Marine Micropaleontology最新文献

Conodonts from Permian-Triassic Boundary (P-TB) beds have been intensively investigated in recent years. Many species survived the end-Permian mass extinction, and some became cosmopolitan in the earliest Triassic. Most studies have focused on common families such as the Gondolellidae and the Achignathodidae, whilst the Ellisonidae is understudied due to the difficulties of reconstructing their multi-element apparatus. Here, we focus on the Ellisonidae from the Meishan, Shangsi and Gaohua sections in South China and find Merrilina (M.) spp. are common taxa. A representative species, M. ultima, previously regarded as a Changhsingian cool-water species, is found in warm, shallow platform settings of the earliest Triassic. Biostratigraphically, M. ultima ranges from the Hindeodus parvus Zone to the Isarcicella staeschei Zone at Meishan and to the I. isarcica Zone at Gaohua, whilst it only occurred in the Clarkina taylore Zone at Shangsi. A compilation of all published data suggests M. ultima firstly appeared in the C. meishanensis-H. praeparvus Zone and went extinct in the I. isarcica Zone. Merrillina spp. occur in various settings and latitudes, indicating that the species were likely cosmopolitan taxa that favoured surface-water habitats and were not restricted to cool waters.

Paleo-reconstructions using element to calcium ratios (Me/Ca) of marine ostracods were usually focused on Mg/Ca and Sr/Ca, whereas paleo-environmental applications using other ostracod Me/Ca including Na/Ca, Ba/Ca, Mn/Ca, Zn/Ca, Ni/Ca, Cd/Ca, Cu/Ca and Cr/Ca have been rather limited due to the lack of a general understanding of the control of physicochemical marine variables on trace-elements uptake. Ba/Ca and Na/Ca were linked to temperature, while Mn/Ca was suggested to be an indicator of redox conditions and used to track oxide contamination in marine shells. The potential of other ostracod ratios as environmental proxies has rarely been investigated. Here, we study the empirical relations between seawater physicochemical variables and several Me/Ca of ostracod shells in shallow marine waters. Our results suggest that shallow sea parameters related to the control of metal concentrations in seawater and sediments such as suspended solids, salinity, electrochemical potential and total carbon are correlated to Me/Ca such as Mn/Ca and Zn/Ca in ostracod shells of Sinocytheridea impressa and Neomonoceratina delicata from Hong Kong coastal waters. Correlations are not always significant for both species, indicating that other factors such as species-specific habitats or biomineralization processes may also play a role in the incorporation of metals. We demonstrate that the combination of multiple linear regressions using several significant sea parameters provides useful information to reconstruct shallow marine conditions including water temperature, salinity, suspended solid and total carbon in sediments. Thus, a detailed description of the marine environment in Hong Kong coastal waters can be achieved.

The Pirabas Formation (Neogene, eastern Brazilian Amazonia) is the only marine Miocene unit in Brazil that crops out on the edge of the equatorial shelf. The formation has a distinctive mixture of carbonate and siliciclastic sediments. The paleodiversity of the deposit includes assemblages of foraminifera, ostracods, decapod crustaceans, mollusks, bryozoans, corals, echinoderms, fish, and sirenids. Microfossils are abundant and palynological studies can contribute to accurate paleoenvironmental reconstructions and biostratigraphic descriptions of the Pirabas formation. Here, we present 17 samples from eight outcrops and one quarry belonging to the Pirabas Formation with a goal to understand their depositional environments and relative ages. We recorded 9 species of dinoflagellate cysts, 7 spore species morphotypes, 59 pollen species morphotypes, 17 species of diatoms, and one species of silicoflagellate. We clustered the samples into two depositional groups, with one group formed by the Capanema quarry, Ponta do Castelo and Fazenda outcrops, deposited in a mesotrophic, shallow, marine environment, with a late early-Miocene age. The second one, formed by Atalaia, Aricuru, Maçarico, and Baunilha Grande outcrops, was deposited in a mesotrophic coastal environment with nearby mangroves; these samples may date to the late middle to late Miocene.

Predicting phytoplankton responses to a changing climate on Tasmania's east coast is presently based on short-term plankton data sets (∼75 years). However, to better predict future phytoplankton composition, it is crucial to understand longer-term variations from geological records. A particularly important group are the coccolithophores given their vital contribution to the oceanic carbon pump.

Here, we expand the archive of coccolithophores in southeast Australian waters by analysing coccolith assemblages in a 268 cm-long marine sediment core collected off Maria Island, Tasmania, using light and scanning electron microscopy in combination with sedimentary ancient DNA (sedaDNA) techniques.

Coccoliths underwent a shift from a cold to warm-water adapted assemblage at ∼8.2 kyrs BP expressed by a transition in species dominance from the cold-water species Gephyrocapsa muellerae to the warmer-water species Emiliania huxleyi Type A. A period of coccolithophore community instability characterised by reduced diversity and species richness was also detected spanning ∼900 yrs. between 6 and 5 kyrs BP. The latter may be associated with a Mid-Holocene warm period in the Southern Ocean as well as sea-level rise changing the study site from a shallow coastal to deep water habitat.

