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The onshore Lusitanian Basin is dominated by two large diapiric salt walls which extend for up to 100 km. Seismic sections indicate that stratal onlap onto an intervening salt pillow initiated in Early Jurassic times. Well-exposed diapir flanks reveal three types of halokinetic-related unconformities (hook, low-angle wedge and high-angle flap-onlap – a new term) of Kimmeridgian to Turonian age, indicating that diapirism was active throughout this period. Stratal dip-fanning and wedge-thinning is predominantly caused by original sedimentary depositional processes with multiple low-angle unconformities (1°–5° pinchout angles) in both carbonate- and clastic-dominated sequences. No significant sedimentary slumping was observed in the clastic-dominated strata but important slumping of flank material is present in the carbonate-dominated sequences. Two tar accumulations are derived from oil trapped in sandstones on the flanks of the São Pedro de Moel and Santa Cruz salt diapirs. These are interpreted to be exhumed, but now biodegraded, oilfields. To our knowledge, these are the only exposed examples of salt-flank hydrocarbon accumulations that have been documented in the literature.
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The relatively well-studied Lusitanian Basin in coastal west-central Portugal can be used as an analogue for the less well-known Peniche Basin in the deep offshore. In this paper the Lusitanian Basin is reviewed in terms of stratigraphy, sedimentology, evolution and petroleum systems. Data comes from published papers and technical reports as well as original research and field observations. The integration and interpretation of these data is used to build up an updated petroleum systems analysis of the basin. Petroleum systems elements include Palaeozoic and Mesozoic source rocks, siliciclastic and carbonate reservoir rocks, and Mesozoic and Tertiary seals. Traps are in general controlled by diapiric movement of Hettangian clays and evaporites during the Late Jurassic, Late Cretaceous and Late Miocene. Organic matter maturation, mainly due to Late Jurassic rift-related subsidence and burial, is described together with hydrocarbon migration and trapping. Three main petroleum systems may be defined, sourced respectively by Palaeozoic shales, Early Jurassic marly shales and Late Jurassic marls. These elements and systems can tentatively be extrapolated offshore into the deep-water Peniche Basin, where no exploration wells have so far been drilled. There are both similarities and differences between the Lusitanian and Peniche Basins, the differences being mainly related to the more distal position of the Peniche Basin and the later onset of the main rift phase which was accompanied by Early Cretaceous subsidence and burial. The main exploration risks are related to overburden and maturation timing versus trap formation associated both with diapiric movement of Hettangian salt and Cenozoic inversion. ON-LINE FULL VERSION http://onlinelibrary.wiley.com/doi/10.1111/jpg.12648/epdf
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The marl-limestone succession that encompasses the Pliensbachian–Toarcian Stage Boundary (Lower Jurassic) and crops out at Peniche (Lusitanian Basin, Portugal), was chosen as one of the candidates for the establishment of Toarcian GSSP. Chemostratigraphy analyses, of the Upper Pliensbachian (spinatum Zone)-Lower Toarcian (levisoni p.p. Zone) portion, were based on total organic carbon (TOC) (68 samples), the isotope carbon (δ13C) and oxygen (δ18O) (38 samples) on the whole rock sample. Presenting an absolute variation of around -2.0‰, the δ13C and δ18O values decrease from the middle part up to the uppermost part of spinatum Zone, with smaller values in the lowermost part of the polymorphum Zone. In the Lower Toarcian the δ13C data shows a positive trend (spread of + 2.0‰) with a maximum value in the middle-upper portion of the polymorphum Zone and a minimum in the lowermost part of the levisoni Zone. The δ18O values show a general tendency to decrease within the polymorphum Zone, with the smallest values observed in the lower portion of the levisoni Zone. In general the TOC values are low, around 0.2%, in the spinatum Zone, upwards they increase to 0.5% in the polymorphum Zone, whilst they decrease again to 0.2% in the lowermost levisoni Zone. Calcareous nannofossils assemblages were investigated in 12 slides of marly samples collected around the Pliensbachian – Toarcian Stage Boundary that, according to the adopted zonation, proposed for NW European, lies in the NJ5b biozone. Abundant and well preserved nannofossils assemblages comprise 12 genera and 18 species. The genera Schizosphaerella and Lotharingius are dominant. Calcivascularis jansae, a characteristic taxon of the Lower Jurassic tethyan nannofossils assemblages, is abundant in the whole investigated interval. Biscutum grande is the other tethyan taxon present in studied succession. The occurrences of C. jansae and B. grande support the tethyan affinity of the calcareous nannofossils assemblages recovered from the Pliensbachian – Toarcian transition sampled at Peniche section.
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The Global boundary Stratotype Section and Point (GSSP) for the Bajocian Stage, formally defined at the base of bed AB11 of the Murtinheira section at Cabo Mondego (Portugal), has been ratified by the IUGS. Multidisciplinary biostratigraphical data, mainly based on ammonite and calcareous nannofossil assemblages, assure worldwide correlations; magnetostratigraphic data increase the correlation power. The position of the boundary coincides with the first occurrence of the ammonite assemblage characterized by Hyperlioceras mundum and related species (H. furcatum, Braunsina aspera, B. elegantula). The boundary lies just below the nanno-horizon of the entry of Watznaueria communis and W. fossacincta, and closely corresponds with an inversion to normal polarity correlated with the up-to-date Jurassic magnetic polarity time scale. An Auxiliary Stratotype Point (ASP) is also selected at the base of bed U10 of the Bearreraig Bay section on the Isle of Skye, Scotland, as the complementary reference for the palaeobiological key of the Bajocian lower boundary, i.e. the evolutionary transition Graphoceras-Hyperlioceras.
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Over 5,000 meters of Jurassic sediments accumulated in the Lusitanian Basin. The Upper Jurassic contains a great variety of fades, ranging from reefs to fluviatile red beds. The basin contains a fully marine sequence (see Fig. 41-1 and Table 41-1), whereas the shelf area exhibits a great variety of shallow marine and continental deposits. The three examples of shoaling deposits described in this paper are from the top of the Montejunto Beds, the Vale Verde Beds and overlying Pholodomya protei Beds, and the top of the Alcobaça Beds.
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The Mesozoic and Tertiary structural and sedimentological evolution of the western Iberian margin can be related to the reactivation of structures within the Hercynian basement. Sedimentary basins probably formed by extensional collapse of the hanging walls of Hercynian thrust sheets. Within the Lusitanian basin, and also offshore, reactivation of north-northeast to south-southwest- and northeast to southwest-trending late Hercynian orogenic strike-slip faults in the basement strongly controlled basin geometry, facies distributions, the site of salt structures, and the location of extensional and compressional faults. The Mesozoic of the Lusitanian basin comprises four unconformity-bounded sequences which are related to extensional events in the evolution of the North Atlantic. Two inversion episodes resulted in the reversal of Mesozoic tensional/transtensional features and were related to the Pyrenean and Betic orogenies. -from Authors