^Paleontologists often refer to faunal stages rather than geologic (geological) periods. The stage nomenclature is quite complex. For an excellent time-ordered list of faunal stages, see[2]
^ abDates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the International Commission on Stratigraphy 2012 time scale. Where errors are not quoted, errors are less than the precision of the age given. Dates labeled with a * indicate boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon: seeList of Global Boundary Stratotype Sections and Points for a complete list.
^Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. The 2009 version of the ICS time chart[3] recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status.
^The start time for the Holocene epoch is here given as 11,700years ago. For further discussion of the dating of this epoch, see Holocene.
^ abcEruptions were most vigorous 6 to 10 million years ago and 2 to 3 million years ago, when most of the basalt was released. Less extensive eruptions continued 0.01 to 1.6 million years ago. The Chilcotin Group were thought to potentially be linked to the Columbia River Basalt Group in the United States, which are coeval and lie across parts of the states of Washington, Oregon, and Idaho to the south.[3] However, its morphology and geochemistry have been proven much similar to other volcanic plateaus such as the Snake River Plain in Idaho and parts of Iceland. [6] K–Ar whole-rock dates demonstrate that several ages of basalt are represented, from Early Miocene (or even Late Oligocene?) to Early Pleistocene, with particularly abundant eruptions about 14 to 16, 9 to 6, and 1 to 3 Ma ago.
^14.8 to 14.5 million years ago, during the Langhian. A major and permanent cooling step occurred between 14.8 and 14.1 Ma, associated with increased production of cold Antarctic deep waters and a major growth of the East Antarctic ice sheet.
^The Columbia River Basalt Group is thought to be a potential link to the Chilcotin Group. The flows can be divided into four major categories: The Steens Basalt, Grande Ronde Basalt, the Wanapum Basalt, and the Saddle Mountains Basalt. The Columbia River flood basalt province comprises more than 300 individual basalt lava flows that have an average volume of 500 to 600 cubic kilometres. The Steens Basalt captured a highly detailed record of the Earth’s magnetic reversal that occurred roughly 15 million years ago. Over a 10,000 year period, more than 130 flows solidified – roughly one flow every 75 years. Most of the flows froze with a single magnetic orientation. However, several of the flows captured substantial variations in magnetic field direction as they froze. One geomagnetic field reversal occurred during the Steens Basalt eruptions at approximately 16.7 Ma, as dated using 40Ar/39Ar ages and the geomagnetic polarity timescale. The Imnaha lavas have been dated using the K–Ar technique, and show a broad range of dates. The oldest is 17.67±0.32 Ma with younger lava flows ranging to 15.50±0.40 Ma. The next oldest of the flows, from 17 million to 15.6 million years ago, make up the Grande Ronde Basalt. The Wanapum Basalt is made up of the Eckler Mountain Member (15.6 million years ago), the Frenchman Springs Member (15.5 million years ago), the Roza Member (14.9 million years ago) and the Priest Rapids Member (14.5 million years ago). The Saddle Mountains Basalt, seen prominently at the Saddle Mountains, is made up of the Umatilla Member flows, the Wilbur Creek Member flows, the Asotin Member flows (13 million years ago), the Weissenfels Ridge Member flows, the Esquatzel Member flows, the Elephant Mountain Member flows (10.5 million years ago), the Bujford Member flows, the Ice Harbor Member flows (8.5 million years ago) and the Lower Monumental Member flows (6 million years ago). Eruptions were most vigorous from 17 to 14 million years ago, when over 99% of the basalt was released. Less extensive eruptions continued from 14 to 6 million years ago.
^ aberupted approximately 31 to 30 Mya, over a period of 1 Myr or less. This was about the time of a change to a colder and drier global climate, a major continental ice-sheet advance in Antarctica, the largest Tertiary sea-level drop and significant extinctions.[7] According to Hofmann et al. (1997),[full citation needed] most of the Ethiopian flood basalts erupted 30 Myr ago, during a short 1 Myr period, to form a vast volcanic plateau. Immediately after this peak of activity, a number of large shield volcanoes developed on the surface of the volcanic plateau, after which subsequent volcanism was largely confined to regions of rifting (Mohr, 1983a; Mohr & Zanettin, 1988).[full citation needed] The rift that opened along the Red Sea and Gulf of Aden separated the Arabian and African continents, and isolated a small portion of the volcanic plateau in Yemen and Saudi Arabia.[8] Volcanic activity continues to the present day along the Ethiopian and Afar rifts.
