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.     

ECHINOID AND CRUSTACEAN BURROWS AND THEIR DIAGENETIC SIGNIFICANCE IN THE MAASTRICHTIAN-DANIAN OF STEVNS KLINT, DENMARK

The increase in species and specimens of fossils in the uppermost part of the Maastrichtian White Chalk is interpreted as a result of reduced depth. The absence of bryozoans, brachiopods, and regular echinoids in the Cerithium Limestone indicates sedimentation in tidal pools. After sedimentation of the Cerithium Limestone, burrowing activity followed. A burrow of Brissopneustes danicus similar to burrows of the recent Echinocardium cordatum is described. Callianassa and its burrows are found in the Upper Danian calcarenite but not in the Lower Danian or Maastrichtian of Denmark. The dominant type of burrows along the Maastrichtian-Danian boundary has presumably been formed by the crustacean Ctenocheles.
The early post-Maastrichtian burrowing activity was succeeded by (1) induration of the bottom sediment and a slight abrasion (2) dissolution of aragonite shells and siliceous sponges, (3) offshore sedimentation and filling of the burrows with Lower Danian chalk mud, bryozoan fragments and other fossil remains, and (4) settling in the deeper part of the soft chalk sediment and precipitation of flint in or around burrows near the surface of the sediment.     

Larval shell morphology of <Emphasis Type="Italic">Inoceramus pictus</Emphasis>: all suspicions confirmed

Inoceramids were eurytopic bivalves and have a wide application as biostratigraphic index fossils in the Upper Cretaceous. Their paleoecology, however, is far from being understood. Here the prodissoconch of Inoceramus pictus is described. It was found in an upper Cenomanian shallow water methane-seep deposit in the Tropic Shale, southern Utah, USA. The larval shell consists of a small prodissoconch-1 and a large prodissoconch-2. The shell morphology indicates a planktotrophic larval phase with wide dispersal potential, and which confirms previous hypotheses of inoceramid larval ecology. Comparison with other inoceramid prodissoconchs shows that larval shell morphology cannot generally explain dispersal, and that more factors must have played a role in the distribution of species.     

The faunal structure of a mid-Cretaceous rudist reef core

The macrofaunal distribution of the mid-Cretaceous El Abra Limestone reef core is quantified from two measured sections in Taninul Quarry, San Luis Potosi, central Mexico. The faunal structure is transitional between typical Lower Cretaceous reefs dominated by corals with low-density rudist bivalve packing; and densely-packed, rudist-dominated Upper Cretaceous reefs. The macrofauna is predominantly associations of unconnected individuals of caprinid rudists, with a low diversity of other shelly mollusks and corals. An examination of the alternation of paleocommunities defined by the dominant caprinid taxa reveals no pattern of biotic succession within the reef core. Large-scale sedimentologic features of mud and debris content, coupled with rudist growth type, suggest that paleocommunities may have been physically controlled.     

Palaeoecology and evolution of Mesozoic salinity-controlled benthic macroinvertebrate associations

Salinity-controlled benthic macroinvertebrate associations are typical of many Mesozoic marginally marine environments. They can be recognized by abiotic criteria (e.g., environmental setting, specific autigenic minerals), by biotic criteria (faunal composition, diversity, shell morphology, size-frequency histograms, taphonomic features, associated micro fauna and microflora), and by isotope geochemistry of shells. Although salinity-controlled associations must have been widespread in the European German Triassic, very little is known about their ecology. They appear to have been dominated by the bivalve Unionites and the brachiopod Lingula. In the Jurassic, brackish-water associations are characterized by bivalves, in particular neomiodontids, corbulids, mytilids, bakevelliids, isognomonids, and oysters. In the Cretaceous, in addition, corbiculid bivalves and gastropods become increasingly abundant. Salinity-controlled benthic macroinvertebrate associations can be used to reconstruct salinity regimes of ancient environments, but emphasis should be placed on an integrated sedimentological and ecological approach, as salinity is rarely the only parameter influencing faunal composition and diversity. Although the species composition of salinity-controlled benthic associations changes distinctly through time, the composition of morphotypes remains surprisingly constant throughout the Mesozoic and up to the Recent, evidence of a conservative evolution of benthic faunas within marginal marine high-stress environments. □ Salinity, benthic associations, palaeoecology, Mesozoic.     

