PÍSEČNÍK U JAVORNÍKU – DRUMLIN SE ZACHOVALOU SUKCESÍ SUBGLACIÁLNÍCH A SUPRAGLACIÁLNÍCH SEDIMENTŮ

Abstract

Písečník Hill (288 m a. s. l.) is an isolated elevation located near the Javorník town close to the NE foothill of the main ridge of the Rychleby Mts. (Eastern Sudetes). It has a shape of a ridge elongated in the SE–NW direction, made of compacted Miocene sands covered by Pleistocene tills and glaciofl uvial sediments. These glacial sediments have been deposited during the Elsterian glaciation (MIS 12) according to the Northern European stratigraphical scale. The presented study is targeted on glacial deposits and the interpretation of the evolution of the Písečník Hill linked to continental glaciation. Facies description has been supplemented by petrographical analyses of the gravel fraction 16–64 mm. The glacial sequence is composed of five members. The first one is a lodgement till (Jk1) with a basal boulder lag, which followed the erosional phase producing elongated scours. Glacitectonic features, such as plucking of underlying Miocene sands and formation of rip-up clasts could be seen in the lodgement till unit. Boulder lag with boulders up to 2 m long originated by blocking of large clasts in compact, plastic, unlithifi ed basement. The second member (Jk2) is a massive to weakly stratifi ed gravely sand, which filled a shallow depression in the lodgement till. These sediments originated by reworking of underlying till material. Members Jk1–Jk2 have been deposited in subglacial environment. Both members are equivalent from the viewpoint of petrological composition – they both contain predominantly local Gierałtow gneiss. The third member (Jk3) is a coarse grained to bouldery gravel. The fourth member (Jk4) is made of a fi ne layer of laminated sand. The last member (Jk5) is a sandy gravel with gently sloping flat clasts. Members Jk3–Jk5 are interpreted as supraglacial sediments deposited with the ice-cored moraine environment. They are rather polymictic from petrological point of view, as they contain material of diverse provenance originating from different parts of the glacier. The clasts are also more variable in roundness with higher content of rounded to well-rounded clasts (“englacial egg gravel facies”). The Písečník Hill represents a drumlin with a core composed of plastic Miocene sand. Features described in the glacial sequence show on the active glacial movement (in subglacial environment), as well as the subsequent decay starting from the ice-cored moraine to the final disappearance of the dead-ice moraine. The drumlin orientation documents the ice sheet advance from the NE.