I * ,Rtt, I April 2004

Rivista Italiana di Paleontologia e Stratigrafia r.,"-. ,rO I ". , t"ìI * ,rtt, I April 2004

SUBOREAL/BOREAL AMMONITE SUCCESSION AT THE OXFORDIAN/KIMMERIDGIAN BOUNDARY IN THE FLODIGARRY SECTION (STAFFIN BAY, ISLE OF SKYE, UK)

BRONISI.A\r A. MATYJA', KEVIN N. PAGE', ANDRZEJ \rIEMBO\rSKI'E JOHN K. \IRIGHT'

Received September 19,20A2; accepted October, 1" 2003

Key-uords: ammonite succession, Oxfordian/Kimmeridgian più antica Ringsteadia-Microbiplices (subboreale), così come dalla pri- boundary, Boreal zonation, Subboreal zonation, biostratigraphical ma comparsa di piccoli Amoeboceras (Plasmatites) - principalmente,4. correlation. praebauhinì (boreale). Un altro livello che può venir considerato come il limite Oxfordiano/Kimmeridgiano é il limite tra bZona a Bauhini e Abstact. The Flodigarry section at Staffin Bay, Isle of Skye, has quella a Kitchini dello schema boreale, cararrerízzato dalla prima com- yielded numerous ammonites both of Subboreal and Boreal affinity. This parsa degli Amoeboceras (Amoebites) del gruppo di A. bayi. Questo li- has enabled close correlation of the Subboreal and Boreal ammonire zo- vello corrisponde al limite di sottozona Planula/Galar dello schema nations, and provided new palaeontological data on levels which may submediterraneo, ossia é vicino al limite Oxfordiano/Kimmeridgiano be considered as a potential GSSP for the Oxfordian/Kimmeridgian correntemente accettato nella Successione Submediterranea. boundary. The traditional Oxfordian/Kimmeridgian boundary placed at the Pseudocordata/Baylei zones boundary of the Subboreal scheme corresponds precisely to the Rosenkrantzi/Bauhini zones boundary of Introduction the Boreal scheme: this level is characterized by appearance of Pictonia together with Prorasenia replacing an older assemblage of Ringsteadia- Due to the well known existence of two definitions Microbiplices (Subboreal), as well as by first occurrence of small-sized Amoeboceras (Plasmatites) - mostly,4. praebaubini (Boreal). A further of the Oxfordian-Kimmeridgian boundary - each defini- level which may be considered as the Oxfordian/Kimmeridgian bound- tion resulting in the location of the boundary ar a differ- ary is the boundary between the Bauhini Zone and Kitchini Zone of the ent stratigraphical level: lower in the Subboreal/Borea| Boreal scheme characterized by first occurrence of Amoeboceras (Amoe- Succession, and higher in the Submediterranean Succes- bites) of rhe A. bayi group. This level corresponds to the Planula/Galar (Matyja \Wierzbowski 1997; subzones boundary of the Submediterranean scheme, i.e. it lies close to sion & Schweigert & Cal- the currently accepted Oxfordian/Kimmeridgian boundary in the Sub- lomon 1997), there was the need for detailed studies of mediterranean Succession. the sections representative of each of these successions. The object of these studies would be to find levels which Riassunto. La sezione di Flodigarry a Staffin Bay, Isola di Skye, could be considered as directly (or closely) corresponding ha fornito numerosi ammoniti di affinità sia subboreale che boreale. to the boundaries in question: the Pseudocordata/Baylei Questo ha permesso una stretta correlazione delle zonazioni ad ammoniti subboreali e boreali, ed ha fornito nuovi dati paleontologici sui zones boundary (traditional Oxfordian/Kimmeridgian livelli che possono venir considerati come potenziali GSSP per il li- stages boundary in îhe Subboreal Succession), and the mite Oxfordiano/Kimmeridgiano. Il tradizionale limite Oxfordiano/ Planula/Platynota zones (or Planula/Galar subzones) Kimmeridgiano posto al limite di zona Pseudocordata/Baylei dello sche- boundary treated as the Oxfordian/Kimmeridgian stag- ma subboreale corrisponde precisamente al limite di zona Rosenkrantzi/ Bauhini dello schema boreale: questo livello é caratterizzaro dalla com- es boundary (or lying close to) in the Submediterranean parsa di Pictonia insieme con Prorasenìa, che rimpiazzano l'associazione Succession. The paper presents the preliminary results

