Calcareous Microfossils Research Articles

A New Preparation Method of Microfauna from Gypsum: Micropaleontological Association from the Middle Miocene Badenian Gypsum Deposits of Paratethys

Evaporitic gypsum deposits represent an important paleoenvironmental record of the Miocene Badenian of the Carpathian Mountains belt. In this study, we developed a nontoxic method to concentrate calcareous microfossils from gypsum (CaSO4·2H2O), by treating the sulfate with ammonium acetate. We applied the newly developed method to gypsum collected from the Evaporitic Formation outcropping northward of Slănic-Prahova in the Eastern Carpathians. For the first time for this formation, we describe a calcareous microfossil assemblage characterized by the presence of planktonic foraminifera as well as cysts and fragments of calcareous algae.

Integrated stratigraphy and paleontology of the lower Miocene Monte León Formation, southeastern Patagonia, Argentina: Unraveling paleoenvironmental changes and factors controlling sedimentation

Marine sedimentary rocks of the lower Miocene Monte León Formation of southeastern Patagonia (Austral Basin), Argentina are important geological archives for better understanding regional tectonics, paleoenvironments, oceanography, and climate. In this paper, we describe assemblages of invertebrates, palynomorphs, foraminifera, ostracods and calcareous nannofossils in a stratigraphical and sedimentological framework, which suggest deposition during a transgressive-regressive cycle. From base to top, the lowermost outcropping deposits of the Punta Entrada Member represent an inner shelf environment, formed during a transgressive phase. The zone of maximum flooding is marked by a high diversity of protoperidiniaceans (heterotrophic) and offshore dinoflagellate cysts, an increase in the percentage and size of planktonic foraminifera, and a decrease in shallow water benthic foraminifera. Regressive deposits in the upper part of the Punta Entrada Member exhibit a progradational stratal stacking pattern and are characterized by an upward decrease in bioturbation and in the content of marine invertebrates; the dinoflagellate cyst assemblages point toward shallower and more restricted marine conditions than in underlying deposits. The cycle ends with the Monte Observación Member, which contains an impoverished and mostly reworked fauna of invertebrates. The presence of monospecific reefs of Crassostrea orbignyi, the decrease in dinoflagellate cysts and calcareous microfossils diversity, and the increase of continental palynomorphs suggest progressively shallower conditions and increasing influence of freshwater discharge. Although eustatic controls could have contributed to the sedimentary evolution of the Monte León Formation, the upward regressive trend is interpreted as the result of tectonism linked to the Andean orogeny, which led to the uplift, exhumation, and erosion of the highlands in the west. This is supported by the abundance of pyroclastic material, together with reworked specimens of Upper Cretaceous forams and Upper Cretaceous and middle Eocene dinoflagellate cysts in the upper part of the Punta Entrada Member and in the Monte Observación Member.

Sedimentary record of the Cretaceous–Paleocene arc–continent collision in the northwestern Colombian Andes: Insights from stratigraphic and provenance constraints

The collision of intra-oceanic arcs with continental margins is a primary factor controlling the evolution, modification, and growth of continental crust. Syn- to post-collisional basins are formed on both the oceanic and continental sides of an accretionary orogen as a consequence of tectonic activity, which preserve the associated erosional and exhumation record of the colliding element. During the late Cretaceous–Paleogene, the evolution of the northern Colombian Andes was shaped by an oceanic arc-continent collision as a result of the interaction between the Caribbean and South American plates. The timing and stratigraphic record of the collision have mostly been reconstructed from foreland and hinterland basins. In this contribution, we present the results of an integrated stratigraphic, paleontological, and provenance study of Upper Cretaceous sedimentary sequences accumulated on the oceanic side, to the west of the collisional event. Our results suggest that clastic rocks mainly accumulated in short depositional systems in deep marine settings. Two stratigraphic units can be distinguished: A volcanoclastic unit, composed of dark gray siliceous mudrocks interlayed with thick to medium volcanic-rich sandstone layers, accumulated in a turbidite system . A siliciclastic unit (Urrao Member) composed of dark gray mudrocks, and thin to thick, fine- to medium-grained feldspathic litharenites and lithic arkoses accumulated in the lobes and splays of submarine fans. Polymictic conglomerates and sandstones associated with submarine channels and levees are less common and can be used as stratigraphic markers. The Urrao Member was mostly sourced from igneous, sedimentary, and metamorphic Cretaceous and older rocks forming the continental paleo-margin that was being rapidly exhumed as suggested in previous works. Zircon crystal morphology and depositional ages suggest volcanism simultaneous with sedimentation. The maximum depositional UPb ages of zircons and poorly preserved macro- and microfossils (mollusks and calcareous microfossils) suggest a Coniacian and Campanian–Maastrichtian age for the volcanoclastic and siliciclastic units, respectively; nevertheless, regional paleontological and geochronological data indicate that marine siliciclastic sedimentation continued into the Paleocene. These new data suggest that the late Cretaceous–Paleocene interaction of the Caribbean and South American plates did not trigger considerable and long-lasting uplift/erosion of the colliding oceanic domain and that magmatism was active during collision.

