Ninth International Conference on Permafrost ... - IARC Research

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Thixotropic Wedges or Frost Cracks: A Review from the Pannonian Basin(Hungary, Europe)János KovácsDepartment of Geology, University of Pécs, Pécs, HungarySzabolcs Ákos FábiánDepartment of Physical Geography, University of Pécs, Pécs, HungaryGábor VargaDepartment of Physical Geography, University of Pécs, Pécs, HungaryIstván Péter KovácsDoctoral School of Earth Sciences, University of Pécs, Pécs, HungaryGyörgy VargaDoctoral School of Earth Sciences, University of Pécs, Pécs, HungaryIntroductionThere is a general consensus about the study andinterpretation of soft-sediment deformation structures beinghelpful in paleoenvironmental reconstructions. During theglacial periods of the Pleistocene, Hungary was subjectto a cryogenic environment that produced various relictperiglacial features (Dylik 1963, Pécsi 1964, Tarnocai &Schweitzer 1998, Fábián et al. 2000, Kovács et al. 2007).The reason for the cold climate during these glacial periodsis Hungary’s unique geomorphological setting in thePannonian Basin. The Carpathians, which surround this largebasin, create an almost closed climatic situation, producingclimatic conditions not found elsewhere in Europe. In effect,Dylik seems to imply that the climate in Hungary during theglacial periods of the Pleistocene was somewhat similar tothe recent climate of the dry tundra regions of North Siberia.According to Maarleveld (1976) and Van Vliet-Lanoë et al.(2004), however, the Pannonian Basin was mostly devoid ofcontinuous permafrost during the Quaternary.General SettingIn the Pannonian Basin (Fig. 1), the continental crust isthinner and the stress field more complex, owing to a lateralshift to the east of the basin, which is squeezed between therigid northeast European basement and the Alpine orogene,with transpressional and transtensional phases alternatingfrom the upper Cenozoic to today (Csontos et al. 2002). Thepresent-day seismicity is higher than in northwest Europe,but is still of low magnitude.As a result of the cold climatic conditions (mentionedabove) in the Pleistocene epoch, various types of periglacialfeatures developed and are found in well-preserved relictforms in various deposits. Dylik (1963) summarizes therelict periglacial features of Hungary and discusses theiroriginal development, while Pécsi (1964) provides detaileddescriptions, including diagrams and photographs, of thesefeatures with the locations in which they occur. In the lastdecade, researchers investigated these cryogenic features fortheir implication for past climate (Tarnocai & Schweitzer1998, Fábián et al. 2000, Kovács et al. 2007) and for theirFigure 1. Location of the study sites in Hungary.distinction between tectonic and periglacial deformation(Van Vliet-Lanoë et al. 2004, Horváth et al. 2005, Magyariet al. 2005).MethodsOur interpretation of the periglacial deformationsinvestigated is based on (a) detailed field observations and(b) a synthesis of published data. Polygenetic forms wereanalysed using criteria defined for the periglacial andseismogenic structures. Sections were cleaned and describedusing sedimentological and pedological criteria, with respectto the topographical location and available moisture. Samplesfor grain size analyses and OSL dating were collected fromindividual fill units, and additional samples were collectedfor moisture content and background radiation measurement.The samples were dated at the Geological Institute ofHungary.ResultsThixotropic wedgesThixotropic wedges, developed in fine sandy-to-pebblydeposits, are formed within the sediment but relatively closeto the surface (Montenat et al. 2007). The wedges may be147
