Faunal turnover of intermediate-water benthic foraminifera during the Paleogene in New Zealand

Upper abyssal to lower bathyal benthic foraminifera from Ocean Drilling Program Sites 689 (present water depth 2080 m) and 690 (present water depth 2914m) on Maud Rise (Antarctica) recorded changes in deep-water characteristics at high southern latitudes during the Cenozoic. The benthic foraminiferal faunas show only minor differences as a result of the difference in water depths between the sites, and changes in faunal composition were coeval. These changes occurred at the early/late Paleocene boundary (±61.6 Ma), in the latest Paleocene (±57.5 Ma), in the middle early Eocene (±55.0 Ma), in the middle middle Eocene (±46.0 Ma), in the earliest Oligocene (±36.5 Ma) and in the early middle Miocene (±14.5 Ma). The faunal change at the end of the Paleocene was the most important and has been recognized world-wide. On Maud Rise, the diversity decreased by 50% and many common species became extinct over a period of less than 20 000 years. Diversity increased again during the early Eocene, and reached the same values as in the Paleocene by the middle Eocene. In the middle Eocene the diversity started to decrease, and continued to decrease until the middle Miocene. From the beginning of the middle Miocene until today biosiliceous oozes accumulated and calcareous benthic foraminifera were generally absent, with the exception of part of the late Miocene (±8.5–7.5 Ma) and the Quaternary. Changes in composition of the benthic foraminiferal faunas over a wide depth range (upper abyssal-lower bathyal) probably indicate periods of major changes in the formational processes of the deep waters in the oceans. The earliest Eocene faunas, living just after the major extinction at the end of the Paleocene, are characterized by low diversity and high relative abundance of small species that probably migrated downslope into the deep waters. These faunas, and to a lesser degree those in the early middle Eocene, are characterized by high relative abundance of biserial and triserial species. In contrast, older and younger faunas have high relative abundances of spiral species. This suggests that bottom waters on Maud Rise were poor in dissolved oxygen in the latest Paleocene through early middle Eocene, and that the major extinction of benthic foraminifera at the end of the Paleocene might have resulted from a decrease in availability of dissolved oxygen as a result of warming of the deep waters. Warming might have been caused by a change in sources of deep waters, possibly as a result of plate-tectonic activity. The overall decrease in diversity from middle Eocene through Miocene probably reflects continual cooling of the deep waters. Benthic foraminiferal faunas thus indicate that Cenozoic changes in the deep oceanic waters at high latitudes did not consist of gradual progression from Cretaceous circulation to the present-day patterns of formation of deep water: the benthic faunal changes occurred in discrete steps. Benthic faunal composition indicates that deep water most probably formed at high latitudes during the Maastrichtian—early Paleocene, and from the middle Eocene to Recent, with episodes of deep water formation at low latitudes (warm, salty deep water) during the latest Paleocene and early Eocene.

Planktonic foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the late middle Eocene

