Palaeomagnetic and palaeontological dating of a section at Gioia Tauro,Italy: Identification of the Blake Event

Palaeomagnetic and palaeontological studies on samples withdrawn from a 250-m-long unorientated core from Reggio di Calabria, Italy (38°N, 16°E) are described. The lower 200 m of core penetrated off-shore clays and visual examination of the split sections of core indicated no obvious breaks in deposition. After alternating field demagnetization in 200 Oe the palaeomagnetic inclination log shows the Brunhes/Matuyama boundary at 110 m below which the Jaramillo and Olduvai Events within the Matuyama Epoch are identified. This interpretation of the magnetostratigraphy is supported by palaeontological evidence. The rate of accumulation of clay is estimated to have ranged between about 60 and 190 mm/kyr with an overall average through the Matuyama Epoch of about 90 mm/kyr. Assuming that this average rate continued through the Brunhes Epoch, the age of the top of the clay unit is estimated to be about 90,000 yr B.P. About 5 m from the unconformable top surface of the clay, a split sequence of reversed inclinations is interpreted as a record of the Blake Event, and the overall average deposition rate implies that its duration may have been as long as 50,000 yr. No other reversed event is recorded by the palaeomagnetic inclination log through the Brunhes Epoch, though there are four horizons where shallow positive inclinations are recorded.     

Magnetic polarity stratigraphy of the Fisherman's Cliff and Bone Gulch vertebrate fossil faunas from the Murray Basin, New South Wales, Australia

The Fisherman's Cliff and Bone Gulch Local Faunas are the second and third oldest mammalian fossil assemblages known in the Murray Basin of southeastern Australia. The determination of well constrained ages for these two faunas has been plagued by a lack of diagnostic microfossils or material suitable for isotopic age determinations. Based on previous paleomagnetic data [1,2] the ages of the Fisherman's Cliff and Bone Gulch local faunas were assigned to the Gauss and lower Matuyama Chrons, respectively. However, these dates were not tested by direct magnetostratigraphic studies at either locality. In order to make direct correlations, 22 paleomagnetic and five paleomagnetic sites, respectively, were collected from Fisherman's Cliff and Bone Gulch. Results indicate that the Fisherman's Cliff Local Fauna occurs within a zone of normal magnetic polarity whilst the Bone Gulch Local Fauna occurs within a zone of reversed polarity. By correlation to the Chowilla section, these zones are interpreted to represent the Gauss and lower Matuyama Chrons and ages of 2.47–2.92 and 1.88–2.47 Myr are indicated for the Fisherman's Cliff and Bone Gulch Local Faunas, respectively.     

A detailed paleomagnetic survey of the type location for the Gilsa geomagnetic polarity event

A total of 163 cores have been taken from a maximum of 40 separate lavas in three separate sections of the Jökuldalur, southwest of Egilsstadir, Iceland, and subjected to paleomagnetic analysis and some K-Ar dating. Previous work on the sections by McDougall and Wensink (1966) led to the establishment of the Gilságeomagnetic polarity event, with an age of about 1.60 m.y., during the reversed polarity Matuyama epoch. This earlier study described a possible reversely magnetized lava separating the Gilsáevent from a second normal polarity lava, perhaps representing the Olduvai event. Such a possibility was subsequently a source of speculation from diverse sources concerning the polarity history for the lower Matuyama. The present study indicates clearly that there is no second normal polarity event represented in the sections. Only one normal polarity event is therefore represented in the lower Matuyama of the Jökuldalur, and the age of the lavas involved is confirmed to be approximately 1.58 ± 0.08 m.y. Because of uncertainties in the interpretation of the original K-Ar results from Olduvai Gorge, it is still not possible to be certain that the Olduvai and Gilsáevents are separated in time. An incidental result of the survey is evidence to show that, contrary to recent suggestions by Einarsson (1972), there is no substantial hiatus between the major lower parts of the section and lavas believed to represent extrusions after a regional tilting and peneplanation.     

