OLIGOCENE-MIOCENE CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY AND PALEOECOLOGY FROM THE IBERIA ABYSSAL PLAIN

During Ocean Drilling Program (ODP) Leg 149, five sites were drilled on the Iberia Abyssal Plain in the northeastern Atlantic Ocean. Both Mesozoic and Cenozoic sediments were recovered. Oligocene to Miocene sediments were cored at deepwater Sites 897, 898, 899, and 900. Except for a few intervals, occurrences of generally abundant and well-preserved calcareous nannofossils suggest that the deposition of the turbidite-type sediments occurred above the calcite compensation depth (CCD). One major unconformity in the middle late Miocene is present. Detailed quantitative analyses of calcareous nannofossils are used to determine the changes occurring among the nannoflora in relation to sea-level variation. A succession of 89 biohorizons from the early Oligocene to the late Miocene are defined by combining the biostratigraphic results of the four sites studied in the Iberia Abyssal Plain. One new genus and eight new species are described: Camuralithus, Camuralithus pelliculatus, Ericsonia detecta, Helicosphaera limasera, Sphenolithus akropodus, Sphenolithus aubryae, Sphenolithus cometa, Reticulofenestra circus, and Syracosphaera lamina. Two new variations and seven new combinations are also introduced

Stratigraphy and sedimentology of Miocene phosphate-rich sediments in Malta and southeastern Sicily: paleoceanographic implications for the evolution of the eastern Mediterranean during the early to early late Miocene.

International audienceThe Maltese archipelago and south-eastern Sicily include an Uppermost Oligocene to Upper Miocene hemipelagic sedimentary succession representing the Malta-Hyblean plateau, which limits the eastern Mediterranean to the west. This succession hosts a unique and well-exposed series of condensed and allochthonous phosphate-rich beds, which were formed in a sedimentary regime of erosion, sediment reworking and frequent gravity-flow deposition. The combination of nannofossil biostratigraphy and 87Sr/86Sr isotope stratigraphy allows for the precise attribution of ages to the phosphate deposits and for the distinction of three periods of major phosphogenesis. The first phase occurred between 24·5 and 21 Ma and 25 and 18·9 Ma (clustering of ages between 25 and 22·5 Ma) on Malta and Sicily, respectively. The second and third phases of phosphogenesis are documented from the Maltese Islands and are dated as 17·2 to 13·1 Ma and 10·9 to 9·8 Ma, respectively. The phosphate-rich beds are associated with hiatuses and phases of important condensation which, for the oldest phosphogenic period, envelop the time period of 23·2 to 22 Ma for the Fomm Ir Rhi Bay section (Malta) and from 19·1 to 16·3 Ma for the sections of Sampieri and Modica (Sicily). For the second phase of phosphogenesis on the Maltese Islands, a consistent hiatus was found which embraces the time period of approximately 17 to 15 Ma. Also the third phase of phosphogenesis appears to be associated with a major hiatus, which probably envelops the time period between 12·5 and 10·9 Ma, but a better age control is needed here. The correspondence in timing of the Maltese-Sicilian phases of phosphogenesis with major phases of phosphogenesis outside the Mediterranean realm, to maxima in oceanic phosphorus-burial rates and maxima in the δ13C benthic foraminiferal record suggests that the palaeoceanographic evolution of the eastern Mediterranean was well in phase with that of other ocean basins until at least the early Late Miocene, despite its increasing isolation due to the gradual closure of the Eurasian-Arabian Strait and progressive sea-level fall

(Table 2) Stratigraphic position of midpoints of reddish and beige layers of lithologic cycles in the Loulja-A Section and their astronomical ages after tuning to the ETP and Summer Insolation Curves of the La2004 solution

An integrated high-resolution stratigraphy and orbital tuning is presented for the Loulja sections located in the Bou Regreg area on the Atlantic side of Morocco. The sections constitute the upward continuation of the upper Messinian Ain el Beida section and contain a well-exposed, continuous record of the interval straddling the Miocene-Pliocene (M-P) boundary. The older Loulja-A section, which covers the interval from ~5.59 to 5.12 Ma, reveals a dominantly precession-controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the Mediterranean; the high-resolution and high-quality benthic isotope record allows us to trace the dominantly obliquity-controlled glacial history. Our results reveal that the M-P boundary coincides with a minor, partly precession-related shift to lighter "interglacial" values in d18O. This shift and hence the M-P boundary may not correlate with isotope stage TG5, as previously thought, but with an extra (weak) obliquity-controlled cycle between TG7 and TG5. Consequently, the M-P boundary and basal Pliocene flooding of the Mediterranean following the Messinian salinity crisis are not associated with a major deglaciation and glacio-eustatic sea level rise, indicating that other factors, such as tectonics, must have played a fundamental role. On the other hand, the onset of the Upper Evaporites in the Mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage TG12 and TG11, suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase. Finally, the Loulja-A section would represent an excellent auxiliary boundary stratotype for the M-P boundary as formally defined at the base of the Trubi marls in the Eraclea Minoa section on Sicily

