Erik Flügel

Patterns of Phanerozoic carbonate platform sedimentation

Carbonate platforms changed substantially in spatial extent, geometry, composition and palaeogeographical distribution through the Phanerozoic. Although reef construction and carbonate platform development are intimately linked today, this was not the case for most of the Phanerozoic. Carbonate production by non-enzymatic precipitation and non-reefal organisms is mostly responsible for this decoupling. Non-reefal carbonate production was especially prolific during times of depressed reef growth, balancing losses in reef carbonate production. Palaeogeographical distribution and spatial extent of Phanerozoic carbonate platforms exhibit trends related to continental drift, evolutionary patterns within carbonate platform biotas, climatic change and, possibly, variations in ocean chemistry. Continental drift moved large Palaeozoic tropical shelf areas into higher latitudes, thereby reducing the potential size of tropical platforms. However, the combined global size of carbonate platforms shows no significant decline through the Phanerozoic, suggesting that availability of tropical shelf areas was not a major control of platform area. This is explained by the limited platform coverage of low-latitude shelves (42% maximum) and occasional high-latitude excursions of platform carbonates. We speculate that reduced tropical shelf area in the icehouse tropics forced the migration of the many carbonate-secreting organisms into higher latitudes and, where terrigenous input was sufficiently low, extensive carbonate platform could develop.

Anisian (middle triassic) buildups of the Northern Dolomites (Italy): The recovery of reef communities after the permian/triassic crisis

SummaryAfter the end-Permian crisis and a global ‘reef gap’ in the early Triassic, reefs appeared again during the early Middle Triassic. Records of Anisian reefs are rare in the Tethys as well as in non-Tethyan regions. Most Anisian reefs are known from the western part of the Tethys but there are only very few studies focused on biota, facies types and the paleogeographical situation of these reefs. From the eastern part of the Tethys, Anisian reefs, reefal buildups or potential reef-building organisms have been reported from different regions of southern China. Most of the Anisian reefs known from western and central Europe as well as from southern China seem to be of middle and late Pelsonian age.The study area is situated in the northern Dolomites (South Tyrol, Italy) southeast of Bruneck (Brunico). It comprises the area between Olang (Valdaora) and Prags (Braies). The study is based on detailed investigations of the regional geology, stratigraphy and lithofacies (R. Zühlke, T. Bechstädt) as well as on a comprehensive inventory of Anisian reef organisms (B. Senowbari-Daryan, E. Flügel). These data are used in the discussion of the controls on the recovery of reefs during the early Middle Triassic.Most late Anisian reef carbonates studied are represented by allochthonous talus reef blocks of cubicmeter size. Small biostromal autochthonous mounds are extremely rare (Piz da Peres). The reef mounds as well as most of the reef blocks occur within the middle to late Pelsonian Recoaro Formation. They were formed on the middle reaches of carbonate ramps in subtidal depths, slightly above the storm wave base with only moderate water energy. Most lithotypes observed in the reef blocks correspond to sponge and/or algal bafflestones. Low-growing sessile organisms (Olangocoelia (sponge, alga?), sphinctozoan sponges, bryozoans, soleno-poracean algae, corals) and encrusting epibionts (sponges, porostromate algae, cyanophycean crusts, foraminifera, worms, microproblematica) created low cm-sized biogenic structures (bioconstructions) which baffled and bound sediment. Organic framework was only of minor importance; it is restricted to theOlangocoelia lithotype. Framework porosity was small in these reef mounds. Submarine carbonate cements, therefore, are only of minor importance s compared with Permian or Ladinian reefs. The relatively high number of lithotypes encountered in the reef blocks indicates a high biofacies diversity.Regarding the relative frequency, the diverse biota consist in descending order ofOlangocoelia, sponges (sphinctozoans, inozoans, siliceous sponges), bryozoans, porostromate algae and worm tubes. The sphinctozoans are characterized by small, mostly incrusting forms. The numerical diversity (species richness) is low compared with late Permian or Ladinian and late Triassic sphinctozoan faunas occurring within reefs.Following the sponges, monospecific bryozoans (Reptonoditrypa cauticaSchäfer & Fois) are the most common organisms in the reef limestones. Porostromate algae were restricted to areas within the bioconstructions not inhabited by sponges. The low-diverse corals had no importance in the construction of an organic framework.Surprisingly, microbial crusts are rare or even lacking in the investigated Anisian bioconstructions. This is in contrast to late Permian and Ladinian as well as Carnian reefs which are characterized by the abundance of specific organic crusts. The same comes true for‘Tubiphytes’ which is a common constituent in Permian, Ladinian and Carnian reef carbonates but is very rare in the Anisian of the Olang Dolomites. Instead of‘Tubiphytes’ different kinds of worm tubes (spirorbid tubes, Mg-calcitic tubes and agglutinated tubes) were of importance as epifaunal elements. Macrobial encrustations consisting of characteristic successions of sponges, bryozoans, algae, worm tubes and microproblematica seem to be of greater quantitative importance than in Ladinian reefs.Destruction of organic skeletons (predominantly of bryozoans) by macroborers (cirripedia?) is a common feature.The Anisian reef organisms are distinctly different from late Permian and from most Ladinian reef-builders. No Permian Lazarus taxa have been found.New taxa: Sphinctozoan sponges—Celyphia? minima n.sp.,Thaumastocoelia dolomitica n. sp.,Deningeria tenuireticulata n. sp.,Deningeria crassireticulata n. sp.,Anisothalamia minima n.g. n.sp., Inozoan sponges-Meandrostia triassica n.sp. Microproblematica-Anisocellula fecunda n.g. n.sp., Porostromate alga-Brandneria dolomitica n.g. n.sp.Most of our data are in agreement with the model described byFois & Gaetani (1984) for the recovery of reef-building communities during the Ansian but the biotic diversity seems to be considerably higher than previously assumed.Anisian deposition and the formation of the reef mounds within the Pelsonian Recoaro Formation of the Dolomites were controlled by the combined effects of synsedimentary tectonics and eustatic changes in sea-level. During several time intervals, especially the early Anisian (northern and western Dolomites: tectonic uplift), the early Pelsonian (eastern Dolomites: drowning) and the late Illyrian (wide parts of the Dolomites: uplift and drowning), the sedimentation was predominantly controlled by regionally different tectonic subsidence rates. The amount of terrigenous clastic input associated with synsedimentary tectonics (tectonic uplift of hinterlands) had a major influence on carbonate deposition and reef development. The re-appearance of reef environments in the Olang Dolomites was controlled by a combination of regional and global factors (paleogeographic situation: development of carbonate ramps; decreasing subsidence of horst blocks; reduced terrigenous input; moderate rise in sea-level).

