During the two first Italian Antarctic Expeditions (1985/86 and 1986/87) glacial-geological and geomorphological research has been carried out in the area of Terra Nova Bay. In particular the Cenozoic glacial sediments, the Holocene raised beaches and the Holocene glacier fluctuations have been investigated. Three main glacial drifts have been recognized. The youngest drift consists of a massive matrix-supported diamict extending up to about 350 m a.s.l. on the Northern Foothills, where it contains fragments of Pelecypods and Serpulids; it was deposited by a grounded ice-shelf during the last glaciation. In the interior mountains the upper limit of the drift rises up to about 1000 m a.s.l. The young glacial drift is characterized by frequent ice-cored topography, initial weathering stages, slightly stained granitic boulders without cavernous weathering, exept in the coastal belt. The older drift, very thin and discontinuous, occurs above the previous one, up to about 600 m on the Northern Foothills, and it is characterized by red stained granitic boulders affected by cavernous weathering. A third, oldest drift occurs up to 800 m a.s.l., composed of large and scattered boulders, strongly oxidized and affected by cavernous weathering, locally resting on a strongly developed red paleosol. At higher elevations up to about 1000 m round topped glacialy abraded reliefs, devoid of any glacial cover, can be observed and represent evidence of a still older glacial stage. Holocene beaches raised up to 30 m are well known at Terra Nova Bay (Inexpressible Island and Gerlache Inlet). In addition to the ones described by previous authors, other emerged beaches have been found in several localities on the coast of the Northern Foothills, near Evans Cove and at Edmonson Point. It is possible to distinguish two groups of emerged beaches: the first one consists of the beaches at Inexpressible Island and the Northern Foothills, ranging in altitude up to about 30 m a.s.l.; the second group, not higher than 7 m, is present at the foot of northern and eastern slopes of Mt. Melbourne. In our opinion, higher (and older) beaches are lacking in the Mt. Melbourne region because of recent volcanic activity. Several C-14 ages have been obtained from penguin remains collected in the organic horizons developed on the raised beaches; other C-14 ages were supplied by shells (Pelecypods, Barnacles and Corals) collected in marine sediments. We obtained a range for the glacio-isostatic uplift rate suggesting a value lower than 2.1 mm/yr in the last two millennia and a value lower than 4.5 but greater than 1.8 mm/yr in the four previous millennia. Evidence of Holocene glacier fluctuations have been observed close to the terminal margins of the outlet glaciers, of the ice shelves and of the local glaciers. Groups of Holocene ice-cored moraines document very small fluctuations of the ice extent of the outlet glaciers. The moraines can be differentiated on the basis of weathering degree, color of staining, development of deflation pavements, lichen cover and development of patterned ground. The Hells Gate Ice Shelf and the Nansen Ice Sheet (Shelf) advanced, during Holocene, probably because of the isostatic uplift of the coast. Near the termini of the small local glaciers at least two ice-cored moraines can be observed, showing the same differentiations mentioned above for the outlet glaciers. The moraines of the Strandline Gl. (Tethys Bay) rest on raised beaches and document two advance that were separated by a conspicuous lapse of time. They reached, respectively, a distance of more than 60 m and about 50 m from the present front. On the basis of the relationships between moraines and raised beaches, the oldest moraine has to be younger than about 5800-3800 yr B.P. and both were possibly deposited during the Late Holocene. At the foot of the eastern slope of Mt. Melbourne, near Edmonson Point, a glacier has been studied. On its south side, a complex of ice-cored moraines is to be found. It consists of a thin cover of marine sediments (laminated sands) that contains several articulated shells of Adamussium colbechi and Laternula elliptica. The fossiliferous sediments appear to have been frozen at the sole of the glacier and then entrained forward and laterally up to the surface (37 m a.s.l.), testifying to an advance of the glacier greater than 130 m that must have occured later than 600-1000 yr B.P.
Glacial Geology and Geomorphology of Terra Nova Bay (Antarctica).
