Palynostratigraphy of the Upper Cretaceous and Paleogene Deposits in the South of Western Siberia by Example of Russkaya Polyana Boreholes,Omsk Trough

The detailed study of Boreholes 8, 10, and 2 in the Russkaya Polyana district (Omsk Trough) made it possible to reveal the complex structure of the Upper Cretaceous sediments formed in unstable conditions of the marginal part of the Western Siberian basin. The Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino formations were subjected to palynological analysis and substantiation of their Late Cretaceous age. Eight biostratigraphic units with dinocysts and five units with spores and pollen from the Albian to the Maastrichtian were identified. The joint application of biostratigraphic and magnetostratigraphic methods made it possible to reveal the stratigraphic breaks in the studied sedimentary stratum and to estimate their scope. The age of the Lower Lyulinvor Subformation was specified in the marginal part of the Omsk Trough. The ingression traces of the Western Siberian basin in the Albian were found for the first time in the considered region.     

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.     

Stratigraphy of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit (southwestern Siberia): New data

The results of complex palynological and microfaunistic studies of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit are presented. Geochronologically, the age of the deposits varies from Campanian to Quaternary. It was established that the Slavgorod, Gan’kino, and Jurki (?) formations contain four biostratons in the rank of beds with dinocysts and three biostratons in the rank of beds with spores and pollen. The Cenozoic continental deposits contain four biostratons in the rank of beds, containing spores and pollen. As a result of the study, a large stratigraphic gap in the Cretaceous–Paleogene boundary deposits, covering a significant part of the Maastrichtian, Paleocene, Ypresian, and Lutetian stages of the Eocene, was established. The remnants of a new morphotype of heteromorphic ammonites of genus Baculites were first described in deposits of the Slavgorod Formation (preliminarily, upper Campanian). The distribution features of the different palynomorph groups in the Upper Cretaceous–Cenozoic deposits in the area of study due to transgressive-regressive cycles and climate fluctuations were revealed.     

Magnetostratigraphy of the Campanian–Maastrichtian Bakchar Basin (southeastern West Siberia)

In this paper the results of magnetostratigraphic studies of the Upper Cretaceous penetrated by two wells (S-124 and S-114) drilled in the Tomsk structural-facies zone (Bakchar iron ore deposit) are presented. The obtained biostratigraphic data show that the sediments formed in the Campanian–Maastrichtian time interval. The high-temperature component of the remanent magnetization identified in the rocks allowed us to compile paleomagnetic columns for each well and correlate the columns, using paleontological data, with each other and with the general magnetostratigraphic and magnetochronological scales. In magnetostratigraphic sections of two wells, the Campanian reverse-polarity Slavgorod Formation (R(km)) with a normal-polarity horizon is correlated with Chron C33(r) (top) and C33(n) (bottom) of the Gradstein scale, and the Maastrichtian normal-polarity Gan’kino Formation with a thin reverse-polarity horizon (N(mt)) is correlated with Chron C30 of this scale.     

Paleomagnetism of the Paleogene-Neogene continental sediments of the Om’ basin (southern West Siberia)

The paper presents the results of detailed paleomagnetic studies of the Paleogene-Neogene continental sediments stripped by borehole 8 in southwestern West Siberia (Russkaya Polyana district, Omsk Region), near the Kazakhstan frontier. According to the previous biostratigraphic data, the sediments under study formed from Rupelian to Ruscinian. The results of stepwise thermal demagnetization and alternating-field demagnetization were used to carry out a component analysis of natural remanent magnetization, which revealed characteristic (primary) remanent magnetization (ChRM). The compiled paleomagnetic section, which includes seven regional horizons and same-named formations (Oligocene Atlym, Novomikhailovka, and Zhuravka Formations and Neogene Abrosimovka, Beshcheul, Tavolzhan, and Novaya Stanitsa Formations), was compared with the Cenozoic polarity scale for the West Siberian Plate. This made it possible to assess the completeness of the geologic section of the Paleogene and Neogene continental sediments in borehole 8 and to record the magnetozones and their fragments missing from the magnetostratigraphic section (for some intervals, in absolute chronology). The comparison shows that the magnetostratigraphic section of the studied sediments at the edges of the Om’ basin is approximately twice shorter than that of the basin center.     

