Chronology and dynamics of fluvial style transformation in theYounger Dryas – Holocene transition (lower San River, SEPoland)

Abstract

<p>Reconstruction of fluvial style changes in the San River in the Subcarpathian Basins is based on<br>geomorphological and sedimentological analyses. The time control of alluvial fills and temporal<br>changes in the river channel are derived from radiocarbon and optically stimulated luminescence<br>dating combined with independent pollen-based biochronostratigraphy. The results showed that the<br>alluvial plain of the braided (BR) or braided-meandering (BR-M?) river was abandoned before<br>12,800 cal BP. Large meanders (LM) were cut off in the older part of the Younger Dryas (YD; ca.<br>12,600 cal BP), and in the younger part of this period (ca. 12,450 cal BP). The small meanders (SM)<br>developed at the end of the YD and were abandoned at the onset of the Preboreal (PB; ca.11,550<br>cal BP). The erosion phase at the YD-PB transition, reported from many valleys in Central Europe,<br>was not confirmed in the study area. The full cycle of San River channel transformation (BR (BRM?)-><br>LM->SM); was estimated to be approximately 1200 years. According to the palynological data,<br>open pine forests with birch that survived from the end of the Allerød dominated the landscape of<br>the river valley during the YD cooling and did not undergo major changes during the warming in the<br>early PB. Therefore, we assume that the influence of vegetation changes in the San River channel<br>pattern transformation was nonsignificant. The location of the studied palaeochannels in the<br>floodbasin filled with silty clayey deposits may have influenced the formation of relatively narrow<br>and deep channels, than that of much the wider and shallower meanders from the YD, situated<br>several kilometres downstream of the surveyed sites.</p>