The early Paleogene is characterized by several warming episodes that are evaluated as analogues to the ongoing climate change. Specifically, we focalize on the Middle Eocene Climatic Optimum (MECO, centered at ~40 Ma) which is one of the major Eocene global warming events, characterized by ~4–6°C warming, shifts in the global carbon cycle and rise in atmospheric pCO2. Even though the MECO is a still enigmatic event, studies on paleobiotic effects across this interval are yet rather limited. We present here new quantitative analysis on planktic and benthic foraminifera to evaluate the impact of the MECO on the investigated biotic groups along the Sealza section (Liguria, NW Italy). This succession is interpreted as the result of a drowning ramp that was affected by continuous tectonic activity and offers the exceptional opportunity to compare the biotic variations across the MECO in shallow-water assemblages with the deep-water communities. The MECO interval at Sealza is constrained by the stable isotope oxygen data and by the occurrence of the species Orbulinoides beckmanni that has a range mostly coincident with the MECO event. Planktic foraminiferal abundance is generally scarce, as expected from a shallow-water succession. The most abundant genus is Subbotina, which however records its lowest abundance within MECO interval. We interpret this record as a response to the MECO warming because this genus is a cold-water index. The genera Acarinina and Morozovelloides show low abundance in the lower part of the section, but they record an increase across the MECO interval, as expected by these warm indices. The most abundant genus among benthic foraminifera that are well preserved and easy recognizable, is the epifaunal? Cibicidoides, adapted to oxygenated conditions. This genus records a marked decrease across the MECO. Similarly, the opportunistic genus Heterolepa shows an increase in abundance across the MECO interval. Another abundant genus is Anomalinoides that is very abundant in the lower part of the section but also displays a decrease across the interval corresponding to the MECO but differently from Cibicidoides, it did not recover in the post-MECO and is absent at the top of the section. This suggests that Cibicidoides was more resilient than Anomalinoides which proved to be less flexible to the paleoenvironmental changes induced by the MECO warming. The decrease of Cibicidoides coupled to the increase in abundance across the MECO by the genera Uvigerina and Bolivina, infaunal forms tolerating low-oxygen conditions, possibly indicate less oxygenation at the bottom and a change in the quality of organic matter (i.e., more labile) reaching the seafloor.

The relationship between Large Igneous Provinces (LIPs) and major mass extinctions has long been recognized. The K/Pg boundary (KPB) extinction is particularly notable due to the near-simultaneous occurrence of two major catastrophic events: the Deccan volcanism and the Chicxulub impact. To gain a clearer understanding of how volcanic activity drives environmental stress, this study investigates the influence of the Deccan volcanism on ecosystems. Our approach includes detailed species counts alongside isotopic and geochemical analyses of two well-preserved sections from the Mudurnu-Göynük and Haymana basins in Central Anatolia (Turkey).In the Haymana Basin, δ¹³C measurements from the late Maastrichtian display cyclical fluctuations, reflecting precession-driven climate changes. Each cycle ends with a rapid cooling event, indicated by a positive shift in δ¹⁸O values. Spectral analyses of high-resolution δ¹³C and δ¹⁸O isotopic records from planktonic and benthic foraminifera further confirm the influence of orbital forcing, particularly precession cycles, on Late Cretaceous climate variability. The precession-driven cycles reveal climate variations that influenced primary productivity and ocean stratification. During precessional highs, both planktonic and benthic δ¹³C values increase, accompanied by a decrease in Δ¹³Cplanktonic-benthic values and a shift towards more positive δ¹⁸O values, suggesting enhanced water column mixing. Notably, benthic δ¹³C values are consistently heavier than their planktonic counterparts, which may reflect local upwelling conditions. However, the decreasing trend in productivity marker trace elements such as nickel (Ni) and copper (Cu) raises questions about the persistence and extent of upwelling in the Haymana Basin during this period.Concurrently, a quantitative analysis of planktic foraminifera reveals a progressive decline in species diversity throughout the late Maastrichtian, with an accelerated decline just before the K/Pg boundary. In the Göynük and Okçular sections, this decline in biodiversity coincides with intervals of low magnetic susceptibility, suggesting a possible link to ocean acidification during the late Maastrichtian. The K/Pg boundary is marked by a distinct reddish oxidized layer, 2-3 mm thick, which signals a sequence of critical events: the abrupt disappearance of large, specialized foraminiferal taxa (e.g., globotruncanids, racemiguembelinids, planoglobulinids), an increase in mercury (Hg) levels, and elevated concentrations of trace elements such as iridium (Ir), tellurium (Te), nickel (Ni), chromium (Cr), and cobalt (Co).In terms of the faunal response, we observe peaks in Thoracosphaera and Guembelitria cretacea, indicating a collapsed ecosystem following the K/Pg boundary event. In conclusion, our comprehensive analysis of paleontological, isotopic, and geochemical data demonstrates that the detrimental effects of Deccan volcanism began prior to the Chicxulub impact, predisposing marine ecosystems to the K/Pg mass extinction event.

