Uwagi o czwartorzędzie okolic Jeziora Żarnowieckiego

Abstract

REMARKS ON THE QUATERNARY DEPOSITS NEARBY THE ŻARNOWIEC LAKE Summary There is discussed some remarks on the Quaternary in the vicinity of the Żarnowieckie Lake. The discussed area, is placed in north Poland, about 50 km north-west from Gdańsk. In the neighborhood of Żarnowieckie Lake the bedrock of the Cainozoic complex is built of Cretaceous deposits. The top of Cretaceous layer is flat and there is at 95 -100 m b.s.1. However, this surface is situated lower where the Pleistocene erosion took place. Tertiary sediments are up to 200 m thick. Primary Tertiary surface after Miocene sedimentation reached is located probably at the altitude from 25 to 0 m b.s.l. Higher level surface were due to glaciotectonic elevation. Variations of the sub-Quaternary surface position is about 350 m. This surface is built mainly of Miocene, Oligocene and Eocene sediments. In the deeper depressions it's formed by Cretaceous, Jurassic and Triassic deposits too (e.g. Debek depression). The Debek depression is the place where it was noted the deepest occurrence of Quaternary sediments in Poland. According to S. Ostaficzuk (9) this depression has the eversion character. The valley of Żarnowieckie Lake had a complicated and multi stage genesis. The first stage was Pliocene erosion and probably the direction of this erosion was caused by tectonic processes. However, the scale of this process was small, the flat top of Cretaceous surface indicated it. During the Pleistocene this buried valley was changed by glacial exaration, subglacial erosion, glacial, fluvioglacial and warved accumulation processes and by pressure of advanced inland ice. Contemporary Pleistocene sediments are composed of 5 glacial layers at least. There were layers of glacial tills, fluvioglacial sands and gravels, varve silts and clays. Varved and fluvioglacial deposits are strongly contaminated with Tertiary quartz silts and mica. This substance was washed out from elevation of Quaternary substratum and glacial rafts. Pleistocene sediments, excluding youngest ones, are disturbed often by glaciotectonic processes in the form of small folds, micro faults and polished surfaces. Larger glaciotectonic structures folded the sediments of the Quaternary substratum too.