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Heavy-mineral, mineral-chemical and zircon-age constraints on the provenance of Triassic sandstones from the Devon coast, southern Britain

Morton Andrew, Hounslow Mark W., Frei Dirk

Geologos

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2013

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Vol. 19, No. 1-2

67--85

EN

An integrated heavy-mineral, mineral-chemical and zircon-dating study of the Triassic succession exposed on the south Devon coast, in the western part of the Wessex Basin, indicates derivation from a combination of granitic and metasedimentary lithologies of ages of mostly over 550 Ma. These sources were probably located at a relatively proximal location near the southern margin of the basin. Derivation from more distal sources in the Armorican Massif or local Variscan sources to the west appears unlikely in view of the scarcity of Permo-Carboniferous (Variscan-age) zircons. The Budleigh Salterton Pebble Bed Formation was derived from a different combination of source lithologies than the Otter Sandstone Formation, the former including staurolite-grade metasediments that were absent in the catchment area of the Otter Sandstone. The Devon coast succession has provenance characteristics that differ from equivalent sandstones further east in the Wessex Basin, and from sandstones in the East Irish Sea Basin to the north. These differences indicate that sediment supply patterns to the linked Triassic basin systems in southern Britain are complex, involving multiple distinct sub-catchment areas, and that heavy-mineral studies have considerable potential for unravelling these sub-catchment area sources.

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Heavy minerals as a tool to reconstruct river activity during the Weichselian glaciation (Toruń Basin, Poland)

Weckwerth Piotr, Chabowski Marek

Geologos

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2013

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Vol. 19, No. 1-2

25--46

EN

The heavy-mineral composition of the Weichselian fluvial successions deposited by an ephemeral meandering river and by a sand-bed braided river in the Toruń Basin (central Poland) was analysed. On the basis of a lithofacies analysis, in combination with the composition of the heavy-mineral assemblages, the fluvial processes and river-channel morphology were reconstructed. This allows determining the provenance of the fluvial deposits and the rivers’ discharge regimes. A model is proposed which can explain the changes in the amount of individual minerals in the fluvial sediments of different ages under the conditions of the oscillating Scandinavian ice sheet. The model assumes that, during the ice-sheet advances, the proglacial streams supplied large amounts of heavy minerals that were less resistant to mechanical abrasion. During the main phase of the ice-sheet retreat, the distance between the ice sheet and the Toruń Basin increased, and the amount of non-resistant minerals diminished as a result of sediment reworking in proglacial rivers. Due to the unique location of the Toruń Basin at the front of the Scandinavian ice sheet during the Weichselian glaciation, the heavy-mineral assemblages in the fluvial deposits form a valuable tool for the recognition of the ice-sheet extent.

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Możliwości wykorzystania standardowych badań uziarnienia i cech mineralno-petrograficznych w litodynamicznej interpretacji polskiej strefy brzegowej Bałtyku

Racinowski R., Dobrzyński S.

Zeszyty Naukowe. Marine Sciences / Uniwersytet Szczeciński

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1998

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Nr 4

75-90

EN

Standard lithological investigations of the seashore zone rubble comprise the following analyses: grain size distribution, mineral-petrographic composition, heavy minerals composition, morphometric and morphoscopic characteristics of the cobbles, and abrasion of the quartz grains in the sandy fraction. The rubble shows a marked similarity to the mineral-petrographic composition throughout the Polish Baltic seashore and qualitatively it is linked up with initial Pleistocene material. The morphometric features of the gravels undergo a very rapid transformation in relation to the Pleistocene deposits. The farther away from the place where the glacial deposits are washed out, the smaller the quantity of components of low wear resistance - the gravels become more oblate and smooth. The qualitative composition of the rubble's heavy minerals is linked up with the Pleistocene deposits. As a result of rapid differentiation in the seashore environment there are small rubble centres enriched in heavy minerals (mainly on the shore), mainly garnets, zircon, rutile, disthene, staurolite. The rubble that is not enriched in heavy minerals contain larger quantities of amphiboles, pyroxenes, especially biotite, chlorite and muscovite. In the Polish seashore zone the rubble's thickness ranges from a dozen to several dozen centimetres and it is represented by middle-sized and fine sands. The analysis of its lithodynamic features (based on grain size distribution) shows that it is very susceptible to outwashing. The rank erosion velocities are ca 0,1 - 0,3 m/s. This means that in the shallow subshore (0 - 7m under sea level) the sediment transport starts developing at state of the sea 1 - 30B, and in the deeper subshore (7 - 14m under sea level) at sea of 5 - 60B. Basing on the lithological investigations of the rubble, attempts were made to designate local and regional directions of its displacement. To this end the following were used: indices of grain size distribution (mainly Mz and 1), the compositionof heavy minerals (mainly the heavy mineral's mass in the rubble; content of components with densities over 3,4 g/cm3, 2,9 - 3,4 g/cm3). Also the analyses of petrographic and morphometric composition of the cobbles proved instrumental. The findings on a local scale seem unquestionable, yet on a regional scale they are controversial and susceptible of various interpretations.

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Litodynamiczne zróżnicowanie składu minerałów ciężkich w utworach wschodniej części Mierzei Dziwnowskiej

Racinowski R.

Zeszyty Naukowe. Marine Sciences / Uniwersytet Szczeciński

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1998

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Nr 4

53-73

EN

The paper presents lithodynamic interpretation of the results of investigations into heavy minerals separated from the Dziwnów Sandbar shore substratum (down to a depth of 7m below ground level) and from the shoreface debris (down to a depth of 6m below sea level). The localization of the research stations is shown in Fig.1. In the shore substratum the following three complexes of deposits were separated. Complex I represents the deposits of current shore accumulation (Ia - sand horizon, Ib - sand-gravel horizon). Complex II is sandbar-dune deposit that has accumulated by stages from Middle Holocene to Upper Holocene (IIa - sand horizon, IIb - sand-gravel horizon, IIc - organic deposit horizon). Complex III is formed by Vistulian glaciation boulder clays. Based on the weight content of heavy minerals, the opaque minerals concentration, the muscovite fraction and the concentration of transparent minerals with various hydraulic equivalents the percentage similarity of the sandbar-dune and maritime materials to the boulder clays was determined making use of the Wanke's method. It has been found that, in terms of guality, the deposit of the Complex I and II, s well as those of the shoreface debris exhibit a similarity to the glacial deposits (Complex III). By analogy it is concluded that the sandbar-dune deposits (Complex II) were being formed under lithodynamic conditions similar to those conditions under which the recent shore deposits (Complex I) have been formed. However, during the complex II formation, the sedimentation environment dynamics was weaker than that recent. During the complex II and complex I deposits accumulation, the debris was being transported alongshore from the east to the west. Within the shoreface, apart from areas where the debris deposition or slow transit occur, there are areas where the shoreface caving has clearly taken place. This process is particularly clearly visible within the shore section from 388th km to 390th km. On the shore side this is an area that is most intensively eroded by sea waters and is presently protected against abrasion by means of a complex system of hydrotechnic structures.