Domenico Rio

The Cenozoic palaeoenvironment of the Arctic Ocean

The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm ‘greenhouse’ world, during the late Palaeocene and early Eocene epochs, to a colder ‘icehouse’ world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14 Myr, we find sedimentation rates of 1–2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

Export production of coccolithophores in an upwelling region: Results from San Pedro Basin, Southern California Borderlands

A seven month-long time series sediment trap project was carried out in San Pedro Basin (Southern California Borderlands) in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes. This region is periodically influenced by upwelling, particularly during the spring and early summer. The highest fluxes of both whole coccospheres and individual coccoliths occurred during winter (January-February), a period when the fluxes of diatoms and planktic foraminifera were low. The highest coccolithophore fluxes were recorded in the mid-February with 860 × 106 coccoliths m−2 day−1, 8 × 106 whole coccospheres m−2 day−1, and 80 mg of coccolith carbonate m−2 day−1. Coccolith carbonate fluxes in January and February account for most of the total carbonate fluxes measured during this period. The season of maximum coccolithophore production in this region (winter) is correlated with weak stratification of the upper water column, low total primary production, low nutrient contents, and low temperatures. Emiliania huxleyi and Florisphaera profunda are the two most abundant species in this region. While E. huxleyi displays no distinct seasonal changes in flux, F. profunda shows a clear preference for cold, low nutrient water conditions and low light levels. Helicosphaera spp. flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity.

Plio-Pleistocene Nannofossil Biostratigraphy and Calibration to Oxygen Isotope Stratigraphies from Deep Sea Drilling Project Site 607 and Ocean Drilling Program Site 677

Evolutionary events within early Pleistocene Gephyrocapsa assemblages provide at least four biostratigraphically useful events occurring in the Matuyama Chron after the Olduvai Subchron. We establish an informal taxonomy based on three size groups ( 5.5 µm) resulting in four reproducible biostratigraphic events that reflect episodes of adaptive radiation within the Gephyrocapsa lineage. Four additional, late Pliocene-early Pleistocene events are also investigated. The successful astronomical calibration of oxygen isotope stratigraphies from Deep Sea Drilling Project site 607 and Ocean Drilling Program site 677 in the Matuyama Chron permits calibration of the biostratigraphic events to these uniquely resolved isotope chronologies. Shackleton et al.s [1990] time scale gives the following age estimates (in million years): (reemG) reentrance of medium-sized Gephyrocapsa (1.028, 0.957) (677, 607); (tlG) top large Gephyrocapsa (1.240, 1.227); (blG) base large Gephyrocapsa (1.457, 1.479); (bmG) base medium-sized Gephyrocapsa (1.670, 1.700); (tHS) top H. sellii (1.470, 1.241); (tCM) top C. macintyrei (1.597, 1.640); (tDB) top D. brouweri (1.950) (607 only); (baDT) base acme D. triradiatus (2.153) (607 only). Further comparison with other, less resolved, ∂18O stratigraphies indicate that event reemG is diachronous by 71 kyr, consistently being younger in the mid-latitudes. Event tlG appears synchronous, clustering in stage 37 in all sites. Event blG is slightly older (22 kyr) in the mid-latitudes than in the equatorial Pacific. Also, event bmG is older in the mid-latitudes (30 kyr). Event tHS shows the largest difference, occurring 229 kyr later at site 607, corresponding to 12 isotope stages. The critical paleoisotherm separating “young” from “old” last occurrences of H. sellii was probably located between ∼11°N and 18°N in the Atlantic Ocean. Event tCM is clearly time transgressive, occuring 43 kyr earlier at site 607. Event tDB occurred a few kiloyears within basal Olduvai at site 607.

Mode and tempo of the Paleocene-Eocene thermal maximum in an expanded section from the Venetian pre-Alps

Mode and tempo of an expanded Paleocene Eocene Thermal Maximum section in the Venetian Pre-Alps

An early Eocene carbon cycle perturbation at 52.5 Ma in the Southern Alps: Chronology and biotic response

An early Eocene carbon cycle perturbation at ~52.5 Ma from the southern Alps: Chronology and biotic response

Interplay between tectonics and glacio-eustasy: Pleistocene succession of the Crotone basin, Calabria (southern Italy)

