Wyniki wyszukiwania - BazTech

1

Provenance of quartz debris in the Central Western Carpathians at the end of the Triassic, as indicated by cathodoluminescence colours

Vďačný Marek, Michalík Josef

Acta Geologica Polonica

|

2023

|

Vol. 73, no. 1

103--114

EN

Lithic fragments including quartz grains occur infrequently in the shallow-marine limestone sequence of the Fatra Formation deposited in the tensional intra-shelf depression of the Central Western Carpathians during the Rhaetian. Nevertheless, their study can bring data answering questions of sources, palaeogeodynamic arrangement, and processes at the end of the Triassic. In this study, we examined optically the cathodoluminescence (CL) colours of single quartz grains from the Kardolína section (Tatra Mts, Slovakia). These colours reveal a dominance of grains derived from regionally metamorphosed and plutonic rocks. Grains of hydrothermal and pegmatite origin are less frequent. Some of the quartz grains show recycled cement rims suggesting at least a second cycle origin. This sedimentary basin was situated near to the passive margin formed by the Variscan consolidated terrains of the Vindelician Highlands. Our study of the CL colours of quartz grains contributes to the elucidation of the nature of the rocks of the vanished Vindelician mountain belt.

2

An aeolian or a glaciolacustrine record? A case study from Mieļupīte, Middle Gauja Lowland, northeast Latvia

Nartišs M., Kalińska-Nartiša E.

Geologos

|

2017

|

Vol. 23, No. 1

15--28

EN

In the Middle Gauja Lowland, northeast Latvia, dunes are distributed over a vast glaciolacustrine plain that formed during the retreat of the Fennoscandian ice sheet. Such a direct contact between aeolian and glaciolacustrine sediments can be used to infer depositional settings and decipher to what extent these sediments bear an aeolian component. Our proxies, although preliminary, reveal a limited range of variation in grain-size parameters, a significant presence of quartz grains with silica precipitation and matt-surface grains of various rounding degrees and massive structure combined with horizontal lamination. These are indicative of periglacial-aeolian depositional conditions in the foreland of the Linkuva ice-marginal zone. Sedimentary characteristics do not match a single luminescence date of 9.2±0.6 ka, which significantly postdates the minimum age of the Linkuva ice-marginal zone with 10Be ages between 15.4 and 12.0 ka. Whether deposition started directly after drainage of the Middle Gauja ice-dammed lake or if there is a gap of 2.8–6.2 ka is a matter of debate; only future studies at higher OSL resolution could resolve this.

3

Roundness and matt degree of quartz grain surfaces in (fluvio-)glacial deposits of the Pomeranian Stage (Weichselian) in northeast Germany

Górska-Zabielska M.

Geologos

|

2015

|

Vol. 21, No. 2

117--125

EN

Glacial tills and fluvioglacial sediments deposited by the ice-sheet during the Pomeranian Stage (Weichselian) in northeast Germany have been examined in terms of the degree of abrasion, rounding and frosting of quartz grain surfaces in order to determine the conditions and processes that occurred in the alimentation environment of the fine-grained material, as well as during transport. Strata in the glaciomarginal zone and the hinterland of the Pomeranian Stage in the area represent diverse lithofacies, but have similar textural features. These features illustrate mainly that a high-energy aquatic environment had reacted with glacial deposits prior to their inclusion into the ice mass and deposited in the area covered by the Odra lobe. The lack of regional diversification in the character of quartz grain surfaces in glacial deposits between the German part of the Odra lobe and the remainder of the area analysed is recorded solely in the morphological dimension, i.e. the outlet fragment of the ice-front’s course, but not in textural features of the sediments.

4

Mikromorfologia powierzchni ziarn kwarcowych jako wskaźnik procesów glacjalnych zapisanych w osadach różnej litologii (góry Serra da Estrela, Portugalia)

Woronko B., Vieira G..

Landform Analysis

|

2008

|

Vol. 9

134--136