Devonian carbonate buildup facies in an intra-oceanic island arc (Tamworth Belt, New South-Wales, Australia)

Summary  Biohermal and biostromal buildups were investigated in late Early and Middle Devonian carbonate complexes of the Tamworth Belt. The buildup types and subtypes were studied in three regions (Yarramanbully, Sulcor and, Wyaralong') to clarify their paleo-environmental position. Two stages of development are recognized: Incipient bioherms and bioherms. Incipient bioherms are carbonate buildups with organisms which commonly form true bioherms. They dominate the sediment with small growth forms but are not prolific enough to build large bio-frameworks. Small nodular and globular stromatoporoids characterize the incipient bioherms and are interpreted as stunted growth forms. In one location (‘Wyaralong’) the coarse stromatoporoid calcarenite represents a fore-reef facies, at Sulcor a shallow subtidal setting with moderate water energy can be deduced. The bioherms can be sub-divided into stromatoporoid-, stromatoporoid-Stachyodes-, and stromatoporoid-rugose coral bioherms. Their variable composition probably reflects growth and deposition in different zones of a reef complex and/or different proximity to areas of denundation indicated by high siliciclastic input. In the Tamworth region true bioherms occur only in the Moore Creek Limestone Member (Middle Devonian), and not in older carbonate successions. Biostromes are sub-divided into (1) incipient biostromes with stromatoporoid-heliolitid biostromes and alveolitid biostromes; (2) aggregate biostromes withAmphipora andStachyodes biostromes; (3) stratified biostromes; (4) mixed aggregate/stratified biostromes. The different types of biostromes are not limited to specific time-intervals, but rather to environmental conditions.

Mixed carbonate-clastic facies in the Eocene Kalatar Formation of the southwest Tarim Basin (NW China): tectonic and climatic controls

During the Eocene, the southwest Tarim Basin was a large epicontinental sea as a part of the Turun Sea in the eastern Paratethys. The marine succession of the Kalatar Formation is exposed along the piedmonts of the southern Tian Shan and western Kunlun Shan, and can be subdivided into three members. On the southern side of the Tarim Basin, a non-barrier shore-to-shelf, siliciclastic-dominated system, locally with carbonates and oyster biostromes, developed along the western Kunlun Shan, where river input led to a seaward arrangement of alluvial fan, foreshore, shoreface, and offshore facies. In contrast, on the northern side of the Tarim Basin, a carbonate ramp system formed along the southern Tian Shan, including shallow bioclastic-oolitic grainstone shoals, oyster beds, and red algal rudstones along with a number of evaporite units, which formed under hypersaline tidal-flat and lagoonal conditions. The basin center was a largely moderate deep and low-energy embayment facies. Deposition of the mixed carbonate-siliciclastic Kalatar Formation was controlled by tectonic activity, in particular the development of the Himalayan orogeny with the closure of Paratethys sea-level fluctuations, and arid-humid climate variations.     

Middle paleozoic waulsortian-type mud mounds in Southern Fergana (Southern Tien-Shan,commonwealth of independent states): The shallow-water atoll model