^largest known single-event volcanic eruption with a magnitude of 9.2 . It has been dated to 27.51 Ma ago. This tuff and eruption is part of the larger San Juan volcanic field and Mid-Tertiary ignimbrite flare-up.
^ abIsotopic dating indicates the most active magmatic phase of the NAIP to be ca. 60.5–54.5 Ma (million years ago)[4] (mid-Paleocene to early Eocene) - further divided into Phase 1 (pre-break-up phase) dated to ca. 62–58 Ma and Phase 2 (syn-break-up phase) dated to ca. 56–54 Ma
^ abBasaltic volcanism flowed in two main pulses. The first which occurred ~61 million years ago was of 2 to 106 km3 in total volume, into the current western and southeastern Greenland and northwestern Britain. The second and larger flood basalt flow occurred ~56 to 54 Ma years ago in both eastern Greenland and the Faroe Islands.
^it is speculated[according to whom?] that the present day Iceland hotspot originated as a mantle plume on the Alpha Ridge (Arctic Ocean) ca. 130–120 Ma, migrated down Ellesmere Island, through Baffin Island, onto the west coast of Greenland, and finally arrived on the east coast of Greenland by ca. 60 Ma
^The age of Chicxulub asteroid impact and the Cretaceous–Paleogene boundary (65.5 ± 0.3) coincide precisely. Even the most energetic known volcanic eruption, which released approximately 240 gigatons of TNT (1.0×1021 J) and created the La Garita Caldera, was substantially less powerful than the Chicxulub impact. Gerta Keller[citation needed] of Princeton University argues that recent core samples from Chicxulub prove the impact occurred about 300,000 years before the mass extinction.
^The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 65 million years ago. This series of eruptions may have lasted less than 30,000 years in total. The motion of the Indian tectonic plate and the eruptive history of the Deccan traps show strong correlations. Based on data from marine magnetic profiles, a pulse of unusually rapid plate motion begins at the same time as the first pulse of Deccan flood basalts, which is dated at 67 Myr ago. The spreading rate rapidly increased and reached a maximum at the same time as the peak basaltic eruptions. The spreading rate then dropped off, with the decrease occurring around 63 Myr ago, by which time the main phase of Deccan volcanism ended.
^ abcThe volcanism took place between 139 and 69 million years ago, with the majority of act1ivity appearing to lie between 95 and 88 Ma with peaks at 74-76, 80-82, and 88-90 Ma in decreasing order of importance.[9]
^ abThe HALIP is defined as a long lasting (ca. 50 Ma) diffuse volcanic period punctuated by two distinct volcanic events: the ~120-130 Ma Barremian and the ~80-90 Ma Turonian events. In this contribution, we sub-divided the HALIP into two separate LIPs: (1) the ~120-130 Ma Early Cretaceous BLIP which was related to the opening of the Canada Basin, and (2) the ~80-90 Ma Late Cretaceous SLIP which was related to the formation of the Alpha Ridge.
^ abAlthough they are now separated by thousands of kilometres, Manihiki Plateau and Hikurangi Plateau were then part of the same large igneous province, forming the world's largest oceanic plateau. The Ontong Java Plateau was formed 125–120 million years ago with some secondary volcanism occurring 20–40 million years later.
^ abDetailed stratigraphic studies of Cretaceous black shales from many parts of the world have indicated that two oceanic anoxic events were particularly significant in terms of their impact on the chemistry of the oceans, one in the early Aptian (~120 Ma), sometimes called the Selli Event (or OAE 1a) after the Italian geologist, Raimondo Selli (1916–1983), and another at the Cenomanian–Turonian boundary (~93 Ma), sometimes called the Bonarelli Event which occurred approximately 91.5 ± 8.6 million years ago. One possible cause was sub-oceanic volcanism occurring approximately 500,000 years earlier.
