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Details van artikel 10 van 25 gevonden artikelen
| Titel: |
Late Cainozoic stratigraphy, palaeomagnetic chronology and vegetational history from Lake George, N.S.W. |
| Auteur: |
Singh, G. Opdyke, N. D. Bowler, J. M. |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 28 (1981) nr. 3-4 pagina's 435-452 |
| Jaar: |
1981-11 |
| Inhoud: |
The sedimentary record from Lake George provides the longest relatively continuous Quaternary continental sequence yet available from Australia, and may record one of the longest Upper Cainozoic lacustrine records in the world. Palaeomagnetic analysis of a 36 m core from the lake floor identifies a sequence of deposition extending through the Brunhes and Matuyama, to the Gauss magnetic Chron. A longer core from the same site, but with incomplete recovery, extends to 72 m in lacustrine sediment; the age of the base of this core estimated by extrapolation is between 4.2 and 7 Ma. As there are still older and deeper sediments in the basin, extending to an estimated depth of 134 m, the age of the tectonic formation of the Lake George basin must be reckoned as Middle Miocene or older. The pattern of facies organisation through time demonstrates a phase of deep water deposition extending from the base of the cored sequence (72 m) up to 51.5 m, at which time a major change took place. A disconformity developed at this level, associated with a period of deep weathering and a prolonged phase of slope mantle deposition (from 51.5 to 30.8 m). A gradual return to lacustrine environments, with diminishing proportion of slope wash detritus, resulted in increased rates of deposition coincident with the Jaramillo Subchron at 21.5 m. Thereafter, throughout the Brunhes magnetic Chron, lacustrine conditions dominated, varying from deep to lake dry conditions in a rhythmic fashion, and reflecting the major climatic oscillations of the past 700 000 years, becoming more regular in the past 400 000 years. The pollen analytical record of the upper 8.6 m, covering the last 350 000 years, provides the main framework for the reconstruction of climatic history. The pollen and algal records indicate a sequence of vegetation and lake level changes, in which four major glacial/interglacial cycles are correlated with stages 1 to 10 of the 180 marine record. This provides by far the longest continuous biostratigraphic framework for the Quaternary period in Australia. Comparison between the palaeoclimatic record and the lake level evidence shows that there is no simple correlation between the lake level fluctuations and the glacial/ interglacial oscillations. In fact, major falls in the lake level occured both at the peak of cold glacials and during the warm interglacials. Though the falls in the lake levels during a warm period (interglacial) can be explained by high rates of evaporation, drying during maximum cold can be explained best in terms of a fall in precipitation. Permanent to deep-lake conditions generally occurred during intermediate cool periods following warm intervals, when perhaps the seas were still warm and low rates of evaporation on land prevailed. On the other hand, short periods of shallow to deep lake levels also occurred during warm (interglacial) periods, showing that these were associated with reasonably high rates of precipitation. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 10 van 25 gevonden artikelen
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