System/ Period | Series/ Epoch | Stage/ Age | Age (Ma) | |
---|---|---|---|---|
Paleogene | Paleocene | Danian | younger | |
Cretaceous | Upper/ Late | Maastrichtian | 66.0 | 72.1 |
Campanian | 72.1 | 83.6 | ||
Santonian | 83.6 | 86.3 | ||
Coniacian | 86.3 | 89.8 | ||
Turonian | 89.8 | 93.9 | ||
Cenomanian | 93.9 | 100.5 | ||
Lower/ Early | Albian | 100.5 | ≈113.0 | |
Aptian | ≈113.0 | ≈125.0 | ||
Barremian | ≈125.0 | ≈129.4 | ||
Hauterivian | ≈129.4 | ≈132.9 | ||
Valanginian | ≈132.9 | ≈139.8 | ||
Berriasian | ≈139.8 | ≈145.0 | ||
Jurassic | Upper/ Late | Tithonian | older | |
Subdivision of the Cretaceous system according to the ICS, as of 2017. [1] |
The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction, Cenomanian-Turonian Oceanic Anoxic Event (OAE 2), and referred to also as the Bonarelli Event or Level, [2] was an anoxic extinction event in the Cretaceous period. The Cenomanian-Turonian oceanic anoxic event is considered to be the most recent truly global oceanic anoxic event in Earth's geologic history. [3] There was a large carbon cycle disturbance during this time period, [4] [5] signified by a large positive carbon isotope excursion. [6] [7] [8] However, apart from the carbon cycle disturbance, there were also large disturbances in the ocean's nitrogen, [9] oxygen, [10] phosphorus, [11] [12] [13] sulphur, [14] and iron cycles. [15]
The Cenomanian and Turonian stages were first noted by D'Orbigny between 1843 and 1852. The global type section for this boundary is located in the Bridge Creek Limestone Member of the Greenhorn Formation near Pueblo, Colorado, which are bedded with the Milankovitch orbital signature. Here, a positive carbon-isotope event is clearly shown, although none of the characteristic, organic-rich black shale is present. It has been estimated that the isotope shift lasted approximately 850,000 years longer than the black shale event, which may be the cause of this anomaly in the Colorado type section. [16] A significantly expanded OAE2 interval from southern Tibet documents a complete, more detailed, and finer-scale structures of the positive carbon isotope excursion that contains multiple shorter-term carbon isotope stages amounting to a total duration of 820 ±25 ka. [17]
The level is also known as the Bonarelli Event because of 1-to-2-metre (3 ft 3 in to 6 ft 7 in) layer of thick, black shale that marks the boundary and was first studied by Guido Bonarelli [ it ] in 1891. [18] It is characterized by interbedded black shales, chert and radiolarian sands and is estimated to span a 400,000-year interval. Planktonic foraminifera do not exist in this Bonarelli Level, and the presence of radiolarians in this section indicates relatively high productivity and an availability of nutrients. [19] In the Western Interior Seaway, the Cenomanian-Turonian boundary event is associated with the Benthonic Zone, characterised by a higher density of benthic foraminifera relative to planktonic foraminifera, although the timing of the appearance of the Benthonic Zone is not uniformly synchronous with the onset of the oceanic anoxic event and is thus cannot be used to consistently demarcate its beginning. [20]
Selby et al. in 2009 concluded the OAE 2 occurred approximately 91.5 ± 8.6 Ma, [21] though estimates published by Leckie et al. (2002) are given as 93–94 Ma. [22] The Cenomanian-Turonian boundary has been refined in 2012 to 93.9 ± 0.15 Ma. [23] The total duration of OAE2 has been estimated at 0.9 Myr, [24] 0.82 ± 0.025 Myr, [17] or 0.71 ± 0.17 Myr. [25] At high latitudes, the event lasted for a shorter time: only ~600 kyr. [26]
Biodiversity patterns of planktic foraminifera indicate that the Cenomanian-Turonian extinction occurred in five phases. Phase I, which took place from 313,000 to 55,000 years before the onset of the anoxic event, witnessed a stratified water column and high planktonic foraminiferal diversity, suggesting a stable marine environment. Phase II, characterised by significant environmental perturbations, lasted from 55,000 years before OAE2 until its onset and witnessed a decline in rotaliporids and heterohelicids, a zenith of schackoinids and hedbergellids, a 'large form eclipse' during which foraminifera exceeding 150 microns disappeared, and the start of a trend of dwarfism among many foraminifera. This phase also saw an enhanced oxygen minimum zone and increased productivity in surface waters. Phase III lasted for 100,000 to 900,000 years and was coincident with the Bonarelli Level's deposition and exhibited extensive proliferation of radiolarians, indicative of extremely eutrophic conditions. Phase IV lasted for around 35,000 years and was most notable for the increase in the abundance of hedbergellids and schackoinids, being extremely similar to Phase II, with the main difference being that rotaliporids were absent from Phase IV. Phase V was a recovery interval lasting 118,000 years and marked the end of the 'large form eclipse' that began in Phase II; heterohelicids and hedbergellids remained in abundance during this phase, pointing to continued environmental disturbance during this phase. [27]
