Microfacies analysis and palaeoenvironmental interpretation of Lower Oligocene, shallow-water carbonates (Gornji Grad Beds, Slovenia)

Summary The microfacies and palaeoenvironment of Lower Oligocene carbonates of the Gornji Gradbeds from Slovenia are investigated. These beds form part of a transgressive succession overlying both terrigenous sediments (sand-stones and conglomerates) and marine carbonates of Eocene age as well as transgressing directly over Triassic lime-stones. They are followed by foraminiferal rich marls. The carbonates were investigated using multivariate statistical techniques on point counts of thin sections. They are dominated by poorly sorted biogenic rudstones with pack-/wackestone matrix; pack- and grainstones are subordinate. The biogenic components of the carbonates are dominated by coralline red algae (9 genera with 11 species), corals, small benthic, large benthic, and encrusting foraminifera as well as bivalves. Gastropods, bryozoans, brachiopods, echinoderms, serpulids, and green algae are subordinate. The well preserved components allow details pertaining to taxonomy, growth-forms and taphonomic features to be observed. The following carbonate facies are distinguished: 1) nummulitic, 2) bivalve, 3) foraminiferal—coralline algal, 4) grainstone, 5) coralline alga, 6) coralline algal—coral, and 7) coral facies. All the carbonate facies represent fully marine conditions within the photic zone. They are interpreted with respect to substrate composition and stability, water turbulence, terrigenous input and light.     

Microtaphonomy of bioclasts and paleoecology of microencrusters from Upper Jurassic spongiolithic limestones (External Prebetic,Southern Spain)

Microencrusters and microtaphonomic features of the Oxfordian spongiolithic limestones of the External Prebetic were studied using thin-section analysis. The spongiolithic limestone is a bioclastic-rich packstone with common echinoderm, mollusc and brachiopod remains. The bioclasts show a high fragmentation index and frequent microborings. The encrustation index (E _i) is higher for fragments of serpulids, ammonoids and bivalves, and increases with the initial grain-size of bioclasts. The main microencrusters consist of benthic microbial communities (BMC) and nubeculariids, as well as subordinate calcareous and siliceous agglutinated foraminifera, serpulids and bryozoans. BMC are usually the first colonizers, and encrusting foraminifera mainly appear on bioclasts larger than 2 mm. BMC dominate in well-developed encrustations on upward facing surfaces of larger bioclasts that are also colonized by foraminifera (nubeculariids and Subdelloidina). Bullopora, serpulids and bryozoans are more common on lower surfaces. The fact that the values of encrustation index, encrustation thickness and diversity of the microencrusters increase with the size of bioclasts is related to a higher stability and exposure time of the available bioclastic substrate. The microencruster distribution on upper and lower surfaces of large bioclasts may be related to photic control, space competition and/or predation avoidance.     

Hypothesized Kinetic Models for Describing the Growth of Globular and Encrusting Demosponges

The marine sponges Dysidea avara and Chondrosia reniformis (globular forms) were cultured in the laboratory on a diet of viable Phaeodactylum tricornutum cells and dissolved nutrients (algae and fish powders). Our growth data were combined with literature data for Pseudosuberites andrewsi (a globular sponge) and for the encrusting sponges Oscarella lobularis, Hemimycale columella, and Crambe crambe. The suitability of three growth models—linear, exponential, and radial accretive—for describing the growth of globular and encrusting sponges was assessed. Radial accretive growth was determined to be the best model to describe growth of both encrusting and globular sponges. Average growth rates of 0.051 ± 0.016 and 0.019 ± 0.003 mm/day (calculated as the increase of the radius of the sponge per day) were obtained experimentally for D. avara and C. reniformis, respectively.     

Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus.     

