厩 Magnetic Stages

勿 G . Pavia and R. Enay D efinition of the A alenian-B ajocian Stage boundary

The G lobal boundary Stratotype Section and P oint brought to a conclusion in 1994 w ith the nom ination ot the M urtin- (G SSP) for the Bajocian Stage, formally defined at the heira section at C abo M ondego, Portugal, as the best outcrop for defining the G lobal boundary Stratotype Section and Point (G SSP) base of bed AB Il of the M urtinheira section at Cabo of the Stage. A ft er a positive ballot w ithin the B W G , the resolution M ondego (P ortugal), has been ratif ed ky the IU G S. M ul- w as subm itted to the C ongress ot the International Subcom m ission tidisciplinary biostratigrap hical data, m ainly based on on Jurassic Stratigraphy (ISIS) in M endoza, A rgentina, in O ctober, 1994. In addition to the G SSP , the selection of the B earreraig B ay am m onite and calcareous nannofossil assem blages, section on the Isle ot Skye, Scotland, as the A uxilia r y Stratotype assure w orldw ide correlations; m agnetostratigrap hic Point (A SP) w as also suggested as a com plem entary outcrop w here data increase the correlation p ow er The position of the the palaeobiological key (evolutionary transition w ithin the boundary coincides w ith the fi rst occurrence of the am m onite group G raphoceras-H yperhoceras) for recognizing the B ajocian low er boundary is finely represented. T he consensus at the am m onite assem blage characterized 勿 H yperhoceras M endoza m eeting encouraged subm ission oft he proposal of both the m undum and related species (H . furcatum , B ratinsina B ajocian G SSP and the A SP (Pavia and others, 1995) to the ISJS aspera, B . elegantula). The boundary lies just below the w hich unanim ously accepted the resolution. nanno-horizon of the entry of W au naueria com m unis T his paper gives details on the definitio n o t the B ajocian G SSP recom m ended by the IC S at the end 1995. T he proposal w as for- and W . fossacincta, and closely corresponds w ith an m ally ratified by the IU G S at the m eeting ot the E xecutive C om m it- inversion to norm al polarity correlated w ith the up -to- tee in January ］996. date Jurassic m agnetic p olarity tim e scale. A n A uxiliary Stratotyp e P oint (A SP ) is also selected at the base of b ed T he low er boundary of the B aJocian Stage U 10 of the B earreraig B ay section on the Isle of Skye, Scotland, as the comp lem entary referencefor the p alaeo- The original definition ot the B ajocian Stage dates back to 1850 biological key of the Bajocian lower boundary, i.e. the (d'O rbigny, 1842-5 1, p. 606, and 1849-52. pp. 477, 483; see R ioult, evolutionary transition G raphoceras-H yperhoceras. 1980 for references) w ith geographic references to B ayeux and the area around C aen, N W France. In the Jurassic C olloquium held in Luxem bourg, R ioult (1964) proposed the section at Sainte-H onorine- des-Pertes, near B ayeux, as the stratotype of the Bajocian Stage In tro d u c tio n H ow ever, Pavia (in C resta and Pavia, 1994, p. 93) observed that stratigraphic condensation and fossil rew orking dictate exclusion ot any section in the area of B ayeux as the stratotype of the Stage. M ultidisciplinary research on the boundary stratotype, developed O n the basis of am m onite fossil assem blages, the E uro p e a n over m any years by the B ajocian W orking G roup (B W G ), w as B ajocian presently com prises seven 'Standard Zones' (Figure 1),

厩 MP AO GL ANRE TITIYC S│ T A G E S │ E u r o p e a n│ S t a n d a r d Z o n e s │ │ │ │ │ │ │ 百 │ 日＾丁。0 N│ I’ A N │ ││ │｝ │ U │ P a rk in e n n i-q n n r-k im z n n i 7 n n r- │ │ │ ├───────┤ │ │ 三 B 呈 │ f l'A rn │rd ia na m q ran fi an a 7│nnp│ │ │ │ │ ．． A │ │rE │ 4 Z t r ja n n │ i , ta r .q .,c z n i r i & P n .- z P 7 n np.│ │ │ ├───────┤I＿│ │ │ ││ │ │

口．．． │ │ J R ├──────────────────────────────────┤ │ ├─┼─┤ 0 │ │ S t e│ p h │a├───────┤no ceras hum p hti e s│ian um Z on e │ 竺 C │ │ M ite s s a│uze i Z on e │ │ │ │ │ I L │ │ │ │ ├───────┤ │ │ ．门．．．．． │ │ A 0 │ │ │ │ │ │

冈 W │ │ │ ├───────┤ │ │ F ig u r e I B a j o c ia n a m m o n i t e │ E │ │ │ │ │ │ │ │ │ │ │W i│tch e fi a la e v iu s c u l│a Z o│n e S t a n d a r d Z│ o n e s i n E u r op e c o r re l a te d │ R │ │ ││ ├───────┤ │ w i th m a│gnetic p olarity tim e scale 州yperfioceras discites Zone│ │ │ (m o d ifi│ e d f r o m G r a d st ei n a n d│ o th e r│s , │ │ A A L E N I A、 │ ｛ 19│9 4; q 绍， 1 9 95│). │ │