Summary Several Waulsortian-type mud mounds nearly 500 m thick and about 5 km long occur in the Middle Paleozoic carbonate section of the Aktur nappe in the mountains on the right bank of Isfara river. These buildups form a well developed barrier system that stretches along the South Ferganian carbonate platform margin and divides the carbonate complex into a fore-reef and a back-reef part. The time of the mounds' most active growth was from the Late Silurian (Ludlow) to the Middle Devonian (Eifel). Three main facies types can be recognized in the mud mounds: 1. micritic core facies, 2. sparitic flank facies and 3. loferitic capping facies. The central massive or crudely bedded part of the mounds consists of white or light grey clotted micrite. Macrofossils are rare. The sparitic flank facies in contrast consists of coarse and densely packed crinoidal wackestone-floatstones with some brachiopod shell debris. Solitary rugose corals, tabulate corals, stromato-poroids and fragments of mollusks are also abundant. The tops of the mounds are usually covered with loferitic pelmicrites or oolitic grainstone caps. Stromatactis-like structures are very rare and poorly developed in the South Ferganian mud mounds. However, almostin all such mounds horizons of calcitic breccias can be found. In order to explain all the features found in the Fergana mounds an ‘atoll-like’ model has been proposed which starts the evolution of the mud mounds with a small nucleus bioherm. The main stage of the evolution corresponds to an atoll-like structure developing on the surface of shallow water platforms. White clotted micrite of the mound core facies is interpreted as a accumulation of fine-grained sediment in an inner lagoon flanked by crinoidal bar deposits. The mound flank facies represents the atoll rim deposits from where the carbonate mud is derived. The capping loferitic facies is considered as tidal flat deposit that developed on top of the buildups during the last stage of its evolution. The knoll shape of the mounds is explained by the retreat of the atoll flanking crinoidal bars back into the inner lagoon during the rise in sea level. Stromatactis-like structures of small cavities filled with sparry calcite owe their existence to burrowing organisms. Calcitic breccias are interpreted as paleokarst collapse breccias. They indicate that the tops of the mud mound became subaerially exposed. Other evidence for a subaerial exposure can be seen in the occurrence of Variscian ‘black and white’ limestone gravel on the tops of some mud mounds. According toWard et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands.     

High-frequency cycles in Upper-Miocene ramp-temperate carbonates (Sorbas Basin,SE Spain)

Uppermost-Tortonian temperate carbonates occur at the southern margin of the Sorbas Basin (Almería, SE Spain). These carbonates, included in the Azagador Member, formed in a gentle, shallow-water ramp. Six facies cycles in ramp deposits comprise alternating bivalve-shell concentrations and coralline algal beds. The basic cycle reflects the landward advance, as relative sea level rose, of coralline algal deposits, which were the facies of the outer ramp, over bivalve biostromes, which grew in the shallower areas of the mid-ramp. Biostromes were mainly built by oysters and locally by Isognomon. In many cases, however, the removal of smaller shells by storms left only thin, discontinuous patches of large bivalves as residual remains of the oyster biostromes. Some original cycles might be missing due to complete removal of bivalve shells from the biostromes. The six cycles recognised, therefore, should be considered as the minimum number of original cycles in the Azagador carbonates. The available age constraints suggest these cycles were forced by orbital precession or some higher-frequency process. Lithological cycles forced by precession are characteristic of the basinal deposits laterally equivalent to the Azagador carbonates.     

Coralline red algal limestones of the late Eocene alpine Foreland Basin in Upper Austria: Component analysis, facies and palecology

Summary Late Eocene sediments of the Upper Austrian Alpine Foreland Basin discordantly overlie Mesozoic and crystalline rocks, which are deeply eroded and form a distinct pre-Eocene relief. Late Eocene deposits contain red algal limestones with a remarkable lateral extent and a high diversity of sedimentary facies. Towards the south the algal limestones change into more clastic sediments, which are characterized by larger foraminifera and bryozoans. Main components are coralline algal branches and detritus, coralline crusts, rhodoliths, peyssonneliacean aggregates and crusts, nummulitid and orthophragminid foraminifera, corals, bryozoans, as well as terrigenous components. Rank correlation and factor analysis were calculated in order to obtain informations about relations between components. Hierarchical cluster analysis allowed the designation of 17 facies, most of them are dominated by coralline algae. Actualistic comparisons and correlations obtained from statistical analyses allowed the reconstruction of the depositional environments. Main features of the northern area are huge accumulations of unattached coralline algae (branches, rhodoliths, detritus), which are comparable to the present-day “Maerl”-facies. They formed loose frameworks cut by sand channels. The frequency of coralline detritus decreases upsection. Peyssonneliacean algae in higher parts of the profiles show growth-forms that are comparable to peyssonneliaceans of the Mediterranean circalittoral soft bottoms. This succession can be interpreted by an increasing relative sea level. Besides, crustose coralline algal frameworks were growing on morphological highs which are partially comparable to the present-day “Coralligéne de Plateau” of the Mediterranean Sea. In contrast to the northern area, sedimentation rate of the southern area is too low to keep up with rising sea level. The typical succession from nummulitid- to orthophragminid-and bryozoan-dominated facies can be interpreted by an increasing water depth from shallowest subtidal to the deeper photic zone and finally to the aphotic zone.     

