Biotic proxies and geochemistry in lake sediments at the Wolin II/00 site (NW Poland) –...
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indicating that the lake has fluctuated between shallow, saline water and deep, freshwater over the last ca. 90,000 years. X-ray diffraction analysis reveals a cyclical sequence of zones characterised by differing calcite:clay mineral ratios, calcite chemistries and evaporite minerals (halite, trona). The most recent drying began just after the LGM. Cyclicity consistent with precession forcing has been identified (e.g. d 13 C organic ), but other forcing factors are clearly at play. The Sayula record can be compared with marine and terrestrial sequences elsewhere in the NAT and with tropical terrestrial sequences from regions further removed from the direct influence of ice sheets. DISCOVERY OF AN E-W TRENDING PLEISTOCENE BURIED VALLEY IN THE GERMAN BIGHT, SOUTHERN NORTH SEA Jan F. Metzen. Geo-Engineering.Org GmbH, Germany E-mail address: [email protected] During the last 400 kyr large parts of the North Sea shelf area and adjacent northern European lowlands were shaped by glacial carving and melt- water releases, leaving now buried valleys. From 2007 - 2009, extensive Boomer, Chirp and multi-channel air gun reflection seismics were gath- ered in projected wind farm areas within the southern German Bight. This lead to the discovery of three buried glacial valleys. Pseudo-3D mapping of the valley flanks and the geometric orientation to each other show two valley structures running parallel in E-W direction – a major valley in width and length and a smaller one. A third buried valley trends N-S and crosses both E-W trending valleys. This study focusses on the major E-W trending buried valley, which is more than 35 km long and up to 5 km wide. The undulating valley floor is incised down to w300 m in the westernmost part. To the East, the valley bed rises up to <40 m, pinches out to a post-Saalian to Weichselian erosional discordance and splits into some smaller but still buried valley branches. Seismic artefacts and attenuation often hinder direct flank tracing deeper than 60 m. However, the flank geometry gives strong evidence for at least two different erosional processes. The upper valley part is wide open, reaches down to 15 - 40 m and is often V-shaped with shallow flank angles. The lower part has a smaller opening with much steeper flanks; its erosional shape is not clearly of U- or V-type. The sedimentary infill was inferred from seismic facies analysis and validated by CPTu and drill cores. From oldest to youngest, glaciofluvial sands (<5m thick) and sporadic basal till deposits are covered by rhythmitic sediment of clay/silt (>100 m thick). The top layer is also made of these rhythmites but interrupted by interglacial (Holstein?) layers of organic and fossil rich mud. Concluding, this study sheds light on the yet poorly documented relation of E-W trending burried valleys to Elsterian ice sheets in the German Bight. QUATERNARY UPLIFT AND EROSION RATES CONSTRAINED BY U-PB DATED ALPINE SPELEOTHEMS Michael Meyer. Institute of Geology and Palaeontology, Austria E-mail address: [email protected] The effect and relative importance of climate and climate change for the evolution of mountain ranges are subject of an ongoing and intense debate. While horizontal shortening of tectonic plates thickens the buoyant crust and elevates the Earth's surface, erosion of such tectonically accreted belts produces relief and triggers isostatic rebound until equi- librium is reached. Late Cenozoic climate deterioration and in particular the marked climate variability during the Quaternary significantly enhanced erosional unloading with profound consequences for the morpho-tectonic evolution of many active orogens. Hence, reliable esti- mates of the interrelated processes of rock-uplift, surface-uplift and erosion, are highly desirable but difficult to obtain for the Quaternary and often remain poorly constrained especially for calcareous mountain ranges where standard thermochronological techniques are usually not appli- cable. Over the last decade U-rich speleothems have been dated using U-Pb isochron techniques with considerable success. This opens up new vistas for studying landscape evolution and ancient paleoenvironments as no upper dating limit is encountered with this radiometric technique and recent studies show