- Email: [email protected]
Climatic Forcing of Wetland Hydrology during the Holocene Interglacial: Evidence from the Southeastern United States
Abstracts / Quaternary International 279-280 (2012) 462–565
formation of the Sciara del Fuoco depression. We expect that under optimum conditions 40Ar/39Ar dating of basaltic groundmass samples can be used more widely for dating Holocene volcanic events. RECONSTRUCTING FLOOD EVENT CALENDARS FROM MULTI-ARCHIVES APPROACH IN NON-MONITORED AREAS Bruno Wilhelm. EDYTEM, France
535
laminae are varves (correspondence between number of laminae and years). Two periods present noticeable exceptions: the end of the LIA, due to temporary settling of a morainic dam; the 1970-80’s recurrence when reduced sediment supply precluded the formation of varves. RECONSTRUCTING EXTREME FLOOD EVENTS FROM HIGH ALTITUDE LAKE SEDIMENT RECORDS: METHODOLOGICAL ISSUES AND FIRST RESULTS
E-mail address: [email protected]
Torrential flood hazard is expected to increase in the context of global warming. However, long time-series of climate in mountain areas are too sparse to assess reliably recurrence times of such events. Historical documents provide valuable information however they are by nature subjective and variable in quality owing to hazard perception and vulnerability. Even if a critical historian lecture can so supply pertinent flood information, it always persists uncertainties (Mélo et al., this session). To overcome these limits, lake sediments may be used as complementary records. This natural archive has the advantage to be continuous record in which flood events are preserved. Furthermore an objective flood magnitude can be assessed from the thickness of noteworthy event-triggered deposits. However if the recognition of major event-triggered deposits can be simple, a high-resolution dating of these events is more difficult over the historical period due to a lack of chronological markers. In this paper, we present a sediment record study of a French high alpine lake where an important effort was undertaken to date precisely 57 flood events over the last three centuries from the use of historical archives. Local and regional historical archives were going through in order to correlate the thickest sediment deposits triggered by major floods and earthquakes with their potential triggering historic events. Combining this historical dates with the classical dating measurements, we obtain a flood calendar very well-constrained thanks to 19 chronological marks over the last 270 years. This method permitted so to reconstruct a high-resolution flood calendar to assess a reliable frequency of extreme flood events which can be compared with precise climatic parameters. Following this promising results, this method is applying on others sites in the French alpine area and especially close to the well studied Arve's valley with the Lakes Anterne (Sixt) and Blanc (Chamonix). RECONSTRUCTING HIGH RESOLUTION GLACIER ACTIVITY OVER THE LAST CENTURIES FROM A PARTIALLY-VARVED LAKE SEDIMENT SEQUENCE (LAKE BLANC, NW FRENCH ALPS)
Bruno Wilhelm. Université de Savoie/EDYTEM LAB, France E-mail address: [email protected]
Mountain areas are particularly vulnerable to extreme flood hazards. One of the main questions is whether such events will become more frequent in the context of global warming. In this paper we aim at reconstructing flash-flood calendars from five lake sediment records, spreading on a north-south transect in French Alps over the last millennia. Studying flood occurrence from high elevation sediment sequences presents methodological difficulties, such as the absence of established proxies for flood intensity, the erosive destabilization due to human activities and the lack of plant macro-remains for 14C dating. To detect flood-triggered events and to assess their intensity, we used high-resolution geochemical records obtained by X-ray florescence (XRF) core scanning as a grain size proxy. In each lake, specific elements were chosen accordingly to the geological and redox conditions (Ca, Fe, K, Zr). Semi-quantitative XRF measurements were calibrated using independent geochemical methods. We traced organic matter (OM) content using Compton scattering obtained by XRF scanning coupled with infrared spectroscopy and spectrocolorimetry (calibrated by Rock-Eval pyrolysis). In addition to palynological analyses, the OM content was used to disentangle human impact from climate-driven changes in erosion patterns. Finally, an effort was undertaken to combine various dating methods: radionuclides, 14C and the correlation