Rise and fall of rotaliids in the Paleocene-Eocene: the influence of climate and trophic competition

<p>It is largely accepted that climate plays a pivotal role in the diversification of shallow-water communities, with special regards to larger foraminifera (LF), also because increase of surface water temperatures is often accompanied by change in trophic conditions. The shift from widespread eutrophic to oligotrophic conditions in shallow seas probably contributed to the LF differentiation during Paleocene-Eocene times. However, there are few recent attempts to quantify the changes in biodiversity and to correlate them with the global climatic events of the Paleogene. We concentrated our attention on the group of rotaliids, resilient taxa that partially survived after the mass extinction occurred at the end of the Cretaceous.</p><p>Our data show that their differentiation at genus level was very rapid, reaching its maximum already in the late Danian SB2 Zone. Specific diversification, instead, culminated in late Thanetian SB4 Zone. A second peak in specific diversity is recorded during the Cuisian (upper part of the Ypresian), then rotaliid diversity steadily declined, as long as other groups of larger foraminifers, especially <em>Alveolina </em>and <em>Nummulites</em>, became more competitive and proliferated with a large number of species up to the Bartonian SB17 Zone, when a significant drop in rotaliid biodiversity is recorded.</p><p>Differently to other taxonomic groups, i.e., alveolinids and nummulitids, for which a single genus during the whole Eocene generated numerous species, rotaliid genera are usually characterized by a low number of species, possibly due to the re-opening of ecological niches after the abrupt decrease of diversity that followed the PETM event. The competition with other K-strategist LF probably contributed to the decline of rotaliids in the middle Eocene up to the MECO event, where a last dramatic drop is recorded.</p><p>The major changes appear strictly linked to warming events such as the Late Danian Event (LDE, starting of the generic diversification of rotaliids), Paleocene Eocene Termal Maximum (PETM, faunal turnover followed by abrupt decrease in both generic and specific diversity), Early Eocene Climatic Optimum (EECO, increase in number of K-strategists under widespread oligotrophic conditions) and Middle Eocene Climatic Optimum (MECO, ultimate drop in diversity and competition with other larger foraminifers).</p><p>This study was funded by the Italian Ministry of Education and Research (MIUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).</p>

Geochemical and micropaleontological evidence of paleoenvironmental change in the Late Cretaceous Western Interior Seaway from the Niobrara to the Pierre Shale Formation

Deposition of the Upper Cretaceous Niobrara Formation and overlying Sharon Springs Member of the Pierre Shale occurred during transgressive phases within the Western Interior Cretaceous (WIC) Seaway, however their respective geochemical and biological differences are significant. The Niobrara Formation is an alternating calcareous chalk/marl system, biologically defined by fecal pellets and robust foraminifers including Heterohelix globulosa, Globigerinelloides ultramicrus, Hedbergella, Giimbelina and two Archaeoglobigerina species. However, the Sharon Springs is primarily argillaceous in composition with lesser amounts of biogenic calcite and silica. Larger foraminifers within the Sharon Springs are primarily arenaceous whereas foraminifers of the same species found in the Niobrara are dwarfed in the Sharon Springs. Dwarfism of foraminifers species and the presence of dispersed diatoms, which flourish in cold waters, indicate a shift in paleocurrents. Deposition of the Niobrara occurred during times when warm Gulfian currents allowed for carbonate production through the Early Campanian. Paleogeographic maps of the Middle Campanian indicate a southerly restriction of the WIC during the time of the southerly Claggett Transgression. The influx of cold, southerly waters resulted in an environment conducive to diatoms and environmentally stressful to foraminifers. Lithological and geochemical evidence from the Sharon Springs indicates that the cold-water Claggett Transgression resulted in a stratified water column in the middle of the WIC as well as increased organic matter production. Petrographic analysis of preserved organic matter show clumped floccules or flattened amalgamations of floccules in laminated facies. While dispersed amorphous organic matter is also present, flocculation had a major influence on organic matter preservation. Two possible depositional mechanisms, each dependent on water density, probably produced these water conditions. If density contrasts existed between the cold water influx and the warm waters present during the deposition of the Niobrara, the cold waters would have progressed along the bottom of the basin leading to upwelling along the basin margin and basin stratification. If no significant density contrast existed, caballing would occur at the mixing front, leading to downwelling, rapid transport of organic matter to the sea floor, better organic matter preservation and basin stratification.

