Calcareous Nannofossil Assemblages Research Articles

Calcareous nannofossil records and the migration of the Agulhas Return Current during the last 40 kyr

The Agulhas Return Current (ARC) transports warm tropical and subtropical waters eastward into the southern Indian Ocean. It plays a crucial role in the oceanographic connections between the Indian, Atlantic, and Southern oceans. Modern oceanographic observations show that the latitudinal position of the ARC varies interannually. However, its historical positional variations remain poorly understood. Calcareous nannofossils can be a good indicator of ancient current migration, although their record in the Southwest Indian Ocean is poorly studied. This research aims to understand the characteristics and downcore variation of the calcareous nannofossil assemblages and trace the record of the ancient ARC. To achieve these goals, this study analyzed pelagic sediments of multicore 34IV-SWIR-S021MC03, 34IV-SWIR-S032MC04, and 34IV-SWIR-S040MC05 from the Southwest Indian Ocean. A total of 13 nannofossil species have been identified. The assemblages belong to the subtropical convergence zone regime. They are characterized by warm and cold water species, dominated by Emiliania huxleyi, Calcidiscus leptoporus, Gephyrocapsa muellerae, and Florisphaera profunda. According to the AMS14C age model and phytoplankton ecological signatures, this study establishes a calcareous nannofossil indicator to trace the migration of the ancient ARC during the last 40 kyr. The result shows three periods of migration: 40–22 kyr, the ancient ARC was in the far north and was moving southward; 22–14 kyr, a transitional period, the ancient ARC was moving northward; 14–3 kyr, the ARC was moving southward. This further suggests that the migration of the ancient ARC is more complex than the two recognized phases, and there were essential turning points around the last glacial maximum period. It also acknowledges that the ancient ARC is sensitive to interglacial periods and can be influenced simultaneously by the Southern Hemisphere monsoon and westerly winds.

Paleoceanographic Significance of Calcareous Nannofossil Assemblages in the Tropic Shale of Utah during Oceanic Anoxic Event 2 at the Cenomanian/Turonian Boundary

Oceanic Anoxic Event 2 (OAE2) at the Cenomanian/Turonian Boundary (CTB: 93.9Ma) involved the global deposition of organic carbon-rich sediments, a distinctive positive shift in carbon isotope values, and significant species turnover, including changes in calcareous nannofossil assemblages. While it is thought that volcanism triggered organic C-rich sediment deposition during OAE2, it is unclear whether enhanced productivity, increased stratification, of some combination of the two increased organic matter preservation. Calcareous nannofossil assemblages have the potential to qualitatively assess changes in ocean nutrient and temperature conditions to disentangle such ecological dynamics during OAE2. Here we study an expanded section of the Tropic Shale in a drill core in southern Utah near the western margin of the Western Interior Seaway (WIS) to understand how circulation changed during the event and how this may have influenced primary productivity and organic carbon burial. Relative abundance data of well-preserved nannoplankton are complemented with measurements of trace metal, and organic carbon and carbonate concentrations to determine changes in temperature and water column structure, as well as controls on surface water productivity. Detailed statistical analysis helps refine species paleoecologies combined with information from planktic and benthic foraminiferal assemblages and organic biomarkers. Changes in calcareous nannofossil assemblages indicate that near the start of OAE2 the western WIS surface ocean actually cooled for a short time. Following this, surface waters became warmer and more stratified as a Tethyan water mass invaded the seaway. Assemblages suggest that warmth persisted for much of the OAE2 interval, while stratification waxed and waned. The local seaway cooled near the end of OAE2 as Boreal water masses streamed along the western margin. Variations, including the decrease in the abundance of Biscutum constans and short-lived peaks in the abundance of Eprolithus spp. are super regional or possibly global in extent. There is no correlation between calcareous nannofossil assemblages and trace metal concentrations, suggesting they were unaffected by volcanism-related nutrient inputs. Assemblages support other data that suggest increased stratification influenced organic carbon burial in the Western Interior Seaway, and possibly elsewhere, during OAE2.