M a rc h 1 9 9 7 Z 7 w hich have been tentatively correlated w ith the standard ones pro- I T he basal boundary of the H . discites Z one is m arked by an posed for the Pacific Realm (H illebrandt and others in W esterm ann, am m onite assem blage w hich contains the H . m undtan group 1992, p. 254). T he biochronological correlation pow er of the Euro- late representatives of G raphoceras and H aplop leuroceras: pean Standard Zones thus would spread out the palaeobiogeograph- other taxa. like E tihop loceras and H am m atoceratidae, did no t ical sectors w here they are usually recognized and applied. O ther seem so useful for stratotype definition because of w ide bios- bio stratig raphic zonal schem es are in progress, e.g. for calcareous tratigraphic range and low frequency in the Sub- M editerranea n nannofossils, palynom orphs, m oceram id bivalves and others (C resta sequ ence s. and Pavia, 1994 ）． 2 T he M urtinheira section w as provisionally regarded as the m ore T he B ajocian i s d ivided in tw o substages (Pavia in M ichelsen suitable candidate for G SSP w ith the B earreraig B ay section and Zeiss, 1984, p. 65). The European Lower Bajocian encom passes being considered as the auxiliary stratotype. the 4 vperhoceras discites to the Stephanoceras hum phriesianum 3 For these tw o sections, nevertheless, m ore inform ation on bio- Zones. The base of the 且 discites Z one is traditionally used to stratigraphy and m agnetostrati graphy w as to be done. determ ine the base of the substage. F or its recognition, in m any Jur- D uring the B W G m eetings of Portee in Scotland （199 1) and M a r- assic C olloquia (E rlangen 1984, L isboa 1987, Poitiers 199 1, M en- rakech in M orocco (1994) no agreem ent on a single proposal doza 1994) and related B W G m eetings (C resta and Pavia, 1990; w as reach ed . T h e d ile m m a w as that: M orton, 199 1; C resta and Pavia, 1994), the evolution of the I the Bearreraig B ay section is better for docum enting the evolu- am m onite fam ily G raphoceratidae has been stated as providing the tionary lineage w ithin the am m onite fam ily G raphoceratidae highest biostratj graphical resolution. In particular the first occur- and the early developm ent ot H 力,erlioceras} rence of species of the genus 尺yperlioceras, evolved from G rapho- 2 the M urtinh eira section is m o re suitab le fo r d irect corre lation ceras, has been largely accepted as being the biochronological event based on am m onite assem blages; w hich best enables recognition of the basal boundary oft he B aJocian 3 n o a lternativ e cand id ates had been sub m itted . Stage, particularly in the Sub-M editerranean and Sub-B oreal In a postal vote w ithin the BW G , a m ajority o f 6 5.7% favoured P ro vince s. M urtinheira. T he resolution to define the G SSP ot the B ajocian T he re c e n t usage m eans that the H . discites Z one is an A ssem - Stage in the M urtinheira section w as presented during the m eeting of blage Zone in the sense of the International Stratigraphic G uide (Sal- the ISJS (A rgentina. 1994); it w as also suggested that a joint pro- vador, 1994). It is m ainly characterized by species of the Cgenus posal be m ade for the B earreraig B ay section to becom e the B ajocian H yperlioceras. O n the basis of the m ore recent literature, the low er A S P . I n o r der to refine the proposal as m uch as possible, a group of boundary of the H .discites Z one can be assum ed to be m arked by the first occurrence of the am m onite assem blage w ith H Yp erhoceras w orkers m et in C oim bra (Pavia and others, 1995) w ith the aim of niundurn and related species (H .furcatum , B raunAina aspera, B . ele- revising the taxonom y of graphoceratid am m onite specim ens on w hich the B ajocian low er boundary had been form erly recognized at gantula). E arly form s of the evolutionary transition G rapho- C abo M ondego by R ocha and others (in C resta and P avia, 1990, p. ceras-H 力}erfioceras (C allom on and C handler in C resta and Pavia, 49, p1s. 1-4) and by H enriques and others (in C resta and Pavia, 1994, 1990, p. 96; M orton in C resta and Pavia. 1994, p. 79) are referable to the topm ost A alenian. p. 79). B y availability of B uckm an's types and com parative m aterial T w o sectio ns hav e b e e n d em on strated to be the b est fo r record - specially brought by R . Chandler and N . M orton from G reat B ritain (D orset and Skye), it w as possible to im prove and som etim es m od- ing such a biostratigraphic datum : M urtinheira at C abo M ondego in ify previous determ inations of G raphoceratidae listed from C abo Portugal and B earreraig B ay on the Isle of Skye in Scotland. Both M ondego. E ven though rare specim ens referable to 月以〕erfloceras furnish supplem entary biostratigZ'raphic and m agnetostratigraphic had been reported from beds A B 9 and A B IO of the M urtinheira sec- data. The Scottish section, as far as the am m onite biostratigraphy is tion, the m ost significant biostratigraphical change occurs betw een concerned, is lim ited to G raphoceratidae and can be regarded as the bed s A B IO an d A B I L It reco rd s th e fi rst occu rrence of the reference section for the evolution within this fam ily and for the am m onite assem blage w ith H . m undum and related species. This onset of the genus 1}yperlioceras. O n the contrary, the M urtinheira assem blage is precisely correlatable w ith other am m onite succes- section contains m ore diversified am m onite assem blages useful for sions from Sub-M editerranean (e.g. M orocco) and Sub-B oreal (e.g. w orld w ide correlation . D orset, Skye) localities. A s a result of the revision, it has been pro- In conclusion, the lo w er boundary of the H . discites Z one in the posed to define the B ajocian G SSP at the base of bed A B I I of the M u rfi nhe ira sectio n can be u sed to d efi ne th e G S S P for th e base o f M u rtinhe ira section . the B aJocian Stage. In the sam e tim e the section of B earreraig B ay is form ally proposed as the A SP of the B ajocian Stage T he M urtinheira section (w est P ortugal)

