Sponge communities from the Lower Liassic of Adnet (Northern Calcareous Alps, Austria)

The lower slope of the drowned Alpine Adnet Reef was recolonized in Hettangian time by sponge communities of hexactinellid (hexactinosid and lyssacinosid) taxa and a few demosponges. Special taphonomic processes caused an excellent preservation of these sponges. The preservation allows to define several growth forms and to study original spicule configurations of the mainly non-rigid skeletons. Sponge faunas of presumably similar associations are known from adjacent basins, but only by isolated spicules of completely collapsed specimens. In Adnet the sponges are embedded in biodetrital limestones of the Schnöll Formation. Orientation and distribution of the sponges reflect autochthonous faunas that have been mixed with dislocated individuals by local water currents. The predominance of erect sponge types indicates intermediate sedimentation rates and/or occasional high-energy events. Sponge types and community structures are comparable with those ones from Middle Paleozoic mud mounds. Several hiatuses, mostly characterized by ferromanganese crusts have been kept free of sponge settlement. Carbon stable isotopes of the sponge-rich sequence show a small negative δ¹³C_carb excursion that covers the period from Lower Hettangian to Lower Sinemurian.This revised version was published online in May 2005 because several displayed passages had been inadvertently deleted in the original published version.     

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     

A close look at late carboniferous algal mounds: Schulterkofel,Carnic Alps,Austria

Summary During the uppermost Carboniferous and lowermost Permian algal mounds were formed in inner shelf settings of the Carnic Alps (Austria/Italy). A specific mound type, characterized by the dominance of the dasyclad green alga Anthracoporella was studied in detail with regard to geometry, relationship between mound and intermound rocks, composition of the sediment, biota and diagenetic criteria. The two meter-sized mounds studied, occur within depositional sequences of transgressive systems tracts in the Lower Pseudoschwagerina Limestones (uppermost Gzhelian) at the flank of the Schulterkofel. The mounds consist of an Anthracoporella core facies with a spongecrust boundstone facies at the base and at the top. The massive limestones of the Anthracoporella core facies exhibit abundant algal tufts and bushes, frequently in life position. The limestones of the intermound facies represented by thin-bedded bioclastic wackestones and packstones with abundant phylloid algae underlie and overlie the mounds. Intercalations of intermound beds within the mound facies indicate sporadic disruption of mound growth. Onlapping of intermound beds on steep mound flanks indicate rapid stabilization and lithification of mound flanks and the existence of a positive paleorelief. Asymmetrical shape of the mounds may be current controlled. Mound and intermound biota differ in the prevailing algae but are relatively similar with regard to associated foraminifera. Conspicuous differences concern bioerosion and biogenic encrustations. Bothare, high in intermound areas but low in the Anthracoporella core facies. The mounds show no ecological zonation. The mounds grew by in-place accumulation of disintegrated algal material and trapped bioclastic material between erect algal thalli. The comparison of the various Anthracoporella mounds demonstrates that almost each mound had ist own history. Establishing a general model for these mounds is a hazardous venture.     

A new Pliensbachian ichthyosaur from Dorset, England

The first ichthyosaur to be recorded from the Pliensbachian Stage of the English Lower Liassic is described as Leptonectes moorei sp. nov., extending the geological range of Leptonectes to the Pliensbachian. According to criteria for assessing the maturity of ichthyosaurs, it is concluded that L. moorei is an immature individual of a relatively small, slender and short snouted species close to the earlier long-snouted L. tenuirostris (Conybeare) which ranges from the Rhaetian to the Sinemurian. The presence of a short-snouted leptonectid in the Pliensbachian suggests two contrasting patterns of rostral morphology within the clade Leptonectidae in the latest Early Jurassic, rostral reduction within the genus Leptonectes and rostral elongation in Excalibosaurus Eurhinosaurus .     

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.     