Coral-rudist bioconstructions in the Upper Cretaceous Haidach section (Gosau Group; Northern Calcareous Alps, Austria)

Summary In the area of Haidach (Northern Calcareous Alps, Austria), coral-rudist mounds, rudist biostromes, and bioclastic limestones and marls constitute an Upper Cretaceous shelf succession approximately 100 meters thick. The succession is part of the mixed siliciclasticcarbonate Gosau Group that was deposited at the northern margin of the Austroalpine microplate. In its lower part, the carbonate succession at Haidach comprises two stratal packages that each consists, from bottom to top, of a coral-rudist mound capped by a rudist biostrome which, in turn, is overlain by bioclastic limestones and, locally, marls. The coral-rudist mounds consist mainly of floatstones. The coral assemblage is dominated by Fungiina, Astreoina, Heterocoeniina andAgathelia asperella (stylinina). From the rudists, elevators (Vaccinites spp., radiolitids) and recumbents (Plagioptychus) are present. Calcareous sponges, sclerosponges, and octocorals are subordinate. The elevator rudists commonly are small; they settled on branched corals, coral heads, on rudists, and on biolastic debris. The rudists, in turn, provided settlement sites for corals. Predominantly plocoid and thamnasteroid coral growth forms indicate soft substrata and high sedimentation rates. The mounds were episodically smothered by carbonate mud. Many corals and rudists are coated by thick and diverse encrustations that indicate high nutrient level and/or turbid waters. The coral-rudist mounds are capped byVaccinites biostromes up to 5 m thick. The establishment of these biostromes may result from unfavourable environmental conditions for corals, coupled with the potential of the elevator rudists for effective substrate colonization. TheVaccinites biostromes are locally topped by a thin radiolitid biostrome. The biostromes, in turn, are overlain by bioclastic limestones; these are arranged in stratal packages that were deposited from carbonate sand bodies. Approximately midsection, an interval of marls with abundantPhelopteria is present. These marls were deposited in a quiet lagoonal area where meadows of sea grass or algae, coupled with an elevated nutrient level, triggered the mass occurrence ofPhelopteria. The upper part of the Haidach section consists of stratal packages that each is composed of a rudist biostrome overlain by bioclastic wackestones to packstones with diverse smaller benthic foraminifera and calcareous green algae. The biostromes are either built by radiolitids,Vaccinites, andPleurocora, or consist exclusively of radiolitids (mainlyRadiolites). Both the biostromes and the bioclastic limestones were deposited in a low-energy lagoonal environment that was punctuated by high-energy events.In situ-rudist fabrics typically have a matrix of mudstone to rudistclastic wackestone; other biogens (incl. smaller benthic foraminifera) are absent or very rare. The matrix of rudist fabrics that indicate episodic destruction by high-energy events contain a fossil assemblage similar to the vertically associated bioclastic limestones. Substrata colonized by rudists thus were unfavourable at least for smaller benthic foraminifera. The described succession was deposited on a gently inclined shelf segment, where coral-rudist mounds and hippuritid biostromes were separated by a belt of bioclastic sand bodies from a lagoon with radiolitid biostromes. The mounds document that corals and Late Cretaceous elevator rudists may co-occur in close association. On the scale of the entire succession, however, mainly as a result of the wide ecologic range of the rudists relative to corals, the coral-dominated mounds and the rudist biostromes are vertically separated.     

