- Email: [email protected]
Does heavily-grazed vegetation show up in the pollen record?
34
Abstracts / Quaternary International 279-280 (2012) 9–120
speed over land and propagation speed along specific rivers and coastlines are obtained using Markov Chain Monte Carlo algorithms. In this work we also introduce a completely new numerical approach to modelling the first arrival time of a population, which is in good agreement with numerical simulations of Fisher-KPP equation but is orders of magnitude quicker. This new model allows many hundreds of simulations, with differing parameters, to be run in a short period of time; a major step forward for applying more sophisticated statistical techniques to the modelling of the Neolithic of Europe. RECONNAISSANCE U-PB DATING OF MIDDLE-PLEISTOCENETRANSITION GLACIAL TERMINATIONS FROM CORCHIA CAVE (ITALY) SPELEOTHEMS Petra Bajo. University of Melbourne, Australia E-mail address: [email protected]
During the Middle Pleistocene Transition (MPT), the period of glacialinterglacial cycles apparently shifted from w40 kyr to w100 kyr. Much debate has been waged in the last decade as to the causes of this transition. A key to resolving this debate is developing radiometrically dated palaeoclimate records which faithfully preserve the glacial terminations through this interval. Such records would be free of assumptions about orbital tuning. The recent breakthrough in the U-Pb dating of speleothems has opened up a new opportunity to tackle this issue. In this paper, we present a preliminary U-Pb chronology for a number of terminations through the MPT using speleothems from Corchia Cave (Italy). Speleothems from this cave have already yielded useful palaeoclimate records from the latter part of the Quaternary. They contain high concentrations of uranium, very little detrital thorium and relatively wellconstrained initial uranium-series disequilibria, making them relatively easy to date by U-Pb. Our chronologies are based on intensive sampling and, where possible, replicate speleothem records. The latter allows us to splice together multiple speleothem records using their respective isotopic profiles, and, by combining their age models into one, producing a ‘stacked record’ which attempts to minimise overall age uncertainties for the key intervals. THE FIRST FARMERS OF THE NORTH EUROPEAN PLAIN Corrie Bakels. Leiden University, Fac. Archaeology, Netherlands E-mail address: [email protected]
The terrain along the North Sea and the Baltic comprises a complex arrangement of lowland landscapes. It is also characterised by a west-east orientated thermal gradient. A diversity of natural environment leads to differences in what farmers do and the way in which they interact with the natural environment. This is so at present and will have been the same in the past. In her book on the TRB culture (Funnel-Beaker culture), Magdalena S. Midgley states the following: "the TRB settlement pattern demonstrates that the location of individual settlements was clearly bound up with the environmental conditions prevalent in each of the studied regions." But she continues: "there are none the less certain common factors which suggest that, in spite of the great diversity of locally available environments, it is possible to discern some general characteristics of settlement which are relevant to the TRB as a whole." (Midgley 1992, p. 316). It is an aim of this meeting to find out what was shared and what was a regional response. For instance: their crop cultivation is generally described as slash-and-burn cultivation, but this view is under discussion. For instance: the impact of the farmers’ activities on their environment is usually labeled as ‘Iversen landnam’ - and some phases as ‘Troels-Smith landnam’ -, but this is surely too crude. For instance: the problem of rising sea levels which provide another environmental factor, especially felt in the West, in the region of the western neighbours of the TRB people. FORWARD MODELLING OF THE SPELEOTHEM OXYGEN ISOTOPE PALEOCLIMATE PROXY Andy Baker. University of New South Wales, Australia E-mail address: [email protected]
Speleothem oxygen isotope series have recently made substantial contributions to our understanding of changes in the global climate system over the late Quaternary. However, a number of research problems and questions remain outstanding. These include the degree of uncertainty in speleothem oxygen isotope records which are especially apparent over periods of relatively stable climate, but which have largely yet to be fully quantified. Recently, we have started to examine the physical processes that determine water routing through the overlying soil, epikarst and karst aquifer using a lumped hydrological model to describe potential interrelationships between waters routed at different rates between individual sub-surface water stores that differ in their size and drainage characteristics. We demonstrate