Integrated stratigraphic reconstruction for the last 80 kyr in a deep sector of the Sardinia Channel (Western Mediterranean)

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Abstract

A quantitative analysis of planktonic foraminifera, coupled with petrophysical and paleomagnetic measurements and 14C-AMS calibrations, was carried out on a deep core recovered in the Sardinia Channel (Western Mediterranean Sea), during the CIESM Sub2 survey, providing an integrated stratigraphic time-framework over the last 80 kyr. Significant changes in the quantitative distribution of planktonic foraminifera allowed the identification of several eco-bioevents useful to accurately mark the boundaries of the eco-biozones widely recognized in the Western Mediterranean records and used for large-scale correlations. Namely, 10 eco-biozones were identified based on the relative abundance of selected climate-sensitive planktonic foraminiferal species. Sixteen codified eco-bioevents were correlated with Alboran Sea planktonic foraminiferal data and several climatic global events (Sapropel S1, Younger Dryas, Greenland Isotope Interstadial 1, Greenland Isotope Stadial 2, Heinrich event H1–H6) were recognized.

The eco-bioevents together with the 14C-AMS calibrations allowed us to define an accurate age model, spanning between 2 and 83 kyr. The reliability of the age model was confirmed by comparing the colour reflectance (550 nm%) data of the studied record with the astronomically tuned record from the Ionian Sea (ODP-Site 964). A mean sedimentation rate of about 7 cm/kyr included three turbidite event beds that were chronologically constrained within the relative low stand and regressive sea-level phases of MIS 4 and 3. The deep-sea sedimentary record includes a distinct tephra occurring at the base of the core that dates 78 ka cal. BP.

The paleomagnetic data provide a well-defined record of the characteristic remanent magnetization that may be used to reconstruct the geomagnetic paleosecular variation for the Mediterranean back to 83 kyr.

Introduction

Since climate excursions recorded in Northern Hemisphere in the Greenland GISP and GRIP ice cores (GRIP members, 1993) over the last 100 kyr had more or less synchronous effects in the Mediterranean area, many researches have focused on Mediterranean marine cores, with the aim to detect their intensity and impact on the marine environment. During the last glacial period the Mediterranean region experienced rapid modifications in hydrographic conditions in response to fast climatic excursions, such as Heinrich (HE) and Dansgaard–Oeschger (D–O) Stadials (cold) and Interstadials (warm) events (Heinrich, 1988; Dansgaard et al., 1993). In particular, Rohling et al. (1998) and Cacho et al., 1999, Cacho et al., 2000 have proved that the millennial scale D–O and HE directly control the winds and precipitation system on the northern Mediterranean basin. Even during the Holocene the principal climatic events and oscillations of the northern Hemisphere have been clearly traceable in different sectors of the Mediterranean basin sedimentary records (Cacho et al., 1999, Cacho et al., 2000, Cacho et al., 2001; Rohling et al., 2002; Sprovieri et al., 2003, Sprovieri et al., 2006; Perez-Folgado et al., 2003, 2004; Geraga et al., 2005).

A detailed outline of the paleo-environmental changes and their control on marine communities, calibrated by several independent proxies (tephra, sapropel, 14C geochronology), is now available for the Mediterranean area (Buccheri et al., 2002; Ducassou et al., 2007; Emeis et al., 2003; Narcisi and Vezzoli, 1999; Lourens, 2004; Principato et al., 2003; Rohling et al., 2003; Sangiorgi et al., 2006; Sprovieri et al., 2003, Sprovieri et al., 2006, and reference therein). Several codified eco-bioevents, if clearly detected in marine records, can be used as tie points to chronologically constrain the late Pleistocene–Holocene Mediterranean marine sequence. Nevertheless, even if many reference records are available from deep-sea sites, most of them span a short time interval and lack a high resolution detail of the paleo-environmental and paleo-ecological changes before 40 kyr. Recently, Pérez-Folgado et al., 2003, Perez-Folgado et al., 2004 carried out a high-resolution study of the ODP-Site 977, located in the western part of the Alboran Sea, and identified several planktonic foraminiferal eco-bioevents that occurred during the marine isotope stages (MIS) 1–5. These eco-bioevents represent the best tool to correlate deep marine records from different Mediterranean sites.

Many recent studies emphasize the challenge when studying deep-sea records to establish a reliable chronology, even for the deposition of turbidites (Walker, 1992; Beaudouin et al., 2004; Ducassou et al., 2007), and underline the utility to support conventional dating methodologies with different constraints. It is widely accepted that one of the main factors controlling and enhancing turbidite deposition along deep-sea fan is the regression and low stand of sea-level, whereas sea-level rise and highstand phases reduce terrigenous supply to deep-sea systems (Walker, 1992; Richards et al., 1998; Normark et al., 1998).

