Palaeoenvironments of the Mediterranean Basin at the Messinian hypersaline/hyposaline transition: evidence from natural radioactivity and microfacies of post-evaporitic successions of the Adriatic sub-basin Gianluca Sampalmieri, 1 Annalisa Iadanza, 1 Paola Cipollari, 1,2 Domenico Cosentino 1,2 and Sergio Lo Mastro 1 1 Dipartimento di Scienze Geologiche, Universita ` degli Studi Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 Roma, Italy; 2 Istituto di Geologia Ambientale e Geoingegneria, CNR-Roma, Via Salaria km 29,300, 00016 Monterotondo Stazione, Roma, Italy Introduction The Messinian salinity crisis (MSC) was one of the major palaeoceano- graphic events that occurred in the Mediterranean Basin during Neogene times. Different scenarios to explain the mechanisms for developing the evaporitic and the post-evaporitic (p-ev) phases have been suggested (Hsu¨ and Cita, 1973; Nesteroff, 1973; Selli, 1973). Despite a continued debate over the mechanisms, a general consensus (CIESM, 2008) was recently achieved on the main evolutionary stages of the MSC. Starting from the viewpoint of Sicilian stratigraphy (Roveri et al., 2008a), this new MSC scenario com- bines the two-step model of Clauzon et al. (1996) and the well-established chronology of the Messinian events (Krijgsman et al., 1999). According to this model, the MSC developed in two evolutionary steps: (1) Lower Evapor- ites (5.96–5.60 Ma); (2.1) Resediment- ed Evaporites (5.60–5.53 Ma); and (2.2) Upper Evaporites (5.53– 5.33 Ma). Although there is general consensus on the main evolutionary steps of the MSC, the 2.1 sub-step and the palaeo- environments at the hypersaline ⁄ hyposaline transition are scarcely understood. The detailed stratigraphic and palaeoenvironmental analyses re- ported in this article, which were carried out on the p-ev (post- 5.60 Ma) Messinian deposits at Maccarone (Marche, northern Apen- nines) and Colle di Votta (Maiella, Abruzzi, central Apennines), can con- tribute to a better understanding of the palaeoenvironmental conditions in the Mediterranean Basin at the Messinian hypersaline ⁄ hyposaline transition. Geological setting On the Adriatic side of the Apennines, the 16 gypsum cycles recognised in the Romagna sections (Vai and Ricci Lucchi, 1976; Vai, 1988, 1997; Krijgs- man et al., 1999) recorded the MSC in a marginal and shallow area (Vena del Gesso Basin, Fig. 1), at the leading edge of the Apennines (Roveri et al., 2001; Roveri and Manzi, 2006). A similar structural setting, developed in a deeper domain, can be suggested to explain the tectono-sedimentary evolu- tion of the Maccarone area (Marche, northern Apennines). There, above resedimented gypsum beds, lie a succes- sion of fine-grained, mainly barren deposits with intercalations of thin sandstone layer (S. Donato Fm) marls with oligohaline ostracod associations (Lago-Mare biofacies, Casati et al., 1976; Grossi et al., 2008) and evaporitic carbonate beds (Colombacci Fm). These deposits rest below the fully marine early Pliocene Argille Azzurre Fm. At the foreland domain of the Adriatic-verging orogenic system (Maiella Mts, central Apennines), the MSC has been recorded in a marginal and shallow basin. In the Maiella area, an erosional surface separates the Lower Evaporites from the early p-ev Messinian deposits (Sampalmieri et al., 2008). This boundary can be correlated with the Messinian ero- sional surface (MES) recognised throughout the Mediterranean Basin in both offshore (Escutia and Maldo- nado, 1992; Guennoc et al., 2000; Lofi et al., 2005; Maillard et