Volume 37 (2010): Issue -1 (December 2010)
Proceedings of the 2 Asia Pacific Conference on Luminescence Dating, Ahmedabad, India, 2009. Part I Editors Andrzej Bluszcz, Sheng-Hua Li and Ashok Kumar Singhvi

Recent developments in our understanding of the limitations of optically stimulated luminescence as a dating tool are presented alongside summaries of results obtained on other luminescence signals measured in sedimentary quartz grains.

The grain size influence on the number of oxygen vacancies in quartz was investigated by ESR in atmospheric deposition collected at two Japanese cities, Fukuoka and Akita, in 1969 and 1971. The finer grain size fraction shows the highest value of concentration of oxygen vacancies, most closely resembling dust originating in the Taklamakan desert. Month to month and year to year variation of the dependence was also observed which could possibly be attributed to the variation of the mixture ratio of at least two dust sources in China, A conclusive statement can not be made at this stage.

Quartz grains from sediments in Japan are derived from complex mixtures of sources, including volcanic, plutonic, metamorphic and sedimentary rocks. We have measured the OSL signal of quartz grains from modern coastal sediments derived from different source rocks and compared these characteristics with the likely source. Each sample shows a different combination of various OSL components. It is concluded that the source rock affects the characteristics of the OSL components from quartz grains in Japanese sediments. By comparing the LM-OSL signals from volcanic sources with those from various source rocks, it can be deduced that quartz which has a higher fast component ratio is more suitable for dating. We also conclude that volcanic source areas should be avoided.

In the central region of Mainland Kachchh, Western India, the Katrol Hill Fault (KHF) is one of the major E-W trending faults. An understanding of the episodes of reactivation during the past has a bearing on the future seismicity in the region. These reactivations are manifested by offset of elevation of fluvial sediments and scarp-derived colluvium in the Khari River basin, SE of Bharasar (23°11'36.5"N, 69°35'22.6"E). Stratigraphic offsets of the sediments at this site suggest three episodes of reactivation of the KHF during the late Quaternary. Optical dating of samples from sediment strata and top layer of scarp-derived colluvium using Natural Sensitivity Corrected - Single Aliquot Regenerative (NCF-SAR) protocol suggested that these events occurred during the past ~30 ka, with the most recent historic episode around 3.0 ka. Given that a part of the slip recorded in the form of sediments offset, was lost due to erosion after faulting, a lower bound to the time averaged slip rate of the segment of KHF, is inferred to be > 0.23 mm/a during the past 30 ka.

Geomorphology and sedimentary composition of an archeologically important palaeochannel segment of the Vedic Saraswati River in northwestern Haryana have been evaluated and its temporal relation with the surrounding upland examined with the help of OSL dating. Sediment composition and OSL ages suggest that the channel received enough water supply between 5.9 and 4.3 ka ago, and even before. Several lakes and ponds had developed during this period in the surrounding areas. It was a wet phase in this area as well as in Rajastahn. After ~4.3 ka, the river got starved of regular water supply, became sluggish and finally dried up. Reduced water supply, indicative of decreased rainfall, occurred between 4.3 and 3.4 ka ago. The environmental history of the channel might have influenced the Harrapan archeology of the area.

We present the results of luminescence dating of sediments from two cores from the Cauvery Delta in south-east India. Since all natural quartz OSL signals except one sample were in saturation, the elevated temperature post-IR IRSL protocol for K-feldspar was applied to establish a chronology. Internal dose rates of K-feldspar grains were calculated from the measured internal content of potassium, uranium, thorium and rubidium in the bulk of K-feldspar grains using solution ICP-OES and ICP-MS analysis. A substantial scatter in single-aliquot D_e values was observed which is most probably due to the effect of incomplete bleaching of fluvial sediments before burial. A minimum age model was applied to extract possible depositional ages. The study revealed that except an upper layer of Holocene sediments (< 5m), the majority of the upper ~50m of Cauvery delta sediments were deposited between marine isotope stage MIS-5 and MIS-10 or older. The feldspar luminescence ages also indicate the existence of a period of non deposition or erosion in the upper part of the cores.

A record of six discrete middle Holocene floods has been established based on sedimentological and stratigraphical studies in the upper Kaveri catchment at Siddapur. The flood events are represented by six discrete, sharp-bounded, sand-silt couplets. Texturally and geochemically the suite of couplets is quite distinct from the overlying and underlying structureless fluvial deposits. Based on OSL ages the suite of couplets cover the Holocene from ~8 to ~2 ka. Such evidence is not present or reported from any other river originating in the Western Ghat in the Indian Peninsula. We argue that the six couplets represent short-term, high discharge events or flash floods. The initiation of this phase of flash floods broadly corresponds with the southward migration of ITCZ and a gradual decline in Indian summer monsoon precipitation starting at ~7.8 ka. Comparison of the elevation of the highest couplet with the high flood level (HFL) of the 1961 extraordinary flood on Kaveri demonstrates that the 20th century flood was higher than the mid-Holocene palaeofloods.

Electron Spin Resonance (ESR) dating of marine barite in chimneys deposited from hydrothermal vents was attempted to determine the time since hydrothermal activity occurred. In this study, we used Barite (BaSO₄) precipitated in icroenvironments in the chimneys deposited from the hydrothermal vents at the Archaean site in South Mariana spreading centre (12°56.4'N, 143°37.9'E) and at Hakurei site in the Izena caldron (27°15'N, 127°04'E) for ESR measurements. ESR spectrum of marine barite is characterized by an electron-type centre with g values of 2.0034, 2.0022 and 1.9995 attributed to SO₃^-. The signal intensity increased with gamma ray dose. The dose rates of hydrothermal chimneys from the Archaean site and from the Hakurei site were calculated using a model that assumed a grain size and that incorporation of radionuclides after ²²⁶Ra in U series into the chimney, and assuming the efficiency of the defect formation by alpha particles to be the same as that for OSL. The ESR ages were estimated to be 470 years old for barite from the Archaean site and 5670 years old for one from the Hakurei site, although there is a considerable difference between the present ESR ages and the ²¹⁰Pb/²²⁶Ra disequilibrium ages previously reported.

Landforms developed across terrain defining boundary the Main Boundary Thrust (MBT) have imprints of recent tectonic activity. Depositional landforms such as colluvial fan bear signatures of later phases of tectonic activity in the form of faulting of colluvial fan deposits and development of fault scarps. Tectonic geomorphology applied to the MBT zone suggests recent subsurface activity along the MBT and its splay thrusts. Present day tectonic activity of MBT is indicated by ground creeping, thrusting of Lower Siwalik rocks over recent colluvial fan deposit, aligning of series of lakes along splay faults and laterally along a fault, deflected streams, fault scarps and waterfalls. In the present paper we are addressing the tectonic situation in the foothill region of southeastern Kumaun Sub-Himalaya, India based on detailed field work carried out in the region which brought forward some outstanding morphotectonic evidence of neotectonic activities in the MBT zone.