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Integrated stratigraphy and astronomical tuning of theSerravallian and lower Tortonian at Monte dei Corvi

(MiddleÛpper Miocene, northern Italy)

F.J. Hilgen a;�, H. Abdul Aziz b, W. Krijgsman b, I. Ra⁄ c, E. Turco d

a IPPU, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlandsb Paleomagnetic Laboratory, Fort Hoofddijk, Budapestlaan 17, 3584 CD Utrecht, The Netherlandsc Dip. di Scienze della Terra, Univ. ‘G. D’Annunzio’, via dei Vestini 31, 66013 Chieti Scalo, Italy

d Dip. di Scienze della Terra, Universita' di Parma, Parco Area delle Scienze 157/A, 43100 Parma, Italy

Received 3 October 2002; accepted 13 June 2003

Abstract

An integrated stratigraphy (calcareous plankton biostratigraphy, magnetostratigraphy and cyclostratigraphy) ispresented for the Serravallian and lower Tortonian part (MiddleÛpper Miocene) of the Monte dei Corvi sectionlocated in northern Italy. The detailed biostratigraphic analysis showed that both the Discoaster kugleri acme and thefirst influx of Neogloboquadrina acostaensis are recorded at Monte dei Corvi; these events, which passed unobservedin previous studies, play an important role in delineating the Serravallian^Tortonian boundary. Thermal andalternating field demagnetization revealed a characteristic low-temperature component marked by dual polarities. Theresultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the GPTS rangingfrom C5n.2n up to C4r.2r. Unfortunately, the lower part of the section, including the Serravallian^Tortonianboundary interval, did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervalsand a single normal interval are recorded. Using sedimentary cycle patterns in combination with the calcareousplankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping andpreviously tuned section of Monte Gibliscemi on Sicily. The Monte dei Corvi section is dated astronomically bycalibrating the basic small-scale sedimentary cycles to the precession and 65‡N lat. summer insolation time series ofthe La93 solution following an initial tuning of larger-scale cycles to eccentricity. An almost perfect fit is foundbetween the cycle patterns and intricate details, especially precessionôbliquity interference, in the insolation targetbetween 8.5 and 10 Ma. The tuning to precession remains robust for most intervals back to the base of the sectiondated at 13.4 Ma and shows that the section is continuous apart from a possible short hiatus in the Tortonian. Itprovides accurate astronomical ages for all sedimentary cycles, calcareous plankton events, polarity reversals and ashlayers and marks a significant improvement of the recently proposed astronomical calibrations of the Monte dei Corvisection and of parallel sections in the Mediterranean. Astronomical ages for the Ancona and Respighi ashbeds aresignificantly older than previously reported 40Ar/39Ar biotite ages, even if the revised older age for the FCT-san datingstandard of 28.02 Ma is applied. The astronomical dating of the magnetic reversals in the Monte dei Corvi sectionresults in the completion of the astronomical polarity time scale for the last 13 Myr. The Monte dei Corvi section hasrecently been proposed as the stratotype section for the Serravallian^Tortonian boundary despite the moderate to

0031-0182 / 03 / $ ^ see front matter B 2003 Elsevier B.V. All rights reserved.doi:10.1016/S0031-0182(03)00505-4

* Corresponding author. Tel. : +31-30-2535173; Fax: +31-30-2535030. E-mail address: [email protected] (F.J. Hilgen).

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Palaeogeography, Palaeoclimatology, Palaeoecology 199 (2003) 229^264

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poor preservation of the calcareous microfossils and the lack of a reliable magnetostratigraphy across the boundaryinterval. Finally, our study reveals that a single dominantly precession controlled oscillatory climate system isresponsible for late Neogene sapropel formation in the Mediterranean during the last 13.5 million years.B 2003 Elsevier B.V. All rights reserved.

Keywords: astronomical time scale; biostratigraphy; magnetostratigraphy; cyclostratigraphy; chronostratigraphy; Neogene

1. Introduction

The Middle Miocene represents an intriguingperiod of time in the Earth’s history during whichthe present-day ocean-climate system and conti-nental con¢guration took shape. A detailedunderstanding of its history is limited, however,by the accuracy and resolution in dating sedimen-tary archives of that age. Recently climatostrati-graphic criteria were used to obtain an astronom-ical calibration for marine cyclically beddedsuccessions from Ceara Rise (Shackleton andCrowhurst, 1997) and the Mediterranean (Hilgenet al., 2000a; Cleaveland et al., 2002; Caruso etal., 2002; Lirer et al., 2002; Sprovieri et al.,2002a). The astronomical tuning for Ceara Risehas been extended back into the Oligocene(Shackleton et al., 1999) but details of the tuningof the Middle Miocene remain uncertain (Pa«likeand Shackleton, 2000). In the Mediterranean, thetuning has not been extended further back in timethan 14 Ma and, in all cases, the lack of a reliablemagnetostratigraphy prevents Middle Miocene as-trochronology to be applied on a global scale.

A major research e¡ort to improve temporalresolution and accuracy was further made by theMiocene Columbus Project (MICOP; Montanariet al., 1997a). This project was directed at improv-ing the stratigraphy and chronology of theMiocene mainly by dating volcanic ash layersin marine pelagic successions with a goodbiostratigraphic control. Climatostratigraphic cri-teria were not applied in a systematic way andmagnetostratigraphic data are either lacking orof a poor quality. One of the most importantand intensively studied MICOP sections is Montedei Corvi in northern Italy (Montanari et al.,1997b). 40Ar/39Ar incremental heating experi-ments on biotites from two ash layers providedthe necessary ¢rst-order age control (Montanari

et al., 1997b) and the section was proposed as apotential stratotype for the Serravallian, Torto-nian and Messinian global stratotype sectionsand points (GSSPs) by Odin et al. (1997).

Recently, spectral analysis of a high-resolutioncarbonate record provided convincing evidencefor an orbital control in the Monte dei Corvisection (Cleaveland et al., 2002) and an attemptwas made to tune the low-frequency variations incarbonate content to the eccentricity time serieswithin the constraints provided by the 40Ar/39Arbiotite ages of the two ash layers. But the distinctsmall-scale cyclic bedding observed at Monte deiCorvi (Montanari et al., 1997b) suggests that thesection is also suitable for astronomical tuning onthe precession scale. Here we apply the high-res-olution tuning method ^ fully integrated withmagnetostratigraphy and calcareous planktonbiostratigraphy ^ to the Serravallian and lowerTortonian part of the Monte dei Corvi compositeas exposed in the beach section of Montanari etal. (1997b). The integrated approach is importantbecause there is serious doubt about the continu-ity of the succession since neither the ¢rst neo-globoquadrinid in£ux nor the Discoaster kugleriacme recorded at Monte Gibliscemi (Hilgen etal., 2000a) have thus far been found at Montedei Corvi. Our main objectives are to establishan astronomical tuning to precession and insola-tion for the Monte dei Corvi Beach section, totest the tuning of the lower part of this sectionto eccentricity as proposed by Cleaveland et al.(2002) and of parallel sections located elsewherein the Mediterranean (Caruso et al., 2002; Lirer etal., 2002; Sprovieri et al., 2002a), and to clarifythe potential of Monte dei Corvi for de¢ning thelower limit of the Tortonian Stage. Astronomicaldating of the section will further contribute to theintercalibration of the astronomical and 40Ar/39Arradiometric dating methods by providing accurate

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precession ages for ash layers that have alreadybeen dated by 40Ar/39Ar stepwise heating experi-ments on biotites.

2. Geological setting and section

The Miocene succession exposed in the coastalcli¡s of the Conero Riviera south of Ancona innorthern Italy (Fig. 1) is particularly suitable forintegrated stratigraphic studies because it occu-pied a relatively external position with respect tothe developing Apenninic orogen at that time(Montanari et al., 1997b). For this reason thesuccession remained pelagic throughout most ofthe Miocene, being a¡ected by the NE-ward pro-grading orogenic front and associated £ysch-likesedimentation at a late, post-Miocene stage. Theentire succession extends from the Aquitanianinto the Pliocene and contains the Bisciaro (Aqui-tanian to Langhian), Schlier (Langhian to Torto-nian), Euxinic Shale and Gessoso Sol¢fera (Mes-sinian) formations of the northern Apennines(Montanari et al., 1997b).

In this paper we focus on the Serravallian andlower Tortonian part of the succession exposedalong the eastern slopes and in the coastal cli¡s

of Monte dei Corvi described in detail by Mon-tanari et al. (1997b). This interval is particularlywell exposed in the Monte dei Corvi Beach sec-tion of Montanari et al. (1997b), which is com-posed of a cyclic alternation of greenish-graymarls, whitish marly limestones and brown col-ored organic-rich layers (sapropels). In addition,two biotite-rich volcanic ash layers, namedRespighi and Ancona, are present in this part ofthe succession which ranges from NN6 (MNN6b)to NN9 (MNN9) in terms of calcareous nanno-fossil biostratigraphy and from N11 to N16 interms of planktonic foraminiferal biostratigraphy(Montanari et al., 1997b).

3. Cyclostratigraphy

The studied succession is composed of a cyclicalternation of marls, marly limestones and organ-ic-rich beds (Montanari et al., 1997b). The basicsmall-scale cycle is a couplet (0.3^1.0 m thick)which consists of an indurated whitish marly lime-stone and a softer gray to greenish-gray marl (Fig.2). Brownish to blackish colored organic-rich bedsare often (but not always) intercalated in the lime-stones (Fig. 3). In the present paper, these bedsare termed sapropels because they have the sameorigin as sapropels described from the youngerpart of the Mediterranean Neogene (this paper).They were named black shales by Montanari etal. (1997b). While logging the succession, a visualdistinction was made between faint, visible, dis-tinct and prominent sapropels. In doing so, seri-ous problems were encountered due to weather-ing-induced lateral changes in (visual) distinctnessof the sapropels. For this reason we decided tolog that trajectory along which the sapropels aremost clearly discernible. The most problematicinterval starts some 5^10 m east of the ¢shermen’ssheds, and includes the passage underneath thesheds itself. In practice, this part of the trajectoryfollowed rocks exposed in the (present-day) inter-tidal zone. The visual expression of the sapropelsrapidly diminishes or even disappears both in thesubtidal realm as well as in the coastal cli¡s inwhich more weathered rocks are exposed.

The position of a sapropel within a basic cycle

Fig. 1. Location and sample trajectory of the Monte deiCorvi section (MDC, after Montanari et al., 1997b).

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allows to distinguish between a lower (labelled A,below the sapropel) and an upper (B, above) lime-stone bed (Fig. 2). Bed A is not developed in mostof the basic cycles in the lower part of the section.Basic cycles often lack bed B in the interval be-tween 75 and 90 m, while they change into homo-geneous marl-sapropel alternations in the top partof the section west of the ¢shermen’s sheds (Figs.2 and 3). The topmost part of this section,although logged in the more weathered cli¡s, isexcellently exposed along the waterfront. For anadditional check on the basic cycle patterns, ashort freshly exposed parallel section was uncov-ered across the beach by removing 50^100 cmthick loose pebbly beach deposits. The weatheringpro¢le of this parallel section reveals the presenceof additional cycles as more indurated and pro-truding marly limestone beds in homogeneousmarls that are extraordinarily thick (Fig. 4). Basiccycles have been labelled from the base of thesection upward by assigning consecutive numbersto the limestone beds (A, B or AB undi¡erenti-ated) or the corresponding sapropels (Fig. 3).Two thick intervals labelled I and II occur inthe middle part of the section in which the basiccyclicity could not be adequately resolved in the¢eld.

