Warunki sedymentacji formacji dolno kambryjskich piaskowców z Ociesęk i lupków z Kamieńca w Górach Świętokrzyskich

Abstract

Przeprowadzono obserwacje sedymentologiczne skał dolnokambryjskich z otworów wiertniczychKowala 1, Zaręby IG 2 i Wszachów IG 4. Skały te należą do dwóch formacji - piaskowców z Ociesęki łupków z Kamieńca. Z obserwacji wynika, ze piaskowce z Ociesęk powstawały w strefie przejściowej między piaskami litoralnymi a iłami szelfowymi, w morzu niegłębokim, przy umiarkowanym tempie sedymentacji. Łupki z Kamieńca natomiast osadzały się w zbiorniku głębszym, już w strefie szelfu. Przyjmuje się, że ta nagła zmiana sedymentacji mogła być spowodowana czynnikami tektonicznymi.  SEDIMENTARY CONDITIONS OF THE OCIESĘKI SANDSTONE AND KAMIENIECSHALE FORMATIONS (LOWER CAMBRIAN) IN THE HOLY CROSS MTS The paper presents results of sedimentological studies of core material from selected drillings in theKielce-Łagow synclinorium and Chęciny-Klimontów anticlinorium, Holy Cross Mts. The drillingsKowala 1, Zaręby IG 2, and Wszachów IG 4 encountered rocks of two formations of the Lower Cambrian (Holmia-Protolenus stages): Ociesęki Sandstone and Kamieniec Shale Formations. The Ociesęki Sandstone Formation comprises fine- and very fine-grained sandstones and mudstones with thin intercalations of silty claystones and claystones. The rocks display wavy, lenticular and, sometimes, horizontal laminations. Bioturbations are very numerous, being mainly represented by those of the Cruziana and Scolithos assemblages. In some places they are so intense that original structure of rocks is completely obliterated. In the borehole column Kowala 1 a 0.9 m layer of structureless sandstones with conglomerates in upper part was found in the top of this formation.The above described rocks are overlain by those of the claystone-mudstone complex, assigned to the Kamieniec Shale Formation. They are represented by claystones and silty claystones with parallel to somewhat wavy lamination. Traces of organic activity are rather rare here.The results of analysis of sedimentary structures were subsequently used in attempt to reconstruct sedimentary environments of the two formations. The Ociesęki sandstones originated in a transitional zone of littoral sands and shelf clays, in not deep and well ventilated sea and under conditions of moderate rates of sedimentation. The Kamieniec shales were deposited in shelf zone of a deeper basin, under rather quiet hydrodynamic regime. The sudden change in sedimentary conditions under which strata of the two formations originated was probably due to tectonic reasons. This is suggested by the presence of the above mentioned layer of sandstones with conglomerates at the top, found in the borehole column Kowala 1. The layer was formed with contribution of storm waves washing down barrier sediments.Sedimentation of the Ociesęki Sandstone Formation took place in a narrow elevated zone of the seafloor, stretching in the WNW-ESE direction from the vicinities of Kielce in the west to Baranów in the east, and that of the Kamieniec Shale Formation - in parts of the basin which were deeper atthat time.