【正文】 ailable online 23 May 2005Abstract A detailed magnetostratigraphic investigation, coupled with rockmagnetic studies, was carried out on a lacustrine sequence in the eastern Nihewan Basin, Northern China, which contains the Donggutuo and Maliang Paleolithic sites. Magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the lacustrine sequence recorded the late Matuyama and Brunhes chrons. Furthermore, the Maliang artifact layer occurs just below the Brunhes/Matuyama boundary, and the Donggutuo artifact layer is just below the Jaramillo onset. Therefore, the age of the Maliang and Donggutuo artifact layers can be definitely estimated to be about myr and myr, respectively. These two paleomagnetic ages, coupled with previously obtained paleomagnetic data of the Majuangou, Xiaochangliang, Banshan, Lantian, and Xihoudu Paleolithic sites, suggest an expansion and lengthy flourishing of human groups from northern to northcentral China during the entire Early Pleistocene. D 2005 University of Washington. All rights reserved.Keywords: Magnetostratigraphy。 Paleolithic site。 Pleistocene。 Donggutuo。 Maliang。 Nihewan Basin。 North China40Ar/39Ar 年代學(xué)國際國內(nèi)標(biāo)樣的對比標(biāo)定王非 賀懷宇 朱日祥 桑海清 王英蘭 楊列坤(中國科學(xué)院地質(zhì)與地球物理研究所, 北京 100029)摘 要 對四個40Ar/39Ar年齡測定中常用的國際標(biāo)樣Ga1550MMhb1,Lp6, Bern 4M(以Ga1550為基準(zhǔn)樣)和一個國內(nèi)標(biāo)樣BT1(以Lp6為基準(zhǔn)樣),。 Bern 4M 和Lp6的測定結(jié)果表明它們具有穩(wěn)定的40Ar*/39Ak(F值), 所得的年齡結(jié)果接近它們的KAr年齡值: Lp6= Ma。 Bern 4M= Ma。 BT1的年齡譜, Ca/K和C1/K譜以及反等時線的分機(jī)表明,這一樣品的化學(xué)相均勻穩(wěn)定,樣品封閉良好,初始Ar組成接近大氣值,年齡值重復(fù)性好且穩(wěn)定,它的全熔年齡,階段升溫總氣體年齡,坪年齡和反等時線年齡在誤差(2σ)范圍內(nèi)無差別, Ma為BT1的標(biāo)定值.討論了北京492原子能反應(yīng)堆中子量變化情況,結(jié)果表明該反應(yīng)堆中子通量梯度變化大且不穩(wěn)定,須較多的標(biāo)準(zhǔn)進(jìn)行監(jiān)測。測定了該反應(yīng)堆37ArCa和39Ark的產(chǎn)率比系數(shù)(Ca/K轉(zhuǎn)化系數(shù)),這可能和后期492反應(yīng)堆的改造有關(guān).Paleomagnetic and paleointensity study of an Oligocene–Miocenelava sequence from the Hannuoba Basalts in northern ChinaYongxin Pan a,?, Mimi J. Hill b,1, Rixiang Zhuaa Paleomagnetism Laboratory (SKLLTE), Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, Chinab Geomagnetism Laboratory, Department of Earth and Ocean Science, University of Liverpool, Liverpool L69 7ZE, UKReceived 26 July 2004。 received in revised form 16 December 2004。 accepted 29 December 2004Abstract A bined geochronologic, paleomagnetic and paleointensity investigation has been performed on a lava sequence from the Hannuoba Basalts in northern China. Potassium–argon (K–Ar) dating indicates that the lava sequence is of late Oligocene to middle Miocene age (～24–15 Ma). Rock magnetic measurements of thermomagnetic curves, hysteresis properties, saturation isothermal remanent magnetization (SIRM) and backfield demagnetization on representative samples from each lava flow in conjunction with reflected light microscopy observations show the primary carriers of remanence to be finegrained pseudosingle domain titanomagnetite with various titanium contents. Stepwise thermal and alternating field demagnetization successfully isolated stable characteristic remanent magnetization from 40 out of the 43 lava flows, which record 24 paleomagneticallyindependent directions. Data (excluding directions regarded as abnormal/transitional) yield a mean direction of D/I = ?