The late Barremian Halimedides horizon of the Dolomites (Southern Alps, Italy)

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Cretaceous Research 35 (2012) 199—207

The late Barremian H a l i m e d i d e s horizon of the Dolomites (Southern Alps, Italy)

**A lexander L u kenedera *, Alfred U c h m a n b, Christian Gaillard c, D avide O liveroc**

a Natural History Museum, Geological-Palaeontological Department, Burgring 7, 1010 Wien, Austria b Institute o f Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Krakow, Poland

cLaboratoire de Géologie de Lyon, Université Claude-Bernard, Lyon 1, UMR 5276 CNRS, Domaine Scientifique de La Doua, Géode — 2, rue Raphaël Dubois, F-69622 Villeurbanne Cedex, France

A R T I C L E I N F Q A B S T R A C T

A n e w tra c e fossil m a rk e r level, th e H alim edides h o rizo n , is p ro p o se d for th e L ow er C retaceo u s p elag ic to h em ip elag ic su c cessio n o f th e Puez a re a (S o u th e rn Alps, Italy). T he h o riz o n o ccu rs in th e m id d le p a r t o f th e late B a rrem ian Gerhardtia sartousiana Zone (Gerhardtia sartousiana Subzone). It is a p p ro x im a te ly 2 0 c m th ic k a n d re s tric te d to th e u p p e rm o s t p a r t o f th e P uez L im estone M e m b e r (m a rly lim e sto n e s;

H a u te riv ia n —B arrem ian ; Puez F orm ation). It is fixed to th e to p 2 0 c m o f b e d P1/204. T he g re y —w h itish lim e sto n e b e d o f th e G. sartousiana Zone is p e n e tr a te d b y A p tian re d m a rls —siltsto n e s o f th e R edbed M em ber. The h o riz o n is d o c u m e n te d for th e first tim e fro m th e S o u th e rn Alps, in clu d in g th e D olom ites, a n d c a n b e c o rre la te d w ith o th e r M e d ite rra n e a n localities. The tra c e fossil a sse m b la g e o f th is m a rk e r bed w ith th e co -o c c u rre n c e o f H alim edides, Spongeliom orpha a n d Zoophycos sh e d s lig h t o n th e Low er C retaceo u s se d im e n to lo g ic a l h isto ry a n d c u rre n t sy ste m o f th e Puez a re a w ith in th e D olom ites. It also hig h lig h ts th e p a la e o e n v iro n m e n ta l ev o lu tio n o f basin s a n d p la te a u s a n d p ro v id e s in sig h ts in to th e late B a rrem ian interval.

Article history:

Received 29 A ugust 2011

A ccepted in revised form 10 January 2012 Available online 2 February 2012

Keywords:

Halimedides horizon S edim entation discontinuity Late B arrem ian h iatus Lower Cretaceous Dolom ites Italy

1. Introduction

Lower C retaceous pelagic to hem ipelagic sed im en ts cover relatively sm all, restricted areas in th e h ig h er D olom ites (S outhern Alps). In th e S o u th ern Alps, cep h alo p o d -b earin g d ep o sits are m ainly recorded in tw o different facies (Lukeneder, 2010): th e calcareous lim estones o f th e Biancone Form ation (= M aiolica Form ation in th e A ppenines an d basinal settin g s o f th e Southern Alps; see W eissert, 1981) an d th e m o re m arly Puez Form ation ( Lukeneder, 2010). D uring th e late 19th an d early 2 0 th centuries, a rich fauna o f ceph alo p o d s w as collected from Lower Cretaceous sed im en ts o f th is area by Haug (1887,1889) a n d Uhlig (1887). The m o st re c e n t co n trib u tio n s on th e Lower C retaceous o f th e Puez area w e re published d u rin g th e last decade a n d focused on stratigraphy ( Lukeneder an d Aspmair, 2 0 0 6 ), palaeoecology (Lukeneder, 2 0 0 8 ) an d lith o stratig rap h y (Lukeneder, 2010, 2011).

The b io stratig rap h y o f th e Lower C retaceous Puez area is b ased o n m icrofossils (e.g., form inifera), nannofossils an d am m o n ites ( Lukeneder an d Aspmair, 2 0 0 6 ; Lukeneder, 2010, 2011, in p re s s).

* C orresponding author.

