Glacifluviálně-glacilakustrinní sekvence u Vidnavy na severním okraji Žulovské pahorkatiny

Abstract

Glaciofluvial and glaciolacustrine sediments were discovered in a small sandpit situated 800 m SE from Vindava (the Polský kopec Site). Sediments fill two channels located in superposition. Three facies associations (FA) were distinguished in this sedimentary section. The base of the lower channel is formed by gravel lag overlain by gravel-sandy sediments of 3-D dunes and a side bar (FA1). The upper channel infill begins also by basal lag and grades to a fining-upwards sequence from sand to silt (FA2). The sequence is formed from the base up by sediments of small 3-D dunes, A-type ripples, B-type ripples, C-type ripples, and horizontally laminated sediments. The sequence reveals a vertical transition from glaciofluvial (sand) to glaciolacustrine (silt) sedimentation. The sedimentary section is terminated by flat glaciofluvial bedforms (FA3) deposited under upper plane bed conditions. These bedforms arose after the restoration of glaciofluvial conditions. The base of the glaciolacustrine sequence is located at an altitude of ~ 275 m as well as the Old Kaolin Mine Site (850 m SW from the Polský kopec Site) where very similar sediments have been already described. The sediments of both localities represent a proglacial outwash plain in front of the retreating ice sheet (FA1 consists of ~ 23% of erratic rocks), where a relatively large lake, or a system of smaller lakes evolved at the same time.