| 1. |
- Chenot, E., et al.
(författare)
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Diagenetic and detrital influences on clay mineralogy and carbon isotope geochemistry of Campanian-Maastrichtian sediments in the Tremp-Graus Basin (southern Pyrenees, Spain) : [Influencias diagenéticas y detríticas en la mineralogía de las arcillas y en la geoquímica de los isótopos de carbono de los sedimentos del Campaniano-Maastrichtiano de la cuenca de Tremp-Graus (sur de los Pirineos, España)]
- 2022
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Ingår i: Journal of Iberian Geology. - : Springer Science and Business Media LLC. - 1698-6180 .- 1886-7995. ; 48:1, s. 29-43
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Tidskriftsartikel (refereegranskat)abstract
- A 1000 m-thick sequence of Upper Cretaceous sediments outcropping in the Isabena Valley (Tremp-Graus Basin, Spain) has been studied to explore the evolution of environmental conditions that prevailed in this basin. A biostratigraphic study based on calcareous nannofossils was carried out to better constraint the age of the deposits, supplemented by carbon isotope stratigraphy on bulk carbonates. Clay mineral assemblages were identified by X-Ray diffraction combined with organic matter (OM) characterisation by Rock–Eval pyrolysis. The Late Campanian Event and Campanian Maastrichtian Boundary Event are clearly identified from the new δ13Ccarb dataset. The clay assemblage is composed of a complex mixture of chlorite, illite, kaolinite and mixed-layers including illite–smectite and chlorite–smectite. A progressive illitisation of smectite is recorded from the top to the base of the section due to the increasing burial depth. This evolution is consistent with increasing Tmax values of OM evolving from 425 (immature OM) to 449 °C (mature OM) from the top to the base of the section. Thus, detrital minerals are preserved only in the upper part of the section. The clay sedimentation is dominated by smectites likely originating from the Ebro massif, while increasing proportions of kaolinite are recorded from the uppermost Campanian and during the Maastrichtian. This evolution of the clay mineral assemblage is interpreted as a result from a change of source from south to northeast, with contributions from kaolinite-rich weathering profiles (including bauxites) to the northeast of the study area, reflecting a more hydrolysing climate.
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| 2. |
- Simancas, J.F., et al.
(författare)
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The seismic crustal structure of the Ossa-Morena Zone and its geological interpretation
- 2004
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Ingår i: Journal of Iberian Geology. - 1698-6180 .- 1886-7995. ; 30, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- The IBERSEIS deep reflection seismic experiment has provided a crustal image of the Variscan orogen of southwest Iberia. A brief presentation of the entire seismic profile is given, and then the Ossa-Morena Zone (OMZ) and its boundaries are considered. The crust of the OMZ is shown to be divided into an upper crust, characterized by dominantly NE-dipping reflectivity, and a poorly reflective lower crust. The reflectivity of the upper crust has good correlation with the geological cross-section constructed from surface mapping. In the seismic image, the upper crustal geological structures are seen to merge in the middle crust. Nevertheless, the OMZ middle crust is not a mere detachment level, as it shows very unusual features: it appears as a band of strong reflectivity and irregular thickness (the Iberian Reflective Body, IRB) that we interpret as a great sill-like intrusion of basic rocks. The boundaries of the OMZ are considered sutures of the orogen, and their geometrical features, as deduced from geological mapping and the seismic image, are in accordance with the transpressional character of the Variscan collision recorded in SW Iberia. The present Moho is flat, obliterating the root of the orogen.
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| 3. |
- Mil-homens, Mario, et al.
(författare)
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Historical trends in Hg, Pb and Zn sedimentation in the central shelf area of Portugal
- 2008
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Ingår i: Journal of Iberian Geology. - 1698-6180. ; 34:2, s. 287-298
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Tidskriftsartikel (refereegranskat)abstract
- Temporal records of excess 210Pb, and the determination of major (Al and Ca) and trace elements (Zn, Cr, Ni, Pb, Cu and Hg) in two sediment box-cores collected in the central area of the Portuguese shelf at North of the Nazaré canyon (offshore from the Lis River), allow identifying the deposition of various chemical elements normally associated with anthropogenic activities. In order to compensate for the natural sediment variability, heavy metal contents were normalised to Al. Temporal variations of Hg, Pb and Zn (Al-normalised) show an increasing trend since the beginning of the 1920s recording the development of industrial activities. Enrichment factors (EF) were calculated to estimate the level of contamination in these sediments. Mercury is the element with the highest average EF values (EF = 3), followed by Pb (EF = 1.5) and Zn (EF = 1.2). The results indicate that since 1991 64% of total Hg, 44% of total Pb and 24% of total Zn are derived from anthropogenic sources. The average anthropogenic fluxes of Hg, Pb and Zn (0.008, 3, 6 g cm-2yr-1, respectively) for the last 40 years in a ca. 400 km2 area of deposition represent a total accumulation of approximately 30, 12000 and 24400 kg per year of Hg, Pb and Zn, respectively. These results indicate that despite the high-energy conditions and the generally sandy nature of the Portuguese shelf sediments, it is possible to identify significant anthropogenic enrichments in some sediment accumulation areas. These contaminants are not necessarily related to immediate sources but may instead indicate atmospheric and or marine transport from more distant sources.
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