Fabrizio Tremolada

Palaeoceanographic significance of the Tethyan ‘Livello Selli’ (Early Aptian) from the Hybla Formation, northwestern Sicily: biostratigraphy and high-resolution chemostratigraphic records

High-resolution micropalaeontological and chemostratigraphic records for the Hauterivian–Aptian succession outcropping at Calabianca (NW Sicily) provide new insight into the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean. Calcareous nannofossil and planktonic foraminiferal biostratigraphy together with δ13C chemostratigraphy allowed the identification of a hiatus in the Barremian and a major one including most of the Upper Aptian, the entire Lower Albian and part of the Middle Albian. The Livello Selli equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy as well as by the δ13C curve. The multi-proxy record from the Calabianca section is consistent with previous documentation of Tethyan sections, and others worldwide. Early Aptian global events, such as black shale deposition, nannoconid crisis, C isotopic negative spike and positive excursion associated with the OAE1a, increase in abundance of leupoldinids and clavate hedbergellids are superimposed on local/regional events, being strictly related to climate changes and increased run-off. Based on micropalaeontological results and geochemical proxies (Ba, P, V, Ni), the Livello Selli equivalent is interpreted as a high-productivity event associated with variable but overall anoxic/dysoxic conditions in the lower water column. The onset of new physical, chemical and biological conditions in the oceans and of the mid-Cretaceous greenhouse climate are interpreted as consequences of the superplume episode.

Morphometric analyses of Aptian Assipetra infracretacea and Rucinolithus terebrodentarius nannoliths: implications for taxonomy, biostratigraphy and paleoceanography

Abstract Morphometric analyses of Aptian calcareous nannofossils, revealed the occurrence of differently sized specimens of Assipetra infracretacea and Rucinolithus terebrodentarius . The study was conducted on the Cismon core in the Tethys and DSDP Site 463 in the Pacific Ocean with good bio-, magneto- and chemostratigraphic control. Investigation was extended to selected samples from other low-latitude sections/cores to constrain the spatial and temporal distribution of the differently sized morphotypes. Normal- and large-sized specimens display the same ultrastructure, but are clearly separated when maximum diameter is measured. No transitional forms were observed. The large-sized specimens of Assipetra infracretacea and Rucinolithus terebrodentarius are here defined as new subspecies A. infracretacea larsonii and R. terebrodentarius youngii , respectively. Both taxa have FO close to the Barremian/Aptian boundary and LO close to the Aptian/Albian boundary in all investigated sections. They increase in abundance during the Early Aptian with maximum values during OAE 1a and then gradually decrease during the late Aptian. The distribution and abundance of A. infracretacea larsonii and R. terebrodentarius youngii are coeval with major Aptian igneous, geological, geochemical and biotic changes. These nannoliths might, therefore, result from nutrification events and/or physico-chemical reorganization of the mid-Cretaceous ocean.

Reassessing the biostratigraphy and the paleobathymetry of the Gonfolite Lombarda Group in the Como area (northern Italy)

Calcareous nannofossil and foraminiferal analyses have been carried out on outcrops from the type-area of the Gonfolite Lombarda Group (Como, northern Italy). In these marine fine- to coarse-grained elastics, rapidly accumulating at the southern front of the uprising Alpine range during the Oligo-Miocene, a scarce, but reliable, sequence of calcareous nannofossil events has been observed, allowing to refine the previous age assignments. Planktonic foraminifera were found to be extremely rare and provided limited biostratigraphic information. The Villa Olmo Conglomerate and the Chiasso Formation contain the Last Occurrence (LO) of Sphenolithus distentus and the First Occurrence (FO) of Triquetrorhabdulus carinatus, which are characteristic of the nannofossil zones NP24 and NP25 (Chattian), respectively. The lower part of the Como Conglomerate was deposited during the zone NP25, whilst the upper part of the Como Conglomerate straddles the Chattian/Aquitanian boundary in zone NNl. The deposition of the Prestino Mudstones also occurred during zone NNl. However, the upper part of this formation has been dated as Burdigalian during nannofossil zone NN2. The deposition of the upper part of the Val Grande Sandstone has been assigned to the NN3 zone owing to the presence of the taxon Sphenolithus belemnos, which is restricted to NN3. The upper part of the investigated section is characterized by the deposition of the Lucino Conglomerate and its fine-grained members (Lucinasco and Lurate Caccivio Mudstones). The Lucinasco Mudstones have been dated as late Burdigalian corresponding to zone NN4, whilst the overlying Lurate Caccivio Mudstones were deposited during the Langhian part of the zone NN5, based on the presence of S. heteromorphus and the absence of H. ampliaperta. On the whole, the base and the top of the outcropping Gonfolite Lombarda Group result from our study to be younger than hitherto proposed, allowing to resolve certain previous conflicts with the few radiometric dates available for clasts from the Gonfolite Lombarda Group. The depth of deposition was upper bathyal during the Chattian and die Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones.

MAASTRICHTIAN TO EOCENE CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY FROM THE TABIAGO SECTION, BRIANZA AREA, NORTHERN ITALY

Calcareous nannofossil biostratigraphic investigations have been carried out on samples collected from the Tabiago section, Brianza, northern Italy. This section records early Maastrichtian (CC23b nannofossil zone) to early Eocene (NP10 nannofossil zone) calcareous nannofossil assemblages. The Cretaceous-Tertiary transition is characterized by major changes in sedimentation rates and two likely stratigraphic gaps. The Cretaceous Brenno Formation was deposited with a high sedimentation rate (~20 m/m.y.), whilst the Tabiago Formation of Paleogene age records a drastic decrease (~10 m/m.y.). The absence of the CC26 zonal marker Micula prinsii may indicate a stratigraphic hiatus or an extremely condensed level in the latest Maastrichtian. However, only two samples have been collected and analyzed in this interval due to low exposure of the outcrop, and the absence of M. prinsii could be the result of diagenetic overprint or insufficient sampling. A stratigraphic hiatus or a very condensed interval corresponds to the upper part of NP1 nannofossil zone and PƒN foraminiferal Zone and P1a Subzone in the early Paleocene. The poor exposure of the outcrop prevents to precisely locate the zonal boundaries between NP4 and NP5 and between NP9 and NP10 and impedes the documentation of possible further stratigraphic gaps or condensed intervals.