- Email: [email protected]
A Detailed Late-glacial Pollen- Based Climate History from Western North Island, New Zealand
Abstracts / Quaternary International 279-280 (2012) 462–565
493
hemispheric and global climate patterns (including the mid-latitude westerlies, the south-east trades, the ITCZ and ENSO) has been relatively understudied in relation to the YD. This is partly due to a relative paucity of sites that span the LGT. Here we report on lake records from three sites that are relatively evenly distributed on the east Australian margin: Lake Euramoo on the Atherton Tableland (summer rainfall dominated tropics; 17.16 S), Welsby Lagoon, North Stradbroke Island (summer rainfall dominated subtropics; 27.44 S) and north-west crater Tower Hill, western volcanic plains (winter rainfall dominated temperate latitudes; 38.33 S). Our findings, only aspects of which have been reported elsewhere (Turney et al. 2006, QSR 25; Tibby and Haberle 2007, Palaeo x 3 251), are primarily based on diatom records from two of the sites and contiguously measured sediment characteristics (in particular organic content). These indicators were selected as they reflect changes in effective precipitation at short temporal scales. The records from all sites exhibit late glacial “reversals” in effective precipitation, with drier phases occurring against a trend of generally increasing moisture, indicated by reduced sediment organic content and poor diatom preservation. However, none of these coincides with the YD chronozone and together they emphasise the complex nature of the late glacial transition in the Southern Hemisphere.
Proper production rate calibration requires many conditions on samples to be met. K-rich minerals in the samples should contain low level of Ca and 35 Cl to reduce the other 36Cl production pathways. Exposure history (shielding, erosion) of the samples should be clear and preferably simple. Exposure time must be well-determined by other independent methods or the steady state assumption must be justified. In an ideal case, the obtained production rate can be uniquely scaled to any other latitude and altitude, and applied in any possible time span. However, the calculated local production rates can vary within 10% depending on the scaling procedure. Therefore our estimated production rates will be given together with all relevant local parameters. Long term exposed samples of granites from Victoria Land, Antarctica were chosen. Steady state of 36Cl build up and independent dating by 10Be, 26Al and 21Ne make these samples perfect for calibration. Previous calibration based on similar samples gave a value, which is higher than all other available estimates. Verification and explanation of this outlier will be important for 36 Cl dating of long term exposed K-feldspars.
CALCULATION OF SHIELDING FACTORS COSMOGENIC NUCLIDES IN FAULT SCARPS
Robert Tinkler. Massey University, New Zealand
FOR
PRODUCTION
OF
Dmitry Tikhomirov. University of Berne, Switzerland E-mail address: [email protected]
For the last 30 years, Terrestrial Cosmogenic Nuclides (TCN) have successfully been used for geochronology. TCN dating relies on independently calibrated production rates, on semi-empirical scaling factors and on geometrical shielding factors. The computation of scaling factors includes the neutron monitor measurements and requires therefore the use of tabulated data. The geometrical complexity of surrounding environment also forces the use of numerical methods. Special programs were developed to ease the calculation of TCN scaling, shielding and production rates. One of the most challenging TCN applications is the reconstruction of past earthquake histories. In this method, limestone normal fault scarps are used to reconstruct past seismic events that have exposed the foot wall of the scarp. In the simplest case, there is a footwall of infinite height and accumulated colluvium that covers the lower part of the footwall. At the events of earthquakes, the footwall is moving upwards exposing more of its surface. The complexity of the exposure geometry limits the computation of the geometrical scaling factors analytically. Only one discussion dedicated to this computation was recently published. Unfortunately, the average TCN user would need to spend significant time applying the published material to his own case. Therefore we aim with our contribution to provide the reader with a clear protocol and an easy-to-use tool for fault scarp geometrical scaling factors computation. This study consists of a theoretical basis with a reference to previous works and a MATLAB computation code which can be used as stand alone software or as a MATLAB M-file. Geometrical scaling factors are calculated by the program for fast neutron spallation and include all general shielding geometries: topographical shielding, sloped surface, fault scarp surface, colluvium cover, snow cover, self-shielding and erosion. 36
CL PRODUCTION RATE ON FROM VICTORIA LAND
39
A DETAILED LATE-GLACIAL POLLEN- BASED CLIMATE HISTORY FROM WESTERN NORTH ISLAND, NEW ZEALAND
E-mail address: [email protected]