the use of a generic modelling approach, that avoids intractable problems such as site-specific model calibration, but which enables us to perform a sensitivity analysis to quantify hydrological uncertainty across a range of karst systems. This allows us to improve our understanding of stalagmite oxygen isotope data variability and the quantification of the ‘noise’ that is commonly found. Recent model refinements are introduced, demonstrating the utility of our modelling approach to drive forward models of stalagmite oxygen isotopes and the generation of stalagmite oxygen isotope pseudo-proxies. GEOCHEMICAL AND MINERALOGICAL INVESTIGATION OF A RECENTLY EXPOSED SAPROLITE PROFILE IN THE CHILEAN COASTAL RANGE Sophie Baker. Desert Research Institute, United States E-mail address: [email protected]
A new road cut in the Chilean Coastal Range near Valparaiso, Chile has exposed an w8m deep complex weathering profile comprising a saprolite (weathered Carboniferous granitoid) overlain by a w1m layer of fluvial gravels and a w60 cm thick loess. Soil horizons include a well-developed Bt horizon at 20-100 cm depth, and a w1m thick duripan formed mostly in the fluvial gravel layer. A 10Be profile age through the saprolite indicates a minimum exposure age of 2.2 Ma. The chemical weathering observed in the granite generally requires levels of soil moisture typical of a more humid climate than presently exists in the region (semi-arid), while the formation of the duripan in the overlying gravels is compatible with the current climate. Duripan formation likely took place in a dry climate at the maximum depth of penetration of meteoric moisture, and as it proceeded, further limited the downward flux of moisture, requiring that much of the chemical weathering below took place beforehand. The juxtaposition of duripan and saprolite may suggest a change in environmental conditions since the exposure of the granite; however, reconstructing palaeo-environments requires that the effects of the complex geomorphic history on the weathering processes be understood. To investigate the geomorphic and weathering history at this site, we are undertaking geochemical, soil property (particle size, Fe oxides, pH), and mineralogical (bulk and clay) analysis of 16 samples collected down profile. Results so far show that chemical weathering indices (CIA and CIW, based on Al, Na, Ca, and K concentrations) of the saprolite increase towards the surface but do not indicate the intensity of weathering often observed at the top of saprolite sections. This may be the result of conditions unfavorable for intense chemical weathering, or due to truncation of the upper weathering zones prior to fluvial gravel deposition. Clay mineralogy, soil analysis, and meteoric 10Be will help to test these hypotheses. DOES HEAVILY-GRAZED VEGETATION SHOW UP IN THE POLLEN RECORD? Ambroise Baker. University of Oxford, United Kingdom E-mail address: [email protected]
This research aims to assist the establishment of baselines for landscape and ecosystem restoration by contributing to the debates pertaining to the Vera hypothesis and landscape openness within the pollen record. In particular, it attempts to characterise the modern pollen signal produced by heavily-grazed vegetation. This study is focussed on sites within Northern Europe: The New Forest (UK) and the Oostvaardersplassen (The Netherlands), both selected for their differing grazing regimes and histories. The modern pollen
Abstracts / Quaternary International 279-280 (2012) 9–120
35
assemblages from lacustrine sediments and the actual surrounding vegetation were sampled and analysed for quantitative comparison with published Pollen Production Estimates from across the research region. Special attention was paid to the effective flowering of plants under high grazing pressure. In addition, the diversity of Poaceae, in term of species, ecology and growth forms, has also been considered. The scarcity of flowering in grazed plant communities induces a very low pollen deposition onto sediments. For this reason, heavily grazed-vegetation is under-represented in contrast to landscape-wide vegetation and to those plant taxa that avoid biomass removal by large herbivores. Additionally, the low taxonomic resolution of pollen identification for the Poaceae represents a major obstacle in identifying heavily-grazed vegetation. In fact, the numerous Poaceae species and their variable pollen production under different grazing and environmental regimes (when accounted as a mixture) produce a noisy signal. These findings indicate that pollen analysis is a crude tool for tracking grazed vegetation in an open landscape. To improve our understanding, complementary and independent lines of evidences are necessary. Coprophilous fungal spores and phytolith, respectively proxies for grazing pressure and grassland composition, are being developed in order to improve quantitative reconstructions.
