Brittle faulting in the Prince Charles Mountains, East Antarctica: Cretaceous transtensional tectonics related to the break-up of Gondwana

The Lambert Glacier–Amery Ice Shelf occupies a narrow NNE–SSW-orientated fault-bound depression referred to as the Lambert Graben. Deep faults associated with this structure are recognised geophysically, and are interpreted to extend at least 700 km inland from the Antarctic coast. Kinematic and palaeostress data from quartz- and calcite-bearing faults, inferred to represent the surface expression of these deeper structures, suggest that a single faulting event occurred in response to NW–SE-directed extension, oblique to the axis of the graben. The bulk of the movement along these faults was dextral strike slip, accommodating components of both normal and reverse offset. In the northern Prince Charles Mountains, these faults disrupt the Permo-Triassic Amery Group and juxtapose it against Proterozoic basement. Equivalent strike-slip faults in the southern Prince Charles Mountains produce dextrally offset tectonic boundaries and metamorphic isogrades across the Lambert Glacier. The similarity in orientation between the palaeostress field calculated for these faults and the Cretaceous divergence vector between India and Antarctica strongly supports the inference that faulting was of Cretaceous age, and related to the break-up of Gondwana.     

Comparison of the Jurassic and Cretaceous sedimentary cycles of Somalia and Madagascar: implications for the Gondwana breakup

The Jurassic and Cretaceous sedimentary history of northern Somalia and the Morondava Basin of south-western Madagascar have been studied. Both regions display an independent facial development; however, a comparison of the sequential evolution of the Mesozoic sedimentary successions in these two presently widely separated areas reveals a surprisingly high level of similarity, which probably reflects major events during the disintegration of Eastern Gondwana during the Jurassic and Cretaceous. Although in Jurassic times the onset of transgressions and regressions in both areas compares well with eustatic development, major deviations in combination with the tectonic activities of different degrees are observed in the Early and Late Cretaceous synchronously in both regions. Transgressions are observed in Toarcian, Bajocian (not dated in northern Somalia), Callovian, Valanginian (Madagascar only), Aptian and Campanian times. Tectonism is noted before the Aptian and Campanian transgressions in northern Somalia and the Morondava Basin of south-western Madagascar.     

Gondwana to Asia: Plate tectonics,paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through latest Eocene (166–35 Ma)

Using the most up-to-the-date information available, we present a considerably revised plate tectonic and paleogeographic model for the Indian Ocean bordering continents, from Gondwana's Middle Jurassic break-up through to India's collision with Asia in the middle Cenozoic. The landmass framework is then used to explore the sometimes complex and occasionally counter-intuitive patterns that have been observed in the fossil and extant biological records of India, Madagascar, Africa and eastern Eurasia, as well those of the more distal continents.Although the paleogeographic model confirms the traditional view that India became progressively more isolated from the major landmasses during the Cretaceous and Paleocene, it is likely that at various times minor physiographic features (principally ocean islands) provided causeways and/or stepping-stone trails along which land animals could have migrated to/from the sub-continent. Aside from a likely link (albeit broken by several marine gaps) to Africa for much of this time (it is notable, that the present-day/recent biota of Madagascar indicates that the ancestors of five land-mammal orders, plus bats, crossed the > 400-km-wide Mozambique Channel at different times in the Cenozoic), it is possible that the Kerguelen Plateau connected India and Australia–Antarctica in the mid-Cretaceous (approximately 115–90 Ma). Later, the Seychelles–Mascarene Plateau and nearby elevated sea-floor areas could have allowed faunas to pass between southern India and Madagascar in the Late Cretaceous, from around 85–65 Ma, with an early Cenozoic extension to this path forming as a result of the Reunion hot-spot trace islands growing on the ocean floor to the SSW of India. The modelling also suggests that India's northward passage towards Asia, with eventual collision at 35 Ma, involved the NE corner of the sub-continent making a glancing contact with Sumatra, followed by Burma from ~ 57 Ma (late Paleocene) onwards, a scenario which is compatible with the fossil record indicating that India–Asia faunal exchanges began occurring at about this time. Finally, we contend that a number of biologically-based direct terrestrial migration routes that have been proposed for last 15 m.y. of the Cretaceous (Asia to India; Antarctica to Madagascar and/or India) can probably be dismissed because the marine barriers, likely varying from > 1000 up to 2500 km, were simply too wide.     