Microfacies and sequence stratigraphy of the Amapá Formation, Late Paleocene to Early Eocene, Foz do Amazonas Basin, Brazil

On the basis of thin-section studies of cuttings and a core from two wells in the Amapá Formation of the Foz do Amazonas Basin, five main microfacies have been recognized within three stratigraphic sequences deposited during the Late Paleocene to Early Eocene. The facies are: 1) Ranikothalia grainstone to packstone facies; 2) ooidal grainstone to packstone facies; 3) larger foraminiferal and red algal grainstone to packstone facies; 4) Amphistegina and Helicostegina packstone facies; and 5) green algal and small benthic foraminiferal grainstone to packstone facies, divisible locally into a green algal and the miliolid foraminiferal subfacies and a green algal and small rotaliine foraminiferal subfacies. The lowermost sequence (S1) was deposited in the Late Paleocene–Early Eocene (biozone LF1, equivalent to P3–P6?) and includes rudaceous grainstones and packstones with large specimens of Ranikothalia bermudezi representative of the mid- and inner ramp. The intermediate and uppermost sequences (S2 and S3) display well-developed lowstand deposits formed at the end of the Late Paleocene (upper biozone LF1) and beginning of the Early Eocene (biozone LF2) on the inner ramp (larger foraminiferal and red algal grainstone to packstone facies), in lagoons (green algal and small benthic foraminiferal facies) and as shoals (ooidal facies) or banks (Amphistegina and Helicostegina facies). Depth and oceanic influence were the main controls on the distribution of these microfacies. Stratal stacking patterns evident within these sequences may well have been related to sea level changes postulated for the Late Paleocene and Early Eocene. During this time, the Amapá Formation was dominated by cyclic sedimentation on a gently sloping ramp. Environmental and ecological stress brought about by sea level change at the end of the biozone LF1 led to the extinction of the larger foraminifera (Ranikothalia bermudezi).     

Stratigraphic analysis of a fossil Neogoniolithon-capped patch reef and associated facies,San Salvador,Bahamas

An unusual Pleistocene patch reef is exposed in a coastal cliff at Grotto Beach, San Salvador, Bahamas. The reef is a coralline framestone constructed mainly by Porites astreoides together with a few large heads of Diploria strigosa and Montastrea annularis, and is capped by a dense thicket of Neogoniolithon strictum that is interpreted as marking the subtidal/intertidal boundary. The reef is flanked to the northeast by laminated to low-angle cross-laminated intraclastic grainstones and to the southwest by skeletal rudstone of reefal and interreefal derivation. Uranium-series dating of pure aragonite from a Diploria corallum yielded an age of 123 000±9000 years. Reef growth began on an erosional surface underlain by steeply crossbedded eolian grainstone. As the reef grew upward, it also grew laterally over adjacent penecontemporaneous subtidal sediments. The reef was eventually buried by 2.3 m of shallow subtidal and beach sediments that apparently prograded seaward during a highstand, or possibly while sea level was still rising. The shallow subtidal sediments are mainly peloidal, ooidal and skeletal grainstones that are pervasively bioturbated. The overlying beach facies comprises predominantly laminated, sparsely burrowed grainstone. The beach and shallow subtidal facies contain boulders of fine-grained laminated grainstone that are interpreted as storm-tossed blocks of beachrock. Living analogs of the Grotto Beach fossil reef lie off East Beach, San Salvador. Several of these have a flourishing cap of Neogoniolithon that extends above low-tide level and we believe that the Neogoniolithon cap of Grotto Beach reef did likewise. Wherever found in the stratigraphic record this facies should serve to identify the subtidal/intertidal boundary. The uppermost Pleistocene beach sediments associated with Grotto Beach fossil reef lie 5.8 m above present-day mean sea level, which ist strong evidence that this portion of San Salvador has undergone little subsidence since the Grotto Beach section was deposited.     

