Utwory litorinowe w profilu wiertniczym na Helu

Abstract

LITTORINA DEPOSITS IN THE PROFILE OF THE HEL BOREHOLE Summary The paper presents the results of mineralogical studies on Littorina Sea deposits penetrated by a borehole (175 m deep) in the area of the Hel Peninsula. Littorina deposits, occurring at depths 8 to 72 m below sea level, are represented by (from the top downwards): fine grained sands, silty sands and sandy silts. The analysis of mineral composition of these sands failed to show any greater differences in relation to beach and bottom sands known from other parts of Polish Baltic coast. A close comparison of the mineral composition of coeval Littorina deposits from the Mierzeja Wiślana and the Hel Peninsula has shown some discrepancies indicating differences in the facies and age of the deposits forming alimentary areas that is, Oligocene deposits of the Sambian Peninsula in the case of the Mierzeja Wiślana, and (?) the western parts of the Baltic coast and Pleistocene deposits in the case of the Hell Peninsula. An analysis of the whole section of Littorina deposits penetrated by the Hel borehole has shown some changes in mineralogical composition, mainly in the content of micas and in absolute numerical value of the A/G (amphibole-to-garnet) ratio. The largest content of micas and value of the A/G ratio were found to coincide with the basal part of the section (Figs. 1a and 1b). The observed changes in the occurrence of floral and faunal remains appeared to be parallel to the former. This coincidence of the changes in mica content, the A/G ratio and the content of floral and faunal remains in the vertical profile indicates some changes in hydrodynamic regime, that is ceasing of marine currents displayed by cores at the depths about 50 m to 60 m. The action of currents presumably ceased as a result of worsening connections between the Littorina Sea and the Ocean. A sharp boundary found at 40 m depth, connected with disappearance of the faunal remains (in relation to lower parts of the section) does not coincide with the changes in mineralogical composition of the deposits but with the changes in their facies (a transition from the facies of silty sands to fine-grained sands).