Hunters and gatherers, herders and farmers have co-existed in the area during the Holocene. Our understanding of the social dynamics characterizing these communities and their interaction depends greatly on our appreciation of the environment in which they lived. To this end we need to gather long-term information on the distribution and availability of resources. We use geoarchaeology and remote sensing as fundamental tools to support landscape investigations and modeling, and to build a GIS of the area that highlights the main landforms and their relationship to the regional archaeology. The present work combines remote sensing, land cover classification, field landform recognition and physicochemical characterization of soils and sediments to set the foundations for remote geoarchaeological mapping in N Gujarat and other fossil dune regions. It also aims at improving our understanding of settlement location in relation to past climatic and environmental change and to individuate anthropogenic landmarks and potential areas for the recovery of regional palaeoenvironmental records. Our final aim is to inform original models explaining the landscape of NW India as the result of the long-term co-evolution between human occupation and environmental change.
USING NUMERICAL ANALYSES TO DISTINGUISH BETWEEN CLIMATIC AND ANTHROPOGENIC DRIVEN LANDSCAPE CHANGE IN POLLEN DATA: AN EXAMPLE FROM SOUTH-WESTERN TURKEY
Greg Balco. Berkeley Geochronology Center, United States
Johan Bakker. University of Amsterdam/Institute for Biodiversity, Belgium E-mail address: [email protected]
Holocene Vegetation changes are mainly controlled by climate change or human impact, as evidenced by numerous field studies. For the proper assessment of the nature and impact of vegetation changes through time, it is vital to be able to disentangle the influences of man and climate on the vegetation. Within the territory of the ancient city of Sagalassos, located in the Taurus mountain range in SW Turkey, interdisciplinary research has shown that intensive human impact on the vegetation during the Hellenistic-Roman period resulted in the destruction of the natural forest ecosystem. Although minor climatic changes did occur, human impact mostly controlled vegetation change and geomorphic processes. Less is known about the period following the decline of Roman presence and the climatic and anthropogenic influences on the region during this period. Here we present the results of a study focussed on vegetation change during the last 1500 years in two marshes, located near Sagalassos. A numerical approach enabled the creation of a pollen-derived climatic proxy, making it possible to disentangle the impacts of changes in human presence and climate on the vegetation as well as neutralizing the influence of local topography on the way climate change is expressed in a pollen record. Results show a succession of sudden vegetation changes that coincided with well-defined European climate shifts occurring from the end of the Hellenistic-Roman period to the present, including the medieval climate anomaly and the Little Ice Age. Human impact decreased and focussed on pastoralism during dry periods while the Wet MCA showed an increase in fires, crop cultivation and sedimentation rates. The numerical analyses of the high resolution pollen-records thus not only provide a high temporal resolution of vegetation changes, but also a high temporal resolution of climate change not attained before for the wider region. HUMAN-ENVIRONMENT INTERACTIONS IN FOSSIL DUNE REGIONS: GEOARCHAEOLOGY AND REMOTE SENSING FOR THE HOLOCENE PERIOD IN N GUJARAT (INDIA) Andrea Luca Balbo. IMF-CSIC, Spain E-mail address: [email protected]
Within the framework of NoGAP (Nothern Gujarat Archaeological Project), satellite imagery is combined with geoarchaeological investigation in the Little Rann of Kutch (Gujarat, India). NoGAP aims at understanding population dynamics and domestication processes in this semiarid region of NW India where minor changes in monsoon patterns greatly affect seasonal precipitation, soil moisture and ultimately human settlement.