Institute of Geology, University of Varsaw, Al. Zwirki i Vigury 93,02-S9 Slarszawa (Poland). E-mail: [email protected] and Andrzej.Vierzbowski@ìuw.edu.pl Department of Geological Sciences, University of Plymouth, Drake's Circus, Plymouth, PLa 8AA (U.K.). E-mail: [email protected] Department of Geology, Royal Holloway, University of London, Egham, Surrey T\í20 OEX (U.K.). E-mail: [email protected] 274 B. A. Matyja, K. N . Page, A. \X/ierzbozaski k J . K. \X/right

The Staffin Shale has long been known for the rich- ness of its ammonite fauna (Forbes 1851; MacGregor 1934; Anderson & Dunham 1966; Turner 1966; Hud- Flodigerry son & Morton1969: Wright 1973; Sykes 1925; Sykes & Island Callomon 1979; Vrighr 1989; Morton tr Hudson 1995; Wright & Cox 2001). A comprehensive review of the ammonite faunas was given by Sykes & Callomon (1979), Staffin though the details of the amrnonite succession are only at present beins worked out. Ba'' The Oxfordian-Kimmerid gian boundary succession comprises a sequence of bituminous and silty shales with the frequent development of limestone lenses and beds (Fig. 2). Sykes tr Callomon (1979) have shown that this section exhibits the most complete ammonite faunal suc- & cession of the Boreal Province, thus spotlighting irs po- rfi tential for boundary definition. The exposure at Flodigar- 3 rnf. ry, being the most widespread and showing the succession sr.rd o& -o.t to its best advantage, is the site which may be proposed for GSSP status. The section lies within the Trotternish "76 Ridge Site of Special Scientific Inreresr, so thar appropri- ate protection and preservation are assured. The rock platform exposures at Flodigarry presenr- ed initial problems to stratigraphers in that rhe Oxfordian/ Kimmerideian succession is exposed in series of wave-cut platform sections cur rhrough several steeply dipping slipped Fig. 1 - Loc:rlitv nrrps of Staffin Bay and Flodigarrv sectron blocks (Wright 1989, figs 5, 6). Accurare correlarion between slipped blocks is necessary ro establish the con.rplete succession. Currently available maps published by Morton & Hudson (1995) and Wrieht & Cox (2001) are largely based on the of such a study in the Staffin Bay area of the Isle of Skye preliminary maps of \X/right (1973, 1989). \X/ith the advent - typical for the Subboreal/Boreal Succession, and shows of possible GSSP status, the need for rnore detailed study of the the importance of this areain the distinction of a srraro- exposures was obvious, and the necessary field- was type of the Oxfordian-Kimmeridgian boundary. The pa- work completed by the authors in summer 2001. per concentrates mostly on the position of these levels in The detailed strarigraphy of the Flodiearry Shale the Flodigarry section - the most represenrative secrion Member has been set our by Sykes & Callomon (1979) for the area, and it does not include the detailed descrip- and Wright (1989). The currently studied secion has been measured in tion of the whole secrion and ammonires, or a discussion blocks F5 and F6 in the beach at Flodiearry on the detailed stratigraphical correlation of the diverse and it spans Bed SS 33 (upper part) to Bed SS 45 accord- ing standard palaeobiogeographical units. These will constitute a sub- to division of the Staffin Shale Forn-ration ject of a wider study published elsewhere. as summarized by Morton tr Hudson (1995). The ammonite faunas were collected by the aurhors in the Flodi- garry section at 50 successive levels. The faunas include The section studied successive members of the families Aulacostephanidae and Cardioceraridae, making possible recognition of both A prime candidate for designation as the Global the Boreal and Subboreal zones and subzones of Sykes Stratotype Section and Point (GSSP) for the base of tr Callomon (1979), Bìrkelund & Callomon (1985) and the Kimmeridgian Stage is located at Staffin Bay, Isle of Wierzbowski & Smelror (1993), as well as necessitating Skye, U.K. The boundary between Oxfordian and Kim- some modifications to rhese zonal schenes. meridgian strata occurs within the Flodigarry Shale Mem- ber of the Staffin Shale Formation (Tirrner 1966 p. 248; Sykes 1925, p.66), and is exposed in two rock platform Subboreal ammonites and zonal scheme exposures between the villages of Digg, Flodigarry and Kildorais (Fig. 1). That east of Digg is rather small, and The uppermost Oxfordian zone, rhe Pseudocordata covered by seaweed and boulders, and will nor be con- Zone, ts well represented at Staffin by successive faunas sidered further here, as the boundary is particularly well o{ Ringsteadia and ìts microconch counterparr, mostly exposed at Flodigarry east of Kildorais. Microbiplices, and forms transitional between Microbi- Oxfortlian/Kinttneridgian boundarl, at IsLe of Skye 275

