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Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy

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Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy
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  Pleistocene magnetochronology of early hominin sites at Ceprano and FontanaRanuccio, Italy Giovanni Muttoni a, ⁎ , Giancarlo Scardia b , Dennis V. Kent c,d , Carl C. Swisher c , Giorgio Manzi e a Department of Earth Sciences, University of Milan, via Mangiagalli 34, I-20133 Milan, Italy, & ALP   —  Alpine Laboratory of Paleomagnetism, via Madonna dei Boschi 76,I-12016 Peveragno (CN), Italy b Istituto Nazionale di Geo  󿬁 sica e Vulcanologia, Sezione di Milano-Pavia, via Bassini 15, I-20133 Milano, Italy c Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA d Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA e Department of Animal and Human Biology, Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy a b s t r a c ta r t i c l e i n f o  Article history: Received 17 March 2009Received in revised form 21 June 2009Accepted 22 June 2009Available online xxxx Keywords: PleistoceneCepranoFontana RanucciomagnetostratigraphyhomininsItaly Paleomagnetic analyses were conducted on two cores drilled at Ceprano in central Italy where an incompletehominin cranium was discovered in 1994, as well as on two additional cores from the nearby site of FontanaRanuccio that yielded hominin remains associated with an Acheulean industry. No evidence for the 0.78 MaBrunhes – Matuyama boundary was found at Ceprano down to 45 m below the level that yielded the hominincranium. The Ceprano lithostratigraphy and the paleomagnetic age constraints are broadly consistent withthe stratigraphy of the Liri lacustrine sequence of the Latina Valley, constrained by published K – Ar agesbetween ~0.6 and ~0.35 Ma, and according to an age model with magnetic susceptibility supported by pollenfacies data, suggest that the level that yielded the hominin cranium has an age of ~0.45 (+0.05, − 0.10) Ma.Evidence for the Brunhes – Matuyama boundary was found at Fontana Ranuccio about 40 m below thehominin level, consistent with a K – Ar age of ~0.46 Ma reported for this level. Hence the Ceprano and FontanaRanuccio hominin occurrences may be of very similar mid-Brunhes age.© 2009 Elsevier B.V. All rights reserved. 1. Introduction Direct evidence of early hominin occupation in Italy includes anincomplete hominin cranium discovered in 1994 along a roadcut nearCeprano, southeast of Rome (Ascenzi et al.,1996), as well as homininteeth possibly attributed to  Homo erectus  associated with a Mode II(Acheulean) tool industryat the nearby site of Fontana Ranuccio (e.g.,Segre and Ascenzi,1984; Segre, 2004; Segre Naldini et al., 2009). TheCeprano cranium has been variably ascribed to a new species  H.cepranensis  (Mallegni et al., 2003), a late variantof   H. erectus  (Ascenziet al.,1996, 2000)  H. erectus sensu latu  (Clarke, 2000), a possible adultrepresentative of   H. antecessor   (Manzi et al., 2001; Manzi, 2004;Bruner and Manzi, 2005), or to an ancestral morphotype of the  H.heidelbergensis / rhodesiensis  hypodigm (Bruner and Manzi, 2007).Despite its taxonomic uncertainty, the Ceprano cranium is commonlyregarded as representative of one of the oldest hominins thatpopulated Europe (Italy and Spain) at about 1 Ma (Dennell, 2008)and that possibly represented the link between early  Homo  and  H.heidelbergensis , the main type of hominin evidenced in Europe in theMiddle Pleistocene (Manzi, 2004; Bruner and Manzi, 2007; Dennell,2008).Based on stratigraphic and geologic arguments and built on acomplex correlation framework between discontinuous continentalsections,theCepranocraniumwasconsideredbyseveralauthors(e.g.,Ascenzi et al., 1996; Ascenzi and Segre, 1997; Ascenzi et al., 2000;Manzi, 2004) to be older than the oldest Latianvolcanic activity datedin the region to ~0.7 Ma (Carrara et al., 1995; Fornaseri, 1985;Peccerillo, 2005) and therefore close to the Brunhes – Matuyamapolarity chron boundary (0.78 Ma; geomagnetic polarity time scaleincorporating astronomical dating as summarized by Berggren et al.,1995, is used throughout), although no paleomagnetic data wereprovided in support of this interpretation.Preliminary paleomagnetic analyses (DVK) on 8 samples