Paleodepth estimates obtained from empirical age-versus-subsidence curves of oceanic crust allow an independent determination of the paleobathymetric distributions of deep-sea benthic foraminifera. Such backtracking of DSDP sites together with studies of planktonic biostratigraphy, seismic stratigraphy, lithostratigraphy, and isotopic studies allows the placement of benthic foraminifera into a chronologic, paleobathymetric, and paleoceanographic framework. This approach has proven to be successful in recognizing several bathymetrically distinct deep-sea foraminiferal biofacies from the Paleogene of the Atlantic Ocean. Paleocene species have broad bathymetric ranges, but Eocene and Oligocene species tend to be bathymetrically more restricted. Paleocene deep-water benthic foraminifera are predominantly relict Cretaceous taxa. Comparison of Paleocene deep-water benthic foraminiferal faunas with Cretaceous benthic faunas shows that, unlike planktonic organisms, there was no crisis in benthic foraminifera at the end of the Cretaceous. Most of the faunal variation in the Paleocene is attributable to the gradual bathymetric restriction of the shallower Gavelinella beccariiformis assemblage and the bathymetric expansion of the deeper Nuttallides truempyi assemblage. Such depth migrations, both expansions and restrictions, are prominent among the faunal changes noted in deep-sea benthic foraminifera studied to date. A major benthic faunal crisis occurred in the latest Paleocene (Zone P6a) with rapid massive extinctions at the gene ic and specific levels. Most of the extinctions occurred in the shallower G. beccariiformis assemblage containing predominantly Cretaceous relict species; the N. truempyi assemblage was characterized End_Page 515------------------------------ more by appearances than extinctions. Various lines of evidence (seismic, lithostratigraphic, isotopic) indicate that a major, rapid change in abyssal circulation occurred near the end of the Eocene. As modern benthic foraminifera distributions often correlate with modern water-mass distributions, benthic foraminifera may be expected to have responded to the circulation changes. However, the Eocene/Oligocene boundary was not catastrophic for deep-sea benthic foraminifera, and the late Eocene-Oligocene deep-sea fauna evolved in a series of events over several million years. The major faunal abundance change at all depths greater than ~0.5 km (1,600 ft) was the apparently synchronous decrease in abundance of Nuttallides truempyi just above the middle/late Eocene boundary (~38.5 to 40 Ma); this pre-dates by 2 m.y. the major SUP>18O enrichment and the change in abyssal circulation regime inferred from seismic stratigraphic studies. The record in deep abyssal locations (paleodepths > 3 km, 10,000 ft) shows the greatest changes, for here N. truempyi is associated with many endemic deep-water taxa (Abyssammina, Clinapertina, Aragonia, Alabamina dissonata, among others) that decrease in abundance and become extinct prior to the Oligocene. In shallower abyssal depths (2 to 3 km, 6,500 to 10,000 ft), a series of first and last appearances occurred in the late Eocene to earliest Oligocene. In lower bathyal depths (~0.5 to 1.5 km, 1,600 to 5,000 ft), a great number of first appearances occurred in the late Eocene through Oligocene. Oligocene abyssal faunas mark a change from Paleocene (Cretaceous relict) and Eocene taxa (e.g. N. truempyi, Alabamina dissonata, Aragonia spp.) to abyssal assemblages that have many taxa in common with modern assemblages. The Oligocene abyssal fauna is dominated by stratigraphically long-ranging and bathymetrically wide-ranging taxa that survived the extinctions of the Eocene. During the middle Oligocene, Nuttallides umbonifera became important in deep abyssal locations in the North Atlantic and shallow and deep abyssal locations in the South Atlantic. Shallow abyssal Oligocene faunas throughout the Atlantic differ from Eocene faunas primarily by the absence of N. truempyi. Oligocene bathyal (0.5 to 1.5 km, 1,600 to 5,000 ft) assemblages are similar to the Eocene bathyal Lenticulina- ulimina-Osangularia assemblage, although many new taxa appeared in the late Eocene through Oligocene. End_of_Article - Last_Page 516------------

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late middle Eocene and consequent global CO 2 -driven climate change.

