- Email: [email protected]
Late Holocene Records of Dust Accumulation from Middleton Island, Gulf of Alaska
Abstracts / Quaternary International 279-280 (2012) 233–345
monitored during two years through pressure transducers bolted into the platforms. Rocks’ mechanical strength and porosity were also quantified. Additionally, downwearing were measured using a transverse micro erosion meter. The results revealed that the rock resistance must be taken into account when shore platforms are used as a proxy for rmsl, once it controls the height at which platforms develop. The platform surface lowering (downwearing) was up to 3mm/yr at the study area, bioerosion and rocks’ resistance being the main drivers. Therefore, the rocks’ resistance and downwearing rates must be taken into account when the shore platforms’ elevation is used as a proxy for past sea level reconstruction. LATE HOLOCENE RECORDS OF DUST MIDDLETON ISLAND, GULF OF ALASKA
ACCUMULATION
FROM
341
urban area. Methods span from remote sensing and LiDAR to GIS processing of archaeological data, geological field survey and corings. Alluvial chronostratigraphy indicates that the Brenta meanders in Padua were active in the 2nd millennium BC, which implies that the late Bronze Age settlement was on the banks of this major river. 3D modelling of Iron Age and Roman living floors in the underground of the mound shows that the ancient city was at level with the surrounding plain, in a position which was subject to overbank deposition. The lack of floodings in the geoarchaeological record contradicts the presence of such a large river in Padua during the 1st millennium. In agreement with the geomorphic evolution of the alluvial plain, it is probable that the Brenta R. was not flowing anymore through the Iron Age and Roman city and that the underfit Bacchiglione R. was following its abandoned river bed. A STEP BEFORE VENICE: LANDSCAPE RECONSTRUCTION AT ALTINUM
Christopher Moy. U.S. Geological Survey, Woods Hole Coastal and Mar, United States
Paolo Mozzi. University of Padua, Italy
E-mail address: [email protected]
E-mail address: [email protected]
Iron is an important micronutrient that limits the growth of phytoplankton in much of the global ocean. In the Gulf of Alaska (GoA), we have a limited knowledge of the processes that transport iron, and in particular, the role eolian dust plays in delivering iron to the ocean surface. In order to better understand both modern and past mechanisms of dust deposition in the GoA, we examine satellite, NCEP reanalysis, and meteorological station data as well as geochemical data from peat cores collected from Middleton Island (59.43 N, 146.34 W). Widespread dust events have been observed in MODIS satellite imagery emanating from exposed floodplains within the Copper River valley and adjacent glaciated river valleys in southcentral Alaska (AK). Dust events are common in the fall when high pressure in the AK interior and low pressure in the central GoA establish a tight pressure gradient that drives anomalously strong northerly winds. Low river levels and limited snow coverage expose fine-grained glacial sediments that are entrained by winds. MODIS imagery indicates dust reaches beyond the continental shelf, and in many instances, dust plumes have been observed passing over Middleton Island (100 km SSW of the Copper River delta). To better constrain dust deposition from southcentral AK on geologic timescales, we collected cores from an extensive peat bog on Middleton Island, located at the edge of the continental shelf. X-Ray images, bulk density, magnetic susceptibility, and preliminary profiling XRF data indicate significant variations in inorganic or clastic components within the organic peat matrix. Because these cores were collected near the island's topographic high point, we infer that all inorganic constituents are likely delivered as dust. We will present a well-dated, high-resolution scanning XRF profile that will span the middle to late Holocene and monitor downcore variations in terrigenous material that are likely related to Copper River dust events.
Strategically located on the inner margin of the Lagoon of Venice, Altinum was one of the most important cities in the northern Adriatic since the Iron Age to Roman times. The origins of Venice are linked to the migration of the inhabitants, who abandoned the city in the 5th-7th century AD, seeking refuge from Barbarians in the nearby islands. The reconstruction of the ancient landscapes of Altinum is crucial for the definition of modes and timing of the colonization of the lagoon, which finally led to the foundation of Venice around the 9th century AD. Several investigations have been carried out with the collaboration of the Archaeological Superintendency and the support of ARCUS s.p.a. and Regione Veneto. Remote sensing has allowed for a detailed mapping of the city walls, street network, dwellings, public and religious buildings of Roman Altinum. The city stood on a 3.5 m high, 1 km2 wide mound, surrounded by a complex network of rivers and canals. Two large canals, detected with LiDAR, used to cross the urban center, providing direct connection to the lagoon. The harbour was located at the eastern outskirts of the city. Twenty-five corings were carried out in the city and in the harbour to maximum depth of 8 m. The mound consists of superimposed archaeological layers from Protohystory to late Antiquity. The city canals and the harbour basin are filled by 2-5 m of organic-rich clayey silt with abundant plant macro remains and lagoonal shells. The biological proxies of salt/ brackish water vary in the core, suggesting fluctuations in the hydrological conditions; expected sea levels are -1 m asl. at 3000 BP and few decimeters below present in the Roman age. Pollen indicates phases of deforestation; the great diversity of herbaceous plants suggests a variety of human activities in the area (agriculture, farming, gardening) since the beginning of the common era. Some unusual plant remains possibly document trades.