Anthracoporella mounds in the Late Carboniferous Auernig Group,Carnic Alps (Austria)

Summary A heretofore undocumented example of skeletal mounds formed by the dasycladacean algaAnthracoporella spectabilis is described from mixed carbonate-clastic cycles (Auernig cyclothems) of the Late Carboniferous (Gzhelian) Auernig Group of the central Carnic Alps in southern Austria. The massive mound facies forms biostromal reef mounds that are up to several m thick and extend laterally over more than 100 m. The mound facies is developed in the middle of bedded limestones, which are up to 16 m thick. These limestones formed during relative sea-level highstands when clastic influx was near zero. The mound facies is characterized by well developed baffler and binder guilds and does not show any horizontal or vertical zonation. Within the massive mound faciesAnthracoporella is frequently found in growth position forming bafflestones and wackestones composed of abundantAnthracoporella skeletons which toppled in situ or drifted slightly.Anthracoporella grew in such profusion that it dominated the available sea bottom living space, forming ‘algal meadows’ which acted as efficient sediment producers and bafflers. BecauseAnthracoporella could not provide a substantial reef framework, and could not withstand high water turbulence, the biostromal skeletal mounds accumulated in shallow, quiet water below the active wave base in water depths less than 30 m. The massive mound facies is under- and overlain by, and laterally grades into bedded, fossiliferous limestones of the intermound facies, composed mainly of different types of wackestones and packstones. Individual beds containAnthracoporella andArchaeolithophyllum missouriense in growth position, forming “micromounds’. Two stages of mound formation are recognized: (1) the stabilization stage when bioclastic wackestones accumulated, and (2) the skeletal mound stage when the sea-bottom was colonized byAnthracoporella and other members of the baffler and binder guilds, formingAnthracoporella bafflestones and wackestones of the mound facies. A slight drop in sea-level led to the termination of the mound growth and accumulation of organic debris, particularly calcareous algae, fusulinids, crinoids and bryozoans, forming well bedded limestones, which overlie the mound facies     

Foraminiferal biostratigraphy and sequence stratigraphy across the mid-Carboniferous boundary in the Central Taurides,Turkey

The Aladağ Unit is one of the main tectonic units in the Tauride Belt, located in southern Turkey. It includes a continuous Paleozoic carbonate sequence encompassing the mid-Carboniferous boundary, with outcrops being especially well exposed in the Hadim region. The boundary succession lithology is mainly composed of carbonates with intercalated quartz arenitic sandstone layers. Based on foraminifers, four biostratigraphic zones have been defined in the interval from the Upper Serpukhovian to the Lower Bashkirian. These zones are, in ascending order: the Eostaffella ex gr. ikensis—E. postmosquensis Zone (Zapaltyubinsky Horizon, Upper Serpukhovian); the Plectostaffella jakhensis—P. bogdanovkensis Zone, and the Millerella marblensis Zone (Bogdanovsky Horizon, lower Bashkirian); and the Semistaffella sp. Zone (Syuransky Horizon, lower Bashkirian). The mid-Carboniferous boundary occurs between the Eostaffella ex gr. ikensis—E. postmosquensis Zone and the Plectostaffella jakhensis—P. bogdanovkensis Zone. Boundary beds are characterized by eight, repeatedly occurring microfacies types, namely: (1) coated crinoidal packstone; (2) coated bioclastic grainstone; (3) oolitic grainstone; (4) oolitic packstone-grainstone; (5) intraclastic grainstone; (6) mudstone-wackestone; (7) quartz-peloidal packstone; and 8) quartz arenitic sandstone. Based on microfacies stacking patterns, various types of shallowing-upward cycles have been recognized. Depositional sequences and sequence boundaries are correlatable with those described from North America and Russia and Carboniferous global sea-level curves. The duration of cycles has been estimated as 100 ky, suggesting that cycle periodicities correspond to the Milankovitch eccentricity band.     