al., 2006) and on land sections (Guillemin and Hon- zay, 1982; Costa et al., 1986; Cita and Corselli, 1990; Riding et al., 1999; Roveri et al., 2001; Rouchy et al., 2003; Soria et al., 2005; Corne´e et al., 2006). ABSTRACT At the end of the Messinian salinity crisis, changes in the palaeoceanography and palaeoclimate induced a transition from hypersaline to hyposaline conditions in the Mediterranean water body. Detailed investigation of natural radioactivity and microfacies analyses of two early post-evaporitic Messinian sections show that the transition occurred in poorly oxygen- ated and well-stratified water masses. These transitional deposits, which mainly consist of marls and CaCO 3 -rich horizons, are generally well laminated and totally barren in benthic and planktonic fauna. The presence of barite, small (5–8 lm) authigenic framboidal pyrite, and high values of U indicate persistent anoxic conditions during the early post- evaporitic Messinian stage in the Adriatic sub-basin of the Mediterranean Sea. The presence of post-evaporitic well- laminated barren deposits from both Mediterranean border- land sections and ODP sites suggests that these anoxic conditions extended to other sub-basins of the Mediterranean region. Terra Nova, 22, 239–250, 2010 Correspondence: Prof. Domenico Cosentino, Dipartimento di Scienze Geologiche, Universita` degli Studi Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 Roma, Italy. Tel.: +39 06 57338034; fax: +39 06 57338201; e-mail: [email protected]ȑ 2010 Blackwell Publishing Ltd 239 doi: 10.1111/j.1365-3121.2010.00939.x
Transcript
Palaeoenvironments of the Mediterranean Basin at the Messinianhypersaline/hyposaline transition: evidence from naturalradioactivity and microfacies of post-evaporitic successions ofthe Adriatic sub-basin
1Dipartimento di Scienze Geologiche, Universita degli Studi Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 Roma, Italy; 2Istituto di
Geologia Ambientale e Geoingegneria, CNR-Roma, Via Salaria km 29,300, 00016 Monterotondo Stazione, Roma, Italy
Introduction
The Messinian salinity crisis (MSC)was one of the major palaeoceano-graphic events that occurred in theMediterranean Basin during Neogenetimes. Different scenarios to explainthe mechanisms for developing theevaporitic and the post-evaporitic(p-ev) phases have been suggested(Hsu and Cita, 1973; Nesteroff, 1973;Selli, 1973).Despite a continued debate over the
mechanisms, a general consensus(CIESM, 2008) was recently achievedon the main evolutionary stages of theMSC. Starting from the viewpoint ofSicilian stratigraphy (Roveri et al.,2008a), this new MSC scenario com-bines the two-step model of Clauzonet al. (1996) and the well-establishedchronology of the Messinian events(Krijgsman et al., 1999). According tothis model, the MSC developed in twoevolutionary steps: (1) Lower Evapor-ites (5.96–5.60 Ma); (2.1) Resediment-ed Evaporites (5.60–5.53 Ma); and
(2.2) Upper Evaporites (5.53–5.33 Ma).Although there is general consensus
on the main evolutionary steps of theMSC, the 2.1 sub-step and the palaeo-environments at the hypersaline ⁄hyposaline transition are scarcelyunderstood. The detailed stratigraphicand palaeoenvironmental analyses re-ported in this article, which werecarried out on the p-ev (post-5.60 Ma) Messinian deposits atMaccarone (Marche, northern Apen-nines) and Colle di Votta (Maiella,Abruzzi, central Apennines), can con-tribute to a better understanding of thepalaeoenvironmental conditions in theMediterranean Basin at the Messinianhypersaline ⁄hyposaline transition.