Earth pronouncedly warmed just before the beginning of OAE2. [28] The Cenomanian-Turonian interval represents one of the hottest intervals of the entire Phanerozoic eon, [29] and it boasted the highest carbon dioxide concentrations of the Cretaceous period. [30] Even before OAE2, during the late Cenomanian, tropical sea surface temperatures (SSTs) were very warm, about 27-29 °C. [31] The onset of OAE2 was concurrent with a 4-5 °C rise in shelf sea temperatures. [32] Mean tropical SSTs during OAE2 have been conservatively estimated to have been at least 30 °C, but may have reached as high as 36 °C. [33] Minimum SSTs in mid-latitude oceans were >20 °C. [34] This exceptional warmth persisted until the Turonian-Coniacian boundary. [35]
One possible cause of this hothouse was sub-oceanic volcanism. During the middle of the Cretaceous period, the rate of crustal production reached a peak, which may have been related to the rifting of the newly formed Atlantic Ocean. [36] It was also caused by the widespread melting of hot mantle plumes under the ocean crust, at the base of the lithosphere, which may have resulted in the thickening of the oceanic crust in the Pacific and Indian Oceans. The resulting volcanism would have sent large quantities of carbon dioxide into the atmosphere, leading to an increase in global temperatures. Greenhouse gas release was further increased by the degassing of organic-rich sediments intruded into by volcanic sills. [37] Several independent events related to large igneous provinces (LIPs) occurred around the time of OAE2. A multitude of LIPs were active during OAE2: the Madagascar, [38] [39] Caribbean, [40] [41] [42] Gorgona, [43] Ontong Java, [38] and High Arctic LIPs. [44] [45] [46] The abundance of LIPs at this time reflects a major overturning in mantle convection. [47] Trace metals such as chromium (Cr), scandium (Sc), copper (Cu) and cobalt (Co) have been found at the Cenomanian-Turonian boundary, which suggests that an LIP could have been one of the main basic causes involved in the contribution of the event. [48] The timing of the peak in trace metal concentration coincides with the middle of the anoxic event, suggesting that the effects of the LIPs may have occurred during the event, but may not have initiated the event. Other studies linked the lead (Pb) isotopes of OAE-2 to the Caribbean-Colombian and the Madagascar LIPs. [49] An osmium isotope excursion coeval with OAE2 strongly suggests submarine volcanism as its cause; [50] in the Pacific, an unradiogenic osmium spike began about 350 kyr before the onset of OAE2 and terminated around 240 kyr after OAE2's beginning; [51] the osmium isotope data from a highly expanded OAE2 interval in southern Tibet show multiple osmium excursions with the most pronounced one lagging the onset of OAE2 by ≈50 kyr that was probably related to the ocean connectivity change at ~94.5 Ma. [52] Osmium data also reveal that three distinct pulses of intense volcanism occurred ~60, ~270, and ~400 kyr after OAE2's onset, prolonging it. [53] Positive neodymium isotope excursions provide additional indications of pervasive volcanism as a cause of OAE2. [54] Enrichments in zinc further bolster and reinforce the existence of extensive hydrothermal volcanism, [55] as do extreme negative δ53Cr excursions. [56] The absence of geographically widespread mercury (Hg) anomalies resulting from OAE2 has been suggested to be because of the limited dispersal range of this heavy metal by submarine volcanism. [57] A modeling study performed in 2011 confirmed that it is possible that a LIP may have initiated the event, as the model revealed that the peak amount of carbon dioxide degassing from volcanic LIP degassing could have resulted in more than 90 percent global deep-ocean anoxia. [58]
Later on, when anoxia became widespread, the production of nitrous oxide, a greenhouse gas about 265 times more potent than carbon dioxide, drastically increased because of elevated nitrification and denitrification rates. This powerful positive feedback mechanism is what may have enabled extremely hot temperatures to persist in spite of the supercharged organic carbon burial associated with anoxic events. [59]
