Geological Institute

The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic–Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian–Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with formation of the Solonker suture. We evaluate contrasting tectonic models for the evolution of the orogenic belt. Current information provides little support for the main tenets of the one- or three-arc Kipchak model; current data suggest that an archipelago-type (Indonesian) model is more viable. Some diagnostic features of ridge–trench interaction are present in the Central Asian orogen (e.g. granites, adakites, boninites, near-trench magmatism, Alaskan-type mafic–ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, rhyolitic ash-fall tuffs). They offer a promising perspective for future investigations.

There would be few geological studies in which, at some stage, there did not arise a question of timing. The answer is often to be found through direct observation; the principles of superposition and crosscutting relationships apply in determining the order of events on all scales from the microscopic to the macroscopic, from crystallization history to continental assembly. By augmenting those principles with the means to establish sequence and correlation provided by palaeontology, the geologist has the capability, through observation and logical reasoning alone, to determine the relative ages of a great range of geological processes. However, while these techniques make it possible to place geological events in time order, they do not provide an absolute measure of time itself.The measurement of absolute time in geology— geochronology—requires a quantifiable physical process that takes place continuously at a known rate from the time of the event to be dated to the present day. Some cyclic processes, such as the passage of the seasons, leave their imprint in parts of the geological record and can provide detailed, accurate measurements of elapsed time intervals, but they do not permit the measurement of absolute time (age) unless the record is unbroken to the present day or the age of one of the cycles is known by some independent means. The number of annual growth bands in a fossil coral, for example, tells how long that coral once lived, but not when. To measure absolute geologic time, one needs a process that is continuous and unidirectional. The most widely utilized of such processes is natural radioactivity.The concept behind radioisotope geochronology is quite simple. Some of the elements in rocks and minerals have isotopes (atoms of the same atomic number but different mass numbers) that are naturally radioactive-the nuclei of those isotopes are unstable, and liable to break down spontaneously (decay) to an isotope of a different element. If the newly-formed isotope is also unstable, the process continues until a stable nucleus forms.Radioactive decay occurs at rates characteristic of each element and isotope. As far as is known, those rates are independent of any chemical or physical parameters (e.g., pressure, temperature, chemical state etc. ) . The probability that a given nucleus of a given isotope will decay in any given time period is a constant, so the number of decays occurring per unit time is proportional to the number of atoms of that

The metamorphic facies series in regional metamorphism may be classified into the following categories according to an order of increasing rock pressure: (1) andalusite-sillimanite type, (2) low-pressure intermediate group, (3) kyanite-sillimanite type, (4) high-pressure intermediate group, and (5) jadeite-glaucophane type. In Japan and other parts of the circum-Pacific region, a metamorphic belt of the andalusite-sillimanite type and/or low-pressure intermediate group and another metamorphic belt of the jadeite-glaucophane type and/or high-pressure intermediate group run side by side, forming a pair. The latter belt is always on the Pacific Ocean side. They were probably formed in different phases of the same cycle of orogeny. Their origin is discussed. Regional metamorphism under higher rock pressures appears to have taken place in later geological times. The metamorphic facies series of contact metamorphism are briefly discussed.

The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum‐Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from ∼6% in Version 2.0 to ∼11% in Version 3.0.

The inverse problem of three‐dimensional (3‐D) local earthquake tomography is formulated as a linear approximation to a nonlinear function. Thus the solutions obtained and the reliability estimates depend on the initial reference model. Inappropriate models may result in artifacts of significant amplitude. Here, we advocate the application of the same inversion formalism to determine hypocenters and one‐dimensional (1‐D) velocity model parameters, including station corrections, as the first step in the 3‐D modeling process. We call the resulting velocity model the minimum 1‐D model. For test purposes, a synthetic data set based on the velocity structure of the San Andreas fault zone in central California was constructed. Two sets of 3‐D tomographic P velocity results were calculated with identical travel time data and identical inversion parameters. One used an initial 1‐D model selected from a priori knowledge of average crustal velocities, and the other used the minimum 1‐D model. Where the data well resolve the structure, the 3‐D image obtained with the minimum 1‐D model is much closer to the true model than the one obtained with the a priori reference model. In zones of poor resolution, there are fewer artifacts in the 3‐D image based on the minimum 1‐D model. Although major characteristics of the 3‐D velocity structure are present in both images, proper interpretation of the results obtained with the a priori 1‐D model is seriously compromised by artifacts that distort the image and that go undetected by either resolution or covariance diagnostics.

