- Email: [email protected]
East Antarctic ice sheet history derived from sea-level variations before the LGM
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Abstracts / Quaternary International 279-280 (2012) 233–345
diatoms and gastropods indicate that thermal waters feed the lake; ii) during the Late Glacial pollen and macro remains in lacustrine sediments record the forestation and the presence of a thermal flora on the lake shores; cessation of alluvial sedimentation initiates soil formation in the alluvial plain around the lacustrine basin; iii) in the middle Holocene (about 6000-4000 cal BP) an important alluvial event of the Brenta River causes the deposition of ca. 1 m of sediments over the well-developed soil; iv) on these alluvial deposits a new soil develops and the area is interested by Bronze Age frequentation; v) during the Roman age the hydrological conditions of the area and the attractive thermal springs lead to the building of the villa, through reclamation of part of the swampy lake shore by means of 1-2 m thick landfills; vi) a small Medieval settlement develops in the area of the former villa. BENTHIC FORAMINIFERA AS PROXIES OF HOLOCENE PALEOENVIRONMENTAL RECONSTRUCTION IN AUSTRAL FJORD MADRE DE DIOS AND CANAL CONCEPCIÓN:(CHILE) Zúñiga Rival Mireya. University of Barcelona, Germany E-mail address: [email protected]
This study is focussed on the analysis of two sediment cores from the western portion of the Pacific Ocean, one from the fjord Madre de Dios (MDD2-KL: 50 S; 76 60'W; 65 m water depth) and the other from the Canal Concepción (MD07-3124: 50 31‘S 74 58‘W; 564 m). The study is based on micropaleontological analyses of benthic foraminifera and geochemical measurements of stable isotopes (d18O and d13C) and trace elements (Mg/Ca and Cd/Ca) in several infaunal species of benthic foraminifera, mostly Nonionella auris, Buliminella elegantissima, Bulimina marginata and Uvigerina sp. Both studied sequences cover the Holocene period with ultra-high sedimentation rates and our sampling interval provides an average centennial resolution. Results form the fjord Madre de Dios show very consistent patterns in both geochemical and micropaleontological analyses differentiating three different periods along the Holocene. The first interval would correspond to the early Holocene (11-8 cal. ka BP) where N. auris was the dominant species indicating the presence of deep waters relatively well ventilated. For the same interval the Mg/Ca ratios measured in two species (B. marginata and B. elegantissima) indicate temperatures relatively warm. In contrast, after 5 cal ka. BP, the dominat species is B. elegantissima suggesting a deterioration of the deep ventilation and a decrease in the nutrient content while temperatures were cooler. Between 8 and 5 ka BP a transition period is identified with high variability in all the proxies. Results from the Canal Concepción are still in process but Mg/Ca ratios from Uvigerina sp. shows a significant change in the deep water temperature with the presence of warmer water after 5 cal ka BP. THE SHELL BAR IN THE QAIDAM BASIN: ORIGIN AND PALAEOENVIRONMENTAL IMPLICATIONS OF THE CALCAREOUS FOSSILS Steffen Mischke. Institute for Earth and Environmental Science, Uni, Germany E-mail address: [email protected]
The Shell Bar at the southern margin of the Qaidam Basin (Tibetan Plateau, China) is a 1.8 km long, 100 m wide and 2-3 m high ridge consisting of millions of densely-packed bivalve shells. The structure is the only of its kind in the large basin and believed to represent a former large freshwater lake which existed in Marine Isotope Stage 3 and 2. Shells of the bivalve Corbicula are well preserved and often occur as carapaces in life position. However, living Corbicula are typically found in flowing waters, in streams and even large rivers in contrast to the interpretation of the Shell Bar to represent a large lake. The sedimentary matrix of the Shell Bar is fine sand which contains lacustrine ostracod (micro-crustacean) shells from fresh to slightly brackish waters. The common occurrence of Corbicula in flowing waters, and the sandy matrix and ridge-like topography of the Shell Bar are in contradiction to its interpretation as lake remnant and the presence of abundant ostracod shells in the sediments. Three km in the south of the Shell Bar, widely-exposed weakly-cemented sediments of 10 m thickness were investigated in comparison to the Shell Bar sediments for the first time. Silt and sand with cross-bedding and
