Institute of the Earth’s Crust

Periodic assembly and dispersal of continental fragments has been a characteristic of the solid Earth for much of its history. Geodynamic drivers of this cyclic activity are inferred to be either top-down processes related to near surface lithospheric stresses at plate boundaries or bottom-up processes related to mantle convection and, in particular, mantle plumes, or some combination of the two. Analysis of the geological history of Rodinian crustal blocks suggests that internal rifting and breakup of the supercontinent were linked to the initiation of subduction and development of accretionary orogens around its periphery. Thus, breakup was a top-down instigated process. The locus of convergence was initially around north-eastern and northern Laurentia in the early Neoproterozoic before extending to outboard of Amazonia and Africa, including Avalonia–Cadomia, and arcs outboard of Siberia and eastern to northern Baltica in the mid-Neoproterozoic (~760 Ma). The duration of subduction around the periphery of Rodinia coincides with the interval of lithospheric extension within the supercontinent, including the opening of the proto-Pacific at ca. 760 Ma and the commencement of rifting in east Laurentia. Final development of passive margin successions around Laurentia, Baltica and Siberia was not completed until the late Neoproterozoic to early Paleozoic (ca. 570–530 Ma), which corresponds with the termination of convergent plate interactions that gave rise to Gondwana and the consequent relocation of subduction zones to the periphery of this supercontinent. The temporal link between external subduction and internal extension suggests that breakup was initiated by a top-down process driven by accretionary tectonics along the periphery of the supercontinent. Plume-related magmatism may be present at specific times and in specific places during breakup but is not the prime driving force. Comparison of the Rodinia record of continental assembly and dispersal with that for Nuna, Gondwana and Pangea suggests grouping into two supercycles in which Nuna and Gondwana underwent only partial or no break-up phase prior to their incorporation into Rodinia and Pangea respectively. It was only after this final phase of assembly that the supercontinents then underwent full dispersal.

The compression curve of iron is measured up to 205 GPa at 298 K, under quasihydrostatic conditions in a diamond anvil cell. Above 150 GPa, the compression of this metal is significantly higher than previously measured under nonhydrostatic conditions. The same compression curve is also calculated ab initio and the deviation between experiment and theory is clearly established. A formulation of the equation of state of iron over a large pressure and temperature range, based on the current data and existing shock-wave data, is also proposed. Implications for the Earth's core are discussed.

The Paleo-Asian ocean is defined by units located between the Russian (East European), Siberian, Tarim, and Sino-Korean (North China) continents. The study of the composition, age, and structural position of island-arc magmatic rocks, ophiolites, and high-pressure meta-morphic assemblages and their mutual correlations made it possible to identify similarities and differences in the evolution of the Paleo-Asian and Paleo-Pacific oceans. The initial stage of the evolution of the Paleo-Asian ocean defined its opening at 900 Ma, whereas opening of the Paleo-Pacific took place at 750 to 700 Ma. Closing of the Paleo-Asian ocean in the Carboniferous (NE branch) and the Permian corresponds to the main stage of reorganization and reopening of the Paleo-Pacific. The maximal opening of the Paleo-Asian ocean occurred after or simultaneously with the first accretion-collision event at 600 to 700 Ma, resulting from the collision of microcontinents and the Siberian continent. Vendian-Early Cambrian boninite-bearing island-arc complexes occur as lavas, sheeted dikes, and sill-dikes associated with gabbro-pyroxenites and ultramafics. These complexes are widely distributed in the Gornyy Altay, East Sayan, and West Mongolian regions and can be considered fragments of a giant boninite-bearing belt. In the late Early Cambrian, collision of seamounts with an island arc caused the squeezing of the subduction zone and return flows within the accretionary wedge. Serpentinite melange within fragments of ophiolites and high-pressure rocks are typical components of the Late Paleozoic accretionary wedges. Because of Middle Cambrian-Early Ordovician collisional events, two new oceans (Junggar-Irtysh-Kazakhstan and Uralian-South Tien Shan-South Mongolian) were formed. The junction of both oceans in East Mongolia opened to the Paleo-Pacific.

Abstract Pollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 ± 2000 14 C yr bp ) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent ( Prentice et al. , 1996 ). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57°N) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe‐like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south‐western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien‐Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today.