E-mail addresses: alexander.lukeneder@ nhm -w ien.ac.at (A. Lukeneder), alfred.uchman@ uj.edu.pl (A. Uchman), christian.gaillard@ univ-lyon1.fr (C. Gaillard), davide.olivero@univ-lyon1.fr (D. Olivero).

d o i:10.1016/j.cretres.2012.01.002

A d etailed am m o n ite b io stratig rap h y an d zo n atio n w as still m issing because am m o n ites have n o t b een collected b ed -b y -b ed over th e last 150 years. L ukeneder (in press) p resen ts th e resu lts o f th e system atic am m o n ite sam pling a t th e Puez section an d concludes w ith a d etailed am m o n ite zo n atio n o f th a t locality.

A u n iq u e sedim entologic feature occurs in th e m iddle p a rt o f th e Puez Form ation (Lukeneder, 2010). At th e to p o f th e Puez Lim estone M em ber a trace fossil level including n u m ero u s Halimedides is observable in th e w hole o f th e Puez area. The h orizon is p relim i

narily d a te d o n th e basis o f am m o n ites as late B arrem ian from th e Gerhardtia sartousiana Zone (Gerhardtia sartousiana Subzone;

Lukeneder, in p re ss). The tra c e fossil h orizon is restricted to th e u p p e rm o st p a rt o f log P1, b ed P1/204. The la tte r b ed is p e n e tra te d by trace fossils an d filled w ith red se d im e n t from th e overlying Puez R edbed M em ber o f A ptian age. The Halimedides h orizon is described for th e first tim e from th is area an d can be com pared w ith o th e r C retaceous alpine localities w h e re th is trace has b een stu d ied (Gaillard an d Olivero, 2 0 0 9 ).

2. Geological setting and section studied 2.1. Location

The outcrops are situated on th e Puez-O dle-G ardenaccia Plateau in th e D olom ites (m aps T rentino—Alto Adige; South Tyrol; Lukeneder,

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2010). The exact position o f th e m ain outcrop is about 30 km n o rth east of Bolzano (Fig. 1A; E 011°49'15", N 46°35'30"; Lukeneder, 2010).

The grey-, g reen - to red-coloured sedim entary succession o f th e Puez Form ation is located on th e so u th ern side o f th e Piz de Puez. It can be b est studied in ravines called P1, P2 an d P3 (Lukeneder, 2010).

2.2. Geological setting and palaeogeography

The stu d ied sites are o u tcro p s o n th e Puez-G ardenaccia P lateau (Lukeneder, 2010). They are located w ith in th e area o f th e Puez- O dle-G eisler N atural Park in th e n o rth e rn p a rt o f th e Dolomites.

The D olom ites (P erm ian —Cretaceous) a re a n in tern al p a rt o f th e S outhern Alps; th e y are a n o rth e rn Italian m o u n ta in chain th a t em erg ed in th e a fte rm a th o f th e d efo rm atio n o f th e passive c o n tin e n ta l m argin o f th e A driatic (= A pulian Plate) o f th e South A lpine-A pennine Block (D ercourt e t al., 1993; Fourcade e t al., 1993;

Bosellini, 1998; Cecca, 1998; Stam pfli an d Mosar, 1999; Scotese, 2001; Stam pfli e t al., 2002; Bosellini e t al., 2 0 0 3 ). This block w as lim ited by th e Penninic O cean (= A lpine Tethys) to th e n o rth and th e V ardar O cean to th e so u th -e a st (Scotese, 2001; Stam pfli e t al., 2 0 0 2 ). The Puez Form ation includes th re e m em b ers from b o tto m to top: Puez Lim estone, Puez R edbed a n d Puez Marl (Lukeneder, 2010). The succession show s a tran sitio n from lim estones and

m arly lim estones into a m arl-m arly lim esto n e alte rn a tio n in th e u p p e r half o f th e section. A d etailed d escrip tio n o n th e geology an d lith o stratig rap h y is given in L ukeneder (2010). The com plex M ed iterran ean palaeogeography a n d th e presen ce o f m icroplates in th e Tethyan oceanic co rrid o r b e tw e e n Africa an d E urope w as d is

cussed in d etail by Lukeneder (2010, 2011). The Trento Plateau e x ten d s from th e so u th (aro u n d T rento) u p to th e Puez region and w as form erly su rro u n d ed by tw o basins: th e Lom bardia Basin to th e w e st a n d th e Belluno T rough to th e e a st (Lukeneder, 2010).

A ccording to recen t investigations by M uttoni e t al. (2 0 0 5 ), th e Lom bardia Basin (see Fig. 1 for geographic n am es) an d th u s th e a d jac en t Trento P lateau to th e e a st w e re located a t approxim ately 20° N in V alanginian—H auterivian tim es a n d a t alm o st 30° N in th e Aptian.

