WEATHERING AND DENUDATION RATES OF LIMESTONES AND FORMATIVE PROCESSES OF KARST LANDFORMS

本研究试图通过使用方解石中宇宙成因^<36>Cl来量化裸露的碳酸盐岩表面的长期陆上剥蚀。在日本亚热带至亚北极地区的几个非冰川喀斯特地区，从裸露的石尖最上面5cm处采集了碳酸盐样品。用同位素稀释的加速器质谱法测定了方解石中天然Cl和^<35>Cl富集载流子峰的浓度。核素浓度的数量级为10^5-10^6原子g^<-1>，并转换为作用于喀斯特表面的化学和物理过程在10^5年时间尺度上的平均总剥蚀率。剥蚀率为20 ~ 60mmkyr < 1>，以日本中部地区最低。这种趋势表明，在剥蚀过程中，化学（溶解）和物理（碎霜）过程的相对重要性的交替取决于特定地点的因素，如平均温度、年降水量和冻融强度。

This study attempted to quantify long-term subaerial denudation of bare carbonate rock surfaces by using in situ-produced cosmogenic ^<36>Cl in calcite. Carbonate samples were collected from the topmost 5cm of exposed pinnacles at several non-glaciated karst areas in subtropical to subarctic regions in Japan. Concentrations of natural Cl and ^<36>Cl in calcite were determined by accelerator mass spectrometry with isotope dilution with ^<35>Cl-enriched carrier spike. The nuclide concentrations were of the order of 10^5-10^6 atom g^<-1>, and converted to total denudation rates averaged over a 10^5 yr-timescale of chemical and physical processes acting on the karst surfaces. The denudation rates were 20-60mm kyr<-1>, being lowest in the central part of Japan. This tendency indicates the alternation of relative importance of chemical (dissolution) and physical (frost shattering) processes in denudation, depending on site-specific factors such as mean temperature, annual precipitation, and freeze-thawing intensity.