with historic seismic, flood and fire (charcoal counting) events, and Earth's magnetic field secular variation. The study of the northern lakes allowed us to evidence a strong relationship between the occurrence of extreme floods and both annual temperatures and North Atlantic Oscillation (NAO) index: high intensity floods occurred during warm periods and phases of positive NAO signal. In the southern part of transect, the work is in progress, and preliminary results suggest an inverse trend with a higher frequency of extreme events during cold periods, such as the Little Ice Age. CLIMATIC FORCING OF WETLAND HYDROLOGY DURING THE HOLOCENE INTERGLACIAL: EVIDENCE FROM THE SOUTHEASTERN UNITED STATES
Bruno Wilhelm. Université de Savoie/EDYTEM LAB, France E-mail address: [email protected]
Glacier fluctuations are the most spectacular expressions of climatic changes in mountain areas. These fluctuations result in radical changes in hydrological patterns which lead to fast sediment rate changes in lake sediment sequences. To establish a precise chronology permitting to reconstruct this high-frequency variability, continuous varved sequences are largely used. In this paper we propose to present methodologies used to reconstruct glacier activity from a non-continuously varved sediment sequence and to discuss reasons for the disappearance of varves in some parts of the sequence. The sediment is finely laminated with thick interbedded floodand earthquake-triggered deposits. The chronology is based on radioelement measurements, lead contaminations and a comparison of eventtriggered deposits with historic events. The 19 chronological markers obtained over the last 270 years permitted to delimit 14 inter-events periods. During which “continuous” sedimentation rates (i.e. without the event-triggered deposits) evolve abruptly between 0.3 and 2.5 mm/a. A comparison between sediment rates and the fluctuations of the welldocumented Bossons Glacier suggests a strong relationship. During the twentieth century, sediment rate increases correspond to glacier retreat periods and inversely. This result suggests a continuous sediment transfer directly linked to relative glacier melt. However at the end of the Little Ice Age (LIA) we observe an unexpected decrease in sedimentation rate while European glaciers experience a high shrinkage. Frontal moraine freshly discovered may act like a temporary dam. Detailed laminae counting was undertaken from thin section scans. For almost the whole studied period
Debra Willard. USGS, United States E-mail address: [email protected]
Sustainable resource management requires development of boundary conditions that are sufficiently broad to maintain ecosystem function while accommodating climatic and environmental fluctuations. Ideally, boundary conditions would be based on a period of record covered by both instrumental monitoring and proxies from paleo-records such as tree rings and those in sedimentary deposits. We present analysis of vegetation and hydrologic changes during the late Holocene interglacial from wetland sediments of the southeastern United States. Recent calibration studies that correlate hydroperiod, vegetation, and pollen assemblages provide the basis to reconstruct hydrologic fluctuations over subdecadal to millennial time scales. We integrate results from Atlantic Coastal Plain sites that span a latitudinal gradient from subtropical Florida (27 N) to temperate sites in Virginia (39 N) to examine the regional coherence of hydrologic variability. Habitats studied include marshes in central Florida and the Florida Everglades and forested wetlands in North Carolina and Virginia. Pollen evidence from wetland sites indicates centennial-scale fluctuations between wet and dry intervals. In the Florida Everglades, extended periods of drought played a significant role in structuring the modern Everglades landscape. In Atlantic Coastal Plain forested wetlands, hydroperiod fluctuated by an order of magnitude periodically throughout the last 2,400 years. Especially noteworthy hydrologic changes occurred during the Medieval Climate Anomaly, where all study sites became generally drier, and during the Little Ice Age, where the northern sites became wetter while southern sites became drier. The latitudinal transect
536
Abstracts / Quaternary International 279-280 (2012) 462–565
of Holocene climate provides the opportunity to examine spatial differences in hydrologic response to climate events of the Holocene interglacial and a critical context to evaluate the magnitude of anthropogenicallyinduced hydrologic change.