The latest Jurassic–earliest Cretaceous climate and oceanographic changes in the Western Tethys: The Transdanubian Range (Hungary) perspective

AbstractThe Jurassic/Cretaceous transition was characterized by several distinct palaeoenvironmental processes and events, amongst which some of the best known are the late Tithonian–early Berriasian aridization and the late Berriasian tectonic reactivation in the Neotethyan Collision Belt. This study aims to reconstruct the latest Jurassic–earliest Cretaceous palaeoenvironment and its evolution in the area of the Transdanubian Range (Hárskút and Lókút successions, Hungary), and provide new data on the relation between climate changes, palaeoceanography and marine ecosystems. Herein, calcareous nannofossil and geochemical data are presented and put into a geochronological framework in order to evaluate and compare palaeoenvironmental signals recorded in the two studied successions; the resultant scenario is compared with published literature data from both the western Tethyan region and northern Europe. Accordingly, in the Transdanubian Range, the relatively humid climate of the early Tithonian was followed by the late Tithonian–early Berriasian arid phase and the late Berriasian humidification. Besides, two intervals of palaeoceanographic perturbations were documented in the upper Tithonian–lowermost Berriasian (OD I), and the lower/upper Berriasian transition beds (OD II); these are manifested by the record of seafloor hypoxia and elevated accumulations of micronutrients, as well as changes in calcareous nannofossil assemblages. In the view of this study, the most probable trigger of the late Tithonian–early Berriasian aridization was a restriction in the atmospheric circulation (including monsoons), which was forced by climate cooling and lowering thermal gradient between landmasses and the ocean. Under such conditions, the mechanism of a wind‐induced water mixing might become less efficient, driving seawater stratification, seafloor hypoxia and increased burial of nutrients. Although the humid climate of the late Berriasian likely resumed the monsoon‐type circulation, the tectonic reactivation and uplift in the NeoTethyan Collision Belt might have effectively separated the Bakony Basin from the ‘open’ NeoTethys, which hampered the marine circulation and efficient water mixing in the former.

Nannofossils from the Middle Eocene Sabiñánigo Sandstone Formation in the Jaca Basin (southern Pyrenees): biostratigraphy and paleoenvironmental implications

Abstract. This study presents the first detailed data on calcareous nannofossil assemblages from the Sabiñánigo Sandstone Formation in the Jaca Basin (central south Pyrenees). This formation is mainly composed of deltaic and outer-shelf sediments. These siliciclastic deposits contain nannofossil assemblages that are moderately to well-preserved, particularly in fine-grained levels. They contain a calcareous nannofossil assemblage dominated by the species Cyclicargolithus floridanus, Coccolithus pelagicus, Coccolithus formosus, Clausicoccus fenestratus, Zygrhablithus bijugatus, and several species of Sphenolithus and Chiasmolithus. The biostratigraphic results enabled the characterization of the Middle Eocene biohorizons, based on global stratigraphic scales and the improvement of the temporal correlation and lateral evolution of this basin's deposits. The sedimentary sequence of the Sabiñánigo Sandstone was deposited during the Middle Eocene, between the upper part of biozone NP16 and the base of NP17, in the Bartonian. The calcareous nannoplankton assemblage suggests warm and oligotrophic surface waters for the Bartonian interval in the Jaca Basin.

Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene‐Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean

AbstractThe Eocene‐Oligocene transition (EOT; ∼34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continental‐scale ice‐sheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of long‐term surface ocean cooling and trophic conditions, suggesting cause‐effect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a ∼5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warm‐oligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warm‐oligotrophic phase, precursor diversity‐decrease phase, early Oligocene cold‐eutrophic phase, and a steady‐state cosmopolitan phase. The most prominent shift in the assemblages occurred during the ∼550 kyr‐long precursor diversity‐decrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum–EOGM).

Calcareous nannoplankton response to middle-late Eocene climate and sea-level changes in the SW Neo-Tethys