Lateral variability of shallow-water facies and high-frequency cycles in foreland basin carbonate platforms (Pennsylvanian,NW Spain)

The kilometer-sized and 100-meter-thick carbonate platforms of the Escalada Fm. I and II (Middle Pennsylvanian) accumulated in the foredeep of a marine foreland basin during the transgressive phases of 3rd-order sequences and were buried by prograding siliciclastic deltaic systems in the course of the subsequent highstand. The carbonate successions show a general upward trend from grain- to mud-supported carbonates, interfingering landwards with siliciclastic deposits of a mixed siliciclastic-carbonate shelf (Fito Fm.) adjacent to deltaic systems. The spatial variability of the carbonate facies and the high-frequency (4th–5th order) cycles, from the platform margin-outer platform to the deltaic systems, has been interpreted from basin reconstruction. Carbonate facies include skeletal grainstone to packstone, ooidal grainstone, burrowed skeletal wackestone, microbial and algal boundstone to wackestone forming mounds, various algal bafflestone and coral biostromes in areas with siliciclastic input. These high-frequency transgressive–regressive cycles are interpreted to record allocyclic forcing of high-amplitude glacioeustasy because they show characteristic features of icehouse cycles: thickness >5 m, absence of peritidal facies, and in some cases, subaerial exposure surfaces capping the cycles. In the mixed cycles, siliciclastics are interpreted as late highstand to lowstand regressive deposits, whereas carbonates as transgressive-early highstand deposition. The lateral and vertical variability of the facies in the glacioeustatic cycles was a response to deposition in a rapidly subsiding, active foreland basin subjected to siliciclastic input, conditions that might be detrimental to the growth of high-relief carbonate systems.     

The ecology of Cenomanian lithistid sponge frameworks, Regensburg area, Germany

Upper Jurassic‐Lower Cretaceous sponge biostromes and bafflestone mounds were common and widespread in European temperate to tropical marine environments. They declined markedly during the Late Cretaceous. Most sponge frameworks were paucispecific and ecologically simple, with only basic levels of succession or tiering. The occurrence of ecologically complex, lithistid sponge biostromes and mounds in the Cenomanian Quadersandstein Member, Regensburger Grünsandstein of the Saal Quarry, Bavaria, is therefore of special significance. These are ecologically the most complex sponge frameworks yet reported from the Cretaceous. Their size, morphology and ecological organization compare favorably with shallow‐water, sponge‐dominated frameworks in modern seas. The Saal Quarry sponge frameworks are generally associated with firmgrounds and condensed intervals in the transgressive systems tract of the Cenomanian‐Turonian, tectonoeustatic supercycle UZA‐2. The lowest sponge frameworks are up to 1 m high bafflestone mounds consisting of large, irregular, sheet‐ and mound‐like recumbent sponges overlain by diverse, cylindrical, pyriform, upward‐branching forms of Jerea and Siphonia. These biostromes overlie a condensed interval or firmground which locally contains small, in situ pyriform sponges (Jerea pyriformis Lamouroux) as well as Middle Cenomanian Inoceramus etheridgei Woods. The upper sponge frameworks consist of bafflestone mounds up to 4.4 m wide and 1.3 m high, composed of six lithistid sponge morphotypes, possibly representing several species of Jerea and Siphonia. The occurrence of Rotalipora cushmanni in strata overlying the upper sponge framework indicates a Late Cenomanian age. Morphotypes preserve internal sponge morphologies and partially dissolved spicules surrounded by a diagenetic halo of silicified, pelletoid grainstone and/or packstone. Silica cements were derived from spicule dissolution. Different combinations of these morphotypes dominate three to four successional stages of sponge framework growth, and show vertical ecological tiering within communities. This ecological zonation is consistent among frameworks, and is partially or wholly repeated between storm‐related disturbance events.     