At Monte dei Corvi, larger-scale cycles can be

distinguished in addition to the basic cycles andcomprise both small-scale and large-scale sapropelclusters. These clusters are separated by intervalsin which the basic small-scale cyclicity is usuallystill discernible but in which the brownish organicrich layers are generally absent. Sapropel clustersare distinctly present in the lower half and toppart of the section, and are clearly manifested incase sapropels are separately depicted in a litho-logical column and if their visual distinctness istaken into account (Fig. 3). Small-scale clusterscontain 2^4 sapropels (and 5^6 basic cycles) ;large-scale clusters contain several small-scaleclusters (and up to 20 basic cycles) and havebeen labelled informally A to L. Finally, a cycleof intermediate scale is revealed by alternatingthick/thin ^ or present/absent, or distinct/faint ^sapropels in successive basic cycles. This inter-mediate cycle is particularly evident in two inter-vals (i.e. from cycle 38 to cycle 51 in the lowerhalf of the section and from cycle 150 to cycle 176in the upper half of the section). However, thiscycle can also be recognized in other less thickintervals (i.e. cycles 201^203 and 136^145). Pre-vious studies of marine sections of late Mioceneto Pleistocene age in the Mediterranean (Hilgen,1991a; Hilgen et al., 1995; Lourens et al., 1996)have shown that similar sapropel patterns re£ect

Fig. 2. Variations in the internal buildup of basic sedimentary cycles in the Monte dei Corvi section. The position of a sapropelwithin a basic cycle allows to distinguish between a lower (labelled A, below the sapropel) and an upper (B, above) limestonebed.

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Fig. 3. Lithological column of the Monte dei Corvi section showing lithology, sample positions and cycle numbers. Grey shadingin the lithological column marks the softer gray colored homogeneous marls. Whitish beds include both marly limestones andsapropels. Sapropels have been indicated in a separate column which reveals their visual distinctness, ranging from prominent(dark shading) via distinct and visible to faint (light shading) and very faint (no shading). Asterisks (*) mark the position ofpoorly developed cycles observed in the Monte dei Corvi trench section across the beach (see also Fig. 4). A and R mark the po-sition of the Ancona and Respighi ash layers, respectively. I and II indicate the thick intervals in which the basic small-scale cy-clicity could not be adequately resolved.

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the astronomical cycles of precession (basic cycle),obliquity (intermediate cycle) and eccentricity(larger-scale cycles).

4. Calcareous plankton biostratigraphy

Our biostratigraphic analysis of the calcareousplankton (planktonic foraminifers and calcareousnannoplankton) focussed on the lower 93 m ofthe section (Fig. 5) because the biostratigraphyof the younger part has been well documentedin time equivalent sections in the Mediterranean(Hilgen et al., 1995, 2000a,b,c ; Ra⁄ et al., 2003);these sections show a much better preservation

and can be perfectly correlated to Monte dei Cor-vi on the basis of the sedimentary cycle patterns.

4.1. Planktonic foraminifera

Planktonic foraminiferal biostratigraphic stud-ies of the Monte dei Corvi section have been car-ried out previously by Coccioni et al. (1992, 1994)and Montanari et al. (1997b). In these studies, allbiohorizons of Mediterranean zonal schemes forthe Serravallian^Tortonian (e.g. Iaccarino, 1985)were recognized, but the distribution patterns ofthe marker species were not presented. Our aim is(1) to re¢ne and where necessary modify the ex-isting planktonic foraminiferal biostratigraphy ofthe Monte dei Corvi Beach section by presentingthe detailed distribution pattern of the mainmarker species, and (2) to compare the biostrati-graphic results with those of other astronomicallytuned sections in the Mediterranean, in particularthe Monte Gibliscemi section (Hilgen et al.,2000a).

A semi-quantitative analysis was carried out onapproximately 200 samples with an average reso-lution of 1^2 samples per small-scale sedimentarycycle. The sample resolution was higher in theinterval between V52 m and V74 m in whichmost of the bioevents are located. The semi-quan-titative analysis was based on surveying a stan-dard number of ¢elds (27 out of 45) in a rectan-gular picking tray while distinguishing thefollowing abundance categories: Trace (6 3 speci-mens in 9 ¢elds), Rare (3^10 specimens), Com-mon (10^30 specimens), and Frequent (s 30specimens). Preservation is generally poor, theplanktonic foraminifera being strongly recrystal-lized and sometimes deformed and/or broken.Planktonic foraminifera are less abundant butshow a better preservation in the sapropels thanin the marl and limestone layers. Only a few sap-ropel samples are barren in foraminifera. The re-sults of our semi-quantitative analysis are pre-sented in Fig. 5. Taxonomy and distributionpatterns are discussed below and compared withprevious data from the Monte dei Corvi section(Montanari et al., 1997b) and, for the late Serra-vallian to early Tortonian, with data from theMonte Gibliscemi, Case Pelacani, San Nicola Is-

Fig. 4. Comparison of basic cycle patterns in the Monte deiCorvi trench section across the beach and the same intervalin the regular Monte dei Corvi section exposed in the coastalcli¡s.

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land and Ras il-Pellegrin sections (Hilgen et al.,2000a; Caruso et al., 2002; Foresi et al., 2002a,b).In Plate I the main marker species are depictedand compared to better preserved specimens fromother Mediterranean sections (Monte Gibliscemiand Tremiti Islands). Although the preservation israther poor, the diagnostic features of the markerspecies are distinguishable.

4.1.1. Paragloborotalia siakensis andParagloborotalia mayeri

In our previous study of the Monte Gibliscemisection (Hilgen et al., 2000a) we consideredP. siakensis as a junior synonym of P. mayerifollowing the taxonomic concept of Bolli andSaunders (1985). Other authors (e.g. Kennettand Srinivasan, 1983; Iaccarino, 1985; Foresi etal., 1998), however, follow the species concept ofBlow (1969), who regarded P. siakensis andP. mayeri as distinct species. All these authorshave a di¡erent opinion about the distributionrange and phylogeny of P. mayeri. Blow (1969)and Kennett and Srinivasan (1983) reported astratigraphic distribution of P. mayeri rangingfrom N9 to N13 and N4 to N14, evolving fromeither Globorotalia peripheroronda or P. siakensis,respectively. In the Mediterranean, P. mayeri wasrecorded in a short interval within the distributionrange of Globorotalia partimlabiata (N13) in themiddle Serravallian (e.g. Foresi et al., 1998, 2001,2002a,b). Foresi et al. (2001) suggest a possibleevolution of this species from G. partimlabiata.All this indicates that the controversy is stillopen and further studies are necessary to betterunderstand taxonomy, phylogeny and stratigraph-ic distribution of P. mayeri sensu Blow (1969).

At Monte dei Corvi, we observed forms refer-able to P. mayeri with a distribution range similarto that found on Malta and Tremiti Islands(Foresi et al., 2001, 2002a,b; see Plate I, ¢g. 3).We kept the two species distinct in order to com-pare our data with those of other Mediterraneansections. However, the scarcity and poor preser-vation of the specimens referable to P. mayeri donot o¡er new evidence which might contribute tosolve the taxonomic and biostratigraphic prob-lems.

P. siakensis is a long ranging species but itsdistribution pattern reveals marked changes ofbiostratigraphic signi¢cance. P. siakensis is absentin the lowermost part of the section but is abun-dant and almost continuously present in two in-tervals higher in the succession between 5.58 m(Acme I Bottom) and 33.16 m (Acme I Top)and between 40.48 m (Acme II Bottom) and52.70 m (Acme II Top). These two peak intervalshave recently been found in other Mediterraneansections by Foresi et al. (2002a,b). The top of thesecond interval corresponds to the abundancedrop of P. mayeri sensu Bolli and Saunders(1985) ( =P. siakensis in this work) recorded incycle 387 at Monte Gibliscemi and dated at12.006 Ma (Hilgen et al., 2000a). The correlationis con¢rmed by the G. partimlabiata increase andthe Globoturborotalita apertura^Globigerinoidesobliquus gr. peak, which immediately follow theP. siakensis drop both in the Monte dei Corviand Monte Gibliscemi sections, as well as onTremiti Islands (Foresi et al., 2002a).

The last occurrence (LO) of P. siakensis atMonte dei Corvi is not a clear-cut event as atMonte Gibliscemi. Typical specimens of P. sia-kensis disappear at 72.23 m where we placed theLO of the species. The P. siakensis LO as de¢nedabove in the Monte dei Corvi section is found inthe same relative position as at Monte Gibliscemi.Atypical and poorly preserved specimens of thespecies, which are discontinuously present up to80 m, are possibly reworked.P. mayeri sensu Blow (1969) is found as trace

element over a short stratigraphic interval. Fol-lowing a single occurrence at 28.69 m, the speciesis almost continuously present from 38.64 m up to43.59 m. The LO of a single and atypical speci-men is found at 51.35 m. The ¢rst and last occur-rences of P. mayeri cannot be considered reliableevents since they are based on scattered occur-rences and poorly preserved specimens. Despitethe scarcity of the species, however, the P. mayeridistribution range between 38.64 m and 51.35 m isin agreement with that observed on Malta andTremiti Islands (Foresi et al., 2002a,b) if com-pared with the distribution ranges of P. siakensisand G. partimlabiata.

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4.1.2. Globorotalia partimlabiataThe ¢rst occurrence (FO) of G. partimlabiata is

recorded at 28.69 m and the position of this bio-event is well comparable with that reported byMontanari et al. (1997b) at about 22 m abovethe Respighi Level. The taxon shows a sharp de-crease in abundance at 59.55 m, about 2 m belowthe Ancona ash. Montanari et al. (1997b) placedtheir G. partimlabiata LO at a comparable posi-tion just below the ash. Foresi et al. (2002a) ob-served the same sharp decrease in abundance ofG. partimlabiata at Tremiti Islands; according totheir taxonomic concept, this level represents theactual LO of the species although they ¢nd lesstypical representatives at higher levels which theylabelled G. cf. partimlabiata. According to Foresiet al. (2001) these atypical forms could be refer-able to G. challengeri. In our opinion these youn-ger specimens, even if smaller in size, can beincluded in the morphological variation ofG. partimlabiata. At Monte dei Corvi, G. par-timlabiata vanishes higher up in the section, at90.84 m, and its distribution pattern compareswell with that observed at Monte Gibliscemi.

4.1.3. Globigerinoides subquadratusG. subquadratus occurs very rarely and is scat-

tered in the lower part of the section but becomes

more abundant from about 57 m up to 63.56 m.At this level the last common occurrence (LCO)of the species is placed resulting in a slightly lowerposition (about two cycles) than at Monte Gibli-scemi. In the Monte dei Corvi section the actualposition of this event may be obscured by thepresence of very poorly preserved samples andeven a barren sample directly above this level.The distribution pattern of G. subquadratus com-pares well with that recorded on Tremiti Islands(Foresi et al., 2002a) and in the Case Pelacanisection on Sicily (di Stefano et al., 2002).

4.1.4. Globoturborotalita apertura^Globigerinoides obliquus group

We lumped G. apertura, G. decoraperta andG. obliquus under this label to maintain a stabletaxonomic concept even under poor preservationconditions and to compare the distribution pat-tern of this taxon with that observed at MonteGibliscemi (Turco et al., 2001). This group, whichoccurs very rare and scattered in the lower part ofthe section, becomes more continuous and abun-dant from about 51 m upwards. Following a ma-jor in£ux located just above the top of the secondpeak interval of P. siakensis, it becomes trulyabundant and continuously present from 65.18 mup to the top of the section. The ¢rst regular

Plate I.

1. Paragloborotalia siakensis (LeRoy): 1a spiral view, 1b axial view, and 1c umbilical view; Monte dei Corvi section,sample It 20383, 8.13 m.

2. Paragloborotalia siakensis ( =P. mayeri in Hilgen et al., 2000a): 2a spiral view, 2b axial view, and 2c umbilical view;Monte Gibliscemi section, sample It 18516.

3. Paragloborotalia mayeri (Cushman and Ellisor) sensu Blow (1969): 3a spiral view, 3b axial view, and 3c umbilical view;Tremiti Islands, sample TTA-86 (after Foresi et al., 2002a).

4. Globorotalia partimlabiata Ruggieri and Sprovieri: 4a umbilical view, 4b axial view, and 4c spiral view; Monte dei Corvisection, sample It 20413, 28.69 m.

5. Globorotalia partimlabiata Ruggieri and Sprovieri: 5a umbilical view, 5b axial view, and 5c spiral view; MonteGibliscemi section, sample It 18553.

