Benthic Foraminifera Research Articles

A New Epistemological Insight of the Coniacian-Santonian Oceanic Anoxic Event (OAE3)

Eighteen planktic and eleven benthic foraminiferal species were recorded from the dark grey to black shale facies of the Matulla Formation in Abu Zeneima area, West-Central Sinai, Egypt. The faunal assemblage is dominated by cosmopolitan whiteinellids, marginotruncanids, Dicarinellids, Contusotruncanids and Heterohelicids. The planktic species with high taxonomic diversity were used to zone the Coniacian and Santonian stages, as well as define the Coniacian/ Santonian boundary, while benthic foraminifera is of minor contribution in age assignment. The stratigraphic analysis of the relations and ranges of these fauna led to the recognition of five biozones<i>; Dicarinella primitiva</i> or <i>Huberella huberi</i> or <i>Marginotruncana</i> <i>sinuosa</i> for the Coniacian, while <i>Dicarinella concavata</i> and <i>Dicarinella asymetrica</i> for the Santonian. Also, the Coniacian/Santonian boundary was delineated, considering the appearance of <i>Dicarinella</i> <i>concavata</i> and disappearance of <i>Huberella huberi</i>, as well as the<i> </i>increase of Marginotruncanids (<i>M. renzi, M. sigali, M. marginata, M. pseudolinneiana</i>….etc.). Furthermore, the black shales found in the middle part of the Matulla Formation were attributed to the Coniacian-Santonian Oceanic Anoxic Event (OAE3). The occurrence of black shales with planktic foraminifera during the Coniacian–Santonian interval in several countries belonging to five continents, was the main impetus to render this event a global event.

Potential impacts of cable bacteria activity on hard-shelled benthic foraminifera: implications for their interpretation as bioindicators or paleoproxies

Abstract. Hard-shelled foraminifera are protists able to build a calcareous or agglutinated shell (called a “test”). Here we study the impact of sediment acidification on calcareous test preservation. For this study, sediment cores were sampled in the macrotidal Auray estuary located on the French Atlantic coast. Living and dead foraminifera were quantified until 5 cm depth and discriminated using the Cell-Tracker™ Green vital marker. The pH and oxygen profiles combined with quantitative polymerase chain reaction (qPCR) suggested that cable bacteria were most likely to cause the acidifying process. Cable bacteria (CB) are filamentous bacteria coupling sulfide oxidation to oxygen reduction over centimetre distances, generating a strong pH gradient within the first few centimetres of the sediment that could affect the microhabitats occupied by benthic foraminifera. On two different intertidal mudflats, volumetric filament densities have been estimated. They were comparable to those observed in the literature for coastal environments, with 7.4 ± 0.4 and 74.4 ± 5.0 m cm−3 per bulk sediment, respectively. Highly contrasting sediment acidification (from low to very intense) was described from 1.0 to 2.4 ΔpH. This seems to lead to various dissolution stages of the foraminiferal calcareous test from intact to fully dissolved tests revealing the organic lining. The dissolution scale is based on observations of living Ammonia spp. and Haynesina germanica specimens under a scanning electronic microscope. Furthermore, dead foraminiferal assemblages showed a strong calcareous test loss and an organic lining accumulation throughout depth under low pH, hampering the test preservation in deep sediment. These changes in both living and dead foraminiferal assemblages suggest that cable bacteria must be considered in ecological monitoring and historical studies using foraminifera as bioindicators and paleoenvironmental proxies.

Intrasediment gypsum in subtidal offshore carbonates as a witness of basin-wide evaporitic precipitation. The case of the southern Variscan foreland basin (mid-Carboniferous)