Phanerozoic reef evolution: Basic questions and data base

SummaryAn up-dated data base is a matter of importance and urgency in order for encouraging a process-oriented approach to the study of reef evolution.The evolution of reefs is a major section of a Priority Program of the Deutsche Forschungsgemeinschaft devoted to ‘Global and regional controls of biogenic sedimentation’. Biological, paleontological and geological approaches in the study of ancient and modern reefs are needed for providing a better understanding of the following basic questions:- Biological and non-biological processes responsible for the construction and destruction of recent reefs. Studies should be focused on those processes which might also be regarded as important controls in the history of fossil reefs.- Paleontologicla data describing the changes in the biological controls of reef development over time. Studies should aim for a better understanding of major crises in the reef ecosystem during the earths history.- Geological factors governing the short-term and long-term development of reefs. Studies should be concentrated on the controls of reef accretion by sea-level fluctuations, climatic changes and possible changes in early diagenetic factors. The Reef Bibliography presented includes more than 4000 references dealing with Cambrian to Pleistocene reefs and more than 750 references referring to processes relevant to the interpretation of ancient reefs.The constraints of reef evolution will become clearer through intensivying comparative studies of reefs of different ages. The new data base should encourage this comparative research approach.

Evolution of Triassic reefs: Current concepts and problems

SummaryThe paper is concerned with some key questions resulting from current studies of Triassic reefs and reef biota. A survey of the distribution of the reefs in time and space (Figs. 1–2) indicates the existence of Anisian buildups (starting in the Pelsonian), and significantly restricted to the southern part of Europe. Ladinian and Carnian reefs exhibit a larger distribution pattern, including Europe, Asia and western North America as well as Peru. Even broader is the distribution of Norian and Rhaetian reefs, which are known from many parts of the Tethys but have been studied in detail only in Europe, Central Asia and in western North America, The exact age of many Triassic reefs is controversial because of the strong facies control of reef biota. The composition of the framebuilding fauna (especially calcisponges and corals) can only differentiate an Anisian to Carnian time interval from a Late Upper Triassic interval.The current state of research is characterized geographically by strongly biased information (more than 75 % of the Triassic reefs studied in more detail are situated in the Alpine-Mediterranean region and in the Cordilleran of western North America). Information about the composition of the framebuilding and binding communities as well as about facies types is generally good, but there is a strong need for more study of the reef-dwelling organisms and especially of the diagenetic history of reef carbonates.Triassic reefs exhibit five principal reef categories, which are distinguished by morphology and paleogeographical setting: 1. Carbonate ramps with biostromes, 2. Mud Mounds. 3. Reef Mounds, differentiated into knoll reefs and patch reefs. 4. Atolls. 5. Barrier Reef Complexes. Fig. 4 may be used to classify Triassic reefs with respect to morphology and paleogeographical location of the buildups. Most Triassic reefs described up to now are situated in a shelfedge position and in back-platform positions. Foreslope positions and platform margin settings were formed prior to platform and back-platform settings.The palecological interpretation of the reef biota is made more difficult by the rarity of systematic paleontological studies of many Triassic reefs. Difficulties arise even for the main reefbuilding groups: Calcisponges (only the European sphinctozoans have been studied in detail), corals (the problem of the beginning of coralzooxanthellae symbiosis should be clarified), and algal crusts as secondary framebuilders (without Recent counterpartsl).The relative importance of reefbuilders changes throughout time (Figs. 5–6); this is indicated by the different abundances of primary and secondary framebuilders, and also by different reef communities. Upper Triassic reefs seem to be characterized by at least six main communities, whereas Anisian to Carnian reefs exhibit eight communities. Only a few associations may be regarded as long-lived units. Reef communities reflect ecological successions characterizing various stages in the formation of organic buildups (stabilization, colonization, diversification, and domination). A general trend can be seen in the existence of a vertical sequence showing predominantly encrusting and low-diverse biota at the base of the reef formation, and more diverse but vertically zoned biota within the higher levels.Numerical and faunal diversity of reef biota indicate the existence of regular gradients over different parts of Triassic reef complexes. Diversity seems to be