Sejsmotektoniczne osady i struktury w kredowych piaskowcach niecki śródsudeckiej

Jurand Wojewoda

Abstrakt


SEISMOTECTONIC DEPOSITS AND STRUCTURES IN THE CRETACEOUS SANDSTONES OF THE INTRA-SUDETIC BASIN

Summary
Alongshore drift and seasonal storm surges were the dominant factors affecting the sedimentation in the NE part of Upper Cretaceous epicontinental Bohemian Sea during the Turonian. A development of gigantic bedforms - accumulation terraces, and of sandy sequences originated as a result of offshore progradation of these forms, was strongly influenced by fault activity of the basin floor. The resultant sandstones are abundant in seismites - deposits and structures reflecting synsedimentary seismic activity.
Two groups of seismites are distinguished: orthoseismites - produced in situ as a direct effect of a seismic shock, and paraseismites - resultant from a redeposition following the shock. Superficial orthoseismites (shallow penetrating fissures and cracks, convolutions, circular and elongate collapse structures) penetrate the sediment to a depth generally not exceeding 2 metres and form seismic horizons most often in sandstones of the under- and overscarp facies of the accumulation terraces. Penetrating orthoseismites ( deeply penetrating fracture and fault zones, rotational slides) comprise the whole thicknesses of sandstone lithosomes and are located directly above the basement faults. As superficial paraseismites considered are some sand flow deposits. The processes involved in the formation of the seismites described are local fluidization and dewatering of sediments of the accumulation terraces. The orientation of the seismically induced structures is usually concordant with that of major fault of the basement.

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