5 research outputs found
The very high alluvial formation of early Pleistocene age in the Creuse River Valley at Eguzon (Indre) : cryoturbation patterns, préhistorique occupation sites and absolute dating
Malgré des conditions de prospections difficiles, de nombreux témoins des nappes alluviales de la vallée de
la Creuse ont Ă©tĂ© reconnus dans la rĂ©gion dâEguzon, sur la bordure nord, trĂšs bocagĂšre, du Massif central. Ceux de la
trĂšs haute nappe alluviale situĂ©s entre 90 et 110 m dâaltitude relative ont Ă©tĂ© les mieux prĂ©servĂ©s, certains atteignant jusquâĂ
15 m dâĂ©paisseur
A « Pont-de-Lavaud », un cailloutis fluviatile occupant une dĂ©pression du socle cristallophyllien altĂ©rĂ©, Ă
mi-pente du versant ouest dâun interfluve, a Ă©tĂ© conservĂ© sur une faible Ă©paisseur. Des fouilles ont Ă©tĂ© effectuĂ©es entre
1983 et 1995 et ont mis en évidence, dans la partie supérieure du sédiment, dans un état de conservation exceptionnel,
des habitats préhistoriques riches en industries archaïques sur quartz du trÚs ancien Paléolithique et au-dessous, des figures
cryogĂ©niques de types divers (cercles de pierres, structures polygonales, injections dâaltĂ©rites du substratâŠ) ainsi
quâune industrie de mĂȘme typologie mais dispersĂ©e et moins abondante.
Les Ă©tudes gĂ©ologiques entreprises sur le site et Ă lâĂ©chelle rĂ©gionale permettent de rattacher cet ensemble Ă la
base de la trĂšs haute nappe de 90-110 m, sa position actuelle sâexpliquant par le basculement Ă une date rĂ©cente dâun
bloc faillé du substratum. Les mesures de datations absolues effectuées par la méthode de résonance paramagnétique
électronique (R.P.E.) sur les témoins les mieux conservés de la trÚs haute nappe donnent à celle-ci un ùge de 1 à 1,2 million
dâannĂ©es. Celles obtenues sur les vestiges de la base et sur le site lui-mĂȘme sont comprises entre 0,9 et 1 million
dâannĂ©es, diffĂ©rence attribuĂ©e Ă leur forte pĂ©dogenĂšse. Ces rĂ©sultats confirment lâappartenance de ce niveau alluvial Ă la
derniÚre partie du PléistocÚne inférieur et permettent de classer les habitats de « Pont-de-Lavaud » parmi les plus anciens
dâEurope actuellement connus
Late Triassic (Carnian) corals from Timor-Leste (East Timor): their identity, setting, and biogeography
Late ArtinskianâEarly Kungurian (Early Permian) warming and maximum marine flooding in the East Gondwana interior rift, Timor and Western Australia, and comparisons across East Gondwana
© 2016Substantial new information is presented on upper ArtinskianâKungurian deposits in Timor-Leste and in the Canning, Southern Carnarvon and northern Perth basins of Western Australia. These basins, situated between about 35°S and 55°S palaeolatitude, formed part of the East Gondwana interior rift, a precursor to the rift that 100 my later formed the Indian Ocean in this region. Timor lay near the main axis of the East Gondwana interior rift, whereas the Western Australian basins were marginal splays from the rift axis. The main depocentres developed as a result of faulting that was initiated during the Late Pennsylvanian. Detailed lithostratigraphic and biostratigraphic analyses have been made on the newly recognized Bua-bai limestone and the type Cribas Group in Timor, the Noonkanbah Formation in the Canning Basin, the Byro Group in the Merlinleigh Sub-basin of the Southern Carnarvon Basin, and the Carynginia Formation in the northern Perth Basin. In Timor the succession, which is highly disrupted by faulting, was deposited under open-marine conditions probably in a shelfâbasin setting. Restricted, very shallow-water seas flooded the Canning Basin and the MerlinleighâByroâIrwin sub-basins of the Southern Carnarvon and northern Perth basins and had highly variable oxygen levels and salinities typical of estuarine environments. A similar pattern of warming and bathymetric change is recognized in all studied basins. During the early part of the late Artinskian cool conditions prevailed, with water temperatures 0â4 °C forming sea ice in the MerlinleighâByroâIrwin rift. Rapid warming during the latter part of the late Artinskian was accompanied by maximum marine flooding close to the ArtinskianâKungurian boundary. Climatic and bathymetric conditions then allowed carbonate mounds, with larger fusulines and a variety of algae, to develop in the northern part of the rift system, and Tubiphytes, conodonts, and brachiopods with Tethyan affinities to migrate into the marginal-rift basins despite the generally adverse water quality at these depositional sites. Comparison between the stratigraphic record from the East Gondwana interior rift and coeval records from Lhasa and Sibumasu indicate a similar pattern of climate change during the Carboniferous to end Cisuralian. Similar trends probably are present in Eastern Australia although there is confusion over the correlation of some units