羌塘盆地双湖地区早中侏罗世过渡期碳同位素波动及成因研究

藏北双湖县巴岭乡地区出露一套深水相黑色页岩地层,包括下侏罗统曲色组和中侏罗统色哇组二个组地层单元。根据菊石化石控制的生物地层时代,下伏曲色组划归Pliensbachian-Toarcian 阶,上覆色哇组级代表Aalenian-Bajocian 期沉积,二者之间为连续沉积,是目前西藏特提斯域菊石化石控制程度最高的中下侏罗统地层。野外实测了索布查J₂/J₁界线剖面,按2m间距采集了148件样品,室内开展了无机碳（δ¹³C_carb）和有机碳（δ¹³C_kero）分析,目的是揭示早侏罗世末期到中侏罗世初期这一时段的古海洋演化过程。研究结果表明,曲色组沉积期古海水δ¹³C_DIC偏正,而色哇组δ¹³C_DIC偏负,J₂/J₁界线上下δ¹³C_carb值显示阶步式负向偏移的特点。根据相关分馏方程计算,Toarcian期海洋浮游植物繁盛,δ¹³C_DIC偏正_,海水营养盐NO₃浓度偏低,而Aalenian期海洋浮游植物衰减,δ¹³C_DIC偏低,NO₃浓度升高。沉积有机质或干酪根碳同位素δ¹³C_kero在J₂/J₁界线上下与δ¹³C_carb变化趋势一致,也具有由高值逐渐偏低的特点,但δ¹³C_carb和δ¹³C_kero变化曲线的波峰和波谷并不同步,这是因为海源和陆源有机质相对含量高低变化所致。文中根据碳同位素质量平衡方程,定量的描述了索布查界线剖面陆源和海源有机质比例的变化过程,讨论了曲色组和色哇组烃源岩在油气勘探中的意义。     

藏东类乌齐地区辉长岩:冈瓦纳大陆北缘晚古生代裂解的记录

青藏高原处于冈瓦纳大陆与劳亚大陆的交汇部位,是研究冈瓦纳大陆裂解与聚合过程的关键地区。晚古生代伴随着特提斯洋的打开与扩张,冈瓦纳大陆北缘发生了广泛的裂解作用。大陆板内岩浆作用是超大陆裂解的重要证据。在青藏高原内部已有二叠纪大陆板内特征基性岩的报道,它们是该裂解事件的记录。然而,根据目前的相关报道,这些岩石主要出露在青藏高原的西部,以羌塘和潘伽地区为主,在其他地区尚无相关报道。首次报道的藏东类乌齐地区早二叠世辉长岩LA-ICP-MS锆石U-Pb定年结果显示,辉长岩的形成年龄为280±2Ma。全岩地球化学资料表明,辉长岩具有与典型大陆板内玄武岩类似的地球特征。辉长岩具有明显正的锆石εHf(t)值(5.1~11.5),暗示其岩浆起源于亏损的地幔源区。结合区域地质资料,认为类乌齐辉长岩是冈瓦纳大陆北缘早二叠世裂解的产物。因此,早二叠世大陆板内基性岩浆作用在青藏高原东部也有出露,它们是在羌塘-潘伽地幔柱活动的作用下,冈瓦纳大陆北缘裂解与班公湖-怒江洋打开和扩张的结果。     