DYNAMICS OF ANTARCTICA
STICK-SLIP
MOTION,
WHILLANS
ICE
STREAM,
J. Paul Winberry. Central Washington University, United States E-mail address: [email protected]
DEVELOPMENT OF A METHOD TO QUANTIFY UV-B FLUX DURING THE QUATERNARY USING UV-B ABSORBING COMPOUNDS CONTAINED IN FOSSIL PINUS SPP. SPOROPOLLENIN Kathy J. Willis. Long-Term Ecology Laboratory, Institute of Biodive, United Kingdom E-mail address: [email protected]
UV-B radiation currently represents approximately 1.5% of incoming solar radiation. However, significant changes are known to have occurred in the amount of incoming radiation both on recent and geological timescales due to stratospheric ozone loss, solar activity1, Milankovitch oscillations, volcanic events and variations in cloud cover. Estimates from modelling suggest that in some intervals of time (e.g. End Permian), incoming UV-B could have been up to 80% higher than present2. If these estimates are correct then the impact on terrestrial ecosystems could have been profound3. Up until now it has not been possible to reconstruct a detailed measure of UV-B radiation through time. Instrumental records of UV-B radiation only extend back to the 1920s and modelling of past UV-B radiation is extremely difficult due to the unknown spatial variation in cloud and ash cover over time. Some success has recently been obtained in determining short-term variations (<200 yrs) through the measurement of UV-B absorbing compounds contained in the sporopollenin of fossil pollen4. However, it has not been possible to obtain a systematic continuous record through time from one fossil species. In a recent study we aimed to determine the suitability of fossil Pinus spp.pollen to record variations in UV-B flux through the Cenozoic. Due to the large size of the grain (and therefore extraction from sedimentary sequences without the use of chemicals), and its long fossil history, we hypothesised that this grain could provide a good proxy for recording past variations in UV-B flux. Preliminary results indicate the excellent potential of this species for providing a quantitative record of UV-B variation during the Quaternary. THE RURRAND FAULT AND THE 1756 DÜREN EARTHQUAKES PALEOSEISMOLOGICAL STUDIES IN THE LOWER RHINE EMBAYMENT Jonas Winandy. RWTH Aachen University, Germany E-mail address: [email protected]
The Rurrand Fault (Rurrandverwerfung) in the Lower Rhine Embayment located between Aachen and Cologne possibly indicates the Düren earthquake sequence. In 1756 several strong events took place in western Germany. At least two people died and hundreds of houses were destroyed. The earthquakes were felt as far as Strasbourg and London, therefore, a magnitude of at least 6 is reasonable. However, to date the seismic source is not clear. Recurrence intervals for active faults in the study area are estimated to be in the order of tens of ka. Due to relatively high erosion rates active faults are often not visible in the field. Therefore, seismic hazard might be underestimated. During road construction works in 2010 archaeological remains (Neolithic, Iron Age, Roman and Medieval) were found in the immediate vicinity of the Rurrand Fault, which was also disclosed by the archaeological trenches. Beside the Rhine Graben this fault is one of the most prominent NW-SE trending normal faults with a morphological expression in the area. We found Holocene surface-near sediments with significant offsets covered by thin colluvial sediments. A complex fault geometry was observed during the archaeological excavations. Growing displacement of the major fault downsection suggest at least two major, surface-rupturing earthquakes along the Rurrand Fault in the Holocene/Late Pleistocene. Additional data were collected with shallow geophysical methods. We applied DC geoelectrics and georadar in order to image the deeper parts of the fault zone. Airborne laserscanning data allow creating a high-resolution DEM. The morphological expression of the fault, the shallow depths of the offset sediments, and geophysical data led us to conclude on very recent seismicity along this active fault, despite radiocarbon and luminescence dating of sediment samples are still in progress.
The stick-slip motion and associated seismic emissions of Whillans Ice Stream (WIS), West Antarctica are two of the many recent observations of unexpected ice sheet behavior that are challenging traditional models of rapid glacier motion. Here we find that the WIS slip events repeatedly nucleate from a sticky-spot located in the middle of the ice stream, acting similar to an asperity in traditional models of earthquake physics. This region shows less motion than surrounding areas during the inter-slip periods, thus, concentrating stress and producing a pulse of seismic energy at the onset of slip. The propagating rupture breaks through an additional asperity in the northern part of the ice stream, producing another pulse of seismic energy 6-12 minutes after initiation. Both asperities are regions of higher hydraulic potential than surrounding regions, suggesting they may have greater bed friction due to reduced water lubrication. Tidal pacing of the stress accumulation combined with fault healing controls the applied stress at failure, with higher stress giving faster propagation of the rupture front and higher slip velocities; these differences are reflected in the timing of the teleseismic arrivals. Our results highlight both the great sensitivity of large ice streams to small changes in external forcing and the importance of limited regions of the subglacial bed in controlling their motion, as well as providing insights to the mechanics of repeating earthquakes. ECOLOGICAL MODELS IN PALEONTOLOGY: ASSESSING INFORMATION ON THE EXTINCTION OF SOUTH AMERICAN MEGAMAMMALS THROUGH ITS POTENTIAL DISTRIBUTION PATTERNS Gisele Winck. Universidade do Estado do Rio de Janeiro, Brazil E-mail address: [email protected]
