Boulders Research Articles

Late Quaternary environmental dynamics in Lenin Peak area (Pamir Mountains, Kyrgyzstan)

The Pamir Mountains include peaks exceeding 7000 m, such as Lenin Peak (7134 m) in the northern Zaalai Range. Here, we examine the distribution of soils and geomorphological processes and landforms in its northern slope, from the highest glaciated environments until Alai valley floor. We present the first geomorphological map of the study area as well as an accurate description the main geomorphological units in order to reconstruct landscape dynamics in the area from Quaternary cold stages until present-day. Five main units are distributed: (1) valley floor (2900–3040 m), an area that must have been ice-free during Quaternary glaciations and is currently being reshaped by glaciofluvial processes, with a large alluvial fan reworked by aeolian activity; (2) hummocky terrain (3040–3500 m) including two moraine systems left by a piedmont glacier during the Last Glaciation as well as hilly deposits originated by a catastrophic rockfall event; (3) U-shaped glacial valley (3500–3800 m), including some moraine ridges as well as a sedimentary cover composed of glacial till that is being eroded by fluvial and mass-wasting processes; (4) high mountain valleys (up to 4600–4800 m) adjacent to the main valley floor with small cirque and alpine glaciers and widespread periglacial processes in ice-free environments; (5) glaciers flowing from the Lenin Peak summit until the foot of the mountain, where they form a debris-covered (surge-type) glacier. The existence of abundant glacial, periglacial and rockfall deposits (moraines, till, erratic boulders) allows inferring five different environmental stages since the Last Glaciation. The latest glacial advances took place during the 20th century and the Little Ice Age and deposited two moraine systems near the glacial front. The occurrence of active rock glaciers and protalus lobes indicates that the limit of permafrost conditions is now located at 3400–3500 m, with seasonal frozen ground in lower areas.

Про змінення положення південної границі Дніпровського (риського) зледеніння

On the basis of newly discovered factual material, this paper analyses the issue of the reassigning the position of the southern border of distribution of the Dnieper (Riss) glacial tongue, which is considered the southernmost glacier tongue of the glacial period in Europe. The article provides critical analysis of the history of glacial theory and the contribution of scientists from different countries. The article analyses the evolution of the views of researchers - from the drift origin of boulder-loam deposits, described in works by R Murchison, C Lyell, D Tilas and C Darwin, to the idea of glacial origin, the first supporters of which included Pierre Martel, Jean-Andre Deluc, Bernhard Friedrich Kuhn, Ignaz Venets , Albrecht Bernardi, Louis Agassiz and others. The paper evaluates the contribution of Russian scientists who studied continental glaciations, including P O Kropotkin, S M Nikitin, O O Inostrantsev, P Y Armashevsky, N I Krishtofovich, G E Shurovsky, F B Schmidt and others. The article also presents the position of V G Pazynych, an opponent of glacier theory, on the numerous differences of opinion in the interpretation of the framework of the theory and on the necessity of developing a complex model of glaciations, which would include consideration of both exaration and drift. This article presents for the first time the results of solving the problem of restoring the geological relic, the “Domotkanski valuny” [lit. Domotkan boulders – translator`s note] as an important object of geological heritage on the southern border of the Dnieper glacial tongue. The paper presents a study of Kalytva mountain as a terminal moraine formation, which was formed during the Dnieper glacial epoch. Kalytva mountain is a fine example of manifestations of glaciotectonic activities, moraine,fluvio- and limno - glacial deposits with erratic boulders and paleogenic outliers. The article proves the possibility of division of the Dnieper climatolith into lower, -middle, and upper Dnieper stadials and shows the correspondence of limno-glacial deposits, moraine and fluvio-glacial deposits of the middle Dnieper stadials to the upper part of the “Shevchenkivska suite”. We have shown that the periglacial zone situated to the south of the line Volnohorsk-Petrykivka-Yurivka is characterized by absence of boulder loams, by much more homogenous and weathered section of sub-aerial Quaternary deposits and by a lens of fluvio-glacial deposits. The discovery of the artificial outcrop of limno glacial moraine deposits between Spasske and Podhorodne villages enables us not only to determine the main clearly-manifested differences between eolian and limnetic loams but also to delineate more precisely the borders of the periglacial zone of the Dnieper glaciations, which was earlier marked almost 100 km to the north – in the region of the Orel river far from its confluence with the Dnieper. Field studies in the interfluve between the Dnieper, Kilchen and Samara found significant evidence for proving that the southern border of the periglacial zone of the Dnieper Glacial Epoch lies considerably further south than had been assumed previously.