Im proving the proposal for the G SSP The relevance ot the sections of C abo M ondego w as firstly pointed out by M outerde and others (1972) and all the subsequent w orks Since 1988, B W G m em bers have m et in Italy (C resta and P avia, strongly em phasized its im portance for correlation w ith other 1990), Scotland (M orton, 199 1) and M orocco (C resta and P avia, provinces (e.g. R ocha and others in C resta and Pavia, 1990, p. 49; 1994) both to discuss the biostratigraphical key for the recognition of H enriques, 1992; H enriques and others in C resta and Pavia, 1994, p. the B ajocian basal boundary and to develop a com m on proposal for 63; H enriques and others, 1996), based on the richness in am m onites defining the B ajocian G SSP according to the G uidelines of the ICS w hich show both north-E uropean and M editerranean afi nities. T he (C ow ie and others, 1986). m ain stratigraphic data, useful to define the B ajocian G SSP, are here In 1988 at Piobbico, ce n t ral Italy, several sections w ere docu- sum m arized from Pavia and others (1995). m ented: D igne, south-eastern France, by G . Pavia; B arranco de Agua Larga, southern Spain, by A . Linares and J. Sandoval; W utach, R ecom m ended stratotype southern G erm any, by G . D iet]; D orset, southern E ngland, by J. C allom on and R . Chandler; Bearreraig Bay, Isle of Skye, Scotland, by C abo M ondego is located on the Portuguese A tlantic coast, 40 kin N . M orton; M urtinheira, C abo M ondego, Portugal, by R. Rocha and w est ofC oim bra and 7 km north ofF igueira da Foz. T he M urtinheira collaborators. D iscussion for defining the B ajocian low er boundary section is at the foot ot C abo M ondego clift , south-w est of the vil- stratotype centred on the sections ot Isle of Skye and C abo M on- lage of M urtinheira (Figure 2). T here is exceptional exposure along dego. The conclusions were brought together in a docum ent sup- the cliffs and inland for about 5 km (the northern flank of Serras da ported by m ost of the participants: B oa V iagem and A lhadas) w ithout significant facies variation or

EPisodes, Vol. 20, no.］ 1 8 structural com plication. T he beds are m onoclinal and dip at about 400 m . T he A alenian-B ajocian section corresponds to a m ore-or- 30' S.25 T he precise geographical location of the G SSP is show n on less rythm ic alternation of gray lim estones and m arls (C alcbrios e th e 1 : M 000-scale topographic m ap of V ais (sheet 238A ) by coordi- m argas do C abo M ondego form ation), som etim es very fossiliferous n a te s 二 134 .4 , P ＝ 3 5 9 .2 . (am m onites, brachiopods), w ith bioturbation m arks, coal fragm ents, T h e s u c c e ss io n c o n s ists of m arine sedim ents ranging from dissem inated pyrite and rare celestite nodules. Strata are norm ally U pper T oarcian to M iddle C allovian w ith a thickness exceeding thin (0.15 to 0.25 m ) and the stratification surfaces are m ore-or-less regular. A t the L usitanian B asin organization scale, the 蒸U ； Aalem an-Bajocian boundary is placed w ithin the M egasequence F (Soares and others, 1993) betw een discontinuity 6, w hich m arks a generalized absence of the base of m id-A alenian L. m urchisonae Zone, and discontinuity 7 placed tow ards the top of the H . discites Z o n e . T h e A alenian-B ajocian boundary is defined at 77.8 m from the 瞿 base of the section m easured along the coast (H enriques, 1992), at the base of bed A B I I of form er w orks (e.g. H enriques and others in R ocha and Scares, 1988, p. 243) or bed M 337 of recent w orks (e.g. 一e H enriques and others in C resta and Pavia, 1994, p. 63) (Figures 3 蒸瘾）杯补！ and 4). /9i软叹 4 从公二创 A m m on ite record 黝 I 竺二二．妨 T he am m onite assem blages in the C abo M ondego sections (R ocha 垦渔葬﹃ and others in C resta. and Pavia, 1990, p. 49, pls. 1-4) have several 沙攫}} :4 1, 嵌 biostratig raphic advantages: 洲 I the m aterial is quite abundant and easy to sam ple; 2 it is w ell preserved as internal m oulds providing easy identification; C ab o 3 in general, it includes individuals representing different ontoge- M ondeg o netic stages; this fact is particularly evident for m icroconchs 编 w hich are m ore frequent due to paleoecological and taphono m ic r e a so n s ; 鬃准韧矍蒸曝 4 am m onites can be sam pled in w idespread m icritic lim estone 阶； beds and are contem poraneous w ith the sedim ent, as they cor r e- 羁R7 _l_' : 门卜曰厂、 spond to resedim ented elem ents in the taphonom ic sense of Fer- C - 的钊 } . I- 甜濒 nandez Lopez (1991). .4- do C abo M w degc 瞥髯马瑟藻七夕鬓 The definition of th e A alem an- B ajocian boundary at bed 展 A B I I is based on am m onite biostratigraphy (Figure 5). In particular, it m arks the first occurrence of the assem blage w ith H yp erlioceras 瓦 - " 合' 弓萦粤群舞翼 m undum and related species (H . furcatum , B raunsina asp era, B. elegantula), even though the genus H yperhoceras m akes early appear- Figure 2 Location of t he M urtinheira section in the northern ance in the underlying beds A B 9 and A B 10, according to F ernandez part of t he C abo M ondego cliff ( arrow ), 7 km north of F iguera Lopez and others (in R ocha and Soares, 1988, p. 301). T he H . da Foz, w est P ortugal. 1:25000 top ographic m ap of Vais, sheet m undum assem blage also contains other均perlioceras taxa and late 238 A , coordinates M =134.4, P =359.2. representatives of G rap hoceras and H aplopleuroceras, as w ell as species of Zurcheria, P arazurcheria and Fontannesia. Less frequent am m onites of the basal B ajocian refer to genera E uhoploceras, Son-

