新疆吉木萨尔大龙口非海相二叠系—三叠系界线层段古地磁特征

通过对吉木萨尔县大龙口非海相二叠系-三叠系界线上下地层磁性特征的研究,在梧桐沟组-锅底坑组共发现78个极性异常,其中以负极性为主,间隔了一系列的正极性和过渡极性.梧桐沟组上部以负极性为主,间隔了2个正极性和过渡极性.这可与巴基斯坦盐岭和四川广元上寺的大隆组下部对比,即相当于Da段.梧桐沟组顶部和锅底坑组底部,正、负极性变化频繁,极性特征可与巴基斯坦盐岭和四川广元上寺大隆组中部对比,即相当于Db段.锅底坑组下部以负极性为主,间隔了2个正极性段,可与四川广元上寺大隆组中上部对比,即相当于Dc段.锅底坑组中下部以负极性为主,上部夹1个正极性段,可与四川广元上寺大隆组上部磁性特征对比,即相当于Dd段.锅底坑组中上部以负极性为主,间隔了4个正极性段,可与四川广元上寺飞仙关组下部对比,即相当于Fa段.根据磁性段的划分对比,将二叠系三叠系界线置于Fa和Dd之间,即本次研究测制剖面的41层和42层之间.根据各岩组的古地磁特征求得岩组形成时的古地磁极:梧桐沟组79.1°N,238.1°;锅底坑组72.3°N,322.2°;下三叠统77.5°N,320.8°.古纬度基本一致,为32°～35°N.     

Magnetostratigraphy of the Middle–Upper Cambrian Verkhnyaya Lena Group and Lower Ordovician Ust-Kut formation in the southern Siberian Platform

The available paleomagnetic data on the Verkhnyaya Lena Group from different areas of the southern Siberian Platform are revised. The group rests unconformably upon the Lower Cambrian strata and is overlain by Lower Ordovician rocks, which determines conditionally the age of its red-colored deposits. Paleomagnetic correlation of composite sections through the region using defined zones of normal and reversed magnetic polarity serves as a basis for development of the magnetostratigraphic scale for the Verkhnyaya Lena Group. The scale includes nine magnetic zones, which play the role of markers; seven of them are traceable in all the examined sections of the southern Siberian Platform. By the distribution of zones with normal (N) and reversed (R) polarity, the magnetostratigraphic scale is subdivided into three parts. Its lower part is represented by reversed polarity, which is characteristic of the second half of the Lower Cambrian. The middle part is characterized by frequently alternating zones with normal and reversed polarity corresponding to the Middle Cambrian. The upper part of the scale corresponds to the interval of reversed polarity characteristic of the Upper Cambrian and Lower Ordovician. The Middle–Upper Cambrian boundary is located near the last N–R reversal of the geomagnetic field in the Cambrian. The magnetostratigraphic scale includes nine orthozones united into three superzones, which are attributed to two hyperzones of magnetic polarity.     

印度阶-奥伦尼克阶界线层型候选剖面--安徽巢湖平顶山西剖面地层序列

位于安徽省中部巢湖市郊的平顶山西剖面被推荐为印度阶-奥伦尼克阶界线的全球层型候选剖面。系统记述了该剖面的地层序列,包括岩石地层、生物地层、磁性地层、碳氧同位素地层和旋回地层等方面的最新研究成果。该剖面包括3个岩石地层单元、7个牙形石带、5个菊石带、3个双壳类带;在剖面下段地层中识别出2个正向磁性带和2个反向磁极性带;与地球轨道天文周期相对应的Milankovitch气候沉积旋回也可以明确地辨认;碳氧同位素δ1 3Ccarb演变呈现两次大的旋回。以牙形石N eospathodus waageni首现定义的印度阶-奥伦尼克阶界线在该剖面上位于三叠系第二个主要的正向极性带近顶部,也接近三叠纪碳同位素δ1 3Ccarb首次正向漂移峰值处     

Paleomagnetism and magnetostratigraphy of Upper Cretaceous and Cretaceous-Paleogene boundary intervals,southern Kulunda basin (West Siberia)

