Stratygrafia i litologia fanerozoiku na Pomorzu Gdańskim

Abstract

Phanerozoic stratigraphy and lithology of the Gdańsk PomeraniaA b s t r a c t . The pre-Phanerozoic basement of the Gdańsk Pomerania (GP) area is built of granitoides and metamorphic rocks of the Paleoproterozoic age. The oldest deposits, lying with a large hiatus on the crystalline basement, are represented by sandstones and conglomerates of Żarnowiec (Smołdzino) Fm of the Uppermost Ediacaran-Lower Cambrian age. They are continental in the lower part changing upwards into marine, with thickness increasing westwards fromzero in the Puck Bay to 175 m near Słupsk. The sandy-siltstone Lower Cambrian sediments, 190 m to > 200 m thick, are subdivided into 3 formations: Kłuków, Łeba and Sarbsko Fms. Shallow-marine sandy-silty-mudstone deposits of the Middle Cambrian (Dębki, Osiec and Białogóra Fms) are over 200 m thick and overlain by a thin, several meters thick complex of dark, bituminous claystones and siltstones with carbonate interbeds and lenses (Piaśnica Fm). A discordance and a small hiatus is found at the base of the Ordovician which is represented here by clay-marly-carbonate deposits, 38–77 m thick. The Ordvician rocks are divided into several formations (successively from the bottom to the top: Słuchów, Kopalino, Sasino and Prabuty Fms) from the Arenig to Ashgill in age. Carbonate clay-siltstone Silurian sediments, lying above with a small hiatus, are subdivided into 4 formations (Pasłęk Claystones and Pelplin, Kociewie and Puck Fms). Thickness of Silurian sediments varies from 1800 m (northern GP) to ca. 1400 m (southern GP) and > 2000 m in the west. The Uppermost Permian rocks lie with a large hiatus on the Silurian complex. The lower part of Permian complex (Rotliegend group) is composed of conglomerates with sandstone and siltstone interbeds, several meters thick and rather limited in areal extent. The upper part (Zechstein group) occurs in the whole GP area, with 300 m series of evaporite deposits of PZ1 cycle dominating in the northern part. The Oldest Halite (Na1) unit, up to 200mthick in several „salt basins”, is a perspective rock body for constructing cavern storages for hydrocarbons. Thickness of PZ1 complex decreases in the southern GP part, where Na1 salts are no more than 80–100mthick. Sulfates + carbonatesand carbonates of PZ2 and PZ3 cycles are several tens of meters thick but the total thickness of the two cyclothemes is up to 200 m, with the Older Halite (Na2) unit being 80–100 m thick. TheMesozoic succession is very reduced in the discussed area, with increased hiatuses and deposit thickness decreasing to the north. The thickest (up to 450 m thick) are here Buntsandstein (Lower Triassic) sandy-silty-claystone series with a few conglomerate interbeds, occurring in sedimentary continuity with the Zechstein ones. They are assigned to 3 formations (Baltic, Pomerania and Połczyn Fms). During the later Triassic and early Jurassic the whole area was a denudated continent. Marine conditions returned in the middle (Bathonian and Callovian) and the early Late Jurassic (Oxfordian), when clastic sediments, 200–400 m thick in the south, were accumulated. The next continental episode took place during the late Jurassic and early Cretaceous Marine Cretaceous succession begins with clastics of the Albian, followed by Cenomanian glauconite sandstones and Turonian siltstones and marls. The Upper Cretaceous complex, with thickness varying from 400 m in Gdańsk block to 500 m near Tczew, is dominated by fine clastics with subordinate gaizes. The Cenozoic (Paleogene and Neogene) rocks (clays, silts to fine sandstones, 100–200 m thick) are overlying the Cretaceous complex with a hiatus. They are covered with the postglacial Quaternary sediments diversified in lithology and thickness up to 100 m.