盆，书

游髓．腻 A B 12 勇交 I

A B I I

A B IO

A B 9

F igure 3 The G SSP of the B ajocian Stage (arrow indicates bed A ll) in the alternating lim estones and m arls of the M urtinh eira F ig ure 4 The position of the G SSP of t he B ajocian Stage at the section, foot oft he Cabo M ondogo cliff. base of b ed A I I (arrow ) in the M urtinheira section.

M a rc h 1 9 9 7 1 9

CA B O M O N D E G O │ I │ z0 山 ││ M u rtin he ira │ 目＿． ‘‘ 卜 .2 O │ │ │ │ s ec tio n │ 心卜奋二 j ．《 │ │ │ │ 嵘卜＿匆目的一～执卜声公舫 │ │ │ │ │ 一｛一｛一撒｛｛-50 '51 4 一鑫Ib eUCIL Us- 09C} 1 AC80 Itl . t L2 - │ │ │ ││ ， I ‘，i ．一｝ ’ 一一 │ ’ │ 的 2 │ │ │ │ │ │ 吕甲，4 下 ’ 毖 │ 山＜ │ │ │ │ │ │ │ ．，蚕，：心 │ │ │ 卜│ O │ ││ │ I’ ，⋯ V 0 │ │ │ │ │ │ │ │

I ，，．一一，．甲I ．，甲＿． │ │ │ │ O 山＜ │ │ ││ │ │ │ │ │ │ │

二 I ： I ：：：：：．：：：：．： │ │ │ │ │ │ │ │

二 │ │ │ │ 乏＜ │ │ │ │ │ │ │

叶． │ │ │ │ 习乏 │ │ │ │ │ │ │ 注山 │ │ │ │ │ │ │ │ │ │ │ 乏泛 │ │ │ │ │ │ │ │ │ │ －J ││ │ │ │ │ │ │ │ │ │ 、、．沪││ │ │ │ │ │ │ │ │ │ 芝 │ │ │ │ │ │ │ │ │ │ │ 二 │ │ │ │ │ │ │ │ │ │ │ S│ │ │ │ │ │ │ │ │ │ │ Z │ │ │ │ │ │ │ │ │ │ │ 0 │ │ │ │ │ │ │ │ │ │ │ ｝一｝：1 ．＿1【‘二│：一；斗：│．：│：│ │’二二．1│1一│：’I J0口、 │ Z │ │ │ │ │ │ │ │ │ │ │ │ │ │ F igure 5 D istribution of t he m ost sIig n}抓cant am m oni”tes throug‘h’ the A a．le nian- B ajocian boundary in the M urtinheira section.的．，│ │ │ │ │ │ │

ninia, 'D ocidocerw ’，Pelekodites, N annoceras, Praestrigites, B rad- change in the nannofloral assem blages suggest continuous sedim en- fordia, 'A sthenoceras', P rotoecotrausies and Trilobiticeras. tation across the boundary. as confirm ed also by sedim entololay.

