Marine Micropaleontology最新文献

In this paper we compare the diversity of Floian (Lower Ordovician) conodonts from the Precordillera with that of the Cordillera Oriental, Argentina. The comparative analysis is restricted to the middle Floian Stage Slice (Fl2) from correlative intervals: Oepikodus evae Zone (Juanognathus variabilis Subzone) in the Precordillera and the Gothodus andinus Zone in the Cordillera Oriental. For the comparative analysis, absolute frequency tables of the conodont data from published articles and collections under study, were prepared. These include four sections of the Precordillera with 13 samples recovered from the middle section of the carbonate San Juan Formation, and six sections of the Cordillera Oriental with 28 samples from the middle-upper section of the shaly Acoite Formation. Diversity patterns and indices were generated from absolute frequencies using the software PAST 4.03. Remarkable differences in the species richness and diversity between coeval communities of referred basins are displayed. Comparisons with other basins elsewhere suggest that the paleolatitudinal gradient is not a major factor controlling changes in diversity, which may be due to a response to the complex interaction of biological and physico-chemical factors.

Benthic foraminifers living in euphotic coastal and shelf environments commonly occur in association with macrophytes (macroalgae and seagrasses), and many lineages have evolved morphologic adaptations to thrive in such habitats. Species that did not occur in the Mediterranean Sea prior to recent centuries, commonly known as “introduced” or “alien” species, are now widespread, and some are so abundant that they are altering coastal habitats. With accelerating climatic change and warming of Mediterranean surface waters, recognizing how invasive algal and foraminiferal species are affecting sedimentation and microenvironments has become increasingly urgent. This project examined 18 sets of sediment samples collected in the Abu Qir coastal area east of Alexandria for comparison with a previous assessment of live assemblages within the macroalgae. Overall, 68 foraminiferal species were identified, of which sixteen species were categorized as epiphytic. The hyaline epiphytic Elphidium crispum was the most common species found in sediments from the platform, while the porcelaneous free-living Quinqueloculina auberiana dominated sediments from the small bay. Eleven introduced foraminiferal species were recorded, one of which, Amphistegina lobifera, was commonly found, especially in the platform sediment samples. Taxa recorded live (stained) in platform sediments were predominantly (>10% each) Peneroplis, Amphistegina and Elphidium, while bay sediments were dominated by Quinqueloculina, followed in order by Elphidium, Amphistegina and Peneroplis. The assemblage differences from previously reported live assemblages associated with macralgae, compared with live and dead assemblages in sediments, appear to reflect hydrodynamic influence of sediment sorting and resistence of larger taxa to physical degradation.

The common brackish water ostracods Cyprideis torosa and Loxoconcha elliptica frequently occur together in high abundances in marginal marine environments. Seasonality of calcification differs between species and can have important implications for palaeotemperature reconstructions. There are existing palaeotemperature calibrations for both genera. However, the Loxoconcha spp. Mg/Ca temperature calibration has not thus far been applied to L. elliptica. The equation for Loxoconcha spp. does not rely on a known Mg/Ca_water value, unlike the calibration for C. torosa, suggesting it may be possible to reconstruct temperatures without an estimation of Mg/Ca_water, which is potentially particularly beneficial in environments that have highly dynamic Mg/Ca_water. However, the calibration has only been applied in environments with marine-like Mg/Ca_water. Demonstrating the applicability of the equation in marginal marine environments (with Mg/Ca_water 3–5 mol/mol) and tracking the seasonal calcification of L. elliptica alongside C. torosa, therefore, has the potential to improve uncertainty in seasonal palaeotemperature reconstructions. Here, we compare previous monitoring of C. torosa with L. elliptica from the same collections. We demonstrate that the Mg/Ca temperature calibration for Loxoconcha spp. is appropriate to use with L. elliptica. Mg/Ca-inferred temperatures broadly track spring temperatures and suggest spring calcification. Cyprideis torosa Mg/Ca-inferred temperatures record the range of expected temperatures between spring and autumn. When analysing multiple single valves of L. elliptica and C. torosa simultaneously, the maximum Mg/Ca_C.torosa can, therefore, be used to reconstruct maximum summer temperatures, the minimum Mg/Ca_C.torosa to reconstruct autumn temperatures, and the Mg/Ca_L.elliptica to reconstruct the range in spring temperatures.

This work introduces graphical methods documenting density, diversity (species richness combined with heterogeneity) and similarity in combined diagrams for estimating the influence of environmental and taphonomic factors in living (LAs) and dead (DAs) assemblages. In this paper, the diagrams compare: 1) densities per 1 g of sediment expressed in cubic squares; 2) diversities based on rarefaction species richness (x-axis) and Shannon H rarefaction (y-axis), both extended to infinity by the logistic Hull equation, and 3) similarity diagrams based on cosine measures (x-axis) and Spearman correlation coefficients (y-axis). Diagrams were exemplified for LAs and DAs found at 53 stations along channels and intertidal areas of the Aveiro Lagoon (Portugal). Eight ‘routes’ characterized by different trends in the distribution of the analyzed biotic parameters were recognized in six regions of the Aveiro Lagoon: ‘port area’, ‘central lagoon’, ‘northeast lagoon’, ‘northern and southern extremities of the lagoon’ and ‘city area’. In addition, Detrended Correspondence Analyses (DCA) based on diversity diagrams were performed to show the influence of environmental parameters, especially grain size, salinity, and pH, on the average species composition in each route. The comparative diagrams allow deduction about the impact of parameters that simultaneously affect LAs and DAs, such as hydrodynamics, post-mortem tests dissolution, physicochemical parameters, excessive contribution of organic matter, oxygen depletion, and pollution by metals. Based on these diagrams, the most favorable environments due to the most remarkable development and diversity of LAs and DAs are located in protected coves of the Aveiro Lagoon mouth.

