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Cretaceous Research 46 (2013) 1e10

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Cretaceous Research

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Exceptionally favourable life conditions for macrobenthos during theLate Cenomanian OAE-2 event: Ichnological record from the BonarelliLevel in the Grajcarek Unit, Polish Carpathians

Alfred Uchman a,*, Francisco J. Rodríguez-Tovar b, Nestor Oszczypko a

a Jagiellonian University, Institute of Geological Sciences, Oleandry Str. 2a, PL-30-063 Kraków, PolandbDepartamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, 18002 Granada, Spain

a r t i c l e i n f o

Article history:Received 20 June 2013Accepted in revised form 17 August 2013Available online

Keywords:Oceanic anoxic eventsIchnologyCretaceousCarpathians

* Corresponding author.E-mail addresses: alfred.uchman@uj.edu.pl (A

(F.J. Rodríguez-Tovar), nestor.oszczypko@uj.edu.pl (N.

0195-6671/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.cretres.2013.08.007

a b s t r a c t

Pelagic and hemipelagic sediments of the Bonarelli Level (uppermost Cenomanian) in the Sztolnia section(Grajcarek Unit, Polish Carpathians) contain trace fossils of the Zoophycos ichnofacies, including (indescending order of abundance): Chondrites (smaller and larger forms), Planolites, Thalassinoides, Palae-ophycus, Taenidium, Teichichnus, and Zoophycos. They occur in thick bioturbated layers, which are inter-bedded with rare, thin layers of unbioturbated black shales. The black shale layers mark the BonarelliLevel and are interpreted as a record of anoxia or dysoxia. Coeval sections in the Western Tethys containsimilar trace fossils but they are less abundant and these sections are characterized by thicker unbio-turbated black shale layers and thinner bioturbated layers. This confirms the exceptionally favourable lifeconditions in sediments of the Sztolnia section, which do not record strong global anoxia during the OAE-2 event. Such favourable conditions were probably caused by effective oxygenation of pore waters anddeep burial of organic matter, which are a consequence of high rates of accumulation and the palae-ogeographical location of the section on a flank of a submarine high, under strong circulation.

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1. Introduction

Cretaceous oceanic anoxic events are worldwide phenomena,usually characterized by the presence of black-shale facies, and bysignificant ecological and evolutionary biotic changes (e.g.,Schlanger and Jenkyns, 1976; Arthur et al., 1990). An especiallysignificant event at the CenomanianeTuronian boundary interval isresponsible for faunal extinctions and turnovers inasmuch of aseries of significant environmental perturbations, includingincreased volcanic activity, changes of circulation, climate andproductivity (Schlanger and Jenkyns, 1976; Jenkyns, 1980; Arthuret al., 1990; Tsikos et al., 2004; Mort et al., 2007 and referencestherein). It is classified as a second-order, stepwise marine massextinction event affecting different groups of organisms (Harriesand Kauffman, 1990; Kauffman and Erwin, 1995; Kauffman andHart, 1996; Harries and Little, 1999; Wan et al., 2003). These bi-otic changes are relatedmostly to the Oceanic Anoxic Event 2 (OAE-2), which is recorded in the highest Cenomanian as a package ofdark anoxic shale horizons named the Bonarelli Level.

. Uchman), fjrtovar@ugr.esOszczypko).

All rights reserved.

The Bonarelli Level is not uniform, and the number, thicknessand lateral range of anoxic horizons varying as shown by high-resolution ichnological analyses in the western Tethys realm, inthe Silesian Unit of the Polish Carpathians (Uchman et al., 2008),Betic Cordillera in Spain (Rodríguez-Tovar et al., 2009a,b) and theGubbio area in the Apennines of Italy (Monaco et al., 2012). In allthese cases, a dozen anoxic, mostly black shale horizons are inter-calated with lighter, bioturbated, dysoxic or oxic horizons withinthe Bonarelli Level, which is 1e2.5 m thick. The anoxic horizonsdominate in these sections.

In this paper an exceptional section of the Bonarelli Level,Sztolnia section of the Grajcarek Unit, Polish Carpathians (Fig. 1), ispresented and discussed, including the incidence of particulartopographic and palaeoceanographic conditions. Its anoxic hori-zons are thin, less numerous, occupying only a small percentage ofthe section (Fig. 2), and the intercalated intervals display highertrace fossil diversity (Figs. 3 and 4) than in other sections. Suchdevelopment of the Bonarelli Level points to an exceptional sea-floor environment. Its presentation contributes to the general pic-ture of the OAE-2 event, demonstrating that conditions duringOAEs are not persistently and globally anoxic or euxinic, and thatthere is local geographic and temporal variation in environmentalchanges.