Late Mesozoic extension in NE Asia resulted in the development of a large extensional province. Metamorphic core complexes (MCCs) are the major features in this province and have 40 Ar/ 39 Ar ages of 130–110 Ma for the mylonites and U‐Pb zircon ages of 150–110 Ma for the integral granitic intrusions. Based on this and previous studies, this paper summarizes major characteristics of these MCCs and recognizes a regional kinematic shear sense. Most MCCs in the Transbaikalia region, Sino‐Mongolia border tract, and the northwest‐central portion of the North China craton (NCC) show a top‐to‐the‐southeast (SE) shear, whereas those in the eastern and southern NCC locally underwent top‐to‐the‐northwest (NW) shear. The three largest basins (Songliao, Huabei and Ordos) in North China are located in the transitional zone between domains of opposing shear sense. We interpret the extension in the Transbaikalia, Sino‐Mongolia tract and northwestern part of the NCC to reflect late‐orogenic collapse of thickened crust following Middle‐Late Jurassic collision along the Okhotsk suture. The southeastward extension is probably controlled by crustal‐scale top‐to‐the‐SE tangential shear. The transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage (ecc, i.e., C′) in sub‐horizontal ductile shear zones late in orogenic crustal thickening. The combined effect of gravitational loading and thermal‐uplifting is considered to be the origin of the late‐or post‐orogenic collapse. The top‐to‐the‐NW extension in the NE of the NCC might reflect antithetic sub‐extensional zones or Mesozoic back‐arc extension as a far‐field effect of Cretaceous Pacific plate subduction.

Fossil pollen data supplemented by tree macrofossil records were used to reconstruct the vegetation of the Former Soviet Union and Mongolia at 6000 years. Pollen spectra were assigned to biomes using the plant‐functional‐type method developed by Prentice et al . (1996). Surface pollen data and a modern vegetation map provided a test of the method. This is the first time such a broad‐scale vegetation reconstruction for the greater part of northern Eurasia has been attempted with objective techniques. The new results confirm previous regional palaeoenvironmental studies of the mid‐Holocene while providing a comprehensive synopsis and firmer conclusions. West of the Ural Mountains temperate deciduous forest extended both northward and southward from its modern range. The northern limits of cool mixed and cool conifer forests were also further north than present. Taiga was reduced in European Russia, but was extended into Yakutia where now there is cold deciduous forest. The northern limit of taiga was extended (as shown by increased Picea pollen percentages, and by tree macrofossil records north of the present‐day forest limit) but tundra was still present in north‐eastern Siberia. The boundary between forest and steppe in the continental interior did not shift substantially, and dry conditions similar to present existed in western Mongolia and north of the Aral Sea.

Abstract The standard form of the Scherrer equation, which has been used to calculate the mean thickness of the coherent scattering domain (CSD) of illite crystals from X-ray diffraction (XRD) full width data at half maximum (FWHM) intensity, employs a constant, K sh , of 0.89. Use of this constant is unjustified, even if swelling has no effect on peak broadening, because this constant is valid only if all CSDs have a single thickness. For different thickness distributions, the Scherrer “constant” has very different values. Analysis of fundamental particle thickness data (transmission electron microscopy, TEM) for samples of authigenic illite and illite/smectite from diagenetically altered pyroclastics and filamentous illites from sandstones reveals a unique family of lognormal thickness distributions for these clays. Experimental relations between the distributions’ lognormal parameters and mean thicknesses are established. These relations then are used to calculate the mean thickness of CSDs for illitic samples from XRD FWHM, or from integral XRD peak widths (integrated intensity/maximum intensity). For mixed-layer illite/smectite, the measured thickness of the CSD corresponds to the mean thickness of the mixed-layer crystal. Using this measurement, the mean thickness of the fundamental particles that compose the mixed-layer crystals can be calculated after XRD determination of percent smectitic interlayers. The effect of mixed layering (swelling) on XRD peak width for these samples is eliminated by using the 003 reflection for glycolated samples, and the 001, 002 or 003 reflection for dehydrated, K-sa-turated samples. If this technique is applied to the 001 reflection of air-dried samples (Kubler index measurement), mean CSD thicknesses are underestimated due to the mixed-layering effect. The technique was calibrated using NEWMOD©-simulated XRD profiles of illite, and then tested on well-characterized illite and illite/smectite samples. The XRD measurements are in good agreement with estimates of the mean thickness of fundamental particles obtained both from TEM measurements and from fixed cations content, up to a mean value of 20 layers. Correction for instrumental broadening under the conditions employed here is unnecessary for this range of thicknesses.

