Calcareous Nannofossil Abundance Research Articles

Assessing temporal transition between microgranular and hyaline tests of calcareous microplankton during the Late Jurassic

Calcareous microplankton increased in abundance during the latest Jurassic, coinciding with the increase in abundance of calcareous nannofossils and with the onset of deposition of pelagic calcareous oozes. However, the timing and causes of the shift from microgranular tests of the earliest microplankton (chitinoidellids) to hyaline tests of calpionellids are obscured because the ultrastructure of two-layered praecalpionellids that occur during the Tithonian is poorly documented. Here, we investigate the ultrastructure of chitinoidellids and praecalpionellids from Upper Tithonian deposits in the Western Carpathians. We show that (1) the chitinoidellid microgranular layer is formed by elongated, euhedral, densely-packed, nanometric needles rather than by fragments of calcareous nannofossils, (2) two-layered chitinoidellids (Semichitinoidella) are formed by an internal microgranular layer (identical to that of Chitinoidella) and by an external hyaline prismatic layer, and (3) two-layered Praetintinnopsella exhibits an internal hyaline layer (with densely-packed, equant microcrystals) and an external layer formed by a dark organic rim. The external layer in Praetintinnopsella thus does not have any relation to the microgranular layer in chitinoidellids and the external hyaline layer of Semichitinoidella is not equivalent in structure to the hyaline layer of Praetintinnopsella. As both single-layer and two-layered chitinoidellids appear prior to the first appearance of Praetintinnopsella but still co-occur with this genus in the lowermost Upper Tithonian deposits, the origin of two-layered Praetintinnopsella either reflects a major transformation in biomineralization towards larger and more packed crystals during their earlier divergence from the chitinoidellid lineage or an origination of two-layered tests with a hyaline layer from an independent non-chitinoidellid ancestor.

Spatio-temporal variability of alkenone and calcareous nannofossil abundance records across the southeastern Philippines: Insights on alkenone production and paleoceanographic reconstructions.

Spatio-temporal variability of alkenone and calcareous nannofossil abundance records across the southeastern Philippines: Insights on alkenone production and paleoceanographic reconstructions.

Middle Paleocene-early Eocene inter-regional correlations and palaeoclimatic changes in eastern Tethys Sea: Calcareous nannofossil evidence for Paleocene-Eocene Thermal Maximum (PETM) and sea-level change from the western Tarim Basin, NW China

Calcareous nannofossil assemblages from the interval covering the middle Paleocene to early Eocene (P/E), studied in sediments from two sections located in the western Tarim Basin (Kuzigongsu and Bashibulake), indicate that the record of the PETM (Paleocene-Eocene Thermal Maximum) is inscribed in a transgression-regression cycle. A large sea transgression occurred concomitant to the Qimugen Formation, according to earlier studies. Here we present detailed evidence of richness and abundance of calcareous nannofossils to study the PETM and sea-level change in the western Tarim Basin. The gradually increasing sea level from the base of the Qimugen Formation is dated to the nannofossil zones NP7 to 9a (Thanetian), in which the first occurrences of H. riedelii and of D. multiradiatus have been recorded. The highstand of the sea level cycle coincides with increasing Discoaster spp. amounts near the Paleocene/Eocene boundary (NP9a-10), which is dated by the occurrence of RD assemblages (namely, Rhomboaster spp. and Discoaster araneus group). Evidence of regression, observed in the top of Qimugen Formation (NP10–11) corresponds to low abundance and diversity of nannofossils, and is characterized by a rapid increase of Micrantholithus spp. in the assemblage. Inter-regional correlations between the two sections show that in the Tianshan Mountain area the highest relative sea level occurred near the middle part of NP9a.

Microfossil fragmentation across the Paleocene-Eocene transition at ODP Site 1209 (North Pacific): Implication for reconstructing nannofossil fluxes.

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).

Biostratigraphy and Paleoenvironmental Reconstruction at the Gebel Nezzazat (Central Sinai, Egypt): A Paleocene Record for the Southern Tethys

