This paper presents the first study of nonmarine ostracods recovered from the Danian of the upper Yacoraite Formation (Balbuena IV sequence) Salta Basin. Six species were identified: Ilyocypris ...triebeli, Ilyocypris argentiniensis, Neuquenocypris (Alleniella)? sp. 1; Neuquenocypris (Alleniella)? sp. 2; Penthesilenula sp. and four indeterminate species. The ostracod fauna shows fluctuations in abundance, diversity, and preservation associated with different phases of the paleolake evolution. This distribution, clearly delineated by the depositional facies, corroborates previous geochemical analyses and high-resolution sequence stratigraphy developed for the section. In general, the most abundant occurrences of ostracods coincide with high-frequency transgressive tracts of the lake system, which form long-term wettest interval of the upper Yacoraite Formation.
•First study with ostracods for the Balbuena IV sequence of the Yacoraite Formation, Salta Basin, Argentina.•Six nonmarine ostracods species are identified.•Temporal distribution of ostracods is in agreement with U/Pb radiometric dating.•Ostracod abundance is correlated with the climatic fluctuations of the dry and wet periods of the paleolake.
The planktic foraminifera from two sedimentary sequences of the Upper Cretaceous recovered by the Deep Sea Drilling Project (DSDP) Leg 80, Site 549 and Site 550 (Hole 550B) in the Goban Spur region ...were analysed in order to refine and integrate the zonal schemes for this area of the North Atlantic Ocean. In the studied intervals, 75 samples were analysed, and 88 species of planktic foraminifera were recognized, enabling the identification of the following biostratigraphic zones: Rotalipora cushmani (upper Cenomanian); Helvetoglobotruncana helvetica (lower Turonian); Dicarinella concavata (upper Turonian–Coniacian); Dicarinella asymetrica (upper Coniacian–Santonian); Racemiguembelina fructicosa and Abathomphalus mayaroensis (upper Maastrichtian). Two intervals in Hole 550B are likely correlative to composite biozones Pseudoguembelina palpebra/Gansserina gansseri (Campanian–Maastrichtian) and Racemiguembelina fructicosa/Abathomphalus mayaroensis (upper Maastrichtian). These zones indicate that the studied intervals were deposited from the late Cenomanian to the late Maastrichtian. The presence of high values (>6.6%) of Total Organic Carbon (TOC) in section 549-27-1 might be related to the Oceanic Anoxic Event 2 (OAE 2), globally recorded across the Cenomanian–Turonian boundary transition. The extinction of the Rotaliporidae family was observed in both sections and was associated with the onset of OAE2 in Site 549.
•Recovery of planktonic foraminifera in the Cenomanian-Maastrichtian interval of Goban Spur, with eight biozones having been recognized.•Variations in the planktonic foraminifera assemblages related to taphonomic processes.•Faunal crisis during the Cenomanian/Turonian transition.•Elevated values of TOC (6.6%) in the Cenomanian/Turonian transition associated to a Global Anoxic Event (OAE 2).