F FÈ ciÈE a F ll -.-s S F FES= >ì €é& SÈ ÈÈEÈs:= _c ar .^ (EÍ ÈRÈ*È€s HÈIEES=*àsSgS bà.8 e el*= F; gHÈ€€€€Èrenre -=o=a-cc **sÉa€l È=H *=On*ÈSSS €S€EEEÈ€ _Jm SRRXFQè HsHD;EÈÈ Èsssfifitr €5€strtr€5 Boreal Zones Subboreal Zones

Kitchini ili -,+ i L- ll 41 1i: ee{Q q) -cr 39 q)

= ,l; cca 38

: Baylei (Ît Bauhini C" Uf2.7 I (g

CD '- 2 o-36 :clm . o riJ IJ- eA \JJ r-=- I 0 I I I Rosenkrantzi Pseudocordata

Fio t Stratiur;lphical distribution of,rurnronit.'s .rnd biostr;rtisruphic;rl interpretation of Flodigarry section; grey blocks ìndicate the intervals of unccrt.rìn bi,'rrr.rtr g,r'rphic.rl intcrpretltion

plices and Prorasenìa. The earliest Ringsteadia, consisting steadia cf . psewdocordata (Blake tc Hudleston), Microbi- of Ringsteadia caledonica Sykes & Callon.ron, is indica- plices anglicus Arkell and Microbiplices sp. may be treated tive of the Caledonica Subzone, the lowest subzone of as indicative of the Pseudocordata Subzone. The upper- the Pseudocordata Zone. A slightly younger fauna with nrost subzone of the Pseudocordata Zone, the Evoluta

Ri n gst eatli a bran de s i Salfeld and M i oobip lìc e s m ì crob ip lex Subzone is also present. It is marked by the occurrence (Quenstedt) and Ringsteadia pseudoyo Salfeld are char- of Ringsteadia epoluta Salfeld together with forms tran- acteristic of the Pseudoyo Subzone. Faunas with Ring- sitional between Microbiplices and Prorasenia. 'Wierzbouski 276 B. A. Matyja, K. N . Page, A. &. J . K. Wright

