Marine Micropaleontology最新文献

This study examines the variations in relative abundance, test size, and biomass of the species Bolivina ordinaria (Foraminifera) over the last 112 ka BP on the northern slope of the Pelotas Basin, Southern Brazil. The analyses were based on 651 individuals from 42 samples distributed along the cores SIS-249 (Marine Isotope Stage 5 to 3) and SIS-188 (Marine Isotope Stage 3 to 1). Bolivina ordinaria was the most abundant species of the Bolivinitidae family in these cores, particularly during warmer periods (MIS 1 and 5). Nine other species of this family were identified: B. compacta, B. doniezi, B. lowmani, Bolivina sp., B.striatula, Brizalina sp., Brizalina spinescens, Brizalina subaenariensis, and Brizalina subspinescens. Larger test lengths were observed during MIS 3 in the both cores. The summed biomass was higher during MIS 5 in the SIS-249 core and lower during MIS 3 in the SIS-188 core. The fluctuations observed in the relative abundance and summed biomass of B. ordinaria are consistent with the oscillations in total organic carbon flow, and the variations in primary productivity between the interglacial and glacial periods. The results suggest that this infaunal species is favored by the regular supply of refractory organic matter during warmer periods but faces increased competition from shallow infaunal and epifaunal species during glacial periods, when the flow of labile organic matter increases.

A serious threat affecting the Mediterranean Sea is the migration of Indo-Pacific marine species through the Suez Canal following its opening in 1869. This phenomenon gives extreme causes for concern as many non-indigenous species are highly invasive and seriously threaten native biodiversity. Particularly insidious are small-size taxa such as benthic foraminifera, which are able to invade wide areas un-noticed.

The objective of this study is to evaluate the stage of invasion of non-indigenous foraminifer Amphistegina lobifera and the re-colonization of Amphistegina lessonii in two islands of the Pelagian Archipelago (Central Mediterranean) where both species were first recorded in 2005.

Absolute abundances quantified in seabed and algal samples collected in 2014 were compared with those detected in 2005 and 2009. Results show that, in the innermost part of the neritic environment, amphisteginids were so abundant and widespread as to have replaced native benthic foraminifera just a few years after earlier reports.

On Lampedusa Island, Amphisteginids seem to compete mainly with other symbiont-bearing foraminifera, such as the milioliid Peneroplis pertusus and Peneroplis planatus; we hypothesize that the different algal symbionts housed by the invasive species could play an important role in the invasion success in the Mediterranean Sea. In the most severe case of amphisteginid invasion, as seen around the volcanic island of Linosa, the accumulation of their carbonatic remains is causing a sedimentation switch: increasing the content of white carbonatic sands and replacing the black volcanic substrates, as already observed in Indian Ocean atolls.

This study reveals moderate yet important variations in Watznaueria barnesiae coccolith and central unit size throughout the Aptian–late Cenomanian (27 my) time interval in western Tethys. A new statistical approach was applied to determine whether non-random size trends apply to these metrics and to identify possible links between their variation and fertility or temperature. During OAE 1a, W. barnesiae coccoliths were the smallest and the most elliptical, with reduced central unit size. A further minor size decrease occurs during OAE 1b but not during OAE 1d. From the middle Albian to the middle Cenomanian, larger and less elliptical coccoliths are observed, with unchanged central unit dimensions. These results, together with concomitantly larger size changes in Biscutum constans confirm that W. barnesiae is a tolerant taxon. High-frequency, high-amplitude paleoenvironmental changes during the Aptian–early Albian indicate that temperature and fertility – either individually or in combination – had no direct impact on the mean coccolith size and potentially other factors affected coccolith size. Instead, lower nutrients with lower temperatures probably played a role in promoting larger W. barnesiae but smaller B. constans coccoliths during the middle Albian–Cenomanian. The size and ellipticity changes during OAE 1a and 1b were the strongest, likely resulting from ocean acidification and trace metal inputs, in addition to (or independently of) fertility and temperature variations.