The Cretaceous/Tertiary boundary stratotype section at El Kef, Tunisia: how catastrophic was the mass extinction?

Since the advent of the Deep Sea Drilling Project, late Mesozoic and Cenozoic benthic foraminifera have been recovered from cores drilled in the Indian, Pacific, and Atlantic Oceans. These faunas represent a broad range of low-middle latitude depositional environments from water depths of about 1,500 to 5,000 m. At the present time, analysis of fossil deep-sea benthic foraminifera is in a nascent stage. However, it is evident that many taxa occur in all the world's oceans, have easily recognized shell morphologies, and are generally more preservable than planktonic foraminifera. The major drawbacks to benthic species in biostratigraphic investigations are their long duration per species, compared to planktonic species, and the taxonomic confusion surrounding many taxa.In the Cretaceous there was little difference between deep ocean and continental slope faunas. Important stratigraphic markers, such as the Bolivinoides lineage, Bolivina incrassata, Gavelinella and Gyroidinoides species established in North America and Europe, were present in the deep ocean. Following a major evolutionary turnover in the early Paleogene, deep-sea faunas became less similar to those of continental margin as many new lower bathyal-abyssal genera evolved. Tertiary stratigraphic boundaries, including the top of the Paleocene, middle Eocene, top of the Eocene, upper Oligocene, and middle Miocene, are readily identifiable. After the middle Miocene, benthic foraminifera changed little and it is difficult to subdivide late Neogene faunas. End_of_Article - Last_Page 700------------

<p><b>Seismic tomography is a powerful tool for understanding Earth structure. In New Zealand, velocity models derived using ray-based tomography have been used extensively to characterize the complex plate boundary between the Australian and Pacific plates. Advances in computational capabilities now allow us to improve these velocity models using adjoint tomography, an imaging method which minimizes differences between observed and simulated seismic waveforms. We undertake the first application of adjoint tomography in New Zealand to improve a ray-based New Zealand velocity model containing the Hikurangi subduction zone and the North Island of New Zealand.</b></p> <p>In support of this work we deployed the Broadband East Coast Network (BEACON), a temporary seismic network aimed at improving coverage of the New Zealand permanent network, along the east coast of the North Island. We concurrently develop an automated, open-source workflow for full-waveform inversion using spectral element and adjoint methods. We employ this tool to assess a candidate velocity model’s suitability for adjoint tomography. Using a 3D ray-based traveltime tomography model of New Zealand, we generate synthetic seismic waveforms for more than 10 000 source–receiver pairs and evaluate waveform misfits. We subsequently perform synthetic checkerboard inversions with a realistic New Zealand source–receiver distribution. Reasonable systematic time shifts and satisfactory checkerboard resolution in synthetic inversions indicate that the candidate model is appropriate as an initial model for adjoint tomography. This assessment also demonstrates the relative ease of use and reliability of the automated tools.</p> <p>We then undertake a large-scale adjoint tomography inversion for the North Island of New Zealand using up to 1 800 unique source–receiver pairs to fit waveforms with periods 4–30 s, relating to minimum waveform sensitivities on the order of 5 km. Overall, 60 geographically well-distributed earthquakes and as many as 88 broadband station locations are included. Using a nonlinear optimization algorithm, we undertake 28 model updates of Vp and Vs over six distinct inversion legs which progressively increase resolution. The total inversion incurred a computational cost of approximately 500 000 CPU-hours. The overall time shift between observed and synthetic seismograms is reduced, and updated velocities show as much as ±30% change with respect to initial values. A formal resolution analysis using point spread tests highlights that velocity changes are strongly resolved onland and directly offshore, at depths above 30 km, with low-amplitude changes (> 1%) observed down to 100 km depth. The most striking velocity changes coincide with areas related to the active Hikurangi subduction zone.</p> <p>We interpret the updated velocity model in terms of New Zealand tectonics and geology, and observe good agreement with known basement terranes, and major structural elements such as faults, sedimentary basins, broad-scale subduction related features. We recover increased spatial heterogeneity in seismic velocities along the strike of the Hikurangi subduction zone with respect to the initial model. Below the East Coast, we interpret two localized high-velocity anomalies as previously unidentified subducted seamounts. We corroborate this interpretation with other work, and discuss the implications of deeply subducted seamounts on slip behavior along the Hikurangi margin. In the Cook Strait we observe a low-velocity zone that we interpret as a deep sedimentary basin. Strong velocity gradients bounding this low-velocity zone support hypotheses of a structural boundary here separating the North and South Islands of New Zealand. In the central North Island, low-velocity anomalies are linked to surface geology, and we relate seismic velocities at depth to crustal magmatic activity below the Taupo Volcanic Zone.</p> <p>This new velocity model provides more accurate synthetic seismograms and additional constraints on enigmatic tectonic processes related to the North Island of New Zealand. Both the velocity model itself, and the underpinning methodological contributions, improve our ever-expanding understanding of the North Island of New Zealand, the Hikurangi subduction zone, and the broader Australian-Pacific plate boundary.</p>

