Sedymentacja margli z Węgierki
Abstract
Sedimentation of Węgierka Marls (Late Senonian, Polish Flysch Carpathians)
The Węgierka Marls (Late Senonian) occur in the upper part of the profile of the Inoceramian Beds in the outer, north-eastern zone of the Skole nappe (Fig. 1). Three lithological types are distinguished in the Węgierka Marls, namely:
— bedded sandy marls, several metres to several tens of metres thick, occurring among alternating turbidite sandstones and shales;
— slump blocks and balls of sandy marl occurring in pebbly mudstone and sandy mudstone beds;
— single (beds of sandy marl, resting on top of pebbly mudstone or sandy mudstone beds, among alternating turbidite sandstones and shales.
The petrographic character, (Fig. 2) the heavy mineral assemblage (Table 1) and the chemical composition of all three lithological types of marl is similar. The macrofauna of the Węgierka Marls (Table 2) is represented by nectonic forms (ammonites, belemnites) and benthic epifauna with rare représentants of infauna. The palaeoecological analysis of the faunal assemblage indicate a shallow marine basin with partly consolidated bottom and significant turbulence of near-bottom water, as indicated by predominance of suspension feeders. The microfauna of the Węgierka Marls forms a rich assemblage (Tables 3, 4 and 5) consisting of calcareous planctonic (numerous) and benthic foraminifera, radiolarians, diatoms, arenaceous foraminifera (very rare), ostracods (rare) and sponge spicules (numerous). The foraminiferal tests are often damaged. The palaeoecological analysis of the microfaunal assemblage indicate the outer shelf as the sedimentary environment of the Węgierka Marls. There are no significant differences in the microfaunal assemblages between the three lithological types of the Węgierka Marls. Marls with abundant infauna represented by the ichnogenera Chondrites and Fucusopsis are occurring in association with turbidite sandstones and mudstones (Fig. 3) in the same profiles as the Węgierka Marls. The marls with infauna contain a microfaunal assemblage consisting mainly of arenaceous benthic foraminifera (Table 6 and Table 7). Both the ichnofaunal assemblage and the microfaunal assemblage indicate bathyal depth of the sedimentary basin. It is concluded therefore, that the sedimentary material of the Węgierka Marls accumulated originally in a shallow-water — neritic part of the basin and was subsequently redeposited in a deep-water — bathyal part of the basin. The slump blocks and balls of the Węgierka Marls in pebbly mudstones are clearly redeposited. The material of single beds of marl is redeposited by turbidity currents as indicated by grading of the sand admixture in the marls, and their association with typical turibidite beds. These beds were probably formed by redeposition of unconsolidated sandy marl sediment, which was dispersed to form turbidity currents during transport by subaqueous mass sediment flow. The bedded marls are interpreted as olistoliths of the neritic sediment transported by sliding, possibly from active fault scarps, into the bathyal part of the basin.
The Węgierka Marls (Late Senonian) occur in the upper part of the profile of the Inoceramian Beds in the outer, north-eastern zone of the Skole nappe (Fig. 1). Three lithological types are distinguished in the Węgierka Marls, namely:
— bedded sandy marls, several metres to several tens of metres thick, occurring among alternating turbidite sandstones and shales;
— slump blocks and balls of sandy marl occurring in pebbly mudstone and sandy mudstone beds;
— single (beds of sandy marl, resting on top of pebbly mudstone or sandy mudstone beds, among alternating turbidite sandstones and shales.
The petrographic character, (Fig. 2) the heavy mineral assemblage (Table 1) and the chemical composition of all three lithological types of marl is similar. The macrofauna of the Węgierka Marls (Table 2) is represented by nectonic forms (ammonites, belemnites) and benthic epifauna with rare représentants of infauna. The palaeoecological analysis of the faunal assemblage indicate a shallow marine basin with partly consolidated bottom and significant turbulence of near-bottom water, as indicated by predominance of suspension feeders. The microfauna of the Węgierka Marls forms a rich assemblage (Tables 3, 4 and 5) consisting of calcareous planctonic (numerous) and benthic foraminifera, radiolarians, diatoms, arenaceous foraminifera (very rare), ostracods (rare) and sponge spicules (numerous). The foraminiferal tests are often damaged. The palaeoecological analysis of the microfaunal assemblage indicate the outer shelf as the sedimentary environment of the Węgierka Marls. There are no significant differences in the microfaunal assemblages between the three lithological types of the Węgierka Marls. Marls with abundant infauna represented by the ichnogenera Chondrites and Fucusopsis are occurring in association with turbidite sandstones and mudstones (Fig. 3) in the same profiles as the Węgierka Marls. The marls with infauna contain a microfaunal assemblage consisting mainly of arenaceous benthic foraminifera (Table 6 and Table 7). Both the ichnofaunal assemblage and the microfaunal assemblage indicate bathyal depth of the sedimentary basin. It is concluded therefore, that the sedimentary material of the Węgierka Marls accumulated originally in a shallow-water — neritic part of the basin and was subsequently redeposited in a deep-water — bathyal part of the basin. The slump blocks and balls of the Węgierka Marls in pebbly mudstones are clearly redeposited. The material of single beds of marl is redeposited by turbidity currents as indicated by grading of the sand admixture in the marls, and their association with typical turibidite beds. These beds were probably formed by redeposition of unconsolidated sandy marl sediment, which was dispersed to form turbidity currents during transport by subaqueous mass sediment flow. The bedded marls are interpreted as olistoliths of the neritic sediment transported by sliding, possibly from active fault scarps, into the bathyal part of the basin.