The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative ...importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.
The long‐ranging nannoplankton genus Discoaster went extinct in the early Pleistocene, one of the most significant events in the Cenozoic nannofossil record. The causal factors of this extinction are ...poorly constrained, at least partially because the ecology of Discoaster is not well understood. We investigate the relationship between the extinction and environmental changes by comparing a suite of high‐resolution nannofossil assemblage data at four Ocean Drilling Program sites to published environmental proxy records. Through the use of multivariate analysis, we determine Discoaster shared environmental preferences with the extant species Florisphaera profunda which thrives in the lower photic zone near the nutricline in locations where the water column is stratified. We show that the last occurrence of Discoaster was globally diachronous, rather than synchronous as previously thought, and likely took place in the equatorial Atlantic Ocean. We propose that the demise of Discoaster was a two‐stage process. A decrease in sea surface temperatures and increase in climate variability led to a global decline in Discoaster abundance. The extinction event itself correlates to shoaling of the nutricline as signified by a decrease in the carbon isotopic gradient between surface and thermocline foraminifera. We hypothesize that the combination of global cooling and a shoaling of the nutricline greatly reduced Discoaster's deepwater niche and contributed to its extinction. This may suggest that ocean stratification and the depth of the nutricline are important contributors to overall nannoplankton diversity.
Key Points
Final species of Discoaster preferred a deep habitat close to the nutricline
Discoaster declined with cooling; extinction related to shoaling of nutricline
The extinction of Discoaster was globally diachronous
The earliest Paleocene record of calcareous nannoplankton presents a unique opportunity to understand the evolutionary recovery of life from mass extinction. Nannoplankton were devastated at the ...Cretaceous/Paleogene boundary and their subsequent recovery can be studied in great detail because of their abundance in sediments, continuous stratigraphic occurrence, and near global distribution. Here we determine when and where new species of nannoplankton originated and how they dispersed following the Cretaceous/Paleogene mass extinction. Initially, we focus our efforts on North Pacific and South Atlantic deep sea sites with orbital age control to compare the precise timing and dynamics of the recovery between the locations. We then broaden our investigation to six sites from different basins and a variety of environments to study global patterns of the initial recovery. Our results show that many taxa in key Paleogene lineages originated in the North Pacific Ocean and that assemblages comprised primarily of new Paleogene taxa were not observed at other sites for several hundred thousand years. Survivors that were adapted to eutrophic post extinction conditions rapidly expanded in Southern Hemisphere sites where they dominated assemblages for most of the initial recovery. We therefore hypothesize that groups of survivors formed regionally incumbent assemblages in the Southern Hemisphere that limited diversification and dispersal of new Paleogene taxa. The end of survivor dominance correlates to the recovery of the biologic pump and subsequent decrease in surface ocean nutrient concentration 300–400 Kyr after the boundary. Only after survivors were removed did new Paleogene nannoplankton assemblages become abundant globally. Our results indicate that competition from regionally incumbent survivors was as an important control on the K/Pg recovery of nannoplankton.
Phytoplankton assemblages in shallow marine environments are being impacted by anthropogenic climate change, but long-term outcomes of these changes are uncertain. Investigation of past neritic ...calcareous nannoplankton can help us understand the fate these ecosystems face. In this study, a Canonical Correspondence Analysis (CCA) of calcareous nannofossils and X-ray fluorescence geochemistry was used to determine how past planktonic ecosystems were influenced by paleoenvironmental parameters on the eastern side of the Late Cretaceous Western Interior Seaway in the Cenomanian (ca. 95–93 Ma). Samples were collected every 10 cm from the Graneros Shale Greenhorn Formation at an outcrop in northwestern Iowa to determine high resolution changes in assemblages and paleoenvironments. Nannofossil diversity outside of a few small intervals ranges is high (generally 30–60 species) with abundant small Biscutum constans, confirming other publications that show elevated diversity in Cretaceous nearshore settings. The CCA results imply assemblages were most influenced by terrigenous influence, wet vs. dry climate, and changes in water mass source. Cretaceous nannofossil paleoecology was also revised based on the CCA results. Size differentiation of nannofossil taxa may highlight more complexity in environmental preferences that have been largely overlooked. After the initial transgression of the Greenhorn Sea into the region, the climate became wetter and terrigenous influence in the area was high. The peak of terrigenous influence corresponds with elevated nannofossil diversity but a lack of microfauna, which may indicate a similar oceanographic setting to the modern Gulf of Mexico nearshore dead zone. As sea level continued to rise above this point, nannoplankton assemblages indicate a potential shift to a higher productivity, stratified water column. As the muddy Graneros Shale transitioned to a further offshore chalky Greenhorn Formation, a normal marine, cosmopolitan nannofloral assemblage became established. Nannofossil and geochemical evidence indicates high productivity from upwelling might be related to the change of deposition to chalk in the Greenhorn Formation. While only a single outcrop was investigated, the novel use of an integrated micropaleontological and geochemical analysis has shed light on the dynamics of how phytoplankton ecosystems were established and modified in shallow marine environments of the Cretaceous and could have important implications on modern shallow marine settings.
Display omitted
•Cenomanian nannofossils and geochemistry from the northwestern Iowa were investigated.•Multivariate statistical analysis revised nannofossil paleoecology.•Terrigenous influence, climate, and water mass controlled assemblages.•Evidence suggests development of a nearshore dead zone like environment.•Diversity was high, and communities were divided by depth and sediment tolerance.
