Abstract Micritic sediments containing dark, discrete, organic-rich burrows, situated in a light grey background carbonate mud, were deposited over a broad geographical area in deep-shelf, bathyal and basinal environments in the western margin of the Tethys Ocean during the Early and Middle Jurassic. These hemipelagic deposits represent a distinct depositional regime marked by low-energy, soft-bottom and only locally dysoxic environments. Still, it is unclear whether the trace-fossil assemblages occurring in these deposits pertain to a network of several community types – the ichnotaxa differing from basin to basin – or to a single community of environmentally broad-ranging, burrow-producing species. Lower Jurassic trace-fossil assemblages are found in the Western Carpathians and in the Subbetic, Betic Cordillera: that is, in basins separated by more than 2000 km in their original palaeogeographical areas. The stereotypical Chondrites and Zoophycos trace-fossil assemblages that occur in the analysed deposits share two ichnogenera of distinctive morphology ( Lamellaeichnus and Teichichnus ). Agglutinated foraminifera Bathysiphon occurs together with the described trace-fossil assemblage and determines the epibenthic palaeoenvironmental conditions. In the Western Carpathians, a Lamellaeichnus -dominated assemblage alternates with a Zoophycos -dominated assemblage in small, metre-scale cycles in the upper Pliensbachian, and the proportion of the Zoophycos assemblage increases stratigraphically upwards, probably owing to reduced basin ventilation during the early Toarcian. Within the southern Iberian palaeomargin, represented by the Betic Cordillera, Zoophycos is scarce in the facies.

A bed by bed analysis of the Bonarelli Level (late Cenomanian) in the Bottaccione Gorge and the Contessa Valley (Gubbio, Italy, area) reveals ichnofabric variations that follow lithofacies changes. Ichnofabric analysis has been approached in ~60 samples for every section, using thin sections of rocks and wet cut surfaces for three-dimensional observations. The ichnofabric includes five ichnotaxa: Chondrites isp., Planolites isp., Thalassinoides isp., Trichichnus linearis , and Zoophycos isp.; their abundance and preservation fluctuate with the substrate consistency, oxygen content, and productivity. The ichnotaxa are absent in many beds that show primary lamination and were deposited under true anoxic conditions, but it is surprising that they are present in many thin beds inside the Bonarelli interval (10 in Bottaccione and 14 in Contessa). In the underlying and overlying Scaglia Bianca (late Cenomanian) carbonate deposits, the presence of a totally bioturbated background, together with superimposed discrete trace fossils (the same ichnotaxa as in the Bonarelli Level), reveals the absence of anoxic conditions (except for cherty layers), but the presence of minor fluctuations between aerobic and slightly dysaerobic conditions is marked by changes in ichnotaxa abundance.