ripple and horizontal stratification in its lower part and carbonate-rich, massive silt with abundant freshwater ostracod shells in its upper part attest their fluvial and lacustrine origin. Many of the ostracod species from the Shell Bar were also recorded from the sediments in the south of the Shell Bar, and the simultaneous accumulation of autochthonous bivalve shells from stream-dwelling mussels and allochthonous ostracod shells transported from the sediments in the south of the Shell Bar in a stream is inferred to explain the co-occurrence of Corbicula shells and ostracod remains. As a consequence, the Shell Bar is regarded to represent a stream deposit. New OSL data indicate that the Shell Bar was formed during MIS 5 (see abstract by Lai et al.). EAST ANTARCTIC ICE SHEET HISTORY DERIVED FROM SEA-LEVEL VARIATIONS BEFORE THE LGM Hideki Miura. National Institute of Polar Research, Japan E-mail address: [email protected]
It has been well known that the age at which the northern hemisphere ice sheets was the greatest was at the Last Glacial Maximum (LGM). In CLIMAP model, Antarctic ice sheet is also considered to have advanced synchronously to the edges of continental shelf margin at the LGM. However, the geological evidence of East Antarctic ice sheet (EAIS) history of LGM and pre-LGM is sparse. We have studied the stratigraphic relationship between raised beach sediments including in situ fossil shells and glacial sediments around the Lützow-Holm Bay region, East Antarctica. The AMS radiocarbon dating ages of in situ fossil shells are clearly classified into two groups; the younger group is 3-8 kyrs BP. Any marine layers and in situ fossil shells were not disturbed by ice sheet loading or scouring. In addition, glacial sediments associated with the greatest ice advance can be observed under marine beds including older fossils. These facts indicate that the age at which the EAIS was the greatest was older than 46 ka not LGM, and the advance of the EAIS was not as dramatic as the advance of northern hemisphere ice sheets during the last glacial. The sea-level observations around the Lützow-Holm Bay region using the relationship between heights and ages of in situ fossil shells indicate the existence of a sea-level high stand of about 10 m around 46 kyrs BP. These near-field sea-level variations can also provide important constraints on the melting history of EAIS before the LGM using numerical calculation. PACIFIC PALEOCLIMATE NORTH AND SOUTH. POLAR TWINS OR BIPOLAR SEESAW? OR SOMETHING ELSE? Alan Mix. College of Oceanic and Atmospheric Sciences, Orego, United States E-mail address: [email protected]
Paleoceanographers have put a lot of effort into understanding past changes in the Atlantic circulation, and much progress has been made; although plenty of puzzles remain, it is clear that changes in the subsurface circulation, and resulting changes in interhemispheric heat transport influence (and are influenced by) surface temperature and salinity and global climate. The Pacific has proven to be more difficult to understand. Does the Atlantic drive the Pacific, as suggested by some early models, or are the responses opposite as suggested by other models, or something else? Was there glacial (or deglacial, or interglacial) formation of intermediate (and perhaps deep) water in the Pacific? What caused productivity changes, and does it matter to global CO2? How does hypoxia relate to physical circulation and/or biological production? Here we will have a look at the transition from the last ice age to the present in the Pacific, focusing mostly on the high latitudes of both hemispheres, and will attempt to generate some spirited discussion and perhaps clear a bit of the confusion. Given predictions for future growth of Pacific hypoxia in the Anthropocene, it is important that we get this right. OFFSHORE FAULT MODELING USING LATE QUATERNARY MARINE TERRACE RECORDS IN THE CRUSTAL SHORTENING ZONE OF NORTHEAST JAPAN BACK-ARC Takahiro Miyauchi. Chiba University, Japan E-mail address: [email protected]
