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- Berglund, Mikael
(författare)
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Litorina Sea shore displacement and pollen analytical indications of forest succession during the Mid-Holocene in Gästrikland, east central Sweden
- 2010
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Ingår i: GFF. - Stockholm : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 132:3, s. 213-226
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the mid-Holocene shore level history and vegetation development in Gästrikland, east-central Sweden. This is investigated using sediment and microfossil records and 14C datings. The time span covered is c. 8000-5000 cal yr BP. Vegetation history during this time includes an increase in Tilia pollen 6500-6300 cal yr BP and a decrease in Ulmus and Corylus c. 5500 cal yr BP. The former change coincides with a sharp drop in relative sea level (RSL) of some 5 m; this RSL drop can be correlated to the regression from the L3 transgression of the Litorina Sea, identified in other areas around the Baltic Sea. The possible connections between RSL and climate (in particular changes on a maritime-continental continuum), as indicated by new pollen data and other records, are investigated. The new material shows, in comparison to other pollen records from southern and central Scandinavia, unusually high percentages of Tilia, Ulmus and Corylus pollen, but less Quercus. The change in pollen spectra around 5500 cal yr BP can be correlated to the northern European “elm decline”. A regional cooling is recorded in widespread data for this time, but observations suggest that other factors must be considered here, including disease and change in the physical landscape due to the ongoing land uplift.
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| 2. |
- Green, Paul F., et al.
(författare)
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Post-breakup burial and exhumation of the southern margin of Africa
- 2017
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Ingår i: Basin Research. - : Wiley-Blackwell. - 0950-091X .- 1365-2117. ; 29:1, s. 96-127
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Tidskriftsartikel (refereegranskat)abstract
- Despite many years of study, the processes involved in the development of the continental margin of southern Africa and the distinctive topography of the hinterland remain poorly understood. Previous thermochronological studies carried out within a monotonic cooling framework have failed to take into account constraints provided by Mesozoic sedimentary basins along the southern margin. We report apatite fission track analysis and vitrinite reflectance data in outcrop samples from the Late Jurassic to Early Cretaceous sedimentary fill of the Oudtshoorn, Gamtoos and Algoa Basins (Uitenhage Group), as well as isolated sedimentary remnants further west, plus underlying Paleozoic rocks (Cape Supergroup) and Permian-Triassic sandstones from the Karoo Supergroup around the Great Escarpment. Results define a series of major regional cooling episodes. Latest Triassic to Early Jurassic cooling which began between 205 and 180 Ma is seen dominantly in basement flanks to the Algoa and Gamtoos Basins. This episode may have affected a wider region but in most places any effects have been overprinted by later events. The effects of Early Cretaceous (beginning between 145 and 130 Ma) and Early to mid-Cretaceous (120-100 Ma) cooling are both delimited by major structures, while Late Cretaceous (85-75 Ma) cooling appears to have affected the whole region. These cooling events are all interpreted as dominantly reflecting exhumation. Higher Late Cretaceous paleotemperatures in samples from the core of the Swartberg Range, coupled with evidence for localised Cenozoic cooling, are interpreted as representing Cenozoic differential exhumation of the mountain range. Late Cretaceous paleotemperatures between 60 degrees C and 90 degrees C in outcropping Uitenhage Group sediments from the Oudtshoorn, Gamtoos and Algoa Basins require burial by between 1.2 and 2.2 km prior to Late Cretaceous exhumation. Because these sediments lie in depositional contact with underlying Paleozoic rocks in many places, relatively uniform Late Cretaceous paleotemperatures across most of the region, in samples of both basin fill and underlying basement, suggest the whole region may have been buried prior to Late Cretaceous exhumation. Cenozoic cooling (beginning between 30 and 20 Ma) is focussed mainly in mountainous regions and is interpreted as representing denudation which produced the modern-day relief. Features such as the Great Escarpment are not related to continental break up, as is often supposed, but are much younger (post-30 Ma). This history of post-breakup burial and subsequent episodic exhumation is very different from conventional ideas of passive margin evolution, and requires a radical re-think of models for development of continental margins.
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