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B. Gary Hoyle Daniel C. Fisher Harold W. Borns Jr. Lisa L. Churchill-Dickson Christopher C. Dorion Thomas K. Weddle 《Quaternary Research》2004,61(3):277-288
Remains identified as those of a woolly mammoth (Mammuthus primigenius) dated at 12,200 ± 55 14C yr B.P. were recovered while excavating in a complex sequence of glaciomarine sediments in Scarborough, Maine, USA. The mammoth was found in the top meter of a fossiliferous unit of mud and sand laminites. These sediments were deposited during a marine regressive phase following the transgression that accompanied northward retreat of the margin of the Laurentide ice sheet. A Portlandia arctica valve from the underlying transgressive unit provides a minimum age of 14,820 ± 105 14C yr B.P. for local deglaciation. The mammoth, an adult female, died in midwinter with no evidence of human involvement. Tusk growth rates and oxygen-isotope variation over the last few years of life record low seasonality. The mammoth was transported to the site as a partial carcass by the late-glacial proto-Saco River. It sank in a near-shore setting, was subjected to additional disarticulation and scattering of elements, and was finally buried in sediments reworked by the shallowing sea. 相似文献
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Two mammoth sites from the central Great Plains of North America, each containing one adult Columbian mammoth (Mammuthus columbi), were excavated from Last Glacial Maximum (LGM) loess and fine-grained alluvial deposits, respectively. Taphonomic data from both sites indicate that the mammoth skeletons exhibit numerous spirally fractured limb elements. Dynamic loading points are present on midshafts of large limb bones. Bone flakes produced from the partial thickness of thick cortical bone are also present. Hypotheses of carnivore activity, mammoth trampling, and human-induced fracturing are evaluated as possible causes of the fractured limb bone. Testing the hypotheses using modern data from actualistic taphonomic studies of elephant skeletons, paleontological data from two proboscidean natural death sites, experimental data from elephant bone fracturing, and archaeologically derived data concerning late Pleistocene human modification of mammoth limb bone indicates that the first two hypotheses can be rejected, while the third hypothesis is supported. 相似文献
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Seismicity pattern in north Sumatra-Great Nicobar region: In search of precursor for the 26 December 2004 earthquake 总被引:1,自引:0,他引:1
Sujit Dasgupta Basab Mukhopadhyay Auditeya Bhattacharya 《Journal of Earth System Science》2007,116(3):215-223
We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant,
intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found
to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day
short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term
quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991)
of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just
before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake. 相似文献
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The ecological implications of a Yakutian mammoth's last meal 总被引:1,自引:0,他引:1
Bas van Geel Andr Aptroot Claudia Baittinger Hilary H. Birks Ian D. Bull Hugh B. Cross Richard P. Evershed Barbara Gravendeel Erwin J.O. Kompanje Peter Kuperus Dick Mol Klaas G.J. Nierop Jan Peter Pals Alexei N. Tikhonov Guido van Reenen Peter H. van Tienderen 《Quaternary Research》2008,69(3):361-376
Part of a large male woolly mammoth (Mammuthus primigenius) was preserved in permafrost in northern Yakutia. It was radiocarbon dated to ca. 18,500 14C yr BP (ca. 22,500 cal yr BP). Dung from the lower intestine was subjected to a multiproxy array of microscopic, chemical, and molecular techniques to reconstruct the diet, the season of death, and the paleoenvironment. Pollen and plant macro-remains showed that grasses and sedges were the main food, with considerable amounts of dwarf willow twigs and a variety of herbs and mosses. Analyses of 110-bp fragments of the plastid rbcL gene amplified from DNA and of organic compounds supplemented the microscopic identifications. Fruit-bodies of dung-inhabiting Ascomycete fungi which develop after at least one week of exposure to air were found inside the intestine. Therefore the mammoth had eaten dung. It was probably mammoth dung as no bile acids were detected among the fecal biomarkers analysed. The plant assemblage and the presence of the first spring vessels of terminal tree-rings of dwarf willows indicated that the animal died in early spring. The mammoth lived in extensive cold treeless grassland vegetation interspersed with wetter, more productive meadows. The study demonstrated the paleoecological potential of several biochemical analytical techniques. 相似文献