On a global scale, the Crotone basin preserves one of the best-developed and most complete Pleistocene marine records available in outcrop, as important as those in California, New Zealand, and Japan. A deformed, markedly cyclothemic, lower to middle Pleistocene succession is present in the territory of San Mauro Marchesato (Crotone area, southern Italy), showing an overall shallowing trend from slope mudstones to marginal marine and continental deposits. Preservation and high resolution of cyclothems occurred through the interaction between high-amplitude relative sea-level fluctuations, a particular pattern of differential subsidence due to intrabasinal tectonics, and high rates of sediment supply. The studied succession was laid down in the Crotone basin under an extensional tectonic regime, following a major, middle Pliocene contractional phase probably of transpressional nature. Two major unconformities, locally accompanied by angular discordances, occur within the succession. The former, centered at ca. 1.2 Ma, is thought to reflect the opening of the San Mauro subbasin within the Crotone basin in the early Pleistocene, following dextral transtensional motion along north- to north-northeast–trending faults. The latter, with a hiatus lasting from ca. 0.65 to 0.45 Ma, may reflect the decoupling of the Calabrian block with respect to Adria and Sicily, allowing further advancing of the Calabrian arc in the Ionian area, where subduction could continue until the present time. The lower part of the succession (the H. sellii and “large Gephyrocapsa ” Zones, from ca. 1.67 to ca. 1.23 Ma) consists of slope to outer-shelf monotonous mudstones and is bounded at the top by the first unconformity, whose gap suppresses the upper part of to locally the entire “large Gephyrocapsa ” Zone (1.608–1.235 Ma) and the lower part of the “small Gephyrocapsa ” Zone (1.235–0.96 Ma). A number of cyclothems developed in an outer- to inner-shelf environment within the “small Gephyrocapsa ” Zone. Biomagnetostratigraphic constraints strongly support a correlation between the condensed sections of cyclo thems and MIS (marine isotope stage) 33 to MIS 25. From the base of the P. lacunosa Zone (at ca. 0.96 Ma) upward, the succession rapidly becomes sand dominated, a change that can be confidently correlated with the major climatic shift associated with MIS 24 to MIS 22. In the following succession, two tephra layers, named “Pitagora ash” and “Parmenide ash,” provide mappable isochronous surfaces across the subbasin. The sedimentary record is remarkably cyclo themic, characterized by a stack of simple or composite, seaward-prograding, sand- dominated tongues and intervening aggradational deposits related to transgressive-deepening episodes. The cyclothems can be confidently correlated with the oxygen isotope record up to the Matuyama-Brunhes inversion, i.e., up to MIS 19, whereas the stratigraphic record postdating MIS 19 has poorer chronological constraints. Dating is provided by tracing the Parmenide ash in the deeper-water coeval succession of the southern part of the Crotone basin, where the deposits including the ash can be correlated by means of nannofossil biostratigraphy with termination V (transition from MIS 12 to MIS 11). The second unconformity marks an abrupt increase in the proximal character of the sedimentary deposits forming the cyclothems, which incorporate increasing amounts of marginal-marine to continental deposits in the upper part of the subbasin infill. Several lines of direct and indirect evidence indicate that, in spite of the dramatic role of tectonics in shaping stratigraphic architecture, the roles of tectonics and eustasy can be disentangled, owing to the different time scales of the tectonic events and the high-frequency, high-amplitude glacio- eustatic Pleistocene cycles. Interaction between intrabasinal tectonics and high rates of sediment supply allowed forced regressive and possibly also lowstand systems tracts to be preserved in some cyclothems, particularly in the lower part of the succession, an unusual fact in shelf deposits. Considering the far younger age of marine terraces on the Ionian side of Calabria when compared to the Tyrrhenian side, it is thought that, during ongoing subduction of the Ionian crust, a wave of uplift and related extensional tectonics migrated southeastward in the rear of the frontal accretionary wedge.

Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes

Calcareous nannofossils have provided a powerful biostratigraphic tool since the 1950s and 1960s, when several milestone papers began to highlight their potential use in dating Cenozoic sediments ...