different in coeval reefs of different paleogeographical position (Fig. 7) and also changes over time (higher diversities during the Norian and Rhaetian). The provinces of Triassic framebuilders can be inferred only for Late Triassic reefs, and seem to be better expressed by non-coral associations (calcisponges, hydrozoans, tabulozoans) than by rather cosmopolitan coral faunas.The evolution of Triassic reefs seems to have been triggered by the co-operation of some major biological innovations, which include the development of binding organisms (necessary for the stabilization phase of reef formation); reinstatement of colony building and special growth types which were lost during the Upper Permian; increase of diversity of reefbuilders over time; rapid evolution of secondary framebuilders during the Norian and Rhaetian; and development of hermatypic corals during the Triassic.ZusammenfassungDie ältesten triadischen Riffe sind aus dem Anis (Pelson) bekannt; anisische Riffe sind bisher nur aus den Alpen und aus den Westkarpathen beschrieben worden. Ladinische und karnische Riffe besitzen eine weitaus größere Verbreitung (Europa, Asien, westliches Nordamerika, Peru); noch größer ist die Verbreitung norischer und rhätischer Riffe. Die biostratigraphische Einstufung vieler Riffe ist schwierig; die riffbildenden Organismen (insbesondere Kalkschwämme und Korallen sowie Mikroproblematika und auch Foraminiferen) gestatten nur die Trennung von Anis bis Karn und Nor-Rhät.Der gegenwärtige Untersuchungsstand ist durch eine Konzentration der Arbeiten Uber Trias-Riffe im alpin-mediterranen Raum und im westlichen Nordamerika gekennzeichnet. Die Information über die Zusammensetzung der gerüstbildenden und sedimentbindenden Faunen sowie über die Riffbildner-Assoziationen ist im allgemeinen gut; es fehlen jedoch neue Untersuchungen über die Riffbewohner. Das gleiche gilt für dringend notwendige Arbeiten über die diagenetische Entwicklung der Riffkarbonate.Die triadischen Riffe lassen sich fünf, durch Gestalt und paläogeographische Position unterschiedenen Riff-Typen zuordnen: 1. Biostrome auf Karbonatrampen. 2. Stillwasserbioherme (Mud Mounds). 3. Riffhügel-strukturen (Reff Mounds), differenziert in Knollenriffe (Knoll Reefs) und Fleckenriffe (Patch Reefs). 4. Atolle. 5. Barrier-Riffkomplexe. Fig. 4 bietet eine Möglichkeit, triadische Riffe im Hinblick auf die paläogeographische Lage und die Gestalt der Riffkörper zu klassifizieren. Die meisten bis jetzt beschriebenen Riffe entstanden in einer Schelfrandposition oder im Rücken ausgedehnter Plattformen (back-platform position). Am oberen Schelfhang und am Plattformrand gebildete Riffe treten früher (bereits im Ladin) auf als Plattformriffe und Riffe in Becken hinter der Plattform.Die palökologische Interpretation der Rifforganismen wird durch die Seltenheit von genauen paläontologischen untersuchungen vieler Riffe erschwert; auch bei den wichtigsten riffbildenden Gruppen treten ungeklärte Probleme auf: Kalkschwämme (bisher wurden nur die Sphinctozoen der europäischen Vorkommen genauer untersucht), Korallen (die Frage der Entstehung der Korallen-Zooxanthellen-Symbiose) und Algen-Krusten als sekundäre Gerüstbildner (keine rezenten Vergleichsmöglichkeiten!).Die relative Bedeutung der Riffbildner (Fig. 5–6) hat sich in der Zeit geändert; dies wird auch in den, in der Mehrzahl auf die Zeitbereiche Anis-Karn oder Nor-Rhät beschränkten “Riffbildner-Assoziationen” deutlich, die teilweise verschiedene Stadien der Riffentwicklung repräsentieren. Eine allgemeine, sowohl in der Mitteltrias als auch in der Obertrias erkennbare Entwicklungsrichtung ist dadurch gekennzeichnet, daß in der vertikalen Folge der Riffe ein durch inkrustierende und geringdiverse Organismen charakterisiertes Anfangsstadium durch höher diverse aber vertikal und lateral zonierte Assoziationen abgelöst wird.Bei Berücksichtigung der numerischen und der Faunen-Diversität der Riffbildner wird die Existenz von Diversitätsgradienten innerhalb der Riff-Komplexe deutlich. Innerhalb von gleichalten Riffen unterschiedlicher paläogeographischer Position (Fig. 7) scheinen Diversitätsunterschiede aufzutreten, desgleichen bei Riffen gleicher Position aber von unterschiedlichem Alter. Die Existenz von “Provinzen” innerhalb der triadischen riffbildenden Gruppen kann nur für die Zeit der oberen Trias vermutet werden; Kalkschwämme, Hydrozoen und Tabulozoen scheinen hier bessere Hinweise zu liefern als die weitgehend kosmopolitischen Korallen.Die Entwicklung der Trias-Riffe wurdeaußer durch großräumige paläogeographische Veränderungen während der Mitteltrias (Beginn des Rifting)—im wesentichen durch das Zusammenwirken eimger, von der Evolution der Rifforganismen abhängiger Neuerungen beeinflußt, zu denen die Entstehung von sedimentbindenden Assoziationen (erforderlich als Pioniergemeinschaften in der Stabilisierungsphase), die Wiederherstellung der im oberen Perm verlorenen Fähigkeit zur Ausbildung von Kolonien und von bestimmten Wuchsformen, die Zunahme der Diversität in der Zeit, die rasche Entwicklung der sekundären Gerüstbildner während des Nor und des Rhät, und schließlich die Entstehung von hermatypen Korallen gehören.