We investigate the response of calcareous nannoplankton to the middle-late Eocene transition in the SW Neo-Tethys and compare our data to published results from X-ray diffraction (XRD) analysis, element content from X-ray fluorescence (XRF) and the abundance of microfossils in the coarse fractions of the sediment. The nannofossil assemblage is mainly composed of Reticulofenestra spp. (avg. 44%), Sphenolithus spp. (avg. 20%), Discoaster spp. (avg. 18%) and Pontosphaera spp. (avg. 10%). The Relative abundance of Zygrhablithus bijugatus and the Chiasmolithus ratio are used with the visual assessment to evaluate the preservation. The Sphenolithus-Reticulofenestra turnover occurred before the MECO at the Lutetian-Bartonian boundary. Besides the significant influence of an evolutionary gradient caused by the disappearance of numerous species of Sphenoliths, Discoasterids, and Coccolithaceae, and the first appearance of multiple species of reticulofenestrids, paleoenvironmental conditions imposed a significant impact on the calcareous nannofossil assemblages. The abundance of ostracods and the planktic/benthic foraminifera ratio depict relative sea-level changes. The microfossil assemblages and the lithological composition of the sediments track paleoclimatic and paleoenvironmental changes across the Lutetian to Priabonian. Dry conditions marked the middle Lutetian, followed by increased variability in hydrolyzing conditions during the late Lutetian and early Bartonian. An eutrophic and restricted ecosystem with high fine-grained material input is suggested for the Priabonian.

Microfossils and biostratigraphy of the Upper Cretaceous Coon Creek Formation Lagerstätte, Mississippi Embayment, USA

Abstract The Upper Cretaceous Coon Creek Formation type-locality in McNairy County, Tennessee, is an exceptional marine invertebrate Lagerstätte that was deposited in a nearshore reentrant into the ancestral continent of Appalachia. Extensive taxonomic analysis of the macrofauna has been done for over 100 years. However, documentation of the microfossil component at the type-locality has largely been ignored. This paper provides analysis of calcareous microfossils (benthic and planktonic foraminifera, calcareous nannofossils and ostracods) and palynomorphs (pollen, spores, algal remains and dinoflagellates) for detailed age control and information regarding environment of deposition. The Coon Creek type-locality is late Campanian (76.8–76.0 Ma) in age and was deposited in 35–60 m water depths. Calcareous nannofossil assemblages suggest that there was an influence of colder water through time, possibly by a connection to the northern Western Interior Seaway. The complex interplay between currents of the Gulf of Mexico and the Western Interior Seaway, upwelling and runoff influenced the palaeoenvironment. Increased influx of freshwater palynomorphs near the top of the section suggests placement proximal to the palaeoshoreline and that weathering increased through time. Changes in the dinoflagellate assemblage may be linked to a mosasaur mass mortality event and the presence of a harmful algal bloom.

Surface water mass dynamics at IODP Site U1313 through Principal Component Analysis: Evidence from coccolith assemblages in the ∼25–7 kyr interval

Coccolith assemblages from Integrated Ocean Drilling Program Site U1313 (North Atlantic; 41°0′N, 32°57.4′W) are analysed to assess temporal changes in surface water conditions from the Last Glacial Maximum (LGM) to the Middle Holocene (∼25–7 kyr). We perform Principal Component Analysis (PCA), involving both calcareous nannofossil assemblage data and other paleoenvironmental proxies. We reconstruct sea-surface dynamics using calcareous nannofossil assemblage variations and comparison with other previously published proxy data from Site U1313 including C37:4 alkenone, dolomite/calcite and quartz/calcite ratios, Uk’37 SST, as well as the sedimentation rate.We use variations in paleoproductivity proxies, cold and warm water group abundance, and the PCA results to infer North Atlantic Current (NAC) and North Atlantic Transitional Waters (NATW) migration through the studied interval. These proxies are also used to highlight variations in the Subtropical Gyre dynamics. Warming episodes are recorded during the LGM and Heinrich Stadial (HS) 1 as a result of northward expansion of the Subtropical Gyre. High coccolithophore productivity episodes characterize HS 1 and 2, and are concomitant with increasing terrigenous input. Both processes are considered a consequence of iceberg influence, which transport nutrients and ice-rafted debris to the area. A southward shift of the Subpolar Front and NAC favour the expansion of cold water from 25.3 ka to the end of the Younger Dryas, whereas the early Holocene is characterized by NATW influence resulting from northward migration of the NAC and Azores Current.

