Sedimentology and trace element geochemistry of shallow-marine carbonates: an approach to paleoenvironmental analysis along the Pagny-sur-Meuse Section (Upper Jurassic, France)

The Middle Oxfordian formations of the eastern edge of the Paris Basin (France) contain mostly shallow-marine carbonate sediments. A detailed sedimentological study of the Pagny-sur-Meuse section reveals five major environments that make up a depositional profile succession grading from tidal-flat to distal lagoon/oolithic shoal. Stratigraphic cycles were established and illustrate variations of the A/S ratio (accommodation rate/sedimentation rate) and hence variations of accommodation space. Geochemical analyses (Sr, Mg, Fe, and Mn) have been conducted along a part of the section. Statistic analysis of the geochemical data (box diagrams and principal component analysis, PCA) are used to investigate similarities between the variations of trace element contents and depositional environments. An analysis of variance (ANOVA) is used to test whether the amounts of trace elements are related to the depositional environments. The relationship is highly significant for Sr, Fe, and Mn. A number of a posteriori tests are performed with this ANOVA to compare the geochemical data for each environment. Tidal-flats and distal lagoon/oolithic shoal transition are the most significantly discriminated environments. Differences among the lagoonal environments are less obvious. Despite (1) an open diagenetic system that explains the low Sr values and (2) the possible influence of clays on Fe–Mn contents in the upper part of the section, some of the variations in Sr and Fe–Mn seem to reflect changes in depositional environment. A number of hypotheses are proposed about the relations between trace elements and paleoenvironmental parameter records: Sr contents may illustrate variations of paleosalinity in depositional environments, whereas Fe and Mn contents seem to record variations of specific low detrital inputs coming from isolated islands submitted to pedogenesis. Low Sr content coupled with relatively high Fe and Mn contents is indicative of low salinity environment near subaerially exposed islands, located in the proximal part of a reconstructed theoretical depositional profile. Conversely, high Sr content coupled with relatively low Fe and Mn contents reflect a more open marine environment in the distal part of the same profile. Such analysis based on trace element geochemistry does not constitute a model but it shows that Sr, Fe, and Mn can partially record indications about paleoenvironmental conditions in shallow-marine carbonates.     

Quantification of high-frequency sea-level fluctuations in shallow-water carbonates: an example from the Berriasian–Valanginian (French Jura)

When quantifying sedimentary processes on shallow carbonate platforms, it is important to know the high-frequency accommodation changes through time. Accommodation changes in cyclic successions are often analysed by simply converting cycle thickness to Fischer plots. This approach is not satisfactory, because it does not account for differential compaction, possible erosion, sea-level fall below the depositional surface, or subtidal cycles. An attempt is made here to reconstruct a realistic, high-frequency accommodation and sea-level curve based on a detailed facies and cyclostratigraphical analysis of Middle Berriasian to Lower Valanginian sections in the French Jura Mountains. The general depositional environment was a shallow-marine carbonate platform on a passive margin. Our approach includes the following steps: (1) facies interpretation; (2) cyclostratigraphical analysis and identification of Milankovitch parameters in a well-constrained chronostratigraphic framework; (3) differential decompaction according to facies; (4) estimation of depth ranges of erosion and vadose zone; (5) estimation of water-depth ranges at sequence boundaries and maximum flooding intervals; (6) estimation of mean subsidence rate; (7) classification of depositional sequences according to types of facies evolution: ‘catch-up’, ‘catch-down’, ‘give-up’, or ‘keep-up’; (8) classification of depositional sequences according to long-term sea-level evolution: ‘rising’, ‘stable’, ‘falling’; (9) calculation of ‘eustatic’ sea-level change for each depositional sequence using the parameters inferred from these scenarios, assuming that sea-level cycles were essentially symmetrical (which is probable in Early Cretaceous greenhouse conditions); (10) calculation of a sea-level curve for each studied section; (11) comparison of these curves among each other to filter out differential subsidence; (12) construction of a ‘composite eustatic’ sea-level curve for the entire studied platform; (13) spectral analysis of the calculated sea-level curves. Limitations of the method are those common to every stratigraphic analysis. However, the method has the potential to improve the original cyclostratigraphical interpretations and to better constrain the high-frequency sea-level changes that control carbonate production and sediment fluxes.     