The study presents new paleomagnetic data on the Upper Cretaceous and Cretaceous-Paleogene boundary intervals of the southern Kulunda basin (Alei area), which were obtained from core samples collected from a 305-m-thick section penetrated in two wells. The paleomagnetic sections of each well were compiled and correlated based on the characteristic remanent magnetization (ChRM). Paleomagnetic, geological, stratigraphic, and paleontological data were used to compile the Upper Cretaceous and Cretaceous-Paleogene magnetostratigraphic section of the southern Kulunda basin. The magnetostratigraphic section consists of five magnetozones, one normal polarity zone, and four reversed polarity zones spanning the Upper Cretaceous and Lower Paleogene. The lower part of the Gan’kino Horizon, showing normal polarity, forms a single normal polarity magnetozone N. The upper part of the Gan’kino Horizon comprises two reversed polarity magnetozones (R₁km and R₂mt). The Talitsa and Lyulinvor Formations of Lower Paleogene age correspond to two reversed polarity magnetozones (R₁zl and R₂i). The compiled Upper Cretaceous and Lower Paleogene magnetostratigraphic section was correlated with the geomagnetic polarity time scale. Two options were considered for correlating the lower normal polarity part of the section with geomagnetic polarity time scale of Gradstein.     

Magnetostratigraphic Study of Meishan Permian-Triassic Section, Changxing, Zhejiang Province, China

INTRODUCTIONBecause many P/ T boundary sections around the worldare stratigraphically unconformed,som e possible exceptionsdeveloped in Greenland,Iran,Russia and South China are ofcourse of international importance.Especially successive sedi-ments from the L ate Paleozoic to Early Mesozoic widely ap-peared in South China,for example,the Meishan Section inChangxing County,Zhejiang Province,and som e analogies inGuangyuan,Wulong and Shangsi counties,Sichuan Province.Some geologists…     

The Permian–Triassic boundary in the Central European Basin: magnetostratigraphic constraints

Some stratigraphic interpretations concerning correlation of the Permian–Triasssic transition beds from the Central European, Boreal and Tethyan Basins are inconsistent with the existing magnetostratigraphic data. In addition, the suggestion that the Permian–Triassic boundary is located in the lower part of the Calvörde Formation of the Central European Basin cannot be supported by magnetostratigraphic data. Results of magnetostratigraphic correlation show that in the Polish part of the Central European Basin the Permian–Triassic boundary is close to the boundary between the uppermost Zechstein and the Lower Buntsandstein. It is located within the reversed magnetozone ‘PZr1’ identified in the upper part of the Rewal Formation. In the German part of the Central European Basin the Permian–Triassic boundary can be located within the reversed magnetozone ‘zrz’ that covers most of the Bröckelschiefer. A higher stratigraphic location of this boundatry, i.e. inside the lowermost Buntsandstein, requires a reversed polarity record to be found within the basal Triassic normal polarity zone.     

哈尔滨荒山剖面第四纪地层研究

哈尔滨荒山剖面是东北地区第四纪典型剖面,因缺乏绝对年龄数据,关于其地层划分及时代还有不同认识.对荒山剖面进行了系统的磁性地层学研究,并与AMS14C、OSL等年代学数据相结合,重新厘定了荒山剖面第四纪地层的年代框架.结果表明,荒山剖面记录了Matuyama负极性时晚期至Brunhes正极性时的沉积,B/M界线位于剖面下部46.7 m,剖面起始沉积年龄早于0.90 Ma.根据AMS14C和OSL年龄确定了全新统和上更新统的底界,对第四纪岩石地层单位的分层标志及顶、底年龄进行了分析,确定第四纪各个岩石地层单位的时代分别为:坦途组的年龄为~12 ka BP,顾乡屯组的年龄为12~79 ka BP,哈尔滨组的年龄为79~138 ka BP,上荒山组的年龄为138~580 ka BP,下荒山组的年龄>900 ka BP.据此建立了荒山剖面第四纪地层系统,为区域地层对比提供依据.      

