Planktic Foraminiferal Assemblages Research Articles

THE MIDDLE EOCENE CLIMATIC OPTIMUM (MECO) IMPACT ON THE BENTHIC AND PLANKTIC FORAMINIFERAL RESILIENCE FROM A SHALLOW-WATER SEDIMENTARY RECORD

We present here new quantitative analyses of planktic and benthic foraminifera to assess the impact of the Middle Eocene Climatic Optimum (MECO, ~40 Ma) on these biotic groups studied along a shallow-water succession rich in larger benthic foraminifera (Sealza, Liguria, NW Italy). The MECO is one of the major Eocene global warming events, characterized by ~4–6°C warming, shifts in the global carbon cycle, and rise in atmospheric pCO2. The Sealza succession is interpreted as the product of a drowning ramp influenced by tectonic activity and provides an exceptional chance to compare biotic variations in shallow-water assemblages with deep-water communities across the MECO. In the section, the MECO interval is tentatively constrained by stable isotope oxygen data and calcareous plankton biostratigraphy. The marked decline in abundance of the epifaunal benthic Cibicidoides across the lower-middle part of the MECO suggests a decrease in oxygenation at the seafloor. Further evidence of oxygen depletion is the increase in organic matter content (TOC) of the sediment and the presence of infaunal genera Uvigerina and Bolivina. The planktic foraminiferal assemblages record the MECO warming in the upper water column as the mixed-layer warm index genera Acarinina and Morozovelloides markedly increase in abundance. In the post-MECO interval, here poorly exposed, cooler conditions are indicated by the dominance of the cold-water index genus Subbotina. Remarkably, Acarinina decline in abundance in the upper MECO interval and never recover. The MECO perturbance permanently impacted the benthic and planktic communities at Sealza that exceeded the tipping point to move to a new regime, thus proving the fauna to be not resilient, but also not recording any extinctions.

Impact of early Danian environmental perturbations on mid-latitude planktic foraminiferal assemblages from the ODP Site 1262 (South Atlantic Ocean)

Impact of early Danian environmental perturbations on mid-latitude planktic foraminiferal assemblages from the ODP Site 1262 (South Atlantic Ocean)

Disentangling multiproxy temperature reconstructions from the subtropical North Atlantic

Reliable reconstruction of past sea surface temperature (SST) is of prime importance for understanding the Earth’s sensitivity to external forcing. Yet, it remains a major challenge in paleoceanography because comparison between SST estimates from different proxies reveals mismatches and raise the question as to what the contrasting proxies actually record. A better understanding of these mismatches in the light of seasonal occurrence of the proxy bearing organisms (archives) and water mass changes help to assess climate models. Here, we analyze data from the last deglaciation using a sediment core site situated at the northern boundary of the North Atlantic subtropical gyre influenced by fast latitudinal migrations of the subtropical Azores Front (AF) and resulting changes in water masses that may affect the SST records. Differences between the SST estimates from different deglacial SST reconstructions obtained from (1) Mg/Ca in planktic foraminifer tests, (2) alkenone UK′37, and (3) planktic foraminifer assemblages (SIMMAX), are assumed to result from the ecology of the proxy bearing organisms, and are assessed for the impact on different SST reconstructions from local seawater δ18O (δ18Ow) reconstructions. The general trends of SSTs from all four proxies confirm the well-known deglacial succession of warm and cold events. Mismatches between amplitudes of temperature changes are explained by differences in the phenology of the proxy-bearing organisms and local changes in hydrography. The combination of δ18O SST from the three different archives of δ18Ow reconstructions may cause offsets that exceed the climate driven signals.