Organic-walled dinoflagellate cyst biostratigraphy of the upper Eocene to lower Oligocene Yazoo Formation, US Gulf Coast

Abstract. New data from a continuously cored succession, the Mossy Grove core, near Jackson, central Mississippi, recovered ∼137 m of marine clays (Yazoo Formation), spanning ∼5 Ma and including the critical Eocene–Oligocene transition (EOT) event. These clay-rich sediments yield well-preserved calcareous microfossil and palynomorph assemblages. Here, we present a new organic-walled dinoflagellate cyst (dinocyst) biostratigraphic framework, including the recognition of 23 dinocyst bioevents. These are integrated with new age constraints based on calcareous nannofossil biostratigraphy and a reassessment of the existing radiometric dates and planktonic foraminiferal biostratigraphy, permitting the establishment of a robust and significantly refined age model for the core. According to this new age model, a major increase in sedimentation rate – from ∼2.1 to ∼4.7 cm kyr−1 – is observed at a core depth of ∼89.1 m (∼34.4 Ma). In the new age model the section is significantly older than previously thought, by up to 1 Ma, with the Eocene-Oligocene boundary (∼33.89 Ma) placed ∼34 m below the level previously identified. With these more accurate age estimates, future isotopic and palaeoecological work on this core can be more precisely integrated with other, globally distributed records of the EOT.

Dinoflagellate cyst evidence for the age, palaeoenvironment and paleoclimate of a new Cretaceous–Paleogene (K/Pg) boundary section at the Bou Angueur syncline, Middle Atlas, Morocco

In this paper, we present results of a palynological analysis of the phosphate succession from the northern flank of the Bou Angueur syncline in the Middle Atlas (central Morocco). The studied interval yielded a well-preserved and diverse palynological content, dominated by dinoflagellate cysts (dinocysts), allowing a detailed taxonomic study of dinocyst and a new biostratigraphic dating of the section. The studied section is assigned to the upper Maastrichtian–Danian interval. A new, relatively complete K/Pg boundary transition was recognized. The succession at the Bou Angueur syncline was compared to Tethyan K/Pg boundary sections, such as the K/Pg boundary Global Stratotype Section and Point (GSSP) at El Kef (NW Tunisia) and Ouled Hadou section (NE Morocco). The dinocyst marker events used for the identification of the late Maastrichtian include the first occurrences of Cordosphaeridium inodes subsp. inodes, Deflandrea galeata and Glaphyrocysta perforata and those used for the early Danian include the first occurrences of Carpatella cornuta, Cassidium fragile, Danea californica, Lanternosphaeridium reinhardtii and Senoniasphaera inornata.The organic-walled dinocyst-producing dinoflagellates did not undergo the K/Pg mass extinction resulting from a large meteoritic impact. They enable us to interpret the environmental and climatic changes in the earliest Danian, while calcareous microfossils could not, since they are partially or completely extinct. We thus describe seven palynological assemblages, reflecting paleoenvironmental and paleoclimatic changes, inferred from changes in relevant ecological parameters, including changes in the relative abundance of selected dinocyst groups, often used as paleoenvironmental indicators. An inner to middle neritic marine environments alternated with several short phases of more offshore conditions is deduced for the late Maastrichtian and earliest Danian and an open outer neritic marine environment during a transgressive regime in the latest Danian. Several dinocyst events were recognized in the studied interval, among which remarkable blooms of tropical warm-water and high-latitude cold-water dinocyst taxa are interpreted herein as ecological responses, related to global climatic changes, including a global warming episode during the late Maastrichtian and the well-known brief global cooling following the K/Pg boundary Chicxulub impact.

