First evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) from the Ionian Zone,western continental Greece

Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes) and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate—black shale succession of the Ionian Zone (western Greece), provide the first evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich (44.5 wt% TOC), carbonate-free black shale, near the Cenomanian–Turonian boundary within the Vigla limestone formation (Berriasian–Turonian). Compared to the ‘Bonarelli’ black-shale interval from the type locality of OAE2 in Marche–Umbria, Italy, this black shale exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched δ¹³C values for both bulk organic matter (−22.2‰) and specific organic compounds are up to 5‰ higher than those of underlying organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian–Turonian black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N₂-fixing cyanobacteria in Cretaceous oceans during the Cenomanian–Turonian and early Aptian oceanic anoxic events.     

Evidence of bottom-redox conditions during oceanic anoxic event 2 (OAE2) in Wadi Bazina,Northern Tunisia (Southern Tethyan margin)

Detailed chemostratigraphy across the Cenomanian-Turonian boundary in northern Tunisia points to several prevailing paleoceanographic conditions during the deposition of organic-rich beds of Bahloul Formation. The sedimentological study shows that there is no correlation between color and CaCO₃ content because both dark and light-colored intervals of Bahloul Formation are carbonate-rich. Stable isotope analysis displays a positive carbon isotope excursion characterized by four significant peaks (I to IV) which are ranging from 3.2 to 3.5‰. These peaks represent episodes of elevated rates of organic carbon burial during the C/T oceanic anoxic event (C/T boundary OAE2). The Cenomanian-Turonian boundary could be situated between the third isotopic peak and the filament event. The total organic carbon (TOC) measurements show values ranging from 0.28 to 6.19% with average value of 3.5%. This indicates that the Bahloul Formation shale is a very good oil source rock. The Hydrogen Index (HI) values range from 359 to 698 mg HC/g TOC. The T _max values range from 390 to 438 °C. Binary diagrams HI vs. T _max indicate a type II with values falling within the immature organic-matter range. The concentrations major elements reveal low values of Ti and K. The correlation between Al and Ti and K shows a significant correlation pointing to homogeneous provenance. Primary productivity indicators (Cu, Ba, and Ni) record its association with organic matter. Redox-sensitive elements such as U, V, and Mo and the high values of V/(V + Ni) ratio indicate a strongly reducing environment which led to the better preservation of the organic matter.     

Foraminifers and radiolarians across the Albian-Cenomanian and Cenomanian-Turonian Boundaries (Northern Peri-Tethys)

Changes in morphological diversity and taxonomic composition of late Albian-early Turonian foraminiferal and radiolarian assemblages from the northern Peri-Tethys are considered. Several stages are defined in evolution of planktonic foraminifers: polytaxic (Albian-Cenomanian), oligotaxic (Cenomanian-Turonian boundary period), and polytaxic (Turonian). The Albian-Cenomanian stage was characterized by intense development of rotaliporids representing an intricate group of planktonic foraminifers, which became extinct in the terminal Cenomanian. An intense speciation of the radiolarian genus Crolanium and last occurrences of its most species, the index species C. cuneatum included, was characteristic of the terminal Albian. Spheroid and discoid radiolarians were dominant in the Cenomanian, while the Turonian was marked by intense development of all the radiolarian morphotypes.     

Carbon isotope records of the early Albian oceanic anoxic event (OAE) 1b from eastern Tethys (southern Tibet,China)

The early Albian Oceanic Anoxic Event (OAE), i.e., OAE1b, is well documented in western Tethys and in the primary North Atlantic Ocean, but has not yet been reported from eastern Tethys. In this paper, we present bulk carbon isotope data of hemipelagites to examine if it was recorded in eastern Tethys. Samples were taken from the upper Chuangdepu Member (nannofossil zone CC8) of the lower Gyabula (former Shadui) Formation at the Bangbu section, Qonggyai, southern Tibet of China. The δ¹³C values mainly range from −0.6‰ to 1.8‰ with a maximum of 1.87‰ and a minimum of −0.69‰. Three stages of carbon isotope evolution were distinguished with three boundaries. By the constraint of the stratigraphic sequence and nannofossil biostratigraphic zone CC8, the rapid δ¹³C change and correlation with western Tethys and Atlantic Ocean together suggest that these three boundaries of the carbon isotope evolution probably correspond to three subevents of the early Albian OAE1b, and the subevent levels of upper Kilian, Paquier, and Leenhardt are recorded in eastern Tethys (southern Tibet). The fact that the amount of δ¹³C shift is less by ∼1.5–2.0‰ in eastern Tethys than in western Tethys and Atlantic Ocean is interpreted as a result of possible cool sea surface (∼14–16 °C) of the southeastern Tethys (northern Indian passive margin of Greater India), which was probably located in a medium–high latitude during the Albian, leading to low primary productivity. The recognition of OAE-1b from Tethys Himalaya can improve our understanding of the Tethys and global paleoclimatic and paleoceanographic changes during the mid-Cretaceous.     

