly with the selected donor catchments to successfully estimate the required GIUH parameters. Moreover, our results showed that drainage network characteristics can be used to identify the influence of geomorphological dispersion on the dynamics of catchment response.  相似文献