Skamieniałości śladowe w oksfordzkich wapieniach płytowych okolic Krakowa
Abstract
TRACE FOSSILS FROM THE OXFORDIAN PLATY LIMESTONES NEARBY KRAKÓW
Summary
Two main facies could be distinguished in the Middle Oxfordian carbonate deposits in the southern part of the Cracow Upland, i.e., the rocky limestones and the platy limestones. The rocky limestones are recognized as ancient microbial-sponge mudmounds-type buildups. The platy limestones are white slightly marly spiculitic wackestones deposited in basins among the bioherms. The platy limestones were deposited below the normal wave base. Their fossils are dominated by nectonic forms, i.e. ammonites and belemnites, whereas benthic forms are subordinate and dominated by siliceous spongia, brachiopods and thin-shell pelecypods. Distinct trace fossils and bioturbation mottling structures (fossitextura deformativa) may be distinguished in the platy limestones. The latter, up to 5 degree of intensity, are common in certain beds. The following ichnotaxa occur, as follows: Thalassinoides ichnosp., Palaeophycus tubular is Hall, ?Skolithos ichnosp., Chondrites ichnosp. They are opportunistic forms, produced by deep-burrowing tracemakers. The shallower burrows are obliterated due to intense in faunal reworking of sediment with in near-bottom layer. Thus, the described trace fossil assemblage is only representation of the deepest tiers of burrows. Further diagenetic processes have caused a strong additional obliteration of burrows. ?Skolithos was produced probably by late burrower in firm sediment. This is indicated by commonly occurring in filling of their tubes by calcite cement. The described trace fossils assemblages confirm that platy limestones originated in calm environment beneath normal wave base, with soft bottom.
Summary
Two main facies could be distinguished in the Middle Oxfordian carbonate deposits in the southern part of the Cracow Upland, i.e., the rocky limestones and the platy limestones. The rocky limestones are recognized as ancient microbial-sponge mudmounds-type buildups. The platy limestones are white slightly marly spiculitic wackestones deposited in basins among the bioherms. The platy limestones were deposited below the normal wave base. Their fossils are dominated by nectonic forms, i.e. ammonites and belemnites, whereas benthic forms are subordinate and dominated by siliceous spongia, brachiopods and thin-shell pelecypods. Distinct trace fossils and bioturbation mottling structures (fossitextura deformativa) may be distinguished in the platy limestones. The latter, up to 5 degree of intensity, are common in certain beds. The following ichnotaxa occur, as follows: Thalassinoides ichnosp., Palaeophycus tubular is Hall, ?Skolithos ichnosp., Chondrites ichnosp. They are opportunistic forms, produced by deep-burrowing tracemakers. The shallower burrows are obliterated due to intense in faunal reworking of sediment with in near-bottom layer. Thus, the described trace fossil assemblage is only representation of the deepest tiers of burrows. Further diagenetic processes have caused a strong additional obliteration of burrows. ?Skolithos was produced probably by late burrower in firm sediment. This is indicated by commonly occurring in filling of their tubes by calcite cement. The described trace fossils assemblages confirm that platy limestones originated in calm environment beneath normal wave base, with soft bottom.