Benthic diversity patterns in oxygenation gradients: an example from the Middle Jurassic of Switzerland

Etter, W. 1995 11 30 Benthic diversity patterns in oxygenation gradients: an example from the Middle Jurassic of Switzerland.
A high-resolution study of the lower Opalinum Clay (Aalenian, Middle Jurassic) of northern Switzerland revealed a pattern of macrobenthic diversity and abundance which does not conform with the dysaerobic-biofacies models currently in use. The upper dysoxic zone contains an association of moderate diversity and moderate abundance which, with increasing oxygen depletion, is replaced by an association dominated by a few peak opportunists (tiny epibenthic bivalves and presumably small annelids) at high abundances but very low diversity. In the lower dysoxic zone, abundance drops to very low levels, but diversity rises again to quite high values. The rather high diversity of the lower dysaerobic biofacies is explained in part by the presence of specialized chemosymbiontic species. The pattern documented in the lower Opalinum Clay has been calibrated by sedimentologic, taphonomic, ichnologic, and microfaunal evidence. It contradicts equilibrium models, which postulate gradual or even linear decreases in both abundance and diversity with increasing oxygen-depletion of the bottom water. The equation of rising diversity with improved oxygenation can be misleading and can yield erroneous results in the reconstruction of ancient bottom-water oxygenation. □ Dysaerobic biofacies, high-resolution study, diversity, chemosymbionts, equilibrium and non-equilibrium models .     

Oncoid-dwelling foraminifera from Late Jurassic shallow-water carbonates of the Northern Calcareous Alps (Austria and Germany)

Oncoidal limestones with different oncoid types are ubiquitous in back-reef open-lagoonal and, to a minor amount, in closed-lagoonal facies of the Late Jurassic Plassen Carbonate Platform of the Northern Calcareous Alps. A common feature of the oncoids from moderately to well-agitated open-lagoonal habitats are incorporated small trochospiral benthic foraminifers, tentatively assigned to trochamminids, switched between individual micritic layers. Their life style is discussed concluding a specialized feeding on cyanophytes on the outer side of the oncoids and later becoming biomurated by successive sheet formations due to oncoid growing.     

Lacustrine microporous micrites of the Madrid Basin (Late Miocene,Spain) as analogues for shallow-marine carbonates of the Mishrif reservoir Formation (Cenomanian to Early Turonian,Middle East)

Shallow-marine microporous limestones account for many carbonate reservoirs. Their formation, however, remains poorly understood. Due to the lack of recent appropriate marine analogues, this study uses a lacustrine counterpart to examine the diagenetic processes controlling the development of intercrystalline microporosity. Late Miocene lacustrine microporous micrites of the Madrid Basin (Spain) have a similar matrix microfabric as Cenomanian to Early Turonian shallow-marine carbonates of the Mishrif reservoir Formation (Middle East). The primary mineralogy of the precursor mud partly explains this resemblance: low-Mg calcites were the main carbonate precipitates in the Cretaceous seawater and in Late Miocene freshwater lakes of the Madrid Basin. Based on hardness and petrophysical properties, two main facies were identified in the lacustrine limestones: a tight facies and a microporous facies. The tight facies evidences strong compaction, whereas the microporous facies does not. The petrotexture, the sedimentological content, and the mineralogical and chemical compositions are identical in both facies. The only difference lies in the presence of calcite overgrowths: they are pervasive in microporous limestones, but almost absent in tight carbonates. Early diagenetic transformations of the sediment inside a fluctuating meteoric phreatic lens are the best explanation for calcite overgrowths precipitation. Inside the lens, the dissolution of the smallest crystals in favor of overgrowths on the largest ones rigidifies the sediment and prevents compaction, while partly preserving the primary microporous network. Two factors appear essential in the genesis of microporous micrites: a precursor mud mostly composed of low-Mg calcite crystals and an early diagenesis rigidifying the microcrystalline framework prior to burial.     