Tracings of the north of Europe: Robert Chambers in search of the Ice Age

SUMMARYScottish publisher and naturalist Robert Chambers pursued an amateur interest in geology through much of his life. His early measurements of raised beaches in Scotland earned him membership in the Geological Society of London in 1844, a recognition much appreciated by the anonymous author of the ‘scandalous’ Vestiges published the same year. Although familiar with emerging ice age theories, Chambers remained with most British geologists a sceptic through the 1840s, even after a trip to the glaciers of the Alps in 1848, which nevertheless prepared him for the turning point, which came in 1849 during an extensive field trip in Norway and Sweden. Here a wealth of observations left him in no doubt that vast glaciers had formerly covered Scandinavia, polishing cliffs, scouring striations, depositing old moraines and erratic boulders. This also led him to a new glacial reading of the British landscape, and with the ardent conviction of a fresh convert he became one of the most vocal supporters of glacial theory in Britain in the 1850s at a time when the iceberg drift theory for boulder transport was still favoured by most prominent British geologists. While Chambers through his popular Chambers’s Edinburgh Journal communicated his travels and ice age vision to a wide audience, and also pointed out ice age evidence on guided excursions around Edinburgh, he did not enter this new vision into subsequent editions of Vestiges, probably in order not to reveal its author. This paper explores Chambers’s contributions to the ice age debate, his field trips and the genesis of his convictions, and evaluates his impact on the scientific debate.

Influencia de la glaciación en la red de drenaje: el ejemplo de los valles de Respina y Rebueno (Alto Porma, Cordillera Cantábrica, noroeste de España)

En el presente trabajo se aborda el estudio de dos valles en la cuenca del río Porma, en la vertiente meridional de la Cordillera Cantábrica, norte de España. El primero de ellos, el de Respina, presenta múltiples evidencias glaciares, como circos, morrenas, cubetas, till o bloques erráticos que demuestran la importancia que tuvo la glaciación en ese valle. El segundo, el de Rebueno, apenas cuenta con restos glaciares y están restringidos a la zona de cabecera. La comparación de los perfiles longitudinales y transversales de ambos valles, pone de manifiesto la importancia que tuvo la glaciación en la configuración del relieve actual del valle de Respina, contrastando con las formas fluviales generadas en el valle de Rebueno. En ambos se dieron procesos distintos que configuraron un relieve con importantes diferencias a pesar de su proximidad y similares características. Además, el trabajo aborda la influencia que la glaciación ha tenido en la configuración actual de la red de drenaje, aspecto que apenas ha sido analizado previamente, y que en este caso se concreta en el desvío del río Respina y la creación de un nuevo valle, como consecuencia de una potente acumulación morrénica procedente de la lengua glaciar del valle de Silván. Se trata de un ejemplo muy significativo de la importancia que tuvo la glaciación en la red fluvial.

Modelling the diversion of erratic boulders by the Valais Glacier during the last glacial maximum

ABSTRACTIn this study, a modelling approach was used to investigate the cause of the diversion of erratic boulders from Mont Blanc and southern Valais by the Valais Glacier to the Solothurn lobe during the Last Glacial Maximum (LGM). Using the Parallel Ice Sheet Model, we simulated the ice flow field during the LGM, and analyzed the trajectories taken by erratic boulders from areas with characteristic lithologies. The main difficulty in this exercise laid with the large uncertainties affecting the paleo climate forcing required as input for the surface mass-balance model. In order to mimic the prevailing climate conditions during the LGM, we applied different temperature offsets and regional precipitation corrections to present-day climate data, and selected the parametrizations, which yielded the best match between the modelled ice extent and the geomorphologically-based ice-margin reconstruction. After running a range of simulations with varying parameters, our results showed that only one parametrization allowed boulders to be diverted to the Solothurn lobe during the LGM. This precipitation pattern supports the existing theory of preferential southwesterly advection of moisture to the alps during the LGM, but also indicates strongly enhanced precipitation over the Mont Blanc massif and enhanced cooling over the Jura Mountains.