The Bashilsky swell: an Upper Pleistocene extrusion in the Verkhnechegemskaya caldera (Northern Caucasus)

This work describes a young extrusive massif in the uppermost reaches of the Chegem River (Bashilauzu-su River), which had been considered as a feeder of the great sequence of Upper Pliocene rhyolite ignimbrites of the Verkhnechegemskaya caldera. The Upper Pleistocene age of the stratum, extrusive origin of automagmatic breccias and fluidolites, as well as its difference from rhyolites of the caldera are proven. The Bashilsky swell, located in the Late Pleistocene glacial trough, is evidence of young volcanism in this area, which has not been previously proposed.     

A 400-km-long piggyback basin (Upper Aptian–Lower Cenomanian) in the Eastern Alps

The Late Aptian to Early Cenomanian Tannheim–Losenstein basin constitutes an early, deep-marine piggyback trough which formed on the Cretaceous orogenic wedge of the Eastern Alps. The narrow basin extended over more than 400 km from the western part of the Northern Calcareous Alps into the Western Carpathians (Slovakia), as suggested by similarities in stratigraphy – e.g. the common coarsening upward succession of marls, sandstones, and conglomerates – and by similarities in timing of deformation and the uniform composition, e.g. similar heavy mineral assemblages. The coarsening-upward succession resulted from the progradation of a coarse-grained slope apron into a hemipelagic basin. The composition of detrital material constitutes evidence for a uniform source area to the north, along the entire length of the basin, comprising continental basement, Mesozoic sediments and remnants of ophiolites. The basin formation marked the onset of compression along the northern Austroalpine plate boundary.     

A new species of Platanus from the Cenomanian(Upper Cretaceous) in eastern Heilongjiang,China

The stratigraphic division and sequence of the Upper Cretaceous sediments in eastern Heilongjiang Province,China,have been ambiguous and controversial,mainly due to a lack of biostratigraphically useful fossils and related radiometric dating.A new species of angiospermous fossil plant.Platanus heilongjiangensis sp.nov.,from Qitaihe in eastern Heilongjiang has been found in sediments conformably above which zircons from a rhyolitic tuff has been dated by U-Pb radiometric methods as 96.2± 1.7 Ma.indicating that the Upper Houshigou Formation is of Cenomanian age.This discovery not only provides new data to improve our stratigraphic understanding of the Houshigou Formation,but also shows that Platanus flourished in the early Late Cretaceous floras of the region.This new study also indicates active volcanism taking place in the eastern Heilongjiang region during the Cenomanian of the Late Cretaceous.     

Biotic response to the latest Cenomanian drowning and OAE2: A case study from the Eastern Desert of Egypt

The changes in macrofauna and microfauna, before, during and after the latest Cenomanian global Oceanic Anoxic Event (OAE2), from the Eastern Desert of Egypt are documented, along with an inferred paleoenvironment. The age of the studied OAE2 interval is constrained by the last occurrence of the marker calcareous nannofossils species Axopodorhabdus albianus along with the previously identified positive δ¹³C excursion from the coeval ammonite Vascoceras cauvini Zone (= Neocardioceras juddii Zone), enabling correlation with the peak ‘b’ of the OAE2. Based on the studied microfaunal assemblages, a warm shallow restricted lagoonal environment with mesotrophic conditions and strong seasonality is inferred. The presence of a rare ammonite (and ostracods) attest to the intermittent introduction of marine waters within this inner ramp setting. In terms of sequence stratigraphy, two 3rd order depositional sequences are recorded. The top surface of the first depositional sequence, at the sequence boundary, SB Ce 5 (the start of the OAE2), is marked by an abrupt faunal change with reduced abundances of the macrofaunal elements. This is in tune with other Egyptian records of relatively smaller loss (10 %) at the Cenomanian-Turonian boundary, as compared to much higher numbers (53–79% of species), globally. This faunal (biotic bottleneck) and lithological change (from siliciclastic-dominated deposits to a largely carbonate-dominated one) at the SB Ce 5 is attributed as a response to the latest Cenomanian drowning (the highest sea-level during the Phanerozoic), that also resulted in the formation of carbonate platform.     