We estimate the potential distribution of 27 South American taxa. The occurrence records were tested with 20 environmental data matrices of the Last Glacial Maximum (LGM). The resulting maps were compared with reconstructions of vegetation coverage of South America during the LGM. Accuracy measures were satisfactory (p<0.05). The group named Tempered comprises Glossotherium robustum, Glyptodon clavipes, Hemiauchenia paradoxa, Mylodon darwini, Pampatherium humboldtii, Toxodon platensis, Macrauchenia patachonica, Panochthus tuberculatus, Megatherium americanum andHaplomastodon platensis. It presents a potential to occur mainly in temperate semi-desert environments, by influence of the minimum temperature of the coldest month. Associated to this group is Hippidion principale and Hippidion devillei, which include distribution on both southern and northeastern SA. The second group named as Intertropical includes Panochthus greslebini, Xenorhinotherium bahiense, Parapanochthus jaguaribensis and Paleolama major. The main variable is temperature annual range and presents higher potential occurrence in tropical semi-desert areas. A third group holds Hoplophorus euphractus and Scelidotherium leptocephalum, and also Andean species: Cuvieronius hyodon, Equus (Amerhippus) andium, Megatherium spp. (several species). The main variable is the annual mean temperature. The fourth group comprises Equus (Amerhippus) neogeus and Glyptotherium sp., influenced mainly by annual precipitation. Haplomastodon waringi and Eremotherium laurillardi present largest distribution in tropical areas of semidesert and savannah, and have greater influence of temperature seasonality and temperature annual range. Megatherium medinae and Lestodon armatus were isolated. All groups have highest potential of distribution mainly in driest areas with open vegetation. Current vegetation maps indicate that these areas have been eliminated or greatly reduced. Stochastic effects may have caused the extinctions. DUST SOURCES TO THE SOUTHERN LATITUDES: SOUTH AMERICA AND AUSTRALIA Gisela Winckler. LDEO of Columbia University, United States E-mail address: [email protected]
Reconstructing climate-related changes in the rate of dust deposition, and in the provenance of the dust, provides critical constraints on hydrology
formation of the Sciara del Fuoco depression. We expect that under optimum conditions 40Ar/39Ar dating of basaltic groundmass samples can be used more widely for dating Holocene volcanic events. RECONSTRUCTING FLOOD EVENT CALENDARS FROM MULTI-ARCHIVES APPROACH IN NON-MONITORED AREAS Bruno Wilhelm. EDYTEM, France
535
laminae are varves (correspondence between number of laminae and years). Two periods present noticeable exceptions: the end of the LIA, due to temporary settling of a morainic dam; the 1970-80’s recurrence when reduced sediment supply precluded the formation of varves. RECONSTRUCTING EXTREME FLOOD EVENTS FROM HIGH ALTITUDE LAKE SEDIMENT RECORDS: METHODOLOGICAL ISSUES AND FIRST RESULTS
E-mail address: [email protected]
Torrential flood hazard is expected to increase in the context of global warming. However, long time-series of climate in mountain areas are too sparse to assess reliably recurrence times of such events. Historical documents provide valuable information however they are by nature subjective and variable in quality owing to hazard perception and vulnerability. Even if a critical historian lecture can so supply pertinent flood information, it always persists uncertainties (Mélo et al., this session). To overcome these limits, lake sediments may be used as complementary records. This natural archive has the advantage to be continuous record in which flood events are preserved. Furthermore an objective flood magnitude can be assessed from the thickness of noteworthy event-triggered deposits. However if the recognition of major event-triggered deposits can be simple, a high-resolution dating of these events is more difficult over the historical period due to a lack of chronological markers. In this paper, we present a sediment record study of a French high alpine lake where an important effort was undertaken to date precisely 57 flood events over the last three centuries from the use of historical archives. Local and regional historical archives were going through in order to correlate the thickest sediment deposits triggered by major floods and earthquakes with their potential triggering historic events. Combining this historical dates with the classical dating measurements, we obtain a flood calendar very well-constrained thanks to 19 chronological marks over the last 270 years. This method permitted so to reconstruct a high-resolution flood calendar to assess a reliable frequency of extreme flood events which can be compared with precise climatic parameters. Following this promising results, this method is applying on others sites in the French alpine area and especially close to the well studied Arve's valley with the Lakes Anterne (Sixt) and Blanc (Chamonix). RECONSTRUCTING HIGH RESOLUTION GLACIER ACTIVITY OVER THE LAST CENTURIES FROM A PARTIALLY-VARVED LAKE SEDIMENT SEQUENCE (LAKE BLANC, NW FRENCH ALPS)
Bruno Wilhelm. Université de Savoie/EDYTEM LAB, France E-mail address: [email protected]
