Last Occurrence Research Articles

The Eocene to Oligocene boundary and paleoclimatic indications based on calcareous nannofossils of Tonasa Formation, South Sulawesi, Indonesia

The biostratigraphy of the Tonasa Formation in the Jeneponto Regency of South Sulawesi, Indonesia, is still poorly known, and there are barren ages, such as much of the Oligocene to Early Miocene. The Tonasa Formation is well exposed along the coast of the Jeneponto Regency, in which the Karama area consists of the most important outcrops of this formation which in this area consists of interbedded marl and limestone. Our study focuses on the biostratigraphy of the Karama area section A based on nannofossil. Samples were collected by measured stratigraphy methods and then subjected to investigation using smear slides. The assemblages of species were determined by semiquantitative analysis. Data analysis obtained three nannofossil datums (boundaries): The First Occurrence (FO) of Sphenolithus pseudoradians NP19/NP20), the First Occurrence of Sphenolithus distentus (CP.16/CP.17), and the Last Occurrence (LO) Sphenolithus predistentus (NP.23/NP.24. The zonal boundary was determined based on calcareous nannoplankton; the Late Eocene to Middle Oligocene boundary of the Tonasa Formation was found in this section. Interestingly, throughout this period, the marker species in this section is Sphenolithus. In addition, the presence of Sphenolithus, Discoaster, and Zygrhablithus bijugatus indicated that the basin was in warm water condition.

Note on the earliest records of genus Macrocephalites Zittel: implications for biostratigraphic correlations

ABSTRACT The Bathonian‒Callovian (Middle Jurassic) genus Macrocephalites Zittel is distributed worldwide, and several of its species are used for inter- and intrabasinal biostratigraphic correlations. Here, the earliest occurrence of genus Macrocephalites, using an integrated approach incorporating data from ammonites, calcareous nannofossils and magnetostratigraphy from the Kachchh Basin of western India is presented. The calcareous nannofossils were extracted from the Macrocephalites triangularis Spath (m) sample, and the magnetostratigraphic data also comes from the same ammonite-bearing bed (Yellow Bed, bed A4), in the core of the Jumara Dome, Kachchh Basin. The sample yielded age-diagnostic calcareous nannofossil taxa with FOs (First Occurrence) of Pseudoconus enigma, Cyclagelosphaera margerelii, Octopodorhabdus decussatus and Watznaueria barnesiae, and the LO (Last Occurrence) of Carinolithus magharensis, thus, bracketing the age of the Yellow Bed between early to early middle Bathonian. An early middle Bathonian age was also proposed previously based on an ammonite assemblage and correlated with the Standard European early middle Bathonian Progracilis Zone. The magnetostratigraphic data yielded an early Bathonian age, but, it is of very low resolution, and possibly re-magnetised. The occurrence of M. aff. triangularis Spath from eastern Crimea from below the Bremeri Zone (middle Bathonian), corroborating the early middle Bathonian age arrived at for the earliest occurrence of M. triangularis in the Kachchh Basin, is also evaluated. The stratigraphic occurrence of a heavily encrusted M. triangularis specimen from Germany, and assigned to the lower Callovian, is also evaluated. The present data suggests that genus Macrocephalites Zittel was already well-established even in the early middle Bathonian, if not earlier, and that a relook/resampling is urgently needed with an integrated approach for southern Tethyan margin localities such as Madagascar and Sula Island.

Biostratigraphy and sedimentation rate estimation of Quaternary sediments of the Krishna-Godavari Basin, Bay of Bengal: Evidence from NGHP-01 Holes 10D, 5C and 3B