<p><b>Seismic tomography is a powerful tool for understanding Earth structure. In New Zealand, velocity models derived using ray-based tomography have been used extensively to characterize the complex plate boundary between the Australian and Pacific plates. Advances in computational capabilities now allow us to improve these velocity models using adjoint tomography, an imaging method which minimizes differences between observed and simulated seismic waveforms. We undertake the first application of adjoint tomography in New Zealand to improve a ray-based New Zealand velocity model containing the Hikurangi subduction zone and the North Island of New Zealand.</b></p> <p>In support of this work we deployed the Broadband East Coast Network (BEACON), a temporary seismic network aimed at improving coverage of the New Zealand permanent network, along the east coast of the North Island. We concurrently develop an automated, open-source workflow for full-waveform inversion using spectral element and adjoint methods. We employ this tool to assess a candidate velocity model’s suitability for adjoint tomography. Using a 3D ray-based traveltime tomography model of New Zealand, we generate synthetic seismic waveforms for more than 10 000 source–receiver pairs and evaluate waveform misfits. We subsequently perform synthetic checkerboard inversions with a realistic New Zealand source–receiver distribution. Reasonable systematic time shifts and satisfactory checkerboard resolution in synthetic inversions indicate that the candidate model is appropriate as an initial model for adjoint tomography. This assessment also demonstrates the relative ease of use and reliability of the automated tools.</p> <p>We then undertake a large-scale adjoint tomography inversion for the North Island of New Zealand using up to 1 800 unique source–receiver pairs to fit waveforms with periods 4–30 s, relating to minimum waveform sensitivities on the order of 5 km. Overall, 60 geographically well-distributed earthquakes and as many as 88 broadband station locations are included. Using a nonlinear optimization algorithm, we undertake 28 model updates of Vp and Vs over six distinct inversion legs which progressively increase resolution. The total inversion incurred a computational cost of approximately 500 000 CPU-hours. The overall time shift between observed and synthetic seismograms is reduced, and updated velocities show as much as ±30% change with respect to initial values. A formal resolution analysis using point spread tests highlights that velocity changes are strongly resolved onland and directly offshore, at depths above 30 km, with low-amplitude changes (> 1%) observed down to 100 km depth. The most striking velocity changes coincide with areas related to the active Hikurangi subduction zone.</p> <p>We interpret the updated velocity model in terms of New Zealand tectonics and geology, and observe good agreement with known basement terranes, and major structural elements such as faults, sedimentary basins, broad-scale subduction related features. We recover increased spatial heterogeneity in seismic velocities along the strike of the Hikurangi subduction zone with respect to the initial model. Below the East Coast, we interpret two localized high-velocity anomalies as previously unidentified subducted seamounts. We corroborate this interpretation with other work, and discuss the implications of deeply subducted seamounts on slip behavior along the Hikurangi margin. In the Cook Strait we observe a low-velocity zone that we interpret as a deep sedimentary basin. Strong velocity gradients bounding this low-velocity zone support hypotheses of a structural boundary here separating the North and South Islands of New Zealand. In the central North Island, low-velocity anomalies are linked to surface geology, and we relate seismic velocities at depth to crustal magmatic activity below the Taupo Volcanic Zone.</p> <p>This new velocity model provides more accurate synthetic seismograms and additional constraints on enigmatic tectonic processes related to the North Island of New Zealand. Both the velocity model itself, and the underpinning methodological contributions, improve our ever-expanding understanding of the North Island of New Zealand, the Hikurangi subduction zone, and the broader Australian-Pacific plate boundary.</p>