四川茂县较场湖相沉积磁性地层初步研究

四川茂县较场剖面厚101.1m,其中湖相沉积厚98.0m,为一套浅黄色-灰色的粉砂、粘土质粉砂和粉砂质粘土层。古地磁测试显示,除2个样品的磁偏角显示负极性外,其余样品的磁偏角全部为正,属布容正极性时,没有出现B/M界线。根据该套地层的岩性、岩相和所处的地貌部位,可以和云南金沙江谷地的龙街组对比,推测其开始沉积的时代为100~120 kaBP.另外,距顶4.0 m处光释光年龄为16.7±1.2 kaBP,推测其结束于10kaBP.湖相沉积历时约100kaBP,是岷江流域出露的末次(间)冰期以来厚度最大的剖面之一。      

准噶尔盆地第三纪磁性地层柱的建立

通过对新疆准噶尔盆地第三系３个剖面古地磁样品的分析、测试，在生物地层学研究的基础上，建立了一条较为完整的第三纪磁性地层柱，标定了各组地质年代，为在不同盆地进行对比，提供了新的依据。     

川滇陆相侏罗系—白垩系界线划分

云南禄丰川街剖面侏罗系-白垩系混合磁极性超带的M19极性带位于安宁组下段顶部．四川泸州纳溪剖面M18r级性亚带位于蓬莱镇组二段上部。上述古地磁界线与马门溪龙、叶肢介、双壳类等所形成的生物界线相吻合。因此陆相侏罗系-白垩系界线在滇中被置于安宁组下段与上段之间或妥甸组上段的2个亚段之间;在四川此界线则被置于蓬莱镇组第二段的中上部。     

新近系谢家阶层型剖面古地磁年代学研究

古地磁测量表明,中国新近系谢家阶界线层型剖面——西宁盆地谢家剖面共记录了18个正极性段与17个负极性段,与标准极性柱中C5Bn.2n—C7n.1n之间的极性带能很好的对应。剖面中谢家组的年龄为17.32—21.58Ma,谢家哺乳动物群的年龄约为21Ma,相当于MN2中期。     

Magnetic polarity stratigraphy of the Pleistocene section at Portland (Victoria), Australia

Three to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along with Globorotalia truncatulinoides within the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre-¹⁴C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.     

The Ensenada and Buenos Aires formations (Pleistocene) in a quarry near La Plata,Argentina

An interdisciplinary study of a section in a quarry near La Plata sheds new light on the geologic, climatic, and biologic evolution of the northeastern Pampean area of Argentina. The stratigraphic succession is composed of seven mainly eolian levels, each one including a soil and separated by a disconformity. Two geosols defined in northern Buenos Aires Province (Hisisa and El Tala) are identified in the Ensenada Formation. The boundary between the Ensenada and Buenos Aires formations is defined by a conspicuous disconformity which overlies the El Tala Geosol. In the section, the boundary between the Tolypeutes pampaeus (Ensenadan) and Megatherium americanum (lower Lujanian) biozones coincides with that of Ensenada and Buenos Aires formations. The boundary between the Matuyama and Brunhes zones of polarity occurs in the upper part of the Ensenada Formation above the Hisisa Geosol. According to geologic evidence, most of the succession was deposited under semiarid to arid climate.     

二连盆地下古近系的磁性地层学研究

古地磁的测试结果表明,蒙古高原二连盆地努和廷勃尔和与呼和勃尔和地区剖面早古近纪地层共记录了5个正极性段与6个负极性段,通过与2004年标准极性年代表对比,确认其可与C21r-C26r之间的极性带对应。脑木根组以晚古新世沉积为主,同时接受了始新世最早期部分沉积及少许中古新世;阿山头组跨越了早—中始新世,持续时间较长;伊尔丁曼哈组的时代为中始新世。同时,确定了含Lambdopsalis,Prionessus及Palaeostylops的化石层的时代为晚古新世最早期;Gomphos层的年龄大致与古新世-始新世界线的年龄相当。     

