230Th dating of gypsum from lacustrine, brackish-marine and terrestrial environments

The (NH4)2CO3 exchange reaction and double-spike MC-ICP-MS method for gypsum U–Th dating

“…3. The 238 U content of these standards ranges from 40 ng g −1 (FGD-1) to 1823.6 ng g −1 (TIG-1), with a median value of 159.9 ng g −1 , which is consistent with the previous studies (the average value is below 200 ng g −1 ), [7][8][9] indicating a generally low 238 U content in gypsum materials. The low 238 U content in gypsum oen results in a large sample size in U-Th dating chemical protocols, leading to difficulties in sample digestion and time consumption.…”

“…In recent years, the method has been applied to evaporates such as gypsum and halite as well. [7][8][9][10][11][12][13][14] Gypsum (CaSO 4 $2H 2 O) is a common evaporate mineral in an array of geological settings, such as saline lakes, springs in terrestrial environments and coastlines, and deltas from marine environments. Due to its widespread, gypsum has been widely used as a tracer of marine, lacustrine, and terrestrial environment evolutions.…”

“…8,12,[15][16][17][18][19] However, previous studies have demonstrated some challenges associated with the U-Th dating of gypsum. 7,11,14,20 The rst challenge is how to digest gypsum into the solution completely and rapidly. Due to the low U content of gypsum (generally below 200 ng g −1 ), a large sample size is required to obtain sufficient 230 Th and 234 U nuclides, which will lead to difficulties in sample digestion, and time consumption.…”

“…The re-crystallization of gypsum during the chemical treatment may lead to the incomplete separation and purication of U and Th from the matrix, resulting in an unmanageable and variable yield of U and Th. To address these challenges, various chemical approaches have been proposed, such as digesting in pure water, 13,14 digesting in acids, [7][8][9]21,22 including HF-HClO 4 -HNO 3 , aqua regia, 0.5 M hot HCl, and 7 M HNO 3 , and digesting in magnesium salts. 20 Each approach has its disadvantages, such as digesting gypsum samples with pure water or 0.5 M HCl is oen time-consuming, digesting with HF-HClO 4 -HNO 3 , aqua regia, and 7 M HNO 3 is easily attacks detrital silicates when using these concentrated acids, which may result in Th contamination from detritals.…”

PXCG-1 and PXCG-2: two reference materials for gypsum U–Th dating

“…Previous studies have developed several techniques for dating gypsum materials, such as Electron Spin Resonance (ESR) dating, Thermoluminescence (TL) dating, and U-Th disequilibrium dating (also called 230 Th dating or 238 U-234 U-230 Th dating). [8][9][10][11][12][13][14][15][16][17][18] Among these methods, U-Th dating is a more promising technique due to the high analytical precisions conducted by mass spectrometry and the accurate half-lives known for 238 U, 234 U and 230 Th nuclides. [19][20][21][22] With the increasing application of U-Th dating in gypsum materials, some challenges of this method have become evident.…”