New Zealand is recognised as a critical location for investigating the timing and magnitude of Quaternary climate fluctuations in the southern hemisphere. Although there are a considerable number of published palaeoenvironmental records from New Zealand, relatively few sediment cores have been extracted from the west of the North Island, and very few cores that span 30,000 years have been extracted in New Zealand. Therefore, more, high resolution multiproxy records that span long continuous periods of time are needed. An 18m core extracted from Eltham Swamp, Taranaki in the western North Island promises to yield information regarding climate change and successional dynamics of vegetation following volcanic and anthropogenic disturbance. Zones of the core can be reliably dated using tephrochronological techniques and radiocarbon dating. The core spans at least 32,000 years and thus covers significant climatic events documented in ocean cores, ice cores and terrestrial records from both the northern and southern hemispheres. Here we present progress on a new high resolution multiproxy palaeoenvironmental record from Eltham Swamp that will improve understanding of climate change in New Zealand and the wider southern hemisphere region over the last 32,000 years. Central to this research is a high resolution pollen record to investigate the magnitude and timing of climate fluctuations over the last 30,000 years in the Taranaki region. Detailed analysis of the record over the last glacial-interglacial transition provides insights into climate variation during time periods associated with the Antarctic Cold Reversal and Younger Dryas Chronozone and provides potential for qualitative and quantitative environmental reconstructions in response to climate change and volcanic eruptions. FIRST PEOPLING OF THE NORTH ATLANTIC FRINGES; PALAEOENVIRONMENTAL AND ARCHAEOLOGICAL EVIDENCE FROM ORKNEY, SCOTLAND Eileen Tisdall. University of Stirling, United Kingdom
K IN LONG TERM EXPOSED SAMPLES
Dmitry Tikhomirov. University of Berne, Switzerland E-mail address: [email protected]
The surface exposure dating of K-rich minerals like K-feldspar and biotite with the cosmogenic 36Cl is presently limited by poorly known rate of 36Cl production from 39K. 36Cl is produced in situ from 39K by secondary cosmic rays in following nuclear reactions: high energy spallation, negative muon capture and thermal neutron capture. At the surface major contribution to 36 Cl production is made by spallation reactions, while the negative muon capture dominates below 2 meters of rock. Previously published 36Cl production rates on 39K by spallation reactions lies in wide band of numbers between 1258 and 22818 at$g(K)-1$yr-1. Obviously, more accurate evaluation of 36Cl production rate from 39K is essential.
E-mail address: [email protected]
Recent archaeological excavations on Stronsay, Orkney, northeast Scotland have revealed a late Mesolithic-Neolithic campsite, with cultural artefacts suggesting a link between these peoples and Mesolithic Scandinavian culture. In close proximity to the archaeological excavations an intact organic sediment sequence lies buried beneath dune sands, consisting of a weathered till surface with evidence for soil development and subsequent accumulation of organic rich lacustrine mud. These sediments are periodically interrupted and capped by wind blown sand, deposition likely representing increasing storm frequency. We present a landscape reconstruction for the time of early occupation on Stronsay. The palaeoenvironmental record provides an insight into resource availability and the attractiveness of this coastal site for settlement and continued occupation. This study is part of an interdisciplinary approach and utilises a range of techniques including pollen and chironomid analysis, high
493
hemispheric and global climate patterns (including the mid-latitude westerlies, the south-east trades, the ITCZ and ENSO) has been relatively understudied in relation to the YD. This is partly due to a relative paucity of sites that span the LGT. Here we report on lake records from three sites that are relatively evenly distributed on the east Australian margin: Lake Euramoo on the Atherton Tableland (summer rainfall dominated tropics; 17.16 S), Welsby Lagoon, North Stradbroke Island (summer rainfall dominated subtropics; 27.44 S) and north-west crater Tower Hill, western volcanic plains (winter rainfall dominated temperate latitudes; 38.33 S). Our findings, only aspects of which have been reported elsewhere (Turney et al. 2006, QSR 25; Tibby and Haberle 2007, Palaeo x 3 251), are primarily based on diatom records from two of the sites and contiguously measured sediment characteristics (in particular organic content). These indicators were selected as they reflect changes in effective precipitation at short temporal scales. The records from all sites exhibit late glacial “reversals” in effective precipitation, with drier phases occurring against a trend of generally increasing moisture, indicated by reduced sediment organic content and poor diatom preservation. However, none of these coincides with the YD chronozone and together they emphasise the complex nature of the late glacial transition in the Southern Hemisphere.
Proper production rate calibration requires many conditions on samples to be met. K-rich minerals in the samples should contain low level of Ca and 35 Cl to reduce the other 36Cl production pathways. Exposure history (shielding, erosion) of the samples should be clear and preferably simple. Exposure time must be well-determined by other independent methods or the steady state assumption must be justified. In an ideal case, the obtained production rate can be uniquely scaled to any other latitude and altitude, and applied in any possible time span. However, the calculated local production rates can vary within 10% depending on the scaling procedure. Therefore our estimated production rates will be given together with all relevant local parameters. Long term exposed samples of granites from Victoria Land, Antarctica were chosen. Steady state of 36Cl build up and independent dating by 10Be, 26Al and 21Ne make these samples perfect for calibration. Previous calibration based on similar samples gave a value, which is higher than all other available estimates. Verification and explanation of this outlier will be important for 36 Cl dating of long term exposed K-feldspars.