Micropaleontology is crucial branch of Earth Sciences, with a pivotal role in the success of the oil and gas industry over the decades. This sector of paleontology is based on the taxonomical ...description of microfossils, which encompass fossils with size variation from 0.001 mm to 1 m. Normally these microorganisms have a high rate on preservation, thus they are widely accepted as reliable evidence to infer about paleodepositional settings and paleoclimate change. Furthermore, microfossils are critical to understanding the evolution through time, being many of them recognized as index fossil and providing useful biozones to correlation. Since 1950, microfossils have been taxonomically described mainly by stereomicroscopes. However, as the technology progress, traditional ways to study these organisms are challenged and improved by nondestructive three-dimensional imaging techniques, as X-ray tomographic microscopy (SRXTM), three-dimensional X-ray microscopy (3D-XRM), the X-ray computed microtomography (microCT) and X-ray computed nanotomography (nanoCT). Recently, one of the most compelling research areas in micropaleontology is the desire to automatize and enhance the details of systematic classification. Thereby, an increasing number of researches have applied the high-resolution X-ray analysis aiming to improve the morphological, taxonomic and taphonomic examination. Most of them have detailed the enhancement provided by the technique when compared with the standard microscopes, and raised questions about the traditional characters used on the microfossil systematic taxonomy. Nevertheless, even with the surpassing detail on microfossil characterization, the application of microCT has been hampered by the costs and sometimes by the needs of specific computer skill. Thus, this research has evaluated the use of microCT as the technique to classify a random bulk of microfossil (comprising foraminifers, ostracods, radiolarians, gastropods and echinoderms) with no further software treatment. No standard microscope analysis was performed. Despite chemical composition of microfossils, most of the specimens morphology, especially internal structures, have been easily acquired and analyzed. 96% of the microfossils of the dataset were identified at least on genus level. Irrespective of the deepness of detail, when considering the overall taxonomic identification, the microCT seems to be effective as the standard microscope. Nonetheless, when problematic specimens are evaluated, the microCT seems to be a more reliable and practical tool than other methods as Scanning Electron Microscopy. Thus, the technique can be used solo or as a complementary method to the stereomicroscope. Additionally, the high-resolution has the potential to lead to the expected automatized micropaleontology, since they can provide numerous images in several planes. This may create a strong database necessary to machine learning and computer identification.
•Random bulk of microfossils are evaluated through microCT.•No further computer treatment on microfossil image.•microCT effective method to microfossil identification.
The Cretaceous-Paleogene (K-Pg) boundary extinction event affected planktic foraminiferal assemblages worldwide in a dramatic way, but deep sea benthic foraminiferal assemblages were not ...significantly impacted. However, possible impacts of massive early Danian volcanic eruptions, such as those related to the Deccan Traps, on benthic foraminiferal assemblages are not yet explored. Here we present geochemical and benthic foraminiferal data across the K-Pg boundary and within the earliest Danian interval at Deep Sea Drilling Project (DSDP) Site 356, located on the São Paulo Plateau, western South Atlantic Ocean. Maastrichtian to Danian benthic foraminiferal assemblages are well-preserved and suggest deposition at middle to lower bathyal paleodepths, under an oligotrophic regime with well-oxygenated bottom water conditions. As expected, the K-Pg boundary event did not significantly affect benthic foraminiferal assemblages at Site 356. However, during the early Danian, benthic foraminiferal species richness, heterogeneity, diversity and equitability presented overall opposite trends in relation to the Hg/TOC and Hg/CaCO3 ratios, as well as Hg concentrations, which we consider proxies for intensity of volcanic activity. Our results suggest a possible response of Danian middle to lower bathyal benthic foraminiferal assemblages at Site 356 to changes in bottom water condition possibly associated with massive volcanism eruptions.
•Geochemical characterization Mercury and Hg/TOC and Hg/CaCO3 ratio in deep-marine at Site 356 (São Paulo Plateau).•Benthic foraminiferal assemblages suggest an oligotrophic regime with well-oxygenated bottom water conditions.•Changes in benthic foraminiferal assemblages in bottom water condition possibly associated with massive volcanism eruptions.