that U-rich cave calcites are not as rare as previously thought. Here we present 2 Ma-old U-Pb dated speleothems which were recovered from a high-alpine glacially sculptured landscape at the northern rim of the Alps. The petrographic, isotopic and organic charac- teristics of these samples call for environmental and climatic conditions during speleothem formation vastly different from today's. We calculate rates for rock- and surface-uplift (and hence erosion rates) using an isotopic modelling approach and show that cave calcites are a unique archive to constrain the magnitude of these vertical changes in mountain ranges composed of carbonate rocks. BIOTIC PROXIES AND GEOCHEMISTRY IN LAKE SEDIMENTS AT THE WOLIN II/00 SITE (NW POLAND) – RECONSTRUCTION OF THE HOLOCENE CLIMATE AND HYDROLOGICAL CHANGES Kamila Mianowicz. University of Szczecin, Poland E-mail address: [email protected] Multi-proxy dataset of palaeoecological records obtained in the Wolin II/ 00 site is a valuable source of information on past environmental changes at the mouth of the Odra River, S. Baltic coast. Pollen, including NPPs, plant and faunal macroremains and geochemical composition of the deposits are the base for the reconstruction. Different groups of proxies enable cross- validation of indicator values of particular fossil taxa. The Ellenberg's ecological numbers for species determined through plant macrofossils are used as a supplementary method to reconstruct changes in the water level. Since the beginning of the Holocene a shallow freshwater body has existed on the site. The sediment composition reflects several periods of a higher or lower water table in the lake. The water level distinctly increased at c. 10,000, 6800, 3800, 1000 and 900 14 C BP. The first water level rise was due to climate change, while the second was probably an indirect result of the Littorina transgression in the southern Baltic Sea. This palaeohydrological event is reflected by the abundance of freshwater faunal macroremains and green algae composi- tion. Causes of the water level rise dated to 3800 14 C BP as well as two other events at the beginning of the second millennium AD are still unclear, and both the drivers of a local range and more regional factors might be concerned. The low water level periods occurred at c. 8800-6800 14 C BP, 4300-3800 14 C BP and 1900-1000 14 C BP. The hiatus covering the second part of the Boreal period and the first half of the Atlantic period, was caused by a shift from humid to drier climate. The next two slowdowns of sedimentation rate probably resulted from local factors. In the uppermost part of the profile lake sediments are replaced by a peat layer containing large proportion of weeds and useful plant macroremains; these are traces of the early medieval human activity at the site. QUATERNARY GEOLOGY, PALEOSEISMOLOGY AND EARTHQUAKE HAZARDS IN REGIONS WITH MODERATE ACTIVE TECTONICS AND HIGH VULNERABILITY: THE SEISMIC LANDSCAPE OF THE PO PLAIN Alessandro Maria Michetti. Dipartimento di Scienze Chimiche e Ambientali, Uni, Italy E-mail address: [email protected] Quaternary Geology, paleoseismology and seismic landscape modeling are vital tools for assessing seismic hazards, particularly in regions characterized by moderate tectonic activity. For instance, this is the case of several areas in Western Europe, including Northern Italy and Switzerland, which are also densely populated, and characterized by a territorial setting in which industry is dominant, and includes the presence of several critical infrastructures and facilities. We illustrate this point using the results of more than 10 years of paleoseismological research in the Po Plain, the most economically developed area in Italy. The seismicity of the Po Plain is characterized by two strong Middle Ages earthquakes, the January 3,1117, Verona, and the Christmas 1222, Brescia, seismic events, both having epicentral intensity of IX to X MCS. Coseismic environmental effects, such as drainage changes, ground rupture and landslides, have been reported by historical sources. However, the iden- tification of the causative faults for these events is still unclear; the possibility that earthquakes of a similar size might affect other areas of Abstracts / Quaternary International 279-280 (2012) 233–345 325
Transcript of Biotic proxies and geochemistry in lake sediments at the Wolin II/00 site (NW Poland) –...
