Geo&Bio (Dec 2023)
The first record of the trace fossils Cochlichnus from the Pennsylvanian continental and marine deposits in the Donets Basin, Ukraine
Abstract
Sinusoidal trace fossils Cochlichnus anguineus are described for the first time from marine and continental siltstones and sandstones of the Mospyne and Smolyanynivka formations (late Bashkirian, Early Pennsylvanian) in Luhansk Oblast, eastern Ukraine (central Donets Basin). Previously, in Ukraine, Cochlichnus anguineus was recorded in the early Bashkirian Buzhanka Formation of the Lviv Paleozoic Trough. Cochlichnus isp. is known from the Ediacaran of western Ukraine. The studied ichnofossils come from four localities representing sedimentary sequences of shallow marine, lagoonal, and lacustrine terrigenous rocks. The ichnogenus Cochlichnus Hitchcock, 1858 is known from the Precambrian to Holocene and were generally distributed in non-marine environments in the Carboniferous, although it has been recorded in a wide range of environments, from lacustrine (Mermia Ichnofacies) to marine (Cruziana Ichnofacies). In the Pennsylvanian deposits of eastern Ukraine, these trace fossils are predominantly found in lacustrine black shales, but also in lagoonal siltstones and shallow marine sandstones and siltstones. Cochlichnus has been interpreted as traces of grazing, feeding, and locomotion, and it is suggested that traces, depending on the environmental conditions and potential producers, may be combinations of all these ethological categories. Potential producers of Cochlichnus include worms sensu lato, as well as nematodes, annelids, insect larvae, or cyclostomates. In modern freshwater basins, traces morphologically similar to Cochlichnus are produced by nematodes and dipteran larvae. It seems that nematodes and/or annelids are the most likely producers of the studied Cochlichnus, since representatives of Diptera are not known in the Carboniferous. In the Donets Basin, Cochlichnus anguineus usually co-occurs with the trace fossils Lockeia, Planolites, and Palaeophycus. Sometimes these ichnofossils are found on the layer surfaces bearing microbially induced sedimentary structures together with Taphrhelminthopsis and Aulichnites.
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