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). [1]
OAE1b had three main subevents: the Kilian, Paquier, and Leenhardt. The Kilian subevent was defined by a negative δ13C excursion from about 2-2.5% to 0.5-1.5% followed by a gradual δ13C rise in the Atlantic Ocean, [2] though the magnitude of these carbon isotope fluctuations was higher in areas like the Basque-Cantabrian Basin. [3] The Paquier subevent was the most extreme subevent of OAE1b, [4] exhibiting a δ13C drop of ~3% in marine organic matter [5] and of 1.5-2% in marine carbonate [3] , which was succeeded by a gradual positive δ13C excursion. The Leenhardt subevent was the last OAE1b subevent and is associated in the eastern Tethys Ocean with a negative δ13C excursion of 0.09‰ to -0.48‰ followed by a positive δ13C excursion to 0.58%, [6] although the magnitude of the carbon isotope shifts varies considerably in other marine regions, the negative δ13C excursion being around 1% in the Atlantic [7] and western Tethys [8] but ~4% in the Basque-Cantabrian Basin [3] and ~3% in the Andean Basin. [9]
Pulsed volcanic activity of the Kerguelen Plateau is suggested to be the cause of OAE1b based on mercury anomalies recorded from this interval. [10] Five different mercury anomalies relative to total organic carbon are known from strata from the Jiuquan Basin spanning the OAE1b interval, strongly supporting a causal relationship with massive volcanism. [11] Prominent negative osmium isotope excursions coeval with biotic changes among planktonic foraminifera further confirm the occurrence of multiple episodes of submarine volcanic activity over the course of OAE1b. [12] Nonetheless, volcanism is not unequivocally supported as OAE1b's mainspring. Mercury anomalies associated with OAE1b have been interpreted by some to reflect mineralisation associated with salt diapirism instead of volcanism. [13] Another line of evidence contradicting the volcanism hypothesis involves the massive diachrony between thallium isotope records and intervals of deoxygenation. [14]
Global warming intensified chemical weathering, leading to increased terrestrial inputs of organic matter into oceans and lakes. This promoted eutrophication that rapidly depleted bodies of water of dissolved oxygen. [15] A contemporary increase in 187Os/188Os reflects an increase in continentally derived, radiogenic osmium sources in the ocean, confirming an increase in terrestrial runoff. [16]
Alternatively, rather than volcanism, some research points to orbital cycles as the governing cause of OAE1b. It has been hypothesised that enhanced monsoonal activity modulated by Earth's axial precession drove the development of OAE1b. Evidence supporting this explanation includes regular variations in detrital and weathering indices between humid intervals of high weathering and anoxia and drier intervals of decreased weathering and better oxygenated waters; these variations are suggested to correspond to precession cycles. [17] A different analysis of orbital forcing purports the long eccentricity cycle as the most significant orbital driver of monsoonal modulation. [18] δ18O records in planktic foraminifera from the Boreal Ocean show a 100 kyr periodicity, indicating that the short eccentricity cycle governed the ingression of hot Tethyan waters into the Boreal Ocean and consequent Boreal warming. [19] The 405 kyr eccentricity cycle appears to have dominated the advance and retreat of anoxia in the Vocontian Basin. [20]
The tectonic isolation of the Atlantic and Tethys Oceans restricted their ventilation, enabling their stagnation and facilitating ideal conditions for thermohaline stratification, which would in turn promote the widespread development of anoxia during a speedily warming climate. [21]
OAE1b's coincidence with a peak in a 5-6 Myr oscillation in marine phosphorus accumulation suggests that enhanced phosphorus regeneration may have been one of the causal factors behind the development of widespread anoxia. As more phosphorus built up in marine environments and caused spikes in biological productivity and decreases in dissolved oxygen, it caused a strong positive feedback loop in which phosphorus deposited on the seafloor was recycled back into the water column at faster rates, facilitating further increase in productivity and decrease in seawater oxygen content. Eventually, a negative feedback loop of increased atmospheric oxygen terminated this phosphorus spike and the OAE itself by causing increased wildfire activity and a consequent decline in vegetation and chemical weathering. [22]
Unlike other OAEs during the MKH, such as the OAE1a and the OAE2, OAE1b was not associated with an extinction event of benthic foraminifera. Identical benthic foraminiferal assemblages occur both below and above the black shales deposited in association with OAE1b, indicating that this OAE was limited in its geographic and bathymetric extent. Although some parts of the ocean floor became devoid of life, benthic foraminifera survived in refugia and recolonised previously abandoned areas after the OAE with no faunal turnover. [23] Planktonic foraminifera, however, significantly declined during OAE1b. [24] In the eastern Pacific, the Paquier Level of OAE1b is associated with the demise of heterozoan-dominated carbonate production. [9]
As with other OAEs, OAE1b left its mark on the geologic record in the form of widespread and abundant deposition of black shales. [25] [26] [1]
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.
