An asteroid impact at the end of the Cretaceous caused mass extinction, but extinction mechanisms are not well-understood. The collapse of sea surface to sea floor carbon isotope gradients has been ...interpreted as reflecting a global collapse of primary productivity (Strangelove Ocean) or export productivity (Living Ocean), which caused mass extinction higher in the marine food chain. Phytoplankton-dependent benthic foraminifera on the deep-sea floor, however, did not suffer significant extinction, suggesting that export productivity persisted at a level sufficient to support their populations. We compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the Pacific, Southeast Atlantic, and Southern Oceans. We conclude that end-Cretaceous decrease in export productivity was moderate, regional, and insufficient to explain marine mass extinction. A transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites, and recovery of productivity may have been as fast in the oceans as on land.
Mass extinction at the Cretaceous–Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, ...empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we document a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as amechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth system modeling, indicate that a partial ∼50% reduction in global marine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario reconciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which marine life imprints its isotopic signal onto the geological record.
We investigated the response of late Paleocene‐middle Eocene (~60–37.5 Ma) benthic foraminiferal assemblages to long‐term climate change and hyperthermal events including the Paleocene‐Eocene Thermal ...Maximum (PETM) at Ocean Drilling Program (ODP) Site 865 on Allison Guyot, a seamount in the Mid‐Pacific Mountains. Seamounts are isolated deep‐sea environments where enhanced current systems interrupt bentho‐pelagic coupling, and fossil assemblages from such settings have been little evaluated. Assemblages at Site 865 are diverse and dominated by cylindrical calcareous taxa with complex apertures, an extinct group which probably lived infaunally. Dominance of an infaunal morphogroup is unexpected in a highly oligotrophic setting, but these forms may have been shallow infaunal suspension feeders, which were ecologically successful on the current‐swept seamount. The magnitude of the PETM extinction at Site 865 was similar to other sites globally, but lower diversity postextinction faunas at this location were affected by ocean acidification as well as changes in current regime, which might have led to increased nutrient supply through trophic focusing. A minor hyperthermal saw less severe effects of changes in current regime, with no evidence for carbonate dissolution. Although the relative abundance of infaunal benthic foraminifera has been used as a proxy for surface productivity through bentho‐pelagic coupling, we argue that this proxy can be used only in the absence of changes in carbonate saturation and current‐driven biophysical linking.
Key Points
Seamount assemblages dominated by shallow infaunal suspension feeders
Post‐PETM faunas affected by ocean acidification and changes in current regime
PETM and ETM3 associated with increased food supply through trophic focusing
The early Eocene greenhouse world was marked by multiple transient hyperthermal events. The most extreme was the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), linked to the extinction of the ...globally recognised deep-sea benthic foraminiferal Velasco fauna, which led to the development of early Eocene assemblages. This turnover has been studied at high resolution, but faunal development into the later early Eocene is poorly documented. There is no widely accepted early Eocene equivalent of the Late Cretaceous-Paleocene Velasco fauna, mainly due to the use of different taxonomic concepts. We compiled Ypresian benthic foraminiferal data from 17 middle bathyal-lower abyssal ocean drilling sites in the Pacific, Atlantic and Indian Oceans, in order to characterise early Eocene deep-sea faunas by comparing assemblages across space, paleodepth and time. Nuttallides truempyi, Oridorsalis umbonatus, Bulimina trinitatensis, the Bulimina simplex group, the Anomalinoides spissiformis group, pleurostomellids, uniserial lagenids, stilostomellids and lenticulinids were ubiquitous during the early Eocene (lower-middle Ypresian). Aragonia aragonensis, the Globocassidulina subglobosa group, the Cibicidoides eocaenus group and polymorphinids became ubiquitous during the middle Ypresian. The most abundant early Ypresian taxa were tolerant to stressed or disturbed environments, either by opportunistic behavior (Quadrimorphina profunda, Tappanina selmensis, Siphogenerinoides brevispinosa) and/or the ability to calcify in carbonate-corrosive waters (N. truempyi). Nuttallides truempyi, T. selmensis and other buliminids (Bolivinoides cf. decoratus group, Bulimina virginiana) were markedly abundant during the middle Ypresian. Contrary to the long-lived, highly diverse and equitable Velasco fauna, common and abundant taxa reflect highly perturbed assemblages through the earliest Ypresian, with lower diversity and equitability following the PETM extinction. In contrast, the middle Ypresian assemblages may indicate a recovering fauna, though to some extent persistently disturbed by the lower-amplitude Eocene hyperthermals (e.g., Eocene Thermal Maximum 2 and 3). We propose the name 'Walvis Ridge fauna' for future reference to these Ypresian deep-sea benthic foraminiferal assemblages.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The response of the Earth system to greenhouse-gas-driven warming is of
critical importance for the future trajectory of our planetary environment.
