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Home , Calymmian, Changhsingian, Chattian, Danian, Ectasian, Eoarchean

GeoArabia, Vol. 12, No. 1, 2007 Gulf PetroLink, Bahrain

On the Period and Sub-

Felix M. Gradstein and Stan Finney

INTRODUCTION

Since the publication of ‘A Geologic Scale 2004’ by Gradstein, Ogg, Smith et al. (2004, Cambridge University Press) and sponsored by the International Commission on Stratigraphy (ICS), two stratigraphic science issues have generated some interesting debates:

1. The status of the and Quaternary 2. The standard international subdivision of the Ordovician.

Below, ICS outlines its long-standing and persistent strategy to improve the knowledge and understanding of these historically complex stratigraphic subjects, ultimately leading to consensus- stratigraphic decisions and uniform usage in international geoscience.

GLOBAL AND STAGES FOR THE ORDOVICIAN

Until recently, there was no global standard set of stratigraphic subdivisions for the Ordovician System/ Period. British series/epochs have often been used as de facto nomenclature on stratigraphic correlation charts and geologic time scales. However, these regional subdivisions are not widely adopted outside of the British Isles and related paleobiogeographic regions (e.g. northwestern Gondwana) because the high degree of biogeographic provincialism and paleoecologic differentiation of Ordovician faunas prevent the British series from being correlated with precision and high resolution.

As a result, several independent and very different sets of series and constituent stages were established for the Ordovician System, with each generally applicable to a different paleoplate or modern . Of course, this has greatly confused Ordovician stratigraphy, and often results in imprecise correlations of Ordovician stratigraphic successions. An example is the Argentine Precordillera where British series are traditionally used to correlate Ordovician strata that contain faunas of predominantly Laurentian affinity.

The Subcommission on Ordovician Stratigraphy of ICS has addressed this problem by developing a standard set of Global Series and Stages for the Ordovician System (Figure 1). This task has taken more than 20 and is nearing completion with only one boundary stratotype, that of the base of the Third and Middle Ordovician Series, still to be approved. The process and the rationale are described in Finney (2005). The new global standard is being accepted rapidly and is facilitating reliable global correlations. It provides a common language for discussing Ordovician strata, and geologic events. It is of fundamental importance in advancing research on Ordovician rocks worldwide.

Some workers on Ordovician may lament the loss of the familiar regional classification (e.g. British series, Australian stages, North American series and stages) that they have long used. However, the establishment of the new global classification allows Ordovician geologists to have the best of “both worlds”. The regional classifications remains unchanged, are not lost, and can continue to be used where they work best in describing regional geology. At the same time, the global units, based on cosmopolitan index species, allow for precise, reliable global correlation.

TOWARDS A CONSENSUS FOR THE AND QUATERNARY

Tertiary, Quaternary, Neogene, and units of the stratigraphic column have seen divergent meanings and ad hoc definitions, both scientifically and politically inspired. Whatever the outcome of any scientific debate, it has to be presented and discussed in an organizationally correct way, well-documented, following the existing ICS rules. Hence, let us review the facts.

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Key Graptolite/ Regional Traditional Ma Global Stages British Series British Series (C) Biohorizons After Fortey et al., 1995, 2000 Global Series 443.7 P. acuminatus 445.6 (GSSP - Dobs Linn) N. extraordinarius ASHGILL ASHGILL (GSSP - Wangjiawan)

Katian Upper

D. caudatus 455.8 CARADOC CARADOC (GSSP - Black Knob R.)

Sandbian N. gracilis 460.9 LLANDEILO (GSSP - Fagelsang) LLANVIRN LLANVIRN ORDOVICIAN

U. austrodentatus 468.1 Middle (GSSP - Huangnitang) Third Stage 471.8 B. triangularis (c) ARENIG ARENIG

Floian

478.6 T. approximatus (GSSP - Diabasbrottet) Lower TREMADOC TREMADOC

I. fluctivagus (c) 488.3 (GSSP - Green Point) Figure 1: Ordovician chronostratigraphic chart showing global Series and Stages, both those defined and those proposed; GSSPs that have been defined and biohorizons under consideration for boundaries still to be defined; and correlation to global Series and Stages of regional British series, as redefined by Fortey et al. (1995, 2000), and of traditional British Series.