Brachiopods from cryptic coral reef habitats in the northern Red Sea

In contrast to the Palaeozoic to Jurassic fossil record, modern tropical and subtropical shallow-water brachiopods are typically small-sized and mostly restricted to cryptic habitats in coral reefs, but information on microhabitat-composition is scant. At Dahab, northern Red Sea, living brachiopods of the genus Argyrotheca were only detected on massively encrusted coral colonies attached to encrusting foraminifers and coralline red algae. Three samples from autochthonous sediments underneath coral colonies are comparatively rich in the brachiopod genera Megerlia and Argyrotheca, and additionally show low numbers of Novocrania and Thecidellina. Based on a coarse-grain analysis including more than 16,000 components >1 mm, these brachiopod shells co-occur with skeletal components of 11 higher taxa. Decapods, fixosessile foraminifers, molluscs, scleractinians, and coralline red algae clearly dominate the assemblages. Brachiopods in this study always contribute less than 2% to the sediment composition. This confirms previous results that even in brachiopod habitats the contribution of brachiopod shells to the total sediment composition is almost negligible. Our study indicates that brachiopods co-occur with pteriomorph bivalves and other epifauna in the cryptic habitats with limited space for encrusters or epibionts on the undersides of scleractinians and it tentatively supports the hypothesis of brachiopods preferring habitats with low grazing pressure, because shelly components of grazers (polyplacophorans and regular echinoids) are rare in our samples.     

Microfossil assemblages and relative sea-level fluctuations in a lagoon at the Oxfordian/Kimmeridgian boundary (Upper Jurassic) in the eastern part of the Paris Basin

The Late Oxfordian–Early Kimmeridgian interval of the eastern part of the Paris Basin is characterized by a carbonate succession deposited in shallow-marine platform environments. The Gudmont-Villiers section is represented by deposits ranging from barrier to typical lagoonal environments often poor in macrofossils. Previously unpublished calcareous microfossils are more abundant and provide alternative paleoenvironmental indicators. They also provide a biostratigraphical framework across the Oxfordian–Kimmeridgian boundary. The evolution of microfossil associations (algae and benthic foraminifera) in the lower part of the section, based on statistical analyses, is correlated to the sea-level variations. The first highly diversified association composed of small agglutinated and calcitic foraminifera (miliolids, textulariids, Spirillina, Trocholina, Molherina basiliensis etc.) characterizes high sea-level deposits; a second association richer in large agglutinated foraminifera (Alveosepta jaccardi, Everticyclammina, Nautiloculina oolithica) is significantly abundant in low sea-level deposits. A third association characterizes beds with a significant occurrence of encrusting microorganisms and algae (Lithocodium aggregatum, Troglotella incrustans, Cayeuxia piae, dasycladaceans). The upper part of the section is marked by more argillaceous beds and by the occurrence of one opportunist taxon (Lenticulina). This study shows that the microfauna-flora evolution in an internal carbonate platform environment constitute an efficient tool to determine variations in the relative sea level.     

The role of colony morphology and substratum inclination in the success of Millepora alcicornis on shallow coral reefs

 Millepora species are conspicuous members of shallow coral reefs where they occupy a variety of substrata and produce morphologically complex skeletons. This study focuses on the roles of growth on vertical and horizontal surfaces and the production of encrusting bases and branches (a “sheet-tree” morphology) for the success of the Millepora alcicornis on coral reefs. The effects of inclination were investigated by comparing the size and growth rates of M. alcicornis on vertical and horizontal surfaces at 3–5 m depth, in St. John, US Virgin Islands. The consequences of morphological complexity were investigated by comparing polyp density, chlorophyll content and biomass between encrusting bases and branches; the role of branches in asexual reproduction was also quantified. Colonies on vertical surfaces had larger encrusting bases, longer perimeters and lower densities of branches compared to those on horizontal surfaces. Growth rates also varied significantly between surfaces, largely because colonies on horizontal surfaces shrank in area while those on vertical surfaces increased in area, albeit slowly. Branches were not specialized in comparison to encrusting bases in terms of the density of dactylozooids and gastrozooids, chlorophyll content and biomass, but they were effective asexual propagules. During one storm, 79% of the branches were removed from colonies of M. alcicornis, and 4% attached to the substratum to produce new colonies at a density of ≈0.5 colonies.m^-2. Anecdotal observations suggest that such storms rarely damaged encrusting bases on vertical surfaces, but often destroyed those on horizontal surfaces. Thus, the encrusting bases on vertical surfaces are likely to be large because of greater age rather than faster growth, while those on horizontal surfaces are likely to be small because they are relatively young and short lived. These findings suggest that the success of M. alcicornis is a result, in part, of the beneficial consequences of their “sheet-tree” morphology, that supports: (a) slow growth and resistance to wave damage of encrusting bases on vertical surfaces, and (b) the use of branches as asexual propagules. Accepted: 24 November 1998     