Hyperthermal events – past climate transients with ...global-scale warming
significantly above background climate variability – can provide insights
into the nature and magnitude of these responses. The largest hyperthermal of
the Cenozoic was the Paleocene–Eocene Thermal Maximum (PETM ∼ 56 Ma).
Here we present new high-resolution bulk sediment stable isotope and major
element data for the classic PETM section at Zumaia, Spain. With these data we
provide a new detailed stratigraphic correlation to other key deep-ocean and
terrestrial PETM reference sections. With this new correlation and age model
we are able to demonstrate that detrital sediment accumulation rates within
the Zumaia continental margin section increased more than 4-fold during
the PETM, representing a radical change in regional hydrology that drove
dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is
that detrital accumulation rates remain high throughout the body of the PETM,
and even reach peak values during the recovery phase of the characteristic
PETM carbon isotope excursion (CIE). Using a series of Earth system model
inversions, driven by the new Zumaia carbon isotope record, we demonstrate
that the silicate weathering feedback alone is insufficient to recover the
PETM CIE, and that active organic carbon burial is required to match the
observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic
carbon sequestration coincides with the peak in detrital accumulation rates
observed at Zumaia. Based on these results, we hypothesise that orbital-scale
variations in subtropical hydro-climates, and their subsequent impact on
sediment dynamics, may contribute to the rapid climate and CIE recovery from
peak-PETM conditions.
Open marine sediments deposited during the Cenomanian–Turonian transition are well exposed in the Spanish Baños de la Hedionda section (Betic Cordillera, South Iberian Palaeomargin). Analysis of ...foraminiferal assemblages and geochemical proxies allow inferences on the impact of the Oceanic Anoxic Event 2 (OAE2) in this area of the western Tethys. Three main intervals have been identified corresponding to different lithological units and biozones. (1) The top of the Capas Blancas Member (Rotalipora cushmani Biozone) represents the pre-extinction phase with diverse foraminiferal assemblages and well developed water-column tiering, well-oxygenated, oligotrophic deep-waters and oxygenated to poorly oxygenated, mesotrophic surface-waters. Foraminiferal opportunist species point to a minor event with dysoxic conditions preceding the OAE2. (2) The black radiolaritic shales (Whiteinella archaeocretacea Biozone) consist of a foraminiferal-barren interval, except for the lowermost centimetres where planktic surface-dweller opportunists are common. Redox sensitive elements (Cr/Al, V/Al, U/Th, MoEF, Moaut, UEF and Uaut) and increased TOC values reflect oxygen depleted conditions related to the OAE2. The increase in P/Ti values at the base of this stratigraphic interval indicates an abrupt increase in productivity. High concentrations of radiolarians are congruent with high surface productivity probably related to changes in oceanic circulation and enhanced upwelling currents, as well as subsequent shallowing of the oxygen-minimum zone. The increase in MoEF and Moaut towards the top of the black radiolaritic shales indicates temporal euxinic conditions. (3) A slow, bottom-up recovery of foraminiferal assemblages is inferred at the base of the Boquerón Member (Helvetoglobotruncana helvetica Biozone), with seafloor recolonization by benthic foraminifera being recorded previous to the water column colonization by planktic forms, mainly by intermediate-dwellers typical of mesotrophic waters. The subsequent proliferation of surface-dweller opportunists and deep-dweller opportunists adapted to mesotrophic to eutrophic conditions, and the decrease in planktic foraminiferal diversity, may indicate the persistence of poorly oxygenated conditions in the water column towards the lower-middle part of the H. helvetica Biozone.
Geoconservation and geoethics are two emergent domains in geosciences. During the last decade, both topics have increasingly gained the attention of geoscientists and the society, but the main ...geoethical dilemmas related to the conservation and management of geoheritage are not clearly identified yet. This work aims at providing an overview on the meaning and scope of geoethics and how it intersects geoheritage and the practice of geoconservation. Some case studies
—
many of which are under current debate and have a high potential as geoeducational resources
—
are presented for addressing ethical, social and cultural settings as well as dilemmas affecting geoheritage. We find that there are particular cases (mostly concerning the trade of fossils, and in particular the growing concern about activities that rely on amber from Myanmar) for which a clear dichotomy of views makes them much more problematic and complex. These cases deserve more suitable legal frameworks that help implement more balanced ethical standards and practice guidelines for geoconservation, guarantee human rights and needs in relation to that heritage and contribute to the advancement of geosciences. Particular attention is given to palaeontological heritage, as fossils are among the most threatened elements of the Earth’s diversity and are in need of more effective and statutory protection measures. In the context of geoethics applied to palaeontological heritage, and given the need of a clear understanding of what ethics in palaeontology means, a new concept
—palaeontoethics—
is proposed and formally defined.