The variations in assemblages of calcareous nannofossils are tracked in the Dakhla and Tarawan Formations exposed at Gebel Nezzazat (central Sinai, Egypt). Five calcareous nannofossil biozones, namely NP2/3, NP4, NP5, NP6, and NP7/8 are identified. A distinct marker bed related to the Latest Danian Event (LDE) occurs within the Dakhla Fm. The earliest representative of fasciculiths, Lithoptychius schmitzii, first occurs just below the LDE distinct bed and is followed by the Los of Diantholitha alata, D. mariposa, L. varolii, L. felis, and L. collaris. The abundance of calcareous nannofossils drops within the LDE distinctive bed. The base of Selandian Stage is here approximated at the base of Zone NP5 in concurrence with a sudden drop in the abundance of calcareous nannofossils. No considerable lithological changes are noted across this transition. The absence of subsequent occurrences of L. ulii, L. janii, L. billii, and L. stegostus suggest inconsistent lowest occurrences (Los) of these taxa, insufficient sampling resolution, and/or a hiatus. The base of Thanetian is approximated with the base of Zone NP7/8 in the topmost of Dakhla Fm. No considerable changes in calcareous nannofossil assemblages are associated in correspondence to this transition except the LO of D. mohleri, lowest continuous occurrence (LctO) of Bomolithus megastypus, and the increase in abundance of Heliolithus kleinpellii as well as a sudden drop in abundance within Zone NP7/8. The variations in calcareous nannofossil assemblages at Gebel Nezzazat suggest prevailing warm-water and oligotrophic conditions during the Paleocene and particularly along the Danian Stage that are interrupted by minor fluctuations in paleoclimatic conditions. In particular, the Danian–Selandian transition marks a decrease in warm and oligotrophic conditions that persisted along the Selandian Stage. The Selandian–Thanetian transition shows an increase of warm and oligotrophic conditions prevailed in the Thanetian record. The sudden decrease in abundance of calcareous nannofossils in both the Selandian and Thanetian is likely resulted from an increase in dissolution of carbonates rather than variations in the paleotemperature and/or paleofertility.

Integrated bio- and chemostratigraphy of the Cretaceous – Paleogene boundary interval in the Zagros Basin (Iran, central Tethys)

An expanded Upper Cretaceous – Lower Paleocene succession, which encompasses the Cretaceous – Paleogene boundary (K – Pg), was studied in detail from the Zagros Basin (southwest Iran, central Tethys). In order to characterize the K – Pg transition, high resolution sampling was performed in the upper part of the Gurpi Formation. The studied interval consists of dark grey marly shales and marls with interbedded limestones. Based on calcareous nannofossils, the studied section is attributed to calcareous nannofossil zones CC26b to NP3 (latest Maastrichtian – early Paleogene). High relative abundances of the nannofossil species Micula staurophora (= Micula decussata) in the Maastrichtian part (CC26) might delineate cool surface water conditions, which are followed by an increase in abundance of Micula murus about 2 m below the K – Pg boundary. Reworked Cretaceous taxa were found at the K – Pg boundary and in the overlying Danian (NP 1–3). These findings hamper a reliable determination of the last occurrence of Cretaceous calcareous nannofossil taxa at the K – Pg boundary. The K – Pg boundary is located in the uppermost part of a positive carbon isotope excursion. Diversity and absolute abundances of calcareous nannofossils show a significant decrease at the K – Pg boundary. A bloom of the dinoflagellate cyst Cervisiella operculata (formerly Thoracosphaera operculata), which is indicating environmental stress, is recorded slightly below the boundary. Throughout the lowermost Danian (NP1), the assemblages are dominated by a bloom of small species like Neobiscutum romeinii, Neobiscutum parvulum, Futyania petalosa and small Cruciplacolithus primus. These taxa indicate stressful, and eutrophic surface water conditions throughout the initial recovery phase. The Dan-C2 and Lower C29n events, recorded in the lower Danian NP1 and lower NP2 biozones, are marked by negative carbon isotope excursions. High relative abundances of Prinsius dimorphosus followed by a Coccolithus pelagicus bloom in the full recovery phase (middle Danian, NP 3), are attributed to a short term cooling phase followed by warm surface water environments recorded along with the highest absolute abundance of calcareous nannofossils.

Calcareous nannofossil biostratigraphy of the Late Cretaceous‒early Paleocene interval in the Zagros basin (southeastern Tethys), Iran

