Martin Hanáček

Sedimentary petrological characteristics of lateral and frontal moraine and proglacial glaciofluvial sediments of Bertilbreen, Central Svalbard

Clast petrology, shape, roundness and striation were studied in various types of glacial deposits of Bertilbreen in central Svalbard. Difference between the upper part of lateral moraine and the lower part of lateral and frontal moraine (latero-frontal zone near the ice margin) was determined. The upper part of lateral moraine contains mostly very angular to subangular clasts of blade and icometric shapes without striation traces. Clasts in lower part of lateral moraine and in frontal moraine are mostly subangular and subrounded with isometric shapes. 30–50% of these clasts are striated. Types of source sediments and available bedrock outcrops affect the nature of proglacial glaciolfuvial braidstream sediments. Clast surface striation is preserved. A braided outwash fan formed in the distal part of the braidstream. The clast nature here is affected by the dynamic of the glaciofluvial transport, thus subrounded clasts predominates. Striation is not preserved on clast surfaces here.

New methods to reconstruct clast transport history in differentglacial sedimentary environments: Case study for Old Redsandstone clasts from polythermal Horbyebreen and Bertilbreenvalley glaciers, Central Svalbard

The objective of this study were Little Ice Age (LIA) to recent subglacial tills, glaciofluvial sediments of proglacial sandur, esker sediments and sediments of moraine-mound complexes of Horbyebreen polythermal valley glacier and LIA to recent sediments of lateral moraine, frontal moraine, ice-cored moraine and glaciofluvial sediments of proglacial sandur of Bertilbreen polythermal valley glacier. Fossil (probably early Holocene) subglacial and supraglacial tills and sediments of coarsegrained glaciomarginal delta of Bertilbreen have also been studied. The research focused on Old Red sandstone clasts, for which roundness, shape and striation presence have been investigated. The results from this research led to the proposal of new methodological approaches. It is mainly the covariant plot of striations and RA (the share of striated clasts versus the share of very angular and angular clasts), which effectively differentiate subglacial tills from glaciofluvial sediments and allows for identification of the source material of moraine-mound complexes, especially the oldest, more degraded parts near the maximum LIA glacier extent. The second is the covariant plot of distance and RS index (the distance from the starting point versus the share of subangular and subrounded clasts) to present downstream roundness trends in proglacial glaciofluvial sediments. The research confirmed the crucial role of lithological properties of thinly bedded rocks on the shape of these rock clasts in sediment and a minimum impact of passive and active transport on the clast shape modification.

VÝZNAM VALOUNOVÝCH ANALÝZ LEDOVCOVÝCH SEDIMENTŮ PRO PALEOGEOGRAFICKÉ REKONSTRUKCE PLEISTOCENNÍHO KONTINENTÁLNÍHO ZALEDNĚNÍ JESENICKA

Sediments of Middle Pleistocene continental glaciation at the northern foothill of Rychleby Mts. and Zlate Hory Highland contain clasts of local to Nordic provenance. Local clasts originating from crystalline units of the above-mentioned mountains prevail. These clasts have palaeogeographical importance for a local reconstruction of ice sheet advance directions. General advance direction from NW to SE has been reconstructed basing on local clasts in earlier studies (mainly Gaba 1981a, b; Gaba – Pek 1999). This interpretation has been based on the fact that the shares of clasts of rocks cropping primarily in NW part of the Rychleby Mts. decrease towards the SE. New, in this contribution presented, interpretation reconstructs the ice sheet advance generally from the North to the South, with variations conditioned by local landscape. Glacial sediments have at each site in the NW–SE direction petrological composition, which corresponds to the lithology of a mountain part south of the site of concern. Gieraltow orthogneiss clasts predominate in glacial deposits of the NW part of the main ridge forefield of Rychleby Mts. The share of amphibolites rises significantly in the forefield of the central part of the Rychleby Mts. main ridge. Feldspar and muscovite quartzites dominate in the area of Sokol Ridge and Zlate Hory Highlands. The new interpretation presumes the colluvial, alluvial and fluvial transport of the debris towards the northern and north-eastern mountain forefi eld before the ice sheet advance. Ice sheet advancing from the North eroded and transported this debris towards the South. Preglacial sediments corresponded petrologically to the mountain parts, from which they originated. Thus, glacial sediments have petrological composition, which corresponds to the lithology of those mountain parts, which lies south of the sediment occurrence. Part of the debris has been transported by Nisa Klodzka River from the West towards the East already before the glaciation. The following pattern could be found in the petrological composition of the glacial sediments gravel fraction. Sediments with monotonous composition of local clasts contain low shares of Nordic and Poland clasts (~2–4 %). On the contrary, sediments with polymict composition of local clasts contain relatively high shares of Nordic and Poland clasts (up to 27 %). Monotonous and distant provenance poor sediments originated at places, where the source preglacial deposits must have been petrologically monotonous considering the lithology of source areas. Concurrently, morphologically conditioned preglacial accumulation of vast lithologically monotonous deposits took place at some places (proximal parts of mountain ridges and saddles foothill). Rather polymict and distant provenance clast rich sediments originated during the later phase of ice sheet decay. Debris from the whole ice sheet body, not only from the glacier base or its front, released to the depositional system at that time. Sites with these sediments are located beyond the mountain foothill, where mixing of debris originating from alluvial fans or rivers flowing form the mountain range took place. Petrologically by far more monotonous sediments have been deposited closer to the mountain foothill. Quartz clasts are mostly of local origin and have together with other clasts been part of preglacial sediments. Part of quartz clasts has been reworked from fluvial deposits of present Poland or they might originate from the Nordic areas.

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

Pisecnik Hill (288 m a. s. l.) is an isolated elevation located near the Javornik 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 Pisecnik 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 Gieraltow 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 Pisecnik 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.

GLACIFLUVIÁLNÍ VÝPLAVOVÁ PLOŠINA U KOLNOVIC A JEJÍ SROVNÁNÍ S TERMINOGLACIÁLNÍMI KUŽELY MEZI SOKOLSKÝM HŘBETEM A ZLATOHORSKOU VRCHOVINOU U JESENÍKU

Glaciofluvial sediments at Kolnovice originated on an outwash plain running along the ice sheet front. Its material is variable from petrographical and provenance point of view, as it was deposited from various parts of a wide ice sheet front. This contrasts with petrologically monotonous deposits of terminoglacial fans in this area (Pisecna and Javorna sites), which originate from one marginal lobe of the ice sheet. In addition, the material in terminoglacial fans comes from the direct surroundings of the sites having been transported only a short distance.