A Paleocene coral—algal—sponge reef from southwestern Alabama and the ecology of Early Tertiary reefs

The Late Paleocene Salt Mountain Limestone from southwestern Alabama is a coral-algal-sponge buildup which further characterizes the faunal makeup of early post-Cretaceous reefs. Thin sectioning has disclosed a variety of lithologies, including large foram-algal packstone, algal bindstone, and sponge bafflestone. A low-diversity fauna of massive scleractinian corals caps the sequence, but may be developed intermittently throughout the section as well. The constructional importance of coralline algae and the low diversity of scleractinian corals are characteristic of Paleocene reefs in general. Sponges, however, are virtually unknown in earliest Tertiary sediments. Their abundance in the Salt Mountain demonstrates not only their local contribution to Early Tertiary reefs, but may also reflect an opportunistic response of sponges as reef constructors following the extinction of oligotrophic, rudist-coral reef communities of the Late Cretaceous. □ Paleocene, reef, paleoecology, sponges, extinction.     

Middle Jurassic Porifera from Kachchh, western India

From the Late Bathonian sponge biofacies at Jumara Dome, Kachchh (western India) 11 species of ‘lithistid’, hexactinellinid and calcarean sponges are described. New taxa are the order Sigmatospirida, the genusJumarella, and the speciesJumarella astrorhiza, Mastosia rhytidodes, Radicispongia kraspedophora, andHexactinella prisca. The diverse sponge assemblage is associated with a rich fauna of epibenthic bivalves and brachiopods and formed meadows on fine-grained carbonate substrates. The sponge meadows grew on a carbonate ramp at the lower end of the photic zone, in quiet waters below storm wave base. The rate of sedimentation exceeded that of sponge production. This prevented the development of reef-like bodies. In contrast to Mesozoic sponge reefs, growth of the sponge meadows appears to have been confined to the regressive phases of small transgressive-regressive cycles.     

The barbs (Barbus spp.) of Lake Tana: a forgotten species flock?

Synopsis All living species occupy an ecological niche, and are positioned within a trophic hierarchy. Extinct organisms presumably held similar behavioral and coevolutionary characteristics in the past, and were susceptible to the same kinds of natural ecological pressures operating today. Paleoecological investigations are limited by the incompleteness of the fossil record, and particularly by a lack of behavioral data that are so fundamental to ecological studies of living communities and habitats. Opportunities to examine the coevolutionary structure of ancient communities from empirical data are extremely rare. One such opportunity is provided by the Lower Cretaceous Santana Formation of north-eastern Brazil, a series of richly fossiliferous strata approximately 110 million years old. Many fossil fishes from the Santana Formation contain identifiable prey, including decapod crustaceans and fishes. A trophic hierarchy of these organisms is reconstructed here, and their ecological relationships are discussed. Comparison is made with a similar fish fauna from the Upper Jurassic Solnhofen Limestone of Germany. Low-level, intermediate and high-level predators are identified in each fauna. Predator-prey relationships in the Santana fauna are strongly hierarchical, and are more focussed at the intermediate predator level than in Solnhofen. Comparison with a model of predator-prey relationships between fishes and benthic fauna of the Baltic Sea (which like the Araripe Basin represents a semi-enclosed environment) suggests that heavy predation on teleosts such asRhacolepis, occupying an intermediate trophic level, may have permitted benthic decapods to proliferate and exclude other benthic organisms. Less intense predation on fishes at the intermediate trophic level would allow their numbers to increase, thereby increasing the intensity of predation on the benthos at the base of the trophic hierarchy.     

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.     

Polycopidae (Crustacea,Ostracoda) aus der borealen Oberkreide des mittleren und südlichen Ostseeraumes

Six species of Upper Cretaceous ostracods of the genusPolycope Sars are described, three of which are new. The well preserved shells come from siliceous chalk nodules — erratics of Campanian to Maastrichtian age — and from a boulder of Upper Turonian chalk embedded in a Pleistocene till at Nossentin near Malchow/NE Germany. Their origin is the Danish Polish Trough in the middle and southern Baltic Sea. Due to the large variability of morphological details a wide definition of the genusPolycope as given here is preferred.     

Mud mounds: A polygenetic spectrum of fine-grained carbonate buildups

Summary This research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results. The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic, Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces (e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies. As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate. The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies, considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is restricted in space.     