IMPROVING COSMOGENIC-NUCLIDE BURIAL DATING
E-mail address: [email protected]
Cosmogenic-nuclide burial dating employs a pair of cosmic-ray-produced nuclides that are produced at a fixed ratio in some mineral target, but have different half-lives. For example, Al-26 and Be-10 are produced in quartz at Al-26:Be-10 ¼ 6.75, and have half-lives of 0.7 and 1.4 Ma. If a sample of quartz is exposed at the Earth's surface for a time, Al-26 and Be-10 concentrations conform to the production ratio no matter the duration of exposure. If the sample is then buried deeply enough to stop the cosmicray flux, concentrations decrease due to radioactive decay. The half-lives differ, so the Al-26/Be-10 ratio diverges from the production ratio. Thus, the Al-26/Be-10 ratio can be used to determine when the sample was buried. This method is potentially valuable for dating Quaternary clastic sediments because, in a general sense, all clastic sediments experience surface exposure during sediment generation and transport, followed by burial in a sedimentary deposit. The challenge in realizing this potential is that they often experience more complex histories that include multiple periods of exposure and burial. Complex exposure histories destroy the simple relationship between the Al-26/Be-10 ratio and the duration of the current period of burial. This talk will describe recent improvements in cosmogenic-nuclide burial dating intended to address this and other issues, allowing the method to be applied to more geologic situations and to a broader time range than has so far been possible. These improvements include i) burial-isochron methods, in which one collects sets of samples that differ in some aspects of their exposure history but share others; ii) three-nuclide burial dating, which permits testing of some of the geologic assumptions required to compute a burial age; and iii) burial dating with nuclide pairs other than the commonly used Al-26/Be-10 pair, which allows tuning the method for best precision in the time range of interest. EXTENT AND DEGLACIATION CHRONOLOGY OF THE LAST BRITISH-IRISH ICE SHEET: IMPLICATIONS OF EXPOSURE DATING USING COSMOGENIC ISOTOPES Colin K. Ballantyne. University of St Andrews, United Kingdom E-mail address: [email protected]
Approximately 200 10Be and 36Cl exposure ages pertaining to the extent and chronology of the last British-Irish Ice Sheet (BIIS) are critically reviewed. Despite uncertainties inherent in the use of exposure ages, this approach has demonstrated that at the Last Glacial Maximum (LGM; c. 2621 ka) the BIIS extended over all low ground in Scotland and all (or almost all) of Ireland, consistent with recent models depicting extension of the last BIIS to the Atlantic shelf edge. Almost all exposure ages obtained for high-level sites above trimlines on the mountains of NW Scotland and Ireland pre-date the LGM, confirming that high plateaux in these areas escaped significant glacial erosion, probably under a cover of
Abstracts / Quaternary International 279-280 (2012) 9–120
speed over land and propagation speed along specific rivers and coastlines are obtained using Markov Chain Monte Carlo algorithms. In this work we also introduce a completely new numerical approach to modelling the first arrival time of a population, which is in good agreement with numerical simulations of Fisher-KPP equation but is orders of magnitude quicker. This new model allows many hundreds of simulations, with differing parameters, to be run in a short period of time; a major step forward for applying more sophisticated statistical techniques to the modelling of the Neolithic of Europe. RECONNAISSANCE U-PB DATING OF MIDDLE-PLEISTOCENETRANSITION GLACIAL TERMINATIONS FROM CORCHIA CAVE (ITALY) SPELEOTHEMS Petra Bajo. University of Melbourne, Australia E-mail address: [email protected]
During the Middle Pleistocene Transition (MPT), the period of glacialinterglacial cycles apparently shifted from w40 kyr to w100 kyr. Much debate has been waged in the last decade as to the causes of this transition. A key to resolving this debate is developing radiometrically dated palaeoclimate records which faithfully preserve the glacial terminations through this interval. Such records would be free of assumptions about orbital tuning. The recent breakthrough in the U-Pb dating of speleothems has opened up a new opportunity to tackle this issue. In this paper, we present a preliminary U-Pb chronology for a number of terminations through the MPT using speleothems from Corchia Cave (Italy). Speleothems from this cave have already yielded useful palaeoclimate records from the latter part of the Quaternary. They contain high concentrations of uranium, very little detrital thorium and relatively wellconstrained initial uranium-series disequilibria, making them relatively easy to date by U-Pb. Our chronologies are based on intensive sampling and, where possible, replicate speleothem records. The latter allows us to splice together multiple speleothem records using their respective isotopic profiles, and, by combining their age models into one, producing a ‘stacked record’ which attempts to minimise overall age uncertainties for the key intervals. THE FIRST FARMERS OF THE NORTH EUROPEAN PLAIN Corrie Bakels. Leiden University, Fac. Archaeology, Netherlands E-mail address: [email protected]
