Simonetta Monechi

Calcareous nannofossil zonation of the Jurassic-Cretaceous boundary interval and correlation with the geomagnetic polarity timescale

Abstract Calcareous nannofossil stratigraphy has been investigated in six European land sections and at two Deep Sea Drilling Project Sites (391C and 534A) ranging from the Upper Kimmeridgian to the Lower Valanginian. Most of the sections contain a continuous record of the Jurassic-Cretaceous boundary interval, a time of rapid increase in nannofossil abundance and diversity and allow development of a revised nannofossil zonation scheme for this period. Numerous nannofossil lineages have been studied in detail and the results help to increase potential stratigraphic resolution in this interval. The proposed scheme consists of six zones which are units recognizable in all sections regardless of nannofossil preservation and eleven subzones determinable in all but the most poorly preserved material. Thirty-eight additional biohorizons are proposed based on the stratigraphy of the two DSDP sites. These can be accurately established only in moderately well-preserved material but spotty occurrences of these taxa in other sections may be stratigraphically useful. Most of the sections studied have been investigated magnetostratigraphically and the results of this study allow correlation between nannofossil zonation and the geomagnetic polarity time scale. Magnetostratigraphy indicates that many nannofossil events can be quite precisely determined and are not significantly time-transgressive. Finally, the magnetostratigraphic definitions of two stage boundaries are refined. The Kimmeridgian-Tithonian and Berriasian-Valanginian boundaries are placed within Chrons CM22n and CM15n respectively. Two new genera, Faviconus and Umbria , and seven new species are described: Umbria granulosa, Rhagodiscus nebulosus, Cretarhabdus octofenestratus, Faviconus multicolumnatus, Nannoconus infans, Nannoconus compressus and Nannoconus wintereri . Eight subspecies and three taxonomic emendations are also described.

Late Cretaceous-Eocene nannofossil and magnetostratigraphic correlations near Gubbio, Italy

Abstract Using a modified sample preparation technique, we have been able to establish a detailed lower Campanian to upper Eocene nannofossil stratigraphy in the Bottaccione and Contessa Highway sections near Gubbio. Appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections. Comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in Deep Sea Drilling Project (DSDP) sites suggest that magmetic Subchrons C17N and C25N are missing in the Bottaccione section. The observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron. Absolute abundance, paleobiogeographic restriction, and differential preservation render some of the traditionally used biostratigraphic events less reliable than others.

High-resolution iridium, δ13C, δ18O, foraminifera and nannofossil profiles across the latest Paleocene benthic extinction event at Zumaya, Spain

In the expanded upper Paleocene-lower Eocene section (~ 30 m of Zone P5 sediments) at Zumaya, northern Spain, the highest occurrence of many late Paleocene deep-sea benthic foraminifera species (~40% extinction), coincides with a transition from marl to calcite-free clay. Our high-resolution studies (chemical elements, 613C, 6180, calcareous nannofossils, planktic and benthic foraminifera) show that below the marl-clay transition there is a 40-50 cm thick interval (corresponding to 10-20 kyr) containing a detailed record of a gradual succession of faunal and geochemical events culminating in the benthic extinctions. Planktic foraminiferal and nannofossil changes (e.g., the onset of demise in Fasciculithus genus) occur a few meters below the marl-clay transition. In the limestone 50 cm below the base of the clay, a prominent glauconite maximum indicates that sea-floor oxygenation suddenly decreased. Glauconite continues to be common until the onset of clay deposition. A whole-rock negative 613C shift (1.6%0), most likely reflecting an original sea-water trend, is gradually developed over the 40 cm of greenish brown marls immediately below the clay. At the base of these marls there is a small, significant iridium anomaly of 133 ppt Ir compared with an average background of 38 ppt. In the marls the demise of the Fasciculithus species accelerates, Gavelinella beccariiformis becomes extinct, and the abundance of Acarinina species begins to increase. The superjacent 4 m of clay is devoid of original calcite in its lower part and has a low calcareous content higher up. At calcareous levels in the clay an unusual planktic foraminifera fauna occurs, dominated by Acarinina species. When marl deposition returns, 613C gradually increases and then stabilizes at values about 0.5%o lower than before the isotopic excursion. The 613C excursion spans in total 5 m, probably corresponding to 200-400 kyr. The fasciculiths disappear shortly after the stabilization of 613C. Here we also present a whole-rock 6~3C profile through the entire Paleocene section at Zumaya. The profile is very similar to previous profiles registered in well preserved deep-sea material, suggesting that whole-rock 613C at Zumaya can be used for correlation.

