Geoarchaeological investigations at Studenoe,an Upper Paleolithic site in the Transbaikal Region,Russia

In 1998, geoarchaeological research was carried out at the Upper Paleolithic site of Studenoe in the Transbaikal Region of Russia. The site is divided into three loci situated on two terraces overlooking the Chikoi River. Alluvial sediments beneath the oldest terrace (T₂) consist of two depositional units. Radiocarbon ages indicate that aggradation of the T₂ fill began before 18,000 yr B.P. Alluvial sediments beneath the lower terrace (T₁) range in age from 13,000 to 10,000 yr B.P. and are divided into three depositional units. Both terraces are overlain by Holocene colluvium. Archaeological materials at Studenoe 1/1, 1/2, and 2 include dwellings, hearths, and thousands of bone and stone artifacts assigned to the late Upper Paleolithic through the Bronze Age. Evidence of microblade technology is present in all components of the site. Material from recent excavations of Paleolithic levels in the T₂ fill at Studenoe includes mobiliary art, bone needles, and a large dwelling with four hearth features. © 2003 Wiley Periodicals, Inc.     

Broadband imaging via direct inversion of blended dispersed source array data

Although seismic sources typically consist of identical broadband units alone, no physical constraint dictates the use of only one kind of device. We propose an acquisition method that involves the simultaneous exploitation of multiple types of sources during seismic surveys. It is suggested to replace (or support) traditional broadband sources with several devices individually transmitting diverse and reduced frequency bands and covering together the entire temporal and spatial bandwidth of interest. Together, these devices represent a so‐called dispersed source array. As a consequence, the use of simpler sources becomes a practical proposition for seismic acquisition. In fact, the devices dedicated to the generation of the higher frequencies may be smaller and less powerful than the conventional sources, providing the acquisition system with increased operational flexibility and decreasing its environmental impact. Offshore, we can think of more manageable boats carrying air guns of different volumes or marine vibrators generating sweeps with different frequency ranges. On land, vibrator trucks of different sizes, specifically designed for the emission of particular frequency bands, are preferred. From a manufacturing point of view, such source units guarantee a more efficient acoustic energy transmission than today's complex broadband alternatives, relaxing the low‐ versus high‐frequency compromise. Furthermore, specific attention can be addressed to choose shot densities that are optimum for different devices according to their emitted bandwidth. In fact, since the sampling requirements depend on the maximum transmitted frequencies, the appropriate number of sources dedicated to the lower frequencies is relatively small, provided the signal‐to‐noise ratio requirements are met. Additionally, the method allows to rethink the way to address the ghost problem in marine seismic acquisition, permitting to tow different sources at different depths based on the devices' individual central frequencies. As a consequence, the destructive interference of the ghost notches, including the one at 0 Hz, is largely mitigated. Furthermore, blended acquisition (also known as simultaneous source acquisition) is part of the dispersed source array concept, improving the operational flexibility, cost efficiency, and signal‐to‐noise ratio. Based on theoretical considerations and numerical data examples, the advantages of this approach and its feasibility are demonstrated.     

How rough sea affects marine seismic data and deghosting procedures

Most seismic processing algorithms generally consider the sea surface as a flat reflector. However, acquisition of marine seismic data often takes place in weather conditions where this approximation is inaccurate. The distortion in the seismic wavelet introduced by the rough sea may influence (for example) deghosting results, as deghosting operators are typically recursive and sensitive to the changes in the seismic signal. In this paper, we study the effect of sea surface roughness on conventional (5–160 Hz) and ultra‐high‐resolution (200–3500 Hz) single‐component towed‐streamer data. To this end, we numerically simulate reflections from a rough sea surface using the Kirchhoff approximation. Our modelling demonstrates that for conventional seismic frequency band sea roughness can distort results of standard one‐dimensional and two‐dimensional deterministic deghosting. To mitigate this effect, we introduce regularisation and optimisation based on the minimum‐energy criterion and show that this improves the processing output significantly. Analysis of ultra‐high‐resolution field data in conjunction with modelling shows that even relatively calm sea state (i.e., 15 cm wave height) introduces significant changes in the seismic signal for ultra‐high‐frequency band. These changes in amplitude and arrival time may degrade the results of deghosting. Using the field dataset, we show how the minimum‐energy optimisation of deghosting parameters improves the processing result.     

