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Soft-sediment deformation structures in cores from lacustrine slurry deposits of the Late Triassic Yanchang Fm. (central China)

Yang R., van Loon A. J., Yin W., Fan A., Han Z.

Geologos

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2016

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Vol. 22, No. 3

201--211

EN

The fine-grained autochthonous sedimentation in the deep part of a Late Triassic lake was frequently interrupted by gravity-induced mass flows. Some of these mass flows were so rich in water that they must have represented slurries. This can be deduced from the soft-sediment deformation structures that abound in cores from these lacustrine deposits which constitute the Yanchang Fm., which is present in the Ordos Basin (central China). The flows and the resulting SSDS were probably triggered by earthquakes, volcanic eruptions, shear stress of gravity flows, and/or the sudden release of overburden-induced excess pore-fluid pressure. The tectonically active setting, the depositional slope and the high sedimentation rate facilitated the development of soft-sediment deformations, which consist mainly of load casts and associated structures such as pseudonodules and flame structures. Sediments with such deformations were occasionally eroded by slurries and became embedded in their deposits.

2

Examining Quartz OSL age underestimation for loess samples from Luochuan in the Chinese Loess Plateau

Lai Z., Fan A.

Geochronometria

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2014

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Vol. 41, no. 1

57--64

EN

When using quartz OSL to date loess samples from the Chinese Loess Plateau, it has been reported that the agreement between OSL ages and the independent ages is limited to the samples younger than ~70 ka with a corresponding De of ~230 Gy, and a sample with an expected age of 780 ka was dated to 107 ka, corresponding to 403 Gy. The growth curves of these samples do not sat-urate at doses of 700 Gy, and a linear growth part was observed for doses higher than 200 Gy. How-ever, the maximum measured age of ~100 ka imply that the De determined using this linear part of a growth curve could be problematic, or that the quartz OSL signal is not as stable as previously thought and has a barrier age of ~100 ka. In the current study, we examine the reasons for the age un-derestimation. We examined the shape of growth curves, anomalous fading, thermal stability, etc. The results show that, for the loess samples examined, quartz OSL does not fade anomalously, and the barrier age of ~100 ka is due to the fact that the OSL signals are less thermally stable, the lifetime of 0.311 Ma at 20°C obtained is much smaller than those for quartz samples from other regions such as Australia (~100 Ma).

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Firing temperature of a clay core sample in a bronze tripod from Daxinzhuang Site in China using TL techniques

Wu Y., Jin Z., Fan A., Fang H.

Geochronometria

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2013

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Vol. 40, no. 4

317--321

EN

In this paper, we studied the thermal history of a clay core sample from one leg of a bronze tripod unearthed at Daxinzhuang Site, Shandong, China. The properties of the luminescence signals of quartz depend on the maximum temperature at which the quartz was annealed in the past. We ex-amined the feasibility of measuring the thermoluminescence (TL) sensitivity change of quartz for ex-ploring the firing temperature of archaeological materials. The sensitization factor of the 110°C TL peak (S2/S1) and the ratio of the 210°C TL peak to the 110°C TL peak at different annealing tempera-tures were utilized to unveil the firing temperature in the clay core sample. The firing temperature of the clay core sample was approximately 700°C-800°C, proving the clay core has been fired. This re-sult proved that the clay core has been fired by human agencies and indicated on the temperature of the clay core in drying and firing given by the foundry workers before the actual casting step.