The Latest Danian Event (LDE) or Top Chron C27n hyperthermal event has been identified in the Caravaca section (Southern Spain) by means of calcareous nannofossil biozones (Subzone NTp7b) and the ...recognition of a prominent, negative ~0.6 per mille carbon isotope excursion measured in benthic foraminiferal tests. This is the first time that this Danian hyperthermal event has been identified in a deep-water, middle to lower bathyal setting from the Western Tethyan realm.
The analysis of benthic foraminiferal assemblages shows gradual changes in the assemblages prior to the onset of the LDE and an increase in food supply to the seafloor during the LDE, in agreement with results from shallower Southern Tethyan settings. The benthic assemblage changes across the LDE at Caravaca share some characteristics with other hyperthermal events, including the negative carbon isotope excursion, the increased abundance of buliminids, or the common occurrence of A. aragonensis, an opportunistic species that proliferated during other Paleogene hyperthermal events. In addition, the increased abundance of Nuttallides truempyi, a dissolution-resistant form that thrived during the Paleocene Eocene Thermal Maximum, and the abundance of calcareous infaunal morphogroups, which calcify in less carbonate-undersaturated pore waters, indicate slightly CaCO3-corrosive bottom waters during the LDE.
Turnover of calcareous plankton across the LDE is similar to other sites globally distributed, including the evolution of photosymbiotic foraminiferal lineages and the radiation of the nannofossil “fasciculiths group”. The occurrence of innovative morphostructures (Diantholitha and Lithoptychius) towards the base of the LDE may indicate a more efficient biological pump. This hypothesis is supported by increased percentages of benthic infaunal morphogroups and a decrease in the abundance of oligotrophic species.
A reworked interval has been identified immediately above the LDE. Higher up in the section, benthic and planktic assemblages from the post-LDE interval point to the recovery of the environmental conditions, including a decrease in the food supply to the seafloor.
•The Latest Danian Event is identified for the first time in the Western Tethys.•Benthic foraminiferal turnover is similar to that recorded across other hyperthermals.•Turnover of calcareous plankton is similar to other sites globally distributed.•Innovative morphostructures of nannofossils indicate a more efficient biological pump.•Slightly CaCO3-corrosive bottom waters and higher food flux during the LDE.
We studied Upper Cretaceous and Lower Paleogene benthic foraminifera from the Agost section (southeastern Spain) to infer paleobathymetrical changes and paleoenvironmental turnover across the ...Cretaceous/Paleogene (K/P) transition. Benthic foraminifera indicate uppermost bathyal depths at Agost during the
Abathomphalus mayaroensis Biochron (from about 400 kyr before the K/P boundary) through the early
Plummerita hantkeninoides Biochron (about 120–150 kyr before that boundary). The depth increased to middle bathyal for the remainder of the Cretaceous, and remained so for the Danian part of the studied section (
Parasubbotina pseudobulloides Biochron, at least 200 kyr after the K/P boundary). There were no perceivable bathymetrical changes at the K/P boundary, where ∼5% of the species became extinct, and the species composition of the benthic foraminiferal fauna changed considerably. Below the boundary, infaunal morphogroups constitute up to 65–73% of the faunas. Directly above the boundary, in the black clays of the lower
Guembelitria cretacea Biozone, benthic foraminifera are rare. Several opportunistic taxa (e.g. the agglutinant
Haplophragmoides sp.) have short peaks in relative abundance, possibly reflecting low-oxygen conditions as well as environmental instability, with benthos receiving food from short-lived, local blooms of primary producers. Above the clays through the end of the studied interval, epifaunal morphogroups dominate (up to 70% of the assemblages) or there is an even mixture or epifaunal and infaunal morphogroups. Infaunal groups do not recover to pre-extinction relative abundances, indicating that the food supply to the benthos did not recover fully over the studied interval (about 200 kyr after the K/P boundary). The benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact, which severely destabilized primary producers and the oceanic food web that was dependent upon them.
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