Mountain areas are particularly vulnerable to extreme flood hazards. One of the main questions is whether such events will become more frequent in the context of global warming. In this paper we aim at reconstructing flash-flood calendars from five lake sediment records, spreading on a north-south transect in French Alps over the last millennia. Studying flood occurrence from high elevation sediment sequences presents methodological difficulties, such as the absence of established proxies for flood intensity, the erosive destabilization due to human activities and the lack of plant macro-remains for 14C dating. To detect flood-triggered events and to assess their intensity, we used high-resolution geochemical records obtained by X-ray florescence (XRF) core scanning as a grain size proxy. In each lake, specific elements were chosen accordingly to the geological and redox conditions (Ca, Fe, K, Zr). Semi-quantitative XRF measurements were calibrated using independent geochemical methods. We traced organic matter (OM) content using Compton scattering obtained by XRF scanning coupled with infrared spectroscopy and spectrocolorimetry (calibrated by Rock-Eval pyrolysis). In addition to palynological analyses, the OM content was used to disentangle human impact from climate-driven changes in erosion patterns. Finally, an effort was undertaken to combine various dating methods: radionuclides, 14C and the correlation with historic seismic, flood and fire (charcoal counting) events, and Earth's magnetic field secular variation. The study of the northern lakes allowed us to evidence a strong relationship between the occurrence of extreme floods and both annual temperatures and North Atlantic Oscillation (NAO) index: high intensity floods occurred during warm periods and phases of positive NAO signal. In the southern part of transect, the work is in progress, and preliminary results suggest an inverse trend with a higher frequency of extreme events during cold periods, such as the Little Ice Age. CLIMATIC FORCING OF WETLAND HYDROLOGY DURING THE HOLOCENE INTERGLACIAL: EVIDENCE FROM THE SOUTHEASTERN UNITED STATES
Bruno Wilhelm. Université de Savoie/EDYTEM LAB, France E-mail address: [email protected]
Glacier fluctuations are the most spectacular expressions of climatic changes in mountain areas. These fluctuations result in radical changes in hydrological patterns which lead to fast sediment rate changes in lake sediment sequences. To establish a precise chronology permitting to reconstruct this high-frequency variability, continuous varved sequences are largely used. In this paper we propose to present methodologies used to reconstruct glacier activity from a non-continuously varved sediment sequence and to discuss reasons for the disappearance of varves in some parts of the sequence. The sediment is finely laminated with thick interbedded floodand earthquake-triggered deposits. The chronology is based on radioelement measurements, lead contaminations and a comparison of eventtriggered deposits with historic events. The 19 chronological markers obtained over the last 270 years permitted to delimit 14 inter-events periods. During which “continuous” sedimentation rates (i.e. without the event-triggered deposits) evolve abruptly between 0.3 and 2.5 mm/a. A comparison between sediment rates and the fluctuations of the welldocumented Bossons Glacier suggests a strong relationship. During the twentieth century, sediment rate increases correspond to glacier retreat periods and inversely. This result suggests a continuous sediment transfer directly linked to relative glacier melt. However at the end of the Little Ice Age (LIA) we observe an unexpected decrease in sedimentation rate while European glaciers experience a high shrinkage. Frontal moraine freshly discovered may act like a temporary dam. Detailed laminae counting was undertaken from thin section scans. For almost the whole studied period
Debra Willard. USGS, United States E-mail address: [email protected]
Sustainable resource management requires development of boundary conditions that are sufficiently broad to maintain ecosystem function while accommodating climatic and environmental fluctuations. Ideally, boundary conditions would be based on a period of record covered by both instrumental monitoring and proxies from paleo-records such as tree rings and those in sedimentary deposits. We present analysis of vegetation and hydrologic changes during the late Holocene interglacial from wetland sediments of the southeastern United States. Recent calibration studies that correlate hydroperiod, vegetation, and pollen assemblages provide the basis to reconstruct hydrologic fluctuations over subdecadal to millennial time scales. We integrate results from Atlantic Coastal Plain sites that span a latitudinal gradient from subtropical Florida (27 N) to temperate sites in Virginia (39 N) to examine the regional coherence of hydrologic variability. Habitats studied include marshes in central Florida and the Florida Everglades and forested wetlands in North Carolina and Virginia. Pollen evidence from wetland sites indicates centennial-scale fluctuations between wet and dry intervals. In the Florida Everglades, extended periods of drought played a significant role in structuring the modern Everglades landscape. In Atlantic Coastal Plain forested wetlands, hydroperiod fluctuated by an order of magnitude periodically throughout the last 2,400 years. Especially noteworthy hydrologic changes occurred during the Medieval Climate Anomaly, where all study sites became generally drier, and during the Little Ice Age, where the northern sites became wetter while southern sites became drier. The latitudinal transect
536
Abstracts / Quaternary International 279-280 (2012) 462–565
of Holocene climate provides the opportunity to examine spatial differences in hydrologic response to climate events of the Holocene interglacial and a critical context to evaluate the magnitude of anthropogenicallyinduced hydrologic change.