Ostracods are common yet understudied prey item in the fossil record. We document drill holes in Paleocene (Danian) ostracods from central Argentina using 9025 specimens representing 66 species. ...While the percentage of drilled specimens at assemblage‐level is only 2.3%, considerable variation exists within species (0.3–25%), suggesting prey preference by the drillers. This preference is not determined by abundance because no significant correlation is found between species abundance and drilling percentages. Seven methods were used, some of which are new, to quantify drilling percentages for the abundant and commonly drilled Togoina argentinensis. The resulting range, from 9.9% to 14.6%, suggests that drilling percentages are fairly insensitive to the method used, implying that comparisons across studies are possible. This information, combined with data from the literature, suggests the Cretaceous–Palaeogene mass extinction may have had a limited effect on drilling intensity in ostracods. The cylindrical (Oichnus simplex) and parabolic (O. paraboloides) drill holes from Argentina may have been caused primarily by naticid and possibly muricid gastropods. Two oval drill holes (O. ovalis) are morphologically similar to octopod drill holes, but their small size, the fact that extant octopods are not known to drill ostracods and the absence of such holes in co‐occurring gastropods, preclude ascription to a predator clade. Drill holes are located preferentially in the median and dorsal regions, where most soft tissue, including the adductor muscle, is located. Drilled specimens are statistically taller than non‐drilled specimens for T. argentinensis and larger predators selected larger ostracods. The drilling percentage does not significantly differ in ornamented ostracods.
The Cerro Azul Section provides a continuous record of the Cretaceous-Paleogene (K-Pg) transition in a shallow marine context of the South Atlantic Ocean in the Neuquén Basin. Ostracod assemblages ...were severely affected by environmental changes across the event. Excellent ostracod preservation at the Cerro Azul Section allows to infer paleoecological preferences of four Danian species based on carbon and oxygen stable isotopes. The studied species were Paracypris bertelsae Ceolin and Whatley, 2015, Cytherella spp., Togoina argentinensis and Henryhowella (Wichmannella) meridionalis (Bertels, 1974). To assess the reliability of ostracod δ13C and δ18O values as paleoenvironmental proxies, we pre-characterized valves with micro x-ray microdiffraction (μXRD) and microRaman (μRaman spectroscopy). Togoina argentinensis and Henryhowella (Wichmannella) meridionalis present in their major calcitic compositions, with small differences of crystallinity within intervals of environmental stress, but no authigenic phases formed during diagenesis. δ13C and δ18O values depict clear interspecific differences between smooth specimens and ornamented specimens. These differences in stable isotope values were likely controlled by microhabitat preferences, which would be comparable with patterns described for benthic foraminifera as well as paleonutrients variations, suing Ba/Ti and P/Ti ratios.
•Exceptional preservation of Danian ostracods to evaluate paleoproductivity.•Valves thickness changed according to paleosalinity.•Kerogen was found in Henryhowella valve.•P/Ti and Ba/Ti associated to δ13C.
The Santa Marta Formation (James Ross Island, Antarctica) presents one of the most complete Santonian-Campanian high-latitude marine records in the Southern Hemisphere. Recent micropaleontological ...studies pointed to an unusual preferential preservation of calcareous microfossils, such as foraminifera and nannofossils, in tuffaceous sandstone levels of the Santa Marta Formation. Here we aim to characterize depositional and early diagenetic conditions that influenced preservation of calcareous microfossils within the succession of the Santa Marta Formation (Alpha Member). We used X-ray fluorescence (FRX)-derived elemental ratios, as well as carbonate (CaCO3), total organic carbon (TOC), and total sulfur (TS) contents to characterize sediment properties, as well as X-ray diffraction (XRD)-derived mineralogical analysis. Elemental ratios suggest hydrothermal influence during diagenesis throughout the stratigraphic succession, as indicated by (Fe + Mn)/Ti values > 20. This interpretation is supported by the occurrence of typical low-temperature hydrothermal minerals, such as garronite and heulandite. Contribution of volcanic ashes in the tuffaceous sandstone levels is evidenced by high values of the log (Zr/Ti) ratio, and the presence of volcanogenic minerals. Since stratigraphic levels characterized by the highest abundances and richnesses of calcareous microfossils also present high log (Zr/Ti) values and CaCO3 contents, we hypothesize that the input and subsequent alteration of volcanogenic material (e.g., ashes) acted as a buffer, increasing porewater alkalinity during early diagenesis. Such a chemical mechanism was already described for modern marine sediments deposited under the influence of significant input of volcanogenic materials, and can explain the preferential preservation of calcareous microfossils in tuffaceous sandstones of the Upper Cretaceous Santa Marta Formation.
