Growth rates of pedogenic carbonate coatings on coarse clasts

Abstract

Growth rates of pedogenic carbonate coatings on clasts can be used as a simple quantitative index of soil and sediment age, as well as a chronological framework for palaeoecological reconstructions. They are also probably connected with general intensity of formation of Bk horizons in soils. Previously, data on coating growth rates were restricted ecologically and geographically to desert regions of North America. This paper presents growth rates of Holocene pedogenic carbonate coatings on clasts within an extended range of environments, calculated on the basis of archaeological and radiocarbon dating. The rates, in this study, are higher than in earlier reports. Carbonate coatings can thicken with rates up to 1 mm/1000 years or higher in semi-arid and semi-humid climates. At least five factors are likely to control growth rates: (1) climate, (2) lithology of carbonate parent material, (3) depth under the soil surface, (4) clast size, (5) bulk density and composition of cutans. Favorable factors for comparatively rapid coating thickening seems to be climatic conditions, ranging from semi-arid to semi-humid, high carbonate content of parent material and large size of clasts. There is also an optimal depth of carbonate coating growth in a soil profile. Little information on bulk density and composition of cutans is available, but they appear to play an important role as one of the factors governing growth rates of pedogenic carbonate coatings on clasts.