The m ain investigation area aro u n d Puez is c o m p ared h erein w ith th e w e ll-k n o w n outcrop o f th e Breggia G orge (Figs. 1, 2 ) in Balerna, so u th e rn Sw itzerland (Gandolfi, 1942; Rieber, 1977;

W eissert, 1979, 1981; W eissert e t al., 1979; A rth u r an d Prem oli- Silva, 1982; Gaillard an d Olivero, 2009; Follmi e t al., 2011). The Puez Form ation (Lukeneder, 2010) a t Puez is com parable to th e M aiolica Form ation o f th e Breggia Gorge section (E 009°42'43", N 45°51'20"). A rth u r a n d Prem oli-Silva (1982) first d a te d a bio- stratigraphical gap a t B alerna o f late B arrem ian—early late A ptian

Fig. 1. Locality m ap of th e Lower Cretaceous Puez area. A, Puez area (w hite star) and indicated outcrop position (P1) w ithin the Dolomites, South Tyrol, Italy. B, position of the Puez locality on the Trento Plateau. C, east—w est transect of the Lower Cretaceous plateau—basinal sequence of the South Alpine region. Bozen, Bolzano; Trient, Trento (see B); Col de Puez, Piz de Puez (2913 m). Black stars indicate positions of the Breggia and Puez localities. W hite dashed line marks the course of the Halimedides horizon (Hh).

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A. Lukeneder et al. / Cretaceous Research 35 (2012) 199—207 201

Fig. 2. The Halimedides horizon a t different localities. From the left, the Breggia Gorge section and the Puez P1 and Puez P3 sections, showing the m arker bed and the following hiatus.

o n th e basis o f th e presen ce o f th e planktonic foram inifera Prae- hedbergella luterbacheri an d Globigerinoides ferreolensis b e tw e e n th e low er M aiolica Form ation an d th e overlying m arlsto n es o f th e

"Scaglia v arieg ate”. T herefore th e y assu m ed th a t sed im en tatio n beg an a fter th e gap w ith th e early late A ptian o f th e P. luterbacheri an d G. ferreolensis zones. This com parable lithological change accom panied by a sedim entological gap a t Balerna w as also re p o rte d by Channel e t al. (1993), w ho indicated a h iatu s sp an n in g a t least th e late B arrem ian—early late Aptian.

3. Material

The sam ples studied w ere collected from th e Puez locality (Fig. 1 ).

Bed-by-bed collecting an d a system atic-taxonom ic stu d y provide th e basic d a ta for statistical analysis o f th e investigated am m onites an d trace fossils. Rock sam ples com prising Halimedides, Spongelio- m orpha an d Zoophycos are all from th e to p o f bed P1/204 (Figs. 2 —4 ).

A dditional m aterial w as collected from th e sam e horizon all over th e Puez area, correlated by th e trace fossil assem blage a n d its red truncations. The m aterial w as collected du rin g th e last th ree years w ith in th e FWF p roject P20018-N10 an d is stored in th e South Tyrol M useum o f N atural Sciences an d th e N atural H istory M useum in Vienna. Som e sam ples are housed in th e In stitu te o f Geological Sciences o f th e Jagiellonian U niversity (prefix INGUJP).

3.1. A m m onites

A m m onite d a ta (Lukeneder, 2011, in p re ss) show th a t th e u p p e rm o st b eds o f th e section P1, to p p ed by bed P1/204, belong to th e G. sartousiana Zone (for th e m o st re c e n t Lower Cretaceous am m o n ite zonation, see Reboulet e t al., 2 0 0 9 ). N um erous am m o n ite m oulds from b ed P1/204 o f Melchiorites cassidoides an d Phyllo- paychyceras ladinum (Fig. 5A—D) a re p e n e tra te d by Halimedides.

Traces are filled w ith red (A ptian) foram iniferal silt from th e bed above. The Halimedides an d Spongeliomorpha traces p u n c tu re all of th e am m o n ite specim ens from th e u p p e r to th e low er side. S even

te e n am m o n ites w ere found in b ed P1/204 d o w n to ap p ro x im ately 20 cm below th e top o f th e bed.