The deposition of a substantial amount of clastic sediments in the Krishna Godavari Basin formed a thick layer of nannofossil-rich clay known as the Godavari Clay Formation. This clayey sequence is a treasure trove for unveiling paleoclimatic and paleoceanographic information. Numerous radiometric dates from the topmost portion of this clay (top 27m) are available, covering the last 43 ka. However, the availability of data on age connotation with considerably high resolution for the deeper sediments is rare and is still awaited. In this study, we pursued nannoplankton and planktic foraminiferal investigations on the top 198 m (Hole 10D), 300 m (Hole 3B), and 198 m (Hole 5C) sediments of this basin to generate multiple age data with a relatively high resolution. First Occurrence (FO) and Last Occurrence (LO) of nannoplankton taxa Emiliania huxleyi, Helicosphaera inversa, Helicosphaera sellii, large Gephyrocapsa spp., Pseudoemiliania lacunosa, Reticulofenestra asanoi, and planktic foraminiferal taxa Globorotalia flexuosa and Globigerinella calida are considered as potential index taxa for establishing the bioevents as well as biostratigraphy.Based on these, we have identified nine events from Hole 10D, six events from Hole 3B, and seven events from Hole 5C, which are potential for assigning the relative ages.We also observed two-fold variations in sedimentation rates in all the holes and one hiatus at 110.73 mbsf in Hole 5C, indicating a shift in climate and basinal settings. A high sedimentation rate of greater than 20.59 cm/ka after approximately 0.4 Ma at all the holes is probably linked to the intensification of the Indian summer monsoon across the mid-Brunhes Epoch. The significantly low sedimentation rates (less than 14.62 cm/ka) in older sediment sequences before 0.4Ma is probably related to the relatively weak monsoonal activity. The generated age data, variations in sedimentation rates, and identified hiatus are considered to be potential for delineating paleoclimatic and paleoceanographic changes of this area since the Calabrian Stage.

Late Triassic–Jurassic bivalve biochronology, palaeogeography and palaeoenvironment of the Junggar Basin, NW China

Abstract The middle Mesozoic of the southern Junggar Basin is a source of abundant Late Triassic–Jurassic non-marine and Early Jurassic marine–littoral bivalves. The bivalve chronology provides a framework for dating the strata and documents Early Jurassic transgressions and the end-Triassic mass extinction in the Junggar Basin. The first occurrences (FOs) and last occurrences (LOs) of Utschamiella cf. tungussica and Utschamiella cf. obrutschevi lie in the basal upper Rhaetian. The FOs of Ferganoconcha sibirica , Ferganoconcha subcentralis , Unio manasensis , Unio mirabilis and Waagenoperna are at, and the FOs of Margaritifera isfarensis , Tutuella rotunda and Tutuella chachlovi adjoin, the base of the middle Sinemurian. The LOs of Yananoconcha hengshanensis and Waagenoperna are at the Lower–Middle Jurassic boundary. The LOs of Psilunio , Cuneopsis and F . subcentralis are near the Middle–Upper Jurassic boundary. Non-marine bivalves disappeared in the late Rhaetian, due to a sudden Norian–Rhaetian temperature drop. New forms did not return until the Sinemurian, when the climate warmed. The transgressions created low-relief terrestrial environments, in which organisms including bivalves thrived, leading to the formation of large quantities of coal, oil and gas. The Junggar Basin shifted from Arctic to subtropical latitudes in the Northern Hemisphere between the Early and Middle Jurassic.

Calcareous nannofossils from the Poggio le Guaine core (Umbria-Marche Basin, central Italy): Biostratigraphy and discussions on the bioevents of the Aptian–Albian interval

The calcareous nannofossil biostratigraphy of the Aptian–Albian interval has been continuously applied and developed along the last decades. The shortage of complete and continuous outcropping marine sections and even marine subsurface sections is one of the challenges of the stratigraphic studies of this interval. Taxonomic ambiguities, diachronism and reworking are constantly pointed as challenging aspects for the calcareous nannofossil biostratigraphic studies of this interval. Amid this scenario, the Poggio le Guaine section of the Umbria-Marche Basin (central Italy) stands out by presenting a complete and undisturbed pelagic to hemipelagic marine sedimentary succession of the Aptian–Albian interval. The present work is aimed to provide a detailed biostratigraphic zonation based on calcareous nannofossils, to calibrate the results to other stratigraphic tools of previous published works and to discuss some important bioevents of the Aptian–Albian interval along the PLG core. The following biozones of the calcareous nannofossil reference zonation for the Aptian–Albian interval were recognized: the Chiastozygus litterarius Zone (NC6 Zone), the Rhagodiscus angustus Zone (NC7 Zone), the Prediscosphaera columnata Zone (NC8∗ and NC8 zones), the Axopodorhabdus albianus Zone (NC9 Zone) and the Eiffellithus turriseiffelii Zone (NC10 Zone). The PLG core encompasses the chronostratigraphic interval from the Barremian/Aptian through the Albian/Cenomanian boundaries. Finally, detailed discussions on some important calcareous nannofossil bioevents of this interval were performed, among them: the first occurrence (FO) of Hayesites irregularis, the FO of Hayesites albiensis, the last occurrence (LO) of Conusphaera rothii, the LO of Micrantholithus hoschulzii/Micrantholithus obtusus, the FO of Rhagodiscus achlyostaurion, the FO of Prediscosphaera columnata, the FO of Tranolithus orionatus and the LOs of Assipetra spp.

