| Abstrakt: |
Several ponds were built in the vicinity of the city of Zábřeh (Czech Republic) during the 15th century, all of which disappeared over time, leaving only one (Oborník) that survived to the present day. Currently, the only proof of the existence of these ponds in the landscape are the dams, preserved in varying degrees of quality. Another potential proof of the presence of ponds is pond sediment, the existence and extent of which are the subject of this text. The abandoned Leštinský pond, located to the east of Zábřeh, was chosen for this research. This pond was only captured on the maps from the 1st military mapping, it is no longer depicted on newer maps. Its presence is indicated by a partially preserved dam, which is not very distinct in the landscape but is visible in Lidar images. The pond sediments were investigated through a combination of geological survey (shallow boreholes) and geophysical prospecting (electrical resistivity tomography and ground penetrating radar). A total of 5 drill cores were taken on which magnetic susceptibility, grain size, geochemical composition and spectral reflectance were measured. Four facies were identified based on the lithology and the used analyses. These facies are interpreted as a recent soil (facie P1), pond sediment (facie R) and buried alluvial soil developed on fluvial sediments (facie P2) and coarse-grained sands (facie F). The data from geophysical survey correlates with boreholes lithology and extends this information spacially. Above all, ground penetrating radar (GPR) of facie RF3, interpreted as the base of pond sediments, can be easily observed in GPR profiles. The obtained results provide information about the presence and thickness of the pond sediment. Pond sediment was captured in boreholes at thickness ranging from 12 to 38 cm, with no internal pond sediment stratigraphy being observed. The probable reason for such a limited sediment thickness could be the initially shallow depth of the pond or the pond's summering process ("letnění"), during which no water was present in the pond and the removal of the pond sediment occurred in regular cycles. [ABSTRACT FROM AUTHOR] |