Planktonic and benthic foraminiferal extinction events during the last 100 m.y.

The age, origin, and geologic development of outcropping sedimentary units of the continental slope and rise of the Wilmington Canyon region are assessed from analysis of foraminifera. DSRV Alvin was used to core outcrops and subcrops of strata in the walls and floors of Wilmington, South Wilmington, and North Heyes Canyons. Planktonic and benthic foraminifera were identified and counted in 34 samples and analyzed using Q-mode cluster analysis. Planktonic foraminifera were used to determine age of outcropping strata and surficial watermass conditions at the time of deposition

The Middle Eocene Climatic Optimum (MECO) was an unusual global warming event that interrupted the long‐term Eocene cooling trend ca. 40 Ma. Here we present new high‐resolution bulk and benthic isotope records from South Atlantic ODP Site 702 to characterize the MECO at a high latitude setting. The MECO event, including early and peak warming as well as recovery to background levels, had an estimated ~300 Kyr duration (~40.51 to ~40.21 Ma). Cross‐plots (δ18O vs. δ13C) suggest that the mechanisms driving coupled changes in O and C isotope values across the MECO were weaker or absent before the event. The paleoecological response has been evaluated by quantitative analysis of calcareous nannofossils and benthic foraminifera assemblages. We document a shift in the biogeographical distribution of warm and temperate calcareous nannoplankton taxa, which migrated toward higher latitudes due to increased temperatures during the MECO. Conversely, changes in the organic matter flux to the seafloor appear to have controlled benthic foraminifera dynamics at Site 702. Benthic phytodetritus exploiting taxa increased in abundance coinciding with a positive δ13C excursion, ~150 Kyr before the start of the δ18O negative excursion that marks the start of MECO warming. Our data suggest that paleoecological disturbance in the deep sea predates MECO δ18O excursion and that it was driven by changes in the type and/or amount of organic matter reaching the seafloor rather than by increased temperature.

The benthic foraminiferal turnover and extinction event (BEE) associated with the negative carbon isotope excursion (CIE) across the Paleocene–Eocene Thermal Maximum (PETM) is analyzed in the Zumaia section (Spain), one of the most complete and expanded deep-water sequences known worldwide. New biostratigraphic, paleoecologic, and paleoenvironmental data on benthic foraminifera are correlated to information on planktic foraminiferal and calcareous nannofossil turnover in order to evaluate possible causes and consequences of the PETM. Gradual but rapid extinction of 18% of the benthic foraminiferal species starts at the onset of the CIE, after the initial ocean warming (as inferred from calcareous nannofossils) recorded in the last 46 kyr of the Paleocene. This gradual extinction event culminated ∼10.5 kyr after the onset of the CIE and led to the main BEE, affecting 37% of the species. Therefore, extinctions across the PETM affected a total of 55% of the benthic foraminiferal species at Zumaia. The gradual extinction occurred under inferred oxic conditions without evidence for carbonate dissolution, indicating that carbonate corrosivity and oxygenation of the ocean bottom waters were not the main cause of the event. An interval characterized by dissolution occurs above the main BEE, suggesting that bottom waters became corrosive after the main extinction. Carbonate is progressively better preserved through the overlying deposits, and carbon isotope values gradually return to background levels. These data are consistent with a slow deepening of the carbonate compensation depth after its initial rise owing to abrupt acidification of the oceans. Microfossil data support a rapid onset of the PETM, followed by long-term effects on calcareous plankton and benthic foraminifera.