Calcareous Nannofossil Biostratigraphy of Tonasa Formation at Barru River Traverse, South Sulawesi, Indonesia

DOI:10.17014/ijog.9.3.371-381Barru is one of the areas in South Sulawesi where the stratigraphic sequences of lithology from Mesozoic to recent are well exposed. The Tonasa Formation is quite widespread in this area, and it is interesting to find out its various aspects related to the carbonate rock development. For this reason, the distribution of nannofossils were recorded and the relative age of Tonasa Formation was determined using nannofossil collected by measuring section at Barru River. The calcareous nannofossil assemblages are moderate to poor preserved. A total of twenty-three species were identified from the bottom to the top of the interbedded marl and limestone. The nannofossil assemblage-based biostratigraphy of the studied area was shown by the First Occurrence (FO) and Last Occurrence (LO) of the marker species. As for the results, there were six data found in this study, i.e. FO and LO of Reticulofenestra umbilicus, FO of Sphenolithus pseudoradians, LO of Discoaster saipanensis, LO of Calcidiscus formosus, and LO Reticulofenestra bisectus. Based on the noted nannofossil data, the determined age of Tonasa Formation at Karama area included NP 15 – NN 1 or CP 13 - CN 1a, and equivalent to Middle Eocene until Early Miocene. The result shows important data that will contribute significantly in age constraint of Tonasa Formation

Plio-Pleistocene Planktic Foraminiferal Biochronology of ODP Site 762B, Exmouth Plateau, Southeast Indian Ocean

ABSTRACTThe Indonesian Throughflow region connects the tropical Pacific Ocean with the eastern Indian Ocean, and variability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magnetochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understanding of the coupled histories of the El Niño Southern Oscillation, Western Pacific Warm Pool, Indonesian Throughflow, and the eastern Indian Ocean has greatly benefitted from the chronological framework provided by planktic foraminiferal biostratigraphies from these regions. Ocean Drilling Program (ODP) Hole 762 lies under the influence of the Leeuwin Current, originating from the Indonesian Throughflow. Multiproxy data have been collected from Hole 762B and other nearby sites for paleoceanographic interpretation. However, a detailed planktic foraminiferal biostratigraphy integrated with magnetochronology is not available from this site. We provide here the sequential order of planktic foraminiferal First Occurrence (FO) and Last Occurrence (LO) events, which allowed us to divide the examined section into seven biostratigraphic zones. The biostratigraphy was integrated with magnetostratigraphy using revised ages of magnetochrons, which yielded biochronological age estimates for planktic foraminiferal events. A major planktonic faunal turnover between 3.4 and 2.7 Ma is probably related to the onset of the Northern Hemisphere glaciation and related changes in the Indonesian Throughflow. We have compared our numerical age estimates with published ages from other parts of the world. The diachronism observed probably is related to the local oceanographic setting of ODP Hole 762B, which has been alternatively influenced by changing strengths of the warm Leeuwin Current and the cold west Australian Current. The biochronology established here will be useful for correlating paleoceanographic events in the region.

Santonian‐Campanian dinoflagellate cyst biostratigraphy and paleoenvironment of the Krishna‐Godavari Basin, India

