Ichnology of the Middle Jurassic hiatus concretions from Poland: implications for their formation, exhumation, and palaeoenvironment

In the present study, the Middle Jurassic exhumed carbonate concretions (the so-called hiatus concretions) from the Polish Jura (southern Poland) were studied ichnologically (precursor burrows and their tiering and bioerosion patterns) in order to decipher the palaeoenvironmental conditions leading to their formation and exhumation. The ichnological approach to the concretionary bodies used in this study yielded information on the scale of seafloor erosion and its relative timing compared to the burrow-infilling phase. The bioerosion patterns also provided information on proximal-distal trends and the frequency and strength of currents in the environment below storm wave base, a setting recorded in the monotonous, concretion-bearing siliciclastic sections which is studied here. The significance of the stratigraphic sequence is also briefly discussed based on the horizons containing the hiatus concretions.