Benthic palaeoecology of Danian deep-shelf bryozoan mounds in the Danish Basin

Early Danian cool-water bryozoan mounds exposed in the coastal cliff Stevns Klint in Denmark were formed shortly after the Cretaceous–Tertiary mass extinction. They represent a relatively deep-water, highly diverse benthic ecosystem within the epeiric seaway that covered the Danish Basin. The mounds are 50–110 m long and reached a height of about 5–10 m above the seafloor; they are asymmetrical with a steep southern and a gentle northern flank, and were dominated by small suspension feeders. The benthic elements generally occur as fragments set in a carbonate mud matrix. The main skeletal contributors are delicate branching bryozoans with minor contributions of bryozoan sheets, and nodular/arborescent bryozoans. Locally abundant octocorals occur on the mound crests and upper parts of the steep flanks. Echinoids are present in minor amounts, but are locally abundant. Serpulids, crinoids, asteroids, brachiopods, bivalves, massive calcareous sponges, and benthic foraminifers are generally minor contributors to the benthic mound fauna. Influx of planktonic foraminifers, coccoliths and other planktonic organisms was high and was probably a major source of nutrient supply to the mainly suspension-feeding benthic fauna.

The faunal association reflects a relatively low energy environment with a high, possibly seasonal influx of particulate nutrients. The best growth conditions with respect to nutrient influx were on the mound crest and upper steep flank reflected by the diverse and relatively largest benthic faunal elements. Periodic reworking and winnowing occurred across the entire mound structure but most prominent on the gentle northern flanks limiting the benthic growth and notably the colony density and size of delicate branching bryozoans. Vagile benthic faunas were also adapted to different areas on the mound. Irregular echinoids preferred the intermound areas within fine-grained wackestone–packstone facies where they ploughed through the sediment, whereas regular echinoids were epifaunal and preferred the upper parts of the mounds, possibly feeding mainly on bryozoans. Skeletons of both groups became concentrated at the toe of the steep flanks and in the intermound areas by physical reworking during major storms.

Changes in faunal composition on the mound crests occurred rhythmically on both small and large scale during mound growth. Rhythmically recurring faunal assemblages reflect alternating hydrodynamic conditions on the seafloor with respect to nutrient influx and energy, which probably were linked to short-term seasonal and long-term climatic variations; the long-term alternation may be within the Milankovitch frequency band. Blooming events of bryozoan sheets resulted from relatively short periods with large amounts of available food and suitable substrate. Successful colonisation by octocorals on the other hand reflected longer-term favourable conditions on the mounds possibly associated with overall higher energy levels.

A possible Pleistocene analogue to the bryozoan-dominated Danian mounds occurs at the shelf-slope break of the Great Australian Bight. Both of these cool-water mound systems deviate from most other biogenic mounds known from the fossil record in their non-cemented nature, regular geometry and a lack of core and flank facies.     

Aggregated Clumps of Lithistid Sponges: A Singular,Reef-Like Bathyal Habitat with Relevant Paleontological Connections

The advent of deep-sea exploration using video cameras has uncovered extensive sponge aggregations in virtually all oceans. Yet, a distinct type is herein reported from the Mediterranean: a monospecific reef-like formation built by the lithistid demosponge Leiodermatium pfeifferae. Erect, plate-like individuals (up to 80 cm) form bulky clumps, making up to 1.8 m high mounds (1.14 m on average) on the bottom, at a 760 m-deep seamount named SSS. The siliceous skeletal frameworks of the lithistids persist after sponge death, serving as a complex 3D substratum where new lithistids recruit, along with a varied fauna of other sessile and vagile organisms. The intricate aggregation of lithistid mounds functions as a “reef” formation, architecturally different from the archetypal "demosponge gardens" with disaggregating siliceous skeletons. Leiodermatium pfeifferae also occurred at two additional, close seamounts (EBJ and EBS), but, unlike at SSS, the isolated individuals never formed accretive clumps. The general oceanographic variables (temperature, salinity, dissolved nutrients, chlorophyll, and oxygen) revealed only minimal between-seamount differences, which cannot explain why sponge abundance at SSS is about two orders of magnitude higher than at EBJ or EBS. Large areas of the dense SSS aggregation were damaged, with detached and broken sponges and a few tangled fishing lines. Satellite vessel monitoring revealed low fishing activity around these seamounts. In contrast, international plans for gas and oil extraction at those locations raise serious concerns over the need for protecting urgently this unique, vulnerable habitat to avoid further alteration. Modern lithistids are a relict fauna from Jurassic and Cretaceous reefs and the roots of the very genus Leiodermatium can be traced back to those fossil formations. Therefore, understanding the causes behind the discovered lithistid aggregation is critical not only to its preservation, but also to elucidate how the extraordinary Mesozoic lithistid formations developed and functioned.     

