Rekonstrukcja dynamiki procesów eolicznych i czasu ich trwania na podstawie wybranych cech teksturalnych osadów wydmy w Cięciwie
Abstract
Badania cech teksturalnych osadów wydmy w Cięciwie oparto na analizie minerałów ciężkich, uziarnieniu oraz obtoczeniu ziarn kwarcowych dwóch frakcji (0,8–1,0 mm i 0,4–0,63 mm). Na podstawie wyników analizy minerałów ciężkich i wartości wskaźnika wietrzeniowego określono położenie gleby kopalnej allerödzkiej (tab.l) rozdzielającej dwie serie wydmowe ze starszego i młodszego dryasu (ryc. 2). Analiza lamin o różnej wielkości ziarna pozwoliła wydzielić laminy grubo- i drobnoziarniste. Rozróżnia je średnia średnica ziarna (Mz) o wartości 1,7 phi (0,3 mm) (ryc. 3). Na podstawie wartości średniej średnicy ziarna i stopnia wysortowania określono dynamikę i prędkość wiatru przeważającego w czasie starszego i młodszego dryasu oraz holocenu. W czasie starszego dryasu przeważał wiatr o dużej zmienności (5–10 m/sek), gdy tymczasem w czasie młodszego dryasu i holocenu warunki były bardziej ustabilizowane (5–6 m/sek). Różny stopień obtoczenia ziarn kwarcowych we frakcji 0,8–1,0 mm i 0,4–0,63 mm w obrębie lamin grubo- i drobnoziarnistych (ryc. 4, 5) wskazuje, że były one w różny sposób transportowane, przy różnych prędkościach wiatru (tab. 2) i ulegały niejednorodnej obróbce. W celach porównawczych analogiczne badania przeprowadzono dla osadów budujących zmarszczki eoliczne w okolicach Khargi w Egipcie.
RECONSTRUCTION OF THE DYNAMICS OF AEOLIAN PROCESSES AND OF THEIR DURATION ON THE BASIS OF SELECTED TEXTURAL FEATURES OF THE DEPOSITS WITHIN THE DUNE AT CIĘCIWA (EASTERN POLAND)
Summary
The investigations of textural features of the deposits of the dune at Cięciwa were grounded on the analysis of heavy minerals, as well as on the grain size distribution of deposits and on the rounding of quartz grains in two fractions, N 8–1.0 mm and 0.4–0.63 mm. Allowing for the composition of heavy minerals and the value of weathering index, the position of the Alleröd fossil soil was established (Table l), separating two dune series, from older and younger Dryas (Fig. 2). The examination of laminae built of grains of various size enabled to distinguish coarse and fine grain laminae. These laminae were distinguished on the basis of the limiting value of average grain diameter 1.7 phi (0.3 mm) (Fig. 3). Regarding the average grain size and the sorting degree, the dynamics and velocity of wind was defined that prevailed during the older and younger Dryas and the Holocene. During the older Dryas the wind of high variability (5–10 m/sec) prevailed, whereas during the younger Dryas and the Holocene the conditions were more stable (5–6 m/sec). The degree of rounding of quartz grains differed in the fractions 0.8–1.0 mm and 0.4–0.63 mm, in coarse and fine grain laminae (Fig. 4, 5); thus pointing to a different way of their transportation at various wind velocities (Table 2) so that their abrasion was not uniform. For the sake of comparison, analogical examinations were carried out concerning deposits that form aeolian ripplemarks in the region of Kharga, Egypt.
RECONSTRUCTION OF THE DYNAMICS OF AEOLIAN PROCESSES AND OF THEIR DURATION ON THE BASIS OF SELECTED TEXTURAL FEATURES OF THE DEPOSITS WITHIN THE DUNE AT CIĘCIWA (EASTERN POLAND)
Summary
The investigations of textural features of the deposits of the dune at Cięciwa were grounded on the analysis of heavy minerals, as well as on the grain size distribution of deposits and on the rounding of quartz grains in two fractions, N 8–1.0 mm and 0.4–0.63 mm. Allowing for the composition of heavy minerals and the value of weathering index, the position of the Alleröd fossil soil was established (Table l), separating two dune series, from older and younger Dryas (Fig. 2). The examination of laminae built of grains of various size enabled to distinguish coarse and fine grain laminae. These laminae were distinguished on the basis of the limiting value of average grain diameter 1.7 phi (0.3 mm) (Fig. 3). Regarding the average grain size and the sorting degree, the dynamics and velocity of wind was defined that prevailed during the older and younger Dryas and the Holocene. During the older Dryas the wind of high variability (5–10 m/sec) prevailed, whereas during the younger Dryas and the Holocene the conditions were more stable (5–6 m/sec). The degree of rounding of quartz grains differed in the fractions 0.8–1.0 mm and 0.4–0.63 mm, in coarse and fine grain laminae (Fig. 4, 5); thus pointing to a different way of their transportation at various wind velocities (Table 2) so that their abrasion was not uniform. For the sake of comparison, analogical examinations were carried out concerning deposits that form aeolian ripplemarks in the region of Kharga, Egypt.