Abstract Precambrian granulites of the Aldan shield in southern Yakutia, USSR, form a massif of 200,000 km 2 bounded by younger fold‐belts to the south, west and east. The massif consists of several blocks that reflect a primary heterogeneity of composition and differences in structural and thermodynamic evolution of different parts of the area. According to structural and petrological data the massif can be divided into two megablocks: eastern Aldan and western Aldan. They are separated by a narrow meridional fold‐belt. Structural evolution of this central zone was determined by the geodynamics of the mega‐blocks and was completed in the late Archaean. Towards the south, this central zone is ‘transformed’into the relatively small Sutam block adjoining the Stanovoy fold‐belt that bounds the Aldan shield on the south. The Sutam block is separated from the other structural units of the Aldan shield by a system of north trending grabens filled by post‐Archaean sediments. The Aldan shield is composed of Archaean high‐grade granulites, while the Stanovoy fold‐belt, to the south, consists of highly foliated Proterozoic rocks metamorphosed under relatively lower‐grade conditions. However, relics of the granulites are mapped within the fold‐belt. They contain high‐grade assemblages (e.g. Opx + Sil + Qz, Sap + Qz, Opx + Gr + Sil, etc.). One of the relics, the Tokskii block, which is only slightly touched by diaphthoresis, is located in the southeastern part of the Stanovoy fold‐belt. Metamorphic conditions of the Tokskii block are compared with those of the Sutam block and a similar evolution of the units is revealed. Mineral assemblages and mineral compositions do not vary within each unit, but they change in a north‐south direction. The Opx + Sil + Qz assemblage has been found only in Sutam and Tok, but not in eastern Aldan and western Aldan. The Sap + Qz assemblage has been found in the Tokskii block but has not yet been found in the Sutam block. The pyrope content in garnets, from metapelites of both blocks, is significantly higher than that from the Aldan (eastern and western blocks) rocks to the north. The most important assemblages from different units of the Aldan shield have been studied using the electron microprobe in order to unravel the metamorphic evolution of the granulites and thus to deduce the thermodynamic regime of this evolution. A geodynamic model for the Aldan shield is discussed in terms of Archaean island arc development.

We present new geodetic results of crustal velocities over a large part of northern Asia based on GPS measurements in the Baikal rift zone and Mongolia spanning the 1994–2002 period. We combine our results with the GPS velocity field for China of Wang et al. [2001] and derive a consistent velocity field for most of Asia. We find contrasted kinematic and strain regimes in Mongolia, with northward velocities and N‐S shortening in westernmost Mongolia but eastward to southeastward motion and left‐lateral shear for central and eastern Mongolia. This eastward to southeastward motion of central and eastern Mongolia is accommodated by left‐lateral slip on the E‐W trending Tunka, Bolnay, and Gobi Altay faults (2 ± 1.2 mm yr −1 , 2.6 ± 1.0 mm yr −1 , and 1.2 mm yr −1 , respectively) and by about 4 mm yr −1 of extension across the Baikal rift zone. Consequently, ∼15% of the India‐Eurasia convergence is accommodated north of the Tien Shan, by N‐S shortening combined with dextral shear in the Mongolian Altay and by eastward displacements along major left‐lateral strike‐slip faults in central and eastern Mongolia. We find a counterclockwise rotation of north and south China as a quasi‐rigid block around a pole north of the Stanovoy belt, which rules out the existence of an Amurian plate as previously defined and implies <2 mm yr −1 of left‐lateral slip on the Qinling Shan fault zone.