Hettangian (Early Jurassic) Dinosaur Tracksites from the Mecsek Mountains,Hungary

A rare example of a North American Jurassic hardground is found in the Carmel Formation of southwestern Utah. The Carmel hard‐ground was formed across a carbonate lagoon from an oolitic shoal seaward to a subtidal shelly facies landward. It has an abundant bivalve fauna consisting of thick layers of encrusters (the oyster Liostrea and the plicatulid Plicatula), borers (the ichnofossil Gastro‐chaenolites with the mytilid Lithophaga often preserved inside), and nestlers (the mytilid Modiolus). A rare soft‐bodied bryozoan (Arach‐nidium) is preserved by bioimmuration in the attachment scars of Liostrea; this is the first bioimmuration recorded from the Jurassic of North America, and the first bioimmuration recorded from a hard‐ground. The phoronid boring Talpina is present in some Liostrea shells; it was apparently excavated after the death of these oysters. The Carmel hardground community does not contain other fossils, such as serpulids, brachiopods, foraminiferans, and skeletal bryo‐zoans, typical of Jurassic hardgrounds elsewhere. It represents a low diversity molluscan community developed in a restricted marine environment.     

Middle Miocene warm-temperate carbonates of Central Paratethys (Mt. Zrinska Gora, Croatia): paleoenvironmental reconstruction based on bryozoans, coralline red algae, foraminifera, and calcareous nannoplankton

Carbonate deposits from Zrin in the Mt. Zrinska Gora were deposited in the SW part of the Central Paratethys Sea during the Middle Badenian (Middle Miocene). The studied section contains a rich fossil community of non-geniculate coralline red algae (Subfamily Melobesioideae), bryozoans, benthic and planktonic foraminifera, echinoderms, ostracods, molluscs, and calcareous nannoplankton. Based on lithological variations and changes in the biogenic components, four facies associations (FA) are distinguished. Their distribution points to skeletal production and sedimentation on a middle to proximal outer carbonate ramp. The main lithological feature of the section is an alternation of two lithofacies: fully lithified grainstone–rudstone and packstone, and semi-lithified rudstone–floatstone with a carbonate sandy matrix. Depositional environments on the ramp were periodically influenced by minor high-frequency sea-level changes and/or changes of hydrodynamic conditions, which are suggested as the driving mechanisms causing the alternation of the two lithofacies. Vertically in the succession, the two lithofacies alternate to give three thinning- and fining-upward units. The lower part of each unit is formed of a rhodolith and coralline algal FA, which passes upwards into a bryozoan-coralline algal FA and/or FA of bioclastic packstone-grainstone. Based on the vertical upward change in FAs, each unit can be interpreted as a deepening-upward sequence. Patterns in the relative abundance of bryozoan colony growth form (vinculariiform, cellariiform, adeoniform, membraniporiform, celleporiform, and reteporiform), size and abundance of rhodoliths and coralline branches, and benthic foraminifera are interpreted by comparison with data from modern and fossil environments. Based on these data, a water depth range for each FA is interpreted, providing evidence of low-frequency relative sea-level changes. It is hypothesized that relative sea-level fluctuated in the water depth range from 30 to 80 m, and in the uppermost part of the section, rich in planktonic foraminifera and calcareous nannoplankton, possibly deeper. Causes of the low-frequency relative sea-level fluctuations and the general deepening trend observed within the succession cannot be interpreted based on one section; however, they may be related to the subsidence of the depositional basin. The benthic biotic communities are a vertical alternation of rhodalgal and bryorhodalgal associations, and this is attributed to relative sea-level fluctuations. These biotic associations gave rise to warm-temperate carbonates of the Middle Badenian N9 planktonic Zone (Orbulina suturalis, O. universa) and NN4–NN5 nannoplankton Zones (Sphenolithus heteromorphus).     