Late Pleistocene outburst floods from Issyk Kul, Kyrgyzstan?

AbstractElevated shorelines and lake sediments surrounding Issyk Kul, the world's second largest mountain lake, record fluctuating lake levels during Quaternary times. Together with bathymetric and geochemical data, these markers document alternating phases of lake closure and external drainage. The uppermost level of lake sediments requires a former damming of the lake's western outlet through the Boam gorge. We test previous hypothesised ice or landslide dam failures by exploring possible links between late Quaternary lake levels and outbursts. We review and recompile the chronology of reported changes in lake site, and offer new ages of abandoned shorelines using 14C in bivalve and gastropod shells, and plant detritus, as well as sand lenses in delta and river sediments using Infrared Stimulated Luminescence. Our dates are consistent with elevated lake levels between ~45 ka and 22 ka. Cosmogenic 10Be and 26Al exposure ages of fan terraces containing erratic boulders (>3 m) downstream of the gorge constrain the timing of floods to 20.5–18.5 ka, postdating a highstand of Issyk Kul. A flow‐competence analysis gives a peak discharge of >104 m3 s–1 for entraining and transporting these boulders. Palaeoflood modelling, however, shows that naturally dammed lakes unconnected to Issyk Kul could have produced such high discharges upon sudden emptying. Hence, although our data are consistent with hypotheses of catastrophic outburst floods, average lake‐level changes of up to 90 mm yr–1 in the past 150 years were highly variable without any outbursts, so that linking lake‐level drops to catastrophic dam breaks remains ambiguous using sedimentary archives alone. This constraint may readily apply to other Quaternary lakes of that size elsewhere. Nonetheless, our reconstructed Pleistocene floods are among the largest reported worldwide, and motivate further research into the palaeoflood hydrology of Central Asia. Copyright © 2017 John Wiley & Sons, Ltd.

Glacial stages and post-glacial environmental evolution in the Upper Garonne valley, Central Pyrenees.

The maximum glacial extent in the Central Pyrenees during the Last Glaciation is known to have occurred before the global Last Glacial Maximum, but the succession of cold events afterwards and their impact on the landscape are still relatively unknown. This study focuses on the environmental evolution in the upper valley of the Garonne River since the Last Glaciation. Geomorphological mapping allows analysis of the spatial distribution of inherited and current processes and landforms in the study area. The distribution of glacial records (moraines, till, erratic boulders, glacial thresholds) suggests the existence of four glacial stages, from the maximum expansion to the end of the glaciation. GIS modeling allows quantification of the Equilibrium Line Altitude, extent, thickness and volume of ice in each glacial stage. During the first stage, the Garonne glacier reached 460m in the Loures-Barousse-Barbazan basin, where it formed a piedmont glacier 88km from the head and extended over 960km2. At a second stage of glacier stabilization during the deglaciation process, the valley glaciers were 12-23km from the head until elevations of 1000-1850m, covering an area of 157km2. Glaciers during stage three remained isolated in the upper parts of the valley, at heights of 2050-2200m and 2.6-4.5km from the head, with a glacial surface of 16km2. In stage four, cirque glaciers were formed between 2260m and 2590m, with a length of 0.4-2km and a glacial area of 5.7km2. Also, the wide range of periglacial, slope, nival and alluvial landforms existing in the formerly glaciated environments allows reconstruction of the post-glacial environmental dynamics in the upper Garonne basin. Today, the highest lands are organized following three elevation belts: subnival (1500-1900m), nival (1900-2300m) and periglacial/cryonival (2300-2800m).

