- Email: [email protected]
Reconnaissance U-Pb dating of Middle-Pleistocene-Transition glacial terminations from Corchia Cave (Italy) speleothems
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
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