The Cerro Azul Section provides a continuous record of the Cretaceous-Paleogene (K-Pg) transition in a shallow marine context of the South Atlantic Ocean in the Neuquén Basin. Ostracod assemblages were severely affected by environmental changes across the event. Excellent ostracod preservation at the Cerro Azul Section allows to infer paleoecological preferences of four Danian species based on carbon and oxygen stable isotopes. The studied species were Paracypris bertelsae Ceolin and Whatley, 2015, Cytherella spp., Togoina argentinensis and Henryhowella (Wichmannella) meridionalis (Bertels, 1974). To assess the reliability of ostracod δ¹³C and δ¹⁸O values as paleoenvironmental proxies, we pre-characterized valves with micro x-ray microdiffraction (μXRD) and microRaman (μRaman spectroscopy). Togoina argentinensis and Henryhowella (Wichmannella) meridionalis present in their major calcitic compositions, with small differences of crystallinity within intervals of environmental stress, but no authigenic phases formed during diagenesis. δ¹³C and δ¹⁸O values depict clear interspecific differences between smooth specimens and ornamented specimens. These differences in stable isotope values were likely controlled by microhabitat preferences, which would be comparable with patterns described for benthic foraminifera as well as paleonutrients variations, suing Ba/Ti and P/Ti ratios.

The Island of Rhodes, located in the Eastern Mediterranean Sea, is affected by an active convergent plate boundary. In this context, marine sediments of Plio-Pleistocene age have been uplifted and are outcropping along the eastern coast of Rhodes. These archives provide an excellent opportunity to unravel the hydrological and climatic changes of the region during the late Pliocene. Our results provide new evidence for a more humid climate and an increased precipitation on the island during times of Northern Hemisphere summer insolation maxima and related sapropel formation in the Mediterranean deep sea. The periodic occurrence of eutrophic conditions at the shelf and upper slope off Rhodes is indicated by the recurrent dominance of eutrophic indicator species (of the genera Bolivina, Eubuliminella and Rectuvigerina), simultaneously with a decline in diversity and oligotrophic indicator species. These conditions resulted from higher primary productivity, triggered by local effects, such as enhanced precipitation and river run-off, which consequently favors the appearance of eutrophic taxa. The ∆δ¹³C records of the epibenthic foraminifera Cibicidoides pseudoungerianus and the shallow infaunal species Uvigerina peregrina indicate a slight productivity decrease towards younger times.

Seagrasses are marine angiosperms documented in shallow-marine, soft bottom settings across the Cenozoic. They proliferated globally after their divergence from other alismatid monocots in the late Cretaceous followed by an adaptation to the marine environment. Detailed evaluation of seagrasses in the geological archives is of utmost importance to understand their responses to climatic and environmental alterations in the deep time perspective. Here we examine the lower Miocene Quilon Limestone from the Kerala Basin (southwest India) that encompasses a Pseudotaberina-Halimeda floatstone signalling a robust photozoan foralgal skeletal assemblage. This is characterized by the dominant soritid foraminifer Pseudotaberina and the calcareous green alga Halimeda, in association with other foraminifera and representatives from various biotic groups that indicate a tropical seagrass paleoenvironment. Abundant soritids together with various bryopsidalean Halimeda species indicate light and temperature as the major ecological drivers regulating the Quilon Limestone seagrass paleocommunity during the early Miocene (Burdigalian). The spatio-temporal distribution patterns of Halimeda also indicate temperature as the most prominent ecological constraint determining its dispersal and evolution at multiple latitudes. A well illuminated substrate is envisaged to support the development and calcification of the Halimeda thalli. Abundance of K-strategist foraminifera with minor occurrence of suspension-feeding bryozoans and some gastropods, bivalves indicate a low-nutrient environment.

We investigate the response of calcareous nannoplankton to the middle-late Eocene transition in the SW Neo-Tethys and compare our data to published results from X-ray diffraction (XRD) analysis, element content from X-ray fluorescence (XRF) and the abundance of microfossils in the coarse fractions of the sediment. The nannofossil assemblage is mainly composed of Reticulofenestra spp. (avg. 44%), Sphenolithus spp. (avg. 20%), Discoaster spp. (avg. 18%) and Pontosphaera spp. (avg. 10%). The Relative abundance of Zygrhablithus bijugatus and the Chiasmolithus ratio are used with the visual assessment to evaluate the preservation. The Sphenolithus-Reticulofenestra turnover occurred before the MECO at the Lutetian-Bartonian boundary. Besides the significant influence of an evolutionary gradient caused by the disappearance of numerous species of Sphenoliths, Discoasterids, and Coccolithaceae, and the first appearance of multiple species of reticulofenestrids, paleoenvironmental conditions imposed a significant impact on the calcareous nannofossil assemblages. The abundance of ostracods and the planktic/benthic foraminifera ratio depict relative sea-level changes. The microfossil assemblages and the lithological composition of the sediments track paleoclimatic and paleoenvironmental changes across the Lutetian to Priabonian. Dry conditions marked the middle Lutetian, followed by increased variability in hydrolyzing conditions during the late Lutetian and early Bartonian. An eutrophic and restricted ecosystem with high fine-grained material input is suggested for the Priabonian.