The extensive work carried out during more than a decade by the International Subcommission on Ordovician Stratigraphy has resulted in a new global classification of the Ordovician System into three series and seven stages. Formal Global Boundary Stratotype Section and Points (GSSPs) for all stages have been selected and these and the new stage names have been ratified by the International Commission on Stratigraphy. Based on a variety of biostratigraphic data, these new units are correlated with chronostratigraphic series and stages in the standard regional classifications used in the UK, North America, Baltoscandia, Australia, China, Siberia and the Mediterranean-North Gondwana region. Furthermore, based mainly on graptolite and conodont zones, the Ordovician is subdivided into 20 stage slices (SS) that have potential for precise correlations in both carbonate and shale facies. The new chronostratigraphic scheme is also tied to a new composite δ13C curve through the entire Ordovician.

On the basis of synchronization of three carbon-14 (14C)-dated lacustrine sequences from Sweden with tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta14C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.

The Central Asian Orogenic Belt is one of the largest accretionary terrains on Earth and records a ca. 800 Ma history of arc and microcontinent accretion, from south to north, during evolution and closure of the southwest Pacific-type Paleo-Asian ocean in the period ca. 1020 to ca. 325 Ma. We contest the evolutionary model for the belt proposed by previous authors in terms of a single, long island arc.

Geological and geophysical observations imply Cenozoic subduction of intact Eurasian continental lithosphere, approximately 300 km in downdip length and including relatively thin (20–25 km) continental crust, beneath the Pamir. An inclined seismic zone dips at about 45° south-southeastward to a depth of 150 to 200 km beneath the Pamir and projects to the surface near the northern margin of the Pamir. The downdip length of the seismic zone of about 300 km implies a comparable amount of subduction of lithosphere in late Cenozoic time. The seismicity and tectonically most active part of the Pamir and its surroundings follows the northern margin of the Pamir. Quaternary offsets on faults and repeated geodetic observations suggest that roughly half of India’s present 44-mm/a convergence with Eurasia is absorbed by localized crustal shortening and underthrusting at this zone.