Pleistocene /Series

In 1985, a joint working of the International Commision on Stratigraphy (ICS) and INQUA (now the International Union for Quaternary Research) formally proposed the base of the Pleistocene. The basal boundary level is the top of sapropel layer ‘e’ in the Vrica section, , , just above top of magnetic polarity C2n (Olduvai) and the level of the calcareous nannofossil brouweri (base Zone CN13). Above are the lowest occurrences of medium-sized species of the calcareous nannofossil Gephyrocapsa and the extinction level of the planktonic foraminifer extremus. Based on the orbitally tuned sedimentary cycles in the Vrica section, the of the boundary is 1.806 Ma. The formal definition was ratified in 1985, and published in the journal Episodes (1985, vol. 8, no. 2, p. 116–120).

The base-Pleistocene proposal and ratification explicitly stated that the boundary decision was “isolated from other more or less related problems, such as … the status of the Quaternary within the chronostratigraphic scale”.

The Pleistocene is an Epoch/Series unit in the International Stratigraphic Chart (see www.stratigraphy. org), with a lower rank than Neogene, Quaternary and .

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Cenozoic Periods/Systems

The Cenozoic currently has two ratified Period/System-level divisions: (1) the ( through ) had its base ratified in 1991, and (2) the Neogene ( through Recent) had its base ratified in 1996.

Neogene Period/System The Neogene in Italy, which originally included the regional stage, had no well-defined “top”. Renevier (the first chair of what has become now ICS) and some others at the end of the 1800s had the Neogene extending to the Recent. This usage is shown in old textbooks by Krumbein and Sloss.

From the literature, the Neogene extending to the , has a long , and is not in any way a novelty, as outlined clearly in Episodes (2005, vol. 28, no. 2, p. 118-120). Hence, 2004 adopted this usage to strengthen late Cenozoic stratigraphic subdivisions, and included a potential definition of the Quaternary.

Tertiary and Quaternary The Tertiary and Quaternary have been consistently recognized by International Geological Congresses of the century. However, there has been no clarification of their rank. This uncertain status of the former Quaternary and Tertiary within the chronostratigraphic scale was indicated in the 1985 base-Pleistocene ratification.

The joint INQUA-ICS Task Force on the base of the Quaternary in 2005 unanimously recommended moving Quaternary down to 2.6 May at base . The official position of INQUA (March 2006) is that “The base of the Quaternary should be placed at the current base of GSSP Gelasian Stage (currently in the Pliocene) at MIS 103.” The official voting of ICS was also 100% for placing the base of the Quaternary at this level. Therefore, both ICS and INQUA are in total agreement on the definition of the span of Quaternary.

The joint INQUA-ICS Task Force was evenly divided on whether the Quaternary, as defined above, should be given the rank of period or of sub-era. The INQUA Executive decided in May 2005 that “the Quaternary and Tertiary should have the status of sub-eras”, then in March 2006 changed its mind and took the position that “the Quaternary must be a full formal chronostratigraphic unit, the appropriate status for which is the Period (or System).” However, the official voting of ICS on this recommendation generated a 70% majority vote in favor of sub-era.

At present, the Quaternary is a formal sub-era of the Cenozoic time scale. It is the interval of oscillating climatic extremes (glacial and interglacial episodes) that was initiated at about 2.6 Ma (set equal to base of Gelasian stage), therefore it encompasses the and Pleistocene epochs and the late Pliocene. Its base is equivalent to the formally ratified base of the Gelasian Stage at Monte San Nicola, Gela, , Italy; it correlates with Marine Isotopic stage 103, and base of magnetic polarity chronozone C2r (Matuyama). See also Episodes vol. 28, no. 2, p.118-120, 2005.

The ICS charts, database and website now indicate this status and duration of the Quaternary (Figure 2).

