Late Frasnian Petit-Mont Member carbonate mounds occur in the southern part of the Dinant Synclinorium and in the Philippeville Anticline (SW Belgium). These mounds are 30 to 80 m thick and 100 to 250 m in diameter. They are embedded in shale, nodular shale and argillaceous limestone. Based on facies mapping of 14 buildups and related off-mound sediments, these mounds typically started from below the photic and storm wave base zones and builtup into shallow water environments. Above an argillaceous limestone substrate, the first carbonate mound facies consists of spiculitic wackestone with stromatactis (PM1), which becomes progressively enriched in crinoids and corals (PM2), then in peloids, stromatoporoids and cyanobacteria (PM3). PM4 consists of algal -coral -peloid wackestone and packstone with green algae and thick algal coatings. A core of algal and microbial bindstone (PM5) sporadically occurs within large mounds. The uppermost part of these mounds may show a recurrence of facies PM2 and PM1. PM1 to PM3 are coloured red by hematite derived from microaerophilic iron bacteria; PM4 and PM5 are grey. The transition from the aphotic to the cyanobacterial photic zone is recorded in the succession PM2 -PM3; the transition from the cyanobacterial to the green algal photic zone is recorded by PM3 -PM5. Storm wave base was reached within PM3 and fair-weather wave base within PM5. This paleobathymetric interpretation suggests a depth of 100 -150 m during initial establishment of PM1. Three types of mounds can be distinguished on the basis of geometry and facies architecture: (1) ''Les Bulants''-type mounds display a continuous vertical facies succession (PM2 -3 -4 -5) and low relief; (2) although exhibiting the same facies succession as ''Les Bulants'', ''Les Wayons''-type mounds show a distinct relief with steep flanks and bioclastic talus; (3) ''St.-Rémy'' mounds consist exclusively of PM1 and PM2, bioclastic flank deposits are not observed. From (1) to (3), these mound types represent successive deepening down a ramp. Biostratigraphic correlation on a regional scale provides good evidence that relative sea-level changes largely controlled lateral and vertical transitions of facies. Beyond that, hypoxic conditions are indicated by the sponge and iron-bacteria consortium in lower parts of the mounds. This is in agreement with the general assumption of stratified water masses during Late Frasnian, preceding the prominent Lower Kellwasser crisis. Cementation began with a radiaxial synsedimentary cement. A fringe of meteoric phreatic cement, initially nonluminescent, then with a bright orange luminescence, occurs in all mounds. It is contemporaneous with a nonluminescent pervasive cement of grainstones deposited in littoral areas. Differentiation between the (reducing) mounds and the (oxidizing) littoral area resulted from better aquifer circulation in sedimentary bodies close to the recharge area. Late burial cements occlude all the remaining porosity and are contemporaneous with the opening of the Variscan fr...

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Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea‐level variations. This paper explores the link between magnetic susceptibility, depositional setting and environmental parameters. These environmental parameters include distal–proximal transects, microfacies successions and fourth‐order trends on different carbonate platform types (platform, ramp, carbonate mound or atoll) during different Devonian stages (Eifelian, Givetian and Frasnian). Average magnetic susceptibility values over a distal–proximal‐trending facies succession vary markedly with depositional setting. On carbonate platforms, average magnetic susceptibility generally increases towards the top of shallowing‐upward sequences. On a distal–proximal transect, average magnetic susceptibility is intermediate for the deepest facies, decreases for the reef belts and increases to a maximum in the back‐reef zone. In ramps and atolls, magnetic susceptibility trends clearly differ; average magnetic susceptibility generally decreases towards the top of shallowing‐upward sequences and is highest in the deepest facies. The strong relationship between magnetic susceptibility, facies and sequences implies a strong environmental influence. However, the different responses in the different platform types suggest that sea‐level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values. Other primary or secondary processes also probably influenced magnetic mineral distribution. Primary processes such as carbonate production and water agitation during deposition are probably key factors. When carbonate production is high, the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases. High water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values. These parameters explain the lowest values observed on the reef platform, inner ramp and atoll crown, which are all in areas characterized by higher carbonate production and greater water agitation during deposition. The lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown. However, other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal. Diagenesis can change magnetism by creating or destroying magnetic minerals. However, the influence of diagenesis probably is linked strongly to the primary facies (permeability, amount of clay or organic matter) and probably enhanced the primary signal. The complexity of the signal gives rise to correlation problems between different depositional settings. Thus, while magnetic susceptibility has the potential to be an important correlation tool, the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and ...

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The sedimentary–diagenetic structure stromatactis is widespread in Palaeozoic spiculitic carbonate mud mounds, but occurs only sporadically in Mesozoic sponge carbonate mud mounds. Comparative analysis of Palaeozoic and Mesozoic stromatactis limestones suggests that this variation results from the degree of siliceous sponge skeletal rigidity and the amount of internal sediment accumulation in the original cavity network. Partial to entire filling by internal sediment resulted in a continuum, from a small amount of internal sediment and large amount of cement (stromatactis, common in the Palaeozoic), to only internal sediments (aborted stromatactis, common in the Mesozoic). These observations match independent lines of evidence concerning the siliceous sponge evolution and sediment recycling (e.g. bioerosion) across the Palaeozoic to Mesozoic biotic revolution.

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Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focuses on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced This article is protected by copyright. All rights reserved.

The major part of the Hanonet Formation is deposited on a mixed siliciclasticcarbonate detrital ramp, whereas the top is dominated by carbonate-rimmed shelf-related sedimentation. The transition corresponds roughly to the Eifelian-Givetian boundary. This work is based on two stratigraphic sections located in the southern part of the Dinant Synclinorium. Petrographic study leads to the definition of 11 microfacies, which demonstrate important sedimentological differences existing between the sections. A curve showing microfacies evolution is interpreted in terms of changing bathymetry. An environmental model depicts the lateral transition from a multiclinal carbonate ramp (to the east) to a forereef setting (to the west). Magnetic susceptibility was used to establish accurate stratigraphic correlations between the two sections. It also leads to an appreciation of the relative importance of eustatic sea-level change and local sedimentation rate. The combined interpretation of the microfacies curves and the magnetic susceptibility provides a new view of the sedimentary dynamics of the studied sections and, in a more general way, a better understanding of the processes responsible for magnetic susceptibility variations in carbonate rocks.