Serpulid-bryozoan-foraminiferal biostromes controlled by temperate climate and reduced salinity: Middle miocene of the Styrian Basin,Austria

Summary Reduced salintiy and a temperate climate prevailed during the Sarmatian in the Styrian Basin, the westernmost embayment of the Central Paratethys. At its northern margin (in the study area) tectonic processes initiated a transgression causing the incision of a cliff into the metamorphic basement and the formation of a carbonate buildup in the latest Sarmatian. The buildup consists of two serpulid-bryozoan-foraminiferal biostromes separated by a microbialite. Serpulids, bryozoa and the encrusting foraminifer Sinzowella caespitosa (Steinmann) as well as microbial mats formed a rigid framework, in which biogenic debris and siliciclastics were baffled. The different biota show complex growth relationships. Stromatolitic crusts and laminated micritic microbial crusts with birdseyes grew in a small sheltered lagoon. The upper biostrome is truncated by a ravinement surface of eustatic orgin and is overlain by ooid grainstone. The buildup drowned during maximum sea-level rise.     

Storm-dominated deposition of the Lower Jurassic crinoidal limestones in the Krížna unit, Western Tatra Mountains, Poland

The Lower-Middle Jurassic of the Krína unit in the Western Tatra Mts. (southern Poland) shows considerable facies variation. Crinoidal grainstones of variable thickness (up to 12 m) are one of characteristic facies. They occur above spiculites which were deposited below storm wave base on the slopes of elevated horsts. First single beds of crinoidal limestones occur within spiculites. They were deposited as event beds, generated probably by storms. The overlying thick complex of well-sorted grainstones composed almost entirely of crinoidal ossicles display widespread erosional bed amalgamation, hummocks and locally wave-formed ripples. The above characteristics are the effects of multiple reworking and winnowing of fine crinoidal material by oscillatory currents related to storms. This proves that the sedimentation of the crinoidal grainstones took place between the storm and the fair-weather wave bases. The vertical transition from spiculites with intercalations of crinoidal limestone beds towards the crinoidal grainstones is interpreted as the result of a shallowing upward trend. Since this trend is opposite to the global Early Toarcian transgression, this could be related to an uplift due to local block tectonic activity. The evidence for that is diversification of facies in the Krína Basin, as well as submarine slumps recorded in spiculites. The location of Krína Basin on relatively low northern latitude and on western edges of great Tethys Ocean during Early Jurassic enabled the formation of the crinoidal tempestites.     

Sedimentology,magnetic susceptibility and isotopes of a Middle Frasnian carbonate platform: Tailfer section,Belgium

Summary  The Tailfer section (Belgium, northern border of the Dinant Synclinorium) exposes Middle Frasnian shallow-water limestones. This paper proposes a sedimentological analysis based on classical petrology, which leads to the identification of 19 fourth order sequences, forming three third order system tracts. This sedimentological analyses is complemented by carbon isotopic and magnetic susceptibility (MS) data (based on the relation between MS and lithogenic input). Each system tracts is characterised by a particular evolution of the isotope and MS curve:

Iron microbial communities in Belgian Frasnians carbonate mounds

Summary The Belgian Frasnian carbonate mounds occur in three stratigraphic levels in an overall backstepping succession. Petit-Mont and Arche Members form the famous red and grey “marble” exploited for ornamental stone since Roman times. The evolution and distribution of the facies in the mounds is thought to be associated with ecologic evolution and relative sea-level fluctuations. Iron oxides exist in five forms in the Frasnian mounds; four are undoubtedly endobiotic organized structures: (1) microstromatolites and associated forms (blisters, veils...), possibly organized in “endostromatolites”; (2) hematitic coccoids and (3) non dichotomic filaments. The filaments resemble iron bacteria of theSphaerotilus-Leptothrix “group”; (4) networks of dichotomic filaments ascribable to fungi; (5) a red ferruginous pigment dispersed in the calcareous matrix whose distribution is related to the mound facies type. The endobiotic forms developed during the edification of the mounds, before cementation by fibrous calcite. The microbial precipitation of iron took place as long as the developing mounds were bathed by water impoverished in oxygen.     