SIX-CHAMBERED VOLUTION OF THE MAASTRICHTIAN PLANKTIC FORAMINIFERAL PLUMMERITA SPECIES IN THE TETHYS

Brönnimann (1952), from Trinidad, was distinguished the last six-chambered volition of the genus Rugoglobigerina (R. reicheli, R. pustulata, R. hexacamerata) as a separate group from another last five-chambered volition with spine-like prolongation of ultimate and penultimate chambers Plummerita hantkeninoides group (P. hantkeninoides, P. costata, P. inflata). Later on, the Rugoglobigerina reicheli specimen belongs to the genus Plummerita due to its spine-like prolongation of ultimate and penultimate chambers, while the other two species R. hexacamerata and R. pustulata don’t have these distinguished characters of the genus Plummerita. In this study, added to P. reicheli of Brönnimann, three new species of the planktic foraminiferal assemblage of six-chamber volution of the Plummerita reicheli group are presented: Plummerita reicheli (Trinidad), P. caribbeanica (Porto Rico). P. spainica (Spain) and P. tunisica (Tunisia).

Four and five-chambered evolution of the late maastrichtian planktic foraminiferal Plummerita species in the Tethys

Brönnimann1 proposed two groups from Trinidad, which have spine-like prolongation of ultimate and penultimate chambers of the diagnostic latest Maastrichtian planktonic foraminiferal genus Plummerita. As a separate group of this genus, some of it has the last six-chambered volition in Plummerita reicheli group (P. reicheli, P. pustulata, and P. hexacamerata). The same author also proposed another group related to this genus, with the last five-chambered volution: P. hantkeninoides group (P. hantkeninoides, P. costata and P. inflata). Nonetheless, another third group was also added to these Plummerita assemblages, where Anan2 added a distinct species of Plummerita from the Duwi section, the Red Sea coast of Egypt, P. haggagae, which differs from the other species of the Plummerita by its four-chambered volution in the last whorl. In the current study, an attempt is made to identify three new species of the planktic foraminiferal assemblages of five-chambers volution, P. hantkeninoides group (P. hodae, P. kellerae, P. premolisilvae) is believed here to be new, as well as another one four-chamber volution, P. haggagae group (P. elkefensis, n. sp.), which described from many localities in the Southern Tethys (Tunisia, Egypt, Iraq), and Northern Tethys (Italy). The biostratigraphy, paleogeography, paleoecology, and paleobathymetry of the recorded Plummerita members in different Tethyan localities are presented and discussed.

Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

Abstract. Planktic foraminifera are widely used in paleoceanographic and paleoclimatic studies. The accuracy of such reconstructions depends on our understanding of the organisms' ecology. Here we report on field observations of planktic foraminiferal abundances (>150 µm) from five depth intervals between 0–500 m water depth at 37 sites in the eastern tropical Indian Ocean. The total planktic foraminiferal assemblage here comprises 29 morphospecies, with 11 morphospecies accounting for 90 % of the total assemblage. Both species composition and dominance in the net samples are broadly consistent with the published data from the corresponding surface sediments. The abundance and vertical distribution of planktic foraminifera are low offshore western Sumatra and increase towards offshore southern Java and the Lesser Sunda Islands (LSI). Average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while that of Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper-water-column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well mixed offshore Java–LSI (upwelling). Overall, the inferred habitat depths of selected planktic foraminifera species show a good agreement with those from sediment trap samples and from surface sediments off Sumatra, but not with those from surface sediments off Java–LSI. The discrepancy might stem from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by a plankton net to seasonal and interannual variability as recorded in sediment traps, and how these changes are transferred and preserved in deep-sea sediments.

Monsoon-related changes in surface hydrography and productivity in the Bay of Bengal over the last 45 kyr BP