DYNAMICS OF ANTARCTICA
STICK-SLIP
MOTION,
WHILLANS
ICE
STREAM,
J. Paul Winberry. Central Washington University, United States E-mail address: [email protected]
DEVELOPMENT OF A METHOD TO QUANTIFY UV-B FLUX DURING THE QUATERNARY USING UV-B ABSORBING COMPOUNDS CONTAINED IN FOSSIL PINUS SPP. SPOROPOLLENIN Kathy J. Willis. Long-Term Ecology Laboratory, Institute of Biodive, United Kingdom E-mail address: [email protected]
UV-B radiation currently represents approximately 1.5% of incoming solar radiation. However, significant changes are known to have occurred in the amount of incoming radiation both on recent and geological timescales due to stratospheric ozone loss, solar activity1, Milankovitch oscillations, volcanic events and variations in cloud cover. Estimates from modelling suggest that in some intervals of time (e.g. End Permian), incoming UV-B could have been up to 80% higher than present2. If these estimates are correct then the impact on terrestrial ecosystems could have been profound3. Up until now it has not been possible to reconstruct a detailed measure of UV-B radiation through time. Instrumental records of UV-B radiation only extend back to the 1920s and modelling of past UV-B radiation is extremely difficult due to the unknown spatial variation in cloud and ash cover over time. Some success has recently been obtained in determining short-term variations (<200 yrs) through the measurement of UV-B absorbing compounds contained in the sporopollenin of fossil pollen4. However, it has not been possible to obtain a systematic continuous record through time from one fossil species. In a recent study we aimed to determine the suitability of fossil Pinus spp.pollen to record variations in UV-B flux through the Cenozoic. Due to the large size of the grain (and therefore extraction from sedimentary sequences without the use of chemicals), and its long fossil history, we hypothesised that this grain could provide a good proxy for recording past variations in UV-B flux. Preliminary results indicate the excellent potential of this species for providing a quantitative record of UV-B variation during the Quaternary. THE RURRAND FAULT AND THE 1756 DÜREN EARTHQUAKES PALEOSEISMOLOGICAL STUDIES IN THE LOWER RHINE EMBAYMENT Jonas Winandy. RWTH Aachen University, Germany E-mail address: [email protected]
The Rurrand Fault (Rurrandverwerfung) in the Lower Rhine Embayment located between Aachen and Cologne possibly indicates the Düren earthquake sequence. In 1756 several strong events took place in western Germany. At least two people died and hundreds of houses were destroyed. The earthquakes were felt as far as Strasbourg and London, therefore, a magnitude of at least 6 is reasonable. However, to date the seismic source is not clear. Recurrence intervals for active faults in the study area are estimated to be in the order of tens of ka. Due to relatively high erosion rates active faults are often not visible in the field. Therefore, seismic hazard might be underestimated. During road construction works in 2010 archaeological remains (Neolithic, Iron Age, Roman and Medieval) were found in the immediate vicinity of the Rurrand Fault, which was also disclosed by the archaeological trenches. Beside the Rhine Graben this fault is one of the most prominent NW-SE trending normal faults with a morphological expression in the area. We found Holocene surface-near sediments with significant offsets covered by thin colluvial sediments. A complex fault geometry was observed during the archaeological excavations. Growing displacement of the major fault downsection suggest at least two major, surface-rupturing earthquakes along the Rurrand Fault in the Holocene/Late Pleistocene. Additional data were collected with shallow geophysical methods. We applied DC geoelectrics and georadar in order to image the deeper parts of the fault zone. Airborne laserscanning data allow creating a high-resolution DEM. The morphological expression of the fault, the shallow depths of the offset sediments, and geophysical data led us to conclude on very recent seismicity along this active fault, despite radiocarbon and luminescence dating of sediment samples are still in progress.