Abstracts / Quaternary International 279-280 (2012) 233–345 325
indicating that the lake has fluctuated between shallow, saline water anddeep, freshwater over the last ca. 90,000 years. X-ray diffraction analysisreveals a cyclical sequence of zones characterised by differing calcite:claymineral ratios, calcite chemistries and evaporite minerals (halite, trona).The most recent drying began just after the LGM. Cyclicity consistent withprecession forcing has been identified (e.g. d13Corganic), but other forcingfactors are clearly at play. The Sayula record can be compared with marineand terrestrial sequences elsewhere in the NATandwith tropical terrestrialsequences from regions further removed from the direct influence of icesheets.
DISCOVERY OF AN E-W TRENDING PLEISTOCENE BURIED VALLEY INTHE GERMAN BIGHT, SOUTHERN NORTH SEA
Jan F. Metzen. Geo-Engineering.Org GmbH, GermanyE-mail address: [email protected]
During the last 400 kyr large parts of the North Sea shelf area and adjacentnorthern European lowlands were shaped by glacial carving and melt-water releases, leaving now buried valleys. From 2007 - 2009, extensiveBoomer, Chirp and multi-channel air gun reflection seismics were gath-ered in projected wind farm areas within the southern German Bight. Thislead to the discovery of three buried glacial valleys. Pseudo-3D mapping ofthe valley flanks and the geometric orientation to each other show twovalley structures running parallel in E-W direction – a major valley inwidth and length and a smaller one. A third buried valley trends N-S andcrosses both E-W trending valleys.This study focusses on the major E-W trending buried valley, which ismore than 35 km long and up to 5 km wide. The undulating valley floor isincised down to w300 m in the westernmost part. To the East, the valleybed rises up to <40 m, pinches out to a post-Saalian to Weichselianerosional discordance and splits into some smaller but still buried valleybranches. Seismic artefacts and attenuation often hinder direct flanktracing deeper than 60 m. However, the flank geometry gives strongevidence for at least two different erosional processes. The upper valleypart is wide open, reaches down to 15 - 40 m and is often V-shaped withshallow flank angles. The lower part has a smaller opening with muchsteeper flanks; its erosional shape is not clearly of U- or V-type. Thesedimentary infill was inferred from seismic facies analysis and validatedby CPTu and drill cores. From oldest to youngest, glaciofluvial sands (<5 mthick) and sporadic basal till deposits are covered by rhythmitic sedimentof clay/silt (>100 m thick). The top layer is also made of these rhythmitesbut interrupted by interglacial (Holstein?) layers of organic and fossil richmud.Concluding, this study sheds light on the yet poorly documented relationof E-W trending burried valleys to Elsterian ice sheets in the German Bight.
QUATERNARY UPLIFT AND EROSION RATES CONSTRAINED BY U-PBDATED ALPINE SPELEOTHEMS
Michael Meyer. Institute of Geology and Palaeontology, AustriaE-mail address: [email protected]
The effect and relative importance of climate and climate change for theevolution of mountain ranges are subject of an ongoing and intensedebate. While horizontal shortening of tectonic plates thickens thebuoyant crust and elevates the Earth's surface, erosion of such tectonicallyaccreted belts produces relief and triggers isostatic rebound until equi-librium is reached. Late Cenozoic climate deterioration and in particularthe marked climate variability during the Quaternary significantlyenhanced erosional unloading with profound consequences for themorpho-tectonic evolution of many active orogens. Hence, reliable esti-mates of the interrelated processes of rock-uplift, surface-uplift anderosion, are highly desirable but difficult to obtain for the Quaternary andoften remain poorly constrained especially for calcareous mountain rangeswhere standard thermochronological techniques are usually not appli-cable. Over the last decade U-rich speleothems have been dated using U-Pbisochron techniques with considerable success. This opens up new vistasfor studying landscape evolution and ancient paleoenvironments as noupper dating limit is encountered with this radiometric technique andrecent studies show that U-rich cave calcites are not as rare as previously
thought. Here we present 2 Ma-old U-Pb dated speleothems which wererecovered from a high-alpine glacially sculptured landscape at thenorthern rim of the Alps. The petrographic, isotopic and organic charac-teristics of these samples call for environmental and climatic conditionsduring speleothem formation vastly different from today's. We calculaterates for rock- and surface-uplift (and hence erosion rates) using anisotopic modelling approach and show that cave calcites are a uniquearchive to constrain the magnitude of these vertical changes in mountainranges composed of carbonate rocks.