Palynological investigation in the lower jurassic of the vicentinian alps (Northeastern Italy)

The present paper emphasizes the applicability of palynological data as an aid to the solution of the problems related to the correlation of non-ammonitiferous Liassic strata in the Southern Alps with the ammonoid-based standard stages as recognized in the outer-Alpine part of Europe.In the Noriglio Grey Limestone Formation of the Vicentinian Alps, northeastern Italy, rich and well-preserved Liassic palynological assemblages can be abundantly found in the marly intercalations of its upper part; in the lower part palynological assemblages have appeared to be very rare. A qualitative and quantitative analysis of the assemblages has indicated the presence of a single palynological assemblage zone. Minor compositional differences do not warrant a zonal subdivision.The overall composition of the assemblages is characterized by the general dominance of Circulina and smooth trilete spores in combination with a large amount of relatively rarely occurring forms of spores, pollen grains and other acid-resistant microfossils.Because of the presence of rich and well-preserved material, it has been possible to detect a relatively wide range of variability within species of Tigrisporites, Foveosporites, Porcellispora and Crassosphaera.Among the forms which could not be matched with previously described taxa the new formgenus Skarbysporites is formally erected together with the new species Skarbysporites elsendoornii, Skarbysporites puntii, Foveosporites visscheri and Tigrisporites jonkeri. Moreover, an emended diagnosis of Circulina is proposed, implicating the assignment to this formgenus of most forms generally included in Classo pollis. Also the generic diagnosis of Tigrisporites is emended.An evaluation of the Liassic palynological assemblages from the outer-Alpine part of Europe with special reference to their potential in characterizing the ammonoid-based chronostratigraphical subdivisions may indicate that two temporal subdivisions of the Liassic Series on the basis of palynological characteristics are now slowly becoming discernable: an assemblage zone characterizing the Hettangian, Sinemurian and Lower Pliensbachian, and an assemblage zone characterizing the Upper Pliensbachian and Toarcian.Because of the possibility of a correlation with the latter zone, the assemblages from the Noriglio Grey Limestone Formation can be reasonably regarded to be indicative of a Late Pliensbachian—Toarchian age of the source-strata.When considering the ammonoid evidence from the overlying “Cape San Vigilio Oolite” it may be concluded that the upper part of the lower subdivision of the Noriglio Grey Limestone Formation and the Rotzo Member represent the Upper Pliensbachian—Lower Toarcian.Because of its potential in correlating non-ammonitiferous strata from the Southern Alps with the successions in northwestern Europe, it is believed that palynology may earn a prominent place in regional Liassic chronostratigraphy.     

ENDOSYMBIOTIC CALCIFYING BACTERIA: A NEW CUE TO THE ORIGIN OF CALCIFICATION IN METAZOA?

Sponges show the highest diversity of associated bacteria among marine invertebrates. Immunological evidence traces the origin of the sponge bacterial symbioses to the Precambrian era. Hence, sponges appear to be ideally suited for studying the evolutionary origins of prokaryote–metazoan associations. Sponges produce either calcareous or siliceous skeletons, which only coexist in a relict group of demosponges, the sclerosponges. We report here, for the first time, intensive calcification in nonsclerosponge siliceous demosponges. Calcification is mediated by endosymbiotic bacteria (calcibacteria) located in archeocyte‐like sponge cells. These calcibacteria are devoid of bacterial walls and divide within sponge cells until they became surrounded by a calcitic sheet, being subsequently extruded to the sponge subectosomal (subepithelial) zone. Thousands of bacteria‐produced calcitic spherules cover the surface of the host sponges, forming a cortex‐like structure that mimics a rudimentary peripheral skeleton. Calcibacteria are vertically transferred to the sponge larvae during embryogenesis. Calcium detoxification may have generated this symbiotic association, with some additional benefits for the sponges, such as skeletal formation and deterrence from predation. This unique symbiosis holds implications for sponge biology and may advance discussions on the role of bacteria in early biocalcification processes in metazoans.     