QUO VADIS

In September 2006, the ICS appointed a three-person late Cenozoic task force to highlight and summarize the past confused definitions of the Quaternary, and the possible path for ICS to follow to improve international stratigraphic clarity. The task force consists of Dr. Brad Pillans (Chair of the INQUA Commission on Stratigraphy), Dr. Phil Heckel (Chair of the Subcommision on of ICS) and Dr. Alexey S. Tesakov (Late Cenozoic stratigraphy specialist, Geology Department, Russian Academy of Sciences, Moscow). A dozen formal steps are to be considered, including the definitions of:

• Pleistocene and its base and rank; • Quaternary and its base and rank;

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INTERNINTERNATIONAATIONAL STRL STRATIGRAPHICATIGRAPHIC CHA CHARTRT ICS ICS InternationalInternational Commission Commission on Stratigraphy on Stratigraphy m m m m m m m m a a

r r m m m m m m m m s s s s s s e e e e e e e e d d d d d d d d h h h h h h m m m m m m m m e e e e e e P P P P P P P P A A e e e e e e e e E E c c c c c c e e e e e e e e e e e e e e h h h h h h h h n n n n e e n n n n e e e e o o o o o o o o e e e e e e e e a a a a a a a a g g g g g g a a a a a a a a i i i i i i i i i i i i i i - - S S S S S S S S S S t t t t t t t t t t t t t t t t h h h h h h h h r r r r r r r r r r r r r r o o o o o o g g g g g g g g r r r r r r r r o o o o g g o o o o g g g g t t t t t t t t a a a a a a b b s s s s s s s s o o o o o o o o S S S S S S S S S S t t t t t t M M M M M M M M e e e e e e p p p p p p E E E E E E E E e e e e e e e e A A A A A A A A a a E E A A a a A A E E E a E a A A E a E a y y y y y y y y u u n n n n n n n n r r r r r r r r S S S S S S G G G G G G G G G G S S S S S S E E E E E E P P P P P P P P o o o o o o o o S S S S S S S S S S E E E E E E E E E E E E E E E E 145.5 ±4.0145.5 ±4.0 359.2 ±2.5359.2 ±2.5 542 542 HoloceneHolocene Tithonian FamennianFamennian EdiacaranEdiacaran * * 0.0118 0.0118 150.8 ±4.0150.8 ±4.0 Upper Upper 374.5 ±2.6374.5 ±2.6 ~630 ~630 y y Neo- Neo- r r Upper Upper Upper UpperKimmeridgianKimmeridgian Frasnian CryogenianCryogenian a a 155.7 ±4.0155.7 ±4.0 385.3 ±2.6385.3 ±2.6 proterozoicproterozoic n n 850 850

n n 0.126 0.126 r r

PleistocenePleistoceneMiddle Middle OxfordianOxfordian a a Givetian Tonian i i e e t t 161.2 ±4.0161.2 ±4.0 391.8 ±2.7391.8 ±2.7 1000 1000 0.781 0.781 n Middlen Middle c c a a i i

Lower Lower CallovianCallovian o o Eifelian Stenian u u o o 1.806 1.806 164.7 ±4.0164.7 ±4.0 v v 397.5 ±2.7397.5 ±2.7 1200 1200 Q Q z z c c Meso- Meso- e e Gelasian Gelasian i i BathonianBathonian

Emsian o o Ectasian s s r r 2.588 2.588 Middle Middle 167.7 ±3.5167.7 ±3.5 D D 407.0 ±2.8407.0 ±2.8 proterozoicproterozoic 1400 1400 s s e e e e t t