Although a majority of biologists are convinced that a mass extinction is underway on earth today, the human history with direct observatory data is too short to predict its future trends. At least five mass extinctions occurred during the Phanerozoic Eon, causing the rapid extinction of at least 75% of existing marine species; they also seriously affected species diversity on land once the terrestrial ecosystem developed. The causes and consequences of these mass extinctions have become the most useful analogs for understanding whether the current global ecosystem is experiencing an extinction event. Previous multidisciplinary studies of the extinction patterns of fossil groups and concurrent environmental changes of the five mass extinctions during the past 500 million years (occurring in the end-Ordovician, Late Devonian Frasnian-Famennian, end-Permian, end-Triassic, and end-Cretaceous) suggested that no catastrophic event wiped out all organisms on earth. However, all five mass extinctions were associated with serious environmental deterioration and major paleoclimatic changes. The end-Ordovician mass extinction, occurring 445.2–443.8 million years ago, consists of two phases separated by an interval dominated by the cold Hirnantia fauna. The wax and wane of glaciation and associated widespread anoxia were the major causes of the two phases of the end-Ordovician mass extinctions. The Late Devonian mass extinction consists of a few different events from the Givetian to the Devonian-Carboniferous boundary, of which the most important is the Kellwasser event around the Frasnian-Famennian boundary. This extinction most seriously affected the coral and stromatoporoid reefs, and caused the extinction of two brachiopod orders (Pentamerida and Atrypida). As of yet, there is no consensus on the cause of this extinction event. Global cooling related to the widespread development of the terrestrial vegetation ecosystem and marine anoxia are the two most plausible scenarios. Although impact events were reported from a few horizons in the Late Devonian, they cannot account for the multiple phases of the Late Devonian mass extinctions. The end-Permian mass extinction about 252 million years ago has been universally documented as the most serious, which caused the disappearances of about 95% of all marine and 75% of all terrestrial species. Based on the latest high-precision geochronology data from South China, this extinction happened within an interval of less than 61 thousand years. This extinction was associated with a sharp negative excursion of δ 13Ccarb. A rapid temperature rise of 6–8 °C also occurred within the extinction interval. The Siberian Traps eruption and volcanism in South China, triggered by the dispersal of the supercontinent Pangea, is the most plausible explanation for the end-Permian mass extinction. The end-Triassic mass extinction at 201.564±0.015 Ma also seriously affected both marine and terrestrial ecosystems. Amphibians and reptiles both suffered a great loss during this extinction, and they were subsequently replaced by highly diverse dinosaurs. Marine conodonts and Ceratitida became extinct, and the sponge Demospongea and the brachiopod order Spiriferinida were also greatly affected. Recent studies suggest that the extinction stage may have extended over 10–20 million years, and the volcanism of the Central Atlantic Magmatic Province may be the cause. The end-Cretaceous mass extinction has been the best-known event among the general public because it caused the extinction of various dinosaurs that prevailed during the Mesozoic Era. The cause of this extinction has been documented as the extraterrestrial Chicxulub impact event. However, detailed paleontological studies suggested that the extinction is more likely to have been caused by another major volcanism event, the massive eruption of the Deccan Traps. In summary, global changes in atmospheric CO2 and paleotemperature (both icehouse and greenhouse), oceanic acidification, sea-level changes, and anoxia triggered by massive volcanic eruptions are the most plausible causes of the past extinctions. Massive volcanism not only ejected a huge amount of CO2 and volcanic sulfates, but also caused a massive release of thermogenic CO2 and methane stored in the deposits of inland basins and continental shelves. Extraterrestrial impact, supernova explosion, and solar flares could instantaneously wipe out all organisms on earth, but they are not the main causes of the five mass extinctions experienced in the history of the earth.