Abstract: This review has been undertaken in order to present some interpretations about the biostratigraphy of the smaller foraminifers belonging to four classes present during the Permian: Fusulinata, Miliolata, Nodosariata and Textulariata. Biostratigraphic markers of these classes are principally known in the orders and superfamilies of Lasiodiscoidea, Bradyinoidea and Globivalvulinoidea (Fusulinata), Cornuspirida (Miliolata), and in the entire class Nodosariata. The class Textulariata is too little known during the Permian to play a significant biostratigraphical role: nevertheless, the appearance of the order Verneulinida is probably an important bioevent. The main genera among the lasiodiscids are Mesolasiodiscus , Lasiodiscus , Lasiotrochus , Asselodiscus , Pseudovidalina , Xingshandiscus and Altineria ; the bradyinoids Bradyina and Postendothyra ; the globivalvulinoids Globivalvulina , Septoglobivalvulina , Labioglobivalvulina , Paraglobivalvulina , Sengoerina , Dagmarita , Danielita , Louisettita , Paradagmarita , Paradagmaritopsis and Paremiratella ; the miliolates Rectogordius , Okimuraites , Neodiscus , Multidiscus , Hemigordiopsis , Lysites , Shanita and Glomomidiellopsis , and the tubiphytids and ellesmerellids, which might be specialized miliolate and cyanobacterium consortia, with reference to microstructures and phylogenies of these groups. The Nodosariata markers belong to Nodosinelloides , Tezaquina , Polarisella , Geinitzina , Pachyphloia , Rectoglandulina , first true Nodosaria , Langella , Pseudolangella , Calvezina , Cryptoseptida , Cylindrocolaniella , Colaniella , Frondina and Ichthyofrondina , but their lineages are too poorly understood to permit an accurate biostratigraphic use at the present time. The superfamily Geinitzinoidea is emended. Finally, palaeobiogeographical implications based on Shanita , Colaniella and Altineria are given.

Abstract As important components of extinct as well as modern reefs, the measurement of changes in the composition of reef biota is crucial in order to evaluate the influence of extrinsic factors on the marine communities. The dramatic abiotic changes in the eastern and northern Pangea was mirrored by a gradual transition from a photozoan to a heterozoan association and the appearance of cool- (temperate-) water carbonates both in reef and carbonate ramp environments. Analyses of large skeletal and microbiotic components as well as microfacies succession were used for detailed explanation of reef structure, especially for lesser-known heterozoan skeletal mounds. The youngest skeletal mounds are recognized in the Roadian. The stable isotope data demonstrated a negative oxygen shift between latest Sakmarian and late early Artinskian coinciding with the end of P2 glaciation. The multiplicative nature of the event included the series of successive changes of extrinsic factors such as ice melting in interglacial episodes, eustatic ocean level rise, change of oceanic circulation and decrease of water temperature. The late Artinskian and subsequent Kungurian climatic impacts in the Northern Hemisphere were irreversible for the photozoan biota and prevented its further development. Roadian (Guadalupian) bryonoderm extended skeletal mounds developed in rather warm-water environments.

Abstract One unresolved conceptual problem in some Palaeozoic sedimentary strata is the boundary between the concepts of “shell concentration” and “reef”. In fact, numerous bioclastic strata are transitional coquina–reef deposits, because either distinct frame-building skeletons are not commonly preserved in growth position, or skeletal remains are episodically encrusted by “stabilizer” (reef-like) organisms, such as calcareous and problematic algae, encrusting microbes, bryozoans, foraminifers and sponges. The term “parabiostrome”, coined by Kershaw, can be used to describe some stratiform bioclastic deposits formed through the growth and destruction, by fair-weather wave and storm wave action, of meadows and carpets bearing frame-building (archaeocyaths, bryozoans, corals, stromatoporoids, etc.) and/or epibenthic, non-frame-building (e.g. pelmatozoan echinoderms, spiculate sponges and many brachiopods) organisms. This paper documents six Palaeozoic examples of stabilized coquinas leading to (pseudo)reef frameworks. Some of them formed by storm processes (generating reef soles, aborted reefs or being part of mounds) on ramps and shelves and were consolidated by either encrusting organisms or early diagenesic processes, whereas others, bioclastic-dominated shoals in barrier shelves, were episodically stabilized by encrusting organisms, indicating distinct episodes in which shoals ceased their lateral migration.