C a lca reou s n an n o fossil reco rd M agnetostratigraphy D etailed studies across the A alenian- Bajocian boundary have been T he succession of the A alenian-B ajocian boundary has been sarn- published recently by H enriques and others (in C resta and Pavia, pled in a total thickness of 16 m . T he intensity of rock m agnetization 1994, p. 63). The nannofossil assem blages are dom inated by speci- in the M urtinheira section is generally weak (between 6.7 x 10-5 and m ens of Schizosphaerella punctulata, Lotharingius contractus, L. 2,2 x 10-4 A/m). but it is m easurable using a triaxial high-sensivity velatus, Triscutum tiziense, B iscutum depravatum and D iscorhabdus cryogenic m agnetom eter (C C L-G M 400). T he m agnetic stabilitv of criotus. The genera C rep idolithws and C arinolithus, w hich dom inate the sam ples has been investigated by increm ental therm al dem ag- the early Jurassic assem blages, are rare. The results point to a grad- netisation. The m ajority ot sam ples carry tw o principal com ponents ual turnover across the A alenian-B ajocian boundary w ith change in of m agnetisation. T he low er stability com ponent is progressivelly nannofossil dom inance rather than abrupt appearences and/or disap- rem oved during dem agnetisation in average up to 250'C and appears pearences of taxa. T his change is initiated by the W atznaueriacea in to represent a norm al polarity overprint near the local present C,eo- the upper G . concavum Z one, from w here the genus Lotharingius is m agnetic field. T he high stability com ponent direction results to be m ore and m ore replaced by W at,7naueria and 0 7clagelosphaera. sim ilar to the D ogger direction indicated for the Iberian Peninsula S e ve ral na nn o -h oriz on s h av e b ee n d etected at th e (Schott and others, 198 1）after applying the bedding-tilt correction A alem an-B ajocian transition. based on the onset of different species (average 40' tow ards 130'）．Then it is clear that this com ponent rep- of W atznauena (Figure 6). T w o nanno-horizons are observed in the resents the record oft he geom agnetic field polarity at the tim e of sed- G . concavum Zone, defined by the appearence of W ovata (A B 1) im entation. T he values of the natural rem anent inagnetisation have and W aft. conununis (A B 3). Six nanno-horizons characterize the H . positive inclinations; but during dem agnetisation about 30% of the do cites Z one. Som e data can be pointed out:议fiossacincta and W ． sam ples changes polarity and finally there are tw o groups of clear aff. m anivitae are observed from sam ple A B 13: the entry of W . coin- opposite polarity. m unis is recorded in sam ple A B 14 ; the first occurrence of W . britan- The final res ul t s ot the palaeom agnetic field polarity record of nica is observed in sam ple A B 17 } W . m anivitae appears in sam ple the A alenian-B ajocian boundary at C abo M ondego are show n in A B 3 4 . Figure 7. The B ajocian low er boundary, at the base of bed A B I I ot Th e p resence of form s such as W . aft. com m urns and W ．aff. th e M urtinh eira section , co incides w ith an inversio n fro m rev ersed to m anivitae. precursory of the nom inate species, and the gradual norm al polarity, w hich can be correlated w ith the JLIraSSiC m alanetic

Episodes, Vol. 20,；，‘，．I 2 0

芝！ e located at the base of bed U 10 in the low er U dairn Shale M em ber, 之！I nu J．四 a，亏︶I 12.4 rn above the base of the section recently revised by M orton (in ‘ ～ u 之仑e E 之 u 之．。 O 。 B 住．． Pavia and others, 1995). Fossils are preserved in scattered calcareous u ‘ s 遥 u 日亡之之之 n n n 。 l n 之 u 亏 n o d u le s d 和︸互。互它亡空。巴之 es ‘ 仍之 u、 el 之旦 s 。．巴。句．七．之七． 0 七 IJ 卜 ej d s 0 a ．。注 q U e e n 之．通渔电．．． M ajor character 甸 P P d t t t 0 七 t 之自 s ‘ ．‘ ． e 5 e e d ‘ ．～o 之．吕匀之之． n n s 。 f a ．甸．勺． E 勺． T he first occurrence of the am m onite assem blage w ith H 力〕erlio- o 写切亡亡亡 u 亡 o C u zl o 之坦之之 zJ ﹄ z 月之心。。。月肠，月勺 ceras m undum and related species is w ell docum ented. T his overlies 。 5 ～肠盏互互劝奋力夺勺奋卜加 5 51 0 Q 一一一一 a 一一 an assem blage w ith H . incisuin w hich m arks the first step in the evo-

lutionary lineagZ}e G raphoceras to I乃,perlioceras at the topom ost 人M M O N IT E S │S A M P LE S │ │ 1 ．月．｜、 1 ． A alem an. In particular, the follow ing biostratigraphical m arkers are 1 1 ！仍 A B 4 0│ │ │ 一｜ 1 ．！ registered: (1) top bed U 9 (I rn below the A SP): first occurrence of 百．山 A B 3│9 │ │ 一十．卜 A S 3 8││ │ 幽．！ H . incisum (M )- rotabilis (m ) and H . m icca; (2) bed U 10: first

刽． U A S 3 6 │ │ 十 ‘ occurrence of H . m undum , H . furcatum , B . aspera; (3) m iddle bed 闷．仍 A S 3│4 │ │ 凶二 U 16 (9 m above the A SP): transition from H , m undum to H . walkeri; O A S 3 2 │ │ │ ｜酬 r 1 (4) m iddle bed U 18 (11 m above the A SP): last representatives of G . A S 30 │ │ │ ｜！．冈 es 1 A S 2 8 │ │ │ ｜州 es lim itatuni (M )- carbatinum (in ). 1 es．． A S 2 5 │ │ │｜侧十 es 十 A S 2 3 │ │ │ 闷乡 C o rrela tio n A S 2 1 │ │ │ 1 1 酬． A S 1 9 │ │ │ J ｜闷！． A S 17 │ │ │｜ l In sum m ary, the m ain biostratig raphical features of the A SP are: 凶． l A S 1 6 │ │ │ 侧 es I A m nionites- R epresentatives of H am m atoceratidae and Son- 由． e ． A S 1 5 │ │ │ 冈 1 j 角 1 l ， ninidae, although rare, im prove correlations w ith the G SSP. 四，月 A S 1 4 │ │ │ 闷 1 1 A 日 13 │ │ │ 酬酬 2 B ivalves- Fossil assem blages found in the low er part of the 剑陌 U dairn Shale M em ber show a significant change in the bivalv e A S 12 │ │ │ 日国 A S 10 │ │ │ 旧酬 com position from the G . concavum Z one into the H . discites A S 1 1 │ │ 酬│ 冈 Z one. In particular, M ytiloceram us po忡 locus first appears n e ar 叼四芝 A S 8 │ │ │ 闷侧 the base of the B ajocian (top of bed U 9). The species is also 匀 A S 7 │ │ │ 恻冈＞ A B 6 │ │ │ 酬 present at the base of the B ajocian in north G erm any (M etz, 《 A S 4 │ │ │ 日 1994, pers. com m .), confirm ing its biostratigraphical potenti al in 0 A S 3 │ │ │ 目 Europe. Inoceram ids are w idely used for M iddle Jurassic bio- 以之 A R I │ │ │ 侧 stratigraphy in eastern R ussia and the circum -Pacific (D am bor e - O A D 1 3│ │ │ 闷 O A D 1 0 │ │ │ 国 nea and others in W esterm ann, 1992), w here 从 polyplocus is A D 7 │ │ │创 recorded from the U pper A alem an P. tugurense Zone. A D 5 │ │ │ 3 M icrofo ssils- G oo d results ha ve been ob tained w ith fora m inif- era, dinoflagellates, spores/pollen and calcareous nannofossils For exam ple, the base ot the B ajocian is m arked by radiation o f F igure ‘Selected calcareous nanno/ossil F O at the gonyaulacacean cysts, and the boundary lies w ithin the N J8b A alenian-B ajocian boundary in the M urtinheira section n an no fossil S ub zo n e. (m odifi ed from H enriques and others in Cresta and Pavia, 4 Sequence stratigraphy- The A alenian-B ajocian boundary is 1994少． placed w ithin the genetic sequence D of the H ebrides B asin (M orton and others, 1987).