Widespread calcite and quartz pseudomorphs, interpreted as originally gypsum crystals, occur within hemipelagic calci-mudstone accumulated in subtidal offshore environments in the broad marine foreland basin developed on the southern flank of the Ouachita–Alleghanian–Variscan Orogen during mid-Carboniferous times, which acted as a marine corridor connecting the Panthalassa and Palaeo-Tethys Oceans during the Mississippian, and progressively narrowed during the assembly of Pangea. In this study, 67 outcrops of radiolaria-bearing calci-mudstone deposits that contain calcite and quartz pseudomorphs located in northern Spain and southern France were studied to constrain the gypsum spatial distribution and sedimentological features. The recognised microfacies indicate intrasediment gypsum precipitation, accompanied by less abundant bottom-grown precipitates and gypsum cumulates, in extensive offshore, probably several ten to a few hundred metres deep, basinal environments. Gypsum precipitation took place during a short-lived temporal episode during the early Bashkirian time (Voznesenkian), which can be correlated, on the basis of benthic foraminifera, with the coastal (inter- to supratidal) gypsum evaporites identified in NW Africa (Tindouf and Reggan successions in Morocco and Algeria) that would represent the shallow-water counterparts. The occurrence of gypsum precipitates both in offshore hemipelagic calci-mudstones of the Variscan foreland basin and in inter- to supratidal environments of the epeiric Sahara Platform indicates that hypersaline conditions affected vast marine areas, roughly coinciding with the estimated age of closure of the Panthalassa and Palaeo-Tethys marine connection. Therefore, the studied succession represents the trace of a basin-wide evaporitic episode extending for hundreds of kilometres driven by foreland basin restriction, mid-Carboniferous sea-level fall and arid climate. This study provides new insights for the interpretation of gypsum precipitates in offshore marine environments encountered in the Phanerozoic and whose genesis is poorly understood.

A comparative approach employing microCT for the analysis of Cenozoic foraminifera from the Brazilian carbonate equatorial platform

Worldwide, some of the largest hydrocarbon reservoirs are located in tropical neritic carbonate deposits. Biostratigraphic and paleoenvironmental analyzes of these sedimentary records are often based on the study of foraminiferal assemblage. Foraminifera-based biozones are widely employed in the oil industry to support drilling processes that, alongside petrophysical prospecting, define interval favorable for exploiting hydrocarbon resources. Both scientific research and the petroleum industry, however, usually apply traditional petrographical and paleontological methods to analyze microfossil assemblages, especially for large benthic foraminifera. New, faster, and more accurate methods based on microCT analyzes have emerged as a valuable high-output tool to obtain high-resolution microfossil records for biostratigraphy and paleoenvironmental reconstructions. This method is also useful for the development of digital databases for artificial intelligence applications. MicroCT analyzes, therefore, lead to faster identification of foraminifera assemblage and support digital access to international foraminifera repositories and reference collections, introducing a new dimension in micropaleontological research.

Multi‐proxy palaeoenvironmental reconstruction of the Skagerrak from the Lateglacial to Middle Holocene

This study uses a multiproxy approach including the first use of 187Os/188Os, %C37:4 biomarkers, carbonate content, sedimentological grain size, geochemical X‐ray fluorescence and microfossil benthic foraminifera species combined with radiocarbon dating, measured on six cores from across the Skagerrak, in order to study the Lateglacial to Middle Holocene history of the area. A new chronostratigraphic framework is developed based on the appearance of specific benthic foraminifera species along with changes in carbonate/X‐ray fluorescence and grain size data. This allowed the correlation of cores based on a series of radiocarbon dated tie points. Analysing the cores together reveals several events recorded in the Skagerrak including: (i) an increased freshwater input (bracketed between 13.3 and 11.3 cal. ka BP) signified by radiogenic 187Os/188Os values, high %C37:4 values and an increase in sand content; (ii) the Glomma drainage event, signified by a sudden appearance of Valvulineria as well as higher %C37:4; and (iii) the opening of the Danish Straits and English Channel leading to the development of modern‐day conditions and circulation patterns in the Skagerrak, signified by the appearance of Hyalinea balthica and a fall in %C37:4.

Foraminiferal biofacies distribution in the outer channel of Chilika Lagoon, Odisha, India

Benthic foraminiferal assemblages are widely used as a proxy to monitor the coastal environment’s health. The current work involves the seasonal distribution of foraminifera in the outer channel sector of the Chilika Lagoon, Odisha during 2017–2018. The outer channel is marine as the sea mouth is nearby. Altogether 28 species of benthic foraminifera are identified, among which dominant are Ammonia spp. The other calcareous taxa are Elphidium spp, Quinqueloculina sp., Haynesina spp., Pararotalia sp., Hanzawaia sp., Nonionellina sp. and agglutinated forms such as Miliammina sp., Trochammina sp. and Textularina sp. are found in moderate abundance. Based on the pre-monsoon abundance, the cluster analyses show two distinct biofacies zones in the studied area. Total foraminiferal number (TFN) increases during pre-monsoon compared to post-monsoon months. A trend of decreasing abundance was observed in TFN, mainly calcareous taxa towards the inner part of the lagoon, that is, away from the sea mouth.