Abstract Shelled phosphorites of Early Cambrian age are common in the Avène-Mendic autochthonous unit (Marcory Formation) and the Mélagues nappe ( “Heraultia beds” of the Lastours Formation), northern Montagne Noire (France). Palaeogeographically, the concentration of phosphate took place along the shelf edge between a stable inner platform (southern Montagne Noire) and an unstable slope-to-basin sea floor preserved in the northern Montagne Noire. Petrography, back-scattered SEM (scanning election microscopy) and elemental mapping by EDS (energy dispersive system) show that the phosphorites were generated by repeated alternations of low sedimentation rates and condensation forming hardgrounds, in situ early diagenetic phosphogenesis, winnowing and polyphase reworking of previously phosphatized skeletons and hardground-derived clasts. The succession of repeated cycles of sedimentation, phosphate concentration and reworking led to multi event phosphate deposits rich in allochthonous particles. Associated accumulations of exhumed and reworked pyrite clasts reflect final deposition in a mainly dysaerobic substrate.

Abstract All bioherms from the Early Cambrian (Botoman) Matoppa Formation of the Nebida Group in SW Sardinia were previously thought to be dominated by Epiphyton. However, at “La Sentinella” (Serra Scoris Hill), they are composed of Girvanella, Razumovskia, Botomaella and Renalcis, with Epiphyton and archaeocyaths as accessory components. This association forms two unusual types of crust boundstone, consisting of stacked flat or curved crusts and saucer-like archaeocyaths delimiting shelter cavities. Dendrolitic Renalcis archaeocyath–cement boundstone caps the bioherm. Analysis of the La Sentinella reef complex and comparison with similar constructions from Mongolia (Zuune Arts, Salaany Gol), Nevada (Stewart's Mill, Battle Mountain), Mexico (Sonora) and China (Tianheban Formation) suggest that episodic deposition of fine-grained siliciclastic or carbonate sediment followed by periods of non-deposition enabled the calcimicrobial rafts and crusts to colonize the substrate and then provide synoptic relief for the development of a dendrolitic Renalcis–cement framework. “La Sentinella” is one of the rare examples of Cambrian reef complex displaying community replacement, from an initial stage of thrombolitic and/or flat-stacked microbial crusts on a muddy substrate to an arched microbial crust system, to a more resistant Renalcis–cement boundstone. Such bioherms reflect an open-shelf, shallow-marine environment of increasing energy.

Abstract Exposures of the Botoman (Lower Cambrian), Lemdad and Issafen formations on the Lemdad syncline, southern High Atlas, provide an excellent example of the interactions between tectonic events, magmatic activity and carbonate productivity. The major factors that controlled the nucleation of carbonate factories on the Botoman High Atlas platform were: (i) synsedimentary tectonism, as normal faulting resulted in tilting of fault blocks causing irregular topographies and subsequent sharp erosion; (ii) volcanism, because pyroclastic influx smothered carbonate factories except in distal areas of the platform or during quiescent episodes of volcanic activity; and (iii) the influence of successive shoaling parasequences. The Botoman reefs exhibit a wide range of external morphologies, including tabular (biostromes) and domal (bioherms and patches) boundstones, which do not exceed 3.5 m of thickness. Although archaeocyathan–microbial reefs only developed under clear-water conditions, microbial reefs grew also under turbid-water conditions. Domal and digitate stromatoids, Girvanella crusts, Epiphyton bushes and thromboid–stromatoid intergrowths document the ability of some microbial communities to develop heterotrophic strategies when submitted to a moderate terrigenous input. Turbidity was a major ecological factor that constrained development of filter/suspension-feeder and phototrophic organisms, but not necessarily of benthic non-phototrophic microbial communities.