Accurate interpretation of origination and extinction of fossil species is crucial to answering a variety of questions in paleontology. Fossil datums, the observed age of first or last occurrences, ...are subject to sampling error as a result of preservation and low abundances near range endpoints. This sampling error can cause local range offset, an age difference between the observed first or last occurrence of a species and its true origination or extinction. Here, we develop and test a new technique, the Probable Datum Method (PDM), that can be used to assess the extent of local range offset for nannofossil species. The PDM estimates the original abundance of a taxon and its probable true age of first or last occurrence. The PDM uses a model in which original abundance is related to count abundance through preservation and the counting process. This model is empirically parameterized, including an experimental determination of false positive and error rates of a nannofossil count. The model is simulated then inverted to estimate likely original abundance and true datum age from count abundance data. We first test the PDM in a positive control experiment with known parameter values. This experiment shows that the PDM is robust and returns known values accurately. Next we apply the method to the origination of nannoplankton after the Cretaceous/Paleogene boundary to test whether first occurrences were synchronous between widely spaced locations. The PDM results suggest that observed diachrony of K/Pg originations cannot be explained by the effects of local range offset; rather, in some cases they indicate truly diachronous first occurrences between localities. Although the technique was developed to analyze nannoplankton ranges, the statistical nature of the PDM, its experimentally derived parameters, and its parsimonious nature should make it applicable to many micropaleontological studies that interpret patterns of origination and extinction.
Nannofossils of the North American Late Cretaceous Western Interior Seaway have been extensively studied, but these investigations have primarily focused on the diverse communities of the Niobrara ...and Greenhorn sea-level highstands. We lack a firm understanding of the nature of early nannofossil communities from the initial stages of the transgression, and of how the diverse assemblages of the Coniacian–Santonian became established. We investigated nannofossils in a core from the San Juan Basin, New Mexico, with concentrated sampling across this transgression. We then compared nannofossil assemblages from the initial transgression of the seaway to the more established, cosmopolitan assemblages of the Niobrara highstand. The initial stages of transgression were characterized by unusual, low-diversity assemblages dominated by holococcoliths and seldom reported and previously undescribed species of hetero- and holococcoliths. Herein, we describe five new species and one new genus from these assemblages: Ahmuellerella frankiae sp. nov., Gartnerago waszczakii sp. nov., Orastrum schollei sp. nov., Pharus clarescopoli sp. nov., and Wisea sanjuanensis gen. et sp. nov. These initial assemblages transitioned to more cosmopolitan, higher-diversity assemblages, coincident with an unconformity that likely represents subaqueous erosion or prolonged non-deposition. Above this unconformity, the nannoplankton were abundant, diverse, and characterized by open-marine, cosmopolitan taxa that persisted through the Coniacian and Santonian. X-ray fluorescence data collected from the core show a high abundance of the detrital elements Al and Ti in the section, indicating substantial detrital clay input into the area, coincident with deposition of the holococcolith-dominated assemblages. The detrital influence lessened as cosmopolitan nannoplankton became more abundant in the area. We suggest that the initial holococcolith-rich assemblages are representative of a shallow-marine, potentially hyposaline, turbid or unstable environment. Such assemblages have been observed from the Late Turonian elsewhere in northern New Mexico and may represent typical pioneer nannofloras of the Late Cretaceous Western Interior marine transgressions. Our integrated investigation of nannofossils and X-ray fluorescence geochemistry adds to the meager knowledge base of pioneer nannofloral communities in the initial phases of continental marine transgression.
•The San Juan Basin core used in this study contains unique nannofloral assemblages of Late Turonian age.•Holococcoliths dominated the nannofloras during the initial transgression of the Niobrara Seaway.•These opportunistic pioneer assemblages were adapted to neritic environments.•The transition to cosmopolitan, open-ocean nannofloral assemblages was observed.•This transition corresponded to a decline in detrital sedimentation in the area.
Marine ecosystems are facing dire consequences from anthropogenic climate change. However, the long-term impacts on marine phytoplankton are uncertain, especially concerning extinction risk and how ...communities will recover when faced with large-scale extinction. Calcareous nannoplankton, an important group of eukaryotic phytoplankton, are especially at risk given their sensitivity to changes in environmental conditions and susceptibility to ocean acidification. Nannoplankton have an extensive and detailed fossil record dating to the Mesozoic and can be used to investigate how phytoplankton have responded to past environmental and ecological perturbations. This focuses on the fossil record of nannoplankton to understand the relationship between climate change and nannoplankton extinction and how nannoplankton communities recover following mass extinction. (Abstract shortened by ProQuest.)
Recurrent Primary Intrasellar Paraganglioma Schueth, Elizabeth A.; Martinez, Daniel C.; Kulwin, Charles G. ...
Case reports in otolaryngology,
07/2020, Letnik:
2020
Journal Article
Recenzirano
Odprti dostop
We describe a case of an 81-year-old male presenting with bitemporal visual field defects and blurry vision in the right eye. The patient was found to have a recurrent primary paraganglioma in the ...sellar and suprasellar region requiring a repeat transsphenoidal endoscopic resection. Immunohistochemical examination confirmed paraganglioma with the classic zellballen appearance which stained positive for chromogranin, synaptophysin, and S-100 in the periphery. Paragangliomas (PGLs) in the sella turcica are a rare entity; only 19 cases have ever been reported in the literature. PGLs in the sellar region are often misdiagnosed or diagnosed in a delayed fashion. Earlier diagnosis of this locally aggressive tumor and meticulous debulking can prevent morbidity secondary to the tumor’s compressive effects. This report highlights the effectiveness of surgical interventions in treatment of paragangliomas. More research is still needed to determine the need for adjuvant therapies such as radiation.
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