Diverse and well-preserved assemblages of organic-walled dinoflagellate cysts have been recovered from the Matulla Formation (Coniacian – Santonian), Gulf of Suez, Egypt. Among the abundant dinoflagellate cyst assemblages, the new species Odontochitina elbeialyi sp. nov. and Odontochitina ornata sp. nov. (Family Ceratiaceae) are described. The two new species are unique by having a granulate periphragm and three prominent horns. The horns are truncated distally and devoid of striae, ridges and perforations. Odontochitina elbeialyi sp. nov. is characterized by a weakly expressed tabulation on the pericyst indicated by the occasional presence of sutural lines or low ridges indicating the cingulum (two transverse ridges), at plate boundaries. Odontochitina ornata sp. nov. differs from the former, particularly by its clear tabulation, which is corniform gonyaulacoid and more strongly expressed by sutural ridges, and by rare short (rudimentary) sutural (mostly gonal) nipple-like, to truncated processes. Based on the current material, Odontochitina elbeialyi sp. nov. and Odontochitina ornata sp. nov. have short stratigraphic ranges and may therefore be considered as stratigraphic markers for the late Santonian (Late Cretaceous). Their comparison with all formally published species of the genus Odontochitina is presented and discussed, and the associated relevant dinoflagellate cyst taxa are also indicated. The paleoenvironmental significance of the Odontochitina elbeialyi sp. nov. and Odontochitina ornata sp. nov. is discussed.

The present paper outlines the results of a detailed study of calcareous nannofossils and small foraminifera made on Campanian marine deposits from the southwestern part of the Transylvanian Basin, Romania, part of the marine-to-continental transitional Petrești succession that yielded the oldest temporally well-constrained continental vertebrate remains in this area. These results are integrated with new and previously published palynostratigraphic information as well as with novel detrital zircon geochronometry data. All three groups of fossils (calcareous nannofossils, small foraminifera, and palynomorphs) convergently indicate an early to middle Late Campanian age for the marine part of the Petrești section. Based on detrital zircon analyses, the most likely maximum depositional age of the studied deposits is 76 ± 1.7 Ma, thus confirming the age supported by microfossil assemblages. Palaeoenvironmental interpretation of the fossil assemblages recovered from the marine part of the Petrești section suggests that despite their flysch-like facies, these beds were deposited in a continental shelf setting, under suboxic conditions and frequent fluctuations in nutrient supply to the seafloor, but quite stable environmental conditions within the water column. The synthesis of all currently available biostratigraphic and geochronologic data from the Petrești succession suggests a middle-late Late Campanian start for the expansion of the emergent land areas that made up the latest Cretaceous Hațeg Island, earlier than previously accepted dates (Maastrichtian) for this event. Furthermore, it documents the establishment of a diversified continental vertebrate faunal assemblage by the second half of the Late Campanian on these emergent lands while also providing further evidence for a later, post-Campanian arrival of certain iconic Hațeg Island dinosaur groups such as titanosaurs and hadrosauroids. Finally, our data show that kogaionid multituberculate mammals were already members of the earliest known Hațeg Island faunas, extending the fossil record of this group from the Maastrichtian into the later part of the middle Late Campanian.

While they are extremely abundant and ecologically important, the epiphytic foraminifera of tropical reefs are still poorly known. The present study describes the foraminiferal assemblages associated with macroalgae on tropical reefs of the Brazilian coast. Samples of four species of macroalgae, two foliose (Padina antillarum and Ulva lactuca) and two corticated (Palisada perforata and Gelidiella acerosa), were collected from intertidal sandstone reefs at Pina, Enseada dos Corais, and Toquinho (Northeastern Brazil). Overall, only 13.3% of the 708,754 foraminifera specimens were alive, belonging to 37 species, with dominance of Rosalina anglica. Most tests were hyaline-perforate and conical in shape, and most species were permanently or temporarily sessile. The majority of living foraminifera were attached to the surface of Palisada and Gelidiella, and no attached specimens were found in either Padina or Ulva. The species richness and abundance of the living foraminifera varied significantly among the macroalgae, occurring the high values in P. perforata. The assemblages varied significantly between the two species of corticated macroalgae, and between the corticated and foliose species, but not between the two foliose algae. Some of the specimens of Glabratella and Rosalina were reproducing, and had juveniles attached to the parental test. This is the first study to focus on the ecological interactions of the epiphytic foraminifera of the tropical southern Atlantic Ocean, and its results indicate that the characteristics of the epiphytic assemblages can be used as a proxy for the understanding of the structure and function of microbenthic communities on tropical reefs.