Abstract In the abandoned slate quarry of Guernanic, Gourin (Morbihan, France), a single horizon (Upper Member of the Schistes de Postolonnec Formation) has yielded an exquisitely preserved Llandeilian (Middle Ordovician) echinoderm assemblage composed of the ophiuroid Taeniaster armoricanus sp. nov. and the mitrate Mitrocystella incipiens. These two groups of echinoderms represent the first fossils formally described from the Middle Ordovician of the Gourin area. The brittlestar T. armoricanus sp. nov. is the third and oldest ophiuroid reported so far in the Palaeozoic of the Armorican Massif. The mitrate Mitrocystella is also described for the first time from western Brittany. Taphonomic features of this ophiuroid–stylophoran aggregation suggest that it probably corresponds to the rapid burial of a life assemblage in an otherwise quiet and moderately deep setting (shelf) below, but close to, storm wave base. This echinoderm association represents the oldest evidence for a gregarious mode of life for ophiuroids, as well as the oldest indisputable example of a mixed ophiuroid–stylophoran meadow.

Abstract Silurian reefs are well known to comprise frame-building corals, stromatoporoids and algae, but also a range of calcimicrobial components and micritic sediments of possible microbial origin. The margins of Wenlock patch reefs tend to have diffuse edges that grade into the surrounding bedded facies because of talus shed from the reefs. However, portions of patch reefs show sharp-bounded reef margins, with bedded limestones terminating abruptly against the reef edge. Examples of sharp boundaries where the reef comprises only carbonate mudstone–wackestone with poorly-defined gross fabric, and containing no metazoan framework, have been found in Wenlock patch reefs the UK and Gotland. Although in some cases the micrite may demonstrate a peloidal structure, in others there is no clear structure, broadly fitting the aphanitic (structureless) type of fabric found in leiolites (suspected microbial facies that show no structure). The fabrics are interpreted to have been formed by microbial mediation of micrite precipitation as part of reef construction, and are therefore automicrites. In all cases the sharp reef edges indicate coherence of the micritic fabric, interpreted as a lithified wall against which bedded limestones were deposited. This arrangement supports published interpretations of pronounced topography of Wenlock patch reefs, and shows the presence of steep, vertical and, possibly, overhanging reef margins, formed prior to bedded sediment accumulation. Thus, there is likely to have been a time interval between reef formation and deposition of bedded sediments, possibly caused by reef upward growth in transgressive settings, followed by catch-up of bedded limestone deposition.

Abstract Palaeozoic sediments of Austria are separated by the Periadriatic Fault into Eastern Alpine (Upper, Middle and Lower Austroalpine) and Southern Alpine units. We herein present six case studies showing up the different development of shallow-marine communities with special regard to carbonate factories and shell pavements occurring in both regions during the Siluro-Devonian time span. Upper Silurian-Upper Devonian deposits of the Eastern Alps comprise accumulations of serpulid tubes (Southern Burgenland) and Septatrypa pavements, Amphipora mounds, coral-stromatoporoid–biostromes and Stachyodes–auloporoid beds regarded as pioneer reef communities (Graz Palaeozoic), respectively. Lower Silurian strata of the Southern Alps consist of pelagic sediments persisting to the Upper Silurian and therefore differ from contemporaneous successions in the Eastern Alps. Intercalated in Ludlow orthocerid limestone beds Cardiola pavements appear (Carnic Alps). Within the Lower Devonian sequence, mounds were built by baffling calcareous algae and tabulozoan communities. Coral–stromatoporoid patch reefs occur during the Pragian, Givetian and Frasnian stages.

Abstract The major part of the Hanonet Formation is deposited on a mixed siliciclastic–carbonate 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 fore-reef 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.