•Tuffaceous sandstones of the Santa Marta Fm. are rich in calcareous microfossils.•Volcanic ash input and related diagenetic processes increased porewater alkalinity.•Low temperature hydrothermal activity influenced early diagenesis.
In the present study, the planktonic foraminiferal distribution in a core section representing an interval between the Cretaceous/Paleogene (K/Pg) boundary and the end of the Paleocene ...(Danian/Selandian) from DSDP Site 356 (São Paulo Plateau, South Atlantic) was analyzed. The results point towards a gradual recovery of the marine pelagic ecosystem in the aftermath of the K/Pg mass-extinction event. The changes in distribution patterns and composition of the Danian planktonic foraminiferal assemblages are primarily related to the instability and changing conditions of oceanic surface waters. The quantitative analyses of the planktonic foraminifera showed that a series of speciation events took place in the Danian immediately after the K/Pg boundary, marking three distinct main intervals: (i) in the Pα zone, evidenced by the predominance of specimens that likely inhabited the most superficial portions of the water column (mixed layer), represented mainly by microperforated taxa (Globoconusa, Guembelitria, Parvularugoglobigerina and Woodringina). The occurrence of this group suggests poorly stratified water masses and a water column with meso-eutrophic conditions. In this interval, the first appearance of spines in the planktonic foraminifera (Eoglobigerina, of the family Globigerinidae) evidences the development of a carnivorous habit; (ii) between zones P1a and P2 there is a continuous increase of species that inhabited the lower portion of the water column, in the thermocline and sub-thermocline, suggesting the recovery of the pelagic ecosystem with the development of a more stratified water column in mesotrophic to oligotrophic conditions; (iii) from zone P3 onwards, most of the planktonic foraminifera inhabited the lowest portions of the water column, together with the first occurrences of mixed-layer endosymbiont-bearing species such as Morozovella, Acarinina and Igorina.
•Paleocene planktonic foraminifera were well preserved.•Studied interval shows evolutionary trend of assemblage vs recovery of marine ecosystem.•Diversity and evenness showed a relationship with instability in the water column and after termination of the K/Pg boundary.•Paleocene planktonic foraminiferal evolution reconstructed at Site 356.
The possibility of a collapse (or marked weakening) of the Atlantic Meridional Overturning Circulation (AMOC) within a few centuries boosted the interest of the scientific community on the responses ...of different compartments of the climate system to past AMOC collapses (or marked weakening). The most recent examples of such periods are Heinrich Stadial 1 (HS1,18-15 ka BP; near-collapsed AMOC) and the Younger Dryas (YD, 12.9-11.7 ka BP; markedly weakened AMOC). Here, we present data from elemental ratios, spectral reflectance, organic biomarkers, sea surface temperatures and planktonic foraminiferal assemblage from two marine sediment cores recovered from the western tropical South Atlantic Ocean spanning the last ca. 20 kyr. The recovered sediments record the responses of eastern tropical South American hydroclimate, western tropical South Atlantic productivity and sea surface temperatures to changes in AMOC strength associated with HS1 and the YD. Our data show that both periods were characterized by wetter conditions over eastern tropical South America associated with increased continental runoff compared to the Last Glacial Maximum. High sea surface temperatures during HS1 and the YD are in line with marked AMOC decreases that led to heat accumulation in the surface layer of the western South Atlantic Ocean, facilitating increased precipitation over eastern tropical South America. Our data demonstrate for the first time that intense runoff during HS1, and hence nutrient transfer to the ocean, affected the pelagic ecosystem, likely increasing primary productivity in the otherwise oligotrophic western tropical South Atlantic Ocean. Our study demonstrates a tight coupling between marine and terrestrial processes in the eastern South American realm during periods of strong climate instability.
