- Email: [email protected]
Glacial history of Sør Rondane Mountains in Dronning Maud Land, East Antarctica: a geomorphologic reconstruction supported by surface exposure age observations
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Abstracts / Quaternary International 279-280 (2012) 462–565
most suitable tectonic basins to reconstruct past sea-level changes because it has been subsided over 1 mm/y during the last 900 ka and filled with alternation of fluvial and marine sediments. A 601-m core GS-NB-1 was collected from the western part of the Nobi-tilted basin in 1998. A comprehensive core analysis composed of lithostratigraphic classification, magnetostratigraphic and tephrostratigraphic studies, pollen and diatom analysis, and 14C dating has revealed the subsurface stratigraphy of the basin. Magnetic stratigraphy indicates the Matsuyama/Brunhes transition (ca. 783 ka) at the core depth of around 545 m. The core contained volcanic ash layers of Sakura (ca. 520 ka) and Azuki (ca. 850 ka), which are representative widespread tephras in Japan. Variations in grain size of sediments in NB1 core clearly reflect eustatic sea-level changes. The core contained ten gravel layers with a thickness of over 5 m, which deposited during the glacial periods of MIS 2, 6, 8, 10, 12, 14, 16, 18, 20 and 22. Magnitude of sea-level low stands was estimated from records of mean maximum grain size of the gravel layers. In contrast silt and clay layers deposited during the interglacial periods. Large accommodation space produced by continuous basin subsidence of about 1m/ka has been filled with coarse fluvial sediments and with fine marine and/or lacustrine sediments alternatively. The cyclostratigraphy of the basin indicates that effects of sea-level change have been quickly transmitted to the basin by rivers through active fluvial processes. Reconstructed sea-level carve will be provided in this presentation. LAST 600 KA TERRESTRIAL ENVIRONMENT CHANGES RECONSTRUCTED FROM ANALYSIS OF THE UWA BASIN-FILL SEDIMENT, SW JAPAN Toshihiko Sugai. The University of Tokyo, Japan E-mail address: [email protected]
The Uwa basin located at the upper most reaches of the Hijikawa River, Shikoku Island, has thick Quaternary terrestrial sediments of over 100 meter with many widespread tephras. We investigated two long sediment cores with the length of over 100 m drilled at an interval of a few hundred meters. Chemical composition of the volcanic glasses in the two cores were analyzed by SEM-EDS and correlated with wide spread tephras whose fall ages have been well-established. Major element, TOC:TN, and grain size of the cores were analyzed and microfossils such as pollen, diatom was studied. From 600 to 250 ka, Uwa basin was mainly lake. At the last stage of the lake period (during MIS8), coarse sediment supply from the surrounding slopes covered the basin floor. Since 250 ka, lake water rarely spread and the basin has been peaty marsh. For the lake period (600250 ka) lake water shrank and peat deposited in glacial periods (MIS12, 10, 8). Since 250 ka, much more organic rich material deposited in Glacial periods (MIS6, 2) while lake water spread in MIS5. In addition, TS values which fluctuate with TOC values are high in organic rich layers deposited in glacial periods under the relatively dry conditions. These results indicate that Uwa basin's deposits have continuously recorded 100 ka Glacial/InterGlacial climate cycles during the last 600 ka. SOUTH ASIAN MONSOON VARIABILITY DURING THE PAST 800 KYR REVEALED BY ROCK MAGNETIC PROXIES Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
A rock magnetic investigation was carried out on a sedimentary core taken from the distal portion of the Bengal Fan in order to reconstruct the South Asian monsoon variability during the past 800 kyr. The 10.2 m long piston core MR0503-PC3, recovered at a water depth of 4400 m, consists of clay to silty clay with minor amounts of nannofossils. An age model for the MR0503-PC3 core is established by correlating a relative paleointensity record of the core (Suganuma et al., 2008) to the global paleointensity stack “Sint-800” (Guyodo and Valet, 1999). The age model is consistent with the published ages of tephra layers intercalated in the core, and show continuous sedimentation during the past 800 kyr. Temporal variations in rock magnetic proxies for the magnetic concentration (ARM, IRM, and HIRM), the grain size (Mrs/Ms), and the composition (S0.3 T and S-0.1 T) show that the amount of fine-grained magnetite increased during interglacial stages, and then gradually decreased toward the following glacial maxima. This indicates that the supply of fine-grained magnetite probably originated from areal expansion and/or increased