Outcrop to petrography scale and new age constraint of the Jatisamit Mélange in the Luk Ulo area, Central Java, Indonesia

To resolve the formation of the Luk Ulo Mélange in the Karangsambung area of Central Java, the matrix-dominated Jatisamit Mélange, which is a member of the Luk Ulo Mélange, was examined. Outcrop and petrographic observations of sandstone boudins and their shale matrix from the Jatisamit Mélange were used to assess deformational mechanisms and formation. We suggest the Jatisamit Mélange underwent three deformation phases: (1) formation of a web structure in the sandstone boudins through a cataclasis mechanism; (2) formation of boudins and cleavage through a ductile deformation; and (3) formation of open fractures and Riedel shears through pressure increasing. These deformations occurred at relatively low to medium temperatures during progressively increasing differential stress. Using illite crystallinity, the matrix of the Jatisamit Mélange has a maximum metamorphic temperature of 150–200 °C (diagenesis zone) at a 4–5 km depth. In addition, calcareous nannofossil assemblages of the Jatisamit Mélange and other related rock units in Karangsambung suggest a depositional matrix age of middle Eocene–early Oligocene. Therefore, the mixing of the Luk Ulo Mélange occurred not earlier than the middle Eocene–early Oligocene at a shallow structural level in the suture zone during the collision of the southeastern margin of Sundaland with the Gondwana micro-continent.

Impact of Thermal Maturation of the Upper Cretaceous Bituminous Limestone of Attarat Um Ghudran Central Jordan on Calcareous Nannofossil Preservation.

Oil shale deposits of the Late Cretaceous from three boreholes in central Jordan were examined to assess the impact of thermal maturation on the content of nannofossils. Thermal activity has been shown to have a strong effect on organic matter content and composition but its effect on calcareous nannofossil assemblages remains inconclusive. This study aims to determine the impact of thermal maturation on nannofossil assemblages and to compare this to an estimated maturity level based on bulk geochemical analysis. Micropaleontological and geochemical analyses were conducted on 31 samples from three oil shale wells drilled in Attarat Um Ghudran central Jordan. Several types of nannofossil preservation have been recorded, including dissolution, overgrowth, and breakage. In the Jordan oil shale sections, nannofossils exhibit a variety of preservation types, with intense dissolution in the middle part of the study sections. The vast majority of the samples had high TOC enrichment, with 29 samples exceeding values of >10%. Kerogen recovery and quality from the oil shale are very good, with a predominance of fluorescent amorphous organic matter (AOM) and minor algal components. The low fluorescence preservation index (FPI), which is 1 in most of the samples, indicates that alteration occurred due to intense thermal activities in the study interval. The palynomorph and AOM fluorescence, ranging from a spore coloration index (SCI) of 3 to 5, suggest that the studied samples were approaching the oil window. A correlation between the nannofossil preservation and geochemical parameters shows a predominance of poorly preserved nannofossils along with high total organic carbon contents and an elevated hydrogen index (HI). We show that low FPI values and a higher level of maturity are associated with poor nannofossil preservation, suggesting that nannofossils, in conjunction with petrographic analysis of kerogen, could be used as a rapid screening technique for estimating levels of oil-shale maturity. The nature of the tectonism in the study area, including faulting and a metamorphosed zone, enhanced the maturity, which might explain why the nannofossils were so significantly affected.

Benthic foraminifera across the Albian–Cenomanian transition and their paleoceanographic significance during OAE1d in the western Tethys (Umbria–Marche Basin, Italy)

The benthic foraminiferal assemblages from the upper Albian-lower Cenomanian interval of the Scaglia Bianca Formation in the Monte Petrano (MP) and Le Brecce (LB) sections (Umbria–Marche Basin; Italy) provide a detailed record of the faunal changes across the Oceanic Anoxic Event 1d (OAE 1d). Fluctuations in abundance, diversity, and species composition reflect variations in bottom-water oxygenation and organic carbon fluxes. Benthic foraminifera are integrated with planktonic foraminifera, calcareous nannofossils, and geochemical proxies to reconstruct the bottom and surface water conditions across the OAE 1d in the Umbria–Marche Basin.The pre-OAE 1d interval was characterized by benthic foraminifera that thrived under stable mesotrophic condition in bottom waters. In surface waters, planktonic foraminifera indicate dominant mesotrophic conditions in agreement with calcareous nannofossil assemblages suggesting a regime of higher fertility under cooler conditions.During the OAE 1d interval, benthic foraminifera display an increase in the abundance of infaunal taxa, suggesting mesotrophic conditions in bottom waters. Nevertheless, within the Pialli Level, the six laminated black-to-dark grey shale horizons (MP1/LB1 to MP6/LB6), benthic foraminifera are absent or highly impoverished (MP1, MP2, MP4, MP6, LB5, LB6), suggesting hypoxic/anoxic conditions in bottom waters. Planktonic foraminifera in this interval reflect mesotrophic to oligotrophic conditions under the presence of an expanded mixed layer and deeper thermocline in the surface waters. Calcareous nannofossils record warm conditions and lower fertility starting just prior to and across the OAE 1d. However, higher values of fertility are recorded in the black-to-dark grey shales MP3/LB3, MP4/LB4 and MP5/LB5 of the Pialli Level.The post-OAE 1d interval is marked by an increase in the diversity of benthic foraminifera, indicating a restoration of the oxygen conditions in a continuous mesotrophic regime in bottom waters. The surface waters experienced oligotrophic conditions based on the planktonic and calcareous nannofossils.A minor discrepancy between benthic foraminifera and geochemical reconstruction of oxygenation levels of bottom waters was recorded, especially in the Pialli Level. The benthic microfaunas appear to be very sensitive to very short-term oxygen depletion at the seafloor when geochemical proxies suggest temporary suboxia. This might indicate that very rapid redox changes are not resolved by bulk elemental data. Otherwise, benthic foraminifera might be much more responsive to very low concentrations of oxygen in bottom waters and temporarily disappear under strong suboxia before reaching fully anoxic conditions.