Emiliania huxleyi coccoliths displayed the highest total relative abundance, but less prevalent larger taxa (Calcidiscus, Coccolithus, Helicosphaera) accounted for >50% of total estimated coccolith CaCO₃ sequestration, indicating that relatively scarce, densely calcified species do the ‘heavy-lifting’ of this process. Analysis of sedaDNA revealed coccolithophores contributed ∼44% to the total palaeo eukaryote composition, underlining their importance as part of the marine ecosystem in the study region. The detection of oceanographic shifts and subsequent coccolithophore assemblage composition, including past transitions of species dominance, offer valuable insight into the biological future of southeast Australian waters.

Studies on pollen in marine surface sediments are important for understanding the distribution mechanisms of pollen and spores into the ocean, and they are also useful in micro-paleontological studies. In this study, high-resolution palynological analysis of marine surface sediment samples from the south and southeastern inner-shelf regions of Hainan Island was performed to understand the distribution mechanism of marine surface pollen and its relationship with terrestrial vegetation. The results indicated that fern spores are the most common type, followed by tree pollen and herbaceous pollen. A majority of total pollen and spore concentrations are dominated by fern spores because the sample sites are highly concentrated with Microlepia and Polypodiaceae spores, mainly due to anthropogenic activities. The variation in tree pollen concentrations (especially for Pinus, Quercus, and Castanopsis) suggested that these pollen grains were transported mainly by wind patterns and rivers from Hainan Island. The pollen concentrations and percentage analysis in the study area showed that the inner-shelf sites have higher values than far offshore sites, reflecting a relationship between modern pollen distribution patterns and nearby landmass vegetation. Based on the principal component analysis of the resulting pollen and spore percentages, there are two main factors affecting the pollen distribution around the study area: possible human activities that have modified Hainan Island and wind–river transport toward the study area. This is the first study to discover that the presence of fern spores across the shelf is unusual, implying widespread lateral mixing in the south and southeastern Hainan Island inner-shelf region.

The complex topography of submarine canyons may result in different composition of benthic foraminifera assemblages. To understand how trophic, hydrological and sedimentological conditions in submarine canyons can influence the distribution of benthic foraminifera, and to use this information to corroborate paleoenvironmental interpretations for the Holocene, we investigated recent benthic foraminiferal assemblages (total fauna >63 μm) and sedimentological data in two canyons (CANWN and CAND) in the Espírito Santo Basin (ESB) between 18°20′ and 21°20′ S. Surface sediment samples (0–2 cm) were collected inside the canyons (150 to 1300 m water depth) and in shelf-slope adjacent transects (50 to 1300 m water depth). The density, taxonomic diversity, and assemblage composition of benthic foraminifera change with depth and location. The distinct ecological preferences of the most abundant taxa allowed us to recognize five benthic foraminiferal groups. Three groups (V, III, and I) are present in different bathymetric sectors; Group V: outer shelf (50 m), Group III: upper, and middle – lower slope (150 to 400 m), and Group I: middle – lower slope (1000 to 1300 m). Groups II and IV show no characteristic bathymetric distribution and are present only in CAND and in CANWN, respectively. Group V consists of Hanzawaia boueana, Peneroplis planatus, and Quinqueloculina lamarckiana; Group III is dominated by Globocassidulina rossensis and Trifarina spp.; Group I consists of Globocassidulina crassa, Bolivina lowmani, Gavelinopsis versiformis, Alabaminella weddellensis, and Epistominella exigua. The main species in Group II (CAND, 150, 1000 to 1300 m) are Trifarina angulosa, Globocassidulina subglobosa, and Discorbis vilardeboanus. Group IV (middle – lower CANWN, 1000 to 1300 m), consists mainly of agglutinated species Glomospira charoides, Rhabdammina abyssorum, and Psammosphaera fusca. Our data suggest that the quantity (and quality) of food supply, hydrodynamic conditions and sediment properties are the main drivers controlling the bathymetric distribution of benthic foraminiferal assemblages in both canyons. The middle – lower CANNW revealed unstable trophic conditions, related to terrigenous sediment input due to turbidity currents. In CAND, the foraminiferal assemblages ecology indicated sufficient organic matter supply that favors species establishment and diversity, indicating a more productive and less unstable environment than in CANWN.