A High‐Resolution Geomagnetic Relative Paleointensity Record From the Arctic Ocean Deep‐Water Gateway Deposits During the Last 60 kyr

AbstractWe present a paleomagnetic and rock magnetic data set from two long sediment cores collected from Bellsund and Isfjorden contourite drifts located on the eastern side of the Fram Strait (western Spitsbergen margin). The data set gave the opportunity to define the behavior of the past geomagnetic field at high latitude and to constrain the palaeoclimatic events that occurred in a time framework spanning marine isotope stage 3 to the Holocene. A high‐resolution age model was reconstructed by coupling 26 radiocarbon ages and high‐resolution relative paleointensity and paleosecular variation of the geomagnetic field records for the last 60 kyr. We show the variation of the geomagnetic field at high latitudes, pointing out variability during periods of regular paleosecular variation (normal polarity) as well as during the most recent geomagnetic excursions, and we provide a high‐resolution record of the Laschamps excursion. Cross‐cores correlation allowed us to outline major, climate‐related, sedimentary changes in the analyzed stratigraphic sequence that includes the meltwater events MWP‐1a and MWP‐19ky, and the Heinrich‐like events H1, H2, H4, and H6. This contribution confirms that rock magnetic and paleomagnetic analysis can be successfully used as a correlation and dating tool for sedimentary successions at high latitudes, where accelerator mass spectrometry dates and oxygen isotope analyses are often difficult to obtain for the scarcity of calcareous microfossils and the uncertainties related to data calibration may be significant, as well as the complexity of water mass characteristics and dynamics through climate changes.

BP Gulf of Mexico Neogene Astronomically-tuned Time Scale (BP GNATTS)

AbstractThis paper introduces an integrated Neogene microfossil biostratigraphic chart developed within post-merger BP for the Gulf of Mexico Basin and is the first published industrial framework “fully-tuned” to orbital periodicities. Astronomical-tuning was accomplished through a 15-year research program on the Ocean Drilling Program’s (ODP) Leg 154 sediments (offshore NE Brazil) with sampling resolution for calcareous nannofossils and planktonic foraminifera ∼20 k.y. and 40 k.y. (thousand year), respectively. This framework extends from the Late Oligocene (25.05 Ma) to Recent at an average Chart Horizon resolution for the Neogene of 144 k.y., approximately double that of published Gulf of Mexico biostratigraphic charts and a fivefold increase over the highest resolution global calcareous microfossil biozonation. Such resolution approximates that of fourth to fifth order parasequences and is a critical component in the verification of seismic correlations between mini-basins in the deep-water Gulf of Mexico. Its utility in global time-scale construction and correlation has been proven, in part, by application of the scheme in full to internal research for the Oligocene–Miocene boundary interval on the global boundary stratotype section and point (GSSP) in northern Italy and offshore wells in the eastern Mediterranean Sea. This step change in Neogene resolution, now at the level of cyclostratigraphy (the orbital periodicity of eccentricity) and the magnetostratigraphic chron, demonstrates the potential for calcareous microfossil biostratigraphy to more consistently reinforce correlations of these time scale parameters. The integration of microfossil disciplines, consistent taxonomies, and rigorous analytical methodologies are all critical to obtaining and reproducing this new level of biostratigraphic resolution.

Pliocene integrated chronostratigraphy from the Anno Formation, Awa Group, Boso Peninsula, central Japan, and its paleoceanographic implications

The Pliocene climate is one of the best analogs for the climate of a globally warmer future. Here, we present a new Pliocene integrated chronostratigraphy from the Anno Formation in the uppermost Awa Group, which is distributed throughout the Boso Peninsula, central Japan, based on paleomagnetic and benthic foraminiferal oxygen isotope records. This new chronostratigraphy provides valuable constraints for paleoceanographic and paleoclimatic studies in the northwestern Pacific Ocean, where the number of paleoceanographic records is limited due to the lack of calcareous microfossils from deep-sea sediment cores, with the exception of some plateaus at water depths above the calcite compensation depth (CCD). Paleomagnetic results indicate that the Anno Formation corresponds to the period extending from the Nunivak normal polarity subchronozone (4.493–4.631 Ma) to Chron C2An.2n (3.116–3.207 Ma), which is just above the Mammoth reversed polarity subchronozone. Although foraminifera are not found in the middle Anno Formation, our oxygen isotope records from the upper and lower Anno Formation demonstrate the recording of glacial–interglacial cycles. However, the amplitude of our δ18O profile is much larger than that of the LR04 stack, with similar to slightly lower glacial values and much lower interglacial values. This observation implies that the bottom water had lower δ18O values and/or a warmer water mass during interglacials compared with global average deep-water regions.