6. Neogloboquadrina acostaensis s.s. (Blow): 6a spiral view, 6b axial view, and 6c umbilical view; Monte dei Corvi section,sample It 20530, 62.28 m.

7. Neogloboquadrina acostaensis s.s. (Blow): 7a spiral view, 7b axial view, and 7c umbilical view; Monte Gibliscemi section,sample It 18575.

8. Globorotalia peripheroronda Blow and Banner: 8a umbilical view, 8b axial view, and 8c spiral view; Monte dei Corvisection, sample It 20397, 17.95 m.

9. Globorotalia peripheroronda Blow and Banner: 9a umbilical view, 9b axial view, and 9c spiral view; Tremiti Islands,sample It 19597.

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occurrence (FRO) of the group is placed at thislevel, which is in the same relative position as insection Gibliscemi.

Our G. apertura^ G. obliquus gr. FRO corre-sponds to the FRO of G. obliquus obliquus re-corded on Tremiti Islands (Foresi et al., 2002a)and in the Case Pelacani section (di Stefano etal., 2002), and is considered to be a very usefulevent in the Mediterranean area (e.g. Foresi et al.,1998; Sprovieri et al., 2002a,b). In addition, theG. apertura^G. obliquus gr. FRO marks a signi¢-cant change in species composition of the oligo-trophic tropical-subtropical planktonic foraminif-eral assemblage related to the global coolingassociated with the Mi-5 oxygen isotope event(Turco et al., 2001).

4.1.5. Globorotaloides falconarae/CatapsydraxparvulusG. falconarae was ¢rst described by Giannelli

and Salvatorini (1976) from the Mediterraneanarea. Small-sized specimens of G. falconarae arevirtually indistinguishable from C. parvulus, de-scribed by Bolli (1957) from Trinidad. For thisreason, Zachariasse (1992) and Hilgen et al.(1995) considered G. falconarae as a junior syno-nym of C. parvulus. Later on, Hilgen et al. (2000a)suggested that G. falconarae and C. parvulus arehomeomorphs and phylogenetically unrelated. Infact, G. falconarae seemed to have evolved fromGloboquadrina sp.1 around 11.5 Ma, whereas therange of the low-latitude C. parvulus extends backinto the early Miocene. Recently, Foresi et al.(2001) embraced again the idea of synonymy be-tween G. falconarae and C. parvulus based ontheir morphological resemblance and suggestedthat the C. parvulus holotype as ¢gured by Bolli(1957) is actually a juvenile form, which apparent-ly di¡ers from the G. falconarae holotype in walltexture.

In the Mediterranean area, similar forms, la-belled either G. falconarae or C. parvulus, havebeen found in sections of Langhian (Fornaciariet al., 1997; Foresi et al., 2001) and late Serraval-lian to Tortonian age (Hilgen et al., 1995, 2000a;Foresi et al., 2002a). The same distribution is alsoobserved at Equatorial Atlantic Site 926 (Turco etal., 2002) and at North Atlantic Site 397 (Foresi

et al., 1998, 2001). Apparently, these forms areabsent in the Mediterranean and low-latitude At-lantic Ocean during the early Serravallian.

However very rare small-sized specimens refer-able to G. falconarae/C. parvulus are discontinu-ously present in the lower Serravallian at Montedei Corvi, in an interval older than the base ofsection Gibliscemi. The taxon becomes continu-ously present from 60.34 m upward and is moreabundant from 79.48 m up to the top of the sec-tion. The rare occurrence of the taxon in the low-er Serravallian calls our previous suggestionsabout the origin of G. falconarae and the homeo-morphysm between G. falconarae and C. parvulusinto question. In fact, we may better reconsiderthem as C. parvulus following the earlier conceptof Zachariasse (1992) also because similar formsextend back into the Langhian. However theirpresence in the lower Serravallian has only beenevidenced at Monte dei Corvi (this study) but noton the Tremiti Islands or Malta (Foresi et al.,2002a,b,c). Further studies are necessary to betterdocument the exact distribution range of this tax-on in order to re-evaluate the synonymy betweenC. parvulus and G. falconarae.

4.1.6. Neogloboquadrina groupWe maintained the same subdivision of the

Neogloquadrina group in four types as in ourstudy of the Gibliscemi section (Hilgen et al.,2000a): large-sized N. atlantica, small-sized N. at-lantica, N. acostaensis sensu strictu (s.s.) and theso-called four-chambered type. The latter is in-cluded in N. acostaensis according to our conceptof the species (for more details on taxonomy, seeHilgen et al., 2000a). Recently, it has been pro-posed to label our large- and small-sized N. atlan-tica as N. atlantica atlantica and N. atlanticapraeatlantica respectively, while the four-cham-bered type was lumped together with N. acostaen-sis s.s. (Foresi et al., 2002c). However, we pre-ferred to maintain our previous taxonomicsubdivision of neogloboquadrinids to better com-pare their distribution with Monte Gibliscemi.

At Monte dei Corvi, neogloboquadrinids ¢rstoccur at 59.80 m directly above a drop in theabundance of G. partimlabiata like in section Gi-bliscemi. The neogloboquadrinids are mainly rep-

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resented by small-sized N. atlantica and, to a less-er extent, the four-chambered type. N. acostaensiss.s. is very rare and ¢rst occurs at 60.34 m, i.e. ata slightly younger level with respect to the othertwo Neogloboquadrina types.

The distribution pattern of the Neogloboquadri-na group at Monte dei Corvi is very similar tothat observed at Monte Gibliscemi. They are con-tinuously present between 59.80 and 63.84 m (¢rstin£ux) but become very rare and are discontinu-ously present from 64.23 to 73.11 m, where thebase of the second in£ux is placed. Neogloboqua-drinids represent a major component of theplanktonic foraminiferal assemblage from thislast level up to the top of the section. However,the base of the second neogloboquadrinid in£uxcoincides with the FO of large-sized N. atlanticaat Monte dei Corvi, whereas the same event pre-dates the large-sized N. atlantica FO at MonteGibliscemi (Hilgen et al., 2000a). This discrepancyis most likely due to the very poor preservation ofthe samples in the interval directly below 73.11 m.

Changes in coiling direction of the neoglobo-quadrinids observed at Monte Gibliscemi areeasily recognized at Monte dei Corvi con¢rmingtheir biostratigraphic signi¢cance in the Mediter-ranean region; they are randomly coiled between59.80 and 63.84 m and predominantly dextrallycoiled between 73.11 and 89.18 m. The neoglobo-quadrinids reveal further changes in coiling direc-tion in the uppermost part of the section, namelyfrom dextral to sinistral at 89.82 m and from sin-istral to dextral at 91.53 m.

The distribution range of large-sized N. atlanti-ca and the position of the last regular occurrence(LRO) of small-sized N. atlantica are in goodagreement with the position of the same eventsat Monte Gibliscemi. The large-sized N. atlanticaFO is placed at 73.11 m and the LO at 77.81 m.The taxon is intermittently present and shows anumber of abundance peaks in sapropel layers.The LRO of small-sized N. atlantica at 83.32 mis a distinct event and is found in the same posi-tion as in section Gibliscemi. In contrast, theFRO of N. acostaensis, as de¢ned at Monte Gi-bliscemi, is considered a less distinct and easilyrecognizable event even though it has been iden-ti¢ed at Case Pelacani (Caruso et al., 2002).

4.1.7. Globorotalia scitula and Globorotaliamenardii group

Beside the distribution of the main biostrati-graphic markers, we analyzed the distribution pat-tern of the G. scitula and G. menardii groups be-cause of their potential biostratigraphic value.The G. scitula group is present throughout thesection except for an interval between 10.04 mand 24.30 m where it is extremely rare and dis-continuously present. The presence of the G. sci-tula gr. in the lower part of the section in combi-nation with the concomitant absence ofP. siakensis might be a valuable biostratigraphictool to characterize the lower Serravallian belowthe base of the ¢rst acme interval of P. siakensisdown to the LRO of G. peripheroronda. The samepattern of the G. scitula gr. and P. siakensis hasalso been recorded at Tremiti Islands (unpub-lished data).

The G. menardii group occurs very scattered inthe lowermost 20 m of the section, but becomesmore abundant although discontinuously presenthigher up in the section. The group vanishes atabout 83 m at a stratigraphic level that approxi-mates the LRO of N. atlantica (small-sized), i.e.similar to the Monte Gibliscemi section (Turco etal., 2001).

4.1.8. Globorotalia peripheroronda in£uxesWe observed two short in£uxes of G. periphe-

roronda at 8.13 m and 17.95 m in our section.These two in£uxes have also been recognized onTremiti Islands in the correlative sedimentarycycles (unpublished data), thus showing their po-tential value for high-resolution biostratigraphiccorrelations in the Mediterranean. The G. periphe-roronda LO has been recorded and dated astro-nomically at 13.39 Ma on Malta (Sprovieri et al.,2002a; Foresi et al., 2002b), i.e. at a level olderthan the base of our Monte dei Corvi section.Both our in£uxes occur in the ¢rst acme intervalof P. siakensis, while the G. peripheroronda LO ofForesi et al. (2002b) is found well below this in-terval.

4.2. Calcareous nannofossils

Calcareous nannofossil assemblages of Monte

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dei Corvi were previously analyzed by Fornaciariet al. (1996) in a biostratigraphic study of theMediterranean Middle Miocene. Through a quan-titative analysis of the same samples studied indetail by Coccioni et al. (1992) and Montanariet al. (1997b), they recognized the following bio-horizons in the Serravallian to lower Tortonianpart of the section, listed from older to youngeras follows: Calcidiscus premacintyrei last commonoccurrence (LCO); Calcidiscus macintyrei ¢rst oc-currence (FO); Coccolithus miopelagicus LCO;Helicosphaera walbersdorfensis last occurrence(LO); Helicosphaera stalis ¢rst common occur-rence (FCO); Discoaster bellus group FO, and;Discoaster hamatus FO.

In this study we analyzed the nannofossil as-semblages in selected intervals of the sectionwith the purpose to re¢ne the previous biostratig-raphy, and examine additional biohorizons suchas the Discoaster kugleri FCO and LCO and theCyclicargolithus £oridanus LO. Analyses focusedmainly on the lower part of the section and onintervals that overlap stratigraphically with theGibliscemi section.

Quantitative data were collected on selectedsamples using standard techniques for smear slidepreparation and a polarizing light microscope.Abundances of the index species were obtainedby counting the number of specimens of each in-dex species per unit area of the slide. The distri-bution patterns of the selected marker species(Fig. 5) allow to locate the position of the bio-stratigraphic useful events.

Identi¢cation of the nannofossils was often ob-scured by the strong overgrowth that a¡ected theassemblages especially in samples from the marlsand marly limestones. This generally poor preser-vation prevented us from obtaining reliable dataon some index species. In addition, it was notpossible to obtain reliable data on the distributionof small helicoliths like H. stalis and H. walbers-dorfensis, whose specimens were only sporadically

encountered. Discoasterids are present through-out the studied interval but are generally rareand poorly preserved. Identi¢cation of Discoasterspecies was possible only in samples from the sap-ropel layers. Placoliths belonging to the Coccoli-thus and Calcidiscus genera are present as minorsecondary components in the assemblages where-as Reticulofenestra and Dictyococcites prevail :peaks in abundance of small specimens of thelatter two genera were observed in some intervalswithin the marly limestones.

Results of the biostratigraphic analysis and thebiohorizons identi¢ed are reported below and dis-cussed in comparison with previous data fromMonte dei Corvi (by Fornaciari et al., 1996) andwith biostratigraphic data from the Monte Gibli-scemi, Case Pelacani, Tremiti Island and Ras il-Pellegrin sections (Hilgen et al., 2000a; Caruso etal., 2002; Foresi et al., 2002a,b) and the openocean.

