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An assessment of the luminescence sensitivity of Australian quartz with respect to sediment history

Fitzsimmons K. E.

Geochronometria

2011

Vol. 38, no. 3

199-208

This study provides a preliminary systematic characterisation of OSL sensitivity, with re-spect to sediment history, of single grains of Australian quartz from a variety of source rocks and depositional contexts. Samples from two distinct lithologies and with relatively short modern sedi-mentary histories were compared in an examination of the influence of rock type on OSL sensitivity. Sediments derived from weathered sandstone were found to be brighter than those from metamor-phosed schists, suggesting that sensitivity may be inherited from the source rock and its earlier sedi-mentary history. Secondly, quartz from the same source, but different modes of deposition, was com-pared to assess the effect on sensitivity of nature of exposure to light during the most recent bleaching event. Quartz grain sensitivity appears not to vary depending on the mode of sediment deposition, suggesting that the nature of exposure to light during deposition is less important in the sensitisation process. This study highlights the complexity and variety of natural sedimentary quartz, demonstrat-ing the limitations of an investigation based solely on OSL sensitivity. Further systematic investiga-tion into the physical, geological and geomorphological characteristics of sediments is proposed to better understand the mechanisms of luminescence sensitisation in quartz.

The morphology of fossil pebbles as a tool for determining their transport processes (Koźmin South lignite open-cast pit, central Poland)

Widera M.

Annales Societatis Geologorum Poloniae

2010

Vol. 80, No 3

315-325

The Koźmin South lignite open-cast pit is the southernmost exposure of Palaeogene (lower Oligocene) deposits in central Poland. This study is focused on Palaeogene pebbles of the so-called Koźmin Gravels, rede- posited in the Neogene sands. These pebbles are not known from the adjacent territory of central Poland and they vary in petrographic composition, shape and surface texture. The classification of the pebble-size particle form is determined as DI/DL (elongation ratio) and DS/DI (flatness ratio). A great number of pebbles are disc-shaped (oblate-shaped) and blade-shaped or they can be classified as platy, bladed and very bladed pebbles. The oblate-prolate index (OP) is less than -2 for 45% of the particles (typical of beach pebbles), the mean sphericity (yp) is 0.56 (typical of beach pebbles), and the mean roundness (RWt) is 0.73 (typical of beach pebbles). The data obtained from SEM analysis of quartz pebble surface micromorphology are characteristic of high mechanical energy of the littoral environment. The surface of some pebbles is excellently polished with v-shaped indentations and grooves. The average composition of the heavy mineral fraction occurring with these pebbles is marked by the predominance of zircon (exceeding 70%). All the above-mentioned data, in the light of extensive literature, indicate that more morphological features of the analysed pebbles have been inherited from the littoral/beach environment. Moreover, a detailed petrographic study was very useful for determining the prove-nance of these pebbles. The most characteristic rocks are greyish-blue quartzes. They are known only from the Sudetes Mts., situated on the NE slope of the Bohemian Massif. Thus, the rock fragments were transported at least 300 km by rivers from the Sudetes to the littoral/beach zone of the Palaeogene sea. Then, the residually-marine beach pebbles were redeposited into the Neogene debris flow and/or fluvial deposits. The present-day area of the Koźmin South lignite open-cast pit was tectonically active at that time.