U-TH dating and physical properties of stalagmites from Amphoe Ban Rai, Changwat Uthai Thani : Paleoclimate implication

Abstract

Stalagmite is the one of advantaged paleoclimate and paleoenvironmental implication proxies. Our purposes are study the physical properties of stalagmites from Amphoe Ban Rai, Changwat Uthai Thani and select the stalagmites for paleoclimate implication. We have surveyed 20 caves and observed its physical properties ‒ shape, color, and texture. We collected 3 stalagmite samples, nearly symmetrical shape, in the same cave. Physical properties assessment was done both before and after cutting process which including of texture, color, growth layer. Following by drilling process, we drilled 8 points and each points were replicated. Powdered samples went to the chemistry and measurement process via U-Th method. The ages shows the precipitation in part of late Pleistocene epoch (87000-105000 a. BP) and the large error (±970-7700 a.). Consequently, the time interval between top and bottom of each samples were overlapped. The precipitation of calcite might occur in open system in which disequilibrium that lead 230Th/232Th ratio ranges 27-273 and 238U concentration ranges 40-181 ppb. Generally, the low of 230Th/232Th ratio represent a contamination (Jeffrey et al., 2004) and 238U concentration should be at least 100-200 ppb. (Shen et al., 2002; H. Cheng et al., 2013). These induce the large error and unsuitable for study further. Eventually, this study reveals that this area consists of the oldest stalagmite in Thailand by now and all of the samples provide the age nearly with each other which represent the precipitation ages of all samples and might be composed of variety ages but undiscovered.