Fig. 1. A, Position of the studied area in the AlpineeCarpathian and Panonian realm. B, Geological sketch map of the Ma1e Pieniny Mts. and �Lubovnianska Vrchovina (based onBirkenmajer, 1979, supplemented and modified by Oszczypko et al., 2010, 2012).

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2. Geological setting

In the Polish Carpathians, the Inner and Outer (Flysch) Carpa-thians are separated by the Pieniny Klippen Belt (PKB) suture zone(Fig. 1), whose succession consists of Jurassic to Upper Cretaceouspelagic and flysch deposits (Birkenmajer, 1986). In the Ma1e Pieninymountain range, the PKB succession is separated from the MaguraNappe of the Outer Carpathians by a narrow, strongly deformedzone, distinguished as the Grajcarek Unit (Birkenmajer, 1977, 1986)or Grajcarek thrust sheets (Oszczypko et al., 2010, 2012). TheGrajcarek thrust-sheet succession consists of Jurassic, Cretaceousand Palaeocene pelagic and flysch deposits belonging to theMagura succession (Birkenmajer, 1977, 1986). Dark shales of the so-called Black Flysch, belonging to the Szlachtowa and Opaleniecformations, are characteristic components of the Grajcarek thrustsheets. They have been dated alternatively to Lower and MiddleJurassic (Birkenmajer and Pazdro, 1968; Birkenmajer et al., 2008) orto “middle” Cretaceous (Sikora, 1962, 1971; Oszczypko et al., 2004,2012), being a subject of long-lasting controversy. Nevertheless, atleast part of these deposits occurs with sedimentological continuitybelow the Upper Cretaceous red and variegated shales of theMalinowa Shale Formation (TuronianeCampanian) and is distin-guished as the “Cenomanian Key Horizon” (Sikora, 1962, 1971; seealso Oszczypko et al., 2012), which corresponds to the BonarelliLevel.

The Sztolnia section (called also the “small waterfall section”)starts with a 3e4m thick succession of dark-grey marly shales witha few intercalations of micaceous sandstones belonging to theuppermost part of the Szlachtowa Formation (GPS co-ordinates:N49�24.0820; E20�31.5370). It is overlain by thin intercalations ofgrey, marly shales, sideritic limestones and grey greenish, non-calcareous shales with pyrite concretions that together representthe Opaleniec Formation. The “Cenomanian Key Horizon” startswith an 80 cm-thick interval of green and grey, non-calcareousmanganiferous radiolarian shales, which are capped by lenses oflight green radiolarites with remarkable pyritization (Fig. 4F),covered by a cherty limestone, which are together 15 cm thick(Fig. 2). Above, the proper Bonarelli Level begins at the base of thefirst black shale intercalation, which is 2.75 cm thick. The BonarelliLevel comprises 10e35 cm-thick layers of cherty, partly “spotty”limestones intercalated with black shales, grey marly shales andgreen non-calcareous shales at the top (Fig. 2). Twelve black shaleintercalations are present; the thickest of which attains 15 cm. Thetopmost black shale layer marking the top of the Bonarelli Level isoverlain by green and red non-calcareous shales of the MalinowaShale Formation. The Malinowa Shale Formation is dominated byred mudstones, which become marly to the south. These sedimentsrepresent the Cretaceous oceanic red beds. Sediments of thestudied interval resulted from pelagic and hemipelagic sedimen-tation, beyond the range of gravitational flows.

Fig. 2. The studied Sztolnia section.

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Fig. 3. Trace fossils (all in the totally bioturbated background) and ichnofabrics on cut and wet surfaces of the studied section. Trace fossils: Chondrites e larger form (Chl),Chondrites e smaller form (Chs), Halimedides (Ha), Palaeophycus (Pa), Planolites (Pl), Taenidium (Ta), Teichichnus (Te), Thalassinoides (Th), Zoophycos (Zo). Fe2S in C e pyrite. Samples:A: SZ-4c, B: SZ-3a, C: SZ-1a, D: SZ-9, E: SZ-1b, F: SZ-26, G: SZ-1b.