Permian-Triassic boundary interval as a model for forcing marine ecosystem collapse by long-term atmospheric oxygen drop

Ecological traits of reefs across the Permian-Triassic boundary interval coincide with a modeled decline of atmospheric oxygen throughout the Permian Period. Selective extinction and recovery patterns within the reef system are observed both at the end of the middle Permian (end-Guadalupian) and at the Permian-Triassic boundary. The end-Guadalupian event selectively affected corals and broke down the cool-water carbonate factory. Sponges, however, were largely unaffected and bloomed in reefs toward the end of the Permian. The end-Permian total destruction of the metazoan reef system only left behind poorly diverse microbial communities. The temporal reef patterns are thus similar to spatial patterns of modern benthic communities approaching oxygen minimum zones. This observation suggests that a decline in oxygen concentrations was at least partly involved in the destruction of reefs, even where there is no direct evidence of oceanic anoxia.

A Middle Permian calcisponge/algal/cement reef: Straža near bled, Slovenia

SummarySiddle Permian reef limestones exposed at the localities of the Straza quarry, Straża Hill and Bohinjska Bela near Bled (northwestern Slovenia) have been studied with respect to microfacies and paleontological criteria.Allochthonous carbonates (limestone breccia represented by cement-rich litho/bioclastic rudstones; matrix-rich poorly sorted litho/bioclastic rud/floatstones; coarse-grained lithoclastic packstones) are present in far greater quantities than autochthonous carbonates (calcisponge boundstones andArchaeolithoporella/calcisponge boundstones with synsedimentary botryoidal carbonate cements; bioclastic crinoidal packstones) in the Straża quarry. Straza Hill is characterized by fine-arenitic bioclastic grainstones with foraminifera and algae.The biota of these limestones consist of calcareous algae (solenoporaceans, dasycladaceans, epimastoporids) and problematical algae (Archaeolithoporella, Tubiphytes), smaller foraminifera (about 30 species), fusulinid formminifera (withNeoachwagerina craticulifera and the first report of the subgenusMinojapanella (Wutuella) from Europe), calcisponges (sphinctozoans and inozoans, new species:Uvanella? telleri n. sp.), brachiopods (about 12 species also including fixosessile types such asLeptodus nobilis), bryozoans (predominantly Cystoporida and Rhabdomesonia) as well as mollusks (gastropods, pelecypods, rare ammonites), ostracods, rare trilobites, rare rugose corals and abundant crinoids (includingPalermocrinus togatus) and echinoids. Tube-like microfossils of various systematic position can be attributed to nine morphological types (Plate 42). The calcisponges described by Heritsch (1938) from Bohinjska Bela must be partially referred to crinoids according to a revision of the originals.The limestones breccia is characterized by a rather uniform composition (with regard to the microfacies of the lithoclasts), by equigranular lithoclasts (about 80% smaller than 10 mm, about 50% smaller than 5mm), by comparable sorting within different facies types and by a predominance of subangular and rounded lithoclasts with medium to high sphericity values. Interparticle voids within the litho/bioclastic rudstones as well as intraskeletal voids within the calcisponge/algal limestones are filled with botryoidal and radiaxial-fibrous cements differing from the granular cements of pelsparitic clasts.The Straža quarry and Straža Hill exhibit different depositional patterns (alloch-thonous sedimentation together with small areas of autochthonous calcisponge/algal frameworks in the Straża quarry and shallow-water platform carbonates in Straża Hill). The depositional sites of the allochthonous facies types can be compared neither with back-reef environments nor with fore-reef breccia. Both, litho/bioclastic rud- and floatstones and calcisponge/algal boundstones were affected by a contemporaneous synsedimentary cementation; growth and coalescence of botryoids together with algal colonization and the growth of calcisponges may have resulted in the formation of a mixed inorganic/organic buildup, corresponding with “calcisponge/algal/cement reefs”.ZusammenfassungMittelpermische Riffkalke der Lokalitäten Steinbruch Straža, Straža Berg und Bohinjska Bela bei Bled (NW-Slowenien) wurden im Hinblick auf die Mikrofazies und die paläontologischen