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The maximum magnitude, the activity rate, and the Gutenberg-Richterb parameter as earthquake hazard parameters, have been evaluated for Sweden. The maximum likelihood method permits the combination of historical and instrumental data. The catalog used consists of 1100 earthquakes in the time interval 1375–1989. The extreme part of the catalog contains only the strongest historical earthquakes, whereas the complete part is divided into several subcatalogs, each assumed complete above a specified threshold magnitude. The uncertainty in magnitude determination was taken into account. For southern Sweden, the calculations giveb-values of 1.04 (0.05) for the whole area south of 60° N and 0.98 (0.06) for a subregion of enhanced seismicity in the Lake Vänern area. For the whole area north of 60° N, theb-value is 1.35 (0.06) and for the seismicity zone along the Gulf of Bothnia 1.26 (0.06). The number of annually expected earthquakes with magnitude equal to or larger than 2.4 [ML(UPP) or MM(UPP)] is 1.8 for the whole southern Sweden, 1.3 for the Lake Vänern region, 3.7 for northern Sweden, and 2.4 for the region along the Gulf of Bothnia. The maximum expected regional magnitude is calculated to 4.9 (0.5) for a time span of 615 years for southern Sweden and the Lake Vänern subregion, and 4.3 (0.5) for a time span of 331 years for northern Sweden and the Gulf of Bothnia subregion. However, several historical earthquakes with magnitude above 5 in nearby areas of Norway indicate that the seismic potential may be higher. 相似文献
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The occurrence of pyrochlorophyll a and pyrophaeophytins a and b in the bottom sediments of a small eutrophic lake (Priest Pot, Cumbria, U.K.) is reported on the basis of HPLC coinjection with standards. Assignment of pyrophaeophytins a and b was confirmed by FAB mass spectrometric and nuclear magnetic resonance studies of the isolated components and comparison with standards. The co-occurrence of pyrochlorins with their non-pyro counterparts, even in a surface sediment, shows that decarbomethoxylation can occur at the very earliest stages of the Treibs diagenetic pathway linking the chlorophylls and sedimentary porphyrins. 相似文献
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Probabilistic seismic hazard analysis for Bangalore 总被引:5,自引:3,他引:2
This article presents the results of probabilistic seismic hazard analysis (PSHA) for Bangalore, South India. Analyses have
been carried out considering the seismotectonic parameters of the region covering a radius of 350 km keeping Bangalore as
the center. Seismic hazard parameter ‘b’ has been evaluated considering the available earthquake data using (1) Gutenberg–Richter (G–R) relationship and (2) Kijko
and Sellevoll (1989, 1992) method utilizing extreme and complete catalogs. The ‘b’ parameter was estimated to be 0.62 to 0.98 from G–R relation and 0.87 ± 0.03 from Kijko and Sellevoll method. The results
obtained are a little higher than the ‘b’ values published earlier for southern India. Further, probabilistic seismic hazard analysis for Bangalore region has been
carried out considering six seismogenic sources. From the analysis, mean annual rate of exceedance and cumulative probability
hazard curve for peak ground acceleration (PGA) and spectral acceleration (Sa) have been generated. The quantified hazard
values in terms of the rock level peak ground acceleration (PGA) are mapped for 10% probability of exceedance in 50 years
on a grid size of 0.5 km × 0.5 km. In addition, Uniform Hazard Response Spectrum (UHRS) at rock level is also developed for
the 5% damping corresponding to 10% probability of exceedance in 50 years. The peak ground acceleration (PGA) value of 0.121 g
obtained from the present investigation is slightly lower (but comparable) than the PGA values obtained from the deterministic
seismic hazard analysis (DSHA) for the same area. However, the PGA value obtained in the current investigation is higher than
PGA values reported in the global seismic hazard assessment program (GSHAP) maps of Bhatia et al. (1999) for the shield area. 相似文献
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The b-value of the Gutenberg–Richter’s frequency–magnitude relation and the p-value of the modified Omori law, which describes the decay rate of aftershock activity, were investigated for more than 500 aftershocks in the Aksehir-Afyon graben (AAG) following the 15 December 2000 Sultandagi–Aksehir and the 3 February 2002 Çay–Eber and Çobanlar earthquakes. We used the Kandilli Observatory’s catalog, which contains records of aftershocks with magnitudes ≥2.5. For the Çobanlar earthquake, the estimated b-values for three aftershock sequences are in the range 0.34 ≤ b ≤ 2.85, with the exception of the one that occurred during the first hour (4.77), while the obtained p-values are in the range 0.44 ≤ p ≤ 1.77. The aftershocks of the Sultandagi earthquake have a high p-value, indicating fast decay of the aftershock activity. A regular increase of b can be observed, with b < 1.0 after 0.208 days for the Çay–Eber earthquake. A systematic and similar increase and decrease pattern exists for the b- and p-values of the Çobanlar earthquakes during the first 5 days. 相似文献
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Verification of our previous definition of preferred earthquake nucleation areas in Kanto-Tokai, Japan 总被引:2,自引:0,他引:2
We have proposed that points of future initiation of rupture may be mapped, based on minima in local recurrence times, which are equivalent to local maxima in the probability for main shocks to occur. These minima are often controlled by anomalously low b-values (logN = a − bM). Of the Kanto-Tokai area, approximately 12% showed anomalously short recurrence times and was proposed as asperities, based on seismicity up to 1999. During the period 1999–2003.5, about 75% of the earthquakes with M ≥ 3.5 fell into the asperities, earlier defined (for example 19 out of 23 M ≥ 3.8 events). The probability for this to occur by chance is approximately 2 10− 14. This supports our idea that the most likely volumes to produce main shocks may be mapped by minima in local recurrence times. 相似文献