Large-scale organic carbon burial acted as a negative feedback loop that partially mitigated the warming effects of volcanic discharge of carbon dioxide, resulting in the Plenus Cool Event during the Metoicoceras geslinianum European ammonite biozone. [60] Global average temperatures fell to around 4 °C lower than they were pre-OAE2. [31] Equatorial SSTs dropped by 2.5–5.5 °C. [61] This cooling event was insufficient at completely stopping the rise in global temperatures. This negative feedback was ultimately overridden, as global temperatures continued to shoot up in sync with continued volcanic release of carbon dioxide following the Plenus Cool Event, [60] although this theory has been criticised and the warming after the Plenus Cool Event attributed to decreased silicate weathering instead. [62]
Within the oceans, the emission of SO2, H2S, CO2, and halogens would have increased the acidity of the water, causing the dissolution of carbonate, and a further release of carbon dioxide. Evidence of ocean acidification can be gleaned from δ44/40Ca increases coeval with the extinction event, [63] [64] [65] as well as coccolith malformation and dwarfism. [66] Ocean acidification was exacerbated by a positive feedback loop of increased heterotrophic respiration in highly biologically productive waters, elevating seawater concentrations of carbon dioxide and further decreasing pH. [67]
When the volcanic activity declined, this run-away greenhouse effect would have likely been put into reverse. The increased CO2 content of the oceans could have increased organic productivity in the ocean surface waters. The consumption of this newly abundant organic life by aerobic bacteria would produce anoxia and mass extinction. [68] An acceleration of the hydrological cycle induced by warmer global temperatures drove greater fluxes of nutrient runoff into the oceans, fuelling primary productivity. [69] [70] [71] The global environmental disturbance that resulted in these conditions increased atmospheric and oceanic temperatures. Extreme hothouse conditions encouraged ocean stratification. [72] Boundary sediments show an enrichment of trace elements, and contain elevated δ13C values. [73] [74] The positive δ13C excursion found at the Cenomanian-Turonian boundary is one of the main carbon isotope events of the Mesozoic. It represents one of the largest disturbances in the global carbon cycle from the past 110 million years. This δ13C excursion indicates a significant increase in the burial rate of organic carbon, indicating the widespread deposition and preservation of organic carbon-rich sediments and that the ocean was depleted of oxygen at the time. [75] [76] [77] Depletion of manganese in sediments corresponding to OAE2 provides additional strong evidence of severe bottom water oxygen depletion. [55] An increase in the abundance of the planktonic foraminifer Heterohelix provides further evidence still of anoxia. [78] [53] The resulting elevated levels of carbon burial would account for the black shale deposition in the ocean basins. [73] [79] The proto-North Atlantic in particular was a hotbed of carbon burial during OAE2 as it was in later, less severe anoxic events. [80] Though anoxia was prevalent throughout the interval, there were transient periods of reoxygenation during OAE2. [6]
Sulphate reduction increased during OAE2, [15] causing euxinia, a type of anoxia defined by sulphate reduction and hydrogen sulphide production, to occur during OAE2, as revealed by negative δ53Cr excursions, [81] positive δ98Mo excursions, [82] a drawdown of seawater molybdenum, [83] [84] and molecular biomarkers of green sulfur bacteria. [85] [86] [87] Although euxinia was not uncommon in the latter part of the Cenomanian, it only expanded into the photic zone during OAE2 itself. [88]
OAE2 began on the southern margins of the proto-North Atlantic, from where anoxia spread across the rest of the proto-North Atlantic and then into the Western Interior Seaway (WIS) and the epicontinental seas of the Western Tethys. [89] Anoxic waters spread rapidly throughout the WIS due to marine transgression and a powerful cyclonic circulation resulting from an imbalance between precipitation in the north and evaporation in the south. [90] Anoxia was especially intense in the eastern North Sea, evidenced by its very positive δ13C values. [91] Thanks to persistent upwelling, some marine regions, such as the South Atlantic, were able to remain partially oxygenated at least intermittently. [92] Indeed, redox states of oceans vary geographically, bathymetrically and temporally during OAE2. [93]