C o n clu sio n s polarity tim e scale (O gg, 1995). Betw een beds A B I I and A B 23, in the low er H . discites Zone, an interval ot norm al polarity is recorded, T he G SSP of the B ajocian Stage, ratified by the E xecutive C om m it- also in agreem ent w ith Steiner and others (1987). tee of the IU G S in January 1996, has been defined at the base of bed A B 11, at the point located 77.8 m from the base of the M urfinheira section at Cabo M ondego (western Portugal). The section fulfills T he B ajocian A SP in the B earreraig B ay m ost of the requirem ents indicated in the G uidelines of the IC S: section (Scotland) I Succession of m ore than a hundred m eters of rhythm ic altem a- tion of gray lim estones and m arls corresponding to an outer N am e an d geographical location of the A SP zone of sedim entation, beyond the platform , in the m ost subs i d- ing part of northern L usitanian Sub-basin. T he A alem an-B ajo- B earreraig B ay, w est Scotland, eastern coast of the Isle of Skye som e cian boundary is placed w ithin the M egasequence F of the Lusi - 10 km north of Portree. T opographic m ap 1:25000, sheet N G 45/55 tan ian B a sin. (Trottem ish); N ational G rid reference: N G 5170527 1. 2 A bsence of unconform ities in the interval from upperm ost A alenian to low erm ost B ajocian w ith continuous exposure f rom P o sition o f th e A S P U pper Toarcian (Low er Jurassic) to C allovian (M iddle Juras- sic). The upperm ost A alem an (G . concavum Z one) and low erm ost B ajo- 3 C orrelation by m eans of am m onite and calcareous nannofossil cian （拄 discites Z one) occur in a thick sequence of silty shales, the assem blages w hich show significant turnovers at the boundary, U daim Shale M em ber of the B earreraig Sandstone Form ation. T he correlatable w ithin T ethyan and Pacific R ealm s. In particular: outcrops and succession have been described in the proceedings of bed A B I I is m arked by the first occurrence of the am m onite previous B W G m eetings (M orton in C resta and Pavia, 1990, p. 23, assem blage w ith H yperhoceras m undum and related species (H . and 1994, p. 79). T he A uxiliary stratotype Section and Point is 加rcatum , B raunsina aspera, B. elegantula); at about 0.30 m

M a r c h 1 9 9 7 2 了

N 任 5 W N 翎口 4 2 7 二 O (n 8 a 4 1 7 拼／丫产扮尸人卞＼ 4-} 扮尸二＞山口 86 一」︵ E N ︶ u V 旧 84 0－ u一。卜 0 1 3 7 4 ，理 V 的 5 S 。 3 70 - A B 3 3 ．一二一︸。一 3 6 4 一A S 2 9 50 。 3 6 2 0一的 50 召 3 55 一A B2 3 3 5 1 一A B 17 斗。︸二 3 47 一A B 15 任 78 3 4 3 一A 8 1 3 e

一 A B 9 ．的．／． s ．．、 e ︾／ ‘． c＝ 76 ．／任乞 ‘ ／又．勺．，叭 N 一 ‘ 一》． J＝．．扩卜 318 一A D 22 2 ．月忆口 V ﹄，．洲协 U － 74 ．叮〔二 2 ．， 310 一A 0 17 洲． O 山

．． O 304 一A D 7 1 1 山． I--,'．哎 ‘ ｛

﹄ V 1 、．

， 7 2 1 ．．

．．．．，

！！

7 0

0 9 0 18 0 2 7 0 3 6 0 -9 0 0 9 0 0 0 .15 0 .3 -9 0 0 9 0

D e c lin a tio n Inc lin a tio n IV IR N P G V P a laeo latitu d e Inte nsity(m A lm )

F igure 7 M agnetostratigrap hic sequence across th e A alenian-B ajocian boundary in the M urtinheira section (m odifi edfrom H enriques and others in Cresta and Pavia, 1994).