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, 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.
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 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 Andean-Saharan glaciation, also known as the Early Paleozoic Ice Age (EPIA), the Early Paleozoic Icehouse, the Late Ordovician glaciation, the end-Ordovician glaciation, or the Hirnantian glaciation, occurred during the Paleozoic from approximately 460 Ma to around 420 Ma, during the Late Ordovician and the Silurian period. The major glaciation during this period was formerly thought only to consist of the Hirnantian glaciation itself but has now been recognized as a longer, more gradual event, which began as early as the Darriwilian, and possibly even the Floian. Evidence of this glaciation can be seen in places such as Arabia, North Africa, South Africa, Brazil, Peru, Bolivia, Chile, Argentina, and Wyoming. More evidence derived from isotopic data is that during the Late Ordovician, tropical ocean temperatures were about 5 °C cooler than present day; this would have been a major factor that aided in the glaciation process.
Sapropel is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2 wt.% in weight.
The Lau event was the last of three relatively minor mass extinctions during the Silurian period. It had a major effect on the conodont fauna, but barely scathed the graptolites, though they suffered an extinction very shortly thereafter termed the Kozlowskii event that some authors have suggested was coeval with the Lau event and only appears asynchronous due to taphonomic reasons. It coincided with a global low point in sea level caused by glacioeustasy and is closely followed by an excursion in geochemical isotopes in the ensuing late Ludfordian faunal stage and a change in depositional regime.
The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction, Cenomanian-Turonian Oceanic Anoxic Event, and referred to also as the Bonarelli Event or Level, 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. There was a large carbon cycle disturbance during this time period, signified by a large positive carbon isotope excursion. However, apart from the carbon cycle disturbance, there were also large disturbances in the ocean's nitrogen, oxygen, phosphorus, sulphur, and iron cycles.
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 Carnian pluvial episode (CPE), often called the Carnian pluvial event, was an interval of major change in global climate that was synchronous with significant changes in Earth's biota both in the sea and on land. It occurred during the latter part of the Carnian Stage, a subdivision of the late Triassic period, and lasted for perhaps 1–2 million years.
Peregrinella is an extinct Early Cretaceous rhynchonellid genus with scattered, global representation from North America to Europe and Tibet. These brachiopods are stationary epifaunal suspension feeders, its most distinguishing feature is the size, considered to be the largest of all Mesozoic rhynchonellids, which has long puzzled paleontologists because of its unusual morphology, stratigraphic occurrence, and distribution patterns.
The Capitanian mass extinction event, also known as the end-Guadalupian extinction event, the Guadalupian-Lopingian boundary mass extinction, the pre-Lopingian crisis, or the Middle Permian extinction, was an extinction event that predated the end-Permian extinction event. The mass extinction occurred during a period of decreased species richness and increased extinction rates near the end of the Middle Permian, also known as the Guadalupian epoch. It is often called the end-Guadalupian extinction event because of its initial recognition between the Guadalupian and Lopingian series; however, more refined stratigraphic study suggests that extinction peaks in many taxonomic groups occurred within the Guadalupian, in the latter half of the Capitanian age. The extinction event has been argued to have begun around 262 million years ago with the Late Guadalupian crisis, though its most intense pulse occurred 259 million years ago in what is known as the Guadalupian-Lopingian boundary event.
The Calcare di Sogno is a geological formation in Italy, dated to roughly between 182-169 million years ago and covering the Lower Toarcian-Late Bajocian stagess of the Jurassic Period in the Mesozoic Era. Thallatosuchian remains are known from the formation, as well fishes and other taxa.
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 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 Weissert Event, also referred to as the Weissert Thermal Excursion (WTX), was a hyperthermal event that occurred in the Valanginian stage of the Early Cretaceous epoch. This thermal excursion occurred amidst the relatively cool Tithonian-early Barremian Cool Interval (TEBCI). Its termination marked an intense cooling event, potentially even an ice age.
The Steptoean positive carbon isotope excursion (SPICE) is a global chemostratigraphic event which occurred during the upper Cambrian period betwee 497 and 494 million years ago. This event corresponds with the ICS Guzhangian- Paibian Stage boundary and the Marjuman- Steptoean stage boundary in North America. The general signature of the SPICE event is a positive δ13C excursion, characterized by a 4 to 6 ‰ (per mille) shift in δ13C values within carbonate successions around the world. SPICE was first described in 1993, and then named later in 1998. In both these studies, the SPICE excursion was identified and trends were observed within Cambrian formations of the Great Basin of the western United States.
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