Palaeomagnetism of the loess/palaeosol sequence in Viatovo (NE Bulgaria) in the Danube basin

The results of a palaeomagnetic investigation of a 27 m thick loess/palaeosol sequence in Viatovo (NE Bulgaria) are presented in this paper. The sequence consists of topsoil S₀, seven loess horizons (L₁–L₇) and six interbedded palaeosols (S₁–S₆) overlying a red clay (terra rossa) complex. Magnetic viscosity experiments, IRM acquisition, AMS analysis and NRM stepwise alternating and thermal demagnetisation experiments of pilot samples were implemented for precise determination of the characteristic remanence and construction of a reliable magnetostratigraphical scheme. Analysis of IRM acquisition curves using the expectation – maximization algorithm of Heslop et al. [Heslop, D., Dekkers, M., Kruiver, P., van Oorschot, H., 2002. Analysis of isothermal remanent magnetization acquisition curves using the expectation – maximization algorithm. Geophys. J. Int., 148, 58–64] suggests that the best fitting is obtained by three coercivity components. Component 1 corresponds to SD maghemite/magnetite, while component 2 is probably related to the presence of oxidised detrital magnetites. The third component shows varying coercivities depending on the degree of pedogenic alteration of the samples and probably reflects the presence of detrital magnetite grains oxidised at different degree.

The relevance of the Viatovo section as a key representative sequence for the loess cover in the Danube basin is confirmed by the presence of geomagnetic polarity changes in the lower part of the sequence. The youngest one recorded in the seventh loess unit L₇ can be identified as corresponding to the Matuyama/Brunhes palaeomagnetic polarity transition. Two normal magnetozones were found in the red clay complex, probably corresponding to the Jaramillo and Olduvai subchronozones of the Matuyama chron.     

高分辨率洛川剖面黄土磁性地层学

洛川剖面作为经典的黄土剖面,磁极性地层界线的具体位置还不清楚.通过对洛川黄土-古土壤序列以10 cm间隔的古地磁研究,厘定了磁极性界线的具体位置：（1）MB (Matuyama-Brunhes) 界线位于53 m处,S8的上部.（2）Jaramillo位于67.8~72.5 m,上界在S₁₀的上部,其下界位于L₁₃的顶部.（3）Olduvai位于107.2~114.2 m,上界位于S₂₅的顶部,相当于WS₂的上部,其下界位于L₂₉的上部,相当于WL₂的上部.4）并未检测到Matuyama的底界,可能位于红粘土内.     

中国黄土与红色粘土记录的地磁极性界限及地质意义

本文报道由蓝田、陕县、洛川、西峰、平凉、兰州及靖远等剖面获得的古地磁研究结果．主要结论为：１．中国黄土剖面记录了Ｂｒｕｎｈｅｓ正极性带与Ｍａｔｕｙａｍａ负极性带，Ｂｒｕｎｈｅｓ／Ｍａｔｕｙａｍａ极性转换过程位于第８层黄土（Ｌ８）．在段家坡黄土剖面该转换过程对应的地层厚度为０．３７５ｍ，持续时间约６０００ａ．转换过程由３次极性变化构成，每次经历的时间约为４００ａ．２．Ｊａｒａｍｉｌｌｏ正极性亚带（Ｊ）位于标志层Ｌ９至Ｌ１５之间，大约Ｓ１０－Ｓ１３位置．３．Ｏｌｄｕｖａｉ正极性亚带（Ｏ）对应的地层为Ｓ２７－Ｓ３３４．Ｒｅｕｎｉｏｎ正极性亚带（Ｒ）由两部分组成，在蓝田段家坡黄土剖面分别位于Ｌ３６和Ｓ３８５．Ｍａｔｕｙａｍａ负极性带与Ｇａｕｓｓ正极性带界限（Ｍ／Ｇａ）位于黄土和红色粘土交界处，中国黄土的底界年龄为２．４８Ｍａ左右．黄土与红色粘土为整合接触关系．６．黄土下伏的红色粘土记录了Ｇａｕｓｓ正极性带，Ｇｉｌｂｅｒｔ负极性带和古地磁年表编号５（Ｅｐｏｃｈ５）．     

Palaeomagnetism and the age of the Makapansgat hominid site

The time of deposition of the Makapansgat Limeworks site in South Africa, containing several hominid fossils, has an important bearing on hominid phylogeny in Africa. Hence, in an attempt to determine this age, a palaeomagnetic analysis of the site has been performed and the results are reported here. Member 3 (from which most of the important hominid fossils have been recovered) appears to have an age greater than 2.90 Ma and possibly greater than 3.06 Ma but less than 3.32 Ma. Previously it has not been possible to delineate the age of this important member with any degree of accuracy. The most likely position for the underlying Member 2 is in that section of the Gauss normal epoch predating the Mammoth event and having age limits of 3.06–3.32 Ma.     

