A multidisciplinary study of middle Miocene seep-carbonates from the northern Apennine foredeep (Italy) S. Conti a, * , D. Fontana a,1 , A. Gubertini a,2 , G. Sighinolfi a,3 , F. Tateo b,4 , C. Fioroni a,5 , P. Fregni a,6 a Dipartimento di Scienze della Terra, Universita ` di Modena e Reggio, Largo Sant’ Eufemia 19, I-41100 Modena, Italy ,7 b Istituto Geoscienze e Georisorse, CNR, c/o Dipartimento di Geologia, Paleontologia e Geofisica, Universita ` di Padova, Via Giotto, 1, I-35137 Padova, Italy Received 18 June 2003; received in revised form 21 January 2004; accepted 31 March 2004 Abstract Several pelitic intervals are intercalated at various levels within the marly-arenaceous turbiditic successions of the middle Miocene northern Apennine foredeep. They range in thickness from 30 to 200 m, and represent sedimentation on top of ephemeral structural highs related to blind faults. Sediments are made up of hemipelagites and fine-grained turbidites, and include 13 C-depleted carbonates, related to the rising of methane-rich fluids (hydrocarbon seep-carbonates). Large portions of pelitic intervals are involved in chaotic masses by soft sediment deformation (slumps, slides, intraformational breccias), revealing an intense sediment instability during middle Miocene. A stratigraphic, mineralogic and geochemical study was conducted on two of these pelitic intervals (Castagno d’Andrea, Mt Citerna) in order to reconstruct carbonate development, the composition of fluids, and to document the connections between fluid seepage and syndepositional tectonics. This multidisciplinary approach has allowed us to discriminate between the two examined pelitic intervals in terms of age, depositional rates and conditions, organic carbon and post-depositional processes. Seep-carbonates are characterized by chemosymbiotic fossil communities, autoclastic fractures and brecciation; carbonate bodies show complex facies relationships, as indicative of different stages in chemoherm growth. The compositional study evidences the peculiar chemistry of chemoherm carbonates (calcite low in Mg and Sr) compared with carbonates in associated enclosing pelites and with modern chemoherms, in general. The non-carbonate components within the chemoherms are enriched in detrital minerals and depleted in phyllosilicates with respect to the enclosing pelites. The mineralogical changes in the clay component within the brecciated unit of the Castagno d’Andrea chemoherms suggest authigenic precipitation of the Mg-rich phases. 0037-0738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2004.03.010 * Corresponding author. Tel.: +39-59-2055858. E-mail addresses: conti.stefano@unimore.it (S. Conti), fontana.daniela@unimore.it (D. Fontana), gubertini.arianna@unimore.it (A. Gubertini), sighinolfi.giampaolo@unimore.it (G. Sighinolfi), tateo@igg.cnr.it (F. Tateo), fioroni.chiara@unimore.it (C. Fioroni), fregni.paola@unimore.it (P. Fregni). 1 Tel.: +39-59-2055844. 2 Tel.: +39-59-2055863. 3 Tel.: +39-59-2055824. 4 Tel.: +39-49-8272083; fax: +39-49-8272070. 5 Tel.: +39-59-2055854. 6 Tel.: +39-59-2055846. 7 Fax: +39-59-2055887. www.elsevier.com/locate/sedgeo Sedimentary Geology 169 (2004) 1 – 19