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This Sztolnia section has been previously studied by several au-thors (Sikora, 1962, 1971; Birkenmajer and Pazdro, 1968;Birkenmajer, 1977; Oszczypko et al., 2004, 2012; Birkenmajeret al., 2008). The radiolarite layer and “spotty” limestones werepreviously regarded by Birkenmajer (1977, 1986), Birkenmajer andGedl (2007) and Birkenmajer et al. (2008) as tectonic blocksderived from theBraniskoUnit of the PieninyKlippenBelt. However,the Szlachtowa Formation at the Sztolnia section (Oszczypko et al.,2012) contains three foraminiferal assemblages, the oldestbelonging to the OxfordianeTithonian, the intermediate repre-senting the BerriasianeBarremian, and the youngest indicatingAptianeAlbianeCenomanianage. Similar, foraminifera assemblageshave been found in the overlying Opaleniec Formation, with theoldest assemblage belonging to the OxfordianeHauterivian, inter-mediate to the Aptian, and the youngest to the AlbianeCenomanian.The “Cenomanian Key Horizon” contains Cenomanian foraminifera.Also, Cenomanian calcareous nannoplankton (Colomisphaera aff.pokornyi �Rehánek)were found in limestones in theBonarelli Level ofthe studied section (Oszczypko et al., 2012; see also Golonka andSikora, 1981; Oszczypko et al., 2004). The black shale in-tercalations show geochemical features typical of the OAE-2 event(Wójcik-Tabol and Oszczypko, 2010, 2012). Bak (2011) suggestedthat the “spotty” limestones could be an equivalent to the BonarelliLevel.

3. Ichnological analysis

3.1. Synopsis of trace fossils

Ichnological analysiswasbasedon samples collectedbed-by-bedfrom the 4.5 m thick interval starting below and ending above theBonarelli Level. Ichnological and lithological featureswere observedon cut surfaces. The studied samples are housed in the Institute ofGeological Sciences, Jagiellonian University (labelled SZ).

Ten ichnotaxa have been differentiated, showing significantdifferences in abundance and distribution through the studied in-terval. Chondrites (smaller and larger forms), Planolites, and Tha-lassinoides, are the most abundant ichnotaxa. Palaeophycus,Taenidium, Teichichnus, and Zoophycos are rare, andHalimedides andTrichichnus are only sporadically present.

Chondrites is visible as groups of branched bars and spots, whichrepresent dendritically downward branching tunnels. Smaller (lessthan 1 mm, mostly less than 0.5 mm in diameter; Figs. 3BeG and4AeC, IeJ) and larger (1e1.5 mm in diameter; Figs. 3A, E, G and4A, D) forms have been differentiated, that could be tentativelyassigned, respectively, to Chondrites intricatus (Brongniart, 1823)and Chondrites targionii (Brongniart, 1828) (sensu Uchman, 1999).Chondrites is interpreted as being produced by a surface ingestor(Kotake, 1991a) that may be able to live chemosymbiotically indysoxic conditions at the aerobiceanoxic interface (Seilacher, 1990;Fu, 1991).

Halimedides is a straight, horizontal tunnel, 1.2 mm in diameter,with a chamber that is 2.5 mmwide (Fig. 3B). Gaillard and Olivero(2009) interpreted this trace as a deep-sea agrichnion in whichchambers were used for food capture and storage, produced in stiffto firm substrates probably by a small crustacean. Lukeneder et al.(2012) distinguished the Halimedides Horizon within the LowerCretaceous pelagic to hemipelagic succession of the Puez area(Southern Alps, Italy) associatedwith firmgrounds on ancient deep-sea floors. Uchman (1999) discussed taxonomy of Halimedides.

Fig. 4. Other trace fossils and some features of beds on cut and wet surfaces from the studiePalaeophycus (Pa), Planolites (Pl), Taenidium (Ta), Thalassinoides (Th). F, G, Bioturbated radiolarfabric” to black shales. I, A transition from black laminated shales (lam) to bioturbated limesSZ-5c, D: SZ-1b, E: SZ-15a, F: SZ-6, G: SZ-6, H: SZ-8, I: SZ-16, J: SZ-19.

Palaeophycus is a simple, straight or curved, cylindrical tunnelwith a wall, 1.5e3.5 mm in diameter (Figs. 3C and 4I). Palaeophycusis a facies-crossing form, interpreted as an open tube produced bycarnivorous or omnivorous invertebrates, mostly polychaetes(Pemberton and Frey, 1982; Keighley and Pickerill, 1995) or ar-thropods (Morrisey et al., 2012).