3.2. Trace fossils

Halimedides annulata (Vialov, 1971) ( Figs. 2 —5 ) is a m ostly straight, rarely slightly curved, sim ple h orizontal to oblique, exceptionally sub-vertical u n lin ed tu b u la r burrow , 1.0—3.1 m m

w id e (average 2.3 m m ), w ith a series o f h e a rt-sh a p e d o r sub- spherical ch am b e rs th a t are sym m etrically d istrib u te d along th e burrow . The ch am b e rs are 4.8—14 m m w id e (average 7.6 m m ) an d ab o u t 3 —9 m m long (average 4.7 m m ), co n seq u en tly o rie n te d w ith its n arrow ing side in o n e direction, located a t different intervals, ranging m ostly from 7 to 11 m m . However, th e re are intervals w ith o u t ch am b e rs th a t are up to a t least 52 m m long. The tu n n els are filled w ith reddish, stru ctu reless o r rarely p elleted m arlstone.

Locally, th e m argins o f som e b u rro w s display in d istin ct p e rp e n dicular annulations.

The taxonom y o f th is trace fossil w as discussed by U chm an (1999). G aillard a n d Olivero (2009) d escribed Halimedides from different Lower C retaceous horizons in pelagic d ep o sits from th e Alps an d co n sid er th e m as a d ee p -se a agrichnion in w hich ch a m bers w e re u sed for food c ap tu re an d storage, p roduced in stiff to firm su b strates probably by a sm all crustacean.

Spongeliomorpha sp. (Figs. 3C—E, 4A, B, D) is re p re se n te d by h o rizo n tal to su b -h o rizo n tal tubular, rarely branched, straig h t burrow s, 5 —15 m m in diam eter, covered w ith scratch m arks. The scratch m arks are straig h t o r slightly sinuous, 7 —12 m m long, form ing a n an asto m o sin g n etw o rk th a t ru n s along th e burrow , or occurring in sets th a t are oblique to th e course o f th e burrow . The bran ch es are Y-shaped an d seg m en ts b e tw e e n bran ch es are a t least 180 m m long. In som e seg m en ts o f th e burrow s, scratch m arks are n o t visible. In such cases a tran sitio n to Thalassinoides is possible.

The b u rro w is filled w ith a red m arlstone.

Spongeliomorpha is a cru stacean b u rro w p ro d u ced in a firm - ground. It has b e e n synonym ised w ith Thalassinoides an d Ophio- m orpha (e.g., Schlirf, 2 0 0 0 ) b u t m o st au th o rs c o n tin u e to sep arate th e se ichnogenera. The an asto m o sin g scratch m ark p a tte rn is sim ilar to th a t in Spongeliomorpha iberica Saporta, 187 , w h ich is in te rp re te d as having be e n p roduced by sh rim p s scraping m icrobes from th e b u rro w m argin (d e G ibert an d Ekdale, 2010).

Zoophycos sp. (Fig. 4 E, F) is a lobate planar, sp reite stru ctu re oblique in resp ect to th e b e d d in g an d encircled by a m arginal tu n n e l th a t is 4 m m w id e an d filled w ith greenish, in som e cases glauconitic, m arlstone. The sp reite lam inae a re 1 —2 m m w ide, arcuate, an d arran g ed tan g en tially in resp ect to th e m arginal tu n n el. The lobes are 40 to a t least 50 m m w ide, an d som e are at least 80 m m long. Zoophycos s.l. is generally considered a stru ctu re p roduced by, as y e t undiscovered, d ep o sit-feed ers (e.g., Olivero and Gaillard, 1996, 2 0 0 7 ), w hich are referred to as sipunculids (W etzel an d W erner, 1981), polychaete annelids, arth ro p o d s (Ekdale and Lewis, 1991), o r e ch iu ran w o rm s (Kotake, 1992). Kotake (1991)

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2G2 A. Lukeneder et al. j Cretaceous Research SS (2Ql2) l99—2QZ

Fig. 3. A, location of the upperm ost bed of log P1 w ith topm ost bed P1/2G4. B, surface view of Halimedides horizon w ithin log PS, bed PS/21G (= P1/2G4). C, sam ple of bedding plane showing Halimedides (H) and Spongeliomorpha (Sp), bed P1/2G4. D, magnification of C. E, surface of bed P1/2G4 showing Halimedides (H) and Spongeliomorpha (Sp). F, vertical section through cut rock sam ple showing sections of Halimedides and a p enetrated depth of approxim ately 1S cm. Scale bars represent SG cm in A, B, 1 cm in C—F.

show ed th a t som e Cenozoic Zoophycos are p roduced by surface ingestors o f organic d etritu s. The precise ethological in te rp re ta tio n o f th is com plex ichnogenus rem ain s controversial. Brom ley and H anken (2003) suggested th a t th e u p p e r helical p a rt o f a large Pliocene Zoophycos from Rhodes, Greece, is a depo sit-feed in g stru ctu re, an d lateral lobes developing from its lo w er p a rt are sulphide w ells for chem osym biotic bacteria. Zoophycos indicates c o h e re n t sed im en ts (Olivero, 1996; Olivero an d Gaillard, 1996) and can occur in firm ground su b strates in distal settings (M acEachern an d Burton, 2 0 0 0 ).