Deep-time phylogenetic clustering of extinctions in an evolutionarily dynamic clade (Early Jurassic ammonites)

Conservation biologists and palaeontologists are increasingly investigating the phylogenetic distribution of extinctions and its evolutionary consequences. However, the dearth of palaeontological studies on that subject and the lack of methodological consensus hamper our understanding of that major evolutionary phenomenon. Here we address this issue by (i) reviewing the approaches used to quantify the phylogenetic selectivity of extinctions and extinction risks; (ii) investigating with a high-resolution dataset whether extinctions and survivals were phylogenetically clustered among early Pliensbachian (Early Jurassic) ammonites; (iii) exploring the phylogenetic and temporal maintenance of this signal. We found that ammonite extinctions were significantly clumped phylogenetically, a pattern that prevailed throughout the 6.6 Myr-long early Pliensbachian interval. Such a phylogenetic conservatism did not alter--or may even have promoted--the evolutionary success of this major cephalopod clade. However, the comparison of phylogenetic autocorrelation among studies remains problematic because the notion of phylogenetic conservatism is scale-dependent and the intensity of the signal is sensitive to temporal resolution. We recommend a combined use of Moran's I, Pearson's ? and Fritz and Purvis' D statistics because they highlight different facets of the phylogenetic pattern of extinctions and/or survivals.     

The occurrence and role of microencruster frameworks in Late Jurassic to Early Cretaceous platform margin deposits of the Northern Calcareous Alps (Austria)

Late Jurassic reefs are generally assumed to lack “cement crusts”. In the present paper, microencruster frameworks with variable amounts of cement are described from Late Jurassic to Earliest Cretaceous shallow-water carbonates of the Northern Calcareous Alps of Austria. The boundstones are characterized by a specialized and highly diverse community of microencrusters, partly occupying cryptic habitats. Volumetrically of minor importance compared to similar Permo-Triassic examples, Late Jurassic to Earliest Cretaceous microframeworks here reported compare well with cement reefs or cement-supported counterparts of other time intervals. The assumed depositional setting is that of a fore-reef slope environment. Generally, this peculiar microfacies can be integrated in current concepts of Late Jurassic reef classifications. Although more details are still needed for comparison, Late Jurassic microencruster-cement frameworks seem to be typical, but not restricted to the margins of Neotethyan isolated platforms. This work is dedicated to Erik Flügel, former professor of the University of Erlangen, for his fundamental pioneer research on various aspects of microfacies, including poorly known phenomena of ancient cement reefs.     

Continental, brackish and marine carbonates from the Lower Cretaceous of Kolone–Barbariga (Istria, Croatia): stratigraphy, sedimentology and geochemistry

During the Early Cretaceous, wide areas of the Dinaric–Adriatic Carbonate Platform emerged for long periods. The Hauterivian–Barremian carbonates from Kolone–Barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish/palustrine facies. The sequence of the platform is made for the most part by subtidal and intertidal limestones. The bone levels are located in a large depression few meters deep in the uppermost Hauterivian marine limestones. The filling facies of this depression are made by oncolitic rudstones and algal boundstones, which represent marginal lacustrine facies, and by laminated limestones, thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies. The fossil content is characterized by rare charophyte stems, ostracods, gastropods and plant remains, while typical marine fauna is absent. At the Hauterivian–Barremian boundary a major emersion event has been observed, then a slow transgressive phase occurred. The transgressive facies are primarily made by mudstones with ostracods, charophytes and Spirillina (brackish and probably freshwater facies), wackestones with Ophtalmidiidae and rare dasyclad algae, storm layers with gastropods and miliolids and breccia-like dinoturbated beds. Wackstones, packstones and very rich in dasyclad grainstones outcrop at the top of the section, representing the maximum of the transgression. Trace elements content, carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation. In this geological setting, Barium seems to discriminate between brackish and freshwater facies. The isotopic values of the marine carbonates appear to depend on early diagenetic processes, meanwhile lacustrine facies seem to show a weak signal of the depositional environment.     