Pliocene PliocenePiacenzianPiacenzian a a Bajocian Lower LowerPragian CalymmianCalymmian n n r r o o 3.600 3.600 171.6 ±3.0171.6 ±3.0 411.2 ±2.8 411.2 ±2.8 n n 1600 1600

r r

e e ZancleanZanclean u u Aalenian LochkovianLochkovian StatherianStatherian a a c c J J g g P P

i i 5.332 5.332 i i 175.6 ±2.0175.6 ±2.0 1800 1800

o o 416.0 ±2.8416.0 ±2.8

r r e e MessinianMessinian Toarcian Pridoli Pridoli Orosirian o o Paleo- Paleo- 7.246 7.246 183.0 ±1.5183.0 ±1.5 418.7 ±2.7418.7 ±2.7 2050 2050 N N b b z z

proterozoicproterozoic Tortonian PliensbachianPliensbachian LudfordianLudfordian RhyacianRhyacian

c c

11.608 11.608 Lower Lower 189.6 ±1.5189.6 ±1.5 Ludlow Ludlow 421.3 ±2.6421.3 ±2.6 m m 2300 2300 o o i i

SerravallianSerravallian SinemurianSinemurian Gorstian Siderian a a s s o o

n n

Miocene 13.82 13.82 196.5 ±1.0196.5 ±1.0 422.9 ±2.5422.9 ±2.5 2500 2500 c c a a e e z z

i i

LanghianLanghian HettangianHettangian

HomerianHomerian r r 426.2 ±2.4426.2 ±2.4 e e o o 15.97 15.97 199.6 ±0.6199.6 ±0.6 Wenlock Wenlock Neoarchean u u M M

r r l l i i BurdigalianBurdigalian Rhaetian SheinwoodianSheinwoodian n n

20.43 20.43 203.6 ±1.5203.6 ±1.5 2800 2800 S S 428.2 ±2.3428.2 ±2.3 P P e e * *

AquitanianAquitanian Upper UpperNorian Telychian y y n n r r c c c c

23.03 23.03 216.5 ±2.0216.5 ±2.0 c c 436.0 ±1.9436.0 ±1.9 C C

MesoarcheanMesoarchean

a a a a i i i i c c i i i i i i c c

t t Chattian Chattian Carnian LlandoveryLlandoveryAeronian e e

r r s s i i o o o o 28.4 ±0.1 28.4 ±0.1 228.0 ±2.0228.0 ±2.0 o o 439.0 ±1.8439.0 ±1.8 3200 3200 h h

OligoceneOligocene

e e s s c c T T o o z z z z Rupelian Ladinian z z RhuddanianRhuddanian a a r r

33.9 ±0.1 33.9 ±0.1 i i 237.0 ±2.0237.0 ±2.0 443.7 ±1.5443.7 ±1.5 PaleoarcheanPaleoarchean r Middler Middle z z o o o o o o A A

T T PriabonianPriabonian Anisian HirnantianHirnantian r r r r r r e e

245.0 ±1.5245.0 ±1.5 37.2 ±0.1 37.2 ±0.1 o o 445.6 ±1.5445.6 ±1.5 3600 3600

n n e e e e e e

BartonianBartonian Olenekian Upper Upper

e e Katian e e n n

n n n n 249.7 ±0.7249.7 ±0.7 n n Lower limit isLower limit is Eocene 40.4 ±0.2 40.4 ±0.2 Lower Lower l l 455.8 ±1.6455.8 ±1.6 EoarcheanEoarchean g g

a a i i

o o Lutetian Induan not defined not defined a a a a a a SandbianSandbian a a

c c

e e 48.6 ±0.2 48.6 ±0.2 251.0 ±0.4251.0 ±0.4 i i 460.9 ±1.6460.9 ±1.6 l l h h h h h h P P v v

a a Ypresian ChanghsingianChanghsingian DarriwilianDarriwilian o o P P P P 55.8 ±0.2 55.8 ±0.2 P P 468.1 ±1.6468.1 ±1.6

P P LopingianLopingian 253.8 ±0.7253.8 ±0.7 Middle Middle d d Subdivisions Subdivisions of the global of the geologic global recordgeologic are record are

ThanetianThanetian WuchiapingianWuchiapingian r r Stage 3 Stage 3 58.7 ±0.2 58.7 ±0.2 260.4 ±0.7260.4 ±0.7 formally definedformally by defined their lower by their boundar lowery .boundar Each unity. Each unit