The environment of Venice area in the past two million years

A ca. 950 m thick succession that was continuously cored in 1971 in Venice has been revisited, in order to reconstruct the environmental history of the Venice area since about 2.15 Ma. Magnetic polarity stratigraphy, integrated with refined calcareous nannofossil biostratigraphy, provides a firm chronostratigraphic framing of the succession. In order to improve the chronological resolution, we derived astrochronological refinements in the lower Pleistocene sapropel-bearing interval by a comparison with other time-correlative sections in the Mediterranean. The pollen record is used as a proxy of climatic changes and as an indirect tool in the chronological reconstruction in the upper part of the succession. The following history has been inferred: (1) in the late Gelasian (late Pliocene), the depositional area was a strongly subsiding shelf which shoaled to near sea level; (2) following a hiatus of a minimum duration of 0.2 Myr, encompassing most of the Olduvai Subchron, the shelf rapidly drowned to bathyal depths over the early Pleistocene (biozones MNN 19a to 19e: from 1.947 Ma to 0.96 Ma). This interval was characterized by starved sedimentation (less than 10 cm/kyr), represented by hemipelagic muds interbedded with sapropel layers; (3) during most of biozone MNN19f (Pseudoemiliania lacunosa Zone, 0.96–0.42 Ma) a thick package of turbidites was laid down as a result of massive terrigenous input from the eastern Southern Alps; (4) later, in the middle part of Chron 1n (Brunhes), deltaic sedimentation, primarily related to the progradation of the paleo-Po system, led to the progressive infill of the basin. This progradational episode was a major building phase, and ended with the first appearance of continental sediments, tentatively correlated with marine oxygen isotope substage 8.4; (5) the upper part of the succession shows a cyclic organization, with an upward increasing amount of marginal-marine and subaerial deposits. In this interval the Venice area was below sea level during glacioeustatic highstands but became emergent during subsequent major glacioeustatic lowstands. Pollen data support an overall good correspondence of continental sediment packages of sequences with glacial conditions and of maximum flooding intervals with interglacial conditions.

Emergence of Venice during the Pleistocene

The Pleistocene history of sea-level change for the Venice region was reconstructed using an integrated magneto-bio-cyclostratigraphy of lithofacies and a published palynofloral analysis of continuously cored sediments in a 950-meter-deep drill core. The basin in which the Venice region is located collapsed at B1.8 Ma with slow sediment accumulation in the deeper-water starved basin during most of the Matuyama polarity chron but shoaled rapidly in the early and middle Brunhes in response to a major phase of deltaic progradation. The initial transition to continental sediments occurred during a prominent glacioeustatic low-stand that is likely to be MIS 12 (B0.43 Ma) but could be as young as MIS 8 (B0.25 Ma). The Venice area oscillated from below sea level during subsequent major glacioeustatic high-stands to becoming increasingly emergent during major low-stands as the basin continued to fill with marine and continental sediments. Some parts of the Venice area are now emergent for the first time during a glacioeustatic high-stand (i.e., MIS 1 or the Holocene). The total long-term subsidence rate estimated from the VENICE-1 record is less than 0.5 mm/yr, considerably slower than estimates for the Holocene and especially the modern anthropogenic period. r 2002 Elsevier Science Ltd. All rights reserved.

Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes

Calcareous nannofossils are widely used in Cenozoic marine biostratigraphy. At present, the two most widely used calcareous nannofossil biozonations were established approximately 40 years ago. These were derived from marine land sections and Deep Sea Drilling Project rotary cored sediments. Over nearly three decades, we have generated Miocene through Pleistocene calcareous nannofossil data from deep sea sediments in low and middle latitude regions. The sediments used here have been mostly recovered using the advanced piston coring technique, generating less core disturbance and complete recovery via multiple penetration of the sediment column at single sites. A consistent trait in our work on calcareous nannofossil biostratigraphy has been to use semi-quantiative methods in combination with short sample distances, close enough to capture the details of the abundance behaviour of individual calcareous nannofossil taxa. Such data represent the foundation of the new biozonation presented here, which still partly relies on the pioneering work presented by Er lend Martini and David Bukry about 40 years ago. A key aim here has been to employ a limited set of selected biohorizons for the purpose of establishing a relatively coarsely resolved and stable biozonation. We present 31 biozones using a new code system: CNM1-CNM20; Calcareous Nannofossil Miocene biozones 1 through 20. CNPL1-CNPL11; Calcareous Nannofossil Plio-Pleistocene biozones 1 through 11. As the new biozonation encompasses 23 million years, the average biozone resolution becomes 0.74 million years, ranging from 0.15 to 2.20 million years. A single biohorizon is used for the definition of each biozone boundary. Auxiliary markers are avoided, as well as subzones, in order to maintain stability to the new biozonation. Virtually every biozone holds one or several additional biohorizons. These, together with all biozone boundary markers, are assigned age estimates derived chiefly from astronomically tuned cyclostratigraphies.