pedogenic activity in the Ganges and Brahmaputra rivers catchment. Increases during warmer periods suggest intensification of the South Asian summer monsoon during interglacial stages. During marine isotope stages (MIS) 15 to 11, enhancement of fine-grained magnetite and increased hematite and maghemite contributions are observed. These suggest a significant intensification of the South Asian summer monsoon during this period. Our record and other paleoclimatic reconstructions mainly from the low and mid latitudes suggest that a major climatic event possibly occurred prior to the mid-Brunhes event (MBE), but the timing is not synchronous. GLACIAL HISTORY OF SØR RONDANE MOUNTAINS IN DRONNING MAUD LAND, EAST ANTARCTICA: A GEOMORPHOLOGIC RECONSTRUCTION SUPPORTED BY SURFACE EXPOSURE AGE OBSERVATIONS Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
Antarctic ice sheet volume and sea ice extent, are driven by Earth's global climate system, and more regional parameters such as albedo, thermohaline circulation, productivity of marine organisms, and erosion or weathering rate of base rock. Thus a reconstruction of Antarctic ice sheet variability is essential to understand their interactions. Previous studies have estimated a significant decrease in ice sheet thickness during the last several million years (e.g., Liu et al., 2010). However, the geographical extent (volume) of this decrease and its response and feedback to the global climate remain uncertain and topic of debate. In this study, we focus on the past change of the ice sheet thickness at Sør Rondane Mountains in Dronning Maud Land, East Antarctica, because little is known about this region's glaciation history. We carried out a field expedition to investigate the past change of the ice sheet elevation based on detailed geomorphologic evidence, and precise surface exposure ages using the cosmogenic isotopes Be-10 and Al-26. Based on these data, we will discuss a relationship between East Antarctic ice sheet change and the global climate. POST-DEPOSITIONAL REMANENT MAGNETIZATION LOCK-IN FOR MARINE SEDIMENTS DEDUCED FROM BE-10 AND PALEOMAGNETIC RECORDS THROUGH THE MATUYAMA - BRUNHES BOUNDARY Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
Geomagnetic field intensity records from marine sediments have contributed to better understanding variations of the Earth's magnetic field, and have helped to establish age models for marine sediments. However, lock-in of the geomagnetic signal below the sediment-water interface in marine sediments through acquisition of a post-depositional remanent magnetization (PDRM) adds uncertainty to synchronization of marine sedimentary records. Although quantitative models enable assessment of delayed remanence acquisition associated with PDRM processes, the nature of the filter function and the thickness of the PDRM lock-in zone remain topics of debate. We carried out numerical simulations to assess the best-fit filter function and thickness of the PDRM lock-in zone in marine sediments based on a recently published comparison of 10Be flux and relative paleointensity records. Our simulations reveal that a Gaussian function with a 17 cm lock-in zone thickness is the most suitable for representing the PDRM lock-in process in the studied core. They also suggest that the PDRM is not simply locked as a result of progressive consolidation and dewatering of marine sediments, and that the arbitrary lock-in functions (linear, cubic, and exponential) that are often used to model PDRM lock-in starting from the base of the surface mixed layer cannot explain the observed paleomagnetic signal in marine sediments. SPATIAL SCALE OF VEGETATION RECONSTRUCTION USING FOSSIL POLLEN: A VIEW FROM THE LANDSCAPE RECONSTRUCTION ALGORITHM Shinya Sugita. University of Tallinn, Estonia E-mail address: [email protected]