The CIESM core C08 is located at the mouth of the Bizerte Canyon in the Sentinelle Valley in a key position of paleoceanographic and geological significance (Fig. 1). The Sardinia Channel connects the Alboran to the Tyrrhenian Basin and offers a stratigraphic record with the potential to link the eco-stratigraphic and paleoceanographic observations between the Western, Central and Eastern Mediterranean late Pleistocene–Holocene marine records (Perez-Folgado et al., 2004; Sbaffi et al., 2004; Geraga et al., 2005; Asioli et al., 2001; Ariztegui et al., 2000). In fact, a portion of the Modified Atlantic Water (MAW) coming from the Strait of Gibraltar (Bryden and Kinder, 1991), diverges from the part that enters the Eastern Mediterranean and flows through the Sardinia Channel into the Tyrrhenian Sea along the northern Sicilian coast (Millot, 1987), forming a secondary circulation gyre. The circulation system in this sector of the Tyrrhenian Sea is counter-clockwise, with the Levantine Intermediate Water (LIW) inflows lapping on the northern Sicilian coast and the outflow occurring along the eastern Sardinia coast (Pinardi and Masetti, 2000 and references therein).

The core site is also in a strategic position to check the efficiency of a submarine canyon in driving density flow to the deep-sea environment (see below), even if not directly connected to any emerged sector nor to continental shelf (Reading and Richards, 1994). Thus the possibility that such a type of canyon would form a fan can be evaluated, even verifying the significance and the timing of the turbidite deposition.

The aim of this study is to provide a record of integrated stratigraphic data spanning back to about 80 kyr, relative to a deep basin area, based on eco-biozones, 14C-dated ages, event stratigraphy, lithostratigraphy, petrophysical properties and paleomagnetic measurements. Furthermore, the reliability of the reflectance parameter 550 nm% is evaluated as an independent correlation tool for tuning marine records.

Section snippets

Geological setting

Core C08 was collected in the Sentinelle Valley of the Sardinia Channel, 55 km from the mouth of the Bizerte Canyon, equidistant from Sicily, Sardinia and Tunisia (Fig. 1), during the cruise CIESM Sub2 onboard the R/V Urania in December 2005 (38°38.5364′N, 10°21.5576′E—2370 m water depth). In this area a 400-km-long submerged sector of the Apennine–Maghrebian branch of the Alpine orogen separates the Tyrrhenian (Plio-Pleistocene in age) and the Algero Provencąl (Miocene in age) oceanic basins.

Material and methods

The gravity corer entered the uppermost portion of a sedimentary sequence made up with lateral continuous parallel and thin reflectors (Sartori et al., 2001), possibly related to hemipelagic and turbiditic deposition. It recovered about 5.40 m of hemipelagic mud interlayered with three fine-to-medium sand turbidite layers of increasing thickness towards the top of the core (Fig. 2).

Lithostratigraphy and petrophysical properties

The sediment consists for the 95% of hemipelagic mud, ranging in colour from reddish and ochre to light, olive and dark grey; the remaining 5% are turbiditic sand layers (Fig. 2).

The uppermost 0.50 m consists of a reddish mud pervasively oxidized, then about 0.11 m of alternating dark grey and ochre laminated mud, and further below, 0.05 m of fine laminated ochre mud. From about 0.66 m down to 2.40 m olive grey mud occurs with rare dark patches, probably due to bioturbation, while from 2.40 m to the

Planktonic foraminiferal eco-biozonation

Significant changes in the quantitative distribution of the planktonic foraminifera species allowed several authors (Asioli et al., 1999, Asioli et al., 2001; Capotondi et al., 1999; Casford et al., 2002; Principato et al., 2003; Sprovieri et al., 2003; Ducassou et al., 2007) to define eco-biozones useful for fine-scale subdividing of the stratigraphic record. The eco-biozone boundaries are characterized by the temporary appearance or disappearance and/or evident abundance peaks of different

Conclusions

The multidisciplinary study of core C08, recovered from the deep sector of the Sardinia Channel, based on planktonic foraminiferal assemblages, petrophysical (MS, Grape density, 550 nm% reflectance) and paleomagnetic (NRM Intensity, ChRM Inclination, ChRM Declination) data, provides an integrated stratigraphic reference record for the Western Mediterranean Sea that spans back for about 83 kyr. The most important eco-bioevents widely used for large-scale correlation in the Western Mediterranean

Acknowledgements

The authors gratefully acknowledge Lucas J. Lourens of the University of Utrecht for original reflectance data of Ionian cores and Carmine Lubritto of CIRCE Radiocarbon Laboratory, (Caserta, Italy) for 14C-AMS dates. Sincere thanks are also due to Laura Giuliano, who involved some of us in CIESM SUB2 cruise. Captain Vincenzo Lubrano di Lavadera and the crew of R/V Urania, who sailed despite a very rough sea, are kindly acknowledged. Two anonymous reviewers and Patricia Scalfani are sincerely

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