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tpermafrost (which were based on the occurrence of ice-wedgecasts and cryoturbations) in Hungary during the Pleistocene.Based on previously reported periglacial features, the localglacial history and OSL dates, these features suggest thatthe Pannonian Basin was underlain by permafrost duringthe Late Pleniglacial (22,000–18,000 years ago). We acceptthat some of the wedge-shaped sedimentary structures maybe causally related to paleoearthquakes, but the obviouscomplexity of the phenomenon requires caution.Figure 2. (A) periglacial frost wedge (sand wedge); (B)nonperiglacial synsedimentary transtensive fault (thixotropicwedge).very narrow and are recurrent (dm to several dm depth);the wedge pattern may be vertically arranged (Montenatet al. 2007). Tension faults (Fig. 2B) are often mistakenfor frost (cryodesiccation) fissures, evidence of former iceveins, or even ice-wedge casts, but occur rarely in polygonalnetworks and extend deeper in depth (Van Vliet-Lanoë et al.2004). These forms are much narrower than those developedby periglacial thermokarst. Their orientation is parallel orconjugate with tectonic direction (Van Vliet-Lanoë et al.2004).Frost wedgesThe sand wedges found in the Quaternary sedimentshave a polygonal system; consequently they are consideredsand-wedge polygons. The wedges have an average verticaldimension of 1.5–2.0 m, but some are as much as 3 m (Fig.2A). The wedge width was measured at right angle of theaxial plane of the wedge. Additionally these wedges are 25–30 cm and 50–60 cm or slightly more in width. The sandfilledwedge structures have simple V-shapes with rectilinearor slightly curved sides (convex outward) and pointed toes.The fill of the wedges is subvertically laminated, the sanditself is fine- to medium-grained (1–3 φ) and moderatelywell sorted. Some wedges near or at the top contain pebbles.The host strata adjacent to a sand wedge is upturned. In planview, it forms a polygonal network with cracks spaced 2–5m apart. The cracks are irregular and several meters long.ConclusionsSeveral hypotheses for the formation and infill of thewedges were evaluated using detailed physical, stratigraphic,and sedimentological information. The most likelyexplanation for most of the features is that they are relictcryogenic structures formed by thermal-contraction crackingin permafrost, and filled with wind-blown sediments. Thewedges are believed to have formed in the tundra environmentthat existed in the Pannonian Basin during the coldest parts ofthe Würm glaciation. Our observations of relict sand wedgessupport previous inferences for the occurrence of continuousAcknowledgmentsThe authors are grateful to C. Tarnocai and F. Schweitzerfor field assistance and useful communications, and to E.Thamó-Bozsó for supervising the OSL measurements.ReferencesCsontos, L., Benkovics, L., Bergerat, F., Mansy, J.L. &Wórum, G. 2002. Tertiary deformation history fromseismic section study and fault analysis in a formerEuropean Tethyan margin (the Mecsek-Villány areaSW Hungary). Tectonophysics 357: 81-102.Dylik, J. 1963. Magyarország periglaciális problémái.Földrajzi Értesítő 12: 453-464.Fábián, S.Á., Kovács, J. & Varga, G. 2000. Újabb szempontokhazánk periglaciális klímájához. Földrajzi Értesítő49: 189-204.Horváth, Z., Michéli, E., Mindszenty, A. & Berényi-Üveges,J. 2005. Soft-sediment deformation structures in LateMiocene–Pleistocene sediments on the pediment of theMátra Hills (Visonta, Atkár, Verseg): Cryoturbation,load structures or seismites? Tectonophysics 410: 81-95.Kovács, J., Fábián, S.Á., Schweitzer, F. & Varga, G. 2007.A relict sand-wedge polygon site in north-centralHungary. Permafrost and Periglacial Processes 18:379-384.Maarleveld, G. 1976. Periglacial phenomena and the meanannual temperature during the Last Glacial time in theNetherlands. Biuletyn Peryglacjalny 26: 57-78.Magyari, Á., Musitz, B., Csontos, L. & Van Vliet-Lanoë, B.2005. Quaternary neotectonics of the Somogy Hills,Hungary (part I): Evidence from field observations.Tectonophysics 410: 43-62.Montenat, C., Barrier, P., Ott d′Estevou, P. & Hibsch, C.2007. Seismites: An attempt at critical analysis andclassification. Sedimentary Geology 196: 5-30.Pécsi, M. 1964. Chronological problem of the patterned soilsof Hungary. Biuletyn Peryglacjalny 14: 279-293.Tarnocai, C. & Schweitzer, F. 1998. Cryogenic features inCanada and Hungary and their significance for pastclimate. Geografia Fisica e Dinamica Quaternaria21: 84-92.Van Vliet-Lanoë, B., Magyari, A. & Meilliez, F. 2004.Distinguishing between tectonic and periglacialdeformations of quaternary continental deposits inEurope. Global and Planetary Change 43: 103-127.148
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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xvi
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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370Huang, B. 339Hugelius, G. 105, 1
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