O O 471.8 ±1.6471.8 ±1.6 PaleocenePaleoceneSelandianSelandian CapitanianCapitanian Floian of the Phanerozoicof the (~542 Ma (~542 to Present) Ma to andPresent) the and the 61.7 ±0.2 61.7 ±0.2 265.8 ±0.7265.8 ±0.7 Lower Lower 478.6 ±1.7478.6 ±1.7 base of Ediacaranbase of are defined are by defined a basal by Global a basal Global Danian Danian n Guadalupiann GuadalupianWordian TremadocianTremadocian a a Standard StandardSection and Section Point and(GSS PointP (GSS ), whereasP ), whereas 65.5 ±0.3 65.5 ±0.3 i i 268.0 ±0.7268.0 ±0.7 488.3 ±1.7488.3 ±1.7 PrecambrianPrecambrian units are formallyunits are subdivided formally subdivided by by MaastrichtianMaastrichtian m m Roadian Stage 10 Stage 10 70.6 ±0.6 70.6 ±0.6 r r 270.6 ±0.7270.6 ±0.7 absolute ageabsolute (Global age Standard (Global StandardStratigraphic Stratigraphic Age, Age,

~ 492.0 * ~ 492.0 * e e

CampanianCampanian c c KungurianKungurian FurongianFurongianStage 9 Stage 9 GSSA). DetailsGSSA). of Detailseach GSS of eachP are GSS postedP are on posted the on the P P

i i 275.6 ±0.7275.6 ±0.7 ~ 496.0 * ~ 496.0 * 83.5 ±0.7 83.5 ±0.7 ICS websiteICS ( wwwebsitew.stratigraph (www.stratigraphy.org). y.org).

SantonianSantonian o o ArtinskianArtinskian Paibian Upper Upper 85.8 ±0.7 85.8 ±0.7 284.4 ±0.7284.4 ±0.7 501.0 ±2.0501.0 ±2.0 International International chronostratigraphic chronostratigraphic units, rank, units, rank,

z Cisuralianz

names andnames formal and status formal are status approved are approvedby the by the n n ConiacianConiacian SakmarianSakmarian Stage 7 Stage 7 c c a a

89.3 ±1.0 89.3 ±1.0 o o 294.6 ±0.8294.6 ±0.8 ~ 503.0 * ~ 503.0 * InternationalInternational Commission Commission on Stratigraphy on Stratigraphy (ICS) (ICS) i i i i s s

r r

u u Turonian Asselian Series 3 Series 3 e e Drumian and ratifiedand by ratified the International by the International Union of GeologicalUnion of Geological o o b b

l l o o 93.5 ±0.8 93.5 ±0.8 299.0 ±0.8299.0 ±0.8 ~ 506.5 * ~ 506.5 *

Sciences Sciences(IUGS). (IUGS). z z m m e e Gzhelian CenomanianCenomanian Stage 5 Stage 5 a a c c a a n n Numerical Numerical ages of the ages unit of boundaries the unit boundaries in the in the

o o 99.6 ±0.9 99.6 ±0.9 Upper Upper 303.9 ±0.9303.9 ±0.9 ~ 510.0 * ~ 510.0 * - - s s a a

a a i i P P C C n n t t KasimovianKasimovian PhanerozoicPhanerozoic are subject are to subject revision. to Somerevision. stages Some stages u u Albian n n Stage 4 Stage 4 s s n n

e e a a ~ 517.0 * ~ 517.0 *

112.0 ±1.0 112.0 ±1.0 o o 306.5 ±1.0306.5 ±1.0 e e Series 2 Series 2 within the withinOrdovician the Ordovician and and Cambrian will be formally will be formally r r v v e e r r l l P P

Aptian y Middle y MoscovianMiddle Moscovian Stage 3 Stage 3 named uponnamed international upon international agreement agreement on their GSS on theirP GSSP e e C C s s f f 311.7 ±1.1 311.7 ±1.1 ~ 521.0 * ~ 521.0 *