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。     

Stratigraphy and sedimentary environments for cretaceous deposits in the southern part of the Var’egansk Megabar (Western Siberia)

Results of comprehensive studies of the Var’egansk Megabar sections in boreholes which penetrated the upper part of the Pokur Formation and the lower part of the Kuznetsovo Formation are presented. The stratigraphic range of the studied deposits spans the upper Albian-lower Turonian. Palynological and lithofacies studies resulted in the refinement of sedimentary paleoenvironments in the region under study. It has been confirmed that the upper part of the Pokur Formation was formed under coastal-marine conditions; it characterizes mainly different deltaic facies. Sandy rocks of the Pokur Formation upper part mostly formed in delta channels, whereas silty-clayey rocks, in marshy-swamp environments. Deposition of the Kuznetsovo Formation is confined to a major sea transgression, and it proceeded under normal sea conditions.     

北京大兴凸起南部PGZ05钻孔剖面第四纪磁性地层学

对北京大兴凸起南部PGZ05孔(孔深255 m)全孔岩心进行了磁性地层、岩石地层、AMS14C测年研究,在系统性的古地磁样品采集(440块岩样)、处理和测试基础上,分析认为255 m的岩心记录了布容正向极性时(Brunhes)、贾拉米洛(Jaramillo)极性亚时、奥尔都维(Olduvai)极性亚时和高斯正极性时(Gauss)。在此磁性年代框架上,结合AMS14C测年及岩性特征,对PGZ05钻孔剖面进行第四纪地层划分,确定下更新统、中更新统、上更新统和全新统的分布深度及年代,将更新统的底界(Q/N)定位于181. 35 m处,亦为一重要岩性(棕红色半固结黏土)界限,中更新统、上更新统、全新统的底界分别定位于75. 60 m、57. 20 m、17. 35 m处。研究成果为大兴凸起南部第四纪地层划分与对比、古地理环境演变及区域地层研究提供了可靠的地层年代学框架,具有重要地质意义。     

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.     

Sedimentation Model of Rocks of the Pokur Formation: Basis for the Prediction of Filtration-Volumetric Characteristics (Upper Cretaceous,West Siberia)

The HC-rich Upper Cretaceous rocks in the West Siberian petroliferous basin comprise genetically heterogeneous sediments, resulting in the specificity of morphology, structure, and properties of natural reservoirs therein. One of the possible techniques for more reliable predictions of reservoir rock characteristics is the utilization of results of sedimentation modeling based on the complex interpretation of borehole and seismic data. The paper presents an example of the realization of such approach for refining the structure of oil-and-gas pools in the Pokur Formation of the Russko-Chasel megaswell.     

Upper Cretaceous deposits in the northwest of Saratov oblast,Part 1: Litho- and biostratigraphic analysis of the Vishnevoe section

The work is dedicated to multidisciplinary study of Upper Cretaceous deposits exposed at the day surface in a ravine near the village of Vishnevoe, the Petrovsk district of Saratov oblast. The exposed section includes deposits of the Bannovka, Mozzhevelovyi Ovrag, Mesino-Lapshinovka, Rybushka, Ardym, Lokh formations and of the Borisoglebsk sequence first distinguished in the Volga River basin. Age ranges of the formations studied are confirmed or defined more precisely (the Ardym and Lokh formations) based on fossil faunas of cephalopods, bivalves, radiolarians, planktonic and benthic foraminifers. The middle-upper Coniacian range of the Borisoglebsk sequence is substantiated. Distribution of brachiopods, sponges, radiolarians, ostracodes and calcareous nannoplankton in the section is established. Radiolarian assemblages are used to distinguish biostratigraphic subdivisions corresponding in rank to faunal beds. Based on nannofossil assemblages, zones and subzones of standard zonations after Perch-Nielsen (1985) and Burnett (1998) are established. Stratigraphic ranges of certain radiolarian, ostracode and calcareous nannoplankton taxa are verified.     