4.2.1. Cyclicargolithus £oridanus LOWe observed very rare specimens of C. £orida-

nus in the basal part of the section just below theRespighi ash layer. It is di⁄cult to ascertainwhether their presence is due to reworking or rep-resents the uppermost part of the C. £oridanusdistribution range. Nevertheless, the presence ofspecimens of Reticulofenestra pseudoumbilicus inthe same interval and its gradual upward increasein abundance suggest that the basal part of thesection is very close to the C. £oridanus LO. Thisis in agreement with data from open ocean sites,in which the decrease (LCO) and extinction (LO)of C. £oridanus are linked to the appearance (FO)and increase (FCO) of R. pseudoumbilicus. Al-though the exit of C. £oridanus and entranceR. pseudoumbilicus are recorded at di¡erent strati-graphic levels in di¡erent oceanic areas (see Ra⁄et al., 1995), their distribution ranges are invaria-bly associated (R. pseudoumbilicus increases justabove the sharp decrease in C. £oridanus).

Fig. 5. Semi-quantitative distribution patterns of planktonic foraminiferal marker species and quantitative distribution patterns ofcalcareous nannofossil marker species against depth in the Monte dei Corvi section. No data indicates that the species has notbeen counted in that particular interval.

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Relative to the base of the ¢rst acme interval ofP. siakensis, the observed specimens of C. £orida-nus are found at a higher stratigraphic level thanthe C. £oridanus LCO recorded in the Ras il-Pel-legrin section on Malta (Foresi et al., 2002b), in-dicating that they are similar to the sporadicspecimens often encountered above the LCO ho-rizon (Fornaciari et al., 1996).

4.2.2. Calcidiscus macintyrei FO, and Calcidiscuspremacintyrei LO and LCO

The usefulness of the C. macintyrei FO, and theC. premacintyrei LO and LCO for biostrati-graphic subdivision of the Mediterranean Mio-cene was investigated and discussed in detail byFornaciari et al. (1996). These authors used theC. premacintyrei LCO to de¢ne their MNN6/7zonal boundary and showed that it is concomitantwith or occurs just above the C. macintyrei FO, asin records from the open ocean (see discussion inFornaciari et al., 1996). Both biohorizons arenot clear-cut, and the weakness of the signals be-comes particularly evident if nannofossil assem-blages are poorly preserved, thus complicatingbiostratigraphic observations. Moreover, theC. macintyrei distribution is known to be biogeo-graphically controlled (Ra⁄ et al., 1995), which inaddition a¡ects the degree of reliability of bioho-rizons associated with the species.

The previous study of the Monte dei Corvi sec-tion by Fornaciari et al. (1996) documented thedistribution of both index species. The extinctionpattern of C. premacintyrei, the appearance pat-tern of C. macintyrei and the position of bothbiohorizons relative to each other agree wellwith data available from the Mediterranean andthe open ocean (Ra⁄ et al., 1995). In the presentstudy we analyzed the Calcidiscus index species inall samples available from the lowermost 51 m inour section. Calcidiscus specimens are generallyrare and completely missing in many samples re-sulting in an intermittent distribution pattern(Fig. 5). As a consequence, the biostratigraphicsignal is weak for both index species, but thetwo biohorizons nevertheless maintain their recip-rocal positions, with the C. macintyrei FO re-corded at 41.72 and the C. premacintyrei L(C)Oat 42.07 m. These data agree with the results of

Fornaciari et al. (1996), who recognized the twobiohorizons in the interval 11 to 14 m below theAncona ash layer.

Relative to the base of the second P. siakensisacme interval, our C. macintyrei FO and C. pre-macintyrei L(C)O correspond rather well with theC. macintyrei FCO and C. premacintyrei LO re-ported by Foresi et al. (2002a) from Tremiti Is-lands. However they occur at a much higher levelthan the C. macintyrei FO and C. premacintyreiLCO reported from Tremiti Islands and Malta;the latter events are located just above theG. partimlabiata FO (Foresi et al., 2002a,b). Thesedi¡erences at least partly re£ect the di⁄cultiesencountered in accurately de¢ning and pinpoint-ing these events in the Mediterranean due to theweakness of the biostratigraphic signal.

4.2.3. Discoaster kugleri FCO and LCOThe presence of D. kugleri passed unobserved

in the previous study of the Monte dei Corvi sec-tion because the species was known to be veryrare and therefore not considered useful for bio-stratigraphic purposes in the Mediterranean Mio-cene (Fornaciari et al., 1996). Moreover discoast-erids are rare and poorly preserved at Monte deiCorvi. The usefulness of the D. kugleri biohori-zons for biostratigraphic subdivision of the Med-iterranean Miocene was ¢rst demonstrated by Hil-gen et al. (2000a). In their study of sectionGibliscemi, they recorded a short interval inwhich D. kugleri is continuously present often inelevated numbers. The astronomical ages for theD. kugleri FCO and LCO at Gibliscemi are con-sistent with the astronomical ages obtained forthe same events in the low-latitude open ocean,where the species is common in a short intervaland the two biohorizons are clearly documented(Ra⁄ et al., 1995; Backman and Ra⁄, 1997). Inthe light of these ¢ndings, a detailed analysis wascarried out at Monte dei Corvi with the purposeto detect the D. kugleri range in this section. Ourinvestigation concentrated on samples from thesapropel layers, in which the preservation of dis-coasterids is considerably better than in samplesfrom the marly limestone beds. We obtained aclear picture of the distribution pattern of D. ku-gleri (see Fig. 5), despite the poor preservation of

PALAEO 3178 18-9-03


the specimens and the fact that the species ispresent in low numbers only. The short intervalin which the species is found extends from 55.31to 63.36 m, where the FCO and LCO biohorizonsare placed, respectively.

The position of these events corresponds wellwith the positions of the same events reportedfrom the Gibliscemi, Case Pelacani and TremitiIsland sections (Hilgen et al., 2000a,b,c; Foresiet al., 2002a; Caruso et al., 2002).

4.2.4. Coccolithus miopelagicus LROThe position and pattern of the LRO of C. mio-

pelagicus is similar to that observed at MonteGibliscemi and is consistent with the foraminiferaldata. The biohorizon is close to the P. mayeri LO(it occurs just above it, at 75.55 m). The species isscarce and irregularly distributed in the upperpart of its range and marked by decreases inabundance (it disappears for short intervals) justbelow the LRO biohorizon. Our analysis resultedin a more detailed picture of the distribution ofC. miopelagicus than reported by Montanari et al.(1997b), who placed the LCO of C. miopelagicus

(equivalent to our LRO) at a somewhat lowerstratigraphic position, about 10 m above the An-cona ash layer. Relative to the foraminiferal data,the C. miopelagicus LCO is also reported from alower stratigraphic level in the Case Pelacani sec-tion (Caruso et al., 2002).

4.2.5. Helicosphaera stalis FCO andHelicosphaera walbersdorfensis LO

The determination of the distribution patternsof these two species of small helicoliths in theiruppermost (for H. walbersdorfensis) and lower-most (for H. stalis) ranges was hampered by pres-ervation problems and di¡erences in the compo-sition of the nannofossil assemblages. At Montedei Corvi, the biostratigraphic signal is unclearmainly due to the discontinuous presence of theindex species rather than to the poor preservationof the assemblage. Scattered presences of H. wal-bersdorfensis and H. stalis were recorded at di¡er-ent levels within the studied interval, i.e. below77 m and above 85 m, respectively. We failed todetect the two successive events (or the reversal inabundance between the two species) in our high

Fig. 6. Representative examples of thermal (TH) and alternating ¢eld (AF) demagnetization diagrams. Closed (open) symbolsrepresent the projection of vector end-points on the horizontal (vertical) plane; values denote temperature in degrees Celsius (‡C).(No) tc indicates that (no) tectonic correction for the bedding tilt has been made.

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resolution sample set, despite the fact that theyhave previously been recorded in the same section(Fornaciari et al., 1996) and elsewhere in theMediterranean (Fornaciari et al., 1996; Hilgenet al., 2000a). The distribution of these small hel-icoliths seems to be controlled by environmentalfactors even over a limited geographic area (with-in the Mediterranean). Similar discrepancies inthe distribution of small helicoliths have been ob-served between sedimentary successions from thelate Miocene in the Mediterranean (Ra⁄, unpub-lished data).

4.2.6. Discoaster hamatus FO and Discoasterbellus group FO

The appearance of the ¢ve-rayed discoasterids(D. bellus gr. FO) in the Mediterranean has beenconsidered a fairly reliable event (Fornaciari etal., 1996). It is succeeded by the D. hamatus FO,an event which is usually di⁄cult to pinpoint dueto the rareness of the marker species. Despite theinferred reliability of the D. bellus gr. FO, wefailed to recognize this biohorizon at Monte deiCorvi. Single specimens of Discoaster cf. belluswere recorded in some samples (at 87.24, 88.48,90.09, and 90.37 m). These scattered presences arefound in the same position as the oldest ¢ve-rayeddiscoasterids at Monte Gibliscemi (Hilgen et al.,2000a).

5. Magnetostratigraphy

The Monte dei Corvi section has previouslybeen subjected to a detailed paleomagnetic studyby Montanari et al. (1997b). Applying standarddemagnetization techniques, they concluded thatthe magnetic intensity was too weak to yield use-ful information on the magnetic polarity and thatthe natural remanent magnetization (NRM) wasalready largely removed at a temperature of200‡C. Nevertheless, several samples showedsouthwesterly declinations and negative inclina-tions, but these directions were considered as anoverprint. Furthermore, rock magnetic experi-ments revealed that there was no signi¢cant di¡er-ence in magnetic mineralogy or grain sizethroughout the section (Montanari et al., 1997b).

A pilot study on a limited number of orientedhand samples similarly revealed weak to veryweak NRM intensities, but also some levels withopposite reversed and normal polarity directions.In view of its manifest importance we resampledMonte dei Corvi with an approximate resolutionof one sample per cycle (that is 20 kyr) despitethese rather discouraging results. All 192 sampleswere taken with a portable drill and a generatoras power supply. Evidently, the 40‡ tilt (beddingorientation 110/42; strike/dip) will help to distin-guish primary (pre-tilt) from secondary (post-tilt)components.

Stepwise alternating ¢eld (AF) demagnetizationwas applied to at least one specimen per level.Small steps of 5 mT were applied up to 30 mT,followed by steps of 10 mT up to a maximum¢eld of 100 mT. In addition, thermal (TH) de-magnetization was applied to the second specimen(when available) with temperature increments of20‡C after an initial heating step to 100‡C. Sam-ples were heated and cooled in a laboratory-built,shielded furnace with a residual ¢eld of less than

Fig. 7. Plotted directions of the secondary and ChRM com-ponent showing the non-antipodality of the latter. The 95%con¢dence ellipse for the normal and reverse mean directionsis indicated. Statistical information: N, number of samples;Dec., declination; Inc., inclination; k, Fisher’s precision pa-rameter, K95, radius of the 95% con¢dence cone.

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Fig. 8. Magnetostratigraphy of Monte dei Corvi and correlation to CK95. In the polarity column black (white) denotes normal(reversed) polarity intervals and cross-hatching denotes intervals of unde¢ned polarity.

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30 nT. The NRM was measured at each step witha horizontal 2G Enterprises DC SQUID cryogen-ic magnetometer. NRM directions were deter-mined by means of principal component analysisand magnetization vectors were avaraged usingFisher statistics to calculate the mean directionper component.

The initial NRM invariably revealed very weakintensities ranging between 0.05 and 0.6 mA/m. Itproved impossible to determine the magneticcomponents from Zijderveld diagrams in a signi¢-cant number of samples ( T 25%); directionsshowed so much scatter that it was not even pos-sible to determine their polarity (Fig. 6; PCOR088). Most samples from the lower half of thesection 9 but several levels from the upper halfas well 9 revealed a normal polarity componentin geographic coordinates (Fig. 6; PCOR 170) butthe orientation of this component often changedinto meaningless directions following tectonic cor-rection (tc) for the bedding tilt. We interpret thiscomponent as a secondary post-tilt overprintprobably related to the present-day ¢eld.Although directions show some scatter in all sam-ples, the average direction of this secondary com-ponent approximately coincides with the expecteddirection at the location (43‡N; inclination of 62‡see also Fig. 7).