taken(CCS) from the ~1 m-thick roadcut section that yielded the hominincraniumgaveunstabledirectionssavefor threesamplescharacterizedbyanormalmagneticpolaritycomponent(seebelow),butthesectionwas too short to con 󿬁 rm reliability of the magnetic results ordetermine any correlation with the geomagnetic polarity time scale.To address these issues, we organized the drilling of two long cores atCeprano, where expanded sections are not exposed, with the aim toestablish a magnetic polarity stratigraphy and therefore provideconstraints on the age of the Ceprano hominin fossil. Here we reportthe paleomagnetic data used to construct age models of sedimenta-tion for the Ceprano 1 and Ceprano 2 cores that bring a revision of theage of the Ceprano cranium. By exploiting the opportunity provided Earth and Planetary Science Letters xxx (2009) xxx – xxx ⁎  Corresponding author. E-mail address:  giovanni.muttoni1@unimi.it (G. Muttoni). EPSL-09896; No of Pages 14 0012-821X/$  –  see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2009.06.032 Contents lists available at ScienceDirect Earth and Planetary Science Letters  journal homepage: www.elsevier.com/locate/epsl ARTICLE IN PRESS Please cite this article as: Muttoni, G., et al., Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy,Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2009.06.032  by two additional cores taken in 2004 by A.G. Segre at the earlyhominin site of Fontana Ranuccio, we also searched for the Brunhes – Matuyama boundary at this locality. 2. Geological setting  The Ceprano and Fontana Ranuccio sites are located in the LatinaValleyabout90 kmand50 kmsoutheastofRome,respectively(Fig.1A).The Latina Valley consists of several extensional tectonic basins,including the Ceprano basin (hosting the Ceprano site) and the Anagnibasin (hosting the Fontana Ranuccio site). These basins, bounded byhorsts of Mesozoic to Miocene limestones (Segre and Ascenzi, 1984;Carraraet al.,1995; Ascenzi et al.,1996;Segre, 2004),developed mainlybetweentheLatePlioceneandtheearlierpartoftheMiddlePleistocene(Carrara et al.,1995; Galadini and Messina, 2004) and were character-ized by regional volcanic activity [Alban Hills (Latian) and Ernici-Roccamon 󿬁 na magmatic provinces] since about 0.6 Ma (e.g., Giannetti,2001; Peccerillo, 2005; Rouchon et al., 2008) (Fig.1A). The Anagni basin, where the Fontana Ranuccio site is located, isbounded to the southeast by the Sgurgola-Ferentino bedrock ridgethat possibly acted as a dam for lacustrine and  󿬂 uvial sedimentationduring the Early Pleistocene (Alberti et al., 1975) (Fig. 1B). These lacustrine-alluvial sediments, which we encountered in our drillingsat Fontana Ranuccio (units 2 – 3; see below), were covered by MiddlePleistocenepyroclastics,datedatFontanaRanucciobetween0.528Maand 0.487 Ma (K-Ar, Biddittu et al.,1979; see below) and attributed tothe Alban Hills magmatic province (~0.6 – 0.02 Ma; Peccerillo, 2005;Fig.1A,B), and by travertine (Segre and Ascenzi,1984). The Ceprano basin is comprised broadly between the Ceprano siteand the Roccamon 󿬁 na volcanic complex (Fig.1A,C) and was the locusof extensive lacustrine sedimentation during the Middle Pleistocene  – the Liri lacustrine sequence (Devoto, 1965; Carrara et al., 1995)  – Fig.1.  (A) Simpli 󿬁 ed geologic map of the Latina Valley (adapted from Segre, 2004) with indication of the drill sites (C = Ceprano 1 and Ceprano 2; FR = Fontana Ranuccio 1 andFontanaRanuccio2).Thestratigraphicsettingoflacustrinedeposition intheLatinaValleyduringthePleistoceneisalsoindicatedintherightpanel.(B)Digitalelevationmodelof theAlban Hills-Anagni basin area; the white shaded area represents the inferred distribution of the  N ~0.6 Ma lacustrine deposition in the Anagni basin (FR = Fontana Ranuccio 1 andFontana Ranuccio 2). (C) Digital elevation model of the Roccamon 󿬁 na volcano-Ceprano basin area; the white shaded area represents the inferred distribution of the  b ~0.6 Malacustrine deposition in the Ceprano basin (C = Ceprano 1 and Ceprano 2).2  G. Muttoni et al. / Earth and Planetary Science Letters xxx (2009) xxx –  xxx ARTICLE IN PRESS Please cite this article as: Muttoni, G., et al., Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy,Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2009.06.032  possibly triggered by the damming of the southeastern outlet of theLatina