Integrated biostratigraphic and physical stratigraphic framework: a high definition correlative tool for the Lago Mare deposits

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1 Integrated biostratigraphic and physical stratigraphic framework: a high definition correlative tool for the Lago Mare deposits Gennari R., Iaccarino S. M., Roveri M., Manzi V., Grossi F. The post-evaporitic phase (p-ep or Stage 2 of Roveri et al., in press) of the Messinian Salinity Crisis (MSC) starts at 5.6 Ma according to Krijgsman et al. (1999), based on the age, astronomically calibrated, of the top of the Lower Evaporites. In the Northern Apennine, this onset is characterized, on the basin margin, by the erosion and sub-aerial exposition of the Lower Evaporites, generating, at points, a hiatus embracing almost all the p-ep (e.g. Monticino quarry, Vena del Gesso basin); this erosional surface is generally characterized by angular discordance and is known as the intra- Messinian unconformity or Messinian Erosional Surface (MES in Mediterranean subsurface, Lofi et al., 2005). In the foredeep settings its correlative conformity is recognized at the base of a complex of reworked gypsum (gypsarenites and chaotic gypsum, Manzi et al., 2007, Roveri et al., 2006a and b). The upper boundary of the p-ep is represented by the end of the MSC, and coincides with the return to fully marine conditions in the whole Mediterranean (Iaccarino et al., 1999, Gennari et al., submitted); according to tentatively tuning of the Mio-Pliocene boundary with insolation curve, this transition lasted less than one sedimentary cycle (Roveri et al. 2006a). However, the isotopic signal suggests that fresh water masse still influenced the Mediterranean marine water at least during the first cycle of the Zanclean (Pierre et al. 2006) even at the Eraclea Minoa section (Sicily, Italy), the GSSP of the Zanclean stage (Van Couvering et al. 2000). The term post-evaporitic fits well in the Northern Apennine contest, where the salt unit and the Upper Evaporites are lacking; actually, it involves a physical-stratigraphic concept, being constrained between the MES at its base and the Messinian/Zanclean boundary (MZB) at its top. The Lago Mare expression adopted for this stratigraphic unit is related to the paleonvironmental meaning, but it is often used as a synonymous of p-ep (see Orsazg-Sperber, 2006 for a review of the term). Roveri et al. (2008) used the term Stage 2 for the Messinian deposits postdating the Lower Evaporites (marginal and deep member of Manzi et al., 2007) and splitted it in Stage 2.1 (p-ev 1 subunit) and 2.2 (p-ev 2 sub-unit); the former, has at its base resedimented evaporites feeding the emerging Lower Evaporites, followed by fine-grained siliciclastic deposits, in Northern Apennine, and by the salt unit in the central and western Mediterranean basin. P-ev 2 sub-unit is mainly characterized by cyclic deposition of coarse- and fine-grained decametric siliciclastic couplets, thought to be driven by alternating wet and dry conditions related to precessional cyclicity.