Early Triassic peritidal carbonate sedimentation on a Panthalassan seamount: the Jesmond succession,Cache Creek Terrane,British Columbia,Canada

The Jesmond succession of the Cache Creek Terrane in southern British Columbia records late Early Triassic peritidal carbonate sedimentation on a mudflat of a buildup resting upon a Panthalassan seamount. Conodont and foraminiferal biostratigraphy dates the succession as the uppermost Smithian to mid-Spathian. The study section (ca. 91 m thick) is dominated by fine-grained carbonates and organized into at least 12 shallowing-upwards cycles, each consisting of shallow subtidal facies and overlying intertidal facies. The former includes peloidal and skeletal limestones, flat-pebble conglomerates, stromatolitic bindstones, and oolitic grainstone, whereas the latter consists mainly of dolomicrite. The scarcity of skeletal debris, prevalence of microbialite, and intermittent intercalation of flat-pebble conglomerate facies imply environmentally harsh conditions in the mudflat. The study section also records a rapid sea-level fall near the Smithian-Spathian boundary followed by a gradual sea-level rise in the early to mid-Spathian.     

Response of triassic reef coral communities to sea-level fluctuations, storms and sedimentation: Evidence from a spectacular outcrop (Adnet, Austria)

Summary The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg Austria has been repeatedly referred to as one of the most spectacular examples of an ancient ‘autochthonous’ coral reef structure. The ‘Tropfbruch’ quarry is probably the best outcrop for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach (combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater detail with data from modern coral reefs investigated by corresponding quantitative surveys. Three unconformities and three well-defined ‘reef growth stages’ reflecting the vertical and lateral development of the reef structure were differrentiated using transects: Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ and the great thickness of this interval. The massive coralPamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branchingRetiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean algaDiplopora adnetensis and by the decreasing size ofRetiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as a major control mechanism. Stage 2, separated from stage 1 by an unconformity caused by partial subaerial exposure and karstification, is characterized by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform. Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment led to a reduction of reef growth. Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the input of platform sediment. The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by small-scale sea level changes, storm activity and sedimentation. The vertical changes in reef community structures correspond to a sequence of ‘allogenic replacements’. The Adnet reef structure should not be regarded as a general model of Alpine Upper Rhaetian reefs, because of the particular setting of the patch reef. Only the ‘capping beds’ of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria similar to Adnet. Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of theRetiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity of corals subsequent to breaks in settlement, segration patterns of corals indicating ‘contact avoidance’, toppling of large coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water depths.     

Facies mosaic in the inner areas of a shallow carbonate ramp (Upper Jurassic,Higueruelas Fm,NE Spain)

The internal facies and sedimentary architecture of an Upper Jurassic inner carbonate ramp were reconstructed after the analysis and correlation of 14 logs in a 1 × 2 km outcrop area around the Mezalocha locality (south of Zaragoza, NE Spain). The studied interval is 10–16 m thick and belongs to the upper part of the uppermost Kimmeridgian–lower Tithonian Higueruelas Fm. On the basis of texture and relative proportion of the main skeletal and non-skeletal components, 6 facies and 12 subfacies were differentiated, which record subtidal (backshoal/washover, sheltered lagoon and pond/restricted lagoon) to intertidal subenvironments. The backshoal/washover subenvironment is characterized by peloidal wackestone–packstone and grainstone. The lagoon subenvironment includes oncolitic, stromatoporoid, and oncolitic-stromatoporoid (wackestone and packstone) facies. The intertidal subenvironment is represented by peloidal mudstone and packstone–grainstone with fenestral porosity. Gastropod-oncolitic (wackestone–packstone and grainstone) facies with intercalated marl may reflect local ponds in the intertidal or restricted lagoon subenvironments. Detailed facies mapping allowed us to document 7 sedimentary units within a general shallowing-upward trend, which reflect a mosaic distribution, especially for stromatoporoid and fenestral facies, with facies patches locally more than 500 m in lateral extent. External and internal factors controlled this heterogeneity, including resedimentation, topographic relief and substrate stability, combined with variations in sea-level. This mosaic facies distribution provides useful tools for more precise reconstructions of depositional heterogeneities, and this variability must be taken into account in order to obtain a solid sedimentary framework at the kilometer scale.