Wyniki wyszukiwania - BazTech

1

Lithostratigraphic classification of the Tsodilo Hills Group: a Palaeo- to Mesoproterozoic metasedimentary succession in NW Botswana

Wendorff Marek, Świąder Andrzej

Geology, Geophysics and Environment

|

2019

|

Vol. 45, no. 4

305--318

EN

The Tsodilo Hills Group strata exposed in the Tsodilo Hills are an association of meta-arenites, metaconglomerates, quartz-mica schists, sandstone, red siltstone and sedimentary breccia deposited on an open siliciclastic marine shelf between the Late Palaeoproterozic and Late Mesoproterozoic, and outcropping in NW Botswana. The succession is dominated by three micaceous quartzite units interlayered with subordinate lenses and wedges of other rock types. Facies gradients from S to N are expressed by: decreasing content of muscovite at all levels of metasediment organisation from thin wedge-shaped units to thick quartzite complexes, as well as a decrease in pebble content and increase in arenaceous matrix in some metaconglomerate beds, matching regional palaeotransport direction. Well-rounded pebbles of extrabasinal rocks are flat, suggesting redeposition from a beach environment. Lenticular conglomeratic bodies with erosional lower boundaries represent infills of local incisions in the sandy bottom sediments. The abundance of laterally discontinuous lithological units reflects shelf palaeotopography controlled and modified by deposition and migration of large bed forms, ranging from megaripple marks (or submarine dunes) to sand waves. Deposition was influenced by tides and two regressive events. The older regression resulted in a marker unit of tidal mudflat-related red-bed facies: mudstone, siltstone, channel-fill sandstone and sedimentary breccia. The second regression is indicated by a tabular conglomerate marker reflecting increased input of coarse terrigenous material.

2

Najpłytsze podłoże krystaliczne polskiej części platformy wschodnioeuropejskiej w strefie podlaskiej

Cymerman Z.

Przegląd Geologiczny

|

2017

|

Vol. 65, nr 12

1529--1535

EN

The intensive development of studies on the crystalline basement of the Polish part of the East European Platform started only in the mid-1950s. These studies were based on geophysical research that preceded planned deep drilling projects. Twenty-five drill holes were located along four sections called: Białowieża, Kruszyniany, Sokółka and Krasnopol. The aim of this article is to re-evaluate drilling materials in the light of a variety of data, mainly structural data obtained from 20 boreholes from the first three "drilling sections”. All these sections were located on the Belarus-Lithuanian Elevation where the crystalline basement occurs at the shallowest depths. Special attention was paid to the recognition of ductile shear zones, SM foliation, LM mineral lineation and kinematic indicators. The results of the studies made it possible to identify the direction of tectonic transport, mainly with the top-to-SW, S and W, and deformation regimes in the boreholes of the Podlasie Belt. The main deformations have been related to a compressional regime in the amphibolite and granulite facies of regional metamorphism during the Svecofennian orogeny. It is suggested for the future to combine the research efforts of specialists from different fields of geological sciences. However, due to the scarcity of core material from old drillings, the most important are new deep boreholes that will provide a lot of drilling material to explain the geological structure and the evolution of the Proterozoic basement of NE Poland.

3

Seismic and non-seismic soft-sediment deformation structures in the Proterozoic Bhander Limestone, central India

Sarkar S., Choudhuri A., Banerjee S., Van Loon A. J., Bose P. K.

Geologos

|

2014

|

Vol. 20, No. 2

89--103

EN

Numerous soft-sediment deformation structures occur within the Proterozoic Bhander Limestone of an intracratonic sag basin in a 750 m long section along the Thomas River, near Maihar, central India. Part of these deformation structures have most probably a non-seismic origin, but other structures are interpreted as resulting from earthquake-induced shocks. These seismic structures are concentrated in a 60 cm thick interval, which is interpreted as three stacked seismites. These three seismites are traceable over the entire length of the section. They divide the sedimentary succession in a lower part (including the seismites) deposited in a hypersaline lagoon, and an upper open-marine (shelf) part. Most of the soft-sediment deformations outside the seismite interval occur in a lagoonal intraclastic and muddy facies association. The SSDS within the seismite interval show a lateral continuity. They record simultaneous fluidisation and liquefaction. The bases of each of the three composing seismite bands are defined by small-scale shear folds, probably recording an earthquake and aftershocks. The presence of the three seismite bands at the boundary between the lagoonal and the overlying open-marine oolitic facies association suggests that the seismic event also triggered basin subsidence.