We present here the first long Quaternary record of organic-walled dinoflagellate cyst assemblages analysed from sediment cores retrieved during the International Ocean Discovery Program (IODP) Expedition 381 in the Gulf of Corinth. Site M0078A is located in the central part of the Gulf of Corinth (GoC), a semi-isolated marine basin that was repeatedly isolated and reconnected to the Mediterranean Sea during the Quaternary glacial/interglacial cycles. Our results show that dinoflagellate cysts are sorted in two major ecogroups, each group alternating between marine and isolated/brackish conditions. The marine intervals are characterised by high dinocyst diversity whereas the isolated intervals are dominated by taxa thriving in low-salinity conditions such as Spiniferites cruciformis and Pyxidinopsis psilata. In several of these assemblages, S. cruciformis is so prevalent that it forms almost monospecific assemblages. The low salinity dinocyst assemblages are reported for the first time outside the Ponto-Caspian region and they show a close affinity to modern assemblages from the Black Sea, Caspian Sea and Marmara Sea. The alternations between marine and brackish conditions recorded in the Gulf of Corinth reflect changes in surface water salinity (SSS) and temperature (SST), in response to the Quaternary glacial-interglacial cycles. These seem to be in good agreement with regional and global marine isotope and sea-level records. Our findings suggest that the study region sensitively responds to climate forcing at orbital time scales and that local factors most likely drive shifts in dinoflagellate species composition and diversity.

The Paleocene-Eocene period was punctuated by several hyperthermal events likely triggered by massive injection of greenhouse gases, the best-known being the PETM (∼56 Ma). Environmental changes during hyperthermals severely impacted planktonic organisms, especially calcareous nannoplankton producing tiny calcite platelets. These calcite platelets (coccoliths) accumulate at the sea floor and constitute a major component of deep-sea sediments. As calcareous nannoplankton contribute to the biological carbon pump and carbonate counter pump, a better knowledge of their production dynamics in surface ocean and their dissolution throughout the water column is pivotal to produce realistic carbon budgets across hyperthermal events. In this work, we quantitatively assessed calcareous nannofossil abundances and nannofossil fragments from deep sea sediments of late Thanetian to early Ypresian age (55.63–57.42 Ma) from ODP Site 1209 (North Pacific). We developed a new method, based on the shape and number of fragments, to reconstruct an all-inclusive nannofossil absolute abundance (including entire specimens and fragments) in the sediments. The reconstructed values of absolute abundance estimated integrating fragments are on average 25% higher. We also analysed different dissolution proxies (planktonic foraminifera fragmentation, benthic/planktonic ratios, coarse fraction). The fragmentation of planktonic foraminifera does not covary with nannofossil fragmentation, suggesting distinct controlling factors. Foraminiferal proxies and nannofossil assemblages point to episodes of intense dissolution across the PETM as well as during an event pre-dating the PETM by 300–700 kyrs that we identify as the Late Paleocene Event (LPE).

The composition of planktonic foraminiferal assemblages in surface sediments of the Mediterranean Sea shows a pronounced zonal gradient. This gradient is different from what is observed in the open ocean, indicating that the assemblage composition may respond to environmental variables other than the otherwise dominant surface water temperature. Here we make use of a dataset of census counts of 18 taxonomic categories in 124 surface-sediment samples extracted from the ForCenS database to understand the main environmental factors affecting the composition of recent Mediterranean planktonic foraminiferal assemblages. The tested explanatory variables include temperature, salinity, chlorophyll, nitrate and phosphate concentrations in the surface waters, temperature, nitrate and phosphate concentrations at depth and thermal, salinity and density vertical gradients. The composition of the assemblages is aligned along two environmental gradients and redundancy analysis reveals that the tested variables explain a large portion (>70%) of the variance in the compositional data. The first environmental gradient reflects the nutrient content in the deep waters, affecting nutrient availability in the productive zone, while the second gradient is driven by higher (northern area) and lower (southern area) upward nutrient advection due to differences in density stratification, conditioned by the regional hydrography. Although sea surface temperature is the most reconstructed environmental variable from fossil assemblages of planktonic foraminifera, it seems to play a secondary role in the Mediterranean Sea. This, has implications for reconstructions of past oceanographic conditions in this region, opening up the possibility to reconstruct productivity instead, or next to, temperature.

Study of the South Pacific Ocean sediments from IODP Expedition 378, Holes U1553A and U1553B, shows 19 late Eocene to late Oligocene silicoflagellate species. The late Eocene includes Corbisema tajmahalii n. sp., observed over a ∼ 8.4 m interval and proposed as a new subzone within the Corbisema apiculata Zone. The new species is characterized by the presence of basal ring that has three sides and an arrowhead-shaped outline with the two minor-axis corners more closely spaced. This study has found the first known Bachmannocena double skeleton, in corner-aligned configuration that suggests evolutionary relationship with the Corbisema triacantha group of Cenozoic silicoflagellates. Also observed is the apparent early evolution of Stephanocha raupii at ∼29.6 Ma, derived from a skeletal diversity related to Distephanopsis crux, thus the species is here transferred to Distephanopsis (abbreviated as Ds.). Silicoflagellate skeletal abundance declines after the Eocene-Oligocene boundary, with generally low abundance except for two sediment samples immediately below the Ds. raupii n. comb. first appearance.