AbstractThe present study deals with the biostratigraphic framework of Late Cretaceous sediments of the subsurface Well (DNG) “A” (2085–1840 m depth) from the Raghavapuram/Chintalapalli Shale of the Krishna‐Godavari Basin and analyzed the palynological assemblage. The recorded palynological assemblage is dominated by marker dinoflagellate cyst viz. Areoligera coronata, Areoligera senonensis, Heterosphaeridium spinaconjunctum, Nelsoniella aceras, Nelsoniella semireticulata, Odontochitina porifera, Xenascus ceratioides, and Xenascus gochtii species. The last occurrence (LO) of significant species of dinoflagellate cysts is considered for the biostratigraphic establishment. On the basis of dinoflagellate cyst biostratigraphy, the examined sequences correspond to the Santonian‐Campanian age. The dominance of gonyaulacoid dinoflagellate cysts is interpreted in terms of sea‐level fluctuation and other paleoenvironmental signals through this biostratigraphic establishment. The recorded dinoflagellate cysts indicate the outer neritic, cool depositional environment. The sea‐level rise, recorded in our study is linked with the transgressive phase during the Late Cretaceous (Santonian‐Campanian) period.

Integrated biostratigraphy for the Santonian/Campanian boundary interval, the Kurdistan Region, northeast Iraq

The first high-resolution integrated biostratigraphic study for Santonian/Campanian sediments of the Tabin section in the Kurdistan Region, northeast Iraq is provided. The study, based on 28 closely spaced samples, combines data from planktic foraminifers (25 species), calcareous nannofossils (32 species) and two ammonite genera in the Kometan Formation, marking the Santonian/Campanian boundary (S/C boundary) in the Kurdistan Region. In the absence of the crinoid Marsupites testudinarius, the proposed boundary marker, secondary markers such as calcareous nannofossils, planktic foraminifers and ammonites, have been used to establish a multi-stratigraphic biozonation for the late Santonian–early Campanian duration. Based on the occurrences of calcareous nannofossils, three biozones are identified — Lucianorhabdus cayeuxii (late Santonian), Calculites obscurus (latest Santonian–earliest Campanian), and Broinsonia parca parca (early Campanian). Seven calcareous nannofossil bioevents and three planktic foraminiferal bioevents are also identified. The Santonian/Campanian boundary is marked by: (a) the LO (Last Occurrence) of the planktic foraminifera D. asymetrica, (b) the FOs (First Occurrence) of the calcareous nannofossil species B. parca parca and B. parca constricta, (c) the extinction of several planktic foraminiferal species of Dicarinella and Marginotruncana, (d) the abundance and diversification of the planktic foraminifera genera, Globotruncana and Globotruncanita at the beginning of the Campanian, and (e) the disappearance of the ammonite genus Texanites, 0.5 m below (i.e., at 19 m) the disappearance of all Dicarinella and Marginotruncana species in the study section. Similar to several other Tethyan sections, the FO of B. parca parca is above the LOs of D. concavata and D. asymetrica; the LO of D. asymetrica is used here to mark the S/C boundary

Late Eocene to early Oligocene calcareous nannofossil biostratigraphy of the Cerro Colorado Formation, Austral basin, Argentina

This paper documents calcareous nannofossil assemblages and the bioevents recorded in the Austral basin of Tierra del Fuego, Argentina. Fifty samples from the type section of the Cerro Colorado Formation were analyzed. Nannoflora is moderately preserved and indicates a late Eocene to early Oligocene age for sedimentary rocks of this formation. Biostratigraphic results are based on distribution patterns of calcareous nannofossils assemblages, permitting comparison with the Southern Ocean zonations and some correlations with standard schemes. Our biostratigraphic interpretation shows an almost complete stratigraphic section spanning from the Priabonian to Rupelian Stages and calcareous nannofossil Chiasmolithus oamaruensis to Blackites spinosus zones, or the low latitude zones of Martini NP18 to NP21. The oldest fossiliferous rocks from the type locality of the Cerro Colorado Formation contain Chiasmolithus oamaruensis indicating nannofossil Zone NP18. The Eocene/Oligocene boundary was placed between the last occurrence (LO) of Reticulofenestra oamaruensis and the increasing in abundance (IB) of Reticulofenestra daviesii. Samples taken from the top of the section belong to the Estancia María Cristina Beds have Cyclicargolithus abisectus. During the late middle to late Eocene a hiatus is suggested between the Cerro Colorado and Leticia formations evident by a 39 Ma detrital zircon age dating, and the first occurrence (FO) of Dictyococcitesbisectus. Furthermore, the presence of C. abisectus in the Estancia María Cristina Beds suggests an unconformity with the underlying Cerro Colorado Formation as previously inferred by stratigraphic relationships.