Kriterien untersucht.Allochthone Karbonate (feinkörnige Kalkbrekzien mit zemenstreichen, litho/bioklastischen Rudstones; matrixreichen schlecht sortierten, litho/bioklastischen Rud/Floatstones; grobkörnigen lithoklastischen Packstones) überwiegen im Steinbruch Straža deutlich im Vergleich mit autochthonen Karbonaten (Kalkschwamm-Boundstones undArchaeolithoporella/Kalkschwamm-Boundstones mit synsedimentären botryoidalen Karbonatze. menten; bioklastische Crinoiden-Packstones). Am Berg Straža treten feinarenitische bioklastische Grainstones mit Foraminiferen und Algen auf.Fauna und Flora dieser Kalke besteht aus Kalkalgen (Solenoporaceen, Dasycladaceen, Epimastoporen) und problematischen Algen (Archaeolithoporella, Tubiphytes), Kleinforaminiferen (etwa 30 Arten), Fusuliniden (mitNeoschwagerina craticulifera und der erstmals in Europa nachgewiesenen UntergattungMinojapanella (Wutuella)), Kalkschwämmen (Sphinctozoen und Inozoen; neue Art:Uvanella? telleri n. sp.), Brachiopoden (etwa 12 Arten, darunter auch fixosessile Formen wieLeptodus nobilis), Bryozoen (überiegend Cystoporida und Rhabdomesonida) sowie aus Mollusken (Gastropoden, Muscheln, sehr seltene Ammoniten, Ostrakoden, seltene Trilobiten und rugose Korallen, häufige Crinoiden (darunterPalermocrinus togatus) und Echinoideen. Röhrenförmige Mikrofossilien verschiedener systematischer Stellung können neun morphologischen Typen zugeordnet werden (Tafel 42). Ein Teil der von Heritsch (1938) aus Bonhinjska Bela beschriebenen Kalskschwämme muß aufgrund der Revision des Originalmaterials zu Crinoiden gestellt werden.Die Kalkbrekzien zeichnen sich durch eine ziemlich einheitliche Zusammensetzung aus, wenn man die Mikrofazies der Lithoklasten betrachtet. Weitere Merkmale sind die auffallend gleiche Größe der Lithoklasten (80% der Lithoklasten sind Kleiner als 10 mm, etwa 50% kleiner als 5 mm), eine vergleichbare Sortierung innerhalb der verschiedenen Faziestypen und das Überwiegen von subangularen und gerundeten Lithoklasten mit mittleren bis hohen Sphaerizitätswerten. Sowohl die Interpartikelporen in den litho/bioklastischen Rudstones als auch die Hohlräume in den sessilen Organismen der Kalkschwamm/Algen-Kalke sind mit botryoidalen und radiaxial-fibrösen karbonatischen Zementen gefüllt, die sich deutlich von den granularen Zementen in den pelsparitischen Lithoklasten der Kalkbrekzie unterscheiden.Die Kalke des Steinbruchs Straža und vom Berg Straža sind unterschiedlichen Ablagerunsbereichen zuzuordnen (allochthone Sedimentation und kleinflächige Bildung von Schwamm/Algen-Gerüsten im Steinbruch Straža und flachmarine Plattformkarbonate am Berg Straža). Der Sedimentationsraum der allochthonen Karbonate entspricht weder backreef-Bereichen noch Vorriffbereichen. Eine Sedimentation auf einer Karbonatrampe mit vorausgehendem selektivem Sedimenttransport ist wahrscheinlich. Da sowohl die Kalkschwamm/Algen-Boundstones als auch die litho-bioklastischen Rudstones von der intensiven, zeitgleichen Zementation betroffen waren, kann davon ausgegangen werden, daß das Wachstum und die Verschmelzung von Zement-Botryoiden zusammen mit der wiederholten Besiedlung der Zemente durch Algen (Archaeolithoporella, Tubiphytes) und dem Wachstum von Kalkschwämmen zur Bildung von “Kalkschwamm/Algen/Zement-Riffen” geführt haben.“Algen/Zement-Riffe” sind unter den sieben im Perm auftretenden Riffhaupttypen (Kalkschwamm/Algen-Riffe,Tubiphytes/Algen-Riffe, Stromatolithen-Riffe, Bryozoen/Algen-Riffe,Palaeoaplysina-Riffe, Riffe mit phylloiden Algen, Korallen-Riffe) von besonderer Bedeutung, da sie offensichtlich zeitgebundene organogene Strukturen darstellen. Kalkschwamm/Algen-Riffe undTubiphytes/Algenkrusten-Riffe, die durch inkrustierende Algen und rasche synsedimentäre Karbonatzementation gebildet wurden, sind bisher nur aus dem Zeitbereich Oberes Unter-Perm (Artinsk) bis Untere Ober-Trias (Karn) bekannt. Permische und mittel- bis tief-obertriadische Algen/Zement-Riffe stimmen nicht nur in der quantitativen Bedeutung der frühdiagenetischen Karbonatzemente überein, sondern zum Teil auch im Vorkommen von gleichen oder von nahe verwandten Arten bei Kalkschwämmen, Algen und Tubiphyten. Viele permische und mitteltriadische Algen/Zement-Riffe entstanden am Rand von Karobontplattformen im Bereich des oberen Hanges (Upper Capitan Reef, U.S.A.; Anisische Riffe in den Dolomiten). Wie die Untersuchung des Straza-Riffes bei Bled zeigt, scheint jedoch auch eine Position auf Karbonatrampen denkbar zu sein.

