Development of the SAR TT-OSL procedure for dating Middle Pleistocene dune and shallow marine deposits along the southern Cape coast of South Africa   总被引：1，自引：0，他引：1  

Zenobia Jacobs  Richard G. Roberts  Terry J. Lachlan  Panagiotis Karkanas  Curtis W. Marean  David L. Roberts 《Quaternary Geochronology》2011,6(5):491-513

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.  相似文献   

Mississippi Valley regional source of loess on the southern Green Bay Lobe land surface, Wisconsin     

Peter M. Jacobs  Joseph A. Mason  Paul R. Hanson   《Quaternary Research》2011,75(3):574-583

Loess has been recognized on the glacial land surface of the Green Bay Lobe for over 100 yr, but no systematic explanation of the source of the loess has been advanced. Intriguingly, the loess on the Green Bay Lobe land surface is thicker than predicted by regional thinning trends from the Mississippi Valley and is geographically separated from much loess of southwest Wisconsin by a sandy region devoid of loess. Mapping based on soil survey interpretation indicates that the loess occurs above an escarpment marking the eastern end of the sandy loess-free region. Particle size fining trends demonstrate that the loess was transported by northwesterly winds. Clay mineralogy of the Green Bay Lobe loess is distinctly different than glaciogenic sediments and matches loess of the Mississippi Valley, indicating a regional source and long distance transport of the loess. We propose the loess was transported from the regional source along a surface of transport produced by migration of eolian sand through low-relief landscapes including the glacial Lake Wisconsin basin. Eolian sand migration caused repeated entrainment of dust leading to east-southeastward transport. The loess accumulated above an escarpment that limited sand mobility and re-entrainment of loess beyond this topographic barrier.  相似文献   

Revealing the temporal dynamics of subsurface temperature in a wetland using time-lapse geophysics     

Heather Musgrave  Andrew Binley 《Journal of Hydrology》2011,396(3-4):258-266

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The ~4-ka Rungwe Pumice (South-Western Tanzania): a wind-still Plinian eruption     

Karen Fontijn  Gerald G. J. Ernst  Costanza Bonadonna  Marlina A. Elburg  Evelyne Mbede  Patric Jacobs 《Bulletin of Volcanology》2011,73(9):1353-1368

The ~4-ka trachytic Rungwe Pumice (RP) deposit from Rungwe Volcano in South-Western Tanzania is the first Plinian-style deposit from an African volcano to be closely documented focusing on its physical characterization. The RP is a mostly massive fall deposit with an inversely graded base. Empirical models suggest a maximum eruption column height H _T of 30.5–35 km with an associated peak mass discharge rate of 2.8–4.8 × 10⁸ kg/s. Analytical calculations result in H _T values of 33 ± 4 km (inversion of TEPHRA2 model on grain size data) corresponding to mass discharge ranging from 2.3 to 6.0 × 10⁸ kg/s. Lake-core data allow extrapolation of the deposit thinning trend far beyond onland exposures. Empirical fitting of thickness data yields volume estimates between 3.2 and 5.8 km³ (corresponding to an erupted mass of 1.1–2.0 × 10¹² kg), whereas analytical derivation yields an erupted mass of 1.1 × 10¹² kg (inversion of TEPHRA2 model). Modelling and dispersal maps are consistent with nearly no-wind conditions during the eruption. The plume corner is estimated to have been ca. 11–12 km from the vent. After an opening phase with gradually increasing intensity, a high discharge rate was maintained throughout the eruption, without fountain collapse as is evidenced by a lack of pyroclastic density current deposits.  相似文献   

The use of the Schmidt Hammer and Equotip for rock hardness assessment in geomorphology and heritage science: a comparative analysis   总被引：1，自引：0，他引：1  

Heather Viles  Andrew Goudie  Stefan Grab  Jennifer Lalley 《地球表面变化过程与地形》2011,36(3):320-333

Rapid, field‐based measurements of rock hardness are of use in investigating many geomorphological and heritage science problems. Several different methods are now available for taking such measurements, but little work has been done to assess their comparability and strengths and weaknesses. We review here the capabilities of two types of Schmidt Hammer (Classic N type and Silver Schmidt BL type) alongside two types of Equotip (standard type D and Piccolo) for investigating rock hardness in relation to rock weathering on various types of sandstone and limestone, as well as basalt and dolerite. Whilst the two Schmidt hammers and the two Equotips show comparable results when tested at 15 individual sites, interesting differences are found between the Equotip and Schmidt Hammer values which may reveal information about the nature of weathering on different surfaces. Operator variance is shown to be an issue in particular for the Equotip devices, which also exhibit higher variability in measurements and necessitate larger sample sizes. Carborundum pre‐treatment also has varying effects on the data collected, depending on the nature of the surface studied. The Equotip devices are shown to be particularly useful on smaller blocks and in situations where edge effects may affect Schmidt Hammer readings. We conclude that whilst each device contributes to geomorphological research, they do not necessarily produce comparable information. Indeed, using Schmidt Hammer and Equotip in combination and looking at any differences in results may provide invaluable insights into the structure of the near‐surface zones and the nature of weathering processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Naming conventions in geomorphology: contributions and controversies in the sandstone landscape of Zhangjiajie Geopark,China     