Calcareous nannofossil biostratigraphy reveals a continuous depositional record through the Upper Cretaceous‒Paleocene succession in the Zagros Basin; southwest Iran (southeastern part of the Neo-Tethys), especially through the Cretaceous‒Paleogene and the Danian‒Selandian boundaries. The upper part of the Gurpi Formation and the lower part of the Pabdeh Formation were investigated. Calcareous nannofossil assemblages from these formations are characterized by abundant, diverse and moderate- to well-preserved forms with Tethyan affinities. This study concentrates on two sections (the Gurpi and Kabir-Kuh sections) in the west and southwest of Iran in the Zagros Basin, which span biozones CC25c/UC20bTP to NP6/NTp10B in the Kabir-Kuh and CC25b/UC20aTP to NP5/NTp9 in the Gurpi section. Late Maastrichtian nannofossil abundance and diversity in the studied intervals is high with a sharp decrease slightly above the K/Pg boundary. The K/Pg boundary interval is marked by the FO of Biantholithus sparsus, an acme of the dinoflagellate cyst Thoracosphaera operculata, a notable decrease in Cretaceous calcareous nannofossil abundance and diversity, and the appearance of new Paleocene taxa. An increased abundance of Thoracosphaera is recorded similar to that in the El Kef (Global Stratotype Section and Point, GSSP, for the K/Pg boundary), Ellés (auxiliary section), Egypt, Atlantic Ocean and sections elsewhere in the world. Reworked Cretaceous calcareous nannofossils are recorded from the base of the Danian along with the new Paleocene species. The Danian‒Selandian boundary is marked by the appearance of Lithoptychius ulii, Lithoptychius pileatus and Lithoptychius janii at the base of NTp8C; this level is also marked by the second radiation of Fasciculithus. Azam Mahanipour [a_mahanipour@uk.ac.ir], Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman, Iran; Mohammad Parandavar [parandavar.m@gmail.com], Paleontological Research Department, Exploration Directorate of Oil and Gas, NIOC, Tehran; Mohamed Youssef [myousefgeology@gmail.com], Department of Geology, Faculty of Science, South Valley University, 83523 Qena, Egypt.

The Late Miocene to Early Pliocene “Humid Interval” on the NW Australian Shelf: Disentangling Climate Forcing From Regional Basin Evolution

AbstractPre‐Quaternary paleoclimate studies in Australia mainly focus on terrestrial records from the southeastern part of the continent. IODP Expedition 356 drilled on the northwestern Australian shelf, yielding Miocene‐Pleistocene paleoclimate records in an area where climate archives are scarce. Postexpedition research revealed a dry‐to‐humid transition across the latest Miocene and early Pliocene (start of the “Humid Interval”). However, the complex tectonic history of the area makes these interpretations challenging. In this study, we investigate late Miocene to early Pliocene sediment cores from two sites that are only 100 km apart but situated in two adjacent basins (Northern Carnarvon and Roebuck Basins). Combining lithofacies study, time series analysis of potassium content (K wt%), and calcareous nannofossil abundance counts (N/g), this work disentangles the complex interplay between basin evolution and climate change between 6.1 and 4 Ma. Overall, the investigated proxies show high correlation between both sites, except during 6.1–5.7 Ma. During this interval, Site U1463 records a gradual increase in K wt%, correlated with basin deepening, whereas Site U1464 records an abrupt rise in K wt% at ~6 Ma. We explain this diachronicity by differential basin subsidence. The tectonic interplay with our paleorecords makes it difficult to pinpoint the exact onset of the “Humid Interval,” but we conclude that K wt% and coccolith abundances at Site U1464 indicate that a fluvial deposition system was already established since at least 6 Ma. This age is consistent with data supporting a southward movement of the Intertropical Convergence Zone rain belt at ~7 Ma.

Calcareous nannofossil and foraminiferal trace element records in the Sorbas Basin: A new piece of the Messinian Salinity Crisis onset puzzle

The Messinian Salinity Crisis (MSC) was an extreme event that affected the Mediterranean Sea during the late Miocene, leading to massive evaporite deposition across the basin. Here we focus on the Perales section (Sorbas Basin, Western Mediterranean), using calcareous nannofossil (CN) and foraminiferal geochemical analyses to trace the paleoenvironmental dynamics culminating in the MSC onset. Orbital and tectonic forcing drove the CN fluctuations that correlated with the lithological quadripartite precessional cycle. Our integrated analysis reveals that cyclical sapropel deposition was triggered by an increase in marine productivity, followed by an increase in freshwater input and the development of a Deep Chlorophyll Maximum (DCM). The overlying marl records the protracted freshwater input that led to the shallowing of the DCM, decreasing organic carbon export and promoting seafloor re-oxygenation. Stratification, acting as a barrier, trapped part of the river-sourced nutrients below the photic zone. The subsequent gradual decrease in temperature promoted the disruption of the stratification, mixing nutrients upward into the photic zone and promoting diatom proliferation and preservation. When the reservoir of dissolved silica was exhausted, bioturbated marls were deposited at the top of the cycle. In the last pre-evaporitic cycle (UA34) the usual lithological cyclicity is obliterated; however the precessional footprint is revealed by CN fluctuations, suggesting that sapropel-like deposition lasted for most of the cycle. This cycle also records a succession of CN abundance peaks (MSC onset bioevent), as already recorded in several Mediterranean sections approximately at the MSC onset, suggesting that the same paleoenvironmental changes triggered the evaporitic phase in the whole Mediterranean. This bioevent marks the last step of water exchange reduction with the Atlantic (restriction pulse), which increased the sensitivity of the Mediterranean to freshwater input and associated nutrient delivery, culminating in a further increase in marine productivity.