Geological setting
On the Adriatic side of the Apennines,the 16 gypsum cycles recognised in theRomagna sections (Vai and RicciLucchi, 1976; Vai, 1988, 1997; Krijgs-man et al., 1999) recorded the MSC ina marginal and shallow area (Vena delGesso Basin, Fig. 1), at the leadingedge of the Apennines (Roveri et al.,2001; Roveri and Manzi, 2006).Asimilar structural setting,developed
in a deeper domain, can be suggested toexplain the tectono-sedimentary evolu-
tion of the Maccarone area (Marche,northern Apennines). There, aboveresedimented gypsum beds, lie a succes-sion of fine-grained, mainly barrendeposits with intercalations of thinsandstone layer (S. Donato Fm) marlswith oligohaline ostracod associations(Lago-Mare biofacies, Casati et al.,1976; Grossi et al., 2008) and evaporiticcarbonate beds (Colombacci Fm).These deposits rest below the fullymarine early Pliocene Argille AzzurreFm.At the foreland domain of the
Adriatic-verging orogenic system(Maiella Mts, central Apennines), theMSC has been recorded in a marginaland shallow basin. In the Maiellaarea, an erosional surface separatesthe Lower Evaporites from the earlyp-ev Messinian deposits (Sampalmieriet al., 2008). This boundary can becorrelated with the Messinian ero-sional surface (MES) recognisedthroughout the Mediterranean Basinin both offshore (Escutia and Maldo-nado, 1992; Guennoc et al., 2000; Lofiet al., 2005; Maillard et al., 2006) andon land sections (Guillemin and Hon-zay, 1982; Costa et al., 1986; Cita andCorselli, 1990; Riding et al., 1999;Roveri et al., 2001; Rouchy et al.,2003; Soria et al., 2005; Cornee et al.,2006).
ABSTRACT
At the end of the Messinian salinity crisis, changes in thepalaeoceanography and palaeoclimate induced a transitionfrom hypersaline to hyposaline conditions in the Mediterraneanwater body. Detailed investigation of natural radioactivity andmicrofacies analyses of two early post-evaporitic Messiniansections show that the transition occurred in poorly oxygen-ated and well-stratified water masses. These transitionaldeposits, which mainly consist of marls and CaCO3-richhorizons, are generally well laminated and totally barrenin benthic and planktonic fauna. The presence of barite, small
(5–8 lm) authigenic framboidal pyrite, and high values of Uindicate persistent anoxic conditions during the early post-evaporitic Messinian stage in the Adriatic sub-basin of theMediterranean Sea. The presence of post-evaporitic well-laminated barren deposits from both Mediterranean border-land sections and ODP sites suggests that these anoxicconditions extended to other sub-basins of the Mediterraneanregion.
The p-ev Messinian deposits analy-sed in this paper come from twoItalian sections sampled on the Adri-atic side of the Apennines (Fig. 1): theColle di Votta section (Maiella,Abruzzi, central Apennines) and theMaccarone section (Marche, northernApennines).The Colle di Votta section (Fig. 2)
starts from the bottom of the LowerEvaporites (Sampalmieri et al., 2008).The p-ev deposits of the Colle di Vottasection mainly consist of thinly lami-
nated greyish-brown pelites with car-bonates as concretions and lenses inits lower part.The Maccarone section (Fig. 3)
starts a few metres below the 5.5-Mavolcaniclastic layer (Odin et al., 1997)and contains the Messinian ⁄Zancleantransition at the top. The section,which was previously studied byCasati et al. (1976) and Bassetti et al.(1994), was recently investigated forits pollen and dinocyst content (Ber-tini, 2006) and for its ostracod assem-
blages (Grossi et al., 2008). Moreover,the significance of the section in theMediterranean Messinian stratig-raphy was discussed by Popescu et al.(2007) and Roveri et al. (2008b).
Materials and methods
The p-ev Messinian deposits of theMaccarone and Colle di Votta sec-tions were sampled at regular spacing(50 cm) and investigated using a mul-tidisciplinary approach involving
(b)
(a)
Fig. 1 Simplified structural scheme of the circum-Mediterranean region, with location of the central-northern Apennines (a);geological scheme of the central and northern Apennines showing the location of the study sections (b).
Messinian palaeoenvironments of the Mediterranean Basin • G. Sampalmieri et al. Terra Nova, Vol 22, No. 4, 239–250
microfacies analysis, compositionalanalyses [X-ray Diffraction and En-ergy Dispersive X-ray microprobe](EDAX Inc., Mahway, NJ, USA)and natural radioactivity (NRD) char-acterisation (both field and laboratoryanalyses) to improve our knowledgeof the palaeoenvironment during thehypersaline ⁄hyposaline transition ofthe MSC.The NRD measurements were per-
formed using an integral 2¢¢ · 2¢¢ NaI(Tl) Gamma Scintillator equippedwith a field spectrometer that detectsthe contribution of each natural radio-active element (238U, 232Th and 40K).The c-ray values were measured every20 cm with count times of 120 s. Afield spectrum was obtained with a
count time of 20 min and comparedwith laboratory analyses performedusing an HPGe c-spectrometer, whichprovides more accurate measurementsof radioactivity on 59 selectedsamples.