Triassic Reefs of the Tethys

The evolution of Triassic reefs started with a long-lasting global crisis of the metazoan reef ecosystem after the Permian—Triassic mass extinction (about 12 Ma), followed by a relatively rapid recovery during the Middle Triassic. Reef systems were differentiated during the Upper Triassic but were severely affected by a global crisis at the Triassic—Jurasic boundary. The present contribution is focused on the biological controls of Triassic reefs, particularly in the Tethyan realm, and on the major changes in reef ecosystems recorded by differences in reef types and reef biota. The term “reef” as used in this chapter refers to bioconstructions characterized by (1) biological control during the formation of the structure (predominantly by sessile benthic organisms), (2) a laterally restricted topographic relief, and (3) (inferred) rigidity of the structure.

Problems with reef models: The late triassic steinplatte “Reef” (Northern Alps, Salzburg/Tyrol, Austria)

SummaryThe Late Triassic limestones of the Steinplatte near Waidring at the Austrian/German boundary have become a classical example of an ancient reef, formed at a carbonate shelf margin (“framebuilt reef rim”).Evaluation of the stratigraphic framework and the investigation of cliff wall sections, together with the analysis of microfacies, paleontological and geochemical data, result in a very different interpretation of the depositional history. A “non-reef” model is favoured: Bioclastic deposition on a carbonate ramp grading into a slope.The Steinplatte is made up of three depositional units: 1) Kössen facies; 2) mound facies, the apparently massive carbonates of the Oberrhätkalk; 3) capping facies, the upper-most strata of the Oberrhätkalk.The Kössen facies comprises predominantly fine-grained lithobioclastic packstones. Changes in microfacies types and in sedimentary structures indicate an increase in water energy trough time. Local biostromal “mounds” (“A-, B-, and C-reefs”; mounds at the base of the Steinplatte cliff) were formed at the same stratigraphical level. Influence of these low relief mounds on the sedimentation in adjacent areas was subordinate except for a mound at the southwestern corner of the Steinplatte acting as a mounding nucleus on the carbonate ramp of the Kössen facies.The mound facies makes up the bulk of the Oberrhätkalk of the Steinplatte. It consists predominantly of fine- and medium-grained bioclastic carbonate sands, shell coquinas and some thin, small-scaled autochthonous boundstone structures (predominantly calcisponge limestones). Patches of dendroid corals occur in the lowermost mound facies. The source of most coral bioclasts and fine-grained coral debris, occurring within various levels of the mound facies, probably were coral patches high on the slope or on a platform. Several shell beds as well as a conspicuous “White Bed” can be used as time lines in the reconstruction of the depositional events. Sedimentation on a depositional slope is indicated by the predominance of northward dipping beds in the area of the western cliff wall. To the south (west of Wieslochsteig) horizontal bedding becomes more evident, pointing to a change from ramp to platform edge type sedimentation.The capping facies comprises thick-bedded strata dipping off and wrapping around the northern and eastern sides of the mound-shaped surface of the mound facies. These strata were deposited sobsequent to a change in sea level on the moundshaped surface of the mound facies. The capping facies differs from the mound facies in attidude, increase in bioclastic coated grainstones with abundant algae and in the occurrence of “coral gardens” representing a veneer on parts of the mound facies. Sea-level fluctuations are indicated by repeated vadose diagenesis and by distinct upslope-down-slope zonations of the biota.The general facies model of the Steinplatte is shown in Fig. 33. It corresponds to a development from a carbonate ramp (prior to the deposition of Shell Bed III) to a slope, probably grading into a platform to the south.The non-reef character of the mound facies of the Steinplatte limestone is accentuated by the lack of organic frames (in the coral thickets), the lacking influence of calcisponge frames on adjacent sediments, lack of ecological successions, and by the predominance of skeletal sediment consisting of mollusk, echinoderm and allochthonous coral debris, in contrast to only small amounts of frameworks.General implications of the Steinplatte study to the investigation of ancient “reefs” concern the interpretation of “potential frame-building” organisms as actual frame-builders and the interpretation of so-called “reef-detritus”.ZusammenfassungDie Faziesentwicklung der obertriadischen Kalke im Gebiet der Steinplatte bei Waidring (Kammerköhr-Sonntagshorngruppe) an der Grenze von Tirol, Salzburg und Bayern wird seit den Arbeiten vonVortisch (1926),Ohlen (1959) undPiller (1981a) als Modell für die Ausbildung eines Riffes am Übergang einer Plattform in ein Becken betrachtet.Eine Neuuntersuchung unter Berücksichtigung der stratigraphischen Beziehungen zwischen den Kössener Schichten und dem Oberrhätkalk sowie der Lagerungsverhältnisse der Oberrhätkalke führte zu einem in wesentlichen Punkten abweichenden Sedimentationsmodell und zu einer Interpretation als zeitliche Folge von Karbonatrampe und (Plattform-)Hang mit bioklastischer Sedimentation ohne ausgedehnte Riffstrukturen (Fig. 33).Die Untersuchungen