辽西晚三叠世末—中侏罗世崩塌-滑坡-泥石流沉积及其构造意义

燕山板内造山带东部辽西、冀北地区，晚三叠世末—中侏罗世期间发生了两次大规模的滑坡、泥石流沉积和成群的巨大岩块崩塌事件。辽西晚三叠世—早侏罗世邓杖子组是一套以碳酸盐岩砾岩为主的崩塌、泥石流、滑坡及深水浊积岩序列，邓杖子组中砾岩的砾石成分自下而上表现出明显的变化规律，即邓杖子组下部砾岩砾石时代新而上部砾岩砾石时代老。其中最新的砾石成分是来自于邓杖子组之下的晚三叠世水泉沟组的安山岩，砾石时代的倒序显示同构造剥蚀-沉积的特点。同时，邓杖子组沉积组合也反映出伸展盆地的沉积特点。邓杖子组沉积后不久，在辽西—冀北的其他地区，还发育许多早—中侏罗世巨大的崩塌岩块，野外见到的最大岩块延伸长度超过4km。崩塌、滑坡、泥石流及成群发育的巨大崩塌岩块都是在地壳快速隆升过程中发生的同构造沉积记录，这从构造-沉积学的角度显示燕山地区在早中生代曾经发生过强烈快速隆升。     

A stable isotope record from freshwater lake shells of the eastern Tibetan Plateau, China, during the past two centuries

Lake Xingcuo is a small, closed, hardwater lake situated in the eastern Tibetan Plateau. Stable isotope data (δ¹⁸O and δ¹³C) from the freshwater snail Gyraulus sibirica (Dunker) in a 34-cm-long, radioactive isotope-dated sediment core represent the past 200 years of Lake Xingcuo environmental history. Carbon and oxygen isotope ratios in the shells of the snail yield information on the isotopic composition of the water in which the shell was formed, which in turn relates to climatic conditions prevailing during the snail's life-span. Living and fossil shells from Lake Xingcuo were collected. δ¹⁸O values in the living shells from Lake Xingcuo are in equilibrium with ambient waters, while δ¹³C values may trace snail dietary carbon. On comparing δ¹⁸O and δ¹³C in the shell of Gyraulus sibirica with monitored data for the period 1954-1995, we found that the δ¹⁸O composition in the shell is an efficient proxy revealing air temperature during the warmer months from April to September. There is a positive correlation between the δ¹⁸O in the shells of Gyraulus sibirica and the running average temperature of the warmer months. Climatic variability in the eastern Tibetan Plateau for the past two centuries has been inferred from the δ¹⁸O record from the freshwater snails in the sediments of Lake Xingcuo. As such, the last 200 years' palaeoclimatic record for this region can be separated into three periods representing oscillations between warm and cool conditions consistent with the Guliya ice record in the Tibetan Plateau.     

The motion of Adria during the Late Jurassic and Cretaceous: New paleomagnetic results from stable Istria

The motion of Adria, the largest lithospheric fragment in the Central Mediterranean region, has played an important role in the tectonic development of the surrounding mountain chains and even of distant areas, like the Eastern Alps or the Pannonian basin. The available paleomagnetic data were insufficient to constrain this motion, except in a general way. In this paper, new paleomagnetic results are presented from one of the stable parts of Adria which emerge from the Adriatic Sea. The results were obtained on weakly magnetic platform carbonates of the mud-supported type, collected from 21 geographically distributed localities.The results, combined with mean paleomagnetic directions from selected localities from a pioneer study in Istria that were chosen using statistical criteria, were divided into three age groups (Tithonian–Aptian, Albian–Cenomanian, Turonian–Coniacian). The paleomagnetic poles calculated for each of them (Tithonian–Aptian): λ(N) = 47°, (E) = 275°, k = 67, α₉₅ = 9.4°, N = 5; Albian-Cenomanian: λ(N) = 58°, (E) = 253°, k = 145, α₉₅ = 4.3°, N = 9; Turonian–Coniacian: λ(N) = 63°, (E) = 261°, k = 50, α₉₅ = 7.3°, N = 9) reveal a moderate shift during the Cretataceous, which is comparable with that calculated from the African reference poles. However, the Istrian apparent polar wander path is slightly displaced from the African curve, as a consequence of about 10° counterclockwise rotation of Istria, with respect to Africa. This rotation angle is more that 10° smaller than the difference measured for the Mid-Late Eocene between the paleomagnetic direction of platform carbonates from Istria and the African reference direction. This difference may be the consequence of a small clockwise rotation of Istria, with respect to Africa, most probably at the end of Cretaceous.     