4. Discussion

4.l. The Halimedides horizon: trace fossil com m unity on the surface o f bed Pl/2Q4

The d e n sity o f b u rro w s is high on th e surface o f th e b ed and Halimedides is clearly th e d o m in a n t ichotaxon (Figs. S, 4 ). Hal- im edides an d Spongeliomorpha cross over each o th e r an d probably illu strate th e sam e colonization phase. Halimedides is a rhabdogly- phid trace fossil com m only d escribed from flysch d ep o sits and

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Fig. 4. A—D, rock samples from Halimedides horizon a t Puez (P1/2G4) comprising Halimedides (H) and Spongeliomorpha (Sp). E, F, Zoophycos (Zoo, log P4) is 1S cm in diameter. Scale bars represent 1 cm.

p reserv ed as a hypichnial convex relief. U nder th e se conditions, Halimedides are p red ep o sitio n al b u rro w s partially preserv ed after ero sio n o f th e sea floor. In th e sections studied, b u rro w s related to th is ichnogenus are preserv ed as ep ich n ia o r en d ich n ia n ear th e top surface o f a b ed com p o sed o f pelagic m ud. M ost o f th e b u rro w s p e n e tra te d up to 30 m m below th e m ark er bed surface, b u t som e to a t least 70 m m . Spongeliomorpha exhibit scratch m arks. The surface show s u nroofed burrow s. The ab sence o f a roof can be explained by ero sio n b u t no sm oothing by c u rre n ts is observed. A collapse of roofs o r b u rro w in g o n th e b o u n d aries o f tw o lithologies is an altern ativ e explanation. No fragm ents o f collapsed roof have been

en c o u n te re d in th e stu d ied sections. Such fragm ents could have b e e n w in n o w ed aw ay by c u rre n ts b u t th e p ro b lem o f sm oothing retu rn s. Thus a b u rro w in g b e tw e e n tw o lithologies, i.e., b etw e e n firm limy m u d an d soft red m arl is th e m o st p robable explanation.

4.2. Are trace fossils reliable indicators fo r sedim ent consistency?

Halimedides v ery probably o ccurred in different kinds o f en v i

ro n m en ts. However, th e v ery stro n g sim ilarities (taphonom y, posi

tio n in th e bed, m orphology) occurring w ith specim ens from different C retaceous pelagic d ep o sits from th e Alps (G aillard and

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Fig. 5. A, m ould of the am m onite Melchiorites cassidoides p enetrated by Halimedides (H). B, Melchiorites cassidoides penetrated by Halimedides. C, Phyllopachyceras ladinum penetrated by Halimedides; left, lateral view; right, longitudinal, polished cross-section. D, Phyllopachyceras ladinum penetrated by Halimedides; left, dorsal view; right, lateral view.

Scale bars represent 1 cm.

Olivero, 2 0 0 9 ) allow in terestin g com p ariso n s an d possible co n clu sions to be m ade. First, it has b een su p p o sed th a t th e co-occurrence o f Halimedides an d Spongeliomorpha probably indicates a d eep -sea en v iro n m e n t w ith pelagic deposits. The association o f th is ichnofauna w ith a b u n d a n t am m onites, th e ab sence o f a d iverse b en th o s an d th e v ery fine-grained se d im e n t confirm th is in terp re tatio n . Both Halimedides an d Spongeliomorpha occurring on th e u p p e r surface o f th e bed 2 0 4 also clearly indicate a firm ground, as observed in o th e r C retaceous b ed surfaces (Gaillard an d Olivero, 2 0 0 9 ). Spongeliomorpha exhibits visible scratch m arks a tte stin g to th is second s ta te m e n t b u t fine scratch m arks, w hich m ay be observed on C retaceous specim ens o f H alimedides from so u th  e a ste rn France, are n o t visible b ecause o f th e filling o f th e burrow . Following th e se data, th e u p p e r surface o f bed 204 clearly illustrates a d e e p -se a su b strate exhibiting th e Glossifungites ichnofacies (Seilacher, 1967; P em b erto n e t al., 2004; M acEachern e t al., 2 0 0 7 ), w hich is typical of firm ground (e.g., Buatois an d M angano, 2011). By co m p ariso n w ith o th e r k n o w n specim ens, Halimedides from th e Puez area are clearly "sparsely c h a m b e re d ” (Table 1). The associa