The boundary between the PseudocordataZone and rantzi Spath but below the earliest occurrence o{ Amoe- the Baylei Zone (Fig. 2), i.e. the boundary between the boceras (Plasmatites) spp. and above the last occurrence Subboreal Oxfordian and Kimmeridgian, lies in the 0.5 m of Amoeboceras marstonezse Spath, is solved here by the thick interval between the last occcurrence of Ringsteadia recognition of the Rosenkrantzi Subzone of the Rosenk- - Ringsteadia eaoluta Salfeld (1.65 m and possibly 1.47 m rantzi Zone. below Bed 36) and the first occurrence of Pictonia - Pic- The Bauhini Zone of the lowermost Boreal Kim- tonia sp. nov. (1.08 m below Bed 36). meridgian is characterised by the occurrence of srnall- The Baylei Tone is marked by the occurrence of sized Amoeboceras spp. of the subge nus Plasmatires (Fig. ammonites of the genus Pictonia and Prorasenia. Of spe- 2). Am oebo c eras (P lasmatite s) praebauh in i (Salf eld) fir st cial interest is recognition of the oldest known Pictonia appears from 1.17 to 1.04 m below Bed 36. Amoeboceras fauna so far discovered (Pictonia sp. nov.) which directly rosenhrantzi Spath and Amoeboceras schulginae Mesezh- precedes the appearan ce of Pictonia densicostata Buckman nikov also occur, and continue up to O. 1Z n-r above Bed in the Flodigarry section (Fig. 2). The new species dif- 36. The Oxfordian/Kimmeridgian boundary in the Bo- fers from the very close Pictonia densicostata Buckman real sense thus lies between 1.65 m (last occurrence of in character of outer whorl which shows more regular Amoeboceras rosenhrantzi Spath withou t Plasmatites) and and stronger ornamentation and is more tightly coiled. 1.17 m below Bed 36, in almost exactly the same interval Full description of the new species will be presented else- of strata where the boundary in the Subboreal sense was where, but this finding confirms the previous suggesrions deduced to lie (see above). The main part of the Bauhi- that the Staffin Bay sections in Scotland are much more niZone, continuing up (Fig.2), contains Amoeboceras complete than the English sections where a hiatus must bawhini (Oppel), Amoeboceras praebawhini (Salfeld) and occur at the boundary of the Pseudocordata and Baylei Amoeboceras lineatum (Quenstedt). A thin faunal horizon Zones (e.g. Arkell 1956). with numerous Amoeboceras aff . schulginae Mesezhnikov The boundary between the Baylei Zone and the is situated in the middle of the zone. Cymodoce Zone in the Subboreal Province lies within The appearance still higher of Amoeboceras (Amoe- the continuous lineage Pictonia-Rasenia at the base of bites) bayi Birkelund Er Callomon and Amoeboceras the Rasenia inconstans horizon. It thus occurs at Flodi- (Amoebites) cricki (Salfeld) is indicative of the Bore- garry above the last occurrence of Pictonia, of the baylei/ al Kitchini Zone as originally defined by Mesezhnik- normandiana group and below the first ocurrenc e of Rase- ov (1968; see also Vierzbowski & Smelror 1993). The nia inconstans Spath. boundary between the Bauhini and Kitchini Zones runs through the 0.8 m of strata between 0.5 and 1.3 m above Bed 40 (Fig. 2). The youngest Amoeboceras (A,moebites) subkitcbini Spath in the upper part of the Flodigarry sec- Boreal ammonites and zonal scheme tion, found above Bed 44, is indicative of the higher part The Upper Oxfordian part of the sequence stud- of the KitchiniZone. ied contains tv/o zones, the Regulare and Rosenkrantzi Zones, and the Lower Kimmeridgian is represented again by two zones, the Bauhini and Kitchini Zones. The Regu- Correlation between Subboreal and Boreal zonal lare Zone shows the occurrence of evolute, densely and schemes regularly rlbbed Amoeboceras of the Amoeboceras regulare (Sykes Er 1979). The section studied at Flodigarry shows very group Callomon Still higher the first ^ specimens of Amoeboceras marstonense Spath, indicative complete ammonite succession consisting of successive of the lower part of the overlying