Objective identification of Lepidocyclina (Foraminifera) species from the Eocene of Cuba based on growth-invariant morphometric characters

Megalospheric specimens of Lepidocyclina from seven localities in western and central Cuba were morphometrically investigated using 11 growth-independent characters for equatorial sections of nepionts and 19 growth-independent and invariant characters describing equatorial sections of neanic chamberlets. This provides a complete geometric reconstruction of the equatorial morphology for lepidocyclinids. Specimens were objectively (to be precise, intersubjectively) classified by clustering and ordination methods resulting in four morphologically homogenous groups. These unprejudiced groups are then subjectively identified as Lepidocyclina macdonaldi, L. pustulosa, L. ariana and L. ocalana following the taxonomic rules and checked for significant differences. The D/P-ratio (deuteroconch/protoconch) separates L. ocalana (D/P ≥ 1) from L. pustulosa (D/P ≅ 1), L. macdonaldi and L. ariana (D/P < 1). The form of neanic chamberlets differentiates both L. macdonaldi and L. pustulosa possessing arcuate chamberlets from L. ariana and L. ocalana with spatulate chamberlets. The smaller sized characters isolate L. pustulosa from the other species. Lepidocyclina macdonaldi has the longest stratigraphical range occurring from ABZ 9 to ABZ 16 (American larger Benthic foraminifera Zonation). Lepidocyclina ariana is restricted to ABZ 12, while L. pustulosa and L. ocalana range from ABZ 13 to ABZ 16 and ABZ 15 to ABZ 16, respectively. An evolutionary trend could be detected in nepionts of L. macdonaldi starting from slightly smaller nepionts at the first appearance to significantly larger nepionts at the end of the Priabonian. Additionally, the arcuate chamberlets arranged in rows transform from not connected to connected. Differences within L. ocalana can be explained by environmental influences due to the palaeogeographical position of samples.

Comprehensive Facies Analysis and Depositional Environment Modeling of the Eocene Dammam Formation in Central to Southern Iraq

The Dammam Formation holds immense geological significance, as it spans across a substantial portion of southern Iraq, encompassing a vast area. This formation stands out as the primary aquifer source in the region. To gain a comprehensive understanding of its sedimentology, a comprehensive study was conducted using 310 samples extracted from various boreholes. These boreholes, including Kr-1, Kr-c.q., Nj-20, Ns-13, Ns-24, R-742, and Ru-509. The lithology of the Dammam Formation is limestone, dolomitic limestone, and dolomite rocks, which are also used as raw materials in the manufacture of cement. The microfacies analysis was carried out on Lower-Upper Eocene carbonate rocks along a center-south transect in Iraq. This analysis establishing larger benthic foraminifera enables to reconstruction of the paleoenvironmental model and to show the evolution of a platform along the depth gradient. The analysis revealed the presence of five primary microfacies within the Dammam Formation, each offering unique insights into its composition. These microfacies include Lime-mudstone, Wackestone, Packstone, Floatstone, and Rudstone, all of which contribute to a comprehensive understanding of the formation’s sedimentary makeup. Moreover, this in-depth examination uncovered an additional eight submicrofacies. The benthic foraminiferal assemblages within the Dammam Formation provide valuable insights into the progressive shifts along an ecological gradient, indicating a gradual transition from shallower, more protected (inner) shelf environments to deeper, more open (outer) shelf settings. Within the inner shelf, one can observe the prevalence of orbitolitids, alveolinids, and, to some extent, small miliolids, indicative of this relatively shallow and sheltered environment. Moving towards the inner ramp or shoal region, the foraminiferal composition is characterized by robust nummulitids, signifying the distinctive conditions of this particular zone. From a paleoenvironmental perspective, the Dammam Formation reflects deposition in a diverse range of environments, including peritidal inner ramp areas, lagoons, shoals, restricted-marine platforms, and open marine interior platforms. This variability underscores the complexity of the formation’s geological history and the diverse conditions under which its sediments accumulated over time.