tio n o f Halimedides an d Spongeliomorpha re p re se n ts a n om ission suite o f trace fossils according to Bromley (1996) w h e re bu rro w s w e re em p laced d u rin g a period o f n o n -deposition. The h iatu s occurring a t th e to p o f bed 2 04 is m arked by an om ission horizon th a t is directly overlain by th e red A ptian Puez Redbed M em ber. This illustrates a t least a long period o f n o n -d ep o sitio n co rresp o n d in g to a p a rt o f th e G. sartousiana Zone a n d th e e n tire Im erites giraudi Zone. The succession o f trace fossils in th e suite is confirm ed by th e

cro ss-cu ttin g relationships. Zoophycos is cross-cut by Halimedides (Fig. 4 F), an d Halimedides seem s to be m o re frequently cross-cut by Spongeliomorpha (Fig. 4A, B). T hese observ atio n s confirm th a t Zoo- phycos traces w ere form ed in a softer b u t probably c o h eren t substrate, possibly a stiffground (Olivero, 1996; Olivero an d Gaillard, 1996; Gaillard an d Olivero, 2 0 0 9 ). Also, som e Zoophycos are considered as a distal expression o f th e Glossifungites ichnofacies (M acEachern an d Burton, 2 0 0 0 ).

4.3. Age and duration o f the late Barremian hiatus

At th e Puez section th e Gerhardtia sartousiana Zone ranges from bed P1/194 up to th e en d o f log P1 w ith b ed P1/204. The low er b o u n d ary is fixed by th e first ap p earan ce o f th e zonal index a m m o n ite G. sartousiana in b ed P1/194 (Lukeneder, 2011). Based on th e am m o n ite assem blage a n d fu rth e r lithological an d m icrofossil analysis, th e u p p e r tw o am m o n ite subzones, i.e., th e G. provincialis an d H emihoplites feraudianus subzones, are probably missing, a h iatus occurring a t th e to p o f log P1 after bed P1/204. Bed P1/204 is directly overlain by A ptian sedim ents. H alimedides p e n e tra te d m oulds o f th e a m m o n ites M elchiorites cassidoides an d Phyllo- paychyceras ladinum (Fig. 5A—D). These can be found w ith in bed P1/204 d o w n to ap p ro x im ately 20 cm below th e top, indicating th e m ax im u m d e p th o f th e H alimedides burrow s. If th e age m odel for a m m o n ite zones from Ogg e t al. (2 0 0 8 ), in ad d itio n to se d im e n ta tio n rates given by L ukeneder an d Rehakova (2004) for such hem ipelagic sedim ents, are considered, it can be assu m ed th a t th e

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Table l

M easurem ents o f Halimedides o bserved in fine grained pelagic deposits from d ifferent localities. C ham ber d istance in Halimedides is m e a n t to reflect consistency o f sea-floor sedim ents.

seafloor/locality

tu n n el d iam eter

L

c h am b er length

W

ch am b er w id th

S

ch am b er spacing

d u ra tio n o f se d im en tatio n o f th e u p p e rm o st 20 cm o f b ed P l/2 0 4 is ap p ro x im ately 2 0 0 ,0 0 0 -3 0 0 ,0 0 0 years.

It w as also n o ted by W issler e t al. (2 0 0 2 ), based o n a ch em o - stratig rap h ic perspective, th a t th e sed im en tatio n , an d c o n seq u en tially th e stratigraphy, w as less co n tin u o u s th a n generally assu m ed d u rin g th e Barrem ian. At th e strato ty p e o f th e B arrem ian (Angles), late B arrem ian sed im en ts rep resen tin g ap p ro x im ately 2 m yr are m issing (W issler e t al., 2 0 0 2 ). According to W issler e t al. th e gap is m o st probably located w ith in th e I. giraudi Zone.

The h iatus in th e m id G. sartosuiana Zone is com parable to situ  ations in so u th -east Spain (Com pany e t al., 1994), w h e re in th e Capres section th e G. sartousiana (including H. feraudianus Subzone) an d th e Imerites giraudi zones are co ndensed to w ith in only 2 m.

The co n d en sed low er p art w as d eterm in ed by th e index species of G. sartousiana (Heinzia sartousiana in Com pany e t al., 1994). Litho

logical differences observed in th e Puez area are clearly a conse

quence o f a n altered palaeoceanography and, therefore, reflect sea-level fluctuations d u rin g th e early Cretaceous, especially w ith in th e early late B arrem ian (G. sartousiana Zone; Lukeneder, in p ress). A ccording to W eissert (pers. com m ., 2011) th e hiatuses aro u n d th e Southern Alpine chain m o st probably reflect pulses in episodic b o tto m w a te r cu rren t activity.

