Climatic and sea level controls on Late Quaternary eolian activity on the Agulhas Plain, South Africa   总被引：1，自引：0，他引：1  

Andrew S. Carr  David S.G. Thomas 《Quaternary Research》2006,65(2):252-263

Located at the interface between the temperate westerly and sub-tropical climate systems, South Africa's winter rainfall zone (WRZ) is a key location in understanding Late Quaternary atmospheric circulation dynamics. Inactive eolian deposits in the WRZ, comprising pan-fringing lunette and coastal dunes, were investigated to establish their depositional ages and utility as paleoenvironmental indicators. The resulting optical luminescence chronology reveals episodic lunette accretion at 60,000-45,000 yr, 12,000-13,000 yr, 2800-2600 yr, 1200 yr, and <1000 yr, with coastal dune ages clustering at 4100-4700 yr.Episodes of lunette and coastal dune accretion on the Agulhas Plain are temporally distinct, reflecting differing fundamental controls on their activity. Comparisons to previously published data also reveal that the lunettes differ in age from more ancient coastal eolianites. Lunette deposition is asynchronous between locations, reflecting the topographic and hydrological setting of the individual pans. In near-coastal settings, with limited surface recharge, lunette accretion appears to be at least partially controlled by sea level induced changes in groundwater levels. Those pans with more significant surface recharge (particularly from fluvial systems) may produce less ambiguous paleoenvironmental records, with pan status more strongly reflecting regional hydrological conditions. Lunette orientation is indicative of strong westerly winds during both the Pleistocene and Holocene. Lunette accretion would have been promoted by reduced on-shore moisture transport during the summer months, enhancing rainfall seasonality. Such conditions would have been promoted by increased continentality as the Agulhas Bank was exposed during low sea level stands.  相似文献   

Primary geochemical and mineralogical dispersion in the vicinity of the Lady Loretta Zn-Pb-Ag deposit, Northwest Queensland     

G.R. Carr   《Journal of Geochemical Exploration》1984,22(1-3)

Lady Loretta is a stratiform Zn-Pb-Ag deposit occurring within carbonate- and pyrite-rich argillaceous rocks of the southern part of the Lawn Hill Platform, northwestern Queensland. The deposit consists of a single massive sulphide lens within a steep-sided basinal structure and contains reserves of 8 690 000 tonnes of ore at 18.1% Zn, 6.7% Pb and 110 g t⁻¹ Ag.The proportion of pyrite-rich layers in the host rocks increases progressively from about 2% at 150 m stratigraphically below the ore to > 90% in the top 10 m of the footwall rocks. Hanging-wall rocks contain up to 20% pyrite-rich layers for at least 100 m above the ores. Siderite is the carbonate phase present within the ore and within the host rocks in an aureole that extends from 75 m beneath to 50 m above the ore. Both older and younger rocks are dolomitic. The two carbonate phases do not occur together within unmineralized host rocks although they may coexist within veins. Siderite contains up to 13 mol% ZnCO₃ and 32 mol% MgCO₃. There is an antipathetic relationship between Zn and Mg, the latter increasing with distance from the ore.Zinc and, to a lesser extent, Hg, Pb, Ag and Ba show extensive primary dispersion within the host rocks. Within the plane of sedimentation, haloes vary in width from 50 m to 1.5 km and these dispersions are thought to be dependent on the shape of the sedimentary basin floor at the time of exhalative activity. Perpendicular to the sedimentary layering, Zn and Hg show the most extensive primary dispersion with anomalous values extending up to 100 m into the footwall and at least 50 m into the hanging wall.  相似文献   

Monte Carlo simulation of small air-mass showers     

H. C. Vaughan  G. R. White  P. H. Carr 《Pure and Applied Geophysics》1982,120(2):261-272

The present model permits simulation of any geographic region and the symmetrical or random positioning of any number of rain gauges. The operator has the option of entering precipitation parameters: rain cell diameter, duration, rain swath length, vector angle, and precipitation amount for any number of discrete showers. In a series of computations the model generates (1) a random first echo location and resulting rain swath, which is superimposed on a specific grid of rain gauges; (2) the number of rain gauge receiving a hit; and (3) the number of undetected rain events within an area.By use of a portion of the Iowa climatological rain gauge network and parameters derived from radar and rain gauge observations the model shows that only 7% of single cell showers are detected by the existing sampling grid.Journal Paper No. J-10378 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project 2449.A portion of this paper was presented at the 93rd Annual Meeting of the Iowa Academy of Science, April 1981.  相似文献   

Unprecedented recent warming rate and temperature variability over the east Tibetan Plateau inferred from Alpine treeline dendrochronology     

Shi  Chunming  Masson-Delmotte  Valérie  Daux  Valérie  Li  Zongshan  Carré  Matthieu  Moore  John C. 《Climate Dynamics》2015,44(5-6):1367-1379

Climate Dynamics - Despite instrumental records showing recent large temperature rises on the Tibetan Plateau (TP), only a few tree-ring temperature reconstructions do capture this warming trend....  相似文献   

Igpet software for modeling igneous processes: examples of application using the open educational version     

Carr  Michael J.  Gazel  Esteban 《Mineralogy and Petrology》2017,111(2):283-289

Mineralogy and Petrology - We provide here an open version of Igpet software, called t-Igpet to emphasize its application for teaching and research in forward modeling of igneous geochemistry....  相似文献   

A dating intercomparison study on Late Stone Age coastal midden deposits,South Africa     

Mark D. Bateman  Andrew S. Carr  Colin V. Murray‐Wallace  David L. Roberts  Peter J. Holmes 《Geoarchaeology》2008,23(6):715-741

The southern and western coastlines of South Africa have an extensive archaeological record with many sites associated with widespread eolian deposits. While much of this rich archaeological record is based on cave sites, evidence of Late Stone Age occupation is additionally preserved in the form of open‐site shell middens. We present here a comparative study of the application of amino acid racemization (AAR), optically stimulated luminescence (OSL), and radiocarbon analyses to three Late Stone Age (LSA) midden sites found within dunes on the southern coastline of South Africa. Preliminary geochronological analyses suggest that middens offer opportunity to fill in gaps in what is still a fragmentary archaeological record. Results show OSL and radiocarbon ages in good agreement, illustrating the potential to date not only the middens but also the surrounding dunes that constituted the dwelling sites. AAR results show increasing ratios with age and also that the application of paired shell and “whole rock” AAR can provide insights into the degree of biogenic sediment recycling at buried midden sites. However, the work also highlights that caution is required when OSL sampling sediment associated with middens which may have undergone human disturbance and that further work is required to improve the regional marine reservoir correction for radiocarbon dating in this part of South Africa. The study also illustrates that AAR will only provide useful data provided that middens have been sufficiently deeply buried to overcome fluctuations in environmental variables that affect the racemization rate and that inter‐genus comparisons should be avoided. © 2008 Wiley Periodicals, Inc.  相似文献