First record of Oceanic Anoxic Event 2 in the Eastern Carpathians: implications for chemostratigraphic and biostratigraphic correlations

This study aims to investigate a marlstone and claystone succession located at the southern end of the Eastern Carpathians, a region where oceanic anoxic event 2 (OAE2) has not been pointed out so far. Toward the upper half of this succession, a 17-cm-thick black shale was identified. The investigated depositional interval lies within the late Cenomanian–early Turonian, encompassing the UC3d up to UC7 nannofossil zones. The δ13C values fluctuated between 2.06‰ and 3.89‰, showing a positive isotope excursion that was assigned to OAE2. The δ13C isotope curve displays the following intervals: pre-excursion, first build-up, trough, second build-up, plateau, and post-excursion. Within the second build-up interval of OAE2, a substantial shift in CaCO3 values, accompanied by high concentrations of total organic carbon and a significant decline in the abundance and diversity of calcareous nannofossil assemblages, was observed. The nannofossil turnover related to OAE2 climax revealed predominance of Watznaueria barnesiae and temporary disappearance from the record of surface-water higher fertility taxa, such as Biscutum constans, Zeugrhabdotus erectus, and Discorhabdus ignotus. Above OAE2, peaks of Eprolithus floralis, followed by increased abundance of Eiffellithus turriseiffelii and Nannoconus spp., were identified. In the lower part of the studied succession (i.e., the upper Cenomanian UC3d nannofossil subzone), during the pre-excursion characterized by low δ13C values and less negative δ18O values, a small group of nannofossils more related to mid- and high-paleolatitudes, such as Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum, is present, always showing a low abundance.

Integrated biostratigraphy (orbitolinids, calcareous nannofossils, and palynomorphs) of the Lower Cretaceous Sarcheshmeh Formation, western Koppeh-Dagh Basin, NE Iran

An integrated biostratigraphy using orbitolinids, calcareous nannofossils, and dinoflagellate cysts was conducted on the Lower Cretaceous Sarcheshmeh Formation in two stratigraphic sections from the western Koppeh-Dagh Basin (NE Iran). The analyzed successions consist mainly of deep-marine shales and marlstones with intercalations of thin-bedded orbitolinid-bearing limestones. These strata yielded common to abundant and fairly well to well-preserved calcareous nannofossil assemblages. The aforementioned assemblages led to the identification of parts of the NC6 and NC7a biozones that can be correlated with parts of the CC7a and CC7b zones. The organic-walled dinoflagellate cysts also show well-preserved and relatively diverse assemblages in the studied sections that corresponded to the Odontochitina operculata Zone. Additionally, within the limestone intercalations of the Sarcheshmeh Formation, two index species of orbitolinids, Praeorbitolina cormyi Schroeder, and P. wienandsi Schroeder, were recorded, indicating the presence of the Praeorbitolina cormyi Zone. According to the literature, these recognized biozones are compatible with the ammonite zones of Deshayesites forbesi, Deshayesites deshayesi, and Dufrenoyia furcata, as well as the Globigerinelloides blowi and Leupoldina cabri planktonic foraminiferal zones. By the compilation of all acquired data, an age of late early Aptian (late Bedoulian) is deduced for the Sarcheshmeh Formation in the studied sections.