Age Assignment of the Lycoptera- bearing Bed

In the Yanliao area, the occurrence of the Nestoria-Keratestheria fauna and the Eoparacypris- Luanpingella-Darwinula assemblage in the Dabeigou Formation s.s., a Rb-Sr isochron age of 145.2 Ma for the Baiqi Formation and a complete stratigraphic sequence-all this proves that the Lycoptera-bearing bed overlies the Upper Jurassic. The Jehol fauna comprises the primitive Trigonioidids fauna, Eosestheria fauna, Lycoptera fauna et al., and their own laws of evolution expound that they belong to Cretaceous faunas. The associations of Eosestheria with Yanjiestheria, Lycoptera with Eosestheria, and Kuntulunia with Yanjiestheria as well as the occurrence of early angiosperms and sporo - pollen in the Fuxin Formation and its equivalents also demonstrate that the Lycoptera-bearing, bed should be assigned to the Cretaceous. The confirmation of the existence of Aucellina in the Jixi Group and the correlation of Trigonioidids and Cypridids with those in the equivalent strata of Japan and Western Europe have also been     

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。     

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。     

Late Permian magnetostratigraphy on the eastern Russian platform

The Late Permian is characterized palaeomagnetically by the transition from the long-lasting Permo-Carboniferous reversed polarity superchron (PCRS; also called: Kiaman reversed superchron) to the subsequent Permo-Triassic mixed polarity superchron, often called Illawarra mixed polarity superchron. Many discussions have been devoted to the exact time of the onset of the Illawarra reversals. Apparently contradictory data have been obtained from magnetostratigraphic sediment successions formed in different environments in many regions of the world. These sediments have been dated using classical geological or palaeontological correlation methods without the possibility of absolute age control because volcanogenic materials are missing. Application of the local or regional stratigraphic schemes leads to difficulties and apparent diachronous age estimates of the end of the PCRS. This paper shows that in agreement with earlier investigations, the continental red beds of the Upper Permian Tatarian stage on the eastern Russian platform record the Kiaman/Illawarra boundary. The Illawarra reversal sequence measured in a type section at the Volga river can be correlated well with the corresponding polarity pattern found in the Tethyan realm if one assumes a longer duration of the Tatarian than previously suggested.     

Cretaceous complexes of the frontal zone of the Moneron-Samarga Island arc: Geochemical data on the basalts from the deep borehole on Moneron Island, the Sea of Japan

The variations of petrogenic oxides and trace elements have been studied in the Cretaceous volcanic rocks recovered by a deep borehole from the depth interval of 1253–4011 m on Moneron Island. The volcanic section is subdivided into two complexes: the Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous Complex occur below 1500 m. Chemically, they belong to low-potassium island arc tholeiites, and their trace element distribution suggests their formation in a suprasubduction mantle wedge under the influence of water fluids that were subsequently released from subducted sediments and oceanic plate during the dehydration of subducted sedimentary rocks and oceanic basalts and, finally, mainly from basalts. The Early Cretaceous basalts from the borehole are interpreted as ascribing to the frontal part of the Moneron-Samarga island arc system. The volcanic rocks of the Late Cretaceous Complex are situated at depths above 1500 m. They also were formed in a suprasubduction setting, but already within the East Sikhote-Alin continental-margin volcanic belt that was initiated after the accretion of the Moneron-Samarga island arc system to the Asian continent. The island-arc section of the Moneron borehole contains basaltic andesite dikes, which are geochemically comparable with the Early-Middle Miocene volcanic rocks of Southwestern Sakhalin.     

