Depositional environments of loesses from the Sandomierz section, SE Poland, based on lithological and SEM studies

摘要

The litology of the Sandomierz section deposits have been examined, with SEM analysis performed on 4 quartz grain-size classes. All of the Sandomierz deposits contain predominant quartz grains with signs of aeolian transport. This refers both to morainic till and muds underlying the loess section as well to loesses themselves along with soil complexes. A much smaller, although significant contribution comprises redeposited grains with features of a high energy beach environment. Their content increases up section. During sedimentation of the LMg (younger upper loess) deposits (later part of the Vistulian Glaciation) wind strength was increasing. This is indicated by the upwards increasing content of coarser fractions within the interval, with simultaneously improved sorting, as well as by the increased contribution of garnets and the greater content of zircon and rutile at the top. The increasing contribution of aeolian quartz grains, the considerable content of grains redeposited from a beach environment and the decreasing amount of post-sedimentary features all suggest increased wind speed. Low variability in the shape of the 1-0.5 mm quartz grains from the LMg horizon indicates short transport and a similar nearby source of material. Alimentary areas for this horizon were composed of young Pleistocene muds and tills. A change in depositional conditions is observed at the LMs/LMg boundary (upper part of the Vistulian Glaciation). During deposition of the LMs (younger middle loess) horizon, wind strength decreased, as shown by the content of heavy minerals and the smaller mean grain-size along with the reduced content of aeolized quartz grains.