Results
Colle di Votta section
The 20-m-thick p-ev succession fromthe Colle di Votta section consists ofterrigenous-carbonate deposits, whichare essentially barren. As a whole, theterrigenous sediments are dominatedby calcite and quartz, with subordi-nate quantities of clay minerals(mainly smectite), plagioclase and
Fe-dolomite. Analysis of microfaciesalso revealed the occurrence of bo-tryoidal-shaped grains with a calciticcore and a rim made up of crypto-crystalline Fe–Mn–Ni oxides(Fig. 4a,b).The carbonates show a mineralogy
dominated by pure calcite, with aminimal amount of aragonite andpore-filling chalcedony. Framboidalpyrite, barite and celestite occur aswell. Framboids of pyrite occur eitheras single isolated elements (Fig. 4c) oras composite framboids (Fig. 4d). Inspiteof theirhomogeneousmineralogy,the carbonates exhibit a complexframework of microfacies (Fig. 4e,f).Thecarbonate facies,mainlybrecciatedlimestones, from the Colle di Votta
200 µm
(a)
(f)
50 µm
(d)
5 µm
(c)
Ca
Ca
Ca, Sr
Ca, Sr
v
pg
pg
mb
1 mm
(e)
mbmb
p
mc
mc
v
is
mc
is
1 mm
(b)
200 µm
Ca
c-ox
Fig. 4 Colle di Votta section. Detrital grains from the fine-grained p-ev1 deposits: (a) botryoidal-shaped grains, with (b) a calciticcore (Ca) and a rim made up of cryptocrystalline Fe–Mn–Ni oxides (c-ox), determined by EDAX microprobe. (c) Isolatedframboid of pyrite, and (d) composite framboids of pyrite from a carbonate concretion. (e,f) Thin section microphotographs ofcarbonate concretions: the original sediment is mainly represented by a somewhat microbrecciated muddy carbonate (mb);pseudomorphs (p), often lenticular pseudomorphs after gypsum (pg), dispersed organic matter and calcitic unidentified detritalgrains represent the most common elements within the mudstones. A peloidal inclusion-rich microcrystalline cement (mc)interrupts the distribution of the muddy sediment through sharp irregular surfaces (is); sparry calcitic veins (v) cut themicrosparitic cement and the microbrecciated muddy sediment. A fluid-induced instantaneous brecciation could account for boththe textural features (localised brecciation, autochthonous nature of the angular clasts) and the isotopic moderately negative d13Cvalues (Table 1).
Terra Nova, Vol 22, No. 4, 239–250 G. Sampalmieri et al. • Messinian palaeoenvironments of the Mediterranean Basin
section show light d18O values, rangingfrom )1.65 up to )8.74& PDB(Table 1).In the Colle di Votta section, the
NRD of the p-ev deposits show strongdifferences with respect to the under-lying evaporitic deposits, which exhi-bit the typical cyclic profile indicatedby the alternation of primary gypsumbeds and sapropelitic layers (Fig. 2).The background of the NRD in-
creases in the uppermost part of thesection, moving from 22 counts persecond (Cps) up to 42 Cps. NRDmeasurements in the p-ev depositsyielded high values of radioactivity inboth carbonates (20–63 Cps) and theirhost terrigenous sediments (21–70 Cps). Field NRD spectra on the
carbonate facies show 238U-dominant(up to 8 p.p.m.) radioactivity. Con-versely, the c-signal of the terrigenousdeposits is mainly from 40K, 238U and232Th.