Triassic palynoevents in the circum-Arctic region

Triassic successions of the present-day Arctic contain abundant and diverse assemblages of nonmarine palynomorphs that have provided important biostratigraphic information. Dinoflagellate cyst are biostratigraphically useful in marine intervals in the Upper Triassic. Based on published records, we present a compilation of 78 last occurrences (LOs), first occurrences (FOs), and some abundance events that are anticipated to have correlation potential in the Arctic region. Palynological work has been carried out in many Arctic areas, with extensive palynological research published on the Triassic successions of the Norwegian Barents Sea and Svalbard. An updated, recent palynological zonation scheme exists for that region, integrating previous schemes and illustrating the chronostratigraphic value of palynology in the Triassic. For the Lower and Middle Triassic, good ammonoid control ties the palynological zones to the chronostratigraphic scale. Independent control is sparse, and resolution is lower in the Upper Triassic, so that palynology is commonly the only biostratigraphic discipline available for chronostratigraphic dating and correlation.

Dinoflagellate cyst biostratigraphy of Upper Cretaceous turbiditic deposits from a part of the Bąkowiec section in the Skole Nappe (Outer Carpathians, southern Poland)

Dinoflagellate cysts from turbiditic deposits of the Ropianka Formation in an interval of the Bąkowiec section (Skole Nappe, Outer Carpathians, southern Poland) have been analyzed. This interval, previously attributed to the Cretaceous–Paleogene boundary transition based on planktic and benthic foraminifera, contains organic-walled dinoflagellate cysts (dinocysts) of a latest Campanian age. The difference in age, revealed here between foraminifera and dinocyst findings, is considered as an unresolved dilemma, which is pending some explanations, probably on the basis of further multidisciplinary studies envisaged in the same outcrop. The palynological content is well preserved and rich in dinocyst cyst taxa, including 37 upper Campanian index species among 92 species in total. The dinocyst assemblages observed in this interval are similar to those previously recognized in biostratigraphically well-calibrated sections of Western Europe. The dinocyst marker events enabled a correlation of the studied interval with the Samlandia mayi dinocyst Zone of Slimani (2001a), which is an equivalent to the Belemnitella minor Zone in the northwestern Europe. These dinocyst events include the first occurrences (FOs) of Kleithriasphaeridium truncatum, Nematosphaeropsi philippotii, Samlandia carnarvonensis, Samlandia mayi and last occurrences (LOs) of Corradinisphaeridium horridum, Raetiadinium truncigerum, Odontochitina operculata and Xenascus ceratioides subsp. ceratioides. The palynological content shows significant reworking of Campanian dinocyst taxa and a richness in palynodebris of continental origin, which are likely related to deposition by turbiditic currents.

Permian palynoevents in the circum-Arctic region

Permian palynofloras are recorded around the present-day Arctic and are typically dominated by taeniate and non-taeniate pollen, with intervals of spore domination. The assemblages show close similarities around the Arctic. Based on the published record, we present a compilation of 23 last occurrences (LOs), first occurrences (FOs), and some abundance events. These are anticipated to have regional correlation potential. In general, the Permian palynofloras of the Arctic have not been extensively studied, and the resolution is low due to a general lack of independent age control.

Carboniferous palynoevents in the circum-Arctic region

The Carboniferous of the present-day Arctic yields an abundant and diverse association of terrestrial palynomorphs, particularly from Mississippian successions. Relatively few sections have been studied. However, those published so far demonstrate considerable similarities in the palynofloras between Arctic regions. Based on the published record, we present a compilation of 31 last occurrences (LOs), first occurrences (FOs), and some abundance events that have correlation potential around the Arctic. The chronostratigraphic resolution is relatively low, and the lack of independent age control hampers exact age assignments. But for most of these successions, palynology is the only dating tool available.