Influence of Clay, Calcareous Microfossils, and Organic Matter on the Nature and Diagenetic Evolution of Pore Systems in Mudstones

AbstractMudstones exert a fundamental control on the flow of both aqueous and nonaqueous fluids in sedimentary basins. Predicting their flow and storage properties requires an understanding of pore size and connectivity, yet there are very few quantitative descriptions of pore systems of mineralogically and texturally well‐characterized mudstones. We use a combination of electron microscopy, mercury injection capillary pressure porosimetry, and CO2 sorption methods to generate a quantitative description of the size distribution, connectivity, and evolution of pore systems in a sequence of Posidonia Shale mudstones buried to 100–180 °C. We place the pore data into a detailed mineralogical, petrographical, and textural context to show that the nature and evolution of porosity and pore systems can be described in terms of associations with clay‐rich, microfossil‐rich, and organic matter‐rich domains, common to many mudstones. Pore size distributions are described by power laws, and pore systems are well connected across the full nanometer‐micrometer spectrum of pore sizes. However, connected networks occur primarily through pores <10 nm radius, with typically 20–40% of total porosity associated with pores with radii < ~3 nm, within both organic matter and the clay matrix. Clay‐rich, microfossil‐rich, and organic matter‐rich domains have distinct pore size distributions which evolve in very different ways with increasing thermal maturity. We suggest that the flow of aqueous and nonaqueous fluids depends not only on the overall connectivity of pores but also the larger‐scale connectivity and wetting state of clay‐rich, microfossil‐rich, and organic matter‐rich domains.

Palinotaxonomia da seção cretácea a neogena da Bacia de Pelotas, Brasil: cistos de dinoflagelados das ordens Ptychodiscales e Gonyaulacales

Cistos de dinoflagelados são comumente utilizados para a obtenção das idades relativas, correlações e interpretações paleoambientais das seções cretáceas e paleógenas da margem continental brasileira. Contudo, as informações micropaleontológicas da Bacia de Pelotas são referentes, na sua maioria, a microfósseis calcários. Nesta segunda contribuição, o detalhamento sistemático e descritivo das associações de cistos de dinoflagelados das ordens Ptychodiscales e Gonyaulacales é apresentado, a partir da análise 535 amostras de dois poços (BP-01 e BP-02) perfurados pela Petrobras S.A. na porção offshore da Bacia de Pelotas. Os níveis analisados mostraram-se ricos e diversificados, possibilitando o reconhecimento 137 espécies de cistos de dinoflagelados. Em maior número, cistos pertencentes à Ordem Gonyaulacales totalizaram 76 gêneros, 133 espécies, além de três subespécies. Dois gêneros e quatro espécies foram conferidos à Ordem Ptychodiscales. Do total de táxons descritos, 72 são citados pela primeira vez para as bacias brasileiras. As associações reconhecidas indicaram idades entre o Crétaceo e o Neogeno, tendo como base as ocorrências de E. dettmanniae, D. acuminatum e O. indigena para o Cretáceo; D. californica, D. carposphaeropsis e E. reticulata para o Paleoceno; B. longissimum, M. fimbriatum e M. perforatum para o Eoceno; C. galea, C. aubryae e H. obscura para o Mioceno. R. actinocoronata e A. andalousiensis, registradas em níveis pós miocênicos da bacia, são indicativas de idades mais jovens, possivelmente posicionadas entre o Plioceno e o Pleistoceno.