The terrain along the North Sea and the Baltic comprises a complex arrangement of lowland landscapes. It is also characterised by a west-east orientated thermal gradient. A diversity of natural environment leads to differences in what farmers do and the way in which they interact with the natural environment. This is so at present and will have been the same in the past. In her book on the TRB culture (Funnel-Beaker culture), Magdalena S. Midgley states the following: "the TRB settlement pattern demonstrates that the location of individual settlements was clearly bound up with the environmental conditions prevalent in each of the studied regions." But she continues: "there are none the less certain common factors which suggest that, in spite of the great diversity of locally available environments, it is possible to discern some general characteristics of settlement which are relevant to the TRB as a whole." (Midgley 1992, p. 316). It is an aim of this meeting to find out what was shared and what was a regional response. For instance: their crop cultivation is generally described as slash-and-burn cultivation, but this view is under discussion. For instance: the impact of the farmers’ activities on their environment is usually labeled as ‘Iversen landnam’ - and some phases as ‘Troels-Smith landnam’ -, but this is surely too crude. For instance: the problem of rising sea levels which provide another environmental factor, especially felt in the West, in the region of the western neighbours of the TRB people. FORWARD MODELLING OF THE SPELEOTHEM OXYGEN ISOTOPE PALEOCLIMATE PROXY Andy Baker. University of New South Wales, Australia E-mail address: [email protected]
Speleothem oxygen isotope series have recently made substantial contributions to our understanding of changes in the global climate system over the late Quaternary. However, a number of research problems and questions remain outstanding. These include the degree of uncertainty in speleothem oxygen isotope records which are especially apparent over periods of relatively stable climate, but which have largely yet to be fully quantified. Recently, we have started to examine the physical processes that determine water routing through the overlying soil, epikarst and karst aquifer using a lumped hydrological model to describe potential interrelationships between waters routed at different rates between individual sub-surface water stores that differ in their size and drainage characteristics. We demonstrate the use of a generic modelling approach, that avoids intractable problems such as site-specific model calibration, but which enables us to perform a sensitivity analysis to quantify hydrological uncertainty across a range of karst systems. This allows us to improve our understanding of stalagmite oxygen isotope data variability and the quantification of the ‘noise’ that is commonly found. Recent model refinements are introduced, demonstrating the utility of our modelling approach to drive forward models of stalagmite oxygen isotopes and the generation of stalagmite oxygen isotope pseudo-proxies. GEOCHEMICAL AND MINERALOGICAL INVESTIGATION OF A RECENTLY EXPOSED SAPROLITE PROFILE IN THE CHILEAN COASTAL RANGE Sophie Baker. Desert Research Institute, United States E-mail address: [email protected]
A new road cut in the Chilean Coastal Range near Valparaiso, Chile has exposed an w8m deep complex weathering profile comprising a saprolite (weathered Carboniferous granitoid) overlain by a w1m layer of fluvial gravels and a w60 cm thick loess. Soil horizons include a well-developed Bt horizon at 20-100 cm depth, and a w1m thick duripan formed mostly in the fluvial gravel layer. A 10Be profile age through the saprolite indicates a minimum exposure age of 2.2 Ma. The chemical weathering observed in the granite generally requires levels of soil moisture typical of a more humid climate than presently exists in the region (semi-arid), while the formation of the duripan in the overlying gravels is compatible with the current