Maceral and calcareous nannofossil assemblages as proxies of late Rupelian (Oligocene) environmental changes in the Paratethys: An example from a section of the Menilite Formation in the northern Outer Carpathians

The Menilite Formation (Oligocene) of the Skole Nappe in the Polish Carpathians was deposited in the Paratethys. Deep-sea unbioturbated fine-grained carbonates of the Dynów Marl Member contain cold-water calcareous nannoplankton from Zone NP23 (Rupelian), including Reticulofenestra ornata and Pontosphaera fibula, which are typical of brackish waters in the Paratethys. It is likely that the water column was brackish in the upper part and fully marine and anoxic in the lower part. The Dynów Marl Member records the maximum isolation of the Paratethys from the oceanic circulation (the Upper Solenovian Event). The overlying green mudstones (probably the Krępak Member) are shallowly bioturbated. They contain fully marine, warm-water calcareous nannoplankton from Zone NP24. The environmental change (marine/brackish) is reflected in the quantity and type of organic matter. The abundance and preservation of organic matter are very high (TOC varies from 2.7 wt % to 26 wt %; HI values are >300 mg HC/g TOC) in brown, laminated shales, which were accumulated in saline anoxic conditions. The macerals in the shales are predominantly composed of the liptinite group, including lamalginite, telalginite, liptodetrinite, and bituminite. These macerals are primarily derived from planktonic and benthic algae as well as bacteria. The percentages of vitrinite and inertinite, originating from terrestrial sources, range up to 10% and 0.5%, respectively. The macerals are much less abundant in marls of the Dynów Marl Member because of dispersion in the carbonate groundmass during the calcareous nannoplankton blooms in brackish surface waters. The overall liptinite (mainly liptodetrinite and lamalginite) contribution is 77%–99.7%. Vitrinite and inertinite contents are in average 4.6% and 0.3%, respectively. Macerals are also infrequent in the overlying green mudstones, likely because of oxidation and consumption by organisms in warmer waters.

Biostratigraphical investigation of middle-early Miocene sediments from a section of AK-1 well, onshore Niger Delta: Insights from calcareous nanofossils

Biostratigraphic analysis was carried out on KA-1 well, onshore Niger Delta Basin of Nigeria. A total of forty (40) ditch cutting samples were collected from the studied section at 30 feet depth intervals with the studied section ranging from 7590-4800feet. The objectives of this study are to determine the age and biozonation of the studied section. Using simple smear slide method, the samples were processed and analyzed for nannofossils using a reflected binocular microscope. Calcareous nannofossil assemblages from the well are of low diversity and abundance. Some depths yielded almost monospecific assemblages while some have no records of calcareous nannofossils. Species include Helicospharea ampliaperta, Sphenolithus heteromorphus, Cyclicargolithus floridanus, Helicospharea scissura and Discoaster deflander. These belong to the NN4 zone of middle to early Miocene age. Keywords: Biozonation, Calcareous nannofossils, Helicospharea ampliaperta, Oligotrophic, Niger Delta.

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.

Changes in calcareous nannofossil assemblages linked to dramatic climate change over the Paleocene–Eocene Thermal Maximum in the Taramsa Section, Central Nile Valley, Egypt

Changes in calcareous nannofossil assemblages linked to dramatic climate change over the Paleocene–Eocene Thermal Maximum in the Taramsa Section, Central Nile Valley, Egypt

CALCAREOUS NANNOFOSSIL TAXONOMY AND BIOSTRATIGRAPHY OF THE TOARCIAN-LOWER BAJOCIAN COLLE DI SOGNO SECTION (LOMBARDY BASIN, SOUTHERN ALPS, ITALY)

