Abstract Cretaceous rocks crop out extensively in the three main Alpine orogenic belts of Spain: the Betic Cordillera, the Pyrenees and the Iberian Ranges. These rocks, deformed during Cenozoic Alpine convergence, are almost entirely sedimentary (with the exception of rare volcanic and meta-morphic rocks) and were deposited in an enormous variety of environments ranging from alluvial fans to pelagic seas. There were four main basins – Betic, Pyrenean, Basque-Cantabrian and Iberian (Fig. 12.1 ) – each of which originated in Triassic and Jurassic times in response to continental break-up at the start of the Alpine cycle. They subsequently underwent a polyphase evolution in the Cretaceous period when palaeo-geography and sedimentation in Iberia were strongly influenced by the relative movements of the contiguous Eurasian and African plates. Initiation of the North Atlantic spreading in earliest Cretaceous time led to a decrease in relative sinistral motion between Iberia and Africa (e.g. Ziegler 1988 a ). This was followed by a phase of rapid counterclockwise rotation of Iberia relative to Europe and the progressive opening of the Bay of Biscay, which lasted from late Aptian to early Campanian times (e.g. Olivet 1996 ). Finally, a third phase of basin evolution was heralded by the onset of Late Cretaceous oblique convergence between Africa and Europe (e.g. Savostin et al . 1986 ; Reicherter & Pletsch 2000 ). In addition to this changing tectonic setting, other factors, such as climate and eustasy, were also important controlling influences. The Cretaceous climate of Iberia

Abstract: Facies, fossils, morphology, lamination features, microstratigraphy, and composition of phosphate and iron-manganese nodules and crusts found in condensed limestones associated with stratigraphie discontinuity surfaces in Mesozoic successions of the Betic Cordillera of southern Spain, demonstrate that these structures are not diagenetic concretions, but biosedimentary microbial accretions (stromatolites) that grew rhythmically at the sediment-water interface in pelagic environments. These structures accreted by bacterially mediated precipitation of authigenic minerals, by trapping and binding of fine-grained, pelagic, siliciclastic, and carbonate particles, and by encrustation of benthic foraminifera. SEM examination of stromatolite laminae reveals the presence of dense accumulation of spheroidal, ovoidal, and sausage-shaped strings of micrometer-sized bodies with a bacteria-like size and shape. XRD and microprobe (BSE and X-ray images) studies show the presence of authigenic minerals such as francolite, goethite, hematite, barite, pyrite, and glauconite, among others. Authigenic clays and complex poorly crystalline Fe-Mn-Al- (Si)-oxyhydroxides are always closely associated with these minerals. Marine authigenesis in stromatolites of the pelagic realm was achieved through microbially mediated synsedimentary precipitation of poorly crystalline or amorphous phases that preceded crystallization of the observed minerals. Deposition of finegrained metals and silicate precipitates on bacterial surfaces favored preservation of microbial remains as external moulds. After degradation of bacterial organic matter, other components, such as francolite, nucleated within empty bacterial cells and other voids from bacterially precipitated amorphous precursors. Texture, mineralogy, and chemistry indicate the vertical and temporal evolution of the physicochemical conditions during the synsedimentary bacterial precipitation of amorphous precursors and the oscillations of the oxic-anoxic boundary (usually from oxic to postoxic conditions, although sometimes sulfidic conditions have been registered, allowing pyrite precipitation) during which the maturation of authigenic mineral phases took place. In conclusion, periods of very low sedimentation rate, now seen as sequence boundaries and/or transgressive surfaces in Mesozoic Alpine-Mediterranean paleomargins, favored accretion of stromatolites in the pelagic realm and bacterially mediated precipitation of a wide spectrum of authigenic minerals that provide abundant information about paleoceanography, sedimentation, and early diagenesis in open marine mesozoic environments.