It has been hypothesised that the Cenomanian-Turonian boundary event occurred during a period of very low variability in Earth's insolation, which has been theorised to be the result of coincident nodes in all orbital parameters. Barring chaotic perturbations in Earth's and Mars' orbits, the simultaneous occurrence of nodes of orbital eccentricity, axial precession, and obliquity on Earth occurs approximately every 2.45 million years. [94] Numerous other oceanic anoxic events occurred throughout the extremely warm greenhouse conditions of the Middle Cretaceous, [95] and it has been suggested that these Middle Cretaceous ocean anoxic events occurred cyclically in accordance with orbital cycle patterns. [94] The mid-Cenomanian Event (MCE), which occurred in the Rotalipora cushmani planktonic foraminifer biozone, has been argued to be another example supporting this hypothesis of regular oceanic anoxic events governed by Milankovitch cycles. [95] The MCE took place approximately 2.4 million years before the Cenomanian-Turonian oceanic anoxic event, roughly at the time when an anoxic event would be expected to occur given such a cycle. [94] Geochemical evidence from a sediment core in the Tarfaya Basin is indicative of the main positive carbon isotope excursion occurring during a prolonged eccentricity minimum. Carbon isotope shifts smaller in scale observed in this core likely reflected variability in obliquity. [96] Ocean Drilling Program Site 1138 in the Kerguelen Plateau yields evidence of a 20,000 to 70,000 year periodicity in changes in sedimentation, suggesting that either obliquity or precession governed the large-scale burial of organic carbon. [97] Within the OAE2 positive δ13C excursion, short eccentricity scale carbon isotope variability is documented in a significantly expanded OAE2 interval from southern Tibet; [17] periodic negative δ13C excursions paced by the short eccentricity cycle are easily detectable in southwestern Utah too. [98]
The phosphorus retention ability of seafloor sediments declined during OAE2, [11] [99] revealed by a decline in reactive phosphorus species within OAE2 sediments. [100] The mineralisation of seafloor phosphorus into apatite was inhibited by the significantly lower pH of seawater and much warmer temperatures during the Cenomanian and Turonian compared to the present day, which meant that significantly more phosphorus was recycled back into ocean water after being deposited on the sea floor during this time. This would have intensified a positive feedback loop in which phosphorus is recycled faster into anoxic seawater compared to oxygen-rich water, which in turn fertilises the water, causes increased eutrophication, and further depletes the seawater of oxygen. [12] The influx of volcanically erupted and chemically weathered sulphate into the ocean also inhibited phosphorus burial by increasing hydrogen sulphide production, [101] which hinders the burial of phosphorus through sorption to iron oxyhydroxide phases. [14] OAE2 may have occurred during a peak in a 5-6 Myr cycle governing phosphorus availability; at this and other peaks in this oscillation, an increase in chemical weathering would have increased the marine phosphorus inventory and sparked a positive feedback loop of increasing productivity, anoxia, and phosphorus recycling that was only ended by a negative feedback of increased atmospheric oxygenation and wildfire activity that decreased chemical weathering, a feedback which operated on a much longer timescale. [13] Enhanced phosphorus recycling would have resulted in an abundance of nitrogen fixing bacteria, increasing the availability of yet another limiting nutrient and supercharging primary productivity through nitrogen fixation. [102] The ratio of bioavailable nitrogen to bioavailable phosphorus, which is 16:1 in the present, fell precipitously as the ocean transitioned from being oxic and nitrate-dominated to anoxic and ammonium-dominated. [59] A potent feedback loop of nitrogen fixation, productivity, deoxygenation, nitrogen removal, and phosphorus recycling was created. [9] Bacterial hopanoids indicate populations of nitrogen fixing cyanobacteria were high during OAE2, providing a rich supply of nitrates and nitrites. [103] Negative δ15N values reveal the dominance of ammonium through regenerative nutrient loops in the proto-North Atlantic. [104]
In the present day, sulphidic waters are generally prevented from spreading throughout the water column by the oxidation of sulphide with nitrate. However, during OAE2, the inventory of seawater nitrate was lower, meaning that chemolithoautotrophic oxidation of sulphides with nitrates was inefficient at preventing the spread of euxinia. [105]
A marine transgression in the latest Cenomanian resulted in an increase in average water depth, causing seawater to become less eutrophic in shallow, epicontinental seas. Turnovers in marine biota in such epicontinental seas have been suggested to be driven more so by changes in water depth rather than anoxia. [106] Sea level rise also contributed to anoxia by transporting terrestrial plant matter from inundated lands seaward, providing an abundant source of sustenance for eutrophicating microorganisms. [107]