CALCULATION OF SHIELDING FACTORS COSMOGENIC NUCLIDES IN FAULT SCARPS
Robert Tinkler. Massey University, New Zealand
FOR
PRODUCTION
OF
Dmitry Tikhomirov. University of Berne, Switzerland E-mail address: [email protected]
For the last 30 years, Terrestrial Cosmogenic Nuclides (TCN) have successfully been used for geochronology. TCN dating relies on independently calibrated production rates, on semi-empirical scaling factors and on geometrical shielding factors. The computation of scaling factors includes the neutron monitor measurements and requires therefore the use of tabulated data. The geometrical complexity of surrounding environment also forces the use of numerical methods. Special programs were developed to ease the calculation of TCN scaling, shielding and production rates. One of the most challenging TCN applications is the reconstruction of past earthquake histories. In this method, limestone normal fault scarps are used to reconstruct past seismic events that have exposed the foot wall of the scarp. In the simplest case, there is a footwall of infinite height and accumulated colluvium that covers the lower part of the footwall. At the events of earthquakes, the footwall is moving upwards exposing more of its surface. The complexity of the exposure geometry limits the computation of the geometrical scaling factors analytically. Only one discussion dedicated to this computation was recently published. Unfortunately, the average TCN user would need to spend significant time applying the published material to his own case. Therefore we aim with our contribution to provide the reader with a clear protocol and an easy-to-use tool for fault scarp geometrical scaling factors computation. This study consists of a theoretical basis with a reference to previous works and a MATLAB computation code which can be used as stand alone software or as a MATLAB M-file. Geometrical scaling factors are calculated by the program for fast neutron spallation and include all general shielding geometries: topographical shielding, sloped surface, fault scarp surface, colluvium cover, snow cover, self-shielding and erosion. 36
CL PRODUCTION RATE ON FROM VICTORIA LAND
39
A DETAILED LATE-GLACIAL POLLEN- BASED CLIMATE HISTORY FROM WESTERN NORTH ISLAND, NEW ZEALAND
E-mail address: [email protected]
New Zealand is recognised as a critical location for investigating the timing and magnitude of Quaternary climate fluctuations in the southern hemisphere. Although there are a considerable number of published palaeoenvironmental records from New Zealand, relatively few sediment cores have been extracted from the west of the North Island, and very few cores that span 30,000 years have been extracted in New Zealand. Therefore, more, high resolution multiproxy records that span long continuous periods of time are needed. An 18m core extracted from Eltham Swamp, Taranaki in the western North Island promises to yield information regarding climate change and successional dynamics of vegetation following volcanic and anthropogenic disturbance. Zones of the core can be reliably dated using tephrochronological techniques and radiocarbon dating. The core spans at least 32,000 years and thus covers significant climatic events documented in ocean cores, ice cores and terrestrial records from both the northern and southern hemispheres. Here we present progress on a new high resolution multiproxy palaeoenvironmental record from Eltham Swamp that will improve understanding of climate change in New Zealand and the wider southern hemisphere region over the last 32,000 years. Central to this research is a high resolution pollen record to investigate the magnitude and timing of climate fluctuations over the last 30,000 years in the Taranaki region. Detailed analysis of the record over the last glacial-interglacial transition provides insights into climate variation during time periods associated with the Antarctic Cold Reversal and Younger Dryas Chronozone and provides potential for qualitative and quantitative environmental reconstructions in response to climate change and volcanic eruptions. FIRST PEOPLING OF THE NORTH ATLANTIC FRINGES; PALAEOENVIRONMENTAL AND ARCHAEOLOGICAL EVIDENCE FROM ORKNEY, SCOTLAND Eileen Tisdall. University of Stirling, United Kingdom
K IN LONG TERM EXPOSED SAMPLES
Dmitry Tikhomirov. University of Berne, Switzerland E-mail address: [email protected]
The surface exposure dating of K-rich minerals like K-feldspar and biotite with the cosmogenic 36Cl is presently limited by poorly known rate of 36Cl production from 39K. 36Cl is produced in situ from 39K by secondary cosmic rays in following nuclear reactions: high energy spallation, negative muon capture and thermal neutron capture. At the surface major contribution to 36 Cl production is made by spallation reactions, while the negative muon capture dominates below 2 meters of rock. Previously published 36Cl production rates on 39K by spallation reactions lies in wide band of numbers between 1258 and 22818 at$g(K)-1$yr-1. Obviously, more accurate evaluation of 36Cl production rate from 39K is essential.
E-mail address: [email protected]
Recent archaeological excavations on Stronsay, Orkney, northeast Scotland have revealed a late Mesolithic-Neolithic campsite, with cultural artefacts suggesting a link between these peoples and Mesolithic Scandinavian culture. In close proximity to the archaeological excavations an intact organic sediment sequence lies buried beneath dune sands, consisting of a weathered till surface with evidence for soil development and subsequent accumulation of organic rich lacustrine mud. These sediments are periodically interrupted and capped by wind blown sand, deposition likely representing increasing storm frequency. We present a landscape reconstruction for the time of early occupation on Stronsay. The palaeoenvironmental record provides an insight into resource availability and the attractiveness of this coastal site for settlement and continued occupation. This study is part of an interdisciplinary approach and utilises a range of techniques including pollen and chironomid analysis, high