High-resolution magnetostratigraphy and micropalaeontology across the J/K boundary strata at Brodno near ilina, western Slovakia: summary of results

This study summarizes the final results of magnetostratigraphic and micropalaeontological investigations of the Tithonian/Berriasian boundary (J/K) limestones at the locality of Brodno near ilina, Western Carpathians, West Slovakia. The aim is to prepare the background for correlation of a Late Tithonian and Early Berriasian biostratigraphic zonation with global magnetoevents (manifested in detailed magnetostratigraphic profiles) between the Tethyan realm and other regions, particularly the Boreal and Pacific realms. Suitable physical properties of the limestones studied, a favourable geological setting and rich microfossil assemblages (calpionellids) at Brodno (magnetozones M21r to M18r) allowed a systematic collection of new data on the original synoptic section, which now has the character of a high-resolution profile across the J/K boundary. Two reverse subzones detected within magnetozones M20n and M19n are named ‘Kysuca Subzone’ and ‘Brodno Subzone’, respectively. Both can be correlated with analogous subzones in the M-sequence of marine anomalies. Their existence can also be confirmed in the Bosso Valley section in Umbria, central Italy. A detailed study of the interval between magnetozones M20n and M17r in the Bosso Valley profile is presently in its final stage. Both magnetostratigraphic profiles, from the Brodno and Bosso Valley localities, were thoroughly investigated in the intervals close to the J/K boundary and are still unique among continent-based profiles in the detection and precise definition of both reverse subzones within M20n and M19n. Samples collected from the boundary strata of the reverse Kysuca Subzone at Brodno indicated a transition from N (R) to R (N) polarity of the Earth's palaeomagnetic field within a time interval of c. ±5 ka. Limestone samples (total number N=368) were subjected to progressive thermal demagnetization in 10–12 thermal fields and to subsequent multi-component analysis of remanence. The C-component, as the carrier of palaeomagnetic directions, was determined in the temperature interval of 300° to 540°, or possibly 580°C. Magnetomineralogical analyses of pilot samples and unblocking temperatures determined for all samples showed that magnetite is the carrier of remanent magnetization. The positions of the individual events of calpionellid stratigraphy relative to the global magnetic polarity timescale are precisely defined. The base of the Calpionella Standard Zone, which is considered a provisional J/K boundary indicator in ammonite-free sections in the Tethyan realm, lies within magnetozone M19n at the level of 35% of its local thickness. None of the boundaries in the calpionellid zonation coincides precisely with any of those in the palaeomagnetic zonation, but the first appearance ofCalpionella grandalpina , indicating the base of the Intermedia Subzone, lies in close proximity to the base of magnetozone M19r.     

New data on the magnetostratigraphy of the Jurassic–Cretaceous boundary interval,Nordvik Peninsula (northern East Siberia)

The results of this study were used to identify a reversed polarity magnetozone, referred to as M17r, in Berriasian sections of the Nordvik Peninsula (northern East Siberia) within the normal polarity magnetozone (M18n) from previous studies. The new magnetozone embraces the Volgian–Ryazanian boundary (Chetaites chetae/C. sibiricus zonal boundary). It was also found that the former magnetozone M17r at Nordvik, which includes the C. sibiricus/Hectoroceras kochi zonal boundary should correspond to magnetozone M16r. Using magnetostratigraphic and biostratigraphic criteria proves that the Boreal C. sibiricus Zone is correlated with at least the major part of the Tethyan Tirnovella occitanica Zone, and the Boreal H. kochi Zone is correlated with the lower part of the Malbosiceras paramimounum Subzone of the Tethyan Fauriella boissieri Zone.     

New sedimentological, bio-, and magnetostratigraphic data on the Jurassic-Cretaceous boundary interval of Eastern Crimea (Feodosiya)

The first compiled composite section comprises continuous succession of upper Tithonian-lower Berriasian strata (Jacobi Zone) from different isolated outcrops of the Feodosiya area. Based on new magnetostratigraphic and sedimentological data, the paleomagnetic section is correlated with succession of M20r, M19n, M19r, M18b chrons and M18n.1r Subchron (“Brodno”). The thorough complex bio- and magnetostratigraphic correlation of the upper Tithonian-lower Berriasian interval (Jacobi Zone) carried out through the Western Tethys and Eastern Paratethys provided grounds for first defining age analogs of the Durangites Zone in the Crimean Mountains and specifying location of the boundary between the Jurassic and Cretaceous systems, as well as for determining late Tithonian age of strata in the Dvuyakornaya Bay section barren of fossils.     