Astronomical forcing of Northwest African climate and glacial history during the late Messinian (6.5-5.5 Ma)

High-resolution physical, chemical and biological-based climate proxies from the Ain el Beida (AEB) section in Atlantic Morocco reveal the imprint of the three main orbital parameters precession (19–23 kyr), obliquity (41 kyr) and eccentricity (95–125 and 400 kyr) between 6.5 and 5.5 million years before present (Ma). The precession-related variations are most prominently reflected in the color reflectance and chemical composition of the sediment, showing that precession minimum configurations lead to more humid climate conditions in Northwest Africa probably related to the Atlantic system, while more arid climate conditions prevailed during precession maxima. In addition, precession-bound changes in planktonic foraminifera and calcareous nannofossil assemblages indicate that sea surface temperature (SST) increased during the humid phases, while productivity conditions increased during the dry periods. The clear imprint of the short and long-term eccentricity cycles is explained by a non-linear climatic response to the precession forcing with overall more humid climate conditions during eccentricity maxima. The obliquity-controlled variations in SST and aridity conditions concur with glacial–interglacial variability that is conspicuously recorded in both planktonic and benthic δ18O records of AEB. The observed warm and wet climates during interglacial periods most likely reflect the direct ice driven thermal response to the reduced ice sheets and more active Atlantic depressions. Similar as during the Pliocene and Pleistocene, obliquity-controlled variations in the planktonic and benthic carbon isotope (δ13C) records of AEB are inversely related to the oxygen isotope records with more depleted values during glacial stages, although with a small lag. The close correspondence between the δ13C records of AEB and other open ocean sites (i.e., Sites 982 and 926) may therefore point to large-scale glacial-controlled variations in the deep-sea carbon reservoir. Superimposed on the orbital variations, the imprint of the – onset of the – Messinian Salinity Crisis can be traced by a marked ~ 1.0‰ negative excursion in planktonic δ13C at 6.0 Ma, followed by a prominent peak in Ti/Al at ~ 5.97 M

Revised astrochronology for the Ain el Beida section (Atlantic Morocco): No glacio-eustatic control for the onset of the Messinian Salinity Crisis

Glacio-eustatic sea level lowering has often been proposed as a key mechanism for explaining the onset of the Mediterranean evaporites during the Messinian Salinity Crisis (MSC). To examine the role of glacio-eustacy during the progressive isolation of the Mediterranean in more detail, we reinvestigated the Ain el Beida quarry section that is located at the Atlantic margin of Morocco and therefore free of destructive MSC-related complications. The section consists of deep marine, cyclically bedded (reddish/beige), silty marls of late Messinian age. The reddish layers reveal the same characteristic signals as found in the Mediterranean sapropels (Globigerinoides spp. maxima and δ¹⁸O minima), suggesting that they correspond to precession minima and, hence, (boreal) summer insolation maxima.We have established an integrated stratigraphy (calcareous plankton biostratigraphy, magnetostratigraphy, stable isotope stratigraphy and cyclostratigraphy) and an astronomical tuning of the Ain el Beida section by using conventional techniques and calibration methods. The astronomical ages for the biostratigraphic events and paleomagnetic reversals are in good agreement with the Mediterranean chronology, and confirm our cyclostratigraphic correlations. Stable isotope analyses reveal that the peak glacial stages TG22 and TG20 clearly post-date the initiation of the Messinian evaporites in the Mediterranean and that there is no evidence for a glacio-eustatic control for the onset of the MSC.Only the TG12-11 transition seems to correspond to a major intra-MSC event, i.e. the beginning of the Upper Evaporites. The typical Lago Mare facies of the Upper Evaporites was thus deposited during warmer climate conditions and associated higher global sealevel stands