Plio-Pleistocene sedimentary record from the Northwind Ridge: new insights into paleoclimatic evolution of the western Arctic Ocean for the last 5 Ma

Sediment core HLY0503-03JPC from the top of the Northwind Ridge provides the first confirmed Plio-Pleistocene record from the western Arctic Ocean, with calcareous microfossils uniquely preserved to ca. 5 Ma. Results are compared to nearby core P1-93AR-P23 from the ridge slope, which was previously used to reconstruct early Quaternary sea-ice conditions in the region (Polyak et al. in Quat Sci Rev 79:145–156, 2013), and is now re-dated to at least the late Pliocene. Ages were estimated primarily from strontium isotope stratigraphy on benthic foraminifers. Based on multiple physical, paleomagnetic, elemental geochemical, and paleobiological (foraminifers) proxies, we identify three major stratigraphic divisions (Units 1, 2a, and 2b) roughly representing upper to middle (“glacial”) Quaternary, lower Quaternary to Pliocene, and lower Pliocene to possibly upper Miocene (undated). Benthic foraminiferal assemblages were utilized to evaluate paleo-sea-ice conditions, while other proxies were used to interpret paleocirculation and sediment transport processes. Early Quaternary and older sediments indicate diminutive effect from glaciations, reduced sea-ice conditions, and a periodic strong current impact on the ridge top, possibly due to an enhanced Atlantic water flow. Ages derived from the first foraminiferal tests appearing at ca. 5 Ma likely indicate a redeposition pulse that we attribute to the onset of Pacific water throughflow via the Bering Strait. A large hiatus above this level in JPC3 spans most of the Pliocene. The Unit 2a/1 boundary, estimated to ca. 0.8 Ma, is marked by an abrupt faunal and sedimentary change, which is consistent with the major climatic shift that occurred during this time (Mid-Pleistocene Transition). Unit 1 exhibits a strong control from glacial cyclicity, with a progressive expansion of the Laurentide Ice Sheet primarily affecting the study region, and mostly perennial sea-ice conditions. Overall results suggest that the Pliocene and early Pleistocene may provide relevant paleoclimatic analogs for the rapidly changing Arctic environments of today.

Late Holocene paleoceanography in the Chukchi and Beaufort Seas, Arctic Ocean, based on benthic foraminifera and ostracodes

Calcareous microfossil assemblages in late Holocene sediments from the western Arctic continental shelf provide an important baseline for evaluating the impacts of today’s changing Arctic oceanography. This study compares 14C-dated late Holocene microfaunal assemblages of sediment cores SWERUS-L2-2-PC1, 2-MC4 and 2-KL1 (57 mwd), which record the last 4200 years in the Herald Canyon (Chukchi Sea shelf), and HLY1302-JPC-32, GGC-30, MC-29 (60 mwd), which record the last 3000 years in the Beaufort Sea shelf off the coast of Canada. Foraminiferal and ostracode assemblages are typical of Arctic continental shelf environments with annual sea-ice cover and show relatively small changes in terms of variability of dominant species. Important microfaunal changes in the Beaufort site include a spike in Spiroplectammina biformis coinciding with a decrease in Cassidulina reniforme in the last few centuries suggesting an increase of Pacific Water influence and decreased sea-ice. There is low-amplitude centennial-scale variability in proportions of benthic foraminiferal species, such as C. reniforme. In addition to these species, Cassidulina teretis s.l., Elphidium excavatum clavatum and Stainforthia feylingi are also common at this site. At the Herald Canyon site in the last few centuries, C. reniforme peaks around 150 years BP and then decreases while Spiroplectammina earlandi spikes and Acanthocythereis dunelmensis decreases also suggesting an increase in Pacific Water influence and decreased sea-ice at this site. This site also includes Buccella spp. and Elphidium excavatum clavatum. Differences in benthic foraminifera and ostracode species dominance between the two sites may be due to a greater influence of Pacific Water in the Chukchi shelf, compared to the more distal Beaufort shelf, which is also affected by the Beaufort Gyre and the Mackenzie River.