above the boundary, bed A B 13 regis te rs the first occurrence of Cresta, S, and Pavia, G , eds., 1990, Proceedings of the m eeting on Bajocian nannofossils W atznaueria fossacincta and W . aff. m onivitae. stratigraphy: M em orie Descrittive delta C arta G eologica Italiana, v. 40, 282 pp. 4 W ell correlatable palaeornagnetic results w ith an inversion from Cresta, S, and Pavia, G , eds., 1994, Proceedings of the 3rd international m eet- reversed to norm al polarity exactly at the low er boundary of the ing on A alenian and Bajocian stratigraphy: M iscellanea del Servizio G eo- B ajocian Stage. logico d'Italia, v. 5, 321 pp. 5 E asy accessibility of the section w ell exposed on the clif at Fernandez Lopez, S, 1991, T aphonom ic concepts for a theoretical C abo M ondego. w hich is subject to m arine erosion. biochronology: Revista Espahola de Paleontologia, v. 6, pp. 37一9. G radstein, F M , A gterberg, F P, O gg, J G . H ardenbol, J, V een, P van, Thierry, 6 C lassification of the C abo M ondego area as a N atural M onu- J, and H uang, Z, 1994, A M esozoic tim e scale: Journal of G eophysics m ent is in progress. A form al petition w as subm itted to the Pr e s- Research, v. 99, pp. 24,051-24,074 ． ident of the Portuguese Republic in 1994. H enriques, M H } 1992, Biostratigrafia e Paleontologia (A m m onoidea) do T he B earreraig B ay section (Isle of Sky e , w est Scotland) has A aleniano em Porlugal (Sector Setentrional da B acia Lusitaniana): PhD been accepted as the B ajocian A SP w ithin the sam e G SSP proposal Thesis, Coim bra University, IN IC , 301 pp. H enriques, M H , Linares, A , Sandoval, J, and Ureta, M S, 1995, The Aalen- It provides fine docum entation of the am m onite lineage G rapho- ian in the Iberia (Betic, Lusitanian and Iberian Basins), in Riccardi, A C , ceras-H 对，erlioceras, and com plem entary biostratigraphical data ed ., A dvances in Jurassic R esearch: G eoR esearch F orum , Transtec P ub- m ainly related to the onset of the bivalve M ytiloceram us polyplocus lications Ltd, Switzerland, v 1-2, pp. 139- 150. near the boundary. M ichelsen, 0 , and Zeiss, A , eds.. 1984. Proceedings of the international sym - posium on Jurassic stratigraphy: G eological Survey ofD enm ark, 3 vols. M orton, N , ed., 199 1, C onference on A aienian and Bajocian stratigraphy: Birkbeck C ollege, London U niversity, 129 pp. A cknow ledgem ents M orton, N , Sm ith, R M , Golden, M , and Jam es, A V , 1987. Com parative stratigraphic study of the Triassic-Jurassic sedim entation and basin evo- T he present report is the result of hard w ork by m any m em bers of the lutio n in the B ritish Isles, in B roo ks, J, and G lennie, K , eds., Petroleum G eology of N orth W est Europe: G raham and Trotm an, London, pp. B ajocian W orking G roup including R . C handler, S. Fernandez 6 9 7 - 7 0 9 . L opez, M .H . H enriques, N . M orton, R . M outerde and R . R ocha, w ho M outerde, R, R uget, C, and C aloo, B , 1972, Les lim ites d'& ages. Exam en du together w rote the G SSP proposal subm itted for ratification by the probl6m e de la lim ite A al6nien-B ajocien: M 6m oires du BR G M ., v. 77, IC S. T his proposal w ill be published in extended form in the very pp. 59-68 n ear future . O gg, J G , 1995, Phanerozoic m agnetic polarity tim e scale: G lobal Earth Physics, A Handbook of Physics C onstants, A G U Reference Shelf 1, pp. 2 4 0 - 2 7 0 . O rbigny, A d', 1842-51, Pal6ontologie franqaise. Terrains jurassiques. 1, R ef e r e n c es C6phalopodes: M asson ed., Paris. 2 vols. O rbigny, A d', 1849-52, C ours 616m entaire de pal6ontologie et de g6ologie Cow ie, J W , Z iegler, W , Boucot, A J, Bassett, M G , and Rem ane, J, 1986, stratigraphique: M asson ed., Paris, 2 vols. G uidelines and statutes of the International Com m ission on Stratigraphy Pavia, G , C handler, R . Fernandez Lopez, S, H enriques, M H, M orton, N (IC S): Courier Forschunginstitut Senckenberg. v. 83, pp. I一14. M outerde, R, and Rocha, R , 1995, A proposal for the global boundary