Maccarone section
The p-ev1 fine-grained deposits aremainly characterised by clay minerals,with 65–80% of smectite, as well ascalcite, quartz, plagioclase and mini-mal amounts of Fe-dolomite andpyrite. Within the p-ev1 deposits, itis possible to distinguish three blackshale horizons (2–5 m thick), whichshow sub-millimetric laminations,high organic-matter content and au-thigenic framboidal pyrite. These
organic matter-rich horizons containcarbonate layers 5–20 cm thick thatconsist mainly of calcite and Fe-dolo-mite (Figs 5a and 6). These carbonatelayers show a microcrystalline texturewith crystals ranging from 5 to 20 lm(Fig. 5b,c). Framboidal pyrite is wellrepresented in both the black shalehorizons and the carbonate layers.Moreover, aggregate crystals of bariteup to 100 lm in size (Fig. 5b) andisolated detrital crystals of quartz,K-feldspar and mica have been ob-served. The microcrystalline texture ofthe carbonate layers together withtheir d18O values, which rangebetween )0.08 and +2.41& PDB(Table 1), suggests that these carbon-ate horizons were deposited underarid and evaporative conditions. Inaddition, the negative d18O meanvalue ()2.5& PDB) from the p-ev1deposits points to a water mass with astrong continental signature (Cosenti-no et al., 2009).The p-ev1 NRD profile (Fig. 3)
shows a high-frequency cyclical signalwith small deflections in correspon-dence with the thin sandstone inter-calations. In the p-ev1 deposits, thehighest c-ray values come from thevolcaniclastic layer (52–65 Cps).Field spectra of NRD were ac-
quired on different lithologies andshowed variable contributions from238U, 232Th and 40K. Both the bluish-grey and black shales are mainlycharacterised by NRD due to 40Kwith a large amount of 238U andvariable contributions of 232Th.
Discussion
The p-ev Messinian sections discussedin this article are characterised by bothorganic matter-rich marls and carbon-ate facies. The fine-grained depositsfrom these two sections are quitesimilar in mineralogical compositionand show almost the same values ofNRD. They are rich in organic matterand are generally barren in benthicbiota, indicating high organic carbonpreservation in low-oxygen bottomwater (Emerson and Hedges, 1988),which is probably because of highorganic matter input from continentalweathering. Abundant plant remainshave been observed in both analysedsections and a rich pollen flora con-sisting of 130 taxa was identified in theMaccarone section (Bertini, 2006).
Table 1 Stable isotope and carbonate composition of samples from three organic
matter-rich horizons of the Maccarone section (MC) and from carbonates of the
Colle di Votta section (RM). Dataset from Cosentino et al. (2009).
Lithology Sample
d18O
(& PDB
calcite)
d13C
(& PDB
calcite) CaCO3(%) MgCa(CO3)2(%)
p-ev Maccarone
Grey shale MC 246 )2.62 )1.38 17.72 2.13
Grey shale MC 245 )1.29 )1.58 21.57 2.60
Grey shale MC 244 )0.98 )2.03 21.31 4.72
Grey sandstone MC 243 )2.46 )2.74 31.07 5.91
Marl MC 242 1.35 )6.34 42.63 5.20
Carbonate MC 241 1.33 )6.37 62.15 3.78
Marl MC 240 2.41 )8.66 46.22 1.89
Marl MC 239 1.31 )4.97 39.03 0.14
Black shale MC 238 0.50 )4.34 7.96 9.21
Marl MC 237 0.56 )4.90 48.79 1.42
Grey shale MC 236 )2.30 )0.33 16.44 1.42
Grey shale MC 235 )2.87 )0.41 17.98 1.42
Grey shale MC 188 )2.17 )0.49 21.57 0.94
Grey shale MC 187 )3.00 )0.73 34.15 1.42
Carbonate MC 186 1.95 )8.76 72.93 3.80
Black shale MC 185 )2.87 )1.01 17.98 1.42
Black shale MC 184 )1.02 )0.58 37.24 1.42
Grey shale MC 166 )1.53 )1.06 21.57 2.60
Carbonate MC 165 )0.08 )0.96 63.68 2.12
Black shale MC 164 0.12 )1.59 23.37 4.96
Carbonate MC 163 0.38 )1.20 73.19 2.60
Black shale MC 162 1.65 )2.80 25.94 12.28
Black shale MC 161 1.30 )3.12 20.29 5.90
Black shale MC 160 0.59 )3.96 11.30 8.97
Black shale MC 159 )1.38 )0.75 14.64 2.36
Black shale MC 158 )2.51 )2.55 30.05 1.89
p-ev Colle di Votta
Brecciated carbonate RM 49 )5.00 )15.68 – –
Brecciated carbonate RM 48 )5.14 )7.37 – –
Yellow mud carbonate RM 47 )6.85 )7.62 – –
Grey laminated marl RM 46 )1.65 )6.19 – –
Red laminated shale RM 45 )8.74 )10.89 – –
Brecciated carbonate RM 43 )3.92 0.59 – –
Brecciated carbonate RM 34 )4.44 )17.99 – –
Messinian palaeoenvironments of the Mediterranean Basin • G. Sampalmieri et al. Terra Nova, Vol 22, No. 4, 239–250
These findings testify to strong conti-nental runoff during wet climateepisodes.
