Nannofossil Assemblages Research Articles

Early Miocene (Burdigalian) Dinoflagellate Cysts from the Kerala Basin, Southwest India: Indicators of Marine Ingression at the Onset of the Mid-Miocene Climate Optimum (MMCO)

Abstract In the present study, the assemblages of organic walled dinoflagellate cyst (dinocysts) and calcareous nannofossils from Quilon Formation, Kerala Basin, south-western India are analyzed for age interpretation and reconstruction of the depositional environment. The integrated biostratigraphy based on dinocysts and calcareous nannofossils from the same sediment samples indicates that the studied succession was deposited during the early Miocene (middle Burdigalian, ~19-17.5 Ma) time. The dinocyst assemblages contain abundant taxa (Cleistosphaeridium, Polysphaeridium, Lingulodinium, Homotryblium and Spiniferites) that range from shallow inner to outer neritic marine zone. The abundance of autotrophic, thermophilic taxa suggests relatively high surface water temperatures and high nutrient availability. The dinocyst assemblage in the lower part of the studied succession is dominated by Cleistosphaeridium spp., Polysphaeridium spp., Spiniferites spp., Homotryblium spp. and Lingulodinium spp. An increase in the relative abundances of outer neritic dinocyst taxa such as Spiniferites, Achomosphaera and Hystrichokolpoma in the upper part of the succession suggests a change towards more open marine conditions created during marine ingression. The interpreted marine ingression along the south-western Indian coast probably corresponds to the initial small pulses of transgression at the onset of the long-term global sea-level maximum related to the Mid-Miocene Climatic Optimum (MMCO).

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.

THE DISTRIBUTION RANGE OF CALCAREOUS NANNOFOSSIL SPECIES <em>RETICULOFENESTRA PSEUDOUMBILICUS</em> IN THE MIOCENE: AN EXAMPLE OF ECOLOGICAL INFLUENCE ON EVOLUTIONARY DEVELOPMENT

Reticulofenestra pseudoumbilicus is a Neogene calcareous nannofossil species whose highest stratigraphic occurrence (Top) is a reliable biohorizon in the Pliocene, calibrated at 3.82 Ma. The species is present in the stratigraphic record from at least the Middle Miocene, within an interval around the biohorizon Top Sphenolithus heteromorphus, calibrated at 13.53 Ma, but its lower distribution range is not precisely delineated. The study of nannofossil assemblages in sediment cores from Integrated Ocean Drilling Program IODP Site U1338 (eastern equatorial Pacific) indicates a lower stratigraphic position for the evolutionary emergence (Base) of R. pseudoumbilicus, detected in the Early Miocene with an estimated age of 16.46 Ma. This age results from a new astronomically tuned chronology, which dates the deepest sediments at Site U1338 to 16.67 Ma. Base R. pseudoumbilicus is followed above by a temporary disappearance of the taxon until a re-entrance after ~3 Myr. This lengthened stratigraphic range has been confirmed by data from other locations at low and mid-latitudes in the Atlantic. The distribution range of R. pseudoumbilicus, lasting ~13 Myr during the Neogene, is thus characterized by a variable pattern of repeated occurrences and disappearances. Comparison to benthic foraminifera δ18O and δ13C records suggests a control by global climatic/environmental conditions on these events, particularly by temperature variations. The recurrent presence of R. pseudoumbilicus at stratigraphically different intervals could represent an example of iterative evolution, expressed as repeated speciation events that are in part influenced by complex external factors related to the dynamic climate and environmental evolution during the Miocene.

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

The Paleocene-Eocene period was punctuated by several hyperthermal events likely triggered by massive injection of greenhouse gases, the best-known being the PETM (∼56 Ma). Environmental changes during hyperthermals severely impacted planktonic organisms, especially calcareous nannoplankton producing tiny calcite platelets. These calcite platelets (coccoliths) accumulate at the sea floor and constitute a major component of deep-sea sediments. As calcareous nannoplankton contribute to the biological carbon pump and carbonate counter pump, a better knowledge of their production dynamics in surface ocean and their dissolution throughout the water column is pivotal to produce realistic carbon budgets across hyperthermal events. In this work, we quantitatively assessed calcareous nannofossil abundances and nannofossil fragments from deep sea sediments of late Thanetian to early Ypresian age (55.63–57.42 Ma) from ODP Site 1209 (North Pacific). We developed a new method, based on the shape and number of fragments, to reconstruct an all-inclusive nannofossil absolute abundance (including entire specimens and fragments) in the sediments. The reconstructed values of absolute abundance estimated integrating fragments are on average 25% higher. We also analysed different dissolution proxies (planktonic foraminifera fragmentation, benthic/planktonic ratios, coarse fraction). The fragmentation of planktonic foraminifera does not covary with nannofossil fragmentation, suggesting distinct controlling factors. Foraminiferal proxies and nannofossil assemblages point to episodes of intense dissolution across the PETM as well as during an event pre-dating the PETM by 300–700 kyrs that we identify as the Late Paleocene Event (LPE).

