ELSEVIER Tectonophysics 263 (1996) 235-248 TECTONOPHYSICS Paleostress characterization of the "Wallachian phase" in its type area(southeastern Carpathians, Romania) J.-C. Hippolyte a,*, M. Sandulescu b Tectonique Quantitatil~e, CNRS URA 1759, T26-E1, Case 129, Uni~,ersit~ P. et M. Curie, 4 Place Jussieu, 75252 Paris, France b Romanian Geological Institute, Str. Caransebes 1, Sector 1, 78344 Bucharest, Romania Received 15 May 1995 Abstract The "Wallachian phase" is defined in the East Carpathians, a convex to the east mountain belt in Romania, as a tectonic event occurring between Pliocene and Quaternary times. This event formed folds and minor thrusts, structures that are usually located in internal parts of the somewhat older fold-and-thrust belt structure. This location contrasts with the location one would predict from their recent age, and contrasts with the older, Cretaceous-middle Tortonian, piggyback thrust mode of propagation. In the southeastern Carpathians, this late overstep sequence of thrusting resulted from a modification in the stress field. Our data indicate that the direction of compression changed from NW-SE to N-S during middle-Tortonian time. This is further supported by stratigraphic dating of structures, and thereby paleostresses, indicating that the Wallachian episode was not a brief event at the Pliocene-Quaternary boundary, but lasted from middle Tortonian to early Pleistocene. 1. Introduction The Carpathian chain is an Alpine fold-and-thrust belt forming a convex to the east arc, extending in central Europe between the Alps to the west and the Balkans to the southeast (Fig. 1). It wraps around the Pannonian and the Transylvanian Basins. Two seg- ments of this belt cross Romania: the South Carpa- thians and the East Carpathians (Fig. 1). They formed from late Cretaceous to Quaternary, reflecting short- ening between the Fore-Apulian block and Europe. Two principal compressional periods are recognized in the fold-and-thrust belt, the Dacidian (late Creta- * Corresponding author ceous) and the Moldavian (Miocene) periods (Sandulescu, 1980). Most models of the Carpathian Pannonian region consider that the Neogene compressional deforma- tion of the Carpathians is an accommodation of the coeval extension and strike-slip displacement in the Pannonian Basin (Horvfith and Royden, 1981; Kovfics, 1982; Balla, 1985). According to Sand- ulescu (1980), the structures of the Carpathian belt also reflect differential block movements in the fore- land (Fig. 1) since late-Cretaceous time. Determina- tion of the paleostresses in the inner basins, in the fold-and-thrust belt and in its foreland, is an impor- tant objective since it may reveal the connections between the tectonic processes in these different structural areas. 0040-1951/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S0040- 195 1(96)0004 1-8