Testing the application of quartz and feldspar luminescence dating to MIS 5 Japanese marine deposits

Thiel, C.*; Tsukamoto, Sumiko*; Tokuyasu, Kayoko; Buylaert, J.-P.*; Murray, A. S.*; Tanaka, Kazuhiro*; Shirai, Masaaki*

The applicability of both quartz and feldspar luminescence dating was tested on twenty-five samples from a marine succession now forming a cliff at Oga Peninsula, Honshu Island, Japan. The quartz shows thermal instability and linear modulated optically stimulated luminescence (LM-OSL) analysis revealed the dominance of a slow component. When compared with independent age control provided by two marker tephra, the quartz OSL ages grossly underestimated the depositional age. In contrast, potassium (K)-rich feldspar is a suitable dosimeter when measured using post-IR infrared stimulated luminescence (IRSL) at 225C, but it was found that the fading corrected ages calculated using dose rates based on sieved grain-size still underestimate. SEM analyses on the feldspar extracts revealed that the grains are amorphous with small crystalline inclusions; using standard internal dose rate parameters, this would result in a too large dose rate. Three different dose rate scenarios were considered for calculation: (1) sieved grain size (90-180m) and 12.50.5% K. (2) smaller grain size (4020m) and measured K concentration (60.5%), and (3) smaller grain size consistent with the observed crystal dimensions (4020m) and 12.50.5% K. The final dose rate scenario produces fading corrected ages that agree well with independent age control.