Astronomically forced paleoclimate and sea-level changes recorded in the continental margin of the South China Sea over the past ∼23 m.y.

The Earth has witnessed the emergence of continental-sized ice sheets, starting with Antarctica and gradually extending to both hemispheres over the past 40 million years. These ice accumulations have had a dramatic impact on both paleoclimate and sea level, substantially influencing sediment deposition in the continental margins. However, understanding sediment accumulation on an orbital scale in continental margins remains limited because of the scarcity of high-resolution, chronologically constrained sedimentary records. Here, we conducted a highly resolved cyclostratigraphic analysis based on natural gamma radiation (GR) series in depth domain at the continental margin of the South China Sea. We established a 22.8 m.y.-long high-resolution astronomical time scale spanning from the Miocene to the Quaternary by tuning the GR records to the global deep-sea benthic foraminifera carbon isotope curves and the 405 k.y. eccentricity cycles. The m.y.-scale sea-level changes since the Miocene were reconstructed through the sedimentary noise modeling of the 405-k.y.-tuned GR series. These reconstructions aligned with regional and global sea-level changes. The phase correlation between the filtered 1.2 m.y. cycles of sea-level change curves (dynamic noise after orbital tuning and ρ1 median models) from δ13Cbenthic and tuned GR series and the 1.2 m.y. obliquity amplitude modulation cycles revealed a shift from an anti-phase to an in-phase relationship across the middle Miocene climate transition (ca. 13.8 Ma), suggesting extensive expansion of the Antarctic ice sheet played a key role. In addition, a shift from an in-phase to an anti-phase relationship during the late Miocene (ca. 8 Ma and 5.3 Ma), indicating ephemeral expansion of the Arctic ice sheets or the changes in carbon cycle involving the terrestrial and deep ocean carbon reservoirs, might be the primary driver of eustatic changes. Furthermore, obliquity forcing and changes in meridional gradients in insolation that transported poleward flux of heat, moisture, and precipitation increased ice accumulation in both pole ice sheets and nonlinearly transferred high-latitude signals to low-latitude regions. This phenomenon is supported by the observation of strong obliquity signals in low latitude during global climate cooling interval. Our results suggest that m.y.-scale sea-level variations respond to astronomically induced climate change and ice sheet dynamics of both poles. This work contributes a highly resolved low-latitude geological archive to the future reconstruction of paleoclimate evolution on a global scale.

Environmental DNA metabarcoding of foraminifera for biological monitoring of bottom water and sediments on the Takuyo-Daigo Seamount in the northwestern Pacific

Foraminifera are adapted to a wide range of environments, and environmental DNA (eDNA) metabarcoding of foraminifera should facilitate development of new environmental indicators. In this study, we used eDNA metabarcoding to evaluate the discrepancy between planktic and benthic foraminifera molecular communities identified in bottom water and short sediment cores. The molecular community was compared to foraminiferal shells in sediment traps set on the seafloor. Samples were collected in June and August around the Takuyo-Daigo Seamount in the western subtropical Pacific Ocean. Approximately 40% of amplicon sequence variants (ASVs) pertained to unknown foraminiferal lineages in sediment samples, compared with only 22% in bottom water. Bottom water contained benthic foraminifera and taxonomically unassigned lineages, which were attributed to resuspended particles. In bottom water, 100 ASVs were assigned to planktic foraminifera. ASVs assigned to Candeina nitida were most abundant and accounted for 36%–86% of planktic foraminiferal ASVs. In sedimentary DNA, Globigerinita glutinata was the most abundant among 33 ASVs of planktic foraminifera. However, transparent shells in sediment traps contained more spinose species, such as Globigerinoides ruber, whereas C. nitida was not found and few G. glutinata were detected. This discrepancy between the three samples may be due to the species-specific preservation, to polymerase chain reaction biases, and/or to low abundance of planktic foraminifers. In sedimentary DNA, 893 ASVs were assigned to high-level foraminiferal taxa. Among benthic foraminiferal lineages, monothalamids were most abundant, as reported in other deep-sea regions. Molecular communities formed one cluster above the boundary at which ASVs sharply decrease across the three cores. Our results suggest that depth within the sediment core can affect foraminiferal ASVs, but the distance between sites up to 200 m did not strongly affect ASVs of sedimentary DNA at least above the boundary at which ASVs sharply decrease. Sequences of foraminiferal DNA in sediment decreased linearly in core PC02-A1, but exponentially in core PC03-B3. The decline of foraminiferal ASVs may reflect both the decreases in numbers of living foraminifera and degradation of DNA in sediment, related to the particle mixing depth.