Abstract Semiempirical equations of state (EoS) of Au, Pt, MgO, NaCl-B1, and NaCl-B2 based on expanded Mie–Grüneisen–Debye approach, which are consistent both with the Mie–Grüneisen–Bose–Einstein approach and the thermochemical, X-ray, ultrasonic and shock-wave data in a wide pressure-temperature range, have been constructed. It is shown that to determine the volume dependence of the Grüneisen parameter, not only shock-wave and static compression data, but also experimental information on heat capacity, bulk moduli, volume, and thermal expansion coefficient at zero pressure need to be taken into account. Intrinsic anharmonicity is of great importance at construction of EoS at high temperatures and x=V/V 0>1. Cross-comparison of the current equations of state with independent measurements shows that these EoS may be used as the internally consistent and independent pressure scales in a wide range of temperatures and pressures. Keywords: Expanded Mie-Grüneisen-Debye EoSPressure scalesGrüneisen parameterIntrinsic anharmonicityGoldPlatinumMagnesium oxideSodium chloride Acknowledgements The authors thank Artem Oganov (ETH, Zurich, Switzerland) as the first reader of this manuscript and Kenichi Takemura (NIMS, Tsukuba, Japan) for sharing raw x-ray diffraction data. P.D. thanks A.D., who took the liberty of presentation of part of this work for COMPRES workshop in Geophysical Laboratory in January 2007. This work was supported by the Russian Foundation for Basic Research, grants No. 05-05-64491 and No. 08-08-00147.

We have constructed semiempirical equations of state of Al, Au, Cu, Pt, Ta, and W, which within experimental error bars describe the available shock-wave, ultrasonic, x-ray, and thermochemical data in the temperature range from $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ up to the melting temperature and to compression $x=V∕{V}_{0}=0.5--0.7$. The comparison of the calculated room-temperature isotherms for these metals with quasihydrostatic measurements supports recently proposed ruby pressure scales. We recommend a new ruby pressure scale in the form $P=A(\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}∕{\ensuremath{\lambda}}_{0})\ifmmode\times\else\texttimes\fi{}(1+m\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}∕{\ensuremath{\lambda}}_{0})$ with parameters $A=1884\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $m=5.5$. The cross check on independent data confirms the obtained PVT equations of state of Ag, Al, Au, Cu, Pt, Ta, W, $\mathrm{MgO}$, and diamond. The equations of state of these materials obtained here provide accurate and versatile means for calibrating pressure at all temperatures below the melting point. Furthermore, they can be used for accurate tabulation of thermodynamic properties (heat capacities, entropies) of these reference substances in a wide P-T range.

Inna Safonova, Reimar Seltmann, Alfred Kröner, Dmitry Gladkochub, Karel Schulmann, Wenjiao Xiao, Juyong Kim, Tsuyoshi Komiya, Min Sun. Episodes 2011;34:186-96. https://doi.org/10.18814/epiiugs/2011/v34i3/005

The level of intraplate seismicity in Japan generally shows a positive correlation with the density of Quaternary faulting. In southwest Japan, where intraplate seismicity is concentrated on land, rates of seismic moment release ( ) are similar when calculated from either the 400‐year historical record of seismicity or geologically determined slip rates of Quaternary faults. A data set of 18 earthquakes with seismic moments (M 0 ) ranging from ∼0.01 to 3×10 27 dyn cm shows a relationship between rupture length l and M 0 (log M 0 = 23.5+1.94 · log l ). When seismic moment on each Quaternary fault is assumed to occur in discrete events every T = M 0 / years (where M 0 is estimated for a rupture extended over the entire fault length, and is proportional to the slip rate of each Quaternary fault), the moment frequency distribution of earthquakes (log N =A − B · log M 0 ) predicted from the geologic record is virtually identical to that seen with the 400‐year record of seismicity. In contrast, if it is assumed that earthquakes on each fault occur according to the Gutenberg‐Richter relation, we obtain poor agreement with the observed seismicity. Thus, while regional seismicity satisfies the relation log N =A − B · log M 0 (or equivalently, log N = a − b · log M, where M is magnitude), it appears that seismicity on individual faults does not. This further implies that the primary factor that leads to the magnitude frequency distribution in regional seismicity studies is the relative distribution of the slip rates and lengths of preexisting faults.

In Gobi Altay and Altay, Mongolia, several flat surfaces, worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m, suggests disruption of a single large-scale surface. New thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during Jurassic time. The Gobi Altay and Altay flattopped massifs are tectonically and geomorphologically unique. Their preservation for ~150 m.y. implies that no further tectonic movements occurred before the onset of the last deformation episode, 5 ± 3 m.y. ago. It also suggests that very low erosion rates were maintained by a dry climate over millions of years.