Rosenkrantzt Zone members of both the Cardioceratidae and Aulacostepha- have been found. nidae represented by numerous specimens. This makes The RosenkrantziZone has had a chequered exist- possible close correlation of the Boreal and Subboreal ence since it was first defined as the range zone oÍ Amoe- zonal schemes. boceras rosenbrantzi Spath by Sykes & Surlyk ( 1 926). Sykes The Pseudocordata Zone (Subboreal) corresponds & Callomon (1979) divided it into two subzones, a low- to a part of the Regulare Zone plus the whole Rosenk- er Marstonense Subzone characterised by the co-occur- rantztZone (Boreal). The first appearance of the ammo- rence of Amoeboceras marstonense Spath and Amoeboceras nites of the genus Pictonia indicative of the base of the rosenbrantzi Spath, and an upper Bauhini Subzone, marked BayleiZone (Subboreal) is recognized at the same level as by the incoming of members of rhe Amoeboceras (Plas- the first appearance of Amoeboceras (Plasmatires) indica- matites) group. Following Birkelund & Callomon (1985), tive of the Bauhini Zone (Boreal). The next marked fau- the strata containing.,4 moeboceras (Plasmatites) spp. were nal boundary distinguished by incoming of small Amoe- removed from the RosenkrantztZone and placed in the boceras (Amoebites) of Amoeboceras bayi group is char- lower Kimmeridgian Bauhini Zone. The problem of the acteristic of the base of the Kitchi ni Zone (Boreal). This stratigraphic interval containing Amoeboceras rosenb- boundary does not correspond to any distinct faunistic Oxfordian/Kimmeridgian boundary at Isle of Skye 277 level in the Subboreal succession, being placed within up- between Oxfordian and Kimmeridgian is at the base of per part of the Baylei Zone. The Baylei/Cymodoce zonal the Kitchini Zone of the Boreal scheme where the first boundary of the Subboreal scheme is thus considerably s mall-sized,4 m o e b o c era s (Am o e b ite s) of the .,4. b ay i gr oup higher than the Bauhini/Kitchini zonal boundary of the appear. Choosing of any of these levels as the Oxfordian/ Boreal scheme. Kimmeridgian boundary requires further detailed studies of the Submediterranean Succession to recognize their correlation potentials. It should be remembered that Summary and conclusions the base of the Boreal Kitchini Zone corresponds to the Planula/Galar Subzone boundary (Schweigert & Callo- The coastal exposure at Flodigarry, Isle of Skye, mon 1997; Matyja & \Vierzbowski 2002) treated until fulfils the principal criteria (Remane et al. 1996) for def- the early sixties as the Oxfordian/Kimmeridgian bound- inition as GSSP for the base of the Kimmeridgian Stage. ary in the Submediterranean Succession, and lying fairly The section is well exposed, relatively thick, lacks any close to the currently accepted Oxfordian/Kimmeridgian major hiatus, has not been subject to synsedimentary boundary in the Submediterranean sense. disturbance and has been subject to only minor, faulted, tectonic disturbance. It contains an abundance of well- Ackno.oledgemenrs. \We wish to thank Mr. S. Purdey of SERAD preserved marine fossils, and does not show abrupt facies (Portree) for permission to sample the sections and Mr. A. Turner, changes. Scottish Natural Heritage (Portree) for providing the necessary legal The traditional candidate level for the boundary be- consents. The authors ere grateful for financial support enabling the tween Oxfordian and Kimmeridgian is at the base of the field-studies from the Royal Society, and from the Faculty of Geology of the University of Warsau', which supported the stay in Britain of Bauhini/Baylei Zones, as characterised by the association B.A. Matyja and A. Vierzbowski. The authors are also grateful to the of Amoeboceras (Plasmatires) spp., Pictonia spp. and Pro- journal referees Dr. Ewa Glowniak and Dr. Guillermo Melendez for rasenia spp.. A further candidate level for the boundary suugestions and conrmen!s.

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