The biostratigraphic framework of CSDP-003 well, Central Swamp Depobelt, Niger Delta, Nigeria

The biostratigraphic framework of CSDP-003 well, Central Swamp Depobelt was investigated to establish the stratigraphic sequences penetrated in the well and the age of the sequences based on calcareous nannofossils recovered. The study was carried out with 138 ditch cuttings from the well and was prepared with the standard simple smear-slide technique of calcareous nannofossil sample preparatory method. The slides produced from the samples were viewed and 31 calcareous nannofossils were recovered which were used to characterize the well into 3 NN zones, following base (Last Downhole Occurrence/First Appearance Datum (LDO/FAD) of Sphenolithus heteromorphus, Top (First Downhole Occurrence/Last Appearance Datum (FDO/LAD) of Helicosphaera ampliaperta, and Top (First Downhole Occurrence/Last Appearance Datum (FDO/LAD) of Sphenolithus heteromorphus corresponding to NN3, NN4, and NN5 biozones respectively. Three Maximum Flooding Surfaces (MFS) and two Sequence Boundaries (SB) were delineated and their ages were determined using the diagnostic forms. MFS 17.40Ma was noted with high abundance and diversity of calcareous nannofossils and explosive events (ACME) of Sphenolithus heteromorphus, Helicosphaera ampliaperta, Sphenolithus moriformis, and Helicosphaera cartari at 2804m within NN4 zone, MFS 15.90Ma was identified based on abundance and diversity peak at 2429m corresponding to explosive events (ACME) of Sphenolithus heteromorphus, and Sphenolithus moriformis within NN4 zone while MFS 15.00Ma was delineated based on abundance and diversity peak with Helicosphaera cartari ACME at 1957m. The Sequence Boundary's SB 16.5 Ma (latest Burdigalian) and SB 15.5 Ma (Langhian) were delineated based on rare to non-occurrence of calcareous nannofossil at 2530m and 2228m respectively. ‬‬

Depositional mechanisms for upper Miocene sediments in the South China Sea central basin: Evidence from calcareous nannofossils

Abstract In 2014, the International Ocean Discovery Program (IODP) Expedition (Exp.) 349 discovered carbonate layers at sites located in the South China Sea (SCS) central basin. Preliminary results from shipboard investigation showed that most of these carbonate layers are calcareous nannofossil ooze and interpreted them as turbidites. However, more detailed studies are required to determine their depositional mechanisms and paleoenvironmental implications. In this study, we have analyzed CaCO3 content, calcareous nannofossil abundance, assemblage composition and preservation in carbonate and clay samples from the upper Miocene sections of Site U1433 in the SCS central basin. We confirm that these carbonate layers are of turbidity current genesis but are not typical nannofossil ooze, while the clays represent regular in situ deep sea sediments. The study interval spanned approximately from 10 to 5 million years before present (Ma). Calcareous nannofossil abundance and assemblage are used to reconstruct the evolution of the upper seawater structure in the SCS central basin. Our results indicate that the seawater shifted from strongly stratified to well-mixed due to enhanced monsoon. This shift was accompanied by an increase in pelagic productivity at ~8 Ma. This environmental change is critical for component variations of the carbonate turbidites since we suggest that these turbidites mainly sourced from periplatform ooze in the southern SCS composed by of mixed neritic and pelagic particles. The neritic and pelagic CaCO3 production have inversed responses to the change of seawater environment in the SCS and thus cause the component variations in the carbonate turbidites of Site U1433.