The Loess in the Qinling Mountains and Its Records of Palaeoenvironmental Changes

The Fengzhou loess section is very typical in the Qinling Mountains. The section, which is about 82 m thick and underlain by Neogene red clays, consists of 33 layers of loess and 33 layers of palaeosol. It covers the Brunhes normal polarity zone and Matuyama reversed polarity zone, and the B/ M boundary is located in the middle part of loess layer 8 (L8). The loess of the Matuyama reversed polarity zone records the Jaramillo, Olduvai and Reunion normal polarity subchrons. The boundary between the Matuyama reversed polarity zone and Gauss normal polarity zone (M / Ga) appears on the lithological boundary between loess and Neogene red clays. Loess accumulation in the Fengzhou section started before 2.48 Ma B.P. Based on the stratigraphical structure, the material composition and magnetic susceptibility curve of the Fengzhou loess section, the palaeoclimatic changes during the last 2.48 Ma in the Qinling Mountains are subdivided into 66 cold-dry and warm-humid stages, equivalent to 33 climatic cycles. The     

The upper Volgian Substage in Northeast Siberia (Nordvik Peninsula) and its Panboreal correlation based on ammonites

Section of the middle and upper Volgian substages and basal Boreal Berriasian in the Cape Urdyuk-Khaya (Nordvik Peninsula) is largely composed of dark argillites substantially enriched in C_org. Characteristic of the section is a continuous succession of ammonite, foraminiferal, ostracode, and dinocyst zones known also in the other Arctic areas. Boundaries of the upper Volgian Substage are recognizable only based on biostratigraphic criteria. The succession of the middle Volgian Taimyrosphinctes excentricus to basal Ryazanian Hectoroceras kochi zones is characterized. The range of the substage is revised. The lower Exoticus Zone, where ammonites characteristic of the Nikitini Zone upper part in the East European platform have been found, is referred to the middle Volgian Substage. Newly found ammonites are figured. Two possible positions of the Jurassic-Cretaceous boundary in the Arctic region, i.e., at the lower and upper boundaries of the Chetae Zone at the top of the upper Volgian Substage, are discussed.     

辽西朝阳地区含鸟化石层附近侏罗—白垩系磁性地层研究

本文通过对辽西朝阳地区含鸟化石层附近侏罗-白垩系蓝旗组、土城子组、义县组地层共1252块古地磁样吕的测试与分析，建立了以上沉积地层的磁极性序列，发现蓝旗组、土城子组地层的磁极性序列具有频繁的正、反极性、而义县组则为单一正极性，结合现有古生物和同位素年龄资料，对比国际中生代地磁极性年表，表明土城子组的磁极性序列相当于提塘期、基末里期、牛津期和卡洛期，其主体的地质时代应属晚侏罗世（J3），土城子组底部的地质时代应属中侏罗世（J2)；并且根据义县组含鸟化石层以上层位的磁性地层研究结果，认为义县组含鸟化石的正极性带可与M16正极性时相对应，义县组含鸟类化石层的时代应属早白垩世早期，辽西白垩系/侏罗系界线很有可能位于义县组/土城子组之间。     

黄土高原黄土、红色粘土与古湖盆沉积物关系

本文通过磁性地层学、古生物地层学、沉积学的对比研究，讨论了中国黄土高原地区黄土，红色粘土与该区重要古湖盆之一，古三门湖堆积物之间关系，并分析气候环境对它们的影响。主要结论如下：１）红色粘土与上覆黄土可以是连续沉积，并呈相渐变关系。２）中国黄土与三门组记录了布容正极性带与松山负极性带。Ｂ／Ｍ界限位于Ｌ８，Ｊ亚带位于标志层Ｌ９与Ｌ１５之间，大约Ｓ１０－Ｓ１３之间，Ｏ亚带位于Ｓ２２－Ｓ３３，或三门组之中。Ｍ／Ｇａ界限对应于黄土与红土界限。并基本对应于三门组与游河组界限。３）红色粘土（三趾马红粘土）并非仅仅是中新世保德期沉积物。它包括上新统与中新统，上新世静乐组记录了高斯正极性带，吉尔伯特负极性带，中新世蓝田组记录了Ｅｐｏｃｈ５。４）古三门湖堆积包括早更新世早期三门组（１．２０—２．５０Ｍａ，松山负极性带），上新世晚期游河组（２．５０—３．５０Ｍａ，高斯正极性带），更早期的三门湖沉积未出露。三门组与午域黄土为同期异相沉积，记录了松山负极性带，游河组则与该区上部红色粘土（静乐组上段）为同期异相沉积，记录了高斯正极性带     