Facies of Liassic sponge mounds, central High Atlas, Morocco

Summary Liassic sponge mounds of the central High Atlas (Rich area, northern Morocco) have a stratigraphic range from the Lower/Upper Sinemurian boundary interval up to the lower parts of the Lower Pliensbachian (Carixian). The base of Liassic sponge mounds consists of a transgressive discontinuity, i.e., a condensed section of microbioclastic wackestones with firm- and hardgrounds, ferruginous stromatolites, sponge spicules and ammonites. The top of Liassic sponge mounds is an irregular palaeorelief covered by cherty marl-limestone rhythmites, namely hemipelagic spicular wackestones with radiolaria. In the Rich area, section Foum Tillicht, the sponge mound succession has a total thickness of about 250 meters. Within this succession we distinguished between three mound intervals. The lower mound interval shows only small, meter-scale sponge mounds consisting of boundstones with lyssakine sponges, commensalicTerebella and the problematicumRadiomura. This interval forms a shallowing-upward sequence culminating in a bedded facies withTubiphytes, calcareous algae (Palaeodasycladus), sponge lithoclasts, coated grains, and thin rims of marine cement. The middle mound interval is aggradational with decametric mounds and distinct thrombolitic textures and reefal cavities. The mound assemblage here consists of hexactinellid sponges, lithistid demosponges, non-rigid demosponges,Radiomura, Serpula (Dorsoserpula), Terebella, encrusting bryozoa, and minor contributions by calcareous sponges, and excavating sponges (typeAka). Thrombolites are dendrolitic and may reach sizes of several tens of centimeters, similar to the maximum size of siliceous sponges. The upper mound interval appears retrogradational and geometries change upsection from mound shapes to flat lenses and level-bottom, biostromal sponge banks. The biotic assemblage is similar to that of the middle mound interval and there is no difference between mound and bank communities. The demise of sponge mounds is successive from regional spread in the Sinemurian to more localised spots in the Lower Pliensbachian. This reduction correlates with an increasing influence of pelagic conditions. At Foum Tillicht, sponge mounds lack any photic contribution and there is virtually no differentiation into subcommunities between mound surface and cavity dwelling organisms. There is some evidence that the heterotrophic food web of mound communities was sourced by oxygen minimum zone edge effects, namely microbial recycling of essential elements such as N and P. Basin geometry suggests a waterdepth of several 100's of meters, well below the photic zone and possibly only controlled by the depth range of the oxygen minimum zone. Palaeoceanographic conditions of well-stratified deeper water masses diminished gradually during widespread transgression across the Sinemurian to Pliensbachian boundary culminating in the Lower Pliensbachianibex ammonite zone.     

Non‐actualistic wood‐fall associations from Middle Jurassic of Poland

Kaim, A. 2010: Non‐actualistic wood‐fall associations from Middle Jurassic of Poland. Lethaia, Vol. 44, pp. 109–124. The oldest modern‐type wood‐fall (sunken wood) associations so far known, were reported from the Upper Cretaceous of Japan. Here, four Middle Jurassic fossil associations collected from logs of sunken driftwood are documented from clay and silt sediments of the Cz?stochowa Ore‐bearing Clay Formation in Poland. The associations are composed of almost entirely different set of molluscs when compared to modern examples of wood‐fall communities. The exceptions are leptochitonid polyplacophorans and alleged cocculinoid gastropods, both of which are typical of modern sunken wood communities. It is hypothesized here that the associations represent Jurassic wood‐fall communities, which in contrast to their modern counterparts do not contain associated chemosymbiotic animals. This disparity results from the absence of xylophagain wood‐boring bivalves, which since the Cretaceous have produced significant amounts of faecal pellets, the decomposition of which increases the amount of sulphide around sunken driftwoods. The associations are considered as benthic rather than pseudoplanktonic because the wood logs were colonized only on their upper side, the abundant crinoids belong to benthic genera rather than to pseudoplanktonic, associations include numerous infaunal organisms, and there are too many clingers in the associations. The most typical and numerous members of the investigated associations are the gastropods Cosmocerithium and Astandes, both having uncertain taxonomic positions. It is suggested here that Cosmocerithium could be a grazer of bacterial mats, and represents an ecological counterpart of modern Provannidae. □chitons, cocculinoids, deep sea, ecology, evolution, Wood‐fall communities.     