High‐resolution upper Pliocene to Pleistocene calcareous nannofossil biostratigraphy in Ocean Drilling Program Hole 1146A in the South China Sea

AbstractWe established a high‐resolution calcareous nannofossil biostratigraphy for the late Pliocene–Pleistocene by analyzing a 242 m‐thick, continuous sedimentary succession from Ocean Drilling Program Site 1146, Hole A, in the South China Sea (SCS). A total of 14 calcareous nannofossil datums were detected in the SCS succession. They are, in descending order: first occurrence (FO) of Emiliania huxleyi, last occurrence (LO) of Pseudoemiliania lacunosa, LO of Reticulofenestra asanoi, FO of Gephyrocapsa parallela, FO of R. asanoi, LO of large Gephyrocapsa spp., FO of large G. spp., FO of Gephyrocapsa oceanica, FO of Gephyrocapsa caribbeanica, LO of Calcidiscus macintyrei, LO of Discoaster brouweri, LO of Discoaster pentaradiatus, LO of Discoaster surculus, and LO of Discoaster tamalis. The FO of E. huxleyi was not precisely detected due to poor preservation and dissolution of nannofossils in the underlying strata. We refined the previous calcareous nannofossil biostratigraphy in the SCS by identifying Gephyrocapsa species and four evolutionary extinction events of the genus Discoaster. The proposed calcareous nannofossil biostratigraphy correlates with those reported in other terrestrial and marine areas/sites and global benthic foraminiferal δ18O records. The age–depth curves based on nannofossil biostratigraphy indicate a significant increase in the sedimentation rates at the LO of R. asanoi (0.91–0.85 Ma). The timing of this increase corresponds to reef expansion in the Ryukyu Islands linked to a stepwise increase in Kuroshio Current intensity. This timing is broadly coeval with a sea surface temperature increase of ∼2 °C in the northwestern Pacific due to expansion of the Western Pacific Warm Pool towards the north and south subtropical regions. This can be explained by increased weathering and erosion of terrestrial areas in glacial periods and increased rainfall causing higher sediment transport in interglacial periods, which were both linked to Middle Pleistocene Transition‐related climatic changes.

Pleistocene Calcareous Nannofossil Biostratigraphy and Gephyrocapsid Occurrence in Site U1431D, IODP 349, South China Sea

We reinvestigated the Pleistocene calcareous nannofossil biostratigraphy of Site U1431D (International Ocean Discovery Program (IODP) Expedition 349) in the South China Sea (SCS). Twelve calcareous nannofossil Pleistocene datums are identified in the site. The analysis confirms that the last occurrence (LO) of Calcidiscus macintyrei is below the first occurrence (FO) of large Gephyrocapsa spp. (>5.5 μm). The FO of medium Gephyrocapsa spp. (4–5.5 μm) is also identified in the samples through morphometric measurements, which was unreported in shipboard results. Magnetobiochronologic calibrations of the numerical ages of LO of Pseudoemiliania lacunosa and FO of Emiliania huxleyi are underestimated and need reassessment. Other potential markers such as a morphological turnover of circular to elliptical variants of Pseudoemiliania lacunosa and a small Gephyrocapsa acme almost synchronous with the FO of Emiliania huxleyi may offer biostratigraphic significance in the SCS. The morphologic changes in Gephyrocapsa coccoliths are also examined for the first time in Site U1431D. Placolith length and bridge angle changes are comparable with other ocean basins, suggesting that morphologic changes are most likely evolutionary novelties rather than being caused by local climate anomalies.

Evidence for three successive upper Barremian–lower Aptian rudist faunas in the Urgonian-type deposits of southeastern France and their stratigraphic value

The stratigraphic reappraisal of the Urgonian-type carbonate platform series of southeastern France, based on new ammonite discoveries, supports a precise dating of the Brouzet-les-Alès, Orgon and Rustrel upper Barremian–lower Aptian rudist faunas. The Brouzet-les-Alès fauna consists of an assemblage dominated by Homopleura and Agriopleura species spanning the Toxancyloceras vandenheckii Zone and the two lower subzones of the Gerhardtia sartousiana Zone (Gerhardtia sartousiana and Gerhardtia provincialis subzones). The Orgon fauna is characterised by an impoverished requieniid–monopleurid assemblage (missing Agriopleura) restricted to the upper part of the Gerhardtia sartousiana Zone (= Hemihoplites feraudianus Subzone). The Rustrel fauna records the outbreak of caprinid rudists, ascribed to the Martelites sarasini Subzone of the Martelites sarasini Zone, though some its key taxa locally extend into the lower Aptian. The definition of these rudist faunas is based on the combined First Occurrence (FO) or Last Occurrence (LO) of cardinal species and the co-occurrence of subordinate taxa. Two main faunal changes are recognized, viz. the regional disappearance of Agriopleura (collapse of the Bouzet-lès-Alès fauna) and the beginning of the family Caprinidae (Rustrel fauna). Both faunal changes have a widespread records along the western European Tethys margins and coincide with large-scale environmental perturbations.