Dinoflagellate biostratigraphy at the Campanian-Maastrichtian boundary in Zumaia,northern Spain

Dinoflagellate cyst assemblages from a well-exposed uppermost Cretaceous section at Zumaia (northern Spain) provide a basis for comparison with previous biostratigraphic and magnetostratigraphic studies on the problematic location of the Campanian-Maastrichtian boundary in the section. The position of the last occurrence of Corradinisphaeridium horridum and first common occurrence of Alterbidinium acutulum, correspond well with the bioevents defining the Campanian-Maastrichtian boundary in the Global boundary Stratotype Section and Point of Tercis les Bains (130 km to the North). Together with other age-diagnostic dinoflagellate cyst bioevents, we suggest that the boundary should be placed between 239.75 and 224.75 m below the Cretaceous-Palaeogene boundary, about 46 m lower than an interpretation based on the first occurrence of the planktonic foraminifer Pseudoguembelina palpebra and the last occurrence of the nannofossil Broinsonia parca subsp. constricta. A conspicuous acme of the dinoflagellate cyst Thalassiphora cf. delicata is encountered around the lower-upper Maastrichtian boundary (calibrated by foraminiferal, calcareous nannoplankton and magnetic polarity data), which may prove to be a useful correlatable event.     

Magnetostratigraphy and lithostratigraphy of the Laño vertebrate-site: Implications in the uppermost Cretaceous chronostratigraphy of the Basque-Cantabrian Region

Here we present the magnetostratigraphic dating of the Laño locality (Condado de Treviño, northern Iberian Peninsula), one of the most noteworthy Campanian-Maastrichtian vertebrate sites of Europe. A composite section of 75 m thickness (Laño quarry) constructed from multiple, overlapping profiles and a continuous one (Faido) have been sampled for magnetostratigraphy. Thermal demagnetization techniques were systematically applied to 161 standard specimens and allowed characterizing the characteristic remanent magnetism, mostly carried out by magnetite. The palaeomagnetic signal is slightly scattered due to variety of lithologies, but the primary character can be guaranteed, since the normal and reverse directions are pseudo antiparallel; 346, 28 (α₉₅: 11.9°, k: 5.3) and 175, −35 (α₉₅: 16.4°, k: 4.6). Reliable samples allowed us to build the local polarity sequence made of eight magnetozones that has been used to correlate to the Global Polarity Time Scale. The age of the lower part of the Laño-village succession is basal late Campanian (Hoplitoplacenticeras marroti ammonite zone) and fits with the long reversed zone that must correlate to Chron C33r. The pattern of magnetozones allows tracking the section up to C30r at the upper part of the profile. In this correlation, the Laño vertebrate site is regarded as latest Campanian in age as it falls within the C32n (≈72–73.5 Ma). The combined lithostratigraphic and magnetostratigraphic analyses have yielded additional conclusions regarding the vertebrate assemblages that are representative of the Late Campanian of the Iberian Peninsula, in addition to highlight an older occurrence in Europe of some vertebrate groups such as salamandrid lissamphians and anguid lizards (or amphisbaenians).     

“鄂西地区一个含早期人类和巨猿化石的新地层单位——高坪组”的商榷

程捷等人(2004)报道了鄂西建始地区高坪龙骨洞的发掘和研究情况,并试图建立一个新的岩石地层单位——高坪组,建组的主要依据是将龙骨洞A剖面获得的地磁极性柱与标准磁性年表的松山反极性世的早期进行对比,即龙骨洞极性柱上部和中部的正极性事件分别与奥都威和留尼旺极性亚时对比。根据这种对比方案,可以计算出龙骨洞A剖面的平均沉积速率,结果发现该剖面的沉积速率变化很大,特别是留尼旺亚时的沉积速率远远大于相邻时间段的沉积速率,这与龙骨洞的沉积环境稳定以及相对应的地层岩性一致等相矛盾,因此,这一极性对比方案值得商榷,高坪组的年代存在不确定性。如果将龙骨洞A剖面的两个正极性事件与布容期和贾拉米诺极性亚时相对比,可以获得较均匀的沉积速率,由此可推算出的龙骨洞古人类年龄大约在1.1—1.4Ma之间,其时代与中国其他大部分地区的古人类年龄也比较相近。