Changes in foraminiferal assemblages and environmental conditions during the T-OAE (Early Jurassic) in the northern Lusitanian Basin, Portugal

The foraminiferal assemblages and other microfossils from the Rabaçal area (Maria Pares section) in the Lusitanian Basin (Portugal) provide new insights regarding the Toarcian Oceanic Anoxic Event (T-OAE). Complementary analysis of the δ13C, total organic carbon (TOC) and geochemical redox and palaeoproductivity proxies reflect environmental changes that affected the microfossil assemblages. Detailed analyses of foraminiferal assemblages (their diversity, abundance, morphogroups and lifestyle) and geochemistry led us to discern phases of the biotic crisis and subsequent stages of recovery. Environmental instability, which began in the lattermost part of the Polymorphum Zone, is marked by a lesser abundance of foraminifera and ostracods, increased opportunist foraminifera, fluctuations in TOC values and the enrichment factor of phosphorous (PEF), as well as the onset of a negative carbon isotopic excursion (CIE). The peak phase of the biotic crisis corresponds with the lowest values for foraminiferal diversity and abundance (including a barren sample for benthic microfossils). The abundance and diversity of echinoderms, brachiopods, dinoflagellate cysts and calcareous nannofossils dropped sharply during the peak phase. This biotic crisis also entails extinction of the Order Metacopina and a local disappearance of echinoderms and brachiopods. Anoxic conditions at sea bottom did not develop, given the almost continuous record of foraminifera and trace fossils, yet oxygen-depleted conditions occurred. The lower part of the Levisoni Zone contains thin nodular limestones corresponding to a tempestitic–turbiditic facies. In this context, the re-oxygenation of bottom waters was favoured, as indicated by the presence of Thalassinoides and the low values of TOC and redox-sensitive elements (Mo, Ni and U). The survival phase in the wake of the biotic crisis is characterized by greater diversity and abundance of foraminifera and echinoderms (holothuroids and ophiuroids). The lowest δ13C values are recorded during this phase, with a dominance of opportunist (Eoguttulina) and facultative opportunist (Paralingulina tenera) foraminifera. Finally, recovery after the biotic crisis is evidenced by high values for specialists and potentially deep infaunal foraminifera, indicating oxic conditions in the sediment.

Mid-Cretaceous paleoenvironmental changes in the western Tethys

Abstract. We present a continuous record of surface water temperature and fertility variations through the latest Barremian–Cenomanian interval (ca. 27 Myr) based on calcareous nannofossil abundances from the western Tethys. The nannofossil temperature index, calibrated with TEX86 sea surface temperatures, suggests that warmest (34–36 ∘C) conditions were reached during oceanic anoxic event (OAE) 1a onset, the Aptian–Albian boundary interval hyperthermals (113, Kilian level and Urbino level OAE 1b) and during a ca. 4 Myr long phase in the middle Albian. Coolest temperatures (29 ∘C) correspond instead to the late Aptian. Generally warm conditions characterized the Albian followed by a progressive cooling trend that started in the latest Albian (at the Marne a Fucoidi–Scaglia Bianca Formation transition). Temperate conditions occurred in the Cenomanian with frequent short-term variations highlighted by abundance peaks of the cold-water nannofossil species E. floralis and R. parvidentatum. Mid-Cretaceous surface water fertility was rather fluctuating and mostly independent from climatic conditions as well as from black shales intervals. Intense warming and fertility spikes were systematically associated only with black shales of OAE 1a and of the Aptian–Albian boundary hyperthermals. The Albian–Cenomanian rhythmic black shales are, in fact, associated with varying long-term climatic and fertility conditions. The similarity of western Tethys climatic and fertility fluctuations during OAE 1a, OAE 1b, the middle Albian and OAE 1d with nannofossil-based records from other basins indicated that these paleoenvironmental conditions were affecting the oceans at supra-regional to global scale.

CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY AND PALEOCEANOGRAPHY OF THE TOARCIAN OCEANIC ANOXIC EVENT AT COLLE DI SOGNO (SOUTHERN ALPS, NORTHERN ITALY)

We present calcareous nannofossil biostratigraphy and abundances for the Upper Pliensbachian-Lower Toarcian interval, including the Toarcian Oceanic Anoxic Event (T-OAE), represented by the Fish Level at Colle di Sogno (N Italy). In addition to biohorizons identifying NJT 5 and NJT 6 nannofossil zones, the first occurrences of C. superbus and D. striatus constrain the onset and the end of the T-OAE, respectively. We propose the last occurrence of M. jansae as additional event to approximate the end of the T-OAE at lower latitudes. Quantitative data highlight the “ Schizosphaerella decline” marking the Pliensbachian/Toarcian boundary and the “ Schizosphaerella crisis” at the onset of the T-OAE as supplementary biohorizons. S. punctulata and M. jansae constitute most of the micrite in the interval below the Fish Level, which is marked by an increase in abundance of small coccoliths remaining abundant in the overlying interval, with limited contributions of S. punctulata, while M. jansae disappears. Principal Component Analysis implemented nannofossil paleoecological and paleoenvironmental reconstructions. The latest Pliensbachian was characterized by stable oligotrophic conditions favourable to calcification at low p CO 2 levels promoting the proliferation of deep-dwelling and highly-calcified S. punctulata . During the earliest Toarcian an initial pulse of continental run-off introduced terrigenous material favouring the intermediate-dweller M. jansae and the low-salinity adapted Calyculus . Higher nutrient concentrations and ocean acidification magnified during the T-OAE, stimulatying mesotrophic low-calcified coccolith-producers and suppressing k-strategist deep- to intermediate-dwellers. After the T-OAE, partial recovery of calcareous nannoplankton indicates still perturbed conditions. Ecosystem modifications anticipated the T-OAE of ~1 million years with species origination and major changes in assemblages.