The longest voyage: Tectonic,magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia

The tectonic evolution of the Indian plate, which started in Late Jurassic about 167 million years ago (~ 167 Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety of plate tectonic events such as: continental breakup, sea-floor spreading, birth of new oceans, flood basalt volcanism, hotspot tracks, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be investigated. Plate tectonic maps are presented here illustrating the repeated rifting of the Indian plate from surrounding Gondwana continents, its northward migration, and its collision first with the Kohistan–Ladakh Arc at the Indus Suture Zone, and then with Tibet at the Shyok–Tsangpo Suture. The associations between flood basalts and the recurrent separation of the Indian plate from Gondwana are assessed. The breakup of India from Gondwana and the opening of the Indian Ocean is thought to have been caused by plate tectonic forces (i.e., slab pull emanating from the subduction of the Tethyan ocean floor beneath Eurasia) which were localized along zones of weakness caused by mantle plumes (Bouvet, Marion, Kerguelen, and Reunion plumes). The sequential spreading of the Southwest Indian Ridge/Davie Ridge, Southeast Indian Ridge, Central Indian Ridge, Palitana Ridge, and Carlsberg Ridge in the Indian Ocean were responsible for the fragmentation of the Indian plate during the Late Jurassic and Cretaceous times. The Réunion and the Kerguelen plumes left two spectacular hotspot tracks on either side of the Indian plate. With the breakup of Gondwana, India remained isolated as an island continent, but reestablished its biotic links with Africa during the Late Cretaceous during its collision with the Kohistan–Ladakh Arc (~ 85 Ma) along the Indus Suture. Soon after the Deccan eruption, India drifted northward as an island continent by rapid motion carrying Gondwana biota, about 20 cm/year, between 67 Ma to 50 Ma; it slowed down dramatically to 5 cm/year during its collision with Asia in Early Eocene (~ 50 Ma). A northern corridor was established between India and Asia soon after the collision allowing faunal interchange. This is reflected by mixed Gondwana and Eurasian elements in the fossil record preserved in several continental Eocene formations of India. A revised India–Asia collision model suggests that the Indus Suture represents the obduction zone between India and the Kohistan–Ladakh Arc, whereas the Shyok-Suture represents the collision between the Kohistan–Ladakh arc and Tibet. Eventually, the Indus–Tsangpo Zone became the locus of the final India–Asia collision, which probably began in Early Eocene (~ 50 Ma) with the closure of Neotethys Ocean. The post-collisional tectonics for the last 50 million years is best expressed in the evolution of the Himalaya–Tibetan orogen. The great thickness of crust beneath Tibet and Himalaya and a series of north vergent thrust zones in the Himalaya and the south-vergent subduction zones in Tibetan Plateau suggest the progressive convergence between India and Asia of about 2500 km since the time of collision. In the early Eohimalayan phase (~ 50 to 25 Ma) of Himalayan orogeny (Middle Eocene–Late Oligocene), thick sediments on the leading edge of the Indian plate were squeezed, folded, and faulted to form the Tethyan Himalaya. With continuing convergence of India, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene Period during the Neohimalayan phase (~ 21 Ma to present), creating a series of north-vergent thrust belt systems such as the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust to accommodate crustal shortening. Neogene molassic sediment shed from the rise of the Himalaya was deposited in a nearly continuous foreland trough in the Siwalik Group containing rich vertebrate assemblages. Tomographic imaging of the India–Asia orogen reveals that Indian lithospheric slab has been subducted subhorizontally beneath the entire Tibetan Plateau that has played a key role in the uplift of the Tibetan Plateau. The low-viscosity channel flow in response to topographic loading of Tibet provides a mechanism to explain the Himalayan–Tibetan orogen. From the start of its voyage in Southern Hemisphere, to its final impact with the Asia, the Indian plate has experienced changes in climatic conditions both short-term and long-term. We present a series of paleoclimatic maps illustrating the temperature and precipitation conditions based on estimates of Fast Ocean Atmospheric Model (FOAM), a coupled global climate model. The uplift of the Himalaya–Tibetan Plateau above the snow line created two most important global climate phenomena—the birth of the Asian monsoon and the onset of Pleistocene glaciation. As the mountains rose, and the monsoon rains intensified, increasing erosional sediments from the Himalaya were carried down by the Ganga River in the east and the Indus River in the west, and were deposited in two great deep-sea fans, the Bengal and the Indus. Vertebrate fossils provide additional resolution for the timing of three crucial tectonic events: India–KL Arc collision during the Late Cretaceous, India–Asia collision during the Early Eocene, and the rise of the Himalaya during the Early Miocene.     