^The plateau was produced by the Kerguelen hotspot, starting with or following the breakup of Gondwana about 130 million years ago. The Kerguelen Plateau was formed starting 110 million years ago from a series of large volcanic eruptions.
^This volcanic rocks are formed from the eruption of Kerguelen hot spot in the early Cretaceous age. The similarity between the geochemical data of Rajmahal volcanis and lavas of the Kerguelen plateau confirms this. The lava pile of ~230 m thickness in the Rajmahal Hills, Jharkhand, and alkalic basalts in the Bengal Basin were emplaced at ~118 Ma.
^The original basalt flows occurred 128 to 138 million years ago. The basalt samples at Paraná and Etendeka have an age of about 132 Ma.
^ abAges were determined by 40Ar/39Ar analysis on plagioclase (Knight et al. 2004), (Verati et al. 2007), (Marzoli et al. 2004).[full citation needed] These data show indistinguishable ages (199.5±0.5 Ma) from Lower to Upper lava flows, from central to northern Morocco. Therefore the CAMP is an intense and short magmatic event. Basalts of the Recurrent unit are slightly younger (mean age: 197±1 Ma) and represent a late event. According to magnetostratigraphic data, the Moroccan CAMP were divided into five groups, differing in paleomagnetic orientations(declination and inclination) (Knight et al. 2004).[full citation needed] Each group is composed by a smaller number of lava flows (i.e., a lower volume) than the preceding one. These data suggest that the CAMP were created by five short magma pulses and eruption events, each one possibly < 400 years (?) long. All lava flow sequences are characterized by normal polarity, except for a brief paleomagnetic reversal yielded by one lava flow and by a localized interlayered limestone in two distinct section of the High Atlas CAMP.
^Although composed of many different rocks types, of various composition, age, and tectonic affinity, it is the late Triassic flood basalts that are the defining unit of Wrangellia. These basalts, extruded onto land over 5 million years about ~231–225 Ma.
^This massive eruptive event spanned the Permian-Triassic boundary, about 250 million years ago, and is cited as a possible cause of the Permian-Triassic extinction event. The Siberian Traps are considered to have erupted via numerous vents over a period of roughly a million years or more. The source of the Siberian Traps basalt has variously been attributed to a mantle plume which impacted the base of the earth's crust and erupted through the Siberian Craton, or to processes related to plate tectonics. Another possible cause may be the impact that formed the Wilkes Land crater, which may have been contemporaneous and would have been antipodal to the Traps. However, there are already other suggested candidates for giant impacts at the Permian–Triassic boundary, for example Bedout off the northern coast of Western Australia, although all are equally contentious.
^The eruptions that produced the Emeishan Traps began c. 260 million years ago (Ma). In volume, the Emeishan Traps are dwarfed by the massive Siberian Traps, which occurred, in terms of the geological time scale, not long after, at c. 251 Ma. Nonetheless, the Emeishan Traps eruptions were serious enough to have global ecological and paleontological impact. The Emeishan Traps are associated with the so-called end-Guadalupian Extinction or end-Capitanian mass extinction.[10] Emeishan volcanism was active at 258–246 Ma
^After restoring the center of the Skagerrak-Centered Large Igneous Province (SCLIP)using a new reference frame, it has been shown that the Skagerrak plume rose from the core–mantle boundary (CMB) to its ~300 Ma position.[18] The major eruption interval took place in very narrow time interval, of 297±4 Ma. This rift formation coincides with the Moskovian/Kasimovian boundary and the Carboniferous Rainforest Collapse.
^occurred around 305 million years ago in the Carboniferous period.
^The Hangenberg event sits on or just below the Devonian/Carboniferous boundary and marks the last spike in the period of extinction. It is marked by an anoxic black shale layer and an overlying sandstone deposit.[18] Unlike the Kellwasser event, the Hangenberg event affected marine and terrestrial habitats.
^the extinction pulse that occurs near the Frasnian/Famennian boundary.