In contrast, samples from the uppermost partof the section revealed a straightforward reversedcomponent that decays linearly towards the originin ¢elds between 10 and 60 mT and temperaturesbetween 100 and 260‡C (Fig. 6; PCOR 192). Di-rections were obtained following tectonic correc-tion, indicating that the component is pre-tilt, andtherefore most likely of primary origin. In addi-tion, no evidence is found at all of a secondaryoverprint. Other levels revealed a reversed compo-nent in the same ¢eld/temperature range, but anadditional secondary normal overprint is present(Fig. 6; PCOR 163). This secondary componentcould be largely removed at very low ¢elds (0^10mT) and temperatures (0^120‡C). Demagnetiza-tions showing normal pre-tilt directions are ob-served in the upper part of the section, especiallyin the interval between 75 and 95 m. (Fig. 6;PCOR 123), although their quality is less as inthe reversed uppermost part. Isolated normal

components mainly show north to northeast de-clinations and a rather disorderly decay towardsthe origin, thereby hampering a reliable determi-nation of the direction.

Summarizing, sediments from section Montedei Corvi revealed a complex NRM behaviorwith two partly overlapping components. Itproved possible to isolate a characteristic compo-nent marked by dual polarities. This characteristicremanent magnetization (ChRM) componentshows two clusters located in the SE and NEquarters of an equal area plot (Fig. 7). The non-antipodal behavior can be explained by overlap-ping unblocking temperature spectra of a primarycomponent and the secondary (post-tilt) overprintmaking it impossible to completely isolate the pri-mary ChRM component. We thus assume thatthis component records the ancient geomagnetic¢eld, even though it does not pass the reversaltest. Mean directions of the ChRM should there-fore be treated with caution when interpreted interms of tectonic rotations.

Plotting the ChRM directions in stratigraphicorder reveals three isolated intervals of reversedpolarity in the lowermost 60 m of the section,which is dominated by secondary components(Fig. 8). By contrast, 14 polarity reversals are re-corded in the uppermost 60 m, which reveal aprolonged interval of normal polarity between75 and 90 m (Fig. 8). This interval has a minimumduration of 700 kyr if the small-scale cycles arerelated to precession. Accepting a precession ori-gin for the sedimentary cyclicity, we can correlatethe normal polarity interval with chron C5n.2n,because it is the only normal chron in this part ofthe geomagnetic polarity time scale (GPTS) with aduration in excess of 700 kyr (Cande and Kent,1995). The three small normal subchrons between90 and 100 m then correspond to C5n.1n,C4Ar.2n and C4Ar.1n and the uppermost normalpolarity interval at 114 m to cryptochron C4r.2r-1(Fig. 8). Unfortunately, all these normal polarityintervals are marked by one or two samples only.This indicates that some caution is required hereeven though the correlative subchrons in theGPTS (CK95: Cande and Kent, 1995) show rel-atively short durations varying between 40 and100 kyr.

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In conclusion, the magnetostratigraphic calibra-tion of the upper part of section Monte dei Corvito CK95 seems rather straightforward. However,signi¢cant discrepancies occur in the relativelength of the subsequent polarity intervals. In par-ticular the reversed intervals at 90^92 and 101^

107 m are too long when compared to the patternin the GPTS. But our cyclostratigraphic interpre-tation does not point to higher sedimentationrates in these intervals. The two most logical ex-planations for the observed discrepancies there-fore are: (1) errors in the CK95 pattern due to

Fig. 9. Cyclostratigraphic and (calcareous plankton) biostratigraphic correlations between the ^ upper part of the ^ Monte deiCorvi section and section Gibliscemi. Numbered calcareous plankton events refer to the numbers for the same events in Table 2.

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changes in sea£oor spreading rates and/or di⁄cul-ties in determining the boundary of short sub-chrons in sea£oor anomaly pro¢les, and (2) errorsin determining the exact position of the reversalboundaries in section Monte dei Corvi. In view ofthe relatively low sample resolution and the poorquality of many of the demagnetizations, we pres-ently favor the second option. Whatever its origina much higher sample resolution with at least ¢velevels per cycle is necessary to solve the observeddiscrepancies.

6. Astronomical tuning

6.1. Correlation to section Gibliscemi andastronomical origin of the cyclicity

Biostratigraphic correlations between Montedei Corvi and the Gibliscemi section located onSicily are straightforward. The calcareous plank-ton biostratigraphy of Monte dei Corvi revealsthe same order of events as in section Gibliscemi(Figs. 5 and 9). Biostratigraphic tie points wereemployed as a starting point to correlate the sec-tions cyclostratigraphically in detail. The cyclo-stratigraphic correlations are generally straight-forward because the cycle patterns are identicalor nearly identical. Minor discrepancies are mostlikely related to the locally intense deformation insection Gibliscemi which prevented us from log-ging the entire succession in a perfectly reliableway. Our correlations show that most of the bio-events are recorded in the correlative cycle in bothsections (Fig. 9). The cyclostratigraphic correla-tions in addition reveal that the normal polarityintervals at 94 and 100 m correlate with two nor-mal polarity intervals in section Gibliscemi A pre-viously identi¢ed as C4Ar.1n and C4Ar.2n whilethe normal polarity interval at 113 m correlateswith the short normal polarity interval in sectionMetochia previously identi¢ed as C4r.2r-1(Krijgsman et al., 1995). Clearly these correlationscon¢rm both the primary character of the inferredChRM component and the magnetostratigraphiccalibration to CK95.

In principle, cyclostratigraphic correlationscould have been established independently from

the biostratigraphic and magnetostratigraphicdata by using characteristic details in the cyclepatterns alone. This is especially true for the toppart of the section, i.e. the interval from cycle 146to 203 (Fig. 9). The similarity in the cycle patternscannot be explained other than that the brownishorganic-rich layers at Monte dei Corvi correspondto sapropels ^ and associated gray marlbeds ^ atMonte Gibliscemi. This relationship is con¢rmedby rare in£uxes of large-sized Neogloboquadrinaatlantica which are recorded in a limited numberof (successive) sapropels at Monte Gibliscemi andin the correlative brownish layers at Monte deiCorvi. It is for these reasons that we adoptedthe term sapropel instead of black shales for thebrownish layers at Monte dei Corvi.

The correlations between Monte dei Corvi andMonte Gibliscemi con¢rm the astronomical con-trol on the sedimentary cyclicity. Further con¢r-mation comes from the 40Ar/39Ar dating of bio-tites from the Respighi and Ancona ash layers,dated at 12.86 and 11.43 Ma, respectively (Mon-tanari et al., 1997b). Application of these agesresults in an average period of close to 20 kyrfor basic cycles in the interval between the ashlayers and, hence, of V40 kyr for the intermedi-ate cycle and of V100 and V400 kyr for thelarger-scale cycles. This outcome is consistentwith results of spectral analysis on a high-resolu-tion carbonate record which point to a similarorbital control if the 40Ar/39Ar ages of the ashlayers are taken as age calibration points to com-pute the carbonate time series (Cleaveland et al.,2002).

6.2. Astronomical tuning

Now that the astronomical origin of the sedi-mentary cyclicity at Monte dei Corvi has beenwell substantiated, determination of phase rela-tions between sedimentary cycles and individualastronomical parameters is a logical next step inan astronomical tuning procedure. For Monte deiCorvi, these phase relations can be ascertainedthrough the detailed correlations to section Gi-bliscemi and the fact that phase relations areknown for sapropels in the latter section (Hilgen,1991a; Hilgen et al., 1995, 2000a; Lourens et al.,

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Fig. 10. Tuning of sapropel clusters in the Monte dei Corvi section to eccentricity maxima in the eccentricity time series of solu-tion La90ð1;1Þ (Laskar, 1990; Laskar et al., 1993). Small-scale clusters are calibrated to 100-kyr maxima, large-scale clusters (A^L)to 400-kyr maxima.

PALAEO 3178 18-9-03


Fig. 11. Detailed tuning of the basic small-scale sedimentary cycles in the upper half of the Monte dei Corvi section to the pre-cession and insolation time series of solution La93ð1;1Þ. Also shown are the positions of the calcareous plankton events. Numbersrefer to the numbers for the same events in Table 2. S^T indicates the recently proposed Serravallian/Tortonian boundary (Torto-nian GSSP).

PALAEO 3178 18-9-03


1996). The observed link between sapropels atMonte dei Corvi and Monte Gibliscemi impliesthat they correspond to minima in the precessionindex and, thus, to 65‡N lat. (boreal) summer in-solation maxima, and that small-scale and large-scale sapropel clusters correspond to 100-kyr and400-kyr eccentricity maxima, respectively. Finally,alternating thick/thin ^ or present/absent, or dis-tinct/faint ^ sapropels in successive basic cyclesare related to obliquity maxima/minima and,thus, to high/low-amplitude (boreal) summer in-solation maxima, due to precession-obliquity in-terference.

Using these phase relations and the existingtuning for the sapropels at Monte Gibliscemi asstarting point, we ¢rst tuned sapropel clusters atMonte dei Corvi to 400-kyr and 100-kyr eccen-tricity maxima (Fig. 10). Both small-scale andlarge-scale clusters were identi¢ed using di¡eren-ces in visual expression of the sapropels and theirpreferred occurrence in bundles. To correctly in-terpret sapropel clusters in terms of eccentricityrelated patterns, we assumed that a 400-kyr eccen-tricity cycle corresponds to approximately 20 ba-sic cycles and a 100-kyr cycle to 4^6 basic cycles.In general, recognition of sapropel clusters andthe ensuing calibration to eccentricity are straight-forward, apart for the interval between 72 and87 m in which identi¢cation of clusters is moreproblematic. The ¢rst-order astronomical calibra-tion of this interval to eccentricity was achievedby taking the number of basic cycles and the de-tailed correlations to section Gibliscemi in addi-tion into account. Sapropel clusters could againbe unambiguously recognized lower in the section(Fig. 10).

The problematic identi¢cation of sapropel clus-ters in the middle part of the section can be ex-plained by di⁄culties encountered in logging thepart of the trajectory underneath the ¢shermen’ssheds and the fact that it corresponds to a max-imum in amplitude of the 1.2-Myr obliquity cycle,around 10.8 Ma. In addition, the 400-kyr mini-mum at 10.9 Ma is weakly developed with rela-tively high eccentricity values, most likely due tothe 2.4-Myr eccentricity maximum around 10.7Ma. As a consequence, the amplitude of the pre-cession and insolation variations are enhanced for

a prolonged period of time, thus generating con-ditions that are less favorable for the formationand thus identi¢cation of sapropel clusters.

We then succeeded by calibrating the individualbasic cycles to precession and insolation startingfrom the top of the section downward. The result-ing tuning is presented in Figs. 11 and 12. It de-viates in detail from the astronomical tuning ofsection Gibliscemi as discussed below. This is notunexpectedly in view of the locally intense defor-mation at Gibliscemi. Nevertheless, the correla-tions con¢rm that Gibliscemi represents a contin-uous succession despite the deformation.

6.2.1. Cycles 176^203Cyclostratigraphic correlations between Monte

dei Corvi and Monte Gibliscemi are unambiguousin this interval. The initial tuning of Monte Gi-bliscemi looks convincing but, alternatively, Gi-bliscemi cycles G33 to G44 may be tuned oneprecession (insolation) cycle older. A reconnais-sance of Monte Gibliscemi (upward extension ofsection Gibliscemi C, following the trajectory ofSprovieri et al., 1996) revealed the presence of anextra cycle between our cycles G44 and G45 whilethe remaining homogeneous marlbed remainsthicker than the average homogeneous marlbedof regular basic cycles. This implies that the olderoption is in better agreement with the cyclostrati-graphic data (Fig. 11) and thus that the initialtuning of Monte Gibliscemi has to be slightlymodi¢ed in this interval. The modi¢ed tuning isconsistent with the almost regular thickness of thehomogeneous marlbed between the sapropels ofcycles 184 and 185 at Monte dei Corvi, but resultsin a less good ¢t with the insolation patterns forcycles 192 to 193.

