科研之友
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摘要
The transition region between regressive and transgressive barriers on the northern and central coastal sectors of Rio Grande do SW (RS) in southern Brazil is represented by a 170 km long stretch of coast where the barrier shows a general aggradational/stationary (a/s) behavior on a long term time scale. In this study, approximately 50 km of this transition region was analyzed at four sites: Tramandai, Jardim do Eden, Cidreira and Dunas Altas. All barriers began forming around 7.8 - 7.2 ka. The northernmost site (Tramandai) has a typical a/s stratigraphy, and barrier morphology is dominated by transgressive dunefields. Ten km to the south, at Jardim do Eden, the barrier shows a transgressive stratigraphy, and barrier morphology is also dominated by transgressive dunefields. At Tramandai the maximum barrier height is around 4 m, with a maximum of 6 m, while at Jardim do Eden it averages 6 m, with a maximum of 11 m. Further to the south, 10 km from Jardim do Eden, the barrier at Cidreira shows a dominant transgressive stratigraphy developed in the last 7 ka, but with evidence of a relatively small regression (similar to 600 m). Barrier height averages 10 m, reaching 20 m due to the existence here of a large transgressive dunefield. And finally, at around 30 km to the south of Cidreira, the a/s barrier of Dunas Altas occurs. Barrier morphology here is dominated by transgressive dunefields, with a surface height of around 8 m, but fronted by the largest and highest foredunes (around 8-10 m) in Rio Grande do Sul. The Dunas Altas coastline has regressed around 600 m in the last 7.8 ka. The Holocene barrier analyzed in this study, along a 50 km segment shows a general a/s behavior in the last 7.8 ka. The long time of a relatively stationary condition allowed the barrier to grow vertically by accumulation of aeolian deposits of at least four phases of transgressive dunefield development.
- 出版日期2013