Facies variability in Lower Liassic carbonate successions of the Western Dinarides (Croatia)

Summary In the Western Dinarides the Lower Liassic carbonates are underlain by Upper Triassic “Hauptdolomit”, whereas the first appearance of the foraminiferOrbitopsella praecursor (Gümbel) marks the beginning of the Middle Liassic. Their composition, observed at several localities in Western Croatia, shows a correlation of sedimentation events, which took place during Early Liassic on the Adriatic-Dinaridic carbonate platform. Facies variability is interpreted as result of autocyclic sedimentary processes on which the carbonate platform reacted by periodical oscillations of sea-bottom near the fair-weather wavebase. As a consequence, the Lower Liassic carbonate successions in the Dinarides is characterized by stacking of two main types of coarsening-upward parasequences: (1) the basal part of the Lower Liassic succession is represented by parasequences composed of mudstones or pelletal-bioclastic wackestones as their lower members, and peloidal-bioclastic wackestone/packstones to grain-stones as their upper members; and (2) the upper part of the Lower Liassic succession with parasequences consisting of mudstones or pelletal-bioclastic wackestones overlain by ooid grainstones. Judging from the composition of parasequences and thickness relations of their members, the first type is interpreted to comprise late transgressive system tract (ITST) and/or early highstand system tract (eHST), while the second type corresponds to a late highstand system tract (1HST) and/or early lowstand system tract (eLST) of a third-order sequence.     

Triassic/Jurassic carbonates from the Hochfelln Mountain (Northern Calcareous Alps)—its facies, silicified fauna and implications for the end-Triassic biotic crisis

A suite of Early Mesozoic (Late Triassic, Norian to Early Jurassic) calcareous beds was studied from the Hochfelln Mountain in the Northern Calcareous Alps (NCA, South Germany). The Hauptdolomit Group consists of thick peritidal deposits and is overlain by basin deposits of the Rhaetian Kössen Formation and Rhaetian reefoidal limestone with corals. Unlike many other sections in the Tethys realm, coral growth seems to continue into the Jurassic or starts again relatively early within the Early Jurassic. Silicified corals and other marine invertebrates are present in the calcareous, micritic Hochfelln Beds. A re-examination of previously collected ammonite material indicates the presence of Coroniceras sp. which suggests an Early Sinemurian age for the Hochfelln Beds. Abundant sponge spicules (spiculites) suggest that sponges were the source for the silicification. The site produced one of the most diverse Early Jurassic (Sinemurian) gastropod faunas of the NCA (25–30 species, some undescribed). The relatively diverse Early Sinemurian gastropod fauna and coral growth indicate rapid recovery from the end-Triassic biotic crisis.     

A microbial model for the Lower Devonian stromatactis mud mounds of the Montagne Noire (France)

Summary Lower Devonian mud mounds and stromatactis fabrics are exceptionally well exposed in quarry walls and industrially sawed blocks in the Montagne Noire in southern France. Interlayered red biomicrites and white to grey sparitic calcites form mounds up to 70 m high. The red biomicrites contain predominantly bryozoans, sponges and echinoderms. The sparitic layers show typical features of stromatactis fabrics, as outlined byBathurst (1982). We recognize two types of stromatactis fabrics: (1) Stromatactis type A: exentsive cavity systems filled by multiple cement generations, which are interpreted to be related to microbial mats, and (2) Stromatactis type B: smaller patches of blocky spar which are mainly diagenetic in origin, but show characteristic features of stromatactis. Type A is far more important in terms of rock volume. The cyclic interlayering of red biomicrites and sparitic layers is supposed to result from frequent changes in the composition of the mound biota. The bryozoan/sponge community was displaced by short term propagations of microbial mats during times of extremely low sedimentation. Sedimentation and thus the biotic community was probably determined by high frequency (6th order) sea level changes. Despite these changes, mound growth continued, because once established the ecological advantage over the surroundings was maintained by both communities alternating with each other. The microbial mats and the cavities they left after their decay were important for the stabilization of the mounds, the latter allowing for enormous quantities of dissolved carbonate to be transported and precipitated. We anticipate a close interrelation between mound formation and stromatactis formation, and we believe that it is not incidential that both, mud mounds and stromatactis, are mainly restricted to the same interval, namely the Paleozoic.     

