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La méthode de datation IRSL sur feldspaths alcalins (40-60 mm) est appliquée aux loess du Pléistocène supérieur et moyen récent (< 300 ka) de deux séquences loessiques du sud-est de la Roumanie, à Mircea Voda et à Mostistea, dans la continuité des datations IRSL réalisées à Tuzla dans la même région (Balescu et al., 2003). L'ensemble des âges IRSL obtenus, corrigés pour le fading, confirme que les loess L1, L2 et L3 se sont mis en place dans le sud-est de la Roumanie au cours des trois derniers cycles glaciaires du Pléistocène (MIS 2 à 4, MIS 6, MIS 8) et que le sol du Dernier Interglaciaire dont la position stratigraphique était controversée, correspond au pédocomplexe S1. Ces résultats impliquent la validité d'une chronologie longue au détriment d'une chronologie courte dans laquelle les pédocomplexes S1 et S2 étaient attribués au Dernier Glaciaire (Conea, 1969). Cela amène donc à reconsidérer la chronologie des occupations de plein air du Paléolithique moyen de la Roumanie qui jusqu'à présent, a été limitée au dernier cycle glaciaire. Enfin, ces résultats IRSL confirment que le début de la sécheresse en contexte interglaciaire dans le sud-est de la Roumanie, attesté par l'apparition du premier pédocomplexe steppique de type chernozem (S2) au sein des séquences loessiques, remonte au MIS 7.

ABSTRACT:Popa, L., Panaiotu, C.E. and Grădinaru, E. 2014. An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis. Acta Geologica Polonica, 64 (2), 189-206. Warszawa.A well-developed Triassic carbonate platform is exposed in the eastern part of the Tulcea Unit, in the Cimmerian North Dobrogean Orogen, southeastern Romania. Facies analysis of the 200 m thick succession of lower Middle Anisian limestones exposed in a large limestone quarry south of the village of Mahmudia suggests a transition from upper slope towards toe-of-slope carbonate facies, reflecting sea-level fluctuations and tectonic tilting. The slope is dominated by in situ microbialites in the upper portion, consisting of reefal boundstone facies, and by molluscan coquina and cement boundstones. A key role is played by the cosmopolitan micro-encruster Tubiphytes, which became common in the aftermath of the mass extinction at the Permian/Triassic boundary, and by autochthonous micrite and synsedimentary marine cement. The absence of metazoan reef builders, such as sponges and corals, reflects the fact that microbes were the first organisms to recover after the Permian/Triassic crisis under unusual marine conditions and that their main role in reef formation was sediment stabilization along the upper slopes. The lower slope is mostly detrital, being dominated by platform-derived bioclastic rudstones and crinoidal floatstones, which are interbedded with basinal carbonate hemipelagics. The toe-of-slope is composed of pelagic wackestones framed by thin tongues of intraclast breccia. All these observations are in agreement with the slopeshedding model described for the Pennsylvanian microbial margin in Asturias (northern Spain) and the AnisianLadinian flat-topped, steep-rimmed Latemar platform (Dolomites, Italy).As most of the Anisian reefs were described from western and eastern Tethys (Southern Alps, Hungary, China), the occurrence of the early Middle Anisian Tubiphytes-reef from North Dobrogea (Romania) contributes to resolving the puzzle of the geographic distribution of reef recovery in the Middle Triassic.

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