The South China Sea (SCS) is sensitive to the East Asian monsoon (EAM) and changes in the Western Pacific. However, because of the difficulty of sampling and lack of data in the central SCS, many uncertainties remain the primary driving force of paleoclimatic variations. Here, a sediment core JL136, from the central SCS, was used to evaluate variations of sea surface temperature (SST) and salinity (SSS) during the Holocene, and then the corresponding influencing factors were analyzed, based on measured Mg/Ca ratio and stable isotopic compositions (δ¹⁸O and δ¹³C) of planktonic foraminifera Globigerinoides ruber sensu stricto (s.s.). The results show that the Mg/Ca-SST change is consistent with the speleothem δ¹⁸O records across most Asian monsoon regions on the Holocene long-term trend, revealing that the central SCS record is a response to the East Asian Summer Monsoon (EASM) intensity changes induced by Northern Hemisphere summer insolation (NHSI) variation. During the early Holocene (11.6–8.8 ka), SSS was low with an average of 32.7 psu, which may be related to palaeogeographic variations with sea level changes and the increased coastal water due to the opening of the Taiwan Strait. During the mid-late Holocene, high salinity ocean water was fully exchanged with the SCS due to the influence of high sea level, with an overall higher salinity in the SCS compared with the early Holocene (average 33.8 psu). In addition, the SSS broadly showed an increasing trend, which may be mainly controlled by the weakening EASM intensity and the decreasing precipitation during the low NHSI.

The subsurface middle Eocene - early Miocene succession in the N. El Faras - 1X Well, drilled in the Qattara Depression at the northern part of the Western Desert, Egypt (Southern Tethyan Province, STP), was studied for its ostracode content to infer changes in paleobathymetry as well as paleobiogeographic reconstructions. This succession is composed mainly of three lithostratigraphic units, as the upper part of the Apollonia Formation (middle to late Eocene), the Dabaa Formation (late Eocene and Oligocene) and the lower part of the Moghra Formation (early Miocene). The stratigraphical distribution, paleoenvironmental and paleobiogeographical significance of the ostracode faunas from the Oligocene interval of the study area are documented for the first time. Fifty seven ostracode species belonging to 36 genera were identified in this succession. Among them, two new species were described. The vertical distribution of these ostracode species enabled the recognition of seven local biozones. Qualitative and quantitative statistical analysis of ostracode associations revealed a depositional depth ranging from the inner to outer neritic setting. Considering the CONISS cluster analysis, six ecozones were established. During the middle and late Eocene, the paleobiogeographical affinities of the Egyptian ostracodes from N. El Faras-1X× Well succession with that of the Southern Tethyan countries suggest a direct connection between Egypt and the countries of the Southern Tethyan Province. This connection facilitated the dispersal and exchange within this province. The low ostracode similarity between the STP and the Northern Tethyan Province (NTP) suggests a slight connection and exchange between them. The in common occurrence of these ostracodes with that of Somalia is attributed to the connection between the STP and Somalia via the Tethyan Seaway, which facilitated the dispersal and exchange of the middle Eocene ostracodes. The similarity between the Egyptian ostracodes (STP) and that of South America and the Caribbean Sub-Province indicates a direct connection between those provinces across the Gibraltar Strait and through the North Equatorial Oceanic Water Current during that time. During the Oligocene, the low ostracode similarity between the STP and the NTP may be attributed to a more or less restricted connection. Also, the low similarity indicates a continuation of the mild connection between the STP and the South America and Caribbean Sub-Province across the Gibraltar Strait and through the North Equatorial Current. During the early Miocene, the similarity of the recorded ostracodes of the STP with that of the NTP suggests a continuous connection between the two provinces. Also, there was a connection between the South America and Caribbean Sub-Province and the North American Province through the North Equatorial Current and the warm Gulf Stream within the Caribbean Sea.