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.

Neogene-Quaternary Mediterranean calcareous nannofossil biozonation and biochronology: A review

The present study focuses on calcareous nannofossil biostratigraphy of the last 23 Myr in the Mediterranean region and is intended as a review paper in which an updated zonation is presented. This includes the improvements in biostratigraphic classification achieved in the last decades. The proposed biozonal scheme incorporates the biochronologic data derived from the integration of biostratigraphically useful events with radiometric datings, magnetostratigraphy and astronomically tuned cyclostratigraphy. This biochronology directly derives by previous compilations and includes improved data and ages derived from recent studies based on high resolution quantitative analysis of nannofossil assemblages. The presented zonal scheme consists of 21 biozones and 35 subzones spanning the last 23 Myr, named according to the well-established code-system MNN (Mediterranean Nannofossil Neogene) for the Miocene and Pliocene time interval and MNQ (Mediterranean Nannofossil Quaternary) for the Pleistocene and Holocene. In addition, a revision of the nannofossil biostratigraphy at the Oligocene/Miocene transition is given, with the introduction of Zone MNP26 (Mediterranean Nannofossil Paleogene), as a result of the different age assigned to the Oligocene/Miocene chronostratigraphic boundary. This zonation provides a significant bio-chronostratigraphic resolution of about 0.5 Myr, corresponding to a degree of precision functional for dating sedimentary successions and, therefore, useful for geological studies (e.g. geological mapping, temporal scanning of geological phasis). The biostratigraphic resolution can be furtherly improved through integration with the analogous scheme recently established for planktonic foraminifers.

Calcareous nannofossils, planktonic foraminifera, and revised stratigraphy of the Eocene Çayraz Formation; the final stage of marine sedimentation in Central Anatolia, Turkey

New field observations and discovery of calcareous nannofossils and planktonic foraminifera from the 'shallow-marine' Çayraz Formation (Haymana Basin, Central Anatolia), a contributing Eocene section to the shallow benthic zonation (SBZ) in the Tethys, allow us to revise its stratigraphy and establish an integrated biostratigraphic scheme for the first time. The hemipelagic marls in the uppermost part of the Eskipolatlı Formation that underlies the Çayraz Formation yielded nannofossil assemblages of Zone CNE3, pinning down the initiation of the Çayraz shelf system into the 'middle' Ypresian. The prominent marly part (Member B) between the carbonate-clastic packages of the Çayraz Formation with prolific occurrences of larger benthic foraminifers (LBFs) (Members A below and C above) yielded calcareous nannofossils suggesting Zone CNE6 (late Ypresian). We show that the mixed carbonate-siliciclastic sequence with abundant LBFs in the upper part of the formation (Member C) is overlain by newly discovered hemipelagic marls (here named as Member D). These marls yielded calcareous nannofossils indicating Zone CNE9 and CNE10 for the lower and Zone CNE12(?Lutetian) for the upper samples. The same beds yielded planktonic foraminifers indicating Zone E8 for the lower and Zone E9 for the upper samples. We conclude that shallow-marine sedimentation in the Çayraz section ended in the 'middle' Lutetian, challenging the previous Bartonian records by LBFs. A new lithostratigraphic scheme consisting of four members with distinctive lithological and biotic characteristics is proposed for the Çayraz Formation: two main shelf systems (Members A and C), each followed by deep-marine sedimentation (Members B and D).