125.0 ±1.0125.0 ±1.0 i i M M limits. Mostlimits. sub-Series Most sub-Series boundaries boundaries (e.g., Middle (e.g., Middle

BarremianBarremian n Lowern BashkirianLower Stage 2 Stage 2 and Upperand Aptian) Upper are Aptian) not formally are not defined. formally defined. Lower Lower 130.0 ±1.5130.0 ±1.5 o o 318.1 ±1.3318.1 ±1.3 Series 1 Series 1 ~ 534.6 * ~ 534.6 *

b b Colors are Colors according are according to the Commission to the Commission for the for the HauterivianHauterivian - Upper- SerpukhovianUpper Stage 1 Stage 1 r r n n 542.0 ±1.0542.0 ±1.0 s s i i 136.4 ±2.0136.4 ±2.0 a a 326.4 ±1.6326.4 ±1.6 a a i i GeologicalGeological Map of the Map World of the (ww Wworld.cgm (www.orgw.cgm). w.org). s s p p

ValanginianValanginian s Middles MiddleVisean Visean i i C C This chartThis was chart drafted was by drafted Gabi Ogg. by Gabi Intra Ogg. Cambrian Intra Cambrian unit ages unit ages p p The listed The numerical listed numerical ages are fromages 'Aare Geologic from 'A Geologic 140.2 ±3.0140.2 ±3.0 i i 345.3 ±2.1345.3 ±2.1 M M s s with * are withinformal, * are andinformal, awaiting and ratified awaiting def ratifiedinitions. definitions. BerriasianBerriasian Lower TLowerournaisianTournaisian Time ScaleTime 2004', Scale by 2004',F.M. Gradstein, by F.M. Gradstein, J.G. Ogg, J.G. Ogg, 145.5 ±4.0145.5 ±4.0 359.2 ±2.5359.2 ±2.5 Copyright © Copyright2006 International © 2006 International Commission Commission on Stratigraphy on Stratigraphy A.G. Smith,A.G. et al.Smith, (2004; et al.Cambridge (2004; Cambridge University University Press). Press). Quaternary*:Quaternary*: Formal chronostratigraphic Formal chronostratigraphic unit sensu joint unit ICS-INQUsensu jointA ICS-INQUtaskforce (2005)A taskforce and ICS.(2005) and ICS. Tertiary*: InformalTertiary*: chronostratigraphic Informal chronostratigraphic unit sensu Aubry unit sensu et al. Aubry(2005, etEpisodes al. (2005, 28/2). Episodes 28/2).

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INTERNINTERNATIONAATIONAL STRL STRATIGRAPHICATIGRAPHIC CHA CHARTRT ICS ICS InternationalInternational Commission Commission on Stratigraphy on Stratigraphy m m m m m m m m a a

r r m m m m m m m m s s s s s s e e e e e e e e d d d d d d d d h h h h h h m m m m m m m m e e e e e e P P P P P P P P A A e e e e e e e e E E c c c c c c e e e e e e e e e e e e e e h h h h h h h h n n n n e e n n n n e e e e o o o o o o o o e e e e e e e e a a a a a a a a g g g g g g a a a a a a a a i i i i i i i i i i i i i i - - S S S S S S S S S S t t t t t t t t t t t t t t t t h h h h h h h h r r r r r r r r r r r r r r o o o o o o g g g g g g g g r r r r r r r r o o o o g g o o o o g g g g t t t t t t t t a a a a a a b b s s s s s s s s o o o o o o o o S S S S S S S S S S t t t t t t M M M M M M M M e e e e e e p p p p p p E E E E E E E E e e e e e e e e A A A A A A A A a a E E A A a a A A E E E a E a A A E a E a y y y y y y y y u u n n n n n n n n r r r r r r r r S S S S S S G G G G G G G G G G S S S S S S E E E E E E P P P P P P P P o o o o o o o o S S S S S S S S S S E E E E E E E E E E E E E E E E 145.5 ±4.0145.5 ±4.0 359.2 ±2.5359.2 ±2.5 542 542 HoloceneHolocene TithonianT ithonian FamennianFamennian EdiacaranEdiacaran * * 0.0118 0.0118 150.8 ±4.0150.8 ±4.0 Upper Upper 374.5 ±2.6374.5 ±2.6 ~630 ~630 y y Neo- Neo- r r Upper Upper Upper UpperKimmeridgianKimmeridgian FrasnianFrasnian CryogenianCryogenian a a 155.7 ±4.0155.7 ±4.0 385.3 ±2.6385.3 ±2.6 proterozoicproterozoic n n 850 850 n n 0.126 0.126 r r