gründen sich auf Profilaufnahmen und Beprobung von 32 Lokalitäten (Fig. 4), darunter von drei Profilen in der Westwand und Südwand der Steinplatte. Mikrofazies und Fossilinhalt wurden in mehr als 400 Großschliffen untersucht Zusätzlich wurden rasterelektronenmikroskopische und geochemische Daten eingesetzt.Grundsätzlich können im Gebiet der Steinplatte drei Ablagerungseinheiten unterschieden werden: (1) Kössen Fazies (als Unterlage und laterales Äquivalent der Oberrhätkalke), (2) “Mound Facies” (die Masse des Oberrhätkalkes der Steinplatte umfassend), und (3) “Capping Facies” (den obersten, deutlich gebankten Abschnitt der Oberrhätkalke mit Massenvorkommen von Thecosmilien-Rasen (“Fischers Coral Garden” an der Nordflanke der Steinplatte; Coral Garden an der Ostflanke des Plattenkogels) umfassend).Die überwiegend durch bioklastische und biolithoklastische Packstones und Wackestones gekennzeichnete Kössen Fazies läßt sich nach Komponentengröße und Fossilinhalt 14 Mikrofaziestypen zuordnen, deren vertikale Abfolge auf eine Zunahme in der Wasserenergie sowohl nördlich der Steinplatte (Referenzprofil 6, Lokalität 10) als auch im Wieslochsteigprofil (Lokalität 25) hinweist. An der Westseite der Steinplatte verzahnen sich Kössener Fazies und Kalke der Mound Facies. Der Beginn der Oberrhätkalk-Sedimentation ist durch einen im gesamten Raum entwickelten Horizont mit lokalen biostromalen Buildups gekennzeichnet (“B-reef”, “C-reef” und Buildups an der SW-Ecke der Steinplatte-Aufschlußbasis). Diese Buildups sind durch unterschiedliche Biota gekennzeichnet. Ihr sedimentäres Relief und ihre Bedeutung als Sedimentlieferant für die Umgebung waren gering.Die Mound Facies ist überwiegend durch bioklastische Karbonatsande (Wackestones, Packstones, Grainstones; seltener Floastones und Rudstones) sowie durch kleindimensionierte autochthone organogene Buildups (biostromale Boundstones) gekennzeichnet. Die meisten Buildups werden durch Kalkschwämme, Tabulozoen und inkrustierende Organismen aufgebaut. Kalkschwamm/Tabulozoen-Boundstones treten vereinzelt an der Basis der Mound Facies und häufiger, zum Teil übereinandergesetzt, im Profil C der Steinplatte-Südwand (Lokalität 22) auf. Sie besitzen keine Bedeutung als Sedimentlieferanten für die Umgebung.Thecosmilia Buildups sind in der Mound Facies sehr selten. Der in vielen Proben beobachtbare “Korallenschutt” läßt sich nicht von den in der Mound Facies auftretenden, vorwiegend solitären oder plattigen Korallen ableiten. Der Anteil der Korallen am Gesteinsvolumen liegt häufig unter 20%. Anhäufungen von Muschel- und Brachiopoden-Schalen finden sich in bestimmten Horizonten, die zum Teil lateral verfolgbar sind.Für den größen Teil der Mound Facies im Bereich zwischen der Verzahnung mit der Kössen Fazies und dem Gebiet nördlich vom Wieslochsteig ist eine Hangsedimentation nachweisbar (Einfallen zwischen etwa 15 und 25°N).Die an die Mound Facies angelagerte Capping Facies repräsentiert den jüngsten Abschnitt der Steinplatte-Sedimentation. Es handelt sich um nur wenige Meter mächtige, gebankte Kalke, in welchen bioklastische Grainstones und Korallen-Kalke dominieren. Die Capping Facies läuft fächerförmig um das hügelförmige Relief der Mound Facies von N gegen NE nach E herum. Kennzeichnend für die Capping Facies sind ausgedehnte Korallen-Rasen und eine an paläontologischen und faziellen Merkmalen erkennbare bathymetrische Zonierung. Sedimenttransport am Hang wird durch einen an der Nordflanke der Steinplatte aufgeschlossenen Rutschkörper angezeigt. Im Vergleich mit der Mound Facies und der Kössen Facies sind Hinweise auf frühe vadose Diagenese häufiger.Eine Rckonstruktion der Sedimentationsgeschichte muß folgende Tatsachen berücksichtigen:Unterscheidung von drei Ablagerungseinheiten; Anlagerung (on-lapping) der Capping Facies an die Mound Facies; Hangsedimentation sowohl der Mound Facies als auch der Capping Facies; Sedimentransport am Hang; überwiegend Sedimentation von Bioklasten und Lithoklasten; Abnahme der nichtkarbonatischen Beeinflussung (ausgedrückt durch CaCO3-Gehalt und K-Werte) und Zunahme der Häufigkeit frühdiagenetischer Lösung von der Kössen Facies zur Capping Facies.Wichtige Voraussetzungen für die Rekonstruktion der Ablagerungsgeschichte sind ferner die Interpretation der Boundstone-Strukturen (organogene Gerüste im Falle der Kalkschwamm/Tabulozoen Boundstones, jedoch keine organogene Gerüste im Falle der Thecosmilien-Rasen), die unterschiedliche Bedeutung der Bioklasten (Korallen-“Schutt”, Kalkschwamm-Detritus, Foraminiferen, Kalkalgen, Schalen) und Lithoklasten (angulare bis runde mikritische Komponenten, Durchschnittsgröße zwischen 200 und 500 μm; entstanden durch Aufarbeitung von Karbonatschlamm und Schlammaggregaten am Hang sowie durch Umlagerung von transportierten, mikritisierten Bioklasten) und die Intensität der Bioerosion (in der Mound Facies bei etwa 30% der Bioklasten; Mikro- und Makrobohrer).Die Erkennung von Zeitlinien innerhalb der Mound Facies ist durch einen lateral aus den Kössener Schichten durch die Mound Facies verfolgbaren lithologischen Leithorizont (“White Bed”) sowie durch sieben schalenreiche Horizonte (“shell beds” I bis VII) möglich. Als wichtiger Horizont läßt sich Shell Bed III vom Profil A im Übergangsbereich Kössen Facies/Mound Facies bis zum Wieslochsteig verfolgen.Die Entwicklung der Sedimentation in der Zeit läßt sich in neun Stadien beschreiben:Die Sedimentation der Mound Facies begann mit der Bildung eines isolierten Kalksc