Latest Hauterivian foraminiferal and calcareous nannofossil assemblages and bioevents from the Pseudothurmannia beds (Central Western Carpathians, Slovakia): A prelude to the Faraoni event

A diverse and abundant assemblage of deep-water agglutinated foraminifera (DWAF) has been recovered from an uppermost Hauterivian ammonite-rich horizon (Pseudothurmannia ohmi Biozone) from the Central Western Carpathians. The section records the last occurrence of the calcareous nannofossil species Litraphidites bollii (Thierstein) preceding the Faraoni anoxic level. Various morphogroups of agglutinated foraminifera show changes in response to trophic regime shift and decreasing oxygenation of the bottom and pore waters in a relatively short time-series. The DWAF data were compared with calcareous nannofossil assemblages and foraminifera analysed from thin sections (calcareous benthic and planktonic foraminifera). Four ecozones were identified, each with a specific taxonomic composition of foraminiferal assemblages. The zone-to-zone changes include fluctuations in the richness and relative abundance of morphogroups and planktonic foraminifera, and dwarfism in certain groups of foraminifera.

Oceanic anoxic event 2 in Sergipe-Alagoas Basin, Brazil: New paleoecological insights from calcareous nannofossils assemblages

A boring core (UFRJ-2-LRJ-01-SE) from the Sergipe-Alagoas Basin, Brazil, is one of the best and most expanded sections of the late Albian–early Turonian age within South America and includes one of the few records of Oceanic Anoxic Event 2 (OAE 2) in the South Atlantic Ocean. The aim of this study is to revise the calcareous nannofossil biostratigraphy and reconstruct paleoclimatic-paleoceanographic patterns based on the quantitative analysis of nannofossil assemblages performed on 78 samples throughout the core UFRJ-2-LRJ-01-SE. The biostratigraphic revision corroborates the previously defined late Albian–early Turonian age for the studied section, however, a hiatus (∼ 4.7 Ma) has been identified, omitting the latest Albian–early Cenomanian time interval including OAE 1d. In addition, we confirm the occurrence of the OAE 2 interval within the studied section. Also, the revised nannofossil biostratigraphy integrated with chemostratigraphy pointed out the presence of the Middle Cenomanian Event (MCE), previously identified as the Lower Cenomanian Anoxic Event (LCAE). The relative abundances of selected calcareous nannofossil taxa suggest a prevalence of warmer surface waters during the late Albian and cooler conditions during the middle Cenomanian–early Turonian. The integration of diversity, species richness, Shannon diversity, equitability, nutrients (NI) and temperature (TI) indices separated four intervals recording different paleoecological conditions. The comparison with western Tethys data shows similarity between the temperature and fertility trends recognized in the studied section, suggesting global climate changes and similar fluctuations in ocean fertility during the late Albian–early Turonian.

Oldest Asian Record of Snapping Shrimps (Malacostraca: Alpheidae) from the Kutch Basin, Western India and Associated Biota: Biostratigraphic, Paleoenvironmental and Paleoecological Significance

AbstractThe oldest Asian record of alpheid shrimps, assigned to genus Alpheus, based on snapping claw fingertips from the Miocene Khari Nadi Formation in the Kutch Basin, western India reported herein, extends the fossil record of the family Alpheidae from Asia by ∼22 million years. An early Miocene (Aquitanian) age is estimated based on the associated assemblage of calcareous nannofossils, Sphenolithus disbelemnos, Cyclicargolithus floridanus, and Reticulofenestra haqii. The co‐occurring microbiota includes bony fish otolith remains, identified as “genus Gobiidarum”, isolated teeth of Dasyatis rays, Sphyrna sharks, and teleosts, ctenoid and placoid scales, ostracods, belonging to the genera Paractinocythereis, Alocopocythere, Ruggieria, Aglaiocypris, Bairdoppilata, and echinoid spines. Taken together, the microfossil assemblage and data from chemical analyses using Energy Dispersive Spectroscopy, X‐Ray Diffraction and Wavelength Dispersive X‐Ray Fluorescence of host and associated lithologies suggests prevalence of a shallow (neritic) to coastal marine (intertidal) depositional paleoenvironment. The present investigation also provides the oldest fossil evidence on the co‐occurrence of Alpheus and gobiids (based on otoliths) that strongly advocates that the mutualistic association between these animal groups had developed by the Aquitanian.

