Rola kompakcji w ocenie mobilności neotektonicznej pogórzy karpackich

Abstract

COMPACTION OF MIOCENE MOLASSES AND NEOTECTONIC MOBILITY OF THE POLISH CARPATHIAN FOOTHILLS Summary In marginal part of the Polish Carpathians there occur predominantly clay-sandy autochthonous Miocene molasses, mostly Badenian-Sarmatian in age, that underlie overthrust flysch nappes. The thickness of these molasses is up to 2000 m (Figs. 1, 3). Examination of acoustic logs of some 200 drillholes made it possible to estimate the changeable porosity of deposits in question. The relationship between porosity and depth follows an exponential trend (Fig. 2), representing the so-called normal trend of compaction (cf. 7). Overburden of Miocene molasses by 200 m to 7,000 m thick flysch nappes (Fig. 4) resulted in intensive compaction of the former, ranging from 0 to ca. 400 m (Figs. 5, 6). The greatest compaction characterizes eastern part of the Carpathian Foothills (Fig. 6), more specifically the Dynów Foothills (150 - 300 m). Zones showing increased compaction values coincide, to a large extent, with neotectonic structures inferred from residual base level maps of different orders (cf. 17). The low-compaction areas are confined to neotectonic elevations (Figs. 6, 7). Increased subsidence east of the Dunajec River valley (Figs. 6, 7), induced by large thicknesses of molasse series and, hence, increased compaction rates, explains the lack of positive differences among base-Ievel surfaces in this region. The influence of compaction upon shaping of morphostructures in the West Outer Carpathians is negligible as compared to that in the East Carpathians. The Late Miocene through Quaternary mobility of blocks in the platform basement of the East Carpathians seems to have been compensated and partly suppressed by large thicknesses of Miocene molasses. These processes have also found their reflection in near-surface structure of the flysch cover.