Valley (Devoto,1965; Carrara et al.,1995) by the Roccamon 󿬁 navolcanic complex, active between ~0.6 and ~0.15 Ma (De Rita andGiordano,1996; Giannetti, 2001; Giordano et al., 2006; Rouchon et al.,2008) (Fig. 1C). Hominin footsteps were recently found in an ash deposit of the Roccamon 󿬁 na volcanic complex (Mietto et al., 2003)and dated by  40 Ar/ 39 Ar on single leucite crystals to 0.345±0.006 Ma(Scailletetal.,2008).TheLirilacustrinesequence,asrecognizedintheCeprano site area, consists of three main lithostratigraphic units withatotalmaximumthicknessof~100 minthetype-area(Devoto,1965).At the base of the sequence is a white calcareous mud withinterbedded black graded tephras ( “ lower lacustrine mud ”  of  Devoto,1965; lacustrine basinal facies), passing upward to cross-beddedyellow sand, gravel and calcareous mud ( “ typical lacustrine facies ”  of Devoto,1965;  󿬂 uvial and nearshore lacustrine facies), and capped bylacustrine travertine and calcareous mud, locally rich in organicmatter ( “ late lacustrine facies ”  of  Devoto, 1965; nearshore lacustrineand/or marsh facies).In our drilling at Ceprano, we encountered a sequence of lithological units (1 – 4; see below) that are interpreted as represent-ing, from top to bottom, the  “ late lacustrine facies ”  (unit 1), the “ typical lacustrine facies ”  (unit 2), and the  “ lower lacustrine mud ” (unit 4) of the Liri lacustrine sequence of  Devoto (1965). The Lirilacustrine sequence is constrained by K – Ar ages on fallout (non-reworked) tephra layers of 0.570±0.011 Ma and 0.583±0.011 Ma(sample BIF 124 on leucite) from the  “ lower lacustrine mud ”  and0.354±0.007 Ma and 0.359±0.007 Ma (sample BIF171 on K-feld-spar) from the  “ late lacustrine facies ”  (Carrara et al., 1995; Interna-tional Conventional Constants used for age calculation from Steigerand Jager, 1977). Although we could not  󿬁 nd conclusive evidence of (laterally discontinuous?) tephra layers in the Ceprano cores (i.e., inunit 1  ≈  “ late lacustrine facies ”  and in unit 4  ≈  “ lower lacustrinemud ” ), the available radiometric age constraints (Carrara et al.,1995)bracket the Liri lacustrine deposition at Ceprano in a time windowbroadly comprised between ~0.6 and ~0.35 Ma.In summary, the Anagni basin, where the Fontana Ranuccio site islocated, hosted lacustrine sedimentation before, and during the earlystages of, the Alban Hills volcanic activity, i.e. roughly before 0.5 – 0.6 Ma, whilst the Ceprano basin, where the Ceprano site is located,hosted lacustrine sedimentation during the Roccamon 󿬁 na volcanicactivity broadly between ~0.6 and ~0.35 Ma. Therefore, we mightexpect to  󿬁 nd the Brunhes – Matuyama polarity reversal in thelacustrine deposits of Fontana Ranuccio and exclusively normalpolarity of the Brunhes chron in the lacustrine deposits of Ceprano. 3. Lithostratigraphy of cores DrillingatCeprano1wascarriedoutafewmeterstothesoutheastof the roadcut that yielded the hominin cranium (Fig. 2). The homininstratigraphiclevelwastracedlaterallyintothecorestratigraphyatabout1.5 m below the ground surface; drilling further penetrated theunderlyingsedimentstoatotaldepthof48 mwithatotalcorerecoveryof 97% (drilling details in Online Table 1). Ceprano 1 is characterized byfourmainlithologicunits(Fig.3).Theupperpartofthecore(unit1;0.3 – Fig. 2.  Physical correlation of the Ceprano 1 and Ceprano 2 cores placed in a detailed topographic context. Lithology and suceptibility data show the lateral consistency of thepredominantlynormal polarity interval(positive ChRM inclinations) thereinretrieved (blackisnormal polarity,whiteisdubious reverse polarity;see discussion). The discoverysiteand stratigraphic position of the Ceprano cranium are indicated.3 G. Muttoni et al. / Earth and Planetary Science Letters xxx (2009) xxx –  xxx ARTICLE IN PRESS Please cite this article as: Muttoni, G., et al., Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy,Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2009.06.032  12.6 m)consists of  󿬁 neto medium-grained,well-sorted sands,possiblypertaining to meandering  󿬂 uvial channels, interbedded with massivepackages of oxidized silty clays with carbonate nodules, and brownorganic-rich clays, ascribable to  󿬂 oodplain and marsh environments,respectively(thisunitshouldcorrespondtothe “ latelacustrinefacies ” of Devoto, 1965 with associated