Episodes, Vol. 20, no. I 2 2

s tratotype section and point (GSSP) oft he Bajocian (M iddle Jurassic) and G iulio Pavia is P rofessor of Palae- the A alenian-B ajocian boundary: D ocum ent subm itted to the ISJS (ICS, ontology at the U niversity of T orino. IU G S), Torino, 29 pp. H is researches have been m ainly R ioult, M , 1964, Le stratotype du Bajocien, in Colloque du Jurassique, Lux- co nc en tra ted o n m id -J u ra ssic em bourg 1962: M dm oires de Flnstitut G -D . de L uxem bourg, pp. am m onite taxonom y and biostratig- 2 39 - 25 8 . Rioult, M , 1980, Bajocien, in Cavelier, C, and Roger, J, eds., Les Etages raphy, and m ore recently on the frangais et leur stratotypes: M 6m oires du B RG M ., v. 109, pp. 73-83. interaction of taphonom ic studies Rocha, R B da, and Snares, A , eds., 1988, Proceedings of the 2nd Intem a- and biochronology. H e chaired the tional Sym posium on Jurassic Stratigraphy: Lisboa, Coim bra, IN IC, 2 Bajocian W orking Group for ten v o ls. years and coordinated the activity Salvador, A , ed., 1994, International Stratigraphic Guide. A guide to strati- for the selection of the B ajocian graphic classification, term inology and procedure. 2nd Edition: G eologi- G S S P selection. In 199 6 he w as cal Society of A m erica, 214 pp. elected as the Chairm an of the Sub- Schott, J J, M ontigny, R , and Thuizat, R , 1981, Paleom a.anetism and Potas- com m ission on Jurassic Stratigra- sium -A rgon age oft he M essejana dike (Portugal and Spain): angular lim - ita tio n to th e ro tatio n o f th e Ib e ria n P e n in su la sinc e th e M id d le Ju ra ssic : phy of t he IC S. Earth Planet Science Letters, v. 53, pp. 457-470. Soares, A , R ocha, R B da, Elm i, S, Henriques, M H , M outerde, R , A lm eras, Y , R uget, C , M arques, J, D uarte, L, C arapito, M C , and Kullberg, J C , R aym ond E nay is P rofessor of 1993, Le sous-bassin nord-lusitanien (Portugal) du Trias au Jurassique G eology at the University of Lyon. m oyen: histoire d'un "rift avortV : C. R. A cadenue des Sciences de Paris, H e h as un d erta ken resea rch o n ser. 11, v. 317, pp. 1659-1666. Steiner, K M , O gg, J G , and Sandoval, J, 1987, Jurassic m agnetostratigraphy, UpperJ urassic am m onite taxonom y, 3. B athom an-Bajocian of C arcabuey, Sierra H arana and Cam pillo de biostratigrap 勿，and palaeobio- A renas (Subbetic C ordillera, southern Spain): Earth Planet Science Let- geography. H e chaired the O xfor- ters, v. 82, pp. 357-372. than W orking G roup for six years W esterm ann, G E G , ed., 1992, The Jurassic of the circum -Pacific: C am - until he w as elected C hairm an of t he bridge U niversity Press, 676 pp. Subcom m ission on Jurassic Stratig- raphy. D uring two four-year term s he encouraged the selection of G SSP s for the Jurassic Stage. That for the B ajocian is thefi rst of t hese.

-nW,wutchison ‘Y oung Scientist’F und

W illiam W att Hutchison, "Hutch" to his many friends around the world, was a Scots-born Canadian geologist whoI s-er -ved ana户a and tliel目甲5 ’n myra户dynam‘c anq creatve ways.丫os凡n otab y, he servea．a s‘ne iuu3 3ecretary Uenerai kj9io- 1，匕U）at a p votal t，m e于n 手tsn，story, anQ as IU 夕尧rres，Qent咬1夕8传-产98 7）. 1 he．s am e boundiess energy, enlhusiasm ,”KIII in com m un‘cat，ons, and． ab，1，ty．t o Ioster team w or性．t at cnaracten zea nis w orK w i［n 甲e W U N aiso carried him - to p-re enIu n-e ntI, sc，ent，lic＿a m ，n｛stratve pos，tlons n tne ana件lan U overnm ent, w nere，乒e servea as L)irec［or t.jeneral ot the G eological 万urvey o1 U anada and as A sslstant D epu ty m inister o r h arth Sciences. H is d istinguished career w as tenrunated in I };08 I b in t e n d e d t o p r o m o te th e pr o - porting their participation in hfimeisps uioOnortniaamenl teog lIfyrU oH dGwuetSahc-th sop' safo tl nad tshseotesr ewe ardgivsei chn oegsnf,f 5wme2rae,srn f iotctolelrs oei.swo Ttuaihnbsegl yi fi saohru ps untang 3ind fsbeuceriln eI seUntfirtGiucsgiStasg ra lifeur oswpm oiftch ea th srcoea aun H mncuedetrm c.thoienri swaolon fro l"duYn boduyant isgou nSpcientist F oundation" attended the 28th International G eological C ongress (IG C) in W ashington, D .C ., in 1989. C urrently, incom e earned as interest on the H utchison fund is insufficient to su st ain com parable grants every four years w ithout seriously eroding the principal. For that reason, the IU G S m ade no grants from the fund for the 30th IG C , prefer- ring instead to strengthen the fund by allow ing it to earn interest for a longer period of tim e and by appealing for donations from the international geologic com m unity. It is expected that grants from the fund w ill again support deserving young sci- entists to attend the 31st IG C in the year 2000. T he H utchison "Y oung Scientist Foundation" is a w orthy cause that honors a fine, caring m an and a distinguished, public-spirited scientist and adm inistrator. The foundation also celebrates and pro- m otes those things that gave H utch the m ost professional satisfaction: geology, international scientific collaboration, and stim ulating young m inds. ．‘ 二＿＿．⋯ ＿，＿二＿，⋯ ＿， T h e IU U S w elcom es contribution s to tile h utcnison ’Y oung Ncientist v ounaation. r ie a s e sena aonations to :

D r. John A . R einerm ind P .O . B ox 890 Leesburg, V A 20 178 U SA F ax: + 1 703 777 4463 T e l: + 1 7 0 3 77 7 14 9 1

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M a rch 19 97