In contrast to the similar palaeo-environments across both sectionssuggested by analyses of the fine-
grained deposits, the carbonate faciesin the two sections are characterisedby different textures and d18O values,
Black shales
Fe-dolomite layer
(a)
Kfl
p
P
D
D
P
P
P
D
P(c)
D
D D
D
Ba
Kfl
D
P
P
Ba
5 µm
(b)
D
DD
Ca
Mg
Ca
Fe
(d)
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00
Fig. 5 Maccarone section. (a) Outcrop of the p-ev1 deposits containing black shale and Fe-dolomite layers; (b) SEM image in theBackscattered Scanning Electron (BSE) mode of a Fe-dolomite sample from the uppermost portion of the p-ev1 deposits (whitedots are framboids of pyrite; see the close-up in the insert box) (P, pyrite; D, Fe-dolomite; Kfl, K-feldspar; Ba, barite); (c) SEMimage in the BSE mode of a Fe-dolomite sample showing microcrystalline texture (P, pyrite; D, Fe-dolomite; Kfl, K-feldspar); (d)EDAX microprobe semi-quantitative spot analysis of a Fe-dolomite sample (Ca – calcium; Mg – magnesium; Fe – iron).
Fig. 6 X-ray pattern of (hkl) (104) reflection for MC 186-1 sample (Maccarone section); the reflection peak is placed betweendolomite and ankerite.
Terra Nova, Vol 22, No. 4, 239–250 G. Sampalmieri et al. • Messinian palaeoenvironments of the Mediterranean Basin
which indicate different genetic pro-cesses. The texture and stable isotopeanalysis of the carbonate facies fromthe Maccarone section (Table 1) pointto an evaporative environment,whereas the brecciated carbonate ele-ments from the Colle di Votta section,which are characterised by negatived18O values, are related to more com-plex processes most likely connectedwith a fluid-rich diagenetic environ-ment with high pore-fluid pressure.Mineralogy provides additional
clues to the palaeoenvironmental con-ditions at the time of deposition. Inboth analysed sections, authigenicdolomite and pyrite are present, pro-viding useful information about thepalaeoenvironment. At continentalmargins, dolomite forms as a primaryprecipitate or by replacing precursorCa and Ca–Mg carbonates where porefluids become suboxic to anoxic (Ba-ker and Kastener, 1981; Burns andBaker, 1987). Moreover, the dimen-sional analysis carried out on somepopulations of framboidal pyriteshows a mean diameter of 4–8 lm,which is typical of dysaerobic condi-tions with anoxic bottom waters(Wilkin et al., 1996, 1997; Wilkinand Barnes, 1997; Bond et al., 2004;Wignall et al., 2005). Barite andMn–Fe oxyhydroxide occurring with-in the p-ev deposits of the Colle diVotta section can form in situ byinorganic precipitation, either on thebasin floor or within unconsolidatedsediments. Barite can inorganicallyprecipitate directly from the water
Fig. 7 Results of the NRD laboratory analyses performed on both Colle di Votta and Maccarone Messinian deposits. U ⁄Th vs. %authigenic U (Uaut) indicate mainly anoxic conditions during the sedimentation of the p-ev1 Messinian deposits of the studysections. The disoxic ⁄anoxic transition (U ⁄Th = 1.3; Jones and Manning, 1994) separates the sandstone of the Maccarone sectionfrom other p-ev1 deposits. Many of the sapropel layers within the Lower Evaporites were sedimented in disoxic conditions.