The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late middle Eocene and consequent global CO 2 -driven climate change.

THE PALEOCENE–EOCENE THERMAL MAXIMUM: NEW DATA ON MICROFOSSIL TURNOVER AT THE ZUMAIA SECTION, SPAIN

The benthic foraminiferal turnover and extinction event (BEE) associated with the negative carbon isotope excursion (CIE) across the Paleocene–Eocene Thermal Maximum (PETM) is analyzed in the Zumaia section (Spain), one of the most complete and expanded deep-water sequences known worldwide. New biostratigraphic, paleoecologic, and paleoenvironmental data on benthic foraminifera are correlated to information on planktic foraminiferal and calcareous nannofossil turnover in order to evaluate possible causes and consequences of the PETM. Gradual but rapid extinction of 18% of the benthic foraminiferal species starts at the onset of the CIE, after the initial ocean warming (as inferred from calcareous nannofossils) recorded in the last 46 kyr of the Paleocene. This gradual extinction event culminated ∼10.5 kyr after the onset of the CIE and led to the main BEE, affecting 37% of the species. Therefore, extinctions across the PETM affected a total of 55% of the benthic foraminiferal species at Zumaia. The gradual extinction occurred under inferred oxic conditions without evidence for carbonate dissolution, indicating that carbonate corrosivity and oxygenation of the ocean bottom waters were not the main cause of the event. An interval characterized by dissolution occurs above the main BEE, suggesting that bottom waters became corrosive after the main extinction. Carbonate is progressively better preserved through the overlying deposits, and carbon isotope values gradually return to background levels. These data are consistent with a slow deepening of the carbonate compensation depth after its initial rise owing to abrupt acidification of the oceans. Microfossil data support a rapid onset of the PETM, followed by long-term effects on calcareous plankton and benthic foraminifera.

Calcareous nannofossil turnover around the Paleocene/Eocene transition at Alamedilla (southern Spain)

A high resolution biostratigraphic study of calcareous nannofossil assemblages has been performed on the Alamedilla section in southern Spain across the Paleocene/Eocene transition. The identification of numerous and well differentiated events together with a major calcareous nannofossil turnover suggest the Alamedilla section to represent one of the most expanded and continuous sections straddling the P/E boundary. Quantitative analyses have revealed a change in the species richness and fluctuations in abundance of important paleoecological species.

The Eocene-Oligocene Boundary in the Umbrian Pelagic Sequences, Italy

Publisher Summary Detailed biostratigraphic and paleomagnetic studies on Eocene–Oligocene pelagic sequences from Umbria (Central Italy) revealed that deposition across the Eocene–Oligocene boundary was continuous and undisturbed in that area. This chapter presents the data from eight stratigraphic sequences spanning the interval from the Early to Middle Eocene boundary through the Early Oligocene with specific emphasis on the events at the Eocene–Oligocene boundary. To have a complete biostratigraphic and paleomagnetic record, the Contessa highway section was sampled upwards into the northwestern quarry—that mirrors the Contessa quarry of Lowrie—where the Eocene–Oligocene boundary is undisturbed. Lithologically, the scaglia formation is very monotonous except for the major color changes. Visual correlations among sections are limited to minor changes that are not easily detected. Some of these changes, however, appear to be of larger (not local) significance.