Quantitative biostratigraphy of Upper Albian to Lower Cenomanian (Cretaceous) calcareous nannofossils of mid-latitude regions

Late Albian - early Cenomanian calcareous nannofossil assemblages from five mid-latitude localities (23-35 degrees) were analyzed using probabilistic and deterministic methods to produce comprehensive and quantitative biostratigraphic sequences that were compared to the widely used 'CC' and 'UC' calcareous nannofossil zonation schemes. This was done to examine their fidelity and general applicability for mid-latitude biostratigraphy and determine whether these quantitative methods can increase the resolution of said schemes. Four biozones spanning the upper Albian through middle Cenomanian were determined using unitary associations (UAs) and ranking and scaling (RASC) optimum sequence from which last appearance datum (LAD) of – Gartnerago stenostaurion, first appearance datum (FAD) – Lithraphidites eccentricus, and LAD – Staurolithites mutterlosei were determined to be reliable early Cenomanian markers at mid-latitudes, while the FAD and LAD of Calculites anfractus are unreliable bioevents and should not be used as a secondary marker for the Albian - Cenomanian boundary. In addition, we have revised the stratigraphic position of the FAD of L. eccentricus, which was previously assigned to the middle-Cenomanian. The proposed FAD was shortly after the Albian - Cenomanian boundary, before the FAD of Corollithion kennedyi. We conclude that UAs are more robust than RASC bioevents for this time sequence; however, both methods do not account for the asynchronicity of depositional and biotic chances. Despite these caveats, combining the results for both methods has proven to be a powerful quantitative biostratigraphic tool.

Calcareous Nannofossils from the Shiranish Formation at Bekhaer anticline, Dhouk area, Northern Iraq

Calcareous nannofossils are examined up on the Shiranish Formation from the Bekhaer anticline in Northern Iraq. The study area includes about 55 meters to find calcareous nannofossils assemblages, from which (36) species have identified.
 Three biozones are postulated based on the above studied assemblages, in order of biozones: Tranolithus phacelosus biozone; Reinhardites levis biozone; Arkhangelskiella cymbiformis biozone. From a regional perspective, these biozones were connected with other calcareous nannofossils biozones, leading to the conclusion that the section is Late Campanian-Maastrichtian in age.

Early Cretaceous climate in North Africa: Insights from the calcareous nannofossils in the atlantic passive margin of Morocco

The Early Cretaceous was a time of marked changes in global climate and carbon cycle. To reconstruct the paleoclimate in North Africa, four well-dated stratigraphic sections in the Atlantic passive margin of Morocco (Essaouira-Agadir Basin) were investigated. Calcareous nannofossil assemblages were used as indicators for medium-term climatic fluctuations. The spatiotemporal changes of key taxa, nannofossil assemblages, and the Temperature and Nutrient Indices (TI and NI) were used to reconstruct the paleoclimate. Nonmetric Multidimensional Scaling and permutational analysis of variance (PERMANOVA) indicated that only early Albian assemblage was significantly different from Barremian and Aptian ones. A steady but gradual decrease in sea surface temperature and increase in nutrients and diversity from the Barremian to the early Albian was observed. The opening of the Atlantic Ocean between Africa and South America has allowed the intrusion of cold waters and higher latitudinal taxa, where warm oligotrophic Aptian times were followed by a cool eutrophic condition in the Albian. The sea-level highstand in the Early Albian may have increased water circulation and intrusion of the upwelling induced, nutrients-rich cold-water, where surface water fertility increased significantly. Consequently, nannofossil diversity increased.

Late Tithonian nannofossils from Dejen area, the Blue Nile Basin, central western Ethiopia

The Jurassic rocks exposed in the Blue Nile Basin (central western Ethiopia), particularly the thick, fossiliferous and widely distributed Antalo Limestone Formation (ALF) has recently been dated between early Callovian and late Tithonian based on the occurrence of calcareous nannofossils from the Mugher section near Dejen, Ethiopia. However, the top part of the ALF is not well exposed at Mugher; in this study, the top part of the ALF was sampled at the Kurar section (150 km north of Mugher). It yielded a nannofossil assemblage containing Helenea chiastia, whose first occurrence (FO) marks the base of the Tithonian NJT16a calcareous nannofossil subzone, and Faviconus multicolumnatus, whose FO is near the base of the NJ15b subzone and corresponds with the FO of the Tithonian zonal marker Polycostella beckmannii recorded at the Mugher section. This age is also corroborated by the presence of recently recorded calpionellids (Bonetinae subzone) and the presence of late Tithonian ammonites, Djurjuriceras cf. sinuosum Tavera and Oxylenticeras Spath from the Kurar section. Hence, the upper part of the ALF exposed at the Kurar and Mugher sections are of late Tithonian age, although at the Mertule Mariam section (60 km northwest of the Kurar section), late Berriasian calpionellids were recently found from the top part of the ALF.