Temporal variations of mixed-layer planktic foraminiferal abundances in a sediment core from the western Bay of Bengal (off Krishna – Godavari Basin) are used to reconstruct surface hydrographic structure and productivity in response to the changes in seasonal monsoon precipitation and wind intensity over the last 45 kyr BP. The faunal proxy records (abundances of eutrophic and oligotrophic species/group and G. bulloides / G. ruber ratio) exhibit millennial-scale variations during the late Glacial, deglacial and Holocene periods. Our results show that the surface hydrographic conditions and productivity varied in concert with the Northern Hemisphere climatic events (Dansgaard-Oeschger (D O) oscillations and Heinrich (H) events). The productivity in the late Glacial period between 44 and 19 kyr BP in general was higher compared to the deglacial and Holocene. Within the late Glacial period, we record high productivity during the cold phases of the D O cycles (43–41, 35–34, 28.5–28, 27–25 kyr BP), North Atlantic Heinrich events (39.5–38.5 kyr BP, H4; 31.5–30 kyr BP, H3; 24–23 kyr BP, H2) and during the Last Glacial Maximum (22–19 kyr BP). These productivity maxima are related to the pronounced advection of nutrient-rich subsurface waters to the euphotic zone induced by the intensified Northeast (NE) Monsoon winds in non-stratified/weakly stratified surface ocean conditions due to reduced Southwest (SW) Monsoon precipitation and freshwater influx. Our faunal record suggests a major reorganization of seasonal monsoon wind circulations after 16 kyr BP, when the SW monsoon intensified and concomitantly the NE monsoon weakened. Enhanced SW monsoon precipitation and freshwater flux to the Bay of Bengal between 15 and 13 kyr BP, a period broadly corresponding to the warm Bølling-Allerød (B/A) event, resulted in strong stratification of mixed-layer water and oligotrophic conditions. An increase in productivity between 13 and 11 kyr BP (equivalent to the cold Younger Dryas (YD) event) is attributed to intensified mixing of weakly stratified mixed layer waters by NE monsoon winds. During the early Holocene between 9 and 6 kyr BP, intensified SW monsoon precipitation and high fluvial discharge resulted in strongly stratified, nutrient-poor waters in the mixed-layer and a conspicuous reduction in productivity. However, a moderate increase in productivity is recorded between 5 and 3 kyr BP, when the SW monsoon intensity and associated fluvial discharge gradually declined and ocean surface stratification weakened resulting in conditions favourable for NE monsoon winds induced mixing. Overall, our results show that the alternating periods of intensified SW monsoon precipitation and NE monsoon wind circulation modulated the surface hydrographic structure and productivity patterns in the Bay of Bengal. • A 45 kyr planktic foraminiferal assemblage record from the western BoB. • Millennial scale variations in surface hydrography and productivity. • Seasonal monsoon precipitation & wind intensity modulate productivity pattern. • The productivity variation pattern is characterized by D O oscillations. • Productivity maxima occurred during cold stadials.

Quantitative analysis of Calabrian planktic foraminifer assemblages and paleoecology of the Eastern Mediterranean from the onshore epibathyal sedimentary archives (Mersin, Turkey)

The youngest epibathyal marine deposits in the Eastern Mediterranean Region giving Calabrian age have been recently discovered in the southern Central Anatolian Plateau, Turkey. Hence the Calabrian planktic foraminifer paleoecology of the Eastern Mediterranean surface waters has not been investigated yet. This study reports the planktic foraminifer assemblages of the two Calabrian aged marine successions in the Mersin district in southern Turkey and their ecological properties in the Eastern Mediterranean sea-surface waters in terms of various ecological parameters such as temperature and nutrient availability. The multivariate statistical analysis revealed that the older marine succession, Gülnar East, is represented by four main assemblages: Globorotalia spp. assemblage, Globigerinella spp. assemblage, Globigerina spp. assemblage, and Orbulina spp. Assemblage; whereas the second and the younger section, Tol, is represented by three assemblages: Globigerinoides spp. and Globigerinella obesa assemblage, Orbulina spp. and Globigerinodes spp. assemblage, and Orbulina spp. assemblage. Examining the statistical correlations between the assemblages, three ecological factors for the Gülnar East section and one ecological factor for the Tol section were identified.

Planktic Foraminiferal Biostratigraphy of the Upper Part of the Damlouk Member, Ratga Formation, Western Desert, Iraq

The basinal part of the Damlouk Member upper sedimentary cycle of the Ratga Formation exposed in the Qaim area of the Iraqi western desert is examined. The studied section consists of marlstone, marly and phosphatic limestone, and planktic foraminifera-rich limestone beds. Detailed study of the planktic foraminiferal assemblages of these rocks revealed the occurrences of (30) species belonging to (11) genera. The stratigraphic distribution of these species permits the recognition of three biozones. These are from the lower to upper part of the section: - Acarinina bullbrooki Zone, (Middle Lutetian), Morozovelloides lehneri Zone, (Late Lutetian), Globigerinatheca semiinvoluta – Hantkenina alabamensis Zone, (Early Bartonian). These zones indicate that the studied section of the Ratga Formation (Damlouk Member) is of Middle-Late Lutetian to Early Bartonian age. These biozones are correlated with different local and regional studies.

