Warunki sedymentacji osadów prekambru i kambru w północnej Polsce

Krzysztof Jaworowski

Abstrakt


DEPOSITIONAL CONDITIONS OF PRECAMBRIAN AND CAMBRIAN SEDIMENTS IN NORTHERN POLAND

Summary
The studied sequences display three stages in sedimentation:
(1) Origin of red-brown sandstones of the Żarnowiec Series which rests directly on the crystalline basement. The series, dated at the Vendian and lower part of Lower Cambrian (older than the Holmia Zone), has originated in an environment of alluvial fans. Its rocks gradually pass upwards into upper Lower Cambrian. Transitional deposits have originated in continental-marine environment, an environment of alluvial fan spreading directly into transgressing sea.
(2) Origin of light-gray sandstones, dark mudstones and interlaminated mudstones and sandstones. The rocks, dated at the Lower and Middle Cambrian, were deposited in marine environment influenced by tides. They are comparable with modern deposits of sand tongues and shelf muds known from southern North Sea. They are separated from overlaying Upper Cambrian by a sedimentary gap corresponding to the Paradoxides forchhammeri and, partly, P. paradoxissimus Zones.
(3) Origin of black claystones and gray limestones with a thin sandstone layer at the base. The rocks, dated at the Upper Cambrian (Agnostus pisiformis - Peltura scarabaeoides Zones), originated in wide, shallow marine reservoir under reducing conditions.
Precambrian and Cambrian rocks of northern Poland represent sedimentary formations related to an early stage of Caledonian tectonic cycle. They indicate sedimentation in stable platform area under conditions of semiarid and humid climate. Using W.J. Chain terminology, it may be stated that the Żarnowiec Series corresponds to red bed subformation, i.e. one of the basic varieties of basal continental formation. Younger Lower Cambrian rocks and those of the Middle and Upper Cambrian represent terrigenous transgressive marine formation. It may be further precised that the section displays two transgressive-regressive cycles: one, comprising marine Lower and Middle Cambrian rocks, and another, comprising Upper Cambrian ones.

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