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

Early Jurassic coccolith diversification and response to pre-Toarcian environmental changes: A perspective from the Paris Basin

The early Jurassic saw large fluctuations in global temperature, sea-level and bottom-water oxic conditions prior to the Toarcian-Oceanic Anoxic Event (T-OAE), in several oceanic basins of NW Europe. Links between such changes, ocean nutrient concentrations and progressively increasing abundance and diversity of calcareous nannoplankton remain unclear. We have investigated the early Jurassic nannofossil assemblages of the Paris Basin across the mid-Sinemurian to lowermost Toarcian. Comparisons to geochemical proxy data let us decipher evolutionary trends from paleoenvironmental responses, test paleoecological affinities of coccolith species and improve our understanding of paleoenvironmental changes. Despite a strong evolutionary trajectory of the coccolith assemblages, multivariate analyses allowed to identify taxa indicating cold (Parhabdolithus, Crucirhabdus, Crepidolithus pliensbachensis), open ocean (Mitrolithus elegans, Mitrolithus lenticularis, Crepidolithus crassus sensu lato, Crepidolithus granulatus (both variants), Crepidolithus crucifer) and high fertility conditions (placoliths: Bussonius, Lotharingius, Similiscutum novum, Similiscutum finchii). Our data support that: (1) stable cool conditions persisted through the Upper Sinemurian, (2) progressive warming and high sea-levels onsetting across the Sinemurian/Pliensbachian transition, persisting to the lower margaritatus ammonite zone (AZ) may have favored the evolution of placoliths, (3) a first significant increase in abundance of placoliths was triggered in the stokesi ammonite subzone (ASz) by elevated fertility levels which preceded immediately the late Pliensbachian organic matter preservation interval (OMPI), (4) the OMPI and remaining subnodosus ASz were characterized by warm temperatures but low fertility surface waters, (5) another large increase in abundance of placoliths suggests again higher fertility levels across the uppermost margaritatus AZ, spinatum cold event and lowermost Toarcian.

Calcareous nannofossils of the late Eocene to early Oligocene from the Pabdeh and Asmari transition in Dezful Embayment (southwestern Iran): Evidence of a climate cooling event

Calcareous nannofossil assemblages have been investigated in the uppermost Eocene to the lowest Oligocene in the Marun oil field in the Dezful Embayment (south‐west Iran). The studied interval includes shales, marlstones and limestones. Seventeen genera and 35 species of calcareous nannofossils have been determined. Regarding the succession of nannofossil bioevents, the studied interval ranges from the late Eocene (Priabonian, CNE18 Zone or NP18 Zone) to the early Oligocene (Rupelian, CNO2 Zone, or NP22 Zone). A high relative abundance of warm water taxa (such as Sphenolithus spp., Discoaster spp. and Helicosphaera spp.) is recorded in the late Eocene, while towards the Eocene–Oligocene boundary (EOB), an increase in the relative abundance of cool and temperate taxa (such as Reticulofenestra spp., Cyclicargolithus floridanus, Dictyococcites bisecta and Markalius inversus) is identified. A marked decrease in the abundance of warm water taxa along with a decrease in species diversity indicates that the cooling event at the EOB in the Marun oil field in Iran is similar to other parts of the world (Tethys realm).

Calcareous nannofossil biostratigraphy and paleogeographic significance in the lower Maastrichtian of the Miechów Trough (southern Poland)

Biostratigraphic analysis of calcareous nannofossils from the Pełczyska section in the Miechów Trough (southern Poland) has revealed that the entire section covers the lowermost Maastrichtian. The UC16bTP Tethyan subzone is designated based on the presence of Broinsonia parca constricta Hattner, Wind and Wise, 1980, reworked remains of Uniplanarius trifidus (Stradner) Hattner and Wise in Wind and Wise, 1983 and the simultaneous lack of Eiffellithus eximius (Stover) Perch-Nielsen, 1968. The studied section spans also the interval between the LO of Zeugrhabdotus praesigmoides Burnett, 1997 and the FO of Prediscosphaera mgayae Lees, 2007 (UC16 S3 Boreal subzone). Quantitative analysis of nannofossil assemblages has shown the dominance of cold water species (up to 50%), e.g., Micula decussata Vekshina, 1959, Prediscosphaera spp., Arkhangelskiella spp., Calculites obscurus (Deflandre) Prins and Sissingh in Sissingh, 1977 and Lucianorhabdus cayeuxii Deflandre, 1959. In the early Maastrichtian, the studied area was more influenced by cool water masses from the Boreal Province rather than by warm water from the Tethyan Province. The significant predominance of cold water taxa and the elevated presence of Prediscosphaera cretacea (Arkhangelsky) Gartner, 1968 also supports the hypothesis of climate cooling in the early Maastrichtian.