Table 2 Summary of concentrations of Up.p.m., Thp.p.m. and % K2O.
mass in microenvironments contain-ing decaying organic matter (Bishop,1988). These palaeoenvironmentalindications in both sections generallypoint to dysaerobic conditions in astratified water mass.The NRD data from the analysed
sections provide additional informa-tion for the reconstruction of thepalaeoenvironment at the p-ev1 Mes-sinian stage. U ⁄Th ratio is a proxy fordeducing redox conditions in a depo-sitional environment (Jones and Man-ning, 1994; Wignall, 1994) and is alsosensitive to the input of detrital grains.The 238U content is primarily relatedto processes of organic matter enrich-ment (authigenic uranium, Uaut) andsecondarily to the input of detritalgrains (Udet). In contrast, 40K and232Th are ascribed entirely to theclastic fraction. The Uaut was calcu-lated using the formula Uaut = Utot )Udet (Wignall, 1994), where Udet isTh ⁄3 because in the sedimentary rocksUdet is 1 ⁄3 of Th content. From apalaeoenvironmental point of view, theNRDdata from both analysed sectionsare consistent with anoxic environmen-tal conditions (U ⁄Th > 1.3; Jones andManning, 1994), indicated by a highpercentage of Uaut within the p-ev1deposits (Fig. 7, Tables 2 and 3).Fine-laminated deposits, generally
barren in benthic biota, are well knownfrom the Messinian deposits of thewhole Mediterranean Basin. Thesetypes of deposits were recovered inseveral western Mediterranean ODPsites (Iaccarino and Bossio, 1999) andin the Tyrrhenian abyssal plain (ODPSite 652; Borsetti et al., 1990; Citaet al., 1990) as well as in the Mediter-ranean borderlands (Vismara-Schillinget al., 1976; Fortuin et al., 1995; Bas-setti et al., 1994, 1998; Roveri et al.,2001; Cosentino et al., 2005).The stratigraphy of ODP Site 652
allows for the palaeoenvironmentalreconstruction of the Central Mediter-ranean Basin at the end of the MSC tobe compared with the results presentedin this paper. According to Borsettiet al. (1990) and Kastens and Mascle(1990), the pre-Pliocene successiondrilled at Site 652 belongs to the Mes-sinian. A conglomerate body of 10 mthickness separates an upper portioncharacterised by light mudstone ⁄ siltcouplets containing rare brackishwater forms (Cyprideis sp. and Ammo-nia beccarii tepida) from a lower por-
Table 2 (continued)
Lithology Sample Up.p.m. % K2O Thp.p.m.
Brecciated carbonate RM 49 4.27 0.76 0.09
Yellow laminated marl CV 1 3.46 7.29 0.79
Vacuolar carbonate CV 2 3.59 1.65 0.22
Volcaniclastic layer CV 6 3.67 17.75 5.02
Volcaniclastic layer CV 7 1.95 12.94 2.58
Volcaniclastic layer CV 8 2.09 10.93 2.44
Grey marl CV 9 4.18 6.84 0.95
Grey marl CV 11a 7.36 7.88 0.91
Grey laminated marl CV 12 8.30 6.76 0.67
p-ev Maccarone
Volcaniclastic layer MC 16 3.50 17.79 3.96
Volcaniclastic layer MC 16a 3.28 18.50 4.21
Volcaniclastic layer MC 17 2.81 17.25 3.56
Sandstone MC 49 a 1.50 10.37 1.30
Sandstone MC 100 a 0.95 11.02 0.95
Sandstone MC 137 1.12 11.76 1.24
Black shale MC 161 3.31 14.89 1.06
Black shale MC 166 4.46 16.02 1.37
Carbonate MC 186 1.84 4.21 0.36
Black shale MC 242 4.82 14.84 1.33
Sand MC 243 1.93 12.06 1.09
Grey shale MC 244 1.58 16.41 1.64
Table 3 Summary of U ⁄Th and Th ⁄K ratios, and Uaut and Udet contents.
