Trace-fossils and minor discontinuities in a marl limestone rhythmite, Lower–Middle Kimmeridgian, southern Spain

In a fine-grained Lower to Middle Kimmeridgian marly limestone rhythmite succession, with scarce benthos, fluctuations in ecological and depositional conditions that affected the substrate are detected by analysing trace-fossil assemblages. The dominant grey mudstones with Chondrites and Planolites superimposed on lumpy matrix sediments indicate both late colonisation of dysaerobic mixed layers and the completeness of the stratigraphic record. Major disruptions in rhythmic deposition and substrate colonisation are recorded at the base of thick intercalations of marls in sedimentary packages that were related to tectonic instability. Minor disruptions affected only the deposition of the overlying limestone beds. The trace-fossils reveal changes in the ecological and depositional conditions affecting the substrate during deposition of monotonous marly limestone rhythmites at levels of resolution higher than biostratigraphic, ecostratigraphic and taphonomic resolution. This research demonstrates the application of trace-fossil analysis to approach stratigraphic completeness (maturation) in homogeneous marly limestone rhythmites.