BIOTIC PROXIES AND GEOCHEMISTRY IN LAKE SEDIMENTS AT THEWOLIN II/00 SITE (NW POLAND) – RECONSTRUCTION OF THEHOLOCENE CLIMATE AND HYDROLOGICAL CHANGES
Kamila Mianowicz. University of Szczecin, PolandE-mail address: [email protected]
Multi-proxy dataset of palaeoecological records obtained in the Wolin II/00 site is a valuable source of information on past environmental changesat the mouth of the Odra River, S. Baltic coast. Pollen, including NPPs, plantand faunal macroremains and geochemical composition of the deposits arethe base for the reconstruction. Different groups of proxies enable cross-validation of indicator values of particular fossil taxa. The Ellenberg'secological numbers for species determined through plant macrofossils areused as a supplementary method to reconstruct changes in the water level.Since the beginning of the Holocene a shallow freshwater body has existedon the site. The sediment composition reflects several periods of a higheror lower water table in the lake.The water level distinctly increased at c. 10,000, 6800, 3800, 1000 and 90014C BP. The first water level rise was due to climate change, while thesecond was probably an indirect result of the Littorina transgression in thesouthern Baltic Sea. This palaeohydrological event is reflected by theabundance of freshwater faunal macroremains and green algae composi-tion. Causes of thewater level rise dated to 3800 14C BP as well as two otherevents at the beginning of the second millennium AD are still unclear, andboth the drivers of a local range and more regional factors might beconcerned.The low water level periods occurred at c. 8800-6800 14C BP, 4300-380014C BP and 1900-1000 14C BP. The hiatus covering the second part of theBoreal period and the first half of the Atlantic period, was caused by a shiftfrom humid to drier climate. The next two slowdowns of sedimentationrate probably resulted from local factors.In the uppermost part of the profile lake sediments are replaced bya peat layer containing large proportion of weeds and useful plantmacroremains; these are traces of the early medieval human activity atthe site.
QUATERNARY GEOLOGY, PALEOSEISMOLOGY AND EARTHQUAKEHAZARDS IN REGIONS WITH MODERATE ACTIVE TECTONICS ANDHIGH VULNERABILITY: THE SEISMIC LANDSCAPE OF THE PO PLAIN
Alessandro Maria Michetti. Dipartimento di Scienze Chimiche e Ambientali,Uni, ItalyE-mail address: [email protected]
Quaternary Geology, paleoseismology and seismic landscape modelingare vital tools for assessing seismic hazards, particularly in regionscharacterized by moderate tectonic activity. For instance, this is the caseof several areas in Western Europe, including Northern Italy andSwitzerland, which are also densely populated, and characterized bya territorial setting in which industry is dominant, and includes thepresence of several critical infrastructures and facilities. We illustrate thispoint using the results of more than 10 years of paleoseismologicalresearch in the Po Plain, the most economically developed area in Italy.The seismicity of the Po Plain is characterized by two strong Middle Agesearthquakes, the January 3, 1117, Verona, and the Christmas 1222, Brescia,seismic events, both having epicentral intensity of IX to X MCS. Coseismicenvironmental effects, such as drainage changes, ground rupture andlandslides, have been reported by historical sources. However, the iden-tification of the causative faults for these events is still unclear; thepossibility that earthquakes of a similar size might affect other areas of