Trace fossils from the Baltoscandian erratic boulders in SW Poland

Many well preserved trace fossils were found in erratic boulders and the fossils preserved in them, occurring in the Pleistocene glacial deposits of the Fore-Sudetic Block (Mokrzeszow Quarry, Świebodzice outcrop). They include burrows ( Arachnostega gastrochaenae , Balanoglossites isp., ? Balanoglossites isp., ? Chondrites isp., Diplocraterion isp., Phycodes isp., Planolites isp., ? Rosselia isp., Skolithos linearis , Thalassinoides isp., root traces) and borings ? Gastrochaenolites isp., Maeandropolydora isp., Oichnus isp., Osprioneides kampto , ? Palaeosabella isp., Talpina isp., Teredolites isp., Trypanites weisei , Trypanites isp., ? Trypanites isp., and an unidentified polychaete boring in corals. The boulders, Cambrian to Neogene (Miocene) in age, mainly came from Scandinavia and the Baltic region. The majority of the trace fossils come from the Ordovician Orthoceratite Limestone, which is exposed mainly in southern and central Sweden, western Russia and Estonia, and also in Norway (Oslo Region). The most interesting discovery in these deposits is the occurrence of Arachnostega gastrochaenae in the Ordovician trilobites (? Megistaspis sp. and Asaphus sp.), cephalopods and hyolithids. This is the first report of Arachnostega on a trilobite (? Megistaspis ) from Sweden. So far, this ichnotaxon was described on trilobites from Baltoscandia only from the St. Petersburg region (Russia). Arachnostega on a trilobite ( Asaphus ), a cephalopod and hyolithids is from Russia or Estonia. Another interesting ichnotaxon is Balanoglossites , which also was encountered in the erratic boulders from the Ordovician Orthoceratite Limestone of Sweden. So far, this ichnotaxon was known only from Russia (St. Petersburg region). Some rare borings (e.g., Osprioneides kampto , ? Palaeosabella isp.) also were found in glacial erratics of Silurian stromatoporoids, excellent outcrops of which are located in Gotland (Sweden) and Saaremaa (Estonia). In addition, stromatoporoid/coral, coral/coral and some new fossil associations are reported. The material studied probably was transported from the N, the NE, and less commonly from the NW.

Late Pleistocene and Holocene Glacier Extent in the Georgian Caucasus

This article presents the information of the Georgian Caucasus glaciation at the Late Pleistocene and Holocene period (～126,000-11,700 calendar years ago). Our primary aim was to numerically reproduce the ice extent deduced from geological and geomorphological mapping. We used the analog method with the 30 m resolution SRTM DEM (Shuttle Radar Topography Mission Digital Elevation Model). In addition, the rates of glaciation of those times are identified based on the stadial moraines and erratic boulders. The current investigation has revealed that in the Late Pleistocene, the central and western Caucasus characterized the highest glaciation, while the eastern Caucasus boasted the lowest glaciated area, and in the southern Georgia’s highland glaciation has almost the same form as there is in the Eastern Caucasus today. The longest glaciers were located in the Enguri (Nenskra ～36 km, Mulkhura ～35.1 km, Dolra ～34.5 km), Kodori (Sakeni ～25 km, Klichi ～20 km, Marukhi ～17.3 km) Rioni (Buba ～23 km, Kirtisho ～20.5 km, Jejora ～17.5 km) and Tergi (Devdoraki ～38.5 km, Suatisi ～32 km) river basins. We found, that topography thresholds related to the elevation and hypsometry of individual catchments controlled the gradient of the rate of glacier expansion in the domain at that time.