Calcification processes of siliceous sponges in Viséan Limestones (Counties Sligo and Leitrim,Northwestern Ireland)

Summary In the Lower Carboniferous limestones and shales of the Benbulben Range, Counties Sligo and Leitrim, northwestern Ireland, a suite of carbonate nodules, about 1 to 4 cm in diameter, has been sampled and investigated by thin sectioning. The nodules consist of micritic, peloidal and fenestral fabrics. Many of them contain relics of desma bearing demosponges and hexactinellid sponge skeletons. The nodules are interpreted as calcified siliceous sponges. Micrite and peloids have been formed via microbial activity during the decay of the soft sponge tissue. The actual processes are deduced from Recent examples investigated at Lizard Island, Autralia, byReitner (1993). The skeletal opal was dissolved very early. In places where the skeleton was already embedded in micrite the spicules are preserved as molds cemented by granular ferroan calcite. The nodules were extensively inhabited by agglutinating polychaetes and bored by sponges. Micrite clasts have been exported to the surrounding seafloor before the sponges were completely covered by sediments. Fenestral fabrics represent primary sponge cavities, that may be enlarged due to volume reduction of the soft tissue during calcification. Some originated from non-calcification of decaying tissue. The granular calcite cement, filling the fenestral fabrics, contains relics of spicules and faintly visible peloids floating unsupportedly in the cement. These peloids were probably produced in situ by calcification of organic mucilages that filled the cavities almost entirely. It is evident that most diagenetic processes occurring within the sponges happened on the seafloor, most likely within the still living individuals. Possibly the nodules represent a precursor stage of mud mound development.     

Growth history of Lower Mississippian Waulsortian mounds: Distribution,stratal patterns,and geometries,New Mexico

Summary The factors controlling the localization and growth of Lower Mississippian Waulsortian mounds have been difficult to establish because of limited exposure of individual mounds and mound-bearing platforms in western Europe, where the Waulsortian facies have been studied most intensively. Mounds on the Lower Mississippian homoclinal ramp of the Lake Valley Formation in the Sacramento Mountains, however, are exposed exceptionally well at platform, outcrop, and mound scales in an area roughly 5 km by 20 km, and provide the opportunity to better understand these aspects of Waulsortian mounds. Mounds occur in the northern 2/3 of the essentially continuous 32 km dip transect of the ramp. Mounds grew in an outer ramp setting below wave base, predominantly in the deeper part of the photic zone. Mounds range from broad composites of laterally back-stepping subunits on the shallow part of the ramp to taller and more vertically stacked composite structures down-ramp. The composite nature of the mounds is documented by distinct stratal units that have characteristic facies and geometries common to mounds throughout the transect. As a result, mound growth and form can be described in terms of several primary controlling parameters—submarine topography, water circulation (upwelling of nutrients and oxygen rich waters; oxygen deficient bottom waters), light penetration and the distribution of phototrophic microorganisms, and fluctuations in accommodation. Episodic mound growth is documented by diastems bounding the stratal units within the mounds as well as by the long-established useage of Alamogordo, Nunn, and Tierra Blanca phases of mound growth, correlative with the contemporaneous level-bottom units. However, mound growth that has been correlated with the level-bottom Nunn Member in reality took place during the late stage of deposition of the Alamogordo Member, and nondeposition or erosion occurred on the mounds during deposition of the Nunn Member. Mounds in the shallower (northern) part of the ramp grew primarily on the margins of a broad, low, intra-ramp topographic high, which had been defined previously from facies and isopach trends in underlying strata. Both the margins and the irregular topography of the high are reflected in the distribution, growth geometries, and facies patterns of the mounds, and by the facies and thickness trends of the strata enclosing the mounds. The siting of individual mounds on the shallower part of the ramp was controlled by local topography on and along the margins of the intra-ramp high. Mound growth along the margin began at or just behind local highs, retrograded onto the intra-ramp high, and then prograded onto the basinward side of the initial mound. The lesser height and more pronounced backstepping of mounds on the shallower part of the ramp, in contrast to mounds that grew more vertically and with less back-stepping down ramp suggest that growth and overall morphology were also controlled by accommodation.     