K – Ar ages of ~0.35 Ma of  Carrara et al.,1995; see above). Below is a lacustrine sequence (unit 2; 12.6 – 34.5 m)starting with coarse gyttja and low-energy alluvial deposits (12.6 – 16.4 m) underlain by laminated mud and normal-graded sands,interpreted as turbidites (lacustrine basinal facies; 16.4 – 30.8 m), andcarbonate tufa with plant macroremains (lacustrine nearshore facies;30.8 – 34.5 m);unit2shouldcorrespondtothe “ typicallacustrinefacies ” of Devoto(1965).From34.5to38.0 m(unit3),thecorecomprisessandytoclayeygravelswithpoorlyroundedpebbles,possiblypertainingtoanalluvialfandeposit.Finally,from38.8to48.0 m(unit4)thecoreconsistsof consolidated laminated marls interpreted as a lacustrine deposit,which should correspond to the  “ lower lacustrine mud ”  of  Devoto(1965) with associated K – Ar ages of ~0.6 Ma (Carrara et al., 1995; see Fig. 3.  Stratigraphic synthesis of the Ceprano 1 core with (A) lithology and stratigraphic position of paleomagnetic samples taken for analysis, (B) magnetic susceptibility,(C) weighted NRM intensity,(D) unblocking temperature spectraof the ChRM component, and (E) inclinationvalues of the ChRM component used for polarity interpretation (blackis normal polarity, white is dubious reverse polarity; see discussion). The stratigraphic position of the Ceprano cranium is indicated at the top of the Ceprano 1 core.4  G. Muttoni et al. / Earth and Planetary Science Letters xxx (2009) xxx –  xxx ARTICLE IN PRESS Please cite this article as: Muttoni, G., et al., Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy,Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2009.06.032  above). According to a preliminary palynological study, the Ceprano 1core from meter levels 14 to 24 within lacustrine unit 2 yielded forestpollen associations of temperate climatic conditions (with, amongothers,  Carpinus ,  Ulmus , deciduous  Quercus ,  Alnus ,  Corylus , and  Hedera )compatible with an interglacial period (Margari et al., 2008).Drilling at Ceprano 2 (details in Online Table 1) penetrated 36 m of sedimentsabout140 mnorthwestofCeprano1(Fig.2)totestthelateralcontinuityof thesedimentarysuccession.TheCeprano2coredisplaysafour-fold lithostratigraphic subdivision (interrupted by non-recoverygaps) broadly similar to that observed at Ceprano 1 (Fig. 4) andconsisting of alluvial deposits (unit 1; 0 – 11.3 m), lacustrine deposits(unit 2; 14.9 – 27.8 m), poorly recovered sandy to clayey gravels (unit 3;27.8 – 31.5 m), and laminated marls (unit 4; 35.3 – 36.0 m).Fontana Ranuccio 1 and Fontana Ranuccio 2 were drilled respec-tively ~50 m to the east and ~100 m to the west of the site thatyielded hominin teeth and Acheulean tool assemblages (Fig. 5). Thearchaeological layer at this site, dated by K – Ar on leucites to 0.458±0.006 Ma (Biddittu et al., 1979; Segre and Ascenzi, 1984), isinterbedded in a succession of weathered volcanoclastic andvolcanic layers, outcropping along quarry terraces #2 and #3,capped by tuff (locally known as  tufo litoide ) and resting above apyroclastic deposit (locally known as  pozzolana ) attributed to theLatian-Alban volcanic activity (Segre Naldini et al., 2009) (Fig. 5). This pyroclastic deposit is dated between 0.487±0.008 Ma (top)and 0.528±0.006 Ma (base) by K – Ar on leucites from samples fromquarry outcrops (Biddittu et al., 1979), thus providing a maximumage consistent with the direct date on the archaeological level(Fig. 5). In detail, Fontana Ranuccio 1 (Fig. 6, upper panel; Online Table 1) consists, from top to bottom, of ~1 m of deposits reworkedby quarry activity followed down-section by the pyroclastic deposit Fig. 4.  Stratigraphic synthesis of the Ceprano 2 core with (A) lithology and stratigraphic position of paleomagnetic samples taken for analysis, (B) magnetic susceptibility,(C) weighted NRM intensity,(D) unblocking temperature spectraof the ChRM component, and (E) inclinationvalues of the ChRM component used for polarity interpretation (blackis normal polarity, white is dubious reverse polarity; see discussion).5 G. Muttoni et al. / Earth and Planetary Science Letters xxx (2009) xxx –  xxx ARTICLE IN PRESS Please cite this article as: Muttoni, G., et al., Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy,Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2009.06.032
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