Paleoenvironmental changes recorded at a late Maastrichtian marine succession of northern South America

One of the major environmental and biotic turnovers of the Phanerozoic occurred at the Cretaceous-Paleogene (K-Pg) boundary, being the focus of countless scientific studies that addressed the timing, causes and consequences of this global event. Paleoenvironmental conditions that preceded the K-Pg boundary, however, have been less studied, especially at low latitudes. In order to help reconstructing late Maastrichtian marine environments along the equatorial South American margin, we apply micropaleontological and geochemical techniques to a stratigraphic core that recovered the Colón Formation in northern Colombia. Low abundance foraminiferal assemblages were overall dominated by benthic taxa (Maastrichtian local biozones Siphogenerinoides bramletti and Ammobaculites colombiana), and the planktonic species Guembelitria cretacea. Ostracod assemblages were mainly composed of the genera Veenia, Cytherella, Paracypris, and Cythereis. Calcareous nannofossils were typical of Upper Cretaceous low-latitude successions, with low abundance and diversity assemblages dominated by Micula staurophora, Kamptnerius magnificus and Cervisiella operculata. Sediment elemental ratios (Zr/Rb, Fe/Ca and Sr/Ba), as well foraminiferal, ostracod and nannofossils assemblages, indicate a shallowing upward trend, characterized by a transition from inner platform settings to sublittoral conditions. Input of terrigenous sediments and weathering intensity also increased upward in the section, probably related to the uplift pulses of the Andean orogeny. Proportions of benthic infauna, as well the V/Cr ratio and the distribution of redox-sensitive trace metals (Ni, Cu) along the core, mostly indicate suboxic bottom water conditions in the Colón Formation.

High-amplitude water-level fluctuations at the end of the Mediterranean Messinian Salinity Crisis: Implications for gypsum formation, connectivity and global climate

The formation and dissolution of salt giants impacts ocean chemistry on thousand-million year timescales. Gypsum precipitation and weathering changes the oceanic calcium concentration with implications for the carbon cycle and global temperatures. However, the connectivity of salt giants with the global ocean is necessarily restricted, making the timing of Ca2+ extraction and return more uncertain. Here we reconstruct the final phase of gypsum precipitation of the Late Miocene Mediterranean Salt Giant using micropaleontology, sedimentology and 87Sr/86Sr analyses on the most complete record preserved at Eraclea Minoa on Sicily and explore its implications for global climate. Precessional gypsum-marl couplets (Upper Gypsum) characterize the last 200 kyrs (Stage 3) of the Messinian Salinity Crisis (MSC; 5.97–5.332 Ma) in both intermediate (500–1000 m) and deep (>1000 m) Mediterranean basins. The interbedded selenitic gypsum layers contain well-preserved calcareous nannofossil assemblages dominated by Reticulofenestra minuta, a marine species which tolerates stressful conditions. Marine water is also required to explain the gypsum 87Sr/86Sr data, which describe a small range of ratios (0.708704–0.708813) lower than coeval ocean water. Mass-balance calculations indicate that during gypsum precipitation, the Atlantic made up ≤20% of a Mediterranean (“Lago-Mare”) water mass dominated by low salinity discharge from large river systems and Eastern Paratethys. This suggests episodic extraction of calcium and sulfate ions from the ocean throughout MSC Stage 3. The marls commonly contain shallow (30–100 m) brackish-water ostracods of Paratethyan (Black Sea) origin. Marls with Paratethyan ostracods are also found in both marginal (<500 m) and deep Mediterranean settings. This indicates that marl-deposition was not synchronous across the basin, but that it occurred in intermediate and deep basins during base-level lowstands at insolation minima and on the shallow Mediterranean margins during insolation maxima-driven highstands. These high-amplitude base-level fluctuations exposed the evaporites to weathering, but ponded the products in the Mediterranean basin until reconnection occurred at the beginning of the Pliocene.