^With the K-Ar technique, ages ranging from 338 to 367 Ma with uncertainties on the order of 5 Ma were obtained.[11] With the 40Ar/39Ar technique, integrated ages range from 344 to 367 Ma, with uncertainties on the order of 1 Ma, and two samples yielded plateaus, i.e. the best determined ages, at 360.3 ± 0.9 and 370.0 ± 0.7 Ma. Three out of four ages yielded by the two separate methods are in agreement within uncertainties. One sample yields incompatible ages and could be from a later, altered dyke event. The 40Ar/39Ar plateau age of 370.0 ± 0.7 Ma (conventional calibration) or 373.4 ± 0.7 Ma (recalculated per Renne et al., 2010), the most reliable age obtained in this study, is compatible with recent determinations of the Late Devonian extinction events at the end-Frasnian (~ 376 ± 3 Ma). These results underscore a need for further work, in progress.
^Impact craters, such as the Kellwasser-aged Alamo and the Hangenberg-aged Woodleigh, cannot generally be dated with sufficient precision to link them to the event.
^The Lau event started at the beginning of the late Ludfordian, a subdivision of the Ludlow stage, about 420 million years ago. It coincided with a global low point in sea level, is closely followed by an excursion in geochemical isotopes in the ensuing late Ludfordian faunal stage and a change in depositional regime. Profound sedimentary changes occurred at the beginning of the Lau event; these are probably associated with the onset of sea level rise, which continued through the event, reaching a high point at the time of deposition of the Burgsvik beds, after the event.
^The Mulde event was a secundo-secundo event,[3] and marked the second of three1 relatively minor mass extinctions during the Silurian period. It coincided with a global drop in sea level, and is closely followed by an excursion in geochemical isotopes. Its onset is synchronous with the deposition of the Fröel formation in Gotland.
^The Ireviken event was a minor extinction event at the Llandovery/Wenlock boundary (mid Silurian, 433.4 ± 2.3 million years ago). The event lasted around 200,000 years, spanning the base of the Wenlock epoch. It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. Subsequent to the first extinctions, excursions in the δ13C and δ18O records are observed; δ13C rises from +1.4‰ to +4.5‰, while δ18O increases from −5.6‰ to −5.0‰ .
^estimated to be 2.023 billion years (±4 million years).
^ abcThese unit names were taken from the Lunar geologic timescale and refer to geologic events that did not occur on Earth. Their use for Earth geology is unofficial. Note that their start times do not dovetail perfectly with the later, terrestrially defined boundaries.
^The “Cryptic era” is an informal geologic term, like the “Precambrian”. It has no official definition.
References
^Courtillota, Vincent E.; Renneb, Paul R. (January 2003). "Sur l'âge des trapps basaltiques" [On the ages of flood basalt events]. Comptes Rendus Geoscience. 335 (1): 113–140. Bibcode:2003CRGeo.335..113C. doi:10.1016/S1631-0713(03)00006-3.
^Bradley S. Singer; Malcolm S. Pringleb (1996). "Age and duration of the Matuyama-Brunhes geomagnetic polarity reversal from incremental heating analyses of lavas". Earth and Planetary Science Letters. 139 (1–2): 47–61. Bibcode:1996E&PSL.139...47S. doi:10.1016/0012-821X(96)00003-9. We have obtained 40Ar/39Ar isochron ages using incremental heating techniques on groundmass separates, phenocryst-poor whole rock samples, or plagioclase, from eight basaltic to andesitic lavas that erupted during the Matuyama-Brunhes (M-B) polarity transition at four geographically dispersed sites. These eight lavas range from 784.6 ± 7.1 ka to 770.8 ± 5.2 ka (1 σ errors); the weighted mean, 778.7 ± 1.9 ka, gives a high-precision age that is remarkably consistent with revised astronomical age estimates for the M-B polarity transition
^Courtillot, Vincent; Kravchinsky, Vadim A.; Quidelleur, Xavier; Renne, Paul R.; Gladkochub, Dmitry P. (2010). "Preliminary dating of the Viluy traps (Eastern Siberia): Eruption at the time of Late Devonian extinction events?". Earth and Planetary Science Letters. 300 (3–4): 239–245. Bibcode:2010E&PSL.300..239C. doi:10.1016/j.epsl.2010.09.045.