The stick-slip motion and associated seismic emissions of Whillans Ice Stream (WIS), West Antarctica are two of the many recent observations of unexpected ice sheet behavior that are challenging traditional models of rapid glacier motion. Here we find that the WIS slip events repeatedly nucleate from a sticky-spot located in the middle of the ice stream, acting similar to an asperity in traditional models of earthquake physics. This region shows less motion than surrounding areas during the inter-slip periods, thus, concentrating stress and producing a pulse of seismic energy at the onset of slip. The propagating rupture breaks through an additional asperity in the northern part of the ice stream, producing another pulse of seismic energy 6-12 minutes after initiation. Both asperities are regions of higher hydraulic potential than surrounding regions, suggesting they may have greater bed friction due to reduced water lubrication. Tidal pacing of the stress accumulation combined with fault healing controls the applied stress at failure, with higher stress giving faster propagation of the rupture front and higher slip velocities; these differences are reflected in the timing of the teleseismic arrivals. Our results highlight both the great sensitivity of large ice streams to small changes in external forcing and the importance of limited regions of the subglacial bed in controlling their motion, as well as providing insights to the mechanics of repeating earthquakes. ECOLOGICAL MODELS IN PALEONTOLOGY: ASSESSING INFORMATION ON THE EXTINCTION OF SOUTH AMERICAN MEGAMAMMALS THROUGH ITS POTENTIAL DISTRIBUTION PATTERNS Gisele Winck. Universidade do Estado do Rio de Janeiro, Brazil E-mail address: [email protected]
We estimate the potential distribution of 27 South American taxa. The occurrence records were tested with 20 environmental data matrices of the Last Glacial Maximum (LGM). The resulting maps were compared with reconstructions of vegetation coverage of South America during the LGM. Accuracy measures were satisfactory (p<0.05). The group named Tempered comprises Glossotherium robustum, Glyptodon clavipes, Hemiauchenia paradoxa, Mylodon darwini, Pampatherium humboldtii, Toxodon platensis, Macrauchenia patachonica, Panochthus tuberculatus, Megatherium americanum andHaplomastodon platensis. It presents a potential to occur mainly in temperate semi-desert environments, by influence of the minimum temperature of the coldest month. Associated to this group is Hippidion principale and Hippidion devillei, which include distribution on both southern and northeastern SA. The second group named as Intertropical includes Panochthus greslebini, Xenorhinotherium bahiense, Parapanochthus jaguaribensis and Paleolama major. The main variable is temperature annual range and presents higher potential occurrence in tropical semi-desert areas. A third group holds Hoplophorus euphractus and Scelidotherium leptocephalum, and also Andean species: Cuvieronius hyodon, Equus (Amerhippus) andium, Megatherium spp. (several species). The main variable is the annual mean temperature. The fourth group comprises Equus (Amerhippus) neogeus and Glyptotherium sp., influenced mainly by annual precipitation. Haplomastodon waringi and Eremotherium laurillardi present largest distribution in tropical areas of semidesert and savannah, and have greater influence of temperature seasonality and temperature annual range. Megatherium medinae and Lestodon armatus were isolated. All groups have highest potential of distribution mainly in driest areas with open vegetation. Current vegetation maps indicate that these areas have been eliminated or greatly reduced. Stochastic effects may have caused the extinctions. DUST SOURCES TO THE SOUTHERN LATITUDES: SOUTH AMERICA AND AUSTRALIA Gisela Winckler. LDEO of Columbia University, United States E-mail address: [email protected]
Reconstructing climate-related changes in the rate of dust deposition, and in the provenance of the dust, provides critical constraints on hydrology