Abstract The facies architecture, sedimentary dynamics and palaeogeographic evolution were reconstructed for a number of middle-late Frasnian carbonate mounds from the south side of the Dinant Synclinorium (Belgium). Nine facies were recognized in the buildups, each characterized by a specific range of textures and assemblage of organisms: spiculitic wackestone with stromatactis (facies Pm1), which becomes progressively enriched in crinoids and corals (Pm2); grey or pinkish limestone with stromatactis, corals and stromatoporoids (A3–L3, Pm3); grey limestone with corals, peloids and dasycladales (A4–L4, Pm4); grey, microbial limestone (A5–L5, Pm5); grey limestone with dendroid stromatoporoids (A6–L6); grey, laminar fenestral limestone, (A7–L7); and grey, bioturbated limestone (A8–L8). Sedimentological evidence suggests that facies Pm1 and Pm2 correspond to iron bacteria–sponge-dominated communities, developing in a quiet aphotic and hypoxic environment. A3–L3 developed between storm and fair-weather wave base, in an oligophotic environment. Facies A5–L5 developed close to fair-weather wave base. Facies A6–L6 and the fenestral limestone A7–L7 correspond to an environment with slightly restricted water circulation. Facies A8–L8 developed at subtidal depths in a quiet, lagoonal environment. The main differences between the middle and late Frasnian mounds concern facies architecture, and are a consequence of different palaeoceanographic settings. The large flattened middle Frasnian Arche and Lion buildups show limited vertical differentiation, large-scale progradation features, extensive exportation of material towards off-reef environment and development of inner lagoonal facies. They grew offshore from a well-developed carbonate platform with a healthy carbonate factory. Middle Frasnian sea-level fluctuations were relatively mild, and sedimentation was able to keep up with sea-level rise. At the opposite extreme, during the late Frasnian, severe eustatic rises, together with rising oceanic hypoxic conditions, were responsible for frequent collapses of the carbonate factory, drowning of the middle Frasnian carbonate platform, and development of buildups with relatively limited lateral extension, high vertical facies differentiation, low potential for material exportation and high content in microaerophilic iron bacteria.

Abstract In the Belgian Namur–Dinant Basin the boundary between the Lustin Formation and the Aisemont Formation (in the Lower rhenana conodont Biozone) corresponds to a fall followed by a rise in sea level, leading to the first recorded late Frasnian coral crisis. The Aisemont Formation records a transgressive–regressive cycle. Prior to the crisis most of the colonial rugose corals were members of the Family Disphyllidae, but these were largely replaced by corals belonging to the Phillipsastraeidae. Among these Frechastraea colonized all environments of the basin and was the main constructor of a biostromal reef in its northernmost proximal area, in the fair-weather wave zone. Corals did not encrust each other and therefore were not firmly attached, but they hug tightly the substrate (a dead coral colony) and rest closely on it to resist to the turbulence of waves. During the Silurian and Devonian, up until the late Frasnian crisis, shallow-water reefs in turbulent water were usually built by encrusting stromatoporoids, whereas rugose corals were restricted to waters of lower energy. Indeed, they were unable to encrust substrates, unlike stromatoporoids and post-Palaeozoic scleractinians, and to live in turbulent habitats. In Belgium argillaceous sedimentation prevented the development of stromatoporoids and provided an opportunity for the corals to colonize empty niches and to construct biostromes in relatively high-energy environments. At the same time Alveolites and stromatoporoids were dominant in a mid-proximal environment below the fair-weather wave base, but within the storm wave zone, where they also constructed biostromes.

Abstract Reef development in the Famennian and Carboniferous successions of Belgium is more common than previously thought, and 10 broad time intervals of reef development can be differentiated. Reef formation is due to a variety of reef fabrics. Microbial communities are important for most reef frameworks, and often crucial for formation and stabilization of frameworks. Larger skeletal frameworks are rare. However, the interaction of skeletal bioconstructors and microbial communities is common, and results in successful reef building. However, microbial communities are still the backbone of these reefs. The majority of reefs are small, and a significant number formed in environments of restricted marine facies. Large reefs developed only in the late Tournaisian and late Viséan. Their initiation and formation was controlled by the geometry of the shelf. Three hierarchical levels, discussed below under the headings paleobiology, local environment, and regional and global environment, controlled reef formation. Important limiting factors were relative water depth, sea-level oscillations, climate, shelf geometry and the needs of the individual bioconstructor. In general, Belgian reef diversity reflects the global picture, but significant differences can be recognized in the different time slices. In particular, the abundance of middle Viséan reefs is a unique feature. The onset of the Variscian orogeny terminated all reef development in Belgium, and reefs younger than late Viséan are unknown.

