The Przemyśl sigmoid and possibilities of hydrocarbon exploration

Abstract

The Flysch Carpathians drastically bend from the southeastern to southern direction in the Przemyśl region, and then at Dobromil take the southeastern direction again (Fig. 1). This sharp bend is called the Przemyśl sigmoid and results from the topography of deep Precambrian basement (J. Kusmierek, R. Ney, 1988). A fold-block structure of the basement has recently been examined by seismic survey and boreholes (Figs. 2-5). The consolidated basement rises from the east towards north-west from a depth of 10000-12000 m south of Dolina, up to about 3000 m in the vicinity of Przemyśl and 600 m near Leżajsk. Its southern flank plunges to the south in a stepwise arrangement. The basement blocks are the obstacle to the thrusting Carpathian orogen which accomodated against the shape of the basement. The marginal Carpathians along with the Borislav-Pokutse unit and the Lower Miocene deposits form a common orogen extending from Borislav towards both the east and west (K. Tolwinski, 1937). Possibilities of western extension of the unit into the. area of Poland in the vicinity of Przemyśl and some aspects of the occurrence of Miocene deposits and, perhaps, deep folds south of Przemyśl, are discussed here. These problems are related to hydrocarbon accumulation.