Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Relief and flood loams composition
Abstract
The grain size distribution of overbank sediments of the recent flood plains of rivers in NE Bohemia reflects not only the geology of the source area but the relief energy of both the source and the sedimentation areas. From this point of view the flood plain loams can be divided into 3 groups: loams of highlands (areas with altitude differences 150-300 m), loams of hilly areas (altitude differences 80-150 m), and loams of platform areas (differences max. 75 m). In sediments of the first group silty sands prevail with the Mz around 0.18 mm and sorting degree s1 3.0; in the second group clayey-silty sands to clayey-sandy silts are dominant with the Mz around 0.03 mm and sorting degree s1 3.2 on average. In platform areas silty clays to clayey-sandy silts are dominant with the average mean size Mz 0.002-0.01 mm and sorting degree s1 around 2.5. The clay mineralogy shows prevailing illite in highlands, while kaolinite is dominant in platform areas. The maturity index expressed by the Al2O3 /Na2O ratio is increasing from highland areas through hilly country to platforms having average values 7, 12.5 and 20.7 respectively.