Attenuation mechanisms in fractured fluid-saturated porous rocks: a numerical modelling study

Seismic attenuation mechanisms receive increasing attention for the characterization of fractured formations because of their inherent sensitivity to the hydraulic and elastic properties of the probed media. Attenuation has been successfully inferred from seismic data in the past, but linking these estimates to intrinsic rock physical properties remains challenging. A reason for these difficulties in fluid-saturated fractured porous media is that several mechanisms can cause attenuation and may interfere with each other. These mechanisms notably comprise pressure diffusion phenomena and dynamic effects, such as scattering, as well as Biot's so-called intrinsic attenuation mechanism. Understanding the interplay between these mechanisms is therefore an essential step for estimating fracture properties from seismic measurements. In order to do this, we perform a comparative study involving wave propagation modelling in a transmission set-up based on Biot's low-frequency dynamic equations and numerical upscaling based on Biot's consolidation equations. The former captures all aforementioned attenuation mechanisms and their interference, whereas the latter only accounts for pressure diffusion phenomena. A comparison of the results from both methods therefore allows to distinguish between dynamic and pressure diffusion phenomena and to shed light on their interference. To this end, we consider a range of canonical models with randomly distributed vertical and/or horizontal fractures. We observe that scattering attenuation strongly interferes with pressure diffusion phenomena, since the latter affect the elastic contrasts between fractures and their embedding background. Our results also demonstrate that it is essential to account for amplitude reductions due to transmission losses to allow for an adequate estimation of the intrinsic attenuation of fractured media. The effects of Biot's intrinsic mechanism are rather small for the models considered in this study.     

Permafrost distribution and temperature in the Elkon Horst,Russia

The Elkon Horst is a geological structure that consists of heterogeneous strata with highly variable geocryological and temperature conditions. Gaining accurate knowledge of permafrost distribution patterns within this structure is of both scientific and practical importance. In mountainous terrain, the ground thermal regime is controlled by both surface and subsurface conditions. Surface conditions include snow cover characteristics, the presence or absence of vegetation, vegetation density, etc.. In contrast, subsurface conditions involve rock lithology or petrography, density, quantity and depth of fissures, groundwater, etc.. This article examines ground thermal regimes in various geomorphological settings based on temperature measurement data from geotechnical boreholes. The occurrence and extent of permafrost were evaluated for the entire horst area using direct and indirect methods. The maximum permafrost thickness measured in the Elkon Horst is 330 m, and the estimated maximum is 450 m at higher elevations. Thermophysical properties were determined for the major rock types, and the geothermal heat flux was estimated for the study area. The thermal conductivities were found to vary from 1.47 to 4.20 W/(m·K), and the dry bulk densities to range between 2,236 kg/m~3 and 3,235 kg/m~3. The average geothermal heat flux was estimated to be 44 mW/m~2.     

Climate signals in sediment mineralogy of Lake Baikal and Lake Hovsgol during the LGM-Holocene transition and the 1-Ma carbonate record from the HDP-04 drill core