Lithology Sample U ⁄ Th Th ⁄ K Uaut (p.p.m.) Udet (p.p.m.) % Uaut
tion consisting of dark shales with sandand silt interbeds and completely bar-ren in autochthonous fossils (Borsettiet al., 1990). According to Cosentinoet al. (2006), the pre-Pliocene depositsatODPSite 652 correlatewith the thickMessinian Lago-Mare successiondrilled at theMondragone 1 well (Gar-igliano Plain). The analyses presented
Table 3 (continued)
Lithology Sample U ⁄ Th Th ⁄ K Uaut (p.p.m.) Udet (p.p.m.) % Uaut
Black shale MC 161 3.115 0.071 2.96 0.35 89.30
Black shale MC 166 3.248 0.086 4.00 0.46 89.74
Carbonate MC 186 5.144 0.085 1.72 0.12 93.52
Black shale MC 242 3.611 0.090 4.37 0.44 90.77
Sand MC 243 1.778 0.090 1.57 0.36 81.25
Grey shale MC 244 0.961 0.100 1.03 0.55 65.32
Fig. 8 Correlation panel among the study sections (Maccarone and Colle di Votta), Mondragone 1 well, and ODP Site 652. Datafrom: Borsetti et al. (1990), Cosentino et al. (2006), Grossi et al. (2008) and this paper.
Messinian palaeoenvironments of the Mediterranean Basin • G. Sampalmieri et al. Terra Nova, Vol 22, No. 4, 239–250
in this paper allow for a more precisecorrelation, and indicate that palaeo-environmental conditions that charac-terised the Maccarone and Maiellasections also characterised the CentralMediterranean at Site 652 (Fig. 8).
Conclusions
In the Maccarone and Colle di Vottap-ev deposits, the high U-content, thepresence of small authigenic framboi-dal pyrite and barite, the occurrenceof fine laminations, the lack of benthicbiota and high U ⁄Th ratios (>1.3,Fig. 7) point to a strongly anoxicenvironment under arid conditions.The arid conditions of the p-ev1episode were frequently interruptedby more humid phases responsiblefor the increase in extra-basinal detri-tal grains (U ⁄Th �1). This palaeo-climatic scenario is in accordance withthe pollen records at the Maccaronesection (Bertini, 2006), which point toa drier phase punctuated by short-term humidity fluctuations, indicatedby frequent alternation between herbsand subtropical to warm arborealtaxa.The possible correlation between
the Maccarone section and ODP Site652 suggests an extension to the Cen-tral Mediterranean Basin of thestrongly anoxic environment and thepalaeoclimatic scenario reconstructedfor the Messinian Adriatic sub-basinfrom the Maccarone and Colle diVotta sections.The higher NRD values of p-ev1
(high Uaut), in comparison with thesapropelitic layers of the Lower Evap-orites (low Uaut), could be explainedby the development of more restrictedconditions in the circulation of theMediterranean water mass as a con-sequence of the complete closure ofthe Gibraltar Strait at the evapo-ritic ⁄post-evaporitic transition.
Acknowledgements
Quantitative measurements of NRD wereperformed at the Geochemical Laboratoryof Roma Tre University. The facilities ofthe LIME of Roma Tre University wereutilised for SEM and EDAX microprobeanalyses. The manuscript benefited fromhelpful reviews by T.F. Schildgen and fouranonymous referees. This research wasfinancially supported by MiUR (PRIN2006 – local coordinator D. Cosentino).
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Received 28 September 2009; revised versionaccepted 9 March 2010
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