Synthetic Na-rich birnessite (NaBi) and its low pH form, hexagonal birnessite (HBi), were studied by X-ray and selected-area electron diffraction (XRD, SAED). SAED patterns were also obtained for synthetic Sr-exchanged birnessite (SrBi) microcrystals in which Sr was substituted for Na. XRD confirmed the one-layer monoclinic structure of NaBi and the one-layer hexagonal structure of HBi with subcell parameters a = 5.172 Aa, b = 2.849 Aa, c = 7.34 Aa, beta = 103.3 degrees and a = 2.848 Aa, c = 7.19 Aa, gamma = 120 degrees , respectively. In addition to super-reflection networks, SAED patterns for NaBi and SrBi contain satellite reflections. On the basis of these experimental observations, structural models for NaBi and HBi are proposed. NaBi consists of almost vacancy-free Mn octahedral layers. The departure from the hexagonal symmetry of layers is caused by the Jahn-Teller distortion associated with the substitution of Mn (super 3+) for Mn (super 4+) . The supercell A = 3a parameter arises from the ordered distribution of Mn (super 3+) -rich rows parallel to [010] and separated from each other along [100] by two Mn (super 4+) rows. The superstructure in the b direction of NaBi type II (B = 3b) comes from the ordered distribution of Na cations in the interlayer space. The maximum value of the layer negative charge is equal to 0.333 v.u. per Mn atom and is obtained when Mn (super 3+) -rich rows are free of Mn (super 4+) . The idealized structural formula proposed for NaBi type II is Na (sub 0.333) (Mn (super 4+) (sub 0.722) Mn (super 3+) (sub 0.222) Mn (super 2+) (sub 0.055) )O 2 . NaBi type I has a lower amount of Mn (super 3+) and its ideal composition would vary from Na (sub 0.167) (Mn (super 4+) (sub 0.833) Mn (super 3+) (sub 0.167) )O 2 to Na (sub 0.25) (Mn (super 4+) (sub 0.75) Mn (super 3+) (sub 0.25) )O 2 . Satellites in SAED patterns of NaBi crystals result from the ordered distribution of Mn (super 4+) and Mn (super 2+) pairs in Mn (super 3+) -rich rows with a periodicity of 6b. The structure of HBi consists of hexagonal octahedral layers containing predominantly Mn (super 4+) with variable amounts of Mn (super 3+) and layer vacancies. The distribution of layer vacancies is inherited from the former Mn (super 3+) distribution in NaB. Interlayer Mn cations are located above or below vacant layer sites. The driving force of the NaBi to HBi transformation is probably the destabilization of Mn (super 3+) -rich rows at low pH.

Abstract Domestication of horses fundamentally transformed long-range mobility and warfare 1 . However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling 2–4 at Botai, Central Asia around 3500 bc 3 . Other longstanding candidate regions for horse domestication, such as Iberia 5 and Anatolia 6 , have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 bc , synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association 7 between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 bc 8,9 driving the spread of Indo-European languages 10 . This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium bc Sintashta culture 11,12 .

Abstract Olique-texture electron diffraction examination of K-saturated dioctahedral smectites after 70–100 wetting-drying cycles allows the determination of cation distribution between trans and cis octahedra of the 2:1 layers. Studies of smectites with different compositions has revealed a wide variety of occupancies of the available octahedral sites.

By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of 2500 at 1 Hz and 200 000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w 3 at 40 epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.

Abstract The structure of 6-line and 2-line ferrihydrite (Fh) has been reconsidered. X-ray diffraction (XRD) curves were first simulated for the different structural models so far proposed, and it is shown that neither of these corresponds to the actual structure of ferrihydrite. On the basis of agreement between experimental and simulated XRD curves it is shown that Fh is a mixture of three components: (i) Defect-free Fh consisting of anionic ABACA . . . close packing in which Fe atoms occupy only octahedral sites with 50% probability; the hexagonal unit-cell parameters are a = 2-96 Å and c = 9-40 Å, and the space group is P 1c. (ii) Defective Fh in which Ac 1 Bc 2 A and Ab 1 Cb 2 A structural fragments occur with equal probability and alternate completely at random; Fe atoms within each of these fragments have identical ordered distribution with in the hexagonal super-cell with a = 5.26 Å. (iii) Ultradispersed hematite with mean dimension of coherent scattering domains (CSD) of 10-20 Å. The main structural difference between 6-line and 2-line Fh is the size of their CSD which is extremely small for the latter structure. Nearest Fe-Fe distances calculated for this new structural model are very close to those determined by EXAFS spectroscopy on the same samples.

A newly discovered Paleolithic site on the Yana River, Siberia, at 71 degrees N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This age is twice that of other known human occupations in any Arctic region. Artifacts at the site include a rare rhinoceros foreshaft, other mammoth foreshafts, and a wide variety of tools and flakes. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought.