Planolites is a simple, straight or curved, cylindrical tunnel, 2e3mm, rarely 4mm in diameter, without wall (Figs. 3A, CeE and 4A).Planolites, a facies-crossing form, is an actively filled burrowinterpreted as a pascichnion, probably produced by diverse, mainlysoft-bodied invertebrates, occurring in a wide range of environ-ments (Pemberton and Frey, 1982; Keighley and Pickerill, 1995).

Taenidium is a cylindrical burrow, 4 mm in diameter, withoutwall, with a meniscate fill (Figs. 3D, E and 4C). Taenidium is acommon facies-crossing Phanerozoic trace fossil produced prob-ably by vagile deposit feeders, in some cases maintaining aconnection to the sediment surface or to shallowly burrowingworms keeping pace with sediment accumulation (Locklair andSavrda, 1998). See D’Alessandro and Bromley (1987) and Keighleyand Pickerill (1994) for taxonomical discussion.

Teichichnus, a burrow 5 mm wide, shows fill composed ofstacked laminae (Fig. 3E). Teichichnus is usually interpreted as afeeding structure, and is assigned tentatively to wormlike depositfeeders that migrated upward from a horizontal to subhorizontaltunnel (e.g., Pemberton et al., 2001). This form is common in lowershoreface to offshore environments, but has also been recored onmodern continental slopes (Wetzel, 1981).

Thalassinoides is visible on cut surfaces as larger spots and bars,mostly 7e10 mm, rarely up to 18 mm in diameter (Figs. 3A, D and4A, B, D, E, I), which represent mostly horizontal, branched bur-rows. The fill of some Thalassinoides is preferentially reworked withChondrites. Thalassinoides is mainly interpreted as a domichnial andfodinichnial structure produced by crustaceans, mostly decapods(Frey et al., 1984; Bromley, 1996), occurring in a great variety ofmarine environments from the intertidal to the deep sea (Fürsich,1973; Ekdale, 1992; Schlirf, 2000).

Trichichnus is a poorly preserved, thin (less than 1 mm in diam-eter), cylindrical, pyritized burrow. Trichichnus is regarded asdomichnial burrows of marine meiofaunal deposit feeders (Frey,1970), the tracemaker possibly being a chemosymbiont (Uchman,1995). Trichichnus is a eurybathic marine trace fossil that is com-mon in fine-grained sediments, occurring more deeply in sedimentsthat have been interpreted as very poorly oxygenated, that McBrideand Picard (1991) suggested as having a more opportunistic char-acter than Chondrites. See Uchman (1999) for taxonomic discussion.

Zoophycos is visible as dark, horizontal or oblique, stacked stripesup to 1mm thick, inwhich spreite structures are occasionally visible(Fig. 3F, G). Theyconsist of cross sections of complex helical burrows.Zoophycos is generally considered as a structure produced by someas-yet undiscovered deposit feeder that has been referred tosipunculids (Wetzel and Werner, 1981), polychaete annelids, ar-thropods (Ekdale and Lewis, 1991), and echiurans (Kotake, 1992).The precise ethological interpretation of Zoophycos remains stillcontroversial, being considered as standard fodinichnia (Seilacher,1967; Wetzel and Werner, 1981; Ekdale and Lewis, 1991; Oliveroand Gaillard, 1996), as fermentation structures produced by sur-face ingestors of organic detritus (Kotake, 1989, 1991b), or mostrecently, as chemosymbiotic structurewhose lowermost lobes havebeen interpreted as sulphide wells for bacteria (Bromley andHanken, 2003; Pervesler and Uchman, 2004).

d section. Trace fossils: Chondrites e larger form (Chl), Chondrites e smaller form (Chs),ite with pyrite crystals in F. H, A transition from bioturbated limestones with the “spottytones with the “spotty fabric”. J, Laminated black shales. Samples: A: SZ-1b, B: SZ-9, C:

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3.2. Distribution of trace fossils

Trace fossils through the studied interval of the uppermostOpaleniec Formation and the Cenomanian Key Horizon reveal agenerally similar ichnologic assemblage, with fluctuating compo-sition changes, but showing corresponding variations in abundance(Fig. 2). The abundance was estimated on the basis of density oftrace fossil cross sections on the observed surfaces.