Energy flow to two abundant consumers in a subtropical oyster reef food web

Oyster reefs are among the most threatened coastal habitat types, but still provide critical habitat and food resources for many estuarine species. The structure of oyster reef food webs is an important framework from which to examine the role of these reefs in supporting high densities of associated fishes. We identified major trophic pathways to two abundant consumers, gray snapper (Lutjanus griseus) and crested goby (Lophogobius cyprinoides), from a subtropical oyster reef using stomach content and stable isotope analysis. The diet of gray snapper was dominated by crabs, with shrimp and fishes also important. Juvenile gray snapper fed almost entirely on oyster reef-associated prey items, while subadults fed on both oyster reef- and mangrove-associated prey. Based on trophic guilds of the gray snapper prey, as well as relative δ¹³C values, microphytobenthos is the most likely basal resource pool supporting gray snapper production on oyster reefs. Crested goby had omnivorous diets dominated by bivalves, small crabs, detritus, and algae, and thus were able to take advantage of prey relying on production from sestonic, as well as microphytobenthos, source pools. In this way, crested goby represent a critical link of sestonic production to higher trophic levels. These results highlight major trophic pathways supporting secondary production in oyster reef habitat, thereby elucidating the feeding relationships that render oyster reef critical habitat for many ecologically and economically important fish species.     

Coral reef encruster communities and carbonate production in cryptic and exposed coral reef habitats along a gradient of terrestrial disturbance

Encrusting calcareous organisms such as bryozoans, crustose coralline algae (CCA), foraminiferans, and serpulid worms are integral components of tropical framework-building reefs. They can contribute calcium carbonate to the reef framework, stabilise the substrate, and promote larval recruitment of other framework-building species (e.g. coral recruits). The percentage cover of encrusting organisms and their rates of carbonate production (g m⁻² year⁻¹) were assessed at four sites within a coastal embayment, along a gradient of riverine influence (high-low). As the orientation and type of substrate is thought to influence recruitment of encrusting organisms, organisms recruiting to both natural (the underside of platy corals) and experimental substrates were assessed. The effect of substrate exposure under different levels of riverine influence was assessed by orientating experimental substrates to mimic cryptic and exposed reef habitats (downwards-facing vs upwards-facing tiles) at each site. Cryptic experimental tiles supported similar encruster assemblages to those recruiting to the underneath (cryptic side) of platy corals, suggesting that tiles can be used as an experimental substrate to assess encruster recruitment in reef systems. Encruster cover, in particular CCA, and carbonate production was significantly higher at low-impact (clear water), high wave energy sites when compared to highly riverine impacted (turbid water), low wave energy sites. Cryptically orientated substrates supported a greater diversity of encrusting organisms, in particular serpulid worms and bryozoans. The inverse relationships observed between riverine inputs and encrusters (total encruster cover and carbonate production) have implications for both the current and future rates and styles of reefal framework production.     

POST-LARVAL CEMENTATION IN THE OSTREIDAE AND ITS IMPLICATIONS FOR OTHER CEMENTING BIVALVIA

Despite the polyphyletic acquisition of the cemented habit inthe bivalves, the actual mechanism of post-larval cementationhas remained obscure. This study examines the mechanism of attachmentin the dissoconchs of members of the Ostreidae. It is demonstratedthat a thin periostracal sheet, preformed at the mantle margins,is secreted throughout the cementation process and that theeventual cement is calcareous rather than composed of mucopolysaccharide.The cement structure is reminiscent of ‘inorganic’diagenetic cavity fill cements. The composition of the cementis remarkably similar to that of the oyster shell, indicatingthat it is derived from the same extrapallial fluid. A mechanismis proposed to account for these observations, invoking a permeableperiostracum which allows the ‘leakage’ of extrapallialfluids. This means of cementation has interesting implicationsfor the evolution of the cemented habit in the bivalves, andin other encrusting taxa as well as for our understanding ofbiomineralization processes. ¹Present address: Department of Earth Sciences, University ofCambridge, Downing Street, Cambridge, CB23EQ (Received 29 September 1990; accepted 11 June 1991)     

The Role of Encrusting Coralline Algae in the Diets of Selected Intertidal Herbivores

Kalk Bay, South Africa, has a typical south coast zonation pattern with a band of seaweed dominating the mid-eulittoral and between two molluscan-herbivore dominated upper and lower eulittoral zones. Encrusting coralline algae were very obvious features of these zones. The most abundant herbivores in the upper eulittoral were the limpet, Cymbula oculus (10.4 ± 1.6 individuals m⁻²; 201.65 ± 32.68 g.m⁻²) and the false limpet, Siphonaria capensis (97.07± 19.92 individuals m⁻²; 77.93 16.02 g.m⁻²). The territorial gardening limpet, Scutellastra cochlear, dominated the lower eulittoral zone, achieving very high densities (545.27 ± 84.35 m⁻²) and biomass (4630.17 ± 556.13 g.m⁻²), and excluded all other herbivores and most seaweeds, except for its garden alga and the encrusting coralline alga, Spongites yendoi (35.93 ± 2.26% cover). In the upper eulittoral zone, encrusting coralline algae were only present in the guts of the chiton Acanthochiton garnoti (30.5 ± 1.33%) and the limpet C. oculus (2.9 ± 0.34%). The lower eulittoral zone limpet, Scutellastra cochlear also had a large percentage of encrusting coralline algae in its gut with limpets lacking gardens having higher (45.1 ± 1.68%) proportions of coralline algae in their guts than those with gardens (25.6 ± 0.8%). Encrusting coralline algae had high organic contents, similar to those of other encrusting and turf-forming algae, but higher organic contents than foliose algae. Radula structure, grazing frequencies as a percentage of the area grazed (upper eulittoral 73.25 ± 3.60% d⁻¹; lower eulittoral 46.0 ± 3.29% d⁻¹), and algal organic content provided evidence to support the dietary habits of the above herbivores. The data show that many intertidal molluscs are actively consuming encrusting coralline algae and that these seaweeds should be seen as an important food source.     

Exposure of seawalls to waves within an urban estuary: effects on intertidal assemblages

Abstract Despite being largely protected from sea swell by headlands, shores within Sydney Harbour, New South Wales, Australia are subjected to considerable wave action from wind waves and the numerous recreational and commercial boats and ships using the waterways. The aim of this study was to test whether assemblages on artificial shores, that is, seawalls, either exposed to or sheltered from waves would show similar patterns to those published for natural shores exposed to or sheltered from sea swell. Specifically, the hypotheses were tested that sheltered seawalls would have greater cover of algae, whereas exposed seawalls would have greater cover of sessile invertebrates and greater abundance of mobile invertebrates. It was found that encrusting algae had greater cover on sheltered seawalls, whereas cover of turfing algae was greater on exposed walls. Sessile filter‐feeders generally had greater cover on exposed seawalls, although a dominant space occupier, the oyster Saccostrea glomerata, showed either no difference, or greater cover on sheltered seawalls among different locations. The pattern for the dominant grazer on seawalls, the pulmonate limpet Siphonaria denticulata showed the predicted pattern low on the shore, but the opposite pattern at mid‐tidal levels. Despite some inconsistencies the results were similar to those predicted from studies on natural shores, showing that assemblages on urban structures respond to wave action in a way that is predictable from studies on natural shores. Experiments were carried out where assemblages were transplanted to sites with differing exposure to waves to determine whether differences in recruitment or post‐recruitment mortality were responsible for patterns of difference. We found that some sessile invertebrates did not survive when transplanted to sheltered seawalls, suggesting that difference in survival of organisms was responsible for observed patterns. This was not, however, found when the experiment was repeated at other locations. It is likely that processes affecting the assemblages are temporally and spatially very variable, or that more than one process interacts to cause observed patterns. Identifying such complexity requires rigorously structured sampling designs and appropriate manipulative experiments.     

Importance of foraminifera for the formation and maintenance of a coral sand cay: Green Island, Australia

 CaCO₃ production by reef-building organisms on Green Island Reef in the Great Barrier Reef of Australia is estimated and compared with the contribution of benthic foraminifera to the sediment mass of the vegetated sand cay. Major constituents of the cay are benthic foraminifera (mainly Amphistegina lessonii, Baculogypsina sphaerulata, and Calcarina hispida), calcareous algae (Halimeda and coralline algae), hermatypic corals, and molluscs. Among these reef-building organisms, benthic foraminifera are the single most important contributor to the sediment mass of the island (ca. 30% of total sediments), although their production of CaCO₃ is smaller than other reef-building organisms. Water current measurements and sediment traps indicate that the velocity of the current around Green Island is suitable for transportation and deposition of foraminiferal tests. Abundant foraminifera presently live in association with algal turf on the shallow exposed reef flat, whose tests were accumulated by waves resulting in the formation and maintenance of the coral sand cay. Accepted: 30 June 1999     

Upper Eocene larger foraminiferal–coralline algal facies from the Klokova Mountain (southern continental Greece)

Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms. They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids, a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells.     

An Upper Miocene siliciclastic-carbonate ramp: depositional architecture, facies distribution, and diagenetic history (Capo Vaticano area, southern Italy)

During the Late Miocene, the marginal areas of the Mediterranean Basin were characterized by the development of mixed siliciclastic-carbonate ramps. This paper deals with a temperate siliciclastic-carbonate ramp (late Tortonian–early Messinian in age) which crops out in the Capo Vaticano area, Southern Apennines (Italy). Carbonate components are mainly represented by calcitic skeletal fragments of coralline red algae, bryozoans, bivalves, and larger foraminifera, whereas corals, brachiopods, echinoderms, and planktonic foraminifera are subordinate. In the studied ramp, the depositional geometries of the main unit, the ‘Sabbie gialle ad Heterostegina’, show a gradual steepening from low/middle (dip about 2–5°) to steep slope settings (up to 25°). The microfacies observations, the quantitative analyses of the main biogenic components as well as the rhodolith shapes and growth forms allowed the differentiation between the middle and the outer ramp depositional setting and the refining of the stratigraphic framework. The middle ramp is characterized by coralline red algal debris packstone facies often associated with larger foraminiferal floatstone/packstone facies, while the outer ramp is characterized by rhodolith floatstone/rudstone facies. These facies pass basinward into typical open-marine deposits (planktonic foraminiferal facies). The taxonomic composition of the coralline red algal assemblage points to a temperate paleoclimate and emphasizes the Miocene Mediterranean phytogeographic patterns. The absence of non-skeletal grains (ooids and green algae), the paucity of Porites patch reefs, the rare occurrence of primary marine cementation, all confirm that the studied ramp was poorly lithified within a warm–temperate setting. The flat depositional profile of the ramp can be related to the absence or paucity of primary marine carbonate cements.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

Evolution of an isolated carbonate bank during Oligocene,Miocene and Pliocene times,Cayman Brac,British west Indies

Summary Modern carbonate sedimentation in the Caribbean Sea commonly occurs on banks that are surrounded and isolated by deep oceanic water. This depositional regime also occurred during the Tertiary, and many islands, such as Cayman Brac, have sequences that evolved in such settings. Cayman Brac is a small (about 39 km²) island, located on the Cayman Ridge, that has an exposed Oligocene to Pliocene succession which encompasses three unconformity-bounded formations. The upper Lower Oligocene Brac Formation is formed ofLepidocyclina limestones and sucrosis dolostones that locally contain numerous bivalves and gastropods. The overlying Lower to Middle Miocene Cayman Formation is formed of pervasively dolomitized mudstones to grainstones that contain an abundant, diverse biota of corals, gastropods, bivalves, foraminifera, and algae. Rhodolites are locally common. The Pliocene Pedro Castle Formation is formed of limestones, dolostones, and dolomitic limestones that contain a biota which is similar to that in the Cayman Formation. The unconformities between the formations represent substantial periods of time during which the previously deposited carbonates were lithified and eroded to produce karst terrains. All facies in the Brac, Cayman, and Pedro Castle formations on Cayman Brac developed on a bank that was no more than 20 km long and 3 km wide. There is no evidence of reef development other than isolated thickets ofStylophora and/orPorites and no systematic stratigraphic or geographic changes in the facies patterns of the formations. Comparison with modern Caribbean banks shows that the depositional regime was primarily controlled by water depth and energy levels. Limestones of the Brac Formation probably accumulated in low-energy conditions in water less than 10 m deep. The overlying Cayman Formation contains facies that formed in water 15 to 30 m deep with good cross-bank circulation. The Pedro Castle Formation formed in slightly shallower water (5–25 m) and lower energy conditions. The disconformities between the packages correlate with world wide eustatic drops in sea level.     

Upper Triassic reefs of the Oman Mountains: Data from the South Tethyan margin

Summary The Upper Triassic reefal limestones of the Oman Mountains were investigated with respect to their microfacies, palaeontology and community structure. The reef fauna described and figured for the first time occurs in parautochthonous slope deposits of the Arabian platform (Sumeini Group) and in allochthonous reefal blocks (‘Oman Exotics’, Hawasina Complex). The ‘Oman Exotics’ are tectonically dislocated blocks, derived from isolated carbonate platforms on seamounts in the Hawasina basin or in the South Tethys Sea. The lithofacies and fauna of these blocks comprise a cyclic platform facies with megalodonts, reef and reef debris facies. The reefal limestones are dated as Norian/Rhaetian by benthic foraminiferal associations (Costifera, Siculocosta, Galeanella) and typical encrusting organisms (Alpinophragmium, Microtubus). Some small ‘Oman Exotics’ are of Carnian age. The shallow-marine organisms include scleractinian corals of different growth forms, ‘sphinctozoans’, ‘inozoans’ chaetetids, spongiomorphids, disjectoporids and solenoporacean algae as the main reef builders, various encrusters like microbes, foraminifers, sponges and many different problematical organisms for the stabilisation of the reef framework and a group of dwellers including benthic foraminifers, gastropods, bivalves and a few dasycladacean algae. The reef communities are characterized by the coverage of organisms and distributional pattern. Analogies with the coeval reef deposits from the European part of the Tethys have been recognized. Some species, now collected in Oman, were also reported from American and Asian localities.     

Cenomanian/Turonian sponge microbialite deep-water hardground community (Liencres,Northern Spain)

Summary A benthic community of sessile metazoans dominated by coralline sponges (e.g.Acanthochaetetes andVaceletia) is found within a Cenomanian-Turonian deep water hardground succession cropping out at the coastal area of the Bay of Biscay near Santander. The characteristic K-strategic community exhibits a very close taxonomic relationship with modern communities from the Pacific realm, which allows for a comparison with Recent environmental conditions. The sponge community was associated with automicrites, microbialites, and thin mineralized limonitic biofilms. This biofacies is typically found in cryptic niches of reefal buildups (“telescoping”). The iron-rich biofilms had a strong electrochemical corrosive ability which explains the distinct submarine dissolution patterns. The hardground conditions are controlled, in part, by strong contour current regimes linked with extremely oligotrophic water masses. This system was established during the drowning of a distal carbonate ramp during the early Middle Cenomanian (A.rhotomagenese zone). In the uppermost portion of the hardground (Late Cenomaian, upperR. cushmani zone) the coralline sponge community was replaced by thick limonitic stromatolites with numerous encrusting foraminifera (Miniacina-type) and by colonies of the problematic iron bacteriumFrutexites. This event is accompanied by an increase of terrigenous influx and detrital glauconite, indicating a fundamental change in food web, and terminates the sponge dominated basal hardground interval. Thehardground was buried by hemipelagic sediments during the Middle Turonian (upperR. kallesi zone). Dedicated to the memory of Prof. Dr. JostWiedmann     

Palynological and physico‐chemical characterisation of honeys from the north‐west of Santa Cruz (Argentinean Patagonia)

Very close similarities between the fossil genera Callimothallus Dilcher, 1965 and Microthallites Dilcher, 1965 and recent representatives of the green algae Ulvella P. L. &; H. M. Crouan, 1859, seem to rule out the assumption that fossil, disciform and radiate palynomorph microfossils are representatives of microthyrioaceous fungi. On the basis of the morphology of fossil Ulvella, a model of the general morpohlogy of encrusting, palynomorph algae is constructed. The model includes 5 morphological characters that may only be applied to encrusting life-forms and in particular not to planktonic algae. These characters, therefore, in future palynological research may serve to distinguish benthic algae from planktonic algae. A new fossil alga, Ulvella nannae sp. nov. is described.