Zonal stratigraphy and biogeography of the West Siberian Oxfordian based on ammonites

The Oxfordian Stage of West Siberia contains Boreal ammonites Cardioceratidae. The authors’ bank of paleontological data includes ~ 500 definitions of Cardioceratinae, permitting a considerable refinement of the official Oxfordian regional zonal scale. The lower substage is divided into the Cardioceras (Scarburgiceras) obliteratum, C. (S.) scarburgense, and C. (S.) gloriosum Zones instead of beds with C. (S.) spp., whereas the C. (Cardioceras) percaelatum and C. (C.) cordatum Zones are recognized instead of beds with C. (C.) spp. We have found new ammonites typical of the Middle Oxfordian C. (Subvertebriceras) densiplicatum and C. (Miticardioceras) tenuiserratum Zones. The first of these zones is divided into two subzones. The Upper Oxfordian includes the Amoeboceras glosense and A. serratum Zones instead of beds with A. spp., and the A. regulare Zone and beds with A. rosenkrantzi are recognized instead of the A. ex gr. regulare Zone. The genus Ringsteadia (Aulacostephanidae) is observed only in the northwestern part of the region, along the eastern slope of the North Urals; therefore, two upper units of the biostratigraphic scale correspond to beds with Ringsteadia marstonensis.In the Oxfordian, West Siberia and northern Siberia belonged to the North Siberian province of the Arctic realm. Only in the latest Oxfordian did the northwestern West Siberian basin become part of the Boreal-Atlantic realm, as evidenced by the distribution of Ringsteadia on the eastern slope of the Cis-Polar Urals.     

Detailed biostratigraphy of Triassic deposits in the Lena lower reaches (northern Yakutia)

Triassic sections of the Lena lower reaches (northern Yakutia) were studied. Stratigraphy and paleontology of the Triassic deposits were refined and described in detail, and their age was constrained by different fauna groups. The first detailed local Triassic biostratigraphic scheme is reported, which includes ammonoid, nautiloid, and bivalve zones and subzones and foraminifer beds. The scheme is compared with the Canadian Triassic Zonal and Standard (International) Scales.     

Fluvial and permafrost history of the lower Lena River,north-eastern Siberia,over late Quaternary time

Arctic warming and permafrost thaw visibly expose changes in the landscape of the Lena River delta, the largest Arctic delta. Determining the past and modern river regime of thick deltaic deposits shaping the Lena River mouth in north-eastern Siberia is critical for understanding the history of delta formation and carbon sequestration. Using a 65 m long sediment core from the delta apex a set of sedimentological techniques is applied to aid in reconstructing the Lena River history. The analysis includes: (i) grain-size measurements and the determination of the bedload composition; (ii) X-ray fluorescence, X-ray diffractometry, and magnetic susceptibility measurements and heavy mineral analysis for tracking mineral change; (iii) pH, electrical conductivity, ionic concentrations, and the δ¹⁸O and δD stable isotope composition from ground ice for reconstructing permafrost formation. In addition; (iv) total and dissolved organic carbon is assessed. Chronology is based on; (vi) radiocarbon dating of organic material (accelerator mass spectrometry and conventional) and is complemented by two infrared – optically stimulated luminescence dates. The record stretches back approximately to Marine Isotope Stage 7. It holds periods from traction, over saltation, to suspension load sedimentation. Minerogenic signals do not indicate provenance change over time. They rather reflect the change from high energy to a lower energy regime after Last Glacial Maximum time parallel to the fining-up grain-size trend. A prominent minimum in the ground ice stable isotope record at early Holocene highlights that a river arm migration and an associated refreeze of the underlying river talik has altered the isotopic composition at that time. Fluvial re-routing might be explained by internal dynamics in the Lena River lowland or due to a tectonic movement, since the study area is placed in a zone of seismic activity. At the southern Laptev Sea margin, onshore continental compressional patterns are bordering offshore extensional normal faults.     

Biostratigraphy of Jurassic-Cretaceous boundary sediments in the Eastern Crimea

The Dvuyakornaya Formation section in the eastern Crimea is described and subdivided into biostratigraphic units based on ammonites, foraminifers, and ostracodes. The lower part of the formation contains first discovered ammonites of the upper Kimmeridgian (Lingulaticears cf. procurvum (Ziegler), Pseudowaagenia gemmellariana Olóriz, Euvirgalithacoceras cf. tantalus (Herbich), Subplanites sp.) and Tithonian (?(Lingulaticeras efimovi (Rogov), Phylloceras consaguineum Gemmellaro, Oloriziceras cf. schneidi Tavera, and Paraulacosphinctes cf. transitorius (Oppel)). Based on the assemblage of characteristic ammonite species, the upper part of the formation is attributed to the Berriasian Jacobi Zone. Five biostratigraphic units (zones and beds with fauna) distinguished based on foraminifers are the Epistomina ventriosa-Melathrokerion eospirialis Beds and Anchispirocyclina lusitanica-Melathrokerion spirialis Zone in the upper Kimmeridgian-Tithonian, the Protopeneroplis ultragranulatus-Siphoninella antiqua, Frondicularia cuspidiata-Saracenaria inflanta zones, and Textularia crimica Beds in the Berriasian. The Cyrherelloidea tortuosa-Palaeocytheridea grossi Beds of the Upper Jurassic and Raymoorea peculiaris-Eucytherura ardescae-Protocythere revili Beds of the Berriasian are defined based on ostracodes. A new biostratigraphic scale is proposed for the upper Kimmeridgian-Berriasian of the eastern Crimea. The Dvyyakornaya Formation sediments are considered as deepwater facies accumulated on the continental slope.     