Biostratigraphy and Paleoecology of the Sinjar Formation (Late Paleocene-Early Eocene) in the Dokan and Sinjar Areas, Iraq

Biostratigraphy of the Sinjar Formation is investigated in two sections (Dokan and Sinjar) from northeastern and northwestern Iraq, respectively. Two hundred samples from all the limestones and marl that form the main lithological components of the studied sections were collected. The studied limestones and marl are rich in microfossils. Through thin sections, we were able to identify thirty species of benthic foraminifera and fifteen species of other microfossils (coral, algae, mollusca, bryozoa, and echinoids) at Dokan section, and fifty-one species of benthic foraminifera and thirty species of other microfossils at Sinjar section. 3 biozones were distinguished from both sections 1-Biozone A: Kathina sp.- Lockhartia hunti Assemblage zone (SBZ 5) (Dokan section); (Kathina pemavuti - Lockhartia hunti Assemblage zone (Sinjar section), 2- Biozone B: Idalina sinjarica Total Range zone (SBZ 6-7) and 3-Biozone C: Alveolina globosa- Alveolina pasitisilata Concurrent Range Zone (SBZ8-10). These zones indicate the Late Paleocene –Early Eocene age of the Sinjar formation. The biostratigraphic correlations in the studied sections are based on benthic foraminiferal zonations. Showed the correlation comparison between the biostratigraphic zones of the commonly used benthic zonal scheme around the Late Paleocene -Early Eocene in and outside of Iraq. paleoecological studies suggest that the carbonate sedimentation of the Sinjar Formation thrived in 18-25oC, with mesophotic to oligophobic light, under an oligotrophic to mesotrophic middle ramp environment with normal marine to slightly saline and at water depths from 40 - 80 m. Stable isotopic carbon (δ13C) and oxygen (δ18O) data revealed generally hot conditions with high productivity during the deposition of the Sinjar Formation accompanied by an abrupt change in paleoenvironmental conditions across the Paleocene-Eocene contact.

Benthic foraminiferal assemblages in the coastal zone of the yellow river delta: Environmental significance and characteristics of microbial diversity

Unicellular eukaryotes known as benthic foraminifera have sophisticated survival mechanisms and ecological environmental indicators. Ten surface samples from the Yellow River Delta's coastal region were taken for this study to analyze the distribution of foraminifera in relation to environmental factors and to examine their microbial diversity. We looked at the physicochemical aspects of the environment at each sampling site (such as pH, TN, TOC, EC, δ13C, δ15N, PAHs, etc.), and we employed 16S rRNA high-throughput sequencing analysis to look into the interactions between microbial communities and foraminiferal species. The findings demonstrated that the Yellow River Delta's advantage benthic foraminiferal species were Quinqueloculina complanata, Ammonia beccarii, and Ammonia aomoriensis, and that TOC and TN were significant determinants of the distribution of benthic foraminiferal communities. PAH enrichment in the coastal zone effects on microbial communities and benthic foraminifera are not yet readily apparent. Sediment organic carbon and nitrogen isotope analysis revealed that marine plankton may be the dominant source of organic matter in the coastal zone sediments in the research area, which was made up of both land-based and marine organic matter. It implies that foraminifera have some environmental indicators, especially when combined with the distributional traits of the benthic foraminiferal assemblages and their considerable association with environmental parameters. The findings revealed that Q. complanata was found in the Yellow River water-affected estuarine coastal zone, A. aomoriensis was significantly influenced by sediment organic matter content and reflected the estuarine and nearshore environments and the combination of Ammonia beccarii-Ammonia aomoriensis-Elphidium excavatum assemblage indicated a semi-open intertidal shallow marine environment. Additionally, benthic foraminifera showed a responsive association with microorganisms, indicating that microbial diversity may be one of the driving forces behind benthic foraminifera's ability to adjust to environmental changes. The findings of this study will open up new avenues for research into the environmental importance of coastal zone ecosystems and for understanding how benthic foraminiferal communities survive.