Integrated stratigraphy of the Oligocene pelagic sequence in the Umbria-Marche basin (northeastern Apennines, Italy): A potential Global Stratotype Section and Point (GSSP) for the Rupelian/Chattian boundary

The Oligocene represents an important time period from a wide range of perspectives and includes significant climatic and eustatic variations. The pelagic succession of the Umbria-Marche Apennines (central Italy) includes a complete and continuous sequence of marly limestones and marls, with volcaniclastic layers that enable us to construct an integrated stratigraphic framework for this time period. We present here a synthesis of detailed biostratigraphic, magnetostratigraphic, and chemostratigraphic studies, along with geochronologic results from several biotite-rich volcaniclastic layers, which provide the means for an accurate and precise radiometric calibration of the Oligocene time scale. From this study, the interpolated ages for the Rupelian/Chattian stage boundary, located in the upper half of Chron 10n at meter level 188 in the Monte Cagnero section, and corresponding to the O4/O5 planktonic foraminiferal zonal boundary, are 28.36 Ma (paleomagnetic interpolation), 28.27 ± 0.1 Ma (direct radioisotopic dating), and 27.99 Ma (astrochronological interpolation). These ages appear to be slightly younger than those reported in recent chronostratigraphic time scale compilations. The Monte Cagnero section is a potential candidate for defining the Chattian Global Stratotype Section and Point (GSSP) and some reliable criteria are here proposed for marking the Rupelian/Chattian boundary according to International Union of Geological Sciences (IUGS) recommendations.

Late Cretaceous flysch deposits of the Northern Apennines, Italy: age of inception of orogenesis-controlled sedimentation

Abstract Calcareous nannofossils have proved to be very effective in determining the age of Cretaceous flysch sequences of the Northern Apennines. Here, we focus on the beginning of flysch sedimentation, which replaced previous pelagic deposition during the Late Cretaceous convergence stage. In all the examined sequences an early to late Campanian age has been determined for the bases of the flysch formations, implying an essentially synchronous start of orogenesis-controlled sedimentation within the Ligurian Apenninic (Ligurian) Ocean Basin. Data obtained from the siliciclastic turbidite sequence (Vat Lavagna/Mt. Gottero Sandstones) overlying Jurassic ophiolites and sedimentary cover, indicate continuous sedimentation from earliest Campanian to early Paleocene. Thus, either a forearc or ‘dormant trench’ tectonic setting seems to be required for this sequence. Regarding the calcareous Helminthoid Flysch, a minor diachrony in the basal ages suggest a general younging from south to north. The onset ages of flysch sedimentation range from early Campanian (Southern Tuscany Flysch), to early-middle Campanian (Mt. Caio/Ottone Flysch), to latest Campanian (S. Remo, Mt. Antola, Mt. Cassio, Mt. Caio/Orocco Flysch). This diachrony could be the consequence of Late Cretaceous-early Tertiary transcurrent tectonics in the Apenninic Basin and/or of multiple source areas (from both the European/Iberian and Adriatic margins). These tectonic implications are in agreement with the kinematic evidence of a transpressional regime along the Iberian/Adriatic plate boundary (Apenninic sector) during the Late Cretaceous.

Mediterranean fossil whale falls and the adaptation of mollusks to extreme habitats

The hypothesis that sunken carcasses of Mesozoic marine reptiles and Cenozoic whales acted as evolutionary stepping stones to deep-sea reducing habitats is underlain by the question of whether vent-like, chemosymbiotic specialization fi rst evolved at shelf depths. Fossil skeletons of large whales have long been known from ancient shallow-water strata, but they have never been considered as a source of information on ecosystem development. We present a study on a 3 Ma old fossil whale fall and a survey of other Pliocene fossil skeletons to show that the associated biota is dominated by heterotrophs, with subsidiary chemoautotrophs. The taphonomy of the Mediterranean shelf whale falls shows some differences with respect to deep-water studies. Quantitative analyses of abundance data within a large data set on fossil and modern mollusk families confi rm that deep- and shallow-water communities at reducing habitats are composed of a different set of taxa, i.e., specialists occurring only below the shelf break. Mediterranean carcasses sunken in coastal settings do not seem to be favorable for the evolution of whale-fall specialists among the mollusks. The situation reverses as the shelf break is approached.