The Upper Jurassic of the Laptev Sea: interregional correlations and paleoenvironments

The Late Jurassic evolution of Boreal and Arctic basins is reflected in the widespread deposition of organic-rich black shales (source rocks). In this connection, the priority should be placed on the development and refinement of zonal schemes for the Upper Jurassic of the Laptev Sea coast based on ammonites, foraminifers, ostracods, dinocysts, and spores and pollen from reference sections as the basis for stratigraphic, paleogeographic, and facies studies. The Upper Jurassic and Lower Cretaceous reference section of interest is located on the left side of the Anabar Bay of the Laptev Sea (Nordvik Peninsula, Urdyuk-Khaya Cape). An uninterrupted and continuous section from Upper Oxfordian to Lower Valanginian is exposed in coastal cliffs and consists mainly of silty clay deposits with abundant macro- and microfossils. A reliable biostratigraphic subdivision of the Upper Jurassic interval of this section was taken as the basis for the assessment of the correlation potential of different fossil groups and subsequent interregional correlations, facies analysis, and detailed paleogeographic reconstructions of the study area. The analysis of variations in the composition of macrobenthic communities and microphytoplankton and terrestrial palynomorph assemblages and the biofacies analysis allowed the reconstruction of the evolution of marine paleoenvironmental settings in the western part of the Anabar–Lena sea and in the terrestrial settings in the adjacent land area of Siberia.     

Latest Jurassic to earliest Cretaceous paleoenvironmental changes in the Southern Carpathians, Romania: regional record of the late Valanginian nutrification event

Fluctuation in calpionellid, foraminiferal, and nannofossil diversity and abundance are documented in two successions located in the eastern part of the Upper Jurassic–Lower Cretaceous carbonate platform of the Southern Carpathian area, Romania. The lower part of the studied sections consists of upper Tithonian–upper Berriasian bioclastic limestones. This age is supported by the presence of the calpionellid assemblages assigned to the Crassicollaria, Calpionella, and Calpionellopsis Zones. Based on biostratigraphical data, a gap was identified within the uppermost Berriasian–base of the upper Valanginian (the interval encompasses the Boissieri, Pertransiensis, Campylotoxum, and lower part of the Verrucosum ammonite Zones). Hence, the upper Tithonian–upper Berriasian bioclastic limestones are overlain by upper Valanginian–lower Hauterivian pelagic limestones (the interval covered by the NK3B and NC4A nannofossil Subzones). A detailed qualitative and semiquantitative analysis of the nannoflora was carried out over this interval. To estimate the surface water fertility conditions, the nannoplankton-based nutrient index (NI) was calculated. The fluctuation pattern of NI allow us to recognize four phases in the investigated interval, as follows: (1) phase I (covering the lower part of the NK3B nannofossil Subzone and the upper part of the Verrucosum ammonite Zone, respectively) is characterized by low values of the NI (below 20%), by the dominance of the genus Nannoconus in the nannofloral assemblages (between 60–70%), and moderate abundance of Watznaueria barnesae (up to 23%), while the high-fertility nannofossils constitute a minor component of the assemblages; (2) phase II (placed in the NK3B nannofossil Subzone, extending from the top of Verrucosum ammonite Zone, up to the lower part of the Furcillata ammonite Zone) is characterized by increase of NI above 30%, a decrease of nannoconids (up to 50% at the top), while Watznaueria barnesae increases in abundance up to 27%. The fertility proxies (Diazomatolithus lehmanii, Zeugrhabdotus erectus, Discorhabdus rotatorius, and Biscutum constans) represent again a minor component of the recorded nannofloras (less than 7% in both sections), but they have an ascending trend; (3) phase III (which encompasses the boundary interval of the NK3B and NC4A nannofossil Subzones, corresponding to the upper part of the Furcillata ammonite Zone) contains higher NI values (over 35%, and up 52% towards the base of this phase), an abrupt nannoconid decrease (down to 20%), higher abundance of Watznaueria barnesae (over 30%), while the fertility nannofossils became an important nannofloral component, jointly amounting to almost 20%; (4) phase IV (identified within the NC4A Nannofossil Zone and corresponding to the boundary interval of the Furcillata and Radiatus ammonite Zones) is characterized by a decrease of NI to 25%, a recovery of the nannoconids up to 40%, a decline in abundance of Watznaueria barnesae to 25%, together with a pronounced drop of fertility taxa, which make together no more than 8%. We assume that maximum of eutrophication in the studied interval from the Southern Carpathians was in the Furcillata ammonite Zone. Notably, within the phases 2 and 3, the morphological changes identified in the benthic foraminiferal assemblages (the predominance of flattened morphologies, together with the presence of conical and trochospiral inflated forms), as well as the occurrence of the Zoophycos trace fossils and pyrite framboids, indicate dysaerobic conditions. In the Southern Carpathians, the late Valanginian–early Hauterivian biogeographical changes are coeval with the initiation of the carbonate platform drowning.     