The study of lepidocyclina (eulepidina) (foraminifera) from middle Oligocene to lower Miocene of South Albania

There are studied too many samples from Ionian Zone (geological outcrops and drilling wells) and Koma depression containing Larger Foraminifers, Lepidocyclina (Eulepidina) subgenus. For their study, determination to species level, biometrie and counting measurements known in literature are used. According to proposal (for Mediterranean region) we suggest that in south Albania also can be separated the following species and subspecies: - Lepidocyclina-(Eulepidina) formosoides DOUVILLE R. - Lepidocyclina-(Eulepidina) dilatata (MICHELOTTI) - Lepidocyclina-(Eulepidina) dilatata (MICHELOTTI) var concentrica SILVESTRI For the specimens of microsphaeric generation (B-Form, diameter more than 5 centimeter) maintained the typological concept of classification and were attributed to the species Lepidocyclina (Eulepidina) elephantine LEMOINE and DOUVILLE (1904). They are given briefly the deposition conditions of the shells of this subgenus in flysch (Ionian Zone and mollasic deposits (Korria depression) Middle Oligocene- Lower Miocene age. The paper has been accompanied by means 3 plates.

Bleaching in foraminifera with algal symbionts: implications for reef monitoring and risk asessment

Reef-dwelling larger foraminifers share key characteristics with reefbuilding corals: they are prolific producers of calcium carbonate, they are physiologically dependent upon algal endosymbionts, and representatives of both groups have suffered bleaching episodes in recent decades. Since 1991, bleaching has been observed in populations of Amphistegina in all subtropical oceans, with peak bleaching in 1992 and secondary peaks in 1998 and 2005. Amphistegina populations exhibiting chronic, intermediate-intensity bleaching characteristically show anomalously high incidences of shell breakage, shell deformities, evidence of predation, and microbial infestation. Asexual reproduction is profoundly affected; broods from partly bleached parents typically have fewer individuals, many of which are anomalous in shape and size. Key differences between bleaching in corals and Amphistegina are that corals typically bleach by expelling their symbionts, while Amphistegina bleach when damaged symbionts are digested, and that mass coral bleaching requires high light but correlates most consistently with elevated temperatures, while bleaching in Amphistegina is induced by light. Amphistegina are particularly sensitive to the shorter (300-490 nm) wavelengths of solar radiation, which have increased in intensity relative to longer visible wavelengths (>;490-700 nm) in clear reef waters over the past 30 years as a consequence of stratospheric ozone depletion. Abundances and visual assessments of Amphistegina populations can be used as a low-cost risk-assessment tool. These protists are sensitive to environmental conditions over days to weeks, and provide a method to quickly distinguish between water quality (local) and photo-oxidative (global) stresses. Risk assessments based on the combined use of in situ measurements and low-cost indicators can provide resource managers with essential information to decide when more costly chemical or molecular procedures are needed to determine local sources of stress.

Biostratigraphy of Late Maastrichtian larger foraminifers in Jamaica and the importance of <i>Chubbina</i> as a Late Maastrichtian index fossil

The succession of larger foraminifers from the White Rock River Bridge section of the Guinea Corn Formation (Late Maastrichtian) in Jamaica, West Indies, contains: Sulcoperculina dickersoni (Palmer), Ayalaina rutteni (Palmer), Orbitoides cf. megaloformis Papp &amp; Küpper, Vaughania cubensis Palmer and Chubbina cardenasensis (Barker &amp; Grimsdale). A. rutteni occurs in the lower beds and C. cardenasensis occurs in the upper beds. The orbitoid foraminifer Or. cf. megaloformis is restricted to the middle beds. The White Rock River Bridge Section can be correlated to the standard Guinea Corn successions using lithological/biostratigraphic markers and rudist marker beds, and linked ages derived from Sr-isotope values. This indicates that Or. cf. megaloformis occurs in the last 1.3 Ma of the Cretaceous in the Caribbean and that its evolution was retrograde compared to coeval populations in Europe. The first appearance of Chubbina represents a valuable datum since the genus occurs in various different biofacies (both with and without orbitoid foraminifers) and allows correlation in the Caribbean, Central America and Florida.