Supplement of groundwater erosion of coastal gullies along the Canterbury coast (New Zealand) : a rapid and episodic process controlled by rainfall intensity and substrate variability

Abstract

Luminescence samples were prepared under subdued red light condition in the luminescence laboratory from Cluj-Napoca, Romania. The material from the ends of each sample tube was used for gamma spectrometry and water content measurements whereas polymineral fine grains (4-11 µm) and coarse (63-90 µm) K-feldspars were extracted from the inner part. Samples were first treated with hydrochloric acid (10% concentration) for calcium carbonate removal, followed by a treatment with hydrogen peroxide (30% concentration) in order to remove the organic matter. All samples were wet sieved in order to collect the finer (<63 µm) and coarser (>63 µm) grains. Polymineral fine grains (4-11 µm) were obtained by settling using Stoke’s law and centrifuging in distilled water (Frechen et al., 1996; Lang et al., 1996). Coarser grains in the range of 63-90 µm was obtained through dry sieving. For coarse K-rich feldspars extraction, an etching with HF (10% concentration) for 40 min was employed to remove the coating and alpha irradiated layer, and the material was then rinsed for 40 min with HCl (10% concentration) to remove any precipitated fluorides. K-feldspar enriched extracts were then separated using a heavy liquid solution with ρ<2.58 g/cm3