Determining the habitat depth of the planktic foraminifera Dentoglobigerina altispira in the eastern Arabian Sea during the middle Miocene

Tests of planktic foraminifera are important tracers for reconstructing past oceanic environments. It is essential to have accurate information of the habitat depth of the planktic foraminiferal species whose isotopic and elemental signatures are being used to infer past climatic and oceanographic conditions. The planktic foraminifera species Dentoglobigerina altispira is a very common component of Miocene and Pliocene tropical to warm subtropical planktic foraminiferal assemblages but different findings exist about the habitat depth of this species from shallow to deep water. For that reason, comparative stable carbon and oxygen isotope analyses of four coexisting planktic foraminifera species from National Gas Hydrate Program Expedition Site 01 (Site NGHP-01-01A) were performed in order to reconstruct the habitat depth of D. altispira in the eastern Arabian Sea for the middle Miocene (~16–12.5 Ma). The D. altispira oxygen isotope values are on average higher than those of the shallow water reference species Trilobatus sacculifer and Globigerinoides obliquus, but still significantly lower than those for the deeper dwelling species Dentoglobigerina venezuelana. This suggests that D. altispira inhabited a deeper habitat depth than the estimated habitat depth for modern T. sacculifer in the eastern Indian Ocean (~50 m). Paired D. altispira and T. sacculifer Mg/Ca data reveal lower Mg/Ca and thus colder temperatures for D. altispira than for T. sacculifer, also suggesting that D. altispira calcified at a greater water depth than T. sacculifer. The data of this study suggest that D. altispira inhabited the lower mixed layer and/or upper thermocline in the eastern Arabian Sea during the middle Miocene.

Evaluation of deep-water environmental conditions during the latest Maastrichtian-early Danian: Insights from the western south atlantic ocean

The Cretaceous-Paleogene (K-Pg) boundary extinction event affected planktic foraminiferal assemblages worldwide in a dramatic way, but deep sea benthic foraminiferal assemblages were not significantly impacted. However, possible impacts of massive early Danian volcanic eruptions, such as those related to the Deccan Traps, on benthic foraminiferal assemblages are not yet explored. Here we present geochemical and benthic foraminiferal data across the K-Pg boundary and within the earliest Danian interval at Deep Sea Drilling Project (DSDP) Site 356, located on the São Paulo Plateau, western South Atlantic Ocean. Maastrichtian to Danian benthic foraminiferal assemblages are well-preserved and suggest deposition at middle to lower bathyal paleodepths, under an oligotrophic regime with well-oxygenated bottom water conditions. As expected, the K-Pg boundary event did not significantly affect benthic foraminiferal assemblages at Site 356. However, during the early Danian, benthic foraminiferal species richness, heterogeneity, diversity and equitability presented overall opposite trends in relation to the Hg/TOC and Hg/CaCO3 ratios, as well as Hg concentrations, which we consider proxies for intensity of volcanic activity. Our results suggest a possible response of Danian middle to lower bathyal benthic foraminiferal assemblages at Site 356 to changes in bottom water condition possibly associated with massive volcanism eruptions.

