High-resolution chronology for the Mesoamerican urban center of Teotihuacan derived from Bayesian statistics of radiocarbon and archaeological data     

Laura E. Beramendi-Orosco  Galia Gonzalez-Hernandez  Linda R. Manzanilla  Avto Goguitchaishvili 《Quaternary Research》2009,71(2):99-107

A high-resolution ¹⁴C chronology for the Teopancazco archaeological site in the Teotihuacan urban center of Mesoamerica was generated by Bayesian analysis of 33 radiocarbon dates and detailed archaeological information related to occupation stratigraphy, pottery and archaeomagnetic dates. The calibrated intervals obtained using the Bayesian model are up to ca. 70% shorter than those obtained with individual calibrations. For some samples, this is a consequence of plateaus in the part of the calibration curve covered by the sample dates (2500 to 1450 ¹⁴C yr BP). Effects of outliers are explored by comparing the results from a Bayesian model that incorporates radiocarbon data for two outlier samples with the same model excluding them. The effect of outliers was more significant than expected. Inclusion of radiocarbon dates from two altered contexts, 500 ¹⁴C yr earlier than those for the first occupational phase, results in ages calculated by the model earlier than the archaeological records. The Bayesian chronology excluding these outliers separates the first two Teopancazco occupational phases and suggests that ending of the Xolalpan phase was around cal AD 550, 100 yr earlier than previously estimated and in accordance with previously reported archaeomagnetic dates from lime plasters for the same site.  相似文献   

SHRIMP U–Pb zircon geochronological evidence for Neoarchean basement in western Arnhem Land, northern Australia     

Julie A. Hollis  Chris J. Carson  Linda M. Glass 《Precambrian Research》2009,174(3-4):364-380

The Pine Creek Orogen, located on the exposed northern periphery of the North Australian Craton, comprises a thick succession of variably metamorphosed Palaeoproterozoic siliciclastic and carbonate sedimentary and volcanic rocks, which were extensively intruded by mafic and granitic rocks. Exposed Neoarchean basement is rare in the Pine Creek Orogen and the North Australian Craton in general. However, recent field mapping, in conjunction with new SHRIMP U–Pb zircon data for six granitic gneiss samples, have identified previously unrecognised Neoarchean crystalline crust in the Nimbuwah Domain, the eastern-most region of the Pine Creek Orogen. Four samples from the Myra Falls and Caramal Inliers, the Cobourg Peninsula, and the Kakadu region have magmatic crystallisation ages in the range 2527–2510 Ma. An additional sample, from northeast Myra Falls Inlier, yielded a magmatic crystallisation age of 2671 ± 3 Ma, the oldest exposed Archean basement yet recognised in the North Australian Craton. These results are consistent with previously determined magmatic ages for known outcropping and subcropping crystalline basement some 200 km to the west. A sixth sample yielded a magmatic crystallisation age of 2640 ± 4 Ma. The ca. 2670 Ma and ca. 2640 Ma samples have ca. 2500 Ma metamorphic zircon rims, consistent with metamorphism broadly coeval with emplacement of the volumetrically dominant ca. 2530–2510 Ma granites and granitic gneisses. Neoarchean zircon detritus, particularly in the ca. 2530–2510 Ma and ca. 2670–2640 Ma age span, are an almost ubiquitous feature of detrital zircon spectra of unconformably overlying metamorphosed Palaeoproterozoic strata of the Pine Creek Orogen, and of local post-tectonic Proterozoic sequences, consistent with this local provenance. Neoarchean zircon is also a common detrital component in Palaeoproterozoic sedimentary units across much of the North Australian Craton suggesting the existence of an extensive, if not contiguous, Neoarchean crystalline basement underlying not only a large part of the Pine Creek Orogen, but also much of the North Australian Craton.  相似文献   

Thermal observations of Saturn's main rings by Cassini CIRS: Phase, emission and solar elevation dependence     

Nicolas Altobelli  Linda J. Spilker  Cedric Leyrat  Stuart Pilorz 《Planetary and Space Science》2008,56(1):134-146

Two and a half years after Saturn orbit insertion (SOI) the Cassini composite infrared spectrometer (CIRS) has acquired an extensive set of thermal measurements (including physical temperature and filling factor) of Saturn's main rings for a number of different viewing geometries, most of which are not available from Earth. Thermal mapping of both the lit and unlit faces of the rings is being performed within a multidimensional observation space that includes solar phase angle, spacecraft elevation and solar elevation. Comprehensive thermal mapping is a key requirement for detailed modeling of ring thermal properties.To first order, the largest temperature changes on the lit face of the rings are driven by variations in phase angle while differences in temperature with changing spacecraft elevation are a secondary effect. Ring temperatures decrease with increasing phase angle suggesting a population of slowly rotating ring particles [Spilker, L.J., Pilorz, S.H., Wallis, B.D., Pearl, J.C., Cuzzi, J.N., Brooks, S.M., Altobelli, N., Edgington, S.G., Showalter, M., Michael Flasar, F., Ferrari, C., Leyrat, C. 2006. Cassini thermal observations of Saturn's main rings: implications for particle rotation and vertical mixing. Planet. Space Sci. 54, 1167-1176, doi: 10.1016/j.pss.2006.05.033]. Both lit A and B rings show that temperature decreases with decreasing rings solar elevation while temperature changes in the C ring and Cassini Division are more muted. Variations in the geometrical filling factor, β, are primarily driven by changes in spacecraft elevation. For the optically thinnest region of the C ring, β variations are found to be nearly exclusively determined by spacecraft elevation. Both a multilayer and a monolayer model provide an excellent fit to the data in this region. In both cases, a ring infrared emissivity >0.9 is required, together with a random and homogeneous distribution of the particles. The interparticle shadowing function required for the monolayer model is very well constrained by our data and matches experimental measurements performed by Froidevaux [1981a. Saturn's rings: infrared brightness variation with solar elevation. Icarus 46, 4-17].  相似文献   