THE RIVERS OF PADUA: GEOARCHAEOLOGICAL INVESTIGATION OF A FLUVIAL CITY
LATE CENOZOIC PALAEOCLIMATE AND ECOSYSTEMS AS ARCHIVED IN THE KALKKOP IMPACT CRATER LAKE FACIES: EASTERN CAPE, SOUTH AFRICA
Paolo Mozzi. University of Padua, Italy E-mail address: [email protected]
Ponani Mthembi. Council for Geoscience, South Africa E-mail address: [email protected]
In the Venetian Plain, human activities interfered with the hydrographic network since the 1st millennium BC, when important cities developed along rivers and lagoons. Padua is a fluvial city encased within two meanders built by the large Brenta R. and later occupied by the minor Bacchiglione R. Any understanding of the role played by the environment in the foundation and development of the city must rely on the reconstruction of the palaeohydrography. With origins tracing back to the late Bronze Age, ancient Padua experienced a major development in the Iron Age between the 9th-6th century BC, when it became an important urban centre. Since the 2nd century BC it was one of the main Roman cities in NE Italy. The stacked layering of archaeological deposits until the Middle Ages resulted in the upbuilding of a 7- m-thick, 1 km2- wide anthropogenic mound, which occupies the whole city centre. A research project funded by Fondazione Cariparo has allowed the integrated analysis of the alluvial and archaeological record in and around the
Impact cratering is one of the fundamental surface forming and modifying processes on all solid bodies in the solar system. In South Africa both cosmic impact and endogenic Crater Lake deposits of various ages occur and these craters include the Palaeoproterozoic Vredefort, Early Cretaceous Morokweng crater, and Middle Pleistocene Tswaing and Kalkkop craters. The Kalkkop impact crater is w50km south of Graaff Reneit and formed in Permo-Triassic lower Beaufort strata of the Karoo Supergroup and it is the main focus for this project. It is w650m in diameter and was made by a meteorite with a diameter of w60m (a rule of thumb is that the meteorite is one tenth the diameter of the crater that it made), smaller than Tswaing crater at 1.13km. Drill cores show that the Kalkkop Crater mainly comprise finely laminated carbonate with thin debris flows, underlain by a breccia succession formed during the impact. The latest core was drilled in mid-1992 and this 89 m long core will be studied in detail. A U-series date of w250 Ka (Middle Pleistocene) was obtained at the
monitored during two years through pressure transducers bolted into the platforms. Rocks’ mechanical strength and porosity were also quantified. Additionally, downwearing were measured using a transverse micro erosion meter. The results revealed that the rock resistance must be taken into account when shore platforms are used as a proxy for rmsl, once it controls the height at which platforms develop. The platform surface lowering (downwearing) was up to 3mm/yr at the study area, bioerosion and rocks’ resistance being the main drivers. Therefore, the rocks’ resistance and downwearing rates must be taken into account when the shore platforms’ elevation is used as a proxy for past sea level reconstruction. LATE HOLOCENE RECORDS OF DUST MIDDLETON ISLAND, GULF OF ALASKA
ACCUMULATION
FROM
341
urban area. Methods span from remote sensing and LiDAR to GIS processing of archaeological data, geological field survey and corings. Alluvial chronostratigraphy indicates that the Brenta meanders in Padua were active in the 2nd millennium BC, which implies that the late Bronze Age settlement was on the banks of this major river. 3D modelling of Iron Age and Roman living floors in the underground of the mound shows that the ancient city was at level with the surrounding plain, in a position which was subject to overbank deposition. The lack of floodings in the geoarchaeological record contradicts the presence of such a large river in Padua during the 1st millennium. In agreement with the geomorphic evolution of the alluvial plain, it is probable that the Brenta R. was not flowing anymore through the Iron Age and Roman city and that the underfit Bacchiglione R. was following its abandoned river bed. A STEP BEFORE VENICE: LANDSCAPE RECONSTRUCTION AT ALTINUM
Christopher Moy. U.S. Geological Survey, Woods Hole Coastal and Mar, United States
Paolo Mozzi. University of Padua, Italy
E-mail address: [email protected]
E-mail address: [email protected]
Iron is an important micronutrient that limits the growth of phytoplankton in much of the global ocean. In the Gulf of Alaska (GoA), we have a limited knowledge of the processes that transport iron, and in particular, the role eolian dust plays in delivering iron to the ocean surface. In order to better understand both modern and past mechanisms of dust deposition in the GoA, we examine satellite, NCEP reanalysis, and meteorological station data as well as geochemical data from peat cores collected from Middleton Island (59.43 N, 146.34 W). Widespread dust events have been observed in MODIS satellite imagery emanating from exposed floodplains within the Copper River valley and adjacent glaciated river valleys in southcentral Alaska (AK). Dust events are common in the fall when high pressure in the AK interior and low pressure in the central GoA establish a tight pressure gradient that drives anomalously strong northerly winds. Low river levels and limited snow coverage expose fine-grained glacial sediments that are entrained by winds. MODIS imagery indicates dust reaches beyond the continental shelf, and in many instances, dust plumes have been observed passing over Middleton Island (100 km SSW of the Copper River delta). To better constrain dust deposition from southcentral AK on geologic timescales, we collected cores from an extensive peat bog on Middleton Island, located at the edge of the continental shelf. X-Ray images, bulk density, magnetic susceptibility, and preliminary profiling XRF data indicate significant variations in inorganic or clastic components within the organic peat matrix. Because these cores were collected near the island's topographic high point, we infer that all inorganic constituents are likely delivered as dust. We will present a well-dated, high-resolution scanning XRF profile that will span the middle to late Holocene and monitor downcore variations in terrigenous material that are likely related to Copper River dust events.