Surname as 'cancer risk' in extreme isolates: example from the island of Lastovo, Croatia

The aim of this study was to analyze whether there are surnames which appear more frequently among the ancestors of cancer cases in a small isolate, in comparison to the ancestral surnames of the healthy controls, using the classic case-control design. The chosen setting was the island of Lastovo, Croatia, located more than 100 kilometers from the nearest coastal region. The period of study was 1970-1995, during which a total of 76 cancer cases were recorded in a population of approximately 800. The comparison of surname frequencies was performed in current and in five ancestral generations. The leading hypothesis was that, if inbreeding and common ancestry contributed to the development of the disease, then those phenomena should be reflected in increasing frequency of some surnames among ancestors, identifying the 'hidden' consanguinity, or 'following' cancer-promoting genes on the Y-chromosome. The results imply that there are surnames representing a classic "risk" for cancer, but also those "protecting" from its development, which all underscores the importance of founder effect and genetic predisposition to the disease in a small, reproductively isolated population. All of the results become more evident and increasingly significant when analyzed in more distant ancestral generations.     

Panmixia: an example from Dawson's burrowing bee (Amegilla dawsoni) (Hymenoptera: Anthophorini)

Dawson's burrowing bee is a large, fast-flying solitary nesting bee endemic to the arid zone of Western Australia. In this study the population structure of the species was examined with molecular markers. Using eight microsatellite loci, we genotyped 531 adult female bees collected from 13 populations of Dawson's burrowing bee, Amegilla dawsoni, across the species range. The mean number of alleles per locus ranged from 4 to 38 and expected heterozygosity was uniformly high with a mean of 0.602. Pairwise comparisons of F(ST) among all 13 populations ranged from 0.0071 to 0.0122 with only one significant estimate and an overall F(ST) of 0.001. The entire sample collection was in Hardy-Weinberg equilibrium and there was no evidence of inbreeding with a mean F(IS) of 0.010. The mating and nesting behaviour of this bee suggests that gene flow would be limited by monandry and the fact that almost 90% of females mate immediately on emergence. Nevertheless there is obviously sufficient gene flow to maintain panmixia, and we suggest that this results from infrequent and unreliable rainfall in the species range, which causes the bees to congregate at limited food resources, allowing a small number of unmated females from one emergence site to come into contact with males from another population. In addition, when drought eliminates food resources near an emergence site, the whole population may move elsewhere, increasing gene flow across the species range.     

Osmunda (Osmundaceae) from the Triassic of Antarctica: an example of evolutionary stasis

Compressed specimens of the fern Osmunda are described from the Triassic of the Allan Hills, Antarctica. The specimens consist of a once pinnate, deeply pinnatifid fertile frond as well as several sterile specimens. Six pinnae are present on the partial fertile rachis, with two sterile pinnae above four fertile pinnae. Both sterile and fertile specimens are virtually identical to the modern species Osmunda claytoniana. Entire fronds are fragmentary; the longest is 21 cm in length. Sterile pinnae are alternate and deeply pinnatifid, with slightly toothed pinnules and dichotomous venation. Fertile pinnae are 1-1.3 cm long, once pinnate, and lack vegetative lamina. Sporangia are clustered, each 300-375 um in diameter, and possess a transverse annulus 6-8 cells long; dehiscence is by a vertical slit. Fronds arise from a rhizome 4 cm long by 1 cm wide; two croziers are present on the rhizome. Two frond segments up to 6 cm long and three deeply pinnatifid pinnae are present on the uppermost part of one rachis. Pinnules are ~4 mm long and 2-3 mm wide. The presence of this Osmunda species in the Triassic demonstrates stasis of frond morphology, both fertile and vegetative, for the genus.     

New bibionomorpha (Insecta: Diptera) from the Jurassic of Asia

The new species Protorhyphus rohdendorfi sp. nov. (Protorhyphidae), Mesorhyphus handlirschi sp. nov., and M. hennigi sp. nov. (Anisopodidae), Procramptonomyia ponomarenkoi sp. nov. and P. kovalevi sp. nov. (Procramptonomyiidae) are described from the Upper Jurassic deposits of Mongolia (Shar Teg); some features of Archirhyphus asiaticus Rohdendorf, 1964 are revealed. The latter two species are also known from the locality of Karatau (Kazakhstan, J_2/3). The genus Tega Blagoderov, Krzemi??ska, and Krzemi??ski, 1993 is transferred from the family Cramptonomyiidae into Anisopodidae (Teginae subfam. nov.).     