6.2.2. Cycles 146^176These cycles can be unambiguously correlated

and tuned. The cycle pattern is dominated by ba-sic and intermediate scale cycles and re£ects pre-cession/obliquity interference with alternatingthick/thin (or present/absent, or distinct/faint)sapropels in successive basic cycles. Clearly, theinterference is not perfect over the entire interval,but switches intermittently by one cycle (i.e. atcycles 168^170 and 162^163). However, despite

PALAEO 3178 18-9-03


Table 1aAstronomical ages of sapropel (or as-sociated calcareous marlbed) mid-point of the basic sedimentary cyclesaccording to the La93ð1;1Þ solution (ofcycles in the stratigraphic overlapwith section Gibliscemi)

Age MdC Gib_m Gib_o

38 548 203 51 5138 568 202 50 5038 590 201 49 4938 619 ^ ^ ^38 641 200 48 4838 662 199 47 4738 683 198 46 4638 705 197 45 4538 734 ^ ^ 4438 756 196 44 4338 777 195 43 4238 797 194 42 4138 816 193 41 ^38 832 ^ ^ 4038 852 192 40 3938 872 191 39 3838 892 190 38 3738 907 189 37 3638 926 188 36 3538 947 187 35 3438 968 186 34 3338 990 185 33 ^39 018 184 32 3239 040 183 31 3139 061 182 30 3039 083 181 29 2939 107 180 28 2839 133 179 27 2739 154 178 26 2639 176 177 25 2539 198 176 24 2439 225 175 23 2339 249 174 22 2239 269 173 21 2139 288 172 20 2039 305 ^ ^ ^39 325 171 19 1939 348 ^ ^ ^39 371 170 18 18

(Continued)

Age MdC Gib_m Gib_o

39 396 169 17 1739 418 168 16 1639 440 167 15 1539 464 166 14 1439 487 165 13 1339 510 164 12 1239 532 163 11 1139 555 162 10 1039 580 161 9 939 602 160 8 839 624 * ^ 739 644 159 7 639 660 * ^ ^39 679 * 6 539 700 * ^ 439 728 158 5 339 751 * 4 239 773 157 3 139 795 156 2 039 817 155 1 3139 843 154 0 3239 866 153 31 3339 888 152 32 3439 909 151 33 3539 932 150 34 3639 959 149 35 3739 980 148 36 38310 002 147 37 39310 023 146 38 310310 041 ^ 39 ^310 057 ^ 310 311310 076 ^ ^ 312310 095 ^ 311 313310 114 145 312 314310 132 144 313 315310 152 143 314 316310 172 142 315 ^310 193 141 316 ^310 209 140 317 317310 223 139 318 318310 244 138 319 319310 266 137 320 320310 287 136 321 321310 308 135 ^ 322310 338 134 322 323

(Continued)

Age MdC Gib_m Gib_o

310 359 133 323 324310 379 132 324 325310 400 131 325 326310 419 130 326 ^310 435 129 ^ 327310 453 128 327 328310 473 127 328 329310 492 126 329 330310 511 125 330 331310 530 124 331 332310 550 123 332 333310 570 122 333 334310 586 121B 334 ^310 602 121A 335 335310 623 120 336 336310 644 119 337 337310 665 118 338 338310 687 117 ^ ^310 716 116 339 339310 737 115 340 340310 759 114 341 341310 779 113 342 342310 799 112B 343 343310 812 112A ^ ^310 832 111 344 344310 852 110 345 345310 873 109 346 346310 892 108 347 347310 910 107 348 348310 928 106 349 349310 948 105 350 350310 968 104 351 351310 984 ^ ^ ^311 002 103 352 352311 023 102 353 353311 043 101 354 354311 064 100 355 355311 093 99 356 356311 116 98 357 357311 137 97 358 358311 158 96 359 359311 178 95 ^ ^311 195 ^ ^ ^311 209 94 360 360311 230 93 361 361

(Continued)

Age MdC Gib_m Gib_o

311 251 92 362 362311 270 91 363 363311 289 90 ^ ^311 307 ^ ^ ^311 327 89 ^ ^311 346 88 ^ ^311 361 87 364 364311 380 86 365 365311 401 85 366 366311 422 84 367 367311 443 83 368 368311 471 82 369 369311 493 81 370 370311 515 80 371 371311 536 79 372 372311 558 78 373 373311 586 77 374 374311 608 76 375 375311 629 75 376 376311 650 74 377 377311 667 73 ^ ^311 683 72 378 378311 703 71 ^ ^311 723 70 ^ ^311 741 69 ^ ^311 757 68 379 ^311 778 67 380 379311 799 66 ^ 380311 821 65 381 ^311 846 64 382 381311 870 63 383 382311 892 62 ^ 383311 913 61 384 ^311 936 60A ^ 384311 961 60 385 385311 984 59 386 386312 006 58 387 387

Ages refer to the age of the correlativeprecession minimum.Gib_o shows the ages of the sedimentarycycles at Monte Gibliscemi according to theinitial tuning (Hilgen et al., 2000a), Gib_mshows the ages according to the slightly re-vised tuning presented in this paper.

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its complexity, the cycle pattern shows an almostperfect ¢t with the insolation target. The excellent¢t becomes particularly evident if the parallel sec-tion across the beach is taken into account. Thissection reveals additional (‘missing’) cycles, whichlack the sedimentary expression of a sapropel dueto weak insolation forcing, as indurated marlbeds(Fig. 4). The indurated beds are intercalated inhomogeneous marls that are thicker than marl-beds of regular basic cycles (Fig. 11).

Despite the unambiguous correlations, the com-plex cycle pattern is not fully identical to the pat-

tern observed at Monte Gibliscemi. Detailed com-parison of the cycle patterns led to a modi¢cationof the tuning of the Gibliscemi cycles as follows.Cycles G7/G8, like their counterparts at Montedei Corvi, must represent double cycles, despitetheir almost regular thickness in the original logof section Gibliscemi A. Revisiting Monte Gibli-scemi showed that the thickness of these cyclesvaries laterally in section Gibliscemi C, with asystematic increase towards the east, thus render-ing support to the alternative interpretation thatthey represent double cycles. The reduced thick-ness of these cycles in section Gibliscemi A is atleast partly related to deformation which led to atectonic reduction of this part of the succession.However, the reduced thickness of the same cyclesat Monte Giammoia, located some 10 km east ofGibliscemi, and of the overlying cycle (G9) bothat Monte Gibliscemi and at Monte Giammoiaindicates that a temporary reduction in sedimen-tation rate must have played a role as well. De-spite these complications, the cyclostratigraphiccorrelations between Monte dei Corvi and MonteGibliscemi are straightforward and con¢rmed indetail by the planktonic foraminiferal biostratig-raphy.

The dominance of precession/obliquity interfer-ence patterns in this interval is related to the min-imum in eccentricity of the 2.4-Myr eccentricitycycle reached at 9.5 Ma. During such a minimum,the amplitude of the 100-kyr cycle is strongly re-duced, resulting in a relatively low and constantprecession amplitude, and precession/obliquity in-terference in the insolation target (see also Hilgenet al., 1995, 2000c).

6.2.3. Cycles 132^146This is the only interval in which the sedimen-

tary succession might be discontinuous. Themarlbed above the sapropel of cycle 145 containsseveral rounded sapropel ‘£akes’ embedded in anotherwise homogeneous marl. In principle, suchrounded components can either be explained byresedimentation or by burrows ¢lled with sapro-pelitic sediment. Our detailed bed-to-bed correla-tions to Monte Gibliscemi indicate that theMonte dei Corvi section contains less cycles inthe interval from cycle 136 to 146 than the corre-

Table 1bAstronomical ages of sapropel (or associated calcareousmarlbed) mid-point of the basic sedimentary cycles accordingto the La93ð1;1Þ solution (of older cycles)

Age MdC Age MdC

312 028 57 312 761 31312 051 56 312 784 30312 077 55 312 811 29312 098 54 312 832 28312 118 53 312 853 27312 137 52 312 873 26312 156 ^ 312 892 n.d.312 178 ^ 312 907 25312 202 ^ 312 927 24312 226 ^ 312 947 23312 248 51 312 965 22312 270 50 312 983 21312 293 49 313 003 20312 317 48 313 024 19312 340 47 313 044 18312 361 46 313 062 17312 384 45 313 076 16312 407 44 313 096 15312 433 43 313 117 14312 454 42 313 138 13312 474 41 313 159 12312 494 40 313 175 n.d.312 511 39 313 191 11312 531 38 313 211 10312 551 ^ 313 232 9312 569 ^ 313 252 8312 583 ^ 313 271 7312 604 ^ 313 288 6312 625 37 313 307 5312 646 36 313 327 4312 669 35 313 345 3?312 696 34 313 363 2?312 718 33 313 382 1?312 739 32

Ages refer to the age of the correlative precession minimum.

PALAEO 3178 18-9-03


lative interval at Monte Gibliscemi (Fig. 9). Morespeci¢cally our correlations show that cycles G-11to G-9 (or G-8) lack sedimentary expression atMonte dei Corvi. The lack of sedimentary expres-sion of these cycles can be explained by the lowamplitude of the precession/insolation forcing inthis interval which corresponds to the 400-kyr ec-centricity minimum around 10.1 Ma. But in thatcase it remains unexplained why the correlativesapropel of the prominent cycle G-11 is not de-veloped. Alternatively, the section might be punc-tuated by a hiatus with a maximum duration of80 kyr. In that case, the thick homogeneousmarlbed of cycle 145 is interpreted as a slumplevel and the hiatus placed at the base of thisbed. Nevertheless, we consider the former optionthat the homogeneous marlbed represents normalmarine pelagic sedimentation more likely becauseno further indications for a sedimentary slumpwere found in the homogeneous marlbed of cycle145. Note that cycles 140^145 can equally well betuned one precession-insolation cycle younger.

To overcome the potential problem of the hia-tus, we continued with the tuning of Monte Gi-bliscemi to older levels until cycles were reachedthat could be unambiguously correlated to Montedei Corvi again on the basis of the cycle patterns(136 to 139 that correlate with G-18 to G-21).Evidently, these older cycles re£ect precession-obliquity interference. The tuning of these cycleshowever is less straightforward because the inter-ference pattern is not manifest in the insolationtarget, even if an uncertainty of one or two cyclesin the tuning is assumed (Fig. 9). The most likelyexplanation for this discrepancy is that details,such as precession/obliquity interference, becomeless reliable in our preferred solution La93ð1;1Þ(Laskar, 1990; Laskar et al., 1993), because majoruncertainties in the tuning can be excluded. Theinterference pattern as can be inferred from thesedimentary cyclicity only becomes visible after asigni¢cant reduction of the (present-day) tidal dis-sipation term from 1 to 0.5 (or an equivalent re-duction in the dynamical ellipticity). But, in thatcase, the almost excellent ¢t with insolation getslost for the interval encompassing cycles 146^176.As a consequence, details in the insolation timeseries re£ecting precession/obliquity interference

can no longer be employed with certainty forthe tuning of older cycles.

6.2.4. Cycles 86^132This interval includes the di⁄cult and problem-

atic passage beneath the ¢sherman’s sheds. Wepreferred to log this trajectory instead of the tra-jectory followed by Montanari et al. (1997b)above the sheds, because the latter trajectory ismore weathered. This stronger weathering ex-plains the almost complete lack of sapropels intheir log of the same interval.

The tuning of this interval is di⁄cult in so farthat the basic cycle patterns do not allow to dis-tinguish sapropel clusters in a routine way, asmentioned in the section on the ¢rst-order astro-nomical calibration to eccentricity. The detailedtuning to precession is based on the number ofbasic cycles, the tuning of the interval stratigraph-ically directly below and above, and the tuning ofthe correlative part of the Gibliscemi section. Inaddition, the identi¢cation of basic cycles showinga minimum contrast in lithology that correspondto 100-kyr eccentricity minima played an impor-tant role in the tuning of this interval (cycles 99,103, 112, 117 and 121). Intricate details of thecycle pattern re£ecting precession/obliquity inter-ference are not observed in the insolation target.

6.2.5. Cycles 52^86The tuning of the basic cycles to precession is

straightforward. No good match with insolationis found, however, most likely because precession/obliquity interference is not reliably resolved inthis interval (see above).

