Benthic foraminiferal morphogroups of mid to outer shelf environments of the Late Jurassic (Prebetic Zone, southern Spain): Characterization of biofacies and environmental significance

Benthic foraminiferal assemblages belonging to a mixed carbonate–siliciclastic shelf succession of the Oxfordian (Upper Jurassic) in the Prebetic, southern Spain, were analyzed. The faunal data, obtained on thin sections of strongly lithified sediments, allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions. Eleven morphogroups were differentiated according to shell composition, general morphology, number of chambers and mode of coiling. Paleoenvironmental analysis combines these features with inferred life-style (epifaunal, shallow infaunal and deep infaunal) and feeding strategy (suspension-feeder, deposit-feeder, herbivores, etc.) of the foraminifera. Analogies and differences regarding previously established morphogroup systems could be outlined accordingly.

In the Prebetic Oxfordian, distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the South-Iberian paleomargin, indicating that nutrient supply was the most important factor controlling morphogroup development. The mid shelf settings are dominated by epifaunal active herbivores–phytodetritivores, in shallow to deep substrate position of the redox boundary. The outer shelf is dominated by agglutinated and infaunal detritivore-bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary. Particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas.     

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.     

Microhermal nodules of <Emphasis Type=Italic>Renalcis</Emphasis>-like calcimicrobes from Oxfordian limestones of the Sierra Madre Oriental (Novillo Formation,Mexico)

Microhermal nodules very similar to those from the Oxfordian Smackover Formation are volumetrically important constituents of the Novillo Formation exposed in eastern Central Mexico. The nodules occur within a micritic limestone succession (Novillo Limestone). Coalescence of adjacent nodules leads to a delicate self-supported frame. Microhermal nodules consist of both microbial carbonate and clustered digitate and branching chambered microfossils. The latter occur in the form of crust-like agglomerations or bushy growth habit in small growth-framework cavities created by accretionary microbialites. Main growth patterns are branching upward, downward facing and pendant. Like Renalcis, the microfossils apparently resulted from the activity of calcimicrobes. Terebella, encrusting foraminifers, and Tubiphytes form part of the microhermal biota and occur as subordinate faunal components. The association developed on the floor of a calm, shallow-marine lagoon with restricted water interchange and reduced oxygenation at the sediment–water interface.     

Paleocene reefs on the Maiella Platform Margin, Italy: An example of the effects of the cretaceous/tertiary boundary events on reefs and carbonate platforms

Summary Reef facies, reef types and their biotic associations in the Maiella platform margin (central Italy) provide qualitative evidence for a significant reef decline across the Cretaceous/Tertiary (K/T) boundary, and indicate two phases of reef recovery during the Paleocene. Rudists dominated the reef community until the latest Cretaceous. A significant sea-level fall around the time of the K/T boundary is documented by a truncation surface associated with emersion. During sea-level highstands in the Danian to Early Thanetian and, more extensively, during the Late Thanetian, coral-algal patch-reefs grew along the platform margin and top. Already in the Danian to Early Thanetian, the reef communities were more diverse and the constructional types more evolved than previously known from this time. Differences between the Danian to Early Thanetian coral association, the Late Thanetian association, and Late Cretaceous coral faunas may have ecological or evolutionary causes. Repeated emergence produced a complex diagenetic history in the Danian to Lower Thanetian limestones. All Paleocene reefs were displaced by gravitative redeposition. Coral-algal reefs are less important in the Early to mid Eocene, when alveolinid foraminifera dominated on the Maiella shelf. Reefs on the Maiella platform diversified and attained large sizes in the Late Eocene to Early Oligocene, as known from other Mediterranean platforms. The external controls on the Late Cretaceous to Oligocene evolution and demise of reef communities that are most easily demonstrated with our data are sealevel fluctuations and climate change. We propose that the change in reef biota and reef types across the K/T boundary and during the Early Tertiary were important causes of the parallel changes in platform growth style.     

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.     

Calcareous nannofossil biostratigraphy of the Thomel Level (OAE2) in the Lambruisse section, Vocontian Basin, southeast France

The Thomel Level of the Lambruisse section in the Vocontian Basin (southeast France), which is marked by intercalations of black shales and organic-rich marls, accumulated during the oceanic anoxic event 2 (OAE2) occurring in the Cenomanian-Turonian (C-T) boundary interval. Calcareous nannofossil biostratigraphic investigation of this interval revealed a total of five nannofossil zones, corresponding to the UC3-UC8 zones (Middle Cenomanian-Middle Turonian) as defined by Burnett. Biostratigraphically important taxa observed in the section include Cretarhabdus striatus, Axopodorhabdus albianus, Lithraphidites acutus, Corollithion kennedyi, Helenea chiastia, Quadrum gartneri, Q. intermedium, Eiffellithus eximius, Eprolithus octopetalus and E. eptapetalus. The two nannofossil events commonly used in the delineation of the C-T boundary, namely the LO of H. chiastia and the FO of Q. gartneri, occur less than 2 m apart in the studied section. These two bioevents define the limits of the UC6 nannofossil Zone and occur within the Whiteinella archaeocretacea foraminifer Zone. Previous litho- and chemostratigraphic analyses indicate that the δ¹³C profile of the section corresponds well with changes in lithofacies and fluctuations in the total organic carbon (TOC) and calcium carbonate content of the section. Initial increase in the δ¹³C values occurs within the UC3-UC4a undifferentiated zone, coinciding with the onset of the deposition of the organic-rich sediments of the Thomel Level and a drastic decline in the CaCO₃ values. The plateau of high δ¹³C values, on the other hand, occurs within the UC5 zone, between the LO of C. kennedyi and the LO of H. chiastia (and FO of Q. gartneri). This interval of high δ¹³C values also corresponds to the interval of high TOC and low CaCO₃ values. The integrated nannofossil, planktonic foraminifer and δ¹³C data provide a precise biostratigraphic and chemostratigraphic framework of the C-T boundary in the Lambruisse section that can be used in future studies in the Vocontian Basin and allow correlations with other well-studied C-T boundary sections.     