/?, with α95 = ? and κ = , corresponding to a paleomagnetic pole at ?E, ?N with dp = ? and dm = ?, consistent with previously published paleomagnetic poles for the North China Block. The modified Thellier method with systematic partial thermoremanent magnetization (pTRM) checks and pTRMtail checks was conducted on 72 selected samples. Reliable paleointensity estimates from four lava flows yield a mean virtual dipole moment of (177。)1022Am2, suggesting moderately low intensity of the geomagnetic field. This is in good accord with reliable paleointensity datasets for the late Oligocene to middle Miocene (30–15 Ma), but lower than the average for middle Miocene to Pliocene age (15–2 Ma). It thus appears that at some point in the midMiocene there was a transition where the field intensity changes between these two states, although many more data are needed to confirm this. 169。 2005 Elsevier . All rights reserved.Partial anhysteretic remanent magnetization (pARM) of synthetic single and multidomain magnetites and its paleoenvironmental significance LIU Qingsong1,2,3 YU Yongjae4 Pan Yongxin2 Zhu Rixiang2 Zhao Xixi31. Institute for Rock Magnetism and Department of Geology and Geophysics, University of Minnesota,MinneapolisMN 55455,USA 2. Paleomagnetism and Geochronology Laboratory (SKLLE), Institute of Geology and Geophysics, Chinese Academy of Sciences,Beijing100029,China 3. Department of Earth Sciences and Institute of Geophysics and Planetary Physics, University of California,Santa CruzCA95064,USA 4. Geosciences Research Division, Scripps Institution of Oceanography,La JollaCA,USAAbstract：In order to isolate magnetic signals carried by singledomain (SD) ferrimagnetic (FM) minerals from multidomain (MD) FM minerals, we developed a few parameters using partial anhysteretic remanent magnetization (pARM). Because MD fraction contains only soft (easy to be demagnetized) coercivity spectrum, pARM(20 mT) was sensitive in eliminating MD contributions. Ratio of pARM(5 mT, 10 mT)/pARM(0, 5 mT) is useful in quantifying a relative abundance of mass ratio between SD and MD fractions. These new proxies can quickly characterize the details of grain size distribution of magnetic minerals in paleoclimatic and paleomagnetic studies.利用相對靜力學(xué)強(qiáng)度測定1998年5月11日印度核爆的當(dāng)量趙連鋒 王衛(wèi)民 李娟 姚振興中國科學(xué)院地質(zhì)與地球物理研究所, 北京, 100029摘 要 核爆當(dāng)量是核試驗的重要參數(shù)之一。許多地震學(xué)家對1998年5月11日在印度的Pokhran地區(qū)的核試驗（POK2）進(jìn)行研究，給出了12~60Kt的當(dāng)量估計，近5倍的估計偏差引起了較為廣泛的關(guān)注?；谌驍?shù)字地震臺網(wǎng)寬頻帶體波資料，我們通過波形反演計算等效震源模型參數(shù)，包括靜力學(xué)強(qiáng)度、特征頻率、以及震源深度和P波在自由表面的反射系數(shù)，并利用相對的靜力學(xué)強(qiáng)度估算了POK2事件的當(dāng)量。我們發(fā)現(xiàn)Lay [1]在美國Nevada試驗場（NTS）獲得的相對靜力學(xué)強(qiáng)度與當(dāng)量的經(jīng)驗公式更適合印度核試驗當(dāng)量估計，并據(jù)此計算了這次試驗的當(dāng)量約36千噸（Kt）。這一結(jié)果支持1998年