BARONI, CARLO;
1987-01-01
Abstract
During the two first Italian Antarctic Expeditions (1985/86 and 1986/87) glacial-geological and geomorphological research has been carried out in the area of Terra Nova Bay. In particular the Cenozoic glacial sediments, the Holocene raised beaches and the Holocene glacier fluctuations have been investigated. Three main glacial drifts have been recognized. The youngest drift consists of a massive matrix-supported diamict extending up to about 350 m a.s.l. on the Northern Foothills, where it contains fragments of Pelecypods and Serpulids; it was deposited by a grounded ice-shelf during the last glaciation. In the interior mountains the upper limit of the drift rises up to about 1000 m a.s.l. The young glacial drift is characterized by frequent ice-cored topography, initial weathering stages, slightly stained granitic boulders without cavernous weathering, exept in the coastal belt. The older drift, very thin and discontinuous, occurs above the previous one, up to about 600 m on the Northern Foothills, and it is characterized by red stained granitic boulders affected by cavernous weathering. A third, oldest drift occurs up to 800 m a.s.l., composed of large and scattered boulders, strongly oxidized and affected by cavernous weathering, locally resting on a strongly developed red paleosol. At higher elevations up to about 1000 m round topped glacialy abraded reliefs, devoid of any glacial cover, can be observed and represent evidence of a still older glacial stage. Holocene beaches raised up to 30 m are well known at Terra Nova Bay (Inexpressible Island and Gerlache Inlet). In addition to the ones described by previous authors, other emerged beaches have been found in several localities on the coast of the Northern Foothills, near Evans Cove and at Edmonson Point. It is possible to distinguish two groups of emerged beaches: the first one consists of the beaches at Inexpressible Island and the Northern Foothills, ranging in altitude up to about 30 m a.s.l.; the second group, not higher than 7 m, is present at the foot of northern and eastern slopes of Mt. Melbourne. In our opinion, higher (and older) beaches are lacking in the Mt. Melbourne region because of recent volcanic activity. Several C-14 ages have been obtained from penguin remains collected in the organic horizons developed on the raised beaches; other C-14 ages were supplied by shells (Pelecypods, Barnacles and Corals) collected in marine sediments. We obtained a range for the glacio-isostatic uplift rate suggesting a value lower than 2.1 mm/yr in the last two millennia and a value lower than 4.5 but greater than 1.8 mm/yr in the four previous millennia. Evidence of Holocene glacier fluctuations have been observed close to the terminal margins of the outlet glaciers, of the ice shelves and of the local glaciers. Groups of Holocene ice-cored moraines document very small fluctuations of the ice extent of the outlet glaciers. The moraines can be differentiated on the basis of weathering degree, color of staining, development of deflation pavements, lichen cover and development of patterned ground. The Hells Gate Ice Shelf and the Nansen Ice Sheet (Shelf) advanced, during Holocene, probably because of the isostatic uplift of the coast. Near the termini of the small local glaciers at least two ice-cored moraines can be observed, showing the same differentiations mentioned above for the outlet glaciers. The moraines of the Strandline Gl. (Tethys Bay) rest on raised beaches and document two advance that were separated by a conspicuous lapse of time. They reached, respectively, a distance of more than 60 m and about 50 m from the present front. On the basis of the relationships between moraines and raised beaches, the oldest moraine has to be younger than about 5800-3800 yr B.P. and both were possibly deposited during the Late Holocene. At the foot of the eastern slope of Mt. Melbourne, near Edmonson Point, a glacier has been studied. On its south side, a complex of ice-cored moraines is to be found. It consists of a thin cover of marine sediments (laminated sands) that contains several articulated shells of Adamussium colbechi and Laternula elliptica. The fossiliferous sediments appear to have been frozen at the sole of the glacier and then entrained forward and laterally up to the surface (37 m a.s.l.), testifying to an advance of the glacier greater than 130 m that must have occured later than 600-1000 yr B.P.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