Abstracts / Quaternary International 279-280 (2012) 233–345
diatoms and gastropods indicate that thermal waters feed the lake; ii) during the Late Glacial pollen and macro remains in lacustrine sediments record the forestation and the presence of a thermal flora on the lake shores; cessation of alluvial sedimentation initiates soil formation in the alluvial plain around the lacustrine basin; iii) in the middle Holocene (about 6000-4000 cal BP) an important alluvial event of the Brenta River causes the deposition of ca. 1 m of sediments over the well-developed soil; iv) on these alluvial deposits a new soil develops and the area is interested by Bronze Age frequentation; v) during the Roman age the hydrological conditions of the area and the attractive thermal springs lead to the building of the villa, through reclamation of part of the swampy lake shore by means of 1-2 m thick landfills; vi) a small Medieval settlement develops in the area of the former villa. BENTHIC FORAMINIFERA AS PROXIES OF HOLOCENE PALEOENVIRONMENTAL RECONSTRUCTION IN AUSTRAL FJORD MADRE DE DIOS AND CANAL CONCEPCIÓN:(CHILE) Zúñiga Rival Mireya. University of Barcelona, Germany E-mail address: [email protected]
This study is focussed on the analysis of two sediment cores from the western portion of the Pacific Ocean, one from the fjord Madre de Dios (MDD2-KL: 50 S; 76 60'W; 65 m water depth) and the other from the Canal Concepción (MD07-3124: 50 31‘S 74 58‘W; 564 m). The study is based on micropaleontological analyses of benthic foraminifera and geochemical measurements of stable isotopes (d18O and d13C) and trace elements (Mg/Ca and Cd/Ca) in several infaunal species of benthic foraminifera, mostly Nonionella auris, Buliminella elegantissima, Bulimina marginata and Uvigerina sp. Both studied sequences cover the Holocene period with ultra-high sedimentation rates and our sampling interval provides an average centennial resolution. Results form the fjord Madre de Dios show very consistent patterns in both geochemical and micropaleontological analyses differentiating three different periods along the Holocene. The first interval would correspond to the early Holocene (11-8 cal. ka BP) where N. auris was the dominant species indicating the presence of deep waters relatively well ventilated. For the same interval the Mg/Ca ratios measured in two species (B. marginata and B. elegantissima) indicate temperatures relatively warm. In contrast, after 5 cal ka. BP, the dominat species is B. elegantissima suggesting a deterioration of the deep ventilation and a decrease in the nutrient content while temperatures were cooler. Between 8 and 5 ka BP a transition period is identified with high variability in all the proxies. Results from the Canal Concepción are still in process but Mg/Ca ratios from Uvigerina sp. shows a significant change in the deep water temperature with the presence of warmer water after 5 cal ka BP. THE SHELL BAR IN THE QAIDAM BASIN: ORIGIN AND PALAEOENVIRONMENTAL IMPLICATIONS OF THE CALCAREOUS FOSSILS Steffen Mischke. Institute for Earth and Environmental Science, Uni, Germany E-mail address: [email protected]
The Shell Bar at the southern margin of the Qaidam Basin (Tibetan Plateau, China) is a 1.8 km long, 100 m wide and 2-3 m high ridge consisting of millions of densely-packed bivalve shells. The structure is the only of its kind in the large basin and believed to represent a former large freshwater lake which existed in Marine Isotope Stage 3 and 2. Shells of the bivalve Corbicula are well preserved and often occur as carapaces in life position. However, living Corbicula are typically found in flowing waters, in streams and even large rivers in contrast to the interpretation of the Shell Bar to represent a large lake. The sedimentary matrix of the Shell Bar is fine sand which contains lacustrine ostracod (micro-crustacean) shells from fresh to slightly brackish waters. The common occurrence of Corbicula in flowing waters, and the sandy matrix and ridge-like topography of the Shell Bar are in contradiction to its interpretation as lake remnant and the presence of abundant ostracod shells in the sediments. Three km in the south of the Shell Bar, widely-exposed weakly-cemented sediments of 10 m thickness were investigated in comparison to the Shell Bar sediments for the first time. Silt and sand with cross-bedding and