6.2.6. Cycles 37^52The detailed tuning of these cycles is compli-

cated because they are sandwitched in betweenthe two thick intervals (I and II) in which thebasic small-scale cyclicity could not be resolvedin the ¢eld and which correspond to two succes-sive 400-kyr eccentricity minima at 12.15 and12.55 Ma. In principle, this shortcoming couldhave been overcome because the sapropel patternis very characteristic and dominated by preces-sion^obliquity interference. However, as statedabove, it is unlikely that such interference patterns

PALAEO 3178 18-9-03


are reliably resolved in La93ð1;1Þ this far back intime. As a consequence, several options exist forthe tuning of cycles 38^51. The small-scale sapro-pel cluster of cycles 43^46 can be calibrated to themost distinct albeit weakly developed 100-kyr ec-centricity maximum at 12.35 Ma. Using this con-straint, the cycles 38^51 can be tuned in one wayonly (Fig. 12). But an alternative option is tocorrelate these cycles one or two precession cycles

older (see also Fig. 12). The latter preferred tun-ing is based on ongoing studies of parallel sectionson San Nicola Island (Tremiti islands, AdriaticSea, Italy) in which the cyclostratigraphy of theproblematic intervals I and II is better resolved(unpublished data).

Dominance of precession^obliquity interferenceover the precession/eccentricity syndrome is asso-ciated with the minimum in eccentricity related to

Table 2Astronomical ages of calcareous plankton bioevents in the Monte dei Corvi section and comparison with the ages of the sameevents in section Gibliscemi and in other sections from the Mediterranean

No. Species Event Cycle Position MdC age MG age RIPS (2002)

Planktonic foraminifer18 Neogloboquadrina group s/d 150^152 91.00^91.525 9.888^9.932 ^ ^17 Globorotalia partimlabiata LO 150 90.84^91.00 9.932^9.945 9.913 T 0.003 [11.80]16 Neogloboquadrina group d/s 145 89.005^89.82 10.024^10.114 10.011 T 0.002 ^15 Neogloboquadrina atlantica s.s. LRO 126^127 83.32^83.54 10.473^10.492 10.473 T 0.001 ^^ Neogloboquadrina acostaensis s.s. FRO ^ ^ ^ 10.554 T 0.003 10.5514 Neogloboquadrina atlantica l.s. LO 110 77.81^78.205 10.832^10.852 10.850 T 0.002 ^13 Neogloboquadrina atlantica l.s. FO 96^97 72.95^73.11 11.137^11.148 11.121 T 0.003 11.1512 Neogloboquadrina group 2nd in£ux96^97 72.95^73.11 11.137^11.148 11.178 T 0.003 ^11 Paragloborotalia siakensis LO 94^95 72.225^72.39 11.178^11.195 11.205 T 0.004 11.2110 Globoturborotalita apertura^

Globigerinoides obliquus gr.FRO 78^79 64.87^65.18 11.538^11.548 ^ 11.54

9 Globigerinoides subquadratus LCO 76^77 63.555^63.84 11.586^11.599 11.539 T 0.004 11.548 Neogloboquadrina group FO 67^68 59.55^59.80 11.757^11.766 11.781 T 0.002 11.807 Paragloborotalia siakensis IIAE 57^58 52.70^52.86 12.006^12.012 ^ 12.006 Paragloborotalia mayeri LO 56 51.345^51.54 12.048^12.055 ^ 12.145 Paragloborotalia siakensis IIAB 42 40.09^40.48 12.444^12.454 ^ 12.384 Paragloborotalia siakensis IAE 37 33.155^33.735 12.612^12.625 ^ 12.583 Globorotalia partimlabiata FO 30 28.135^28.685 12.770^12.784 ^ 12.622 Paragloborotalia mayeri F(C)O 30 28.135^28.685 12.770^12.784 ^ 12.341 Paragloborotalia siakensis IAB 4^5 5.295^5.58 13.307^13.313 ^ 13.22

Calcareous nannofossil^ Discoaster neohamatus FO ^ ^ ^ 9.826 T 0.003 ^^ Discoaster hamatus FO ^ ^ ^ 10.150 T 0.002 ^^ Helicosphaera stalis FCO ^ ^ ^ 10.717 T 0.002 10.71^ Catinaster coalitus FO ^ ^ ^ 10.738 T 0.001 10.74^ Helicosphaera walbersdorfensis LCO ^ ^ ^ 10.743 T 0.003 10.76f Coccolithus miopelagicus LRO 104 75.55 10.968 10.977 T 0.002 11.18/19e Discoaster kugleri LCO 76 63.365^63.555 11.599^11.608 11.604 T 0.002 11.60d Discoaster kugleri FCO 61 55.13^55.31 11.910^11.917 11.889 T 0.004 11.90c Calcidiscus premacintyrei L(C)O 44^45 42.065^42.335 12.384^12.394 ^ 12.51b Calcidiscus macintyrei FO 43^44 41.355^41.72 12.407^12.419 ^ 12.57a Cyclicargolithus £oridanus L(C)O? 6^7 7.05^7.89 13.259^13.279 ^ 13.39

We calculated ages of individual samples by means of linear interpolation between succession age calibration points. As calibra-tion points we used the ages of precession minima and assigned them to the correlative sapropel mid-point. We used the mid-point of the corresponding limestone bed for cycles which do not have a sapropel. We assigned the age to the base of limestonebed if no sapropel is present and only limestone bed B developed as is the case in a limited number of cycles from the lowerpart of the section.

PALAEO 3178 18-9-03


Fig. 12. Detailed tuning of the basic small-scale sedimentary cycles in the lower half of the Monte dei Corvi section to the pre-cession and insolation time series of solution La93ð1;1Þ. Also shown are the positions of the calcareous plankton events. Numbersrefer to the numbers for the same events in Table 2. R and A indicate the Respighi and Ancona ashbeds. S^T indicates the re-cently proposed Serravallian/Tortonian boundary (Tortonian GSSP).

PALAEO 3178 18-9-03


the 2.4-Myr cycle around 12.2 Ma (Fig. 9). Thisrelationship is similar to that observed for theinterval which encompasses cycles 150^176 andcorresponds to the next younger 2.4-Myr eccen-tricity minimum.

6.2.7. Cycles 4^37Despite the uncertainty in the tuning of cycles

38^51, the tuning of cycles 4^37 to precession isunambiguous again. This is due to the applicationof the larger-scale eccentricity related cycles for a¢rst-order astronomical tuning, thus preventing adownward accumulation of errors in the tuning.In this case, the potential error in the tuning iseven eliminated because there is only one optionfor the tuning of the sapropels in the small-scaleclusters of large-scale clusters A and B to preces-sion. The age for the base of our section arrives at13.4 Ma.

7. Discussion

The astronomical tuning in combination withthe integrated stratigraphic correlations to sectionGibliscemi reveal that the Monte dei Corvi sec-tion is continuous within the resolution of theapplied cyclostratigraphic framework, except forthe presence of a possible hiatus with a maximumduration of 80 kyr in the Tortonian. Our initialconcern about the continuity of the section basedon the absence of the ¢rst neogloboquadrinid in-£ux and the D. kugleri acme remains unwar-ranted. The di¡erent biostratigraphic outcome ofthe present study, which does reveal the presenceof both the ¢rst neogloboquadrinid in£ux as wellas the D. kugleri acme must be explained by acombination of sample density, preservation,taxonomic concept and rarity of marker species.Typical D. kugleri was initially reported to be ab-sent (Montanari et al., 1997b) but re-examinationof the samples revealed that rare and atypicalspecimens similar to D. kugleri are present in alimited number of samples directly below the An-cona ashbed (D. Rio and E. Fornaciari, pers.comm.). Unfortunately, a more detailed analysiswas hampered by the scarceness of discoasteridsin combination with the generally poor preserva-T

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r.

PALAEO 3178 18-9-03


tion of the calcareous nannofossils. Like in sec-tion Gibliscemi, typical N. acostaensis is rare inthe interval marked by the ¢rst neogloboquadri-nid in£ux and can easily be missed when preser-vation is moderate to poor as in Monte dei Corvi.The other neogloboquadrinids (small-sized N. at-lantica and four-chambered morphotypes) havemost likely been included in P. continuosa byMontanari et al. (1997b).

7.1. Astronomical time scale

The tuning provides astronomical ages for allsedimentary cycles, calcareous plankton bioeventsand magnetic reversals recorded in section Montedei Corvi (Tables 1a,b^3). Ages of bioevents arein good to excellent agreement with tuned agesobtained for the same events in the Gibliscemiand Case Pelacani sections (Hilgen et al., 2000a;Caruso et al., 2002) but di¡er from ages in paral-lel sections in the Mediterranean for the time in-terval older than 12 Ma (Table 2, see discussionbelow). Comparison with the tuned ages for thesame events at Ceara Rise con¢rms previous no-tions of a strong diachrony of some importantzonal marker events, such as the FO of the neo-globoquadrinids and the LO of P. mayeri, and thealmost perfect synchrony of other events, such asthe FO and LCO of D. kugleri and the G. subqua-dratus LCO.

The astronomical ages for the magnetic rever-sals in the younger part of the section are in goodagreement with astronomical ages for the samereversals in the Gibliscemi and Metochia sections(Table 3) apart from C4Ar.2n(y) which is signi¢-cantly younger. The present study in additionprovides direct astronomical ages for reversals

that were not recorded in the latter sections dueto adverse magnetic properties. Unfortunately,the lower half of the Monte dei Corvi sectiondid not provide a reliable magnetostratigraphyalthough several short intervals with reversed po-larities and a single short interval with normalpolarities were recorded. Astronomical ages forthe short normal polarity interval overlap withtuned ages for a normal polarity interval in thecontinental Orera section in Spain that corre-sponds to cryptochron C5r.2r-1n (Abdul Aziz etal., 2003). Tuned ages for the intervals of reversedpolarity are consistent with the astronomicallydated magnetic reversal history of Orera (AbdulAziz et al., 2003); these intervals correspond to(parts of) C5r.3r, C5An.1r and C5Ar.1r. The re-sults of the present study in combination with thetuned magnetostratigraphy of the Orera sectionresult in the completion of the astronomical po-larity time scale for the last 13 Myr.

The tuning in addition provides ages for theAncona and Respighi ash layers that have previ-ously been dated by 40Ar/39Ar incremental heat-ing experiments on biotites at 11.43 and 12.86Ma, respectively (Montanari et al., 1997b). Theastronomical and 40Ar/39Ar ages are comparedwith one another in Table 4. This comparisoncon¢rms earlier notions that astronomical agesare older than the 40Ar/39Ar ages, at least if pre-viously widely accepted ages for mineral datingstandards are used. The discrepancy is reducedbut not completely eliminated if revised, olderages for the monitor dating standard (Fish Can-yon Tu¡ sanidine) are applied (Renne et al.,1998). The astronomical ages would ¢t with anage of V28.50 Ma for the FCT which is in re-markable good agreement with the U/Pb age of

Table 4Astronomical ages of the Ancona and Resphigi ashbeds and comparison with 40Ar/39Ar ages of biotites from the same ash layers

Ash layer Ar/Ar Astronomical age

27.84 28.02 28.50 Cleaveland Revised Ours

Ancona 11.43 11.50 11.70 11.56 11.67 11.688Respighi 12.86 12.94 13.16 12.98 13.28 13.296

12.94* 13.02* 13.25*

Biotite ages have been calculated using ages of 27.84, 28.02 and 28.50 Ma for the FCT-san monitor dating standard. Revisedages of Cleaveland et al. (2002) based on the modi¢ed tuning presented in Fig. 13. Asterisks indicate ages for the Respighi ash ifthe slightly discrepant oldest age is included in the calculation (see Montanari et al., 1997b).

