Zespoły mineralne procesów diagenezy i wietrzenia w iłach oligoceńskich okolic Szczecina

Abstract

MINERAL ASSEMBLAGES OF DIAGENETIC AND WEATHERING PROCESSES IN THE OLIGOCENE CLAYS OF THE SZCZECIN AREASummaryOligocene septarian clays (Fig. 1) in the Szczecin area are recovered for building ceramics. Mineral assemblages, frequently detrimental to the ceramics production, have been found in the clays. The present studies have been based chiefly on materials from the Niebuszewo brick-yard (Fig. 2) where the most differentiated assemblages have been observed. Mineralogical studies, chiefly DTA revealed calc-dolomitic concretions (Figs. 3-5), sideritic concretions (Fig. 6), iron sulphides both dispersed and in concretions, jarosites (Fig. 7) and gypsum.The assemblages differ as to their origin. According to the present author the calc-dolomitic and sideritic concretions and iron sulphides were formed in the early diagenetic stage and subsequently were subject to alterations related to surficial processes. As a result of the surficial processes a part of the carbonate concretions has been dissolved, the iron .oxides oxidized, while jarosites and gypsum have been formed.Within the clay sediments sequence 3 zones have been distinguished differing as to the content of the discussed assemblages (Fig. 8).In the uppermost zone I jarosites, gypsum, and occasional secondary calcareous concretions have been observed, gypsum being the main detrimental agent in ceramics production.In zone II gypsum, iron oxides and densely veined calc-dolomitic concretions – septaria – are found.Zone III – represented by .original sediments contains iron oxides and carbonate concretions that have a deleterious mechanical effect. The extent of those zones is chiefly controlled by the intensity of weathering processes.