climate. Duripan formation likely took place in a dry climate at the maximum depth of penetration of meteoric moisture, and as it proceeded, further limited the downward flux of moisture, requiring that much of the chemical weathering below took place beforehand. The juxtaposition of duripan and saprolite may suggest a change in environmental conditions since the exposure of the granite; however, reconstructing palaeo-environments requires that the effects of the complex geomorphic history on the weathering processes be understood. To investigate the geomorphic and weathering history at this site, we are undertaking geochemical, soil property (particle size, Fe oxides, pH), and mineralogical (bulk and clay) analysis of 16 samples collected down profile. Results so far show that chemical weathering indices (CIA and CIW, based on Al, Na, Ca, and K concentrations) of the saprolite increase towards the surface but do not indicate the intensity of weathering often observed at the top of saprolite sections. This may be the result of conditions unfavorable for intense chemical weathering, or due to truncation of the upper weathering zones prior to fluvial gravel deposition. Clay mineralogy, soil analysis, and meteoric 10Be will help to test these hypotheses. DOES HEAVILY-GRAZED VEGETATION SHOW UP IN THE POLLEN RECORD? Ambroise Baker. University of Oxford, United Kingdom E-mail address: [email protected]
This research aims to assist the establishment of baselines for landscape and ecosystem restoration by contributing to the debates pertaining to the Vera hypothesis and landscape openness within the pollen record. In particular, it attempts to characterise the modern pollen signal produced by heavily-grazed vegetation. This study is focussed on sites within Northern Europe: The New Forest (UK) and the Oostvaardersplassen (The Netherlands), both selected for their differing grazing regimes and histories. The modern pollen
Abstracts / Quaternary International 279-280 (2012) 9–120
35
assemblages from lacustrine sediments and the actual surrounding vegetation were sampled and analysed for quantitative comparison with published Pollen Production Estimates from across the research region. Special attention was paid to the effective flowering of plants under high grazing pressure. In addition, the diversity of Poaceae, in term of species, ecology and growth forms, has also been considered. The scarcity of flowering in grazed plant communities induces a very low pollen deposition onto sediments. For this reason, heavily grazed-vegetation is under-represented in contrast to landscape-wide vegetation and to those plant taxa that avoid biomass removal by large herbivores. Additionally, the low taxonomic resolution of pollen identification for the Poaceae represents a major obstacle in identifying heavily-grazed vegetation. In fact, the numerous Poaceae species and their variable pollen production under different grazing and environmental regimes (when accounted as a mixture) produce a noisy signal. These findings indicate that pollen analysis is a crude tool for tracking grazed vegetation in an open landscape. To improve our understanding, complementary and independent lines of evidences are necessary. Coprophilous fungal spores and phytolith, respectively proxies for grazing pressure and grassland composition, are being developed in order to improve quantitative reconstructions.
Hunters and gatherers, herders and farmers have co-existed in the area during the Holocene. Our understanding of the social dynamics characterizing these communities and their interaction depends greatly on our appreciation of the environment in which they lived. To this end we need to gather long-term information on the distribution and availability of resources. We use geoarchaeology and remote sensing as fundamental tools to support landscape investigations and modeling, and to build a GIS of the area that highlights the main landforms and their relationship to the regional archaeology. The present work combines remote sensing, land cover classification, field landform recognition and physicochemical characterization of soils and sediments to set the foundations for remote geoarchaeological mapping in N Gujarat and other fossil dune regions. It also aims at improving our understanding of settlement location in relation to past climatic and environmental change and to individuate anthropogenic landmarks and potential areas for the recovery of regional palaeoenvironmental records. Our final aim is to inform original models explaining the landscape of NW India as the result of the long-term co-evolution between human occupation and environmental change.