Kieselschwämme aus dem unterjurassischen Misonekalk der Trento-Plattform (Südalpen): Taxonomie und phylogenetische Relevanz

The Lower Jurassic Misone Limestone of the Trento Platform (Southern Alps, Italy) contains a siliceous sponge fauna which is here described. Besides the well-known Moroccan sponge carbonates, these Lower Jurassic spongioliths from the Trento Platform are presently the second mass occurrence of siliceous sponges, which is known from the southern margin of the Tethys. They differ from each other in regard of the composition of the sponge fauna and the absence of microbial crusts in the spongioliths of the Trento Platform. There, hexactinosans and lithistid demosponges occur in equal proportions. Sphinctozoans are another very characteristic element. Because of the richness in both sphinctozoans and siliceous sponges, the Trento occurrences may be considered as a transitional fauna between the late Palaeozoic-Triassic sponge fauna dominated by sphinctozoans and the post-Liassic sponge fauna dominated by more modern groups of siliceous sponges. Two new siliceous sponge genera with their species are established:Misonia baldensis n. gen. n. sp. (Hexactinosa) andBenacia princeps n. gen. n. sp. (lithistid Demospongiae). The rarity of siliceous sponge dominated spongioliths in the Early Jurassic is due to the restricted occurrence of low energy, deeper shelf areas.     

A high‐stress shelly fauna associated with sponge mud‐mounds in the Coniacian Arnager Limestone of Bornholm,Denmark

The benthic macrofaunas of the Upper Cretaceous chalk of NW Europe show characteristically high species‐richnesses and commonly high densities. They are predominated by bivalves, brachiopods, polychaetes, echinoids, crinoids, asteroids, sponges and towards the end of the Cretaceous also by bryozoans. The mound‐bedded chalk of the Coniacian Arnager Limestone on the island of Bornholm in the Baltic Sea, Denmark, differs from this general picture. It was deposited on a small fault block adjacent to the main Bornholm block, which was emerged during much of the Mesozoic and thus occupied a much more proximal position than most other Upper Cretaceous chalks in NW Europe. The Arnager Limestone contains a unique, exceptionally rich and well‐preserved fauna of mainly hexactinellid, lyssacinosan sponges. The low mud‐mounds are interpreted as formed by baffling and trapping of fine sediment particles by the dense sponge thickets. In contrast, the associated shelly fauna is unusually sparse, of very low richness and extremely low density, except for inoceramid bivalves. It represents a strongly depauparated version of the shelly faunas of contemporaneous chalks in NW Europe. The rare specimens of non‐inoceramid shelly species are interpreted to represent occasional successful spatfalls of benthic species from the deeper‐water chalk farther offshore in the Baltic area. The sponge mud‐mounds of the Arnager Limestone show remarkable resemblances with modern sponge mounds recently discovered on the continental shelf of western Canada. They form an important link between the well‐known older Mesozoic sponge mud‐mounds or ‘reefs’ and the modern mounds and are among the youngest examples of Mesozoic sponge mounds.     

Depth-related ecological zonation of a carboniferous carbonate ramp: Upper Viséan of Béchar Basin,Western Algeria