Abstract The La Joya Formation of the Sierra Agua Verde, Sonora (NW Mexico) is late Atokan in age, equivalent to the early late Moscovian (Podolskian) and fusulinid biozone A3. In this alternance of cherty limestones and thin shaly beds, fusulinellid or anchicodiacean ('phylloid algae') wackestones–packstones and crinoidal rudstones–grainstones are the predominant microfacies, but chaetetid boundstones are conspicuous. These chaetetid occurrences of the Sierra Agua Verde are compared with the accumulations of Arizona, Texas, Kansas and Nevada (USA), and the Cantabric Cordillera (Spain). In Sonora, the environments with chaetetids were quiet, and located below wave base. Shallower facies with staffellids and Komia generally top the chaetetids. Because of the associated micritic deposits, the chaetetids have inhabited probably a soft or firm substrate. As a result of the disphotic–aphotic reconstructed environments, the possible symbionts of the chaetetids are more probably heterotrophic bacteria than autotrophic algae. The most comparable ecological conditions exist in the Atokan Marble Falls Formation of central Texas (USA). Chaetetids are not mentioned in the southern suspect terranes of Mexico, but were possibly present because these regions were located along the probable migration way to Peru, the southernmost area where Pennsylvanian chaetetids are known.

Abstract In the Sierra Agua Verde, central Sonora state, NW Mexico, the La Joya Formation exhibits an alternation (100 m thick) of calcareous siltstone and fossiliferous limestone with nodular cherts. This latter contains an abundant and diverse late Atokan (i.e. Podolskian = early late Moscovian, Middle Pennsylvanian) fossil assemblage composed of phylloid algae, fusulinids, chaetetids, tabulate corals, gastropods, fenestellid bryozoans, spiriferid and productid brachiopods, crinoids and conodonts. The crinoidal beds constitute a good example of a regional encrinite. They include several species of the parataxonomic stem form-genera Cyclocaudex, Cyclocrista, Heterosteleschus, Mooreanteris, Pentagonopterix, Preptopremnum, Cycloscapus and Pentaridica. Their preservation indicates the combination of preburial decay on the sea floor and post-burial decay within the sediment. The high degree of silicification of the crinoids indicates that they were possibly associated with siliceous organisms (Porifera?), not preserved in the assemblages. The studied thanatocoenosis is typical of tropical shallow seas, and reveals strong biogeographical affinities with the assemblages of the midcontinental and southern regions of the USA. Particularly, the Atokan crinoids of central Sonora are similar to those from Kansas and Texas, confirming the close palaeogeographic connection of southern USA and northern Mexico during the Middle Pennsylvanian.

Abstract: Sedimentary dykes in the Permian reef complexes of the Russian platform are well preserved and important in providing information about reef growth, the reef biota and, particularly, cavity-dwelling organisms and sediment sources. Two main fissure assemblages are recognized with N80° and N170° (late Asselian–early Sakmarian) and N130°–140° and N60° (Sakmarian–Artinskian) orientations. These contemporaneous orthogonal dyke sets present orientations corresponding to the regional tectonic fabric and a tectonic origin for fracturing associated with the foreland basin development. The largest dykes record eight lithofacies and several stages of fracture opening. Stromatoids and centimetre-thick deposits of peloidal grainstones–packstones (thromboids), which form in situ within microbial laminae on the fissure walls, preceded filling by skeletal and terrigenous sediments. The fissures contain a well-preserved biota similar to the Lower Permian cavity-dwelling organisms observed within the reef. The coelobiontic habitat was episodically enlarged by successive synsedimentary fracturing episodes reflecting several phases of encrustation and infill of recurrent lithofacies. The pioneer microbialites grew when nothing else was deposited in the fissures immediately after fracturing. Gastropods and ostracods occur as dense clusters, probably indicating in situ growth, or are considered as reworked material from the subsurface. Others organisms, such as crinoids, bryozoans, Tubiphytes, conodonts, brachiopods, ammonoids and spiculate sponges, are also found within fractures as reworked shells and skeletons, indicating that they were washed in from the overlying sea floor. The biota in the dykes is mainly represented by the dweller guilds living on the reef surface, whereas members of the binding and frame-building guilds are poorly represented. The dykes formed during reef development and the last stage of argillaceous wackestone sedimentation within the fractures is related to a major flooding event corresponding to upper Artinskian drowning of the Russian platform. Biostratigraphically significant fossils in the dykes date the ages of the host rock and of the fissure formation and filling from late Asselian to upper Artinskian. The Tratau reef thus provides an instructive example of the interaction between carbonate accumulation and tectonic events.

