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Soares D.M.,University of Cardiff | Alves T.M.,University of Cardiff | Terrinha P.,IPMA Instituto Portugucs do Mar e da Atmosfera
Earth and Planetary Science Letters | Year: 2012

Regional (2D) seismic-reflection profiles and borehole data are used to characterise the syn- to post-rift transition in the shallow offshore Porto Basin, and in deep-offshore regions of West Iberia and Newfoundland (East Canada). The interpreted data highlight the development of a regional stratigraphic surface at the time of complete lithospheric breakup between West Iberia and Newfoundland. This surface, usually called "breakup unconformity", is renamed in this work as Lithospheric Breakup Surface (LBS), on the basis that: (1) it is not always developed as an unconformity and (2) all lithosphere is involved on the breakup process, not only the continental crust. Depositional changes occur across the LBS in association with Late Aptian lithospheric breakup, which is marked by the deposition of a breakup sequence (BS) rather than a single stratigraphic surface. Stratigraphic correlations between strata in shallow and deeper parts of the two margins lead us to propose the breakup sequence (BS) as representing the transitional period between lithospheric breakup and the establishment of thermal relaxation as the main process controlling subsidence on divergent continental margins. The results in this work are important for other continental margins as they demonstrate that during lithospheric breakup significant quantities of sediment bypassed the inner proximal margins of West Iberia and Newfoundland on their way to the outer proximal margin. In addition, the interpreted data show that complete lithospheric breakup between conjugate margins is recorded by similar tectono-stratigraphic events. In Iberia and Newfoundland, these events are associated with reservoir successions in sediment overfilled basins and with carbon-rich strata ('. black shales') in sediment-starved basins. © 2012 Elsevier B.V.

Martins M.,New University of Lisbon | Martins M.,IPMA Instituto Portugucs do Mar e da Atmosfera | Costa P.M.,New University of Lisbon | Raimundo J.,IPMA Instituto Portugucs do Mar e da Atmosfera | And 3 more authors.
Ecotoxicology and Environmental Safety | Year: 2012

Dredging operations in harbours are recurrent to maintain accessibility and navigational depths. One of the main environmental risks of these operations is the remobilization of contaminants trapped in the sediments, rendering them more bioavailable to the biota. However, regulatory policies regarding the contamination risk of dredging chiefly apply to the disposal of dredged materials rather than the direct impact of the procedure itself. In order to assess the ecotoxicological risk of harbour dredging operations in a polluted estuary (the Tagus, W Portugal), the present study compared bioaccumulation and biomarker responses in field-deployed mussels before and after the beginning of operations, complemented by sediment characterization and risk analysis based on standardized sediment quality guidelines. The results revealed a very significant increase in genotoxicity and oxidative stress from the beginning of dredging onwards, which was accompanied by increased bioaccumulation of toxicants, especially polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Overall, the results indicate the importance of surveying the direct impacts of these procedures on local contamination, especially considering these sediments had been previously classified as "trace contaminated", according to normative guidelines, and therefore safe for disposal. This study shows the importance of obtaining both chemical and biological data in standard monitoring procedures and that the remobilization of contaminants by dredging operations may be grossly underestimated, which calls for caution when assessing the impact of these activities even in low to moderately polluted areas. © 2012 Elsevier Inc.

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