Summary Following the demise of the stromatoporoid-coral reef community in Late Frasnian time, Lower Carboniferous carbonate shelf profiles possessed a ramp geometry, with major organic buildups represented by mud-rich mounds. Microfacies petrography of the exceptionally well-preserved Upper Viséan (Lower Carboniferous) carbonate ramp of the Béchar Basin, Algerian Sahara, may well contribute significantly to our understanding of the paleoecological zonation of Carboniferous non-rimmed platforms, and of the still enigmatic mounds commonly referred to as Waulsortian banks or mounds. Facies are grouped into two broad groups: (a) a mound facies group which comprises sponge wackestone-bafflestone, sponge-fenestellid bafflestone-wackestone, crinoid wackestone-packstone, and bedded flanks of intraclastic wackestone-packstone, all four facies composing the actual mud-rich mounds, and (b) a supramound facies group composed of coral-microbial framestone, crinoid packstone-grainstone, algal-foraminiferal grainstone and oolite grainstone. Calcareous algae are important bathymetric indicators and are used to delineate three bathymetric zones based on light penetration: the aphotic zone, which contains no calcareous algae; the dysphotic zone, where there is little ambient light, and which is characterized by the presence of red algae (Fasciella, Ungdarella, Stacheia, Epistacheoides) and absence of green algae; and the euphotic zone, which receives the full spectrum of sunlight, and is characterized by the occurrence of both green algae (Koninckopora, Kamaenella, Kamaena, Palaeoberesella, Calcisphaera, Anthracoporellopsis, Issinella, Exvotarisella) and red algae. Integration of algal zonation, distribution of the other biota, and recurrence of distinct assemblages, enable recognition of seven depth-related benthic assemblages. Together with the physical properties of the facies, the benthic assemblages were used to define seven bathymetric zones, from upper to lower ramp: (1) algal assemblage (upper ramp); (2) crinoid-ramose bryozoan assemblage (mid-ramp); and (3) productid brachiopod assemblage, (4) colonial rugose coral-microbial encruster assemblage, (5) crinoid-fenestellid assemblage, (6) sponge-fenestellid, and (7) sponge assemblage (lower ramp). The vertical zonation of the mud-rich mounds and associated facies differ from that reported from the classical Upper Tournaisian-Lower Viséan Waulsortian mound-bearing successions.     

Upper Sinemurian and Lower Pliensbachian ammonite faunas from Herford-Diebrock area (NW Germany)

At Herford-Diebrock a section from the Upper Sinemurian (Raricostatum to Aplanatum Subzone) to the Lower Pliensbachian (Polymorphus Subzone) is studied in respect of its ammonite faunas. Precise correlations in terms of faunal horizons are carried out between Yorkshire and SW Germany through Hessische Straße. Special emphasis is given to the taxonomical position ofEoderoceras armatum (Sowerby).Eoderoceras miles (Simpson) is now placed in synonymy withSowerby’s species. The section does not fulfill the requirements for the GSSP of the Sinemurian/Pliensbachian boundary.     

BRYOZOAN MUD-MOUNDS FROM THE UPPER ORDOVICIAN JIFARAH (DJEFFARA) FORMATION OF TRIPOLITANIA, NORTH-WEST LIBYA

Abstract:  A bryozoan fauna from carbonate mud-mounds is described from subsurface well cores from the Upper Ordovician (Lower Ashgill) Jifarah (Djeffara) Formation of Tripolitania, north-west Libya. Among a diverse assemblage dominated by trepostomes, nine species of bryozoans are identified, including Jifarahpora libyensis gen. et sp. nov. Delicate and robust branching, encrusting and nodular bryozoan growth forms are all common. The bryozoan-rich limestones are mostly mudstones and wackestones, with bafflestone and floatstone textures, but the mounds apparently lack organic framework and microbial fabrics. Regional geophysical data indicate rapid thickness changes between wells, where mound complexes locally up to 100 m thick had limited topographic relief over the surrounding sea floor. The mounds formed in a high-latitude, cool-water carbonate belt that extended widely across the northern margin of Gondwana. Quaternary analogues from the Great Australian Bight suggest that these early Ashgill mounds may have developed in slope environments during an episode of glacial lowstand that preceded the late Ashgill, Hirnantian glacial event.     

An unusual brachiopod assemblage in a Late Jurassic (Kimmeridgian) stromatactis mud-mound of the Eastern Carpathians (Hăghimaş Mountains), Romania

An unusual fossil assemblage dominated by superabundant rhynchonellid brachiopods in a stromatactis mud-mound is recorded from the Hăghimaş Mountains (Eastern Carpathians), Romania. The mound mainly consists of bioclastic wackestones to packstones with a very rich macrofauna including crinoids, sponges, juvenile ammonites, and echinoids. The brachiopods represent a low-diversity but high-abundance association, dominated by the rhynchonellids Lacunosella and Septaliphoria. The taphonomical features of the fossil assemblage indicate an autochthonous fauna, with successive generations of brachiopods in life position and complete well-preserved individuals in different growth stage alongside an accessory population of crinoids and sponges. Brachiopod-brachiopod endosymbiotic life strategy is documented for the first time from a post-Paleozoic brachiopod assemblage. The mound reveals abundant stromatactis, filled by radiaxial fibrous or drusy calcite cement and internal polymud sediments. This is the first Late Jurassic (Kimmeridgian) stromatactis mud-mound identified in the Eastern Carpathians.     