A phosphogenic event occurred in the Bohemian Cretaceous Basin during the peak of oceanic anoxia. Phosphorus liberation in the pore water environment, several centimetres below the interface between seafloor sediments and the water column, enabled the precipitation of phosphate through biological mediation by microorganisms. [108]
Strontium and calcium isotope ratios both indicate that silicate weathering increased over the course of OAE2. Because of its effectiveness as a carbon sink on geologic timescales, the uptick in sequestration of carbon dioxide by the lithosphere may have helped to stabilise global temperatures after global temperatures soared. [109] Particularly so at high latitudes, where the increase in weatherability was very pronounced. [110]
The event brought about the extinction of the pliosaurs, and most ichthyosaurs. Coracoids of Maastrichtian age were once interpreted by some authors as belonging to ichthyosaurs, but these have since been interpreted as plesiosaur elements instead. [111] Dolichosaurids became rare after OAE2, whereas mosasauroid diversity bloomed in its aftermath. [112] Tethysuchians experienced a significant faunal turnover, and post-OAE2 tethysuchians tended to inhabit warmer environments compared to pre-OAE2 tethysuchians. [113]
Although the cause is still uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years, causing the extinction of approximately 27 percent of marine invertebrates, including certain planktic and benthic foraminifera, mollusks, bivalves, dinoflagellates and calcareous nannofossils. [68] Planktonic foraminifera suffered from the expansion of oxygen minimum zones; [8] those that dwelt in deeper waters were especially hard hit. [114] In Whadi El Ghaib, a site in Sinai, Egypt, the foraminiferal community during OAE2 was low in diversity and dominated by taxa that were extremely tolerant of low salinity, anoxic water. [115] In the southeastern Indian Ocean, off the coast of Australia, the planktonic foraminifer Microhedbergella was highly abundant, [116] while Heterohelix thrived in reducing waters in the South Atlantic, [78] [53] as well as in the Chalk Sea. [7] The benthic foraminifera Gavelella berthelini and Lingulogavelinella globosa dominated during deoxygenated conditions in Poland. [10] The alterations in diversity of various marine invertebrate species such as calcareous nannofossils are reflective and characteristic of oligotrophy and ocean warmth in an environment with short spikes of productivity followed by long periods of low fertility. [117] A study performed in the Cenomanian-Turonian boundary of Wunstorf, Germany, reveal the uncharacteristic dominance of a calcareous nannofossil species, Watznaueria, present during the event. Unlike the Biscutum species, which prefer mesotrophic conditions and were generally the dominant species before and after the C/T boundary event; Watznaueria species prefer warm, oligotrophic conditions. [118] In the Ohaba-Ponor section in Romania, the presence of Watznaueria barnesae indicates warm conditions, while the abundances of Biscutum constans, Zeugrhabdotus erectus, and Eprolithus floralis peak during cool intervals. [117] Sites in Colorado, England, France, and Sicily show an inverse relationship between atmospheric carbon dioxide levels and the size of calcareous nannoplankton. [119] Radiolarians also suffered heavy losses in OAE2, one of their highest diversity losses in the Cretaceous. [120] Bivalves declined significantly in diversity during the leadup to the δ13Corg peak of OAE2. [121] Rudist bivalves suffered high extinction rates combined with low origination rates during OAE2. [122]
The diversity of trace fossils sharply plummeted during the beginning of the Cenomanian-Turonian boundary event. The recovery interval after the anoxic event's conclusion features an abundance of Planolites and is characterised overall by a high degree of bioturbation. [123]
At the time, there were also peak abundances of the green algal groups Botryococcus and prasinophytes, coincident with pelagic sedimentation. The abundances of these algal groups are strongly related to the increase of both the oxygen deficiency in the water column and the total content of organic carbon. The evidence from these algal groups suggest that there were episodes of halocline stratification of the water column during the time. A species of freshwater dinocyst—Bosedinia—was also found in the rocks dated to the time and these suggest that the oceans had reduced salinity. [124] [125]