Boreal-tethyan correlation of the Jurassic-Cretaceous boundary interval by magneto- and biostratigraphy

As a result of detail sampling and paleomagnetic study of the 27-m-thick section of Jurassic-Cretaceous boundary beds in the Nordvik Peninsula (Anabar Bay, Laptev Sea), a succession of M-zones correlative with chrons M20n-M17r is established for the first time in the Boreal deposits. Inside the normal polarity zone corresponding to Chron M20n, a thin interval of reversed polarity, presumably an equivalent of the Kysuca Subzone (M20n.1r), is discovered. The other thin interval of reversed polarity established within the next normal polarity zone (M19n) is correlated with the Brodno Subzone (M19n.1r). The same succession of normal and reversed polarity zones has been discovered recently in the Jurassic-Cretaceous boundary beds of the Tethyan sections: in the Bosso Valley (Italy), at the Brodno (Slovak Republic) and Puerto Escaño (Spain) sites. Correlation of successions established lead us to conclusion, that the Jurassic-Cretaceous boundary corresponds in the Panboreal Superrealm to a level within the Craspedites taimyrensis Zone of the upper Volgian Substage. Hence, the greatest part of Volgian Stage should be included into the Jurassic System. Biostratigraphic data do not contradict this conclusion.     

The bivalve Buchia and the Jurassic-Cretaceous boundary in the boreal province

Eight successive Buchia zones (buchiazones) are recorded in the stratigraphic interval from the base of the Middle Volgian substage (Late Jurassic), up to the base of the Early Valanginian (Early Cretaceous). These zones, reading from the base upwards include: mosquensis, russiensis, taimyrensis, obliqua, unschensis, okensis, jasikovi and tolmatschowi. The lower boundary of each of these zones was examined to choose one of them as the most suitable for recognising the Jurassic-Cretaceous boundary. Preference was given to the base of the okensis zone, because it corresponds to the base of the ammonite zone of Hectoroceras kochi, and it is situated near the boundary between the Volgian and the boreal Berriasian stages. B. okensis is very easily recognised in field sections, and also is good for boreal-tethyan correlation. The base of the inflata zone and of its North Pacific chronostratigraphic analogue, the pacifica zone, is also ideal for correlation, but is too young and corresponds to the base of the Valanginian stage. The bases of other buchiazones are assessed and found unsatisfactory.     

松辽盆地及周缘地区侏罗系/白垩系界线区域对比特征探讨

松辽盆地及周缘地区是白垩纪时期全球最大的陆地出露区,是开展陆相J/K界线研究的理想地区.但是,受制于盆内埋深大、盆缘露头出露不佳等原因,松辽盆地及周缘地区J/K界线发育区域及层段仍然存在较大争议.同时,对于陆相J/K界线划分与对比这样的重大疑难问题,其研究很难一步到位.总结一套影响广泛、区域对比性强的J/K界线区域对比...     

Quaternary stratigraphy of the buried valleys of the lower Red Deer River,Alberta, Canada

The Quaternary fills of the buried valleys of southern Alberta and Saskatchewan have provided a wealth of information for the reconstruction of the glacial-interglacial record of the western plains of Canada, and this paper reports on the previously unstudied stratigraphy of the buried Calgary Valley and its former tributaries in the lower Red Deer River area. We attempt to differentiate Empress Group sediments, which potentially relate to pre-glacial, interglacial/ interstadial and post-glacial lake and river deposition, using sedimentology, stratigraphy and palaeoecology. Twenty-nine stratigraphical logs indicate that Empress Group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the Calgary Valley, located 15 km to the north of Dinosaur Provincial Park. Radiocarbon dates of 52.4 ka, 27.4 ka and > 42.4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid-Wisconsinan in age. However, outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials/interstadials and that older (even pre-glacial) sediments could have survived. Subglacial channels, recognisable on air photographs, largely coincide with buried valley positions due to the preferential excavation of the Quaternary sediment by meltwater and are filled with post-glacial lake sediment from which a radiocarbon date of 16 ka BP was obtained. Pre-glacial and glacial/post-glacial Empress Group sediments are lithologically indistinct but cover a large time span in southern Alberta.     

