Pierre Saint-Marc

Late exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappes

New thermochronological and structural studies were conducted to quantify the cooling and late exhumation histories of the Internal Zone of the western Betic Cordilleras. The study was carried out in the Ojen-Marbella region where the Ojen and Los Reales nappes of the Alpujarride Complex outcrop. 40Ar39Ar single-grain analyses of muscovite and biotite display plateau ages of 19 Ma, on the same rocks. Apatite fission-track datings give ages of 18-16 Ma for the last step of cooling below 110°C, and confined track measurements indicate a very rapid cooling between 110° and <60°C. The combination of both data suggests a fast cooling phase at 19-16 Ma with a gradient higher than 100°C/Ma between 500 ± 50°C and <60°C. This fast cooling was associated with extensional tectonics accommodating thinning of the metamorphic alpine-type pile of nappes. The exhumation rate ranges from 1 to 3 km/Ma during the 19-18 Ma interval and is close to 1 km/Ma in the 18-16 Ma interval. Moreover an uplift of the Ojen and Los Reales units began after the Early Pliocene (5 Ma). The sediments sealing the strike-slip contact forming the boundary between the Alpujarride Complex and the Neomumidian Formation of Early Miocene age contain Early Pliocene planktonic formainiferal assemblages (Zone N18). Benthic formainiferal assemblages of these sediments, actually outcropping at 150 m above sea level, indicate a deposition in the upper bathyal zone ranging from 200 to 600 m water depth. Our conclusions confirm and precise the exhumation processes during the 19 to 16 Ma interval, and uplift of the Internal Zones since 5 Ma.

Continental block collision in the eastern arm of Sulawesi (Indonesia). Structure and geodynamic interpretation

Abstract Recent investigations in East Indonesia lead us to consider the eastern arm of Sulawesi as the result of a collision between two continental blocks: the Tokala block to the west and the Banggai–Sula block to the east. The Tokala block results from the Oligocene obduction of an ophiolitic Asiatic basin onto the passive margin of a Gondwanian block (Banda block), with collision with the Asiatic active margin (western arm of Sulawesi) near the end of the Oligocene or at the beginning of the Miocene. The Tokala Block was then collided by the Irian Jaya derived Banggai–Sula block in the Early to Middle Pliocene times or later.

Stratigraphic succession of the Australian margin between Kai and Aru islands (Arafura Sea, eastern Indonesia) interpreted from Banda Sea II cruise dredge samples

Abstract A fairly complete sedimentary succession (3000–4000 m thick) off the Australian margin east of Kai Besar island (Arafura Sea) is documented from micropalaeontological analysis of samples from eight dredges collected during the Banda Sea II cruise on board Baruna Jaya III. Sediments indicate shelf environment, with siliciclastic probably Late Carboniferous-Early Permian sediments, Jurassic-Cretaceous black shales, open-marine pelagic sediments from Late Albian to Mid-Late Eocene age and shallow water platform carbonate deposited during Early Miocene. From Late Miocene to Holocene times pelagic sediments were deposited. Because samples were dredged, stratigraphic gaps in the succession can only be inferred, but the general sedimentary sequence is similar to that of surrounding areas in the Arafura Sea, as known from exploratory wells.

Cretaceous of eastern and southeastern Sulawesi (Indonesia): new micropaleontological and biostratigraphical data

Abstract New field-data has led to the identification of outcrops of pelagic carbonates with planktonic foraminifera and calcareous nanoplankton of Albian and Campanian-Maastrichtian age in strongly tectonized areas in eastern and southeastern Sulawesi. Most species are described for the first time from this region. The new information indicates no major difference in the facies of the eastern and southeastern arms of Sulawesi. Rather similar facies are also recorded in numerous places in eastern Indonesia and in the distal Australian shelf during Late Cretaceous times.

Biostratigraphy and paleoenvironment of foraminiferal assemblages from neogene and quarternary deep-sea sediments collected during the nautimate cruise (Pacific Ocean, off Mexico, 18°N-21°N). Geodynamic implications

Abstract Deep-sea dives with the submersible Nautile allow to reconstruct the lithostratigraphic series, and to collect samples of plutonic rocks and sediments along the inner wall of the Acapulco trench, off Mexico (Manzanillo area, 18°N-19°N, Pacific Ocean). Plutonic rocks are unconformably overlain by brown and grey sandstones and siltstones, constituting a continuous sequence of sediments, several hundreds meters thick. Assemblages of planktonic foraminifera give a late Miocene-early Pliocene age for the lowest part of the sedimentary sequence. Benthic foraminifera indicate that the minimum depth of deposition was located into the middle bathyal zone. Characteristic species are the following: Bolivina foraminata, Bulimina mexicana, Galliherina avigerinaformis, Gyroidina healdi, Hansenisca rotundimargo, Nodogenerina lepidula, Parafrondicularia miocenica, Fontbotia wuellerstorfi, Plectofrondicularia californica, Protoglobobulimina pseudotorta, Pyrgo murrhina, Siphonodosaria advena. These assemblages are dominated by endofaunic species (bolivinids, buliminids, uvigerinids and cassidulinids) and oxygen-minimum zone indicators (Buliminella subfusiformis, Epistominella smithi, Uvigerina subperegrina). These late Miocene-early Pliocene sediments were probably deposited into the oxygen-minimum zone, at the boundary between the lower and upper parts of the middle bathyal zone, corresponding approximately to a depth of 1000 m. Their present position (between 2500 and 4000 m) reveals a strong and rapid subsidence of this area (between 1500 and 3000 m) since the early Pliocene. These stratigraphic and paleoenvironmental results indicate the importance of these stepwise downward movements of this zone since Eocene. An additional study of late Miocene-Quarternary foraminiferal sediments collected during deep-sea dives conducted to the North (South of Tres Marias Islands, 20°N-21°N) gives complementary data on the stratigraphy and paleoenvironment of these deposits. It completes the understanding of the complex geodynamic history affecting the western boundary of the North America plate.