The Rossello composite: a Mediterranean and global reference section for the Early to early Late Pliocene

A high-resolution magnetostratigraphy (planktonic foraminiferal) biostratigraphy and cyclostratigraphy is presented for the Pliocene Trubi marls in the Punta di Maiata section on Sicily. The integrated stratigraphy of the Rossello composite section of Hilgen ([1], Newslett. Stratigr., 17, 1987) is thereby completed. This composite section provides an unprecedented high-quality reference section for the Early to early Late Pliocene, containing a continuous sequence ranging from below the Thvera Subchron into the Matuyama Chron (4.86-2.45 Ma).The Punta di Maiata section extends from the Sidufjall Subchron of the Gilbert into the Gauss Chron (4.50-3.30 Ma). Linear interpolation between paleomagnetic datum planes in this section yields first-order age estimates of 3.72 (±0.01) and 3.59 (±0.01) Ma for the last common occurrence (LCO) and the actual last occurrence (LO) of Globorotalia margaritae.In addition, this age of 3.59 Ma provides an accurate age for the Zanclean-Piacenzian (Z/P) boundary, provided the LO of G. margaritae is maintained as a criterion to define this boundary in the Mediterranean. Irrespective, however, of the criterion used, the Punta di Maiata and Punta Piccola subsections of the Rossello composite are at present the most suitable sections to be designated as stratotypes for the Z/P boundary. The global significance of the Rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the Trubi sedimentary cycles with the astronomical record.     

山西襄汾大柴更新统剖面划分的新观点

对山西襄汾丁村文化遗址群内大柴剖面进行的磁性地层学研究表明,松山与布容的极性界线（M/B）出现在距剖面顶部45 m处;磁化率对比结果显示,此位置正好与S8上部对应.由这种极性和磁化率的对应结果可推断,下、中更新统（Q₁/Q₂）的地层分界也应在距剖面顶部45 m处的S8上部,而不是传统上认为的Q₁/Q₂的地层分界,在距剖面顶部80 m处.这种以古地磁学为基础的新的划分方案,对丁村遗址群的对比以及丁村遗址年代的最终确定都有重要的指示意义.根据其沉积环境和地层特征推断,采样部位下部的磁化率低值带应为水成黄土.而岩石磁学研究结果显示,磁铁矿、赤铁矿和热不稳定性磁赤铁矿是大柴剖面沉积物中主要的磁性矿物;磁铁矿和赤铁矿同为高温稳定性磁性载体.     

Secular changes,polarity epochs and tectonic movements as indicated by palaeomagnetic studies of Hungarian rock samples

Summary The paper contains an outline of the palaeomagnetic investigations in Hungary including some of their geophysical and geological applications. More than 500 samples of volcanic rocks were studied by usual palaeomagnetic techniques. The rocks investigated belong to three different geological periods — the Quaternary — upper Tertiary, the middle Miocene and the lower Cretaceous. The palaeomagnetic data obtained for the individual localities are summarized in the Appendix.Paper presented at the IAGA Symposium Madrid, September 1969.     

No evidence for a 0.8–0.9 m.y. old micro-australite layer in deep-sea cores

Fission-track and⁴⁰Ar—³⁹Ar dating of Australasian tektites indicates that the australites are older than the rest of the Australasian tektites. Some authors have suggested, therefore, that there should be two microtektite layers in the Australasian region: a younger layer approximately synchronous with the Brunhes/Matuyama geomagnetic reversal boundary (previously described in the literature) and an older layer of Australian microtektites (micro-australites) below the Brunhes/Matuyama reversal boundary and perhaps associated with the end of the Jaramillo event. Fifteen cores already known to contain a layer of Australasian microtektites at or slightly above the Brunhes/Matuyama reversal boundary were searched for an 0.8 to 0.9 m.y. old micro-australite layer. No evidence for this layer was found. Thus, the data do not support the conclusion that the Australasian tektites were produced by two impact events at different times.     

Short geomagnetic episodes in the Matuyama epoch

Two short geomagnetic episodes in the middle Matuyama epoch have been identified within thin (4.3-mm) sections of two deep-sea calcareous sediment cores taken in the western equatorial Pacific. Both cores are correlated by magnetostratigraphic and micropaleontological methods. Magnetic stability and paleomagnetic reliability are tested by alternating field demagnetization of natural remanent magnetization as well as by the ratios of intensities of anhysteretic remanent magnetization to those of saturation isothermal remanent magnetization. One episode is dated to be 1.06 m.y. BP. The other is identified to be about 1.94 m.y. BP, which is presumably in agreement with the Reunion event. Both episodes seem to be accompanied by conspicuous drops in field intensity. Possible correlation of field intensity with biological productivity in the ocean is also postulated from the present paleomagnetic results.     