Two-Tiered Transition of the North Atlantic Surface Hydrology during the Past 1.6 Ma: Multiproxy Evidence from Planktic Foraminifera

Analyses of planktic foraminiferal assemblage data, test morphology, and stable oxygen isotopes from the Integrated Ocean Drilling Program (IODP) Site U1304 in the North Atlantic reveal a stepwise regional migration of the oceanic fronts around 0.6 Ma and 0.4 Ma, i.e., during Marine Isotope Stages (MISs) 15 and 11, respectively. Both changes of planktic foraminiferal assemblages and shell carbonate isotopes indicate that the cold Arctic waters in general persisted at IODP Site U1304 from 1.6 to 0.6 Ma (MIS 15), even though the warmer waters originating from the Atlantic waters episodically bathed Site U1304 during the interglacial periods. During the time-interval from ca. 0.6 to 0.4 Ma (MISs 15–11), an alternating dominance of Artic and Atlantic waters at the Site U1304 has been suggested from isotopic evidence. In MIS 11, the dominant planktic foraminiferal species Neogloboquadrina pachyderma experienced a short-term but significant decrease in test size. The test-size change may have been caused by accelerated reproduction in more favorite feeding conditions over the long-lasting interglacial period around the Subarctic Front. This finding is supported by the presence of massive diatoms oozes in the same time-interval. The modern-type glacial/interglacial change of the surface water system established since ca. 0.4 Ma (MIS 11) followed the Mid-Brunhes Event.

Foraminiferal Biostratigraphy of the Uppermost Cretaceous Period, Duhok Area, Kurdistan Region, North of Iraq

A relatively complete Late Maastrichtian succession of the upper part of the Shiranish Formation (Upper Cretaceous) in the Duhok area is investigated for the planktic foraminiferal assemblages. This studied interval consists mainly of bluish shale, marl, and thin beds of hard marly limestone all with grey-blue color. The upper contact of the Shiranish Formation is conformable with the overlies Danian Aaliji Formation. Based on the recorded planktic foraminifera and their ranges, the studied succession is subdivided into three main biozones of the latest Maastrichtian age, these zones are Pseudoguembelina hariaensis (CF3) Interval Zone, Pseudoguembelina palpebra (CF2) Interval Zone, and Plummerita hantkeninoides (CF1) Total Range Zone. These zones show continuous and complete Upper Cretaceous sediments, which are preserved in the Bade section of the Duhok area

Mediterranean faunal evolution and biochronological events during the last 24 kyr

We generated high-resolution biochronological records in the Mediterranean Sea covering the period extending to the Late-glacial. The present study is based on micropaleontological, sea-surface temperature (SST) and oxygen isotopic analyses performed along three well-dated deep-sea cores: REC1353, KET80–19 and MD84–641 recovered in the Siculo-Tunisian Strait, Tyrrhenian Sea and Levantine Basin, respectively. The quantitative distributional patterns of planktic foraminifera permitted to identify seven biozones based on the apparition and/or disappearance of the main specific taxa or by their noticeable abundance peaks. Abundance records display that major changes in planktic foraminiferal assemblages have a similar pattern mainly in central and western basins. In particular, four recognized bio-events can be used to establish or to improve the chronology of Mediterranean deep-sea cores. The comparison of the SST estimates and foraminiferal records with those of NGRIP ice-core shows a similarity between the Greenland climate and the Mediterranean hydrology. This indicates that the main climate changes recorded in the North Atlantic are globally in phase with those observed in the Mediterranean region.

The equatorial Indian Ocean upper water-column structure influenced by cross-basinal water exchange over the last ~40000 years

The central equatorial Indian Ocean (CEIO) is influenced by both, summer and winter monsoon and is known for cross basin exchange of water between the Arabian Sea (AS) and the Bay of Bengal (BoB). Here, we present planktic foraminiferal assemblage record from a sediment core (SSD-044/GC-01, 5°N; 77°E) from the CEIO, which is in the pathway of this cross-basin water exchange, in order to reconstruct changes in upper water column structure during the last 43 ka, at millennial year timescales. Our data displays an increase in ratio of mixed layer eutrophic to mixed layer oligotrophic foraminifer species from MIS (Marine Isotope Stage) 3 to MIS 2 which further decreased sharply during the last deglaciation and remained low thereafter. This trend matches well with the sedimentary Corg content which is interpreted as a productivity signal, in line with other studies from this region. Furthermore, the relative abundance of thermocline foraminifer species displayed highest values during MIS 3, a decrease through the MIS 2, a sharp decrease through the early deglaciation and an increase thereafter into the Holocene. Our records suggest that the increased productivity at this site seems to be fed by nutrient injection from nutricline to the photic zone which manifests in a corresponding increase in thermocline foraminifera species. The nutrient injection to the photic zone maybe a result of increased vertical/convective mixing due to increased flow of cooler/high-salinity BoB water probably caused by decreased freshening of the BoB during glacials. Furthermore, our data suggests a warm, stratified upper water column and low surface nutrient (oligotrophic) conditions during the last deglaciation and the Holocene.