Deglaciation of Boknafjorden, south‐western Norway

ABSTRACTWe present 30 10Be ages from glacial erratic boulders to constrain the deglaciation of the Scandinavian Ice Sheet in the Boknafjorden region, south‐western Norway. The southern part of the island Karmøy, located at the mouth of this fjord system, became free of glacier ice before 16 ka, probably because of the sudden break up of the Norwegian Channel Ice Stream at 20–18 ka. The ice sheet margin then stabilized at the fjord mouth until a second retreat phase commenced at or slightly before 16 ka. A calving bay developed in Boknafjorden after 16 ka, and in the course of the next millennium the ice front retreated to the inner fjord branches. In contrast, a major outlet glacier that filled the Hardangerfjorden farther to the north did not start to retreat from the fjord mouth until after 15 ka, probably in response to the Bølling warming. Thus, not only did Boknafjorden experience major retreat before Bølling warmth, but there was a variable response of south‐western fjord glaciers in Norway consistent with prior observations of non‐climatic forcing of marine‐terminating outlet glaciers.

Stretched exponential relaxation of viscous remanence and magnetic dating of erratic boulders

AbstractViscous remanence continuously increases with the duration of reorientation of rocks, and the remanence gets partially overprinted in rocks parallel to the Earth's magnetic field. This overprinted viscous remanence is unblocked at a certain temperature that enables the estimation of the time required for the rock to acquire the magnetism, by assuming the exponential law of Néel's single‐domain theory. However, previous results of dating the rocks by the exponential law have shown older ages than radiometric or cosmogenic exposure ages. Néel's exponential decay law is applicable to a system whose magnetic grains have an identical relaxation time. However, in real systems, the expected behavior is not usually observed because relaxation times vary for individual grains. Moreover, the variation of viscous remanence with the logarithmic law for a distribution of relaxation times is predicted to be concave downward. Here we found that the stretched exponential law, exp{−(t/τ)1 − n} with 0 ≤ n < 1, explains previously published data on viscous decay. The observed stretched exponential relaxation can be interpreted in terms of the global relaxation of a system containing many relaxing species, each of which decays exponentially in time with a specific fixed relaxation rate. Using this law, we derived an extended time‐temperature relationship of magnetite involving the Néel's exponential decay law with n = 0 and a system containing many relaxing times with variable n. The extended time‐temperature relationship shows that the age of a coral tsunami boulder with high anomalous unblocking temperatures can be fitted with an assigned radiometric age.

The deep accumulation of 10Be at Utsira, southwestern Norway: Implications for cosmogenic nuclide exposure dating in peripheral ice sheet landscapes

AbstractCosmogenic nuclide exposure dating is a widely used method for constraining past ice sheet histories. We scrutinize a recently published data set of cosmogenic 10Be data from erratic boulders in Norway used to constrain the deglaciation of the western Scandinavian Ice Sheet to 20 ka. Our model of the 10Be inventory in glacial surfaces leads us to conclude that the chronology may be afflicted by the deep subsurface accumulation of 10Be during long‐lasting ice‐free periods that resulted in 10Be ages >10% too old. We suggest that the majority of the dated erratic boulders contain a uniform level of inherited muon‐produced 10Be and were derived from bedrock depths >2.5 m and most likely ~4 m. The implication of our finding is that for landscapes that experience long ice‐free periods between brief maximum glacial phases, glacial erosion of >5 m is required to remove detectable traces of inherited 10Be.

Geomorphic Records along the General Carrera (Chile)–Buenos Aires (Argentina) Glacial Lake (46°–48°S), Climate Inferences, and Glacial Rebound for the Past 7–9 ka: A Discussion