Surfaces and atmospheres of the outer planets, their satellites and ring systems     

Athena Coustenis  Sushil Atreya  Cécile Ferrari  Linda Spilker 《Planetary and Space Science》2008,56(1):1-2

  相似文献   

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation,Gale crater,Mars     

Kathryn M. Stack  John P. Grotzinger  Michael P. Lamb  Sanjeev Gupta  David M. Rubin  Linda C. Kah  Lauren A. Edgar  Deirdra M. Fey  Joel A. Hurowitz  Marie McBride  Frances Rivera‐Hernndez  Dawn Y. Sumner  Jason K. Van Beek  Rebecca M. E. Williams  Robin Aileen Yingst 《Sedimentology》2019,66(5):1768-1802

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10³ to 10⁷ Earth years.  相似文献   

Incorporating inland flooding into hurricane evacuation decision support modeling     

Yang  Kun  Davidson  Rachel A.  Vergara  Humberto  Kolar  Randall L.  Dresback  Kendra M.  Colle  Brian A.  Blanton  Brian  Wachtendorf  Tricia  Trivedi  Jennifer  Nozick  Linda K. 《Natural Hazards》2019,96(2):857-878

Natural Hazards - Formal engineering hurricane evacuation studies have not typically considered inland flooding explicitly, though it has been shown repeatedly to be a major cause of damage and...  相似文献   

Use of plants in the European Palaeolithic: A review of the evidence     

Joyce A. Tyldesley  Paul G. Bahn 《Quaternary Science Reviews》1983,2(1):53-81

The varied evidence available for the different uses to which plant materials were put during the European Palaeolithic is summarised. Actual remains of plants are more abundant than is generally realised, while the indirect clues provided by tools, human teeth and artistic depictions help to fill out the picture.  相似文献   

An estuarine benthic index of biotic integrity (B-IBI) for Chesapeake Bay   总被引：2，自引：0，他引：2  

Stephen B. Weisberg  J. Ananda Ranasinghe  Daniel M. Dauer  Linda C. Schaffner  Robert J. Diaz  Jeffrey B. Frithsen 《Estuaries and Coasts》1997,20(1):149-158

A multimetric benthic index of biotic integrity (B-IBI) was developed using data from five Chesapeake Bay sampling programs conducted between 1972 and 1991. Attributes of the index were selected by comparing the response of 17 candidate measures of benthic condition (metrics) between a set of minimally affected reference sites and at all other sites for which data were available. This procedure was conducted independently for each of seven habitats defined by salinity and substrate. Fifteen of the 17 candidate metrics differed significantly between reference sites and other sites for at least one habitat. No metric differed significantly in all seven habitats; however, four metrics, species diversity, abundance, biomass, and percent of abundance as pollution-indicative taxa, differed in six habitats. The index was calculated by scoring each selected metric as 5, 3, or 1 depending on whether its value at a site approximated, deviated slightly from, or deviated greatly from conditions at the best reference sites. Validation based on independent data collected between 1992 and 1994 indicated that the index correctly distinguished stressed sites from reference sites 93% of the time, with the highest validation rates occurring in high salinity habitats.  相似文献   

Raised Coral Terraces at Malakula, Vanuatu, Southwest Pacific, Indicate High Sea Level During Marine Isotope Stage 3   总被引：2，自引：0，他引：2  

Guy Cabioch  Linda K Ayliffe   《Quaternary Research》2001,56(3)

The occurrence of a series of raised coral reefs from the uplifted island of Malakula (Vanuatu, SW Pacific) provide an opportunity to examine sea-level fluctuations over at least the past 120,000 years. Thirteen fossil coral samples from Malakula were analyzed by the thermal ionization mass spectrometry (TIMS) U/Th dating technique, yielding information on sea levels during late marine isotope stage 3 and early stage 4. Our findings are in good agreement with sea-level estimates from raised coral terraces in Papua New Guinea and the recent sea-level reconstruction from the deep-sea sedimentary δ¹⁸O records. In particular, our coral data appear to confirm that sea levels at about 45,000–50,000 yr B.P. were only 30 to 60 m below the present level. Combined with other evidence of sea-level change, our data provide a strong case for much higher sea levels and therefore markedly reduced continental ice volume at 47,000 to 49,000 years ago.  相似文献   

The Upper Pennsylvanian Pittsburgh Coal Bed: Resources and Mine Models     

Watson  William D.  Ruppert  Leslie F.  Tewalt  Susan J.  Bragg  Linda J. 《Natural Resources Research》2001,10(1):21-34

The U.S. Geological Survey recently completed a digital coal resource assessment model of the Upper Pennsylvanian Pittsburgh coal bed, which indicates that after subtracting mined-out coal, 16 billion short tons (14 billion tonnes) remain of the original 34 billion short tons (31 billion tonnes) of coal. When technical, environmental, and social restrictions are applied to the remaining Pittsburgh coal model, only 12 billion short tons (11 billion tonnes) are available for mining. Our assessment models estimate that up to 0.61 billion short tons (0.55 billion tonnes), 2.7 billion short tons (2.4 billion tonnes), and 8.5 billion short tons (7.7 billion tonnes) could be available for surface mining, continuous mining, and longwall mining, respectively. This analysis is an example of a second-generation regional coal availability study designed to model recoverability characteristics for all the major coal beds in the United States.  相似文献