Fossil pollen records provide baseline information on the past changes in vegetation and land cover in various spatial scales. Commonly used
Abstracts / Quaternary International 279-280 (2012) 462–565
most suitable tectonic basins to reconstruct past sea-level changes because it has been subsided over 1 mm/y during the last 900 ka and filled with alternation of fluvial and marine sediments. A 601-m core GS-NB-1 was collected from the western part of the Nobi-tilted basin in 1998. A comprehensive core analysis composed of lithostratigraphic classification, magnetostratigraphic and tephrostratigraphic studies, pollen and diatom analysis, and 14C dating has revealed the subsurface stratigraphy of the basin. Magnetic stratigraphy indicates the Matsuyama/Brunhes transition (ca. 783 ka) at the core depth of around 545 m. The core contained volcanic ash layers of Sakura (ca. 520 ka) and Azuki (ca. 850 ka), which are representative widespread tephras in Japan. Variations in grain size of sediments in NB1 core clearly reflect eustatic sea-level changes. The core contained ten gravel layers with a thickness of over 5 m, which deposited during the glacial periods of MIS 2, 6, 8, 10, 12, 14, 16, 18, 20 and 22. Magnitude of sea-level low stands was estimated from records of mean maximum grain size of the gravel layers. In contrast silt and clay layers deposited during the interglacial periods. Large accommodation space produced by continuous basin subsidence of about 1m/ka has been filled with coarse fluvial sediments and with fine marine and/or lacustrine sediments alternatively. The cyclostratigraphy of the basin indicates that effects of sea-level change have been quickly transmitted to the basin by rivers through active fluvial processes. Reconstructed sea-level carve will be provided in this presentation. LAST 600 KA TERRESTRIAL ENVIRONMENT CHANGES RECONSTRUCTED FROM ANALYSIS OF THE UWA BASIN-FILL SEDIMENT, SW JAPAN Toshihiko Sugai. The University of Tokyo, Japan E-mail address: [email protected]
The Uwa basin located at the upper most reaches of the Hijikawa River, Shikoku Island, has thick Quaternary terrestrial sediments of over 100 meter with many widespread tephras. We investigated two long sediment cores with the length of over 100 m drilled at an interval of a few hundred meters. Chemical composition of the volcanic glasses in the two cores were analyzed by SEM-EDS and correlated with wide spread tephras whose fall ages have been well-established. Major element, TOC:TN, and grain size of the cores were analyzed and microfossils such as pollen, diatom was studied. From 600 to 250 ka, Uwa basin was mainly lake. At the last stage of the lake period (during MIS8), coarse sediment supply from the surrounding slopes covered the basin floor. Since 250 ka, lake water rarely spread and the basin has been peaty marsh. For the lake period (600250 ka) lake water shrank and peat deposited in glacial periods (MIS12, 10, 8). Since 250 ka, much more organic rich material deposited in Glacial periods (MIS6, 2) while lake water spread in MIS5. In addition, TS values which fluctuate with TOC values are high in organic rich layers deposited in glacial periods under the relatively dry conditions. These results indicate that Uwa basin's deposits have continuously recorded 100 ka Glacial/InterGlacial climate cycles during the last 600 ka. SOUTH ASIAN MONSOON VARIABILITY DURING THE PAST 800 KYR REVEALED BY ROCK MAGNETIC PROXIES Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
A rock magnetic investigation was carried out on a sedimentary core taken from the distal portion of the Bengal Fan in order to reconstruct the South Asian monsoon variability during the past 800 kyr. The 10.2 m long piston core MR0503-PC3, recovered at a water depth of 4400 m, consists of clay to silty clay with minor amounts of nannofossils. An age model for the MR0503-PC3 core is established by correlating a relative paleointensity record of the core (Suganuma et al., 2008) to the global paleointensity stack “Sint-800” (Guyodo and Valet, 1999). The age model is consistent with the published ages of tephra layers intercalated in the core, and show continuous sedimentation during the past 800 kyr. Temporal variations in rock magnetic proxies for the magnetic concentration (ARM, IRM, and HIRM), the grain size (Mrs/Ms), and the composition (S0.3 T and S-0.1 T) show that the amount of fine-grained magnetite increased during interglacial stages, and then gradually decreased toward the following glacial maxima. This indicates that the supply of fine-grained magnetite probably originated from areal expansion and/or increased