An 800-year record of benthic foraminifer images and 2D morphometrics from the Santa Barbara Basin

The Santa Barbara Basin is an extraordinary archive of environmental and ecological change, where varved sediments preserve microfossils that provide an annual to decadal record of the dynamics of surrounding ecosystems. Of the microfossils preserved in these sediments, benthic foraminifera are the most abundant seafloor-dwelling organisms. While they have been extensively utilized for geochemical and paleoceanographic work, studies of their morphology are lacking. Here we use a high-throughput imaging method (AutoMorph) designed to extract 2D data from photographic images of fossils to produce a large image and 2D shape dataset of recent benthic foraminifera from two core records sampled from the center of the Santa Barbara Basin that span an ~800-year-long interval during the Common Era (1249–2008 CE). Information on more than 36,000 objects is included, of which more than 22,000 are complete or partially-damaged benthic foraminifera. The dataset also includes other biogenic microfossils including ostracods, pteropods, diatoms, radiolarians, fish teeth, and shark dermal denticles. We describe our sample preparation, imaging, and identification techniques, and outline potential data uses.

Meiofauna community structure in the Yellow Sea Cold Water Mass and non‐Yellow Sea Cold Water Mass

This study investigated meiofaunal community structure over a large area of the Yellow Sea and East China Sea for 45 stations from 2021 to 2022. Meiofaunal densities were 34 ± 15–1610 ± 378 ind./10 cm2. Nematodes (67.3%) were the most dominant taxa, followed by benthic foraminifera (12.0%) and benthic harpacticoids (8.8%). The study was conducted in various sedimentary environments. Median grain size, water depth, and environmental characteristics (TOC, TN, Hg, Sr) were identified as influencing meiofauna community structure. The Yellow Sea and East China Sea, where this study was conducted, contain a variety of currents and the Yellow Sea Cold Water Mass (YSCWM) in the central waters. YSCWM and non-YSCWM areas differed in their meiofauna community structure. Even within the YSCWM region, we found differences in benthic community structure due to a variety of environmental factors. The meiofaunal taxon most affected by Sediment temperature was benthic foraminifera. Identifying foraminifera in paleo-oceanographic environments can indicate past expansion and contraction of YSCWM. Meiofauna have been used to monitor changes in marine ecosystems due to their sensitivity to changes in the surrounding environment. Meiofauna index (N/C ratio, MPI) were identified as appropriate for use in the study area.

A benthic foraminifera perspective of the Late Miocene-Early Pliocene Biogenic Bloom at ODP Site 1085 (Southeast Atlantic Ocean)

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0–3.5 Ma) was a phase of high marine biological productivity documented globally at multiple ocean sites, related to an increase in nutrient input and/or a significant reorganization of nutrients in the oceans. Here, we studied the Biogenic Bloom at Ocean Drilling Program (ODP) Site 1085 in the Southeast Atlantic Ocean, additionally providing an updated age model based on calcareous nannofossil biostratigraphy. During the event, we identified four intervals characterised by distinct benthic foraminiferal assemblages, suggesting changes in paleoenvironmental/paleoceanographic conditions. The Biogenic Bloom extends from 8.1 to 3.0 Ma at Site 1085, as detected by different proxies such as linear sedimentation rates, carbonate mass accumulation rates, benthic foraminiferal indices and assemblage data. The inferred paleoenvironmental changes allowed us to differentiate four intervals within the Biogenic Bloom. From 8.1 to 5.2 Ma and from 3.8 to 3.0 Ma, the high benthic foraminiferal accumulation rates (BFARs) and the abundance of phytodetritus-exploiting taxa point to highly seasonal phytoplankton blooms. Between 5.2 and 4.8 Ma, we document short-term fluctuations between well‑oxygenated conditions with transient input of phytodetritus and phases of low oxygen eutrophic conditions. Between 4.8 and 3.8 Ma, a decrease in opportunistic species and an increase in eutrophic taxa likely suggest a switch to a higher food supply to the seafloor. Our data shows that the onset of the Biogenic Bloom was synchronous with other global well-dated records and its end appears to align with other Atlantic records. Lastly, our findings support the hypothesis that the Biogenic Bloom was not a single productivity event, but a complex event made up of several short-lived, high-productivity regimes with different driving forces.

