Spatial and temporal facies evolution of a Lower Jurassic carbonate platform, NW Tethyan margin (Mallorca, Spain)

The variety of depositional facies of a Lower Jurassic carbonate platform has been investigated on the island of Mallorca along a transect comprising six stratigraphic profiles. Twenty-nine facies and sub-facies have been recognized, grouped into seven facies associations, ranging in depositional environment from supratidal/terrestrial and peritidal to outer platform. Spatial and temporal (2D) facies distribution along the transect reflects the evolution of the carbonate platform with time showing different facies associations, from a broad peritidal platform (stage 1) to a muddy open platform (stage 2), and finally to a peritidal to outer carbonate platform (stage 3). Stage 1 (early Sinemurian to earliest late Sinemurian) corresponds to a nearly-flat peritidal-shallow subtidal epicontinental platform with facies belts that shifted far and fast over the whole study area. The evolution from stage 1 to stage 2 (late Sinemurian) represents a rapid flooding of the epicontinental shallow platform, with more open-marine conditions, and the onset of differential subsidence. During stage 3 (latest Sinemurian), peritidal and shallow-platform environments preferentially developed to the northeast (Llevant Mountains domain) with a rapid transition to middle-outer platform environments toward the northwest (Tramuntana Range domain). Stages 1 and 3 present facies associations typical of Bahamian-type carbonates, whereas stage 2 represents the demise of the Bahamian-type carbonate factory and proliferation of muddy substrates with suspension-feeders. The described platform evolution responded to the interplay between the initial extensional tectonic phases related to Early Jurassic Tethyan rifting, contemporaneous environmental perturbations, and progressive platform flooding related to the Late Triassic–Early Jurassic worldwide marine transgression and associated accommodation changes

56. Morphology and Basement Structures of the Goban Spur Continental Margin (Northeastern Atlantic) and the Role of the Pyrenean Orogeny

A new bathymetric map, based mainly on Seabeam data, has been established for the Goban Spur area during a postcruise survey of DSDP Leg 80. Using both Seabeam data and a new series of eight seismic profiles obtained perpen-dicular to the continental margin, we have constructed a new detailed structural map of the Goban Spur continental margin which clearly reveals Caledonian and Variscan trends. Both the thinning of the Goban Spur continental crust, from Early Cretaceous (late Cimmerian phase) to middle Albian time, and subsequent widening of the adjacent oceanic domain, from middle Albian to Campanian time, resulted from tensional movements in a N70 ° direction which fol-lowed Caledonian trends. During the rifting phase, the tops of the tilted fault blocks remained close to sea level. The rapid subsidence of the margin seems to have occurred in the early Albian during the last stage of rifting. Eocene intraplate deformation affected the whole Goban Spur continental margin, but is particularly evident at the Pastouret Ridge, a reactivated oceanic fracture zone. The oceanic domain underwent a slight intraplate compression, which fractured the old oceanic crust through its entire thickness, probably along previous zones of weakness, such as fracture zones

Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1–2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ~2 ‰ (13C enrichment) which took place between ~91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies