Ján Schlögl

Analyzing Variations in Cephalopod Abundances in Shell Concentrations: The Combined Effects of Production and Density-Dependent Cementation Rates

Abstract Upper Jurassic ammonoid shell concentrations on pelagic carbonate platforms formed by the mixture of well-preserved and moldic shells provide a unique opportunity to evaluate the effects of average shell durability and productivity on variations in shell abundance preserved in the fossil record. High abundance of primary cement has significantly negative statistical effects on taphonomic alteration, reducing the proportion of ammonoid shells affected by Fe-staining and syndepositional dissolution. High proportions of internal borings indicate that shell concentrations were not rapidly buried. Significantly negative effects of taphonomic alteration on ammonoid shell-packing density and spatial variations in shell-bed thickness show that variations in ammonoid abundance are related to variations in production and destruction rates rather than to variations in sediment dilution. The close spatial association of dissolved aragonite shells and precipitated calcite in shell-rich deposits and the higher proportion of dissolved molds in shell-poor beds demonstrate the simultaneous action of dissolution and cementation in the semiconsolidated mixed layer. These relationships imply positive feedback between the high abundance of ammonoid shells and the low rate of shell destruction, with dissolved carbonate ions from high aragonite input reducing the rate of ammonoid dissolution and providing a local source for carbonate cement. Cementation has the strongest positive relationship with shell-packing density in rank correlations and generalized linear models. Proportions of ammonoid embryonic stages and early juveniles have smaller but significantly positive statistical effects on shell-packing density in simple regressions. We hypothesize that (1) ammonoid shell concentrations correspond to long-term peaks in ammonoid production, with aragonite dissolution buffering the pore-water chemistry, and (2) the increase in ammonoid production rates was related to intervals with average high fecundity coupled with high juvenile mortality.

Middle Jurassic stromatactis mud-mound in the Pieniny Klippen Belt (Western Carpathians)

SummaryA stromatactis mud-mound has been found near Slavnické Podhorie in the Czorsztyn Unit of the Pieniny Klippen Belt (Western Carpathians, Slovakia). Its stratigraphic range is Bathonian to Callovian and it is one of the youngest known true stromatactis mud-mounds. The complete shape the mound is not visible since the klippe is a tectonic block encompassed by younger Cretaceous marls. The matrix is micritic to pelmicritic mudstone, wackestone to packstone with pelecypods, brachiopods, ammonites, and crinoids. An important component of the mound is stromatactis cavities that occur as low as the underlying Bajocian-Bathonian crinoidal limestones. The stromatactis cavities are filled by radiaxial fibrous calcite (RFC) as well as in some places by internal sediment and, finally, by clear blocky calcite. Some cavities remain open with empty voids in the centres. In some stromatactis cavities, tests of cavedwelling ostracodsPokornyopsis sp. were found, surrounded by the latest stages of the RFC. This indicates that stromatactis cavities formed an open network enabling migration of the ostracods and their larvae over a period of time.Except in the case of the stromatactis cavities, there are numerous examples of seeming recrystallizationsensu Black (1952) and Ross et al. (1975) and Bathurst (1977). The radiaxial fibrous calcite encloses patches of matrix and isolated allochems. The RFC crystals are oriented perpendicularly to the substrate whether it is a cavity wall or enclosed allochems. This means that the RFC crystals could not grow from the centre of the cavity outward as postulated by Ross et al. (1975). There are also numerous “floating” isolated allochems, which are much smaller than the surrounding RFC crystals. The explanation involving three-dimensional interconnection of allochems seems to be unlikely. In the discussed mud-mound there is a conflict between apparently empty cavities that had to exist in the sediment and seeming “recrystallization” related to the same RFC that forms the initial void filling. The authors favor an alternative explanation of the “recrystallization”. We presume that the allochems served as nucleation points on which the crystals started to grow. Obviously, the allochems and the micritic patches were different from the surrounding material. RFC crystals (either short-or long-bladed) of the “recrystallization” spar grew at the expense of decaying microbial mucillages. The mucus can enclose peloids, allochems, or whole micritic patches that “floated” in the cavity and served as nucleation sites for the RFC crystals. The entire mud-mound represents a microbially bound autochthonous micritic mass; the stromatactis and stromatactis-like cavities originated where purer mucillage patches occurred, giving rise to open spaces. Such features as the morphological variety of stromatactis fabrics, the pervasive penetration of the sparry calcite into matrix, and the enclosure of the “floated” allochems and mudstone patches by sparry calcite, seem to provide support for the presence of mucus aggregates within the mound body. The mucus might be related to protozoans rather than to sponges or other well organized metazoan organisms.Occurrence of the stromatactis cavities in the underlying Bajocian-Bathonian crinoidal limestones support the inference on biological origin of the stromatactis fabrics. The alternative inorganic models of stromatactis origin (e.g., internal erosion or water-escape) are hardly applicable to the sediment formed by crinoidal skeletal detritus.

Early Tithonian Serpulid-Dominated Cavity-Dwelling Fauna, and the Recruitment Pattern of the Serpulid Larvae

Abstract A Lower Tithonian cavity-dwelling community from pelagic carbonate platform deposits of the Czorsztyn Unit, Western Carpathians, represents a succession of mostly solitary coelobite organisms, dominated by scleractinian corals and small-sized serpulids during the initial recruitment stage, and by serpulids during the following recruitment stages. These bioconstructors were accompanied with other suspension feeders: thecideidine brachiopods, oysters, bryozoans, sponges, crinoids and sessile foraminifers. The boundary between the first and the second recruitment stage represents an interval of aggregate growth interruption, when a thin sheet of cyclostome bryozoans developed. Corals and serpulids Neovermilia and Vermiliopsis are primary bioconstructors; all other associated organisms profited from the free spaces between the serpulid tubes. The aggregates were already bioeroded, mineralized and encrusted during their growth. Serpulid larvae show a special recruitment pattern. Their tubes were observed attached on the inner surfaces of adult serpulid tubes only. Possible causes of such a larval behaviour involve several physical, biological or chemical factors. Except for the first recruitment stage, the rest of the succession seems to be physically controlled by the gradual infilling of cavities.

Venezuelan sandstone caves: a new view on their genesis, hydrogeology and speleothems

Caves in arenites of the Roraima Group in Venezuela have been explored on the Chimanta and Roraima plateaus (tepuis). Geological and geomorphological research showed that the most feasible method of caves genesis was the winnowing and erosion of unlithified or poorly lithified arenites. The unlithified arenitic beds were isolated by well-cemented overlying and underlying rocks. There is a sharp contrast between these well-lithified rocks and the loose sands which form the poorly lithified to unlithified beds. They are only penetrated by strongly lithified pillars which were cemented by vertical finger flow of the diagenetic fluids from the overlying beds. Such finger flow is only typical for loose sands and soils where there is a sharp difference in hydraulic conductivity. The pillars exhibit no signs of further dissolution. The caves form when the flowing water accesses the poorly lithified beds through clefts/crevices. Collapse of several superimposed winnowed-horizons can create huge subterranean spaces. Futher upward propagation of the collapses can lead to large collapse zones which are commonly observed on the tepuis. Dissolution is also present but it probably plays neither a trigger role, nor a volumetrically important role in the cave-forming processes. The strongest dissolution/reprecipitation agent is condensed atmospheric moisture which is most likely the main agent contributing to growth of siliceous speleothems. As such, it can be active only after, but not before the cave is created. Siliceous speleothems are mostly microbialites except for some normal stalactites, cobweb stalactites and flowstones which are formed inorganically. They consist of two main types: 1. fine-laminated columnar stromatolite formed by silicified filamentous microbes (either heterotrophic filamentous bacteria or cyanobacteria) and 2. a porous peloidal stromatolite formed by Nostoc-type cyanobacteria. The initial stages of encrusted shrubs and mats of microbes were observed, too, but the surrounding arenitic substrate was intact. This is strong evidence for the microbial mediation of silica precipitation.

A late Burdigalian bathyal mollusc fauna from the Vienna Basin (Slovakia)

A late Burdigalian bathyal mollusc fauna from the Vienna Basin (Slovakia) This is the first record of a bathyal mollusc fauna from the late Early Miocene of the Central Paratethys. The assemblage shows clear affinities to coeval faunas of the Turin Hills in the Mediterranean area and the Aquitaine Basin in France. The overall biostratigraphic value of the assemblage is hard to estimate due to the general very poor knowledge of Miocene bathyal faunas. Several species, however, are known from deep water deposits of the Middle Miocene Badenian stage as well. This implies Early Miocene roots of parts of the Middle Miocene deep water fauna and suggests a low turnover for bathyal mollusc communities at the Early-Middle Miocene boundary. The nassariid gastropod Nassarius janschloegli Harzhauser nov. sp. and the naticid gastropod Polinices cerovaensis Harzhauser nov. sp. are introduced as new species.

Bathyal sponges from the late Early Miocene of the Vienna Basin (central Paratethys, Slovakia)

Here we report, for the first time, a very rich and diversified sponge assemblage from late Early Miocene deposits of a central part of the Vienna Basin (Paratethys) in Slovakia. Bodily preserved sponges are described as a new genus and species Paracinachyrella fossilis (Tetiliidae, Demospongiae). Dissociated spicules reveal the presence of the “soft” demosponges that belong to families Tetillidae, Theneidae, Geodiidae, Samidae, Thrombidae, Thoosidae, Agelasidae, Myxillidae, Bubaridae, and Tedaniidae, the lithistid family Pleromidae, and an undetermined rhizoclone-bearing lithistid. Fragments of dictyonal skeleton indicate the presence of hexactinellid sponges that belong to the families Farreidae and Euretidae, and lychniscosan sponges. We estimate that at least 16–19 different species of siliceous sponges inhabited this region of the Central Paratethys during the latest Burdigalian. Most of these sponges are reported for the first time from the Miocene of the Paratethys. This sponge fauna has clear Tethyan affinities and indicates the existence of connection between Paratethys and Tethys during the latest Burdigalian, as well as the presence of open marine, deep-water, bathyal conditions in this part of the Vienna Basin.KurzfassungWir beschreiben eine neue, sehr reiche und diverse Schwamm-Assoziation aus Ablagerungen des späten Unter-Miozän des zentralen Teils des Wiener Beckens (Paratethys) in der Slowakei. Körperlich Schwämme werden als neue Gattung und Art Paracinachyrella fossilis (Tetiliidae, Demospongiae) beschrieben. Disassoziierte Nadeln belegen die Anwesenheit von “weichen” bzw. skelettlosen Demospongiern, die zu den Familien Tetillidae, Theneidae, Geodiidae, Samidae, Thrombidae, Thoosidae, Agelasidae, Myxillidae, Bubaridae und Tedaniidae sowie zu den lithistiden Familien Pleromidae und einem unbestimmten Rhizoclon-tragenden Lithistiden gehören. Bruchstücke dictyonaler Skelette sprechen für die Anwesenheit hexactinellider Schwämme, die zur Familie Euretidae und lychniscosen Schwämmen gehören. Wir schätzen, dass mindestens 16-19 verschiedene Arten von kieseligen Schwämmen diese Region der zentralen Paratethys während des jüngsten Burdigal besiedelten. Die meisten dieser Schwämme werden zum ersten Mal aus dem Miozän der Paratethys beschrieben. Diese Schwamm-Fauna zeigt klare Affinitäten und spricht für eine offene Verbindung zwischen Paratethys und Tethys während des jüngsten Burdigal und impliziert, dass offen marine, tiefe, bathyale Bedingungen in diesem Teil des Wiener Beckens vorherrschten.

Early and Middle Callovian ammonites from the Pieniny Klippen Belt (Western Carpathians) in hiatal successions: unique biostratigraphic evidence from sediment-filled fissure deposits

In the Pieniny Klippen Belt (West Carpathians), the upper Middle Jurassic (Callovian) sediments are mostly represented by deep-water radiolarites that were deposited in slope and basinal environments of the Kysuca Basin in the northwestern Tethys. The contemporaneous depositional conditions from shallow environments of the Czorsztyn Ridge are poorly known owing to the Upper Bathonian – Lower Oxfordian hiatus that is extensively developed in the Pieniny Klippen Belt. However, submarine fissures (neptunian dykes) related to extensional fracturing were filled with unlithified carbonate during this period and thus provide unique information about sediments and fossil assemblages that are otherwise missing in normal stratigraphic position. In hiatal successions, such sediments were not deposited on exposed surfaces owing to sediment bypassing and winnowing. The absence of borings and encrusters on the walls of the dykes indicates that such fissures were filled relatively rapidly with sediment, thus also enhancing preservation of fossil assemblages. In addition to brachiopods, bivalves, and gastropods, some dykes contain ammonites that represent biostratigraphic zones that were not recorded in the West Carpathians until now. They include the Lower Callovian Gracilis Zone and the Middle Callovian Coronatum Zone. Ammonite assemblages in the Callovian dykes are dominated by phylloceratids and lytoceratids. Ammonitina are almost exclusively represented by microconchs or juveniles. This size-selective preservation can reflect sorting of shells within fissures that eliminated large-sized microconchs and macroconchs, and/or higher susceptibility to damage of large-sized ammonites on the exposed sea-floor. Relatively rare kosmoceratid ammonites that are preserved in the Lower Callovian assemblages indicate that the Czorsztyn Ridge was situated within the area of the Subboreal influence.

Massartella hirsuta sp. nov. (Ephemeroptera: Leptophlebiidae: Atalophlebiinae) and new data on mayflies of Guyana Highlands

Description and figures of the larva and egg of Massartella hirsuta sp. nov. (Ephemeroptera: Leptophlebiidae) from the south-eastern part of Grand Sabana region (Venezuela) are presented. Diagnostic characters distinguishing the larvae of this species from other known Massartella species include a heavy row of setae along the entire outer margin of the mandibles. This character, among others, will also distinguish the new species from undescribed species of Massartella from the sandstone table mountains. Two well-defined species groups of the genus Massartella can be distinguished in the Guyana Highlands: (1) M. venezuelensis group including M. venezuelensis and M. hirsuta sp. nov., and (2) M. devani group containing M. devani and undescribed taxa from Mt. Roraima and Mt. Chimantá plateaus. The first group seems to be distributed in uplands (∼1000 m a.s.l.), while the second group appeared to be restricted to the thermal refugia above 2000 m a.s.l. The origin of Massartella species in Guyana Highlands is discussed.

Deep-Water Chondrichthyans from the Early Miocene of the Vienna Basin (Central Paratethys, Slovakia)

Sampling of latest Burdigalian (Miocene) silty clays from the Malé Karpaty Mountains in the Slovakia revealed a deep-water, low diversity shark fauna. The fauna is dominated by teeth of very small squaliform sharks, including two new species, Eosqualiolus skrovinai sp. nov. and Paraetmupterus hurvathi sp. nov. The generic composition of the squaliform fauna is more similar to that known from the Eocene than that of today, suggesting a post-early Miocene faunal turnover within this clade, at least locally. Nectobenthic, non squaliform sharks are rare, but include the new sawshark species Pristiuphurus striatus sp. nov., while minute teeth of an enigmatic taxon described here as Nanuceturhinus tuberculatus gen. et sp. nov. probably indicate the presence of a previously unrecorded planktivore. The unusual composition of the fauna, with the complete absence of taxa known to be of medium to large size, suggests an unusual, and probably very stressed, palaeoenvironment.

Stratigraphy, plankton communities, and magnetic proxies at the Jurassic/Cretaceous boundary in the Pieniny Klippen Belt (Western Carpathians, Slovakia)

Abstract A well preserved Upper Tithonian–Lower Berriasian Strapkova sequence of hemipelagic limestones improves our understanding of environmental changes occurring at the Jurassic/Cretaceous boundary in the Western Carpathians. Three dinoflagellate and four calpionellid zones have been recognized in the section. The onset of the Alpina Subzone of the standard Calpionella Zone, used as a marker of the Jurassic/Cretaceous boundary is defined by morphological change of Calpionella alpina tests. Calpionellids and calcified radiolarians numerically dominate in microplankton assemblages. The first occurrence of Nannoconus wintereri indicates the beginning of the nannofossil zone NJT 17b Subzone. The FO of Nannoconus steinmannii minor was documented in the lowermost part of the Alpina Subzone. This co-occurrence of calpionellid and nannoplankton events along the J/K boundary transition is typical of other Tethyan sections. Correlation of calcareous microplankton, of stable isotopes (C, O), and TOC/CaCO3 data distribution was used in the characterization of the J/K boundary interval. δ13C values (from +1.09 to 1.44 ‰ VPDB) do not show any temporal trends and thus show a relatively balanced carbon-cycle regime in sea water across the Jurassic/Cretaceous boundary. The presence of radiolarian laminites, interpreted as contourites, and relatively high levels of bioturbation in the Berriasian prove oxygenation events of bottom waters. The lower part of the Crassicolaria Zone (up to the middle part of the Intermedia Subzone) correlates with the M19r magnetozone. The M19n magnetozone includes not only the upper part of the Crassicollaria Zone and lower part of the Alpina Subzone but also the FO of Nannoconus wintereri and Nannoconus steinmannii minor. The reverse Brodno magnetosubzone (M19n1r) was identified in the uppermost part of M19n. The top of M18r and M18n magnetozones are located in the upper part of the Alpina Subzone and in the middle part of the Ferasini Subzone, respectively. The Ferasini/Elliptica subzonal boundary is located in the lowermost part of the M17r magnetozone. A little bit higher in the M17r magnetozone the FO of Nannoconus steinmannii steinmannii was identified.