Ichnodiversity is generally higher below the Bonarelli Level inthe uppermost Opaleniec Formation and the lower part of theCenomanian Key Horizon, including all the identified ichnotaxa.This part of the studied interval is characterized by rare Palae-ophycus, Taenidium, Teichichnus, and Zoophycos, and very rare Hal-imedides and ?Trichichnus, which are restricted to these beds. Theremaining ichnotaxa, i.e. Chondrites (larger and smaller), Planolites,and Thalassinoides, occur frequently through the Cenomanian KeyHorizon.

Fig. 5. Comparison of the Bonarelli Level from the Sztolnia section with other sections of tha(marked in grey). Based on Uchman et al. (2008) for the Barnasiówka section, Carpathians,Cordillera, Spain, and on Monaco et al. (2012) for the Bottaccione and Contessa sections, C

In the Bonarelli Level as a whole, the trace fossil assemblagerecords the disappearance of the very rare, but previously recordedHalimedides and ?Trichichnus, and decrease in abundance, to veryrare, single records of Palaeophycus, Taenidium, Teichichnus, andZoophycos. From the remaining ichnotaxa, only Chondrites (largerand smaller) maintains a continuous and abundant record, whilePlanolites and Thalassinoides show decreasing abundance and lesscontinuous records with respect to the layers below the BonarelliLevel. The trace fossil diversity drops significantly in the blackshales, until they completely disappear and primary laminationsare recorded. The total disappearance of trace fossils and thepresence of primary lamination are more common in the middlepart of Bonarelli Level (basal part of bed SZ-7 and upper part of bedSZ-19), and probably also in the upper part (bed SZ-29). Occa-sionally, in the lowermost part of the level (bed SZ-8) and in theuppermost part (bed SZ-32), trace fossils crosscut finely laminatedsediment.

t level the western Tethys, with indication of number of ichnotaxa and anoxic horizonsPoland, Rodríguez-Tovar et al. (2009a,b) for the Hedionda and El Chorro sections, Beticentral Apennines, Italy.

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Above the Bonarelli Level, corresponding to the lowermost partof the Malinowa Formation, the diversity and abundance of tracefossils is similar to that registered in the upper part of the Cen-omanian Key Horizon. However, these data must be consideredwith caution due to outcrop limitations.

Fig. 6. Palaeogeographic situation of the Grajcarek Zone during the Late Cenomanian. A, Sketon Stampfli et al., 2002, modified, in the Carpathian part based on Golonka et al., 2000, moMaZ, Manin Zone; Mr, Marmarosh Massif; PiZ, Pieniny Zone; Si, Silesian Basin; SiR, SilesianBirkenmajer, 1986, modified).

4. Interpretation and discussion

The trace fossil assemblage, which includes Zoophycos, isdominated by fodinichnia and chemichnia, and is interpreted asbelonging to the Zoophycos ichnofacies (Seilacher, 1967), which is

ch map of the European part of the Tethys, with location of the cross section in B (baseddified). Abbreviations: CzR, Czorsztyn Ridge; ExR, Egzotic Ridge; GrZ, Grajcarek Zone;Ridge; Sk, Skole Basin. B, Palaeogeographic cross section of the study region (based on

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typical of slopes and basin plains beyond the range of turbidites orsubmarine slopes (Wetzel and Uchman, 2012). Long-lastingpelagic sedimentation in the Grajcarek Unit succession suggestsinstead a submarine high, because the central part of the adjacentMagura Nappe is characterized by turbiditic sedimentation at thattime. Also, the long existence of a basin plain without turbiditiccurrents in a narrow basin is less probable. The trace fossilassemblage is dominated by only four ichnotaxa (larger andsmaller Chondrites, Planolites, and Thalassinoides) forming thebasic constituents of the infauna. The presence of fodinichnia(Planolites), domichnia/fodinichnia (Thalassinoides) and chem-ichnia (Chondrites) point to diverse adaptations to the availabilityof food in the sediment. This tracemaker community shows nosignificant changes in diversity during the Bonarelli Level depo-sition with respect to prior times, except for disappearance of thevery rare Halimedides and ?Trichichnus, and the decrease inabundance of Palaeophycus, Taenidium, Teichichnus, and Zoo-phycos. Thus, as a general pattern, the Bonarelli Level as a wholedoes not represent significant palaeoenvironmental changes forthe tracemaker community, except for the minor components. Inthis generally habitable environment for the macrobenthicinfauna, significant, but sporadic disruption to the community canbe envisaged. The community was eliminated or limited duringdeposition of black shales due to anoxia or dysoxia, but itsdisappearance does not necessarily mean a lack of bioturbation.Some black shale layers are massive, without primary lamination(e.g., bed SZ-24), suggesting shallow bioturbation in surficialsoupy sediment, in which preservation of trace fossils is impos-sible. After these short, episodic disturbances, the communitywas easily restored during deposition of limestones or marlyshales. The improvement of oxygenation was probably rapid insome beds, because trace fossils crosscut the primary lamination.