Research Article| July 01, 1991 Zircon response to diamond-pressure metamorphism in the Kokchetav massif, USSR J. C. Claoué-Long; J. C. Claoué-Long 1Research School of Earth Sciences, Australian National University, GPO Box 4, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar N. V. Sobolev; N. V. Sobolev 2Institute of Geology and Geophysics, USSR Academy of Sciences Siberian, Division 630090 Novosibirsk 90, USSR Search for other works by this author on: GSW Google Scholar V. S. Shatsky; V. S. Shatsky 2Institute of Geology and Geophysics, USSR Academy of Sciences Siberian, Division 630090 Novosibirsk 90, USSR Search for other works by this author on: GSW Google Scholar A. V. Sobolev A. V. Sobolev 3Vernadsky Institute of Geochemistry, USSR Academy of Sciences, Kosigin str. 19, 117975 Moscow, USSR Search for other works by this author on: GSW Google Scholar Geology (1991) 19 (7): 710–713. https://doi.org/10.1130/0091-7613(1991)019<0710:ZRTDPM>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. C. Claoué-Long, N. V. Sobolev, V. S. Shatsky, A. V. Sobolev; Zircon response to diamond-pressure metamorphism in the Kokchetav massif, USSR. Geology 1991;; 19 (7): 710–713. doi: https://doi.org/10.1130/0091-7613(1991)019<0710:ZRTDPM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Ultrahigh-pressure metamorphism of the diamond-bearing gneisses in the Kokchetav massif, USSR, has been dated at 530 ±7 Ma (2&sgr,) by SHRIMP ion-microprobe analysis of metamorphic zircons. Zircon xenocrysts as old as 2000 Ma have retained original isotopic compositions through the extreme metamorphic conditions and indicate that the protolith that was buried to diamond-forming pressures included Early Proterozoic components. Highly variable reset-ting of U-Pb isotopic systems in zircon xenocrysts at the time of metamorphism suggests that diffusive lead loss had commenced but was incomplete, a disequilibrium observation consistent with relatively transient exposure of the rocks to extreme crustal depths. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

We have studied the high-pressure behavior of periclase (MgO) using density functional simulations within the generalized gradient approximation. The static and thermal $(P\ensuremath{-}V\ensuremath{-}T)$ equation of state, B1-B2 transition pressure, elastic constants, Gr\"uneisen parameter, and the intrinsic anharmonic parameters were calculated from static and ab initio molecular dynamics simulations. The simulations were performed using the projector augmented-wave and pseudopotential methods with different descriptions of the Mg atom (``small core'' and ``large core''). The errors of large-core pseudopotentials increase with pressure and are mainly due to the overlap between the Mg semicore (2p) orbitals and the valence orbitals, both of the same Mg atom and of the neighboring O atoms, rather than core deformation or core-core overlap effects. In agreement with previous works, we find that MgO remains in the B1 (``NaCl'') structure at all pressures existing within the Earth, and transforms into the CsCl-type structure at 509 GPa. Direct ab initio calculations avoid the simplifying assumptions inherent to many empirical treatments of thermoelasticity and allowed us to assess some of the common assumptions. We present a detailed qualitative analysis of the effects of intrinsic anharmonicity and analyze the validity of the Mie-Gr\"uneisen approximation at high temperatures.