MORFOLOGÍA, BIOMETRÍA Y TAXONOMÍA DE FORAMINÍFEROS PLANCTÓNICOS DEL DANIENSE BASAL: Palaeoglobigerina n. gen.

El Daniense basal contiene asociaciones oligotáxicas con foraminíferos planctónicos de pequeño tamaño (< 150 μm) y de morfología muy simple, derivadas de la radiación evolutiva acontecida tras el evento de extinción en masa del límite Cretácico/Paleógeno (K/Pg). Se ha revisado la clasificación taxonómica de este grupo de foraminíferos después de realizar análisis biométricos y morfológicos para delimitar las especies. Este estudio y la distribución bioestratigráfica de las especies están basados en material y muestreos de alta resolución de algunos de los cortes del límite K/Pg más continuos del mundo. Se propone Palaeoglobigerina n. gen. para incluir a pequeñas especies de globigerínidos trocoespiralados, de pared lisa microperforada y 3-4 cámaras en la última vuelta de espira, que aparecen en las Zonas de Guembelitria cretacea y de Parvularugoglobigerina eugubina (Daniense basal). Se han reconocido, descrito e ilustrado veintidós especies: cinco de Guembelitria, dos de Hedbergella, dos de Woodringina, dos de Chiloguembelina, cinco de Palaeoglobigerina n. gen. y seis de Parvularugoglobigerina.

The environmental factors limiting the distribution of shallow-water terebratulid brachiopods

AbstractThe Cenozoic genusTerebratulaseems to be an exception to the post-Permian trend in brachiopod retreat to offshore habitats, because it was species rich and numerically abundant in warm-temperate shallow-water environments in the Mediterranean and the Paratethys realms. This was so despite the general dominance of bivalves and the pervasive bioturbation and predation pressure during the Neogene.Terebratula, however, went extinct in the Calabrian (Pleistocene). The optimal environmental conditions forTerebratuladuring its prime are poorly known. The Águilas Basin (SE Spain) is an ideal study area to investigate the habitat ofTerebratula, because shell beds of this brachiopod occur there cyclically in early Pliocene deposits. We evaluate the paleoecological boundary conditions controlling the distribution ofTerebratulaby estimating its environmental tolerances using benthic and planktic foraminiferal and nannoplanktic assemblages and oxygen isotopes of the secondary layer brachiopod calcite. Our results suggest thatTerebratulain the Águilas Basin favored oligotrophic to mesotrophic, well-oxygenated environments at water depths of 60–90 m. Planktic foraminiferal assemblages and oxygen isotopes point to sea-surface temperatures between ~16°C and 22°C, and bottom-water temperatures between 17°C and 24°C. The analyzed proxies indicate thatTerebratulatolerated local variations in water depth, bottom temperature, oxygenation, productivity, and organic enrichment.Terebratulawas probably excluded by grazing pressure from well-lit environments and preferentially occupied sediment-starved, current-swept upper offshore habitats where coralline red algae were absent. Narrow temperature ranges ofTerebratulaspecies might have been a disadvantage during the high-amplitude seawater temperature fluctuations that started about 1 Ma, when the genus went extinct.