Biotic characteristics of the Sinian-Cambrian boundary beds in China and the boundary problems

There is general agreement that the first appearance of various small shelly fossils should be used to help delineate the beginning of the Cambrian Period. The history of research on this stratigraphic topic in China is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside China.The sections across the Precambrian—Cambrian (Sinian—Cambrian) boundary are described with notes on fossils in: (1) Tianzhushan section, Yichang, Hubei; (2) Maidiping section, Emli, Sichuan; (3) Wangjiawan section, Jinning County, Yunnan; and (4) Kunyang section, Yunnan.This is followed by a consideration of the biotic characteristics of Sinian—Cambrian Period. The history of research on this stratigraphic topic in China is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside China. This is followed by a consideration of the biotic characteristics of Sinian—Cambrian boundary beds, with respect to stratigraphy as well as organic evolution. The Precambrian—Cambrian boundary in China is estimated to have an age of 615 ± 20 Ma.It is commented that the above sections are qualified to be important candidates for the selection of the Sinian—Cambrian boundary stratotype and are also important working reference sections for the international Precambrian—Cambrian boundary stratotype.     

Cambrian stratigraphy of Kashmir and its boundary problems

The biostratigraphy of the Cambrian of Kashmir based on trilobite assemblage zones and trace fossils has been attempted. Faunal gaps occur in lower part of Lower Cambrian, upper Lower Cambrian, lower Middle Cambrian and upper part of Upper Cambrian. In the Lower Cambrian Cruziana—Rusophycus and Redlichia Zones, in the Middle Cambrian Solenopleura—Tonkinella, Tonkinella—Anomocare, Anomocare—Bailiella and Bolaspidella Zones, and in the Upper Cambrian Chuangia and Dikelocephalites Zones are recognized. The position of intrasystem boundaries is also discussed. While the various taxa have lithological preferences and are not necessarily found in a continuous sequence, an attempt has been made to interpret the ranges of different genera. The affinities of the fauna with that of other Cambrian basins of the world are discussed. It is concluded that the bulk of the fauna is of a cosmopolitan nature.     

A revision of the lower Cretaceous stratigraphy of Lebanon

The lithostratigraphic nomenclature of the lower Cretaceous strata of Lebanon is completely revised. Four formations are defined in place of the existing complex of informal nomenclature. In ascending order these are the Chouf Sandstone Formation, the Abeih Formation, the Mdairej Limestone Formation and the Hammana Formation. The Hammana Formation is subdivided into a lower Dahr el Beidar Member and an upper Knisseh Member.     

黑龙江东部侏罗—白垩系界线附近地层研究新进展

<正> 近年来,随着饶河东安镇具国际性对比标准的海相侏罗—白垩系界线的确定及其相关生物组合带的建立(孙革等,1989),黑龙江省东部地区的海相—海陆交互相—陆相的侏罗—白垩系界线及其附近地层的研究,不断取得新的进展。研究成果之一是,鸡西盆地城子河组时代属早白垩世。在其典型剖面(穆棱河北岸路堑剖面)的城子河组下部,发现含早白垩世凡兰吟—戈特里夫期(Valanginian-Hauterivian)沟鞭藻的海相层(孙学坤、     

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.     

An inlier of Jurassic rocks at the bottom of the Lena River valley

An inlier of Jurassic rocks is identified for the first time at the surface of the first terrace above a floodplain composed of Holocene sediments on the left side of the Lena River. It represents a block of Jurassic rocks similar compositionally to rocks in outcrops on the left slope of the river valley. It is shown that the block was displaced along faults in the Holocene. The rocks of the inlier are deformed, and the Paleogene–Neogene sequence covering the plateau (altitude approximately 200 m) is displaced in the stepwise mode to the level corresponding to the bottom of the Lena River valley (altitude approximately 100 m). The Holocene alluvium enveloping the inlier belongs to the constratal type being up to 40 m thick. Steep faceted morphostructures on the left slope of the Lena River valley coincide with the faults. The left slope of the valley is crossed exclusively by young incisions. It is assumed that Holocene movements may be reactivated in the future.     

The Jurassic/Cretaceous boundary in northern Siberia and Boreal-Tethyan correlation of the boundary beds

There is no international consensus regarding the GSSP for the Berriasian, the basal stage of the Cretaceous System. Any of the events discussed by the international expert community can be regarded as a marker of the Jurassic/Cretaceous boundary: a phylogenetic change of taxa, paleomagnetic reversal, or isotopic excursion. However, the problem of identification of this level in Boreal sections can be solved only using a combination of data obtained by paleontological and nonpaleontological methods of stratigraphy (bio-, chemo-, magnetostratigraphy, etc.). With any of the accepted markers, the Jurassic/Cretaceous boundary in Siberian sections will be within the upper part of the regional Bazhenovo Horizon. The least interval of the uncertainty of the position of this boundary in Siberian sections will be ensured by the selection of one of two markers: biostratigraphic (base of the Pseudosubplanites grandis Subzone) or magnetostratigraphic (base of the M18r magnetozone).