临夏盆地新近纪郭泥沟剖面磁组构特征及其环境意义

临夏盆地在东亚新生代地层、古气候、古生物研究方面占有举足轻重的地位.本文对盆地东部的郭泥沟剖面进行了详细的岩石磁学和磁组构研究,以揭示从早中新世到早上新世临夏盆地的沉积演化过程.郭泥沟剖面沉积物中的磁性矿物有磁铁矿、磁赤铁矿、赤铁矿和针铁矿,但剩磁载体以磁铁矿和赤铁矿为主.从上庄组和东乡组的褐红色粉砂质粘土到柳树组和何王家组的褐黄色粘土,赤铁矿含量呈现降低的趋势,与沉积物颜色变化一致.郭泥沟剖面沉积物磁组构类型为正常沉积磁组构.结合岩石磁学结果和磁组构参数特征可揭示临夏盆地早中新世-早上新世沉积的演化过程：早中新世上庄组为稳定湖相沉积,古水流方向为NNW,与南北向的大夏河方向一致;中中新世气候发生较明显的干湿波动,形成了东乡组的褐红色湖相粉砂质粘土夹粉砂、砂和青灰色泥灰质粘土条带,古水流方向主要为NNW,沉积过程主要受大夏河控制;中中新世晚期,受青藏高原构造运动影响,沉积相由湖相细粒沉积物转变为虎家梁组河流相砂砾层;同时,盆地的水动力条件也发生改变,晚中新世柳树组湖相沉积过程同时受南北向大夏河和东西向洮河控制,两个方向近垂直的河流共同作用导致柳树组内沉积各向异性度较低,面理和线理均不发育,磁化率最大轴偏角分布比较分散,磁组构确定的古流向为东西向和南北向;早上新世期间,由于受青藏高原隆升影响,沉积了何王家组下部的河流相砂砾层;受构造抬升影响,大夏河重新主导何王家组上部洪泛平原相沉积过程,水动力条件较为单一稳定,古流向主要为N向,与大夏河流向一致.     

兰州地区晚第三纪磁性地层与古环境意义

兰州地区位于黄土高原和青藏高原的过渡带,其第三纪地层对研究风尘沉积发育和青藏高原隆升都有着特殊的意义.本研究以0.5 m间距对兰州盆地皋兰山剖面240 m的晚第三纪地层进行古地磁样品采集,古地磁样品共计422个;以50 ℃为间隔从室温至500 ℃用热退磁仪和超导磁力仪完成了皋兰山剖面样品的系统热退磁和剩磁测量.结果表明皋兰山剖面上部地层的实测极性柱出现2个负极性大段中间夹着4个正极性小段,其特点与Gilbert时的典型特征完全一致,并且两端未完全出露的正极性分别与Chron2A.3n和Chron3An.1n相对应,最终确定皋兰山剖面的年代为6～3.5 Ma.由此推断,皋兰山剖面顶部的五泉砾岩形成大约开始于3.5 Ma,五泉砾岩底界年代的确定,为青藏高原的A幕运动提供了地质证据.皋兰山剖面深度602 m处出现由河湖相砂岩向以风成红粘土为主常夹有薄层砂岩的地层转变,通过岩性地层及年代的推断,兰州地区的风尘序列堆积发育的年代至少为7 Ma,与黄土高原风尘序列堆积底界8～7 Ma基本一致,说明了兰州地区与黄土高原在风尘序列堆积过程中具有统一性.     

Paleomagnetic stratigraphy of Pliocene Centerville Beach section,northern California

Samples from the upper two-thirds of the approximately 1900 m thick Neogene section exposed south of Centerville Beach on the northern California coast have predominantly reversed detrital remanent magnetism. Fossil evidence suggests a lower Pliocene through lower Pleistocene age for the section. The combined paleomagnetic and fossil data indicate that a large part of the section was deposited during the Matayama reversed epoch (2.4-0.7 million years ago). Samples from correlative sections exposed a few kilometers inland from the Centerville Beach section have a predominantly normal polarity and appear to have been remagnetized. The Centerville Beach section is important because it may serve as a standard with which to compare both other on-land Pliocene sections from western North America and nearby Deep Sea Drilling Project cores.     