Late Cretaceous Calcareous Nannofossil Biostratigraphy and Paleoecology in the Northwestern Desert, Egypt

The Upper Cretaceous succession of the northwestern desert in Egypt comprises two distinctive formations distributed throughout the studied subsurface succession. These formations are the Abu Roash and the Khoman from base to top, respectively. The examination of the studied samples resulted in the identification of thirty-six calcareous nannoplankton species belonging to twenty-three genera. Based on calcareous nannoplankton assemblages, the studied El-Noor-1 borehole succession was subdivided into seven calcareous nannoplankton biozones. These biozones were correlated with those recorded in Egypt and in other parts of the world. The analyses of calcareous nannofossils revealed the presence of hiatuses between the Late Santonian and Late Campanian. Abundance, diversity, preservation, fertility indices and temperature indices of the Late Cretaceous calcareous nannofossils were analyzed to determine the paleoecology of the studied succession. According to the calcareous nannoplankton content, the studied successions are subdivided into five ecozones. The environment of each ecozone is interpreted. The environmental indicators point to warmer climate oligotrophic environments for the Lucianorhabdus cayeuxii, Reinhardtites levis, Arkhangelskiella cymbiformisand Micula murus zones and cooler climate eutrophic environments for the Quadrum trifidum, Tranolithus orionatus and Lithraphidites quadratus zones.

Pattern and timing of the Early Jurassic calcareous nannofossil crisis

abstract Article history:Received 27 April 2014Received in revised form 12 June 2014Accepted 23 June 2014Available online 30 June 2014Keywords:Early ToarcianCalcareous nannofossilsBiocalcification crisisCarbonate production TheToarciancalcareousnannofossilcrisisassociatedwiththeearlyToarcianOceanicAnoxicEvent(T-OAE)intheEarlyJurassicperiodisthoughttorepresentoneofthemostimportantbiocalcificationcrisesduringtheMesozo-ic,occurringsimultaneouslywithaprofounddisturbanceofthecarboncycle.However,thecausesarestillunderdebate, particularly with regard to the pattern, timing of the biocalcification crisis, relative roles of intrinsic andextrinsic processes as drivers of the crisis, and also causal mechanisms of the T-OAE.In this study, a new quantification of Toarcian calcareous nannofossil abundance and size is presented for theSancerre borehole (Paris Basin, France). Beyond the recognition of a severe biocalcification crisis defined bythe major drop in abundance, and the reduction in size of the most important pelagic carbonate producerSchizosphaerella punctulata, for the first time, this study proposes an insight into the pace and timing of thenannoplanktoncrisis.AtSancerre,thecarbonateproductionofthelowerToarciansedimentspreviouslyattribut-ed to obliquity forcing of climate allows to estimate a duration of ~210 kyr for the biocalcification crisis andof ~120 kyr for the shift towards lower carbon isotope values. The onset of the biocalcification crisis marked bya fertility event lasted~60kyr,andthe calciumcarbonate valuesremainedlow for ~150 kyr;thesubsequent re-covery of carbonate and nannoplankton lasted ~60 kyr and N550 kyr, respectively. Additionally, a link betweenthe biocalcification crisis, the seawater palaeotemperature, and the carbon isotope steps can be demonstrated.This covariance provides compelling evidence of fundamental change in the response of the climatic warmingand the carbon cycle systems triggering the biocalcification crisis. These observations indicate that thebiocalcification crisis can be regarded as a direct or indirect consequence of a global warming. Moreover, a defi-ciency of the biological pump is proposed here as a complementary casual mechanism for explaining thenegative carbon-isotope excursion.© 2014 Elsevier B.V. All rights reserved.Contents1. Introduction 572. TheSancerreborehole:geologicalsettingandpalaeogeographyoftheParisBasin 573. Materialandmethods 583.1. Quantificationofnannofossilabundanceandvolume 583.2. Analyticalanalysis 584. Results 594.1. Calcareousnannofossilpreservation 594.2. Stratigraphicdistributionofthecalcareousnannoplankton 594.3. Clusterandprincipalcomponentanalyses 594.4. Evolution of Schizosphaerella size 605. Discussion 605.1. ThecalcareousnannoplanktonresponsetotheT-OAEenvironmentalchanges 605.1.1. Patternsinnannofossilassemblageswithinpre-eventstableenvironmentalconditions 605.1.2. TheT-OAEperturbationasrecordedbynannofossilassemblages 605.1.3. Theenvironmentalrecoveryasrecordedbynannofossilassemblages 605.2. Expressionandevolutionofthebiogeniccarbonateproduction 615.3. AtimescaleforthenannoplanktoncrisisacrosstheT-OAE 61