The paper by Bourgois et al. (2016) presents new cosmogenic isotope concentrations data that permit them to propose a scenario for the post-glacial evolution of the Lago General Carrera/Buenos Aires (LGCBA). In this comment, we do not discuss the validity of the proposed ages, although ages deduced from cosmogenic isotope concentrations may be affected by complex history, particularly when they are obtained in erratic boulders or dropstones (Putkonen & Swanson, 2003; Delmas et al., 2011). We simply note here basic geomorphological evidence challenging the complex scenario proposed by Bourgois et al. (2016), and showing that the LGCBA has never been endorheic following the retreat of the main glacial tongue. This observation has significant implications on the post-glacial climatic evolution of that area. As observed by Bourgois et al. (2016) and several previous authors (e.g., Caldenius, 1932; Turner et al., 2005; Hein et al., 2010), shorelines around the lake evidence periods of higher water levels. In the Rio de Las Dunas and Rio Los Maitenes area, Bourgois et al. (2016) note four major terrace levels corresponding to fan deltas whose elevation vary from 500 meters above sea level (m-asl) for the highest T4 terrace, to ~300 m-asl for the lower terrace, the present-day elevation of the lake being 201 m-asl. They propose that the four fan deltas formed in a short time period between 13.7 +/-0.8 ka and 10.9 +/-1.3 ka, i.e. in less than 1000 years per fan delta. In the discussion section of their paper, Bourgois et al. (2016) propose that the three higher terraces (T2-T4) accumulated in ice-walled lake environment, while a major ice-tongue still existed along the lake. They note that the T1 shoreline is largely preserved all around the lake, and they propose that this terrace formed during an endorheic period. The fan delta corresponding to the present-day elevation of the lake (T0 according to the terminology of Bourgois et al. (2016)) would be much more recent, less than 6.7 ka-old. Between the appearance of the T1 and T0 fan deltas, Bourgois et al. (2016) propose that a glacial advance occurred, followed by a tremendous rise of the level of the lake that would have reached elevations larger than 500 m in the Rio de Las Dunas area, i.e. above T4. At that time, according to Bourgois et al. (2016), despite this elevation is now higher than the present-day elevation of the Perito Moreno outlet towards the Atlantic Ocean, the lake would still have been endorheic. Then, Bourgois et al. (2016) conclude that the posterior isostatic rebound uplifted the Rio de Las Dunas area with respect to Perito Moreno from more than 135 m.

Alkali basalts and enclosed ultramafic xenoliths near Ushuaia, Tierra Del Fuego, Argentina.

At the southernmost part of Tierra del Fuego a few outcrops and erratic boulders of alkali basaltic rocks with ultramafic enclaves have been studied. Alkali basalt plugs or pipes hitherto identified are scarce, and host rocks are constituted by slates that belong to Mesozoic deposition. The petrography, texture and composition of the basalt and xenoliths were investigated by petrographic microscope and electron microprobe analysis. Xenocrysts of amphibole and alkali feldspar, phenocrysts of nepheline, olivine, spinel, phlogopite and Fe–Ti minerals (10 %) and a diversity of xenoliths, mainly lherzolitic, pyroxenite and wehrlitic nodules (15 %), but also from metamorphic rocks provenance, are contained in the basalt groundmass (75 %). This finer-grained material is made up of laths or needles of plagioclase, pyroxene, opaque minerals, apatite and glass, with intersertal, hyalopilitic and pilotaxitic. Locally, rock has an even granoblastic texture. Former amygdules are filled by analcite, zeolites, sodalite and calcite. The normative classification, based on nepheline content, conclude that this rock is an alkali basalt. The chemical classification, considering immobile elements as Zr/TiO2 versus Nb/Y indicate an alkali basalt too and plots over the TAS diagram fall in the foidite (Na-rich or nephelinite) and basanite fields. The REE patterns are fractionated (La/Yb primitive mantle normalized is approximately 30). The K–Ar isotopic technique on individual macrocrysts gave ages of 146 ± 5 Ma (amphibole) and 127 ± 4 Ma (alkali feldspar); and K–Ar whole rock datum reported 8.3 ± 0.3 Ma. Nevertheless, fertile samples show geochemical features typical of deep derived material thus, based on the position in the actual tectonic setting, indicate that the basalt is older than its isotopic age.