The Middle-Upper Eocene in the Northern Plateau of the Bahariya Depression, Western Desert (Egypt) and correlation with other Tethyan sectors

This study describes the paleoenvironmental evolution of the Middle-Upper Eocene succession exposed along the northern plateau of the Bahariya Depression (Western Desert, Egypt). Based on detailed field observations and facies analysis, twenty-one facies were recognized and grouped into five facies associations: tidal flat to restricted marine (FA1), lagoonal (FA2), ramp crest (FA3), middle ramp (FA4), and siliciclastic-dominated foreshore–shoreface (FA5). These facies associations were developed in a gently dipping mixed siliciclastic-carbonate ramp which was connected with siliciclastic coastal-shelf depositional system. The biogenic assemblages described in the Middle-Upper Eocene deposits show a mixing of photozoan and heterozoan associations, indicating euphotic to mesophotic inner to mid-ramp settings under mesotrophic-oligotrophic conditions. The succession shows a transition from photozoan to heterozoan carbonates and a shift towards inner ramp settings. The formation and the evolution of the northern Bahariya platform reflect the complex interplay of synsedimentary tilting due to post-Middle Eocene inversion phase, high-frequency sea-level changes, transition from warm to humid climate and paleoecological parameters. The sedimentation pattern including distinct lateral changes in facies and thicknesses are largely controlled by tectonics. Long-term sea level changes were responsible for the unconformities associated with major regressions. The Middle-Upper Eocene strata display a characteristic up-section increase in clastic input from the hinterlands through tectonic uplift and/or a change to a cooling climate. The shift to a colder climate, which was a result of a global temperature decrease, led to the maximum northward retreat of the Neo-Tethys Ocean. During the Eocene epoch, carbonates dominated by Larger Benthic Foraminifera (LBF) were prevalent along the entire Tethyan margins. This was linked to a decline in coral reef formations. Comparisons with other southern and western-central Tethyan sectors showed that small coral reef build-ups in widely scattered localities could exist in broad LBF-rich ramps. Consequently, zooxanthellate corals were only able to flourish locally in marginal environments under specific ecological conditions.

Modeled foraminiferal calcification and strontium partitioning in benthic foraminifera helps reconstruct calcifying fluid composition

Foraminifera are unicellular organisms that inhabit the oceans. They play an important role in the global carbon cycle and record valuable paleoclimate information through the uptake of trace elements such as strontium into their calcitic shells. Understanding how foraminifera control their internal fluid composition to make calcite is important for predicting their response to ocean acidification and for reliably interpreting the chemical and isotopic compositions of their shells. Here, we model foraminiferal calcification and strontium partitioning in the benthic foraminifera Cibicides wuellerstorfi and Cibicidoides mundulus based on insights from inorganic calcite experiments. The numerical model reconciles inter-ocean and taxonomic differences in benthic foraminifer strontium partitioning relationships and enables us to reconstruct the composition of the calcifying fluid. We find that strontium partitioning and mineral growth rates of foraminiferal calcite are not strongly affected by changes in external seawater pH (within 7.8–8.1) and dissolved inorganic carbon (DIC, within 2100–2300 μmol/kg) due to a regulated calcite saturation state at the site of shell formation.

Short-term middle Eocene (Bartonian) paleoenvironmental changes in the sedimentary succession of Olivetta San Michele (NW Italy): the response of shallow-water biota to climate in NW Tethys

This study focuses on the paleontological content of the middle Eocene (Bartonian) carbonate–siliciclastic sediments of the Capo Mortola Calcarenite Formation from Olivetta San Michele (Liguria, Italy). Along the succession, there are significant paleoecological changes triggered by the variation in neritic input as a consequence of tectonic and climatic instability. Among microfossils, nummulitids prevail, followed by orthophragmines, smaller benthic, and planktonic foraminifera, whereas mollusks and ichnofossils are the most abundant macrofossils. The sudden changes in the benthic communities due to the progressive increase in fluvial input are recorded throughout the sedimentary succession. An increase in water turbidity caused stressful conditions for autotrophic taxa, reducing their size and abundance. In contrast, filter feeders became dominant, suggesting an increase in dissolved and suspended nutrients. Ichnological analysis shows environmental fluctuations controlled by the transport of neritic material offshore, thus confirming the general deepening trend of the studied succession. In the upper part of the succession, we recorded an alternation between gravity flows and marly sediments that are interpreted as short-term alternations between low and intense precipitations. The gravity flows yield taxa such as larger benthic foraminifera (LBF), smaller benthic and planktonic foraminifera, mollusks, and corals. In turn, marls display only a few LBF and abundant smaller benthic and planktonic foraminifera. In these intervals, the increase in planktonic foraminifera also suggests a deepening of the carbonate ramp coinciding with a reduction of light that did not favor the development of LBF. These changes are probably related to the climatic dynamics that occurred in the Bartonian in the western Tethys.