From Middle Jurassic heating to Neogene cooling: The thermochronological evolution of the southern Alps

The Dolomite region is located in the Southern Alps, which were affected by Mesozoic extensional tectonics and by consequent thermal perturbations. In this work, vitrinite reflectance and apatite fission-track analysis are used to estimate the thermal evolution. These methodologies have been applied to the Permo-Mesozoic succession, which crops out along the TRANSALP seismic profile. The regional distribution of the organic matter maturity seems to be mainly controlled by different burials reached during the Norian-Liassic extensional phase, in connection with high heat flow values. The best solutions obtained from thermal modelling of both vitrinite and fission-track data suggest that peak of high heat flow occurred during Bajocian–Bathonian ages, when western Tethys was characterized by intrusions of gabbros and plagiogranites and extrusion of tholeiite basalts. This time coincides with the onset of the drifting phase and related thermal subsidence. The following thermal relaxation occurred during continuous sedimentation and the maximum burial does not coincide with peak temperatures. Cooling history has been carefully analysed through apatite fission-track data on samples collected close to the Valsugana overthrust, which document an important exhumation event at about 10 Ma. The related erosion has been analysed through the combined use of arenite petrography and fission-track analysis on detrital samples of the Veneto foredeep succession, which represents the storage of detritus during Tertiary. These data confirm that after Serravalian the Southalpine domain and related covers were affected by subaerial erosion.     

Impact of methane seeps on the local carbon‐isotope record: a case study from a Late Jurassic hemipelagic section

An Oxfordian (Late Jurassic) hemipelagic succession from Beauvoisin (SE France) contains a pronounced, short‐lived negative excursion in the bulk‐carbonate carbon‐isotope record, with an amplitude of 4‰. It was shown previously that the Beauvoisin paleoenvironment was impacted by hydrocarbon seepage. New isotopic data corroborate that methane was a significant constituent of these hydrocarbons. The negative excursion was caused by transient enhanced precipitation of ¹³C‐depleted carbonate, mediated by anaerobic oxidation of methane. Despite its local diagenetic origin, the Beauvoisin excursion is similar in shape and duration to globally recognized negative C‐isotope excursions that have been related to catastrophic, massive dissociation of methane hydrate. Shape and duration of negative excursions therefore cannot be used as an argument when determining their origin if they have not been shown to represent a global perturbation of the carbon cycle.     

Sedimentary record of Late Paleozoic rift and break-up in Northern Gondwana: a case history from the Thini Chu Group and Tamba-Kurkur Formation (Dolpo Tethys Himalaya,Nepal)

The Gottero unit of the Northern Apennines, Italy, is representative of the sedimentary cover of the Ligure-Piemontese oceanic lithosphere. This unit consists of a thick sedimentary sequence that includes Valanginian-Santonian pelagic deposits and Campanian-early Paleocene turbiditic deposits. The latter are overlain by early Paleocene trench deposits related to frontal tectonic erosion of the accretionary wedge slope. This sequence is interpreted as recording trenchward motion of the oceanic lithosphere.

