Marie-Christine Janin

Le Miocène du bassin de Saint-Florent(Corse): Modalités de la transgression du Burdigalien supérieur et mise en évidence du Serravallien

The Miocene series of Corsica deposited after the anti clockwise rotation of the Corsica-Sardinia block,between 18 and 21 Ma (Rehault 1981; Rehault et al. 1984). The study of the Saint-Florent basin (NW corsica) allows to document the conditions of the Miocene transgression and the evolution of the basin. The Saint-Florent sedimentary serie consist of 3 marine formations lying between 2 continental ones. At the base, the continental formation of Fium Albino (150 m) in the northern part of the basin, stratigraphically lies on the Upper Nebbio alpine nappe. It consists of well stratified, red, colluvial deposits from local origin, with interbedded palaeosoils remains. We have very few paleontological evidences, however from geometrical evidence, these series are clearly post nappe and ante Upper Burdigalian. This formation is described here for the first time. At the upper part, the continental formation of Saint-Florent, characterized by well rounded pebbles of rhyolites, lies with an erosional surface truncating different terms of the marine series. It is probably of Lower Tortonian age. The 3 lithostratgraphic units of the marine series are, from the base to the top: the Torra formation (50 m) is characterized by coastal deposits (conglomerate, siltstone, sandstone layers, with debris of oyster, sands with scutella) with sparse micro-fauna and - flora, suggesting an Upper Burdigalian (upper N7/lower N8 Blows zones); the Monte San Angelo Formation (250 m) is a white calcarenite with rhodophytes, its different components - fine and coarse terrigenous detritus, benthic or planktonic bioclasts-having built hydraulic dunes under the action of varying currents in a low water environment. Planktonic foraminifera - rich levels indicate a Langhian age (from N8 to the upper part of the N9 Blows zones); the Farinole Formation (100 m), described here for the first time, is observed only in the northern part of the basin. It consists of marls and clayey sandstones deposited in circalittoral environment. Rich microfauna of benthic and planktonic foraminifera, and rich calcareous nannoplankton evidence the Serravallian (NN7-NN6, Martinis zones). To the east, the basin is limited by a meridian normal fault. On the one hand, synsedimentary deformations in the Torra formation and in the lower part of the Monte San Angelo Formation are located to the north of the basin near the fault. On the other hand, thick subtidal environment deposits of the Torra Formation occure in a shallow water. Thus the subsidence of this Formation is probably controled by the syn-sedimentary activity of the meridian normal fault. Extensional fractures indicating a NE-SW direction of extension.

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.

Geology and geochemistry of a 800 m section through young upper oceanic crust in the North Fiji Basin (Southwest Pacific)

Lagabrielle, Y., Auzende, J.-M., Eissen, J.-P., Janin, M.-C. and Cotten, J., 1994. Geology and geochemistry of a 800 m section through young upper oceanic crust in the North Fiji Basin (Southwest Pacific). In: J.-M. Auzende and T. Urabe (Editors), North Fiji Basin: STARMER French-Japanese Program. Mar. Geol., 116: 113-132. We report the results of geological and structural observations made during one dive of the French submersible Nautile during the STARMER Cruise in 1989 in the vicinity of the 16”40’S triple junction in the North Fiji Basin. This dive provided a spectacular, 800 m continuous section of oceanic crust exposed along the northern wall of a 3000 m deep basin at the eastern branch of the triple junction. A number of volcanic facies have been encountered including massive and pillowed lavas, sheeted dikes and spectacular columnar-jointed massive lavas. Pillowed lavas have been observed only at the base and at the top of the section. The ratio between massive and pillowed basalts is high suggesting that the crust in this area grew mostly during a stage of high eruptive rate. Dikes have been observed in the middle part of the section. They probably do not represent the top of a classical “dike complex” but an isolated set of sheeted dikes, possibly the feeders of overlying flows. The abundance of vertical tectonic breccias observed during the first part of the dive confirms that the basal part of the wall can be regarded as a major tectonic boundary along which occurred significant vertical and strike-slip motions. Micropaleontological data from sedimentary rocks collected during the dive bring new constraints to the evolution of the triple junction. The oceanic crust in the surveyed area is at least as old as 1.9-1.3 Ma, based on the age of sedimentary rocks collected in talus at the base of the wall and observed at the summit of the section. The collected basalts include (1) N-type MORBs, (2) E-type MORBs and (3) BABBs. This emphasizes the heterogeneous nature of the mantle beneath the central NFB. Some portions of the depleted mantle underlying the central NFB triple junction area have recorded contamination from melts or fluids from an ancient subduction zone (probably .the New Hebrides during the opening of the NFB), whereas adjacent mantle areas show the influence from an alkali-enriched source. Such alkali-enriched characters are reported from recent basalts of the northern NFB (South-Pandora ridge-Rotuma island).

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.