A comparison of the Sztolnia section to other sections from thewestern Tethys, including the Barnasiówka section (Silesian Nappe,Carpathians, Poland; Uchman et al., 2008), Hedionda and El Chorrosections (Betic Cordillera, Spain; Rodríguez-Tovar et al., 2009a,b;Rodríguez-Tovar and Uchman, 2011) and the Bottaccione andContessa sections (Central Apennines, Italy; Monaco et al., 2012)show that their trace fossil content is similar, but the number andthickness of bioturbated layers in the Bonarelli Level differ signifi-cantly (Fig. 5). The trace fossil diversity of the Sztolnia section iscomparatively higher, the bioturbated layers are thicker, and thenumber and thickness of anoxic layers are lower. This suggests thatthe environment of the Sztolnia section sediments was morefavourable for macroinfauna than in the other sections. This can beexplained by its palaeogeographical location in the Carpathian partof the Tethys, which was connected to the Ligurian or South Pen-ninic oceanic basins (Fig. 6A). The Grajcarek Zone was situated onthe northern flank of the intrabasinal Czorsztyn Ridge (Fig. 6B). It isnot excluded that such a location would condition effective circu-lation along the ridge and hence improved oxygenation, withoutupwellings. Upwelling was responsible for anoxia in the BeticCordillera during the OAE-2 event (Rodríguez-Tovar et al., 2009b).

The comparison of the thicknesses of the Bonarelli Level indifferent sections (Fig. 5) shows that the greatest thickness is in theSztolnia section, and the smallest in the Gubbio area sections. Thedifferences could result from the rates of accumulation, with thehighest rate in the Sztolnia section. Someone can expect a lowerabundance of trace fossils in sections showing higher rate of accu-mulation due to dilution effect, but the situation is reverse (Fig. 5).This problem can be explained in different way. An increasing in therate of accumulationwould determine more rapid and greater burialof organic matter, which microbial decomposition can lead todecreasing oxygenation of pore waters, but when effective circula-tion can bring oxygenated waters the greater burial of organic matter

can promote deep sediment reworking by infauna (Wetzel andUchman, 2012, and references therein). Deep reworking, in sedi-ment of relatively high consistency, positively influences the pres-ervation of trace fossils (e.g., Bromley, 1996). This is probably anadditional factor influencing the observed record of endobenthic lifein the Sztolnia section. However, the expected increase in burial oforganic matter did not significantly influence oxygenation below thesedimentewater interface. The relatively thin Bonarelli Level in theGubbio area, where the accumulation rate was the lowest, displaysmuch better developed anoxic layers referred to poorer oxygenationof pore waters than in the Sztolnia section.

5. Conclusions

The trace-fossil assemblage in the Bonarelli Level at the Sztolniasection shows no significant reduction in trace-fossil diversity fromthat of the previous assemblage below the Bonarelli Level, exceptfor the disappearance of very rare components and lower abun-dance of the rarer components. Thus, the Bonarelli Level event(OAE-2), as a whole, does not affect significantly the macrobenthictracemaker community. Only episodic disappearance of macro-benthic tracemakers in thin and rare layers of black shales revealshort episodes of anoxia/dysoxia followed by rapid recovery of theichnofauna. The abundance of trace fossils and the reduced anoxiain the Bonarelli Level of the studied section, in comparison to othersections of the western Tethys, confirm the minor influence of theOAE-2 event on local living conditions, which can be related toeffective circulation on the flank of a submarine high, and addi-tionally to deep burial of organic matter.

Acknowledgements

A. Uchman and N. Oszczypkowere supported by the JagiellonianUniversity (DS funds). Research by F.J. Rodríguez-Tovar was sup-ported by Project CGL2012-33281 (Secretaría de Estado de IþDþI,Spain), Project RNM-3715 and Research Group RNM-178 (Junta deAndalucía). Andrew K. Rindsberg (University of West Alabama,Livingston, USA) and Richard Twitchett (Plymouth University, Ply-mouth, UK) provided helpful reviewer comments and proposedseveral improvements of the text.

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Appendix A. Supplementary data

Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.cretres.2013.08.007.