PALAEO 3178 18-9-03


Fig. 13. Correlation of the low-frequency variations in CaCO3 content (of Cleaveland et al., 2002) in the lower part of the Montedei Corvi Beach section to the eccentricity time series of solution La93. Both the initial tuning of Cleaveland et al. (2002);(dashed lines) as well as our revised tuning (solid lines) are shown. Both assume that CaCO3 maxima correspond to eccentricityminima, i.e. similar to the observed phase relation in the Pliocene Trubi Formation on Sicily (Hilgen, 1991b). The smoothedCaCO3 record is based on applying a bandpass ¢lter with a 2.6^18 m width to the CaCO3 depth series shown to the left (seeCleaveland et al., 2002). In addition the large-scale CaCO3 cycle related to 400-kyr eccentricity has been schematically indicated(dotted line). Note that the tuning of Cleaveland et al. (2002) is consistent with the radiometric ages of the ashbeds and that ourtuning is consistent with the 400-kyr eccentricity cycle. Ages of the Ancona (A) and Respighi (R) ashbeds are indicated to theright as follows: 1. astronomical age, this paper; 2. astronomical age of Cleaveland et al. (2002), and 3. 40Ar/39Ar biotite age ofMontanari et al. (1997b). Also indicated are the ages for the N. acostaensis FO (1. our age; 2. astronomical age of Cleaveland etal., 2002) and our astronomical age of the Serravallian/Tortonian (S/T) boundary according to a recent proposal to de¢ne theTortonian GSSP close to the D. kugleri and G. subquadratus LCOs in the Monte dei Corvi section (Hilgen et al., 2003).

PALAEO 3178 18-9-03


Schmitz and Bowring (2001) but which is incon-sistent with previous attempts to intercalibrate ra-dioisotopic and astronomic time (Renne et al.,1994; Hilgen et al., 1997; Steenbrink et al.,1999). Clearly more research is needed to solvethis fundamental problem in geochronometry.

7.2. Alternative tunings

Our tuning deviates from the tuning of the low-frequency variations in a high-resolution carbon-ate record from the lower part of the Monte deiCorvi Beach section to eccentricity proposed byCleaveland et al. (2002). Their tuning, which iswithin error consistent with the 40Ar/39Ar biotiteages of the ash layers, is based on correlatingsuccessive carbonate maxima to 100-kyr eccentric-ity minima but is less convincing when the 400-kyr cycle is examined. In fact their tuning can beeasily adjusted as to make it consistent with ours(see below). The inconsistency in their tuningpartly results from their wish to stay within errorto the published biotite ages while we could ex-tend our existing tuning for the younger part ofthe Mediterranean Miocene. Our alternative tun-ing for the low-frequency variations in carbonatecontent to eccentricity is presented in Fig. 13. Thistuning results in a much better ¢t with the 400-kyreccentricity cycle and seems consistent with ourages for the ash layers. The large discrepancy inthe tuned ages for the N. acostaensis FO is ex-plained by the fact that the ¢rst neogloboquadri-nid in£ux was not recorded by Montanari et al.(1997b).

An apparent mis¢t in the revised tuning isfound slightly above the Ancona ashbed in theinterval between 157 and 160 m (Fig. 13) wherea distinct carbonate maximum corresponds to in-creasing eccentricity values following the 400-kyrminimum at 11.7 Ma. This mis¢t is recognizablein the ¢eld as the ¢rst prominent cape east of the¢shermen’s sheds. This small cape represents thecarbonate maximum but it also contains thesmall-scale sapropel cluster of cycles 74^77 thatcorrelates with the 100-kyr eccentricity maximumat 11.62 Ma. This interval coincides with the oxy-gen isotope event Mi-5 as recorded in section Gi-bliscemi (Turco et al., 2001), suggesting that this

event exerted an additional control on the carbon-ate content in this particular interval.

Discrepant ages of the calcareous planktonevents (Table 2) indicate that our tuning mustalso deviate from the tuning of parallel sectionsin the Mediterranean, which together cover thetime interval between 10.5 and 13.7 Ma (CasePelacani, Caruso et al., 2002; Tremiti, Lirer etal., 2002; Ras il-Pellegrin, Sprovieri et al.,2002a). However, at this stage, it is di⁄cult tocompare both these tunings in detail because ofthe di¡erent biostratigraphic methods applied andthe limited reliability of several events in the crit-ical interval due to the rare and scattered presenceof the marker species. When the ages of the morereliable events (D. kugleri FCO and LCO, Neo-globoquadrina group FO, P. siakensis IAB, IAE,IIAB, IIAE and G. partimlabiata FO) are com-pared, it is clear that the tuning is essentially con-sistent back to 12 Ma but that it starts to deviatefor older time intervals with a maximum discrep-ancy of 160 kyr for the G. partimlabiata FO (Ta-ble 2). The tuning of the Tremiti sections in thecritical interval is based on cycle counts ratherthan on cycle patterns, although eccentricity re-lated signals are taken into account as a checkon the precession tuning. The latter is crucialfor avoiding the accumulation of errors in themore subjective cycle counts by tracing the ex-pression of the eccentricity envelope of the preces-sion amplitude. On Tremiti, cycle counts are com-plicated by the presence of an hiatus (work inprogress), the lack of sedimentary expression ofsome basic cycles and their complex quadripartitebuild-up with often two carbonate minima (onered and one gray) per cycle instead of one asassumed by Lirer et al. (2002). Moreover, the tun-ing is based on less well exposed and therefore lesssuitable sections located on opposite sites of SanNicola Island while an ideal composite sectioncan be constructed using the excellent but di⁄cultto reach exposures along the steep northwest fac-ing cli¡s. Finally, a potential error lies in the reli-ability of the two biostratigraphic events, theP. mayeri FCO and the C. premactintyrei LCO,used as timelines to correlate Tremiti to the olderRas il-Pellegrin section on Malta and extend thetuning further downward.

PALAEO 3178 18-9-03


Although the discrepancies are rather smallfrom a geological perspective they have importantconsequences for ^ the consistency of ^ phase re-lations between the sedimentary cyclicity and theastronomical parameters, and pose serious limita-tions for studies that aim to reconstruct the e¡ectsof astronomical climate forcing. The results of ourstudy indicate that a single orbital induced oscil-latory climate system can be held responsible forNeogene sapropel formation in the Mediterraneanover the last 13.5 million years. A recent climatemodeling experiment of orbital extremes indicatesthat the African monsoon is at least partly re-sponsible (Tuenter et al., 2003), thereby con¢rm-ing earlier ideas of Rossignol-Strick (1983) andPrell and Kutzbach (1987). In addition this studyprovides support for the use of the classical 65‡Nlat. summer insolation curve as a tuning target bydemonstrating an obliquity control on the Africanmonsoon intensity mostly via summer heating ofthe Eurasian continent at latitudes higher than30‡ or even 50‡ (Tuenter et al., 2003).

7.3. GSSPs, APTS and astronomical solutions

Summarizing the demonstrable continuity ofthe succession in the Serravallian^Tortonianboundary interval in combination with the astro-nomical tuning of the cycles strengthens the casefor Monte dei Corvi as a candidate for de¢ningthe Tortonian GSSP as proposed by Montanari etal. (1997b) and Odin et al. (1997), who in additionsuggested to de¢ne the Serravallian and MessinianGSSPs in the same section. Serious shortcomingsare the moderate to poor preservation of the cal-careous plankton, the lack of a reliable magneto-stratigraphy in the lower half of the section and,in case of the Serravallian GSSP, the accessibilityof the Monte dei Corvi High Cli¡ section, whichwas not included in the present study. The Mes-sinian GSSP has recently been de¢ned at the baseof astronomically dated color cycle no. 15 in sec-tion Oued Akrech, located on the Atlantic side ofMorocco (Hilgen et al., 2000b,c). Recently it hasbeen proposed to formally de¢ne the TortonianGSSP in the Monte dei Corvi section at themid-point of the sapropel of cycle 76(www.geo.uu.nl/SNS). This level coincides closely

with the LCOs of D. kugleri and G. subquadratus ;these events are demonstrable (near)synchronousbetween the Mediterranean and low-latitudeocean (Hilgen et al., 2000a).

Despite the moderate to poor preservation, de-tailed biostratigraphic correlations to section Gi-bliscemi ^ characterized by a much better preser-vation ^ were possible, but the preservationconditions certainly hampers to establish a reli-able stable isotope record. The lack of a reliablemagnetostratigraphy in the Serravallian^Torto-nian boundary interval can be overcome withinthe framework of an astronomically tuned inte-grated stratigraphy because a single tuned sectionwith a reliable magnetostratigraphy is su⁄cient tobridge the gap. Tuned ages for reversal bound-aries are not yet available for this interval fromthe marine record but they have been obtainedfrom the continental Orera section in Spain (Ab-dul Aziz et al., 2003).

Finally, the unambiguous tuning of the upperpart of the section, re£ecting precession^obliquityinterference, o¡ers an excellent opportunity for avery detailed comparison between the intricatecycle patterns and di¡erent astronomical solu-tions. The almost perfect ¢t suggests that the idealsolution must be close to solution La93ð1;1Þ withpresent-day values for the dynamical ellipticity ofthe Earth and the tidal dissipation by the Moon.This outcome is in line with previous studies di-rected at testing the accuracy of astronomical so-lutions by means of a detailed statistical compar-ison with sedimentary archives of the orbitalforcing of past climate (Lourens et al., 1996,2001; Pa«like and Shackleton, 2000). But it isalso clear from the present study that serious mis-¢ts start to arise for intervals older than 10 Ma.To explain these mis¢ts we have compared thecycle patterns with the same insolation targetcurve derived from the La90-93 solution butwith di¡erent values for tidal dissipation. Neitherof these curves produced an excellent and con-vincing ¢t with all cycle patterns in the Montedei Corvi Beach section although the di¡erencesin the ages of the insolation peaks remain verysmall in the order of 1^10 kyr. Consequently themis¢ts are di⁄cult to explain other than by smalluncertainties in the astronomical solution itself. A

PALAEO 3178 18-9-03


www.geo.uu.nl/SNS

detailed comparison with a new numerical solu-tion may reveal whether this is indeed the case.

8. Conclusions

The distinct cycle patterns and the calcareousplankton biostratigraphy and magnetostratigra-phy allow the Monte dei Corvi section to be as-tronomically tuned by correlating sedimentarycycles to the precession and insolation time seriesof the La93ð1;1Þ solution. The tuning is unambig-uous for the younger part of the section but maybe o¡ in parts by one or occasionally even twocycles in older parts. Intervals marked by thenear-absence of small-scale sapropel clusters re-lated to the 100-kyr eccentricity cycle and pro-longed dominance of the intermediate cycle andthus precession^obliquity interference correspondto minima in eccentricity related to the 2.4-Myreccentricity cycle. Our tuning marks a signi¢cantimprovement of the recently published astronom-ical calibrations of the Monte dei Corvi section(Cleaveland et al., 2002) and of parallel sectionsin the Mediterranean (Lirer et al., 2002; Sprovieriet al., 2002a).

Astronomical ages for the reversal boundariesin combination with the tuned magnetostratigra-phy of the continental Orera section in Spain (Ab-dul Aziz et al., 2003) results in the completion ofthe astronomical polarity time scale for the last13 Myr. Tuned ages for the Ancona and Respighiash layers are signi¢cantly older (by 250^400 kyr)than published 40Ar/39Ar biotite ages reported forthe same layers.

Finally, our study reveals that the Monte deiCorvi Beach section is an acceptable candidatefor de¢ning the Tortonian GSSP, despite its ob-vious shortcomings, and that a single orbital in-duced oscillatory system is responsible for lateNeogene sapropel formation in the Mediterraneanby continuously a¡ecting (circum-)Mediterraneanclimate throughout the last 13.5 million years.

Acknowledgements

Silvia Iaccarino and Willem-Jan Zachariasse

are thanked for discussion and constructive read-ing of the manuscript. Alessandro Montanari andDavid Bice gratefully sent and discussed the elec-tronic version of ¢gure 3 of the Cleaveland et al.paper. We are further thankful to Maria-BiancaCita, Rudolfo Sprovieri and Finn Surlyk for theircritical reviews which considerably improved themanuscript. Esther van Assen, Tanja Kouwen-hoven and Erwin van der Laan are thanked fortheir help in the ¢eld, Esther in particular forconstructing ‘Dutch’ dams to facilitate loggingof the problematic part of the trajectory under-neath the ¢shermen’s sheds. Unfortunately, thedams were repeatedly destroyed by bow wavesof the ferries.

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