Sub-Quaternary depression in the Lower Narew Region, its age and origin

Abstract

A depression in the sub-Quaternary surface, demarcated by Ostrołęka, Ostrów Mazowiecka and Chorzele, reaches in its bottom 80-120 m b.s.l. and possesses also a branch of the same depth. In the Quaternary substrate there are rocks of the Upper Cretaceous, Palaeogene and Neogene. A significant role for an explanation of the origin of the sub-Quaternary depression is played by a site of fluvial-lake Eopleistocene deposits at Opaleniec near Chorzele. It proves that already during the earliest Quaternary, a well developed fluvial pattern existed in this area and was probably dependent on tectonic foundations. Deep valleys of that time initiated a system of depressions, modified then during the whole Pleistocene. A sub-Quaternary surface is there now a polygenetic surface, developed mainly due to repeated processes of glacial and fluvial erosion. Ice sheet produced deformations played a secondary role in modelling a depression. Glaciotectonic processes were marked particularly at its western and southwestern margins, opposing in general the ice sheet movements.