Calcareous dinoflagellate blooms during the Late Cretaceous 'greenhouse' world-a case study from western Ukraine.

The Late Cretaceous was a unique period in the history of the Earth characterized by elevated sea levels, reduced land area, and significantly high concentrations of atmospheric CO2 resulting in increased temperatures across the globe-a 'Greenhouse World'. During this period, calcareous dinoflagellate cysts (c-dinocysts) flourished and became a ubiquitous constituent of calcifying plankton around the world. An acme in calcareous dinocysts during the Albian to the Turonian coincided with the highest recorded seawater surface temperatures and was possibly linked to conditions that favored calcification and a highly oligotrophic system in European shelf seas. This study examines the potential applicability of c-dinocysts as a proxy for paleoenvironmental conditions based on their assemblage changes plotted against foraminiferal occurrences and microfacies analysis. The material was extracted from the upper Turonian chalk of the Dubivtsi region in western Ukraine. An inverse correlation was observed between species diversity and the number of c-dinocyst specimens. Nutrient availability gradients apparently determined important changes in the calcareous dinocysts distribution. These trophic changes were likely caused by the interplay of eustatic sea-level fluctuations and Subhercynian tectonic activity leading to changeable nutrient inputs from the nearby land.

Mg-rich amorphous to Mg-low crystalline CaCO3 pathway in foraminifera.

Calcium carbonate minerals produced by marine organisms play a central role in the global carbon cycle and carbonate sedimentation, which influence the climate by regulating atmospheric CO2 levels. Foraminifera are important marine single-celled organisms that have produced calcite shells for over 300 million years. Here, we present new observations promoting our understanding for foraminiferal biocalcification by studying Amphistegina lessonii. We integrated in vivo confocal autofluorescence and dye fluorescence imaging with elemental analysis of the cell supporting the concept that the calcite shells of foraminifera are produced via deposition of intracellularly formed Mg-rich amorphous calcium carbonate (Mg-ACC) particles that transform into a stable mineral phase. This process is likely accompanied by the activity of endosymbiotic microalgae and seawater-derived endocytic vesicles that provide calcification substrates such as DIC, Ca2+, and Mg2+. The final transformation of semi-liquid amorphous nanoparticles into a crystalline shell was associated with Mg2+ liberation.

Stable isotopes and predation marks shed new light on ammonoid habitat depth preferences.

Ammonoids are extinct cephalopods with external shells which predominated in many late Paleozoic and Mesozoic marine ecosystems. Stable isotope data from ammonoid shells constitute primary tools for understanding their palaeohabitats. However, in most sedimentary successions globally the aragonitic shells of ammonoids are dissolved during fossilisation process and therefore not available for geochemical studies. We overcome this taphonomic bias by analysing the better preservable calcitic elements of the ammonoid jaws (aptychi). We study moulds and aptychi of two successive members, temporal subspecies in our interpretation, of a scaphitid evolutionary lineage from a Late Cretaceous chalk succession in Poland. In order to reconstruct their habitat depth preferences, we apply the powerful combination of stable isotope data from aptychi and co-occurring benthic and planktic foraminifera with an analysis of predation marks preserved on scaphitid specimens. On this basis we conclude that the populations of the older subspecies led a nektic, and those of the younger subspecies, a nektobenthic lifestyle. The shift in habitat depth preferences took place probably as a response of local populations to the shallowing of the sea. Previous studies largely assumed stable depth preferences for ammonoid species, genera and even higher clades. Our study casts doubts over such generalizations by pointing out that ammonoids could have been more flexible in their depth-related behaviour than anticipated.

Test structure in some pioneer multichambered Paleozoic foraminifera.

Foraminiferal wall microstructures, consistent with the molecular-based high-rank classification, are critical to understanding foraminiferal evolution and advanced taxonomic relationships. Although test structures are well documented for recent, Cenozoic, and some Mesozoic foraminifera, the diagnostic characteristics of Paleozoic taxa are largely unexplored. The majority of calcareous Paleozoic foraminifera have been assigned to the Fusulinata based on questionable homogeneously "microgranular" test wall microstructures, which have never been sufficiently documented for most taxa. We investigated the test structures of exceptionally well-preserved Devonian (Eifelian) Semitextularia thomasi, representing the first calcareous true multichambered (serial) foraminifera, and compared this species with a large fusiform Permian representative of "true" fusulinids (Neoschwagerinidae). The tests of Semitextularia thomasi display lamellar structures that are not observed in any other fossil or recent foraminiferal group. The Paleozoic foraminifera, traditionally referred to one taxon (the class Fusulinata), possess at least three contrasting test wall microstructures, representing separate high-rank taxonomic groups. Fusulinata is most likely a highly polyphyletic group that is in need of taxonomic revision. The term Fusulinata, defined as including all Paleozoic calcareous forms except Miliolida and Lagenata, is not phylogenetically meaningful and should no longer be used or should be restricted to true complex fusulinids with microgranular test structures, which appeared in the Carboniferous.

Mercury spikes as evidence of extended arc-volcanism around the Devonian-Carboniferous boundary in the South Tian Shan (southern Uzbekistan).

Recently, the end-Devonian mass extinction (Hangenberg Crisis, 359 Ma) was identified as a first-order mass extinction, albeit not one of the "Big Five" events. Many marine and terrestrial organisms were affected by this crisis. The cause of this mass extinction is still conjectural and widely discussed. Here we report anomalously high mercury (Hg) concentrations from the South Tian Shan (Uzbekistan), together with correlation using conodont biostratigraphic data. Hg enrichment (to 5825 ppb) was detected in marine deposits encompassing the Hangenberg Crisis. In the Novchomok section, the Hangenberg Crisis interval does not contain typical Hangenberg Black Shales; however, by means of inorganic geochemistry (enrichment of redox-sensitive elements such as Mo, V, and U) we detected an equivalent level despite the lack of marked facies changes. This is the first record of Hg and Hg/total organic carbon anomalies in marly shales, marls and carbonates that are totally independent of facies changes, implying that volcanism was the most probable cause of the Hangenberg Crisis. This conclusion is confirmed by the presence of a negative δ13C excursion, which may reflect massive release of isotopically light carbon from volcanogenic and thermogenic devolatilization likely combined with increased arc-volcanism activity worldwide at the end of the Devonian.

Unlocking the biomineralization style and affinity of Paleozoic fusulinid foraminifera.

Fusulinids are the most diverse, abundant and geographically widespread Paleozoic foraminifera which are widely considered to possess a "homogeneously microgranular" test microstructure composed of subangular grains of several micrometers in size. However, this texture appears to be a diagenetic artifact. Here we describe well-preserved Devonian calcareous fusulinids (Nanicella) from the Holy Cross Mountains (HCM) in central Poland. Foraminifera from Poland in which the primary nature of tests have not been masked by diagenesis are composed of low magnesium calcite spherical grains up to about 100 nanometers in diameter, identical to those observed in Recent and fossil hyaline foraminifera (Rotaliida, Globothalamea). These data call the paradigm of microgranular test microstructure of Foraminifera into question, and suggest a possible phylogenetic relationship between globothalamids and some fusulinids.