Gary Brierley  He Qing Huang  Anze Chen  Simon Aiken  Mike Crozier  Wolfgang Eder  Andrew Goudie  Yuanxu Ma  Jan‐Hendrik May  Piotr Migon  Gerald Nanson  Deli Qi  Heather Viles  Chris Wood  Robert Wray  Guifang Yang  Xiaoping Yang  Guo‐an Yu 《地球表面变化过程与地形》2011,36(14):1981-1984

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The Collision Orogen of Central Dronning Maud Land (Antarctica), a Result of the Assembly of East and West Gondwana     

W. Bauer  J. Jacobs 《Gondwana Research》2001,4(4):573-574

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International Symposium and Field Workshop on Gondwana Evolution and Dispersal, Kochi University, Japan, November 13-15, 2004     

Joachim Jacobs 《Gondwana Research》2005,8(2):293-294

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An alternative use of Kieffer’s lattice dynamics model using vibrational density of states for constructing thermodynamic databases     

Michael H. G. Jacobs  Rainer Schmid-Fetzer  Arie P. van den Berg 《Physics and Chemistry of Minerals》2013,40(3):207-227

We use Kieffer’s model to represent the vibrational density of states (VDoS) and thermodynamic properties of pure substances in pressure–temperature space. We show that this model can be simplified to a vibrational model in which the VDoS is represented by multiple Einstein frequencies without significant loss of accuracy in thermodynamic properties relative to experimental data. The resulting analytical expressions for thermodynamic properties, including the Gibbs energy, are mathematically simple and easily accommodated in existing computational software for making thermodynamic databases. We show for aluminium, platinum, orthoenstatite and forsterite that thermodynamic properties can be represented with comparable accuracy as with Kieffer’s model with the same number of fitting parameters as in the Mie–Grüneisen–Debye model. We demonstrate that the method enables to achieve thermodynamic properties with superior accuracy relative to the Mie–Grüneisen–Debye method. The method is versatile in the sense that it allows incorporating dispersion of Grüneisen parameters. It is possible to extend the formalism to include other physical effects, such as intrinsic anharmonicity in the same way as in vibrational models based on Kieffer’s formalism.  相似文献   

Constraints and deception in the isotopic record; the crustal evolution of the west Musgrave Province,central Australia     

Christopher L. Kirkland  R. Hugh Smithies  Ailsa J. Woodhouse  Heather M. Howard  Michael T.D. Wingate  Elena A. Belousova  John B. Cliff  Rosanna C. Murphy  Catherine V. Spaggiari 《Gondwana Research》2013,23(2):759-781

The Hf and Nd isotopic evolution of the Musgrave Province, central Australia, is used to constrain the timing of crust formation and lithospheric organisation of Proterozoic Australia. The dataset from this region challenges two widely held tenets of Hf and Nd isotope systematics, namely; that crust formation events can only be identified as periods when crystallisation ages correspond to model ages, and that linear Hf evolution arrays away from depleted mantle (along crustal Lu/Hf or Sm/Nd slopes) reflect reworking of the same source.Hf isotopes in Musgrave Province zircon crystals indicate two major crust formation events at c. 1900 Ma and at 1600–1550 Ma. Although no juvenile rocks or crystals are known from c. 1900 Ma, radiogenic addition into the crust at this time is required to account for consistent Nd and Hf evolution patterns, which show no indication of an initially heterogeneous source. Oxygen isotopes in zircon grains confirm that much of the c. 1900 Ma Hf isotopic signal is not compromised by mixtures. Furthermore, the correspondence between mantle extraction and the commencement of reworking of Archean material supports new crust generation at c. 1900 Ma and a coupling between lower and upper crustal processes. The c. 1900 Ma timing of juvenile addition is dissimilar to that in the Albany–Fraser and Arunta Orogens and may reflect continental arc development on the margin of a southern continent.The general Hf isotopic evolution trend of the Musgrave Province apparently reflects reworking from a dominant c. 1900 Ma source with some additional unradiogenic and radiogenic input through time. However, in the 1220–1050 Ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle-derived material. Intracontinental rifts and other regions with sustained very-high temperature crustal recycling processes generate magmatic provinces with extreme HFSE-enrichment. This can have a profound influence on isotopic evolution trends, suppressing typical juvenile addition patterns. Isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within HFSE enriched magmas without diverging isotopic signatures from apparent reworking trends. In the Musgrave Province, the crust had become so HFSE enriched during the prolonged Musgrave Orogeny (1220–1150 Ma) that it was insensitive to mantle input, which is estimated to have been as much as 85% during this event.  相似文献