Ichnology of the Cretaceous Oceanic Red Beds (Outer Western Carpathians, Czech Republic)

Abstract

Large differences in the intensity and overall character of bioturbational structures were found in five facies containing hemipelagic red beds. Red beds (CORB) of the Godula facies of the Silesian Unit and their equivalents (mostly not red) in the Kelč facies of the Silesian Unit and the CORB in the non-calcareous sediments of the Rača Unit display a very low degree of bioturbation. The CORB facies of the Rača Unit, containing calcareous intercalations, displays a very high degree of bioturbation as expressed by a high ichnofabric index. They contain trace fossils Chondrites, Zoophycos, Planolites, Thalassinoides, Palaeophycus, Teichichnus and Phycosiphon. The supply of food obviously acted as the controlling factor. The "calcareous" facies of the CORB of the Rača Unit has a considerably higher proportion of sand-dominated interbeds and also carbonates than the non-calcareous facies. This (especially the presence of carbonates) suggests a relative proximity of food-rich environments and an easy transport of nutrition-rich substrate by turbidite currents into the basin directly, not only by periodical fall-out of dead plankton (which is probably responsible for the rhythmicity of poor colonization horizons in weakly bioturbated units).

Early Cretaceous sedimentary evolution of a pelagic basin margin (the Manín Unit, central Western Carpathians, Slovakia)

“…3) were examined for stable carbon and oxygen isotopes and for organic carbon contents. Ichnofossils were studied on wet rock surfaces and on polished sections of rocks using methods described in Bromley (1970), Mikulá s (1992 and Mikulá s et al (2009). Foraminifers were investigated both in thin sections and on isolated specimens in optical microscope and in SEM.…”

The former presence of organic matter caused its later absence: Burn‐down of organic matter in oceanic red beds enhanced by bioturbation (Eocene Variegated Shale, Carpathians)

“…The observed trace fossil association is quite similar in several instances to those described from oceanic red beds by Leszczyński (), Mikuláš et al . () and Reolid et al . ().…”

“…Nonetheless, there are only a few ichnological studies dealing with such sediments (e.g. Leszczyński & Uchman, , ; Leszczyński, ; Mikuláš et al ., ; Wetzel & Uchman, ; Reolid et al ., ). A reason for the low number of investigations may be due to strong compaction and low colour contrast, both resulting in a low visibility of trace fossils.…”

Dynamic environmental conditions recorded by the trace fossil Teichichnus and event beds during deposition of the basal Vaca Muerta Formation in the central Neuquén Basin (Argentina)

“…It occurs mainly in fully marine settings but also in brackish environments (Goldring, 1971;Netto and Rossetti, 2003). Commonly, Teichichnus is present in muddy sand but occasionally in chalk, marl and deep-sea mud (e.g., Frey and Bromley, 1985;Bromley and Uchman, 2003;Mikuláš et al, 2009). The unknown, supposedly wormlike producers mainly follow a suspension-and/or deposit-feeding mode (Knaust, 2018a).…”