Microfacies and depositional structure of allochthonous carbonate base-of-slope deposits: The late permian Pietra di Salomone megablock, Sosio Valley (Western Sicity)

SummaryThe carbonate breaccias and calcarenites of the extremely fossiliferous Pietra di Salomone megablock southwest of Palazzo Adriano, Sosio Valley (Monti Sicani, Western Sicily) represent debris-flow and turbidite sediments deposited in a base-of-slope position.Microfacies criteria (22 localities, 240 samples) and paleontological data (especially sphinctozoan and inozoan sponges,Tubiphytes, Archaeolithoporella, fusulinids, conodonts) provide evience of long- and short-lasting erosion of Middle to Upper Permian carbonate platform marginal reefs formed by binder/encruster and baffler guilds, probably on the uppermost slope. Subsequent to repeated reworking, lithified material (rudstones, boundstones) was transported downslope by sedimentary gravity flow processes and deposited, possibly, as fillings in channels incised in the deep-water basinal marly sediments of the Torrente San Calogero section adjacent to the Pietra di Salomone outcrop.The coincidence in the biostratigraphical age of the pebbles and the marly matrix of the breccias and of the basinal sediments indicates that the destruction of the platform margins and the platform lasted at least from the Murghabian to the Dzhulfian.The comparison of the reef biota preserved in the Pietra di Salomone limestone with reef biota occurring in Lower Permian allochthonous blocks within the Lercara ‘Formation’ (Cozzo Intronata, River San Filippo) points to a turnover in the composition of algal and sphinctozoan sponge associations after the Artinskian, probably during the lower Middle Permian (Kubergandian).RiassuntoLa Pietra di Salomone è il maggiore fra i famosi blocchi calcarei permiani della Valle del Sosio, ubicato a sudovest di Palazzo Adriano (Monti Sicani, Sicilia occidentale) e noto fin dal secolo scorso per la straordinaria ricchezza di fossili. Questo blocco calcareo risulta costituito da carbonati clastici risedimentati, prevalentemente da debris-flow, alla base di una scarpata.L’analisi delle microfacies e i dati paleontoloigici basati principalmente sulle spugne calcaree,Tubiphytes, Archaeolithoporella, fusulinidi e conodonti, indicano che le aree di alimentazione del materiale clastico erano costituite da complessi di scogliera ubicati al margine di piattaforme carbonatiche del Permiano medio e superiore.Il materiale clastico (per lo più elementi già litificati di rudstones e boundstones) prodottosi in seguito a ripetuti eventi erosivi, è stato trasportato lungo la scarpata mediante flussi gravitativi e potrebbe aver costituito il riempimento di canali incisi nei depositi permiani di bacino rappresentati nella sezione del Torrente San Calogero, contigua alla Pietra di Salomone.I dati biostratigrafici ricavati dagli elementi e dalla matrice marnosa delle brecce e quelli provenienti dai depositi di bacino, indicano che lo smantellamento dei margini della piattaforma si è protratto almeno dal murgabiano allo Giulfiano.Il confronto fra le faune di scogliera presenti nella Pietra di Salomone con quelle del Permiano inferiore presenti nei carbonati clastici della ‘Formazione’ Lercara (Cozzo Intronata, Fiume San Filippo) evidenzia una variazione nella composizione delle associazioni algali e delle spugne calcaree, variazione registrata dopo l’Artinskiano, probabilmente alla base del Permiano medio (Kubergandiniano).

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

SummaryThe 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.