No major change in terrestrial ecosystems is known to have been synchronous with the marine transgression associated with OAE2, although the loss of freshwater floodplain habitat has been speculated to have possibly resulted in the demise of some freshwater taxa. In fossiliferous rocks in southwestern Utah, a local extirpation of some metatherians and brackish water vertebrates is associated with the later marine regression following OAE2 in the Turonian. Whatever the nature and magnitude of terrestrial extinctions at or near the Cenomanian-Turonian boundary was, it was most likely caused mainly by other factors than eustatic sea level fluctuations. [126] The effect of the ecological crisis on terrestrial plants has been concluded to have been inconsequential, in contrast to extinction events driven by terrestrial large igneous provinces. [127] However, while terrestrial plants did persist even during the exceptional warmth, the Plenus Cool Event facilitated a notable expansion of angiosperm-dominated savanna ecosystems. [128]
The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.
An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.
The Triassic–Jurassic (Tr-J) extinction event (TJME), often called the end-Triassic extinction, was a Mesozoic extinction event that marks the boundary between the Triassic and Jurassic periods, 201.4 million years ago, and is one of the top five major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, the entire class of conodonts and 23–34% of marine genera disappeared. On land, all archosauromorphs other than crocodylomorphs, pterosaurs, and non-avian dinosaurs became extinct; some of the groups which died out were previously abundant, such as aetosaurs, phytosaurs, and rauisuchids. Some remaining non-mammalian therapsids and many of the large temnospondyl amphibians had become extinct prior to the Jurassic as well. However, there is still much uncertainty regarding a connection between the Tr-J boundary and terrestrial vertebrates, due to a lack of terrestrial fossils from the Rhaetian (uppermost) stage of the Triassic. Plants, crocodylomorphs, dinosaurs, pterosaurs and mammals were left largely untouched; this allowed the dinosaurs, pterosaurs, and crocodylomorphs to become the dominant land animals for the next 135 million years.
The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 445 million years ago (Ma). It is often considered to be the second-largest known extinction event just behind the end-Permian mass extinction, in terms of the percentage of genera that became extinct. Extinction was global during this interval, eliminating 49–60% of marine genera and nearly 85% of marine species. Under most tabulations, only the Permian-Triassic mass extinction exceeds the Late Ordovician mass extinction in biodiversity loss. The extinction event abruptly affected all major taxonomic groups and caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, echinoderms, corals, bivalves, and graptolites. Despite its taxonomic severity, the Late Ordovician mass extinction did not produce major changes to ecosystem structures compared to other mass extinctions, nor did it lead to any particular morphological innovations. Diversity gradually recovered to pre-extinction levels over the first 5 million years of the Silurian period.
The Late Devonian extinction consisted of several extinction events in the Late Devonian Epoch, which collectively represent one of the five largest mass extinction events in the history of life on Earth. The term primarily refers to a major extinction, the Kellwasser event, also known as the Frasnian-Famennian extinction, which occurred around 372 million years ago, at the boundary between the Frasnian stage and the Famennian stage, the last stage in the Devonian Period. Overall, 19% of all families and 50% of all genera became extinct. A second mass extinction called the Hangenberg event, also known as the end-Devonian extinction, occurred 359 million years ago, bringing an end to the Famennian and Devonian, as the world transitioned into the Carboniferous Period.
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the Sun. These orbital changes modify the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes. In this context, the term "forcing" signifies a physical process that affects the Earth's climate.
An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them. These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating. On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions. Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO2) as the "central external trigger for euxinia."
The Early Cretaceous or the Lower Cretaceous is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma, approximately. The Aptian succeeds the Barremian and precedes the Albian, all part of the Lower/Early Cretaceous.
