Portal de Periódicos da CAPES

A marine Late Jurassic syn-rift succession in the Lusitanian Basin, western Portugal — tectonic significance of stratigraphic signature

1997; Elsevier BV; Volume: 114; Issue: 1-4 Linguagem: Inglês

10.1016/s0037-0738(97)00068-7

1879-0968

Rodmar Ravnås, J. Windelstad, Donatella Mellere, Arvid Nøttvedt, T. Stuhr Sjøblom, R. J. Steel, Raymond C. Wilson,

Geology and Paleoclimatology Research

In the Lusitanian Basin, which is located along the western Iberian margin, rapid subsidence in the Oxfordian-Tithonian resulted from extension related to the opening of the North Atlantic. In the Santa Cruz area, located in the western part of the Lusitanian Basin, the Kimmeridgian syn-rift, marine Abadia Formation and the overlying alluvial Kimmeridgian-Tithonian Praia da Amoreira member of the Lourinhã Formation, were deposited in the middle part of the hangingwall dip slope of a larger half-graben that constitutes the Turcifal subbasin. The marine part of the succession consists of base-of-slope and lower slope mudstones and sandy turbidites, middle slope mudstones, upper slope to shelfal/?shoreline mudstones and sandstones, and fan-deltaic deposits. Two intermediate-scale fining-to-coarsening (FUCU) units are present in the marine strata. The lower FUCU unit represents a normal, base-of-slope/lower slope to upper slope, shoaling-upward succession. The unit reflects the progradation of a hangingwall shelfal ramp and infilling of an inherited rift bathymetry during a period of relative tectonic quiescence. The upper FUCU unit represents an intermediate-scale deepening-shoaling-upward or backstepping-forestepping sequence which is related to a single rift event; the backstepping segment was deposited during a period of increasing basinal subsidence and basin floor tilt rates, the early syn-rotational stage. It consists of submarine channel-fill incised into slumped upper slope sediments, and adjacent overbank deposits. The backstepping segment terminates with a clay-prone marine interval with abundant soft-sediment deformation features, which represent a period of maximum sea-level stand during the rotational climax. The overlying forestepping segment consists of a shoaling-upward, slope to fan-deltaic succession which terminates with alluvial deposits. It represents an interval with decreasing basinal subsidence and basin floor tilt rates, and renewed overbalance of sediment supply, which led to a regression during the late syn-rotational stage. In medial reaches of the hangingwall dip slope, periods of increasing-to-decreasing rift activity are recorded by a backstepping-forestepping package, or a threefold sandstone-mudstone-sandstone lithosome motif. The formation of smaller-scale units superimposed on the intermediate-scale FUCU syn-rotational motif were controlled predominantly by minor fault-controlled subsidence events or higher-frequency faulting events.