Magnetostratigraphic, biostratigraphic, and stable isotope stratigraphy of an Upper Miocene drill core from the Salé Briqueterie (northwestern Morocco): A high‐resolution chronology for the Messinian stage

Abstract

We report a high‐resolution stable isotope, carbonate, magnetostratigraphic, and biostratigraphic record from a 175‐m drill core from the Salé Briqueterie, which is part of the Bou Regreg section in northwestern Morocco. The Salé drill core spans the interval from paleomagnetic Chron C4n partim to C3r (earliest Gilbert), which represents the time leading up to and including the isolation and desiccation of the Mediterranean (i.e., the Messinian salinity crisis). During Chrons C3An and C3Ar (6.935 to 5.894 Ma) the isotope and carbonate signals display quasi‐periodic variations with estimated periods of 40 and 100 kyr, respectively. We interpret the 40‐kyr δ18O variations as reflecting changes in global ice volume caused by obliquity‐induced changes (41 kyr) in solar insolation in polar regions. The 100‐kyr carbonate variations probably represent long‐term modulation of the amplitude of the precessional cycle (∼21 kyr), which is not resolved by our sampling frequency. The cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of Shackleton et al. (1994a) from stage TG24 in Chron C3r (earliest Gilbert) to stage C3Ar.δ18O.18 at the base of Chron C3Ar (6.935 Ma). A major change in paleoceanographic conditions is recorded across the Tortonian/Messinian boundary, which we correlate to Chron C3Bn at 7.04 Ma. Benthic foraminiferal δ18O values increased by an average of 0.4‰ in two steps at 7.17 Ma and 6.8 Ma and δ13C values decreased by 0.7–0.8‰ between 7.1 and 6.8 Ma, representing the late Miocene carbon shift. The first step in δ18O values coincides with an inferred reversal in deep water circulation through the Rifian Corridor, and the second correlates with the base of the Tripoli Formation and onset of “crisis conditions” in the Mediterranean. We suggest that the increase in δ18O values represents, at least in part, an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the Mediterranean. Average δ18O values remained high throughout most of Chrons C3Ar and C3An, reaching maximum δ18O values during isotope stages TG20 and 22 in Chron C3r (earliest Gilbert). The glacio‐eustatic falls associated with these events may have resulted in the complete isolation of the Mediterranean from the world ocean (Shackleton et al., 1994a). Following stage TG12 in the Salé record, there exists a trend toward progressively lower δ18O values that may represent a series of marine transgressions that eventually reflooded the Mediterranean and ended the Salinity Crisis.

Calcareous nannofossil biostratigraphy of the M. del Casino section (northern Apennines, Italy) and paleoceanographic conditions at times of Late Miocene sapropel formation

“…In the Sale Briqueterie drill core (northwestern Morocco), Hodell et al (1994) found the FO of A. primus in Chron C4n.2n whereas Rakic El Bied and Benson (1996) recorded the same event at a slightly younger level, at the C3Bn=C3Br boundary, in the Ain el Beida section located nearby. In the equatorial Pacific and Indian Ocean, the FO of A. primus is recorded in Chron C3Br , while, in the Mediterranean, this event is detected in former Chron 6, equivalent to the C3Bn=C3Br boundary (Flores et al, 1992) (Fig.…”

The Abad composite (SE Spain): a Messinian reference section for the Mediterranean and the APTS

“…This event occurs in the upper part of chron C3An.2n and is useful for Mediterraneanwide correlations. It is older, however, than the same bioevent in the North Atlantic, where it has been recorded immediately after the ®rst coiling change of the neogloboquadrinids (see Sierro, 1985;Sierro et al, 1993;Hodell et al, 1994;Zhang and Scott, 1996) within chron C3An.1r. The progressively restricted connection between the Atlantic and Mediterranean during the Messinian is probably responsible for the earlier disappearance of this species from the Mediterranean.…”

Messinian paleoenvironmental evolution in the lower Guadalquivir Basin (SW Spain) based on benthic foraminifera

“…Nonetheless, the detailed paleogeographic evolution and the precise timing of the different processes leading to the MSC and the later Mediterranean reflooding are still discussed controversially (Riding et al, 1998;Krijgsman et al, 1999a;Aguirre and Sánchez-Almazo, 2004;Braga et al, 2006;Roveri and Manzi, 2006). Various studies addressed the Messinian paleoenvironmental evolution on the Atlantic side of the Rifian corridors (Hodell et al, 1989;Benson et al, 1991;Gebhardt, 1993;Hodell et al, 1994;Barbieri, …”