PleistocenePleistoceneMiddle Middle OxfordianOxfordian a a GivetianGivetian Tonian Tonian i i e e t t 161.2 ±4.0161.2 ±4.0 391.8 ±2.7391.8 ±2.7 1000 1000 0.781 0.781 n Middlen Middle c c a a i i

Lower Lower CallovianCallovian o o Eifelian Eifelian Stenian Stenian u u o o 1.806 1.806 164.7 ±4.0164.7 ±4.0 v v 397.5 ±2.7397.5 ±2.7 1200 1200 Q Q z z c c Meso- Meso- e e GelasianGelasian i i BathonianBathonian

Emsian Emsian o o EctasianEctasian s s r r 2.588 2.588 Middle Middle 167.7 ±3.5167.7 ±3.5 D D 407.0 ±2.8407.0 ±2.8 proterozoicproterozoic 1400 1400 s s e e e e t t

PliocenePliocenePiacenzianPiacenzian a a BajocianBajocian Lower LowerPragian Pragian CalymmianCalymmian n n r r o o 3.600 3.600 171.6 ±3.0171.6 ±3.0 411.2 ±2.841 1.2 ±2.8 n n 1600 1600

r r e e ZancleanZanclean u u AalenianAalenian LochkovianLochkovian StatherianStatherian a a c c J J g g P P

i i 5.332 5.332 i i 175.6 ±2.0175.6 ±2.0 1800 1800 o o 416.0 ±2.8416.0 ±2.8

r r e e MessinianMessinian ToarcianToarcian Pridoli Pridoli OrosirianOrosirian o o Paleo- Paleo- 7.246 7.246 183.0 ±1.5183.0 ±1.5 418.7 ±2.7418.7 ±2.7 2050 2050 N N b b z z

proterozoicproterozoic TortonianTortonian PliensbachianPliensbachian LudfordianLudfordian RhyacianRhyacian c c

11.608 11.608 Lower Lower 189.6 ±1.5189.6 ±1.5 Ludlow Ludlow 421.3 ±2.6421.3 ±2.6 m m 2300 2300 o o i i

SerravallianSerravallian SinemurianSinemurian GorstianGorstian SiderianSiderian a a s s o o

n n

MioceneMiocene 13.82 13.82 196.5 ±1.0196.5 ±1.0 422.9 ±2.5422.9 ±2.5 2500 2500 c c a a e e z z

i i

LanghianLanghian HettangianHettangian

HomerianHomerian r r 426.2 ±2.4426.2 ±2.4 e e o o 15.97 15.97 199.6 ±0.6199.6 ±0.6 WenlockW enlock Neoarchean Neoarchean u u M M

r r l l i i BurdigalianBurdigalian RhaetianRhaetian SheinwoodianSheinwoodian n n

20.43 20.43 203.6 ±1.5203.6 ±1.5 2800 2800 S S 428.2 ±2.3428.2 ±2.3 P P e e * *

AquitanianAquitanian Upper UpperNorian Norian TelychianTelychian y y n n r r c c c c

23.03 23.03 216.5 ±2.0216.5 ±2.0 c c 436.0 ±1.9436.0 ±1.9 C C

MesoarcheanMesoarchean

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e e s s c c T T o o z z z z RupelianRupelian LadinianLadinian z z RhuddanianRhuddanian a a r r

