Jacques Thorez

Smectite composition as a tracer of deep circulation: the case of the Northern North Atlantic

Abstract The link between smectite composition in sediments from the northern North Atlantic and Labrador Sea, and deep circulation is being further investigated through detailed studies of the X-ray pattern of smectites and cation saturations. This allows clear distinction of dominant terrigenous sources associated to the main components of the modern Western Boundary Undercurrent. Time variations of smectite characteristics in two piston cores from the inlet and outlet of the Western Boundary Undercurrent gyre in the Labrador Sea indicate: (1) a more southern circulation of North East Atlantic Deep Water during the Late Glacial; (2) a step by step transition to the modern pattern of deep circulation during the Late Glacial/Holocene transition, with intensification of North East Atlantic Deep Water and Davis Strait Overflow; (3) an expansion of Davis Strait Overflow and Labrador Sea Water circulation in relation to ice surges and deposition of detrital layers; (4) an intensified circulation of North East Atlantic Deep Water during the Younger Dryas; and (5) a very recent increased influence of Denmark Strait Overflow Water beginning between 4.4 and

The biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods (Late Devonian)

Abstract The earliest diversification of tetrapods is dated as Late Devonian based on 10 localities worldwide that have yielded bone remains. At least 18 different species are known from these localities. Their ages span the ‘middle’–late Frasnian to latest Famennian time interval, with three localities in the Frasnian, one at the F/F transition (though this one is not securely dated) and six in the Famennian. These localities encompass a wide variety of environments, from true marine conditions of the nearshore neritic province, to fluvial or lacustrine conditions. However, it does not seem possible to characterize a freshwater assemblage in the Upper Old Red Sandstone based upon vertebrates. Most of the tetrapod-bearing localities (8 of 10) were situated in the eastern part of Laurussia (=Euramerica), one in North China and one in eastern Gondwana (Australia), on a pre-Pangean configuration of the Earth, when most oceanic domains, except Palaeotethys and Panthalassa, had closed.

A depositional and diagenetic model for the Eocene Sulcis coal basin of SW Sardinia

Abstract Detailed sedimentological, mineralogical and petrographical analysis of closely spaced cored boreholes has enabled the development of a revised depositional model for the early Eocene coal-bearing Produttivo Formation of the Sulcis Basin. The deposition of autochthonous-hypautochthonous palustrine-lacustrine coals and associated carbonates was interrupted episodically by sedimentation of allochthonous lithocalcirudites and lithocalcarenites. The latter clastics display characteristic upward shoaling tidal flat sequences related to marine incursions. This interpretation is in contrast to the previously accepted fluvial origin of the detrital episodes. The coarse basal transgressive lag deposits consist of various carbonate intraclasts, dolosparite, grains consisting of calcite cement and euhedral-subhedral evaporite-bearing quartz grains. Combined stable isotope and cathodoluminiscence analysis has revealed a complex diagenetic history for the clastic deposits. The potential extrabasinal or intrabasinal provenance of the clasts, in particular the origin of the evaporite relicts, is discussed. The subtropical-tropical coastal marshes of the Florida Everglades (USA) are proposed as a possible modern analogue for the subbituminous Sulcis coals.

Climatic Indexes on the Basis of Sedimentation Parameters in Geological and Archaeological Section

The need for numerical parameters is a first requisite for mathematical evaluation of climatical evolution.