Biostratigraphic characterization by means of ammonoids of the lower Aptian Oceanic Anoxic Event (OAE 1a) in the eastern Iberian Chain (Maestrat Basin, eastern Spain)

It is now generally accepted that the Oceanic Anoxic Event 1a [OAE 1a] correlates with the lower part of the Leupoldina cabri planktonic foraminiferal Zone. Its calibration against the standard ammonite scale, however, seems to be more problematic. This is due, in part, to the fact that ammonites are scarce and/or of little diagnostic value from a biochronological viewpoint in the lower Aptian pelagic successions where the black shale horizons are better developed.We have been able to characterize OAE 1a geochemically in the relatively shallow water deposits of the eastern Iberian Chain (Maestrat Basin, eastern Spain), where ammonite faunas are rich. The interval corresponding to this event is dominated by the genera Roloboceras and Megatyloceras, accompanied by Deshayesites forbesi and Deshayesites gr. euglyphus/spathi. This assemblage is characteristic of the middle/upper part of the Deshayesites weissi Zone. The first occurrence of the species Deshayesites deshayesi (d'Orbigny), which marks the base of the overlying zone, takes place in our sections some metres above the OAE 1a interval.In the historical stratotype region of Cassis-La Bédoule (southern Provence Basin, southeastern France), the OAE 1a interval is also characterized by the presence of Roloboceras and Megatyloceras. Nevertheless, it has usually been correlated with the D. deshayesi Zone. In our opinion, this discrepancy is due to divergences in the taxonomic assignments of the deshayesitids present in these beds. In fact, the specimens attributed by French authors [Ropolo, P., Conte, G., Gonnet, R., Masse, J.P., Moullade, M., 2000. Les faunes d'Ammonites du Barrémien supérieur/Aptien inférieur (Bédoulien) dans la région stratotypique de Cassis-La Bédoule (SE France): état des connaissances et propositions pour une zonation par Ammonites du Bédoulien-type. Géologie Méditerranéenne 25, 167–175; Ropolo, P., Moullade, M., Gonnet, R., Conte, G., Tronchetti, G., 2006. The Deshayesitidae Stoyanov, 1949 (Ammonoidea) of the Aptian historical stratotype region at Cassis-La Bédoule (SE France), Carnets de Géologie / Notebooks on Geology Memoir 2006/01, 1–46.] to D. deshayesi and D. dechyi can be reinterpreted as belonging to D. forbesi.Following this reinterpretation, the Roloboceras beds (equivalent of OAE 1a) of Cassis-La Bédoule would also correspond to the D. weissi Zone. This age is additionally corroborated by data from southern England [Casey, R., 1961a. The stratigraphical palaeontology of the Lower Greensand. Palaeontology 3, 487–621; Casey, R., 1961b. A Monograph of the Ammonoidea of the Lower Greensand, part III. Palaeontographical Society, London, pp. 119–216], and by our recent observations in Le Teil (Ardèche Platform, southeastern France), where the Roloboceras faunas are also associated with Deshayesites consobrinus and Deshayesites gr. euglyphus, taxa that are characteristic of the D. weissi Zone.     