New insights in the pattern and timing of the Early Jurassic calcareous nannofossil crisis

Abstract The Toarcian calcareous nannofossils crisis associated with the early Toarcian Oceanic Anoxic Event (T-OAE) in the Early Jurassic period is thought to represent one of the most important biocalcification crises during the Mesozoic, occurring simultaneously with profound disturbance of the carbon cycle. However, the causes are still under debate, particularly with regard to the pattern, timing of the biocalcification crisis, relative roles of intrinsic and extrinsic processes as drivers of the crisis, and also causal mechanisms of the T-OAE. In this study, a new quantification of Toarcian calcareous nannofossil abundance and size is presented for the Sancerre borehole (Paris Basin, France). Beyond the recognition of a severe biocalcification crisis defined by the major drop in abundance, and the reduction in size of the most important pelagic carbonate producer Schizosphaerella punctulata , for the first time, this study proposes an insight into the pace and timing of the nannoplankton crisis. At Sancerre, the carbonate production of the lower Toarcian sediments previously attributed to obliquity forcing of climate allows estimating a duration of ~ 210 kyr for the biocalcification crisis and of ~ 120 kyr for the shift towards lower carbon isotope values. The onset of the biocalcification crisis marked by a fertility event lasted ~ 60 kyr, and the calcium carbonate values remained low for ~ 150 kyr; the subsequent recovery of carbonate and nannoplankton lasted ~ 60 kyr and > 550 kyr, respectively. Additionally, a link between the biocalcification crisis, the seawater palaeotemperature, and the carbon isotope steps can be demonstrated. This covariance provides compelling evidence of fundamental change in the response of the climatic warming and the carbon cycle systems triggering the biocalcification crisis. These observations indicate that the biocalcification crisis can be regarded as a direct or indirect consequence of a global warming. Moreover, a deficiency of the biological pump is proposed here, as a complementary causal mechanism for explaining the negative carbon-isotope excursion.

Evaluation of foraminifera and calcareous nannofossils changes across the Late Paleocene/Early Eocene transition at Nag El-Quda section, Upper Nile Valley, Egypt

A quantitative study of calcareous nannofossils, planktonic, and benthic foraminiferal assemblages have been performed on fifty six samples collected from ∼40 m interval across the Paleocene/Eocene transition at Nag El-Quda section in Upper Nile Valley, Egypt. I study this interval to evaluate the faunal and floral changes across the P/E transition. Four biozones of calcareous nannofossils and seven planktonic biozones have been recorded. The benthic foraminifera extinction event (BFEE) and the characteristic datum of both calcareous nannofossils, planktonic foraminifera, have been recognized. The absence of deep-sea benthic foraminifera (Stensioeina beccariiformis), the low abundance of (Angulogavelinella avnimelechi and Gavelinella rubiginosus) and increasing dominance of shallow-marine taxa (buliminids, Loxostomoides applinae) indicate deposition of the interval in shallow water environments (100–150 m depth). The benthic foraminiferal assemblages are dominated by Loxostomoides applinae, buliminids, and Lenticulina spp and indicate dysoxic conditions. Quantitative analyses have revealed a change in the species richness and fluctuations in abundance of foraminifera and calcareous nannofossils.