4

Alkaline rocks of the Ukrainian Shield: Some mineralogical, petrological and geochemical features

Ponomarenko A. N., Kryvdik S. G., Grinchenko A. V.

Mineralogia

|

2013

|

Vol. 44, iss. 3/4

115--124

EN

The Ukrainian Shield (USh) is a typical province of Proterozoic alkaline magmatism where about 50 massifs and occurrences of alkaline rocks and carbonatites have been found. In spite of the wide distribution of Devonian basaltic- and alkaline magmatic rocks in the Dnieper-Donetsk depression adjacent to the USh, and in a marginal zone of the USh adjacent to folded Donbass, only alkaline rocks of Proterozoic age (1.8-2.1 Ga) that have been identified in the central interior of the USh. Some discrete bodies of 2.8 Ga subalkaline rocks also occur in Bogdanivka massif (Azov area). Occurrences of both Proterozoic (prevailing) and Phanerozoic (Devonian) alkaline rocks and kimberlites are only found in the eastern part of the USh (Azov area). Kimberlites in the central part of the Ukrainian Shield (Kirovograd region) are also of Proterozoic age (ca 1.8 Ga). It is this predominance of Precambrian rocks that makes the USh so different from other alkaline provinces where Phanerozoic alkaline rocks and kimberlites commonly prevail over Precambrian rocks. The lack of Phanerozoic alkaline magmatism on USh is poorly understood. Two main complexes of alkaline rocks - alkaline-ultrabasic (carbonatitic) and gabbro- syenitic - are distinguished in the USh. There are also rare occurrences of rock types such as alkaline- and alkaline-feldspar granites that may represent one separate alkaline-granite complex. Alkaline rocks present in the Eastern (Azov) province and in the Western province display essentially different geochemical character. Those of the Eastern province show characteristics typical of alkaline-ultrabasic rocks (e.g. high contents of incompatible rare elements 116 such as Nb, REE, Zr, Y, Sr, whereas those in the Western province are characterized by low contents of Nb and Zr, and REE in some cases. This fact is interpreted as reflecting different geodynamic conditions of their origin. The Eastern rocks were formed in rift settings, the Western rocks in crustal compressional settings (collision, subduction). Various mineral deposits of phosphorus (apatite), niobium, REE, yttrium and zirconium, including unusually rich ores of REE, Y and Zr (Azov and Yastrybetsky) are associated with the alkaline rocks and carbonatites of the USh.

5

Proterozoiczne zmiany retrogresywne zapisane w granulitach i gnejsach podlaskiego kompleksu metamorficznego

Krzemińska E.

Przegląd Geologiczny

|

2001

|

Vol. 49 nr 12

1129-1136

PL

Praca prezentuje wyniki badań petrologicznych oraz dane termobarometryczne granulitów i gnejsów z trzech głębokich otworów wiertniczych z kompleksu podlaskiego, w polskiej części platformy wschodnioeuropejskiej. Zastosowane geotermobarometry rejestrują w granulitach z Mielnika warunki wczesnoretrogresywnego etapu metamorfizmu (T = 650-700oC; p = 5,8-6,2 kbar) oraz regresywnego (T = 520-550oC; p = 4,1-5,2 kbar) etapu metamorfizmu proterozoicznego, datowanego na co najmniej 1527 mln lat. Skonstruowano hipotetyczną ścieżkę p-T dla tego stadium metamorfizmu, porównując otrzymane wyniki z analogicznymi danymi z zachodniej części białorusko-bałtyckiego pasa granulitowego i zachodniolitewskiego masywu granulitowego (rejon Lazdijai).

EN

This paper presents the results o)penological study and thermobarometric data of granulites and gneisses from deep boreholes, from the Podlasie Complex, in Polish part of the East European Craton. Applied geothermobarometers indicate an early-retrograde, near peak (T = 650-700" C, p = 5.8-6.2 kbar) and retrograde stage (T- 520-550°C, p = 4.1-5.2 kbar) of Proterozoic metamorphism (1527 Ma) in the Mielnik granulites. These metamorphic conditions were also compared with those from the Ivje block in the Belarus-Baltic Granulite Belt and Lazdijai area, Western-Lithuanian Granulkę Domain.