The Gottero unit records a pre-Late Oligocene, complex deformation history related to subduction and accretion events. This deformation history has developed through underthrusting (D1a), underplating (D1b and D1c) and later exhumation (D2a and D2b) episodes. The folding phase related to the main underplating sub-phase (D1b) is predated by a sub-phase (D1a) connected to rapid fluid escape and followed by a sub-phase dominated by the development of shear zones (D1c). The D1b sub-phase is characterized by similar folds and a slaty cleavage developed under P/T conditions of 0.4GPa/210°-270 °C. The D1c sub-phase, characterized by west-verging thrusts, is particularly signficative in understanding the dynamics of the Ligure-Piemontese accretionary wedge because it testifies active shortening of the Gottero unit also after its transfer to the prism. In addition, sub-phase D1c represents the transition from the sub-phases connected to accretion and the tectonics dominated by extension, characterized by parallel folds and low-to high-angle normal faults. The gravity driven extension is represented by the D2a and D2b sub-phases and can be interpreted as the result of the thicknening of the Ligure-Piemontese accretionary wedge, produced by continuous underplating at its base but also by shortening of the previously underplated units. These final tectonic events resulted in the exhumation of the Gottero unit to the surface during the Early Oligocene, when this Unit became one of the source areas of the conglomerates deposited in the Tertiary Piedmont basin.

This deformation history suggests the occurrence of a complex sequence of deformations during the transition from accretion to exhumation, even in the intermediate levels of the accretionary wedge.     

Paleomagnetism of Upper Jurassic basalts from Transbaikalia: new data on the time of closure of the Mongol-Okhotsk Ocean and Mesozoic intraplate tectonics of Central Asia

The Upper Jurassic basalts (150–160 Ma) described as the Ichetui Formation over the territory of the Tugnui, Margintui, and Maly Khamar-Daban volcanic structures have been studied paleomagnetically. It is shown that natural remanent magnetization still contains a component which may reflect the geomagnetic field direction at the beginning of the Late Jurassic. This is supported by reversal and conglomerate tests. Calculation of mean paleopole gives: Plat = 63.6°, Plong = 166.8°, α₉₅ = 8.5°. These values well coincide with the data for the Badin Formation from Mogzon depression, which lies east of the study area and approximately dates from the Kimmeridgian-Oxfordian interval of the Late Jurassic. At the same time, those poles statistically differ from the European and Southeast Asian poles of the same age. The available paleomagnetic data suggest that at the beginning of the Late Jurassic the Mongol-Okhotsk Ocean was probably still open. Since the early Late Jurassic the continental blocks of Southeastern Asia and Siberian part of the Eurasian plate had been approaching, with the Siberian domain rotating clockwise. Analysis of the total of data shows that sinistral strike-slip deformations were present not only in southern Siberia but also between the Siberian and European Platforms. Thus, the deformations of the Central Asian crust in the early Late Jurassic reflect the intraplate strike-slip motions coeval with the closure of the Mongol-Okhotsk Ocean and are governed by the clockwise rotation of the Siberian part of the Eurasian plate relative to its European part.     

Middle Jurassic continental to marine transition in an extensional tectonics context: the Genna Selole Fm depositional system in the Tacchi area (central Sardinia,Italy)

In Eastern Sardinia during the early Middle Jurassic, Alpine Tethys opening triggered the rise of a temporary tectonic high. The high collapsed rapidly, was fragmented into separate blocks, and subsequently covered by continental, transitional, and finally shallow marine deposits forming a narrow depositional system comprising the Genna Selole Fm. Present‐day exposures in the southern part of the palaeo‐high allow the sedimentological evolution of the transgressive cover sequence to be ascertained. Initial terrestrial deposits comprise alluvial fan deposits located at the mouths of palaeovalleys. These pass into braid‐deltas and in the coastal areas located between adjacent valleys mouths, palustrine and coastal plain tidally‐influenced environments developed. These environments interfingered laterally and passed seaward into a transitional, siliciclastic to carbonate tidal environment. With the collapse of the tectonic high, the continental to transitional environments were transgressed with deposition of marine carbonates. A comparison with similar coeval deposits of the W‐Mediterranean domain has been undertaken. Copyright © 2015 John Wiley & Sons, Ltd.     