Belemnites and biostratigraphy of the Jurassic-Cretaceous boundary deposits of northern East Siberia: New data on the Nordvik Peninsula

The study of new collections from the Urdyuk-Khaya Cape (Nordvik Peninsula) made it possible to specify the taxonomic composition of belemnites from the Volgian and basal Ryazanian in northern East Siberia. Cylindroteuthis knoxvillensis Anderson, 1945, C. cf. newvillensis Anderson, 1945, and Arctoteuthis tehamaensis (Stanton, 1895) known from northern California, as well as the new species C. venusta sp. nov. and A. britanna sp. nov. are first described from the Arctic region. Belemnite stratigraphy of Jurassic-Cretaceous boundary layers is fundamentally revised, allowing a new refined version of their scale to be proposed as a Boreal standard. Two independent successions of biostratigraphic units are defined in the section interval spanning the uppermost Middle Volgian Substage to the basal Ryazanian Stage: (1) Liobelus russiensis Zone, Lagonibelus gustomesovi and Arctoteuthis porrectiformis beds; (2) Lagonibelus napaensis, Arctoteuthis tehamaensis, and Cylindroteuthis knoxvillensis zones.     

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。     

北京怀柔HR_（88－1）钻孔剖面磁性地层学研究

在系统古地磁样品采集、处理和测量的基础上，运用磁性地层学的研究方法，对北京怀柔地区ＨＲ（８８－１）钻孔剖面进行了详细地层划分，分别确定了该区上新统、下更新统、中更新统和上更新统的分布深度及地质年代。     

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.     

北京怀柔HR_（88－1）钻孔剖面磁性地层学研究

在系统古地磁样品采集、处理和测量的基础上，运用磁性地层学的研究方法，对北京怀柔地区ＨＲ（８８－１）钻孔剖面进行了详细地层划分，分别确定了该区上新统、下更新统、中更新统和上更新统的分布深度及地质年代。     

Paleomagnetism of trap basalts in the northwestern Siberian craton,from core data

We present new paleomagnetic data for continental flood basalts (Siberian traps) obtained from cores of two boreholes in the northwestern Noril'sk area, within the Kharaelakh and Vologochan basins. Paleomagnetic measurements of lava and tuff samples from KhS-59 and SSV-19 boreholes allowed reconstructing and correlating the polarity patterns. Thus multiple paleomagnetic anomalies (PMA) have been discovered as brief polarity changes in narrow intervals of the magnetostratigraphic section above the principle reversal at the boundary between the Ivakin and Syverma Formations.The most prominent anomalies are observed at the bases of the Morongo and Mokulai Formations. The samples from the anomalous intervals differ from those of other intervals neither in rock magnetic properties, nor in mineralogy and magnetic grain sizes. Therefore, the revealed PMA record excursions of the geomagnetic field. Comparison of the results with the Meishan Global Stratotype Section and Point (GSSP) of the Permian–Triassic boundary implies a revision to the P–T position in the trap basalt succession of the Noril'sk area. Judging by the EMF behavior, basalts in this part of the trap province erupted for at least 500 kyr during an interval of stable normal polarity.     

Berriasian Stage of the Crimean Mountains: Zonal subdivisions and correlation

Biostratigraphy of the Berriasian Stage in the Crimean Mountains is specified and substantiated. Fragments of all the standard stage zones (jacobi, occitanica, and boissieri) are distinguished based on the found index species, and position of the Jurassic-Cretaceous boundary is targeted. According to verified distribution of ammonites, the jacobi Zone is divided into the jacobi and grandis subzones crowned by the Malbosiceras chaperi Beds. The Tirnovella occitanica-Retowskiceras retowskyi Beds and overlying Dalmasiceras tauricum Subzone are recognized in deposits of the occitanica Zone. The upward succession of biostratigraphic units established in the boissieri Zone includes the Euthymiceras-Neocosmoceras Beds, Riasanites crassicostatus Subzone, Symphythyris arguinensis and Jabronella sf. paquieri-Berriasella callisto Beds. The last biostratigraphic unit is suggested in this work instead the former Zeillerina baksanensis Beds. Except for the jacobi Zone, the substantiated ammonoid zonation is practically identical to the Berriasian biostratigraphic scale of the northern Caucasus, although the Berriasian-Valanginian boundary has not been defined in the Crimean Mountains based on ammonites. Several marker levels of bivalve mollusks and four biostratigraphic subdivisions of brachiopod scale are distinguishable here. As for the latter, these are (from the base upward) the Tonasirhynchia janini, Belbekella airgulensis-Sellithyris uniplicata, Symphythyris arguinensis, and Zeillerina baksanensis beds.     