Outline volcanic history of the region west of Vatnajökull, Central Iceland

This paper outlines the structure and volcanic geology of a 25 × 50 km region of central Iceland including part of the eastern neovolcanic zone and its western margin. It includes an extinct Brunhes epoch silicic centre, the Hagangas, offset en échelon from a zone of major postglacial basaltic activity forming a northeasterly extension of the Torfajökull centre. Stratigraphic subdivisions restricted to the last 690,000 years comprise, in order of decreasing age, interglacial flood tholeiites, major centres of intraglacial hyaloclastite eruption, and postglacial lavas, which are mostly olivine basalts. The Hagangas centre and interglacial tholeiites lie on crust predominantly of Matuyama age (0.69–2.30 m.y.) but the bulk of the present volcanic activity may be taking place through crust belonging entirely to the present polarity epoch; this latter zone is characterised by normal faulting and extensive hydrothermal alteration. The widespread hydrothermal alteration and voluminous basaltic eruption distinguish this neovolcanic zone from the western zone, and the relationship of the region to growth of the upper crust in Iceland is briefly discussed.     

Rock magnetism and magnetostratigraphy of the loess-sol series of Ukraine (Roksolany,Boyanychi, and Korshev sections)

The results of the rock magnetic and paleomagnetic studies for the Quaternary loess-sol deposits of Ukraine are reported. The magnetic properties of the rocks composing the sections in the Pre-Black-Sea Depression (Roksolany) and Volyn Upland (Boyanychi and Korshev) are compared. Based on the highly precise measurements by modern instruments, the primary magnetization component is isolated in the rocks and its polarity is reliably determined in both the loess and soil horizons. The position of the Matuyama–Brunhes boundary in the Roksolany section is determined at a depth of 46.6 m at the contact of the Lubenskii and Martonoshskii soil horizons. This is consistent with the present-day notions of the group of Ukrainian scientists about the Quaternary stratigraphy of the south of Ukraine and inconsistent with the previous results that placed this boundary at a depth of 34 m in loesses above the PK₇ level.     

Age of New Zealand Pleistocene substages by fission-track dating of glass shards from tephra horizons

Eleven tephras and two pumice-rich horizons interbedded in Pleistocene marine sediments of the Wanganui Basin have been dated using the fission-track method on glass shards. Ages of the lower boundaries of New Zealand Pleistocene marine Substages are 0.45 m.y. (Putikian), 1.06 m.y. (Okehuan), 1.55 m.y. (Marahauan). On the basis of sedimentation rates an estimation of 1.86 m.y. is obtained for the Plio-Pleistocene boundary (Hautawan).     

Implications of a combined biostratigraphic and palaeomagnetic study of the Umbrian Maiolica Formation

The study of a 275.5 m thick section of white, pelagic limestones occupying the valley of the Fonte del Giordano river on the southern slope of Mt. Montagnola has yielded a biostratigraphically controlled clear magnetic reversal pattern after thermal cleaning. The magnetic stratigraphy of the lower 131 m of the section (Calpionellid zones) is correlatable with the M-sequence of oceanic magnetic anomalies between M-19 and M-14. The reversal stratigraphy of the upper 81.5 m of the section (Radiolaria zone) has also been tied to the oceanic polarity time scale by making linear interpolation for a missing 63 m thickness underneath it.Besides the Fonte del Giordano section two Berriasian outcrops each with a different bedding attitude were studied at Gubbio and near Cagli for tectonic tilt test giving positive results. The mean palaeomagnetic pole position for the Late Jurassic/Early Cretaceous after bedding correction is: Φ = 19.1°, Λ = 288.2°, k = 148.7, α₉₅ = 10.2° (N = 3), confirming the presence of a large swing in the polar path, a common behaviour of apparent polar wandering for the peri-Adriatic region during this time.     

泥河湾层磁性地层学研究回顾

泥河湾盆地以富含哺乳动物化石和古人类遗址而引起了古人类学家和地贡学家的广泛关注,泥河湾层是该盆地中发育的一套晚新生代河湖相沉积物．磁性地层学研究结果表明泥河湾层的形成始于高斯正极性世,经历了松山反向极性世,结束于布容正极性世．本文回顾了针时泥河湾层的磁性地层学研究工作,选取了小长梁、东谷坨、郝家台、洞沟、红崖、虎头粱及许家窑等七个剖面作详细介绍,并进行了横向时比．