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Employing Minimum age model (MAM) and Finite mixture modeling (FMM) for OSL age determination of two important samples from Ira Trench of North Tehran Fault

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Fattahi M. , Heidary M. , Ghasemi M.

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tom Vol. 43, no. 1

38--47

EN

Ira trench site is in a point where, the surface trace of North Tehran Fault (NTF) joins the Mosha Fault (MF) in the north-eastern margin of Tehran and can provide important paleosismological information for Tehran. The Ira trench, were divided into 6 packages (I to VI), described, according to their composition, relative and absolute ages. Package I consists of units 23, 25, 26, 27, 28, 29, 30 and 31. The whole package I mainly belongs to Holocene, and provides essential constraints for the recent paleo-earthquake activity of the EMF and NTF zone. Therefore, finding accurate ages for the units of this package is very important. Three colluvial wedges (units 23, 26, 28) are present between 20 and 36.5 m north in package I, which are assigned to 3 episodes of activity on Fault 13. Central age model (CAM) provided OSL ages of 35.0 ± 6.1, 7.3 ± 1.3, 6.4 ± 0.9 and 56 ± 6.5 ka for units 23, 26, 28 and 29, respectively. The conflicting ages of 56 ± 6.5 and 35.0 ± 6.1 ka (for units 23 and 29, respectively) as compared to the underlying younger units suggest that these ages are overestimated. MAM provided OSL ages of 13.1 ± 4.3 and 3.5 ± 0.4 ka for units 23 and 29, respectively. The contribution of the new statistical age model of sample IRA4 to the paleoseismic data is discussed.

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Middle pleistocene stratigraphy in the light of data from the vilkiskes site, eastern Lithuania

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Satkunas J. , Molodkov A.

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tom Vol. 16

94--102

EN

The Vilkiskes outcrop is approximately 40 metres high section of Quaternary sandy sediments, exposed in the slope of the Neris River valley and is located 15 km upstream from the city of Vilnius. The section is composed mainly of sand with one till layer in the middle part. The outcrop is of particular interest due to typical section of sandy formation presumably of lacustrine origin, occurring under the till. This formation is widely distributed in the vast area in between Vilnius city and Nemencine town, according to the data of geological mapping, and represents a particular period of nonglacial sedimentation of Saalian time. The new optically stimulated luminescence (OSL) dates (determined by A. Molodkov), obtained from the Vilkiskes section, fall into the time span of 307-230 and 147-137 ka. The age of the lower part of Vilkiskes lacustrine section (dated 307-230 ka by OSL) looks closest to the two ice free stages, which can be correlated with oxygen isotope stages (OIS) 7 (236-186 ka) and OIS 9 (328-301 ka). Ages of about 147.1 and 136.7 ka are obtained near the immediate contact with the underlying glacial lithocomplex. Assuming OSL ages, conditions of occurrence and palaeopalynological characteristics, the interval of the Vilkiskes outcrop with OSL dates falling into the time span 236-186 ka (OIS 7) can be introduced as the last Middle Pleistocene (Drenthe-Warthe) ice free interval in Lithuania, most probably, separating the Zemaitija and Medininkai stadials. The interval dated 147.1 and 136.7 ka is interpreted as the Pamarys Interstadial that tentatively can be correlated with the Zeifen Interstadial in the Kattegat Depression suggesting the existence of a ?Younger Dryas?-type climate oscillation just prior to the OIS 6/5e boundary.

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Chronology of red dune aggradations of South India and its Palaeo-environmental significance

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Alappat L. , Seralathan P. , Shukla A. D. , Thrivikramji K. P. , Singhvi A. K.

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tom Vol. 40, no. 4

274--282

EN

Red sand dunes occur in the coastal plains of south east and west of Tamil Nadu, India be-tween the co-ordinates of 8°00’ to 9°30’ N; 77°18’ to 79° 00’ E. OSL dating of these sands indicated aggradations between ~16-9 ka and ~9-3 ka in the west and east coasts respectively. Dating results from inland red dunes at the foothills of Western Ghats show a break in deposition at ~6 ka and ag-gradation since ~2 ka. The sand aggradations in the west coast occurred during the transition period when SW monsoon in the area was re-establishing. The dunes attained their stability by 9 ka. In the coastal region, the aggradations were controlled by sea level changes and a local recycling of earlier dunes (in the east coast). In the inland areas, the dune building was controlled by sand supply from fluvial sources.

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Residual OSL signals from modern greenlandic river sediments

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Alexanderson H.

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tom Vol. 26

1-9

EN

Ripple-laminated sandy deposits at shallow water depths in four rivers on Jameson Land, East Greenland were sampled for optically stimulated luminescence (OSL) dating. Silt-sized grains have significantly higher equivalent doses (∼1.1 Gy) than sand grains (∼0.1 Gy). This suggests that coarse grain-size fractions are better bleached and more suitable than fine grains for OSL dating of glaciofluvial/fluvial sediments. A sample from a sidebar deposited during the spring flood yielded 1.0 Gy (∼500 years) while a subaerial deposit was completely zeroed. The spring flood deposit is considered to be most similar to deglacial conditions and incomplete bleaching of this amount (1 Gy) is generally not a significant source of error for sediments of Pleistocene age. Most samples have rather poor luminescence characteristics and are affected by thermal transfer if preheat temperatures at or above 260°C are used.

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Chronostratigraphy of the Vistulian glaciation on the Kujawy Moraine Plateau (Central Poland) based on lithostratigraphic research and OSL dating

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Przegiętka K. R. , Chruścińska A. , Oczkowski H. L. , Molewski P.

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tom Vol. 32

69-77

EN

The subject of the investigations presented here is fixing dilemmatic character (transgressive or recessive) of the Poznań phase of the Vistulian (Weichselian) Glaciation and answering the question about the possibility of lithostratigraphic separation of this phase from the Leszno phase in the region of so called Vistula lob. Here we present the outcomes of the research project carried out on a few tills exposures, which constitute the sedimentological record of the last ice sheet advance on the Kujawy Moraine Plateau. The absolute ages of 17 samples (collected from fluvial deposits uncovered in the geological logs) have been determined by means of the OSL method applying the single aliquots regenerative (SAR) dose protocol. The OSL data are analysed with regard to supposed bleaching conditions at the moment of the last transport and deposition of the material. In conclusion, some remarks on suitability of fluvial sands for OSL dating are made. In most of the investigated sites, there appears to exist only a single till level associated with the main stage of the Vistulian Glaciation. This fact and the results of OSL dating support the hypothesis, that the Poznań phase in Kujawy Moraine Plateau is not a distinct lithostratigraphic unit, but it is a recessive phase of the last glaciation.