Global radiolarian zonation for the Pliensbachian, Toarcian and Aalenian

Jurassic radiolarians from 220 samples in Queen Charlotte Islands, B.C., Williston Lake, B.C., east-central Oregon, Baja California Sur, southern Spain, Austria, Slovenia, Turkey, Oman, Japan and Argentina were studied in order to construct global zonation for the Pliensbachian, Toarcian and Aalenian stages. Well-preserved faunas from continuous stratigraphic sections in Queen Charlotte Islands provide the most detailed record for this time interval, and all collections are tied to North American ammonite zones or assemblages. Collections from nearly all other areas lack independent dating except for early Toarcian carbon-isotope dating in Slovenia and late Aalenian ammonites in Spain.A database of 197 widely distributed updated taxonomic species was used to construct a Unitary Association (UA) zonation for the interval. A global sequence of 41 UAs was obtained for the top of the Sinemurian to the base of the Bajocian. The first and the last UAs represent the Late Sinemurian and the Early Bajocian respectively. The remaining 39 UAs were merged into nine zones (four Early Pliensbachian, one Late Pliensbachian, one Early Toarcian, one Middle-Late Toarcian, and two Aalenian) according to prominent radiolarian faunal breaks and ammonite data. The new zones are the Canutus tipperi - Katroma clara Zone (latest Sinemurian/earliest Pliensbachian); Zartus mostleri - Pseudoristola megaglobosa, Hsuum mulleri - Trillus elkhornensis and Gigi fustis - Lantus sixi zones (Early Pliensbachian); Eucyrtidiellum nagaiae - Praeparvicingula tlellensis Zone (Late Pliensbachian); Napora relica - Eucyrtidiellum disparile Zone (Early Toarcian); Elodium pessagnoi - Hexasaturnalis hexagonus Zone (Middle and Late Toarcian); Higumastra transversa - Napora nipponica Zone (early Aalenian); and Mirifusus proavus - Transhsuum hisuikyoense Zone (late Aalenian). These zones can be correlated worldwide and link previously established UA zonations for the Hettangian-Sinemurian and the Middle to Upper Jurassic. The new zonation allows high-resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of Jurassic radiolarians.     

First evidence of brachiopod diversification after the end-Triassic extinction from the pre-Pliensbachian Internal Subbetic platform (South-Iberian Paleomargin)

Lower Jurassic brachiopods are widely known in the External Betic Zone. Their occurrence was so far virtually restricted to the easternmost Subbetic Zone where they underwent a diversity burst and radiation event during the late Sinemurian–early Pliensbachian interval, leading to a bloom in brachiopod diversity from the early Pliensbachian onwards. Taxonomical and paleobiogeographical analyses performed in a newly recorded assemblage from the most offshore areas of the Subbetic Basin (Granada province, Spain) reveals that this diversification event occurred earlier than expected hitherto, probably in the Turneri–Obtusum chronozones, as similarly observed in the most intra-Tethyan basins such as the Northern Calcareous Alps and Transdanubian Ranges, illustrating the recovery of the background conditions for the establishment of diversified brachiopod communities after the end-Triassic extinction event. A new rhynchonellide species, Alebusirhynchia vorosi nov. sp., is formally described among the ten different taxa recorded for the first time in this area. The Mediterranean paleobiogeographical affinities revealed by the brachiopod assemblage emphasizes that the onset of the Mediterranean/Euro-Boreal bioprovinciality and the initial brachiopod diversification in the pre-Pliensbachian Internal Subbetic platform took place earlier in the Sinemurian as well, following the Euro-Boreal monotypic record previously reported in this region.