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Notes: Comparison of ultrastructures in Pliocene periplatform carbonates from the Bahamas with Silurian limestones from Gotland (Sweden) reveals that despite the differences in primary sediment composition and age, they reflect a similar mechanism of lithification. In both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis. Neither significant compression nor meteoric influence are necessary for the formation of calcite microspar. A model is proposed for the process of microsparitic cementation of fine-grained aragonite needle muds comprising four stages: (1) unconsolidated, aragonite-dominated carbonate mud; (2) precipitation of microspar that engulfs aragonite needles; (3) dissolution of aragonite, resulting in pitted surfaces of the microspar crystals; and (4) slight recrystallization. Our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite.

Notes: Quantitative logs of grain composition for several sections of platform top and flank of the Vercors carbonate platform (Early Cretaceous, SE France) provide platform-to-basin correlation with a resolution of a few metres over an area of 70 km2. Grain composition was determined by point-counting thin sections. Point-count groups that characterize palaeoenvironmental realms (i.e. open sea, platform margin) were defined for the platform–basin trajectory. Grain-composition logs revealed marked peaks in the number of open-sea biota and peaks in ooid abundance. The peaks in open-sea biota correspond to back-stepping intervals and deepening upward facies successions at the platform margin. These peaks probably relate to incipient drowning of the platform and may be used to delineate marine-flooding surface-bounded sequences. Peaks in ooid occurrence show no relationship with the progradation, aggradation or retreat of the platform. Apparently, the oolitic sands were not part of a facies tract that shifted up and down the platform. Instead, they represent a depositional mode that was either on or off. Times of prolific ooid production and shedding probably occurred during wide but shallow submergence of the platform, accompanied by suitable water chemistry. Peaks in both ooids and open-sea biota are excellent markers for platform-to-basin correlation, as they are recorded in successions on the platform top as well as on the flank. Altogether, the grain-composition logs show that each of the lithologically rather similar platform tongues of the Vercors has a unique signature or compositional fingerprint. These compositional fingerprints are most helpful in evaluating the lateral extent of different stratigraphic units. In outcrops of the Vercors platform, the physical tracing of bedding surfaces delineate wedges of toe-of-slope sediments that show a conspicuous thinning towards the platform. However, our correlation shows that these sediment bodies are not truly basin-restricted wedges but have a platform top equivalent. This implies that these units were, at least partly, deposited during high stands of sea level that flooded the platform.

Notes: A 38 m long sediment core (MD992201) retrieved from a water depth of 290 m from the leeward margin of the Great Bahama Bank (GBB; 25°53·49′N, 79°16·34′W) has been investigated for changes in aragonite content. The core covers the Mid to Late Holocene (the past 7230 yr). Sediment lightness (L*-values) was used as a proxy for aragonite content, based on a high linear correlation (R = 0·93) between the X-ray diffraction derived aragonite content and L*-values. The resulting time resolution of the L*-values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top. Detailed time series analysis using Monte Carlo Singular Spectrum Analysis and spectral analysis (Lomb–Scargle Fourier transform) identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr. During the first ∼1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat-topped GBB. Superimposed on a multimillennial signal, related to Holocene sea-level changes, a millennial-scale fluctuation and five quasi-periodic oscillations were detected (∼1·3–2 kyr, ∼500–600 yr, ∼380 yr, ∼260 yr, ∼200 yr and ∼100 yr period). Comparisons with other proxies (e.g. tree ring-Δ14C, 10Be and δ18O in ice cores) provides information on the origin and dynamics of the individual signals. The analysis shows that the ∼200 yr and ∼100 yr signals can be attributed to solar forcing. The ∼260 yr, ∼380 yr and the ∼500–600 yr quasi-periodic signals are found to be of climatic origin, whereas the millennial scale fluctuations remain enigmatic, although solar forcing mechanisms seem likely. The data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the Mid to Late Holocene climate, which in turn controlled sediment input variations found in the Holocene wedge leeward of the GBB. Although these periplatform sediments have a rather uniform appearance, they still contain a large variety of subtle sedimentary variations.

Notes: Core, logging and high-resolution seismic data from ODP Leg 166 were used to analyse deposits of the Neogene (Miocene–Lower Pliocene) Bahamian outer carbonate ramp. Ramp sediments are cyclic alternations of light- and dark-grey wackestones/packstones with interbedded calciturbidite packages and minor slumps. Cyclicity was driven by high-frequency sea-level changes. Light-grey layers containing shallow-water bioclasts were formed when the ramp exported material, whereas the dark-grey layers are dominantly pelagic. Calciturbidites are arranged into mounded lobes with feeder channels. Internal bedding of the lobes shows a north-directed shingling as a result of the asymmetrical growth of these bodies. Calciturbidite packages occur below and above sequence boundaries, indicating that turbidite shedding occurred during third-order sea-level highstands and lowstands. Highstand turbidites contain shallow-water components, such as green algal debris and epiphytic foraminifera, whereas lowstand turbidites are dominated by abraded bioclastic detritus. Gravity flow depocentres shifted from an outer ramp position during the early Miocene to a basin floor setting during the late Miocene to early Pliocene. This change was triggered by an intensification of the strength of bottom currents during the Tortonian, which was also responsible for shaping the convex morphology of the outer ramp. The Miocene and Lower Pliocene of the leeward flank of Great Bahama Bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps. The contrast between its sedimentary patterns and the well-known Upper Pliocene–Quaternary slope facies associations of the flat-topped Great Bahama Bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base-of-slope successions.