白垩纪大洋缺氧事件2(OAE 2)的天文年代学对比研究

白垩纪中期大洋缺氧事件2(OAE 2)是地史时期一次全球性重大古海洋和古气候事件, 记录了地球温室期全球碳循环扰动和地球系统反馈过程的重要信息。由于全球不同剖面OAE 2年代学约束仍存在争议, 制约了对这一全球性事件成因机制的认识。针对上述问题, 本研究选取了全球不同纬度带的8个剖面, 通过对碳同位素和硬等温剩余磁化率数据进行旋回地层分析, 开展了OAE 2天文年代学研究。结果显示, 研究剖面的OAE 2发生时间被约束在94.55~93.98 Ma, 结束时间被约束在93.80~93.17 Ma, 持续时间为430~910 ka, 不同剖面的OAE 2起止时间和持续时间存在差异。火山活动为海洋环境提供了营养物质, 暂时性的全球海洋连通性影响了火山喷发物质搬运, 季风强弱影响了陆源物质风化速率和火山喷发物、陆源剥蚀物的搬运, 故剖面地理位置及其与火山活动区域的距离、海洋连通性和季风活动共同影响OAE 2的起止时间和持续时间。OAE 2的发生阶段大致与短偏心率调制周期极大值时期(即约2.4 Ma超长偏心率周期)或从较大值向极大值过渡时期对应, 且天文理论曲线La2010d中约2.4 Ma超长偏心率周期也为极大值时期或从较大值向极大值过渡时期。在此天文轨道配置下, 气候季节对比性明显增加, 增强的季风降水导致陆地向海洋输送的营养物质增加, 海洋初级生产力提高, 造成海水缺氧, 随后大量有机质的分解进一步导致了O₂消耗, 这些因素的共同作用可能促进了大洋缺氧事件的形成。相反, OAE 2的结束阶段与超长偏心率周期较小值时期对应, 此时气候以低季节性对比为特征, 季风降水减弱, 水柱混合良好, 从而提高海洋中间和底部水域O₂浓度, 这些因素的共同作用可能导致大洋缺氧事件的结束。在OAE 2期间, 天文轨道周期驱动的季风强度的变化, 通过影响陆源物质的剥蚀以及陆源和火山喷发物质的搬运、海洋水体分层状况等, 在OAE 2演化中扮演着重要角色。

     

Radiolarians of the upper Cenomanian and lower Turonian from deposits of the Ananuri Formation, the western Caucasus (Lazarevskoe area)

Diverse radiolarians (over 70 species) are detected in cherty rocks above the bituminous shale horizon, the marker of anoxic event OAE-2 recorded across the Cenomanian-Turonian boundary in the upper part of the Ananuri Formation of flyschoid deposits, the Lazarevskoe area of the western Caucasus. The radiolarian assemblages studied are comparable in composition with radiolarians from concurrent Cenomanian-Turonian boundary strata in other Mediterranean regions (e.g., in the Crimea and Turkey). The lower radiolarian assemblage includes index species Dactyliosphaera silviae of synonymous Cenomanian zone. Alievium superbum present in the upper assemblage is index species of the relevant Turonian zone. Within the studied flyschoid sequence, sediments indicative of the above event (bituminous shales and cherts) are confined to upper elements of flysch rhythms.     

The late Quaternary tephrostratigraphical record of the San Gregorio Magno basin (southern Italy)

Twenty‐one primary pyroclastic layers were found embedded in the lacustrine sediments of the San Gregorio Magno basin (Southern Apennines). These sand‐sized layers were characterised by a noticeable juvenile fragments content and by a sharp basal contact with the underlying clay and silt sediments. The tephra layers have been correlated with terrestrial counterparts from well‐known eruptive events of the Campanian volcanic area, or with reference layers from deep sea sediment cores and from the Monticchio maar sequence. The investigation of the San Gregorio Magno tephra layers made it possible to deduce that lacustrine sedimentation at San Gregorio Magno basin began before 170k yr BP and lasted at least until the emplacement of the Neapolitan Yellow Tuff, which occurred about 15k yr BP. The tephrochronology allowed determination of the varying sedimentation rate that occurred in the basin. Correlation of the lacustrine record with marine sequences has allowed development of a late Quaternary tephrostratotype for southern Italy. Copyright © 2006 John Wiley & Sons, Ltd.     

鄂尔多斯盆地东缘煤层气有利区块优选

鄂尔多斯盆地东缘经过20 a的勘探开发,煤层气仍然没有实现产业化。随着勘探资料的不断丰富,有必要对该区进行煤层气有利区块的优选和重新认识。在前人研究基础上,首先将鄂尔多斯盆地东缘埋深1 500 m区域分为6个区块,选取煤层厚度、含气量、构造条件、水文条件、煤体结构、含气饱和度、储层压力梯度、渗透率和临界解吸压力与储层压力比9个参数作为区块优选指标,结合国内外及研究区实际情况制定了相应的评价临界值。将上述参数作为评价指标集合,以评价单元作为对象集,以有利、较有利和不利作为评级等级集合,然后运用模糊数学综合评判方法得到各评价单元的不同评价参数对评价等级的隶属度,并运用层次分析法确定了各指标的相对权重,最后得到了评价单元对评价等级的隶属度。根据最大隶属度原则,吴堡-柳林属于有利区,大宁-吉县和韩城属于较有利区,准格尔、府谷、河曲-临县属于不利区,吴堡-柳林的煤层气可采性好于大宁-吉县和韩城。因此,建议将吴堡-柳林、大宁-吉县和韩城定为研究区煤层气优先开发区块。     