Proptychopterina (Diptera: Eoptychopteridae) from the Jurassic of Northeastern China

A complete well-preserved male fly from the Jurassic of Daohugou locality (Northeastern China) is described as Proptychopterina opinata sp. nov. The distribution of Proptychopterina is discussed, this genus is re-diagnosed, and a key to species is provided based on the wings.     

Patch reef development in the florigemma-Bank Member (Oxfordian) from the Deister Mts (NW Germany): a type example for Late Jurassic coral thrombolite thickets

Small reefal bioconstructions that developed in lagoonal settings are widespread in a few horizons of the Late Jurassic (Oxfordian) succession of the Korallenoolith Formation, exposed southwest of Hannover, Northwest Germany. Especially the florigemma-Bank Member, “sandwiched” between oolite shoal deposits, exposes a high variety of build-ups, ranging from coral thrombolite patch reefs, to biostromes and to coral meadows. The reefs show a distribution with gradual facies variations along an outcrop belt that extends about 30 km from the Wesergebirge in the NW to the Osterwald Mts in the SE.The patch reefs from the Deister Mts locality at the “Speckhals” are developed as coral-chaetetid-solenoporid-microbialite reefs and represent a reef type that was hitherto unknown so far north of its Tethyan counterparts. They are mainly built up by coral thickets that are preserved in situ up to 1.5 m in height and a few metres in diameter. They contain up to 20 coral species of different morphotypes but are chiefly composed of phaceloid Stylosmilia corallina and Goniocora socialis subordinately. The tightly branched Stylosmilia colonies are stabilized by their anastomosing growth. The coral branches are coated with microbial crusts and micro-encrusters reinforcing the coral framework. Encrusters and other biota within the thicket show a typical community replacement sequence: Lithocodium aggregatum, Koskinobullina socialis and Iberopora bodeuri are pioneer organisms, whereas the occurrence of non-rigid sponges represents the terminal growth stage. The latter are preserved in situ and seem to be characteristic so far poorly known constituents of the Late Jurassic cryptobiont reef dweller community. The distance and overall arrangement of branches seems to be the crucial factor for the manifestation of a (cryptic) habitat promoting such community replacement sequences. Widely spaced branches often lack any encrusting and/or other reef dwelling organisms, whereas tightly branched corals, as is St. corallina, stimulate such biota. Hence, such reefs are well suited for research on coelobites and community sequences of encrusting and cavity dwelling organisms.     

A multi-proxy study of deeper-water carbonates (Upper Jurassic, southern Germany): combining sedimentology, chemostratigraphy and palynofacies

Deeper shelf carbonates are often composed of relatively monotonous successions with few diagnostic sedimentological characteristics. The Upper Jurassic of southern Germany provides a classical example for deeper ramp carbonate environments, dominated by limestone/marl sequences including conspicuous sponge/microbial bioherms. Sedimentological analysis was integrated with stable isotope (O, C) and palynofacies analysis in an attempt to reconstruct the dominant depositional controls (sea level, climate, nutrients) as well as to delineate genetic sequences and their stacking patterns. Small-scale (3–10 m thick), medium-scale (5–25 m thick) and large-scale (45–60 m thick) sequences could be recognised, which all share similar patterns and trends. Oxygen isotopes from bulk rock carbonate samples were interpreted as records of temperature trends which were related to climatically induced sea level fluctuations. A positive oxygen isotope trend (i.e., cooling and associated relative sea-level fall) in combination with increasing absolute palynoclast abundances (increasing proximality) are inferred to mark regressive hemi-sequences. Negative trends in oxygen isotopes (i.e., warming and associated relative sea-level rise) and a decrease in absolute palynoclast abundances (increasing distality) are interpreted to indicate transgressive hemi-sequences. In contrast to the small-scale sequences, the medium-scale sequences could be correlated on a basin-wide scale by means of stable isotope trends and gamma-ray logs. Borehole scans were found to be useful for the recognition of major facies associations and sequence types when core data are not available.