pedogenic activity in the Ganges and Brahmaputra rivers catchment. Increases during warmer periods suggest intensification of the South Asian summer monsoon during interglacial stages. During marine isotope stages (MIS) 15 to 11, enhancement of fine-grained magnetite and increased hematite and maghemite contributions are observed. These suggest a significant intensification of the South Asian summer monsoon during this period. Our record and other paleoclimatic reconstructions mainly from the low and mid latitudes suggest that a major climatic event possibly occurred prior to the mid-Brunhes event (MBE), but the timing is not synchronous. GLACIAL HISTORY OF SØR RONDANE MOUNTAINS IN DRONNING MAUD LAND, EAST ANTARCTICA: A GEOMORPHOLOGIC RECONSTRUCTION SUPPORTED BY SURFACE EXPOSURE AGE OBSERVATIONS Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
Antarctic ice sheet volume and sea ice extent, are driven by Earth's global climate system, and more regional parameters such as albedo, thermohaline circulation, productivity of marine organisms, and erosion or weathering rate of base rock. Thus a reconstruction of Antarctic ice sheet variability is essential to understand their interactions. Previous studies have estimated a significant decrease in ice sheet thickness during the last several million years (e.g., Liu et al., 2010). However, the geographical extent (volume) of this decrease and its response and feedback to the global climate remain uncertain and topic of debate. In this study, we focus on the past change of the ice sheet thickness at Sør Rondane Mountains in Dronning Maud Land, East Antarctica, because little is known about this region's glaciation history. We carried out a field expedition to investigate the past change of the ice sheet elevation based on detailed geomorphologic evidence, and precise surface exposure ages using the cosmogenic isotopes Be-10 and Al-26. Based on these data, we will discuss a relationship between East Antarctic ice sheet change and the global climate. POST-DEPOSITIONAL REMANENT MAGNETIZATION LOCK-IN FOR MARINE SEDIMENTS DEDUCED FROM BE-10 AND PALEOMAGNETIC RECORDS THROUGH THE MATUYAMA - BRUNHES BOUNDARY Yusuke Suganuma. National Institute of Polar Research, Japan E-mail address: [email protected]
Geomagnetic field intensity records from marine sediments have contributed to better understanding variations of the Earth's magnetic field, and have helped to establish age models for marine sediments. However, lock-in of the geomagnetic signal below the sediment-water interface in marine sediments through acquisition of a post-depositional remanent magnetization (PDRM) adds uncertainty to synchronization of marine sedimentary records. Although quantitative models enable assessment of delayed remanence acquisition associated with PDRM processes, the nature of the filter function and the thickness of the PDRM lock-in zone remain topics of debate. We carried out numerical simulations to assess the best-fit filter function and thickness of the PDRM lock-in zone in marine sediments based on a recently published comparison of 10Be flux and relative paleointensity records. Our simulations reveal that a Gaussian function with a 17 cm lock-in zone thickness is the most suitable for representing the PDRM lock-in process in the studied core. They also suggest that the PDRM is not simply locked as a result of progressive consolidation and dewatering of marine sediments, and that the arbitrary lock-in functions (linear, cubic, and exponential) that are often used to model PDRM lock-in starting from the base of the surface mixed layer cannot explain the observed paleomagnetic signal in marine sediments. SPATIAL SCALE OF VEGETATION RECONSTRUCTION USING FOSSIL POLLEN: A VIEW FROM THE LANDSCAPE RECONSTRUCTION ALGORITHM Shinya Sugita. University of Tallinn, Estonia E-mail address: [email protected]
Fossil pollen records provide baseline information on the past changes in vegetation and land cover in various spatial scales. Commonly used