Impact of an invasive alga (Womersleyella setacea) on sponge assemblages: compromising the viability of future populations

The effects of invasive species on native fauna are understudied, even though their consequences should be taken into consideration for the proper conservation and management of marine systems. Furthermore, bioinvasions may have greater consequences if they affect key structural species with slow dynamics such as marine sponges. We propose that reproductive output could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species (i.e. sponges) as a result of biological invasions. The aim of this study was to investigate the effects of invasive algal (Womersleyella setacea) overgrowth on sponge reproduction by comparing the presence of reproductive elements (spermatic cysts, oocytes, embryos, and larvae) in sponges covered by a thick carpet of the invasive algae and in sponges dwelling in the same habitat but without the invasive algae. Three variables were calculated to assess the impact of the invasive alga on sponge reproduction: the reproductive effort, the proportion of individuals in reproduction, and the size of the reproductive structures. We studied eight sponge species representing the main components of the deep rocky reefs of the area. Our results showed that W. setacea had a strong negative effect on sponge reproduction in six out of eight sponge species studied, with lower and even nil reproductive structures on the sponges subjected to the algal overgrowth. Thus, considering that sexual reproduction is necessary for the persistence of most sponge populations, a significant and constant reduction of the reproductive effort may compromise their viability and affect future trends in these benthic systems.     

Shoal‐water dynamics and coastal biozones in a sheltered‐island setting: Upper Devonian Pillara Limestone (Western Australia)

Along the Canning Basin's Lennard Shelf in Western Australia, the 80‐km‐long Oscar Range is composed of folded Palaeoproterozoic quartzite and phyllite and surrounded by limestones of the Great Devonian Barrier Reef including reef complex, related back‐reef and lagoonal deposits of the Frasnian Pillara Limestone. The range represents an exhumed cluster of palaeoislands. Near the east end of the Oscar Range, a palaeoislet is encircled by the Pillara Limestone showing outward dips that dramatically shallow to expose nearly horizontal bedding planes offshore. From shore and outward, the facies zones observed in the Pillara Limestone include unfossiliferous laminated sediments followed by biozones with abundant Amphipora and Stachyodes, and domal stromatoporoids. An additional outermost lagoonal facies with a diverse molluscan fauna preserved in fine limestone/dolostone is described in this study. High‐spired Murchisonia in a time‐averaged assemblage with other gastropods, bivalves, brachiopods and scaphopods dominate this zone. Uneven distribution of biozones is due to intermittent shoals controlled by the complex relief of basement rocks or recent erosion into underlying layers. The orientations of dendroid stromatoporoids and high‐spired gastropods were analysed to appraise the dynamics of prevailing shoal‐water settings on the inner, more sheltered side of the Oscar Range facing the Devonian mainland to the north. Oscillatory wave action is interpreted as the main agent of transport. Palaeocurrent data for the lighter dendroid stromatoporoids suggest that fair‐weather prevailing winds originated from the SE. Pebble clasts, oncoids, bivalves and gastropods indicate episodes of wave agitation and stronger wind from a SE and southerly direction.     

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.     

The bivalve boring Cuenulites amygdaloides nov. isp. in siliceous sponges from the Upper Cretaceous of Germany

Lower Campanian siliceous sponges from epicontinental deposits of the Subhercynian Cretaceous Basin in Germany contain amygdaloidal depressions which are distinguished as a new ichnospecies of the ichnogenus Cuenulites. These bioerosion traces are interpreted as borings of semi-endolithic bivalves, produced without significant rotation movement, probably mostly by chemical action. As there are no signs of tissue reaction in the bored sponges, the structure is considered to be produced post mortem to the sponge, probably in a foreshore-shoreface setting, with redeposition offshore.     

The palaeoecology of the latest Jurassic–earliest Cretaceous hydrocarbon seep carbonates from Spitsbergen,Svalbard

Latest Jurassic–earliest Cretaceous hydrocarbon seeps from Spitsbergen, Svalbard, are known to contain unusual fauna, lacking most of the species characteristic for roughly coeval seep deposits. This study summarizes and analyses the fauna from 16 seep carbonate bodies from Spitsbergen to explain its composition. The seeps formed in a shallow epicontinental sea with widespread deposition of fine‐grained, organic‐rich sediments. They are spread over a relatively large area and are positioned roughly in the same interval, indicating seepage over extensive areas of the palaeo‐Barents Sea. The seep fauna is very species rich and with low dominance, comprising 54 species, with a composition similar to that of Jurassic–Cretaceous normal‐marine environments of other Boreal seas. Seep‐restricted fauna is not abundant and is represented by four species only. Hokkaidoconchids and possible siboglinid worm tubes characteristic for high sulphide fluxes are rare. Apart from seep‐restricted sulphide‐mining lucinid and thyasirid bivalves, chemosymbiosis was also a source of nourishment for background solemyid and nucinellid bivalves, all of which take sulphide from infaunal sources. This all suggests a relatively weak sulphide flux. The high diversity and low dominance of the fauna and significant richness and abundance of background species is typical for shallow water seeps.