Modeling the bulk sediment XRD patterns allows insight into the environmental and depositional histories of two neighboring rift lake basins within the Baikal watershed. Parallel ¹⁴C-dated LGM-Holocene records in Lakes Baikal and Hovsgol are used to discuss the mineralogical signatures of regional climate change. In both basins, it is possible to distinguish ‘glacial’ and ‘interglacial’ mineral associations. Clay minerals comprise in excess of 50% of layered silicates in bulk sediment.The abundance of smectite (expandable) layers in mixed-layer illite–smectites and the total illite abundance are the main paleoclimatic indices in the clay mineral assemblage. Both indices exhibit coherent responses to the Bølling–Allerød and the Younger Dryas. The smectite layer index is not equivalent to the abundance of illite–smectite, because illite–smectite tends to transform into illite. Repeated wetting–drying cycles in soils and high abundance of expandable layers in illite–smectites (>42%) favor the process of illitization. This relationship is clearly shown in both Baikal and Hovsgol records for the first time. The opposite late Holocene trends in illite abundance in Lake Baikal and Lake Hovsgol records suggest that a sensitive optimal regime may exist for illite formation in the Baikal watershed with regard to warmth and effective moisture.The Lake Hovsgol sediments of the last glacial contain carbonates, suggesting a positive trend in the lake's water budget. A progressive change towards lower Mg content in carbonates indicates lowering mineralization of lake waters. This trend is consistent with the lithologic evidence for lake-level rise in the Hovsgol basin.The pattern of mineralogical changes during the past 20 ka is used to interpret bulk sediment and carbonate mineralogy of the long 81-m Lake Hovsgol drill core (HDP-04) with a basal age of 1 Ma. The interglacial-type silicate mineral associations are confined to several thin intervals; most of the sediment record is calcareous. Carbonates are represented by six main mineral phases: calcite, low-Mg calcite, intermediate/high-Mg calcite, dolomite, excess-Ca dolomite and metastable monohydrocalcite. These mineral phases tend to form stratigraphic successions indicative of progressive changes in lake water chemistry. Five sediment layers with abundant Mg-calcites in the HDP-04 section suggest deposition in a low standing lake with high mineralization (salinity) and high Mg/Ca ratios of lake waters. Lake Hovsgol sediments contain the oldest known monohydrocalcite, found tens of meters below lake bottom in sediments as old as 800 ka. This unusual find is likely due to the conditions favorable to preservation of this metastable carbonate.     

A Special Issue on Data Science for Geosciences

Mathematical Geosciences -     

The 27-Day and 22-Year Cycles in Solar and Geomagnetic Activity

We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the 22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution.     

Infrared reflection spectrometry analysis as a non‐destructive method of characterizing minerals and stone materials in geoarchaeological and archaeometric applications

The purpose of this paper is to show the benefits and applications of using mid and far infrared reflection spectrometry (IRS) in the analysis of archaeological materials. Infrared spectral databases do not yet exist for rocks and principal minerals. In support of IRS techniques, a catalogue and new spectral database have been created with over 500 infrared reflection spectra in mid and far ranges from more than 250 different archaeological minerals and stone materials. The reflection spectrum serves as a “fingerprint” of all these materials. This new, non‐destructive method is useful for spectrometric identification and crystal chemical characterization of many rocks and minerals commonly found in archaeological contexts. Three brief examples of IRS analysis of archaeological materials are presented as test cases. It is suggested that IRS could and should become a routine approach in geoarchaeology and archaeometry for identification and provenance studies. © 2009 Wiley Periodicals, Inc.     

Losses of birch foliage due to insect herbivory along geographical gradients in Europe: a climate-driven pattern?

The study reports large-scale geographical variation in foliar damage of Betula pubescens and B. pendula by leaf-chewing and leaf-mining insects in Northern and Central Europe. The data were obtained in late summer of 2004 from 90 study sites located along several latitudinal and longitudinal gradients up to 1275 km in length; repeatability of a pattern detected was checked in 2005. Foliar damage in B. pubescens due to endemic herbivory increased in Fennoscandia from 1–2% at 70°N to 5–7% at 60°N; this pattern was best explained by mean July temperatures. Higher foliar losses in southern Fennoscandia were mostly due to an increase in proportion of damaged leaves, while an average consumption per damaged leaf increased only slightly. Foliar damage in B. pendula in Fennoscandia followed the same pattern as described for B. pubescens, although the overall loss of leaf area was only ca. 70% of that in B. pubescens. In contrast, there was no geographical or climatic pattern in damage of B. pendula by insect herbivores in Central Europe; average foliar losses were around 5% between 48°N and 60°N. These data suggest that damage of northern birch forests by leaf-chewing and leaf-mining insects will at least double with expected climatic warming, while in more southern regions the effects of climate change on birch foliar losses due to insect herbivory may be small or even negligible.