Strategically located on the inner margin of the Lagoon of Venice, Altinum was one of the most important cities in the northern Adriatic since the Iron Age to Roman times. The origins of Venice are linked to the migration of the inhabitants, who abandoned the city in the 5th-7th century AD, seeking refuge from Barbarians in the nearby islands. The reconstruction of the ancient landscapes of Altinum is crucial for the definition of modes and timing of the colonization of the lagoon, which finally led to the foundation of Venice around the 9th century AD. Several investigations have been carried out with the collaboration of the Archaeological Superintendency and the support of ARCUS s.p.a. and Regione Veneto. Remote sensing has allowed for a detailed mapping of the city walls, street network, dwellings, public and religious buildings of Roman Altinum. The city stood on a 3.5 m high, 1 km2 wide mound, surrounded by a complex network of rivers and canals. Two large canals, detected with LiDAR, used to cross the urban center, providing direct connection to the lagoon. The harbour was located at the eastern outskirts of the city. Twenty-five corings were carried out in the city and in the harbour to maximum depth of 8 m. The mound consists of superimposed archaeological layers from Protohystory to late Antiquity. The city canals and the harbour basin are filled by 2-5 m of organic-rich clayey silt with abundant plant macro remains and lagoonal shells. The biological proxies of salt/ brackish water vary in the core, suggesting fluctuations in the hydrological conditions; expected sea levels are -1 m asl. at 3000 BP and few decimeters below present in the Roman age. Pollen indicates phases of deforestation; the great diversity of herbaceous plants suggests a variety of human activities in the area (agriculture, farming, gardening) since the beginning of the common era. Some unusual plant remains possibly document trades.
THE RIVERS OF PADUA: GEOARCHAEOLOGICAL INVESTIGATION OF A FLUVIAL CITY
LATE CENOZOIC PALAEOCLIMATE AND ECOSYSTEMS AS ARCHIVED IN THE KALKKOP IMPACT CRATER LAKE FACIES: EASTERN CAPE, SOUTH AFRICA
Paolo Mozzi. University of Padua, Italy E-mail address: [email protected]
Ponani Mthembi. Council for Geoscience, South Africa E-mail address: [email protected]
In the Venetian Plain, human activities interfered with the hydrographic network since the 1st millennium BC, when important cities developed along rivers and lagoons. Padua is a fluvial city encased within two meanders built by the large Brenta R. and later occupied by the minor Bacchiglione R. Any understanding of the role played by the environment in the foundation and development of the city must rely on the reconstruction of the palaeohydrography. With origins tracing back to the late Bronze Age, ancient Padua experienced a major development in the Iron Age between the 9th-6th century BC, when it became an important urban centre. Since the 2nd century BC it was one of the main Roman cities in NE Italy. The stacked layering of archaeological deposits until the Middle Ages resulted in the upbuilding of a 7- m-thick, 1 km2- wide anthropogenic mound, which occupies the whole city centre. A research project funded by Fondazione Cariparo has allowed the integrated analysis of the alluvial and archaeological record in and around the
Impact cratering is one of the fundamental surface forming and modifying processes on all solid bodies in the solar system. In South Africa both cosmic impact and endogenic Crater Lake deposits of various ages occur and these craters include the Palaeoproterozoic Vredefort, Early Cretaceous Morokweng crater, and Middle Pleistocene Tswaing and Kalkkop craters. The Kalkkop impact crater is w50km south of Graaff Reneit and formed in Permo-Triassic lower Beaufort strata of the Karoo Supergroup and it is the main focus for this project. It is w650m in diameter and was made by a meteorite with a diameter of w60m (a rule of thumb is that the meteorite is one tenth the diameter of the crater that it made), smaller than Tswaing crater at 1.13km. Drill cores show that the Kalkkop Crater mainly comprise finely laminated carbonate with thin debris flows, underlain by a breccia succession formed during the impact. The latest core was drilled in mid-1992 and this 89 m long core will be studied in detail. A U-series date of w250 Ka (Middle Pleistocene) was obtained at the