The isotope record of short- and long-term dietary changes in sheep tooth enamel: Implications for quantitative reconstruction of paleodiets

Quantitative reconstruction of paleodiet by means of sequential sampling and carbon isotope analysis in hypsodont tooth enamel requires a precise knowledge of the isotopic enrichment between dietary carbon and carbon from enamel apatite (ε_D-E), as well as of the timing and duration of the enamel mineralization process (amelogenesis). To better constrain these parameters, we performed a series of controlled feeding experiments on sheep ranging in age from 6 to 24 months-old. Twenty-eight lambs and 14 ewes were fed isotopically distinct diets for different periods of time, and then slaughtered, allowing the timing and rate of molar growth to be determined. High resolution sampling and stable carbon isotope analysis of breath CO₂ performed on six individuals following a diet-switch showed that 70-90% of dietary carbon had turned over in less than 24 h. Sequential sampling and carbon isotopic analysis was performed on the first (M₁) and second (M₂) lower molars of four lambs as well as on the third lower molar (M₃) of 11 ewes. The changes in diet were recorded in all molars. We found that the length of enamel matrix apposition is approximately one-quarter of the final tooth length during crown extension, and that enamel maturation spans slightly less than 3 months in M₁, and 4 months in M₂ and M₃. Portions of enamel in equilibrium with dietary carbon were used to calculate ε_D-E values. Animals on grass silage diets had values similar to previous observations, whereas animal switched to pelleted corn diets had values ca. 4‰ lower, a pattern consistent with lower methane production observed for animals fed concentrate diets. The tooth enamel forward model of Passey and Cerling (2002) closely predicted the amplitude of isotope changes recorded in tooth enamel, but slightly underestimated the rate of isotope change, suggesting that the rate of accumulation of carbonate during maturation may not be constant over time. Although stable isotope profiles in tooth enamel represent underdetermined systems, our results demonstrate that they can provide useful information about dietary variability if the mineralization process is taken into account.     

Growth increment and stable isotope analysis of marine bivalves: Implications for the geoarchaeological record of El Niño

The 1982–1983 El Niño event afforded the opportunity to develop criteria for the recognition of ancient El Niños using mollusks from archaeological sites along coastal South America. A combination of growth increment and stable isotope analyses indicated that elevated sea surface temperatures during large scale El Niños leave a record decodable from the growth patterns of selected bivalve shells. The intertidal venerid Chione subrugosa displayed a pronounced break in the valve margin profile following the 1982-1983 event but provided an inconsistent stable isotope pattern. The subtidal carditid Trachycardium procerum, on the other hand, preserved a discernible and diagnostic growth interruption as well as an expected trend in stable isotope indicators of salinity and temperature change. We conclude that some of the major culturally disruptive El Niño events can be recognized in the geoarchaeological record by these techniques, especially if ancillary information, such as faunal distribution patterns, are also considered. Perhaps the most serious constraint upon application of this approach involves microstratigraphic resolution of shell midden deposits. Stratigraphic sampling of midden material should be accompanied, if possible, by sampling of proximal natural strata. The chances of discovery of major El Niño perturbations in the geoarchaeological record of shell middens is enhanced by the catastrophic nature of such events and by the indication that major El Niños have a high probability of being closely spaced in time.     

内蒙古科尔沁右翼中旗上侏罗统满克头鄂博组木化石新资料

报道了首次在大兴安岭中南段侏罗系火山-沉积地层中发现的木化石。化石产于内蒙古自治区科尔沁右翼中旗地区满克头鄂博组中酸性火山碎屑沉积岩中,经沈阳地质矿产研究所张武研究员详细鉴定,有5属3个已知种和2个未定种。对新发现木化石的主要特征进行了描述,讨论了木化石的时代。综合分析所发现化石的组合特征,认为其时代属中晚侏罗世。这些木化石新材料为大兴安岭地区上侏罗统地层区域对比提供了新的古生物资料依据。