Integrated tephrostratigraphy and stable isotope stratigraphy in the Japan Sea and East China Sea using IODP Sites U1426, U1427, and U1429, Expedition 346 Asian Monsoon

Integrated Ocean Drilling Program Expedition 346 “Asian Monsoon” obtained sediment successions at seven sites in the Japan Sea (Sites U1422–U1427 and U1430) and at two closely located sites in the northern East China Sea (Sites U1428 and U1429). The Quaternary sediments of the Japan Sea are characterized by centimeter- to decimeter-scale dark–light alternations at all sites deeper than 500 m water depth. The sedimentary records from these sites allow an investigation of the regional environmental response to global climate change, including changes in the Asian Monsoon and eustatic sea level. However, the discontinuous occurrence of calcareous microfossils in the deep-sea sediments and their distinct isotope signature that deviates from standard marine δ18O records do not permit the development of a detailed stable isotope stratigraphy for Japan Sea sediments. Here, we present the tephrostratigraphy for the two southernmost sites drilled in the Japan Sea (Sites U1426 and U1427) and for one site drilled in the East China Sea (Site U1429) along with the benthic δ18O isotope stratigraphy for the shallower Site U1427 and the East China Sea Site U1429. Eighteen tephra layers can be correlated between sites using the major-element composition and morphology of volcanic glass shards, and the compositions of grains and heavy minerals. Tephra correlations show that negative δ18O peaks in the Japan Sea correspond to positive glacial maxima peaks in the East China Sea. Using this integrated stratigraphic approach, we establish an orbital-scale age model at Site U1427 for the past 1.1 Myr. The correlation of tephra layers between the shallower Site U1427 (330 m below sea level: mbsl) and the deeper Site U1426 (903 mbsl) in the southern Japan Sea provides the opportunity for further age constraints. Our results show that alternations in sediment color at Sites U1426 and U1427 can be correlated for the past 1.1 Myr with minor exceptions. Thus, the stable isotope stratigraphy established at the shallower Site U1427 can be correlated to Site U1426, and in turn to all sites drilled during Expedition 346, based on correlations of dark–light layering.

Sedimentological and ichnological characterization of muddy storm related deposits: The upper Hauterivian ramp of the Agrio Formation in the Neuquén Basin, Argentina

The lowermost part of the Agua de la Mula Member (upper Hauterivian), Agrio Formation, was studied in distal depositional settings at four locations in the central Neuquén Basin. Detailed sedimentological and ichnological analysis combining field data and microfacies, using petrography, X-ray diffraction, and organic geochemical data allow to recognize two facies associations, representing proximal to distal facies of a mixed, carbonate-siliciclastic homoclinal outer ramp. The distal outer ramp facies association (FA-1) contains mudstones accumulated by suspension settling during periods of high productivity in the water column with calcareous microfossils as fecal pellets and organo-minerallic aggregates. Very thin (<5 mm thick) beds with local skeletal debris and subtle erosional features suggest storm-generated turbidite-like deposits related to bottom currents that interrupted this “low-energy” scenario. Conversely, the proximal outer ramp facies association (FA-2) is mainly composed of illite-rich floccules with terrigenous organic matter derived from the hinterland, probably transported by suspension in the way of benthic fluid mud. The partially bioturbated clay-bearing, silt-rich mudstones are organized into stacked successions of sharp-based, normally graded and very thin (<5 mm thick) beds indicative of erosive waning flows. In these mudstones, the preservation of parallel to curved ripple lamination indicates storm-driven bottom currents that transported mud as bed load into the proximal outer ramp. Some bioturbated mudstones with Phycosiphon incertum demonstrate a close relationship between event bed deposits and oxygenation pulses of the bottom waters by storm-influenced processes.

過去の微小藻類が作る石灰質微化石の結晶方位の解析 : 石灰質ナンノ化石Florisphaera profundaとDiscoaster属の結晶構造とその意味

過去の微小藻類が作る石灰質微化石の結晶方位の解析 : 石灰質ナンノ化石Florisphaera profundaとDiscoaster属の結晶構造とその意味

Neogene dinoflagellate cysts and acritarchs from the high northern latitudes and their relation to sea surface temperature