Glacial geomorphology of the tableland east of the Andes between the Coyle and Gallegos river valleys, Patagonia, Argentina

ABSTRACTWe report the results of geomorphological mapping of the high tablelands of Patagonia east of the Andes and between the Coyle and Gallegos river valleys. The map covers a low-relief area of about 3400 km2 at a scale of 1:85,000. It contributes to knowledge of a landscape shaped by lobes of the Patagonian ice sheet and can be used as a tool for further Quaternary studies. The map was built from remote-sensing data, compiled, and analyzed in geographical information system packages and supported by fieldwork. It features glacial landforms including moraine ridges and belts, ground moraine, outwash plains, outwash fans, meltwater channels, traces of glacial lakes, and erratic boulders. Fluvial, aeolian, and volcanic landforms and structural features were also mapped to provide a complete understanding of the landscape. We define three glacial units that record the frontal positions of former piedmont glaciers. The criteria used to define these units are the morphology, maximum relief, boulder content of moraine ridges, and crosscutting relations.

Identification, characteristics and classification of cryogenic block streams

Cryogenic block streams consist of a stream of rocks superficially resembling a stream deposit but lacking a matrix, usually occurring on a valley or gully floor or on slopes that are less steep than the maximum angle of repose of coarse sediments. They are usually formed on perennially frozen ground, but can also occur as relict landforms. There are three main active kinds forming today, viz ., Siberian and Tibetan dynamic rock streams and lag block streams. During their formation, the blocks in the active Siberian and Tibetan dynamic block streams move downslope at up to 1 m/a. They are forming today on the Tibetan Plateau and in the more arid parts of south-central Siberia, although the processes involved in the movement are different. In the case of the Tibetan type, individual blocks slide downslope over the substrate in winter on an icy coating in areas of minimal winter precipitation. The Siberian type develops in areas of 15–80 cm of winter snow cover and an MAAT (mean annual air temperature) of ?4 ℃ to ?17 ℃. The movement is due to creep of snow and ice and collapse of the blocks downslope during thawing. Lag block streams are formed by meltwater flowing over the surface of sediment consisting primarily of larger blocks with a limited amount of interstitial sediment. The erosion of the matrix is primarily in the spring in areas of higher winter precipitation on 10°–30° slopes. The blocks remain stationary, but the interstitial sediment is washed out by strong seasonal flows of meltwater or rain to form an alluvial fan. The boulders undergo weathering and become more rounded in the process. Lag block streams can also develop without the presence of permafrost in areas with cold climates or glaciers. Block streams also occur as relict deposits in older deposits under various climatic regimes that are unsuitable for their formation today. An example of relict lag block streams with subangular to subrounded blocks occurs in gullies on the forested mountainsides at Felsen in Germany, and is the original 'felsenmeer'. Similar examples occur near Vitosha Mountain in Bulgaria. The 'stone runs' in the Falkland Islands are examples of the more angular relict lag block streams. In both Tasmania and the Falkland Islands, they mask a more complex history, the underlying soils indicating periods of tropical and temperate soil formation resulting from weathering during and since the Tertiary Period. Block streams have also been reported from beneath cold-based glaciers in Sweden, and below till in Canada, and when exhumed, can continue to develop.

PETROGLYPHS OF KHABAROVSK TERRITORY: THE IMPACT OF THE 2013 AMUR AND USSURI FLOODING

The Sikachi-Alyan and Sheremetyevo rock art sites are in the province of Lower Amur and Ussuri rock art. A history of their discovery is sketched, and their state of preservation is described. In 2013, many of them were damaged by extraordinary flooding. The effects of water and temperature fluctuations and of wind erosion are assessed. In Sikachi-Alyan, the main factors of rock art decay were silting of boulders with petroglyphs, and their displacement caused by seasonal rise of water-level and ice-drift. In Sheremetyevo, destruction resulted mainly from bioagents. The removal of lichen revealed new petroglyphs, and known ones were recorded in details. Boulders with rare zoomorphic and anthropomorphic petroglyphs were discovered in the riverside bush and on the floodplain terrace.