Calcareous nannofossil biostratigraphy was conducted in the Toarcian-lower Bajocian interval at Colle di Sogno (Lombardy Basin, Southern Alps, Northern Italy) where the type-section of the Sogno Formation consisting of pelagic marly limestone, marlstone and marly claystone was established. Semiquantitative analyses of calcareous nannofossil assemblages allowed to achieve a high-resolution biostratigraphy based on several biohorizons, including zonal/subzonal markers and additional events. The NJT5 to NJT9 Zones of the standard nannofossil zonation established for the Mediterranean Province were identified. The biostratigraphy obtained at Colle di Sogno was compared to published nannofossil events calibrated with ammonite zones in sections from SE Spain, S France, Portugal and N Algeria. This assessment evidenced some discrepancies in the succession of events of the standard zonation and, furthermore, resulted in the revision of the age of a few datums. Moreover, some new/additional nannofossil biohorizons are proposed as subzonal markers. A morphometric analysis of the genus Watznaueria was conducted to identify diagnostic features for unambiguous species identification. The species W. colacicchii and W. contracta are distinguished on the basis of the coccolith width/central area width ratio, whereas W. britannica britannica is discriminated by the size - as in the original definition of the species - relative to the new subspecies W. britannica minor. The new species W. gaetanii differs from all other Watznaueria taxa by the bridge ultrastructure. In the Toarcian-Aalenian interval a progressive increase in size of Watznaueria specimens is paralleled by the progressive closure of the central area and the modification of the central area structure passing from a cross (W. colacicchii and W. contracta) to a double-button bridge (W. gaetanii) to a single-button bridge (W. britannica). These intrageneric evolutionary innovations accelerated in the Aalenian under stable paleoceanographic conditions and an oligotrophic regime.

Late Paleocene to Middle Eocene Calcareous Nannofossil Assemblages from Península Mitre, Southeastern Austral Basin, Argentina

On the Fueguian Atlantic coast and in the southern Andean fold and thrust belt, the Paleogene is partially represented by numerous turbiditic systems. Between Río Bueno and Cabo Leticia on Península Mitre, the Paleocene-Eocene is represented by the Río Claro Group (Cabo Leticia, La Barca, Punta Noguera and Cerro Ruperto formations) and the Río Bueno Formation; which together constitute a ~1050 m thickness succession. Here, calcareous nannofossil assemblages recovered from 96 samples were analyzed to determine their relative ages. The Cabo Leticia Formation was barren in nannofossils. The upper LB2 Member of La Barca Formation, contained Rhomboaster cuspis and Fasciculithus richardii, frequent in the Paleocene/Eocene boundary (Subzones NP9a/NP9b). Nannofossils recovered from Punta Noguera Formation indicate an early Eocene age (biozones NP9b-NP10), with Fascilulithus tympaniformis, Rhomboaster cuspis and abundant Toweius spp. The Cerro Ruperto Formation provided one productive sample, with specimens of Reticulofenestra spp. and Toweius spp., which indicates an early Eocene age for the formation (biozones NP12-NP13). The Río Bueno Formation yield calcareous nannofossil assemblages characterized by Chiasmolithus eograndis, Chiasmolithus expansus, Toweius spp. and Reticulofenestra spp. which indicates a late early Eocene to middle Eocene age (biozones NP14-NP16). Although the calcareous nannofossil record is discontinuous due to sedimentary facies of the Río Claro Group, our data allow a better age constraint for the investigated formations and to correlate these units with others outcropping and subsurface units in the Austral Basin.

Eocene nannofossils and paleoenvironmental reconstruction of the Kuldana Formation in Yadgar area, Muzaffarabad, northern Pakistan

The Early Eocene Kuldana Formation (KF) consists of variegated color shales, mudstone, and sandstone with limestone interbeds/lenses in the Yadgar area, Muzaffarabad, of Sub-Himalayan foreland basin. We report, for the first time, 20 nannofossil species of 9 genera, discovered from carbonate units of KF. Based on this calcareous nannofossil assemblage, an Early Eocene Ypresian age (NP10) is determined. The presence of Coccolithus, Fasciculithus, Rhomboaster, Tribrachiatus and Sphenolithus indicates dominantly warm water and oligotrophic conditions during deposition of the carbonate units, while the presence of Zeugrhabdotus and Neococcolithes suggests minor cool-water, eutrophic to mesotrophic conditions. Five microfacies were identified based on the field and petrographic investigations of the study section, namely, Nummulitic wacke-packstone microfacies (KMF-1), Assilina wacke-packstone microfacies (KMF-2), Molluscan microfacies (KMF-3), Lime mudstone microfacies (KMF-4), and Ostracode wackestone microfacies (KMF-5), suggesting that the deposition occurred in inner to middle shelf, shallow marine environment.