Microfacies shift in the Late Paleocene–Early Eocene Patala Formation in the Upper Indus Basin (Pakistan): Implications for development of the Ceno-Tethys Ocean

Field observations, petrography, and laboratory interpretations of the Patala Formation were utilized in an integrated petrologic study aimed at deciphering the genesis mechanism and controlling factors of the limestone/shale alternation during the mature development of the Ceno-Tethys Ocean in the Upper Indus Basin of Pakistan. To achieve this goal, the Patala Formation is categorized into four integrated microfacies (MM-I to MM-IV). Multiple cycles of transgression/regression are noted through fluctuations in eustatic sea level, controlled by climate and regional tectonism. Consequently, a deepening, upward retrogradation sequence was deposited on a carbonate platform of the Ceno-Tethys Ocean. The sediments of the Patala Formation exhibit a facies shift from a shallow-marine to a relatively deep-marine platform. It is indicated by the transition in fossils from shallow-marine green algae, trending towards a relatively deeper-shelf comprising benthic foraminifera such as Discocyclina, Ranikothalia, red coralline algae, echinoids (Echinothrix), and Alveolina, species. The deeper species possess robust shells adapted by organisms to maximize oxygen and light at greater depths. Additionally, mineralogical features, including gypsum (deposited in a lagoon within the platform) and pyrite (found in a deep slope toward a deep shelf), confirm deepening upward interpretations. Thermophilic dinoflagellates, thermal dissolution fragments, and hardground surfaces indicate a Paleocene-Eocene Thermal Maximum (PETM; in the lower part, ca. 56 Ma) of the Patala Formation, assigning a relative chronological age from the late Paleocene to early Eocene. These results highlight the joint influence of climate change, sea level rise, and continuous tectonic activity (associated with the Indo-Eurasian collision) on the pattern of sediment filling, and facies shift. Furthermore, the study contributes to understanding sedimentary environments, paleoenvironmental reconstruction, and paleotectonic evolution of the basin. This ideal case study provides a breakthrough advancement in globally comprehending the complex relationships between periodic autocyclic processes and aperiodic allocyclic events.

Living benthic foraminifera from Almirante Câmara and Grussaí canyons and adjacent slope areas (Campos Basin, Southwest Atlantic): Response to trophic and hydrodynamic conditions

Living (rose Bengal stained) benthic foraminiferal faunas, grain size, geochemical parameters (total organic matter, chlorophyll-a, pheophytin-a, molecular markers, and vertical flux of particulate organic matter) were investigated in 14 stations in two submarine canyons Almirante Câmara and Grussaí considered mature and immature, respectively, and on the adjacent continental slope, from 400 to 1300 m water depth, in the southwestern Atlantic Ocean. Samples were retrieved during two campaigns, in the austral winter 2008 and the austral summer 2009. The density, richness, and species composition of the benthic foraminiferal fauna decrease with depth in the canyons and along the adjacent slope transects, reflecting the availability and quality of sedimentary organic matter. Both canyons act as traps of labile organic matter, mainly towards the head of the Almirante Câmara canyon, promoting high specimen density, species richness, and the occurrence of species indicative of pulses of phytodetritus (e.g., Bolivina pacifica, Nonionella opima, and Nonionella stella). Towards the deeper regions of Almirante Câmara canyon and in the adjacent slope area, the lower abundance, diversity, and richness reflect more oligotrophic conditions and an adverse environment in terms of easily metabolizable organic matter. This multiproxy study demonstrates that the canyons in the southeastern Brazilian continental margin play an important role in accumulating organic matter.