Kinematics of the eastern Caucasus near Baku, Azerbaijan

The potential for large, shallow earthquakes and their associated seismic hazard in the eastern Caucasus, an area of dense population and sensitive industrial infrastructure, remains speculative based on historical precedent and current geologic and seismologic observations. Here we present updated and expanded results from a GPS network between the northern edge of the Lesser Caucasus and Greater Caucasus, providing geodetic constraints to the problem. A significant strain rate is observed in a profile over a distance of about 150?km across the Kura Basin. We attribute this to inter-seismic strain accumulation on buried fault structures and present simple elastic dislocation models for their plausible geometry and slip rate based on the known geology, seismicity and the GPS velocities. Due to the close proximity of the strain anomaly to Baku, further observations are needed to determine whether observed contraction is due to inter-seismically locked faults and, if so, implications for the seismic hazard in the region.     

Geochemistry of Cenomanian/Turonian boundary sediments in the mountainous part of Crimea and the northwestern Caucasus

Detailed data obtained on the chemistry of sedimentary rocks from the mountainous part of Crimea and the northwestern Caucasus that were dated at the Cenomanian/Turonian boundary and were formed during Oceanic Anoxic Event 2 (OAE 2) make it possible to calculate the dissolved oxygen concentration in the bottom waters of the sedimentation basin. The enrichment coefficients of trace elements in the black shales are revised and an explanation is suggested for the genesis of the rocks with regard for unusual climatic changes.     

Further evidence of marine Cenomanian,lower Turonian and Maastrichtian in the Upper Benue basin of Nigeria (West Africa)

Field investigations in the Upper Benue rift basin of Nigeria highlight the necessity for a review of the Cenomanian-Turonian biostratigraphy of the area. Three ammonite zones of Vascoceras bulbosum (Reyment), Paravascoceras costatum (Reyment) and Pseudotissotia (Bauchioceras) nigeriensis (Woods) have been recognized at sections exposed at the quarry of the cement factory near the village of Ashaka. The sediments within the Vascoceras bulbosum zone also contain specimens of Exogyra olisiponensis (Sharpe), Kanabiceras septemseriatum (Cragin) and Epengonoceras dumbli (Cragin). These are all indicative of an uppermost Cenomanian age and reveal that at least the lower portion of the Gongila Formation as exposed at Ashaka is faunistically equivalent to the Pindiga Formation as exposed in the type section at Pindiga.The shales in the Gombe region in which Libycoceras ismaeli (Zittel) was found are probably part of the Maastrichtian Fika shales outcropping extensively in the northern part of the area. The discovery of Cyclolithes nov. sp. within Gombe sandstones at Dakiti near Kumo confirm that they are at least partially marine in origin and Maastrichtian in age. This could be considered as an additional evidence in favour of the presence of marine waters in the Upper Benue during the last part of the Cretaceous.     

The geochemical features of terrigenous host rocks at massive sulfide deposits in the eastern Caucasus

Based on a great body of factual data, geochemical peculiarities in the distribution of rare, noble, radioactive, and other trace components in the Lower-Middle Jurassic terrigenous ore-enclosing (hereafter, host) rocks at massive sulfide deposits in the Vostochnyi (eastern) segment of the Greater Caucasus are high-lighted. Study of the Filizchai base metal massive sulfide deposit made it possible to define general regularities of element distribution in the ore body and altered wall rocks that reflect the general geochemical zonality. Concentrations of most components depend on the lithology and wall-rock alteration, distribution of rocks in the section, proximity of the contacting ore, and its mineral composition. Contents of typical elements in host rocks are closely associated with their concentrations in the ore bodies.     

New Alveolinoidea (Foraminifera) from the Cenomanian of Oman

The first alveolinoidean appearing in the Cenomanian Natih Formation of Oman (Adam foothills and southern edge of Jabal Akhdar) are studied in detail. Morphological analysis results in the creation of one new family, Myriastylidae, two new genera, Myriastyla and Alveocella, and four new species, M. omanensis, M. grelaudae, A. wernliana, and Cisalveolina nakharensis. These four new taxa have a short stratigraphic extension restricted to the uppermost part of Natih E unit and are dated early middle Cenomanian by neighboring foraminifers and ammonite levels.