Do different extraction techniques impact planktic foraminiferal assemblages? An early Eocene case study

Abstract Here we report and compare results on planktic foraminiferal assemblages extracted with five disaggregation techniques: acetic acid, H2O2 at 10% and 25% concentration, neosteramina, and liquid N2. The aim is to estimate whether these laboratory procedures can affect the pristine assemblages or add secondary dissolution effects. We apply these five methods on three samples with different carbonate content from the early Eocene Tethyan Terche section (northeast Italy). For each method we assess: (1) the treatment effectiveness in relation to time required to successfully extract planktic foraminiferal tests and preservation; (2) the degree of dissolution through the analyses of three well-known dissolution proxies including the fragmentation index, the planktic benthic ratio and the weight percent coarse fraction; (3) changes in planktic foraminiferal assemblages through genera and species absolute abundances and the evaluation of multiple species diversity indices. Our data demonstrate that acetic acid and neosteramina treatments are the most effective methods as they represent the only ones capable in disaggregating the samples with higher CaCO3 content whereas liquid N2 revealed to be the best treatment to adopt for samples with low CaCO3 content. The best-preserved foraminiferal specimens derive from the acetic acid and neosteramina treatments. Nonetheless, the acetic acid along with H2O2 treatments, at both concentrations, can impact planktic foraminiferal assemblages affecting the diversity or species abundances. Dissolution of planktic foraminifera shows a complex relationship with the initial carbonate content (CaCO3%) of the samples and with the different dissolution susceptibility of the species that can differ according to the laboratory procedures.

Biostratigraphy and lithostratigraphy of Late Cretaceous–Early Palaeogene deposits in Tang-e-Abolhayat, Zagros basin (SW Iran)

In this study, to consider microbiostratigraphy of Cretaceous and Palaeocene planktic foraminifera, a stratigraphic section of the Gurpi and Pabdeh formations named Tang-e-Abolhayat was selected. On the basis of the identified planktic foraminiferal assemblages, seven biozones and two sub-biozones have been recorded (four biozones from the uppermost part of the Cretaceous, (Gurpi Formation), and three biozones from the lower part of the Lower Palaeocene (Pabdeh Formation). The biostratigraphic correlations based on planktic foraminiferal zonations showed a comparison between the biostratigraphic zones in this study and other equivalents of the commonly used planktic zonal scheme around the Cretaceous–Palaeogene in and outside Iran. Biostratigraphic analysis confirms that the studied section is incomplete across the Cretaceous–Tertiary boundary and a hiatus is suggested by the absence of the Plummerita hantkeninoides, Guembelitria cretacea, Parvularugoglobigerina eugubina Zones and Parasubbotina pseudobulloides Subzone (CFl to Pla zones). These absences could reflect the restriction of the above-mentioned zones to shallower settings, slow sedimentation rates or an interval of erosion or no deposition. There is no obvious evidence of erosion. On the other hand, the Pabdeh Formation overlies Gurpi Formation paraconformably.

Delayed calcareous nannoplankton boom-bust successions in the earliest Paleocene Chicxulub (Mexico) impact crater

AbstractThe Cretaceous-Paleogene (K-Pg; 66 Ma) mass extinction was caused by a bolide impact on the Yucatán platform near modern Chicxulub, Mexico. Calcareous nannoplankton, a dominant group of primary producers, were almost eradicated at this time. Post-impact nannoplankton assemblages from Northern Hemisphere sites were characterized by a short-lived series of high-dominance, low-diversity acmes (“boom-bust” successions), which likely represent an unstable post-impact environment. Although these boom-bust successions are a global signal, the mechanisms that controlled the taxonomic switchovers between acmes are currently unknown. Here, we present detailed analyses of calcareous nannoplankton and planktic foraminiferal assemblages in a new K-Pg section from the peak ring of the Chicxulub crater. We show that although nannoplankton assemblages resemble the typical series of acmes at Tethyan sites, the termination of the “disaster” acme in the crater is delayed by at least 500 k.y. The coincidence between shifts in the dominant planktic foraminiferal trophic group and switchovers in nannoplankton boom-bust taxa suggests that this series of acmes may represent a gradual trend toward oligotrophy driven by the global restoration of biological pump efficiency. Thus, the global diachroneity of boom-bust successions likely reflects the differential pacing of biological pump restoration between oceanic basins and settings.