2 The paleonvironmental meaning of the p-ep is still a matter of debate, since its traditional brackish water source (Cita et al., 1978) is questioned by the occurrence of marine fossil record (Aguirre et al., 2004; Carnevale et al., 2006) and by controversial marine isotopic signature of calcareous shell of classical Lago Mare taxa (Melanopsis, Carnevale et al., 2008). Between these two opposite endmember interpretations several authors point to the occurrence of occasional ingression of marine water from the Atlantic into the Mediterranean possibly driven by eustatic sea level changes (Snel et al., 2006 e Popescu, 2003, Muller, 1990, Spezzaferri et al., 1998). Moving from the physical-stratigraphic framework of Roveri et al. (in press), we analysed the microfossil content of several peri-mediterranean basin in order to better define the paleoenvironmental evolution of the Mediterranean area after the deposition of the Lower Evaporites. New ecobiostratigraphic data from the Northern Apennine foredeep, the Crotone basin (Calabria, Italy), the Caltanisetta basin (Eraclea Minoa section, Sicily) and the Nijar basin (southwestern Spain) were framed in a physical stratigraphic scheme allowing long-distance correlation. The stratigraphic distribution of the most important Lago Mare taxa shows an overall uniformity throughout the analysed basins. The p-ev 1 sub-unit is mainly characterized by deposits devoid of fossil record or yielding species of the Biofacies 1, made up of Ammonia tepida and other estuarine benthic foraminifera, Cyprideis agrigentina and other ostracods of the Loxoconcha muelleri Zone of Gliozzi et al. (2006), tolerating high salinity deviation. Relatively deep water setting, unsuitable habitat for most of the eurihaline taxa of Biofacies 1, are inferred to explain their absence in the lower part of the p-ev 1 sub-unit. The regressive trend characterizing the upper part of the p-ev 1 subunit and the resulting basin filling led to a shallow water paleoenvironment. δ 18 O signature from this interval mainly shows negative values indicative of mesohaline to fresh water and points to a strong continental influence. The p-ev 2 sub-unit is characterized by the arrival of the Parathetyan taxa (Biofacies 2) testifying for an important change in the regional drainage pattern and precipitation regime. The ostracod Loxocorniculina djafarovi and the dinocyst Galeacysta etrusca are the most abundant and widespread bioevents recorded within this unit. The occurrence of these taxa is strongly depending on the paleoenvironment, in fact either shallow water and strong salinity variation can prevent their presence. In fact, at Eraclea Minoa section, shallow water matched with cyclical high salinity condition, led to the selenite precipitation and provided the habitat for the persistence of Biofacies 1 during most of the p-ev 2 sub-unit. The cyclic stacking pattern of p-ev 2 sub-unit is reflected also in the superimposition of Biofacies 1 and 2. The former occurs at dry-wet transition during base level fall, when the lowered continental input increases the salinity; the latter within wet phase, during base level rise, when increased run-

3 off dilutes the watermass. The occurrence of Candoninae, a deep-water ostracod group, marks the maximum flooding surface. Marine taxa are widespread, but only occasionally abundant; they are generally considered reworked because of the presence of extinct species (from Cretaceous to the lower Messinian depending on the area), poorly preserved and scattered assemblages and/or for the contemporary presence of ipohaline ostracods. In the Northern Apennine basin, 1-2 m below the MZB, well preserved assemblages mainly composed of planktic foraminifera, identical to the Pliocene assemblages, occur together with common to rare Lago Mare ostracods. This record could represent the first arrival of marine water a few kyr before the Pliocene marine ingression, the occurrence in the same samples of taxa requiring different habitat (oligo- mesohaline ostracods and marine foraminifera) could be interpreted as very rapid variations of salinity, due to the first arrival of Atlantic marine water, or by the persistence of low salinity and cold deep water, allowing Lago Mare ostracods to survive the marine ingression. This hypothesis should be tested on a wider scale, possibly in more distal and deeper settings. References Aguirre, J. and Sánchez-Almazo, I.M., The Messinian post-evaporitic deposits of the Gafares area (Almería-Níjar Basin, SE Spain). Sedimentary Geology, 168: Carnevale, G., Landini, W., Sarti, G., Mare versus Lago-mare: marine fishes and the Mediterranean environment at the end of the Messinian Salinity Crisis. Journal of the Geological Society, London, 163: Carnevale G., Longinelli A., Caputo D., Barbieri M., Landini W, Did the Mediterranean marine reflooding precede the Mio Pliocene boundary? Paleontological and geochemical evidence from upper Messinian sequences of Tuscany, Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 257, Cita, M.B., Wright, R.C., Ryan, W.B.F., Longinelli, A., Messinian paleoenvironments. In: Hsü, K.J., Montadert, L., Garrison, R.E., Fabricius, F.H., Muekker, C., Cita, M.B., Bizon, G., Wright, R.C., Erikson, A.J., Bernoulli, D., Melieres, F., Kidd, R.B. (Eds.), In. Rep. Deep Sea Drill. Proj. 42,