The Caribbean large igneous province (CLIP) consists of a major flood basalt, which created this large igneous province (LIP). It is the source of the current large eastern Pacific oceanic plateau, of which the Caribbean-Colombian oceanic plateau is the tectonized remnant. The deeper levels of the plateau have been exposed on its margins at the North American and South American plates. The volcanism took place between 139 and 69 million years ago (Ma), with the majority of activity appearing to lie between 95 and 88 Ma. The plateau volume has been estimated as on the order of 4 million km3 (0.96 million cu mi). It has been linked to the Galápagos hotspot.
The Cretaceous Thermal Maximum (CTM), also known as Cretaceous Thermal Optimum, was a period of climatic warming that reached its peak approximately 90 million years ago (90 Ma) during the Turonian age of the Late Cretaceous epoch. The CTM is notable for its dramatic increase in global temperatures characterized by high carbon dioxide levels.
Three Western Interior Seaway anoxic events occurred during the Cretaceous in the shallow inland seaway that divided North America in two island continents, Appalachia and Laramidia. During these anoxic events much of the water column was depleted in dissolved oxygen. While anoxic events impact the world's oceans, Western Interior Seaway anoxic events exhibit a unique paleoenvironment compared to other basins. The notable Cretaceous anoxic events in the Western Interior Seaway mark the boundaries at the Aptian-Albian, Cenomanian-Turonian, and Coniacian-Santonian stages, and are identified as Oceanic Anoxic Events I, II, and III respectively. The episodes of anoxia came about at times when very high sea levels coincided with the nearby Sevier orogeny that affected Laramidia to the west and Caribbean large igneous province to the south, which delivered nutrients and oxygen-adsorbing compounds into the water column.
The Neoproterozoic Oxygenation Event (NOE), also called the Second Great Oxidation Event, was a time interval between around 850 and 540 million years ago which saw a very significant increase in oxygen levels in Earth's atmosphere and oceans. Bringing an end to the Boring Billion, an euxinic period of extremely low atmospheric oxygen spanning from the Statherian to the Tonian, the NOE was the second major increase in atmospheric and oceanic oxygen concentration on Earth, though it was not as large as the Great Oxidation Event (GOE) of the Neoarchean-Paleoproterozoic boundary. Unlike the GOE, it is unclear whether the NOE was a synchronous, global event or a series of asynchronous, regional oxygenation intervals with unrelated causes.
The Toarcian extinction event, also called the Pliensbachian-Toarcian extinction event, the Early Toarcian mass extinction, the Early Toarcian palaeoenvironmental crisis, or the Jenkyns Event, was an extinction event that occurred during the early part of the Toarcian age, approximately 183 million years ago, during the Early Jurassic. The extinction event had two main pulses, the first being the Pliensbachian-Toarcian boundary event (PTo-E). The second, larger pulse, the Toarcian Oceanic Anoxic Event (TOAE), was a global oceanic anoxic event, representing possibly the most extreme case of widespread ocean deoxygenation in the entire Phanerozoic eon. In addition to the PTo-E and TOAE, there were multiple other, smaller extinction pulses within this span of time.
The Selli Event, also known as OAE1a, was an oceanic anoxic event (OAE) of global scale that occurred during the Aptian stage of the Early Cretaceous, about 120.5 million years ago (Ma). The OAE is associated with large igneous province volcanism and an extinction event of marine organisms driven by global warming, ocean acidification, and anoxia.
The Breistroffer Event (OAE1d) was an oceanic anoxic event (OAE) that occurred during the middle Cretaceous period, specifically in the latest Albian, around 101 million years ago (Ma).
The Paquier Event (OAE1b) was an oceanic anoxic event (OAE) that occurred around 111 million years ago (Ma), in the Albian geologic stage, during a climatic interval of Earth's history known as the Middle Cretaceous Hothouse (MKH).
The Amadeus Event (OAE1c) was an oceanic anoxic event (OAE). It occurred 106 million years ago (Ma), during the Albian age of the Cretaceous period, in a climatic interval known as the Middle Cretaceous Hothouse (MKH).
The Mid-Cenomanian Event (MCE) was an oceanic anoxic event that took place during the middle Cenomanian, as its name suggests, around 96.5 Ma.
The Hesseltal Formation or Blackcoloured Formation is a Late Cretaceous geological formation from northern Germany. It consists of lithified marls and limestone, with a unique series of black shales deposited in anoxic conditions during the Cenomanian-Turonian boundary event.