Representative diamond‐bearing gneisses and dolomitic marble, eclogite and Ti‐clinohumite‐bearing garnet peridotite from Unit I at Kumdy Kol and whiteschist from Unit II at Kulet, eastern Kokchetav Massif, northern Kazakhstan, were studied. Diamond‐bearing gneisses contain variable assemblages, including Grt+Bt+Qtz±Pl±Kfs±Zo±Chl±Tur±Cal and minor Ap, Rt and Zrn; abundant inclusions of diamond, graphite+chlorite (or calcite), phengite, clinopyroxene, K‐feldspar, biotite, rutile, titanite, calcite and zircon occur in garnet. Diamond‐bearing dolomitic marbles consist of Dol+Di±Grt+Phl; inclusions of diamond, dolomite±graphite, biotite, and clinopyroxene were identified in garnet. Whiteschists carry the assemblage Ky+Tlc+Grt+Rt; garnet shows compositional zoning, and contains abundant inclusions of talc, kyanite and rutile with minor phlogopite, chlorite, margarite and zoisite. Inclusions and zoning patterns of garnet delineate the prograde P–T path. Inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss. Other ultrahigh‐pressure (UHP) indicators include Na‐bearing garnet (up to 0.14 wt% Na 2 O) with omphacitic Cpx in eclogite, occurrence of high‐K diopside (up to 1.56 wt% K 2 O) and phlogopite in diamond‐bearing dolomitic marble, and Cr‐bearing kyanite in whiteschist. These UHP rocks exhibit at least three stages of metamorphic recrystallization. The Fe‐Mg partitioning between clinopyroxene and garnet yields a peak temperature of 800–1000 °C at P &gt;40 kbar for diamond‐bearing rocks, and about 740–780 °C at &gt;28–35 kbar for eclogite, whiteschist and Ti‐bearing garnet peridotite. The formation of symplectitic plagioclase+amphibole after clinopyroxene, and replacement of garnet by biotite, amphibole, or plagioclase mark retrograde amphibolite facies recrystallization at 650–680 °C and pressure less than about 10 kbar. The exsolution of calcite from dolomite, and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c . 420 °C and 2–3 kbar. A clockwise P–T path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to UHP subduction‐zone metamorphism within the diamond stability field. Tectonic mixing may have occurred prior to UHP metamorphism at mantle depths. During subsequent exhumation and juxtaposition of many other tectonic units, intense deformation chaotically mixed and mylonitized these lithotectonic assemblages.

Middle Jurassic to Early Cretaceous deposits from northeastern China have yielded varied theropod dinosaurs bearing feathers. Filamentous integumentary structures have also been described in ornithischian dinosaurs, but whether these filaments can be regarded as part of the evolutionary lineage toward feathers remains controversial. Here we describe a new basal neornithischian dinosaur from the Jurassic of Siberia with small scales around the distal hindlimb, larger imbricated scales around the tail, monofilaments around the head and the thorax, and more complex featherlike structures around the humerus, the femur, and the tibia. The discovery of these branched integumentary structures outside theropods suggests that featherlike structures coexisted with scales and were potentially widespread among the entire dinosaur clade; feathers may thus have been present in the earliest dinosaurs.

Soils in permafrost regions contain twice as much carbon as the atmosphere, and permafrost has an important influence on the natural and built environment at high northern latitudes. The response of permafrost to warming climate is uncertain and occurs on time scales longer than those assessed by direct observation. We dated periods of speleothem growth in a north-south transect of caves in Siberia to reconstruct the history of permafrost in past climate states. Speleothem growth is restricted to full interglacial conditions in all studied caves. In the northernmost cave (at 60°N), no growth has occurred since Marine Isotopic Stage (MIS) 11. Growth at that time indicates that global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.

After its Ediacaran-Early Cambrian assembly, Gondwana was flanked by a system of peripheral orogens, Terra Australis, Avalonian-Cadomian and newly defined North Indo-Australie, which display broad temporal correlations of their lithotectonic records. Prior to assembly, their initial histories were primarily controlled by the early Neoproterozoic breakup of Rodinia with second order variances reflecting the differing relationships of their basement continental blocks to that supercontinent. The Terra Australis Orogen developed on basement blocks that previously occupied interior locations within Rodinia and initial successions record development of a passive continental margin. The North Indo-Australie orogen records a similar history of passive margin development, but at least its Indian portion was likely separate from Rodinia. The basement blocks of the Avalonian-Cadomian Orogen previously occupied exterior locations around Rodinia with initial successions indicating the development of a convergent plate margin. As Gondwana assembled, Avalonian-Cadomian convergence terminated at about the same time as convergence commenced in the Terra Australis and North Indo-Australie orogens. The absence of a complete long-lived contemporaneous subduction girdle around Gondwana likely prevented its breakup, in contrast to Rodinia and Pangea, in which the presence of subduction girdles corresponds with lithospheric extension across the supercontinents as a precursor to their ultimate breakup.