Organic-walled dinoflagellate cysts and acritarchs are a vital tool for reconstructing past environmental change, in particular in the Neogene of the high northern latitudes where marine deposits are virtually barren of traditionally used calcareous microfossils. Yet only little is known about the paleoenvironmental value of fossil assemblages that do not have modern analogues, so that reconstructions remain qualitative. Thus, extracting their paleoecological signals still poses a major challenge, in particular on pre-Quaternary timescales. Here we unravel the relationship between species relative abundance and sea surface temperature for extinct dinoflagellate cyst and acritarch taxa from the Neogene of the Iceland Sea using palynological assemblages and organic geochemical (alkenone) data generated from the same set of samples. The reconstructed temperatures for the Miocene to Pliocene sequence of Ocean Drilling Program Site 907 range from 3 to 26 °C and our database consists of 68 dinoflagellate cyst and acritarch samples calibrated to alkenone data. The temperature range of five extant species co-occurring in the fossil assemblage agrees well with their present-day distribution providing confidence to inferred temperature ranges for extinct taxa. The 14 extinct dinoflagellate cyst and acritarch species clearly exhibit a temperature dependency in their occurrence throughout the analysed section. The dinoflagellate cyst species Batiacasphaera hirsuta, Labyrinthodinium truncatum, Cerebrocysta irregulare, Cordosphaeridium minimum, Impagidinium elongatum and Operculodinium centrocarpum s.s., and the acritarch Lavradosphaera elongatum, which are confined to the Miocene, have highest relative abundances and restricted temperature ranges at the warm end of the reconstructed temperature spectrum. The latter five species disappear when Iceland Sea surface temperatures permanently drop below 20 °C, thus indicating a distinct threshold on their occurrence. In contrast, species occurring in both the Miocene and Pliocene interval (Batiacasphaera micropapillata, Habibacysta tectata, Reticulatosphaera actinocoronata, Cymatiosphaera? invaginata) show a broader temperature range and a tolerance towards cooler conditions. Operculodinium? eirikianum may have a lower limit on its occurrence at around 10 °C. The calibration of species relative abundance versus reconstructed sea surface temperature provides a quantitative assessment of temperature ranges for extinct Miocene to Pliocene species indicating that temperature is a decisive ecological factor for regional extinctions that may explain the frequently observed asynchronous highest occurrences across different ocean basins. It demonstrates that qualitative assessments of ecological preferences solely based on (paleo) biogeographic distribution should be treated with caution. In addition to enhancing knowledge on marine palynomorph paleoecology, this study ultimately improves the application of palynomorphs for paleoenvironmental reconstructions in the Neogene of the Arctic and subarctic seas, a region essential for understanding past global climate.

Characterization of hydrate-bearing sediments recovered from the Shenhu area of the South China Sea

The characteristics of the hydrate-bearing layer are important parameters for gas hydrate exploration and exploitation, which can be provided by laboratory analysis. We have carried out a systematic analysis of modern instruments, including the laser grain size analyzer, X-ray computed tomography, scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, gas chromatography, and isotope mass spectrometry, on the hydrate-bearing sediment samples recovered from the Shenhu area in the South China Sea in 2016. We focused on the structure, hydration number, and gas composition of the gas hydrate samples. We also evaluated the effects of sediments on the occurrence and distribution of gas hydrate. Our results showed that the sediments are much finer than those recovered from the Shenhu area in 2007. Some samples are found to contain calcareous microfossils and foraminifera, which are beneficial for dispersed gas hydrate formation. Whereas the only visible hydrate sample (FC4) has not found any bioclast in the sediments. Based on the Raman data and the XRD analysis, the gas hydrates demonstrate typical structure I (sI) hydrates, with cage occupancies of methane molecules higher than 99.3% in large cages and 81.5%–91.4% in small cages, respectively. The crystal lattice parameter is 11.89 Å with the hydration number being approximately 6.0. Methane is obviously the dominant component, ranging from 97.6% to 99.95% in these samples. Comprehensive study of carbon and hydrogen isotopes suggests that the hydrate-bound gases are from biogenic and thermogenic gases in the study area.

OSTRACODE BIOFACIES AND SHELL CHEMISTRY REVEAL QUATERNARY AQUATIC TRANSITIONS IN THE POZUELOS BASIN (ARGENTINA)