Autochthonous facies and allochthonous debris flows compared: Early oligocene carbonate facies patterns of the Lower Inn Valley (Tyrol, Austria)

Summary This study presents a microfacies analysis and palaco-environmental interpretations of Early Oligocene carbon ates from the Lower Inn Valley Tertiary (“Unterinntal-Terti?r”) of Austria. The well preserved biogenic components allow detailed investigations of component relationships and controlling ecological parameters. The carbonates are dominated by coralline algae, corals, small and large benthic foraminifers, bryozoans and lithoclasts. Bivalves, gastropods, echinoderms, brachiopods and serpulids are subordinate. The limestones are present as A) autochthonous carbonates transgressing directly above the Triassic basement and B) allochthonous debris flows within deeper-water marls. These carbonates are found within the Paisslberg Formation. The Werlberg Member within this formation, pertains to the autochthonous carbonates and larger debris flows. Five facies types are separated following fabric analysis and statistical treatment (correlation, cluster analysis, principal components analysis) of semi-quantitative data consisting of component frequencies of thin sections. Facies distribution patterns are principally controlled by variations in substrate characteristics, turbulence and light along a depth gradient. Reconstruction of facies pattern distribution reveal both lateral and proximal-distal facies trends: coral-coralline algal facies, coralline algal facies as well as foraminiferal facies were situated in shallower environments, laterally adjacent to each other. These grade distally into coralline algal-bryozoan facies, bryozoan facies and finally into mollusc rich marls. Debris flows consisting of reworked material from all of the known facies (bioclastic packstone facies) is restricted to the debris flow and possible represents transport induced differentiation of components and grain size within distal debris flows.     

Analysis of Late Jurassic to Early Cretaceous algal debris-facies of the Plassen carbonate platform in the Northern Calcareous Alps (Germany,Austria) and in the Kurbnesh area of the Mirdita zone (Albania): a tool to reconstruct tectonics and palaeogeography of eroded platforms

A characteristic microfacies of the Late Jurassic to Early Cretaceous allodapic Barmstein Limestone of the Northern Calcareous Alps are clasts of wackestones with numerous fragments of calcareous algae (“algal debris-facies”). According to dasycladale palaeocoenoses, several subtypes comprising different associations can be distinguished. One association is characterized by the debris of an unknown large dasycladalean alga reported as dasycladalean alga indet. sp. 1 from different localities in the Northern Calcareous Alps, typically forming a monospecific assemblage. Another microfacies type contains star-like calcitic bodies tentatively referred to the morphospecies Coptocampylodon pantici Ljubović-Obradović and Radoičić, originally described as being from the Turonian of NW-Serbia. Other Coptocampylodon-like bodies represent the calcified tufts of the laterals of Selliporella neocomiensis (Radoičić). The occurrence of Coptocampylodon pantici-like microfossils in the Late Tithonian to Early Berriasian, shows that obviously different species of dasycladaleans display identical to similar shaped tufts of laterals in transverse sections when becoming fragmented. Coptocampylodon pantici Ljubović-Obradović and Radoičić was observed only from different occurrences of Barmstein Limestone, but not from the autochthonous platform carbonates of the Plassen carbonate platform. The Coptocampylodon algal debris-facies is also reported from the Late Jurassic of Albania, Mirdita zone. Occurrences of different types of algal debris-facies in components of mass-flow deposits can be used as a tool to reconstruct eroded carbonate platforms and tectonics, as demonstrated in the Northern Calcareous Alps and the Albanides. Finally, the general occurrences of algal debris-facies in both settings—intra-Tethyan mostly isolated platforms (Alps, Albanides) vs. extended epeiric platforms (Middle East)—are compared and discussed.     

Homoiohydrous (recalcitrant) seeds: Developmental status,desiccation sensitivity and the state of water in axes of Landolphia kirkii Dyer

The desiccation sensitivity in relation to the stage of development was investigated in embryonic axes from the homoiohydrous (recalcitrant) seeds of Landolphia kirkii. Electrolyte leakage, used to assess membrane damage after flash (very rapid) drying, indicated that axes from immature (non-germinable) seeds were the most desiccation-tolerant, followed by those from mature seeds, while axes from seeds germinated for increasing times were progressively more desiccation-sensitive. Differential scanning calorimetry was used to study the relationship between desiccation sensitivity and the properties of water in the tissues. Axes from immature seeds had a lower content of non-freezable water than that of any other developmental stage and a higher enthalpy of melting of freezable water. For mature and immature axes electrolyte leakage increased at the point of loss of freezable water. At other developmental stages the water content at which electrolyte leakage increased markedly correlated with the other properties of the water, such as the change in the shape of the melting endotherm and the onset temperature. Ultrastructural studies of axes at the various developmental stages showed changes in the degree and pattern of vacuolation, the presence and quantities of lipid and starch, and the degree of endomembrane development. The results are discussed in relation to current hypotheses on the basis of desiccation tolerance.Abbreviation DSC differential scanning calorimetry