Red deer vs. ibex hunting at a seasonal base camp in the Dolomites: Mondeval de Sora, site 1, sector I

Mondeval de Sora is situated in the heart of the Dolomites (south-eastern Alps, Italy) at an altitude of about 2150 m a.s.l.; this site represents a key deposit for the study of occupation and exploitation patterns of mountain areas in the southern slope of the Alps during the early Holocene. This paper contains the results of the study of the faunal assemblages coming from the Sauveterrian levels of sector I, located under the side of the erratic boulder facing south-east. The faunal assemblages of I sector come from two stratigraphic units (SSUU 8 and 31) and are characterised by a great variety of faunal resources: the most represented species are red deer and ibex, the hunting of which was favoured by the optimal location of the site, followed by a moderate quantity of chamois and roe deer. Wild boar is scarce and carnivores (bear, wolf and fox) are rare. The taphonomic analysis of the faunal macro-remains have demonstrated that the processing of animal carcasses, especially of red deer and ibex, were mostly carried out in the site.

Chronology of glaciations in the Cantabrian Mountains (NW Iberia) during the Last Glacial Cycle based on in situ-produced 10Be

The mountain ranges of the Iberian Peninsula preserve a valuable record of past glaciations that may help reconstruct past atmospheric circulation patterns in response to cooling events in the North Atlantic Ocean. Available chronologies for the glacial record of the Cantabrian Mountains, which are mainly based on radiocarbon and luminescence dating of glacial-related sediments, suggest that glaciers recorded their Glacial Maximum (GM) during MIS 3 and experienced a later Last Glacial Maximum (LGM) advance. This LGM extent is not established yet, preventing a fair correlation with available Cosmic Ray Exposure (CRE) based chronologies for the glacial record of the Pyrenees and the Sistema Central.We present a glacial reconstruction and a 10Be CRE chronology for the Porma valley, in the southern slope of the central Cantabrian Mountains. Glacial evidence at the lowest altitudes correspond to erratic boulders and composite moraines whose minimum 10Be CRE age of 113.9 ± 7.1 ka suggests that glaciers were at their maximum extent during MIS 5d, most likely in response to the minima in summertime insolation of the Last Glacial Cycle. Recessional moraines preserved within the glacial maximum limits allow the assessment of subsequent glacier advances or stagnations. The most remarkable advance took place prior to 55.7 ± 4.0 ka (probably at the end of MIS 4), consistently with minimum radiocarbon ages previously reported for lacustrine glacial-related deposits in the Cantabrian Mountains. A limited number of 10Be CRE ages from a composite moraine suggest a possible advance of the Porma glacier coeval with the global LGM; the glacier front attributed to the LGM would be placed within the margins of the previous GM like in the western Pyrenees. Erratic boulders perched on an ice-moulded bedrock surface provided a mean 10Be CRE age of 17.7 ± 1.0 ka, suggesting that part of the recessional moraine sequence corresponds to minor advances or stagnations of the glacier fronts during the Lateglacial period. This recessional response is consistent with deglacial chronologies previously established in the Pyrenees and the Sistema Central, and correlates with the coldest and driest conditions of MIS 2 according to lacustrine records. Finally, a relict rock glacier provided a mean 10Be CRE age of 15.7 ± 0.8 ka for movement cessation of its toe, indicating that periglacial conditions prevailed, at least, until the end of Heinrich Stadial 1/Mystery Interval.

An erratic dropstone of granodiorite with a water-escape structure from a Weichselian terrace along the River Gauja (NE Latvia)

A river terrace of the River Gauja (Latvia), built of Weichselian glaciolacustrine deposits, contains a large number of erratic boulders from the Fennoscandian Shield. These erratic boulders include several types of granites and granodiorites. Some of the granodiorites are so strongly weathered that they fall apart into mm-sized grains of individual minerals when it is attempted to take them out of the host sediment. This strongly weathered nature makes them physically comparable to unconsolidated sand. A consequence is that they may be subjected to soft-sediment deformation. The erratic granodiorite boulder under study here is the first described to show such a soft-sediment deformation structure inside: it has been intruded by a water/sediment mixture composed of the underlying silty/sandy material that must have been liquefied, possibly due to pressure exerted by the overburden, or – more likely – by the weight of the concentration of gravel of which the granodiorite boulder forms a part. The overpressurized water/sediment mixture tried to escape upwards through, among a few other places, the strongly weathered granodiorite, forming an escape structure.