Nowe znaleziska narzutniaków porfiru rombowego z Oslo na terenie północno-zachodniej Polski

Abstract

NEW FINDS OF ERRATICS OF THE OSLO RHOMB PORPHYRY IN NORTH-WESTERN POLAND Summary Two specimens of Oslo rhomb porphyries find on the Wolin Island beach between Międzyzdroje and Grodno are extraordinary finds among the entire population of Scandinavian indicator erratics within glacial sediments in northern Poland. Only around 20 localities of erratics from Oslo have been noted in that part of Poland so far (Schulz, 1973). Unfortunately, the stratigraphy of the Wolin erratics is not known, because they have been found on the stony abrasion shelf at the foot of a cliff. The cliff itself consists of two separate till layers. The petrographical analysis of the lower bed of gray glacial till where rhomb porphyries had been found, point to distinctly north-western direction of an ice sheet advance (50 % of the entire population of erratics from sample 3 derive from western mother regions in the southern Baltic bottom). The analysed indicator erratics form the lower Wolin till represent the south-eastern Sweden and western part of the bottom of Baltic depression. The ice-sheet, approaching from the north, has transgressed on these outcrops before reaching the mother regions of Cretaceous limestones, which are located in the direct vicinity of the Wolin Island. The ample content of western erratics in sampled sediments of the Wolin cliff as well as the Oslo rhomb porphyries are of high interest. Have they come in icebergs (Benn & Evans, 1998, see Donner, 1995) or maybe their presence in glacial sediments should be connected with the Lagerlund’s ice dome (1987, 1995)? Schulz (2003) suggests a ship transport (as ballast stones). The planned detailed petrographical analysis on the Scandinavian erratics of the Wolin cliff should clarify the issue.