Here we present the first use of calcareous microfossils to examine the late Quaternary paleoecology of the endorheic Pozuelos Basin (Argentina). Modern deposition in the basin centers on Laguna de los Pozuelos (LP), a shallow playa-lake that is fed by axial rivers and groundwater and dominantly accumulates siliciclastic sediments. Today, the distribution of limnocytherid and cypridoidean ostracodes across southern LP is strongly influenced by distance to the Rio Cincel delta, whereas the northern end of the playa-lake is characterized by a paucity of ostracodes due to frequent sub-aerial exposure. Ten ostracode biofacies define a sediment core retrieved from LP, which reveal progressive changes in aquatic environments that varied in salinity, depth, and proximity to deltas over the late Pleistocene. Closed lakes occupied the basin from ∼ 37.6–30.7 ka, ∼ 28.0–25.0 ka, and ∼ 23.0–16.6 ka, whereas saline wetlands occurred when these lakes contracted. Extant LP has no analog in the late Pleistocene record; it formed after ∼ 7.2 ka, following a hiatus that removed the Pleistocene–Holocene transition. Paleoecological evidence indicates that the core site was influenced by deltaic inflows from the eastern basin margin until ∼ 24.3 ka, an area where today dry alluvial fans are found. Reorganization of the watershed by normal faulting, most likely at ∼ 18.0 ka, appears to have reduced the influence of these deltaic inflows. Extensional neotectonics, perhaps induced by incorporation of the Pozuelos Basin into the Andean hinterland, is a mechanism that along with tropical climate change is potentially important to water balance and ecology in high-altitude convergent orogenic basins.

Palinotaxonomia da seção cretácea a neogena da Bacia de Pelotas, Brasil: cistos de dinoflagelados da Ordem Peridiniales

Grande parte do conhecimento micropaleontológico da Bacia de Pelotas é referente a microfósseis de parede calcária, o que justifica a necessidade de levantamento sistemático de dados palinológicos. Este trabalho apresenta os resultados palinológicos obtidos a partir da análise de 535 amostras de dois poços perfurados na porção offshore da Bacia de Pelotas, incluindo depósitos do Cretáceo ao Neogeno. Os conjuntos palinológicos reconhecidos são ricos e diversificados, constituídos por esporos (briófitas e pteridófitas), grãos de pólen (gimnospermas e angiospermas), cistos de dinoflagelados, palinoforaminíferos, escolecodontes e esporos de fungos. Como consequência do grande volume de dados gerados, se fez necessário, para efeito de publicação, a compartimentação das informações. Nesta primeira contribuição, cistos de dinoflagelados da Ordem Peridiniales são apresentados, com descrições e fotomicrografias. Dentre os 220 táxons de cistos de dinoflagelados identificados, 76 são referentes à Ordem Peridiniales, compreendendo 31 gêneros, 72 espécies, uma subespécie, além de dois táxons sem determinação específica. Ressaltam-se ainda 24 espécies documentadas pela primeira vez para o Brasil. Considerações bioestratigráficas e paleobiogeográficas são discutidas sinteticamente, tendo como base as associações reconhecidas para o Cretáceo Superior e o Neogeno na margem atlântica americana e regiões próximas ao Círculo Polar Antártico.

Calcareous dinoflagellate cysts from the Tithonian - Valanginian Vaca Muerta Formation in the southern Mendoza area of the Neuquén Basin, Argentina

The Late Jurassic – Early Cretaceous marine sediments of the Andean region show an excellent record of different calcareous microfossils, among which calcareous dinoflagellate cysts stand out. Detailed micropaleontological studies of Vaca Muerta Formation (Early Tithonian – Early Valanginian) in the southern Mendoza Neuquén Basin from three sections are conducted with the aim of establishing a major presence of microfossil representatives from different microfossil groups. The analysis of several thin sections from the outcrops reveals a relatively rich micropaleontological assemblage of calcareous dinoflagellate cysts, as well as levels with poor preserved calpionellids and benthic foraminifera. Particularly, calcareous dinoflagellate cyst includes 24 known species (two of them with two subspecies). Some species with biostratigraphic value of the Tethyan region have been identified also in the Andean region: 1) Committosphaera pulla (Borza) and Parastomiosphaera malmica (Borza) are species known only from Lower Tithonian; 2) Colomisphaera tenuis (Nagy) appears in the latest Early Tithonian; 3) Colomisphaera fortis Řehánek and Stomiosphaerina proxima Řehánek are important markers for the latest Late Tithonian – middle Late Berriasian interval; 4) Stomiosphaera wanneri Borza appears in the middle Late Berriasian; 5) Colomisphaera conferta Řehánek and Colomisphaera vogleri (Borza) appear in the Late Berriasian and marked the Berriasian-Valanginian boundary interval; 6) Carpistomiosphaera valanginiana Borza is a marker for the Lower/Upper Valanginian. More detailed studies of these groups will allow their correlation with Tethyan biozones, and contribute to improve biostratigraphic schemes in the Neuquén Basin.