Fabbi S.*1, Cestari R.2, Chiocchini M.3, Marino M.4 & Pichezzi R.M.4
1 CNR-IGAG; Sapienza Università di Roma
2 StrataGeoResearch srl, INGEO, Università di Chieti-Pescara 3 Università di Camerino
4 Ispra - Servizio Geologico d’Italia
* Corresponding email: simone.fabbi@uniroma1.it
Keywords: Cretaceous, Carbonate platform, Benthic forams.
Five Upper Cretaceous stratigraphic sections have been measured and sampled in the tectonically complex area of Marsia (northern Simbruini Mts.), allowing the reconstruction of a ~60 m thick inner carbonate platform succession.
The section begins with thin bedded dolomitized limestone with Discorbidae, Miliolidae and ostracoda, passing upwards to decimeter-thick wacke-to-packstone limestone with rudist fragments and Nezzazatinella cf. aegyptiaca. Metre-thick rudist float-to-rudstones follow upwards, with in situ assemblages dominated by elongate shells of Radiolites trigeri, occurring both in monospecific levels or associated with Durania arnaudi and Biradiolites angulosus. Microfacies are composed of Moncharmontia cf. compressa, Nummuloculina cf.
irregularis, Spirosigmoilina rajkae and Rotaliidae. Upwards, a stack of thick-bedded limestone with float-to-
rudstone texture occurs, at first characterized by a Biradiolites martellii oligospecific association, evolving in more differentiated rudist assemblages, composed of Sauvagesia sp., B. martellii, Lapeirousella samnitica and rare Vaccinites sp. Sparse bioclastic lenses with nerineids also occur. The associated microfacies is composed of Dicyclina schlumbergeri, M. compressa, Nezzazatinella picardi, Pseudocyclammina sphaeroidea,
Nummoloculina sp., Rotorbinella scarsellai.
The overlying succession is a ~ 45 m thick stack of whitish limestone with floatstone to rudstone texture, containing benthic organisms such as Accordiella conica, Scandonea samnitica, S. mediterranea, Decastronema
barattoloi, Tetraminouxia salentina, Calcarinella schaubi, R. scarsellai, Murgeina apula and Reticulinella fleuryi. Macrofossil assemblages are dominated by rudists, occurring in floatstones with Hippurites sulcatus, Vaccinites fortisi, Plagioptychus paradoxus, Radiolites cf. dario, along with rare massive corals. Significantly,
sparse floatstones characterized by whole regular echinoids occur, and a peculiar horizon is characterized by abundant calcareous sponges (Chaetetids). This testify a heterogeneity of facies and possible perturbations in sea-water circulation, in turn fostering the proliferation of rudists, chaetetids and/or echinoids. Remarkably ~10 m below the top of the section the uppermost Santonian Keramosphaerina tergestina horizon occurs.
The composed succession can be referred to the “N. cf. aegyptiaca and N. cf. irregularis” and “A. conica and R. scarsellai” biozones, encompassing the late Turonian- uppermost Santonian interval.
The section has been reconstructed despite the structural complexity of the area and is only ~60 m thick, resulting very thin if compared with other coeval succession as the S. Maria dei Bisognosi section (~10 km E of Marsia), where the Coniacian-Santonian is >200 m-thick. Such significant difference can be explained
© Società Geologica Italiana, Roma 2018 CONGRESSO SGI-SIMP 2018
35
A 9 million-year-long astrochronological record of the early-middle Eocene
corroborated by seafloor spreading rates
Francescone F.*1, Lauretano V.2, Bouligand C.3, Moretti M.1, Sabatino N.4, Schrader C.5, Catanzariti R.6,
Hilgen F.5, Lanci L.1, Turtù A.7, Sprovieri M.4, Lourens L.5 & Galeotti S.1
1 Dipartimento di Scienze Pure e Applicate, Università di Urbino, Campus Scientifico ‘E.Mattei’ 2 School of Chemistry, University of Bristol, United Kingdom
3 Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Grenoble, France 4 Istituto per l’Ambiente Marino Costiero, Consiglio Nazionale delle Ricerche IAMC-CNR,
Capo Granitola, Campobello di Mazara TP
5 Department of Earth Sciences, Faculty of Geosciences, Utrecht University, The Netherlands 6 Istituto di Geoscienze e Georisorse, CNR
7 Department of Earth and Life Sciences, Vrije Universiteit, Amsterdam, The Netherlands
* Corresponding email: federica.francescone@uniurb.it
Keywords: early-middle Eocene, Umbria-Marche basin, integrated stratigraphy.
The early-middle Eocene (~56-41 Ma) is recorded in the pelagic Scaglia Rossa and Variegata Formations of the Umbria-Marche basin (central Italy). Geochemical and magnetostratigraphic alignment between the Bottaccione section (Gubbio, central Italy) and the Smirra core (Cagli, central Italy) allow us to generate a continuous and well-preserved new record that, combined with previously published data from the same area (Galeotti et al., 2010, 2017), creates a continuous high-resolution record from the Paleocene-Eocene Thermal Maximum (~56 Ma) to the lower part of Chron C21n. Comparison with carbon isotope records from ODP Sites 1258 at Demerara Rise and ODP Site 1263 at Walvis Ridge reveals a satisfactory match, providing further
evidence of the global significance of the long-term trend and superposed perturbations captured by the δ13C
records. The identification of orbitally forced geochemical cycles allow us to develop a 405-kyr tuned age model, thereby extending the astrochronology for these classic Tethyan successions from ~56.0 to ~47.5 Ma. Marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates are used to independently test the astronomical polarity time scale associated with our tuning as well as other polarity time scales. Our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes, while the other time scales generate more gradual variations and also include large and short-term deviations in spreading rates that occur simultaneously in different oceanic basins, implying errors in polarity reversal ages. Refining the timing of these spreading rate changes is very important as it may help determine the causative mechanism for these changes, especially around ~50 Ma which is a period of worldwide changes in the seafloor spreading and also coincides with the beginning of a long-term
decrease in the temperatures and pCO2.
We therefore conclude that Umbria-Marche basin records provide a valuable cyclochronological and astrochronological estimate for the duration of the interval between ~56 to ~47 Ma. The new age model further contributes to the closure of the middle Eocene gap in the Astrochronological Time Scale.
Galeotti, S., Krishnan, S., Pagani, M., Lanci, L., Gaudio, A., Zachos, J.C., Monechi, S., Morelli, G. & Lourens, L. (2010): Orbital chronology of Early Eocene hyperthermals from the Contessa Road section, central Italy. Earth and Planetary Science Letters, 290, 192-200.
Galeotti, S., Moretti, M., Sabatino, N., Sprovieri, M., Ceccatelli, M., Francescone, F., Lanci, L., Lauretano, V. & Monechi, S. (2017): Cyclochronology of the Early Eocene carbon isotope record from a composite Contessa Road-Bottaccione section (Gubbio, central Italy). Newsletters on Stratigraphy, 50, 231-244.