Former plateau ice fields in the Godeanu Mountains, Southern Carpathians: First evidence of glaciated peneplains in the Carpathians

摘要

The existence of plateau ice fields in the Southern Carpathians has long been suggested due to the widespread presence of the Borascu surface in the region. The Borascu surface is a peneplain consisting of flat plateaus in the elevation range of 1800-2200 m a.s.l. It is present throughout the Southern Carpathians with the most typical appearance in the Godeanu Mountains. These plateaus could have served as ice accumulation sites during the Pleistocene glaciations as they were well above the steady-state equilibrium-line altitude (ELA(0)). Direct geomorphological evidence on the existence of plateau ice fields, and thus well founded reconstructions, are absent due to the lack of glacial landforms on the plateaus. In order to test the existence of plateau ice fields a previous geomorphological survey and theoretical ice surface profiles, based on a steady-state perfectly plastic ice flow model, were used. Based on these methods maps and three-dimensional surface models of the former glaciers were created. The ELA(0)s of the paleoglaciers were estimated by the accumulation-area ratio (AAR) method. According to our results, three major ice fields on the central plateaus and several smaller ice fields on wide saddles were present in the Godeanu Mountains during the maximal glaciation. The ice fields fed numerous surrounding valley glaciers. Several independent valley and cirque glaciers, completely separated from the ice fields, were also present further from the central mass of the mountain range. The average ELA0 of the northern, 1855 +/- 2 m a.s.l., and the southern, 1700 +/- 2 m a.s.l., glaciers differed greatly. We suggest that the surprisingly high average ELA(0) of the northern glaciers was mostly caused by the missing lower sections of these paleoglaciers from our reconstructions, due to the destroyed terminal glacial landforms. However, the terminal glacial landforms are quite well preserved in the southern valleys. Thus, the average ELA(0) of the southern paleoglaciers was suitable to correlate the maximal glaciation of the Godeanu Mountains with the maximal glaciation of the neighbouring Retezat Mountains. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.