Planktonic foraminiferal turnover across the Cretaceous-Tertiary boundary in the Vajont valley (Southern Alps, northern Italy)

Planktonic foraminiferal analysis of the Erto section in the Vajont valley (Southern Alps, northern Italy) reveals a relatively complete succession across the Cretaceous–Tertiary (K–T) boundary. The turnover of planktonic foraminiferal fauna was studied for a stratigraphic interval spanning theAbathomphalus mayaroensisZonep.p., Pseudotextularia deformisZone,Guembelitria cretaceaZone,Parvularugoglobigerina eugubinaZone,Eglobigerina eobullioidesSubzone, andParasubbotina pseudobulloidesZonep. p.The extinction of most large, ornate, late Maastrichtian species occurs below a black ‘boundary clay’ (2–4 cm thick); however, part of the Late Cretaceous species, mainly heterohelicidids and hedbergellids, were found over an interval of more than 100 cm above the boundary. Although a relatively high number of species occur for the last time in the main extinction phase, the abundance of these outgoing species is less than 20% of the total population; unkeeled or weakly keeled, simple-shaped forms (heterohelicids, globotruncanellids, hedbergellids) constitute the bulk of the planktonic foraminiferal population both in uppermost Maastrichtian and lowermost Danian beds. The first Tertiary species (‘Globigerina’minutulaand ‘Globigerina’fringa) appear just above the ‘boundary clay’;Parvularuglobigerina eugubinaoccurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of theEoglobigerina eobulloidesSubzone.     

Late Cenozoic paleomagnetism of West Siberian Plate

On the basis of combined (paleomagnetic, lithological, and paleontological) data, a scale of Neogene geomagnetic polarity is proposed for the West Siberian Plate (WSP). It comprises 17 large orthozones of normal and reversed polarity. The scale was compiled by comparing and correlating the Neogene key sections of the Kulunda and Baraba plains, Irtysh regions between Omsk and Pavlodar and near Tara, and Ob’ region near Tomsk. The reliability of paleomagnetic data is confirmed by component analysis of natural remanent magnetization and by a possibility of determining its primary component. In the studied Neogene rocks this is a high-temperature component related to magnetite, hematite, and maghemite, which decays at 420–675 °C. In the period from Early Miocene to Late Pliocene, the Late Cenozoic geomagnetic field reconstructed from NRM vectors for WSP rocks of Neogene age experienced 17 reversals (at the level of orthozone boundaries), with eight regimes of normal polarity and nine regimes of reversed polarity. Comparison of the WSP Neogene scale with Berggren’s scale provided absolute age boundaries of the Late Cenozoic series on the WSP regional stratigraphic scale. The 23.8 Ma boundary between the Oligocene and Miocene is recorded in the regional scale at the sole of the Lyamin beds of the Abrosimovka Formation, at the bottom of Orthochron R₁N₁aq, and the Miocene-Pliocene 5.2 Ma boundary (Chron C3r), in the Novaya Stanitsa Formation (top of the Cherlak beds).     

The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria

A complete ichthyosaur rostrum, with 124 associated teeth, was recently discovered in Laux-Montaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. This specimen also represents the first occurrence of Aegirosaurus outside the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Tooth morphology and wear pattern suggest that Aegirosaurus belonged to the “Pierce II/ Generalist” feeding guild, which was hitherto not represented in post-Liassic ichthyosaurs. Most Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary.     

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。     

冀北滦平陆相侏罗—白垩系生物地层界线及候选层型研究进展

滦平盆地张家沟侏罗—白垩系界线上下为连续沉积的滨浅湖—半深湖序列,介形类和叶肢介类化石丰富,是中国陆相J\K界线理想的层型候选剖面。通过晚侏罗世和早白垩世介形类、叶肢介生物组合及沉积学与成因地层学的综合研究,认为陆相侏罗—白垩系生物地层界线以介形类大个体滦平介Luanpingella的消失、女星介Cypridea的出现,叶肢介Nestoria、Pseudograpta及Keratestheria等的消失以及Eosestheria的始现,扇三角洲平原或前缘亚相或等同亚、微相带的结束为标志。陆相界线层型研究和定义异于海相盆地,陆相环境生物化石的自然缺欠可以通过地层格架建立及沉积亚微相序列高精度地划分、对比予以弥补,并应纳入陆相界线层型的定义中。