The biostratigraphy of the offshore Niger delta during the Late Quaternary: Complexities and progress of dating techniques

The Late Quaternary marine sediments from the Niger Delta lacks an age model using conventional radiocarbon dating due to the rarity of calcareous macrofossils. The proprietary nature of material drilled by companies prospecting for hydrocarbons in the Niger Delta basin, and in the rare cases when samples are available for study as well as freshwater dilution from continental runoff have contributed to this dearth of knowledge. The availability of three shallow marine (∼3 m) gravity cores obtained from the eastern, central, and western parts of the Niger Delta provides the opportunity for biostratigraphy utilising well-preserved marker species of planktonic foraminifera and calcareous nannofossils in the sediments. The last occurrence (LO) of planktonic foraminiferal species Globorotalia truncatulinoides (late Pleistocene) (MIS 2) and the first occurrence (FO) of Globorotalia tumida (Holocene) (MIS 1) are used to identify two interval zones in the gravity cores. The presence of the calcareous nannofossil Gephyrocapsa oceanica (all <3 μm in size) supports a late Pleistocene age (NN19 Zone) for the lower interval. In addition, an increase in the abundance of Emiliania huxleyi up-section is an indication of early Holocene age (NN20-NN21) for the upper interval.

Radiolarian Biostratigraphy and Faunal Turnover across the Early/Middle Miocene Boundary in the Equatorial Pacific

Sedimentary sequences obtained from drilling during Integrated Ocean Drilling Program (IODP) Expedition 320/321, “Pacific Equatorial Age Transect (PEAT)” at eight sites (Sites U1331–1338) in the equatorial Pacific offer an ideal record for reconstructing the evolution of the ocean/climate system throughout the Cenozoic. The sediments drilled at Site U1335 record short-term events of paleoceanographic significance, including the early Miocene climatic optimum (MCO) and the middle Miocene climatic transition (MMCT). Abundant well preserved radiolarians were recovered from the lower Miocene radiolarian Zone RN2 through middle Miocene Zone RN5 at IODP Site U1335. A total of 46 radiolarian datum levels consisting of 20 first occurrences (FOs), 25 last occurrences (LOs), and one evolutionary transition (ET) was recognized within the studied interval at Site U1335. Of these datum levels, 36 radiolarian datum levels were directly tied to the geomagnetic polarity time scale (GPTS) across the early/middle Miocene boundary. The general magnitude of evolutionary change was estimated based on the total turnover rate (the sum of FOs and LOs per 0.5 m.y.) of tropical radiolarians, and two minor faunal turnovers of radiolarian species were recognized between 16.5 and 14.7 Ma and between 13.9 and 13.4 Ma. These faunal turnovers were associated with regional environmental changes such as the increased biological productivity in the equatorial Pacific during the MCO and the MMCT.

Calcareous Nannofossils Biostratigraphy of the Lower Part of Balambo Formation (Lower Cretaceous) in Azmir Anticline - Northeastern Iraq

The present research includes a biostratigraphic study of calcareous nannofossils of the lower part of Balambo Formation (Lower Cretaceous) in Azmir anticline - northeastern Iraq. Lithologically, the lower part of the studied section (Balambo Formation) consists of limestone containing nodules of chert, marly limestone, with intercalations of green and gray-blue shale. In this work, it has been relied on calcareous nannofossils assamblages in biostratigaphy and age determination of this part because it does not contain planktonic foraminifera. First occurrences (FOs) and last occurrences (LOs) of marker species were used to identify biozones. The section was divided into four main biozones and two subzones and its correlation with collection from global, regional, and local biozones. Thus, the age of this part of the formation extends from the Late Early Hauterivian - Late Aptian. These are from older to younger: 1- Speetonia colligata Interval Zone (part) 2- Lithraphidites bollii Interval Zone 3- Micrantholithus hoschulzii Partial range Zone 4- Chiastozygus litterarius Interval Zone Hayesites irregularis Interval Subzone Eprolithus floralis Interval Subzone (part)