4 Gennari, R., Iaccarino, S.M., Di Stefano, A., Sturiale, G., Cipollari, P., Manzi, V., Roveri, M. and Cosentino, D., in press. The Messinian Zanclean boundary in the Northern Apennines. In: Iaccarino S.M., Lugli S., Manzi V., Roveri M. (eds) The Messinian salinity crisis revisited II RCMNS IC PARMA Stratigraphy. Gliozzi, E., Grossi, F. and Cosentino, D., Late Messinian biozonation in the Mediterranean area using Ostracods: a proposal. R.C.M.N.S. International Congress Parma 2006 The Messinian salinity crisis revisited II Abstract Volume, Acta Naturalia De L Ateneo Parmense, 42-2: A.21. Iaccarino S.M., Castradori D., Cita M.B., Di Stefano E., Gaboardi S., McKenzie J.A., 120 Spezzaferri S., Sprovieri R, The Miocene/Pliocene boundary and the significance of the earliest Pliocene flooding in the Mediterranean. Memorie Società Geologica Italiana, 54, Krijgsman,W., Hilgen, F.J., Raffi, I., Sierro, F.J.,Wilson, D.S., 1999a. Chronology, causes, progression of the Messinian salinity crisis. Nature 400 (6745), Lofi, J.,Gorini, C., Berné, S., Clauzon, G., Dos Reis, A.T., Ryan,W.B.F.,Steckler, M.S., Erosional processes and Paleo-environmental changes in the western gulf of Lions (SW France) during the Messinian salinity crisis. Marine Geology 217, Manzi, V., Roveri, M., Gennari, R., Bertini, A., Biffi, U., Giunta, S., Iaccarino, S.M., Lanci, L., Lugli, S., Negri, A., Riva, A., Rossi, M.E., Taviani M., The deep-water counterpart of the Messinian Lower Evaporites in the Apennine foredeep: The Fanantello section (Northern Apennines, Italy). Palaeogeography, Palaeoclimatology, Palaeoecology, 251: Müller, C., Nannoplankton biostratigraphy and paleoenvironmental interpretations from the Tyrrhenian Sea, ODP Leg 107 (western Mediterranean). In Kastens, K.A., Mascle, J., et al., Proc. ODP, Sci. Results, 107: College Station, TX (Ocean Drilling Program), Orszag-Sperber F., Changing perspectives in the concept of Lago-Mare in Mediterranean Late Miocene evolution. Sedimentary Geology ,

5 Pierre C., Caruso A., Blanc-Valleron M.M., Rouchy J.M., Orzsag-Sperber F Reconstruction of the paleoenvironmental changes around the Miocene-Pliocene boundary along a West-East transect across the Mediterranean. Sedimentare Geology , Roveri, M., Lugli, S., Manzi, V., Gennari, R, Iaccarino, S.M, Grossi, F. and Taviani, M., 2006a. The record of Messinian events in the Northern Apennines foredeep basins. R.C.M.N.S. International Congress The Messinian salinity crisis revisited II, Parma Pre-congress Fieldtrip. Acta Naturalia de l'ateneo Parmense, 42-1: Roveri, M., Manzi, V., Lugli, S., Schreiber, B.C., Caruso, A., Rouchy, J.-M., Iaccarino, S.M., Gennari, R., Vitale, F.P., 2006b. Clastic vs. primary precipitated evaporites in the Messinian Sicilian basins. RCMNS IC Parma 2006 The Messinian Salinity Crisis Revisited II Post-Congress Field-Trip. Acta Naturalia De L'Ateneo Parmense, vol. 42 1, pp Roveri, M., Executive summary. In (F. Briand, Ed.): CIESM The Messinian Salinity Crisis mega-deposits to microbiology A consensus report. CIESM Workshop Monographs, 33: Snel E., Mruneanu M., Meulenkamp J.E., Calcareous nannofossil biostratigraphy and magnetostratigraphy of the Upper Miocene and Lower Pliocene of the Northern Aegean (Orphanic Gulf Strimon Basin areas), Greece. Palaeogeography, Palaeoclimatology, Palaeoecology 238, Spezzaferri, S., Cita, M.B., McKenzie, J.A., The Miocene Pliocene boundary in the eastern Mediterranean: results from ODP Leg 160, Sites 967 and 969. In: Robertson, A.H.F., Emeis, K.-C., Richter, C., Camerlenghi, A. (Eds.), Proc. ODP, Sci. Results, vol Ocean Drilling Program, Texas A & M University, College Station, TX, pp van Couvering J.A., Castradori D., Cita M.B., Hilgen F.J. and Rio D., The base of the Zanclean Stage and of the Pliocene series. Episodes, 23 (3),