ripple and horizontal stratification in its lower part and carbonate-rich, massive silt with abundant freshwater ostracod shells in its upper part attest their fluvial and lacustrine origin. Many of the ostracod species from the Shell Bar were also recorded from the sediments in the south of the Shell Bar, and the simultaneous accumulation of autochthonous bivalve shells from stream-dwelling mussels and allochthonous ostracod shells transported from the sediments in the south of the Shell Bar in a stream is inferred to explain the co-occurrence of Corbicula shells and ostracod remains. As a consequence, the Shell Bar is regarded to represent a stream deposit. New OSL data indicate that the Shell Bar was formed during MIS 5 (see abstract by Lai et al.). EAST ANTARCTIC ICE SHEET HISTORY DERIVED FROM SEA-LEVEL VARIATIONS BEFORE THE LGM Hideki Miura. National Institute of Polar Research, Japan E-mail address: [email protected]
It has been well known that the age at which the northern hemisphere ice sheets was the greatest was at the Last Glacial Maximum (LGM). In CLIMAP model, Antarctic ice sheet is also considered to have advanced synchronously to the edges of continental shelf margin at the LGM. However, the geological evidence of East Antarctic ice sheet (EAIS) history of LGM and pre-LGM is sparse. We have studied the stratigraphic relationship between raised beach sediments including in situ fossil shells and glacial sediments around the Lützow-Holm Bay region, East Antarctica. The AMS radiocarbon dating ages of in situ fossil shells are clearly classified into two groups; the younger group is 3-8 kyrs BP. Any marine layers and in situ fossil shells were not disturbed by ice sheet loading or scouring. In addition, glacial sediments associated with the greatest ice advance can be observed under marine beds including older fossils. These facts indicate that the age at which the EAIS was the greatest was older than 46 ka not LGM, and the advance of the EAIS was not as dramatic as the advance of northern hemisphere ice sheets during the last glacial. The sea-level observations around the Lützow-Holm Bay region using the relationship between heights and ages of in situ fossil shells indicate the existence of a sea-level high stand of about 10 m around 46 kyrs BP. These near-field sea-level variations can also provide important constraints on the melting history of EAIS before the LGM using numerical calculation. PACIFIC PALEOCLIMATE NORTH AND SOUTH. POLAR TWINS OR BIPOLAR SEESAW? OR SOMETHING ELSE? Alan Mix. College of Oceanic and Atmospheric Sciences, Orego, United States E-mail address: [email protected]
Paleoceanographers have put a lot of effort into understanding past changes in the Atlantic circulation, and much progress has been made; although plenty of puzzles remain, it is clear that changes in the subsurface circulation, and resulting changes in interhemispheric heat transport influence (and are influenced by) surface temperature and salinity and global climate. The Pacific has proven to be more difficult to understand. Does the Atlantic drive the Pacific, as suggested by some early models, or are the responses opposite as suggested by other models, or something else? Was there glacial (or deglacial, or interglacial) formation of intermediate (and perhaps deep) water in the Pacific? What caused productivity changes, and does it matter to global CO2? How does hypoxia relate to physical circulation and/or biological production? Here we will have a look at the transition from the last ice age to the present in the Pacific, focusing mostly on the high latitudes of both hemispheres, and will attempt to generate some spirited discussion and perhaps clear a bit of the confusion. Given predictions for future growth of Pacific hypoxia in the Anthropocene, it is important that we get this right. OFFSHORE FAULT MODELING USING LATE QUATERNARY MARINE TERRACE RECORDS IN THE CRUSTAL SHORTENING ZONE OF NORTHEAST JAPAN BACK-ARC Takahiro Miyauchi. Chiba University, Japan E-mail address: [email protected]