An in terestin g q u estio n is th e possible relation o f th e ch arac

teristics o f th e observed ichnofauna an d th e d u ra tio n o f th e period o f n o n -deposition. In d e e p -se a pelagic deposits, w h e n slight gaps are n o t proven, th is d u ra tio n can be estim a te d from su b strate consistency. B ioturbation stru c tu re s an d ichnofauna are useful for recognizing soupgrounds, softgrounds, stiffgrounds, firm grounds an d h ard g ro u n d s according to th e n o m en clatu re in tro d u ced by W etzel an d U chm an (1998). In th e H auterivian section from La Charce (so u th -e a st France), w h ich is characterized by regularly in te rb e d d e d calcareous m u d sto n e an d m arlstone, d e n se bio- tu rb a tio n stru ctu res (b u rro w m o ttles) indicate n o rm al softgrounds w h e re a s th e rare o ccurrences o f Zoophycos possibly indicate soft to stiffgrounds. Beds co ntaining Zoophycos are follow ed by beds co n tain in g Halimedides, illustrating possible stiffgrounds related to sh o rt gaps n o t suspected by o th e r m e th o d s (Gaillard and Olivero, 2 0 0 9 ). The sam e succession w ith Zoophycos follow ed by Halimedides is observed in th e Puez area. In th e La Charce area, Halimedides is d en sely cham bered, locally curved a n d clear gaps are n o t proven. In th e Puez area, Halimedides it is q u ite different, i.e., sparsely cham bered, straight, an d associated w ith Spongeliomor- p h a , indicating a firm er su b strate an d a clear gap. This gap co rre

sponds to a p a rt o f th e G. sartousiana Zone an d th e e n tire I. giraudi Zone. A sim ilar situ atio n is k n o w n in a Lower A ptian u n conform ity visible in m any areas o f th e V ocontian Basin (s o u th -e a s t France;

Gaillard an d Olivero, 2 0 0 9 ). W ith in th e localities in th is basin,

Halim edides is also sparsely cham bered, straight, an d associated w ith Spongeliomorpha and, in addition, w ith Rhizocorallium. The gap is very clear but, in som e areas, w ith o u t th e disap p earan ce o f an e n tire am m o n ite zone (u p p e r p a rt o f th e Deshayesites deshayesi Zone follow ing th e low er p a rt o f th e Deshayesites weissi Zone) and, in o th e r areas, w ith th e d isap p earan ce o f several am m o n ite zones (Cotillon, 2010, fig. 3). A no th er exam ple is th e to p surface o f th e B arrem ian M aiolica Form ation (n o rth e rn Italy an d so u th e rn Sw it

zerland). This co rresp o n d s to a long gap an d is also characterized by sparsely ch am b e red a n d straig h t Halimedides associated w ith Spongeliomorpha an d Rhizocorallium. Here, th e h iatus corresponds to a n a b ru p t lithological b reak b e tw e e n lim estones an d m arls an d spans th e late B a rre m ia n -e a rly A ptian according to A rth u r an d Prem oli-Silva (1982) an d Channel e t al. (1993). These au th o rs assu m ed a re s ta rt o f A ptian se d im en tatio n for th e overlying Scaglia m arlsto n es after a gap w ith in th e early late A ptian G. ferreolensis Zone. In th e Puez area, th e ab sen ce o f Rhizocorallium crossing Halimedides an d Spongeliomorpha could indicate a sh o rte r period o f non-deposition.

The d u ratio n o f am m o n ite zones is very variable (Ogg e t al., 2 0 0 8 ).