二叠系长兴阶全球界线层型剖面和点位

二叠系乐平统长兴阶底界全球界线层型和点位(GSSP)确立在我国浙江长兴煤山D剖面长兴灰岩的下部、4a-2层之底,以牙形石演化序列Clarkina longicuspidata-C.wangi中C.wangi的首现为标志。该点位位于长兴组底界之上88cm处,与长兴期特征的■类化石Palaeofusulina sinensis和大巴山菊石类的首次出现层位一致。界线层的碳同位素存在明显的负漂移,正磁极性带出现在吴家坪晚期的反极性带之上。在煤山D剖面以西300m处的C剖面出露较多的龙潭组地层,清晰地反映出龙潭组—长兴组连续的沉积序列,被列为辅助层型剖面。     

旱峡剖面新民堡群的古地磁学研究

根据岩石剩磁测试资料所反映的古地磁场极性变化特征,甘肃玉门旱峡剖面原先厘定为下白垩统的新民堡群包括7个正向极性亚时带和7个反向极性亚时带。通过与国际中生代极性年表和深海沉积物极性年表的对比,新民堡群实际上可分为两个地层单位:以第三个反向极性亚时带为界(从下往上数),下部层段属于上侏罗说(厚约460m),上部层段属下白垩统(厚约636m)。剖面玄武岩脉的喷溢时代应早于中新世,晚于旱白垩世,分为两期岩浆活动。     

Magnetic polarity stratigraphy of the middle Pleistocene (Ensenadan) Tarija Formation of southern Bolivia

The Tarija Formation of southern Bolivia, which is well known for its classic vertebrate faunas, is of prime importance in understanding of the chronology of the Ensenadan Land Mammal Age. This formation consists of well-exposed and relatively fossiliferous sections of clays, clayey silts, sands, gravels, and tuffs which were deposited in a predominately fluviatile regime in a Pleistocene structural basin. Four stratigraphic sections, each measuring 110 m or less, were studied to establish a magnetic polarity stratigraphy. Paleomagnetic samples were collected from the finer-grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less. All paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds (oe). Some specimens were also thermally demagnetized at 200°C or more. Of the 100 sites, 77 were ultimately used to determine the magnetic polarity zonation. Based on the four sections sampled, the Tarija Formation spans a time interval from about 1 my to about 0.7 my B.P. or perhaps younger. The lower half of the composite section is of reversed polarity punctuated by a short normal event. This sequence probably represents the late Matuyama chron with the Jaramillo subchron. The upper part of the section is of normal polarity and represents early Brunhes time. A tuffaceous unit 43 m above the Brunhes-Matuyama boundary yielded a fission track (zircon) age of 0.7 ± 0.2 by B.P. These data indicate that the classic Tarija fauna is middle Pleistocene Ensendan in age.     

中国北方陆相沉积5.30Ma磁性地层序列

本文通过中国北方新第三纪晚期典型剖面的磁性地层研究,建立５．３０Ｍａ以来中国北方陆相沉积积磁性地层序列。中国黄土记录了Ｂｒｕｎｈｅｓ正极性带与Ｍａｔｕｙａｍａ负极性带,年龄约２．５０Ｍａ。静乐红土（包括静乐剖面,榆林剖面,蓝田剖面）对应于Ｇａｕｓｓ正极性带与Ｇｉｌｂｅｒｔ负极性带,年龄约２．５０￣５．３０Ｍａ。三门组记录了Ｍａｔｕｙａｍａ负极性带下段,年龄约１．２０￣２．５０Ｍａ。游河组记录了Ｇａ     

华北吕梁地区汉高山群和小两岭组的地层时代——火山岩锆石U-Pb年龄的约束

华北吕梁地区出露的以陆源碎屑沉积为主的汉高山群为中元古界底界界线层型的理想候选剖面,其时代的确定对认识华北前寒武纪地质演化历史及初始盖层的确定及Nuna超大陆聚散的研究具有重要的意义.目前,汉高山群的时代、划分对比及其意义还存在较大争议.本研究使用SHRIMP(二次离子质谱仪)对汉高山群安山岩中的锆石进行了 U-Pb同...