Abstract— The HF/HCI‐resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed‐system stepped etching (CSSE) in order to better characterise the noble gases in “phase Q”, a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for ( 20 Ne/ 22 Ne) Q . As already suggested by precise earlier measurements (Schelhaas et al. , 1990; Wieler et al. , 1991, 1992), ( 20 Ne/ 22 Ne) Q is the least uniform isotopic ratio of the Q noble gases. The data cluster ∼10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of ( 20 Ne/ 22 Ne) Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar‐Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne‐Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases “Q1” and “Q2” with slightly distinct chemical properties. Ratios (Ar/Xe) Q and (Kr/Xe) Q reflect both thermal metamorphism and aqueous alteration. These parent‐body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar) Q and (Ne/Ar) Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q 2 . Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q 1 and Q 2 must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q 1 may be related to presolar graphite. Phases Q 1 and Q 2 might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the 20 Ne/ 22 Ne ratios cannot be attributed to the carriers Q 1 and Q 2 . The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne‐E(L), and the data confirm the suggestion of Huss (1997) that the 22 Ne‐E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.

Abstract Late Pliocene and Early Pleistocene epochs 3.6 to 0.8 million years ago 1 had climates resembling those forecasted under future warming 2 . Palaeoclimatic records show strong polar amplification with mean annual temperatures of 11–19 °C above contemporary values 3,4 . The biological communities inhabiting the Arctic during this time remain poorly known because fossils are rare 5 . Here we report an ancient environmental DNA 6 (eDNA) record describing the rich plant and animal assemblages of the Kap København Formation in North Greenland, dated to around two million years ago. The record shows an open boreal forest ecosystem with mixed vegetation of poplar, birch and thuja trees, as well as a variety of Arctic and boreal shrubs and herbs, many of which had not previously been detected at the site from macrofossil and pollen records. The DNA record confirms the presence of hare and mitochondrial DNA from animals including mastodons, reindeer, rodents and geese, all ancestral to their present-day and late Pleistocene relatives. The presence of marine species including horseshoe crab and green algae support a warmer climate than today. The reconstructed ecosystem has no modern analogue. The survival of such ancient eDNA probably relates to its binding to mineral surfaces. Our findings open new areas of genetic research, demonstrating that it is possible to track the ecology and evolution of biological communities from two million years ago using ancient eDNA.

Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.

Pressure is durable problem in geology. It has engendered continuing arguments on its mechanism, thermodynamic basis, and geo­ logical significance. Recently, it has drawn renewed attention both for its important role in the diagenesis of sedimentary rocks and for its relation to rock deformation. Pressure is defined as process by which grains dissolve at intergranular or intercrystalline contacts. This process is presumably related to the higher solubility under nonhydrostatic stress at the contacts than at free grain surfaces. The process often, although not always, is accompanied by reprecipitation at adjacent free grain surfaces. Nevertheless, it is not justifiable to treat pressure as recrys­ tallization process. Two common types of pressure are recognized: intergranular pressure and stylolitization. The former, occurring at individual grain contacts, was first described by Sorby (1863) based on experiments and theoretical predictions by Thompson ( l862a,b). The latter produces a surface or contact that is marked by an irregular and interlocking penetration of the two sidcs, and is supposedly formcd diagenctically by differential vertical movement under pressure, accompanied by solution (Bates & Jackson 1980). Here we use the term for surface that involves an of grains (the aggregate stylolite of Park & Schot 1968), originating exclusively by dissolution under nonhydrostatic stress.

Eight time slices of surface‐water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea‐ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep‐sea cores, 20 of which are accelerator mass spectrometry (AMS)‐ 14 C dated and 30 of which have high (>8 cm /kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The δ 18 O and δ 13 C distributions depict three main modes of surface circulation: (1) The Holocene‐style interglacial mode which largely persisted over the last 12.8 14 C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice‐free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S‐N flow across the eastern Iceland‐Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface‐water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene‐style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during δ 18 O event 3.1 and the Bölling. Meltwater phases markedly influenced the European continental climate by suppressing the “heat pump” of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell. An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95PA01453, Variations in Atlantic surface ocean paleoceanography, 50°‐80°N: A time‐slice record of the last 30,000 years, M. Sarnthein et al.) Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.