USING NUMERICAL ANALYSES TO DISTINGUISH BETWEEN CLIMATIC AND ANTHROPOGENIC DRIVEN LANDSCAPE CHANGE IN POLLEN DATA: AN EXAMPLE FROM SOUTH-WESTERN TURKEY
Greg Balco. Berkeley Geochronology Center, United States
Johan Bakker. University of Amsterdam/Institute for Biodiversity, Belgium E-mail address: [email protected]
Holocene Vegetation changes are mainly controlled by climate change or human impact, as evidenced by numerous field studies. For the proper assessment of the nature and impact of vegetation changes through time, it is vital to be able to disentangle the influences of man and climate on the vegetation. Within the territory of the ancient city of Sagalassos, located in the Taurus mountain range in SW Turkey, interdisciplinary research has shown that intensive human impact on the vegetation during the Hellenistic-Roman period resulted in the destruction of the natural forest ecosystem. Although minor climatic changes did occur, human impact mostly controlled vegetation change and geomorphic processes. Less is known about the period following the decline of Roman presence and the climatic and anthropogenic influences on the region during this period. Here we present the results of a study focussed on vegetation change during the last 1500 years in two marshes, located near Sagalassos. A numerical approach enabled the creation of a pollen-derived climatic proxy, making it possible to disentangle the impacts of changes in human presence and climate on the vegetation as well as neutralizing the influence of local topography on the way climate change is expressed in a pollen record. Results show a succession of sudden vegetation changes that coincided with well-defined European climate shifts occurring from the end of the Hellenistic-Roman period to the present, including the medieval climate anomaly and the Little Ice Age. Human impact decreased and focussed on pastoralism during dry periods while the Wet MCA showed an increase in fires, crop cultivation and sedimentation rates. The numerical analyses of the high resolution pollen-records thus not only provide a high temporal resolution of vegetation changes, but also a high temporal resolution of climate change not attained before for the wider region. HUMAN-ENVIRONMENT INTERACTIONS IN FOSSIL DUNE REGIONS: GEOARCHAEOLOGY AND REMOTE SENSING FOR THE HOLOCENE PERIOD IN N GUJARAT (INDIA) Andrea Luca Balbo. IMF-CSIC, Spain E-mail address: [email protected]
Within the framework of NoGAP (Nothern Gujarat Archaeological Project), satellite imagery is combined with geoarchaeological investigation in the Little Rann of Kutch (Gujarat, India). NoGAP aims at understanding population dynamics and domestication processes in this semiarid region of NW India where minor changes in monsoon patterns greatly affect seasonal precipitation, soil moisture and ultimately human settlement.
IMPROVING COSMOGENIC-NUCLIDE BURIAL DATING
E-mail address: [email protected]
Cosmogenic-nuclide burial dating employs a pair of cosmic-ray-produced nuclides that are produced at a fixed ratio in some mineral target, but have different half-lives. For example, Al-26 and Be-10 are produced in quartz at Al-26:Be-10 ¼ 6.75, and have half-lives of 0.7 and 1.4 Ma. If a sample of quartz is exposed at the Earth's surface for a time, Al-26 and Be-10 concentrations conform to the production ratio no matter the duration of exposure. If the sample is then buried deeply enough to stop the cosmicray flux, concentrations decrease due to radioactive decay. The half-lives differ, so the Al-26/Be-10 ratio diverges from the production ratio. Thus, the Al-26/Be-10 ratio can be used to determine when the sample was buried. This method is potentially valuable for dating Quaternary clastic sediments because, in a general sense, all clastic sediments experience surface exposure during sediment generation and transport, followed by burial in a sedimentary deposit. The challenge in realizing this potential is that they often experience more complex histories that include multiple periods of exposure and burial. Complex exposure histories destroy the simple relationship between the Al-26/Be-10 ratio and the duration of the current period of burial. This talk will describe recent improvements in cosmogenic-nuclide burial dating intended to address this and other issues, allowing the method to be applied to more geologic situations and to a broader time range than has so far been possible. These improvements include i) burial-isochron methods, in which one collects sets of samples that differ in some aspects of their exposure history but share others; ii) three-nuclide burial dating, which permits testing of some of the geologic assumptions required to compute a burial age; and iii) burial dating with nuclide pairs other than the commonly used Al-26/Be-10 pair, which allows tuning the method for best precision in the time range of interest. EXTENT AND DEGLACIATION CHRONOLOGY OF THE LAST BRITISH-IRISH ICE SHEET: IMPLICATIONS OF EXPOSURE DATING USING COSMOGENIC ISOTOPES Colin K. Ballantyne. University of St Andrews, United Kingdom E-mail address: [email protected]
Approximately 200 10Be and 36Cl exposure ages pertaining to the extent and chronology of the last British-Irish Ice Sheet (BIIS) are critically reviewed. Despite uncertainties inherent in the use of exposure ages, this approach has demonstrated that at the Last Glacial Maximum (LGM; c. 2621 ka) the BIIS extended over all low ground in Scotland and all (or almost all) of Ireland, consistent with recent models depicting extension of the last BIIS to the Atlantic shelf edge. Almost all exposure ages obtained for high-level sites above trimlines on the mountains of NW Scotland and Ireland pre-date the LGM, confirming that high plateaux in these areas escaped significant glacial erosion, probably under a cover of