Profil permu w północno-zachodniej części Gór Świętokrzyskich

Abstract

THE PERMIAN SEQUENCE IN THE NORTH-WESTERN PART OF THE ŚWIĘTOKRZYSKIE MOUNTAINSSummaryThe examinations of the lower part of the Zechstein (cyclothems ZI and Z2) pierced by seven shallow boreholes in the north-western part of the Świętokrzyskie Mountains (Fig. 1) are reviewed in the present paper. The Zechstein lithological sequences and their stratigraphic correlation are presented in Fig. 2. They have been compared to the complete reference sequences for the Świętokrzyskie Mountains - Tumlin 1 and Tumlin 2 (Fig. 3) - established by K. Pawłowska (1964). In each borehole the Upper Permian commences with conglomerates [1] built of Devonian carbonate and detrital rocks. Everywhere the carbonates are overlain by fine-grained limestones, marly limestones, and marls [la]. These rocks called "the Kajetanów limestones" are highly bituminous with abundant Fe, Pb, and Zn sulphides mineralization. Additionally they contain fine bioclastic limestones intercalations with single ooids. Their thickness varies from 10.5 to 23.5 m. The sediments overlying the Kajetanów limestones bear evidence of a facies differentiation; near Kajetanów (in the marginal part of the depositional basin) these are siltstones, marls, and shaly claystones [lc] about 0.8 m thick, whereas in the Lekomin area (farther from the margin of the basin) - marly limestones, marls, and claystones [1b] that attain the thickness of 9 to 12 m. They correspond to the porous dolomitic limestones and limy dolomites ferruginous at the top reported from the Tumlin area. The number of individual ooids (and oncolites?) in the rocks increases upwards. According to the present authors the material subject to dolomitization (possibly late diagenetic) was a poorly consolidated limy-marly sediment of the [lb] type. Subsequently the rocks were affected by karst processes and the formation of rottenstones was probably promoted by the presence of aggressive sulphates in the aquaeous solution. These processes are supposed to have been controled by dedolomitization. Very likely as this hypothesis seems, it remains to be confirmed by further petrographic studies. The apparent thickness of the above rocks ranges from 7.4 to 9.5 m. The oolitic (and oncolitic?), ferruginous, slightly dolomitized and rotten limestones [1f] (2.4-3.3. m thick) of the Tumlin area correspond to the siltstones, sandstones, limestones, and marls [le] of Kajetanów and Lekomin, the total thickness of which is 0.7 to 2.8 m. The above sediments belong to the ZI cycle the deposition of which was terminated by a short-lived emergence. The younger sediments probably belong to the Z2 cycle. As a result of a subsequent Zechstein ingression sediments of a shallow-marine facies such as claystones, limestones, and marls [2b] were formed. They correspond to limy siltstones, limy-clay siltstones, and variegated-spotty claystones [2a] of the lagoonal-limnic facies that occur in the direct neighbourhood (to the east and north-east). At the top of the clay-carbonate layers in Fig. 2 marked as [2b] "variegated" sediments occur that bear similarities to those described above and comprise siltstones, sandstones, sandy marls with limestones intercalations, and silty claystones [2c]. The analysis of the depositional development of the Zechstein indicates that the transgression entered an area distinctly denuded but still of a differentiated relief. The transgression that invaded the Świętokrzyski continent by embayments rapidly lost its expansive force. In the periodically stagnant waters under reducing conditions (considerable concentrations of decaying organic substance) Fe, Pb, and Zn sulphides accumulated. Towards the end of the Zl cyclothem the Świętokrzyskie water areas slowly lost their connection with the west Polish basin. The younger ingression (probably during the Z2 cyclothem) did not reach as far east as the early Zechstein ingression. In isolated lagoons (that in the peripheral zones formed intermittent limnic lakes) rapidly filled with detrital material "variegated" sediments were formed.Ore mineralization evidences and trace elements contents (Tabs. 1 and 2) have been discussed against the facies development. Syngenetic Fe-Zn-Pb-Cu mineralization related to the basal conglomerate and the bituminous Kajetanów limestones series and epigenetic mineralization of similar mineralogy and sedimentary-catagenic type have been found in the sediments examined: Spectrochemical results provided data on the vertical and horizontal distribution of Zn, Pb, Cu, Ag, Ni, Co, V, Cr, Ba and Sr. According to the present authors the syngenetic Fe, Pb, Zn, and Cu sulphides mineralization and a distinct -bituminization of the Zechstein sediments in the north-western bordderland of the Świętokrzyskie Mountains fully account for the need of further comprehensive studies.