A large collection of conodonts (over 4200 elements) from the Santa Gertrudis Formation of the Cordillera Oriental, NW Argentina, is analyzed. The mostly endemic fauna of this unit and the lack of index species require complex taxonomic and biostratigraphic interpretations. We determined new species apparatuses by reviewing previous literature with a different taxonomic approach: Erismodus saltaensis n. sp., Erraticodon aldridgei n. sp., Gallinatodus elegantissimus n. gen. et sp., Pyramidens cactus n. gen. et sp., P. spinatus n. gen. et sp., Zentagnathus gertrudisae n. sp. Although the lack of key conodont species for intercontinental correlation precludes biostratigraphic assignment to a particular biozone, the overlapping ranges of recorded species restrict the age range to the upper Lenodus variabilis, Yangtzeplacognathus crassus and the lower Eoplacognathus pseudoplanus zones, of middle Darriwilian age (Dw2, Middle Ordovician). The depositional environment of the Santa Gertrudis Formation is primarily a shallow inner platform influenced by waves but not by storms; its paleogeographic location in mid-high latitudes exerts important control over the conodont biofacies, similar to the Arabian Darriwilian faunas of the Gondwanan margin. A narrow marine seaway along the suture zone connecting East and West Gondwana is proposed to explain the evolution of lineages of shallow cold-water conodont faunas from the Middle Ordovician onwards.

Microbial activity can be expressed in a wide range of products and forms including boring structures, biofilm-like subproducts, and framboidal pyrite precipitates. Microendolithic structures, in particular, are found in carbonate hardgrounds including tests of planktonic and benthic foraminifera and their traces can provide an extra paleoenvironmental marker of relative paleobathymetry, oxygenation, and environmental stress. Variegated traces of microbial activity including microborings, framboidal pyrite bacterial subproducts, and probable biofilms were herein studied in tests of benthic foraminifera from dysphotic to aphotic, shelf to an upper bathyal hypoxic environment. Collected material is from 6 localities in the Central Paratethys area, the Czech Republic (LOM-1 Mikulov, Hevlín), Slovakia (DNV, LKŠ-1), and Hungary (Rozalia), ranging from Rupelian to Serravalian. Microendolithic morphology was examined from resin casts obtained from the tests resulting in a total of ten ichnospecies and four other forms for which it was only possible to establish affinity on higher ranks. Levels of oxygen depletion were estimated from Benthic Foraminifera Oxygen index (BFOI). The bacterial origin of pyrite was inferred by morphology, grain size, and ẟS³⁴ values. The number of observed microboring structures gradually reduce with the decrease of oxygen content, while the precipitation of framboidal pyrite were increasing at the same time. Biofilm-like structures, apart from the suggestive morphology, also showed an enriched content of elemental iron, sulfur, and phosphorus. Raman spectroscopy shows similarities with organic pigment spectra and is still under investigation.

The glacial-interglacial siliceous productivity in the Sub-Antarctic Zone (SAZ) of the Southern Ocean (SO) has been proposed to respond to higher dust-bearing iron fluxes and/or basin-wide increased nutrient supply to surface waters. However, long records of diatom productivity are mainly obtained from the Atlantic and Pacific sectors of the SO. We present a new diatom productivity record from the SAZ of the western Indian sector of the SO, where the Antarctic Circumpolar Current strongly interacts with bottom topography to create a productivity hotspot, during the last four glacial-interglacial cycles. Our results show that regional changes in diatom productivity did not follow a glacial-interglacial pattern. It was highest during the Marine Isotope stage (MIS) 6 and MIS4, lowest during MIS10-MIS8 and MIS3-MIS1, whereas intermediate diatom productivity was found during MIS7 and MIS5. Multi-millennial events of high diatom productivity were scattered throughout both the glacial and interglacial periods. Both long-term and rapid diatom productivity changes in the region were disconnected from dust flux changes, but might relate to frontal migrations and SO upwelling intensity changes which have both mediated the silica and iron availability for diatoms. Importantly, our data suggest that front migrations were not homogenous in the SO, especially where these fronts interact with bottom topography. The peculiarity of these productivity hotspots must be considered when drawing SO-wide carbon balance in the past.

The Miocene Climate Optimum (MCO) and the subsequent Miocene Climate Transition (MCT) are important biotic, environmental and geologic events. Here we address whether this holds true for the epicontinental Eastern Paratethys Sea (today's Black – Caspian Sea region). Two Tarkhanian – lower Chokrakian sequences of Middle Miocene age in the Kerch Peninsula were investigated using foraminifera, calcareous nannofossils, molluscs, fish otoliths, spores and pollen, oxygen and carbon stable isotopes and strontium isotope stratigraphy (SIS). Our results show that the marine environment during the Tarkhanian to early Chokrakian in the study area was characterized by open shelf conditions (near upper part of lower sublittoral zone), variable water column stratification and bottom water oxygen levels. Biostratigraphy and new SIS data suggest an age of >15.5 (∼16.0?) – 14.75 Ma for the Tarkhanian, which implies a considerably longer duration (> 0.75 Ma vs. 0.1 Ma) than was previously suggested. The maximum transgression seen in the middle Tarkhanian could be dated to ∼15.5–15.1 Ma and correlates with the highstand of sequence Bur 5/Lan 1 (15.2 Ma) and terminal phase of the MCO. The vegetation indicates a gradual change from subtropical humid (early Tarkhanian) to arid (early Chokrakian) conditions, which reflect the MCT. The climate change in the Eastern Paratethys occurred slightly earlier than in the Central Paratethys, possibly related to the existence of the large flat Eurasian continent.