Abstract The present study provides an example of how Permian benthic carbonate production is controlled by oceanographic factors and climate. After the Permo-Carboniferous glaciation, shallow-marine benthic carbonate production exhibits strikingly different temporal and spatial patterns on the eastern Arabian plate and on isolated platforms of the SW Neo-Tethys. Close to the SE margin of the Arabian plate in the Haushi area, Cisuralian (late Sakmarian– early Artinskian) mixed carbonate-siliciclastic deposits of the Saiwan Formation and Guadalupian (Wordian) marl-carbonate alterations of the Khuff Formation are characterized by dominance of crinoids, brachiopods, bivalves and bryozoans. Scarcity of calcareous algae and zooxanthellate invertebrates indicate that members of the heterozoan association (bryonoderm facies) were responsible for carbonate production. Guadalupian carbonates of the Khuff Formation in the Haushi area show striking compositional differences to lateral equivalents in the subsurface where photozoan carbonates dominate. Contemporaneous carbonates of the Saiq Formation from the Saih Hatat (Oman Mountains) exhibit a twofold composition: siliciclastic sediments contain small tabulate corals of the heterozoan association. Most of the formation is carbonate of the photozoan association with fusulinaceans, smaller foraminifers, calcareous algae, rugose corals and aggregate grains. Lopingian carbonates of the Saiq Formation (Saih Hatat) are dominated by heterozoan carbonate production with crinoids, chaetetids, bryozoans and brachiopods, and resemble heterozoan bryonoderm carbonates. Shallow-water reef carbonates of the Neo-Tethys, preserved as blocks in the Ba'id area (Oman Mountains) and the Batain coast, are contrasting: in the Ba'id area Late Cisuralian-Early Lopingian blocks of photozoan carbonates have been found, containing calcareous sponges, rugose corals, richthofeniid brachiopods and calcareous algae. Cisuralian blocks from the Batain coast are very similar to the heterozoan bryonoderm facies, while Guadalupian reef blocks show striking similarities to photozoan chlorosponge associations. Combining climate modelling data with outcrop data, dominance of heterozoan carbonate production along the rim of Arabian plate and the Neo-Tethys can be explained by cool water during the Cisuralian and local upwelling of nutrient-rich water during the Guadalupian. Formation of Lopingian heterozoan carbonates of the Saiq Formation is least understood but could be the consequence of upwelling of saline and nutrient-rich oceanic bottom water. Comparing the ecological complexity of reefs, chlorosponge reefs built complex frameworks with a variety of ecological niches, if encrusters are present, whereas heterozoan reef communities are comparatively simple in their structure.

Abstract This paper presents biostratigraphical and palaeogeographical correlations, in a post-Hercynian and pre-Cimmerian tectonic framework, between stratigraphic sections of Late Permian age in two important and remote areas, with some considerations concerning neighbouring countries. It concerns mainly the Nikitin sequence (Kuban, Russia) and the Bükk Mountains (Hungary), and describes the carbonate environments, microfauna diversity, foraminiferal assemblages, calcisponge and brachiopod constructions, and gymnocodiacean accumulations. This study is extended to former Transcaucasia (southern Armenia, Georgia and Adzerbadjan), the Alborz Belt in northern Iran, Italy and the Carnic Alps. It emphasizes a relatively simple biosedimentary evolution, which permits a confident palaeogeographic reconstruction. New geochemical results provided some additional markers, in particular small microspherules consisting of Cr/Ni spinels of cosmic origin. They occur in several sections in a defined position at the Permian–Triassic boundary based on biostratigraphic correlations (conodonts, foraminifers, last Permian reefal phenomena). These geochemical data might be related to a possible meteorite impact, Nevertheless, another global alternative phenomenon occurs. From the Latest Permian to the Earliest Triassic, the carbonate production or biomineralization is preferentially concentrated in the confined, intertidal or lagunal zones, and its evolution is relatively progressive from gymnocodiacean accumulations of the Latest Permian to the microbialites of the Earliest Triassic.

Abstract Growth periodicity (cyclomorphic variation) in corals is expressed by various features, among them changes in the distribution of tabulae. A method potentially useful in analysis of periodical environmental changes is proposed herein. Measurement of spaces between tabulae in tabulate corals and preparation of a histogram converted into a trend curve may show relative periodical fluctuations of the environment. Such an analysis, exemplified here on Givetian Pachyfavosites sp. from the Avesnois (northern France), shows that this method may be used as a tool for estimation of environmental changes.