E stim ations for Jurassic an d C retaceous am m o n ite zones are based o n biostratigraphic (Bulot an d Thieuloy, 1993; H antzpergue, 1993), ch ronostratigraphic (Ogg e t al., 2 0 0 8 ) o r sedim entologic (Lukeneder an d Rehakova, 2004; Strasser, 2 0 0 7 ) criteria. Lower Cretaceous am m o n ite zones (Reboulet e t al., 2 0 0 9 ) com pared to d a ta given by Ogg e t al. (2008) lead to estim atio n s varying from 400,000 to 1,400,000 years, b u t frequently are close to 1 myr. Following this average value, th e d u ratio n o f th e period o f n o n -d ep o sitio n in th e Puez area could be 1.5 myr. But o th e r occurrences o f firm grounds w ith Halimedides in th e V ocontian Basin indicate a sh o rter tim e, possibly o n e am m o n ite zone o r less: 0 .5 -1 m yr could be, very approxim ately, th e d u ratio n o f non -d ep o sitio n necessary for th e form ation o f a firm ground in fine-grained pelagic dep o sits and colonization by straight, sparsely ch am b ered Halimedides. If th e com bined d a ta from am m o n ites (Lukeneder, in p ress) an d planktonic foram inifera (Jan Sotak, pers com m . 2011) are considered, a h iatus extends from th e G. sartousiana Zone up to th e foram iniferal zones o f Praehedbergella luterbacheri a n d Globigerinelloides fer- reolensis o f th e earliest late Aptian. Ogg e t al. (2008) assum ed a d u ratio n o f th e approxim ately 5 - 6 m yr for th is interval.

5. Conclusions

The lim esto n e sed im e n ta tio n o f th e Puez Lim estone M em ber e n d s ab ru p tly w ith a significant h iatu s w ith in th e early late B arrem ian Gerhardtia sartousiana Zone (G. sartousiana Subzone).

This h iatu s is m arked a t th e top o f b ed 2 04 by an om ission horizon,

D

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directly overlain by th e red A ptian Puez Redbed M em ber. The horizon co n tain s th e trace fossils H alimedides, Spongeliomorpha and Zoophycos (called h e re th e H alimedides horizon). This situ atio n is com parable to th a t a t o th e r localities in so u th -e a st Spain and M orrocco. The accom panying h iatu s spans th e late B arrem ian—

m id d le/late Aptian. Taking into account com bined d a ta from am m o n ites an d p lanktonic foram inifera th e h iatu s e x ten d s from th e am m o n ite G. sartousiana Zone u p to foram iniferal zones o f Praehedbergella luterbacheri an d Globigerinelloides ferreolensis o f th e earliest late A ptian, w hich a m o u n ts to ap p ro x im ately 5 —6 myr.

O bserved H alimedides characterize a firm ground on an cien t d e e p -se a floors. C olonization by th e H alimedides tracem ark er o ccurred a fte r a relatively long period o f no n -d ep o sitio n . In th e Puez area, Halimedides observed on th e u p p e r surface o f th e bed 20 4 show s tw o in terestin g characteristics: firstly, th e tu n n e l is very straight; secondly th e b u rro w system is sparsely ch am b e red (7 to at least 52 m m b e tw e e n tw o successive cham bers). According to observations o n coeval C retaceous pelagic d ep o sits in s o u th e a ste rn France a n d Sw itzerland, th is m orphology indicates firm - gro u n d s w h ereas d en sely ch am b e red Halimedides are m o re likely to indicate less firm substrates. Such firm grounds colonized w ith Halimedides could indicate a h iatu s th a t lasted from 0.5 to 1 myr.

Using available d a ta from C retaceous pelagic d ep o sits from th e Alps, th e follow ing suite o f trace fossils expressing stiffening to h ard en in g o f th e su b strated in th e m ark er b ed can be proposed:

softground soft- to stiffground stiffground firm ground

firm er firm ground B ioturbation stru ctu res only

Zoophycos

Halimedides (densely cham bered) Halimedides (sparsely cham bered)

+ Spongeliomorpha Halimedides (sparsely cham bered)

+ Spongeliomorpha + Rhizocorallium

Acknowledgements

Thanks are d u e to th e A ustrian Science Fund (FWF) for financial su p p o rt (p ro ject P20018-N10). Sincere th a n k s go to Evelyn Kus- tatscher, Benno B aum garten an d Vito Zingerle (all M useum o f N ature, South Tyrol) for th e ir org an isatio n al help. W e th a n k Michl Laim er (Bozen), official provincial g o v ern m en t for "R aum ordnung, U m w elt u n d Energie”. A rth u r K am m erer an d A strid W ied e n h o fer (all Office for N atural Parks, South Tyrol) provided a digging p erm it in th e Puez-G eisler N atural Park. W e th a n k David J. B atten (M an

ch ester) for revising an d editorial w ork. Very special th a n k s go to th e an onym ous review ers for carefully read in g an d review ing th e m anuscript. Photographs w e re ta k e n by Alice Schum acher (Vienna).

This w o rk is d ed ica ted to O skar Costa (La Villa), w h o passed aw ay too early n e a r his beloved Rifugio Puez in th e a u tu m n o f 2010. AU w as su p p o rte d by The Jagiellonian U niversity (DS funds).

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