Calcareous nannofossil response to the Weissert episode (Early Cretaceous): Implications for palaeoecological and palaeoceanographic reconstructions

Abstract The causal link between changes in calcareous nannofossil abundances, their size and the palaeoenvironmental conditions in the Tethyan Realm across the Valanginian Weissert episode was examined through high-resolution quantitative analyses of the genera Nannoconus and Micrantholithus from the Angles section (Vocontian Basin, SE France). A set of published mineralogical, micropalaeontological and geochemical data from numerous European localities (including nannofossil data from Italy, France and Romania) and from the Atlantic and Pacific Oceans, allows us to propose a coherent palaeoecological and palaeoceanographic model, and to discuss the possible forcing factors behind the palaeoenvironmental changes that occurred during the Valanginian. In the Vocontian Basin, the genus Nannoconus appears to be particularly sensitive to global fertility conditions and local continental input while Micrantholithus is clearly associated with salinity levels. During the first phase of the Weissert episode, a global increase in nutrients, together with a breakdown of the upper water column stratification explains the nannoconid decline. Elevated freshwater fluxes into the Vocontian Basin under warmer and more humid conditions account for pentalith decreases. Low-resolution data on pCO 2 and ocean Ca 2 + concentrations cannot highlight large-magnitude rapid fluctuations in pCO 2 and oceanic Ca 2 + if they exist. However, relatively low pCO 2 levels and high oceanic Ca 2 + concentrations probably helped the recovery of Nannoconus and Micrantholithus from the aftermath of the Weissert episode to the early Hauterivian. The long-term changes observed in the Valanginian nannolith distribution are consistent with increased hydrothermal activity that influenced fertility levels. Low- to mid-latitudinal monsoonal circulation probably contributed to their short-term changes by the way of rapid changes in the chemical weathering pattern that triggered significant fluctuations in turbidity, fertility, and salinity conditions.

RETRACTED: Pattern and timing of the Early Jurassic calcareous nannofossil crisis

abstract Article history:Received 27 April 2014Received in revised form 12 June 2014Accepted 23 June 2014Available online 30 June 2014Keywords:Early ToarcianCalcareous nannofossilsBiocalcification crisisCarbonate production TheToarciancalcareousnannofossilcrisisassociatedwiththeearlyToarcianOceanicAnoxicEvent(T-OAE)intheEarlyJurassicperiodisthoughttorepresentoneofthemostimportantbiocalcificationcrisesduringtheMesozo-ic,occurringsimultaneouslywithaprofounddisturbanceofthecarboncycle.However,thecausesarestillunderdebate, particularly with regard to the pattern, timing of the biocalcification crisis, relative roles of intrinsic andextrinsic processes as drivers of the crisis, and also causal mechanisms of the T-OAE.In this study, a new quantification of Toarcian calcareous nannofossil abundance and size is presented for theSancerre borehole (Paris Basin, France). Beyond the recognition of a severe biocalcification crisis defined bythe major drop in abundance, and the reduction in size of the most important pelagic carbonate producerSchizosphaerella punctulata, for the first time, this study proposes an insight into the pace and timing of thenannoplanktoncrisis.AtSancerre,thecarbonateproductionofthelowerToarciansedimentspreviouslyattribut-ed to obliquity forcing of climate allows to estimate a duration of ~210 kyr for the biocalcification crisis andof ~120 kyr for the shift towards lower carbon isotope values. The onset of the biocalcification crisis marked bya fertility event lasted~60kyr,andthe calciumcarbonate valuesremainedlow for ~150 kyr;thesubsequent re-covery of carbonate and nannoplankton lasted ~60 kyr and N550 kyr, respectively. Additionally, a link betweenthe biocalcification crisis, the seawater palaeotemperature, and the carbon isotope steps can be demonstrated.This covariance provides compelling evidence of fundamental change in the response of the climatic warmingand the carbon cycle systems triggering the biocalcification crisis. These observations indicate that thebiocalcification crisis can be regarded as a direct or indirect consequence of a global warming. Moreover, a defi-ciency of the biological pump is proposed here as a complementary casual mechanism for explaining thenegative carbon-isotope excursion.© 2014 Elsevier B.V. All rights reserved.Contents1. Introduction 572. TheSancerreborehole:geologicalsettingandpalaeogeographyoftheParisBasin 573. Materialandmethods 583.1. Quantificationofnannofossilabundanceandvolume 583.2. Analyticalanalysis 584. Results 594.1. Calcareousnannofossilpreservation 594.2. Stratigraphicdistributionofthecalcareousnannoplankton 594.3. Clusterandprincipalcomponentanalyses 594.4. Evolution of Schizosphaerella size 605. Discussion 605.1. ThecalcareousnannoplanktonresponsetotheT-OAEenvironmentalchanges 605.1.1. Patternsinnannofossilassemblageswithinpre-eventstableenvironmentalconditions 605.1.2. TheT-OAEperturbationasrecordedbynannofossilassemblages 605.1.3. Theenvironmentalrecoveryasrecordedbynannofossilassemblages 605.2. Expressionandevolutionofthebiogeniccarbonateproduction 615.3. AtimescaleforthenannoplanktoncrisisacrosstheT-OAE 61