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ValanginianValanginian s Middles MiddleVisean Visean i i C C This chartThis was chart drafted was bydrafted Gabi byOgg. Gabi Intra Ogg. Cambrian Intra Cambrian unit ages unit ages p p The listed The numerical listed numerical ages are ages from are 'A Geologicfrom 'A Geologic 140.2 ±3.0140.2 ±3.0 i i 345.3 ±2.1345.3 ±2.1 Geological Map of the World (www.cgmw.org). M M s s with * arewith informal, * are informal, and awaiting and awaiting ratified def ratifiedinitions. definitions. BerriasianBerriasian Lower LowerTournaisianTournaisian Time ScaleTime 2004', Scale by 2004', F.M. Gradstein,by F.M. Gradstein, J.G. Ogg, J.G. Ogg, 145.5 ±4.0145.5 ±4.0 359.2 ±2.5359.2 ±2.5 Copyright Copyright© 2006 International © 2006 International Commission Commission on Stratigraphy on Stratigraphy A.G. Smith,A.G.The et listedSmith, al. (2004; numerical et al. Cambridge (2004; ages Cambridge are University from ‘A University GeologicPress). Press). Time Quaternary*:Quaternary*: Formal chronostratigraphic Formal chronostratigraphic unit sensu unit joint sensu ICS-INQU joint ICS-INQUA taskforceA (2005)taskforce and (2005) ICS. and ICS. Scale 2004’, by F.M. Gradstein, J.G. Ogg, A.G. Smith, Tertiary*: InformalTertiary*: chronostratigraphic Informal chronostratigraphic unit sensu unit Aubry sensu et al. Aubry (2005, et Episodesal. (2005, 28/2).Episodes 28/2). et al. (2004; Cambridge University Press).

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• Neogene and its top and rank; • Paleogene rank; • Pliocene and the placement of its stages. The use and position of Gelasian, and re-examination of its definition; • Tertiary and its use and rank.

The task force also may want to advise on a realistic correlation web for the last 5 Ma underlying rational, global subdivisions and hierarchy. The findings of this task force will be presented at the 33th International Geologic Congress in Oslo, Norway in 2008.

Until further notice, geoscientists are advised to follow the ICS stratigraphic scheme outlined in Figure 2.

REFERENCES

Finney, S.C. 2005. Global Series and Stages for the Ordovician system: a progress report. Geologica Acta, v. 3, no. 4, p. 309-316. Fortey, R.A., D.A.T. Harper, J.K. Ingham, A.W. Owen and A.W.A. Rushton 1995. A revision of Ordovician series and stages from the historical type area. Geological Magazine, v. 132, p. 15-30. Fortey, R.A., D.A.T. Harper, J.K. Ingham, A.W. Owen, M.A. Parkes, A.W.A. Rushton and N.H. Woodcock 2000. A revised correlation of Ordovician rocks in the British Isles. Geological Society of London Special Report No. 24, 83 pp.

ABOUT THE AUTHORS

Felix M. Gradstein is Chair of the International Commission on the Stratigraphy. Following retirement from the Geological Survey of Canada and Saga Petroleum Norway, he joined the Natural History Museum. University of Oslo as stratigraphy/micropaleontology professor, where he is developing relational stratigraphic databases for offshore Norway. His activities have included quantitative stratigraphy (he chaired previous IGCP and IUGS programs). Ocean Drilling Program legs in the and Indian oceans, and coordinating compilation of and Phanerozoic geologic time scales. He is an avid skier and offshore sailor. [email protected]

Stan Finney is Chair and Professor of Geological Sciences at California State University at Long Beach. He has served as Chair of the International Subcommission on Ordovician Stratigraphy (1996-2004) and presently serves as Vice Chair of the International Commission on Stratigraphy (2000-2008). He is a specialist on Ordovician graptolite and has published on graptolite taxonomy, paleoecology and paleobiogeography, the Late Ordovician mass extinction, and the stratigraphy and structure of the Roberts Mountains allochthon of north-central Nevada. His recent research utilizes U-Pb of detrital zircons to interpret the paleogeographic and geotectonic history of the Precordillera terrane of western Argentina. [email protected]

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